JP7013303B2 - Force sensor - Google Patents

Description

The present invention relates to a force sensor that detects components in a plurality of directions of an external force and a moment acting on a receiving portion.

A force sensor is used as a means for detecting an external force acting on a predetermined portion such as a joint portion or a tip portion of an arm of an industrial robot or a medical manipulator. As an example of the force sensor, a 6-axis force sensor including an optical displacement sensor is disclosed in Patent Document 1. The force sensor described in Patent Document 1 includes a support portion, a receiving portion, an elastic connecting portion connecting them, and a displacement direction changing mechanism arranged between the supporting portion and the receiving portion. Be prepared. The displacement direction conversion mechanism is provided with a detection target body, and the displacement (movement) of the detection target body is detected by a displacement detection element provided on the support portion so as to face the detection target body. For example, when an external force acts on the receiving portion while the supporting portion is fixed, the elastic connecting portion is elastically deformed, and the receiving portion is displaced with respect to the supporting portion according to the direction and magnitude of the external force. At this time, the displacement direction conversion mechanism also deforms with the deformation of the elastic connecting portion, but the displacement direction of the displacement direction conversion mechanism is a direction orthogonal to the displacement direction of the receiving portion.

Japanese Patent No. 5602582

Although the above-mentioned Patent Document 1 describes an embodiment in which a displacement direction changing mechanism and an elastic connecting portion are separately provided, it is also possible to incorporate the displacement direction changing mechanism into the elastic connecting portion. It is possible to reduce the number of parts and simplify the assembly process. However, in the force sensor in which the displacement direction conversion mechanism is incorporated in the elastic connection portion, the detection target provided in the displacement direction conversion mechanism comes into contact with the displacement detection element depending on the direction of the external force acting on the receiving portion. There is a risk that it will end up.

Here, when a load is applied to a rigid body in a predetermined direction, the value obtained by dividing the load by the amount of displacement in that direction is defined as the rigidity value. A rigid body is less likely to be deformed as the rigidity value is higher. Therefore, in order to prevent the detection target body provided in the displacement direction conversion mechanism from coming into contact with the displacement detecting element, it is necessary to make the displacement conversion mechanism difficult to deform, that is, to increase the rigidity value. Further, the force sensor is strongly required to be thinner and smaller as a whole. It is considered that if a material having high rigidity is used, it is possible to prevent the detection object from coming into contact with the displacement detection element while realizing the thinning (miniaturization) of the entire sensor.

However, using a highly rigid material leads to an increase in cost. In addition, the sensitivity (detection sensitivity) of the force sensor with the displacement direction conversion mechanism incorporated in the elastic connection generally has a positive correlation with the height of the displacement conversion mechanism. It becomes necessary to increase the height of the mechanism, which hinders the thinning of the entire sensor. That is, the force sensor is required to increase the rigidity and the sensitivity, but in general, the sensitivity decreases when the rigidity is increased, and conversely, the rigidity decreases when the sensitivity is increased. There will be a need. Similarly, if an attempt is made to make the entire sensor thinner, the sensitivity is lowered, and if an attempt is made to increase the sensitivity, it becomes difficult to make the entire sensor thinner.

An object of the present invention is to provide a force sensor capable of reducing the thickness of the entire sensor and increasing the sensitivity.

The force sensor according to the present invention has a support portion, a force receiving portion that is displaced with respect to the support portion due to the action of an external force, an elastic connecting portion that connects the support portion and the force receiving portion, and the elastic connection portion. A displacement conversion unit joined to the unit and displaced according to a load input to the force receiving unit, a detection target provided in the displacement conversion unit, a sensor substrate fixed to the support unit, and the sensor. A force sensor equipped with a displacement detecting element mounted on a substrate and detecting a displacement amount of the detection target body, wherein the detection target body is the center of a joint portion between the displacement conversion portion and the elastic connection portion. Is arranged on the side where the joint portion between the elastic connecting portion and the receiving portion is located, rather than a straight line orthogonal to the direction in which the supporting portion and the receiving portion are connected. The straight line forms an angle larger than 0 degrees, and the displacement conversion in the direction in which the distance between the detection target and the support portion in the direction connecting the support portion and the receiving portion is parallel to the straight line. It is characterized by being longer than the height of the part.

According to the present invention, it is possible to achieve both a thinning of the entire force sensor and an improvement in sensitivity.

It is an external perspective view of a force sensor. It is sectional drawing and the plan view explaining the structure of a force sensor. It is a figure explaining an example of the deformation of the elastic connection part in a force sensor. It is a top view of the sensor board of a force sensor. It is a partial cross-sectional view which shows the structure of the force sensor which concerns on Example 1 and the modified example thereof. It is a partial cross-sectional view which shows the structure of the force sensor which concerns on Example 2 and the modified example thereof. It is a figure explaining the relationship between the structure of the force sensor which concerns on Example 3, the reflection surface of a detection object, and the light-receiving surface of a displacement detection element. It is a partial cross-sectional view which shows the structure of the force sensor which concerns on Comparative Examples 1 and 2. It is a partial cross-sectional view which shows the structure of the force sensor which concerns on Comparative Examples 3, 4 and 5. It is a partial cross-sectional view which shows the structure of the force sensor which concerns on Comparative Examples 6 and 7. It is a figure which shows the measurement result of the sensitivity and rigidity about an Example and a comparative example. It is a figure explaining the sensitivity increase effect of a force sensor. It is a graph explaining the relationship between the sensitivity increase rate in a force sensor and the position / posture of a displacement detection element.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, the basic configuration of the force sensor common to the examples and the comparative examples will be described. FIG. 1 is an external perspective view of the force sensor 100. The force sensor 100 includes a substantially cylindrical main body portion 2 and a disk-shaped lower lid 1 that covers the lower portion of the main body portion 2.

For convenience of explanation, as shown in FIG. 1, x-axis, y-axis and z-axis orthogonal to each other are defined. The force sensor 100 has a substantially disk-like or substantially columnar shape, and the thickness direction thereof is the z direction. The x-direction and the y-direction are set so as to divide the force sensor 100 into four quadrants in the xy plane when the force sensor 100 is viewed from the z direction, as will be described later with reference to FIG. The central axis L shown in FIG. 1 is parallel to the z-axis and passes through the center of the xy plane in the force sensor 100.

