Strain wave gearing device provided with torque detection device

Abstract

In a strain wave gearing device (1) in which a flexible external gear (3) is caused to flex into an elliptical shape to partially mesh with a rigid internal gear (2), a torque detection unit (20) of a torque detection device (10) for detecting transmission torque transmitted via the external gear (3) is provided with: strain gauges (11) that are affixed, to the surface of a diaphragm of the external gear, at 16 locations at equiangular intervals of 22.5 degrees in the circumferential direction; and a Wheatstone bridge circuit (21) that combines the outputs of the strain gauges (11) and outputs a torque detection signal (22). This makes it possible to remove eighth-order components of rotation ripple included in the strain gauge output and to accurately detect transmission torque.

Description

Wave gear device equipped with torque detection device

[0001] The present invention relates to a strain gauge type torque detector that detects torque transmitted via a flexible external gear.

[0002] Wave gearing devices equipped with strain gauge-type torque detectors have been proposed in Patent Documents 1 to 3. To accurately detect torque in a wave gearing device, it is necessary to remove rotational ripple, which is a periodic error component contained in the strain gauge output signal and occurs regardless of the transmitted torque, and to improve the linearity of the detected output. Because the wave generator rotates with the external gear bent elliptically, each circumferential portion of the external gear repeatedly displaces with a constant amplitude in the radial direction. Periodic error components are included in the torque detection output due to the displacement of each portion of the external gear that occurs regardless of the transmitted torque. Multiple sets of strain gauges are used to remove such periodic error components.

[0003] In Patent Document 1, two sets of torque detection means, each consisting of a pair of strain gauges arranged at 90-degree intervals on the surface of the external gear, are arranged at positions rotated by an angle of k × 45 degrees (k is an odd number) around the central axis of the external gear, and the transmission torque is calculated based on the combined output of the detection outputs of these two sets of torque detection means. Patent Document 2 proposes a method of adjusting the gain of the output of each detection element to remove periodic errors contained in the detection output obtained by combining the outputs of multiple detection elements. Patent Document 3 proposes a method in which, when the order of the rotational ripple component to be compensated is N (N: positive integer), at least (2N + 1) strain gauges are attached to the external gear, and the outputs are gain-adjusted by an amplifier and then combined to generate a detection signal.

[0004] Japanese Patent No. 3644558 Japanese Patent No. 4569990 Japanese Patent Laid-Open No. 2004-45378

[0005] In the past, errors in the attachment position of strain gauges to the diaphragm of an external gear tended to result in a large second-order component (180-degree period) remaining as rotational ripple. However, recently, the second-order component has almost disappeared from the rotational ripple components included in the torque detection output, and an eighth-order component tends to remain. One reason for this trend is that it has become possible to attach strain gauges to specified locations on external gears with relatively high precision using CCD cameras, etc.

[0006] FIG. 6 shows two examples of measurement results of rotational ripple appearing in the detected torque output measured by the present inventors. FIG. 6(A) is an explanatory diagram showing the attachment positions of strain gauges to a flexible external gear of a strain wave gearing device. Two orthogonal axis strain gauges 102 were attached to the surface of a disk-shaped diaphragm 101 of a cup-shaped or top hat-shaped external gear 100 at eight locations on the same circle, spaced at equal 45-degree intervals. As shown in FIG. 6(B), eight sets of two orthogonal axis strain gauges 102 were connected to form a Wheatstone bridge circuit 103. FIGS. 6(C1) and 6(C2) are graphs showing measurement results of the rotational ripple (%) contained in the detected torque output from the Wheatstone bridge circuit 103 versus the input rotation angle (the rotation angle of the elliptical wave generator). As shown in these graphs, the second-order component of the rotational ripple contained in the detected torque output tends to be almost completely eliminated, with the eighth-order component remaining. In order to further improve the torque detection accuracy by reducing the rotational ripple contained in the transmission torque of the strain wave gear device, it is necessary to reliably remove the eighth-order component of the rotational ripple.

[0007] The object of the present invention has been made in view of this point, and is to provide a strain wave gear device equipped with a torque detection device that can reliably remove the eighth-order component of the rotational ripple contained in the torque detection output and perform torque detection with high accuracy.

