JP2020073880A - Strain gauge and multi-axis force sensor - Google Patents

Abstract

To provide a strain gauge whose occurrence of measurement errors due to changes in ambient temperature is suppressed.SOLUTION: A strain gauge 20 includes a base material 21 and a circuit pattern formed on the base material. The base material has a sensitive area 21s attached to a strain-generating area where strain occurs under the load of a strain-generating member and insensitive areas 21n1 and 21n2 arranged outside the strain-generating area. The circuit pattern includes first direction strain sensing elements X1, X2 forming a first bridge circuit BC1, second direction strain sensing elements Y1, Y2 forming a second bridge circuit BC2 and at least one of first direction fixed resistance elements RX1, RX2 forming the first bridge circuit and second direction fixed resistance elements RY1, RY2 forming the second bridge circuit. The strain-sensitive elements and the fixed resistance elements are made of the same material. The strain sensing elements are formed in the sensitive area and the fixed resistance elements are formed in the insensitive area.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a strain gauge and a multi-axis force sensor including the strain gauge.

  Multi-axis force sensors equipped with strain gauges are widely used in robots, game machines, various measuring machines, and other machines. Patent Documents 1 and 2 disclose an example of a multi-axis force sensor including a strain gauge.

JP, 2010-164495, A Japanese Patent No. 5008188

  In a multi-axis force sensor including a strain gauge, the existence of a measurement error due to a change in ambient temperature has been recognized, and its suppression is desired.

  Therefore, an object of the present invention is to provide a strain gauge in which generation of a measurement error due to a change in ambient temperature is suppressed, and a multiaxial force sensor including the strain gauge.

According to a first aspect of the invention,
The load is attached to the strain-deflecting member and is detected by the first Wheatstone bridge circuit of the load acting in the first direction of the strain-generating member, and in the second direction orthogonal to the first direction of the strain-generating member. A strain gauge used for detection of a load acting by a second Wheatstone bridge circuit,
Base material,
A circuit pattern formed on the substrate,
The base material has a sensitive area attached to a strain generating area where strain is generated by receiving a load of the strain generating member, and a dead area arranged outside the strain generating area,
The circuit pattern forms two first direction strain sensing elements that form a first Wheatstone bridge circuit, two second direction strain sensing elements that form a second Wheatstone bridge circuit, and a first Wheatstone bridge circuit. Including a first direction fixed resistance element and a second direction fixed resistance element forming a second Wheatstone bridge circuit,
At least one of the two first direction strain sensing elements, the two second direction strain sensing elements, and the first direction fixed resistance element and the second direction fixed resistance element is formed of the same material,
The two first direction strain sensing elements and the two second direction strain sensing elements are formed in the sensing area, and at least one of the first direction fixed resistance element and the second direction fixed resistance element is A strain gauge formed in the dead area is provided.

  In the strain gauge according to the first aspect, the circuit pattern includes two first direction fixed resistance elements forming a first Wheatstone bridge circuit and two second direction fixed resistance elements forming a second Wheatstone bridge circuit. Alternatively, the two first direction strain sensing elements, the two second direction strain sensing elements, the two first direction fixed resistance elements, and the two second direction fixed resistance elements are formed of the same material. The two first direction fixed resistance elements and the two second direction fixed resistance elements may be formed in the dead region.

  In the strain gauge according to the first aspect, the circuit pattern may further include at least one terminal, and the at least one terminal may be formed in the dead region.

  In the strain gauge of the first aspect, in the dead region, the at least one terminal is provided on a side opposite to the sensitive region of at least one of the first direction fixed resistance element and the second direction fixed resistance element. May be.

  In the strain gauge of the first aspect, a pair of the dead areas may be provided on both sides of the sensitive area.

  In the strain gauge of the first aspect, the circuit pattern may further include two third direction strain sensing elements or two third direction fixed resistance elements, and the two third direction strain sensing elements or two The third direction fixed resistance element may configure a third Wheatstone bridge circuit by connecting the first Wheatstone bridge circuit and the second Wheatstone bridge circuit.

According to a second aspect of the invention,
Strain plate,
A load acting portion connected to the strain plate,
A multi-axis force sensor including the strain gauge according to the first aspect attached to the strain plate is provided.

  In the strain gauge of the present invention and the multi-axis force sensor including the strain gauge, occurrence of measurement error due to change in ambient temperature is suppressed.