FIG. 2A is a zx cross-sectional view of the force sensor 100. FIG. 2B is a plan view of the force sensor 100 viewed from the upper surface side by seeing through the upper part of the force receiving portion 4 of the force sensor 100. FIG. 2C is a plan view of the force sensor 100 as viewed from the bottom surface side with the lower lid 1 removed.

The main body portion 2 has a support portion 6 having a cylindrical shape, a receiving portion 4 having a substantially disk shape, and an elastic connecting portion 5 connecting the support portion 6 and the receiving portion 4. The lower lid 1 is fixed to the lower surface of the support portion 6, and the fixing portion is composed of the support portion 6 and the lower lid 1. The receiving portion 4 is a movable portion that can be displaced in the z direction with respect to the fixed portion by deforming the elastic connecting portion 5 and can be inclined with respect to the xy plane. The fixed portion is attached to a base (not shown) or the like, and the receiving portion 4 is attached to a robot arm, a manipulator or the like (not shown).

The elastic connecting portions 5 are arranged at four positions in the xy plane around the central axis L at intervals of 90 °. In other words, the elastic connecting portion 5 is arranged in a cross shape in the xy plane so that the heights in the z direction are the same between the supporting portion 6 and the receiving portion 4. Each of the four elastic connecting portions 5 is provided with a displacement direction conversion unit 3 (hereinafter referred to as “displacement conversion unit 3”) which is substantially U-shaped when viewed from the y direction or the x direction. Therefore, in the force sensor 100, more accurately, the elastic connecting portion 5 connects the supporting portion 6 and the receiving portion 4 with the displacement conversion portion 3 interposed therebetween. A detection target is attached to the outer surface of the tip of the displacement conversion unit 3. Hereinafter, the four detection target bodies attached to each of the four displacement conversion units 3 are referred to as detection target bodies 8a, 8b, 8c, and 8d.

The columnar portions project from the four locations of the receiving portion 4 toward the lower lid 1 side (-z direction), and the detection target body is also attached to the tip of each columnar portion. Hereinafter, the four detection target bodies attached to the tips of the four columnar portions are referred to as detection target bodies 8e, 8f, 8g, and 8h. The detection target bodies 8a to 8h are attached to the displacement conversion unit 3 or the columnar portion so as to face the same direction (−z direction) and to be located at the same height in the z direction. A sensor substrate 7 is fixed to the support portion 6, and displacement detection elements 9a to 9h are mounted on the sensor substrate 7 so as to face the detection target bodies 8a to 8h at predetermined intervals in the z direction. Has been done.

When a load (external force or moment) acts on the receiving portion 4, the receiving portion 4 which is a movable portion is displaced with respect to the fixed portion, so that the end portion of the elastic connecting portion 5 on the receiving portion 4 side is displaced. As a result, the detection target bodies 8a to 8d attached to the displacement conversion unit 3 are displaced. The displacement of the detection target bodies 8a to 8d when an external force Fz in the −z direction (direction toward the lower lid 1 side) acts on the force receiving portion 4 will be described with reference to FIG.

FIG. 3 shows the state before and after the deformation of the displacement conversion unit 3 provided with the detection target body 8d when the external force Fz toward the lower lid 1 side is input to the force receiving unit 4 from the y direction. It is a figure. When an external force Fz in the -z direction is input to the receiving unit 4, the detection target body 8a (not shown) is in the y direction, the detection target body 8b (not shown) is in the x direction, and the detection target body 8c (not shown) is-. The detection target body 8d is displaced in the y direction and in the −x direction, respectively. At this time, the displacement amount Δz of the receiving portion 4 in the z direction becomes smaller as the rigidity of the elastic connecting portion 5 increases.

Here, the relative displacement amount of the detection target body 8d with respect to the displacement detection element 9d (not shown) in the direction orthogonal to the normal of the light receiving surface of the displacement detection element 9d (not shown) is defined as “sensitivity”. In the force sensor 100, since the light receiving surface of the displacement detection element 9d (not shown) is orthogonal to the z direction, the sensitivity of the detection target body 8d is given by the displacement amount Δx in the x direction. From FIG. 3, it can be seen that the sensitivity decreases as the height h of the displacement conversion unit 3 decreases. Further, the displacement amount Δx is determined as a distance (interval) between the lines 23 and 24 passing through the center of the surface of the detection target body 8d and orthogonal to the x direction. The height h of the displacement conversion unit 3 having a substantially U-shape is such that the line 21 that bisects the z-direction thickness of the elastic connecting portion 5 and the z-direction thickness of the tip portion of the displacement conversion unit 3 are bisected. It is specified by the distance (interval) between the dividing lines 22.

When the external force Fx in the x direction is input to the receiving unit 4, the detection target bodies 8e to 8h are displaced in the x direction, and when the external force Fy in the y direction is input to the receiving unit 4, the detection target body 8e ~ 8h is displaced in the y direction. When the moment Mx around the x-axis is input to the receiving unit 4, the detection target bodies 8a and 8c are displaced in the −y direction, and when the moment My around the y-axis is input to the receiving unit 4, the detection target body 8b , 8d are displaced in the x direction. When the moment Mz around the z-axis is input to the receiving unit 4, the detection target bodies 8e and 8f are displaced in the y direction and the −x direction, and the detection target bodies 8g and 8h are displaced in the −y direction and the x direction. Displace. In this way, the displacement conversion unit 3 and the elastic connecting unit 5 function as a displacement direction conversion mechanism that converts the direction of the force acting on the receiving unit 4.

