Sensor system and power transmission device

Abstract

To provide a sensor system capable of detecting a failure of a sensor without providing two sensors for the same measurement object.SOLUTION: A sensor system 50 comprises a first sensor and a second sensor, which measure different objects, and a failure detection section 51. The failure detection section 51 detects a failure of either the first sensor or the second sensor. The failure detection section 51 acquires a first output value fluctuating according to a temperature from the first sensor. The failure detection section 51 also acquires a second output value fluctuating according to the temperature from the second sensor. Then, the failure detection section 51 detects the failure of either the first sensor or the second sensor on the basis of whether or not a relationship between the first output value and the second output value is within a predetermined normal range.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sensor system and a power transmission device.

Background Art

[0002] In recent years, the demand for speed reducers mounted on robot joints and the like has been rapidly increasing. Regarding conventional speed reducers, for example, they are described 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 the rotational speed after deceleration. Thereby, it is possible to measure the torque applied to the flexible external gear.

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0003] However, the resistance wire of the strain gauge used for torque measurement has a complex shape that is folded back in a zigzag. For this reason, when the speed reducer is driven, repeated flexural deformation of the flexible external gear may cause a failure such as disconnection in a part of the resistance wire of the strain gauge. When such a failure occurs, the measured value of the strain gauge changes. However, simply detecting a change in the measured value of the strain gauge cannot distinguish whether the change is due to a failure such as disconnection or a change in the torque applied to the flexible external gear.

[0004] Therefore, conventionally, in order to detect a failure of the strain gauge, it has been necessary to arrange two strain gauges at the same location on the flexible external gear and compare the measured values of those strain gauges.

[0005] An object of the present invention is to provide a sensor system capable of detecting a sensor failure without providing two sensors for the same measurement target.

Means for Solving the Problems

[0006] The present invention relates to a sensor system including a first sensor and a second sensor having different measurement targets, a substrate on which the first sensor and the second sensor are mounted, a failure detection unit that detects a failure of either one of the first sensor and the second sensor, and a signal processing unit that corrects a first measurement value, which is a measurement value of the measurement target of the first sensor, using a second measurement value, which is a measurement value of the measurement target of the second sensor. The failure detection unit obtains a first output value that varies according to temperature from the first sensor and a second output value that varies according to temperature from the second sensor, and detects a failure of either one of the first sensor and the second sensor based on whether or not the 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 the strain of the object to which the substrate is fixed, the second sensor is a temperature sensor that detects the temperature of the object, the first sensor has a first resistance wire pattern in which a zigzag structure, in which the ends of adjacent conductive wires in the circumferential direction are alternately connected on the inner or outer side in the radial direction, forms an arc-shaped or annular pattern centered on the central axis of the object to which the substrate is fixed, and the second sensor has a second resistance wire pattern that is arc-shaped or annular centered on the central axis and does not have the zigzag structure to do.

Effect of the Invention

[0007] According to the present invention, output values of a first sensor and a second sensor having different measurement targets are obtained, and a failure of either one of the first sensor and the second sensor is detected based on whether or not the relationship between these output values is within a normal range. Thereby, it is possible to detect a failure of a sensor without providing two sensors for the same measurement target.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, exemplary embodiments of the present application will be described with reference to the drawings. In the present application, the direction parallel to the central axis of the power transmission device is referred to as the "axial direction", the direction orthogonal to the central axis of the power transmission device is referred to as the "radial direction", and the direction along an arc centered on the central axis of the power transmission device is referred to as the "circumferential direction", respectively. However, the above "parallel direction" includes a substantially parallel direction. Also, the above "orthogonal direction" includes a substantially orthogonal direction.

[0010] <1. Configuration of the Power Transmission Device> FIG. 1 is a longitudinal sectional view of a power transmission device 1 according to the first embodiment. FIG. 2 is a cross-sectional view of the power transmission device 1 seen from the A-A position in FIG. 1. This power transmission device 1 is a device that transmits the rotational motion of the first rotational speed obtained from a motor to the subsequent stage while reducing the speed to a second rotational speed lower than the first rotational speed. The power transmission device 1 is used, for example, by being incorporated together with a motor in a joint of a robot. However, the power transmission device of the present invention may be used in other devices such as assist suits and automated guided vehicles.

[0011] As shown in FIGS. 1 and 2, the power transmission device 1 of the present embodiment includes an internal gear 10, a flex gear 20, a wave generator 30, and a sensor board 40.

[0012] The internal gear 10 is an annular gear having a plurality of internal teeth 11 on its inner peripheral surface. The internal gear 10 is fixed to the frame of the device on which the power transmission device 1 is mounted, for example, by screwing. The internal gear 10 is arranged coaxially with the central axis 9. Further, the internal gear 10 is located radially outside the cylindrical portion 21 of the flex gear 20 described later. 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 regarded as a substantially rigid body. The internal gear 10 has a cylindrical inner peripheral surface. The plurality of internal teeth 11 are arranged at a constant pitch in the circumferential direction on the inner peripheral surface. Each internal tooth 11 projects radially inward.

[0013] The flex gear 20 is an annular gear having flexibility. The flex gear 20 is rotatably supported about the central axis 9. The flex gear 20 is an example of the "gear" in the present invention.

