JP2013124946A - Force sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve downsizing and cost reduction while securing high reliability.SOLUTION: An integral structure is prepared by arranging a disk-like force receiver 300 under a disk-like flexure element 100 and connecting the force receiver 300 and the flexure element 100 by a cylindrical connection member 200. A detecting groove G is dug on the inside of a contour line f1 of an upper surface of the flexure element 100. The bottom of the detecting groove G forms a diaphragm part 110 and a square flexure detecting base plate 400 composed of silicon is joined to the upper surface of the diaphragm part 110. The lower surface of the diaphragm part 110 and the lower surface of a sidewall part 120 around the diaphragm part 110 are aligned on the same plane. Piezoresistive elements A are formed along an X axis and a Y axis just close to the outside of a junction part of the connection member 200 on the upper surface of the flexure detecting base plate 400. A bridge circuit utilizing the piezoresistive elements A is formed on a circuit board 500, and a moment component Mx around the X axis, a moment component My around the Y axis and a force component Fz in a Z-axis direction are respectively outputted as bridge voltages.

Description

  The present invention relates to a force sensor, and more particularly to a force sensor that detects a force component in a predetermined axis direction or a moment component around a predetermined axis in an XYZ three-dimensional orthogonal coordinate system.

  In various industrial machines including robots, force sensors that detect forces acting on the joints between arms are used. In particular, in the case of an industrial machine driven by computer control, it is important to detect the force acting on each part separately for a force component in a predetermined axis direction and a moment component around the predetermined axis in a three-dimensional coordinate system.

  As a sensor having a function of independently detecting a three-dimensional force component in each axial direction and a moment component around each axis as described above, for example, Patent Document 1 listed below discloses a piezoresistor formed on a semiconductor substrate. A force sensor using an element is disclosed. In this force sensor, a semiconductor substrate is bonded to a strain generating body in which mechanical bending occurs due to the action of a force to be detected, and a change in the resistance value of a piezoresistive element formed on the semiconductor substrate is detected. The applied force is detected. By devising the position and orientation of the piezoresistive element formed on the semiconductor substrate, a force component in a specific axial direction and a moment component around a specific axis can be detected independently.

  On the other hand, Patent Document 2 uses a structure in which four struts are passed between two parallel substrates, and detects the displacement state of each strut using a capacitive element. A 6-axis type force sensor capable of independently detecting a force component in the coordinate axis direction and a moment component around each coordinate axis is disclosed.

JP-A 63-266325 JP 2004-325367 A

  In recent years, with the miniaturization of industrial machinery, it has been required to reduce the size of the force sensor while ensuring high reliability. Further, from a commercial standpoint, further cost reduction is desired. However, with the force sensor of the type conventionally proposed, it is difficult to achieve further downsizing and cost reduction while ensuring reliability.

  Accordingly, an object of the present invention is to provide a force sensor that can be downsized and cost can be reduced while ensuring high reliability.

(1) A first aspect of the present invention is a force sensor that detects a force component in a predetermined axis direction or a moment component around a predetermined axis in an XYZ three-dimensional orthogonal coordinate system.
A force receiving body that receives a force to be detected, a strain generating body having a diaphragm portion that deforms based on the force received by the force receiving body, a connecting member that connects the force receiving body and the diaphragm portion, and XYZ tertiary A strain detection substrate disposed at the position of the origin O of the original Cartesian coordinate system and joined to the diaphragm, a detection circuit that outputs a force to be detected as an electrical signal,
Provided,
The strain body is constituted by a plate-like member having an upper surface and a lower surface parallel to the XY plane, and a detection groove defined in the central portion of the upper surface of the strain body has a detection groove toward the lower surface side. The diaphragm portion is formed by the bottom portion of the detection groove, the side wall portion is formed around the detection groove, and the lower surface of the diaphragm portion and the lower surface of the side wall portion are located on the same plane,
The force receiving body is arranged below the strain body at a predetermined interval,
The connecting member is constituted by a columnar member arranged on the Z axis, the upper end thereof is connected to the lower surface center portion of the diaphragm portion, and the lower end thereof is connected to the upper surface center portion of the force receiving body,
The strain detection substrate has a top surface and a bottom surface that are parallel to the XY plane, and is joined to the bottom surface of the detection groove so that stress generated by the deformation of the diaphragm portion is transmitted, and a piezoresistive element is provided at a predetermined position on the top surface. Formed,
The detection circuit outputs an electric signal indicating the force received by the force receiving body based on a change in electric resistance of the piezoresistive element.

(2) According to a second aspect of the present invention, in the force sensor according to the first aspect described above,
The force receiving body, the connecting member, and the strain generating body are configured by an integral structure made of the same material.

(3) According to a third aspect of the present invention, in the force sensor according to the first or second aspect described above,
The force receiving member is constituted by a plate-like member having an upper surface and a lower surface parallel to the XY plane,
A screw hole for fixing the strain generating body to the external first object is formed in the side wall portion of the strain generating body,
A screw hole for fixing the force receiving body to the external second object and an instrument for rotating a screw inserted through the screw hole of the strain generating body are inserted into the outer periphery of the force receiving body. An opening is formed,
The screw hole of the strain generating body and the screw hole of the force receiving body are formed at positions where the orthogonal projection projection images on the XY plane do not overlap, and the screw hole of the strain generating body and the opening of the power receiving body are , The orthogonal projection image on the XY plane is formed at the overlapping position.

(4) According to a fourth aspect of the present invention, in the force sensor according to the third aspect described above,
The strain body is constituted by a disk-shaped member having the Z axis as the central axis,
The strain detection substrate is composed of a square substrate centering on the Z axis,
The strain body is formed with a detection groove capable of accommodating a square substrate,
A total of 4 respectively arranged at each outer position of the opposite side on the line connecting the midpoints of a pair of opposite sides of the square and each outer position of the opposite side on a line connecting the midpoints of another set of opposite sides. Each screw hole is formed in the strain body.

(5) According to a fifth aspect of the present invention, in the force sensor according to the first to fourth aspects described above,
An insertion port penetrating from the outside toward the detection groove is provided in the side wall portion of the strain generating body, and the circuit board on which the detection circuit is mounted is inserted and fixed in the insertion port, and the piezoresistive element and the circuit board Wiring is provided between the detection circuit and the detection circuit.

(6) The sixth aspect of the present invention is the force sensor according to the first to fifth aspects described above,
When a projection image is formed by orthographic projection of the upper end surface of the connection member onto the upper surface of the strain detection substrate, at least a part of the piezoresistive element is constituted by a central element disposed in the immediate vicinity of the projection image. It is what you have.

(7) A seventh aspect of the present invention is the force sensor according to the sixth aspect described above,
The central element is arranged at a position where a stress is applied in a direction to be contracted by the action of the detection target component and a first group of central elements arranged at a position where the stress is applied in a direction of extension by the action of the predetermined detection target component. A second group of central elements,
The detection circuit detects the detection target component using a Wheatstone bridge in which the central element belonging to the first group is arranged on the first opposite side and the central element belonging to the second group is arranged on the second opposite side. It is a thing.

(8) The eighth aspect of the present invention is the force sensor according to the seventh aspect described above,
A first central element and a second central element arranged along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A third central element and a fourth central element arranged along the X-axis negative region such that the X-axis direction is the longitudinal direction;
Have
The first to fourth central elements are composed of piezoresistive elements of the same material and the same size,
A detection circuit uses a Wheatstone bridge in which a first central element and a second central element are arranged on the first opposite side, and a third central element and a fourth central element are arranged on the second opposite side. The moment component My around the Y axis is detected.

(9) According to a ninth aspect of the present invention, in the force sensor according to the eighth aspect described above,
A fifth central element and a sixth central element arranged along the Y-axis positive region such that the Y-axis direction is the longitudinal direction;
A seventh central element and an eighth central element arranged along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
Further comprising
The fifth to eighth central elements are constituted by piezoresistive elements of the same material and the same size,
In addition to detecting the moment component My around the Y axis, the detection circuit further arranges the fifth central element and the sixth central element on the first opposite side, and the seventh central element and the eighth central element. The moment component Mx around the X axis is detected using a Wheatstone bridge in which the element is arranged on the second opposite side.

(10) According to a tenth aspect of the present invention, in the force sensor according to the sixth aspect described above,
It further has a reference element made of a piezoresistive element arranged at a position where no significant stress change occurs even when the diaphragm portion is deformed by the action of the force to be detected,
The detection circuit detects the detection target component using a Wheatstone bridge in which the central element is arranged on the first opposite side and the reference element is arranged on the second opposite side.

(11) An eleventh aspect of the present invention is the force sensor according to the tenth aspect described above,
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
A first reference element and a second reference element arranged in the vicinity of the periphery of the strain detection substrate;
Have
The first to fourth central elements are composed of piezoresistive elements of the same material and the same size, and the first to second reference elements are composed of piezoresistive elements of the same material and the same size, In a state where the force to be detected is not acting, the resistance value of the first to second reference elements is set to be twice the resistance value of the first to fourth central elements,
A detection circuit includes a resistance element formed by connecting a first central element and a second central element in series, and a resistance element formed by connecting a third central element and a fourth central element in series. The force component Fz in the Z-axis direction is detected using a Wheatstone bridge arranged on one opposite side and having a first reference element and a second reference element arranged on the second opposite side.

(12) According to a twelfth aspect of the present invention, in the force sensor according to the sixth aspect described above,
A reference element composed of a piezoresistive element arranged at the outer position of each central element with the position of the Z axis as the inner side;
The detection circuit detects the detection target component using a Wheatstone bridge in which the central element is arranged on the first opposite side and the reference element is arranged on the second opposite side.

(13) According to a thirteenth aspect of the present invention, in the force sensor according to the twelfth aspect described above,
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
A first reference element disposed outside the first central element along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second reference element disposed outside the second central element along the X-axis negative region so that the X-axis direction is a longitudinal direction;
A third reference element disposed outside the third central element along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth reference element arranged outside the fourth central element along the Y-axis negative region so that the Y-axis direction becomes the longitudinal direction;
Have
The first to fourth central elements and the first to fourth reference elements are composed of piezoresistive elements of the same material and the same size,
A detection circuit includes a resistance element formed by connecting a first central element and a second central element in series, and a resistance element formed by connecting a third central element and a fourth central element in series. A resistance element formed by connecting a first reference element and a second reference element in series, and a resistance element formed by connecting a third reference element and a fourth reference element in series; The force component Fz in the Z-axis direction is detected using a Wheatstone bridge arranged on the second opposite side.

(14) According to a fourteenth aspect of the present invention, in the force sensor according to the sixth aspect described above,
The strain detection substrate is composed of a silicon single crystal substrate, and the (001) plane of the silicon single crystal substrate is the upper surface of the strain detection substrate.
Each central element is arranged to face the peak direction of the piezoresistance coefficient in the (001) plane,
A reference element composed of a piezoresistive element arranged to face a direction forming 45 ° with respect to the peak direction;
The detection circuit detects the detection target component using a Wheatstone bridge in which the central element is arranged on the first opposite side and the reference element is arranged on the second opposite side.

(15) According to a fifteenth aspect of the present invention, in the force sensor according to the fourteenth aspect described above,
The strain detection board is arranged so that the peak direction of the piezoresistance coefficient is the X-axis or Y-axis direction,
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
First to fourth reference elements arranged such that a direction at 45 ° to the X axis or the Y axis is a longitudinal direction;
Have
The first to fourth central elements and the first to fourth reference elements are composed of piezoresistive elements of the same material and the same size,
A detection circuit includes a resistance element formed by connecting a first central element and a second central element in series, and a resistance element formed by connecting a third central element and a fourth central element in series. A resistance element formed by connecting a first reference element and a second reference element in series, and a resistance element formed by connecting a third reference element and a fourth reference element in series; The force component Fz in the Z-axis direction is detected using a Wheatstone bridge arranged on the second opposite side.

(16) According to a sixteenth aspect of the present invention, in the force sensor according to the sixth aspect described above,
A central element having a first polarity composed of a piezoresistive element that increases in electrical resistance when a stress in an extending direction acts and decreases in electrical resistance when a stress in a contracting direction acts;
A central element having a second polarity composed of a piezoresistive element that decreases in electrical resistance when stress in the extending direction acts and increases in electrical resistance when stress in the contracting direction acts;
Have
The detection circuit detects a detection target component using a Wheatstone bridge in which a central element having a first polarity is arranged on the first opposite side and a central element having the second polarity is arranged on the second opposite side. It is what I do.

(17) According to a seventeenth aspect of the present invention, in the force sensor according to the sixteenth aspect described above,
A first central element and a second central element arranged along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A third central element and a fourth central element arranged along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A fifth central element and a sixth central element arranged along the Y-axis positive region such that the Y-axis direction is the longitudinal direction;
A seventh central element and an eighth central element arranged along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
Have
The first, third, fifth, and seventh central elements are central elements having the same material and the same size and having the first polarity, and the second, fourth, sixth, and eighth central elements are A central element having the same material and the same size and having a second polarity, the resistance values of the first to eighth central elements are set to be equal to each other in a state where a force to be detected is not applied. ,
A detection circuit includes a resistance element formed by connecting a first central element and a third central element in series, and a resistance element formed by connecting a fifth central element and a seventh central element in series. A resistance element formed by connecting the second central element and the fourth central element in series with each other, and a resistance element formed by connecting the sixth central element and the eighth central element in series; The force component Fz in the Z-axis direction is detected using a Wheatstone bridge arranged on the second opposite side.

(18) According to an eighteenth aspect of the present invention, in the force sensor according to the sixth aspect described above,
The strain detection substrate is constituted by a silicon single crystal substrate, the (001) plane of this silicon single crystal substrate is the upper surface of the strain detection substrate, and the peak direction of the piezoresistance coefficient on the (001) plane is the X-axis or Y-axis direction. The strain detection board is arranged so that
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
Fifth and sixth central elements disposed on both sides of the first central element along the X-axis positive region so that the X-axis direction is the longitudinal direction;
Seventh and eighth central elements disposed on both sides of the second central element along the X-axis negative region so that the X-axis direction is the longitudinal direction;
Ninth and tenth central elements disposed on both sides of the third central element along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
Eleventh and twelfth central elements arranged on both sides of the fourth central element along the Y-axis negative region so that the Y-axis direction becomes the longitudinal direction;
First to fourth reference elements arranged such that a direction at 45 ° to the X axis or the Y axis is a longitudinal direction;
Have
The first to twelfth central elements and the first to fourth reference elements are composed of piezoresistive elements of the same material and the same size,
The detection circuit
A resistance element formed by connecting a first central element and a second central element in series and a resistance element formed by connecting a third central element and a fourth central element in series are arranged on the first opposite side. A resistive element formed by connecting the first reference element and the second reference element in series, and a resistive element formed by connecting the third reference element and the fourth reference element in series. The force component Fz in the Z-axis direction is detected using a Wheatstone bridge arranged on the opposite side of
Using a Wheatstone bridge in which the fifth central element and the sixth central element are arranged on the first opposite side and the seventh central element and the eighth central element are arranged on the second opposite side, The moment component My is detected,
Using a Wheatstone bridge in which the ninth central element and the tenth central element are arranged on the first opposite side and the eleventh central element and the twelfth central element are arranged on the second opposite side, The moment component Mx is detected.

