Torque detector for strain wave gearing

Abstract

In the torque detector (5) of the strain wave gearing (1), first and second strain gauges (11, 12) each having an arc shape subtending an angle of 180 degrees are attached to the inner surface (33a) of the diaphragm (33) where strain (elastic deformation) occurs in the external gear (3). First and second dummy strain gauges (13, 14) are attached to the inner surface (34a) of the boss, which is a part of the external gear (3) where strain (elastic deformation) does not occur. These four strain gauges form a full-bridge circuit (8). This makes it possible to realize a torque detector for a strain wave gearing that is easy to manufacture and capable of accurate temperature compensation.

Description

[Technical Field]

[0001] The present invention relates to a torque detector for a strain wave gearing device, and more specifically to a torque detector for a strain wave gearing device that detects torque transmitted via an external gear using a strain gauge attached to the diaphragm of the external gear, which is subject to repeated deflection (elastic deformation) during operation. [Background technology]

[0002] Known strain wave gearing devices include strain wave gearing with a cup-shaped external gear and strain wave gearing with a top-hat-shaped external gear. Strain wave gearing devices are comprised of a rigid internal gear, a flexible external gear positioned inside the rigid internal gear, and a wave generator that radially deflects the external gear to partially mesh with the internal gear and shifts the meshing position of the two gears circumferentially. The external gear is deflected into an elliptical shape by the wave generator with an elliptical profile. The cup-shaped external gear includes a radially flexible cylindrical body with external teeth formed on its outer periphery, a disk-shaped diaphragm extending radially inward from the rear end of the body, and a disk-shaped boss integrally formed at the center of the diaphragm. In the case of a top-hat-shaped external gear, a disk-shaped diaphragm is formed that extends radially outward from the rear end of a radially flexible cylindrical body with external teeth formed on its outer periphery, and an annular boss is integrally formed at the outer periphery of the diaphragm. In either case, the body and the diaphragm are elastically deformable parts, while the boss, which is the attachment part to another member, is a rigid part that does not undergo elastic deformation.

[0003] A known method for detecting the output shaft torque of a strain wave gearing device is to use the strain (elastic deformation) of the external gear. In this method, a strain gauge is attached to an elastically deformable diaphragm in the external gear, and torque is detected based on the output from this gauge.

[0004] In the torque detector described in Patent Document 1 (JP 2000-320622 A), a resistor pattern of a strain gauge is attached to a diaphragm where distortion occurs due to torque applied to an external gear, and a wiring terminal portion formed at the end of the resistor pattern is attached to the surface of a rigid boss located inside the diaphragm where distortion does not occur, thereby preventing breakage of lead wires, etc.

[0005] In the torque detector described in Patent Document 2 (JP 2004-198400 A), strain gauges are attached to the inner surface of a diaphragm in a cup-shaped external gear, and the strain gauges have an arc-shaped or annular pattern that spans an angle of 180 degrees or 360 degrees. Furthermore, Figure 12A of Patent Document 2 proposes a half-bridge configuration using two strain gauges with arc-shaped patterns arranged at 180 degrees. The use of two strain gauges has the disadvantage that temperature drift is likely to occur within the bridge due to changes in the temperature coefficient of the fixed resistor caused by temperature changes. To overcome this drawback, Figure 13 of Patent Document 2 proposes stacking two strain gauges with the same pattern in the same position. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-320622 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-198400 Summary of the Invention [Problem to be solved by the invention]

[0007] Here, in a torque detector for a strain gauge wave gear device that uses strain gauges, when temperature compensation for the strain gauges is performed by arranging two strain gauges with the same pattern overlapping each other in the same position, as proposed in Patent Document 2, it is necessary to overlap the two sets of strain gauges in the same position with high precision. However, it is very difficult to overlap two sets of strain gauges with high precision, and there are cases where temperature compensation cannot be performed reliably.

[0008] An object of the present invention is to provide a torque detector for a wave gearing device that detects torque using a strain gauge attached to the diaphragm of an external gear, which is easy to manufacture and can perform temperature compensation with high accuracy. [Means for solving the problem]

[0009] In the torque detector of the wave gear device of the present invention, two strain gauges are attached to the surface of the diaphragm where strain (elastic deformation) occurs in the external gear, and two dummy strain gauges are attached to the surface of the boss, which is a part of the external gear where strain (elastic deformation) does not occur, and these four strain gauges form a full bridge circuit.

[0010] That is, the present invention is a first strain gauge and a second strain gauge for detecting torque that are attached to the surface of a disk-shaped diaphragm that undergoes elastic deformation during operation in a cup-shaped or top-hat-shaped external gear of a strain wave gearing device; a bridge circuit composed of the first and second strain gauges and a first fixed resistor and a second fixed resistor; It is equipped with each of the first and second strain gauges has a resistor grid pattern in which resistor segments of a predetermined length are arranged at predetermined intervals to describe an arc subtending an angle of 180 degrees; In a torque detector for a strain wave gear device in which the first and second strain gauges are attached to the surface of the diaphragm so as to be point symmetric with respect to the central axis of the external gear, a first dummy strain gauge used as the first fixed resistor; a second dummy strain gauge used as the second fixed resistor; It is equipped with The first and second dummy strain gauges are attached to the surface of the boss of the external gear where no elastic deformation occurs.