[0014] The flexible gear 20 of the present embodiment has a cylindrical portion 21 and a flat plate portion 22. The cylindrical portion 21 extends in a cylindrical shape 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. Since the cylindrical portion 21 has flexibility, it can be deformed in the radial direction. In particular, the tip portion of the cylindrical portion 21 located radially inside the internal gear 10 is a free end, so it can be displaced more greatly in the radial direction than other portions.

[0015] The flexible gear 20 has a plurality of external teeth 23. The plurality of 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 projects radially outward. The number of internal teeth 11 of the internal gear 10 described above and the number of external teeth 23 of the flexible gear 20 are slightly different.

[0016] The flat plate portion 22 has a diaphragm portion 221 and a thick portion 222. The diaphragm portion 221 extends in a flat plate shape radially outward from the axial base end of the cylindrical portion 21 and extends in an annular shape around the central axis 9. The diaphragm portion 221 can be slightly bent and deformed in the axial direction. The thick portion 222 is an annular portion located radially outside 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 the device on which the power transmission device 1 is mounted.

[0017] The wave generator 30 is a mechanism that generates periodic bending deformation in the cylindrical portion 21 of the flexible gear 20. The wave generator 30 has a cam 31 and a flexible bearing 32. The cam 31 is rotatably supported around 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 flexible gear 20. Therefore, the cam 31 and the cylindrical portion 21 can rotate at different rotational speeds.

[0018] 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. Therefore, the cylindrical portion 21 of the flex gear 20 deforms into an elliptical shape along the outer peripheral surface of the cam 31. As a result, the outer teeth 23 of the flex gear 20 mesh with the inner teeth 11 of the internal gear 10 at two locations corresponding to both ends of the major axis of the ellipse. At other positions in the circumferential direction, the outer teeth 23 and the inner teeth 11 do not mesh.

[0019] The cam 31 is connected to the motor directly or via another power transmission mechanism. When the motor is driven, the cam 31 rotates at a first rotational speed about the central axis 9. As a result, the major axis of the above-described ellipse of the flex gear 20 also rotates at the first rotational speed. Then, the meshing position between the outer teeth 23 and the inner teeth 11 also changes in the circumferential direction at the first rotational speed. Also, as described above, the number of inner teeth 11 of the internal gear 10 and the number of outer teeth 23 of the flex gear 20 are slightly different. Due to this difference in the number of teeth, the meshing position between the outer teeth 23 and the inner teeth 11 changes slightly in the circumferential direction for each rotation of the cam 31. As a result, the flex gear 20 rotates about the central axis 9 relative to the internal gear 10 at a second rotational speed lower than the first rotational speed. Therefore, a rotational motion at the decelerated second rotational speed can be extracted from the flex gear 20.

[0020] <2. Regarding the sensor substrate> <2-1. Configuration of the sensor substrate> The sensor substrate 40 is a substrate on which a sensor for detecting the torque applied to the flex gear 20 is mounted. As shown in FIG. 1, in the present embodiment, the sensor substrate 40 is fixed to the circular surface of the disk-shaped diaphragm portion 221.

[0021] FIG. 3 is a view showing the back surface of the sensor substrate 40 facing the diaphragm portion 221 among the front and back surfaces. FIG. 4 is a view showing the front surface of the sensor substrate 40 not facing the diaphragm portion 221 among the front and back surfaces. FIG. 5 is a partial cross-sectional view of the diaphragm portion 221 and the sensor substrate 40.

[0022] The sensor substrate 40 of this embodiment is a flexible printed circuit board (FPC) that can be deformed flexibly. As shown in FIGS. 3 and 4, the sensor substrate 40 has an annular main body portion 41 centered on the central axis 9 and a flap portion 42 protruding radially outward from the main body portion 41. Also, as shown in FIG. 5, the sensor substrate 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. For example, copper or an alloy containing copper is used as the material of the conductor layer 44. The sensor substrate 40 of this embodiment has the conductor layer 44 on both the front and back surfaces of the insulating layer 43.

[0023] Also, as shown in FIG. 5, the sensor substrate 40 is fixed to the diaphragm portion 221 of the flex gear 20 by a double-sided adhesive tape 45. Specifically, the front surface of the diaphragm portion 221 and the back surface of the sensor substrate 40 are fixed via the double-sided adhesive tape 45. The double-sided adhesive tape 45 is formed by shaping a material having an adhesive force into a tape shape and cured to such an extent that it can maintain its shape. By using such a double-sided adhesive tape 45, the work of fixing the sensor substrate 40 to the diaphragm portion 221 becomes easier than when using a fluid adhesive. Also, variations in the fixing work by the operator can be reduced.

[0024] The sensor substrate 40 is mounted with a rotation angle detection sensor S1, a torque detection sensor S2, a temperature sensor S3, and a signal processing circuit 46. Both the rotation angle detection sensor S1 and the torque detection sensor S2 are 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.

[0025] The rotation angle detection sensor S1 has a resistance wire pattern formed on the back surface of the main body 41 that faces the diaphragm portion 221 among the front and back surfaces. That is, the conductor layer 44 on the back surface side includes the resistance wire pattern of the rotation angle detection sensor S1. The torque detection sensor S2 and the temperature sensor S3 have a resistance wire pattern formed on the surface of the main body 41 that does not face the diaphragm portion 221 among the front and back surfaces. That is, the conductor layer 44 on the surface side includes the resistance wire pattern of the torque detection sensor S2 and the resistance wire pattern of the temperature sensor S3.

