Method and device for detecting an imminent tooth meshing fault in a harmonic gearing system, and robot comprising such a device

Abstract

The invention relates to a method and to a device for detecting an imminent tooth meshing fault, in particular a temporary interruption in tooth meshing, in a harmonic gearing system (10), wherein the harmonic gearing system (10) has a wave generator (12), a flexible transmission element (14) with external toothing (14'), and an outer ring (16) with internal toothing (16'), wherein the internal toothing and the external toothing mesh with one another, wherein the flexible transmission element (14) has a first strain sensor (S1) in a first region and a second strain sensor (S2) in a second region diametrically opposite the first region along a circumferential direction (U), wherein the first strain sensor (S1) generates a first signal (ST1) and the second strain sensor (S2) generates a second signal (ST2).

Description

[0001] Method and device for detecting an impending tooth meshing disturbance in a wave gear, robot with such a device

[0002] The invention relates to a method for detecting an impending meshing disturbance, in particular a brief meshing interruption, in a strain wave gear. Furthermore, the invention relates to a device for detecting such a meshing disturbance. Furthermore, the invention relates to a robot with such a device.

[0003] Strain wave gears (also known as stress wave gears, strain wave gears or harmonic reducers) are compact gears used, for example, in the joints of collaborative robots and industrial robots. Such strain wave gears have a wave generator, a flexible transmission element (flexspline) with external teeth, and an outer ring (circular spline) with internal teeth, with torque and speed being transmitted by means of the meshing internal and external teeth. A problem that sometimes occurs during operation of such strain wave gears is so-called "ratcheting," which describes a meshing disturbance between the internal and external teeth, in particular a brief interruption in the meshing, i.e. slipping of the internal teeth relative to the external teeth.Ratcheting can occur, for example, when attempting to transmit excessive torque (“ratcheting torque”) via the strain wave gear. As a result, the wave generator or the flexible transmission element can suffer offset, eccentricity, and / or misalignment. This can result in wear and / or other damage to the strain wave gear, particularly to the internal and / or external gearing, which can reduce the service life of the strain wave gear. In extreme cases, the strain wave gear can suffer irreparable damage, which can lead to operational and / or production downtime. In addition, costs for replacement products as well as for disassembly and reassembly can arise.

[0004] Against this background, the task arises to provide a solution that detects an impending tooth meshing disturbance, in particular a short-term tooth meshing interruption in the form of ratcheting.

[0005] The object is achieved by a method for detecting an impending tooth meshing disturbance, in particular a brief tooth meshing interruption, 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, wherein the internal teeth and the external teeth are in engagement with one another, wherein the flexible transmission element comprises a first strain sensor in a first section along a circumferential direction and a second strain sensor in a second section diametrically opposite the first section, wherein the first strain sensor generates a first signal and the second strain sensor generates a second signal, wherein a first value of a time derivative of the first signal is determined by means of the first signal and a second value of a time derivative of the second signal is determined by means of the second signal,wherein a difference value is calculated from the first value and the second value, wherein the difference value is compared with a predetermined limit value, wherein in the event that the difference value exceeds the limit value, an impending tooth mesh disturbance is detected.,