Next, a method of detecting an external force and a moment in the force sensor 100 will be described. FIG. 4 is a plan view of the sensor substrate 7. The light sources 10a to 10h and the displacement detection elements 9a to 9h are mounted on the sensor substrate 7 as a set of one light source and one displacement detection element. One light source and one displacement detection element of each set may be integrally configured or may be separate bodies. The light sources 10a to 10h are, for example, LEDs, and the displacement detection elements 9a to 9h are photodiodes (PD), but the light sources are not limited thereto. The displacement detecting elements 9a to 9h have a structure in which a plurality of light receiving surfaces, which are light detection surfaces, are arranged in a stripe shape. Although not shown, each of the detection objects 8a to 8h has a reflection surface on which a diffraction grating is formed by a metal reflection film or the like formed on the front surface or the back surface of a substrate such as glass.

The displacement detection elements 9a to 9h and the detection target bodies 8a to 8h are one-to-one, and the reflection surface of the detection target body and the light receiving surface of the displacement detection element are arranged so as to face each other in the z direction. The divergent luminous flux emitted from the light sources 10a to 10h to the detection target bodies 8a to 8h is reflected by the detection target bodies 8a to 8h, and the reflected light from the detection target bodies 8a to 8h is reflected on the light receiving surface of the displacement detection elements 9a to 9h. It forms a diffracted light pattern that is a fringe of light and dark. The arrangement pitch of the light receiving surfaces of the displacement detection elements 9a to 9h corresponds to the quarter period of the diffracted light pattern. Therefore, when the detection target bodies 8a to 8h are displaced in the arrangement direction of the light receiving surfaces of the displacement detection elements 9a to 9h, the diffracted light pattern moves with the displacement. In this way, a two-phase sinusoidal signal (sin, cos) having a phase difference of 90 ° can be obtained from the plurality of light receiving surfaces.

The calculation circuit (not shown) performs an inverse tangent calculation (tan ^-1 ) of the obtained two-phase sinusoidal signal to calculate the displacement amount of the detection target bodies 8a to 8h. The arithmetic circuit further calculates six components (forces in the six-axis direction) of external forces Fx, Fy, Fz and moments Mx, My, Mz from the calculated displacement amount. By installing the detection target bodies 8a to 8d in the displacement conversion unit 3, it is not necessary to separately provide a displacement direction conversion mechanism, so that the cost can be reduced by reducing the number of parts and the force sensor 100 can be used. It is possible to reduce the size.

Next, the force sensor according to the embodiment of the present invention based on the force sensor 100 will be described. The force sensor according to the first to third embodiments described below is generally an improvement in the structure of the displacement conversion unit 3 of the force sensor 100 described above, and accordingly, the detection target bodies 8a to 8d and the displacement detection element. The arrangement of 9a to 9d is devised.

FIG. 5A is a partial cross-sectional view of the force sensor 100A according to the first embodiment, showing the displacement conversion unit 3 to which the detection target body 8d is attached and its vicinity. In the force sensor 100A, the structure of the other elastic connecting portion whose length direction is parallel to the x direction and the structure of the two elastic connecting portions whose length direction is parallel to the y direction are shown in FIG. 5, respectively. Since it is equivalent to the structure shown in (a), the illustration and description will be omitted. The coordinate axes in FIG. 5A correspond to the coordinate axes shown in FIG. 2, so that the right side of the portion shown in FIG. 5A is the central axis L side (not shown). .. For convenience of explanation, in the state of FIG. 5A, it is assumed that the z direction is parallel to the vertical direction and both the x direction and the y direction are parallel to the horizontal direction, which will be described later with the force sense sensors 100B and 100C. The same applies to 100p to 100v.

In the force sensor 100A, the portion where the elastic connecting portion 5 connecting the support portion 6 and the receiving portion 4 (not shown) and the displacement conversion portion 3 are joined is referred to as a joining portion 11, and the force sensor 100B described later is referred to. , 100C, 100p-100v, the same designation is used. Further, a line orthogonal to the direction connecting the support portion 6 and the receiving portion 4 and passing through the center of the joint portion 11, that is, a straight line passing through the x-direction center of the joint portion 11 and parallel to the z-direction is defined as ". It is defined as "joint vertical straight line 12". In the force sensor 100A, the joint portion 11 is provided at the center in the length direction (center in the x direction) of the elastic connecting portion 5. That is, in the x direction, the distance E from the inner peripheral surface of the support portion 6 to the joint portion vertical line 12 is the same as the distance F from the boundary between the elastic connecting portion 5 and the receiving portion 4 to the joint portion vertical line 12. Is set to. Although the details will be described later, the position of the joint portion 11 is not limited to the central portion in the length direction of the elastic connecting portion 5, and is not limited to the support portion 6 side (closer to the outer circumference) or the central axis L side (center) (not shown). It can also be installed near).

The displacement conversion unit 3 is provided with an overhanging portion 15 protruding from the tip end portion on the sensor substrate 7 side toward the central axis L (not shown). The detection target body 8d is attached to the tip surface of the overhanging portion 15 so that the reflection surface that reflects the light emitted from the light source 10d (not shown) is parallel to the z direction. The overhanging portion 15 may be integrally formed with the displacement conversion portion 3, or may be prepared as a separate component and joined to the displacement conversion portion 3. In the force sensor 100A, the detection target body 8d is arranged on the side where the joint portion between the elastic connecting portion 5 and the receiving portion 4 is located, that is, on the central axis L side, rather than the joint portion vertical line 12. The displacement detection element 9d is mounted on the sensor substrate 7 so as to face the detection target body 8d.

In the force sensor 100A, the height h of the displacement conversion unit 3 is defined in the same manner as the force sensor 100 shown in FIG. Here, as shown in FIG. 5A, the vertical distance G of the detection target body 8d with respect to the elastic connection portion 5 is bisected with the z-direction thickness of the elastic connection portion 5 from the center of the surface of the detection target body 8d. It is defined as the length of the perpendicular line drawn on the line 21. Further, the length of the perpendicular line drawn from the surface center of the detection target body 8d to the joint vertical line 12 is defined as the horizontal distance J with respect to the joint vertical line 12 of the detection target body 8d. The height h, vertical distance G, and horizontal distance J of the displacement conversion unit 3 are similarly defined for the force sensor 100B, 100C, 100p to 100v, which will be described later.