(19) According to a nineteenth aspect of the present invention, in the force sensor according to the sixth to eighteenth aspects described above,
The arrangement pattern of each central element is made symmetrical with respect to the XZ plane and the YZ plane.

(20) According to a twentieth aspect of the present invention, in the method of manufacturing an integrated structure used for the force sensor according to the second aspect described above,
In the XYZ three-dimensional Cartesian coordinate system defined in the direction in which the Z axis is directed upward, the material rod is arranged so that the central axis is on the Z axis, and the Z coordinate value exceeds α and falls within the range of less than β. A side machining step for cutting the part from the side so that only the part near the central axis remains,
An upper surface processing stage in which a detection region is defined at the center of the upper end surface of the material rod, and the detection region is cut downward to form a detection groove;
And
The power receiving body is constituted by the portion where the Z coordinate value is α or less, the connecting member is constituted by the portion where the Z coordinate value exceeds α and falls within the range of less than β, and strain is generated by the portion where the Z coordinate value is β or more. It is intended to make up the body.

  The force sensor according to the present invention is configured by a basic structure including a force receiving body, a connecting member, and a strain generating body, and the strain generating body can be realized by a simple structure in which a detection groove is formed on the upper surface. While ensuring reliability, it is possible to reduce the size and cost as compared with the conventional apparatus. In particular, if this basic structure is made up of an integral structure made of the same material, the manufacturing process becomes easier, manufacturing costs can be greatly reduced, and a highly reliable device for connecting each part is realized. can do. In addition, since the diaphragm portion is formed by the bottom portion of the detection groove and the deformation can be electrically detected based on the change in the electric resistance of the piezoresistive element, sufficient detection accuracy can be ensured.

It is a sectional side view which shows an example of the conventional force sensor. FIG. 2 is an exploded side view of the force sensor shown in FIG. 1. FIG. 2 is a top view (upper view (a)) and a side view (lower view (b)) of the basic structure of the force sensor according to the present invention. 3 is a top view (upper view (a)) showing a state in which the cover 180 of the basic structure shown in FIG. 3 is removed, and a side sectional view (lower view (b)) cut along the XZ plane. , Not a cross section, but a region). It is a bottom view of the basic structure shown in FIG. FIG. 6 is a bottom view showing a state where four screws N1 to N4 are inserted through the basic structure shown in FIG. 4 is a top view (upper view (a)) showing a state where the cover 180 of the basic structure shown in FIG. 3 is removed, and a side sectional view (lower view (b)) cut at the position of the cutting line WW (cover bonding). The hatching of the portion 190 does not indicate a cross section but indicates a region). FIG. 4 is a side sectional view on the XZ plane showing a deformation state when a moment component + My around the Y-axis acts on the basic structure shown in FIG. 3. It is a sectional side view in the XZ plane which shows a deformation | transformation state when force component + Fz of a Z-axis direction acts on the basic structure shown in FIG. It is a top view which shows the 1st Example of the piezoresistive element arrangement pattern in the force sensor which concerns on this invention (a hatching shows the formation area of a piezoresistive element, and does not show a cross section). It is a table | surface which shows the change of the resistance value of each piezoresistive element in 1st Example shown in FIG. FIG. 11 is a circuit diagram showing a detection circuit for detecting a moment component My around the Y axis using the first embodiment shown in FIG. 10. FIG. 11 is a circuit diagram showing a detection circuit for detecting a moment component Mx around the X axis using the first embodiment shown in FIG. 10. It is a top view which shows the 2nd Example of the piezoresistive element arrangement pattern in the force sensor which concerns on this invention (the hatching shows the formation area of a piezoresistive element, and does not show a cross section). It is a table | surface which shows the change of the resistance value of each piezoresistive element in 2nd Example shown in FIG. FIG. 15 is a circuit diagram showing a detection circuit for detecting a force component Fz in the Z-axis direction using the second embodiment shown in FIG. 14. It is a top view which shows the 3rd Example of the piezoresistive element arrangement pattern in the force sensor which concerns on this invention (the hatching shows the formation area of a piezoresistive element, and does not show a cross section). It is a table | surface which shows the change of the resistance value of each piezoresistive element in the 3rd Example shown in FIG. FIG. 18 is a circuit diagram showing a detection circuit for detecting a force component Fz in the Z-axis direction using the third embodiment shown in FIG. 17. It is a top view which shows the 4th Example of the piezoresistive element arrangement pattern in the force sensor which concerns on this invention (The hatching shows the formation area of a piezoresistive element, and does not show a cross section.). It is a table | surface which shows the change of the resistance value of each piezoresistive element in the 4th Example shown in FIG. It is a graph which shows the piezoresistance coefficient (electrical resistance change sensitivity with respect to stress distortion) about each crystal plane of a silicon single crystal substrate. FIG. 21 is a circuit diagram showing a detection circuit for detecting a force component Fz in the Z-axis direction using the fourth embodiment shown in FIG. 20. It is a top view which shows the 5th Example of the piezoresistive element arrangement pattern in the force sensor which concerns on this invention (The hatching shows the formation area of a piezoresistive element, and does not show a cross section.). It is a table | surface which shows the change of the resistance value of each piezoresistive element in the 5th Example shown in FIG. FIG. 25 is a circuit diagram showing a detection circuit for detecting a force component Fz in the Z-axis direction using the fifth embodiment shown in FIG. 24. It is a top view which shows the 6th Example of the piezoresistive element arrangement pattern in the force sensor which concerns on this invention (the hatching shows the formation area of a piezoresistive element, and does not show a cross section). FIG. 28 is a circuit diagram showing a detection circuit for detecting a moment component Mx around the X axis, a moment component My around the Y axis, and a force component Fz in the Z axis direction using the sixth embodiment shown in FIG. 27;

  Hereinafter, the present invention will be described based on the illustrated embodiments.

<<< §1. Structure of conventional equipment and its problems >>
Here, first, the structure and operating principle of the force sensor disclosed in the above-mentioned Patent Document 1, which is considered to be the prior art closest to the force sensor according to the present invention, will be described. FIG. 1 is a side sectional view of this conventional force sensor, and FIG. 2 is an exploded side view thereof.

  As shown in FIG. 1, the main structure of the force sensor is a strain generating body 10, a force receiving body 30, a strain detection substrate 40, and a cover 50. The strain body 10 and the force receiving body 30 are both disk-shaped members, and the side view of FIG. 2 shows a state where they are separated and the cover 50 is removed.

  The strain body 10 includes a diaphragm portion 11 composed of a thin washer-like portion, a side wall portion 12 surrounding the periphery thereof, and a column portion 13 extending downward along the central axis. The side wall 12 is formed with through holes H1 and H2 for wiring and through holes H3 and H4 for screwing. On the other hand, the force receiving body 30 is formed with through holes H5, H6, and H7 for screwing at the center and the periphery. The central through hole H5 is for inserting the screw N, and the tip of the screw N is screwed into a female screw formed below the support column 13. Eventually, the force receiving body 30 is joined to the lower end of the column portion 13 by the screw N. In addition, illustration of each through-hole H1-H7 and the screw N is abbreviate | omitted in the side view of FIG.

  A shallow and wide groove G1 is dug on the upper surface of the strain generating body 10, and a strain detection substrate 40 is accommodated in the groove G1. The upper part of the groove G1 is covered with the cover 50. On the other hand, an annular groove G2 is dug on the lower surface of the strain body 10, and the upper part of the groove G2 is a washer-shaped diaphragm portion 11. The diaphragm portion 11 is flexible because it is thin. Therefore, when an external force acts on the force receiving body 30, the external force is transmitted to the diaphragm portion 11 via the support column portion 13, and the diaphragm portion 11 is deformed. The groove G3 dug in the lower surface of the force receiving body 30 is for accommodating the head of the screw N.

  The strain detection substrate 40 is formed of a silicon substrate and is attached to the bottom surface of the groove G1. Therefore, the mechanical deformation generated in the diaphragm portion 11 is transmitted to the strain detection substrate 40 as it is. Piezoresistive elements K1 to K4 are formed at predetermined positions on the upper surface of the strain detection substrate 40. When mechanical deformation occurs in the strain detection substrate 40, the electrical resistances of the piezoresistive elements K1 to K4 change. . Wiring pins 61 and 62 inserted through the through holes H1 and H2 are wired to the piezoresistive elements K1 to K4 via bonding wires 71 and 72, respectively. The lower ends of the wiring pins 61 and 62 are connected to a detection circuit (not shown). In this detection circuit, a change in the electrical resistance of each of the piezoresistive elements K1 to K4 is detected, and the external force acting on the force receiving body 30 is detected. Is done.

  The strain body 10 is fixed to the upper object (not shown) with screws inserted through the through holes H3 and H4, and the force receiving body 30 is fixed to the lower object (not shown) with screws inserted into the through holes H6 and H7. In this case, the force sensor functions to detect an external force applied from the lower object to the upper object.

  A characteristic of this conventional force sensor is that stress (mechanical strain) concentrates at positions L1 to L4 in FIG. 2 in the diaphragm portion 11 when an external force is applied. Here, the positions L1 and L4 are the outer peripheral edges of the washer-shaped diaphragm portion 11, and the positions L2 and L3 are the inner peripheral edges of the washer-shaped diaphragm portion 11. In short, the stress generated in the diaphragm portion 11 based on the external force acting on the force receiving body 30 is concentrated on the end portion. The piezoresistive elements K1 to K4 shown in FIG. 1 are formed at positions corresponding to these positions L1 to L4. Thus, by arranging the piezoresistive elements K1 to K4 at positions where stress is concentrated, high detection sensitivity can be obtained.

  The form of stress generated at each of the positions L1 to L4 of the diaphragm portion 11 varies depending on the direction of the applied external force. However, in the conventional force sensor, the washer-like diaphragm portion 11 is placed inside the washer-like diaphragm portion 11 as described above. Each component of the external force acting on the force receiving body 30 is detected by the bridge circuit using the arranged piezoresistive elements K2, K3 and the piezoresistive elements K1, K4 arranged on the outside.

  However, this conventional force sensor has the following problems. First, in order to be able to detect the stress generated at the outer peripheral edge (positions L1, L4) of the washer-like diaphragm portion 11, the outer dimension of the strain detection substrate 40 is made larger than the outer diameter of the diaphragm portion 11. I must. This is because the outer periphery of the strain detection substrate 40 needs to extend to the outside of the positions L1 and L4 in order to generate sufficient strain at the positions L1 and L4 of the strain detection substrate 40. Further, in order to perform wiring to both ends of the piezoresistive elements K1 and K4, it is necessary to provide a certain amount of margin on the outer peripheral portion of the strain detection substrate 40. As a result, the size of the strain detection substrate 40 has to be increased to some extent as compared with the size of the diaphragm portion 11, which hinders downsizing of the entire apparatus.

  Secondly, since the shape of the basic structure constituted by the strain body 10 and the force receiving body 30 is complicated, the manufacturing process becomes complicated, and the manufacturing cost is inevitably increased. As shown in the drawing, the strain body 10 needs to be processed to form a wide and shallow groove G1 on the upper surface, and to be processed to form an annular groove G2 on the lower surface. In particular, in order to perform the process of forming the groove G2 on the lower surface side, the force receiving body 30 becomes an obstacle. Therefore, it is necessary to prepare the force receiving body 30 as a separate body from the strain generating body 10 and to have a detachable structure. There is. That is, the process of forming the groove G2 on the lower surface of the strain body 10 and then attaching the force receiver 30 below the strain body 10 (in the illustrated example, the force receiver 30 with the screw N). Must be performed on the lower surface of the support column 13). As the processing process and the assembly process become more complicated, the manufacturing cost increases.

  Thirdly, since it is necessary to connect the strain generating body 10 and the force receiving body 30 that are prepared as separate bodies, the reliability of the connection portion must be reduced. For example, when the screw N is connected and fixed as in the illustrated example, if the screw N is slackened, correct detection cannot be performed, and in some cases, the force receiving body 30 is distorted. There is also a risk of falling off the body 10. Therefore, in practice, in addition to fixing with the screw N, it is necessary to fill and fix the adhesive between the two. However, when the adhesive is inserted, there is another problem that hysteresis characteristics appear in the connection portion. Will occur. In particular, when an overload is applied to the apparatus, the adhesive may be partially peeled off, resulting in a hysteresis characteristic that cannot be ignored at the connection portion.

  The present invention is for solving such a problem in a conventional apparatus, and provides a technique for reducing the size and cost while ensuring high reliability.

<<< §2. Basic structure of force sensor according to the present invention >>
Next, the basic structure of the force sensor according to the present invention will be described. FIG. 3 shows a top view (upper view (a)) and a side view (lower view (b)) of the basic structure constituting the force sensor according to the present invention. As shown in the lower side view, main components of the basic structure are the strain body 100, the connection member 200, and the force receiving body 300.

  As shown by the broken line in the drawing, a detection groove G is provided inside the strain body 100, and a diaphragm portion 110 is formed by the bottom of the detection groove G. On the other hand, a side wall 120 is formed around the detection groove G. Further, the strain detection substrate 400 is disposed on the bottom surface of the detection groove G (the top surface of the diaphragm portion 110).

  Here, for convenience of explanation, an XYZ three-dimensional orthogonal coordinate system is defined by taking the origin O at the center position of the strain detection substrate 400 and taking the X, Y, and Z axes in the directions shown in the figure. That is, in the top view of the upper stage, the X axis is defined in the right direction, the Y axis is defined in the upward direction, and the Z axis is oriented in a direction perpendicular to the paper surface. In the lower side view, the X axis is defined in the right direction, the Z axis is defined in the upper direction, and the Y axis is oriented in a direction perpendicular to the paper surface.

  As shown in the upper plan view of the upper stage, the strain body 100 is configured by a plate-like member having an upper surface and a lower surface parallel to the XY plane. On the other hand, in the example shown here, the force receiving body 300 is also constituted by a plate-like member having an upper surface and a lower surface parallel to the XY plane. The force receiving body 300 is not necessarily a plate-like member, but in order to reduce the size of the apparatus, it is practically preferable that the force-receiving body 300 is constituted by a plate-like member having an upper surface and a lower surface parallel to the XY plane. In particular, in the case of the illustrated example, the strain body 100 and the force receiving body 300 are configured by disk-shaped members having the same diameter, and are arranged so that the Z axis is the central axis. In the figure, the force receiving body 300 is completely overlapped with the strain body 100.

  The force receiving body 300 is disposed below the strain generating body 100 with a predetermined interval, and the two are connected by the connecting member 200. The connecting member 200 is constituted by a columnar member (in this example, a columnar member) disposed on the Z-axis, and the upper end thereof is connected to the center of the lower surface of the diaphragm portion 110, and the lower end thereof is a power receiving body. 300 is connected to the center of the upper surface. In the case of the example shown here, the strain body 100, the connecting member 200, and the force receiving body 300 are made of the same material (for example, a metal having a linear expansion coefficient close to that of a silicon substrate such as Kovar or 42-alloy, or stainless steel or aluminum. Etc.) is formed of an integral structure made of a metal. Therefore, the connection part between the strain body 100 and the connection member 200 and the connection part between the connection member 200 and the force receiving body 300 are not joined by an adhesive or the like, but are constituted by a continuous structure made of the same material.

