Strain wave gear and transmission element for same, robotic arm and method for measuring a torque

Abstract

An elastic transmission element is part of a strain wave gear. Such strain wave gears are also referred to as Harmonic Drives. The elastic transmission element is also referred to as a flexspline and has an outer toothing (03). The elastic transmission element is equipped with at least one strain gauge (04) for measuring a mechanical strain on the elastic transmission element. The one strain gauge (04) or the plurality of strain gauges (04) extends at least as a whole about a circumference of a lateral surface or an axial lateral face of the elastic transmission element.

Claims

1. An elastic transmission element of a strain wave gear, wherein an outer toothing is formed on the elastic transmission element, and wherein at least one strain gauge for measuring a mechanical strain of the elastic transmission element is arranged on the elastic transmission element, wherein the at least one strain gauge extends completely around a circumference of the elastic transmission element.

2. The elastic transmission element according to claim 1, wherein the elastic transmission element comprises a hollow-cylindrical part and an annular part extending radially and adjoining the hollow-cylindrical part in an axial direction.

3. The elastic transmission element according to claim 1, wherein the at least one strain gauge has the shape of a circular ring or a cylinder shell.

4. The elastic transmission element according to claim 1 wherein the at least one strain gauge comprises a plurality of strain gauges and a first subset of the plurality of strain gauges extends about a circumference of the elastic transmission element and a second subset of the plurality of strain gauges extends about a circumference of the elastic transmission element.

5. The elastic transmission element according to claim 1 wherein the at least one strain gauge a plurality strain gauges and a number of strain gauges in the plurality of strain gauges is a multiple of four.

6. The elastic transmission element according to claim 5, wherein the plurality of strain gauges form a Wheatstone bridge.

7. The elastic transmission element according to claim 1, wherein the at least one strain gauges extending about the circumference of the elastic transmission comprises two strain gauges forming a Wheatstone half bridge.

8. A strain wave gear having a wave generator that comprises an elliptical disk, a rigid outer ring having an inner toothing and an elastic transmission element according to claim 1.

9. A robotic arm having at least one drivable arm element which is coupled via a strain wave gear according to claim 8.

10. A method for measuring a torque on an elastic transmission element according to claim 1, wherein the at least one strain gauge comprises a plurality of strain gauges and a linear combination of signals of the plurality of strain gauges is formed.

11. The elastic transmission element according to claim 2, wherein the at least one strain gauge extends completely around a circumference of the hollow-cylindrical part.

12. The elastic transmission element according to claim 2, wherein the at least one strain gauge extends completely around a circumference of the annular part.

13. A strain wave gear, comprising: an elliptical disk; a rigid outer ring having an inner toothing; and an elastic transmission element, the elastic transmission element including a plurality of strain gauges extending completely around a circumference of the elastic transmission element.

14. The strain wave gear according to claim 13, wherein the elastic transmission element comprises a hollow-cylindrical part and an annular part extending radially and adjoining the hollow-cylindrical part in an axial direction.

15. The strain wave gear according to claim 14, wherein the plurality of strain gauges extends completely around a circumference of the hollow-cylindrical part.

16. The strain wave gear according to claim 14, wherein the plurality of strain gauges extends completely around a circumference of the annular part.

17. The strain wave gear according to claim 14, wherein the plurality of strain gauges includes a first subset extending completely around a circumference of the hollow-cylindrical part and a second subset extending completely around a circumference of the annular part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further details, advantages and developments arise from the following description of embodiments with reference to the drawing. In the figures:

[0035] FIG. 1 shows a first embodiment of an elastic transmission element;

[0036] FIG. 2 shows a circuit diagram of a connection of the strain gauges shown in FIG. 1;

[0037] FIG. 3 shows a circuit diagram of an alternative connection of the strain gauges shown in FIG. 1;

[0038] FIG. 4 shows a second embodiment of the elastic transmission element;

[0039] FIG. 5 shows a third embodiment of the elastic transmission element;

[0040] FIG. 6 shows a fourth embodiment of the elastic transmission element; and

[0041] FIG. 7 shows a fifth embodiment of the elastic transmission element.

DETAILED DESCRIPTION

[0042] FIG. 1 shows a first embodiment of an elastic transmission element of a strain wave gear. The elastic transmission element, which is also referred to as a flexspline, has the shape of a flanged bushing so that it has a bushing-shaped portion 01 and an adjoining annular or flange-like portion 02. An outer toothing 03 (shown in FIG. 6) which engages in an inner toothing (not shown) of an outer ring of the strain wave gear is formed on the bushing-shaped portion 01.

[0043] In this first embodiment, four strain gauges 04 are arranged on the annular portion 02 of the elastic transmission element, which together extend completely circumferentially about the elastic transmission element. The four strain gauges 04 form a closed circumference on an axial lateral face of the elastic transmission element. Since the four strain gauges 04 in this first embodiment are arranged laterally on the annular portion 02 of the elastic transmission element, they together have the shape of a circular ring, wherein each of the four strain gauges 04 has the shape of a circular ring segment.