5 (b) and 5 (c) are partial cross-sectional views of a first modified example and a second modified example of the force sensor 100A, respectively, and the portions corresponding to the portions shown in FIG. 5 (a) are shown in the table. Has been done. Since the displacement conversion unit 3 of the force sensor 100A has a substantially U-shape, the detection target bodies 8b (not shown) and 8d can detect the force applied to the force receiving unit 4 in the x direction. The detection target bodies 8a and 8c (both not shown) can detect the force applied to the receiving unit 4 in the y direction. On the other hand, in the first modification and the second modification shown in FIGS. 5 (b) and 5 (c), the force sensor 100A is changed to a configuration that does not detect the force acting in the horizontal direction. Is.

The first modification of the force sensor 100A is a displacement conversion unit that intersects the z-direction from the joint portion 11 at a predetermined angle θ and extends linearly in a direction approaching the central axis L (not shown) and the sensor substrate 7. Has 3A. The second modification of the force sensor 100A has a displacement conversion unit 3B extending in the z direction from the joint portion 11 to the sensor substrate 7 (not shown) and then extending in the direction toward the central axis L (not shown). In both the first modification and the second modification, the detection target body 8d is arranged in the displacement conversion unit so that the reflection surface is parallel to the z direction on the central axis L side of the joint portion vertical line 12. Will be done. The displacement detection element 9d (not shown) is arranged so as to face the detection target body 8d in the same manner as in the state shown in FIG. 5A.

FIG. 6A is a partial cross-sectional view of the force sensor 100B according to the second embodiment, and shows a portion corresponding to the portion shown in FIG. 5A. In the force sensor 100B, the structure of the other elastic connecting portion whose length direction is parallel to the x direction and the structure of the two elastic connecting portions whose length direction is parallel to the y direction are respectively. Since it is equivalent to the structure shown in FIG. 6 (a), the illustration and description will be omitted.

In the force sensor 100A, the reflection surface of the detection target body 8d is parallel to the z direction. On the other hand, in the force sensor 100B, the tip surface of the overhanging portion 15 is directed with respect to the z direction so that the reflective surface of the detection target body 8d intersects the z direction at a predetermined angle and faces the sensor substrate 7. It is an inclined surface. The displacement detection element 9d is mounted on the sensor substrate 7 so as to face the detection target body 8d. Since the other configurations of the force sensor 100B are the same as those of the force sensor 100A, overlapping description will be omitted. The vertical distance G and the horizontal distance J in the force sensor 100B are as shown in FIG. 6A according to the definitions described with reference to FIG. 5A.

6 (b) and 6 (c) are partial cross-sectional views of a first modified example and a second modified example of the force sensor 100B, respectively, and the portions corresponding to the portions shown in FIG. 6 (a) are shown in the table. Has been done. Similar to the force sensor 100A, the force sensor 100B can detect the force applied to the force receiving unit 4 in the x-direction and the y-direction. On the other hand, in the first modification and the second modification shown in FIGS. 6 (b) and 6 (c), the force sensor 100B is changed to a configuration that does not detect the force acting in the horizontal direction. Is.

In the first modification of the force sensor 100B, the angle of the light receiving surface of the detection target body 8d is the same as that of the force sensor 100B as compared with the first modification of the force sensor 100A (FIG. 5B). The other configurations are the same, except that they are changed to intersect the z direction at a predetermined angle. In the second modification of the force sensor 100B, the angle of the light receiving surface of the detection target body 8d is the same as that of the force sensor 100B as compared with the second modification of the force sensor 100A (FIG. 5 (c)). The other configurations are the same, except that they are changed to intersect the z direction at a predetermined angle. The displacement detection element 9d (not shown) is arranged so as to face the detection target body 8d in the same manner as in the state shown in FIG. 6A.

FIG. 7A is a partial cross-sectional view of the force sensor 100C according to the third embodiment, and shows a portion corresponding to the portion shown in FIG. 5A. In the force sensor 100C, the structure of the other elastic connecting portion whose length direction is parallel to the x direction and the structure of the two elastic connecting portions whose length direction is parallel to the y direction are respectively. Since it is equivalent to the structure shown in FIG. 7 (a), the illustration and description will be omitted.

The force sensor 100C differs from the force sensor 100B according to the second embodiment in that the light receiving surface of the displacement detection element 9d does not face the reflection surface of the detection target body 8d, but the other configurations are different. Since they are the same, common explanations will be omitted. In the force sensor 100C, the displacement detection element 9d is mounted on the sensor substrate 7 so that the normal of the light receiving surface is parallel to the z direction.

FIG. 7B is a diagram illustrating an optical path between the detection target body 8d and the displacement detection element 9d. The line orthogonal to the reflection surface of the detection target body 8d intersects the light receiving surface of the displacement detection element 9d at an angle η. FIG. 7C is an enlarged view of the displacement detection element 9d. In the force sensor 100C, a diffraction grating 13 having a light receiving surface having an inclination of an angle η formed so as to be parallel to the reflecting surface of the detection target body 8d is arranged on the surface (on the light receiving surface) of the displacement detection element 9d. There is. Therefore, the incident light from the detection target body 8d is refracted by the diffraction grating 13 as shown by the broken line in FIG. 7C, and is vertically incident on the light receiving surface of the displacement detection element 9d. As a result, the optical relationship between the detection target body 8d and the displacement detection element 9d on the force sensor 100C is equivalent to the optical relationship between the detection target body 8d and the displacement detection element 9d on the force sensor 100B. Become. The force sensor 100C can be changed to a configuration that does not detect the force acting in the x direction and the y direction in the same manner as in the first modification and the second modification of the force sensor 100B.

Next, the force sensor 100p to 100v according to Comparative Examples 1 to 7 to be compared with the force sensors 100A to 100C according to the above-mentioned Examples 1 to 3 will be described. 8 (a) and 8 (b) are partial cross-sectional views of the force sensors 100p and 100q according to Comparative Examples 1 and 2, respectively, and the parts corresponding to the parts shown in FIG. 5A are shown. ..

