Method and device for detecting a tooth meshing fault in a wave gear, drive module, robot

Abstract

The invention relates to a method and a device for detecting a tooth engagement fault, in particular a short-term interruption of tooth engagement, in a wave gear (10), wherein the wave gear (10) comprises a wave generator (12), a flexible transmission element (14) with an external toothing (14) and an outer ring (16) with an internal toothing (16), wherein the internal teeth (16) and the external teeth (14) are in engagement with each other, wherein the flexible transmission element (14) has a first strain sensor (S1) which generates a first time series (ST1). Furthermore, the invention relates to a drive module and a robot.

Description

[0001] The invention relates to a method for detecting a tooth engagement fault, in particular a momentary interruption of tooth engagement, in a wave gear. The invention further relates to a device for detecting a tooth engagement fault, in particular a momentary interruption of tooth engagement, in a wave gear. The invention also relates to a drive module with such a device. Finally, the invention relates to a robot with such a drive module.

[0002] Strain wave gears (also known as strain wave gears or harmonic reducers) are compact gearboxes used, for example, in the joints of collaborative and industrial robots. These gears consist of a wave generator, a flexible transmission element (flexspline) with external teeth, and an outer ring (circular spline) with internal teeth. Torque and speed are transmitted via the meshing internal and external teeth. A problem that sometimes occurs during the operation of such gears is ratcheting, which refers to a disruption in the meshing between the internal and external teeth, specifically a momentary interruption of tooth engagement, i.e., slippage of the internal teeth relative to the external teeth.Ratcheting can occur, for example, when attempting to transmit excessive torque (ratcheting torque) using the wave gear. As a result, the wave generator or the flexible transmission element can develop misalignment, eccentricity, and / or malalignment. This can lead to wear and / or other damage to the wave gear, particularly to the internal and / or external gearing, which can reduce its service life. In extreme cases, the wave gear can suffer irreparable damage, potentially resulting in operational and / or production downtime. Furthermore, costs may be incurred for replacement products as well as for disassembly and reassembly.

[0003] Against this background, the task arises to provide a solution that detects a dental procedure disorder, in particular a short-term interruption of the dental procedure.

[0004] The problem is solved by a method for detecting a tooth engagement fault, in particular a brief interruption of tooth engagement, in a wave gear. wherein the wave gear comprises a wave generator, a flexible transmission element with external teeth and an outer ring with internal teeth, where the internal and external teeth are in mesh with each other, wherein the flexible transmission element has a first strain sensor that generates a first time series, where a reference time series is provided, wherein a difference measure between a value of the time series and a reference value of the reference time series or between the time series and the reference time series is determined using the first time series and the reference time series, In the event that the difference falls below a predetermined limit, a dental intervention disorder is detected.

[0005] The wave gear comprises a shaft generator, a flexible transmission element with external teeth, and an outer ring with internal teeth, the internal and external teeth meshing with each other. The internal and external teeth provide the advantage of a compact design for the wave gear. Furthermore, the flexible transmission element includes a first strain sensor. This first strain sensor can be arranged on a flange or a collar sleeve of the flexible transmission element. This offers the advantage that the strain sensor is positioned outside the tooth engagement area and is therefore safe and protected from external forces. The first strain sensor generates a first time series.According to the invention, a reference time series is provided, and a difference measure is determined between a value in the first time series and a reference value in the reference time series, or between the time series and the reference time series, using the first time series and the reference time series. Determining this difference measure offers the advantage of identifying a correlation or similarity between the first time series and the reference time series. If the difference value falls below a predetermined threshold, a gear meshing fault is detected. The advantage of detecting gear meshing faults is that the wave gear can potentially be taken out of service before irreparable damage occurs. This reduces the probability of lengthy operational and / or production downtimes. Furthermore, it avoids costs for both replacement products and disassembly.

[0006] According to an advantageous embodiment of the invention, the time series comprises several time-spaced values, and the reference time series comprises several time-spaced reference values. The number of values ​​and the number of reference values ​​can be the same or different. In particular, the values ​​can originate from a different time period than the reference values.