FIG. 1 shows a wiring pattern of a strain gauge according to an embodiment of the present invention. FIG. 2 is a circuit diagram corresponding to the wiring pattern of the strain gauge of FIG. FIG. 3A and FIG. 3B are explanatory diagrams showing how measurement is performed by the triaxial force sensor according to the embodiment of the present invention. FIG. 4 shows a modification of the wiring pattern of the strain gauge according to the embodiment of the present invention.

<Embodiment>
Embodiments of a strain gauge and a multi-axis force sensor of the present invention will be described with reference to FIGS. 1 to 4 by taking a strain gauge 20 and a three-axis force sensor 100 to which the strain gauge 20 is applied as an example.

FIG. 1 shows a state before the strain gauge 20 is attached to the flexure element 11 (see FIGS. 3A and 3B) of the triaxial force sensor 100. As shown in FIG. 1, the strain gauge 20 includes a rectangular base material 21 and a circuit pattern CP printed on the surface of the base material 21. The base material 21 has a sensitive area 21s and dead areas 21n1 and 21n2 sandwiching the sensitive area 21s, and the circuit pattern CP has six strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ and Z _2. If, comprising four fixed resistor _{RX 1,} RX _2, and RY 1, RY _2, and eight terminals _T 1 through T _8, and a wiring W for connecting them. In the following description, in the strain gauge 20 and the triaxial force sensor 100 including the same, the direction in which the dead areas 21n1 and 21n2 sandwich the sensitive area 21s is defined as the y direction (second direction), and on the surface of the base material 21. In, the direction orthogonal to the y direction is defined as the x direction (first direction). Further, the direction of an axis orthogonal to the x direction and the y direction is the z direction (third direction).

  Here, in the triaxial force sensor 100 shown in FIGS. 3A and 3B, the flexure plate 11 receives a load applied from the outside to the triaxial force sensor 100 via the load acting portion 12. It is a distorted disk shape. The strain in the strain-flexing plate 11 occurs on the front surface and the back surface (upper and lower surfaces orthogonal to the z direction) of the strain-flexing plate 11 and does not occur on the side surface of the strain-flexing plate 11 (the circumferential surface parallel to the z direction) or can be ignored. Small enough. In the present specification, regions such as the front surface and the back surface of the strain-flexing plate 11 in the present embodiment that are distorted by the external load of the strain-flexing plate 11 are referred to as “strain-generating regions”. The strain plate 11 may have any diameter and thickness.

  The load acting portion 12 stands upright in the direction of the rotation axis A (z direction) of the strain-flexing plate 11 from the center of the surface of the strain-flexing plate 11. The load acting portion 12 is a portion that receives a load from the outside to move and causes strain in the strain-flexing plate 11, and is, for example, a prism having a square cross section. The load acting portion 12 is provided on the surface of the strain plate 11 such that the central axis of the prism is aligned with the rotation axis A of the strain plate 11, that is, coaxially with the strain plate 11. The strain plate 11 and the load acting portion 12 are integrally formed of, for example, a synthetic resin material.

  Returning to FIG. 1, the base material 21 is a flexible resin film, for example, and has a central circular sensitive area 21s and a pair of dead areas 21n1 and 21n2 sandwiching the sensitive area 21s. Polyester, polyimide or the like can be used as the resin film. It is also possible to form the sensitive region 21s and the insensitive regions 21n1 and 21n2 from different materials, but these should be formed from the same material so that the temperature characteristics (resistance temperature coefficient, etc.) of all regions are equal. Is desirable. Further, in this case, the sensitive area 21s and the dead areas 21n1 and 21n2 may be integrally cut out from the vicinity of the integrally formed material (for example, a sheet of polyester, polyimide, or the like) to form the base material 21. More desirable. Thereby, the temperature characteristics of each region can be made more uniform.

The sensitive area 21s is an area attached to the back surface of the strain-flexing plate 11, and thus has a diameter equal to or smaller than the back surface of the strain-flexing plate 11. On one surface of the sensitive area 21s, strain sensitive elements (first direction strain sensitive elements) X ₁ and X ₂ sandwich the center c in the x direction, and strain sensitive elements (second strain sensitive elements (second direction) are sandwiched in the y direction. Directional strain sensing elements Y ₁ and Y ₂ are formed, and strain sensing elements (third direction strain sensing element) Z ₁ and Z ₂ are formed along the outer circumference.