[0008] In order to solve the above problems, the present invention provides a strain gear device comprising: a rigid internal gear; a flexible external gear that is cup-shaped or top hat-shaped; a wave generator that bends the external gear into an elliptically shape so that it is partially meshed with the internal gear; and a torque detection device that detects the transmission torque transmitted via the external gear, wherein the torque detection section of the torque detection device comprises: strain gauges attached to 16 locations on the surface of a diaphragm of the external gear, at equal angular intervals of 22.5 degrees, around the central axis of the external gear, in the circumferential direction of the diaphragm; and a bridge circuit that combines the gauge outputs from each of the strain gauges to output a torque detection signal.

[0009] When a torque sensor is mounted as a safety measure in a strain wave gearing device incorporated as a reducer in a human-collaborative robot, it is desirable to have a redundant or dual-system torque sensor to ensure safety even in the unlikely event of a torque sensor failure. In the strain wave gearing device of the present invention, it is also desirable to have a redundant strain gauge-type torque detector to generate two independent systems of detection output. Furthermore, it is desirable that, under normal conditions, the transmitted torque be detected based on a highly accurate output obtained by combining the detection outputs of these two systems.

[0010] In this case, the wave gear device of the present invention comprises, as the torque detection unit, a first torque detection unit and a second torque detection unit that output two independent systems of torque detection signals, and further comprises: an output combining unit that generates a combined signal by combining a first torque detection signal that is the torque detection signal of the first torque detection unit and a second torque detection signal that is the torque detection signal of the second torque detection unit, and a calculation unit that can calculate the transmission torque based on each of the first torque detection signal, the second torque detection signal, and the combined signal.

[0011] The strain gauges may be biaxial orthogonal strain gauges. In this case, the strain gauges each include a pair of first and second strain gauges arranged orthogonally so as to be inclined at 45 degrees in opposite directions relative to the radial direction of the diaphragm. In this case, two systems of detection outputs can be generated as follows: the first torque detection unit includes, as the bridge circuit, a first bridge circuit that combines gauge outputs output from eight pairs of the first and second strain gauges that are arranged at equal angular intervals of 45 degrees to output the first torque detection signal, and the second torque detection unit includes, as the bridge circuit, a second bridge circuit that combines gauge outputs output from the remaining eight pairs of first and second strain gauges that are arranged at equal angular intervals of 45 degrees to output the second torque detection signal.

[0012] Sixteen uniaxial strain gauges can be used as the strain gauges. In this case, uniaxial strain gauges inclined at 45 degrees to one side with respect to the radial direction of the diaphragm and uniaxial strain gauges inclined at 45 degrees to the other side are alternately arranged along the circumferential direction. In this case, two systems of torque detection signals can be generated as follows. That is, the first torque detection unit includes, as the bridge circuit, a first bridge circuit that combines gauge outputs output from eight of the sixteen uniaxial strain gauges to output the first torque detection signal, and the second torque detection unit includes, as the bridge circuit, a second bridge circuit that combines gauge outputs output from the remaining eight uniaxial strain gauges to output the second torque detection signal. Furthermore, if the 16 uniaxial strain gauges are divided into eight strain gauge pairs, each consisting of two adjacent uniaxial strain gauges that are inclined in opposite directions, and these are referred to as the first to eighth strain gauge pairs along the circumferential direction of the diaphragm, the first bridge circuit is formed using two pairs of the first and third strain gauge pairs that are arranged at 90-degree intervals, and two pairs of the sixth and eighth strain gauge pairs that are located at positions rotated by an angle of 135 degrees from the first and third strain gauge pairs, and the second bridge circuit is formed using two pairs of the second and fourth strain gauge pairs that are arranged at 90-degree intervals, and two pairs of the fifth and seventh strain gauge pairs that are located at positions rotated by an angle of 135 degrees from the second and fourth strain gauge pairs.

[0013] In this invention, in a wave gearing device in which a flexible external gear is bent into an elliptical shape and partially meshes with a rigid internal gear, a torque detection device that detects the transmitted torque transmitted via the external gear is used, where strain gauges are attached to the surface of the diaphragm of the external gear at 16 locations circumferentially spaced at equal angular intervals of 22.5 degrees, and the outputs of these strain gauges are combined to generate a torque detection signal. According to this invention, the eighth-order component of the rotational ripple contained in the strain gauge output can be removed, allowing for accurate detection of transmitted torque.

