Method for controlling an output shaft in a drive unit

Abstract

The invention relates to a method (200) for controlling the angular position of an output shaft in a drive unit (100), comprising the steps of: - detecting a change in direction of the drive (5); - detecting the torque transmitted by the flexible ring (6.3) of the strain wave gear immediately after detecting the change in direction by a second sensor (12); - determining a drive period of the drive (5) until expected achievement of the transmitted torsion (14.1, 14.2) of the flexible ring (6.3) based on the first torque; - driving the drive shaft (4) by the drive (5) during the drive period; - detecting a change in the angular position of the output shaft immediately after the end of the drive period by a first sensor (11.1); - controlling the drive using the first sensor (11.1) following the drive period when the change in angular position is detected.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling the angular position of an output shaft in a drive unit having a drive shaft, a drive for driving the drive shaft, and a strain wave gear for transmission from the drive shaft to the output shaft, the strain wave gear having a wave generator operatively connected to the drive shaft, a flexible ring, and a toothed ring connected to the output shaft, the strain wave gear comprising a first sensor for detecting the angular position of the output shaft and a second sensor for detecting the torque transmitted by the flexible ring. The invention also relates to such a drive unit configured to perform the method, and to a robot comprising such a drive unit. [Background technology]

[0002] Drive units are known from the prior art and are used in robotics, particularly for moving robot arms used in industry, laboratory technology, or medical technology. For this purpose, the drive unit is equipped with a strain wave gear to enable a very high transmission ratio between the drive and the robot part to be moved for precise movement. The strain wave gear has a non-circular, in particular elliptical, cross section and a wave generator or wave producer extending into a flexible ring, also known as a flexspline, which is deformed over its entire circumference. The flexible ring has external toothing that engages with the internal toothing of a toothed ring configured as an outer ring only at two outer points of its deformation. Due to the circumferential deformation, the engagement points also rotate, and the number of teeth on the flexible ring and the number of teeth on the toothed ring differ, thereby setting the toothed ring to a rotational movement significantly slower than the rotational movement of the wave generator.

[0003] In this regard, the drive unit is controlled by a control method to move the output shaft to a target angular position as accurately as possible. In this regard, sensors are typically arranged on the drive shaft and the output shaft, serving as actual value transmitters for controlling the drive unit. The sensor on the drive shaft is used for coarse positioning, and the sensor on the output shaft is used for fine positioning. The provision of two sensors is particularly necessary because, when the drive shaft and thus the output shaft are driven, the flexible ring expands in the form of a torsion, especially during acceleration of the drive unit, and this expansion is superimposed on the correlation between the angular position of the drive shaft and the angular position of the output shaft. Therefore, it is impossible to control the output shaft sufficiently accurately using only one of the sensors. An electric motor, particularly an axial-flux motor, is typically used as the drive unit, and an incremental rotary encoder is used as the sensor. A corresponding drive unit is known, for example, from Korean Patent Publication No. 102061693.

[0004] Furthermore, a drive unit having a sensor for detecting the extension of the output shaft is known from JP 6334317. A servo motor with controllable torque is also known from JP 2020-196091. A device for detecting sensor failures is known from JP 5955447. Finally, a device for controlling a motor, the control parameters of which can be automatically set, is known from JP 2003-061377.

[0005] The drawback is that drive units with sensors on the output shaft and on the drive shaft are complex, expensive and require a lot of installation space. Summary of the Invention [Problem to be solved by the invention]

[0006] One object of the present invention is to propose a drive unit which does not have the above-mentioned drawbacks. This object is achieved by a method according to claim 1. Furthermore, this object is achieved by the subject matter of claim 6 and of claim 10. Preferred embodiments can be found in the dependent claims. [Means for solving the problem]

[0007] According to one aspect of the invention, a method for controlling the angular position of an output shaft in a drive unit as described in the introduction comprises the steps of: - detecting a change in the direction of the drive relative to a previous rotation; - detecting the torque transmitted by the flexible ring immediately after detecting the change in direction by the second sensor; - determining a period of time for which the drive device is driven until an expected transmission twist of the flexible ring is achieved based on the first torque; - driving the drive shaft with a drive device over a driving period; - detecting, by a first sensor, a change in the angular position of the output shaft immediately after the end of the driving period; - controlling the drive device using the first sensor following a drive period when a change in angular position is detected; Includes.

[0008] A change of direction means that the drive unit drives or has driven the drive shaft in a first direction before the change of direction, and drives the drive shaft in a second direction opposite to the first direction after the change of direction. A change of direction therefore involves braking and subsequent acceleration of the drive unit. In this respect, direction should always be understood as the direction of rotation. When the drive unit rotates in one direction, at least after an initial phase, the drive shaft, strain wave gear, or all components of the strain wave gear and output shaft also rotate in this direction. In this respect, the leading rotation of the drive unit, with respect to driving the output shaft in the first direction, can exist until just before the change of direction or can precede the change of direction in time.