[0026] The signal processing circuit 46 is arranged in the flap portion 42.

[0027] <2-2. About the 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.

[0028] The four first resistance wire patterns R1 are arranged at equal intervals in the circumferential direction around the central axis 9. Each first resistance wire pattern R1 is an arc-shaped pattern as a whole, in which one conductor extends in the circumferential direction while zigzagging. In the present embodiment, one first resistance wire pattern R1 extends in an angular range of about 45° around the central axis 9. Further, the first resistance wire pattern R1 includes a plurality of first resistance wires r1. The plurality of first resistance wires r1 are arranged at minute 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 connected alternately on the inner or outer side in the radial direction. Thereby, the plurality of first resistance wires r1 are connected in series as a whole.

[0029] The four second resistance line patterns R2 are arranged at equal intervals in the circumferential direction around the central axis 9. Each of the second resistance line patterns R2 is an arc-shaped pattern as a whole, in which one conductor extends in the circumferential direction while zigzagging. In the present embodiment, one second resistance line pattern R2 extends within an angular range of approximately 45° around the central axis 9. The second resistance line pattern R2 includes a plurality of second resistance lines r2. The plurality of second resistance lines r2 are arranged at minute intervals in the circumferential direction. Each second resistance line r2 extends linearly along the radial direction of the flex gear 20. The ends of the second resistance lines r2 adjacent to each other in the circumferential direction are alternately connected on the inner or outer side in the radial direction. Thereby, the plurality of second resistance lines r2 are connected in series as a whole.

[0030] The four second resistance line patterns R2 are arranged concentrically with the four first resistance line patterns R1 and in a region where the first resistance line patterns R1 are not arranged in the circumferential direction. In the present embodiment, the first resistance line patterns R1 and the second resistance line patterns R2 are arranged alternately in the circumferential direction. Then, the four first resistance line patterns R1 and the four second resistance line patterns R2 extend in an annular shape centered on the central axis 9 as a whole.

[0031] FIG. 6 is a circuit diagram of a first bridge circuit C1 including four first resistance line patterns R1. In the example of FIG. 6, the four first resistance line patterns R1 are distinguished and shown as Ra, Rb, Rc, and Rd. The first resistance line patterns Ra, Rb, Rc, and Rd are arranged in this order counterclockwise with Ra being the first one in FIG. 3.

[0032] As shown in FIG. 6, the four first resistance line patterns Ra, Rb, Rc, and Rd are incorporated in the first bridge circuit C1. The first resistance line pattern Ra and the first resistance line pattern Rb are connected in series in this order. The first resistance line pattern Rd and the first resistance line pattern Rc are connected in series in this order. Then, between the + pole and the - pole of the power supply voltage, the column of the two first resistance line patterns Ra and Rb and the column of the two first resistance line patterns Rd and Rc are connected in parallel. Also, the midpoint M11 of the first resistance line pattern Ra and the first resistance line pattern Rb and the midpoint M12 of the first resistance line pattern Rd and the first resistance line pattern Rc are connected to the first voltmeter V1.

[0033] FIG. 7 is a circuit diagram of a second bridge circuit C2 including four second resistance line patterns R2. In the example of FIG. 7, the four second resistance line patterns R2 are shown distinguished as Re, Rf, Rg, and Rh. The second resistance line pattern Re is located between the first resistance line pattern Ra and the first resistance line pattern Rd in FIG. 3. Also, the second resistance line patterns Re, Rf, Rg, and Rh are arranged in this order clockwise with Re being the first in FIG. 3.

[0034] As shown in FIG. 7, the four second resistance line patterns Re, Rf, Rg, and Rh are incorporated in the second bridge circuit C2. The second resistance line pattern Re and the second resistance line pattern Rf are connected in series in this order. The second resistance line pattern Rh and the second resistance line pattern Rg are connected in series in this order. Then, between the + pole and the - pole of the power supply voltage, the column of the two second resistance line patterns Re and Rf and the column of the two second resistance line patterns Rh and Rg are connected in parallel. Also, the midpoint M21 of the second resistance line pattern Re and the second resistance line pattern Rf and the midpoint M22 of the second resistance line pattern Rh and the second resistance line pattern Rg are connected to the second voltmeter V2.

[0035] When the power transmission device 1 is driven, a radially extending portion (hereinafter referred to as the "extending portion") and a radially contracting portion (hereinafter referred to as the "contracting portion") are generated in the diaphragm portion 221. Specifically, two extending portions and two contracting portions are generated alternately in the circumferential direction. That is, the extending portion and the contracting portion are generated alternately at 90° intervals in the circumferential direction. And the locations where these extending portions and contracting portions are generated rotate at the first rotational speed described above.

[0036] 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 strain of the diaphragm portion 221. For example, when the above-described extending portion overlaps a certain resistance wire pattern, the resistance value of that resistance wire pattern increases. Also, when the above-described contracting portion overlaps a certain resistance wire pattern, the resistance value of that resistance wire pattern decreases.

[0037] In the example of FIG. 3, when the contracting portion overlaps the first resistance wire patterns Ra, Rc, the extending portion overlaps the first resistance wire patterns Rb, Rd. Also, when the extending portion overlaps the first resistance wire patterns Ra, Rc, the contracting portion overlaps 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 opposite resistance value changes.