The strain sensitive elements X ₁ and X ₂ are formed in parallel with each other with the y direction as the grid width direction. The strain-sensitive element X ₁ and the strain-sensitive element X ₂ are formed at positions equidistant from the center c, respectively, and are arranged in the x-direction between the strain-sensitive element X ₁ and the strain-sensitive element X ₂ . The distance is larger than the width of the load acting portion 12 in the x direction.

The strain sensing elements Y ₁ and Y ₂ are formed in parallel with each other with the x direction as the grid width direction. The strain sensing element Y ₁ and the strain sensing element Y ₂ are formed at positions equidistant from the center c, respectively, and are arranged in the y direction between the strain sensing element Y ₁ and the strain sensing element Y ₂ . The distance is larger than the width of the load acting portion 12 in the y direction.

Each of the strain sensing elements Z ₁ and Z ₂ has an arc shape, and is formed to face each other in the x direction with the circumferential direction of the sensing region 21s as the width direction of the grid. The strain sensing elements Z ₁ and Z ₂ are arranged on the opposite side (outside) from the center c of the strain sensing elements X ₁ , X ₂ , Y ₁ and Y ₂ .

  The pair of dead regions 21n1 and 21n2 has a shape sandwiching the sensitive region 21s in the y direction.

Fixed resistance elements (first direction fixed resistance elements) RX ₁ and RX ₂ respectively extending in the x direction are formed side by side in the x direction on portions of the surface of the dead area 21n1 far from the sensitive area 21s. Four terminals T ₁ , T ₂ , T ₃ and T ₄ arranged in the x direction are formed in the portion close to the sensitive area 21s. That is, in the dead region 21n1, the fixed resistance elements RX ₁ and RX ₂ are arranged on the opposite side of the terminals T _{1 to} T ₄ from the sensitive region 21s.

Similarly, fixed resistance elements (second direction fixed resistance elements) RY ₁ and RY ₂ extending in the x direction are formed side by side in the x direction on portions of the surface of the dead area 21n2 far from the sensitive area 21s. Therefore, four terminals T ₅ , T ₆ , T ₇ , and T ₈ arranged in the x direction are formed in the portion close to the sensitive area 21s. That is, in the dead region 21N2, a fixed resistance element _RY 1, RY ₂ terminal _T 5 through T _8, are arranged on the opposite side of the sensitive region 21s.

As shown in FIGS. 1 and 2, the wiring W constitutes the first bridge circuit (first Wheatstone bridge circuit) BC1 by connecting the strain sensing elements X ₁ and X ₂ and the fixed resistance elements RX ₁ and RX _2. ing. Further, a terminal T ₁ is provided between the strain sensing element X ₁ and the fixed resistance element RX ₁ , a terminal T ₂ is provided between the strain sensing element X ₁ , X ₂ , and a fixed resistance element RX ₁ , RX ₂ . to the terminal _{T 3,} the terminal _{T 4} is connected between the strain sensitive elements _{X 2} and the fixed resistance element RX _2.

Similarly, the wiring W connects the strain sensing elements Y ₁ and Y ₂ and the fixed resistance elements RY ₁ and RY ₂ to form a second bridge circuit (second Wheatstone bridge circuit) BC2. The terminal T ₈ is between the strain sensing element Y ₁ and the fixed resistance element RY ₁ , the terminal T ₆ is between the strain sensing element Y ₁ and Y ₂ , and the terminal T ₈ is between the fixed resistance element RY ₁ and RY _{2. 7} , the terminal T ₅ is connected between the strain sensing element Y ₂ and the fixed resistance element RY ₂ .

One end of the strain sensing element Z ₁ is connected to the first bridge circuit BC1 between the strain sensing element X ₁ and the fixed resistance element RX ₁ , and the other end is connected to the strain sensing element Y ₁ and the fixed resistance element RY. _{The first} bridge circuit BC2 is connected to the first bridge circuit BC2. Similarly, one end of the strain sensing element Z ₂ is connected to the first bridge circuit BC1 between the strain sensing element X ₂ and the fixed resistance element RX ₂ , and the other end is fixed to the strain sensing element Y _2. It is connected to the second bridge circuit BC2 between the resistive element RY _2. Thus, a first bridge circuit BC1 to a pair of opposite sides portion of the second bridge circuit BC2 respectively sensitive elements Z ₁ strain to another pair of opposite side _portions, a third bridge circuit having Z _2, respectively (Third Wheatstone bridge circuit) BC3.

The strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ included in the circuit pattern CP, the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ , and the wiring W are made of the same material. More preferably, it is formed by a site in the vicinity of one material. This material is, for example, copper, a copper alloy such as copper / nickel, or the like. The circuit pattern CP can be printed on the base material 21 by photoetching, printing, vapor deposition, sputtering or the like.

  The strain gauge 20 is attached to the strain-flexing plate 11 such that the surface of the base material 21 opposite to the surface on which the circuit pattern CP is formed is in contact with the strain-flexing plate 11.

Specifically, the sensitive area 21 s of the base material 21 is attached to the back surface of the flexure plate 11 such that the center c coincides with the rotation axis A of the flexure plate 11. As described above, the distance between the strain sensitive elements X ₁ and X ₂ in the x direction is larger than the dimension of the load acting portion 12 in the x direction, and the distance between the strain sensitive elements Y ₁ and Y _{2 in} the y direction is It is larger than the dimension of the load acting portion 12 in the y direction. Therefore, in the state in which the sensitive portion 21s of the base material 21 is attached to the strain plate 11, the strain sensitive elements X ₁ and X ₂ and the strain sensitive elements Y ₁ and Y ₂ are respectively in the x direction and the y direction. Is arranged in an area outside the load acting portion 12 in the direction where the strain is relatively large. 1 and 4, the contour of the load acting portion 12 in a state where the base material 21 is attached to the strain generating plate 11 is shown by a dotted line, and the load acting portion 12 and the strain sensing elements X ₁ , X ₂ , The positional relationship with Y ₁ and Y ₂ is shown.

In the base material 21 attached to the triaxial force sensor 100, the terminals T ₁ , T ₂ , T ₃ , T ₄ formed in the dead area 21n1 and the terminals T ₅ , T ₆ , T formed in the dead area 21n2. ₇ and T ₈ are exposed to the outside in the radial direction of the flexure plate 11 (that is, to the outside of the flexure region).

  Next, the usage method and operation of the strain gauge 20 and the triaxial force sensor 100 of this embodiment will be described.

When the triaxial force sensor 100 is used as a tactile sensor of a robot hand, for example, the triaxial force sensor 100 is first fixed to the fingertip of the robot hand. Next, the terminals T _{1 to} T ₈ and the signal processing unit (not shown) are connected using the lead wires L _{1 to} L ₈ (FIG. 2), respectively. The terminals T _{1 to} T ₈ and the lead wires L _{1 to} L ₈ can be joined by any method, for example, using solder or anisotropic conductive film (ACF).

The terminals T ₁ and T ₅ are connected to a power supply (not shown) of the signal processing unit by lead wires L ₁ and L ₅ , respectively. Terminals _T 2, _{T 3,} the terminal _T 6, _{T 7,} the terminal _T 4, _{T 8,} respectively, the leads _L 2, _{L 3,} the leads _L 6, _{L 7,} the lead wire _L 4, _{L 8,} signal It is connected to an arithmetic unit (not shown) in the signal processing unit via an amplifier (not shown) in the processing unit.

During operation of the triaxial force sensor 100, the input voltage Ei is applied between the terminals T ₁ and T ₅ by the power supply. The resistance value of each strain sensing element and the resistance value of each fixed resistance element forming the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3 have no deflection in the sensing region 21s of the base material 21. In the state, the terminals T ₂ and T ₃ are adjusted to have the same voltage, the terminals T ₆ and T ₇ to have the same voltage, and the terminals T ₄ and T ₈ have the same voltage. Therefore, in a state where the strain plate 11 is not distorted and the sensitive area 21s is not bent (FIG. 3A), between the terminals T ₂ and T _3, between the terminals T ₆ and T ₇ , and between the terminals T ₆ and T ₇ . There is no potential difference between T ₄ and T ₈ , and the calculation unit does not calculate the strain.

