JP7692863B2 - Force Sensor - Google Patents

Description

This disclosure relates to a force sensor that detects a load.

In equipment such as the arms of industrial robots or medical manipulators, force sensors are used that detect the load acting on each part of the equipment and output an electrical signal. Known force sensors include the strain gauge type force sensor disclosed in Patent Document 1 and the magnetic type force sensor disclosed in Patent Document 2. The force sensor disclosed in Patent Document 1 detects the electrical resistance value of the strain gauge and detects the force that moves the force receiving body of the force sensor and the torque that rotates the force receiving body based on the amount of variation in the magnetic resistance value. The force sensor disclosed in Patent Document 2 includes a magnet and a Hall element that is a magnetic sensor, and detects the force that moves the force receiving body and the torque that rotates the force receiving body by detecting the change in the relative position of the magnet with respect to the magnetic sensor based on the change in magnetic flux density.

Japanese Patent Application Publication No. 57-169643 Japanese Unexamined Patent Publication No. 177232/1983

In the case of the conventional force sensor disclosed in Patent Document 1, since it is necessary to attach a large number of strain gauges to the strain body in the manufacturing process of the force sensor, the structure of the force sensor becomes complicated. In the conventional force sensor disclosed in Patent Document 2, each of the four Hall elements detects the distance from the magnet, and detects the force in each direction of two mutually perpendicular axes and the torque centered on one axis perpendicular to each of the two axes. That is, the force sensor disclosed in Patent Document 2 uses four Hall elements to detect the force in each direction of three axes and the torque centered on one axis. Therefore, in order to detect a total of six components of force, which are the force in each direction of three mutually perpendicular axes and the torque centered on each of the three axes, it is necessary to increase the number of Hall elements, which makes the structure of the force sensor complicated. Thus, the conventional force sensor has a problem in that it is difficult to make it simple in configuration and to be able to detect the force in each direction of three mutually perpendicular axes and the torque centered on each of the three axes.

The present disclosure has been made in consideration of the above, and aims to provide a force sensor that can be made simple in structure and is capable of detecting forces in the directions of three mutually perpendicular axes and torques centered on each of the three axes.

In order to solve the above-mentioned problems and achieve the object, the force sensor disclosed herein comprises a fixed portion, a force receiving portion that receives a load, a thin plate portion provided on the fixed portion, and a bridge portion that connects the force receiving portion to the thin plate portion, and comprises a strain generating body in which at least one of the thin plate portion and the bridge portion is distorted when the force receiving portion receives a load, causing the force receiving portion to move or rotate relative to the fixed portion, a magnet mounting plate fastened to the force receiving portion, a plurality of magnets attached to the magnet mounting plate, a substrate fixed to the fixed portion, and a plurality of magnetic sensors that are each disposed on the substrate and face a magnet one-to-one, and that detect magnetic flux density in each direction of three mutually perpendicular axes.

The force sensor disclosed herein has a simple structure and is capable of detecting forces in the directions of three mutually perpendicular axes and torques centered on each of the three axes.

FIG. 1 is a perspective view showing an external appearance of a force sensor according to a first embodiment; FIG. 1 is an exploded perspective view of a force sensor according to a first embodiment; FIG. 1 is a top view of a force sensor according to a first embodiment; 1 is a bottom view of a force sensor according to a first embodiment; 1 is a cross-sectional view of a force sensor according to a first embodiment; FIG. 1 is a perspective view of a strain body which is a component of a force sensor according to a first embodiment; FIG. 5 is a diagram showing a state in which the substrate and the magnetic sensor are removed from the force sensor shown in FIG. FIG. 1 is a plan view showing a substrate and a magnetic sensor which are components of a force sensor according to a first embodiment;

The force sensor according to the embodiment is described in detail below with reference to the drawings.

Embodiment 1.
Fig. 1 is a perspective view showing the appearance of the force sensor 10 according to the first embodiment. Fig. 2 is an exploded perspective view of the force sensor 10 according to the first embodiment. Fig. 3 is a top view of the force sensor 10 according to the first embodiment. Fig. 4 is a bottom view of the force sensor 10 according to the first embodiment. Fig. 5 is a cross-sectional view of the force sensor 10 according to the first embodiment.