  The petal-like cover 180 depicted in the top view in the upper part of FIG. 3 functions as a lid that covers the upper part of the detection groove G. As will be described later, the planar shape of the detection groove G has a petal shape that is slightly smaller than the contour shape of the cover 180. The detection groove G drawn by a broken line in the lower side view shows the contour position of the detection groove G when the strain body 100 is cut along the XZ plane. As shown in the upper part of FIG. 3, screw holes 151, 152, 153, and 154 are formed in the side wall 120 of the strain body 100 (these screw holes are not shown in the lower side view). The circuit board 500 protruding outward from the side wall 120 of the strain generating body 100 is a board for mounting the detection circuit, and one end of the circuit board 500 reaches the detection groove G.

  The basic structure inside the force sensor will become clearer with reference to FIG. 4 shows a top view (upper figure (a)) showing a state where the cover 180 of the basic structure shown in FIG. 3 is removed and a side sectional view (lower figure (b)) cut along the XZ plane. Has been. Here, in the upper plan view of the upper stage, the hatched portion by dots sandwiched between the petal-like contours f1 and f2 is an area of the cover adhesion portion 190 for adhering the peripheral portion of the lower surface of the cover 180 (Hatching is for indicating a region, not for a cross section).

  As shown in the side sectional view of the lower part of FIG. 4, the cover bonding portion 190 is a stepped portion formed at a position lower than the upper surface of the strain generating body 100 by a dimension corresponding to the thickness of the cover 180. Moreover, the petal-like outline f2 shown in the upper part of FIG. 4 matches the outline shape of the cover 180 shown in FIG. Therefore, if adhesive is applied to the portion of the cover adhesive portion 190 shown hatched in the figure and the cover 180 is fitted to the stepped portion from above, the peripheral portion of the lower surface of the cover 180 is fixed to the cover adhesive portion 190. can do.

  On the other hand, the inner contour f <b> 1 of the cover bonding portion 190 indicates the contour of the detection groove G. That is, a detection area corresponding to the inside of the petal-like contour f1 is defined at the center of the upper surface of the strain body 100, and the detection area is directed toward the lower surface side of the strain body 100. A detection groove G having a uniform depth is formed. The lower side sectional view of FIG. 4 shows a section obtained by cutting the basic structure along the XZ plane, so that only a part of the longitudinal section of the detection groove G appears, but the upper side view of FIG. As described above, the detection groove G has a petal-like planar shape. The depth of the detection groove G is uniform, and a petal-shaped diaphragm portion 110 having a uniform thickness is formed at the bottom of the detection groove G. Since the diaphragm part 110 is thin, when it receives the effect | action of the force used as a detection target, it will bend (mechanical deformation). As illustrated, the lower surface of the diaphragm 110 and the lower surface of the side wall 120 are located on the same plane.

  The strain detection substrate 400 is a square semiconductor substrate having an upper surface and a lower surface that are parallel to the XY plane, and is arranged so that the Z axis is the central axis. As shown in the top view in the upper part of FIG. 4, the petal-like planar shape of the detection groove G is a shape suitable for accommodating the square-shaped strain detection substrate 400. 4, the strain detection substrate 400 is bonded to the bottom surface of the detection groove G (that is, the upper surface of the diaphragm portion 110) so that the stress generated by the deformation of the diaphragm portion 110 is transmitted. (Specifically, the strain detection substrate 400 is bonded to the upper surface of the diaphragm 110 by applying an adhesive to the entire lower surface).

  A piezoresistive element A is formed at a predetermined location on the upper surface of the strain detection substrate 400 (not shown in the lower side sectional view). In the example shown here, the strain detection substrate 400 is configured by a silicon substrate, and the piezoresistive element A can be configured as a region in which P-type or N-type impurities are implanted into the upper surface layer of the silicon substrate. In the example shown in the figure, eight sets of piezoresistive elements A are arranged in the immediate vicinity of the position of the connecting member 200 indicated by a broken line, but the number and arrangement of the piezoresistive elements are not limited to this example. . Regarding the number of piezoresistive elements and variations in arrangement, some examples will be described in §5.

  In short, the strain detection substrate 400 used in the present invention has a top surface and a bottom surface that are parallel to the XY plane, and is joined to the bottom surface of the detection groove G so that stress generated by the deformation of the diaphragm 110 is transmitted. As long as a piezoresistive element is formed at a predetermined position, it is sufficient. On the circuit board 500, a detection circuit (not shown) that outputs an electric signal indicating the force received by the force receiving body 300 based on a change in the electric resistance of the piezoresistive element A is mounted. Specific examples of the configuration of the detection circuit will be described in several embodiments in §5.

  As a result, the force sensor according to the present invention includes a force receiving body 300 that receives a force to be detected, a strain generating body 100 having a diaphragm portion 110 that deforms based on the force received by the force receiving body 300, and a receiving body. The connecting member 200 that connects the force body 300 and the diaphragm unit 110, the strain detection substrate 400 that is arranged at the position of the origin O of the XYZ three-dimensional orthogonal coordinate system and is joined to the diaphragm unit 110, and the force to be detected. A force sensor that detects a force component in a predetermined axis direction or a moment component around a predetermined axis in an XYZ three-dimensional orthogonal coordinate system. It will be.

  Screw holes 151, 152, 153, and 154 formed in the side wall portion 120 of the strain body 100 are through holes (screws are not cut) for fixing the strain body 100 to the first external object. is there. 4 shows a state where screws N1 and N2 are inserted through the screw holes 151 and 152, respectively. Similarly, screws N3 and N4 are inserted through the screw holes 153 and 154, respectively. These four screws N <b> 1 to N <b> 4 are arranged in the female screw in the screw hole formed in the first object (not shown) arranged above the strain body 100 or the upper part of the screw hole. Screw onto the nut. Therefore, the strain body 100 is firmly fixed to the first object (not shown) disposed above by the four screws N1 to N4.

  As shown in the side sectional view of the lower part of FIG. 4, openings 321 and 322 are provided on the outer periphery of the force receiving body 300. Here, the opening 321 is formed at a position directly below the screw hole 151, and the opening 322 is formed at a position directly below the screw hole 152. These openings 321 and 322 are used to insert an instrument (driver) for rotating the screws N1 and N2 inserted through the screw holes 151 and 152. Similarly, an opening 323 for inserting an instrument for rotating the screw N3 is formed at a position directly below the screw hole 153, and a position for rotating the screw N4 at a position directly below the screw hole 154. An opening 324 for insertion of the instrument is formed.

  FIG. 5 is a bottom view of the basic structure shown in FIG. 3, and FIG. 6 is a bottom view showing a state where four screws N1 to N4 are inserted into the basic structure shown in FIG. As described above, an instrument (driver) for rotating the screws N1, N2, N3, and N4 inserted through the screw holes 151, 152, 153, and 154 of the strain generating body 100 is provided on the outer periphery of the force receiving body 300. Openings 321, 322, 323, and 324 (in this example, U-shaped notches formed from the outer periphery of the force receiving member 300 toward the central axis) are formed.

  A user of this force sensor uses these openings 321, 322, 323, 324 to attach four screws N 1 to N 4 from the lower surface side of the force receiving body 300 to the screw holes 151, 152 of the strain generating body 100. , 153, and 154, and the four screws N1 to N4 can be fixed to the first object by rotating with an instrument (driver). FIG. 6 shows a state in which the fixing with the four screws N1 to N4 is completed in this way.

  While the openings 321, 322, 323, and 324 are formed at positions in the X-axis or Y-axis direction, respectively, the force receiving body 300 is located at a position shifted by 45 ° in the outer peripheral portion of the force receiving body 300. Is formed with screw holes 351, 352, 353, and 354 for fixing to the second object disposed below.

  FIG. 7 is a top view (upper view (a)) and a side sectional view (lower view (b)) showing a state where the cover 180 of the basic structure shown in FIG. 3 is removed. Here, the top view in the upper part of FIG. 7 corresponds to the top view in the upper part of FIG. 4 rotated by 45 ° clockwise, and the side sectional view in the lower part of FIG. 7 shows the structure shown in the upper part of FIG. The cross section cut | disconnected in the position of WW is shown. Therefore, screw holes 351 and 352 appear in this side sectional view. Inside the screw holes 351, 352, 353, and 354 formed in the force receiving body 300, female screws are formed, and the tips of the four screws led out from the second object side disposed below. Screwed into the part. Thereby, the force receiving body 300 can be firmly fixed to the second object (not shown) disposed below.

  The contour shape of the detection groove G shown in the lower side sectional view of FIG. 7 is different from the contour shape of the detection groove G shown in the lower side sectional view of FIG. This is because the latter shows a cross section at the position of the cutting line WW, whereas the latter shows a cross section by the XZ plane. The lower side sectional view of FIG. 7 clearly shows how the cover adhesive portion 190 is formed by the step structure generated by the difference between the contours f1 and f2. The side wall 120 of the strain body 100 is provided with an insertion port penetrating from the outside toward the detection groove G, and the circuit board 500 on which the detection circuit is mounted is inserted and fixed in the insertion port. Is also clearly shown. A bonding wire 470 is included between each piezoresistive element A (not shown in the lower side sectional view) provided on the upper surface of the strain detection substrate 400 and the detection circuit provided on the circuit substrate 500. Wiring is applied (if necessary, a bonding pad may be provided on the upper surface of the strain detection substrate 400).

  As shown in FIG. 5, the orthographic projection image of the screw holes 151, 152, 153, 154 of the strain generating body 100 on the XY plane is arranged on the X axis or the Y axis, whereas the force receiving body Orthographic projection images of 300 screw holes 351, 352, 353, and 354 on the XY plane are arranged on an axis obtained by rotating the X axis or the Y axis by 45 °, and the former and the latter are mutually on the XY plane. It is formed at a position that does not overlap. For this reason, interference with the four screws for fixing the strain body 100 to the first object and the four screws for fixing the force receiving body 300 to the second object can be prevented.

  On the other hand, orthographic projection images of the screw holes 151, 152, 153, and 154 of the strain generating body 100 on the XY plane and the XY planes of the openings 321, 322, 323, and 324 provided in the force receiving body 300 are displayed. Are formed at positions overlapping each other. Therefore, the operation | work which inserts a screw in each screw hole, and the operation | work which rotates each screw can be performed using each opening part.

  In the example shown here, the strain body 100 is configured by a disk-shaped member having the Z axis as the central axis, and the strain detection substrate 400 is configured by a square substrate having the Z axis as the central axis. . Then, as shown in the top view in the upper part of FIG. 4, a petal-like detection groove G is formed in the strain generating body 100 so as to accommodate the square strain detection substrate 400. The screw holes 151, 152, 153, 154 of the strain body 100 are arranged at positions avoiding the four petal positions of the petal-like detection grooves G, and space is provided for the disk-shaped strain body 100. An efficient arrangement is realized.

  That is, screw holes 151 and 152 are arranged at respective outer positions of the opposite side on a line connecting the midpoints of a set of opposite sides of the square constituting the strain detection substrate 400 (X axis in the illustrated example). Screw holes 153 and 154 are arranged at positions outside the opposite side on a line connecting the midpoints of a pair of opposite sides (in the example shown, the Y axis). By adopting such an arrangement, it becomes possible to efficiently arrange the square-shaped strain detection substrate 400 and a total of four screw holes inside the disc-shaped strain generating body 100, and the overall size of the apparatus can be reduced. It can contribute to the conversion.

<<< §3. Advantages of force sensor according to the present invention >>
Subsequently, the merit of the force sensor according to the present invention will be described by comparing the structure of the conventional device described in §1 with the structure of the device according to the present invention described in §2. In §1, the problems of the conventional device are listed as factors that hinder downsizing, factors that cause an increase in manufacturing cost, and factors that lower reliability with respect to the connecting portion. However, the force sensor according to the present invention has these problems. Will be resolved. Hereinafter, it demonstrates in order.

  First, in the conventional force sensor, in order to be able to detect the stress generated on the outer peripheral edge (positions L1 and L4 in FIG. 2) of the washer-shaped diaphragm portion 11, the outer dimension of the strain detection substrate 40 is detected. Needs to be larger than the outer diameter of the diaphragm portion 11. This becomes a factor that hinders downsizing of the entire apparatus. In other words, in the conventional apparatus, as shown in FIG. 1, the piezoresistive elements K2 and K3 are arranged inside the strain detection substrate 40, and the piezoresistive elements K1 and K4 are arranged outside as well. It is necessary to prepare a strain detection substrate 40 having a size (a size slightly larger than the diaphragm portion 11) that can arrange the piezoresistive elements K1 to K4 side by side, and the size of the strain generating body 10 is necessarily large. I have to be.

  On the other hand, in the present invention, as shown in the side view in the lower part of FIG. 3, when the positions L5 to L8 are defined, the detection of the stress generated at the outer peripheral edge (positions L5 and L8) of the diaphragm 110 is basically performed. A method of detecting the force acting on the basis of the stress generated at the inner peripheral edge (positions L6 and L7) is employed. Therefore, the piezoresistive element A may be arranged inside the strain detection substrate 400 (positions L6 and L7 in the lower part of FIG. 3) as shown in the top view of the upper part of FIG. In this embodiment, reference elements arranged at different positions are used in combination).

  As described above, in the present invention, since the policy of not detecting the stress generated at the outer peripheral edge (positions L5 and L8) of the diaphragm portion 110 is adopted, it is not necessary to make the size of the strain detection substrate 400 larger than the size of the diaphragm 110. . As can be seen from the side cross-sectional view in the lower part of FIG. 4 and the side cross-sectional view in the lower part of FIG. 7, the strain detection substrate 400 is accommodated in the detection groove G and has a slightly smaller size than the diaphragm portion 110. ing. For this reason, it is possible to reduce the size of the entire apparatus as compared with the conventional apparatus.

  Actually, in the sample made by the inventor of the present application, the strain generating body 100 and the force receiving body 300 are configured by using a disk having a diameter of about 10 mm and a thickness of about 2 to 3 mm, and the strain detection substrate 400 is a square having a side of about 5 mm. It was possible to construct using a silicon substrate. Further, when a stainless steel disk is used as the strain generating body 100, if the thickness of the diaphragm portion 110 is about 1 mm, mechanical deformation having sufficient sensitivity as a force sensor used for a general robot arm or the like is caused. I was able to. Note that the thickness of the strain detection substrate 400 is smaller than the thickness of the diaphragm portion 110 (for example, about half the thickness) so that the mechanical deformation generated in the diaphragm portion 110 can be sufficiently transmitted to the strain detection substrate 400. It is preferable to set to.