[0038] Also, in the example of FIG. 3, when the contracting portion overlaps the second resistance wire patterns Re, Rg, the extending portion overlaps the second resistance wire patterns Rf, Rh. Also, when the extending portion overlaps the second resistance wire patterns Re, Rg, the contracting portion overlaps 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 opposite resistance value changes.

[0039] FIG. 8 is a graph showing the measured value v1 of the first voltmeter V1 of the first bridge circuit C1 and the measured value v2 of the second voltmeter V2 of the second bridge circuit C2. As shown in FIG. 8, the first voltmeter V1 and the second voltmeter V2 each output sinusoidal measured values v1 and v2 that periodically change. The period T of this measured value corresponds to 1 / 2 times the period of the first rotational speed described above. Also, depending on whether the phase of the measured value of the second voltmeter V2 is advanced by 1 / 8 of the period of the first rotational speed (1 / 4 of the period of the measured values v1 and v2) or delayed by 1 / 8 of the period of the first rotational speed (1 / 4 of the period of the measured values v1 and v2) with respect to the phase of the measured value of the first voltmeter V1, the direction of the input rotational motion can be determined.

[0040] Therefore, based on the measured values v1 and v2 of these two voltmeters V1 and V2, the rotational angle of the rotational motion input to the flex gear 20 can be detected. Specifically, for example, a function table associating combinations of the measured values v1 and v2 of the first voltmeter V1 and the second voltmeter V2 with the rotational angle is prepared in advance, and the rotational angle may be output by inputting the measured values v1 and v2 into the function table.

[0041] Also, this rotational angle detection sensor S1 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 the current value corresponding to the combined resistance of the first resistance wire patterns Ra, Rb, Rc, and Rd in the first bridge circuit C1. Specifically, assuming the power supply voltage is Vo and the combined resistance of the first resistance wire patterns Ra, Rb, Rc, and Rd is Rc1, the measured value I1 of the first ammeter A1 is I1 = Vo / Rc1.

[0042] The individual resistance values of the first resistance line patterns Ra, Rb, Rc, and Rd change according to the expansion and contraction of the diaphragm portion 221 described above. However, these combined resistances Rc1 are less affected by the expansion and contraction of the diaphragm portion 221, and the change due to temperature becomes dominant. Therefore, the measured value I1 of the first ammeter A1 fluctuates according to the temperature of the power transmission device 1. This measured value I1 of the first ammeter A1 is an example of the "first output value" in the present invention.

[0043] Also, this rotation angle detection sensor S1 includes 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 the current value corresponding to the combined resistance of the second resistance line patterns Re, Rf, Rg, and Rh in the second bridge circuit C2. Specifically, assuming the power supply voltage is Vo and the combined resistance of the second resistance line patterns Re, Rf, Rg, and Rh is Rc2, the measured value I2 of the second ammeter A2 is I2 = Vo / Rc2.

[0044] The individual resistance values of the second resistance line patterns Re, Rf, Rg, and Rh change according to the expansion and contraction of the diaphragm portion 221 described above. However, these combined resistances Rc2 are less affected by the expansion and contraction of the diaphragm portion 221, and the change due to temperature becomes dominant. Therefore, the measured value I2 of the second ammeter A2 fluctuates according to the temperature of the power transmission device 1. This measured value I2 of the second ammeter A2 is an example of the "first output value" in the present invention.

[0045] <2-3. About the 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 line pattern R3 and a fourth resistance line pattern R4.

[0046] The third resistance line pattern R3 is an arc-shaped or annular pattern as a whole, in which a single conductor extends in the circumferential direction while zigzagging. In the present embodiment, the third resistance line pattern R3 is provided in a range of approximately 360° around the central axis 9. The third resistance line pattern R3 includes a plurality of third resistance lines r3. The plurality of third resistance lines r3 are arranged in the circumferential direction in a posture substantially parallel to each other. Each third resistance line r3 is inclined to one side in the circumferential direction with respect to the radial direction of the flex gear 20. The inclination angle of the third resistance line r3 with respect to the radial direction is, for example, 45°. The ends of the third resistance lines r3 adjacent to each other in the circumferential direction are alternately connected inside or outside in the radial direction. Thereby, the plurality of third resistance lines r3 are connected in series as a whole.

[0047] The fourth resistance line pattern R4 is an arc-shaped or annular pattern as a whole, in which a single conductor extends in the circumferential direction while zigzagging. The fourth resistance line pattern R4 is located radially inward of the third resistance line pattern R3. In the present embodiment, the fourth resistance line pattern R4 is provided in a range of approximately 360° around the central axis 9. The fourth resistance line pattern R4 includes a plurality of fourth resistance lines r4. The plurality of fourth resistance lines r4 are arranged in the circumferential direction in a posture substantially parallel to each other. Each fourth resistance line r4 is inclined to the other side in the circumferential direction with respect to the radial direction of the flex gear 20. The inclination angle of the fourth resistance line r4 with respect to the radial direction is, for example, 45°. The ends of the fourth resistance lines r4 adjacent to each other in the circumferential direction are alternately connected inside or outside in the radial direction. Thereby, the plurality of fourth resistance lines r4 are connected in series as a whole.