The force sensor 100p according to Comparative Example 1 is substantially the same as the force sensor 100 described with reference to FIG. That is, the detection target body 8d and the displacement detection element 9d are arranged so that their respective centers are located on the joint vertical straight line 12, and face each other in the z direction. In the force sensor 100p, the horizontal distance J with respect to the joint vertical line 12 of the detection target body 8d is zero (0) according to the definition described with reference to FIG. 5A. Further, the vertical distance G of the detection target body 8d by the force sensor 100p with respect to the elastic connecting portion 5 is, strictly speaking, a length obtained by adding the thickness of the detection target body 8d to the height h of the displacement conversion unit 3. However, it is considered that the thickness of the detection target body 8d is sufficiently smaller than the height h of the displacement conversion unit 3, and the vertical distance G is the same as the height h of the displacement conversion unit 3 in the force sensor 100p. do.

In the force sensor 100q according to Comparative Example 2, the displacement conversion unit 3 has a support portion from the tip portion on the sensor substrate 7 side so that the detection target body 8d is arranged on the support portion 6 side of the joint portion vertical line 12. An overhanging portion 15 projecting to the 6 side is provided. The detection target body 8d is attached to the tip surface of the overhanging portion 15 so that the reflection surface is parallel to the z direction. Further, the displacement detection element 9d is mounted on the sensor substrate 7 so as to face the detection target body 8d.

9 (a) to 9 (c) are partial cross-sectional views of the force sensor 100r, 100s, 100t according to Comparative Examples 3, 4 and 5, respectively, and are the parts corresponding to the parts shown in FIG. 5A. It is shown. The force sensor 100r according to Comparative Example 3 includes the same displacement conversion unit as the displacement conversion unit 3 and the overhanging unit 15 included in the force sensor 100A according to the first embodiment. Therefore, in the force sensor 100r, the detection target body 8d is arranged on the central axis L side of the joint vertical line 12. However, in the force sensor 100r, the detection target body 8d is attached to the surface facing the sensor substrate 7 at the tip of the overhanging portion 15, and faces the displacement detection element 9d mounted on the sensor substrate 7 in the z direction. In this respect, it differs from the force sensor 100A. In accordance with the definition described with reference to FIG. 5A, the horizontal distance J with respect to the joint vertical line 12 of the detection target body 8d in the force sensor 100r is the joint vertical line from the center of the surface of the detection target body 8d. It is the length of the vertical line drawn to 12. Further, similarly to the force sensor 100p according to Comparative Example 1, in the force sensor 100r, the vertical distance G is assumed to be the same as the height h of the displacement conversion unit 3.

The force sensor 100s according to Comparative Example 4 has a different arrangement of the detection target body 8d and the displacement detection element 9d as compared with the force sensor 100q according to Comparative Example 2, but the other configurations are the same as those of the force sensor 100q. be. In the force sensor 100s, the detection target body 8d is attached to the surface facing the sensor substrate 7 at the tip of the overhanging portion 15, and is arranged on the support portion 6 side of the joint portion vertical line 12. Further, the detection target body 8d faces the displacement detection element 9d mounted on the sensor substrate 7 in the z direction. Similar to the force sensor 100p according to Comparative Example 1, in the force sensor 100r, the vertical distance G is assumed to be the same as the height h of the displacement conversion unit 3.

In the force sensor 100t according to Comparative Example 5, the displacement conversion unit 3 has a support portion from the tip portion on the sensor substrate 7 side so that the detection target body 8d is arranged on the support portion 6 side with respect to the joint portion vertical line 12. An overhanging portion 15 projecting to the 6 side is provided. The force sensor 100t differs from the force sensors 100q and 100s in that the tip surface of the overhanging portion 15 is designed to intersect the z direction at a predetermined angle. The detection target body 8d is attached to the tip surface of the overhanging portion 15t, so that the reflection surface of the detection target body 8d intersects the z direction at a predetermined angle. Further, the displacement detection element 9d is mounted on the sensor substrate 7 so as to face the detection target body 8.

10 (a) and 10 (b) are partial cross-sectional views of the force sensors 100u and 100v according to Comparative Examples 6 and 7, respectively, and are shown by the portions corresponding to the portions shown in FIG. 5 (a). .. In the force sensor 100u according to Comparative Example 6, the positional relationship between the detection target body 8d and the displacement detection element 9d is the same as that of the force sensor 100A according to the first embodiment, and the detection target body 8d is more than the joint vertical line 12. It is arranged on the L side of the central axis. However, the height h of the displacement conversion unit 3 is higher in the force sensor 100u than in the force sensor 100A according to the first embodiment, as shown in the dimensions of each unit described later. Specifically, the force sensor 100u has a structure in which the sum of the distance E and the horizontal distance J described with reference to FIG. 5A is shorter than the height h of the displacement conversion unit 3.

The force sensor 100v according to Comparative Example 7 includes the same displacement conversion unit 3 as the displacement conversion unit 3 of the force sensor 100u according to Comparative Example 6. However, in the force sensor 100v, the reflection surface of the detection target body 8d is orthogonal to the z direction, and the center of the detection target body 8 is arranged so as to be located on the joint vertical line 12. It is different from the force sensor 100u.

Next, the sensitivities of Examples 1 to 3 (force sensor 100A to 100C) and Comparative Examples 1 to 7 (force sensor 100p to 100v) will be described. It should be noted that the detection target bodies attached to each of the four displacement conversion units 3 provided in the force sensor are equivalent, and the displacement detection elements facing each detection target body are also equivalent. The description will be described with the description of "body 8" and "displacement detection element 9".