[0007] In a preferred embodiment of the invention, the difference measure is determined by dynamic time normalization. In principle, a difference measure can be determined using various methods or algorithms, with dynamic time normalization (DTW) being a preferred algorithm. In other words, determining a difference measure using dynamic time normalization allows for the determination of a similarity between two time series. The difference measure can also be referred to as a cost function, since the algorithm seeks the most cost-effective path from the beginning to the end of both time series using a matrix (the difference matrix) of the pairwise difference measures / costs of all values ​​of both time series. Such a path can be obtained by so-called backtracking in a first iteration of the algorithm.For pure cost determination, however, it is only necessary to perform a simple run without backtracking. Optimal agreement between the first time series and the reference time series depends on the lowest possible cost function.

[0008] In an advantageous embodiment of the invention, the difference measure is provided that it is a Euclidean distance or the Mahalanobis distance.

[0009] Another object of the invention is a device for detecting a tooth engagement fault, in particular a brief interruption of tooth engagement, in a wave gear, wherein the wave gear comprises a wave generator, a flexible transmission element with external teeth and an outer ring with internal teeth, where the internal and external teeth are in mesh with each other, wherein the flexible transmission element has a first strain sensor that generates a first time series, where an evaluation device for evaluating the first time series, wherein the evaluation device is configured such that a reference time series is provided, wherein a difference measure between a value of the time series and a reference value of the reference time series or between the time series and the reference time series is determined using the first time series and the reference time series, In the event that the difference falls below a predetermined limit, a dental intervention disorder is detected.

[0010] Another object of the invention is a drive module with an electric motor a wave gear wherein the wave gear comprises a wave generator, a flexible transmission element with external teeth and an outer ring with internal teeth, where the internal and external teeth are in mesh with each other, wherein the flexible transmission element has a first strain sensor, wherein a first time series can be generated by means of the first strain sensor, and with a device described above.

[0011] Another object of the invention is a robot with a drive module described above.

[0012] The same features, advantages and technical effects that have already been explained in connection with the inventive method and its embodiments can be applied individually or in combination to the device, drive module and robot according to the invention.

[0013] Further details and advantages of the invention will be explained below with reference to the exemplary embodiment shown in the drawings. Herein: Fig. 1 schematically a wave gear and a failure to engage between a flexible transmission element and an outer ring. Fig. 2 an embodiment of a flexible transmission element in a perspective view and a schematic top view. Fig. 3 schematically a time series generated by a first strain sensor and a reference time series according to a method according to the invention for detecting a tooth engagement disturbance. Fig. 4 schematically five difference measures determined by means of a time series and a reference time series according to the inventive method for detecting a dental intervention disorder.

[0014] In Fig. Figure 1 shows a typical schematic representation of a wave gear 10. The main components of the wave gear 10 are a wave generator 12, a rigid outer ring 16 (circular spline) with internal teeth 16, and a flexible transmission element 14 (flexspline) arranged between them with external teeth 14, wherein the internal teeth 16 and the external teeth 14 are in mesh with each other. The wave generator 12 comprises a drive shaft and an oval or elliptical disk connected to the drive shaft, on the circumference of which several rolling elements (not shown) are arranged that roll on the inside of the transmission element 14.The flexible transmission element 14 is engaged with the outer ring 16 by the shaft generator 12, whereby each individual tooth of the flexible transmission element 14 is moved out of a gap between two teeth of the outer ring 16 during a 180° rotation of the shaft generator 12 and moves into the next gap (indicated by arrow P in detail D). In this way, the flexible transmission element 14 rotates relative to the outer ring 16 in the opposite direction to the rotation of the shaft generator 12, transmitting a torque between the flexible transmission element 14 and the outer ring 16. The output of the wave gear 10 can be either via the flexible transmission element 14 (with a fixed outer ring 16) or via the outer ring 16 (with a fixed transmission element 14). In the following, the output side always corresponds to the flexible transmission element 14.

[0015] As a result of excessively high torque or another cause, the engagement between the internal teeth 16 and the external teeth 14 can be temporarily lost, causing one tooth of the transmission element 14 to skip several teeth of the outer ring 16 (indicated by the additional arrow P). Such slippage or relative movement between the internal teeth 16 and the external teeth 14 is called ratcheting. While in normal operation without ratcheting, the tooth engagement between the transmission element 14 and the outer ring 16 maintains a strict relationship between the respective angles of rotation, such a disruption in engagement leads to uncontrolled relative rotation and a resulting angular misalignment.