[0048] FIG. 9 is a circuit diagram of a third bridge circuit C3 including a third resistance line pattern R3 and a fourth resistance line pattern R4. As shown in FIG. 9, the third bridge circuit C3 of the present embodiment includes a third resistance line pattern R3, a fourth resistance line pattern R4, and two fixed resistors Rs. The third resistance line pattern R3 and the fourth resistance line pattern R4 are connected in series. The two fixed resistors Rs are connected in series. Then, between the + pole and the - pole of the power supply voltage, the column of the two resistance line patterns R3 and R4 and the column of the two fixed resistors Rs are connected in parallel. Further, the midpoint M1 of the third resistance line pattern R3 and the fourth resistance line pattern R4 and the midpoint M2 of the two fixed resistors Rs are connected to a third voltmeter V3.

[0049] The resistance values of the third resistance line pattern R3 and the fourth resistance line pattern R4 change according to the torque applied to the flex gear 20. For example, when a torque acting in one circumferential direction is applied to the flex gear 20 about the central axis 9, the resistance value of the third resistance line pattern R3 decreases and the resistance value of the fourth resistance line pattern R4 increases. On the other hand, when a torque acting in the other circumferential direction is applied to the flex gear 20 about the central axis 9, the resistance value of the third resistance line pattern R3 increases and the resistance value of the fourth resistance line pattern R4 decreases. Thus, the third resistance line pattern R3 and the fourth resistance line pattern R4 exhibit resistance value changes in opposite directions with respect to the torque.

[0050] When the resistance values of the third resistance line pattern R3 and the fourth resistance line pattern R4 change, the potential difference between the midpoint M1 of the third resistance line pattern R3 and the fourth resistance line pattern R4 and the midpoint M2 of the two fixed resistors Rs changes, so the measured value v3 of the third voltmeter V3 changes. Therefore, based on the measured value v3 of this third voltmeter V3, the direction and magnitude of the torque applied to the flex gear 20 can be detected.

[0051] Further, this torque detection sensor S2 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 the current value corresponding 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, assuming 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 measured value I3 of the third ammeter A3 is I3 = Vo / Rc3.

[0052] The individual resistance values of the third resistance wire pattern R3 and the fourth resistance wire pattern R4 change according to 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 the change due to temperature becomes dominant. Therefore, the measured value I3 of the third ammeter A3 fluctuates according to the temperature of the power transmission device 1. The measured value I3 of this third ammeter A3 is an example of the "first output value" in the present invention.

[0053] <2-4. About ripple correction> When the power transmission device 1 is driven, periodic flexural deformation occurs in the flex gear 20. Therefore, the measured value v3 of the third voltmeter V3 described above includes a component reflecting the torque to be originally measured and an error component (ripple) caused by the periodic flexural deformation of the flex gear 20. The error component changes according to the rotation angle of the rotational motion input to the flex gear 20.

[0054] Therefore, the signal processing circuit 46 performs correction processing for canceling the above error component from the measured value of the third voltmeter V3. FIG. 10 is a diagram conceptually showing the correction processing of the signal processing circuit 46. As shown in FIG. 10, the measured 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. First, the signal processing circuit 46 detects the rotation angle of the rotational motion input to the flex gear 20 based on the measured values v1 and v2 of the first voltmeter V1 and the second voltmeter V2. Then, according to the detected rotation angle, the above-described error component is estimated. After that, the measured 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.

[0055] Note that the signal processing circuit 46 may multiply the measured values v1 and v2 of the first voltmeter V1 and the second voltmeter V2 by predetermined coefficients without calculating the above-described rotation angle, and synthesize them with the measured value v3 of the third voltmeter V3. In this way, since the processing load associated with the calculation of the rotation angle is reduced, the calculation speed of the signal processing circuit 46 can be improved.

[0056] <2-5. About Temperature Correction> As described above, when copper or an alloy containing copper is used as the material of the conductor layer 44, the material cost of the sensor substrate 40 can be suppressed. However, compared with other expensive materials, the resistance value of copper is likely to change with the ambient temperature. Therefore, the sensor substrate 40 of the present embodiment includes a temperature sensor S3 in order to correct the influence of temperature. As shown in FIG. 4, the temperature sensor S3 has a fifth resistance wire pattern R5 extending in an arc shape or an annular shape along the circumferential direction of the flex gear 20.

[0057] FIG. 11 is a circuit diagram of a detection circuit C4 including a fifth resistance line pattern R5. As shown in FIG. 11, one end of the fifth resistance line pattern R5 is connected to the + pole of the power supply voltage. Also, the other end of the fifth resistance line pattern R5 is connected to the - pole of the power supply voltage. Further, the temperature sensor S3 has a fourth ammeter A4. As shown in FIG. 11, the fourth ammeter A4 is connected in series with the fifth resistance line pattern R5. Therefore, the fourth ammeter A4 measures a current value corresponding to the resistance value of the fifth resistance line pattern R5. Specifically, when the power supply voltage is Vo, the measured value I4 of the fourth ammeter A4 is I4 = Vo / R5.

[0058] Since the fifth resistance line pattern R5 is arc-shaped or annular, the resistance value of the fifth resistance line pattern R5 is hardly affected by the torque applied to the flex gear 20, and the change due to temperature becomes dominant. Therefore, the measured value I4 of the fourth ammeter A4 varies according to the temperature of the power transmission device 1. This measured value I4 of the fourth ammeter A4 is an example of the "second output value" in the present invention.

