Method of operating drive system to prevent meshing interference in strain wave gear arrangement

Abstract

The invention relates to a method for operating a drive system comprising an electric machine and a strain wave gear arrangement having a wave generator coupled to the electric machine, a rigid outer ring having inner teeth, and an elastically deformable transmission ring having outer teeth engaging with the inner teeth on the outer ring, the method comprises the following method steps: measuring a torque applied to the transmission ring by means of a torque sensor, detecting a meshing disturbance on the basis of the measured torque and storing a critical torque value that has occurred during the meshing disturbance, determining a torque threshold value, which is less than or equal to the critical torque value, and determining the torque threshold value, which is less than or equal to the torque threshold value. And-controlling the electric machine such that the torque exerted on the transmission ring is below the torque threshold.

Description

Technical Field

[0001] The present invention relates to a method for operating a drive system, wherein the drive system includes an electric motor and a strain wave gear unit. Furthermore, the present invention relates to a drive system having an electric motor and a strain wave gear unit. Background Art

[0002] A strain wave gear unit (also known as a strain wave drive, an elliptical center gear mechanism) can achieve almost backlash-free power transmission with a high transmission ratio, and is therefore particularly suitable for applications that require precise motion and small space requirements. Since a high torque can be generated by a relatively small motor due to the high transmission ratio, a strain wave gear unit can be used to construct a very compact drive mechanism for, for example, a robot.

[0003] The main components of a strain wave gear unit are a wave generator ("wave generator"), a rigid outer ring with internal teeth ("circular spline"), and a transmission ring with external teeth ("flexible spline") arranged between the wave generator and the rigid outer ring. Compared with a rigid gear, the torque transmission between the wave generator and the outer ring is based on elastic deformation. In the torque transmission, the transmission ring is deformed into an oval shape by the wave generator, so that the transmission ring engages with the outer ring on two opposite sides of its circumference. When the wave generator rotates, the transmission ring rolls on the outer ring, so that the torque is transmitted between the transmission ring and the outer ring through the interlocking teeth. Therefore, the transmission ratio of the transmission device is determined by the difference in the number of teeth between the transmission ring and the outer ring.

[0004] If an excessive torque is applied during operation, for example when the gearbox is working under high resistance, the engagement between the transmission ring and the outer ring may be at least partially lost, so that the teeth of the transmission ring skip over the teeth of the outer ring ("ratchet effect"). Although the rotation of the transmission ring and the rotation of the outer ring are strictly coupled during normal operation, this meshing interference will temporarily cause an uncontrolled relative rotation between the two rings. This will produce an unknown angular offset on the output side compared with the drive side, resulting in an inability to precisely control the angular position. Since the condition of the transmission device cannot indicate whether such meshing interference has occurred, it becomes more difficult to find the cause of subsequent failures.

[0005] Against this background, a method is known from JP 2021014876 A, in which the torque acting on the output side of a strain wave gear device is measured and this torque is compared with two threshold values. Exceeding the first threshold value indicates meshing interference, while exceeding the second threshold value indicates that the transmission ring may buckle. The disadvantage of this method is that the critical torque ("ratchet torque") at which meshing interference may occur varies depending on the transmission. On the other hand, this simple threshold method cannot reliably determine whether meshing interference has actually occurred or whether a temporarily occurring high torque decreases without interference. In addition, these meshing interferences can cause damage in the strain wave gear device, where meshing interference is a self-reinforcing phenomenon that increases with the operating time. In repeated work cycles, the locally increased wear on the teeth of the strain wave gear device and the high torque required on the output side lead to an increased likelihood of local meshing interference.

[0006] DE 10 2021 113 139 B3 describes a method for operating an automatic machine device having a transmission and a sensor device, by means of which the torque applied to the transmission is determined. The method includes a determination step and a comparison step, in which the operating parameters of the automatic machine device are adjusted according to the comparison.

[0007] JP 2021-14 876A describes a failure determination device for a wave gear device, which failure determination device includes a torque detector located on the output side of the wave gear device and a determination unit for determining the failure of the wave gear device based on the torque detected by the torque detector.