[0014] Furthermore, in the present invention, in order to remove periodic error components, the multiple sets of strain gauges arranged around the central axis of the external gear are divided into two groups, allowing two independent systems of torque detection signals to be obtained. Furthermore, by combining the two systems of torque detection signals, a three-system output can be obtained, including a high-precision output from which periodic error components have been removed. In this case, transmitted torque detection can be performed with high precision, and even if one detection unit fails, the other detection unit can be used to detect transmitted torque, ensuring safety.

[0015] (A) is a schematic longitudinal cross-sectional view showing a strain wave gear device equipped with a torque detection device to which the present invention is applied, and (B) is a longitudinal cross-sectional view showing an external gear to which the torque detection unit of the torque detection device is attached. (A) is an explanatory diagram showing the attachment positions of 16 sets of strain gauges (biaxial orthogonal strain gauges) that make up the torque detection unit of the torque detection device, and (B) is an explanatory diagram showing a Wheatstone bridge circuit made up of 16 sets of strain gauges (biaxial orthogonal strain gauges). This is an explanatory diagram showing an example of the configuration of a torque detection device for a strain wave gear device configured to obtain two independent systems of detection output. (A) is an explanatory diagram showing the attachment positions of 16 sets of strain gauges (biaxial orthogonal strain gauges) that make up the torque detection unit of the torque detection device, (B) is an explanatory diagram showing a first Wheatstone bridge circuit, and (C) is an explanatory diagram showing a second Wheatstone bridge circuit. (A) and (B) are graphs showing two example simulation results of error components included in torque detection signals. (A) is an explanatory diagram showing the attachment positions of 16 strain gauges (uniaxial strain gauges) that constitute the torque detection unit of a torque detection device, and (B) is an explanatory diagram showing a Wheatstone bridge circuit composed of 16 strain gauges (uniaxial strain gauges). An example of a dual-system torque detection unit composed of uniaxial strain gauges is shown, where (A) is an explanatory diagram showing the arrangement of 16 strain gauges, (B) is an explanatory diagram showing a first Wheatstone bridge circuit, and (C) is an explanatory diagram showing a second Wheatstone bridge circuit. (A) is an explanatory diagram showing biaxial orthogonal strain gauges in a biaxial stacked arrangement, and (B) is an explanatory diagram showing biaxial orthogonal strain gauges in a biaxial planar arrangement. (A) is an explanatory diagram showing the attachment positions of strain gauges on the diaphragm of an external gear, and (B) is an explanatory diagram showing a Wheatstone bridge circuit composed of eight sets of orthogonal biaxial strain gauges. (C1) and (C2) are graphs showing measurement results of rotational ripple (%) included in the torque detection output versus the input rotation angle.

[0016] (Overall configuration) Fig. 1A(A) is a schematic longitudinal sectional view showing a strain wave gear device equipped with a torque detection device to which the present invention is applied, Fig. 1A(B) is a longitudinal sectional view showing an external gear to which a torque detection unit of the torque detection device is attached, Fig. 1B(A) is an explanatory diagram showing 16 sets of strain gauges (biaxial orthogonal strain gauges) that make up the torque detection unit of the torque detection device, and Fig. 1B(B) is an explanatory diagram showing a Wheatstone bridge circuit made up of 16 sets of strain gauges (biaxial orthogonal strain gauges).

[0017] The wave gear device 1 includes a rigid internal gear 2, a flexible external gear 3 coaxially arranged inside the rigid internal gear 2, a wave generator 4 with an elliptical contour fitted coaxially inside the flexible external gear 3, a cross roller bearing 5 that supports the internal gear 2 and the external gear 3 in a state where they can rotate freely relative to each other, a hollow input shaft 6, an end plate 7 arranged on one side in the axial direction, and an end plate 8 arranged on the other side in the axial direction. Both shaft ends of the hollow input shaft 6 are supported by the end plates 7 and 8 via ball bearings 9 a and 9 b, respectively.

[0018] The external gear 3 is top-hat shaped and comprises a cylindrical body 3b on which external teeth 3a are formed, a diaphragm 3c continuous with one end of the cylindrical body 3b and extending radially outward, and an annular boss 3d formed on the outer periphery of the diaphragm 3c. The cylindrical body 3b is bent into an elliptical shape by the wave generator 4, and the external teeth 3a partially mesh with the internal teeth 2a of the internal gear 2. The wave generator 4 comprises a cam plate 4a of a constant width formed integrally with the hollow input shaft 6, and a wave bearing 4b fitted onto the elliptical outer periphery of the cam plate 4a.