The X-axis, Y-axis, and Z-axis are three axes perpendicular to each other. The direction of the arrows on each axis is the positive direction, and the direction opposite to the arrows is the negative direction. In the first embodiment, the positive Z direction is the upward direction, and the negative Z direction is the downward direction. The force sensor 10 shown in FIG. 1 has a cylindrical appearance. The Z-axis is the height direction of the cylinder, that is, the axis in the height direction of the force sensor 10. Note that the shape of the force sensor 10 is not limited to a cylindrical shape, and can be modified as appropriate. FIG. 3 shows the force sensor 10 as viewed from the positive Z direction side. FIG. 4 shows the force sensor 10 as viewed from the negative Z direction side. The cross section shown in FIG. 5 is a cross section taken along line V-V in FIG. 3, which is parallel to the X-axis and Z-axis.

The force sensor 10 comprises a strain body 20, a force receiving body 30 provided on the positive Z direction side of the strain body 20, a magnet mounting plate 40 attached to the strain body 20, a substrate 50 provided on the negative Z direction side of the strain body 20 and the magnet mounting plate 40, a plurality of magnets 60, and a plurality of magnetic sensors 70. The force receiving body 30, the strain body 20, and the substrate 50 are overlapped with each other in the Z direction. The magnet mounting plate 40 is sandwiched between the strain body 20 and the substrate 50.

When a load such as a force or torque to be measured causes distortion in the strain body 20, the position of at least one of the multiple magnets 60 changes via the magnet mounting plate 40. The magnetic flux density detected by the magnetic sensor 70 changes due to the change in the relative position between the magnetic sensor 70 and the magnet 60. The force sensor 10 estimates the applied load based on the amount of change in the magnetic flux density detected by the magnetic sensor 70.

The force receiving body 30 is a structure that receives an external force applied from outside the force sensor 10, i.e., a load. The outer shape of the force receiving body 30 is circular in the XY plane. The force receiving body 30 is made of a metal material such as an aluminum alloy or steel. The screw hole 31 is formed near the center of the force receiving body 30 in the X and Y directions. The screw hole 32 is formed near the outer edge of the force receiving body 30 in the X and Y directions. The force receiving body 30 shown in FIG. 3 has four screw holes 31 and four screw holes 32. The number of screw holes 31 and the number of screw holes 32 are arbitrary.

Figure 6 is a perspective view of the flexure body 20, which is a component of the force sensor 10 according to the first embodiment. The external shape of the flexure body 20 is circular in the XY plane. The flexure body 20 is made of a metal material such as an aluminum alloy or steel. The flexure body 20 includes a force receiving portion 21, four bridge portions 22, four thin plate portions 23, and a fixing portion 25.

The force receiving part 21 is provided at the center of the strain generating body 20 in the X and Y directions. The force receiving part 21 is fastened to the force receiving body 30 by a fastener such as a screw screwed into a screw hole 31 of the force receiving body 30 shown in FIG. 3. The surface of the force receiving part 21 on the positive Z direction side is in contact with the force receiving body 30. The force receiving part 21 receives the load applied to the force receiving body 30. Note that a screw or the like, which is a fastener for fixing the force receiving body 30 to a detection target such as a robot hand such as an electric hand or an air hand, is screwed into the screw hole 32 of the force receiving body 30. The fastener for fastening the force receiving part 21 to the force receiving body 30 and the fastener for fixing the force receiving body 30 to the detection target are omitted in the illustration.

The fixing portion 25 surrounds the outer edges of the strain body 20 in the X and Y directions. Four screw holes 24 are formed in the fixing portion 25. Fasteners such as screws for fixing the fixing portion 25 to a device such as a robot arm are screwed into the screw holes 24. The fasteners for fixing the fixing portion 25 to the device are not shown in the figure.