[0008] DE 10 2019 210 795 A1 describes a strain wave gear device having a vibration sensor, the signal of which is used to determine load data and / or is further processed to provide information about the transmission condition and / or to detect critical operating conditions.

[0009] Against this background, the object is to provide methods and systems that can reduce the likelihood of meshing interference occurring. SUMMARY OF THE INVENTION

[0010] This object is achieved by a method for operating a drive system, wherein the drive system includes an electric motor and a strain wave gear device, which strain wave gear device includes a wave generator coupled to the electric motor, a rigid outer ring having internal teeth, and an elastically deformable transmission ring having external teeth that engage the internal teeth of the outer ring, wherein the method includes the following method steps:

[0011] - Measuring the torque applied to the transmission ring by means of a torque sensor,

[0012] - Detecting meshing interference based on the measured torque and storing the critical torque value that has occurred during the meshing interference,

[0013] - Determine a torque threshold that is less than or equal to the critical torque value, and

[0014] - Control the electric motor such that the torque applied to the transmission ring is below the torque threshold.

[0015] Furthermore, this object is achieved by a drive system having an electric motor and a strain wave gearing, the strain wave gearing including a wave generator coupled to the electric motor, a rigid outer ring having internal teeth, and an elastically deformable transmission ring having external teeth that engage the internal teeth of the outer ring, wherein the drive system is configured to perform the following method steps:

[0016] - Measure the torque applied to the transmission ring by means of a torque sensor,

[0017] - Detect meshing interference based on the measured torque and store the critical torque value that has occurred during the meshing interference,

[0018] - Determine a torque threshold that is less than or equal to the critical torque value, and

[0019] - Control the electric motor such that the torque applied to the transmission ring is below the torque threshold.

[0020] If meshing interference has been detected based on the measured torque, store the critical torque value that has occurred during the meshing interference. This torque value may correspond to the ratchet torque.

[0021] According to the invention, after detecting meshing interference and storing the critical torque value, a torque threshold that is less than or equal to the critical torque value is determined. Subsequently, the electric motor is controlled such that the torque applied to the transmission ring is below or equal to the level of the previously determined torque threshold. This method according to the invention makes it possible to significantly reduce the likelihood of other meshing interferences occurring. In a particularly preferred case, other meshing interferences can be completely avoided by the method and drive system according to the invention.

[0022] The wave generator of the strain wave gear device is particularly formed by a disk which is connected to the drive shaft and has an oval shape, for example an elliptical shape. The disk preferably has a rolling bearing shrunk onto its circumference, which rolling bearing has a thin, elastically deformable raceway and a number of rolling elements. The transmission ring can be, for example, cup-shaped or top-hat-shaped ("top hat" shaped), i.e., the transmission ring is particularly formed by the cylindrical wall of a cup-shaped or top-hat-shaped bushing, which cup-shaped or top-hat-shaped bushing can be made of steel, for example. Thus, these are common design options for the transmission ring, and the common design options can be used to preload the transmission ring relative to the wave generator. In particular, the measured torque can be analyzed and evaluated via an evaluation unit, which determines the change of the torque over time and compares the torque with a reduction threshold. For example, the rate of change over time can be determined and compared with the reduction threshold, particularly by forming the difference or the numerical derivative of the torque measurement values. It is also conceivable to compare and check whether the measured torque has decreased by at least a predetermined amount within a predetermined period of time. The reduction threshold can particularly be a relative reduction threshold, i.e., it is compared and checked whether the measured torque has decreased by at least a predetermined percentage. If the reduction threshold is exceeded, a warning signal is triggered, which warning signal can particularly be transmitted to an external data processing unit, such as the monitoring and control unit of the strain wave gear device.

[0023] The detection of meshing interference can be based on the curve of the torque measured over time on the deformable transmission ring. This represents the dynamic behavior of torque transmission before and during meshing interference. Usually, an excessive torque is formed before meshing interference, which ultimately causes the teeth of the transmission ring to disengage from the outer ring teeth and skip over the outer ring teeth. The accumulated torque decreases significantly within a short period of time. This decrease in torque can be used as a characteristic signal of meshing interference and enables reliable detection of meshing interference.