Next, when a load in the x direction is applied to the load acting portion 12, the load acting portion 12 receives the load and moves, causing strain in the flexure plate 11 (FIG. 3B). At this time, the sensitive area 21s of the base material 21 of the strain gauge 20 attached to the strain-flexing plate 11 is also flexed integrally with the strain-flexing plate 11, and the strain-sensing element X ₁ receives a compressive strain. Stretching strain occurs in the element X ₂ . As a result, the resistance values of the strain sensing elements X ₁ and X ₂ change, and a potential difference is generated between the terminals T ₂ and T ₃ of the first bridge circuit BC1 including the strain sensing elements X ₁ and X ₂ . The calculation unit calculates the amount of strain generated in the flexure plate 11 based on this potential difference and the magnitude of the load acting on the load acting unit 12 in the x direction. At this time, no strain is generated outside the strain generation region, that is, in the dead regions 21n1 and 21n2, and the resistance values of the fixed resistance elements RX ₁ and RX ₂ are constant. Even when a load in the y direction is applied to the load acting portion 12, the magnitude of the similarly applied load in the y direction is obtained.

When a load in the Z direction is applied to the load acting portion 12, the sensitive areas 21s of the strain-flexing plate 11 and the base material 21 are curved so that the centers thereof project, and thus the strain-sensitive elements X ₁ , X _{2 are applied.} , Y ₁ , Y ₂ , Z ₁ , Z ₂ all have elongation strain. As a result, the combined resistance of the first bridge circuit BC1, the combined resistance of the second bridge circuit BC2, and the resistance values of the strain sensing elements Z ₁ and Z ₂ are changed, and the terminals T ₄ and T _{8 of} the third bridge circuit BC3 are changed. There is a potential difference between them. The calculation unit determines the amount of strain generated in the flexure plate 11 based on this potential difference, and the magnitude of the load in the Z direction acting on the load acting unit 12.

Here, the fixed resistance elements RX ₁ and RX _{2 of} the first bridge circuit BC1 and the fixed resistance elements RY ₁ and RY ₂ of the second bridge circuit BC2 are printed on the base material 21, and the strain sensing elements X ₁ and X ₂ are printed. , Y ₁ , and Y ₂ will be described below.

(1) By forming the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , and RY ₂ in this way, the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , and RY ₂ become the strain sensing elements X ₁ and X. It is formed of the same material as ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ and at a position close to these. Here, since the temperature coefficient of resistance indicating the rate of change in resistance value with respect to temperature change is a physical property value that depends on the material, in the present embodiment, the temperature coefficient of resistance of all strain-sensitive elements is equal to the temperature coefficient of resistance of all fixed resistance elements. Further, fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ are formed on the base material 21, and the vicinity of the strain sensing elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ is provided. Therefore, the change in ambient temperature that affects all strain-sensitive elements and all fixed resistance elements is substantially the same. Therefore, when the ambient temperature changes, the resistance values of all the strain sensing elements and the resistance values of all the fixed resistance elements change at the same rate.

In the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3, when the resistance value balance among the resistance elements (strain-sensing element and fixed resistance element) included in each of them changes, between T _{2, T 3,} between the terminals _T 6, _{T 7,} the potential difference between the terminals _T 4, _{T 8} occurs, the strain on the basis of which is detected. Therefore, when the balance between the resistance value of the strain sensing element and the resistance value of the fixed resistance element changes due to a change in ambient temperature, a measurement error may occur due to this change in balance. However, in the present embodiment, when the ambient temperature changes, the ambient temperature changes because the resistance values of all strain-sensitive elements and the resistance values of all fixed resistance elements change at the same rate. Even in such a case, the balance of the resistance value between the elements does not change, and the occurrence of measurement error is suppressed. When the circuit pattern CP is formed, a strain sensing element or the like is formed by using a portion near a material (copper, copper alloy, or the like) prepared as an integral lump, so that the strain sensing element X ₁ , _{X 2, Y 1, Y 2} , Z 1, Z 2, fixed resistor _{RX 1, RX 2, RY 1} , RY 2, the resistance temperature coefficient of the wire W can be more uniform, the occurrence of measurement errors better Can be suppressed.