[0006] The strain wave gear comprises a wave generator, a flexible transmission element with external teeth, and an outer ring with internal teeth, wherein the internal and external teeth mesh with one another. The internal and external teeth provide the advantage of a compact design for the strain wave gear. Furthermore, the flexible transmission element has a first strain sensor in a first section along a circumferential direction and a second strain sensor in a second section diametrically opposite the first section. The first and second strain sensors can be arranged on a flange or on a collar sleeve of the flexible transmission element. In other words, the first and second sections can be formed on the flange or on the collar sleeve, respectively.This has the advantage that the strain sensors are positioned outside the tooth engagement area and are therefore safe and protected from the effects of force. Furthermore, according to the invention, the first strain sensor generates a first signal and the second strain sensor generates a second signal, wherein a first value of a time derivative of the first signal is determined using the first signal and a second value of a time derivative of the second signal is determined using the second signal. A difference value is then calculated from the first value and the second value, and the difference value is compared with a predetermined limit value. If the difference value exceeds the limit value, an impending tooth meshing fault is detected. Individual components of the strain wave gear, in particular the flexible transmission element, can deform under the forces, stresses and torques acting during operation. The deformation orA shape of the flexible transmission element in undisturbed normal operation without meshing disturbances is usually symmetrical, in particular point-symmetrical. In other words, the respective deformation at diametrically opposed sections of the flexible transmission element is equal (large), at least in terms of magnitude. The first signal generated by the first strain sensor and the second signal generated by the second strain sensor are therefore identical, or at least largely equal. A difference value between a first value generated by the first signal and a second value generated by the second signal is therefore zero. Taking into account measurement errors and / or geometric deviations due to manufacturing, operation, and / or wear, the difference value may deviate from zero.The differential value at least does not exceed a specified limit when the strain wave gear is operated in normal, damage-free operation. However, the deformation or shape of the flexible transmission element can be particularly asymmetrical shortly before a tooth meshing disturbance occurs—shortly before ratcheting or before the external toothing of the flexible transmission element slips relative to the internal toothing of the outer ring. In other words, the respective deformation at diametrically opposed sections of the flexible transmission element is no longer equal (large). Rather, in such a case, the differential value exceeds the specified limit, so that an impending tooth meshing disturbance is detected by measurement using the strain sensors.By detecting an impending meshing fault, offsets, eccentricities, misalignments, wear and / or other damage to the strain wave gear can be avoided, thus saving costs. A differentiating element or D element can be used to determine the first and second values ​​using the first and second signals, respectively. Furthermore, it is conceivable for the specified limit value to be dynamic or adjustable, particularly over the course of the strain wave gear's service life. This can, under certain circumstances, sensitize the strain wave gear to a meshing fault. If, for example, impending ratcheting is to be detected with greater certainty, the limit value can be reduced so that the impending meshing fault can be detected even with the smallest asymmetries in the deformation of the flexible transmission element.

[0007] According to an advantageous embodiment of the invention, it is provided that the flexible transmission element has a third strain sensor in a third section along the circumferential direction and a fourth strain sensor in a fourth section diametrically opposite the third section, wherein the third strain sensor generates a third signal and the fourth strain sensor generates a fourth signal, wherein a third value of a time derivative of the third signal is determined by means of the third signal and a fourth value of a time derivative of the fourth signal is determined by means of the fourth signal, wherein a further difference value is calculated from the third value and the fourth value, wherein the further difference value is compared with a predetermined further limit value, wherein in the event that the further difference value exceeds the further limit value, an impending tooth mesh disturbance is detected.In order to detect an asymmetry in the shape or deformation of the flexible transmission element and the associated impending gear meshing disturbance, at least a pair of strain sensors is required. Detection can be optimized with two pairs of strain sensors. It is also conceivable, for example, for the strain gear to have three or four pairs, i.e. a total of six or eight strain sensors, with the strain sensors of each pair being arranged diametrically opposite each other along the circumferential direction. With an increasing number of pairs of strain sensors, there is the advantage that the strain can be detected in a larger area of ​​the flexible transmission element and therefore any asymmetry can be detected in as large an area as possible, preferably across the entire circumference.

[0008] In a preferred embodiment of the invention, it is provided that the first signal is filtered before the first value is determined by means of a first low-pass filter, and / or the second signal is filtered before the second value is determined by means of a second low-pass filter, and / or the third signal is filtered before the third value is determined by means of a third low-pass filter, and / or the fourth signal is filtered before the fourth value is determined by means of a fourth low-pass filter. Preferably, the strain wave gear or the flexible transmission element has four strain sensors, i.e. the first, the second, the third and the fourth strain sensor. Preferably, all four signals are filtered by means of an associated low-pass filter. Preferably, the signals are filtered immediately before they are fed to a differentiator, so that the filtered signals are fed to the differentiator as input variables without further manipulation.It is also conceivable in principle that the wave gear comprises one or more signal amplifiers, wherein the signal amplifiers can in particular be arranged in front of one of the low-pass filters.