[0024] Furthermore, during the detection, the measured torque can be compared with at least one threshold value, where only when it is detected that the threshold value is exceeded, it is determined that the measured torque decreases over time and is compared with a decrease threshold value. The threshold value is used to distinguish the load peaks generated during normal operation from the excessive torques indicating meshing interference or emitting meshing interference signals. For example, during the start-up or stop process, the transmission must overcome the inertia of the load coupled to the outlet side or the output side, which causes a brief increase in torque (start-up / stop torque). If an obstacle appears on the output side, for example, if a robotic arm actuated by a gearbox hits an obstacle, the transmission will briefly resist a high resistance (impact torque) before the collision is recorded. At very high torques, the mechanical load capacity of the transmission ring will eventually be exceeded, resulting in buckling of the transmission ring (buckling torque, torsional buckling, torsional flexural buckling). The ratchet torque is between the impact torque and the buckling torque, and the ratchet torque usually triggers meshing interference. The threshold value used in this method can, for example, correspond to the impact torque or the ratchet torque. Preferably, the threshold value is between the impact torque and the buckling torque, or between the impact torque and the ratchet torque.

[0025] In the method according to the invention, the critical torque value that has occurred during meshing interference, such as the ratchet torque, can be stored in an internal storage unit in or on the strain wave gear device, where the internal storage unit can be arranged in the evaluation unit of the motor on the input side. Alternatively or additionally, it is conceivable that the critical torque value, in particular the critical ratchet torque, can be transmitted to a remote storage unit via a wired or wireless connection.

[0026] According to a preferred embodiment, the torque threshold is determined based on the detected critical torque. In the determination of the torque threshold, the detected critical torque is preferably included. Thus, it is conceivable that a safety factor is stored in the evaluation unit, wherein the safety factor defines the relationship between the detected critical torque and the torque threshold to be determined. For example, it can be set that the torque threshold is determined as a predetermined percentage of the detected critical torque. In order to maintain the efficiency and effectiveness of the strain wave gear device, the percentage should not be set too low, otherwise the strain wave gear device can only transmit a part of the required torque. For example, the percentage can be selected between 80% and 95%. The safety factor or the percentage can be adjusted by the evaluation unit during operation or can be a fixed, empirically determined value. An embodiment with a variable safety factor or percentage is particularly advantageous because, for example, it can be estimated more conservatively as the service life increases. With the extension of the service life and the increase of wear, the possibility of meshing interference increases. Therefore, the safety factor or the percentage in a strain wave gear device with a long operating time can be selected to be lower in order to avoid the occurrence of meshing interference again. For a strain wave gear device with only a few operating hours, the safety factor or the percentage can be selected to be larger because the possibility of meshing interference is smaller. Alternatively, a safety margin can be stored in the evaluation unit, for example, the torque threshold is defined as the absolute value of the difference between the detected critical torque and an absolute value.

[0027] According to a preferred embodiment, it is set that other meshing interferences are detected based on the measured torque and the other critical torque values occurring during these meshing interferences are stored, wherein the torque threshold is additionally determined based on the stored other critical torque values. In this context, meshing interference describes the "sliding" of the teeth of the transmission ring relative to the teeth of the outer ring. In this case, one or more teeth can be skipped in the case of meshing interference, wherein the teeth must be arranged adjacent to each other. Then, the torque threshold is determined based on several, particularly all, stored critical torque values. In this way, for example, if another meshing interference occurs at a critical torque below the currently used torque threshold, the torque threshold can be further reduced. For example, the lowest critical torque value can be determined based on multiple critical torque values, and this lowest critical torque value can then be used to determine the torque threshold.