(2) As in this embodiment, the fixed resistance elements RX ₁ and RX _{2 of} the first bridge circuit BC1 and the fixed resistance elements RY ₁ and RY ₂ of the second bridge circuit BC2 are connected to the dead areas 21n1 and 21n2 of the base material 21. The fixed resistance elements RX ₁ , RX ₂ , RY ₁ , and RY ₂ can be made to act as dummy gauges for temperature compensation in a portion (outside the strain-generating region) where the strain is not generated. Therefore, even when the main body of the triaxial force sensor 100 including the strain plate 11 expands or contracts due to a change in ambient temperature, the strain-sensing elements X ₁ , X ₂ , Y ₁ , due to the expansion or contraction, It is possible to compensate for the change in the resistance value of Y ₂ and suppress the occurrence of measurement errors.

(3) By forming the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , and RY ₂ by printing on the base material 21, the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3 are formed. Each can be formed as a complete closed circuit on the substrate 21.

  In order to make the bridge circuit a closed circuit, the strain-sensitive element that constitutes the bridge circuit is printed on the substrate, and the fixed resistance element that constitutes the bridge circuit is provided outside the substrate, for example, in the signal processing unit. It is necessary to connect the strain sensing element on the base material and the fixed resistance element of the signal processing section by a lead wire or the like. In this case, the wiring on the base material and the lead wire are connected by joining the lead wire to the electrode provided on the base material. The bonding method is limited to solder bonding in which the bonding resistance is practically negligible because it becomes a resistance in the circuit and causes a large strain detection error.

  However, in order to perform good soldering, it is necessary to provide a relatively large electrode on the base material and to secure a pitch between the plurality of electrodes, so that the base material becomes large. In addition, since it is necessary to fill the solder with a certain thickness in order to perform good solder joint, it also hinders the downsizing of the triaxial force sensor.

In contrast, in the present embodiment, the first bridge circuit BC1, second bridge circuit BC2, the third bridge circuit BC3, respectively, is formed as a closed circuit was completed on the substrate 21, the terminal _T 1 through T The connection between the base material 21 and the signal processing unit via ₈ is merely a joint for connecting the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3 to the power supply and the arithmetic unit. Therefore, in the present embodiment, the generation of the joining resistance is allowed at the joints between the terminals T _{1 to} T ₈ and the lead wires L _{1 to} L _8, and any joining method other than the solder joining, for example, an anisotropic conductive film is used. Bonding using can be adopted. By using the anisotropic conductive film, the size of the electrodes, the pitch between the electrodes, and the thickness of the joint can all be suppressed to about one-tenth that in the case of solder joining, so that the triaxial force can be applied. If miniaturization of the sensor 100 is desired, joining with an anisotropic conductive film is advantageous.

  The effects of the strain gauge 20 and the triaxial force sensor 100 of this embodiment are as follows.

In the strain gauge 20 of the present embodiment, since the fixed resistance elements RX ₁ and RX _{2 of} the first bridge circuit BC1 and the fixed resistance elements RY ₁ and RY ₂ of the second bridge circuit BC2 are formed on the base material 21, The effects of the above (2) and (3) can be obtained, and the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , and RY ₂ are the same as those of the strain sensing elements X ₁ , X ₂ , Y ₁ , and Y ₂ . Since it is made of a material, the effect (1) can be obtained.

In the strain gauge 20 of the present embodiment, only the strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ are formed in the sensitive region 21s, and the terminals T _{1 to} T are formed. ₈ and the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , and RY ₂ are formed in the dead areas 21n1 and 21n2. Therefore, the diameter (dimension) of the sensitive area 21s can be reduced, and thus the strain plate 11 of the triaxial force sensor 100 can be reduced. The downsizing of the strain plate 11 leads to downsizing of the triaxial force sensor 100, which is preferable.

In the strain gauge 20 of the present embodiment, since the electrode _T 1 through T ₈ is provided in the dead region 21N1,21n2, if necessary, without increasing the diameter of the sensitive area 21s, electrodes _T 1 ~ The size of T ₈ can be increased to facilitate the work of joining with a lead wire or the like.

  Since the triaxial force sensor 100 according to the present embodiment includes the strain gauge 20, the same effect as that of the strain gauge 20 can be obtained.

  In the above embodiment, the following modified modes can be adopted.

In the strain gauge 20, the strain sensitive elements Z ₁ and Z ₂ may be formed in the dead region 21n1 and / or the dead region 21n2. In this case, since the insensitive areas 21n1 and 21n2 are not bent, the strain sensitive elements Z ₁ and Z ₂ substantially act as fixed resistance elements (third-direction fixed resistance elements).

