Torque detector for strain wave gearing device

Abstract

Provided is a torque detector (5) for a strain wave gear device (1), wherein first and second strain gauges (11, 12), which exhibit an arc shape that expands at an angle of 180 degrees, are affixed to an inner surface (33a) of a deformed (elastically deformed) diaphragm (33) of an externally toothed gear (3). The first and second dummy strain gauges (13, 14) are adhered to an inner surface (34a) of a boss, which is a portion of the external gear (3) where deformation (elastic deformation) does not occur. A full bridge circuit (8) is formed by the four strain gauges. The torque detector for a strain wave gearing device can be easily manufactured and can perform temperature compensation with high precision.

Description

Technical Field

[0001] The present invention relates to a torque detector for a wave gear device. More specifically, the torque detector for a wave gear device uses a strain gauge to detect torque transmitted via an externally toothed gear, wherein the strain gauge is attached to a diaphragm of the externally toothed gear that repeatedly deflects (elastically deforms) during operation. Background Art

[0002] Known wave gear devices include those with cup-shaped external gears and those with top-hat-shaped external gears. These wave gear devices consist of a rigid internal gear, a flexible external gear disposed inside the internal gear, and a wave generator. The wave generator causes the external gear to bend radially, partially meshing with the internal gear, and circumferentially shifting the meshing position of the two gears. The external gear is bent into an elliptical shape by the wave generator, which has an elliptical profile. The cup-shaped external gear includes a cylindrical main body with external teeth formed on its outer circumference, which is radially flexible; a disc-shaped diaphragm extending radially inward from the rear end of the main body; and a disc-shaped boss integrally formed with the center portion of the diaphragm. In the case of a top-hat-shaped externally toothed gear, a cylindrical main body has external teeth formed on its outer circumference, allowing radial deflection. A disc-shaped diaphragm extends radially outward from the rear end of the cylindrical main body, and an annular boss is integrally formed on the outer circumference of the diaphragm. In either case, the main body and diaphragm are elastically deformable, while the boss, which serves as a mounting point for other components, is rigid and non-elastic.

[0003] A method for detecting output shaft torque of a wave gear device using deformation (elastic deformation) of an externally toothed gear is known. This method attaches a strain gauge to an elastically deformable diaphragm in the externally toothed gear, and detects torque based on the output from the strain gauge.

[0004] In the torque detector described in Patent Document 1 (Japanese Patent Gazette No. 2000-320622), the resistor pattern of the strain gauge is adhered to: a diaphragm that is deformed due to the torque applied to the external gear, and the wiring terminal portion formed at the end of the resistor pattern is adhered to: the surface of a rigid boss located on the inner side thereof and that does not deform, so that the wires, etc. will not be broken.

[0005] In the torque detector described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-198400), strain gauges are attached to the inner surface of a diaphragm in a cup-shaped external gear. The strain gauges are arranged in an arcuate or annular pattern, extending over an angle of 180 or 360 degrees. Furthermore, FIG12A of Patent Document 2 shows a half-bridge structure using two strain gauges with arcuate patterns arranged at 180 degrees. Using two strain gauges has the disadvantage that temperature drift caused by changes in the temperature coefficient of the fixed resistor within the bridge structure due to temperature fluctuations is likely to occur. To mitigate this disadvantage, FIG13 of Patent Document 2 shows two strain gauges with the same pattern stacked at the same location.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-320622

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2004-198400 Summary of the Invention

[0010] In a torque detector for a wave gear device using strain gauges, as proposed in Patent Document 2, when temperature compensation is performed by arranging two strain gauges of the same pattern so that they overlap at the same position, it is necessary to accurately overlap the two sets of strain gauges at the same position. However, accurately overlapping the two sets of strain gauges is extremely difficult, and reliable temperature compensation may not be achieved.

[0011] An object of the present invention is to provide a torque detector for a wave gear device that detects torque using a strain gauge attached to a diaphragm of an external gear, wherein the torque detector for the wave gear device is easy to manufacture and can perform temperature compensation with high accuracy.