  The second problem of the conventional force sensor is that the shape of the basic structure is complicated, so that the manufacturing process is complicated and the manufacturing cost increases. As shown in FIG. 2, the strain body 10 needs to be processed to form the groove G1 on the upper surface and to form the groove G2 on the lower surface. That is, in order to form the diaphragm portion 11 by the groove G2 formed on the lower surface side and dispose the strain detection substrate 40 having a size larger than that of the diaphragm portion 11, it is necessary to form the groove G1 on the upper surface side. Eventually, an assembly process is required in which the force receiving body 30 is prepared separately from the strain generating body 10 and the force receiving body 30 is connected after the lower surface of the strain generating body 10 is processed.

  On the other hand, in the present invention, as shown in the side view in the lower part of FIG. Since the lower surface of the diaphragm part 110 and the lower surface of the side wall part 120 are located on the same plane, the lower surface of the strain generating body 100 is a flat surface, and there is no need to dig a groove in the lower surface.

  In fact, in the apparatus according to the present invention, the basic structure composed of the strain generating body 100, the connecting member 200, and the force receiving body 300 can be constituted by an integral structure made of the same material, which greatly reduces the manufacturing cost. be able to. Specifically, this basic structure can be produced by the following process.

  First, a material rod made of a metal material such as Kovar, 42-alloy, stainless steel, aluminum (not necessarily a metal as long as it is a material capable of constituting the diaphragm portion 110 having flexibility) is used. prepare. In the case of the illustrated example, it is preferable to prepare a metal cylindrical bar. Here, for convenience of explanation, as shown in the lower diagram of FIG. 3, an XYZ three-dimensional orthogonal coordinate system in which the Z axis is defined in the upward direction is considered, and on this coordinate system, the central axis is on the Z axis. Let's assume that the rods are arranged so that

  First, a side surface machining step is performed in which a portion of the material bar whose Z coordinate value exceeds α and falls within the range of β is cut from the side surface so that only a portion near the central axis remains. Α and β shown in the side view at the bottom of FIG. 3 indicate positions according to the Z coordinate value. In short, by performing cutting from the side surface on the section between the positions α to β, the cylindrical connection member 200 is formed by the vicinity of the central axis.

  Subsequently, a detection region (region inside the contour f1 shown in the top view in the upper part of FIG. 4) is defined at the center of the upper end surface of the material rod, and the detection region is cut downward. A detection groove G is formed. Then, the force receiving body 300 is constituted by the portion where the Z coordinate value of this material bar is α or less, the connecting member 200 is constituted by the portion where the Z coordinate value exceeds α and falls within the range of β, and Z The strain body 100 can be constituted by a portion having a coordinate value equal to or larger than β, and these become an integral structure made of the same material.

  Finally, if necessary, a process of forming the cover bonding portion 190 on the upper end surface (a process of shallowly digging a region between the contours f1 and f2 shown in the top view in the upper part of FIG. 4), and a screw hole 151 Processing for forming ˜154, 321 to 324 and openings 351 to 354 and processing for forming an insertion port for inserting the circuit board 500 may be performed.

  As described above, in the force sensor according to the present invention, the basic structure can be mass-produced by machining with respect to one material bar. Therefore, the manufacturing process is simplified and the manufacturing cost can be greatly reduced. .

  A third problem of the conventional force sensor is that it is necessary to connect the strain generating body 10 and the force receiving body 30 that are prepared as separate bodies, and the reliability of the connection portion is reduced. is there. If the connection with the screw N is performed as in the example shown in FIG. 1, the reliability of the connection portion is lost due to the loosening of the screw N, and the force receiving body 30 may fall off. Moreover, when both are fixed with an adhesive, a hysteresis characteristic that adversely affects detection occurs.

  In the force sensor according to the present invention, the basic structure including the force receiving body 100, the connecting member 200, and the strain generating body 300 can be constituted by an integral structure made of the same material. With such a configuration of an integral structure, sufficient reliability can be obtained for the connecting portions, and a highly durable device can be realized.

<<< §4. Piezoresistive element arrangement >>
In §2, the configuration of the basic structure of the force sensor according to the present invention has been described. Here, the basic policy regarding the arrangement of the piezoresistive elements provided on the strain detection substrate 400 will be described.

  First, let us consider how the diaphragm 110 is deformed and what stress is applied to the strain detection substrate 400 when an external force is applied to the force sensor described in Section 2. FIG. 8 is a side sectional view on the XZ plane showing a deformation state when the moment component + My around the Y-axis acts on the basic structure shown in FIG. In the figure, the Y axis is an axis that is oriented in the depth direction perpendicular to the paper surface at the origin O.

  In the present application, the sign of the moment component around the specific coordinate axis is positive in the rotation direction for advancing the right screw in the positive direction of the specific coordinate axis. Therefore, in the example shown in the figure, the moment component + My is a force that rotates the force receiving body 300 clockwise about the Y axis as the center axis, and the moment component -My is a force receiving body about the Y axis as the center axis. This is the force to rotate 300 counterclockwise.

  When the moment component + My acts on the force receiving body 300 in a state in which the strain generating body 100 is fixed, the diaphragm 110 and the strain detection substrate 400 are deformed as illustrated. As a result, a stress as indicated by an arrow is applied to the upper surface of the strain detection substrate 400. That is, when attention is focused on the vicinity of the center of the upper surface of the strain detection substrate 400 (the immediate vicinity of the outside of the connection region of the connection member 200), stress in the extending direction (tensile stress) is applied on the left side of the drawing, and shrinking on the right side of the drawing. Stress (compressive stress) is applied. As a result, a change occurs in the electric resistance of the piezoresistive element arranged at each position.

  For example, in the case of a P-type piezoresistive element formed on a silicon substrate, the resistance value increases when a stress in the extending direction acts, and the resistance value decreases when a stress in the contracting direction acts. In the case of an N-type piezoresistive element, the opposite result occurs. Therefore, if a detection circuit for detecting such a change in the resistance value of the piezoresistive element is provided on the circuit board 500, the external force component acting on the force receiving body 300 can be detected as an electric signal.

  The stress applied to each piezoresistive element varies depending on the type of external force component acting on the force receiving body 300. For example, when the negative moment component -My acts, a deformation mode that is reversed from the left and right of FIG. 8 is obtained. FIG. 9 is a side sectional view on the XZ plane showing a deformation state when the force component + Fz in the Z-axis direction acts on the basic structure shown in FIG. When the central portion of the strain detection substrate 400 is pushed upward (Z-axis positive direction) and attention is paid to the vicinity of the center of the upper surface of the strain detection substrate 400, stress is applied in the extending direction at either the left or right position. When a negative force component -Fz (a force component directed downward in FIG. 9) is applied, on the contrary, stress is applied in a contracting direction at either the left or right position.

  As a result of investigation by the inventor of the present application, the strength of the stress generated on the upper surface of the strain detection substrate 400 when various external force components are applied to the force receiving member 300 is concentrated on the outermost portion of the connection region of the connection member 200. There was found. That is, in the top view in the upper part of FIG. 7, the stress concentrates on the outermost portion of the area of the connection member 200 indicated by the broken-line circle. In the example shown in the figure, the eight piezoresistive elements A are arranged in the immediate vicinity of the outside in order to increase the detection sensitivity by arranging the piezoresistive elements at locations where stress is concentrated.

  In the present application, in this way, on the upper surface of the strain detection substrate 400, the piezoresistive element (that is, the upper end surface of the connection member 200 is aligned with the upper surface of the strain detection substrate 400). When a projection image is formed by projective projection, a piezoresistive element arranged in the immediate vicinity of the outside of the projection image is referred to as a “center element”. The eight sets of piezoresistive elements A shown in FIG. 7 are all “central elements”. Since these central elements are arranged at locations where stress is concentrated, they have a high detection sensitivity with respect to an external force component acting on the force receiving body 300.

  The force sensor according to the present invention is premised on performing detection using this central element, and at least a part of the piezoresistive element formed on the strain detection substrate 400 is constituted by the central element. Note that some of the embodiments described below also utilize piezoresistive elements (referred to as “reference elements”) other than the central element. In the drawings of the present application, the “central element” is indicated by reference signs A, B, C, and D, and the “reference element” is indicated by reference signs P, Q, R, and S to distinguish them.

  In practice, the arrangement pattern of the central elements A to D is preferably symmetrical with respect to the XZ plane and the YZ plane. The eight sets of piezoresistive elements A in the example shown in FIG. 7 and the central elements A to D in each example described later are all the same size of resistive elements and are symmetrical with respect to the XZ plane and the YZ plane. An arrangement pattern is formed. If such symmetry is maintained, the offset voltage of the detected value of each axis component output from the bridge circuit described later becomes zero, so that adjustment is facilitated. Further, since the sides of the bridge are the same, the temperature characteristics are also improved.

  By the way, in order to detect the force received by the force receiving body as an electric signal based on the change in the electric resistance of the piezoresistive element, it is preferable to perform difference detection using a bridge circuit as will be described later. This is because the electrical characteristics of the piezoresistive elements also change when the actual usage environment (especially the temperature environment) of the force sensor changes, so if the absolute value of the electrical resistance of each piezoresistive element is used as it is as a detected value, This is because the influence of the environment or the like appears in the detected value as it is, and the correct detected value cannot be output. By using a bridge circuit that can output the difference in change in electrical resistance between the two sets of piezoresistive elements as a detection value and maintaining the bridge in a state where the force to be detected is not acting, This makes it possible to accurately detect the influence of the actual usage environment.

  In the case of the conventional apparatus shown in FIG. 1, the piezoresistive elements K2 and K3 correspond to the central element in the present invention. By using an outer edge element such as the piezoresistive elements K1 and K4, difference detection can be performed. ing. That is, in the conventional apparatus, by utilizing the difference in the stress generation mode between the central portion and the outer edge portion of the strain detection substrate 40, difference detection is performed by arranging piezoresistive elements at both the central portion and the outer edge portion. Is possible.

  On the other hand, in the case of the apparatus according to the present invention, although stress is concentrated at the central portion of the strain detection substrate 400 (the portion immediately outside the connection region of the connection member 200), a slight stress is generated at the outer edge portion. Only occurs. That is, in the case of the conventional apparatus shown in FIG. 2, significant stress generation is observed at all the positions L1, L2, L3, and L4. In the case of the apparatus according to the present invention shown in FIG. However, significant stress generation is not observed at the outer edge portion of the strain detection substrate 400 (in the vicinity of the positions L5 and L8). This is presumably because the outer edge portion of the strain detection substrate 400 does not extend to the positions where the positions L5 and L8 are crotched. For this reason, in order to perform difference detection in the present invention, some device is required. Hereinafter, these devices will be described based on specific examples.

<<< §5. Configuration and detection operation of specific embodiment >>
Here, specific arrangement examples of the piezoresistive elements provided on the strain detection substrate 400 will be described as individual embodiments. Each of the embodiments has a common feature that at least a part of the piezoresistive elements is constituted by a central element (piezoresistive element disposed in the immediate vicinity of the projected image of the upper end surface of the connection member 200). ing. In each of the following embodiments, an example using a P-type piezoresistive element is shown except for the fifth embodiment (of course, an N-type piezoresistive element may be used instead. However, in this case, it is necessary to consider the configuration of the bridge circuit). Each piezoresistive element has a longitudinal direction in which a current flows, and wiring for each piezoresistive element is performed at both ends in the longitudinal direction.

<5-1. First Example>
FIG. 10 is a top view showing a first embodiment of a piezoresistive element arrangement pattern in the force sensor according to the present invention. This arrangement pattern is the same as the arrangement pattern shown in FIG. 4 and FIG. Has been. In addition, the hatching in FIG. 10 indicates the formation region of the piezoresistive elements A1 to A8, and does not indicate a cross section (the same applies to the top view of each strain detection substrate 400 below).

  Specifically, in the case of this embodiment, the first center element A1 and the second center element A1 are arranged on the upper surface of the strain detection substrate 400 along the X-axis positive region so that the X-axis direction is the longitudinal direction. The central element A2, the third central element A3 and the fourth central element A4 arranged along the X-axis negative region so that the X-axis direction is the longitudinal direction, and the Y-axis direction is the longitudinal direction. As described above, the fifth central element A5 and the sixth central element A6 arranged along the Y-axis positive area, and the first central element A5 arranged along the Y-axis negative area so that the Y-axis direction becomes the longitudinal direction. 7 central elements A7 and an eighth central element A8 are provided.

  Here, the 1st-8th center element A1-A8 is comprised by the piezoresistive element of the same material and the same size, The electrical property becomes the same. Therefore, if stress is applied to each element under the same condition, the same resistance value change occurs. Further, the arrangement pattern of the central elements A1 to A8 is symmetrical with respect to the XZ plane and the YZ plane, and the planar pattern shown in the top view of FIG. The axis is also a line-symmetric figure.

  FIG. 11 is a table showing changes in resistance values of the piezoresistive elements A1 to A8 in the first embodiment shown in FIG. Each column in the row labeled “+ Mx” in the figure indicates a change in resistance value when a moment component + Mx about the positive X-axis acts on the force receiving body 300, and each column in the row labeled “+ My”. Indicates a change in resistance value when a moment component + My about the positive Y-axis acts on the force receiving body 300, and each column in the row labeled “+ Fz” indicates the force in the Z-axis positive direction on the force receiving body 300. The resistance value change when the component + Fz acts is shown. Here, “+” indicates that the resistance value increases, “−” indicates that the resistance value decreases, and “0” indicates that the resistance value does not change (for each example described later) The same is true for the table).

  In the table of FIG. 11, it can be easily understood that the result of the column “+ My” becomes like this by looking at the modification of FIG. 8. In consideration of the deformation mode of FIG. 8, in the top view shown in FIG. 10, stress contracting in the longitudinal direction acts on the elements A1 and A2, the resistance value decreases, and stress extending in the longitudinal direction on the elements A3 and A4. It can be seen that the resistance value increases due to the action. On the other hand, for the elements A5 to A8, since the stretching stress in the longitudinal direction is not generated, the resistance value does not change. The reason why the result in the column “+ Mx” is obtained is also the same.

  On the other hand, the fact that the result in the column “+ Fz” is like this can be easily understood by looking at the modification of FIG. If the deformation | transformation aspect of FIG. 9 is considered, in the top view shown in FIG. 10, it turns out that the stress which extends to a longitudinal direction acts on all the central elements A1-A8, and resistance value increases. In addition, when reverse-direction moment components “−Mx” and “−My” and a reverse direction force component “−Fz” are applied, the result of reversing the signs shown in the table of FIG. 11 is obtained. Become.

  Based on the results shown in the table of FIG. 10, it can be seen that the detection circuit shown in FIGS. 12 and 13 can detect the moment component My around the Y axis and the moment component Mx around the X axis.

  In the detection circuit shown in FIG. 12, the first central element A1 and the second central element A2 are arranged on the first opposite side, and the third central element A3 and the fourth central element A4 are arranged on the second opposite side. This is a circuit for detecting the moment component My around the Y-axis using the Wheatstone bridge arranged in FIG. When a predetermined power supply voltage is supplied from the DC power supply E, the terminals Ty1 and Ty2 maintain an equipotential while the bridge maintains the equilibrium condition. However, when the equilibrium state is lost, a potential difference Vy is generated between the two terminals. It will be. This potential difference Vy becomes an electric signal indicating the direction and magnitude of the moment component My around the Y axis.