Even when the strain sensitive elements Z ₁ and Z ₂ act as fixed resistance elements, the detection of the x-direction load using the first bridge circuit BC1 and the detection of the y-direction load using the second bridge circuit BC2 are performed as described above. It can be performed similarly to the form. Also, the Z-direction load can be detected. When a load in the Z direction acts on the load acting unit 12 and the resistance values of the strain detecting elements X ₁ , X ₂ , Y ₁ , and Y ₂ change, the combined resistance of the first bridge circuit BC1 and the second bridge circuit BC2. This is because, even if the combined resistance changes and the resistance values of the strain sensitive elements Z ₁ and Z ₂ are constant, the balance of the resistance values between the elements of the third bridge circuit BC3 changes.

The strain gauge 20 may not have the strain sensing elements Z ₁ and Z ₂ . In this case, for example, the first bridge circuit BC1 and the second bridge circuit BC2 are connected by two arcuate wirings W instead of the strain sensing elements Z ₁ and Z ₂ .

Even when the strain sensing elements Z ₁ and Z ₂ are not present, the detection of the x-direction load using the first bridge circuit BC1 and the detection of the y-direction load using the second bridge circuit BC2 are the same as in the above-described embodiment. It can be carried out. The strain gauge 20 in such a modified form can be used in a biaxial force sensor. Alternatively, in a three-axis force sensor, the third Wheatstone bridge is configured by connecting the first Wheatstone bridge and the second Wheatstone bridge, which are included in the strain gauge of such a modified mode, with a fixed resistance element formed in the signal processing unit. It can also be used.

In the strain gauge 20, the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , and RY ₂ formed in the dead regions 21n1 and 21n2 of the base material 21 leave at least one of them on the base material 21 and the other bases. It may be provided outside the material 21, for example, in the signal processing unit. Even in such an aspect, at least one of the fixed resistance elements RX ₁ and RX ₂ forming the first bridge circuit BC1 and the fixed resistance elements RY ₁ and RY ₂ forming the second bridge circuit BC2 is provided on the base material 21. By providing in the dead area 21n1 and / or 21n2 above, the effect of suppressing the temperature error in the strain gauge 20 and the triaxial force sensor 100 can be exerted.

In the dead region 21n1 provided on one side of the sensitive region 21s in the y direction (second direction), the fixed resistance elements RX ₁ and RX ₂ and the terminals T _{1 to} T ₄ are orthogonal to the y direction (second direction). The fixed resistance elements RY ₁ and RY may be arranged in a row along the x direction (first direction), and in the dead region 21n2 provided on the other side of the sensitive region 21s in the y direction (second direction). ₂ and the terminals T _{5 to} T ₈ may be arranged in a line along the x direction (first direction) orthogonal to the y direction (second direction).

As shown in FIG. 4, fixed resistance elements RX ₁ and RX ₂ may be formed in a portion of the dead area 21n1 close to the sensitive area 21s, and terminals T _{1 to} T ₄ may be formed in a portion far from the sensitive area 21s. That is, in the dead region 21n1, the terminals T _{1 to} T ₄ may be provided on the opposite side of the fixed resistance elements RX ₁ and RX _{2 from} the sensitive region 21s. The same applies to the arrangement of the fixed resistance elements RY ₁ and RY ₂ and the terminals T _{5 to} T _{8 in} the dead area 21n2. By arranging the terminals T _{1 to} T ₈ on the outer side in this way, it becomes easier to join the lead wires and the like to the terminals T _{1 to} T ₈ .

Any one or more of the terminals T _{1 to} T ₈ may be formed in the sensitive area 21s. In this case, it is desirable to provide it in the vicinity of the center c which is attached below the load acting portion 12 and is less likely to cause strain.

In the sensitive area 21s, the strain sensitive elements Z ₁ and Z ₂ may be arranged on the center c side (inner side) of the strain sensitive elements X ₁ , X ₂ , Y ₁ and Y ₂ . Further, each of the strain sensing elements X ₁ , X ₂ , Y ₁ , Y ₂ may be formed in an arc shape so that the width direction of the grid thereof is the circumferential direction of the sensing region 21s. Such a strain gauge 20 can be satisfactorily used by being attached to the flexure plate 11 to which the cylindrical load acting portion 12 having the rotation axis A as its center is connected.

