JP2007315878A - Multi-axis force/moment sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a multi-axis force/moment sensor which does not use spherical kinetic pair structure that is difficult to be applied to linking mechanisms, between coupling members and a base part and a power receiving part, moreover, can obtain linear characteristics approximately equal to those an original Stewart platform structure as for an applied force and strain, and can obtain an appropriate amount of displacement with respect to the applied force, and thereby facilitates application to miniaturization. <P>SOLUTION: Each rod 6 is linked to an upper flange 1 and a lower flange 2 by fastening structures, and each rod 6 is constituted of an elastic ring 5, and an upper linking rod 3 and a lower linking rod 4 in a bar shape which are coupled to both ends of this elastic ring 5, and are arranged on the same axis as the axis of a force that is applied to the rod 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multi-axis force sensor that measures the forces and torques of a plurality of axes applied to an object by measuring strain generated in the object, and in particular, to realize downsizing of the apparatus. is there.

  The basic configuration of a force sensor that measures strain generated in an object by force and torque and measures the magnitude of the force and torque is composed of a structure body and a sensor section that form a sensor body, and an electric circuit section. The structure includes a fixed base portion, a force receiving portion to which an external force acts, and a coupling member that connects the base portion and the force receiving portion. In the force sensor, a structure configured to cause a certain strain or displacement with respect to an applied force is hereinafter referred to as a strain generating body. The sensor unit measures strain and displacement using various sensors attached to the strain generating body. In the electric circuit unit, an output value such as a voltage from the sensor unit is processed or a value is corrected. The force receiving portion is displaced according to the applied external force, and the magnitude of the generated displacement is read by the sensor portion. It is necessary to read displacements at a plurality of locations according to the number of force and torque axes to be measured and the obtained displacement processing method. The correlation between these displacements and external force is obtained theoretically or experimentally in advance, and the value of the force applied from the displacement is obtained using the obtained correlation.

If the force applied to an object of a certain shape is only in one axial direction, the proportional force is established between the applied force and the generated strain in the range of elastic deformation. It is possible to accurately calculate the force applied from the strain. However, when two or more axial forces are applied simultaneously, the relationship between the generated strain and the force becomes non-linear, and the error between the force calculated from the amount of strain and the actual force increases.
Thus, if a linear relationship cannot be obtained between the applied force and the generated strain, for example, as shown in Patent Document 1, for example, it is necessary to perform complicated correction processing in an electric circuit unit. The detection operation becomes complicated.

  In order to cope with such a problem, some device is usually applied to the structure of the strain generating body and the sensor arrangement. For example, in Patent Document 2, six-axis forces and moments, in this case, the three orthogonal axes forces and moments around each axis are placed parallel to each other as the strain generating bodies of the load cell whose measurement target is measured. In addition, a so-called Stewart platform structure is used, which is composed of two discs and six rods that are coupled to each other and are arranged in a pair so as to face each other. In this structure, the six-axis force applied to the disk is expressed by a linear combination of the compression and tensile forces of the six rods. Therefore, by measuring the strain in the axial direction of the six rods with a strain sensor such as a strain gauge, even when a plurality of axial forces act on the disk at the same time, without increasing the calculation error due to force interference, You can know the applied force.

JP-A-3-245028 (see page 1, right column, line 12 to page 2, upper right column, line 5; page 3, left column, lines 16 to 38) JP-A-6-58830 (see paragraphs 0011 to 0014, FIGS. 1 and 2)

Incidentally, there is a demand for downsizing of this type of force sensor depending on its use and the like. The following problems can be considered when trying to realize this demand for miniaturization.
That is, the Stewart platform structure described above is based on the premise that the base part, the force receiving part, and the connecting member (rod) are connected by a so-called ball pair structure such as a ball joint. This is because, when the connection between the rod and the base portion and the force receiving portion is a ball pair, the moment (bending force) is not transmitted from the force receiving portion to each rod, but only the axial force of compression tension is transmitted. This is because each rod only undergoes linear deformation, and as a result, only the linear deformation occurs in the entire strain generating body. However, in order to actually create an ideal ball-pair structure, precise processing is required. Therefore, it is difficult to create ball joints at both ends of the rod, especially when the force sensor is downsized. Costs also increase significantly.