[0012] In the torque detector of the wave gear device of the present invention, two strain gauges are attached to the surface of the diaphragm of the external gear that undergoes deformation (elastic deformation), and two dummy strain gauges are attached to the surface of the boss, which is a portion of the external gear that does not undergo deformation (elastic deformation). The four strain gauges above form a full-bridge circuit.

[0013] Specifically, the present invention comprises: first and second strain gauges for torque detection, which are attached to the surface of a disk-shaped diaphragm that elastically deforms during operation of a cup-shaped or top-hat-shaped externally toothed gear of a wave gear device; and a bridge circuit composed of the first and second strain gauges and first and second fixed resistors.

[0014] The first and second strain gauges each include a resistor grid pattern in which resistor segments of a predetermined length are arranged at predetermined intervals to form an arc extending 180 degrees.

[0015] The first and second strain gauges are attached to the surface of the diaphragm in a point-symmetrical manner with respect to the central axis of the externally toothed gear. The torque detector of the wave gear device is characterized in that:

[0016] comprising: a first dummy strain gauge used as the first fixed resistor, and a second dummy strain gauge used as the second fixed resistor,

[0017] The first and second dummy strain gauges are attached to surfaces of bosses in the externally toothed gear that do not elastically deform.

[0018] Here, the first and second dummy strain gauges can be strain gauges with the same configuration as the first and second strain gauges. In this case, each of the first and second dummy strain gauges comprises an arc-shaped resistor grid pattern, formed by arranging resistor segments of a predetermined length at predetermined intervals to form an arc extending 180 degrees. The first and second dummy strain gauges are affixed to the surface of the boss in a point-symmetrical manner with respect to the central axis of the externally toothed gear. For example, the first and second strain gauges and the first and second dummy strain gauges are concentrically arranged on the same surface of the diaphragm and the boss of the externally toothed gear.

[0019] Alternatively, ordinary uniaxial strain gauges may be used as the first and second virtual strain gauges.

[0020] Effects of the Invention

[0021] The torque detector for a wave gearing device according to the present invention, unlike a torque detection bridge circuit composed of two strain gauges and two external fixed resistors, eliminates the problem of temperature drift caused by the temperature coefficient errors of the external fixed resistors. Furthermore, it eliminates the need for arranging the two strain gauges, each attached to a diaphragm of an external gear, to overlap and overlap the strain gauges in the same position to suppress temperature drift. This makes it possible to achieve a torque detector for a wave gearing device that is capable of highly accurate temperature compensation and is easy to manufacture. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 (A) is a schematic diagram showing the configuration of a wave gear device including a torque detector to which the present invention is applied. Figure 1 (B) is an explanatory diagram showing the meshing state of the internally toothed gear and the externally toothed gear.

[0023] Figure 2 (A) is a schematic longitudinal sectional view of an external gear to which a strain gauge unit of a torque detector is attached. Figure 2 (B) is an explanatory diagram showing a strain gauge unit. Figure 2 (C) is an explanatory diagram showing a full-bridge circuit.

[0024] Figure 3 This is an explanatory diagram showing another example of a wave gear device including a torque detector to which the present invention is applied. DETAILED DESCRIPTION

[0025] Hereinafter, an embodiment of a wave gear device including a torque detector to which the present invention is applied will be described with reference to the drawings.

[0026] Figure 1 (A) is an explanatory diagram showing a wave gear device according to an embodiment. Figure 1 (B) is an explanatory diagram showing the meshing state of the internal gear and the external gear of the wave gear device. Figure 1 As shown in Figures (A) and (B), a wave gear device 1 consists of a rigid internal gear 2, a flexible, cup-shaped external gear 3 positioned inside the internal gear, and a wave generator 4. The wave generator 4 causes the external gear 3 to bend radially, partially meshing with the internal gear 2 and circumferentially shifting the meshing position between the two gears. The wave generator 4, with its elliptical profile, bends the external gear 3 into an elliptical shape, meshing with the internal gear 2 at both ends of the elliptical major axis L. Rotating the wave generator 4, such as by a motor, shifts the meshing position between the internal gear 2 and the external gear 3 circumferentially, causing relative rotation between the two gears 3 and 4 based on the difference in the number of teeth between the two gears. For example, the internal gear 2 is fixed, while the external gear 3 serves as the output element, delivering reduced speed.