Shapes (dimensions) are set for each of the force sensors of Examples 1 to 3 and Comparative Examples 1 to 7 as follows. Common to Examples 1 to 3 and Comparative Examples 1 to 7, the distance E and the distance F are both 14.75 mm. The cross-sectional area of the cross section that appears when the elastic connecting portion 5 is cut in the yz plane is 19.2 mm ² . Further, the cross-sectional area of each of the two cross sections appearing by cutting the two straight line portions parallel to the z direction in the displacement conversion unit 3 on the xy plane is also 19.2 mm ² . Common to Examples 1 to 3 and Comparative Examples 1 to 5, the height h of the displacement conversion unit 3 is 9.1 mm. In Comparative Examples 6 and 7, the height of the displacement conversion unit 3 is 36 mm. Common to Examples 1 to 3 and Comparative Examples 1 to 5, the vertical distance G is 9.1 mm. In Comparative Examples 6 and 7, the vertical distance G is 36 mm. Common to Examples 1 to 3 and Comparative Examples 2 to 5, the horizontal distance J is 9.1 mm. In Comparative Example 6, the horizontal distance J is 14.75 mm. In Comparative Examples 1 and 7, as described above, the horizontal distance J is zero (0). Further, the dimensions specified here are examples, and do not limit the dimensions of each part of the force sensor 100A to 100C according to the first to third embodiments.

A load of 40 N is applied in the −z direction to the receiving unit 4 of the force sensor 100 according to Examples 1 to 3 and Comparative Examples 1 to 7, and the sensitivity detected by the displacement detecting element 9 (detection for the displacement detecting element 9). The relative movement distance of the object 8) was measured. In all force sensors except Example 3, the displacement detection element 9 and the detection target body 8 face each other, so that the normal of the light receiving surface of the displacement detection element 9 and the light receiving surface of the detection target body 8d are facing each other. It is assumed that it is parallel to the normal of.

The measured values of sensitivity and rigidity of Examples 1 and Comparative Examples 1 and 2 are shown in FIG. 11 (a). The "observation direction" in FIG. 11 (a) is the direction in which the detection target body 8 and the displacement detection element 9 face each other except for the third embodiment, and also in FIGS. 11 (b) and 11 (c). The same is true. In the third embodiment, it is the normal direction of the light receiving surface of the detection target body 9. For example, in the first embodiment, since the detection target body 8 and the displacement detection element 9 face each other in a direction parallel to the xy plane (horizontal plane), the observation direction is defined as the horizontal direction.

In the force sensors of Examples 1 and Comparative Examples 1 and 2, the vertical distance G of the detection target body 8 with respect to the elastic connecting portion 5 is the same. It can be seen that in Example 1 in which the detection target body 8 is on the central axis L side of the joint portion vertical line 12, the sensitivity is higher than in Comparative Example 2 in which the detection target body 8 is on the support portion 6 side. Further, it can be seen that the sensitivity of Comparative Example 1 in which the detection target 8 is on the joint vertical line 12 is higher than that of Comparative Example 2, but lower than that of Example 1. From these facts, when the vertical distance G of the detection target body 8 with respect to the elastic connecting portion 5 is equal and the observation direction is the horizontal direction, the detection target body 8 is arranged on the central axis L side of the joint vertical line 12. By doing so, it can be seen that the sensitivity can be increased. Since the rigidity depends on the shape of the displacement conversion unit 3, it is the same for each force sensor.

The measured values of sensitivity and rigidity of Examples 2 and 3 and Comparative Examples 2 and 5 are shown in FIG. 11 (b). In these force sensors, the vertical distance G of the detection target body 8 with respect to the elastic connecting portion 5 is equal. In Example 2 and Comparative Example 5, the angle formed by the normal of the surface (reflecting surface) of the detection object 8 and the joint vertical line 12 is larger than 0 degrees. The sensitivity of Examples 2 and 3 in which the detection target body 8 is on the central axis L side of the joint portion vertical line 12 is higher than the sensitivity of Comparative Examples 2 and 5 in which the detection target body 8 is on the support portion 6 side. Since the rigidity depends on the shape of the displacement conversion unit 3, it is the same for each force sensor.

The measured values of sensitivity and rigidity of Comparative Examples 3, 1 and 4 are shown in FIG. 11 (c). In these force sensors, the vertical distance G of the detection target body 8 with respect to the elastic connecting portion 5 is equal. When the direction of the detection target body 8 is the z direction (vertical direction), whether the detection target body 8 is on the central axis L side of the joint vertical line 12, on the joint vertical line 12, or on the support 6 side is determined. It can be seen that it does not affect the sensitivity. Since the rigidity depends on the shape of the displacement conversion unit 3, it is the same for each force sensor. From the above comparison, the detection target body 8 is arranged on the central axis L side of the joint vertical line 12, and the angle formed by the normal surface of the surface of the detection target 8 and the joint vertical line 12 is from 0 degrees. It can be seen that the sensitivity can be increased by setting a large angle.

The measured values of sensitivity and rigidity of Comparative Examples 6 and 7 are shown in FIG. 11 (d). In these force sensors, the vertical distance G of the detection target body 8 with respect to the elastic connecting portion 5 is equal. In Comparative Example 6, the detection target body 8 is on the central axis L side, but the sensitivity of Comparative Example 6 is lower than that of Comparative Example 7 in which the detection target body 8 is on the joint vertical line 12. Recognize. Further, in Comparative Examples 6 and 7, the rigidity is lowered as compared with Examples 1 to 3 and Comparative Examples 1 to 5, and it is considered that this is due to the difference in the height of the displacement conversion unit 3. Be done. Further, in Comparative Example 6, the horizontal distance (the sum of the distance E (14.75 mm) and the horizontal distance J (14.75 mm)) from the support portion 6 of the detection target body 8 is the height h (36 mm) of the displacement conversion unit 3. Shorter than. When such conditions are met, even if the detection target body 8 is arranged on the central axis L side of the joint vertical line 12, the sensitivity is higher than that of the detection target body 8 on the joint vertical line 12. It can be seen that the effect of increasing is not obtained.

From the comparison of Examples 1 to 3 and Comparative Examples 1 to 7 described above, it can be seen that the sensitivity of the force sensor can be increased by satisfying the following first to third conditions. The first condition is that the detection target body 8 is arranged on the central axis L side of the joint vertical line 12. The second condition is that "the displacement conversion unit 3 is in a non-displacement state and the normal direction (direction orthogonal to the reflection surface) of the surface of the detection object 8 does not face the z direction (vertical direction)". The third condition is "the distance from the inner peripheral surface of the support portion 6 to the detection target body 8 is longer than the height of the displacement conversion portion 3".