  Further, when a displacement sensor is used as a means for measuring deformation of the strain body due to the force applied to the force sensor, the rigidity of the strain body is adjusted so that a displacement that can be measured with sufficient sensitivity is generated. There is a need. In the case of this structure, the rigidity is adjusted by changing the axial rigidity and mounting angle of the rod. However, considering the construction of a small force sensor, since it is necessary to cause a certain displacement with respect to a slight rod length, it is necessary to reduce the rigidity. In order to reduce the rigidity by simply making the rod shape columnar, it is conceivable to select a material having a low Young's modulus. However, since the physical properties of metal materials are limited, the only way to reduce the cross-sectional area is to reduce the rigidity. When the cross section becomes narrower with respect to the rod length, the rigidity against bending and torsion is lower than the rigidity against the axial load, and becomes brittle. For this reason, there is a possibility that the required mechanical strength cannot be maintained due to bending or buckling due to the compressive load, so that it is particularly difficult to use as a strain generating body of a small force sensor.

  The present invention was made to solve the above-described problems, without adopting a structure of a ball pair that is difficult to apply to the coupling mechanism between the base portion and the force receiving portion and the coupling member, With regard to the applied force and strain, linear characteristics almost the same as the original Stewart platform structure can be obtained, and an appropriate amount of displacement can be obtained with respect to the applied force, making it easy to apply to miniaturization. An object is to obtain a multi-axis force sensor.

  A multi-axis force sensor according to a first invention includes a fixed base portion, a force receiving portion to which a load to be detected is applied that is arranged at a predetermined distance from the base portion, and a base portion and a force receiving portion. Based on the mechanical characteristics obtained in advance for the strain generating body, the force receiving portion or a predetermined force of the force received by the force receiving portion from the load is input based on the displacement of each rod. It is a multi-axis force sensor that outputs each axial component, and each rod is connected to the foundation and force receiving portion with a fixed structure, and each rod is against the rigidity in the axial direction of the force applied to the rod. It is composed of an elastic body that increases the rigidity in the bending direction.

  The multi-axis force sensor according to the second invention includes a fixed base portion, a force receiving portion to which a load to be detected is applied that is arranged at a predetermined distance from the base portion, and a base portion and a force receiving portion. Based on the mechanical characteristics obtained in advance for the strain generating body, the force receiving portion or a predetermined force of the force received by the force receiving portion from the load is input based on the displacement of each rod. A multi-axis force sensor that outputs each axial component, wherein each rod is connected to the base portion and the force receiving portion with a fixed structure, and each rod is coupled to an elastic body and both ends of the elastic body. And a rod-shaped connecting rod arranged coaxially with the axis of the force applied to.

  In the multi-axis force sensor according to the first invention, as described above, each rod is composed of an elastic body whose rigidity in the bending direction is larger than the rigidity in the axial direction of the force applied to the rod. Even if the connection between the rod and the foundation and force receiving part is fixed, the rod has a linear characteristic with respect to the applied force and strain that is displaced only in the axial direction while maintaining rigidity against bending and torsion. As a result, the axial stiffness of the elastic body is reduced, and the displacement with respect to the applied force is increased while maintaining the required mechanical strength, so that the displacement can be easily and reliably detected.

  In the multi-axis force sensor according to the second invention, as described above, each rod is connected to the elastic body and a rod-like connection that is coaxially arranged with the axis of the force applied to the rod connected to both ends of the elastic body. Because it is composed of rods, the rigidity of bending and torsion is low only in the vicinity of the connecting part of the connecting rod at the end of the rod when viewed from the rod as a whole, even if the connection between each rod and the foundation and force receiving part is fixed. Because of the structure, the moment of the error factor generated at the binding site is absorbed by the connecting rod and is not transmitted to the elastic body, linear characteristics are obtained with respect to the applied force and strain, the detection operation becomes simple, and as an elastic body By reducing the rigidity in the axial direction, the displacement with respect to the applied force is increased while maintaining the necessary mechanical strength, and the detection of the displacement is easily and reliably performed.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing a 6-axis force sensor according to Embodiment 1 of the present invention. Here, the six-axis force refers to the forces in the axial directions of the x, y, and z orthogonal three axes shown in FIG. There are two plate-like members of an upper flange 1 that receives force as a force receiving portion and a lower flange 2 that is a fixed base portion, and these are connected by six rods 6. The upper flange 1, the lower flange 2, and the rod 6 constitute a strain body.
The rod 6 includes an elastic ring 5 which is an annular structure, an upper connecting rod 3 for connecting the elastic ring 5 to the upper flange 1, and a lower connecting rod 4 for connecting the lower flange 2. The connecting rods 3 and 4 and the flanges 1 and 2 are coupled by a fixing structure such as welding, bolting, cutting out from a pin or an integral member. Since a perfect ball-pair structure is not required, it can be easily realized even in downsizing. The fixing structure is not a joining method such as welding that completely eliminates the degree of freedom, but a joining method having a single axis degree of freedom such as pinning, or a joining method having a biaxial degree of freedom. Even if only two degrees of freedom are reduced, the realization is considerably easier. Note that the reason why linear mechanical characteristics can be obtained as a strain generating body as described above will be described later.