[0059] The signal processing circuit 46 corrects the measured value v3 of the third voltmeter V3 in consideration of not only the above-described rotation angle but also the measured value I4 of the fourth ammeter A4. Specifically, the measured value v3 of the third voltmeter V3 is increased or decreased in a direction to cancel the change due to temperature. In this way, while using inexpensive copper or a copper alloy, the influence of temperature change can be suppressed, and the torque applied to the flex gear 20 can be detected more accurately.

[0060] The fifth resistance line pattern R5 of the temperature sensor S3 is arc-shaped or annular about the central axis 9. For this reason, when the power transmission device 1 is driven, stress is hardly applied to the fifth resistance line pattern R5. Therefore, the fifth resistance line pattern R5 is less likely to have a failure such as disconnection compared to the other resistance line patterns R1 to R4.

[0061] Consider performing temperature correction on the measured value of a voltmeter for a full-bridge circuit as shown in FIG. 13. Let the measured value of the fifth ammeter A5 connected in series with the full-bridge circuit of FIG. 13 be the measured value I5. In order to perform the above-described temperature correction on the measured value v3 of the third voltmeter V3, the temperature correction may be performed based on the measured value I5 of the fifth ammeter A5 instead of the measured value I4 of the fourth ammeter A4. When performing temperature correction based on the measured 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 positions of the resistance wire patterns included in the rotation angle detection sensor S1 and the torque detection sensor S2. Compared with 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. Due to these reasons, a temperature difference occurs between the resistance wire related to the measured value I4 and the resistance wire related to the measured value v3 that is the object of correction. On the other hand, when performing temperature correction based on the measured value I5, the temperature can be detected based on the measured value I5 of the current in the bridge circuit C3 connected to the third voltmeter V3. Therefore, the temperature difference between the resistance wire related to the measured value I5 and the resistance wire related to the measured value v3 that is the object of correction disappears. Thus, the accuracy of temperature correction can be made higher.

[0062] As a temperature correction method, for example, (voltage value after temperature correction) = (voltage value before temperature correction) + f(current value), and it may be increased or decreased in a direction to cancel the change in the voltage value due to temperature. In the case of this embodiment, for example, the measured voltage value may be v3 and the measured current value may be I5. f(current value) is an expression 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, with the sensor substrate 40 fixed to the diaphragm portion 221 of the flex gear 20, the torque detection sensor S2 is placed in a thermostat, 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 drive of the power transmission device 1, and the measured value I5 and the measured value v3 at that time are measured. Then, based on the set of the measured value I5 and the measured value v3 measured for each temperature, an approximate expression for the measured value I5 and the measured value v3 is calculated, and the coefficients of the approximate expression may be used. The approximate expression may be obtained, for example, by performing regression analysis on the measurement data to derive an equation between the measured value I5 and the measured value v3. For regression analysis, for example, the coefficients may be obtained using the least squares method. For example, with the measured value v3 as y, the measured value I5 as x, and a, b, and c as constants, an approximate expression is obtained in the form of y = a(x^2) + bx + c, and the values of a and b may be used as the temperature correction coefficients. Then, when the power transmission device 1 is driven, y may be set as the measured value v3 after temperature correction, x as the measured value I5, and c as the measured value v3 before temperature correction.

[0063] FIG. 12 is a flowchart showing the flow of temperature correction for a method of performing temperature correction based on the measured value of an ammeter connected in series with a bridge circuit. The signal processing circuit 46 acquires the 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, during the drive of the power transmission device 1, the measured value I5 and the measured value v3 are measured. Then, the measured value v3 is temperature-corrected based on the measured value I5 and the temperature correction coefficient with respect to the measured value v3. Then, based on the temperature-corrected measured value v3, the direction and magnitude of the torque applied to the flex gear 20 are detected and output.

[0064] As described above, the method of performing temperature correction based on the measured value of the ammeter connected in series with the bridge circuit is suitable when a resistance wire pattern is fabricated using a material with a low specific resistance such as copper, aluminum, gold, or silver. Further, temperature correction may be performed on the measured value v1 of the first voltmeter V1 based on the measured value I1 of the first ammeter A1. Temperature correction may also be performed on the measured value v2 of the second voltmeter V2 based on the measured value I2 of the second ammeter A2. Also, as shown in FIG. 9, even when the bridge circuit C3 is a half-bridge circuit instead of a full-bridge circuit, an ammeter may be connected in series with the bridge circuit, and temperature correction may be performed as described above.

[0065] <2-6. Regarding Fault Detection> Subsequently, regarding the 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, an explanation will be given. As shown in FIGS. 1, 3, and 4, the signal processing circuit 46 of the sensor substrate 40 is electrically connected to the fault detection unit 51. The fault detection unit 51 is composed of a processor such as a CPU and various memories, a computer, or an electric circuit board. In the present embodiment, the sensor substrate 40 and the fault detection unit 51 constitute a sensor system 50 with a fault detection function.