[0019] When the wave generator 4 rotates in conjunction with the rotation of the hollow input shaft 6, the meshing positions of the gears 2, 3 move circumferentially, and relative rotation occurs between the gears according to the difference in the number of teeth between them. The internal gear 2 is sandwiched between the inner ring 5a of the cross roller bearing 5 and an end plate 7, and these three members are fastened and fixed coaxially in this state. The boss 3d of the external gear 3 is sandwiched between the outer ring 5b of the cross roller bearing 5 and the other end plate 8, and these three members are fastened and fixed coaxially in this state. For example, if the internal gear 2 is fixed so as not to rotate, the external gear 3 rotates, and reduced rotation is output to a load member (not shown) via the end plate 8, which functions as an output shaft.

[0020] (Torque Detection Device) The strain wave gear device 1 is provided with a torque detection device 10 that detects the transmission torque transmitted via the external gear 3. The torque detection device 10 includes a torque detection section 20 attached to the external gear 3 and a signal processing unit 30 located outside the strain wave gear device 1, and the torque detection section 20 and the signal processing unit 30 are connected via cable wiring 40. The torque detection section 20 includes multiple sets of strain gauges 11 and a flexible printed wiring board 12 that are attached to the diaphragm 3 c of the external gear 3.

[0021] 1B(A), 16 sets of strain gauges 11 are arranged at equal angular intervals of 22.5 degrees around the central axis of the diaphragm 3c of the external gear 3. Each strain gauge 11 is protected by a coating layer (not shown) or the like. In this example, the strain gauges 11 are connected to each other by a wiring pattern (not shown) formed on a flexible printed wiring board 12.

[0022] Each strain gauge 11 is an orthogonal biaxial strain gauge. In FIG. 2B , the 16 pairs of biaxial orthogonal strain gauges are labeled clockwise with the symbols (a1, a2), (A1, A2), (b1, b2), (B1, B2), (c1, c2), (C1, C2), (d1, d2), (D1, D2), (e1, e2), (E1, E2), (f1, f2), (F1, F2), (g1, g2), (G1, G2), (h1, h2), and (H1, H2). In each of the orthogonal biaxial strain gauges, the symbols a1, A1, b1, B1, c1, C1, d1, D1, e1, E1, f1, F1, g1, G1, h1, and H1 denote strain gauges inclined at a 45-degree angle to one side of the diaphragm radius line. Symbols a2, A2, b2, B2, c2, C2, d2, D2, e2, E2, f2, F2, g2, G2, h2, and H2 are strain gauges arranged at an angle of 45 degrees to the other side of the diaphragm radius line. As shown in Figure 1B (B), these 16 sets of strain gauges 11 form a Wheatstone bridge circuit 21.

[0023] A torque detection signal 22, which is an output signal of a Wheatstone bridge circuit 21 constituting the torque detection section 20, is supplied to a signal processing unit 30 via a cable wiring 40, as shown in FIG. 1A (A). The signal processing unit 30 calculates a transmission torque based on the torque detection signal 22. The calculated transmission torque is transmitted to a higher-level device (not shown).

[0024] As described above, the torque detection unit 20 of the torque detection device 10 includes strain gauges 11 attached to 16 locations on the diaphragm 3c of the external gear 3 at equal angular intervals of 22.5 degrees, and a Wheatstone bridge circuit 21 configured using these strain gauges 11. A signal is generated by inverting the phase of the eighth-order component of the rotational ripple contained in the strain gauge output, and a torque detection signal 22 is obtained in which the eighth-order component is canceled out. Based on the torque detection signal 22, the transmission torque transmitted via the external gear 3 can be detected with high accuracy.

[0025] (Modification 1 of Torque Detection Device: Dual-System Torque Detection Section) For example, when a torque sensor is mounted as a safety measure in a strain wave gear device 1 incorporated as a reducer in a human-collaborative robot, it is desirable to have a redundant or dual-system torque sensor to ensure safety in the unlikely event that the torque sensor fails. To meet this demand, the strain gauge-type torque detection section 20 of the torque detection device 10 in the strain wave gear device 1 can be duplicated to generate two independent systems of detection output.