  For example, when the moment component + My acts, as shown in the table of FIG. 11, the resistance values of the central elements A1 and A2 decrease and the resistance values of the central elements A3 and A4 increase, so that the terminal Ty1 side is positive and the terminal Ty2 side is positive. A negative voltage Vy is generated. When the counterclockwise moment component -My is applied, the sign of the voltage Vy is reversed. Further, if the applied moment component is large, the absolute value of the voltage Vy is also large.

  Similarly, in the detection circuit shown in FIG. 13, the fifth central element A5 and the sixth central element A6 are arranged on the first opposite side, and the seventh central element A7 and the eighth central element A8 are arranged on the first side. 2 is a circuit that detects a moment component Mx around the X-axis using a Wheatstone bridge disposed on the opposite side of 2. When a predetermined power supply voltage is supplied from the DC power supply E, the terminals Tx1 and Tx2 maintain an equipotential while the bridge maintains the equilibrium condition. However, when the equilibrium state is lost, a potential difference Vx occurs between the terminals. It will be. This potential difference Vx becomes an electric signal indicating the direction and magnitude of the moment component Mx around the X axis.

  Note that when the moment component Mx acts, the resistance values of the central elements A1 to A4 do not change, so the detection circuit shown in FIG. 12 does not erroneously detect the moment component Mx. Further, when the force component Fz is applied, all the resistance values of the central elements A1 to A8 are increased. Therefore, the detection circuit shown in FIG. 12 maintains the equilibrium condition of the bridge and erroneously applies the force component Fz. There is no detection. Similarly, the detection circuit shown in FIG. 13 does not erroneously detect the moment component My and the force component Fz. As described above, the detection circuits shown in FIGS. 12 and 13 can obtain an accurate detection value in which interference of other axis components is eliminated.

  The detection circuits shown in FIG. 12 and FIG. 13 are both circuits that perform differential detection using a Wheatstone bridge, so that each piezoresistive element is changed depending on the actual usage environment (especially temperature environment) of the force sensor. Even if a change occurs in the electrical characteristics, the effect is not output as a detected value. For example, even if the electrical resistance of the eight sets of piezoresistive elements increases or decreases due to temperature changes, these increases and decreases are phenomena that occur for all eight sets of piezoresistive elements. The balanced condition of the bridge circuit is maintained as it is, and no detection voltage is output. As described above, the detection circuits shown in FIGS. 12 and 13 can perform accurate detection without the influence of the actual use environment.

  Since the moment component My detection circuit shown in FIG. 12 and the moment component Mx detection circuit shown in FIG. 13 are completely independent circuits, if only one of the detection is sufficient, the necessary central element and It is sufficient to prepare only the detection circuit. For example, when it is sufficient to detect the moment component My, it is sufficient to prepare the central elements A1 to A4 and the detection circuit of FIG. 12, and it is not necessary to provide the central elements A5 to A8 and the detection circuit of FIG. Further, even when both of the moment components My and Mx are detected using the eight sets of the central elements A1 to A8, the central elements A1 to A4 for detecting the moment component My are made of piezoresistive elements having the same material and the same size. If the central elements A5 to A8 for detecting the moment component Mx are composed of piezoresistive elements having the same material and the same size, all the central elements A1 to A8 are not necessarily composed of piezoresistive elements having the same material and the same size. There is no need to configure it.

  After all, the basic concept of the first embodiment is that the central element is arranged at a position where a stress is applied in a direction in which the central element is extended by the action of a predetermined detection target component (for example, moment component My) ( For example, A3, A4) and a second group of central elements (for example, A1, A2) arranged at positions where stress in the direction of contraction due to the action of the detection target component is applied, and the detection circuit includes: By detecting the detection target component using a Wheatstone bridge in which the central element belonging to the first group is arranged on the first opposite side and the central element belonging to the second group is arranged on the second opposite side, In detecting My or Mx, the difference detection using only the central element is enabled.

<5-2. Second Embodiment>
FIG. 14 is a top view showing a second embodiment of the piezoresistive element arrangement pattern in the force sensor according to the present invention. In this arrangement pattern, two sets of reference elements P1 and P2 are used together with four sets of central elements B1 to B4. The four sets of central elements B1 to B4 are piezoresistive elements arranged in the immediate vicinity of the projected image of the upper end surface of the connection member 200, whereas the two sets of reference elements P1 and P2 are detected objects. This is a piezoresistive element arranged at a position where a significant stress change does not occur even when the diaphragm 110 is deformed by the action of the force.

  In the case of the illustrated example, the reference elements P <b> 1 and P <b> 2 are disposed in the vicinity of the periphery of the strain detection substrate 400. When the structure of the force sensor according to the present invention described in §2 is adopted, as described above, even if various external force components are applied to the force receiving body 300, the stress generated in the strain detection substrate 400 is generated by the connection member 200. There is no significant stress change in the vicinity of the periphery of the strain detection substrate 400, concentrated in the immediate vicinity of the connection portion. Therefore, the resistance values of the reference elements P1 and P2 arranged in the vicinity of the periphery of the strain detection substrate 400 are hardly affected by the action of external force. The second embodiment described here performs difference detection by incorporating such reference elements P1 and P2 into a bridge circuit.

  Specifically, in the case of this embodiment, the first central element B1 disposed along the X-axis positive region on the upper surface of the strain detection substrate 400 so that the X-axis direction is the longitudinal direction, and X The second central element B2 arranged along the X-axis negative region so that the axial direction becomes the longitudinal direction, and the second central element B2 arranged along the Y-axis positive region so that the Y-axis direction becomes the longitudinal direction 3 central element B3, the fourth central element B4 arranged along the Y-axis negative region so that the Y-axis direction is the longitudinal direction, and the first central element B4 arranged near the periphery of the strain detection substrate 400 A reference element P1 and a second reference element P2 are provided.

  Here, the first to fourth central elements B1 to B4 are constituted by piezoresistive elements of the same material and the same size. On the other hand, the first and second reference elements P1 and P2 are composed of piezoresistive elements of the same material and the same size, and the first and second references are made in a state where no force to be detected acts. The resistance values of the elements P1 and P2 are set to be twice the resistance values of the first to fourth central elements B1 to B4. More specifically, in the illustrated example, each of the reference elements P1 and P2 is configured by a piezoresistive element having the same thickness as each of the central elements B1 to B4 and twice the length. Of course, each of the reference elements P1 and P2 may be configured by a piezoresistive element having the same length as each of the central elements B1 to B4 and a thickness of 1/2 times. Alternatively, two piezoresistive elements having the same material and the same size as the central elements B1 to B4 may be used as the reference element P1 or P2.

  Further, the arrangement pattern of the central elements B1 to B4 is symmetrical with respect to the XZ plane and the YZ plane, and the planar pattern of the central elements B1 to B4 shown in the top view of FIG. The figure is line symmetric with respect to the X axis and line symmetric with respect to the Y axis.

  FIG. 15 is a table showing changes in resistance values of the piezoresistive elements B1 to B4, P1 and P2 in the second embodiment shown in FIG. In this table, the fact that the result in the column “+ My” becomes like this can be easily understood by looking at the modification of FIG. If the deformation | transformation aspect of FIG. 8 is considered, in the top view shown in FIG. 14, the stress which shrinks to a longitudinal direction will act on element B1, resistance value will decrease, and the stress which will extend to a longitudinal direction will act on element B2. It can be seen that the resistance value increases. On the other hand, in the elements B3 and B4, since no stretching stress is generated in the longitudinal direction, the resistance value does not change. In addition, as described above, the resistance values of the elements P1 and P2 do not change significantly due to the action of external force. The result in the “+ Mx” column is the same.

  On the other hand, the fact that the result in the column “+ Fz” is like this can be easily understood by looking at the modification of FIG. If the deformation | transformation aspect of FIG. 9 is considered, in the top view shown in FIG. 14, it turns out that the stress which extends to a longitudinal direction acts on all the central elements B1-B4, and resistance value increases. No significant resistance value change occurs in the elements P1 and P2. In addition, when reverse-direction moment components “−Mx” and “−My” and a force component “−Fz” in the reverse direction are applied, a result obtained by reversing the signs shown in the table of FIG. 15 is obtained. Become.

  Based on the results shown in the table of FIG. 15, it can be seen that the detection circuit shown in FIG. 16 makes it possible to detect the force component Fz in the Z-axis direction. This detection circuit includes a resistance element formed by connecting a first central element B1 and a second central element B2 in series, and a resistance formed by connecting a third central element B3 and a fourth central element B4 in series. The force component Fz in the Z-axis direction is detected using a Wheatstone bridge in which the elements are arranged on the first opposite side and the first reference element P1 and the second reference element P2 are arranged on the second opposite side. Circuit. When a predetermined power supply voltage is supplied from the DC power supply E, the two terminals Tz1 and Tz2 maintain an equipotential while the bridge maintains the equilibrium condition. However, when the equilibrium state is lost, a potential difference Vz occurs between the two terminals. It will be. This potential difference Vz is an electric signal indicating the direction and magnitude of the force component Fz in the Z-axis direction.

  As described above, since the resistance values of the elements P1 and P2 are set to be twice the resistance values of the elements B1 to B4, the bridge circuit maintains a balanced state when no external force is applied. . However, when the force component + Fz acts, as shown in the table of FIG. 15, the resistance values of the central elements B1 to B4 increase and the resistance values of the reference elements P1 and P2 do not change, so the terminal Tz1 side is positive and the terminal Tz2 side is positive. A negative voltage Vz is generated. When the force component -Fz in the reverse direction acts, the sign of the voltage Vz is reversed. If the applied force component is large, the absolute value of the voltage Vz is also large.

  Note that when the moment component Mx acts, the resistance value change of the resistance element in which the central elements B3 and B4 are connected in series is canceled, and when the moment component My acts, the resistance element in which the central elements B1 and B2 are connected in series. 16 is canceled out, the detection circuit shown in FIG. 16 does not erroneously detect the moment components Mx and My. As described above, the detection circuit shown in FIG. 15 can obtain an accurate detection value that eliminates interference of other axis components.

  Further, the detection circuit shown in FIG. 15 is a circuit that performs differential detection using a Wheatstone bridge. Therefore, the electrical characteristics of each piezoresistive element are changed depending on the actual usage environment (particularly the temperature environment) of the force sensor. Even if a change occurs, the influence is not output as a detection value. For example, even if the electrical resistances of the four sets of central elements B1 to B4 increase or decrease due to temperature changes, the electrical resistances of the two sets of reference elements P1 and P2 also increase and decrease under the same conditions. The balanced condition of the bridge circuit is maintained as it is, and no detection voltage is output. As described above, the detection circuit shown in FIG. 16 can perform accurate detection without the influence of the actual use environment.

  After all, the basic concept of the second embodiment is significant even when the diaphragm portion 110 is deformed due to the action of the force to be detected (force component Fz in this example) in addition to the central elements B1 to B4. Reference elements P1 and P2 composed of piezoresistive elements arranged at positions where no stress change occurs are further provided, and the detection circuit arranges the central elements B1 to B4 on the first opposite side, and the reference elements P1 and P2 are arranged on the second side. By detecting the component to be detected using the Wheatstone bridge arranged on the opposite side of this, it is possible to detect the difference in detecting the force component Fz.

  According to this basic concept, it is not always necessary to use four sets of the central elements B1 to B4 as the central element. For example, a bridge circuit is formed by the central elements B1 and B2 arranged on the X axis and the reference elements P1 and P2. It can also be configured. In this case, the central elements B1 and B2 arranged on the X axis may be arranged on the first opposite side, and the reference elements P1 and P2 may be arranged on the second opposite side (the resistance values of the reference elements P1 and P2 are Halved). Alternatively, a bridge circuit can be configured by the central elements B3 and B4 and the reference elements P1 and P2 arranged on the Y axis. In this case, the central elements B3 and B4 arranged on the Y axis may be arranged on the first opposite side, and the reference elements P1 and P2 may be arranged on the second opposite side (the resistance values of the reference elements P1 and P2 are Halved).

<5-3. Third Example>
FIG. 17 is a top view showing a third embodiment of the piezoresistive element arrangement pattern in the force sensor according to the present invention. In this arrangement pattern, four sets of reference elements Q1 to Q4 are used together with four sets of central elements B1 to B4. The four sets of central elements B1 to B4 are exactly the same as the central elements B1 to B4 used in the second embodiment, and the piezoresistive elements disposed in the immediate vicinity of the projected image of the upper end surface of the connection member 200. It is. On the other hand, the four sets of reference elements Q1 to Q4 are piezoresistive elements arranged at the outer positions of the central elements B1 to B4 with the Z-axis position as the inner side.

  Here, considering a case where force components Mx, My, and Fz are applied, the behavior of the resistance value change of the reference element arranged at the outer position is the change and increase / decrease in the resistance value of the central element arranged at the inner position. It reverses and the absolute value of the amount of change becomes smaller. As described above, in the basic structure of the apparatus according to the present invention, no significant stress is observed at the outer peripheral edge of the strain detection substrate 400. Therefore, the reference elements Q1 to Q4 are the piezoresistive elements K1 in the conventional apparatus shown in FIG. , K4 cannot be performed. However, as described below, it can function as a reference element for performing difference detection. In the third embodiment described here, difference detection is performed by incorporating reference elements Q1 to Q4 arranged at the outer position into the bridge circuit in addition to the central elements B1 to B4 arranged at the inner position. is there.

  Specifically, in the case of this embodiment, the first central element B1 disposed along the X-axis positive region on the upper surface of the strain detection substrate 400 so that the X-axis direction is the longitudinal direction, and X The second central element B2 arranged along the X-axis negative region so that the axial direction becomes the longitudinal direction, and the second central element B2 arranged along the Y-axis positive region so that the Y-axis direction becomes the longitudinal direction 3 central element B3, the fourth central element B4 arranged along the Y-axis negative region so that the Y-axis direction is the longitudinal direction, and the X-axis positive so that the X-axis direction is the longitudinal direction. The first reference element Q1 disposed outside the first central element B1 along the region, and the second central element B2 along the X-axis negative region so that the X-axis direction is the longitudinal direction Second reference element Q2 arranged outside the Y axis and the third center along the Y axis positive region so that the Y axis direction is the longitudinal direction. The third reference element Q3 arranged outside the element B3 and the fourth reference element arranged outside the fourth central element B4 along the Y-axis negative region so that the Y-axis direction becomes the longitudinal direction. A reference element Q4 is provided.

  Here, the first to fourth central elements B1 to B4 and the first to fourth reference elements Q1 to Q4 are composed of piezoresistive elements having the same material and the same size. The arrangement pattern of each of the central elements B1 to B4 and each of the reference elements Q1 to Q4 is symmetric with respect to the XZ plane and the YZ plane, and eight sets of piezoelectric elements shown in the top view of FIG. The planar pattern of the resistive element is a figure that is line symmetric with respect to the X axis and line symmetric with respect to the Y axis.