[0027] The cup-shaped externally toothed gear 3 comprises a radially flexible cylindrical main body 32 with external teeth 31 formed on its outer circumference, a disc-shaped diaphragm 33 extending radially inward from the rear end of the main body 32, and a disc-shaped boss 34 integrally formed with the center portion of the diaphragm 33. The main body 32 and diaphragm 33 are elastically deformable components that repeatedly flex in the radial direction due to the rotating wave generator 4. The boss 34, which serves as a mounting portion for attaching other components, is a rigid, non-elastically deformable component.

[0028] The torque detector 5 includes a strain gauge unit 6 as a torque detector attached to the cup-shaped externally toothed gear 3 of the wave gear device 1 , and a signal processing unit 7 that processes the output of the strain gauge unit 6 to detect the transmitted torque and outputs the signal to the outside.

[0029] Figure 2 (A) is a schematic longitudinal sectional view of an external gear to which a strain gauge unit of a torque detector is attached. Figure 2 (B) is an explanatory diagram showing a strain gauge unit of a torque detector. Figure 2 (C) is an explanatory diagram showing a full-bridge circuit composed of strain gauges. Referring to these figures, the strain gauge unit 6 is explained to include a first strain gauge 11 (resistor R1), a second strain gauge 12 (resistor R2), a first dummy strain gauge 13 (resistor R3), and a second dummy strain gauge 14 (resistor R4). The first and second strain gauges 11 and 12 are bonded to the inner surface 33a of the elastically deformable diaphragm 33 of the external gear 3. The first and second dummy strain gauges 13 and 14 are bonded to the inner surface 34a of the rigid boss 34 that does not elastically deform, with the inner surface 34a being connected to the inner surface 33a. Therefore, the first and second dummy strain gauges 13 and 14 function as fixed resistors. The first and second strain gauges 11 and 12 and the first and second dummy strain gauges 13 and 14 constitute a full-bridge circuit 8 , and changes in resistance of the first and second strain gauges 11 and 12 caused by deformation of the diaphragm 33 are output as changes in output voltage.

[0030] The first and second strain gauges 11 and 12 are formed by resistor grid patterns 11a and 12a, respectively, formed by arranging resistor segments of a certain length at regular intervals, to form a circular arc extending 180 degrees. The first and second strain gauges 11 and 12 are arranged point-symmetrically about the central axis of the external gear 3 (device central axis 1a). The opposing ends of the first and second strain gauges 11 and 12 are connected to form wiring terminals 51 for lead wire extraction. Wiring terminals 52 and 53 are formed at the opposing ends of the first and second strain gauges 11 and 12, respectively.

[0031] Concentrically arranged inside the first and second strain gauges 11 and 12 are the first and second dummy strain gauges 13 and 14. Specifically, the first and second dummy strain gauges 13 and 14 comprise arc-shaped resistor grid patterns 13a and 14a extending 180 degrees, and are arranged point-symmetrically about the central axis of the external gear 3 (device central axis 1a). The opposing ends of the first and second dummy strain gauges 13 and 14 are connected to the wiring terminal 54. The opposing ends of the first and second dummy strain gauges 13 and 14 are connected to the wiring terminal 52 and the wiring terminal 53, respectively.

[0032] The strain gauge unit 6 of this example has resistor grid patterns 11 a , 12 a , 13 a , and 14 a , wiring terminals 51 to 54 , and the like formed on the surface of a circular base material 61 having a constant width using resistor foil, thin metal wire, or the like.

[0033] Unlike a torque detection bridge circuit composed of two strain gauges and two external fixed resistors, the torque detector 5 of a wave gearing device constructed in this manner eliminates the problem of temperature drift caused by temperature coefficient errors in the external fixed resistors. Furthermore, there is no need to overlap the two strain gauges attached to the diaphragm 33 of the external gear 3 to suppress temperature drift. This eliminates the need for a torque detector for a wave gearing device that can perform temperature compensation with high accuracy and is easy to manufacture.

