JP7707491B2 - Sensor system and power transmission device - Google Patents

Description

The present invention relates to a sensor system and a power transmission device.

In recent years, the demand for reducers to be installed in the joints of robots and the like has been rapidly increasing. A conventional reducer is described, for example, in Japanese Patent Application Laid-Open No. 2004-198400. In this publication, a strain gauge is attached to a flexible external gear that rotates at a reduced rotation speed. This makes it possible to measure the torque acting on the flexible external gear.
JP 2004-198400 A

However, the resistance wire of the strain gauge used to measure torque has a complex shape that is folded back in a zigzag pattern. For this reason, when the reducer is in operation, the flexible external gear repeatedly flexes and deforms, which can cause a failure such as a break in part of the resistance wire of the strain gauge. When such a failure occurs, the measurement value of the strain gauge changes. However, simply detecting the change in the measurement value of the strain gauge makes it impossible to distinguish whether the change is due to a failure such as a break, or due to a change in the torque applied to the flexible external gear.

For this reason, in the past, in order to detect a failure in a strain gauge, it was necessary to place two strain gauges at the same location on the flexible external gear and compare the measurement values of those strain gauges.

The object of the present invention is to provide a sensor system that can detect sensor failure without installing two sensors for the same measurement target.

The present invention provides a sensor device including a first sensor and a second sensor having different measurement objects, a substrate on which the first sensor and the second sensor are mounted, a fault detection unit that detects a fault in either the first sensor or the second sensor, and a signal processing unit that corrects a first measurement value that is a measurement value of the measurement object of the first sensor using a second measurement value that is a measurement value of the measurement object of the second sensor, wherein the fault detection unit obtains from the first sensor a first output value that varies with temperature and obtains from the second sensor a second output value that varies with temperature, and detects a fault in either the first sensor or the second sensor based on whether a relationship between the first output value and the second output value is within a predetermined normal range, the first sensor is a strain sensor that detects a distortion of an object to which the substrate is fixed, and the second sensor is a temperature sensor that detects the temperature of the object, the first sensor has a first resistance wire pattern that is centered on a central axis of the object to which the substrate is fixed and has a bent structure in which ends of adjacent conductors in the circumferential direction are alternately connected on the inside or outside in the radial direction to form an arc-shaped or annular pattern, and the second sensor has a second resistance wire pattern that does not have the bent structure and is centered on the central axis .

According to the present invention, output values of a first sensor and a second sensor, which have different measurement objects, are acquired, and a failure in either the first sensor or the second sensor is detected based on whether the relationship between these output values is within a normal range. This makes it possible to detect a sensor failure without providing two sensors for the same measurement object.

FIG. 1 is a vertical cross-sectional view of the power transmission device. FIG. 2 is a cross-sectional view of the power transmission device. FIG. 3 is a diagram showing the rear surface of the sensor substrate. FIG. 4 is a diagram showing the surface of the sensor substrate. FIG. 5 is a partial cross-sectional view of the diaphragm portion and the sensor substrate. FIG. 6 is a circuit diagram of the first bridge circuit. FIG. 7 is a circuit diagram of the second bridge circuit. FIG. 8 is a graph showing the measurement values of the first voltmeter and the measurement values of the second voltmeter. FIG. 9 is a circuit diagram of the third bridge circuit. FIG. 10 is a diagram conceptually illustrating the correction process. FIG. 11 is a circuit diagram of a detection circuit of the temperature sensor. FIG. 12 is a flowchart showing the flow of temperature correction in a method of performing temperature correction based on the measurement value of an ammeter connected in series with a bridge circuit. FIG. 13 is a modified circuit diagram of the third bridge circuit. FIG. 14 is a diagram conceptually showing inputs and outputs of the failure detection unit. FIG. 15 is a flowchart showing the flow of the failure detection process. FIG. 16 is a graph showing changes in the measurement values. FIG. 17 is a circuit diagram of a detection circuit of a temperature sensor according to a modified example.

Below, exemplary embodiments of the present application will be described with reference to the drawings. In this application, the direction parallel to the central axis of the power transmission device is referred to as the "axial direction", the direction perpendicular to the central axis of the power transmission device is referred to as the "radial direction", and the direction along the arc centered on the central axis of the power transmission device is referred to as the "circumferential direction". However, the above "parallel direction" also includes a direction that is approximately parallel. Furthermore, the above "orthogonal direction" also includes a direction that is approximately orthogonal.

1. Configuration of the power transmission device
Fig. 1 is a longitudinal sectional view of a power transmission device 1 according to a first embodiment. Fig. 2 is a transverse sectional view of the power transmission device 1 as seen from the position A-A in Fig. 1. This power transmission device 1 is a device that transmits rotational motion of a first rotation number obtained from a motor to a subsequent stage while reducing the rotation number to a second rotation number lower than the first rotation number. The power transmission device 1 is used, for example, by being incorporated into a joint of a robot together with a motor. However, the power transmission device of the present invention may also be used in other devices such as an assisted suit or an unmanned transport vehicle.

As shown in Figures 1 and 2, the power transmission device 1 of this embodiment includes an internal gear 10, a flex gear 20, a wave generator 30, and a sensor board 40.

The internal gear 10 is an annular gear having multiple internal teeth 11 on its inner circumferential surface. The internal gear 10 is fixed, for example by screws, to the frame of the device on which the power transmission device 1 is mounted. The internal gear 10 is arranged coaxially with the central axis 9. The internal gear 10 is also located radially outside a cylindrical portion 21 (described later) of the flex gear 20. The rigidity of the internal gear 10 is much higher than the rigidity of the cylindrical portion 21 of the flex gear 20. For this reason, the internal gear 10 can be considered to be a substantially rigid body. The internal gear 10 has a cylindrical inner circumferential surface. The multiple internal teeth 11 are arranged on the inner circumferential surface at a constant pitch in the circumferential direction. Each internal tooth 11 protrudes radially inward.

The flex gear 20 is a flexible, annular gear. The flex gear 20 is supported so as to be rotatable about the central axis 9. The flex gear 20 is an example of a "gear" in the present invention.