  FIG. 18 is a table showing changes in resistance values of the piezoresistive elements B1 to B4 and Q1 to Q4 in the third embodiment shown in FIG. In this table, “+” indicates that the resistance value increases, “−” indicates that the resistance value decreases, and “0” indicates that the resistance value does not change as described above. However, “+ δ” indicates that the resistance value slightly increases, and “−δ” indicates that the resistance value slightly decreases. Here, the slight increase means a small increase amount compared to the increase amount indicated by “+”, and the slight decrease means a small decrease amount compared to the decrease amount indicated by “−”. .

  As described above, in the basic structure of the apparatus according to the present invention, the stress generated in the strain detection substrate 400 is concentrated on the outermost portion of the projected image of the upper end surface of the connection member 200 (the arrangement portion of the central elements B1 to B4). On the outside, the magnitude of the stress is drastically reduced. In the case of the example shown in FIG. 17, the behavior of the resistance value change of the reference elements Q1 to Q4 is obtained by reversing the increase and decrease of the behavior of the resistance value change of the central elements B1 to B4, respectively, and reducing the absolute value of the change amount. . The table shown in FIG. 18 shows such a result. For example, in the column “+ Mx”, the element B3 is “+” and the element B4 is “−”, whereas the element Q3 arranged outside these elements is “−δ” and the element Q4. Is “+ δ”.

  Based on the results shown in the table of FIG. 18, it can be seen that the detection circuit shown in FIG. 19 can detect the force component Fz in the Z-axis direction. This detection circuit includes a resistance element formed by connecting a first central element B1 and a second central element B2 in series, and a resistance formed by connecting a third central element B3 and a fourth central element B4 in series. An element disposed on the first opposite side and a first reference element Q1 and a second reference element Q2 connected in series; a third reference element Q3; a fourth reference element Q4; Is a circuit that detects a force component Fz in the Z-axis direction by using a Wheatstone bridge in which resistance elements formed by connecting the two in series are arranged on the second opposite side. When a predetermined power supply voltage is supplied from the DC power supply E, the terminals Tz3 and Tz4 maintain the same potential while the bridge maintains the equilibrium condition. However, when the equilibrium state is lost, a potential difference Vz is generated between the two terminals. It will be. This potential difference Vz is an electric signal indicating the direction and magnitude of the force component Fz in the Z-axis direction.

  As described above, since the eight elements B1 to B4 and Q1 to Q4 are composed of piezoresistive elements of the same material and the same size, the bridge circuit maintains a balanced state when no external force is applied. . However, when the force component + Fz acts, as shown in the table of FIG. 18, the resistance values of the central elements B1 to B4 are greatly increased and the resistance values of the reference elements Q1 to Q4 are decreased, so that the terminal Tz3 side is positive and the terminal A voltage Vz that is negative on the Tz4 side is generated. When the force component -Fz in the reverse direction acts, the sign of the voltage Vz is reversed. If the applied force component is large, the absolute value of the voltage Vz is also large.

  When the moment component Mx acts, the resistance value change of the resistance element in which the central elements B3 and B4 are connected in series and the resistance element in which the reference elements Q3 and Q4 are connected in series is canceled, and when the moment component My acts Since the resistance value change of the resistance element in which the central elements B1 and B2 are connected in series and the resistance element in which the reference elements Q1 and Q2 are connected in series is canceled, the detection circuit shown in FIG. 19 erroneously detects the moment components Mx and My. Never do. As described above, the detection circuit shown in FIG. 19 can obtain an accurate detection value from which interference of other axis components is eliminated.

  In addition, since the detection circuit shown in FIG. 19 is a circuit that performs differential detection using a Wheatstone bridge, the electrical characteristics of each piezoresistive element can be changed depending on the actual usage environment (especially temperature environment) of the force sensor. Even if a change occurs, the influence is not output as a detection value. For example, even if the electrical resistances of the four sets of central elements B1 to B4 increase or decrease due to temperature changes, the electrical resistances of the four sets of reference elements Q1 to Q4 also increase or decrease under the same conditions. The balanced condition of the bridge circuit is maintained as it is, and no detection voltage is output. As described above, the detection circuit shown in FIG. 19 can perform accurate detection without the influence of the actual use environment.

  After all, the basic concept of the third embodiment is further provided with reference elements Q1 to Q4 made of piezoresistive elements arranged at the outer positions of the respective central elements B1 to B4 with the position of the Z axis as the inner side, and the detection circuit comprises: In detecting the force component Fz by detecting the detection target component using the Wheatstone bridge in which the central elements B1 to B4 are arranged on the first opposite side and the reference elements Q1 to Q4 are arranged on the second opposite side. It is in the point of enabling differential detection.

  According to this basic concept, it is not always necessary to use four sets of the central elements B1 to B4 as the central element. For example, a bridge circuit is configured by the central elements B1 and B2 arranged on the X axis and the reference elements Q1 and Q2. You can also In this case, the central elements B1 and B2 arranged on the X axis may be arranged on the first opposite side, and the reference elements Q1 and Q2 may be arranged on the second opposite side. Alternatively, a bridge circuit can be configured by the central elements B3 and B4 and the reference elements Q3 and Q4 arranged on the Y axis. In this case, the central elements B3 and B4 arranged on the Y axis may be arranged on the first opposite side, and the reference elements Q3 and Q4 may be arranged on the second opposite side.

  Note that in the arrangement of the piezoresistive elements shown in FIG. 17, the closer the positions of the reference elements Q1 to Q4 are closer to the outer peripheral edge of the strain detection substrate 400, the smaller the increase / decrease amount of the resistance value. ”And“ −δ ”will approach“ 0 ”. When “+ δ” and “−δ” become “0”, the third embodiment is eventually an embodiment of the same principle as the second embodiment described above. Conversely, when the positions of the reference elements Q1 to Q4 are moved closer to the center of the strain detection substrate 400, the increase / decrease amount of the resistance value becomes small at first, and after the increase / decrease amount becomes “0” at a certain position, This time, the increase / decrease relationship reverses and the increase / decrease amount increases. In other words, “+ δ” and “−δ” in the table of FIG. 18 are reversed, and the closer to the center, the larger the increase / decrease amount, and the closer to “+” and “−”. This is natural when considering that the configuration in which the reference elements Q1 to Q4 are brought to the outermost part of the connection member 200 becomes the central elements B1 to B4.

  As described above, the detection circuit shown in FIG. 19 can perform the detection function without any trouble even when “+ δ” and “−δ” in the table of FIG. 18 are reversed. For example, when the force component + Fz acts, according to the table of FIG. 18, the resistance values of the central elements B1 to B4 are greatly increased and the resistance values of the reference elements Q1 to Q4 are decreased, but the central elements B1 to B4 are decreased. Since the increase / decrease amount of the resistance value is larger than the increase / decrease amount of the resistance value of the reference elements Q1 to Q4, even if the relationship between “+ δ” and “−δ” in the table of FIG. With the detection circuit 19, a correct detection value of the force component Fz can be obtained.

  However, in this case, as the increase / decrease amount “δ” of the resistance values of the reference elements Q1 to Q4 increases, the detection sensitivity of the detection circuit shown in FIG. 19 decreases. The reference elements Q <b> 1 to Q <b> 4 are preferably arranged on the outer side of the strain detection substrate 400 as much as possible. On the other hand, in performing accurate detection that eliminates the influence of changes in the temperature environment, it is preferable that the reference elements Q1 to Q4 be placed in a temperature environment as close as possible to the central elements B1 to B4. From such a viewpoint, it is preferable to arrange the reference elements Q1 to Q4 as far as possible inside the strain detection substrate 400 (positions close to the central elements B1 to B4).

<5-4. Fourth embodiment>
FIG. 20 is a top view showing a fourth embodiment of the piezoresistive element arrangement pattern in the force sensor according to the present invention. In this arrangement pattern, four sets of reference elements R1 to R4 are used together with four sets of central elements B1 to B4. The four sets of central elements B1 to B4 are exactly the same as the central elements B1 to B4 used in the second embodiment, and the piezoresistive elements disposed in the immediate vicinity of the projected image of the upper end surface of the connection member 200. It is. On the other hand, the four sets of reference elements R1 to R4 are piezoresistive elements arranged in a direction in which the resistance change sensitivity to stress strain is small.

  The fourth embodiment described here performs differential detection by incorporating reference elements Q1 to Q4 arranged in a direction in which the resistance change sensitivity to stress strain is small in addition to the central elements B1 to B4 into the bridge circuit. Is.

  FIG. 21 is a table showing changes in resistance values of the piezoresistive elements B1 to B4 and R1 to R4 in the fourth embodiment shown in FIG. In this table, “+” indicates that the resistance value increases, “−” indicates that the resistance value decreases, and “0” indicates that the resistance value does not change (or “+” or “ The change in resistance value is negligible with respect to the change in resistance value indicated by “−”). Here, all the columns of the four sets of reference elements R1 to R4 are “0”. This is because the arrangement directions of the reference elements R1 to R4 are all in the electric resistance change sensitivity (piezoresistance coefficient) with respect to the stress strain. ) Is facing the smaller direction.

  Actually, in order to implement the fourth embodiment, it is necessary to use a substrate having unique characteristics as the strain detection substrate 400. I will explain this point below. In general, it is known that the electric resistance change sensitivity to stress strain has direction dependency. For example, considering the case where a silicon single crystal substrate is used as the strain detection substrate 400, a large difference occurs in the direction distribution of the electrical resistance change sensitivity depending on the plane orientation when cutting the silicon single crystal substrate.

  FIG. 22 is a graph showing the piezoresistance coefficient (electric resistance change sensitivity to stress strain) for each crystal plane of the silicon single crystal substrate. That is, a silicon single crystal substrate is cut out at a specific crystal plane, and the piezoresistance coefficient in each direction in the cut surface is plotted in correspondence with the distance from the origin O. The top of the figure shows a graph for the (001) plane, the bottom left of the figure shows a graph for the (110) plane, and the bottom right of the figure shows a graph for the (111) plane.

  For example, for the (001) plane, the piezoresistance coefficient has a peak value in each direction of 0 °, 90 °, 180 °, and 270 °. Therefore, the strain detection substrate 400 is configured by using a silicon single crystal substrate cut out so that the (001) plane becomes the upper surface. For example, the direction of 0 ° ([010] direction) is the X-axis positive direction, and 90 ° ([−100] direction) is the Y axis positive direction (in the specification, the minus sign indicating the crystal orientation is attached in front of the numeral 1), and four sets of centers as shown in FIG. If the elements B1 to B4 are arranged, the longitudinal directions of these four sets of the central elements B1 to B4 are all directed to the peak direction of the piezoresistance coefficient, and the stress strain can be detected with good sensitivity.

  On the other hand, in the (001) plane, a piezo in a direction forming 45 ° with respect to the peak direction, such as a 45 ° direction ([−110] direction) or a 135 ° direction ([−1-10] direction). The resistance coefficient is very small. Therefore, in the piezoresistive element arranged so that these directions become the longitudinal direction, the electric resistance change sensitivity to the stress strain becomes very small. In this way, the four sets of reference elements R1 to R4 shown in FIG. 20 are arranged in a direction in which the piezoresistance coefficient becomes very small (a direction that forms 45 ° with respect to the X axis or the Y axis). In the table shown in FIG. 21, the four reference elements R1 to R4 are all “0” because the reference elements R1 to R4 are arranged in such a specific direction. is there.

  Thus, the (001) plane of the silicon single crystal substrate has characteristics that are very convenient for use as the strain detection substrate 400 in the present invention. That is, the piezoresistance coefficient has a characteristic that the peak direction of the piezoresistance coefficient faces two axial directions orthogonal to each other and the piezoresistance coefficient is very small in a direction that forms 45 ° with respect to these two axes. On the other hand, as shown in the lower left graph of FIG. 22, the characteristics of the (110) plane are such that the two axes P and Q indicating the peak direction of the piezoresistance coefficient are not orthogonal to each other. Q cannot be used as it is as the X-axis and Y-axis in the present invention. Further, as shown in the lower right graph of FIG. 22, the characteristic of the (111) plane has no azimuth dependency and the same sensitivity can be obtained in any direction. Therefore, it can be used in the fourth embodiment. Can not.

  Therefore, in the fourth embodiment, the strain detection substrate 400 is constituted by a silicon single crystal substrate cut out by the (001) plane, and the (001) plane becomes the upper surface of the strain detection substrate 400, and the peak direction of the piezoresistance coefficient ( [010] direction and [-100] direction) must be arranged so as to be in the X-axis or Y-axis direction.

  And in this 4th Example, as shown in FIG. 20, on the upper surface of the distortion | strain detection board | substrate 400, it arrange | positioned along the X-axis positive area | region so that a X-axis direction may become a longitudinal direction. The central element B1, the second central element B2 arranged along the X-axis negative region so that the X-axis direction is the longitudinal direction, and the Y-axis positive region so that the Y-axis direction is the longitudinal direction The third central element B3 disposed along the fourth central element B4 disposed along the Y-axis negative region so that the Y-axis direction is the longitudinal direction, and the X-axis or Y-axis. First to fourth reference elements R <b> 1 to R <b> 4 are provided so that the direction forming 45 ° is the longitudinal direction.

  Here, the first to fourth central elements B1 to B4 and the first to fourth reference elements R1 to R4 are composed of piezoresistive elements having the same material and the same size. The arrangement pattern of the central elements B1 to B4 is symmetrical with respect to the XZ plane and the YZ plane, and the plane patterns of the four sets of central elements B1 to B4 shown in the top view of FIG. Is a line symmetry with respect to the X axis and a line symmetry with respect to the Y axis.

  Based on the results shown in the table of FIG. 21, it can be understood that the detection circuit shown in FIG. 23 can detect the force component Fz in the Z-axis direction. This detection circuit includes a resistance element formed by connecting a first central element B1 and a second central element B2 in series, and a resistance formed by connecting a third central element B3 and a fourth central element B4 in series. A first reference element R1 and a second reference element R2 connected in series, a third reference element R3, a fourth reference element R4, Is a circuit that detects a force component Fz in the Z-axis direction by using a Wheatstone bridge in which resistance elements formed by connecting the two in series are arranged on the second opposite side. When a predetermined power supply voltage is supplied from the DC power supply E, the terminals Tz5 and Tz6 maintain an equipotential while the bridge maintains the equilibrium condition. However, when the equilibrium state is lost, a potential difference Vz is generated between the terminals. It will be. This potential difference Vz is an electric signal indicating the direction and magnitude of the force component Fz in the Z-axis direction.

  As described above, the eight sets of elements B1 to B4 and R1 to R4 are composed of piezoresistive elements of the same material and the same size, so that the bridge circuit maintains a balanced state when no external force is applied. . However, when the force component + Fz acts, as shown in the table of FIG. 21, the resistance values of the central elements B1 to B4 increase greatly, and the resistance values of the reference elements R1 to R4 do not change significantly, so that the terminal Tz5 side is positive. A voltage Vz that is negative on the terminal Tz6 side is generated. When the force component -Fz in the reverse direction acts, the sign of the voltage Vz is reversed. If the applied force component is large, the absolute value of the voltage Vz is also large.