The thin plate portion 23 is a flexible thin plate. The thin plate portion 23 is provided closer to the center than the outer edge of the fixed portion 25. The thickness direction of the thin plate portion 23 is the radial direction of the circle that is the outer shape of the strain body 20. The thin plate portion 23 is long in a direction perpendicular to the radial direction. Each of the four thin plate portions 23 is disposed at equal intervals in the circumferential direction. The screw holes 24 are disposed between the thin plate portions 23.

The bridge portion 22 is a flexible bridge. The bridge portion 22 extends radially from the force receiving portion 21 and connects the force receiving portion 21 to the thin plate portion 23. One radial end of the bridge portion 22 is fixed to the outer edge of the force receiving portion 21. The other radial end of the bridge portion 22 is fixed to the center of the thin plate portion 23. Each of the four bridge portions 22 extends in each direction of the cross with the force receiving portion 21 as the center, and is disposed at equal intervals in the circumferential direction. That is, each of the four bridge portions 22 is disposed at equal intervals around the force receiving portion 21.

When the force receiving portion 21 receives a load through the force receiving body 30, the bridge portion 22 and the thin plate portion 23 are elastically deformed. The position or posture of the force receiving portion 21 changes due to the elastic deformation of the bridge portion 22 and the thin plate portion 23. The force receiving portion 21 moves from its position in the initial state in the direction of the force received by the force receiving portion 21 by a distance corresponding to the magnitude of the force received by the force receiving portion 21. Alternatively, the posture of the force receiving portion 21 changes from its position in the initial state to the direction of the torque received by the force receiving portion 21 by a rotation angle corresponding to the magnitude of the torque. The initial state refers to the state before the force receiving portion 21 receives a load. The position refers to the position in each of the X-axis, Y-axis, and Z-axis directions. The posture refers to the orientation state due to rotation around each of the X-axis, Y-axis, and Z-axis.

In this way, when the force receiving portion 21 receives a load, the thin plate portion 23 and the bridge portion 22 are distorted, and the force receiving portion 21 is displaced relative to the fixed portion 25. The displacement of the force receiving portion 21 relative to the fixed portion 25 includes the case where the force receiving portion 21 moves relative to the fixed portion 25 and the case where the posture of the force receiving portion 21 changes relative to the fixed portion 25. When the load is no longer applied to the force receiving portion 21, the force receiving portion 21 returns to its initial position and posture due to the restoring force of the bridge portion 22 and the thin plate portion 23. Note that this is not limited to the case where both the thin plate portion 23 and the bridge portion 22 are distorted when the force receiving portion 21 receives a load, but rather, the force receiving portion 21 is displaced relative to the fixed portion 25 due to the distortion of at least one of the thin plate portion 23 and the bridge portion 22 when the force receiving portion 21 receives a load. When the load on the force-receiving portion 21 is removed, the force-receiving portion 21 returns to its initial position and posture due to the restoring force of at least one of the distorted elements, the bridge portion 22 and the thin plate portion 23.

The detection sensitivity of the force sensor 10 is determined by the flexibility of the thin plate portion 23 and the flexibility of the bridge portion 22. That is, the detection sensitivity of the force sensor 10 depends on the flexibility of the thin plate portion 23 and the flexibility of the bridge portion 22. The thinner the thickness of the thin plate portion 23 or the shorter the Z-direction length of the thin plate portion 23, the higher the flexibility of the thin plate portion 23. The shorter the Z-direction length of the bridge portion 22 or the shorter the length of the bridge portion 22 in the direction perpendicular to the Z axis and the radial direction, the higher the flexibility of the bridge portion 22. However, while the detection sensitivity improves as the flexibility of the thin plate portion 23 and the bridge portion 22 is increased, the thin plate portion 23 and the bridge portion 22 become more susceptible to breakage, and the fatigue life of the force sensor 10 may not be satisfied. The flexibility of the thin plate portion 23 and the bridge portion 22 is set so as to satisfy the detection sensitivity and fatigue life.