The flex gear 20 of this embodiment has a cylindrical portion 21 and a flat portion 22. The cylindrical portion 21 extends cylindrically in the axial direction around the central axis 9. The axial tip of the cylindrical portion 21 is located radially outside the wave generator 30 and radially inside the internal gear 10. The cylindrical portion 21 is flexible and can deform in the radial direction. In particular, the tip of the cylindrical portion 21, which is located radially inside the internal gear 10, is a free end and can therefore be displaced in the radial direction more than other portions.

The flex gear 20 has a number of external teeth 23. The multiple external teeth 23 are arranged at a constant pitch in the circumferential direction on the outer peripheral surface near the axial tip of the cylindrical portion 21. Each external tooth 23 protrudes radially outward. The number of internal teeth 11 of the internal gear 10 described above and the number of external teeth 23 of the flex gear 20 are slightly different.

The flat plate portion 22 has a diaphragm portion 221 and a thick portion 222. The diaphragm portion 221 spreads outward in the radial direction from the axial base end of the cylindrical portion 21 in a flat plate shape, and also spreads in an annular shape around the central axis 9. The diaphragm portion 221 is slightly deformable in the axial direction. The thick portion 222 is an annular portion located radially outward of the diaphragm portion 221. The axial thickness of the thick portion 222 is thicker than the axial thickness of the diaphragm portion 221. The thick portion 222 is fixed, for example by screwing, to a component to be driven of a device in which the power transmission device 1 is mounted.

The wave generator 30 is a mechanism that generates periodic bending deformation in the cylindrical portion 21 of the flex gear 20. The wave generator 30 has a cam 31 and a flexible bearing 32. The cam 31 is supported rotatably about the central axis 9. The cam 31 has an elliptical outer peripheral surface when viewed in the axial direction. The flexible bearing 32 is interposed between the outer peripheral surface of the cam 31 and the inner peripheral surface of the cylindrical portion 21 of the flex gear 20. Therefore, the cam 31 and the cylindrical portion 21 can rotate at different rotational speeds.

The inner ring of the flexible bearing 32 contacts the outer peripheral surface of the cam 31. The outer ring of the flexible bearing 32 contacts the inner peripheral surface of the flex gear 20. As a result, the cylindrical portion 21 of the flex gear 20 is deformed into an elliptical shape that conforms to the outer peripheral surface of the cam 31. As a result, the external teeth 23 of the flex gear 20 mesh with the internal teeth 11 of the internal gear 10 at two locations that correspond to both ends of the major axis of the ellipse. At other circumferential positions, the external teeth 23 do not mesh with the internal teeth 11.

The cam 31 is connected to the motor directly or via another power transmission mechanism. When the motor is driven, the cam 31 rotates around the central axis 9 at a first rotation speed. As a result, the major axis of the ellipse of the flex gear 20 also rotates at the first rotation speed. Then, the meshing position between the external teeth 23 and the internal teeth 11 also changes in the circumferential direction at the first rotation speed. Also, as described above, the number of internal teeth 11 of the internal gear 10 and the number of external teeth 23 of the flex gear 20 are slightly different. Due to this difference in the number of teeth, the meshing position between the external teeth 23 and the internal teeth 11 changes slightly in the circumferential direction for each rotation of the cam 31. As a result, the flex gear 20 rotates around the central axis 9 at a second rotation speed lower than the first rotation speed relative to the internal gear 10. Therefore, a rotational motion of the second rotation speed, which is reduced in speed, can be obtained from the flex gear 20.

<2. Sensor board>
<2-1. Configuration of the sensor board>
The sensor board 40 is a board on which a sensor is mounted for detecting the torque applied to the flex gear 20. As shown in Fig. 1, in this embodiment, the sensor board 40 is fixed to the circular surface of the disk-shaped diaphragm portion 221.

Figure 3 is a diagram showing the back surface of the sensor substrate 40 that faces the diaphragm portion 221. Figure 4 is a diagram showing the front surface of the sensor substrate 40 that does not face the diaphragm portion 221. Figure 5 is a partial cross-sectional view of the diaphragm portion 221 and the sensor substrate 40.

The sensor board 40 of this embodiment is a flexible printed circuit board (FPC) that can be flexibly deformed. As shown in Figs. 3 and 4, the sensor board 40 has a main body portion 41 that is annular about the central axis 9, and a flap portion 42 that protrudes radially outward from the main body portion 41. As shown in Fig. 5, the sensor board 40 has an insulating layer 43 and a conductor layer 44. The insulating layer 43 is made of a resin that is an insulator. The conductor layer 44 is made of a metal that is a conductor. The material of the conductor layer 44 is, for example, copper or an alloy containing copper. The sensor board 40 of this embodiment has the conductor layer 44 on both the front and back surfaces of the insulating layer 43.

As shown in FIG. 5, the sensor board 40 is fixed to the diaphragm portion 221 of the flex gear 20 by double-sided adhesive tape 45. Specifically, the front surface of the diaphragm portion 221 and the back surface of the sensor board 40 are fixed via the double-sided adhesive tape 45. The double-sided adhesive tape 45 is made by molding an adhesive material into a tape shape and hardening it to the extent that it can maintain its shape. By using such a double-sided adhesive tape 45, the work of fixing the sensor board 40 to the diaphragm portion 221 is easier than when a fluid adhesive is used. In addition, the variation in the fixing work depending on the worker can be reduced.

The sensor board 40 is equipped with a rotation angle detection sensor S1, a torque detection sensor S2, and a temperature sensor S3, as well as a signal processing circuit 46. The rotation angle detection sensor S1 and the torque detection sensor S2 are both strain sensors that detect the strain of the diaphragm portion 221, and are an example of the "first sensor" in the present invention. The temperature sensor S3 is a sensor that detects the temperature of the power transmission device 1, and is an example of the "second sensor" in the present invention.