[0028] According to a preferred embodiment, it is provided that during the initial commissioning of the drive system or during the manufacture of the drive system, an initial critical torque value is determined and stored, and a torque threshold is additionally determined based on the initial critical torque value. Since even a single meshing interference can lead to increased wear, it is more desirable to avoid meshing interference for as long as possible. The torque threshold preset before the first operation makes it possible to reduce the likelihood of meshing interference, particularly during the first few hours of operation. For example, the torque threshold can be determined or set based on data obtained experimentally during production, based on empirical values, or based on data determined during the initial startup of the drive system. The initial critical torque value, which serves as the basis for the first torque threshold, can be determined, particularly during a series of experimental tests.

[0029] According to a preferred embodiment, it is provided that when a meshing interference is detected, the torque curve and / or the load curve are additionally stored, and a torque threshold is additionally determined based on the stored torque curve and / or load curve. Storing the torque curve or the load curve makes it possible to detect whether the maximum torque and / or load values repeatedly occur, particularly in certain regions of the internal teeth and / or external teeth, especially when the teeth engage with each other. This allows for the early detection of wear and damage in these specific regions, particularly of the teeth. If wear is detected in a certain region, the torque threshold can be selected such that further wear in this region is minimized or the risk of meshing interference in this region is reduced.

[0030] In a preferred embodiment, the drive system has a position sensor, wherein the position of the wave generator is stored when a meshing interference occurs. With the aid of the position sensor, regions of the transmission ring, particularly the teeth, can be assigned to the meshing interference.

[0031] According to the invention, it is provided that in order to control the electric motor, at least one control parameter, i.e., a control parameter that influences the acceleration behavior and / or the braking behavior of the electric motor, is set according to the determined torque threshold. Alternatively, the control parameter can influence the cycle time for the work cycle.

[0032] According to a preferred embodiment, it is provided that the electric motor is additionally controlled such that the electric motor enters an idling state when an overload torque threshold greater than the determined torque threshold is exceeded and / or when a predetermined overload torque increment is exceeded. The idling state describes a state in which the electric motor does not provide any input-side torque. The electric motor can be switched off such that the electric motor acts as a damper. The idling state is not only relevant for the protection of the strain wave gear device but also for the protection of personnel in applications where the drive system is used in the robotic arm of a collaborative robot. Such a collaborative robot works closely with personnel, and the personnel can be protected by placing the electric motor in the idling state in the event of a collision with the robot.

[0033] In a strain wave gear device, the transmission ring is preferably arranged in a fixed position. The wave generator may be formed as an input end of the strain wave gear device, and the rigid outer ring may be formed as an output end of the wave transmission device. Both the wave generator and the outer ring are preferably mounted such that the wave generator and the outer ring can rotate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other details and advantages of the present invention will be described below with reference to the exemplary embodiments shown in the drawings. In the drawings:

[0035] Figure 1 An exemplary embodiment of a machine tool is shown schematically;

[0036] Figure 2 A schematic cross-sectional view of a strain wave gear device is shown, as well as the perfect tooth engagement during operation;

[0037] Figure 3 A schematic meshing interference and deformation of a transmission ring for measuring torque are shown;

[0038] Figure 4 A cross-sectional view of a drive system is shown;

[0039] Figure 5 A cross-sectional view of a strain wave gear device is shown;

[0040] Figure 6 A first torque curve with meshing interference based on which a torque threshold is determined and another torque curve taking into account the determined torque threshold are shown;

[0041] Figure 7 A second torque curve with meshing interference based on which a torque threshold is determined and another torque curve taking into account the determined torque threshold are shown;

[0042] Figure 8 A load cycle of a drive system is shown;

[0043] Figure 9 Segments from Figure 8 the load cycle are shown;

[0044] Figure 10 A control loop for a drive system is shown; and

[0045] Figure 11 A schematic flowchart of an exemplary embodiment of a method for operating a drive system according to the present invention is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] Figure 1An embodiment of a robot is schematically illustrated, which is designed as an industrial robot 200 having a plurality of arm segments 201, each of which is rotatably connected via a drive module 100. Even though the industrial robot 200 shown here has three arm segments 201 and three drive modules 100, embodiments of industrial robots 200 with different numbers of arm segments 201 and drive modules 100, for example, having four, five, six, or seven arm segments and drive modules, are conceivable. In addition, the drive module 100 can be used for any robot connection. Such an industrial robot 200 is typically used as a collaborative robot that works in close cooperation with humans.