[0034] (Other embodiments)

[0035] The torque detector of the present invention can also be used in a wave gear device having a top-hat-shaped external gear. Figure 3 As shown, a wave gear device 1A includes a rigid internally toothed gear 2A, a top-hat-shaped externally toothed gear 3A, a wave generator 4A, and a torque detector 5A. The top-hat-shaped externally toothed gear 3A comprises a radially flexible cylindrical main body 32A with external teeth 31A formed on its outer circumference, a disc-shaped diaphragm 33A extending radially outward from the rear end of the main body 32A, and an annular boss 34A integrally formed with the outer circumferential edge of the diaphragm 33A. The main body 32A and diaphragm 33A are elastically deformable portions, while the boss 34A, which serves as a mounting portion for attaching the main body to other components, is a rigid, non-elastically deformable portion.

[0036] The torque detector 5A includes a strain gauge unit 6A and a signal processing unit 7A. The strain gauge unit 6A includes a first strain gauge 11A, a second strain gauge 12A, a first dummy strain gauge 13A, and a second dummy strain gauge 14A. The first and second strain gauges 11A, 12A, and the first and second dummy strain gauges 13A, 14A are respectively configured as follows: Figure 1 、 2 The torque detector 5 is similar to the one shown above. The difference is that the first and second strain gauges 11A and 12A are attached to the radially inner surface of the diaphragm 33A, while the first and second dummy strain gauges 13A and 14A are attached to the same surface of the boss 34A, which is radially outer. In this case, the same operational effects as those of the torque detector 5 described above can be achieved.

Claims

1. A torque detector for a wave gear device, the wave gear device comprising: A first strain gauge and a second strain gauge for detecting torque, which are attached to the surface of a disk-shaped diaphragm of a wave gear device, wherein the disk-shaped diaphragm has flexibility such that it repeatedly bends during the operation of a cup-shaped or top-hat-shaped externally toothed gear; and a bridge circuit composed of the first strain gauge, the second strain gauge, a first fixed resistor, and a second fixed resistor; The first strain gauge and the second strain gauge each include a resistor grid pattern in which resistor segments of a predetermined length are arranged at predetermined intervals to form an arc extending 180 degrees. The first strain gauge and the second strain gauge are attached to the surface of the diaphragm in a point-symmetrical manner with respect to the central axis of the externally toothed gear. It is characterized by: The torque detector of the wave gear device includes a first dummy strain gauge used as the first fixed resistor and a second dummy strain gauge used as the second fixed resistor. The first dummy strain gauge and the second dummy strain gauge are attached to a surface of a boss, and the boss has such rigidity that it does not bend during the operation of the externally toothed gear.

2. The torque detector of the wave gear device according to claim 1, wherein: The first and second dummy strain gauges each include an arc-shaped resistor grid pattern in which resistor segments of a predetermined length are arranged at predetermined intervals to form an arc extending 180 degrees. The first dummy strain gauge and the second dummy strain gauge are attached to the surface of the boss in a point-symmetrical manner with respect to the central axis.

3. The torque detector of the wave gear device according to claim 2, wherein: The externally toothed gear is in the cup shape and comprises: a cylindrical main body having external teeth formed on an outer peripheral surface and being flexible in the radial direction; the disc-shaped diaphragm extending radially inward from one end of the main body; and the annular or disc-shaped boss formed integrally with the center portion of the diaphragm. The first strain gauge, the second strain gauge, the first dummy strain gauge, and the second dummy strain gauge are concentrically attached to the surfaces of the diaphragm and the boss on the same side in the direction toward the central axis.

4. The torque detector of the wave gear device according to claim 2, wherein: The externally toothed gear is in the shape of a top hat and comprises: a cylindrical main body having external teeth formed on an outer peripheral surface and being flexible in a radial direction; a disc-shaped diaphragm extending radially outward from one end of the main body; and an annular boss formed integrally with an outer peripheral edge portion of the diaphragm. The first strain gauge, the second strain gauge, the first dummy strain gauge, and the second dummy strain gauge are concentrically attached to the surfaces of the diaphragm and the boss on the same side in the direction toward the central axis.

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