The rotation angle detection sensor S1 has a resistance wire pattern formed on the rear surface of the main body 41 that faces the diaphragm portion 221. That is, the conductor layer 44 on the rear surface includes the resistance wire pattern of the rotation angle detection sensor S1. The torque detection sensor S2 and the temperature sensor S3 have resistance wire patterns formed on the front and rear surfaces of the main body 41 that do not face the diaphragm portion 221. That is, the conductor layer 44 on the front surface includes the resistance wire pattern of the torque detection sensor S2 and the resistance wire pattern of the temperature sensor S3.

The signal processing circuit 46 is located in the flap portion 42.

<2-2. Rotation angle detection sensor>
The rotation angle detection sensor S1 is a sensor that detects the rotation angle of the rotational motion input to the flex gear 20 based on the distortion of the diaphragm portion 221. As shown in Fig. 3, the rotation angle detection sensor S1 includes four first resistance wire patterns R1 and four second resistance wire patterns R2.

The four first resistance wire patterns R1 are arranged at equal intervals in the circumferential direction around the central axis 9. Each of the first resistance wire patterns R1 is an overall arc-shaped pattern in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. In this embodiment, one first resistance wire pattern R1 spreads over an angular range of about 45° around the central axis 9. The first resistance wire pattern R1 also includes multiple first resistance wires r1. The multiple first resistance wires r1 are arranged at small intervals in the circumferential direction. Each first resistance wire r1 extends linearly along the radial direction of the flex gear 20. The ends of the first resistance wires r1 adjacent to each other in the circumferential direction are alternately connected on the inside or outside of the radial direction. As a result, the multiple first resistance wires r1 are connected in series as a whole.

The four second resistance wire patterns R2 are arranged at equal intervals in the circumferential direction around the central axis 9. Each of the second resistance wire patterns R2 is an overall arc-shaped pattern in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. In this embodiment, one second resistance wire pattern R2 extends in an angular range of about 45° around the central axis 9. The second resistance wire pattern R2 also includes multiple second resistance wires r2. The multiple second resistance wires r2 are arranged at small intervals in the circumferential direction. Each second resistance wire r2 extends linearly along the radial direction of the flex gear 20. The ends of the second resistance wires r2 adjacent to each other in the circumferential direction are alternately connected on the inside or outside of the radial direction. As a result, the multiple second resistance wires r2 are connected in series as a whole.

The four second resistance wire patterns R2 are arranged concentrically with the four first resistance wire patterns R1 and in an area in the circumferential direction where the first resistance wire patterns R1 are not arranged. In this embodiment, the first resistance wire patterns R1 and the second resistance wire patterns R2 are arranged alternately in the circumferential direction. The four first resistance wire patterns R1 and the four second resistance wire patterns R2 as a whole extend in an annular shape centered on the central axis 9.

Figure 6 is a circuit diagram of a first bridge circuit C1 including four first resistance wire patterns R1. In the example of Figure 6, the four first resistance wire patterns R1 are distinguished and shown as Ra, Rb, Rc, and Rd. The first resistance wire patterns Ra, Rb, Rc, and Rd are arranged in this order counterclockwise, starting with Ra in Figure 3.

As shown in FIG. 6, the four first resistance wire patterns Ra, Rb, Rc, and Rd are incorporated into the first bridge circuit C1. The first resistance wire pattern Ra and the first resistance wire pattern Rb are connected in series in this order. The first resistance wire pattern Rd and the first resistance wire pattern Rc are connected in series in this order. Then, between the positive and negative poles of the power supply voltage, two rows of the first resistance wire patterns Ra, Rb and two rows of the first resistance wire patterns Rd, Rc are connected in parallel. In addition, the midpoint M11 of the first resistance wire pattern Ra and the first resistance wire pattern Rb, and the midpoint M12 of the first resistance wire pattern Rd and the first resistance wire pattern Rc are connected to the first voltmeter V1.

Figure 7 is a circuit diagram of a second bridge circuit C2 including four second resistance wire patterns R2. In the example of Figure 7, the four second resistance wire patterns R2 are distinguished and shown as Re, Rf, Rg, and Rh. The second resistance wire pattern Re is located between the first resistance wire pattern Ra and the first resistance wire pattern Rd in Figure 3. The second resistance wire patterns Re, Rf, Rg, and Rh are arranged in this order clockwise, starting with Re as the first pattern in Figure 3.

As shown in FIG. 7, the four second resistance wire patterns Re, Rf, Rg, and Rh are incorporated into the second bridge circuit C2. The second resistance wire pattern Re and the second resistance wire pattern Rf are connected in series in this order. The second resistance wire pattern Rh and the second resistance wire pattern Rg are connected in series in this order. Then, between the positive and negative poles of the power supply voltage, two rows of the second resistance wire patterns Re and Rf and two rows of the second resistance wire patterns Rh and Rg are connected in parallel. In addition, the midpoint M21 of the second resistance wire pattern Re and the second resistance wire pattern Rf and the midpoint M22 of the second resistance wire pattern Rh and the second resistance wire pattern Rg are connected to the second voltmeter V2.

When the power transmission device 1 is driven, the diaphragm portion 221 has a portion that expands in the radial direction (hereinafter referred to as the "expansion portion") and a portion that contracts in the radial direction (hereinafter referred to as the "contraction portion"). Specifically, two expansion portions and two contraction portions alternate in the circumferential direction. That is, the expansion portions and contraction portions alternate at 90° intervals in the circumferential direction. The locations where these expansion portions and contraction portions occur rotate at the first rotation speed described above.

The resistance values of the first resistance wire patterns Ra, Rb, Rc, Rd and the second resistance wire patterns Re, Rf, Rg, Rh provided on the back surface of the sensor substrate 40 change according to the radial distortion of the diaphragm portion 221. For example, when the above-mentioned extension portion overlaps with a certain resistance wire pattern, the resistance value of that resistance wire pattern increases. Also, when the above-mentioned contraction portion overlaps with a certain resistance wire pattern, the resistance value of that resistance wire pattern decreases.