  The connecting rods 3 and 4 and the elastic ring 5 are joined by means such as welding or bolting. Alternatively, it is configured by cutting out from an integral member or punching out from a plate-like member. Each rod 6 is arranged at equal intervals along the concentric circumferential direction from the center of the upper flange 1 and the lower flange 2, and the two rods 6 face each other at a predetermined angle with a predetermined angle. It is attached in the form.

  FIG. 2 is a view showing the state where the upper flange 1 is removed in order to display the inside of the force sensor in an easy-to-understand manner. From the lower flange 2, a PD mounting portion 9 which is a portion for mounting the quadrant photodiode PD7 protrudes, and the quadrant photodiode PD7 is mounted here. A diode mounting portion 10 to which a diode D8 that is a light source of the quadrant photodiode PD7 is attached is attached to the upper flange 1, and a diode D8 is attached to the quadrant photodiode PD7 so as to face it. Three pairs of quadrant photodiodes PD7 and diodes D8 are attached so as to be 120-degree rotationally symmetric, and as shown in FIG. 3, coordinate systems xi, yi, zi, i = 1 of the respective diodes D8. 2 and 3 are attached so that the yi-axis direction and the z-axis direction of the coordinate axis of the entire force sensor coincide.

  Next, assuming that the strain body of FIG. 1 has an original Stewart platform structure and the applied force and the generated displacement have a linear relationship, the upper flange to which a load is applied as a multi-axis force sensor. The procedure for detecting the 6-axis force and moment acting on 1 will be described. However, since this part is not a main part of the present invention but is known per se, it will be described only in outline.

A displacement sensor for detecting the displacement generated in the upper flange 1 quadrant photodiode PD7 has got four light receiving regions indicated by S ₁ to S ₄ in FIG. 4, the pin diode D8 to these areas Light focused by the hall is projected. Output signals I _{1 to} I ₄ are obtained according to the light intensity to each light receiving region. When the relative position of the quadrant photodiode PD7 and the diode D8 changes, the ratio of light projection to each light receiving region also changes. Therefore, the displacements Dx and Dy in the x-axis direction and the y-axis direction in the figure are as follows: It is expressed by the relationship.

Dx = I ₁ −I ₂ −I ₃ + I ₄ (1)
Dy = I ₁ + I ₂ −I ₃ −I ₄ (2)

When the six displacements obtained from the three sets of diodes are D∈R ^{6 × 1,} and the six-axis displacement generated in the upper flange 1 by the force is X∈R ^{6 × 1} , the relationship between them is given by expressed.

  Note that r in the above equation is the distance on the xy plane from the center of the upper flange 1 to the light receiving surface of each of the four-division photodiodes PD7 in FIG.

  Due to the above relationship, the displacement of the upper flange 1 can be obtained from the output of the displacement sensor. In the example of FIG. 3, the displacement sensors are shown in a 120 ° symmetrical arrangement, but for example, the arrangement of the displacement sensors can be changed as shown in FIG. When the arrangement of the displacement sensors is changed, a similar effect can be obtained by obtaining a matrix corresponding to the conversion matrix A of Expression (3) according to the arrangement. Here, the quadrant photodiode PD7 and the diode D8 as the light source are given as examples of the displacement sensor. However, the sensor is not limited to this as long as the sensor can measure a two-dimensional displacement. For example, PSD, CCD, The same effect can be obtained with a sensor using capacitance.

  Furthermore, by applying a transformation matrix G obtained from information on the mounting positions of the rods 6 on the upper flange 1 and the lower flange 2, it matches the x, y, z coordinate axis directions applied to the center of the upper flange 1. The relationship between the forces fx, fy, fz and moments Mx, My, Mz around the x, y, z coordinate axes and the axial forces fi, i = 1,. Is done.

  By obtaining the inverse matrix of the transformation matrix G, conversely, the force acting on each rod 6 from the force applied to the upper flange 1 can also be obtained from the following equation.

  In general, the relationship between the displacement X generated in the structure and the applied force F (fx, fy, fz, Mx, My, Mz) is obtained by measuring the displacement when only one of the axial forces is applied. It is expressed as the following equation using a matrix that converts the force and displacement obtained by changing the axial force to apply the force to all axial forces.