[0047] Figure 2 The typical structure of a strain wave gear device 10 is schematically illustrated. The main components of the strain wave gear device 10 are a wave generator 13, a rigid outer ring 11 with internal teeth 1 ("circular spline"), and a flexible transmission ring 12 with external teeth 2 ("flexible spline") arranged between the wave generator and the rigid outer ring. The wave generator 13 is formed by an oval disk connected to a drive shaft, and a number of rolling elements 14 (not shown) are arranged on the circumference of the wave generator and roll on the inner side of the transmission ring 12. The flexible transmission ring 12 is engaged with the outer ring 11 by the wave generator 13, where each individual tooth of the transmission ring 12 moves out of the gap between two teeth of the outer ring 11 during a 180° rotation of the wave generator 13 and moves into the corresponding subsequent gap (indicated by the arrow 3 in section 4). In this way, the transmission ring 12 rotates relative to the outer ring 11 in a direction opposite to the rotation of the wave generator 13, and torque is transmitted between the two rings 11 and 12. The output of the strain wave gear device 10 can be achieved either via the transmission ring 12 (when the outer ring 11 is fixed) or via the outer ring 11 (when the transmission ring 12 is fixed). Hereinafter, the output of the strain wave gear device is formed by the outer ring 11.

[0048] Due to excessive torque, the engagement between the teeth 1 and 2 may be temporarily lost, such that the teeth of the transmission ring 12 can skip several teeth of the outer ring 11 during a meshing interference 62 (indicated by the arrow 62). Although a strict relationship between the corresponding rotation angles is maintained by the teeth between the rings 11 and 12 during normal operation, such a meshing interference results in an uncontrolled relative rotation and the resulting angular offset 64.

[0049] Figure 3Schematically shows the dynamic deformation of the drive ring 12 in different stages of meshing interference. The drive ring 12 is designed as a top hat-shaped bushing ("top hat shape") (see the left figure), the upper edge of the drive ring has external teeth 2, and the external teeth in turn engage with the internal teeth 1 of the outer ring 11. The deformation degree of the cylindrical wall of the drive ring 12 at three consecutive time points and the corresponding states of the teeth 1, 2 are shown. The position of the outer ring 11 is marked by a reference point 34 at the upper edge of the drive ring 12, while the lines 36, 37, 38 represent the corresponding torsions of the drive ring 12. In the first stage, the engagement between the rings 1, 2 remains intact, but an increasing torque accumulates due to the elastic torsion 36 of the drive ring 12. As the torsion increases, the torsional stiffness of the drive ring 12 increases, causing the torque to increase sharply and finally reach the maximum value of the torque at the deformation 37. When this critical value is reached, the meshing interference 62 is triggered, in which the engagement of the teeth 1, 2 is at least partially cancelled, torsion springs back, and the external teeth 2 jump relative to the internal teeth 1. After the jump, the line 38 no longer terminates at the reference point 34 as before, but has an angular offset from this reference point, and this angular offset corresponds to the offset generated between the rotation angles of the two rings 2, 3. Based on this torsion, the torque can be measured by means of a torque sensor 15, such as one or more strain gauges, and utilized in the form of a torque curve 60 that changes with time (see Figure 6 ).

[0050] Figure 4 Shows an embodiment of a drive module 100 for moving the arm section 201 of an industrial robot 200, and this drive module can be used in an industrial robot 200 according to Figure 1 . The drive module 100 includes a transmission device, which is designed as a strain wave gear device 10, a motor 20, and a braking device 30. Another component of the drive module 100 according to this embodiment is an electronic unit 40. The wave generator 13 is formed by an oval disk, and a number of rolling elements 14 are arranged on the circumference of the wave generator, and the rolling elements roll on the inner side of the drive ring 12.