In the example of FIG. 3, when the contracted portion overlaps with the first resistance wire patterns Ra, Rc, the extended portion overlaps with the first resistance wire patterns Rb, Rd. Also, when the extended portion overlaps with the first resistance wire patterns Ra, Rc, the contracted portion overlaps with the first resistance wire patterns Rb, Rd. Therefore, in the first bridge circuit C1, the first resistance wire patterns Ra, Rc and the first resistance wire patterns Rb, Rd show resistance value changes in opposite directions.

In the example of FIG. 3, when the contracted portion overlaps with the second resistance wire patterns Re, Rg, the extended portion overlaps with the second resistance wire patterns Rf, Rh. When the extended portion overlaps with the second resistance wire patterns Re, Rg, the contracted portion overlaps with the second resistance wire patterns Rf, Rh. Therefore, in the second bridge circuit C2, the second resistance wire patterns Re, Rg and the second resistance wire patterns Rf, Rh show resistance value changes in opposite directions.

Figure 8 is a graph showing the measurement value v1 of the first voltmeter V1 of the first bridge circuit C1 and the measurement value v2 of the second voltmeter V2 of the second bridge circuit C2. As shown in Figure 8, the first voltmeter V1 and the second voltmeter V2 output periodically changing sinusoidal measurement values v1 and v2, respectively. The period T of these measurement values corresponds to 1/2 the period of the first rotation speed described above. In addition, the direction of the input rotational motion can be determined based on whether the phase of the measurement value of the second voltmeter V2 leads the phase of the measurement value of the first voltmeter V1 by 1/8 period of the first rotation speed (1/4 period of the measurement values v1 and v2) or lags behind the phase of the measurement value of the first voltmeter V1 by 1/8 period of the first rotation speed (1/4 period of the measurement values v1 and v2).

Therefore, based on the measurement values v1, v2 of these two voltmeters V1, V2, it is possible to detect the rotation angle of the rotational motion input to the flex gear 20. Specifically, for example, a function table that associates the combination of the measurement values v1, v2 of the first voltmeter V1 and the second voltmeter V2 with the rotation angle is prepared in advance, and the measurement values v1, v2 are input to the function table to output the rotation angle.

The rotation angle detection sensor S1 also has a first ammeter A1. As shown in FIG. 6, the first ammeter A1 is connected in series to the first bridge circuit C1. Therefore, the first ammeter A1 measures a current value according to the combined resistance of the first resistance wire patterns Ra, Rb, Rc, and Rd in the first bridge circuit C1. Specifically, if the power supply voltage is Vo and the combined resistance of the first resistance wire patterns Ra, Rb, Rc, and Rd is Rc1, the measurement value I1 of the first ammeter A1 is I1=Vo/Rc1.

The individual resistance values of the first resistance wire patterns Ra, Rb, Rc, and Rd change in response to the expansion and contraction of the diaphragm portion 221 described above. However, the combined resistance Rc1 is less affected by the expansion and contraction of the diaphragm portion 221, and is dominated by changes due to temperature. Therefore, the measurement value I1 of the first ammeter A1 fluctuates in response to the temperature of the power transmission device 1. This measurement value I1 of the first ammeter A1 is an example of the "first output value" in the present invention.

The rotation angle detection sensor S1 also has a second ammeter A2. As shown in FIG. 7, the second ammeter A2 is connected in series to the second bridge circuit C2. Therefore, the second ammeter A2 measures a current value according to the combined resistance of the second resistance wire pattern Re, Rf, Rg, and Rh in the second bridge circuit C2. Specifically, if the power supply voltage is Vo and the combined resistance of the second resistance wire pattern Re, Rf, Rg, and Rh is Rc2, the measurement value I2 of the second ammeter A2 is I2=Vo/Rc2.

The individual resistance values of the second resistance wire patterns Re, Rf, Rg, and Rh change in response to the expansion and contraction of the diaphragm portion 221 described above. However, the combined resistance Rc2 is less affected by the expansion and contraction of the diaphragm portion 221, and is dominated by changes due to temperature. Therefore, the measurement value I2 of the second ammeter A2 fluctuates in response to the temperature of the power transmission device 1. This measurement value I2 of the second ammeter A2 is an example of the "first output value" in the present invention.

<2-3. Torque detection sensor>
The torque detection sensor S2 is a sensor that detects the torque applied to the flex gear 20 based on the distortion of the diaphragm portion 221. As shown in Fig. 4, the torque detection sensor S2 includes a third resistance wire pattern R3 and a fourth resistance wire pattern R4.

The third resistance wire pattern R3 is an arc-shaped or annular pattern in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. In this embodiment, the third resistance wire pattern R3 is provided in a range of approximately 360° around the central axis 9. The third resistance wire pattern R3 also includes a plurality of third resistance wires r3. The plurality of third resistance wires r3 are arranged in the circumferential direction in a substantially parallel posture. Each third resistance wire r3 is inclined toward one side in the circumferential direction with respect to the radial direction of the flex gear 20. The inclination angle of the third resistance wire r3 with respect to the radial direction is, for example, 45°. The ends of the third resistance wires r3 adjacent to each other in the circumferential direction are alternately connected on the inside or outside of the radial direction. As a result, the plurality of third resistance wires r3 are connected in series as a whole.

The fourth resistance wire pattern R4 is an arc-shaped or annular pattern in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. The fourth resistance wire pattern R4 is located radially inward from the third resistance wire pattern R3. In this embodiment, the fourth resistance wire pattern R4 is provided in a range of approximately 360° around the central axis 9. The fourth resistance wire pattern R4 also includes a plurality of fourth resistance wires r4. The plurality of fourth resistance wires r4 are arranged in the circumferential direction in a substantially parallel posture. Each of the fourth resistance wires r4 is inclined toward the other circumferential side with respect to the radial direction of the flex gear 20. The inclination angle of the fourth resistance wire r4 with respect to the radial direction is, for example, 45°. The ends of the fourth resistance wires r4 adjacent to each other in the circumferential direction are alternately connected to each other on the inner side or the outer side in the radial direction. As a result, the plurality of fourth resistance wires r4 are connected in series as a whole.