[0026] Fig. 2A is an explanatory diagram showing an example of the configuration of a torque detection device for a wave gear drive 1 configured to obtain two independent systems of detection output. Fig. 2B(A) is an explanatory diagram showing the attachment positions of 16 sets of strain gauges 11, Fig. 2B(B) is an explanatory diagram showing a first Wheatstone bridge circuit consisting of eight sets of strain gauges that make up the first torque detection unit, and Fig. 2B(C) is an explanatory diagram showing a second Wheatstone bridge circuit consisting of eight sets of strain gauges that make up the second torque detection unit. In Figs. 2A and 2B, parts that are common to the torque detection device 10 shown in Figs. 1A and 1B are assigned the same reference numerals.

[0027] As shown in FIG. 2B(A), the torque detection unit 20 of the torque detection device 10A of this embodiment includes 16 sets of strain gauges 11 (biaxial orthogonal strain gauges) attached to the diaphragm 3c at equal angular intervals of 22.5 degrees. These strain gauges 11 are divided into a first torque detection unit 20A and a second torque detection unit 20B, which output two independent torque detection signals. The first torque detection unit 20A of the torque detection unit 20 includes eight sets of strain gauges 11 arranged at equal angular intervals of 45 degrees, e.g., eight sets of strain gauges 11 designated by symbols (A1, A2), (B1, B2), (C1, C2), (D1, D2), (E1, E2), (F1, F2), (G1, G2), and (H1, H2). As shown in FIG. 2B(B), these eight sets of strain gauges 11 form a first Wheatstone bridge circuit 21A. In this way, the first torque detection unit 20A (first Wheatstone bridge circuit 21A) has the same configuration as the conventional torque detection unit (Wheatstone bridge circuit 103) shown in Figure 6, which is composed of eight sets of strain gauges 102 arranged at equal angular intervals of 45 degrees.

[0028] The second torque detection unit 20B of the torque detection unit 20 includes the remaining eight sets of strain gauges 11, i.e., (a1, a2), (b1, b2), (c1, c2), (d1, d2), (e1, e2), (f1, f2), (g1, g2), and (h1, h2), arranged at equal angular intervals of 45 degrees, forming a second Wheatstone bridge circuit 21B as shown in Fig. 2B(C). The eight sets of strain gauges 11 of the second torque detection unit 20B are arranged at positions rotated 22.5 degrees relative to the eight sets of strain gauges 11 of the first torque detection unit 20A, and the output signal of the second Wheatstone bridge circuit 21B has a phase difference of 22.5 degrees with respect to the output signal of the first Wheatstone bridge circuit 21A.

[0029] Referring to FIG. 2A, a first torque detection signal 22A, which is an output signal of the first Wheatstone bridge circuit 21A constituting the first torque detection section 20A, and a second torque detection signal 22B, which is an output signal of the second Wheatstone bridge circuit 21B constituting the second torque detection section 20B, are supplied to the signal processing unit 30 via cable wiring 40.

[0030] The signal processing unit 30 includes an input port 31 to which the first and second torque detection signals 22A and 22B are input, a first amplifier 32A that adjusts the gain of the first torque detection signal 22A, a second amplifier 32B that adjusts the gain of the second torque detection signal 22B independently of the first amplifier 32A, and an output combiner 32C that combines the gain-adjusted first torque detection signal 23A and the gain-adjusted second torque detection signal 23B to generate a combined signal 23C. The signal processing unit 30 also includes a calculation unit 33 and an output port 34 that calculates a transmission torque based on the gain-adjusted first torque detection signal 23A, the gain-adjusted second torque detection signal 23B, and the combined signal 23C.

[0031] First detection signal 24A, second detection signal 24B, and composite signal 24C (high-precision detection signal), which represent the transmission torque calculated based on first torque detection signal 23A, second torque detection signal 23B, and composite signal 23C, respectively, are output to a higher-level controller (not shown) from output port 34. When first torque detection signal 23A, second torque detection signal 23B, and composite signal 23C are output from output port 34 and the transmission torque value is calculated on the higher-level side, it is also conceivable that composite signal 23C may be generated on the higher-level side.