In the comparison of Examples 1 to 3 and Comparative Examples 1 to 7, in each force sensor corresponding to each example, the vertical distance G with respect to the elastic connecting portion 5 of the detection target body 8 is the height of the displacement conversion portion 3. It is performed under the condition that it is equal to h. Therefore, the first to third conditions indicate the conditions for increasing the sensitivity when the thickness of the entire force sensor (height in the z direction of the force sensor) is the same. The height h of the displacement conversion unit 3 and the sensitivity have a positive correlation. Therefore, in terms of design, the height of the displacement conversion unit 3 is increased in Comparative Example 1 (the thickness of the entire force sensor is thick), and the height of the displacement conversion unit 3 is decreased in Examples 1 to 3. (The thickness of the entire force sensor is thin), and it is possible to obtain the same sensitivity. Further, as can be seen from the above comparison results, the rigidity of the force sensor tends to improve when the height of the displacement conversion unit 3 is low. Therefore, in the force sensor according to the first to third embodiments, it is possible to make the sensor thinner and improve the rigidity while maintaining the sensitivity. On the contrary, the sensitivity can be increased by changing the arrangement of the detection target body 8 as in Examples 1 to 3 without changing the height of the force sensor from the conventional height.

Next, the reason why the first to third conditions contribute to the increase in the sensitivity of the force sensor will be described with reference to FIG. FIG. 12A is a partial cross-sectional view of a force sensor that has an effect of increasing sensitivity. Here, the first modification of the force sensor 100B according to the second embodiment will be taken up. 12 (b) shows the deformation of the elastic connecting portion 5 and the displacement conversion portion 3 after an external force is applied in the −z direction to the receiving portion 4 (not shown) on the right side of the elastic connecting portion 5 of FIG. 12 (a). It is sectional drawing which shows the later state. In FIGS. 12 (a) and 12 (b), hatching in each part is omitted in order to specify the dimensions and the like of each part.

The height h, the distance E, the vertical distance G, and the horizontal distance J of the displacement conversion unit 3 shown in FIG. 12 (a) follow the definitions described with reference to FIGS. 5 (a) and 6 (a). Here, the detection target body 8 is arranged so that the height h of the displacement conversion unit 3 and the vertical distance G are equal to each other. The intersection of the line 21 and the joint vertical straight line 12 is defined as the junction center point 14a, and the distance from the junction center point 14a to the surface center of the detection target body 8 is defined as “w”. Further, the angle formed by the straight line connecting the joint portion center point 14a and the surface center of the detection target body 8 with the joint portion vertical straight line 12 is defined as “β”, and the normal of the reflection surface in the detection target body 8 is in the z direction (joint portion). The angle formed by the vertical line 12) is defined as "γ". The angles β and γ take positive values when the detection target body 8 is on the central axis L side (right side in FIG. 12A) of the joint portion vertical line 12 (not shown), and the support portion 6 It shall take a negative value if it is on the side. Further, it is assumed that the detection target body 8 and the displacement detection element 9 face each other in a state where no external force is applied to the force sensor. As shown in FIG. 12B, the angle formed by the deformed elastic connecting portion 5 with the horizontal plane is defined as “dα”. It is assumed that the joint center point 14a moves to the joint center point 14b after deformation, and the joint vertical line 12 is inclined according to the joint vertical line 12'after deformation.

The locus of the detection target body 8 at the time of deformation can be considered to consist of the following first movement and second movement. The first movement is a movement in the −z direction (downward in the vertical direction) due to the rotation of the joint portion center point 14a by dα about the boundary point between the support portion 6 and the elastic connecting portion 5. The second motion is a motion that rotates by dα around the joint center point 14b after deformation. Since these motions are projected in the direction forming an angle β with respect to the z direction (vertical direction) which is the observation direction by the displacement detection element 9, the detection target body 8 is zx by the first motion and the second motion, respectively. It moves on the plane by the amount represented by the vectors of the following equations 1 and 2. In the following calculation, the height h (= wcosβ) of the displacement conversion unit 3 is assumed to be constant.

The sensitivity is the vector of the sum of the displacements represented by the following equations 1 and 2 projected onto the detection target body 8. The installation direction of the detection target body 8 on the zx plane is represented by the following equation 3. Therefore, if the absolute value of the projection component is taken by adding the displacements of the following equations 1 and 2 to the direction represented by 3 below, and note that J = wsinβ and h = wcosβ, the sensitivity is the following equation 4 It is represented by.

When the detection target body 8 is on the joint vertical line 12 (for example, in the case of the force sensor 100p according to Comparative Example 1), β = 0 degrees, γ = 0 degrees, and w = h, so that the sensitivity is hdα. Will be. Hereinafter, the sensitivity of the force sensor is evaluated using the sensitivity hdα as a reference value.

13 (a) and 13 (b) show a graph of the relationship between the angle β and the sensitivity with respect to a predetermined angle γ. In FIGS. 13 (a) and 13 (b), the sensitivity increase rate on the vertical axis is the value of the sensitivity calculated by the above equation 4 divided by the reference value (= hdα). As can be seen from FIG. 13, when the angle γ takes a positive value under the condition that the height h of the displacement conversion unit 3 takes a positive value, the sensitivity increase rate becomes 1 or more when the angle β takes a positive value. It can be seen that the effect of increasing sensitivity appears remarkably. Further, it can be seen that the larger the angle β (the longer the horizontal distance J), the greater the effect of increasing the sensitivity. On the other hand, even when the angle γ takes a negative value, there is a tendency that the sensitivity increasing effect can be obtained by taking a positive value and increasing the value, but the range of the angle β where the sensitivity increasing effect can be obtained. It can be seen that is limited.