Figure 9 is a circuit diagram of a third bridge circuit C3 including a third resistance wire pattern R3 and a fourth resistance wire pattern R4. As shown in Figure 9, the third bridge circuit C3 of this embodiment includes a third resistance wire pattern R3, a fourth resistance wire pattern R4, and two fixed resistors Rs. The third resistance wire pattern R3 and the fourth resistance wire pattern R4 are connected in series. The two fixed resistors Rs are connected in series. Then, between the positive and negative poles of the power supply voltage, the row of the two resistance wire patterns R3 and R4 and the row of the two fixed resistors Rs are connected in parallel. In addition, the midpoint M1 of the third resistance wire pattern R3 and the fourth resistance wire pattern R4 and the midpoint M2 of the two fixed resistors Rs are connected to a third voltmeter V3.

The resistance values of the third resistance wire pattern R3 and the fourth resistance wire pattern R4 change depending on the torque applied to the flex gear 20. For example, when a torque is applied to the flex gear 20 in one circumferential direction around the central axis 9, the resistance value of the third resistance wire pattern R3 decreases, and the resistance value of the fourth resistance wire pattern R4 increases. On the other hand, when a torque is applied to the flex gear 20 in the other circumferential direction around the central axis 9, the resistance value of the third resistance wire pattern R3 increases, and the resistance value of the fourth resistance wire pattern R4 decreases. In this way, the third resistance wire pattern R3 and the fourth resistance wire pattern R4 show resistance value changes in opposite directions with respect to torque.

When the resistance values of the third resistance wire pattern R3 and the fourth resistance wire pattern R4 change, the potential difference between the midpoint M1 of the third resistance wire pattern R3 and the fourth resistance wire pattern R4 and the midpoint M2 of the two fixed resistors Rs changes, and the measurement value v3 of the third voltmeter V3 changes. Therefore, the direction and magnitude of the torque applied to the flex gear 20 can be detected based on the measurement value v3 of the third voltmeter V3.

The torque detection sensor S2 also has a third ammeter A3. As shown in FIG. 9, the third ammeter A3 is connected in series to the third bridge circuit C3. Therefore, the third ammeter A3 measures a current value according to the combined resistance of the third resistance wire pattern R3, the fourth resistance wire pattern R4, and the two fixed resistors Rs in the third bridge circuit C3. Specifically, if the power supply voltage is Vo and the combined resistance of the third resistance wire pattern R3, the fourth resistance wire pattern R4, and the two fixed resistors Rs is Rc3, the measurement value I3 of the third ammeter A3 is I3=Vo/Rc3.

The individual resistance values of the third resistance wire pattern R3 and the fourth resistance wire pattern R4 change depending on the torque applied to the flex gear 20. However, the combined resistance Rc3 of the third resistance wire pattern R3, the fourth resistance wire pattern R4, and the two fixed resistors Rs is less affected by the torque applied to the flex gear 20, and is dominated by changes due to temperature. Therefore, the measurement value I3 of the third ammeter A3 fluctuates depending on the temperature of the power transmission device 1. This measurement value I3 of the third ammeter A3 is an example of the "first output value" in the present invention.

<2-4. Ripple correction>
When the power transmission device 1 is driven, periodic flexural deformation occurs in the flex gear 20. Therefore, the measurement value v3 of the third voltmeter V3 described above contains a component reflecting the torque that is originally to be measured, and an error component (ripple) caused by the periodic flexural deformation of the flex gear 20. The error component changes depending on the rotation angle of the rotational motion input to the flex gear 20.

Therefore, the signal processing circuit 46 performs a correction process to cancel the above-mentioned error component from the measurement value of the third voltmeter V3. FIG. 10 is a conceptual diagram showing the correction process of the signal processing circuit 46. As shown in FIG. 10, the measurement values v1, v2, and v3 of the first voltmeter V1, the second voltmeter V2, and the third voltmeter V3 are input to the signal processing circuit 46. The signal processing circuit 46 first detects the rotation angle of the rotational motion input to the flex gear 20 based on the measurement values v1 and v2 of the first voltmeter V1 and the second voltmeter V2. Then, the above-mentioned error component is estimated according to the detected rotation angle. Then, the measurement value v3 of the third voltmeter V3 is corrected using the estimated error component. As a result, the torque applied to the flex gear 20 can be output with higher accuracy.

In addition, the signal processing circuit 46 may multiply the measured values v1 and v2 of the first voltmeter V1 and the second voltmeter V2 by a predetermined coefficient and combine them into the measured value v3 of the third voltmeter V3 without calculating the rotation angle described above. In this way, the processing load for calculating the rotation angle is reduced, and the calculation speed of the signal processing circuit 46 can be improved.

<2-5. Temperature correction>
As described above, by using copper or an alloy containing copper as the material for the conductor layer 44, the material cost of the sensor board 40 can be reduced. However, compared to other expensive materials, the resistance value of copper is more likely to change depending on the environmental temperature. Therefore, the sensor board 40 of this embodiment is provided with a temperature sensor S3 to correct the influence of temperature. As shown in FIG. 4, the temperature sensor S3 has a fifth resistance wire pattern R5 that extends in an arc shape or annular shape along the circumferential direction of the flex gear 20.

Figure 11 is a circuit diagram of the detection circuit C4 including the fifth resistance wire pattern R5. As shown in Figure 11, one end of the fifth resistance wire pattern R5 is connected to the positive pole of the power supply voltage. The other end of the fifth resistance wire pattern R5 is connected to the negative pole of the power supply voltage. The temperature sensor S3 also has a fourth ammeter A4. As shown in Figure 11, the fourth ammeter A4 is connected in series to the fifth resistance wire pattern R5. Therefore, the fourth ammeter A4 measures a current value corresponding to the resistance value of the fifth resistance wire pattern R5. Specifically, when the power supply voltage is Vo, the measurement value I4 of the fourth ammeter A4 is I4 = Vo/R5.