X = CF (6)
F = C ⁻¹ X (7)

The matrix C is called a compliance matrix, and C ⁻¹ is called a stiffness matrix. By obtaining the matrix C, it is possible to know the applied force by removing this influence even if a displacement occurs in the other axial direction due to one axial force. However, since the matrix C obtained by this method is obtained from the displacement when only one axial force is applied, an accurate value is not always derived when a plurality of axial forces are applied simultaneously. If the displacement due to each axial force is expressed by linear superposition when other axial forces are applied at the same time, an accurate value can be known from the matrix C.

  When the Stewart platform structure is used as the strain generating body, as shown in the above equation (5), all applied 6-axis forces are converted into uniaxial forces of rod compression or tension. For this reason, even if a plurality of axial forces are simultaneously applied, these axial forces do not act so as to change the displacement characteristics of the structure, and therefore, a linear relationship is established between the respective axial forces and displacements. Therefore, it is possible to know the force applied with high accuracy by the calculation using the matrix C.

By using the relational expression obtained above, that is, based on the detection output D of the displacement sensor using the four-division photodiode PD7, the generated displacement X of the upper flange 1 is obtained by the expression (3). Based on X, the six-axis force applied to the upper flange 1 can be obtained by the equation (7).
Further, the displacement generated in each rod 6 is detected, the force fi generated in each rod 6 is obtained from each displacement and the rigidity of the rod 6, and applied to the upper flange 1 by the equation (4) based on this force fi. It is also possible to determine the 6-axis force.

Next, the structure of the rod 6 that is the main part of the present invention and the mechanical characteristics based on the structure will be described. First, a connection structure between each rod 6 and the upper and lower flanges 1 and 2 will be described.
As described above, this connection structure employs a fixing structure that can be formed relatively easily even when downsized. FIG. 6 shows one rod 6 alone. The connecting portion 20 is a portion connected to the upper flange 1 and the lower flange 2, and is fixedly connected to the flanges 1 and 2 by welding or the like, for example.

As shown in FIG. 6, in the rod 6 according to the first embodiment, the coupling portion 20 is not directly attached to the end portion of the circular elastic ring 5 as an annular shape, but the connecting rod 3 made of a columnar member is interposed therebetween. 4 is provided. The material and dimensions of the connecting rods 3 and 4 are selected so that the strain caused by the load has a sufficient margin with respect to the elastic limit.
The presence of the connecting rods 3 and 4 can reduce the influence of the moment at the connecting portion 20. That is, since the columnar members constituting the connecting rods 3 and 4 have lower rigidity against bending and torsion than the rigidity against compressive load, the entire rod 6 is bent and twisted only in the vicinity of the connecting portion at the end of the rod 6. The structure has low rigidity. For this reason, the moment of the error factor generated at the coupling site is absorbed by the connecting rods 3 and 4 at the end of the elastic ring 5 and is not transmitted to the elastic ring 5. Further, the bending torsional deformation of the connecting rods 3 and 4 occurs only at a small portion at the end of the rod 6, and the axial force is transmitted to the elastic ring 5 through the connecting rods 3 and 4. Therefore, it is possible to obtain the same effect as when the ball pair structure is used at the end of the rod 6 in a pseudo manner.

  In other words, even if both the flanges 1 and 2 and the rod 6 are connected by a fixed structure, the applied force and the generated displacement are linearly equivalent to a Stewart platform that originally has this connection as a ball-pair structure. A relationship is obtained. Therefore, the downsizing of the sensor can be realized easily and simply, and the six-axis force and moment applied to the upper flange 1 by the load can be detected without requiring complicated correction processing.

Next, as the structure of the rod 6 that is the main part of the present invention and the mechanical characteristics based on the structure, the effect of increasing the displacement with respect to the load will be described.
The difficulty in pursuing this increase in the amount of displacement while the rod remains in the shape of a columnar member has been briefly mentioned above, but will be described in more detail here.