[0009] An advantageous embodiment of the invention provides that the first and second strain sensors are each spaced apart by 90 degrees along the circumferential direction from both the third strain sensor and the fourth strain sensor. In other words, a fictitious connecting line between the first and second strain sensors is rotated by 90 degrees relative to another fictitious connecting line between the third and fourth strain sensors. Preferably, all strain sensors are arranged on a circle along the circumferential direction, i.e., the strain sensors are preferably spaced apart by the same radius from a rotational axis of the strain wave gear.However, it is also conceivable that the first and second strain sensors are spaced from the rotation axis by a first radius, while the third and fourth strain sensors are spaced from the rotation axis by a second radius, wherein the second radius can be larger or smaller than the first radius.

[0010] According to a preferred embodiment of the invention, the first and second sections are designed in the shape of a quarter-circle, with the first strain sensor and the second strain sensor detecting strain substantially over a respective angle of 90°. In other words, the strain sensors can each extend 90 degrees along the circumferential direction. Because the strain sensors each extend 90 degrees along the circumferential direction, the deformation and thus also any asymmetry in the deformation of the flexible transmission element can be fully detected.

[0011] In an advantageous embodiment of the invention, each strain sensor comprises a plurality of strain gauges, wherein the strain gauges for each strain sensor are interconnected, in particular, as a bridge circuit. The bridge circuit can be designed, in particular, as a full bridge, i.e., comprising four variable resistors.

[0012] A preferred embodiment of the invention provides that in the event of an impending gear meshing fault, the strain wave gear is taken out of operation. The wave generator of the strain wave gear can in particular comprise a drive shaft and an elliptical disk. If an impending gear meshing fault is detected, the decommissioning can be carried out in particular by decommissioning a drive and thus the drive shaft. Furthermore, if an impending gear meshing fault is detected, the supply of electrical power can be prevented or switched off, which has the same effect as decommissioning the strain wave gear, since in such a case no torque or speed is transmitted. It is therefore conceivable that ratcheting can also be prevented by switching off the power supply sufficiently quickly, which prevents wear or other damage to the strain wave gear.

[0013] A further subject of the invention is a device for detecting an impending tooth meshing disturbance, in particular a brief tooth meshing interruption, 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, wherein the internal teeth and the external teeth are in engagement with each other, wherein the flexible transmission element has a first strain sensor in a first section along a circumferential direction and a second strain sensor in a second section diametrically opposite the first section, wherein a first signal can be generated by means of the first strain sensor and a second signal can be generated by means of the second strain sensor, wherein the device further comprises an evaluation device for evaluating the first and second signals, wherein the evaluation device is configured such thatthat a first value of a time derivative of the first signal is determined by means of the first signal and a second value of a time derivative of the second signal is determined by means of the second signal, wherein a difference value is calculated from the first value and the second value, wherein the difference value is compared with a predetermined limit value, wherein in the event that the difference value exceeds the limit value, an impending tooth meshing disturbance is detected.,

[0014] A further subject of the invention is a drive module with an electric motor, with a wave gear, wherein the wave gear has a wave generator, a flexible transmission element with external teeth and an outer ring with internal teeth, wherein the internal teeth and the external teeth are in engagement with one another, wherein the flexible transmission element has a first strain sensor in a first section along a circumferential direction and a second strain sensor in a second section diametrically opposite the first section, wherein a first signal can be generated by means of the first strain sensor and a second signal can be generated by means of the second strain sensor, and with a device as described above for detecting an impending tooth meshing disturbance.