[0051] The wave generator 13 of the strain wave gear device 10 is coupled to the motor 20, in this case to the rotor shaft 21 of the motor 20. The motor 20 can be designed as an axial flow machine or a radial flow machine.

[0052] The rotor shaft 21 and thus the wave generator 13 are further coupled to a braking device 30 by means of which the rotor shaft 21 can be decelerated and / or fixed. The rotor shaft 21 is also coupled to a position sensor 50 which can be used to determine the position of the rotor shaft 21 and, in this case, the angular position of the rotor shaft. The position sensor 50 is preferably designed as an optical or magnetic rotary encoder or a rotary angle encoder. By the combination of the torque sensor 15 and the position sensor 50, the amount of torque between the rings 11, 12 and the direction of rotation of the wave generator can be detected.

[0053] Figure 5 Details of the strain wave gearing 10 of the drive module 100 according to Figure 4 are shown. It can be seen that a torque sensor 15 is arranged on the elastically deformable transmission ring 12 by means of which the torque applied to the transmission ring 12 is measured. The torque sensor 15 according to this embodiment comprises one or more strain gauges by means of which the applied torque can be measured via the resulting torsion of the transmission ring 12. The torque sensor 15 is connected to an evaluation unit 41 of the drive module 100 which continuously or quasi-continuously receives the measured values of the torque sensor 15. In this embodiment, the evaluation unit 41 is designed as part of the electronic unit 40, see Figure 4 .

[0054] In Figure 6 and Figure 7 , two torque curves 60, 60' varying over time t which may occur when carrying out the method according to the invention are shown. The first torque curve 60 represents an operating situation in which a meshing interference 62 occurs and is detected. The second torque curve 60' represents the corresponding operating situation in which the motor is controlled such that the torque on the transmission ring 12 is below a torque threshold 63 which is determined based on the critical torque value occurring during the meshing interference.

[0055] The torque applied to the transmission ring 12 is measured by means of one or more torque sensors 15. A meshing interference 62 is detected based on the measured torque. The meshing interference 62 can be regarded as damped vibrations in Figure 6 and Figure 7 . The critical torque value occurring in the case of a meshing interference 62, for example in the case of the ratchet torque 61 which occurs when the teeth 1, 2 first "slip past", is stored. The torque threshold 63 is then determined based on the critical torque value, where this value is lower than or equal to the critical torque value 61. As shown by the second torque curve 60', the motor is subsequently controlled such that the torque applied to the transmission ring 12 is below the determined torque threshold 63.

[0056] Figure 6 The embodiment shown inFigure 7 The difference between the embodiments shown in is the second torque curves 60', 60", which occur when the motor is controlled at the torque threshold 63. Although according to Figure 6 the second torque curve 60' of has the same torque increase phase and torque decrease phase as the first torque curve 60, according to Figure 7 the second torque curve 60" of is the result of a control strategy in which the torque increase phase and torque decrease phase are changed compared to the first torque curve 60. This modified control strategy can be achieved, for example, by adjusting the control parameters for controlling the motor.

[0057] Figure 8 illustrates the change in the RPM curve during an exemplary operating cycle 80 of the drive system, as explained in connection with Figure 7 which may be caused by a change in the control parameters. The operating cycle 80 represents the repetitive tasks of the drive system. A first RPM curve 81 corresponding to the first torque curve 62 is shown. In particular, a second RPM curve 62 corresponding to the second torque curve 60" is obtained due to the determination of the torque threshold 63 and the change in the control parameters for the same operating cycle.

[0058] In Figure 8 it can be seen that the acceleration and braking behavior in the second RPM curve 82 has changed compared to the first RPM curve 81.

[0059] Figure 9 shows a section 83 of the curves 81, 82 from Figure 8 It can be seen that the second RPM curve 82 has a lower initial acceleration (84') compared to the first RPM curve 81, the second RPM curve changes to an increasing acceleration (84") compared to the first RPM curve 81 and ends again with a lower acceleration than the first RPM curve 81 at the end of the acceleration process (84'").