[0011] Here, the first and second dummy strain gauges may have a configuration similar to that of the first and second strain gauges. In this case, each of the first and second dummy strain gauges has an arc-shaped resistor grid pattern in which resistor segments of a predetermined length are arranged at predetermined intervals to describe an arc subtending an angle of 180 degrees, and these first and second dummy strain gauges are attached to the surface of the boss so as to be point-symmetric with respect to the central axis of the external gear. For example, the first and second strain gauges and the first and second dummy strain gauges are arranged concentrically on the surfaces of the diaphragm and boss of the external gear on the same side.

[0012] It should be noted that a general single-axis strain gauge can also be used as each of the first and second dummy strain gauges. [Effects of the Invention]

[0013] Unlike constructing a bridge circuit for torque detection using two strain gauges and two external fixed resistors, the torque detector for a wave gearing device of the present invention eliminates the problem of temperature drift caused by temperature coefficient errors in the external fixed resistors. Furthermore, there is no longer a need to place a strain gauge overlapping each of the two strain gauges attached to the diaphragm of the external gear in the same position in order to suppress temperature drift. This makes it possible to realize a torque detector for a wave gearing device that can perform temperature compensation with high precision and is easy to manufacture. [Brief explanation of the drawings]

[0014] [Figure 1] 1A is a schematic diagram showing a strain wave gear device equipped with a torque detector to which the present invention is applied, and FIG. 1B is an explanatory diagram showing the meshing state of an internal gear and an external gear. [Figure 2] FIG. 1A is a schematic vertical cross-sectional view of an external gear to which a strain gauge unit of a torque detector is attached, FIG. 1B is an explanatory diagram showing the strain gauge unit, and FIG. 1C is an explanatory diagram showing a full-bridge circuit. [Figure 3] FIG. 10 is an explanatory diagram showing another example of a strain wave gear device equipped with a torque detector to which the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a strain wave gear device equipped with a torque detector to which the present invention is applied will be described below with reference to the drawings.

[0016] FIG. 1(A) is an explanatory diagram showing a strain wave gear device according to an embodiment, and FIG. 1(B) is an explanatory diagram showing the meshing state of the internal gear and external gear of the strain wave gear device. As shown in Figures 1(A) and 1(B), strain wave gearing 1 is composed of a rigid internal gear 2, a cup-shaped flexible external gear 3 placed inside it, and a wave generator 4 that bends the external gear 3 radially to partially mesh with the internal gear 2 and move the meshing position of the two gears circumferentially. The external gear 3 is bent into an elliptical shape by the wave generator 4, and the external gear 3 meshes with the internal gear 2 at both ends of the major axis L of the ellipse. When the wave generator 4 is rotated by a motor or the like, the meshing position between the internal gear 2 and the external gear 3 moves circumferentially, and relative rotation occurs between the gears 3 and 4 due to the difference in the number of teeth between the gears 2 and 3. For example, the internal gear 2 is fixed and the external gear 3 is used as an output element, outputting reduced rotation from here.

[0017] The cup-shaped external gear 3 comprises a cylindrical body 32 that is radially flexible and has external teeth 31 formed on its outer peripheral surface, a disk-shaped diaphragm 33 that extends radially inward from the rear end of the body 32, and a disk-shaped boss 34 that is integrally formed at the center of the diaphragm 33. The body 32 and diaphragm 33 are elastically deformable parts, and are repeatedly deflected radially by the rotating wave generator 4. The boss 34, which is the attachment part to another member, is a rigid part that does not undergo elastic deformation.

[0018] The torque detector 5 includes a strain gauge unit 6, which is a torque detection section attached to the cup-shaped external gear 3 of the strain gear device 1, and a signal processing section 7 that detects the transmitted torque by processing the output of the strain gauge unit 6 and outputs the result to the outside.

[0019] Figure 2(A) is a schematic longitudinal cross-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 the strain gauge unit of the torque detector, and 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 includes 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 attached 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 attached to the inner surface 34a of a boss 34, which is rigid and does not undergo elastic deformation, and which is 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 form a full-bridge circuit 8, and changes in the resistance of the first and second strain gauges 11 and 12 caused by distortion of the diaphragm 33 are output as changes in output voltage.

[0020] The first and second strain gauges 11, 12 are formed with resistor grid patterns 11a, 12a, each of which has resistor segments of a fixed length arranged at regular intervals, forming an arc-shaped pattern subtending an angle of 180 degrees. The first and second strain gauges 11, 12 are arranged in point symmetry with respect to the central axis of the external gear 3 (device central axis 1a). One ends of the first and second strain gauges 11, 12 that face each other are connected to form a wiring terminal 51 for drawing out lead wires. The other ends of the first and second strain gauges 11, 12 that face each other are formed with wiring terminals 52 and 53, respectively.