[0015] The invention further relates to a robot with a drive module as described above. A robot within the meaning of the invention is, in particular, a collaborative robot or an industrial robot. However, robots within the meaning of the invention can also be other partially or fully automated devices that comprise a device according to the invention. The drive module is preferably configured and / or arranged such that it can move a robot arm of the robot.

[0016] For the device according to the invention, the drive module according to the invention and the robot according to the invention, the same features, advantages and technical effects can be applied individually or in combination as have already been explained in connection with the method according to the invention and its embodiments.

[0017] Further details and advantages of the invention will be explained below with reference to the exemplary embodiments illustrated in the drawings. Herein:

[0018] Fig. 1 shows schematically a wave gear and an engagement disturbance between a flexible transmission element and an outer ring.

[0019] Fig. 2 shows an embodiment of a flexible transmission element in a perspective view and a schematic plan view.

[0020] Fig. 3 shows a flow chart of an embodiment of the method according to the invention for detecting an impending tooth meshing disturbance in a wave gear.

[0021] Fig. 4 shows a schematic representation of the time course of four signals determined by strain sensors.

[0022] Fig. 5 schematically shows the time course of four signals determined by means of strain sensors, four values ​​determined from the signals by time derivative and a difference value determined from the values ​​as well as a further difference value determined from the values.

[0023] Fig. 1 schematically illustrates a typical design of a strain wave gear 10. The main components of strain 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 therebetween with external teeth 14', wherein the internal teeth 16' and the external teeth 14' are in mesh with one another. The wave generator 12 comprises a drive shaft and an oval or elliptical disc connected to the drive shaft, on the circumference of which a plurality of rolling elements (not shown) are arranged, which roll on the inside of the transmission element 14.The flexible transmission element 14 is engaged with the outer ring 16 by the wave generator 12, with each individual tooth of the flexible transmission element 14 being moved out of a gap between two teeth of the outer ring 16 during a 180° rotation of the wave generator 12 and moving into the respective subsequent 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 direction opposite to the rotation of the wave generator 12, whereby a torque is transmitted between the flexible transmission element 14 and the outer ring 16. The output of the wave gear 10 can be effected 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.

[0024] As a result of excessive torque or for another reason, the engagement between the internal gearing 16' and the external gearing 14' may be temporarily lost, causing a 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 gearing 16' and the external gearing 14' is referred to as "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 an engagement disturbance results in uncontrolled relative rotation and a resulting angular misalignment.

[0025] Fig. 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 apart by 90 degrees along the circumferential direction U from both the third strain sensor S3 and the fourth strain sensor S4.All four strain sensors S1, S2, S3, S4 essentially extend over an angle of 90°.

[0026] Fig. 3 shows a flow chart of an embodiment of the method according to the invention for detecting an impending tooth meshing disturbance in a strain wave gear 10. The first, second, third and fourth strain sensors S1, S2, S3, S4 each generate a first, second, third and fourth signal ST1, ST2, ST3, ST4. The four signals ST1, ST2, ST3, ST4 are first filtered by means of a first, second, third and fourth low-pass filter T1, T2, T3, T4. Subsequently,

[0027] - by means of the filtered first signal ST 1 a first value DST 1 of a time derivative of the filtered first signal ST1,

[0028] - by means of the filtered second signal ST2, a second value DST2 of a time derivative of the filtered second signal ST2,

[0029] - by means of the filtered third signal ST3, a third value DST3 of a time derivative of the filtered third signal ST3, and

[0030] - using the filtered fourth signal ST4, a fourth value of a time derivative of the filtered fourth signal DST4 is determined. The four values ​​DST1, DST2, DST3, DST4 are determined using a first, second, third and fourth differentiating element D1, D2, D3, D4. A difference value AD is calculated from the first value DST1 and the second value DST2. Furthermore, a further difference value Ad is calculated from the third value DST3 and the fourth value DST4. The difference value AD is compared with a predetermined limit value G and the further difference value Ad is compared with a further predetermined limit value g. If the difference value AD exceeds the limit value G or the further difference value Ad exceeds the further limit value g, an impending tooth meshing fault is detected and the strain wave gear 10 is taken out of operation by stopping a drive of the wave generator 12.