For example, a general small force sensor having a rated load of about 10 kg has an outer diameter φ of about 70 mm and a height of about 25 mm. When measuring the deformation of a strain generating body using a displacement sensor, it is necessary to cause a certain large deformation with respect to the rated load. The amount of deformation is 25 μm with respect to the rated load in the z-axis direction of 12 kg. For example, when the inclination θ of the rod 6 is 30 °, the rod length is 29 mm or less at the longest. From the formula (5), when a load of 12 kg is applied, a load of about 2.3 kg is applied to each rod 6. In order for each rod 6 to be deformed by 25 μm in the z-axis direction with respect to this load, it is necessary to deform approximately 29 μm in the axial direction of the rod 6. Here, if the material of the rod is a general iron material, its Young's modulus is about 2.1 × 10 ⁵ MPa, so that a displacement of 29 μm occurs on a 29 mm long rod with a load of about 2.3 kg. The cross-sectional area of the rod to be used is 1.1 × 10 ⁻¹ mm ² , and if the rod 6 is cylindrical, the diameter is about 0.37 mm. When the rod 6 becomes thin in this way, the rod 6 may bend when a compressive load is applied, which may cause buckling.

  This is because when the force sensor is downsized, it is necessary to cause a large displacement with a small member with respect to a certain small load, and it is necessary to reduce the rigidity of the rod 6. A method of preventing buckling by preliminarily applying tension to the rod 6 and canceling the applied compressive force is also conceivable, but in this case, a large stress is generated in the rod 6 when a tensile load is applied. For this reason, it is difficult to prevent plastic deformation with respect to the rated load or to increase the safety factor for the load so as to withstand an excessive load. For example, when a 29 mm rod causes a displacement of 29 μm, the strain becomes 0.1%, so it is difficult to increase the safety factor.

In the first embodiment of the present invention, with respect to such a problem that arises in downsizing, by providing the elastic ring 5 in the rod 6, sufficient displacement is generated and stress generated in each part of the member is generated. It is possible to keep the safety factor high while keeping it low.
As shown in FIG. 7, the Young's modulus of the material is E, the radius to the center of the ring is r _r , the width of the ring cross section is b, the thickness is h, and the force f is applied in the direction of the diameter of the elastic ring 5. Suppose that That is, the axis of the force f applied to the elastic ring 5 is parallel to a plane including the ring shape, and the ring shape is line-symmetric with respect to the axis when viewed from a direction perpendicular to the plane. ing. The displacement d in the force direction of the ring at this time is expressed by the following equation.

Further, the maximum strain at this time is generated on the inner surface of the portion where the force is applied to the ring, and the value ε _max is expressed by the following equation.

For example, if r _r = 6.5 mm, h = 0.6 mm, and b = 6.3 mm, the same displacement of about 29 μm is generated for the same load of about 2.3 kg as in the case of examining the rod-shaped rod, The maximum strain at that time is about 0.05%, which is greatly reduced. Thus, by providing the elastic structure portion (elastic ring 5) in the rod, it is possible to prevent buckling and plastic deformation from occurring while causing sufficient displacement with respect to the load. Further, by using spring steel such as SUP10 as a material, it is possible to further increase the allowable strain amount.

  Further, since the elastic structure portion has a ring shape, the rigidity can be easily adjusted by changing the diameter, thickness and width of the ring. The adjustment of the thickness of the ring can be easily performed with a lathe or the like, and it is also easy to process the cylindrical member to a certain width. Therefore, by using a ring-shaped member for the elastic structure portion, a desired elasticity can be obtained. It can be obtained very easily.

  Thus, providing the elastic structure part in the rod also has the following meaning. That is, by increasing the number of members that are deformed by the load, the load applied per unit amount of the members and the amount of displacement to be generated can be reduced. As a result, even when a small number of members need to be displaced like a small sensor, it is possible to configure a strain generating body while preventing buckling and plastic deformation.

In the above description, the upper flange 1 to which the diode D8 is attached is used as the force receiving portion. However, the same effect can be obtained when the lower flange 2 is used as the force receiving portion.
In the above description, the inclinations θ of the rods 6 are all set to the same value. However, the inclinations of the individual rods do not have to be the same, and the same applies to the case where the inclinations of the rods are different. The effect of can be obtained. However, in this case, the transformation matrices G and C in the equations (4) to (7) need to be corrected accordingly.

Embodiment 2. FIG.
FIG. 8 is a diagram showing the rod 6 of the multi-axis force sensor according to Embodiment 2 of the present invention. That is, instead of using a rod-shaped elastic body as the rod 6, a rod having a spring-shaped elastic body 11 formed in a spiral shape as shown in FIG. 8 may be used. In this example, a coil spring formed by winding a wire is used as an elastic body. The amount of deflection δ with respect to the force f of the coil spring is expressed by the following equation, where d is the wire diameter of the coil, D is the average diameter of the coil, n is the effective number of turns, and G is the transverse elastic modulus of the wire material.