Because the fifth resistance wire pattern R5 is arc-shaped or annular, the resistance value of the fifth resistance wire pattern R5 is less affected by the torque applied to the flex gear 20, and temperature-dependent changes are dominant. Therefore, the measurement value I4 of the fourth ammeter A4 fluctuates according to the temperature of the power transmission device 1. This measurement value I4 of the fourth ammeter A4 is an example of the "second output value" in the present invention.

The signal processing circuit 46 corrects the measurement value v3 of the third voltmeter V3, taking into account not only the rotation angle but also the measurement value I4 of the fourth ammeter A4. Specifically, the measurement value v3 of the third voltmeter V3 is increased or decreased in a direction that cancels changes due to temperature. In this way, the torque applied to the flex gear 20 can be detected more accurately by suppressing the effects of temperature changes while using inexpensive copper or copper alloy.

The fifth resistance wire pattern R5 of the temperature sensor S3 is arc-shaped or annular about the central axis 9. Therefore, stress is less likely to be applied to the fifth resistance wire pattern R5 when the power transmission device 1 is in operation. Therefore, the fifth resistance wire pattern R5 is less likely to break down or fail, compared to the other resistance wire patterns R1 to R4.

Consider performing temperature correction on the measurement value of the voltmeter for a full bridge circuit as shown in FIG. 13. The measurement value of the fifth ammeter A5 connected in series with the full bridge circuit of FIG. 13 is the measurement value I5. In order to perform the above-mentioned temperature correction on the measurement value v3 of the third voltmeter V3, the temperature correction may be performed based on the measurement value I5 of the fifth ammeter A5 instead of the measurement value I4 of the fourth ammeter A4. When performing temperature correction based on the measurement value I4, the position of the fifth resistance wire pattern R5 included in the detection circuit C4 of the temperature sensor S3 is different from the position of the resistance wire pattern included in the rotation angle detection sensor S1 and the torque detection sensor S2. Compared to the temperature sensor S3, the resistance wires of the rotation angle detection sensor S1 and the torque detection sensor S2 are longer and self-heating is higher. For these reasons, a temperature difference occurs between the resistance wire related to the measurement value I4 and the resistance wire related to the measurement value v3 that is the subject of correction. In contrast, when temperature correction is performed based on the measurement value I5, the temperature can be detected based on the measurement value I5 of the current of the bridge circuit C3 connected to the third voltmeter V3. Therefore, there is no temperature difference between the resistance wire related to the measurement value I5 and the resistance wire related to the measurement value v3 that is the subject of correction. This makes it possible to improve the accuracy of the temperature correction.

As a method of temperature correction, for example, (voltage value after temperature correction) = (voltage value before temperature correction) + f (current value), and increase or decrease in the direction to cancel the change in the voltage value due to temperature. In the case of this embodiment, for example, the voltage value may be the measured value v3, and the current value may be the measured value I5. f (current value) is an equation including the current value, which is a variable that changes with temperature, and the temperature correction coefficient. To obtain the temperature correction coefficient, for example, the torque detection sensor S2 is placed in a thermostatic chamber with the sensor board 40 fixed to the diaphragm part 221 of the flex gear 20, the power supply voltage is kept constant, and the temperature of the torque detection sensor S2 is changed in a state where no load is applied due to the driving of the power transmission device 1, and the measured values I5 and v3 at that time are measured. Then, based on the set of the measured values I5 and v3 measured for each temperature, an approximation equation for the measured values I5 and v3 is calculated, and the coefficient of the approximation equation may be used. The approximate equation can be calculated, for example, by performing a regression analysis of the measurement data to derive an equation between the measurement value I5 and the measurement value v3. The regression analysis can be calculated, for example, by using the least squares method to find coefficients. For example, the measurement value v3 can be calculated as y, the measurement value I5 as x, and a, b, and c as constants, and an approximate equation can be calculated in the form of y = a(x^2) + bx + c, with the values of a and b being temperature correction coefficients. Then, when the power transmission device 1 is in operation, y can be set to the measurement value v3 after temperature correction, x to the measurement value I5, and c to the measurement value v3 before temperature correction.

Figure 12 is a flow chart showing the flow of temperature correction for a method of performing temperature correction based on the measurement value of an ammeter connected in series with the bridge circuit. The signal processing circuit 46 acquires a temperature correction coefficient. The temperature correction coefficient can be obtained, for example, by the method described above. Then, the power transmission device 1 is driven. Next, while the power transmission device 1 is being driven, the measurement value I5 and the measurement value v3 are measured. Then, the measurement value v3 is temperature corrected based on the measurement value I5 and the temperature correction coefficient. Then, based on the temperature-corrected measurement value v3, the direction and magnitude of the torque applied to the flex gear 20 are detected and output.

As described above, the method of performing temperature correction based on the measurement value of an ammeter connected in series with the bridge circuit is suitable when the resistance wire pattern is made of a material with low resistivity, such as copper, aluminum, gold, or silver. In addition, the measurement value v1 of the first voltmeter V1 may be temperature corrected based on the measurement value I1 of the first ammeter A1. The measurement value v2 of the second voltmeter V2 may be temperature corrected based on the measurement value I2 of the second ammeter A2. Even if the bridge circuit C3 is a half-bridge circuit rather than a full-bridge circuit as shown in Figure 9, an ammeter may be connected in series with the bridge circuit and the temperature correction described above may be performed.

<2-6. Fault detection>
Next, a function of detecting a fault such as a disconnection of the resistance wire pattern in the rotation angle detection sensor S1 and the torque detection sensor S2 described above will be described. As shown in Figures 1, 3, and 4, the signal processing circuit 46 of the sensor board 40 is electrically connected to a fault detection unit 51. The fault detection unit 51 is composed of a computer having a processor such as a CPU and various memories, or an electric circuit board. In this embodiment, the sensor board 40 and the fault detection unit 51 constitute a sensor system 50 with a fault detection function.

Figure 14 is a conceptual diagram showing the input and output of the fault detection unit 51. As shown in Figure 14, the fault detection unit 51 receives the measurement value I1 of the first ammeter A1, the measurement value I2 of the second ammeter A2, the measurement value I3 of the third ammeter A3, and the measurement value I4 of the fourth ammeter A4 from the signal processing circuit 46 of the sensor board 40. The fault detection unit 51 outputs a detection result indicating whether or not the rotation angle detection sensor S1 and the torque detection sensor S2 are faulty based on these measurement values I1, I2, I3, and I4.