[0031] Fig. 4 shows a schematic representation of the time course of four signals ST1, ST2, ST3, ST4, determined by means of strain sensors S1, S2, S3, S4. On the left-hand side of Fig. 4, the four signals ST1, ST2, ST3, ST4 are shown in normal operation N of the strain wave gear 10. The signal courses are cyclical and resemble the course of trigonometric functions. At a certain point in time, the second and third signals ST2, ST3 each have a signal deviation X in their course, with the signal deviations X each circled. Shortly after the signal deviations X, a tooth meshing disturbance or ratcheting R occurs.

[0032] Fig. 5a schematically shows the time course of four signals ST1, ST2, ST3, ST4 determined by means of strain sensors S1, S2, S3, S4. Furthermore, Fig. 5b shows the time course of four values ​​DST1, DST2, DST3, DST4 determined by time derivation of the signals ST1, ST2, ST3, ST4 shown in Fig. 5a. In addition, Fig. 5c shows the time course of a difference value AD determined from the values ​​DST1, DST2 and the time course of a further difference value Ad determined from the values ​​DST3, DST4. A comparison of the difference value AD with the limit value G and a comparison of the further difference value Ad with the further limit value g decides whether the strain wave gear 10 should be taken out of operation. For example, the limit value G and the further limit value g could be set to 0.5, i.e. either +0.5 or -0.5.

[0033] List of reference symbols

[0034] 10 wave gears

[0035] 12 wave generator

[0036] 14 Flexible transmission element

[0037] 14' external toothing

[0038] 14" collar sleeve

[0039] 16 Outer ring

[0040] 16' internal gearing

[0041] D Detail section

[0042] D1 First differentiating term

[0043] D2 Second differentiating term

[0044] D3 Third differentiating element

[0045] D4 Fourth differentiating term

[0046] DST 1 First value of a time derivative of the first signal

[0047] DST2 Second value of a time derivative of the second signal

[0048] DST3 Third value of a time derivative of the third signal

[0049] DST4 Fourth value of a time derivative of the fourth signal

[0050] G Limit value g Additional limit value

[0051] N Normal operation of the strain wave gear

[0052] P Arrow

[0053] P' Further arrow

[0054] R Tooth meshing disorder / ratcheting

[0055] 51 First strain sensor

[0056] 52 Second strain sensor

[0057] 53 Third strain sensor

[0058] 54 Fourth strain sensor ST 1 First signal

[0059] ST2 Second Signal

[0060] ST3 Third Signal

[0061] ST4 Fourth Signal

[0062] T 1 First low-pass filter

[0063] T2 Second low-pass filter

[0064] T3 Third low-pass filter

[0065] T4 Fourth low-pass filter

[0066] X (signal) deviation

[0067] AD difference value

[0068] Ad Additional difference value

Claims

Patent claims 1. A method for detecting an impending meshing disturbance, in particular a brief meshing interruption, in a wave gear (10), wherein the wave gear (10) comprises a wave generator (12), a flexible transmission element (14) with external teeth (14') and an outer ring (16) with internal teeth (16'), wherein the internal teeth and the external teeth are in engagement with one another, wherein the flexible transmission element (14) comprises, along a circumferential direction (U), in a first section, a first strain sensor (S1) and, in a second section diametrically opposite the first section, a second strain sensor (S2), wherein the first strain sensor (S1) generates a first signal (ST1) and the second strain sensor (S2) generates a second signal (ST2),characterized in that a first value (DST1) of a time derivative of the first signal (ST1) is determined by means of the first signal (ST1) and a second value (DST2) of a time derivative of the second signal (ST2) is determined by means of the second signal (ST2), wherein a difference value (AD) is calculated from the first value (DST1) and the second value (DST2), wherein the difference value (AD) is compared with a predetermined limit value (G), wherein in the event that the difference value (AD) exceeds the limit value (G), an impending tooth mesh disturbance is detected.