  Thereby, it is possible to obtain arbitrary rigidity. By using such a spring for the elastic body, the columnar portions of the connecting rods 3 and 4 at both ends thereof and the elastic body can be integrated, so that the rod can be easily formed.

Further, the maximum torsional stress τ _max of the spring is expressed by the following equation where the load is f and the spring index is c = D / d.

Here, κ is the stress correction factor of the whirl.
The maximum torsional stress of the spring is generated inside the spring. For example, if the material is spring steel (G = 7.85 × 10 ⁴ MPa), a spring that produces the same displacement with respect to the same load as the ring shape with a strand diameter of 2.5 mm and an average coil diameter of 5 mm The maximum torsional stress is about 36 MPa, which is sufficiently smaller than the allowable torsional stress of the material of 500 MPa or more, and the amount of strain on the material surface is as small as 0.046%, so that it has an effect of preventing buckling.

Embodiment 3 FIG.
FIG. 9 is a diagram showing a rod 6 of a multi-axis force sensor according to Embodiment 3 of the present invention. Although it is the same cyclic | annular elastic body as previous Embodiment 1, the square frame-shaped elastic body 12 is employ | adopted here instead of circular. Also here, the axis of the force f applied to the frame-like elastic body 12 is parallel to the plane including the frame shape, and the frame shape is symmetrical with respect to the axis when viewed from a direction perpendicular to the plane. It is trying to become.
Here, the height to the center of the frame is H, the horizontal length is L, the thickness of the beam perpendicular to the load is h ₁ , the thickness of the beam parallel to the load is h ₂ , the width is b, and the Young's modulus of the material is When E and I ₁ are the cross-sectional secondary moment of the horizontal beam and I ₂ is the cross-sectional secondary moment of the vertical beam, the deformation amount δ when the load f is applied is expressed by the following equation.

  By adjusting each parameter, a desired displacement with respect to the load f can be obtained. By making the elastic body into such a frame shape, the joint portions between the connecting rods 3 and 4 at both ends and the elastic body 12 become flat, and the work of joining becomes easy.

The maximum stress τ _max is generated at the center of the cross beam, exactly the portion joined to the rod, and the value is expressed by the following equation.

For example, when b = 4 mm, h1 = h2 = 0.852 mm, and E = 2.1 × 10 ⁵ MPa, the maximum strain is about 0.05%, which has the effect of reducing the strain amount compared to a simple columnar structure. .

Embodiment 4 FIG.
FIG. 10 shows a rod 6 of a multi-axis force sensor according to Embodiment 4 of the present invention, and a cantilever structure or a structure in which these are stacked is used as an elastic body. Since the cantilever structure can be easily created by bending or punching a plate-like member, the cantilever structure is easy to manufacture. Further, in the case of the cantilever structure, the elastic member can be efficiently arranged in a small space by being stacked in layers. As a result, many members are gradually deformed with respect to the load, which has the effect of reducing strain and stress per unit member.

Embodiment 5 FIG.
As shown in the first and third embodiments, when an elastic body having a circular shape such as a circle or a quadrangle is adopted as the rod 6, the rigidity in the axial direction to which a force is applied by the elasticity is reduced. Depending on the shape, the rigidity against bending is generally kept high. That is, with respect to the load in the axial direction, adjustment is made so that the rigidity is particularly low, but the rigidity against bending and torsion is maintained, and displacement occurs only in the axial direction. Therefore, compared to a simple column shape, deformation such as bending and torsion is less likely to occur, and the structure is less susceptible to the moment at the coupling portion 20 that causes an error.

FIG. 11 shows an example of the rod 6 in the fifth embodiment. In FIG. 2A, the connecting portion 20 for connecting the both flanges 1 and 2 is directly connected to the elastic ring 5 without using the connecting rods 3 and 4. Further, in FIG. 5B, similarly, the connecting portion 20 is directly connected to the frame-like elastic body 12.
In this case, even if the rod 6 is fixed to both the flanges 1 and 2, the rod 6 has linear characteristics with respect to the force and strain that are displaced only in the axial direction while maintaining rigidity against bending and torsion. The detection operation is simplified, and the axial rigidity of the elastic body is reduced, so that the displacement with respect to the applied force is increased while maintaining the required mechanical strength, and the displacement is easily and reliably detected.