The magnet mounting plate 40 is made of steel material. The magnet mounting plate 40 functions as a yoke that amplifies the magnetic flux density of the magnet 60. The force sensor 10 can improve its detection sensitivity by amplifying the magnetic flux density of the magnet 60 with the magnet mounting plate 40 functioning as a yoke.

As shown in FIG. 5, the magnet mounting plate 40 is fastened to the force receiving portion 21 by a fastener 81 such as a screw. The surface of the force receiving portion 21 facing the negative Z direction is in contact with the magnet mounting plate 40. As the force receiving portion 21 is displaced relative to the fixed portion 25, the magnet mounting plate 40 is also displaced relative to the fixed portion 25. Displacement of the magnet mounting plate 40 relative to the fixed portion 25 includes cases where the magnet mounting plate 40 moves relative to the fixed portion 25 and cases where the attitude of the magnet mounting plate 40 changes relative to the fixed portion 25. As the force receiving portion 21 returns to its initial position and attitude, the magnet mounting plate 40 also returns to its initial position and attitude.

Figure 7 is a diagram showing the force sensor 10 shown in Figure 4 with the substrate 50 and magnetic sensor 70 removed. In the XY plane shown in Figure 7, the magnet mounting plate 40 is cross-shaped. That is, each of the four parts of the magnet mounting plate 40 extends in each direction of the cross. The cross formed by the four parts of the magnet mounting plate 40 is the same as the cross formed by the four bridge sections 22. The center of the cross of the magnet mounting plate 40 is fastened to the force receiving section 21. Note that the magnet mounting plate 40 may have a shape other than a cross as long as it can be fastened to the force receiving section 21 and can fulfill the function of the yoke. The magnet mounting plate 40 may be, for example, a diamond shape.

The substrate 50 shown in FIG. 4 constitutes the bottom surface of the force sensor 10 on the negative Z direction side. The substrate 50 is fixed to the fixed portion 25 of the strain body 20 while being in contact with only the fixed portion 25. The screw holes 51 are formed near the outer edges of the substrate 50 in the X and Y directions. The number of screw holes 51 is arbitrary. As shown in FIG. 5, the substrate 50 is fastened to the fixed portion 25 by fasteners 82 such as screws screwed into the screw holes 51.

The force sensor 10 includes four magnets 60a, 60b, 60c, and 60d shown in FIG. 7. The magnet 60 refers to each of the four magnets 60a, 60b, 60c, and 60d without distinction. Each of the four magnets 60a, 60b, 60c, and 60d is attached to the magnet mounting plate 40. Each of the magnets 60a, 60b, 60c, and 60d is arranged on each of the four parts of the magnet mounting plate 40 that extend in each direction of the cross. Each of the magnets 60a, 60b, 60c, and 60d is arranged on the part of the magnet mounting plate 40 that faces the substrate 50. Each of the magnets 60a, 60b, 60c, and 60d is arranged on the negative Z direction side of the bridge portion 22, that is, on the substrate 50 side of the bridge portion 22. The position of each of the magnets 60a, 60b, 60c, and 60d in the XY plane coincides with the position of each of the bridge sections 22 in the XY plane. Each of the magnets 60a, 60b, 60c, and 60d is disposed at equal intervals in the circumferential direction, similar to each of the four bridge sections 22. In addition, each of the magnets 60a, 60b, 60c, and 60d is disposed at an equal distance from the center of the force receiving section 21.

Each of the magnets 60a, 60b, 60c, and 60d is a permanent magnet or an electromagnet. In the first embodiment, each of the magnets 60a, 60b, 60c, and 60d has a hollow cylindrical shape. Each of the magnets 60a, 60b, 60c, and 60d may have a shape other than a hollow cylindrical shape, and may be a cylindrical shape or a rectangular prism shape without a gap, etc.