[0021] The first and second dummy strain gauges 13, 14 are arranged concentrically inside the first and second strain gauges 11, 12. That is, the first and second dummy strain gauges 13, 14 have arc-shaped resistor grid patterns 13a, 14a that subtend an angle of approximately 180 degrees, and are arranged in point symmetry with respect to the central axis of the external gear 3 (device central axis 1a). One ends of the first and second dummy strain gauges 13, 14 that face each other are both connected to wiring terminal 54. The other ends of the first and second dummy strain gauges 13, 14 that face each other are connected to wiring terminal 52 and wiring terminal 53, respectively.

[0022] In the strain gauge unit 6 of this example, resistor grid patterns 11a, 12a, 13a, 14a and wiring terminal portions 51 to 54 are formed on the surface of a base material 61 in the shape of a circular ring with a fixed width, using resistor foil, thin metal wires or the like.

[0023] Unlike when a bridge circuit for torque detection is configured using two strain gauges and two external fixed resistors, the torque detector 5 of the wave gearing configured in this way eliminates the problem of temperature drift caused by temperature coefficient errors in the external fixed resistors. Furthermore, there is no need to place a strain gauge overlapping each of the two strain gauges attached to the diaphragm 33 of the external gear 3 in the same position in order to suppress temperature drift. This makes it possible to obtain a torque detector for a wave gearing that can perform temperature compensation with high precision and is easy to manufacture.

[0024] (Other embodiments) The torque detector of the present invention can also be used in a strain wave gear device equipped with a top hat-shaped external gear. As shown in Fig. 3, strain wave gearing 1A includes a rigid internal gear 2A, a top-hat-shaped external gear 3A, a wave generator 4A, and a torque detector 5A. Top-hat-shaped external gear 3A includes a cylindrical body 32A with external teeth 31A formed on its outer circumferential surface that is radially flexible, a disk-shaped diaphragm 33A that extends radially outward from the rear end of body 32A, and an annular boss 34A integrally formed on the outer circumferential edge of diaphragm 33A. Body 32A and diaphragm 33A are elastically deformable, while boss 34A, which serves as an attachment point for attachment to other members, is a rigid part that does not undergo elastic deformation.

[0025] 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 and 12A and the first and second dummy strain gauges 13A and 14A are configured in the same manner as in the torque detector shown in FIGS. 1 and 2. The difference is that the first and second strain gauges 11A and 12A are attached to the surface of a diaphragm 33A located on the inside in the radial direction, and the first and second dummy strain gauges 13A and 14A are attached to the surface of the same side of a boss 34A located on the outside in the radial direction. In this case, the same effects as those of the torque detector 5 described above can be obtained.

Claims

1. a first strain gauge and a second strain gauge for detecting torque that are attached to the surface of a flexible disk-shaped diaphragm that repeatedly flexes during operation of a cup-shaped or top-hat-shaped external gear of a strain wave gear device; a bridge circuit composed of the first and second strain gauges and a first fixed resistor and a second fixed resistor; It is equipped with Each of the first and second strain gauges has a resistor grid pattern in which resistor segments of a predetermined length are arranged at predetermined intervals to describe an arc subtending an angle of 180 degrees; In a torque detector for a strain wave gear device in which the first and second strain gauges are attached to a surface of the diaphragm so as to be point symmetric with respect to a central axis of the external gear, a first dummy strain gauge used as the first fixed resistor; a second dummy strain gauge used as the second fixed resistor; It is equipped with A torque detector for a strain wave gear device, characterized in that the first and second dummy strain gauges are attached to the surface of a boss having sufficient rigidity to prevent deflection during operation of the external gear.

2. 2. The torque detector for a strain wave gear device according to claim 1, each of the first and second dummy strain gauges has an arc-shaped resistor grid pattern in which resistor segments of a predetermined length are arranged at predetermined intervals to describe an arc subtending an angle of 180 degrees; A torque detector for a strain wave gear device, characterized in that the first and second dummy strain gauges are attached to the surface of the boss so as to be point symmetrical with respect to the central axis.

3. 3. The torque detector for a strain wave gear device according to claim 2, the external gear is cup-shaped and includes a cylindrical body portion having external teeth formed on its outer peripheral surface and capable of bending in the radial direction, the disk-shaped diaphragm extending radially inward from one end of the body portion, and the annular or disk-shaped boss formed integrally with a central portion of the diaphragm, The first and second strain gauges and the first and second dummy strain gauges are respectively attached concentrically to the surfaces of the diaphragm and the boss facing the same side in the direction of the central axis.

4. 3. The torque detector for a strain wave gear device according to claim 2, the external gear has the top hat shape and includes a cylindrical body portion having external teeth formed on an outer peripheral surface thereof and capable of bending in the radial direction, the disk-shaped diaphragm extending radially outward from one end of the body portion, and the annular boss formed integrally with the outer peripheral edge portion of the diaphragm, The first and second strain gauges and the first and second dummy strain gauges are respectively attached concentrically to the surfaces of the diaphragm and the boss facing the same side in the direction of the central axis of the strain detector of the wave gear device.

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