Embodiment 6 FIG.
In the present invention, a displacement sensor is used instead of a strain sensor, but in order to obtain an accurate measurement value with the displacement sensor, it is necessary to cause a large displacement to some extent. In the previous embodiments, for this reason, the elastic deformation portions 5, 11, 12, and 13 are provided in the rod 6. However, in the sixth embodiment, as shown in FIG. A concave lens 14 is provided between the diode D8 and the quadrant photodiode PD7. By providing this concave lens 14, the spot light 15 is refracted and the amount of displacement observed by the four-division photodiode PD7 is larger than the actual amount of displacement, so that even a slight displacement can be accurately measured. Become. Further, since the amount of displacement required for the upper flange 1 can be reduced, the amount of displacement required for the elastically deformed portion of the rod 6 is also reduced, so that the possibility of yielding due to a load is reduced and the rigidity of the entire sensor is reduced. Therefore, a highly rigid force sensor can be configured.

Embodiment 7 FIG.
In each of the previous embodiments, the displacement of the force receiving portion (upper flange 1) is measured using a two-dimensional displacement sensor, and the relationship between the applied force and the compliance matrix or stiffness matrix (in which the relationship between the applied force and the force is determined in advance) (See formulas (6) and (7)). In the seventh embodiment, separately from such a force derivation method, instead of measuring the displacement of the force receiving portion using a two-dimensional displacement sensor, as shown in FIG. A one-dimensional displacement sensor using a capacitance meter 16 for measuring the displacement generated in FIG. 6 (FIG. 1A) or using a diode D8 and a two-divided photodiode PD17 (FIG. 2B). The applied force can be measured by converting the obtained displacement of the rod 6 into the axial force of the rod 6. In this method, since the force applied to each rod 6 can be measured, the force applied to the force sensor can be obtained by using the above equation (4).
As a result, it is not necessary to obtain a compliance matrix, etc., or to convert the values from the two-dimensional displacement sensor to introduce the displacement of the force receiving portion, so the amount of calculation and labor required to measure the force are greatly reduced. It becomes possible.

Embodiment 8 FIG.
FIG. 14 is a diagram showing a rod 6 according to an eighth embodiment of the present invention. In the force sensor, it is desirable to provide a measure so that plastic deformation does not occur in the strain generating body when an excessive load unintended by the user is applied. In order to meet this requirement, in FIG. 14A, the stoppers 18 extending from the upper and lower connecting rods 3 and 4 and having a hook shape at the center are engaged with each other with a certain gap. Even if a large load is applied and the elastic ring 5 tends to deform greatly, the gap between the stoppers 18 disappears, and the force is received not by the elastic ring 5 but by the stopper 18, so that the elastic ring 5 is further deformed. Can be prevented.
Further, as shown in FIG. 14 (b), a stopper 19 in which a pin-shaped member having a certain outer diameter and a hole-shaped member having an inner diameter obtained by adding a value of an allowable displacement to the outer diameter of the pin-shaped member is provided. Even if it is used, the same effect can be obtained.

  Further, in each modification of the present invention, the elastic body is formed of an annular structure, and the axis of the force applied to the rod is parallel to a plane including the annular shape and is annular when viewed from a direction perpendicular to the plane. When the shape is axisymmetric with respect to the axis, rigidity against bending and torsion is maintained, and a rod that is displaced only in the axial direction is obtained.

  Further, when the annular shape of the annular structure is a circle, the rod is easily manufactured.

  Further, when the annular shape of the annular structure is a quadrangle, the structure of the end portion for connection becomes simple.

  In addition, when the elastic body is formed in a spiral shape centering on the axis of the force applied to the rod, the structure of the end portion for connection becomes simple.

  Moreover, when the elastic body is formed in a cantilever shape, strain and stress per unit member can be reduced.

  In addition, if the rod is provided with a stopper that prevents further elongation of the elastic body when the axial elongation due to the force applied to the rod exceeds a predetermined dimension, even if an excessive load is applied Plastic deformation can be prevented, and the reliability as a sensor is improved.

  Further, the base portion and the force receiving portion are constituted by flat plates arranged in parallel to each other, and six rods are provided along the circumferential direction of the flat plate. The multi-axis force sensor has a load receiving portion that is loaded. Multi-axis force sensor that reliably detects the force and moment of the 6-axis component when outputting a total of 6 components of the force received from each of the three orthogonal axes and the moment around each axis. I can do it.

  In the above description, the multi-axis force sensor that outputs a total of six components including the components in the directions of the three orthogonal axes and the moments around the axes has been described. Needless to say, the present invention can also be applied as a three-axis force sensor for detecting the three components.