[0032] A composite signal 23C obtained by adding together two independent systems of first torque detection signal 23A and second torque detection signal 23B, which have a phase difference of 22.5 degrees, is equivalent to the output of a Wheatstone bridge circuit configured from 16 sets of strain gauges 11 (two-axis orthogonal strain gauges) shown in FIG. 1B(B), and is a high-precision detection output in which rotational ripple error, particularly its eighth-order component, has been removed and linearity has been improved.

[0033] 2C(A) and 2C(B) are graphs showing two examples of simulation results of torque detection using the torque detection device of this embodiment. The graphs plot the percentage (%) of error components contained in the torque detection signal (vertical axis) for each input rotation angle (deg) of the wave generator (horizontal axis). In these graphs, the broken lines La1 and La2 (actual measurements) connecting the circular dots indicate the percentage of error components contained in the first torque detection signal 22A obtained from the first torque detection unit 20A (first Wheatstone bridge circuit 21A). These broken lines La1 and La2 were obtained using the measurement results (actual measurements) when eight sets of strain gauges, as shown in FIG. 6, were arranged at equal 45-degree angles. The broken lines Lb1 and Lb2 (22.5-degree phase) connecting the square dots indicate the percentage of error components contained in the second torque detection signal 22B obtained from the second torque detection unit 20B (second Wheatstone bridge circuit 21B). These broken lines Lb1 and Lb2 are obtained by shifting the phase of the broken lines La1 and La2, which are actual measurements, by 22.5 degrees. The broken lines Lc1 and Lc2 (two-signal addition) connecting the dots marked with x indicate the proportion of error components contained in the composite signal 23C obtained by combining the first torque detection signal 23A and the second torque detection signal 23B.

[0034] As can be seen from these graphs, of the periodic error components contained in the torque detection signal, the second-order component, which appears at a 180-degree cycle, does not show a significant reduction effect compared to when eight sets of strain gauges are arranged at equal 45-degree angles (Figure 6), but it can be seen that the eighth-order component is significantly reduced. In simulation result 1 shown in Figure 2C(A), the eighth-order error component is reduced from ±0.72% to ±0.51%, and in simulation result 2 shown in Figure 2C(B), the eighth-order error component is reduced from ±0.54% to ±0.28%.

[0035] As described above, in the torque detection device 10A of this embodiment, a torque detection mechanism is constructed that can obtain two independent systems of detection signals using 16 sets of strain gauges 11 arranged around the central axis of the external gear 3 in order to remove periodic error components. Even if one sensor system fails, the other can continue to detect the transmitted torque, ensuring safety. Furthermore, by combining the two systems of torque detection signals, accurate torque detection can be performed using a detection output in which periodic error components, especially eighth-order error components, have been significantly reduced.

[0036] (Modification 2 of Torque Detection Device: Use of Single-Axis Strain Gauges) In the torque detection device 10, the greatest improvement in detection accuracy can be expected when orthogonal biaxial strain gauges are used as the 16 strain gauges 11 that make up the torque detection unit 20, as described above. However, orthogonal biaxial strain gauges are expensive, and small sizes, for example, with a diameter of 5 mm or less, are difficult to obtain as standard manufacturer products. For this reason, orthogonal biaxial strain gauges can be difficult to use, particularly in small-sized strain wave gear devices. As a countermeasure to this, the use of single-axis strain gauges can be considered.

[0037] FIG. 3A is an explanatory diagram showing the attachment positions of 16 strain gauges (single-axis strain gauges) that make up the torque detection unit of the torque detection device, and FIG. 3B is an explanatory diagram showing a Wheatstone bridge circuit made up of 16 strain gauges (single-axis strain gauges).

[0038] As shown in Figure 3(A), the torque detection unit 20 of this example includes 16 strain gauges 51 arranged at equal angular intervals of 22.5 degrees around the central axis of the diaphragm 3c of the external gear 3. Each strain gauge 51 is protected by a coating layer (not shown) or the like. The strain gauges 51 are also connected to one another by a wiring pattern (not shown) formed on the flexible printed wiring board 12.