[0016] In Fig. Figure 2 shows an embodiment of the flexible transmission element 14 in a perspective view and a schematic top view. The transmission element 14 has a collar sleeve 14 designed as a flange. The collar sleeve 14 has a first strain sensor S1 in a first section along a circumferential direction U and a second strain sensor S2 in a second section diametrically opposite the first section. Furthermore, the collar sleeve 14 has a third strain sensor S3 in a third section along the circumferential direction U and a fourth strain sensor S4 in a fourth section diametrically opposite the third section. The first and second strain sensors S1, S2 are each spaced 90 degrees apart along the circumferential direction U relative to both the third strain sensor S3 and the fourth strain sensor S4. All four strain sensors S1, S2, S3, S4 extend substantially over an angle of 90°.

[0017] In Fig. Figure 3 schematically depicts a time series ST1 generated by a first strain sensor S1 and a reference time series R according to an embodiment of the inventive method for detecting a tooth engagement defect. Using the first time series ST1 and the reference time series R, a difference is determined between a value in time series ST1 and a reference value in the reference time series R, or between time series ST1 and the reference time series R. If the difference falls below a predetermined limit, G A dental procedure disorder is detected. The reference time series R represents a dental procedure disorder, in this case a so-called ratcheting.

[0018] In Fig. Figure 4 schematically depicts five difference measures 1, 2, 3, 4, 5, determined using a time series ST1 and a reference time series R, according to the inventive method for detecting a dental procedure disorder. Furthermore, the Fig. 4 a given limit difference G , which has the value one. According to the invention, the difference dimension 1 indicates a tooth engagement fault in the wave gear 10, since the difference dimension 1 has a value of approximately 0.3 and thus the specified limit difference. G = falls below 1.0. All in the Fig. The 4 difference measures 1, 2, 3, 4, 5 shown were determined by dynamic time warping (DTW). Reference symbol list 10 wave gears 12-wave generator 14 Flexible transmission element 14 External teeth 14 Collar sleeve 16 outer ring 16 Internal teeth D Detail section S1 First strain sensor S2 Second strain sensor S3 Third strain sensor S4 Fourth strain sensor ST1 First time series P arrow P Further arrow R Reference Time Series Difference Measure G Limit difference

Claims

[1] Method for detecting a tooth engagement fault, in particular a short-term tooth engagement interruption, in a wave gear (10), wherein the wave gear (10) comprises a wave generator (12), a flexible transmission element (14) with an external toothing (14) and an outer ring (16) with an internal toothing (16), wherein the internal teeth (16) and the external teeth (14) are in engagement with each other, wherein the flexible transmission element (14) has a first strain sensor (S1) which generates a first time series (ST1), characterized by that a reference time series (R) is provided, where a difference measure () is determined between a value of the time series and a reference value of the reference time series or between the time series and the reference time series using the first time series (ST1) and the reference time series (R), where, in the case that the difference measure () falls below a predetermined limit difference (6), a dental intervention disorder is detected. [2] Method according to claim 1, characterized by , that the time series (ST1) includes several time-spaced values ​​and the reference time series (R) includes several time-spaced reference values. [3] Method according to any one of the preceding claims, characterized by , that the difference measure () is determined by dynamic time normalization. [4] Method according to any one of the preceding claims, characterized by , that the difference measure () is a Euclidean distance or the Mahalanobis distance. [5] Device (100) for detecting a tooth engagement fault, in particular a momentary interruption of tooth engagement, in a wave gear (10), wherein the wave gear (10) comprises a wave generator (12), a flexible transmission element (14) with an external toothing (14) and an outer ring (16) with an internal toothing (16), wherein the internal teeth (16) and the external teeth (14) are in engagement with each other, wherein the flexible transmission element (14) has a first strain sensor (S1) which generates a first time series (ST1), characterized by an evaluation unit for evaluating the first time series (ST1), wherein the evaluation unit is configured such that a reference time series (R) is provided, where a difference measure () is determined between a value of the time series and a reference value of the reference time series or between the time series and the reference time series using the first time series (ST1) and the reference time series (R), where in the case that the difference measure () is a predetermined limit difference ( G If the value falls below a certain threshold, a dental procedure disorder is detected. [6] Drive module with an electric motor a wave gear (10), wherein the wave gear (10) comprises a wave generator (12), a flexible transmission element (14) with an external toothing (14) and an outer ring (16) with an internal toothing (16), wherein the internal teeth (16) and the external teeth (14) are in engagement with each other, wherein the flexible transmission element (14) has a first strain sensor (S1), wherein a first time series (ST1) can be generated by means of the first strain sensor (S1), and with a device according to claim 5. [7] Robot (1) with a drive module according to claim 6.

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