It is a perspective view which shows the multi-axis force sensor by Embodiment 1 of this invention. It is a perspective view which shows the inside of the sensor of the multi-axis force sensor by Embodiment 1 of this invention. It is a front view which shows the coordinate system of a sensor main body, and the coordinate system of each of three displacement sensors of the multi-axis force sensor by Embodiment 1 of this invention. It is a perspective view which shows the positional relationship and coordinate system of 4 division | segmentation photodiodes and diodes in the multi-axis force sensor by Embodiment 1 of this invention. It is a front view which shows the example of the arrangement | positioning different from the 120 degree symmetrical arrangement | positioning of the coordinate system of a sensor main body and three displacement sensors of the multi-axis force sensor by Embodiment 1 of this invention. It is the front view which showed independently the elastic ring 6 of the multi-axis force sensor by Embodiment 1 of this invention. It is a figure which shows the shape of the elastic ring 6 of Embodiment 1 of this invention. It is the front view which showed the spring-like elastic body 11 by Embodiment 2 of this invention. It is the figure which showed the frame-shaped elastic body 12 by Embodiment 3 of this invention. It is the front view which showed the cantilever-like elastic body 13 by Embodiment 4 of this invention. It is a figure which shows the shape of the elastic ring 6 of Embodiment 5 of this invention. It is the front view which showed the expansion method of the displacement using the concave lens 14 by Embodiment 6 of this invention. It is the front view which showed the structure of the rod 6 using the one-dimensional displacement sensor by Embodiment 7 of this invention. It is the front view which showed the structure of the stoppers 18 and 19 distribute | arranged in the rod 6 by Embodiment 8 of this invention.

Explanation of symbols

1 Upper flange, 2 Lower flange, 3 Upper connecting rod, 4 Lower connecting rod,
5 elastic ring, 6 rod, 7 4-division photodiode PD, 8 diode D,
11 spring-like elastic body, 12 frame-like elastic body, 13 cantilever-like elastic body,
14 concave lens, 16 capacitance meter, 17 split photodiode PD,
18, 19 Stopper, 20 coupling part.

Claims (9)

Strain generation composed of a fixed base part, a force receiving part that is placed a predetermined distance away from the base part and to which a load to be detected is applied, and at least six rods connecting the base part and the power receiving part A multi-axis which includes a body and outputs predetermined axial components of the force received by the force receiving portion from the load with the displacement of the force receiving portion or each rod as an input based on mechanical characteristics obtained in advance for the strain generating body A force sensor,
The connection between each rod and the foundation part and the force receiving part is performed with a fixing structure,
Each said rod was comprised with the elastic body from which the rigidity of a bending direction becomes large with respect to the rigidity of the axial direction of the force applied to the said rod, The multi-axis force sensor characterized by the above-mentioned. Strain generation composed of a fixed base part, a force receiving part that is placed a predetermined distance away from the base part and to which a load to be detected is applied, and at least six rods connecting the base part and the power receiving part A multi-axis which includes a body and outputs predetermined axial components of the force received by the force receiving portion from the load with the displacement of the force receiving portion or each rod as an input based on mechanical characteristics obtained in advance for the strain generating body A force sensor,
The connection between each rod and the foundation part and the force receiving part is performed with a fixing structure,
Each of the rods is composed of an elastic body and a rod-shaped connecting rod that is coupled to both ends of the elastic body and arranged coaxially with an axis of force applied to the rod. The elastic body is formed of an annular structure, and an axis of force applied to the rod is parallel to a plane including the annular shape, and the annular shape is relative to the axis when viewed from a direction perpendicular to the plane. The multi-axis force sensor according to claim 1, wherein the multi-axis force sensor is line symmetric. The multi-axis force sensor according to claim 3, wherein the annular shape of the annular structure is circular. 4. The multi-axis force sensor according to claim 3, wherein the annular shape of the annular structure is a quadrangle. The multi-axis force sensor according to claim 2, wherein the elastic body is formed in a spiral shape centering on an axis of a force applied to the rod. The multi-axis force sensor according to claim 2, wherein the elastic body is formed in a cantilever shape. 8. The stopper according to claim 1, further comprising a stopper for preventing further extension of the elastic body when the axial extension of the rod due to the force applied to the rod exceeds a predetermined dimension. The multi-axis force sensor according to claim 1. The base portion and the force receiving portion are configured by flat plates arranged in parallel to each other, six rods are provided along the circumferential direction of the flat plate, and the multi-axis force sensor is configured to receive the force receiving force. The multi-component according to any one of claims 1 to 8, wherein a total of six components of components in each axial direction of three orthogonal axes and moments around each of the forces received by the portion from the load are output. Axial force sensor.

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