Figure 8 is a plan view showing the substrate 50 and magnetic sensor 70, which are components of the force sensor 10 according to the first embodiment. Figure 8 shows the substrate 50 and the magnetic sensor 70 arranged on the substrate 50, viewed from the positive Z direction. The force sensor 10 includes four magnetic sensors 70a, 70b, 70c, and 70d. Note that the term magnetic sensor 70 refers to each of the four magnetic sensors 70a, 70b, 70c, and 70d without distinction. Each of the four magnetic sensors 70a, 70b, 70c, and 70d is arranged on the substrate 50 and faces a magnet 60a, 60b, 60c, and 60d in a one-to-one relationship.

Each of the four magnetic sensors 70a, 70b, 70c, and 70d is an integrated circuit that detects magnetic flux density in the X-axis, Y-axis, and Z-axis directions. Each of the four magnetic sensors 70a, 70b, 70c, and 70d may be a combination of three Hall elements. Each of the three Hall elements detects magnetic flux density in one axis direction.

The magnetic sensor 70a is disposed facing the magnet 60a. The magnetic sensor 70a is disposed in the magnetic field formed by the magnet 60a. The magnetic sensor 70b is disposed facing the magnet 60b. The magnetic sensor 70b is disposed in the magnetic field formed by the magnet 60b. The magnetic sensor 70c is disposed facing the magnet 60c. The magnetic sensor 70c is disposed in the magnetic field formed by the magnet 60c. The magnetic sensor 70d is disposed facing the magnet 60d. The magnetic sensor 70d is disposed in the magnetic field formed by the magnet 60d.

The position of the magnet 60a changes with the displacement of the magnet mounting plate 40, and the relative position between the magnet 60a and the magnetic sensor 70a changes. The magnetic flux density detected by the magnetic sensor 70a changes as the relative position between the magnet 60a and the magnetic sensor 70a changes. The force sensor 10 detects the change in the position of the magnet 60a in each of the three axial directions based on the amount of change in the magnetic flux density in each of the three axial directions. In this way, the combination of the magnet 60a and the magnetic sensor 70a functions as a three-dimensional position sensor. Each combination of the magnet 60b and the magnetic sensor 70b, the magnet 60c and the magnetic sensor 70c, and the magnet 60d and the magnetic sensor 70d also functions as a three-dimensional position sensor, similar to the combination of the magnet 60a and the magnetic sensor 70a.

The force sensor 10 uses these four three-dimensional position sensors to detect changes in the position of the magnet 60 at four points on the substrate 50. By utilizing the position information acquired by these four three-dimensional position sensors, the force sensor 10 detects the movement of the force receiving part 21 in each of the three axial directions and the rotation of the force receiving part 21 around each of the three axial directions.

The amount of movement of the force receiving unit 21 in response to the magnitude of the force applied to the force receiving unit 21 is measured in advance, thereby obtaining a conversion law that expresses the relationship between the magnitude of the force and the amount of movement. The force sensor 10 obtains the magnitude of the force received by the force receiving unit 21 by converting the amount of movement of the force receiving unit 21 into the magnitude of the force based on this conversion law. In addition, the amount of rotation of the force receiving unit 21 in response to the torque applied to the force receiving unit 21 is measured in advance, thereby obtaining a conversion law that expresses the relationship between the torque and the amount of rotation. The force sensor 10 obtains the torque received by the force receiving unit 21 by converting the amount of rotation of the force receiving unit 21 into torque based on this conversion law. In this way, the force sensor 10 measures the force in each of the three axial directions and the torque centered on each of the three axes.

The magnets 60a, 60b, 60c, and 60d are all positioned at equal distances from the center of the force receiving portion 21 and are equally spaced apart. In addition, the magnetic sensors 70a, 70b, 70c, and 70d face the magnets 60a, 60b, 60c, and 60d in a one-to-one relationship. By arranging the magnets 60a, 60b, 60c, and 60d and the magnetic sensors 70a, 70b, 70c, and 70d in this manner, the constitutive equation of the above conversion law can be made simpler.