[0066] FIG. 14 is a diagram conceptually showing the input and output of the fault detection unit 51. As shown in FIG. 14, the measured value I1 of the first ammeter A1, the measured value I2 of the second ammeter A2, the measured value I3 of the third ammeter A3, and the measured value I4 of the fourth ammeter A4 described above are input to the fault detection unit 51 from the signal processing circuit 46 of the sensor substrate 40. The fault detection unit 51 outputs a detection result as to whether the rotation angle detection sensor S1 and the torque detection sensor S2 are faulty based on these measured values I1, I2, I3, I4.

[0067] FIG. 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 measured value I1 of the first ammeter A1, which is the "first output value", with the measured value I4 of the fourth ammeter A4, which is the "second output value" (step ST1).

[0068] FIG. 16 is a graph showing changes in measured values I1 and I4. When no failure occurs, as in time T1 in FIG. 16, both measured values I1 and I4 change in the same manner with respect to the temperature change of the power transmission device 1. Therefore, when no failure occurs, the measured values I1 and I4 show correlated changes. However, as described above, since the fifth resistance line pattern R5 of the temperature sensor S3 is in an arc shape or an annular shape without corners, it is less likely to have a failure such as a disconnection. On the other hand, since the four first resistance line patterns R1 (Ra, Rb, Rc, Rd) of the rotation angle detection sensor S1 have a complex shape, the possibility of a failure such as a disconnection occurring is relatively high. When such a failure occurs, as in time T2 in FIG. 16, the value of the measured value I1 changes significantly.

[0069] In step ST1, when the relationship between the measured values I1 and I4 is within a predetermined normal range (step ST1: yes), the failure detection unit 51 determines that no failure such as a disconnection has occurred in the four first resistance line patterns R1 (Ra, Rb, Rc, Rd) of the rotation angle detection sensor S1 (step ST2). On the other hand, when the relationship between the measured values I1 and I4 is outside the predetermined normal range (step ST1: no), the failure detection unit 51 determines that a failure such as a disconnection has occurred in any of the four first resistance line 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 of the measured values I1 and I4.

[0070] Next, the failure detection unit 51 compares the measured value I2 of the second ammeter A2 which is the "first output value" with the measured value I4 of the fourth ammeter A4 which is the "second output value" (step ST4). When the relationship between the measured values I2 and I4 is within a predetermined normal range (step ST4: yes), it is determined that no failure such as a disconnection 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, when the relationship between the measured values I2 and I4 is outside the predetermined normal range (step ST4: no), it is determined that a failure such as a disconnection has occurred in any 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 measured values I2 and I4 may be, for example, the difference between the measured values I2 and I4 or the ratio of the measured values I2 and I4.

[0071] Subsequently, the failure detection unit 51 compares the measured value I3 of the third ammeter A3 which is the "first output value" with the measured value I4 of the fourth ammeter A4 which is the "second output value" (step ST7). When the relationship between the measured values I3 and I4 is within a predetermined normal range (step ST7: yes), it is determined that no failure such as a disconnection 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, when the relationship between the measured values I3 and I4 is outside the predetermined normal range (step ST7: no), it is determined that a failure such as a disconnection 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 measured values I3 and I4 may be, for example, the difference between the measured values I3 and I4 or the ratio of the measured values I3 and I4.

[0072] Thereafter, the failure detection unit 51 outputs a detection result regarding the presence or absence of a failure (step ST10). Specifically, a signal indicating the detection result is output from the failure detection unit 51 to an external controller. The detection result may be displayed on a display unit provided in the failure detection unit 51 or the controller.

[0073] As described above, in this sensor system 50, the failure detection unit 51 acquires measurement values I1, I2, I3, which are "first output values" that vary according to temperature, from the rotation angle detection sensor S1 and the torque detection sensor S2, which are "first sensors". Further, the failure detection unit 51 acquires a measurement value I4, which is a "second output value" that varies according to temperature, from the temperature sensor S3, which is a "second sensor" having a measurement target different from that of the "first sensor". Then, based on whether the relationship between the measurement values I1, I2, I3, which are "first output values", and the measurement value I4, which is the "second output value", is within a predetermined normal range, failures of the rotation angle detection sensor S1 and the torque detection sensor S2 are detected.

[0074] In this way, when the measurement values I1, I2, I3 show changes different from the normal changes according to temperature, failures of the sensors corresponding to those measurement values can be detected. Therefore, failures of each sensor can be detected without providing two sensors for the same measurement target. That is, without providing two rotation angle detection sensors S1 at the same location of the flexible gear 20, a failure of the rotation angle detection sensor S1 can be detected. Also, without providing two torque detection sensors S2 at the same location of the flexible gear 20, a failure of the torque detection sensor S2 can be detected.

[0075] <3. Modification Example> As described above, one embodiment of the present invention has been described, but the present invention is not limited to the above-described embodiment.

[0076] In the above embodiment, after executing the failure detection process (steps ST1 to ST6) of the rotation angle detection sensor S1, the failure detection process (steps ST7 to ST9) of the torque detection sensor S2 was executed. However, the order of these failure detection processes may be reversed. Also, the failure detection process (steps ST1 to ST6) of the rotation angle detection sensor S1 and the failure detection process (steps ST7 to ST9) of the torque detection sensor S2 may be executed simultaneously in parallel.

[0077] In addition, the sensor substrate 40 of the above-described embodiment included the rotation angle detection sensor S1 and the torque detection sensor S2. However, the sensor substrate 40 may include 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. Also, the "first sensor" may be another sensor capable of outputting a first output value that varies according to temperature.