[0039] Each strain gauge 51 is a uniaxial strain gauge, and 16 of them are arranged at equal angular intervals of 22.5 degrees around the central axis of the external gear 3. In FIG. 3A , the 16 uniaxial strain gauges are labeled clockwise with the symbols A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1, F2, G1, G2, H1, and H2. The eight uniaxial strain gauges designated by the symbols A1, B1, C1, D1, E1, F1, G1, and H1 are strain gauges inclined at a 45-degree angle to one side of the diaphragm radius line. The eight uniaxial strain gauges designated by the symbols A2, B2, C2, D2, E2, F2, G2, and H2 are strain gauges inclined at a 45-degree angle to the other side of the diaphragm radius line.

[0040] As shown in Fig. 3B, a Wheatstone bridge circuit 21C is formed using these 16 strain gauges 51. A torque detection signal, which is an output signal from the Wheatstone bridge circuit 21C that constitutes the torque detection unit 20, is supplied to a signal processing unit via cable wiring, as in the case shown in Fig. 1AA. The signal processing unit calculates a transmission torque based on the torque detection signal. The calculated transmission torque is transmitted to a higher-level device (not shown).

[0041] Even when single-axis strain gauges attached to 16 locations at equal angular intervals of 22.5 degrees on the diaphragm 3c of the external gear 3 are used as the strain gauges 51, a signal is generated in which the phase of the eighth-order component of the rotational ripple contained in the strain gauge output is inverted, resulting in a torque detection signal in which the eighth-order component is canceled out. The torque transmitted via the external gear can be detected with high accuracy based on the torque detection signal.

[0042] (Modification 3 of Torque Detection Device: Dual-System Torque Detection Section Using Uniaxial Strain Gauges) Figure 4 shows an example of dual-system torque detection section 20 configured using uniaxial strain gauges. Figure 4(A) is an explanatory diagram showing the attachment positions of 16 strain gauges, Figure 4(B) is an explanatory diagram showing a first Wheatstone bridge circuit, and Figure 4(C) is an explanatory diagram showing a second Wheatstone bridge circuit. The signal processing circuit of the torque detection device can be configured in the same way as in the case shown in Figure 2A.

[0043] As shown in Figure 4A, the strain gauges 51 (uniaxial strain gauges) are arranged at 16 locations at equal angular intervals of 22.5 degrees, with gauges inclined 45 degrees to one side of the diaphragm radius line alternating with gauges inclined 45 degrees to the other side in the circumferential direction. When obtaining two detection outputs from the 16 strain gauges 51, eight of the strain gauges 51 arranged at 45-degree intervals are inclined in the same direction. Therefore, if the eight strain gauges 51 arranged at 45-degree intervals are divided into the eight strain gauges 51 arranged at 45-degree intervals and the remaining eight strain gauges 51 arranged at 45-degree intervals, two Wheatstone bridge circuits are formed using the strain gauges inclined in the same direction. This does not allow for the construction of a Wheatstone bridge circuit for generating torque detection signals.

[0044] In this example, the 16 strain gauges 51 in FIG. 4A are divided into eight strain gauge pairs (A1, A2), (B1, B2), (C1, C2), (D1, D2), (E1, E2), (F1, F2), (G1, G2), and (H1, H2), with each pair of adjacent strain gauges tilted in opposite directions. Of these eight strain gauge pairs, two pairs are selected, each located at an angular interval of 90 degrees and surrounded by a dashed-dotted line. For example, the strain gauge pair (A1, A2) (first strain gauge pair) and the strain gauge pair (C1, C2) (third strain gauge pair) are selected, each located within the dashed-dotted line in FIG. 4A. Two pairs of strain gauges are selected, each located 135 degrees rotated from these two strain gauge pairs. For example, the strain gauge pairs (F1, F2) (sixth strain gauge pair) and (H1, H2) (eighth strain gauge pair) located at 90-degree angular intervals and surrounded by the dashed line in Fig. 4(A) are selected. Using the four strain gauge pairs (A1, A2) selected in this way, (C1, C2), (F1, F2), and (H1, H2), a first Wheatstone bridge circuit 21D is assembled as shown in Fig. 4(C), and this is used to configure the first torque detection unit.

[0045] The remaining four strain gauge pairs, namely, the strain gauge pairs (B1, B2) (second strain gauge pair) and (D1, D2) (fourth strain gauge pair) located at angular intervals of 90 degrees and surrounded by dotted lines in FIG. 4(A), and the strain gauge pairs (E1, E2) (fifth strain gauge pair) and (G1, G2) (seventh strain gauge pair) located at angular intervals of 90 degrees, are used to form a second Wheatstone bridge circuit 21E as shown in FIG. 4(B), which is used to configure the second torque detection unit.