[0044] A first strain gauge 11 of the four strain gauges 04, a second strain gauge 12 of the four strain gauges 04, a third strain gauge 13 of the four strain gauges 04 and a fourth strain gauge 14 of the four strain gauges 04 each have a center angle of 90° since the four strain gauges 04 are arranged so as to be circumferentially evenly distributed on the annular portion 02 of the elastic transmission element.

[0045] Possible electrical connections of the four strain gauges 04 are shown in FIGS. 2 and 3.

[0046] FIG. 2 shows a circuit diagram of a connection of the strain gauges 04; 11, 12, 13, 14 shown in FIG. 1. The four strain gauges 04; 11, 12, 13, 14 are linearly connected as a Wheatstone bridge, in particular as a full bridge.

[0047] FIG. 3 shows a circuit diagram of an alternative connection of the strain gauges 04; 11, 12, 13, 14 shown in FIG. 1. The four strain gauges 04; 11, 12, 13, 14 are cross-connected as a Wheatstone bridge, in particular as a full bridge.

[0048] Alternatively, the four strain gauges 04; 11, 12, 13, 14 can be interconnected as a Wheatstone bridge in a half bridge circuit, with the first strain gauge 11 and the second strain gauge 12 forming a first half bridge and the third strain gauge 13 and the fourth strain gauge 14 forming a second half bridge.

[0049] FIG. 4 shows a second embodiment of the elastic transmission element. This second embodiment is primarily the same as the first embodiment shown in FIG. 1 and differs therefrom in that it comprises eight instead of four strain gauges 04. The eight strain gauges 04 extend together completely about the circumference of the elastic transmission element.

[0050] The eight strain gauges 04, in addition to the first strain gauge 11, the second strain gauge 12, the third strain gauge 13 and the fourth strain gauge 14, comprise a fifth strain gauge 15, a sixth strain gauge 16, a seventh strain gauge 17 and an eighth strain gauge 18.

[0051] The eight strain gauges 04; 11, 12, 13, 14, 15, 16, 17, 18 are preferably interconnected as a Wheatstone bridge in a half-bridge circuit, with the first strain gauge 11 and the second strain gauge 12 forming a first half bridge, the third strain gauge 13 and the fourth strain gauge 14 forming a second half bridge, the fifth strain gauge 15 and the sixth strain gauge 16 forming a third half bridge, and the seventh strain gauge 17 and the eighth strain gauge 18 forming a fourth half bridge.

[0052] FIG. 5 shows a third embodiment of the elastic transmission element. This third embodiment is primarily the same as the second embodiment shown in FIG. 4 and differs from it in that it again comprises eight strain gauges 04. The other eight strain gauges 04 also together extend about the entire circumference of the elastic transmission element and together have the shape of a circular ring which is larger than the circular ring formed by the first eight strain gauges 04; 11, 12, 13, 14, 15, 16, 17, 18, wherein the two circular rings are arranged concentrically and at the same axial position.

[0053] The two times eight strain gauges 04, in addition to the first strain gauge 11, the second strain gauge 12, the third strain gauge 13, the fourth strain gauge 14, the fifth strain gauge 15, the sixth strain gauge 16, the seventh strain gauge 17 and the eighth strain gauge 18, comprise a ninth strain gauge 19, a tenth strain gauge 20, an eleventh strain gauge 21, a twelfth strain gauge 22, a thirteenth strain gauge 23, a fourteenth strain gauge 24, a fifteenth strain gauge 25 and a sixteenth strain gauge 26.

[0054] The two times eight strain gauges 04 allow redundant measurement.

[0055] FIG. 6 shows a fourth embodiment of the elastic transmission element. This fourth embodiment is primarily the same as the first embodiment shown in FIG. 1 and differs from it in that the four strain gauges 04 are arranged on the bushing-shaped portion 01 of the elastic transmission element. Therefore, the four strain gauges 04 together have the shape of a cylinder shell.

[0056] FIG. 7 shows a fifth embodiment of the elastic transmission element. This fifth preferred embodiment is primarily the same as the second embodiment shown in FIG. 4 and differs from it in that it has four further strain gauges 04; 19, 20, 22 on the bushing-shaped portion 01 of the elastic transmission element like the fourth embodiment shown in FIG. 6. Thus, the fifth embodiment shown comprises, both on the bushing-shaped portion 01 of the elastic transmission element and on the annular portion 02 of the elastic transmission element in each case, strain gauges 04 which together extend completely circumferentially.

LIST OF REFERENCE SIGNS

[0057] 01 Bushing-shaped portion [0058] 02 Annular portion [0059] 03 Outer toothing [0060] 04 Strain gauge [0061] 11 First strain gauge [0062] 12 Second strain gauge [0063] 13 Third strain gauge [0064] 14 Fourth strain gauge [0065] 15 Fifth strain gauge [0066] 16 Sixth strain gauge [0067] 17 Seventh strain gauge [0068] 18 Eighth strain gauge [0069] 19 Ninth strain gauge [0070] 20 Tenth strain gauge [0071] 21 Eleventh strain gauge [0072] 22 Twelfth strain gauge [0073] 23 Thirteenth strain gauge [0074] 24 Fourteenth strain gauge [0075] 25 Fifteenth strain gauge [0076] 26 Sixteenth strain gauge