  Note that when the moment component Mx acts, the resistance value change of the resistance element in which the central elements B3 and B4 are connected in series is canceled, and when the moment component My acts, the resistance element in which the central elements B1 and B2 are connected in series. Therefore, the detection circuit shown in FIG. 23 does not erroneously detect the moment components Mx and My. In this way, the detection circuit shown in FIG. 23 can obtain an accurate detection value that excludes interference of other axis components.

  Further, the detection circuit shown in FIG. 23 is a circuit that performs differential detection using a Wheatstone bridge. Therefore, the electrical characteristics of each piezoresistive element are changed depending on the actual usage environment (particularly the temperature environment) of the force sensor. Even if a change occurs, the influence is not output as a detection value. For example, even if the electric resistances of the four sets of central elements B1 to B4 increase or decrease due to temperature changes, the electric resistances of the four sets of reference elements R1 to R4 also increase or decrease under the same conditions. The balanced condition of the bridge circuit is maintained as it is, and no detection voltage is output. As described above, the detection circuit shown in FIG. 23 can perform accurate detection without the influence of the actual use environment.

  In order to perform accurate detection that eliminates the influence of changes in the temperature environment, the reference elements R1 to R4 are preferably placed in a temperature environment as close as possible to the central elements B1 to B4. This is why the reference elements R1 to R4 are arranged close to the central elements B1 to B4, respectively, in the example shown in FIG. Of course, as long as the positions of the reference elements R1 to R4 can be arranged at an angle of 45 ° with respect to the X axis or the Y axis, the positions are not limited to the X axis and the Y axis.

  After all, the basic concept of the fourth embodiment is that the strain detection substrate 400 is composed of a silicon single crystal substrate, and the (001) plane of this silicon single crystal substrate is the upper surface of the strain detection substrate 400, and each center The elements B1 to B4 are arranged so as to face the peak direction of the piezoresistance coefficient in the (001) plane, and the reference element R1 includes a piezoresistive element arranged so as to face a direction forming 45 ° with respect to the peak direction. To R4, and the detection circuit detects the detection target component using a Wheatstone bridge in which the central elements B1 to B4 are arranged on the first opposite side and the reference elements R1 to R4 are arranged on the second opposite side. Therefore, it is possible to detect a difference when detecting the force component Fz.

  According to this basic concept, it is not always necessary to use four sets of the central elements B1 to B4 as the central element. For example, one of the central elements B1 and B2 arranged on the X axis and the reference elements R1 to R4 is used. A bridge circuit can be configured by two. In this case, the central elements B1 and B2 arranged on the X axis may be arranged on the first opposite side, and any two reference elements may be arranged on the second opposite side. Alternatively, a bridge circuit may be configured by the central elements B3 and B4 arranged on the Y axis and any two of the reference elements R1 to R4. In this case, the central elements B3 and B4 arranged on the Y axis may be arranged on the first opposite side, and any two reference elements may be arranged on the second opposite side.

  Note that, as shown in the upper graph of FIG. 22, the (001) plane of the silicon single crystal substrate has an advantageous characteristic that the peak directions of the piezoresistance coefficients are directed in two axial directions perpendicular to each other. Therefore, not only in the fourth embodiment described here, but also in other embodiments of the present application, the strain detection substrate 400 having the (001) plane of the silicon single crystal substrate as an upper surface is used, and the piezoresistance coefficient is increased. The peak direction is preferably the X axis or the Y axis.

<5-5. Fifth embodiment>
FIG. 24 is a top view showing a fifth embodiment of the piezoresistive element arrangement pattern in the force sensor according to the present invention. The arrangement pattern itself in the fifth embodiment is the same as the pattern in the first embodiment shown in FIG. That is, the central elements C1 to C8 shown in FIG. 24 are piezoresistive elements arranged in the same positions as the central elements A1 to A8 shown in FIG.

  However, the odd-numbered central elements C1, C3, C5 and C7 are piezoresistive elements having the first polarity, whereas the even-numbered central elements C2, C4, C6 and C8 are: The piezoresistive element has a second polarity opposite to the first polarity. In the figure, the hatching of the central elements C1, C3, C5 and C7 and the hatching of the central elements C2, C4, C6 and C8 are changed in order to show this difference in polarity. Here, the central elements C1, C3, C5 and C7 are P-type piezoresistive elements (elements whose resistance value increases when stress in the extending direction acts and whose resistance value decreases when stress in the contracting direction acts). The central elements C2, C4, C6 and C8 are N-type piezoresistive elements (elements whose resistance value decreases when stress in the extending direction acts and whose resistance value increases when stress in the contracting direction acts). Let's assume that it is configured. In the fifth embodiment described here, difference detection is performed by incorporating central elements having opposite polarities into a bridge circuit.

  Specifically, in the case of this embodiment, the first central element C1 and the second central element C1 are arranged on the upper surface of the strain detection substrate 400 along the X-axis positive region so that the X-axis direction is the longitudinal direction. The central element C2, the third central element C3 and the fourth central element C4 arranged along the X-axis negative region so that the X-axis direction is the longitudinal direction, and the Y-axis direction is the longitudinal direction. As described above, the fifth central element C5 and the sixth central element C6 arranged along the Y-axis positive region, and the first central element C5 arranged along the Y-axis negative region so that the Y-axis direction becomes the longitudinal direction. 7 central elements C7 and an eighth central element C8 are provided.

  Here, the first, third, fifth, and seventh central elements C1, C3, C5, and C7 are central elements having the same polarity and the same size and the first polarity, and the second, fourth, The sixth and eighth central elements C2, C4, C6 and C8 are central elements having the same material and the same size and the second polarity, and in the state where the force to be detected is not acting, The resistance values of the eighth central elements C1 to C8 are set to be equal to each other.

  In addition, the arrangement pattern of the central elements C1 to C8 is symmetrical with respect to the XZ plane and the YZ plane, and the planar pattern of the central elements C1 to C8 shown in the top view of FIG. The figure is line symmetric with respect to the X axis and line symmetric with respect to the Y axis.

  FIG. 25 is a table showing changes in resistance values of the piezoresistive elements C1 to C8 in the fifth embodiment shown in FIG. 25 is compared with the table in FIG. 11, the columns C1, C3, C5, and C7 in FIG. 25 are the same as the corresponding columns in A1, A3, A5, and A7 in FIG. It can be seen that each column of C2, C4, C6 and C8 of 25 is obtained by reversing the sign of the corresponding column of A2, A4, A6 and A8 of FIG. This is because the central elements C1, C3, C5 and C7 having the first polarity are exactly the same elements as the central elements A1, A3, A5 and A7, and the central elements C2, C4 having the second polarity. , C6 and C8 are naturally taken into consideration that they are elements having opposite polarities to the central elements A2, A4, A6 and A8.

  Based on the results shown in the table of FIG. 25, it can be seen that the detection circuit shown in FIG. 26 makes it possible to detect the force component Fz in the Z-axis direction. This detection circuit includes a resistance element formed by connecting a first central element C1 and a third central element C3 in series, and a resistance formed by connecting a fifth central element C5 and a seventh central element C7 in series. An element disposed on the first opposite side, and a second central element C2 and a fourth central element C4 connected in series; a sixth central element C6 and an eighth central element C8; Is a circuit that detects a force component Fz in the Z-axis direction by using a Wheatstone bridge in which resistance elements formed by connecting the two in series are arranged on the second opposite side. When a predetermined power supply voltage is supplied from the DC power supply E, the terminals Tz7 and Tz8 maintain the same potential while the bridge maintains the equilibrium condition. However, when the equilibrium state is lost, a potential difference Vz is generated between the two terminals. It will be. This potential difference Vz is an electric signal indicating the direction and magnitude of the force component Fz in the Z-axis direction.

  As described above, the eight sets of elements C1 to C8 are configured by piezoresistive elements of the same size, and the resistance values are set to be equal to each other when no external force is applied. Maintains equilibrium. However, when the force component + Fz acts, as shown in the table of FIG. 25, the resistance values of the central elements C1, C3, C5, and C7 having the first polarity increase, and the central element C2 having the second polarity. , C4, C6, C8 decreases in resistance value. Therefore, a voltage Vz is generated in which the terminal Tz7 side is positive and the terminal Tz8 side is negative. When the force component -Fz in the reverse direction acts, the sign of the voltage Vz is reversed. If the applied force component is large, the absolute value of the voltage Vz is also large.

  When the moment component Mx acts, the resistance value change of the resistance element in which the central elements C5 and C7 are connected in series and the resistance element in which the central elements C6 and C8 are connected in series is canceled, and the moment component My acts 26, since the resistance value change of the resistance element in which the central elements C1 and C3 are connected in series and the resistance element in which the central elements C2 and C4 are connected in series is canceled, the detection circuit shown in FIG. 26 erroneously detects the moment components Mx and My. Never do. In this way, the detection circuit shown in FIG. 26 can obtain an accurate detection value that eliminates interference of other axis components.

  After all, the basic concept of the fifth embodiment has a first polarity composed of a piezoresistive element in which the electrical resistance increases when the stress in the extending direction acts and the electrical resistance decreases when the stress in the contracting direction acts. From the piezoresistive elements C2, C4, C6, and C8, the electrical resistance decreases when the stress in the extending direction acts and the electrical resistance increases when the stress in the contracting direction acts. A central element having a second polarity, and a detection circuit disposing the central element having the first polarity on the first opposite side, and the central element having the second polarity as the second element. By detecting the component to be detected using the Wheatstone bridge arranged on the opposite side, it is possible to detect the difference in detecting the force component Fz.

<5-6. Sixth Example>
The arrangement of the piezoresistive element and the detection circuit capable of detecting the moment component Mx around the X axis or the moment component My around the Y axis, or both, have been described as the first embodiment so far. The arrangement and the detection circuit of the piezoresistive element that can detect the force component Fx have been described as the second to fifth embodiments. Of course, a force sensor capable of detecting any force component of Mx, My, and Fz can be configured by combining these.

  Here, as a sixth embodiment, only one example of a force sensor capable of detecting all three components of Mx, My, and Fz will be introduced. The example shown here is an example in which the first embodiment and the fourth embodiment are combined. Since the fourth embodiment is used, the strain detection substrate 400 to be used is constituted by a silicon single crystal substrate cut out by the (001) plane, the (001) plane is the upper surface, and the peak direction of the piezoresistance coefficient is X It arrange | positions so that it may become an axis | shaft or a Y-axis direction.

  FIG. 27 is a top view showing the sixth embodiment. In this arrangement pattern, four sets of reference elements S1 to S4 are used together with 12 sets of central elements D1 to D12. Here, the central elements D1 to D4 and the reference elements S1 to S4 correspond to the central elements B1 to B4 and the reference elements R1 to R4 in the fourth embodiment shown in FIG. On the other hand, the central elements D5 to D12 correspond to the central elements A1 to A8 in the first embodiment shown in FIG.

  In the sixth embodiment, the detection circuit shown in FIG. 28 is used. Here, the detection circuit shown in FIG. 28 (a) corresponds to the detection circuit shown in FIG. 13, and the voltage Vx generated between the terminals T1 and T2 becomes a detection value of the moment component Mx around the X axis. . The detection circuit shown in FIG. 28 (b) corresponds to the detection circuit shown in FIG. 12, and the voltage Vy generated between the terminals T3 and T4 becomes a detection value of the moment component My around the Y axis. The detection circuit shown in FIG. 28 (c) corresponds to the detection circuit shown in FIG. 23, and the voltage Vz generated between the terminals T5 and T6 becomes the detection value of the force component Fz in the Z-axis direction.

  Since the specific detection principle of each component has already been described as each example, detailed description is omitted here. In short, in the sixth embodiment, the strain detection substrate 400 is constituted by a silicon single crystal substrate, the (001) plane of the silicon single crystal substrate becomes the upper surface of the strain detection substrate 400, and the piezoresistance coefficient on the (001) plane. The strain detection substrate 400 is arranged so that the peak direction of the X direction is the X-axis or Y-axis direction.

  Then, the first central element D1 arranged along the X-axis positive region so that the X-axis direction becomes the longitudinal direction, and the X-axis negative region so that the X-axis direction becomes the longitudinal direction The second central element D2 that is arranged, the third central element D3 arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction, and the Y-axis direction is the longitudinal direction. The fourth central element D4 disposed along the Y-axis negative region and the first central element D1 disposed on both sides of the first central element D1 along the X-axis positive region so that the X-axis direction is the longitudinal direction. The fifth and sixth center elements D5 and D6 and the seventh and eighth centers disposed on both sides of the second center element D2 along the X-axis negative region so that the X-axis direction is the longitudinal direction Elements D7 and D8 are arranged on both sides of the third central element D3 along the Y-axis positive region so that the Y-axis direction is the longitudinal direction. The ninth and tenth central elements D9, D10 and the eleventh and twelfth elements arranged on both sides of the fourth central element D4 along the Y-axis negative region so that the Y-axis direction is the longitudinal direction. Center elements D11 and D12, and first to fourth reference elements S1 to S4 arranged so that the direction forming 45 ° with respect to the X axis or the Y axis is the longitudinal direction. Here, the first to twelfth central elements D1 to D12 and the first to fourth reference elements S1 to S4 are composed of piezoresistive elements having the same material and the same size.

  On the other hand, the detection circuit for the force component Fz includes a resistance element formed by connecting a first central element D1 and a second central element D2 in series, a third central element D3, and a fourth central element D4. A resistor element connected in series is arranged on the first opposite side, and a resistor element formed by connecting the first reference element S1 and the second reference element S2 in series, the third reference element S3 and the second reference element S3 The force component Fz in the Z-axis direction is detected using a Wheatstone bridge in which a resistance element formed by connecting four reference elements S4 in series is disposed on the second opposite side.

  The detection circuit for the moment component My arranges the fifth central element D5 and the sixth central element D6 on the first opposite side, and the seventh central element D7 and the eighth central element D8. The moment component My around the Y-axis is detected using the Wheatstone bridge arranged on the opposite side of 2. In the detection circuit for the moment component Mx, the ninth central element D9 and the tenth central element D10 are arranged on the first opposite side, and the eleventh central element D11 and the twelfth central element D12 are arranged on the first side. The moment component Mx around the X-axis is detected using a Wheatstone bridge arranged on the opposite side of 2.

  Of course, the sixth embodiment described here shows an example of a combination of the first to fifth embodiments, and various other combinations are possible in practice. For example, the combination of the first embodiment and the second embodiment, the combination of the first embodiment and the third embodiment, the combination of the first embodiment and the fifth embodiment, Mx, My , Fz can be configured to detect a force sensor capable of detecting an arbitrary force component.