2. Method according to claim 1, characterized in that the flexible transmission element (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, wherein the third strain sensor (S3) generates a third signal (ST3) and the fourth strain sensor (S4) generates a fourth signal (ST4), wherein a third value (DST3) of a time derivative of the third signal (ST3) is determined by means of the third signal (ST3) and a fourth value of a time derivative of the fourth signal (DST4) is determined by means of the fourth signal (ST4), wherein a further difference value (Ad) is calculated from the third value (DST3) and the fourth value (DST4), wherein the further difference value (Ad) is compared with a predetermined further limit value (g), wherein in the event that the further difference value (Ad) exceeds the further limit value (g), an impending tooth meshing disturbance is detected.

3. Method according to claim 1 or 2, characterized in that the first signal (ST1) is filtered before the determination of the first value (DST1) by means of a first low-pass filter (T1), and / or the second signal (ST2) is filtered before the determination of the second value (DST2) by means of a second low-pass filter (T2), and / or the third signal (ST3) is filtered before the determination of the third value (DST3) by means of a third low-pass filter (T3), and / or the fourth signal (ST4) is filtered before the determination of the fourth value (DST4) by means of a fourth low-pass filter (T4).

4. Method according to one of claims 2 or 3, characterized in that the first and the second strain sensor (S1, S2) are each spaced apart by 90 degrees along the circumferential direction (U) from both the third strain sensor (S3) and the fourth strain sensor (S4).

5. Method according to one of the preceding claims, characterized in that the first and the second section are quarter-circular in shape, wherein the first strain sensor (S1) and the second strain sensor (S2) detect a strain substantially over a respective angle of 90°.

6. Method according to one of the preceding claims, characterized in that each strain sensor (S1, S2, S3, S4) comprises a plurality of strain gauges, wherein the strain gauges for each strain sensor (S1, S2, S3, S4) are connected to one another in particular as a bridge circuit.

7. Method according to one of the preceding claims, characterized in that in the event of an impending tooth meshing disturbance, the harmonic drive (10) is taken out of operation.

8. Device (100) for detecting an impending tooth meshing disturbance, in particular a short-term tooth meshing interruption, in a wave gear (10), wherein the wave gear (10) comprises a wave generator (12), a flexible A transmission element (14) having an external toothing and an outer ring (16) having an internal toothing, wherein the internal toothing and the external toothing are in engagement with one another, wherein the flexible transmission element (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, wherein a first signal (ST1) can be generated by means of the first strain sensor (S1) and a second signal (ST2) can be generated by means of the second strain sensor (S2), characterized by an evaluation device (20) for evaluating the first and second signals (S1, S2), wherein the evaluation device (20) is configured such thatthat a first value (DST1) of a time derivative of the first signal (ST1) is determined by means of the first signal (ST1) and a second value (DST2) of a time derivative of the second signal (ST2) is determined by means of the second signal (ST2), wherein a difference value (AD) is calculated from the first value (DST1) and the second value (DST2), wherein the difference value (AD) is compared with a predetermined limit value (G), wherein in the event that the difference value (AD) exceeds the limit value (G), an impending tooth mesh disturbance is detected.

9. Drive module with an electric motor, with a wave gear, wherein the wave gear (10) has a wave generator (12), a flexible transmission element (14) with external teeth and an outer ring (16) with internal teeth, wherein the internal teeth and the external teeth are in engagement with each other, wherein the flexible transmission element (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, wherein a first signal (ST1) can be generated by means of the first strain sensor (S1) and a second signal (ST2) can be generated by means of the second strain sensor (S2), and with a device according to claim 8.

10. Robot (1) with a drive module according to claim 9.

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