[0060] In Figure 10 an exemplary control system 1000 for the drive system is shown. The control system 1000 includes a position controller 70, a speed controller 71, a current controller 72, an inverter 73, a converter 74, an RPM speed converter 75, a motor 20, a position sensor 50, a strain wave gear device 10, and a torque sensor 15. The control system 1000 is designed such that it includes three cascaded control loops. The first control loop is the position control loop 70'. Additionally, the control system 1000 has a speed control loop 71' and a current control loop 72'.

[0061] The torque threshold determined within the scope of the method according to the invention can be taken into account in the current control loop. The torque threshold 63 can be fed to the current controller 72 such that the motor 20 is controlled so that the torque applied to the drive ring 12 is below the torque threshold 63. If the control parameters in the method are changed according to the determined torque threshold 63, these changes can affect the speed controller 71 and optionally also the position controller 70.

[0062] Figure 11 A flowchart of an exemplary embodiment of a method 300 for avoiding meshing interference is shown. In an optional first method step 301, an initial torque threshold can be defined during the initial startup of the drive system or during the manufacture of the drive system, which initial torque threshold is regarded as the upper limit of the torque on the drive ring 12 when controlling the motor. The initial torque threshold can be determined by measuring the initial critical torque value or based on empirical values from the same drive system. Thus, the torque threshold 63 can be preset before the drive system is started for the first time, thereby avoiding the first meshing interference 62 in the early stage of operation.

[0063] After the drive system is started, meshing interference may still occur at a specific torque threshold, for example due to wear. In a second method step 302, such meshing interference 62 can be detected. For this purpose, the torque applied to the drive ring 12 is measured by means of the torque sensor 15. In a third method step 303, the critical torque value that occurs during the meshing interference 62 is stored.

[0064] Subsequently, in a first query 304, it is checked whether the measured torque is greater than a predetermined overload torque threshold, or whether the increase in the measured torque is greater than the increase in the predetermined overload torque. If one of these thresholds is exceeded, the motor will enter the idling state 309. After transitioning to the idling state 309, a fifth method step 310 checks whether the current torque value is reasonable for the drive system or is still significantly too high. If the torque value is too high, an emergency shutdown is initiated in a sixth method step 311.

[0065] If the query 305’ is negative, the method 300 continues with a second query 306. The second query 306 checks whether the current torque exceeds the stored ratchet torque 61. The stored ratchet torque 61 describes the last or multiple stored critical torques that have occurred. If the second query 307 is affirmative, the system directly jumps to the sixth method step 311, and in the sixth method step, an emergency shutdown is initiated.

[0066] If the second query 307’ is negative, the process proceeds to a fourth step 308. The fourth method step 308 includes operating the drive system normally by controlling the motor 20 so that the torque applied to the drive ring 12 is below the determined torque threshold 63.

[0067] If multiple meshing interferences 62 occur during the operation of the drive system, all critical torque values that occur during these meshing interferences 62 are stored. Then, based on all the stored critical torque values, the torque threshold 63 for control in method step 308 is determined, for example, by determining the lowest critical torque value and using this lowest critical torque value to determine the torque threshold.