Figure 15 is a flowchart showing the flow of the fault detection process in the fault detection unit 51. The fault detection unit 51 first compares the measurement value I1 of the first ammeter A1, which is the "first output value," with the measurement value I4 of the fourth ammeter A4, which is the "second output value" (step ST1).

Figure 16 is a graph showing the changes in the measured values I1 and I4. When no failure occurs, as shown at time T1 in Figure 16, both the measured values I1 and I4 change in the same way in response to changes in the temperature of the power transmission device 1. Therefore, when no failure occurs, the measured values I1 and I4 show correlated changes. However, as described above, the fifth resistance wire pattern R5 of the temperature sensor S3 is an arc or ring shape without corners, making it less likely to break down, whereas the four first resistance wire patterns R1 (Ra, Rb, Rc, Rd) of the rotation angle detection sensor S1 have a complex shape, making it relatively more likely to break down, such as break down. When such a failure occurs, the measured value I1 changes significantly, as shown at time T2 in Figure 16.

In step ST1, if the relationship between the measured values I1 and I4 is within a predetermined normal range (step ST1: yes), the fault detection unit 51 determines that no fault such as a break has occurred in the four first resistance wire patterns R1 (Ra, Rb, Rc, Rd) of the rotation angle detection sensor S1 (step ST2). On the other hand, if the relationship between the measured values I1 and I4 is outside the predetermined normal range (step ST1: no), it determines that a fault such as a break has occurred in one of the four first resistance wire patterns R1 (Ra, Rb, Rc, Rd) of the rotation angle detection sensor S1 (step ST3). The relationship between the measured values I1 and I4 may be, for example, the difference between the measured values I1 and I4 or the ratio between the measured values I1 and I4.

Next, the fault detection unit 51 compares the measurement value I2 of the second ammeter A2, which is the "first output value," with the measurement value I4 of the fourth ammeter A4, which is the "second output value" (step ST4). If the relationship between the measurement values I2 and I4 is within a predetermined normal range (step ST4: yes), it is determined that no fault such as a break has occurred in the four second resistance wire patterns R2 (Re, Rf, Rg, Rh) of the rotation angle detection sensor S1 (step ST5). On the other hand, if the relationship between the measurement values I2 and I4 is outside the predetermined normal range (step ST4: no), it is determined that a fault such as a break has occurred in one of the four second resistance wire patterns R2 (Re, Rf, Rg, Rh) of the rotation angle detection sensor S1 (step ST6). The relationship between the measurement values I2 and I4 may be, for example, the difference between the measurement values I2 and I4 or the ratio between the measurement values I2 and I4.

Then, the fault detection unit 51 compares the measurement value I3 of the third ammeter A3, which is the "first output value," with the measurement value I4 of the fourth ammeter A4, which is the "second output value" (step ST7). If the relationship between the measurement values I3 and I4 is within a predetermined normal range (step ST7: yes), it is determined that no fault such as a break has occurred in the third resistance wire pattern R3 and the fourth resistance wire pattern R4 of the torque detection sensor S2 (step ST8). On the other hand, if the relationship between the measurement values I3 and I4 is outside the predetermined normal range (step ST7: no), it is determined that a fault such as a break has occurred in the third resistance wire pattern R3 or the fourth resistance wire pattern R4 of the torque detection sensor S2 (step ST9). The relationship between the measurement values I3 and I4 may be, for example, the difference between the measurement values I3 and I4 or the ratio between the measurement values I3 and I4.

Then, the fault detection unit 51 outputs a detection result regarding the presence or absence of a fault (step ST10). Specifically, the fault detection unit 51 outputs a signal indicating the detection result to an external controller. The detection result may be displayed on a display unit of the fault detection unit 51 or the controller.

As described above, in this sensor system 50, the fault detection unit 51 acquires the measurement values I1, I2, and I3, which are the "first output value" that varies with temperature, from the rotation angle detection sensor S1 and the torque detection sensor S2, which are the "first sensor." The fault detection unit 51 also acquires the measurement value I4, which is the "second output value" that varies with temperature, from the temperature sensor S3, which is the "second sensor" that has a different measurement target from the "first sensor." Then, the fault detection unit 51 detects faults in the rotation angle detection sensor S1 and the torque detection sensor S2 based on whether the relationship between the measurement values I1, I2, and I3, which are the "first output value," and the measurement value I4, which is the "second output value," is within a predetermined normal range.

In this way, if the measurement values I1, I2, and I3 show a change that differs from the normal change according to temperature, a failure of the sensor corresponding to that measurement value can be detected. Therefore, a failure of each sensor can be detected without providing two sensors for the same measurement object. In other words, a failure of the rotation angle detection sensor S1 can be detected without providing two rotation angle detection sensors S1 at the same location of the flex gear 20. Also, a failure of the torque detection sensor S2 can be detected without providing two torque detection sensors S2 at the same location of the flex gear 20.

3. Modifications
Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

In the above embodiment, the fault detection process (steps ST1 to ST6) for the rotation angle detection sensor S1 is executed first, followed by the fault detection process (steps ST7 to ST9) for the torque detection sensor S2. However, the order of these fault detection processes may be reversed. Furthermore, the fault detection process (steps ST1 to ST6) for the rotation angle detection sensor S1 and the fault detection process (steps ST7 to ST9) for the torque detection sensor S2 may be executed simultaneously in parallel.

In addition, the sensor board 40 in the above embodiment was equipped with a rotation angle detection sensor S1 and a torque detection sensor S2. However, the sensor board 40 may be equipped with only one of the rotation angle detection sensor S1 and the torque detection sensor S2. In that case, the "first sensor" may be only one of the rotation angle detection sensor S1 and the torque detection sensor S2. In addition, the "first sensor" may be another sensor capable of outputting a first output value that varies depending on the temperature.