In addition to the components described in the first embodiment, the force sensor 10 includes a cover that covers the force sensor 10 from both the positive Z direction and the negative Z direction. An electric circuit connected to the magnetic sensor 70 is provided on the substrate 50. The force sensor 10 further includes an arithmetic circuit that performs calculations based on the above conversion law, and a display unit that displays the results of the calculations. These components can be publicly known, and therefore illustrations and detailed descriptions of these components are omitted.

The force sensor 10 according to the first embodiment can reduce the number of parts and has a simpler configuration than the configuration of Patent Document 1, which requires attaching a large number of strain gauges to the strain body. If the strain gauge is attached directly to the strain body, repeated application of force to the strain gauge can reduce the adhesive strength, causing problems such as the strain gauge peeling off. The force sensor 10 can avoid such problems by eliminating the need to attach strain gauges.

In the configuration of Patent Document 2, since multiple leaf springs are used as the strain generating parts, there is a possibility that the response of the Hall element may vary due to manufacturing variations in the leaf springs. In addition, in the configuration of Patent Document 2, if the gap between the Hall element and the permanent magnet is filled with an elastic body made of a polymer material instead of providing a leaf spring, there is a problem that the fatigue life is shortened because a force acts directly on the elastic body. The force sensor 10 according to the first embodiment detects the movement and rotation of the force receiving part 21 by utilizing the flexibility of the thin plate part 23 and the bridge part 22, so that the response variation caused by manufacturing variations can be reduced. In addition, the force sensor 10 does not need to fill the gap between the magnet 60 and the magnetic sensor 70 with an elastic body made of a polymer material, so that the problem of the fatigue life being shortened can be avoided.

Furthermore, the force sensor 10 includes a plurality of magnets 60a, 60b, 60c, and 60d attached to the magnet mounting plate 40, and magnetic sensors 70a, 70b, 70c, and 70d that detect magnetic flux density in each direction of three mutually perpendicular axes. The force sensor 10 can detect forces in each direction of three mutually perpendicular axes and torques centered on each of the three axes without increasing the number of parts compared to the configuration of Patent Document 2.

As a result, the force sensor 10 according to the first embodiment has a simple structure and is capable of detecting forces in the directions of three mutually perpendicular axes and torques centered on each of the three axes.

The configurations shown in the above embodiments are examples of the contents of this disclosure. The configurations of the embodiments can be combined with other known technologies. Part of the configurations of the embodiments can be omitted or modified without departing from the gist of this disclosure.

10 Force sensor, 20 Strain generating body, 21 Force receiving part, 22 Bridge part, 23 Thin plate part, 24, 31, 32, 51 Screw hole, 25 Fixing part, 30 Force receiving body, 40 Magnet mounting plate, 50 Substrate, 60, 60a, 60b, 60c, 60d Magnet, 70, 70a, 70b, 70c, 70d Magnetic sensor, 81, 82 Fixing device.

Claims (4)

a strain generating body having a fixed portion, a force receiving portion that receives a load, a thin plate portion provided on the fixed portion, and a bridge portion that connects the force receiving portion to the thin plate portion, wherein when the force receiving portion receives the load, at least one of the thin plate portion and the bridge portion is distorted, causing the force receiving portion to move or rotate relative to the fixed portion;
a magnet mounting plate fastened to the force receiving portion;
A plurality of magnets attached to the magnet mounting plate;
A substrate fixed to the fixing portion;
a plurality of magnetic sensors each disposed on the substrate and facing the magnet in a one-to-one relationship, each detecting a magnetic flux density in each of three mutually perpendicular directions;
A force sensor comprising: The strain generating body has a plurality of the bridge portions,
Each of the plurality of bridge portions is disposed at equal intervals around the force receiving portion,
The magnet mounting plate is sandwiched between the strain body and the substrate,
2. The force sensor according to claim 1, wherein each of the plurality of magnets is disposed on a portion of the magnet mounting plate facing the substrate. The force sensor according to claim 1 or 2, characterized in that the magnet mounting plate is made of a steel material. The force sensor according to any one of claims 1 to 3, characterized in that each of the multiple magnets is disposed at equal intervals and at equal distances from the center of the force receiving portion.

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