[0078] In the above-described embodiment, the temperature sensor S3 mounted on the sensor substrate 40 was used 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 arranged at a position different from the sensor substrate 40 may be used as the "second sensor".

[0079] Also, the rotation angle detection sensor S1 may be used as the "first sensor" and the torque detection sensor S2 may be used as the "second sensor". In that case, 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, it is possible to detect that one of the rotation angle detection sensor S1 and the torque detection sensor S2 has failed.

[0080] In the above-described embodiment, the measured values of the ammeter were used as the "first output value" and the "second output value". That is, in the failure detection process of the above-described embodiment, the power supply voltage Vo was kept constant, and the current values reflecting the change in resistance due to temperature were compared. However, the current value may be kept constant, and the voltage values reflecting the change in resistance due to temperature may be compared. For example, the detection circuit C4 of the temperature sensor S3 may be a circuit in which a fifth resistance wire pattern R5 is connected in series to a constant current source 47 and a voltmeter V4 is connected in parallel to the fifth resistance wire pattern, as shown in FIG. 17. And the measured value of the voltmeter V4 may be used as the "second output value". Also, the failure detection unit 51 may calculate temperature estimated values by multiplying the current value or the voltage value by a predetermined coefficient, and compare the calculated temperature estimated values.

[0081] Also, in the above embodiment, the signal processing circuit 46 was mounted on the sensor substrate 40. However, the signal processing circuit 46 may be provided outside the sensor substrate 40. For example, the signal processing circuit 46 may be incorporated in a computer or an electric circuit board constituting the failure detection unit 51.

[0082] Also, in the above embodiment, copper or an alloy containing copper was used as the material of each resistance wire pattern. However, other metals such as SUS and aluminum may be used as the material of the resistance wire pattern. Also, non-metallic materials such as ceramics and resins may be used as the material of the resistance wire pattern. Also, conductive ink may be used as the material of the resistance wire pattern. When using conductive ink, each resistance wire pattern may be printed on the surface of the sensor substrate 40 with the conductive ink.

[0083] Also, in the flexible gear 20 of the above embodiment, the diaphragm portion 221 extended radially outward from the base end portion of the cylindrical portion 21. However, the diaphragm portion 221 may extend radially inward from the base end portion of the cylindrical portion 21.

[0084] Also, in the above embodiment, the sensor substrate 40 was fixed to the flexible gear 20 of the power transmission device 1. However, the sensor substrate 40 may be fixed to a component other than the flexible gear 20.

[0085] In addition, regarding the detailed configuration of the sensor system and the power transmission device, it may be appropriately changed without departing from the spirit of the present invention. Also, the elements appearing in the above embodiments and each modification example may be appropriately combined within a range where no contradiction occurs.

Industrial Applicability

[0086] This application can be used for a sensor system and a power transmission device.

Explanation of Signs

[0087] 1 Power transmission device 9 Central axis 10 Internal gear 20 Flexible gear 30 Wave generator 40 Sensor substrate 41 Body part 42 Flap part 43 Insulating layer 44 Conductor layer 45 Double-sided adhesive tape 46 Signal processing circuit 50 Sensor system 51 Fault detection unit 221 Diaphragm part 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~Rd First resistance wire pattern R2, Re~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

1. A first sensor and a second sensor with different measurement targets, a substrate on which the first sensor and the second sensor are mounted, 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, which is a measurement value of a measurement target of the first sensor, using a second measurement value, which is a measurement value of a measurement target of the second sensor, A sensor system comprising: The failure detection unit obtains a first output value that varies according to temperature from the first sensor and a second output value that varies according to temperature from the second sensor, and based on whether the relationship between the first output value and the second output value is within a predetermined normal range, detects a failure of either the first sensor or the second sensor. The first sensor is a strain sensor that detects the strain of an object to which the substrate is fixed. The second sensor is a temperature sensor that detects the temperature of the object. The first sensor has a first resistance wire pattern in which an arc-shaped or annular pattern is formed by a zigzag structure in which ends of adjacent conductors in the circumferential direction are alternately connected inside or outside in the radial direction around the central axis of the object to which the substrate is fixed. The second sensor has a second resistance wire pattern that is arc-shaped or annular around the central axis and does not have the zigzag structure. A sensor system.

2. The sensor system according to claim 1, wherein the first sensor has a third resistance wire pattern in which the conductor is inclined to one side in the circumferential direction, and a fourth resistance wire pattern in which the conductor is inclined to the other side in the circumferential direction, and constitutes 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. A sensor system.

3. The sensor system according to any one of claims 1 or 2, further comprising a third sensor whose measurement target is different from that of both the first sensor and the second sensor, wherein the third sensor is mounted on the substrate, and the signal processing unit corrects the first measurement value, which is the measurement value of the measurement target of the first sensor, using the third measurement value, which is the measurement value of the measurement target of the third sensor. A sensor system.

4. The sensor system according to claim 3, wherein the first sensor is a sensor that detects torque applied to the object based on the strain of the object. The sensor system, wherein the third sensor is a sensor that detects a rotation angle of a rotational motion input to the object based on distortion of the object.

5. A power transmission device including the sensor system according to any one of Claims 1 to 4, The power transmission device having a gear to which the substrate is fixed.

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