When β> 0, γ = 90 degrees (the detection object 8 and the displacement detection element 9 face each other in the horizontal direction, are on the central axis L side of the joint vertical line 12, and the reflection surface is parallel to the xy plane. Case), the above equation 4 can be modified as the following equation 5. From this, the sensitivity increase condition is expressed by the following equation 6. From this, it can be seen that when the horizontal distance (= E + J) from the detection target body 8 to the support portion 6 is longer than the height h of the displacement conversion unit 3, there is an effect of increasing the sensitivity. That is, the sensitivity of the force sensor according to the present embodiment is expressed by a function of the horizontal distance (E + J) from the detection target body 8 to the support portion 6, and thus the displacement conversion unit 3 is provided with respect to the elastic connecting portion 5. It can be seen that it does not depend on the position of the joint center point 14a. In the above-mentioned Comparative Example 6 in which the height h of the displacement conversion unit 3 does not satisfy the following equation 6, the sensitivity increasing effect cannot be obtained, and the sensitivity is inferior to that of the Comparative Example 7.

When γ = 0 degrees, that is, when the detection target body 8 and the displacement detection element 9 face each other in the z direction in a state where no external force is applied to the receiving unit 4 (not shown), the above equation 4 is as follows. It can be transformed according to Equation 7. From the following equation 7, it can be seen that the sensitivity increase rate is 1 when γ = 0 degrees, regardless of the value of the angle β. This means that the detection target body 8 and the displacement detection element 9 face each other in the z direction under the condition that the height h of the displacement conversion unit 3 is constant (Comparative Examples 1, 3 and 4). Then, it can be seen that the sensitivity is constant regardless of the angle β regardless of the position of the detection target body 8, and the effect of increasing the sensitivity cannot be obtained. This result is in agreement with the result shown in FIG.

By the way, in various devices provided with a force sensor, if the receiving portion is greatly deformed by the force acting on the receiving portion, the elastic connecting portion may vibrate greatly due to its own weight. For example, in an application for detecting a force in a place where the movement is large, such as attaching to the tip of a robot arm or the like, the vibration of the elastic connecting portion appears as noise in the measured value. In addition, when a force sensor is used to detect the force applied to a predetermined part of the robot hand, there is a request to shorten the stroke from the hand mounting portion to the tip of the hand, and the force sensor is used to meet this demand. Is required to be thinner. Further, a human interactive end effector such as a manipulator, which is an example of a medical robot, is required to have a performance capable of detecting a very small force with high accuracy, that is, an improvement in sensitivity.

By configuring the force sensor so as to satisfy the first to third conditions in response to such a requirement, it is possible to increase the sensitivity without increasing the thickness of the entire force sensor while maintaining the rigidity. It will be possible. Conversely, it is possible to reduce the thickness of the entire force sensor while maintaining the sensitivity characteristics. This makes it possible to improve the performance of various devices equipped with a force sensor.

Although the present invention has been described in detail based on the preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various embodiments within the range not deviating from the gist of the present invention are also included in the present invention. included. Further, each of the above-described embodiments is merely an embodiment of the present invention, and each embodiment can be appropriately combined. For example, in the above embodiment, with respect to the combination of the detection target body 8 and the displacement detection element 9, the means for optically detecting the displacement is used, but the means for detecting the capacitance and the magnetic flux density may be used.

3 Displacement conversion unit (displacement direction conversion unit)
4 Receiving part 5 Elastic connection part 6 Support part 7 Sensor board 8,8a to 8h Detection target 9,9a to 9h Displacement detection element 11 Joint part 12 Joint part Vertical line 100A, 100B, 100C Force sensor

Claims (6)

Support part and
A receiving part that is displaced with respect to the support part due to the action of an external force,
An elastic connecting portion that connects the supporting portion and the receiving portion,
A displacement conversion unit that is joined to the elastic connection unit and displaces according to the load input to the force receiving unit.
The detection target provided in the displacement conversion unit and
The sensor board fixed to the support and
A force sensor that is mounted on the sensor board and includes a displacement detection element that detects the amount of displacement of the detection target.
The detection target passes through the center of the joint portion between the displacement conversion portion and the elastic connecting portion, and the elastic connecting portion and the receiving force are more than a straight line orthogonal to the direction in which the supporting portion and the receiving portion are connected. It is placed on the side where the joint with the part is located,
The normal of the detection target and the straight line form an angle larger than 0 degrees.
A force characterized in that the distance between the detection target body and the support portion in the direction connecting the support portion and the receiving portion is longer than the height of the displacement conversion portion in the direction parallel to the straight line. Sensory sensor. Support part and
A receiving part that is displaced with respect to the support part due to the action of an external force,
An elastic connecting portion that connects the supporting portion and the receiving portion,
A displacement conversion unit that is joined to the elastic connection unit and displaces according to the load input to the force receiving unit.
The detection target provided in the displacement conversion unit and
The sensor board fixed to the support and
A force sensor that is mounted on the sensor board and includes a displacement detection element that detects the amount of displacement of the detection target.
The detection target passes through the center of the joint portion between the displacement conversion portion and the elastic connecting portion, and the elastic connecting portion and the receiving force are more than a straight line orthogonal to the direction in which the supporting portion and the receiving portion are connected. It is placed on the side where the joint with the part is located,
The normal of the detection target and the straight line form an angle larger than 0 degrees.
The distance between the detection target and the support in the direction of connecting the support and the receiving portion is the vertical distance from the detection target to the elastic connection in the direction parallel to the straight line. A force sensor characterized by being longer than. The force sensor according to claim 1 or 2, wherein the displacement detecting element and the detection target body face each other. The force sensor according to any one of claims 1 to 3, wherein the angle formed by the normal line of the detection target and the straight line is 90 degrees. A light source for irradiating the detection target with light is provided.
The displacement detecting element is characterized in that it receives the reflected light from the detection target body of the light emitted from the light source to the detection target body and detects the displacement amount of the detection target body. The force sensor according to any one of 4. A light source for irradiating the detection target with light is provided.
The detection object has a reflecting surface that reflects the light emitted from the light source.
The displacement detecting element has a light receiving surface that receives the reflected light from the detection target body and a diffraction grating provided on the surface of the light receiving surface.
The detection target and the displacement detection element are arranged so that the normal of the reflection surface and the normal of the light receiving surface intersect at a predetermined angle.
According to any one of claims 1, 2, 4, and 5, the diffraction grating is characterized in that the reflected light from the detection target is refracted at the predetermined angle and vertically incident on the light receiving surface. The described force sensor.

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