In addition, in the above embodiment, the temperature sensor S3 mounted on the sensor board 40 is defined as the "second sensor." However, the "second sensor" may be another sensor capable of outputting a second output value that varies according to temperature. For example, a temperature sensor such as a thermocouple that is disposed at a position different from the sensor board 40 may be defined as the "second sensor."

Also, the rotation angle detection sensor S1 may be the "first sensor" and the torque detection sensor S2 may be the "second sensor." In this case, it is possible to detect whether either the rotation angle detection sensor S1 or the torque detection sensor S2 is malfunctioning based on whether the relationship between the first output value output from the rotation angle detection sensor S1 and the second output value output from the torque detection sensor S2 is within a predetermined normal range.

In the above embodiment, the measurement value of the ammeter was used as the "first output value" and the "second output value". That is, in the fault detection process of the above embodiment, the power supply voltage Vo was constant, and the current values reflecting the fluctuation of the resistance value due to temperature were compared. However, the current value may be constant, and the voltage values reflecting the fluctuation of the resistance value due to temperature may be compared. For example, the detection circuit C4 of the temperature sensor S3 may be a circuit in which the fifth resistance line pattern R5 is connected in series to the constant current source 47, and the voltmeter V4 is connected in parallel to the fifth resistance line pattern, as shown in FIG. 17. The measurement value of the voltmeter V4 may be the "second output value". In addition, the fault detection unit 51 may multiply the current value or the voltage value by a predetermined coefficient to calculate a temperature estimate, and compare the calculated temperature estimates.

In the above embodiment, the signal processing circuit 46 is mounted on the sensor board 40. However, the signal processing circuit 46 may be provided outside the sensor board 40. For example, the signal processing circuit 46 may be incorporated in a computer or an electric circuit board that constitutes the fault detection unit 51.

In the above embodiment, copper or an alloy containing copper is used as the material for each resistance wire pattern. However, other metals such as SUS and aluminum may be used as the material for the resistance wire pattern. Also, non-metallic materials such as ceramics and resin may be used as the material for the resistance wire pattern. Also, conductive ink may be used as the material for the resistance wire pattern. When conductive ink is used, each resistance wire pattern may be printed on the surface of the sensor substrate 40 with conductive ink.

In the flex gear 20 of the above embodiment, the diaphragm portion 221 extends radially outward from the base end of the cylindrical portion 21. However, the diaphragm portion 221 may extend radially inward from the base end of the cylindrical portion 21.

In the above embodiment, the sensor board 40 was fixed to the flex gear 20 of the power transmission device 1. However, the sensor board 40 may be fixed to a component other than the flex gear 20.

Other details of the configuration of the sensor system and the power transmission device may be modified as appropriate without departing from the spirit of the present invention. Furthermore, the elements appearing in each of the above embodiments and variations may be combined as appropriate without causing any contradiction.

This application can be used in sensor systems and power transmission devices.

REFERENCE SIGNS LIST 1 Power transmission device 9 Central shaft 10 Internal gear 20 Flex gear 30 Wave generator 40 Sensor board 41 Main body 42 Flap portion 43 Insulating layer 44 Conductive layer 45 Double-sided adhesive tape 46 Signal processing circuit 50 Sensor system 51 Fault detection portion 221 Diaphragm portion A1 First ammeter A2 Second ammeter A3 Third ammeter A4 Fourth ammeter C1 First bridge circuit C2 Second bridge circuit C3 Third bridge circuit C4 Detection circuit R1, Ra to Rd First resistance wire pattern R2, Re to Rh Second resistance wire pattern R3 Third resistance wire pattern R4 Fourth resistance wire pattern R5 Fifth resistance wire pattern Rs Fixed resistor S1 Rotation angle detection sensor S2 Torque detection sensor S3 Temperature sensor V1 First voltmeter V2 Second voltmeter V3 Third voltmeter

Claims (5)

A first sensor and a second sensor having different measurement targets;
a substrate carrying the first sensor and the second sensor;
a failure detection unit that detects a failure of either the first sensor or the second sensor;
a signal processing unit that corrects a first measurement value that is a measurement value of the measurement object of the first sensor using a second measurement value that is a measurement value of the measurement object of the second sensor;
A sensor system comprising:
the failure detection unit acquires from the first sensor a first output value that varies with temperature, and acquires from the second sensor a second output value that varies with temperature, and detects a failure of either the first sensor or the second sensor based on whether a relationship between the first output value and the second output value is within a predetermined normal range ;
the first sensor is a strain sensor that detects a strain of an object to which the substrate is fixed;
the second sensor is a temperature sensor that detects a temperature of the object,
the first sensor has a first resistance wire pattern having a bent structure in which ends of conductors adjacent in a circumferential direction are alternately connected on the inside or outside in a radial direction around a central axis of an object to which the substrate is fixed, forming an arc-shaped or annular pattern;
A sensor system , wherein the second sensor has a second resistance wire pattern that does not have the bent structure and is arc-shaped or annular about the central axis . 2. The sensor system of claim 1 ,
The first sensor is
a third resistance wire pattern in which the conductive wire is inclined to one side in the circumferential direction;
a fourth resistance wire pattern in which the conductor is inclined toward the other side in the circumferential direction,
A sensor system comprising a bridge circuit in which the third resistance wire pattern and the fourth resistance wire pattern are electrically connected between a positive electrode and a negative electrode for connection to a power supply voltage. The sensor system according to claim 1 or 2 ,
The apparatus further includes a third sensor having a measurement target different from that of the first sensor and the second sensor,
the third sensor is mounted on the substrate;
The signal processing unit corrects a first measurement value, which is a measurement value of a measurement object of the first sensor, using a third measurement value, which is a measurement object of a third sensor. The sensor system according to claim 3 ,
the first sensor is a sensor that detects a torque applied to the object based on a distortion of the object,
A sensor system, wherein the third sensor is a sensor that detects a rotation angle of a rotational motion input to the object based on a distortion of the object. A power transmission device comprising the sensor system according to any one of claims 1 to 4 ,
A power transmission device having a gear to which the substrate is fixed.