DESCRIPTION OF SYMBOLS 10: Strain body 11: Diaphragm part 12: Side wall part 13: Strut part 30: Power receiving body 40: Strain detection board | substrate 50: Cover 61, 62: Wiring pins 71, 72: Bonding wire 100: Strain body 110: Diaphragm Portion 120: Side wall portions 151 to 154: Screw hole (screw insertion through hole)
180: cover 190: cover bonding part 200: connection member 300: force receiving bodies 321-324: openings 351-354: screw holes (female screw forming holes)
400: Strain detection board 470: Bonding wire 500: Circuit boards A, A1 to A8: Piezoresistive element (central element)
B1 to B4: Piezoresistive element (central element)
C1 to C8: Piezoresistive element (central element)
D1 to D12: Piezoresistive element (central element)
E: DC power supply Fz: Force component in the Z-axis direction f1: Contour line of detection groove (detection region) f2: Outer contour line of cover adhesion part G: Detection grooves G1, G2, G3: Grooves H1 to H7: Through holes K1 to K4: Piezoresistive elements L1 to L8: Position Mx: Moment component around X axis My: Moment component around Y axis N, N1 to N4: Screw O: Origin P1, P2 of XYZ three-dimensional orthogonal coordinate system : Piezoresistive element (reference element)
Q1-Q4: Piezoresistive element (reference element)
R1 to R4: Piezoresistive elements (reference elements)
S1 to S4: Piezoresistive elements (reference elements)
T1 to T6: Output terminals Tx1 and Tx2: Output terminals Ty1 and Ty2 of moment component Mx: Output terminals Tz1 to Tz8 of moment component My: Output terminals Vx of force component Fz: Output voltage Vy corresponding to moment component Mx: Moment component Output voltage Vz corresponding to My: Output voltage corresponding to force component Fz W: Cutting line X: Coordinate axis of XYZ three-dimensional orthogonal coordinate system Y: Coordinate axis of XYZ three-dimensional orthogonal coordinate system Z: Coordinate axis of XYZ three-dimensional orthogonal coordinate system α: Position in the Z-axis direction β: Position in the Z-axis direction ± δ: Small variation in resistance value

Claims (20)

A force sensor for detecting a force component in a predetermined axis direction or a moment component around a predetermined axis in an XYZ three-dimensional orthogonal coordinate system,
A force receiving body that receives a force to be detected; a strain generating body that has a diaphragm portion that deforms based on the force received by the force receiving body; and a connection member that connects the force receiving body and the diaphragm portion; A strain detection substrate disposed at the position of the origin O of the XYZ three-dimensional orthogonal coordinate system and joined to the diaphragm portion; and a detection circuit that outputs a force to be detected as an electrical signal;
With
The strain body is composed of a plate-like member having an upper surface and a lower surface parallel to the XY plane, and a detection region defined at the center of the upper surface of the strain body is for detection toward the lower surface side. A groove is formed, and the diaphragm portion is formed by a bottom portion of the detection groove. A side wall portion is formed around the detection groove, and a lower surface of the diaphragm portion and a lower surface of the side wall portion are flush with each other. Located on top
The force receiving body is disposed at a predetermined interval below the strain body,
The connection member is constituted by a columnar member arranged on the Z axis, the upper end thereof is connected to the lower surface central portion of the diaphragm portion, and the lower end thereof is connected to the upper surface central portion of the force receiving body,
The strain detection substrate has a top surface and a bottom surface that are parallel to the XY plane, and is joined to the bottom surface of the detection groove so that stress generated by deformation of the diaphragm portion is transmitted, and a piezoelectric portion is attached to a predetermined portion of the top surface. A resistance element is formed,
The force sensor is characterized in that the detection circuit outputs an electric signal indicating a force received by the force receiving body based on a change in electric resistance of the piezoresistive element. The force sensor according to claim 1,
A force sensor, wherein the force receiving body, the connecting member, and the strain generating body are constituted by an integral structure made of the same material. The force sensor according to claim 1 or 2,
The force receiving member is constituted by a plate-like member having an upper surface and a lower surface parallel to the XY plane,
A screw hole for fixing the strain body to an external first object is formed in the side wall portion of the strain body,
A screw hole for fixing the force receiving body to an external second object and an instrument for rotating a screw inserted through the screw hole of the strain generating body are inserted into the outer periphery of the force receiving body. And an opening for forming,
The screw hole of the strain body and the screw hole of the force receiving body are formed at positions where the orthogonal projection projection images on the XY plane do not overlap, and the screw hole of the strain body and the force receiving body The force sensor is characterized in that the opening is formed at a position where the orthogonal projection images on the XY plane overlap. The force sensor according to claim 3, wherein
The strain body is constituted by a disk-shaped member having the Z axis as the central axis,
The strain detection substrate is composed of a square substrate centering on the Z axis,
The strain body is formed with a detection groove capable of accommodating the square substrate,
A total of 4 respectively arranged at each outer position of the opposite side on a line connecting the midpoints of a set of opposite sides of the square and each outer position of the opposite side on a line connecting the midpoints of another set of opposite sides. A force sensor in which a plurality of screw holes are formed in a strain body. The force sensor according to any one of claims 1 to 4,
An insertion port penetrating from the outside toward the detection groove is provided in the side wall portion of the strain generating body, and a circuit board on which a detection circuit is mounted is inserted and fixed in the insertion port, and the piezoresistive element and the circuit board A force sensor, wherein wiring is provided between the detection circuit and the detection circuit. The force sensor according to any one of claims 1 to 5,
When the projection image is formed by orthogonal projection of the upper end surface of the connection member onto the upper surface of the strain detection substrate, at least a part of the piezoresistive element is constituted by a central element disposed in the immediate vicinity of the projection image. A force sensor. The force sensor according to claim 6, wherein
The central element is arranged at a position where a stress is applied in the direction of contraction due to the action of the detection target component, and the first group of central elements arranged at a position where the stress is applied in the direction of extension by the action of the predetermined detection target component. A second group of central elements,
The detection circuit detects the detection target component using a Wheatstone bridge in which a central element belonging to the first group is arranged on the first opposite side and a central element belonging to the second group is arranged on the second opposite side. A force sensor characterized by The force sensor according to claim 7, wherein
A first central element and a second central element arranged along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A third central element and a fourth central element arranged along the X-axis negative region such that the X-axis direction is the longitudinal direction;
Have
The first to fourth central elements are composed of piezoresistive elements of the same material and the same size,
The detection circuit has the Wheatstone in which the first central element and the second central element are arranged on the first opposite side, and the third central element and the fourth central element are arranged on the second opposite side. A force sensor that detects a moment component My around the Y-axis using a bridge. The force sensor according to claim 8, wherein
A fifth central element and a sixth central element arranged along the Y-axis positive region such that the Y-axis direction is the longitudinal direction;
A seventh central element and an eighth central element arranged along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
Further comprising
The fifth to eighth central elements are composed of piezoresistive elements of the same material and the same size,
In addition to detecting the moment component My around the Y axis, the detection circuit further arranges the fifth central element and the sixth central element on the first opposite side, and the seventh central element and the A force sensor characterized by detecting a moment component Mx about the X-axis using a Wheatstone bridge in which an eighth central element is arranged on the second opposite side. The force sensor according to claim 6, wherein
It further has a reference element made of a piezoresistive element arranged at a position where no significant stress change occurs even when the diaphragm portion is deformed by the action of the force to be detected,
A force sensor, wherein the detection circuit detects a detection target component using a Wheatstone bridge in which a central element is arranged on a first opposite side and the reference element is arranged on a second opposite side. The force sensor according to claim 10,
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
A first reference element and a second reference element arranged in the vicinity of the periphery of the strain detection substrate;
Have
The first to fourth central elements are composed of piezoresistive elements of the same material and the same size, and the first to second reference elements are composed of piezoresistive elements of the same material and the same size. In the state where the force to be detected is not acting, the resistance value of the first to second reference elements is set to be twice the resistance value of the first to fourth central elements,
A detection circuit includes a resistance element formed by connecting the first central element and the second central element in series, and a resistance element formed by connecting the third central element and the fourth central element in series Are detected on the first opposite side, and the force component Fz in the Z-axis direction is detected using a Wheatstone bridge in which the first reference element and the second reference element are arranged on the second opposite side. Force sensor characterized by. The force sensor according to claim 6, wherein
A reference element composed of a piezoresistive element arranged at the outer position of each central element with the position of the Z axis as the inner side;
A force sensor, wherein the detection circuit detects a detection target component using a Wheatstone bridge in which a central element is arranged on a first opposite side and the reference element is arranged on a second opposite side. The force sensor according to claim 12, wherein
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
A first reference element disposed outside the first central element along the X-axis positive region so that the X-axis direction is a longitudinal direction;
A second reference element disposed outside the second central element along the X-axis negative region so that the X-axis direction is a longitudinal direction;
A third reference element disposed outside the third central element along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth reference element disposed outside the fourth central element along the Y-axis negative region so that the Y-axis direction is the longitudinal direction;
Have
The first to fourth central elements and the first to fourth reference elements are composed of piezoresistive elements of the same material and the same size,
A detection circuit includes a resistance element formed by connecting the first central element and the second central element in series, and a resistance element formed by connecting the third central element and the fourth central element in series Are arranged on the first opposite side, and the resistance element formed by connecting the first reference element and the second reference element in series, the third reference element, and the fourth reference element, A force sensor which detects a force component Fz in the Z-axis direction using a Wheatstone bridge in which resistance elements formed in series are arranged on the second opposite side. The force sensor according to claim 6, wherein
The strain detection substrate is composed of a silicon single crystal substrate, and the (001) plane of the silicon single crystal substrate is the upper surface of the strain detection substrate.
Each central element is arranged to face the peak direction of the piezoresistance coefficient in the (001) plane,
A reference element made of a piezoresistive element arranged to face a direction that forms 45 ° with respect to the peak direction;
A force sensor, wherein the detection circuit detects a component to be detected using a Wheatstone bridge in which the central element is arranged on the first opposite side and the reference element is arranged on the second opposite side. The force sensor according to claim 14, wherein
The strain detection board is arranged so that the peak direction of the piezoresistance coefficient is the X-axis or Y-axis direction,
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
First to fourth reference elements arranged such that a direction at 45 ° to the X axis or the Y axis is a longitudinal direction;
Have
The first to fourth central elements and the first to fourth reference elements are composed of piezoresistive elements of the same material and the same size,
A detection circuit includes a resistance element formed by connecting the first central element and the second central element in series, and a resistance element formed by connecting the third central element and the fourth central element in series Are arranged on the first opposite side, and the resistance element formed by connecting the first reference element and the second reference element in series, the third reference element, and the fourth reference element, A force sensor which detects a force component Fz in the Z-axis direction using a Wheatstone bridge in which resistance elements formed in series are arranged on the second opposite side. The force sensor according to claim 6, wherein
A central element having a first polarity composed of a piezoresistive element that increases in electrical resistance when a stress in an extending direction acts and decreases in electrical resistance when a stress in a contracting direction acts;
A central element having a second polarity composed of a piezoresistive element that decreases in electrical resistance when stress in the extending direction acts and increases in electrical resistance when stress in the contracting direction acts;
Have
The detection circuit uses a Wheatstone bridge in which the central element having the first polarity is arranged on the first opposite side and the central element having the second polarity is arranged on the second opposite side. A force sensor that performs detection. The force sensor according to claim 16, wherein
A first central element and a second central element arranged along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A third central element and a fourth central element arranged along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A fifth central element and a sixth central element arranged along the Y-axis positive region such that the Y-axis direction is the longitudinal direction;
A seventh central element and an eighth central element arranged along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
Have
The first, third, fifth, and seventh central elements are central elements having the same polarity and the same material and the first polarity, and the second, fourth, sixth, and eighth central elements. Is a central element of the same material and the same size and having the second polarity, and the resistance values of the first to eighth central elements are equal to each other in a state where a force to be detected is not applied. Set to
A detection circuit includes a resistance element in which the first central element and the third central element are connected in series, and a resistance element in which the fifth central element and the seventh central element are connected in series Are arranged on the first opposite side, the resistance element formed by connecting the second central element and the fourth central element in series, the sixth central element, and the eighth central element. A force sensor which detects a force component Fz in the Z-axis direction using a Wheatstone bridge in which resistance elements formed in series are arranged on the second opposite side. The force sensor according to claim 6, wherein
The strain detection substrate is composed of a silicon single crystal substrate, the (001) plane of this silicon single crystal substrate is the upper surface of the strain detection substrate, and the peak direction of the piezoresistance coefficient on the (001) plane is the X axis or the Y axis The strain detection board is arranged to be in the direction,
A first central element disposed along the X-axis positive region such that the X-axis direction is a longitudinal direction;
A second central element disposed along the X-axis negative region such that the X-axis direction is the longitudinal direction;
A third central element arranged along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
A fourth central element disposed along the Y-axis negative region such that the Y-axis direction is the longitudinal direction;
Fifth and sixth central elements disposed on both sides of the first central element along the X-axis positive region so that the X-axis direction is the longitudinal direction;
Seventh and eighth central elements disposed on both sides of the second central element along the X-axis negative region so that the X-axis direction is the longitudinal direction;
Ninth and tenth central elements disposed on both sides of the third central element along the Y-axis positive region so that the Y-axis direction is the longitudinal direction;
Eleventh and twelfth central elements disposed on both sides of the fourth central element along the Y-axis negative region so that the Y-axis direction is the longitudinal direction;
First to fourth reference elements arranged such that a direction at 45 ° to the X axis or the Y axis is a longitudinal direction;
Have
The first to twelfth central elements and the first to fourth reference elements are composed of piezoresistive elements of the same material and the same size,
The detection circuit
A resistance element formed by connecting the first central element and the second central element in series; and a resistance element formed by connecting the third central element and the fourth central element in series. A resistance element formed by connecting the first reference element and the second reference element in series, and the third reference element and the fourth reference element connected in series; A force component Fz in the Z-axis direction is detected using a Wheatstone bridge in which the resistance element is arranged on the second opposite side,
Using a Wheatstone bridge in which the fifth central element and the sixth central element are arranged on the first opposite side, and the seventh central element and the eighth central element are arranged on the second opposite side The moment component My around the Y axis is detected,
Using a Wheatstone bridge in which the ninth central element and the tenth central element are arranged on the first opposite side, and the eleventh central element and the twelfth central element are arranged on the second opposite side A force sensor that detects a moment component Mx about the X axis. The force sensor according to any one of claims 6 to 18,
A force sensor, wherein the arrangement pattern of each central element is symmetrical with respect to the XZ plane and the YZ plane. In the manufacturing method of the integral structure used for the force sensor according to claim 2,
In the XYZ three-dimensional Cartesian coordinate system defined in the direction in which the Z axis is directed upward, the material rod is arranged so that the central axis is on the Z axis, and the Z coordinate value exceeds α and falls within the range of less than β. A side machining step for cutting the part from the side so that only the part near the central axis remains;
An upper surface processing step of defining a detection region at the center of the upper end surface of the material rod, and cutting the detection region downward to form a detection groove;
Have
The power receiving body is constituted by the portion where the Z coordinate value is α or less, the connecting member is constituted by the portion where the Z coordinate value exceeds α and falls within the range of less than β, and strain is generated by the portion where the Z coordinate value is β or more. A manufacturing method of an integral structure used for a force sensor, comprising a body.

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