[0068] List of reference signs

[0069] 1 – internal teeth

[0070] 2 – external teeth

[0071] 3 – movement of the teeth of the external teeth

[0072] 4 – section

[0073] 10 – strain wave gear device

[0074] 11 – outer ring

[0075] 12 – transmission ring

[0076] 13 – wave generator

[0077] 14 – rolling element

[0078] 15 – torque sensor

[0079] 20 – electric motor

[0080] 21 – rotor shaft

[0081] 30 – braking device

[0082] 34 – reference point

[0083] 36, 37, 38 – deformation lines

[0084] 40 – electronic unit

[0085] 41 – evaluation unit

[0086] 50 – position sensor

[0087] 60 – torque curve

[0088] 60’ – new torque curve

[0089] 60” – alternative new torque curve

[0090] 61 – ratchet torque

[0091] 62 – meshing interference

[0092] 63 – new torque threshold

[0093] 70 – Position controller

[0094] 70’ – Position control loop

[0095] 71 – Speed controller

[0096] 71’ – Speed control loop

[0097] 72 – Current controller

[0098] 72’ – Current control loop

[0099] 73 – Inverter

[0100] 74 – Converter

[0101] 75 – RPM - Speed converter

[0102] 80 – Duty cycle

[0103] 81 – RPM curve

[0104] 82 – New RPM curve

[0105] 83 – Section of the curve

[0106] 84’, 84’’, 84’’’ – Modified acceleration

[0107] 100 – Drive module

[0108] 200 – Robot

[0109] 201 – Arm section

[0110] 300 – Method for avoiding meshing interference

[0111] 301 – First method step

[0112] 302 – Second method step

[0113] 303 – Third method step

[0114] 304 – First inquiry

[0115] 305 – First inquiry is affirmative

[0116] 305’ – First inquiry is negative

[0117] 306 – Second inquiry

[0118] 307 – Second inquiry is affirmative

[0119] 307’ – Second inquiry is negative

[0120] 308 – Fourth method step

[0121] 309 – Idle state

[0122] 310 – Fifth method step

[0123] 311 – Sixth method step

[0124] 1000 – Control system for the drive system

Claims

1. A method for operating a drive system, wherein, the drive system includes a motor (20) and a strain wave gear device (10), the strain wave gear device having a wave generator (13) coupled to the motor (20), a rigid outer ring (11) having internal teeth (1), and an elastically deformable transmission ring (12) having external teeth (2) that engage with the internal teeth (1) of the outer ring (11), wherein the method has the following method steps: Measuring the torque applied to the transmission ring (12) by means of a torque sensor (15), Detecting a meshing interference (62) based on the measured torque and storing the critical torque value that has occurred during the meshing interference (62), Determining a torque threshold (63) that is less than or equal to the critical torque value, and Controlling the motor (20) such that the torque applied to the transmission ring (12) is below the torque threshold (63), characterized in that, the motor (20) is additionally controlled such that in the case of exceeding the torque threshold (63) or the stored critical torque value, the motor operates in an idling state.

2. The method according to claim 1, characterized in that, the torque threshold (63) is determined based on the detected critical torque.

3. The method according to claim 2, characterized in that, other meshing interferences (62) are detected based on the measured torque, and other critical torque values that occur during these meshing interferences (62) are stored, wherein the torque threshold (63) is additionally determined based on the stored other critical torque values.

4. The method according to claim 2 or 3, characterized in that, during the initial commissioning of the drive system or during the manufacture of the drive system, an initial critical torque value is determined and stored, and the torque threshold (63) is additionally determined based on the initial critical torque value.

5. The method according to any one of the preceding claims, characterized in that, when the meshing interference (62) is detected, a torque curve and / or a load curve are additionally stored, and the torque threshold (63) is additionally determined based on the stored torque curve and / or load curve.

6. The method according to any one of the preceding claims, characterized in that, in order to control the motor (20), at least one control parameter, i.e., a control parameter that affects the acceleration behavior and / or braking behavior of the motor (20), is set according to the determined torque threshold (63).

7. A drive system having a motor (20) and a strain wave gear device (10), the strain wave gear device including a wave generator (13) coupled to the motor (20), a rigid outer ring (11) having internal teeth (1), and an elastically deformable transmission ring (12) having external teeth (2) that engage with the internal teeth (1) of the outer ring (11), wherein, the drive system is configured to perform the following method steps: Measuring the torque applied to the transmission ring (12) by means of a torque sensor (15), Detect meshing interference (62) based on the measured torque and store the critical torque value that has occurred during the meshing interference (62), Determine a torque threshold (63) that is less than or equal to the critical torque value, and Control the electric motor (20) such that the torque applied to the transmission ring (12) is below the torque threshold (63), Control the electric motor (20) such that, in the case where the torque threshold (63) or the stored critical torque value is exceeded, the electric motor operates in an idling state.

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