[0046] By adding up the torque detection signals obtained from these independent first and second torque detection units, it is possible to obtain the same detection results as those obtained by the Wheatstone bridge circuit 21C (see Figure 3(B)) which uses all 16 uniaxial strain gauges.

[0047] (Other Embodiments) The torque detector described above relates to a strain wave gear device equipped with a top hat-shaped external gear. The present invention can be used as a torque detector for a strain wave gear device equipped with a cup-shaped external gear.

[0048] In the above example, the biaxial orthogonal strain gauges used are those of the biaxial stacked arrangement type shown in Fig. 5(A). As biaxial orthogonal strain gauges, those of the biaxial planar arrangement type shown in Fig. 5(B) are also known, and it goes without saying that biaxial orthogonal strain gauges of this type may also be used.

Claims

1. A strain wave gearing device comprising: a rigid internal gear; a flexible external gear in a cup or top hat shape; a wave generator that bends the external gear into an ellipsoidal shape so that it is partially meshed with the internal gear; and a torque detection device that detects the transmitted torque transmitted via the external gear, wherein the torque detection section of the torque detection device comprises: strain gauges affixed to the surface of a diaphragm of the external gear at 16 locations at equal angular intervals of 22.5 degrees around the central axis of the external gear in the circumferential direction of the diaphragm; and a bridge circuit that combines the gauge outputs from each of the strain gauges to output a torque detection signal.

2. A wave gear device according to claim 1, wherein the strain gauge is a two-axis orthogonal strain gauge or a single-axis strain gauge.

3. A strain wave gear device according to claim 1, comprising, as the torque detection section, a first torque detection section and a second torque detection section that output two independent systems of detection signals; an output combining section that generates a combined signal by combining a first torque detection signal that is the torque detection signal of the first torque detection section and a second torque detection signal that is the torque detection signal of the second torque detection section; and a calculation section that is capable of calculating the transmission torque based on each of the first torque detection signal, the second torque detection signal and the combined signal.

4. A wave gear device according to claim 3, wherein the strain gauges comprise 16 pairs of biaxial orthogonal strain gauges, each pair of first and second strain gauges arranged orthogonally so as to be inclined at 45 degrees in opposite directions relative to the radial direction of the diaphragm, the first torque detection unit comprises a first bridge circuit as the bridge circuit that combines gauge outputs output from eight pairs of biaxial orthogonal strain gauges that are arranged at equal angular intervals of 45 degrees to output the first torque detection signal, and the second torque detection unit comprises a second bridge circuit as the bridge circuit that combines gauge outputs output from the remaining eight pairs of biaxial orthogonal strain gauges that are arranged at equal angular intervals of 45 degrees to output the second torque detection signal.

5. A wave gear device according to claim 3, wherein the strain gauges comprise 16 uniaxial strain gauges, and eight uniaxial strain gauges inclined at 45 degrees to one side with respect to the radial direction of the diaphragm and eight uniaxial strain gauges inclined at 45 degrees to the other side are arranged alternately along the circumferential direction of the diaphragm, the first torque detection unit comprises a first bridge circuit as the bridge circuit that combines gauge outputs output from eight of the 16 uniaxial strain gauges to output the first torque detection signal, and the second torque detection unit comprises a second bridge circuit as the bridge circuit that combines gauge outputs output from the remaining eight uniaxial strain gauges to output the second torque detection signal, and the 16 uniaxial strain gauges are divided into eight strain gauge pairs, each consisting of two adjacent uniaxial strain gauges inclined in opposite directions, and these are designated as first to eighth strain gauge pairs along the circumferential direction of the diaphragm, The first bridge circuit is formed using two sets of the first strain gauge pair and the third strain gauge pair, which are arranged at an angular interval of 90 degrees, and two sets of the sixth strain gauge pair and the eighth strain gauge pair, which are located at a position rotated by an angle of 135 degrees from the first and third strain gauge pairs. The second bridge circuit is formed using two sets of the second strain gauge pair and the fourth strain gauge pair, which are arranged at an angular interval of 90 degrees, and two sets of the fifth strain gauge pair and the seventh strain gauge pair, which are located at a position rotated by an angle of 135 degrees from the second and fourth strain gauge pairs.

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