The base material 21 of the strain gauge 20 may have any shape, for example, may have an elliptical shape, and may have only one of the dead areas 21n1 and 21n2. In the base material 21 having only one of the dead areas 21n1 and 21n2, the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ and the terminals T _{1 to} T ₈ can all be formed in this dead area. In addition, the base material 21 may have any shape including a sensitive area attached to the flexure plate of the multi-axis force sensor and a dead area disposed outside the sensitive area.

  The strain gauge 20 of the above-described embodiment can be used as a strain generating member of any sensor other than the multiaxial force sensor.

  As long as the features of the present invention are maintained, the present invention is not limited to the above-described embodiments, and other forms conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention. ..

  INDUSTRIAL APPLICABILITY The strain gauge and the multi-axis force sensor of the present invention can suppress the influence of temperature change in load detection, and can contribute to improvement of stability and reliability in robots, game machines, various measuring machines, and other machines.

11 Strain plate (strain member)
12 Load acting part 20 Strain gauge 21 Base material 21s Sensitive area 21n1, 21n2 Dead area BC1 1st bridge circuit (1st Wheatstone bridge circuit)
BC2 2nd bridge circuit (2nd Wheatstone bridge circuit)
BC3 3rd bridge circuit (3rd Wheatstone bridge circuit)
RX ₁ , RX ₂ fixed resistance element (first direction fixed resistance element)
RY ₁ , RY ₂ fixed resistance element (second direction fixed resistance element)
T _{1 to} T ₈ terminals X ₁ and X ₂ strain sensing element (first direction strain sensing element)
Y ₁ , Y ₂ strain sensitive element (second direction strain sensitive element)
Z ₁ , Z ₂ strain sensing element (third direction strain sensing element)

Claims (7)

The load is attached to the strain-deflecting member and is detected by the first Wheatstone bridge circuit of the load acting in the first direction of the strain-generating member, and in the second direction orthogonal to the first direction of the strain-generating member. A strain gauge used for detecting a load acting by a second Wheatstone bridge circuit,
Base material,
A circuit pattern formed on the substrate,
The base material has a sensitive area attached to a strain generating area where strain is generated by receiving a load of the strain generating member, and a dead area arranged outside the strain generating area,
The circuit pattern forms two first direction strain sensing elements that form a first Wheatstone bridge circuit, two second direction strain sensing elements that form a second Wheatstone bridge circuit, and a first Wheatstone bridge circuit. Including a first direction fixed resistance element and a second direction fixed resistance element forming a second Wheatstone bridge circuit,
At least one of the two first direction strain sensing elements, the two second direction strain sensing elements, and the first direction fixed resistance element and the second direction fixed resistance element is formed of the same material,
The two first direction strain sensing elements and the two second direction strain sensing elements are formed in the sensing area, and at least one of the first direction fixed resistance element and the second direction fixed resistance element is A strain gauge formed in the dead region. The circuit pattern includes two first direction fixed resistance elements forming a first Wheatstone bridge circuit and two second direction fixed resistance elements forming a second Wheatstone bridge circuit,
The two first direction strain sensing elements, the two second direction strain sensing elements, the two first direction fixed resistance elements, and the two second direction fixed resistance elements are formed of the same material. ,
The strain gauge according to claim 1, wherein the two first direction fixed resistance elements and the two second direction fixed resistance elements are formed in the dead region. The circuit pattern further includes at least one terminal,
The strain gauge according to claim 1, wherein the at least one terminal is formed in the dead region.   The strain according to claim 3, wherein in the dead region, the at least one terminal is provided on a side opposite to the sensitive region of at least one of the first-direction fixed resistance element and the second-direction fixed resistance element. gauge.   The strain gauge according to any one of claims 1 to 4, wherein a pair of the dead areas are provided on both sides of the sensitive area. The circuit pattern further includes two third-direction strain sensing elements or two third-direction fixed resistance elements,
The two third direction strain sensing elements or the two third direction fixed resistance elements form a third Wheatstone bridge circuit by connecting a first Wheatstone bridge circuit and a second Wheatstone bridge circuit. The strain gauge according to any one of 1. Strain plate,
A load acting portion connected to the strain plate,
A multi-axis force sensor comprising: the strain gauge according to claim 1 attached to the strain-flexing plate.

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