[0009] When rotating in a first direction, the flexible ring experiences a torsion in the first direction. When rotating in a second direction after the change in direction, the torsion in the first direction of the flexible ring is reduced, and torsion accumulates in the second direction. If there is a time interval between the rotation in the first direction and the rotation in the second direction during which no torque is applied to the flexible ring, the torsion is reduced to a residual value and accumulates in the second direction starting from the residual value during the rotation in the second direction. During the reduction and / or increase of torsion, no or very little driving force is transmitted to the output shaft. Instead, the driving torque is converted into strain energy to accumulate the described torsion. As soon as the transmission torsion on the flexible ring is fully formed, the rotational movement of the output shaft corresponds linearly to the drive. In this regard, transmission torsion is understood to be the torsion of the flexible ring at which the input torque on the flexible ring corresponds to the output torque, i.e., no further torsion occurs.

[0010] The correlation between the torsion applied to the flexible ring and the torque transmitted by the flexible ring exhibits hysteresis during the transition between rotation in a first direction and rotation in a second direction. This means that the correlation between the two variables depends on the direction in which the change between the two rotations occurs. Starting from rotation in the first direction to rotation in the second direction, the course follows a first path, and starting from rotation in the second direction to rotation in the first direction, the course follows a second path. When a change in direction occurs, the correlation changes from the first path to the second path. If the paths coincide when the transmitted torsion is formed, the torsion can be determined at any time during the change in direction, regardless of the change in path. If the path is changed separately from the transmitted torsion, the change between paths occurs over an undefined intermediate path.

[0011] The present invention now recognizes that by considering the torque transmitted by the flexible ring immediately before a change in direction, particularly taking into account the known hysteresis behavior of the torsion of the flexible ring, it is possible to predict how far the drive device must be rotated in the second direction until the transmitted torsion in the second direction is achieved. The corresponding distance or time the drive device must be driven with a known drive force until the transmitted torsion is achieved is referred to herein as the drive period. With this information, it is possible to determine the correlation between the angular position of the drive device and the angular position of the output shaft without a measurable correlation between the drive device and the first sensor on the output shaft. More precisely, the time until the transmitted torsion is achieved, i.e., the drive period, is a control variable for the drive device. Therefore, using the first and second sensors, it is possible to establish a correlation between the angular position of the drive device and the angular position of the output shaft at any time, i.e., until and after the transmitted torsion is achieved according to the aforementioned prediction of the drive period, through the existing linear correlation. This means that the first and second sensors are sufficient to control the drive device. Therefore, no additional sensors are required to detect the angular position of the drive shaft, which simplifies the control of the drive unit and allows the drive unit to be constructed more compactly and cheaper to manufacture.

[0012] In particular, the present invention utilizes the knowledge that the correlation between the twist of the flexible ring and the torque transmitted by the flexible ring during a change in direction is found along a known path of the hysteresis curve, at least after the change in path. If the change in direction immediately follows a rotation in a first direction, particularly with a transmitted twist formed, the correlation will be found on a second path of the hysteresis curve upon detection, thereby allowing the present twist to be determined by detecting the torque. In this regard, it is known that when a transmitted twist is achieved in a second direction, the correlation after a change in direction will be found on the first path of the hysteresis curve, and the transmitted twist and transmitted torque are known. The angular interval between the two twist states through which the drive must be adjusted to twist the flexible ring until the transmitted twist is achieved is therefore known.

[0013] If the torsion of the flexible ring has already been reduced at the time of a change of direction, for example, if a period without any drive precedes this, a situation may exist in which the torsion at the time of the change of direction is found not along one of the known paths of the hysteresis curve, but between these known paths. In this regard, the exact correlation between the torsion of the flexible ring in this situation and the torque transmitted by the flexible ring is not precisely known. From this situation, the present invention can still achieve sufficiently accurate control of the drive by using information from the first and second sensors to assume a correlated hysteresis error and use this hysteresis error to estimate the torsion at the time of the change of direction. In this regard, it is known that a correlation is found between the first and second paths of the hysteresis curve, and therefore the hysteresis error is determined or can be determined by this limit. The transmitted torsion through which the flexible ring must be twisted remains known.

[0014] According to one aspect of the invention, the drive is driven starting from a change in direction over a drive period, and then a transmission twist is achieved. As soon as the transmission twist is achieved, the second sensor can be used to directly control the drive. In a particularly preferred embodiment, the drive unit operates in error mode until the drive period is completed, and if the drive period ends and no change in the angular position of the output shaft is detected by the first sensor at the end of the drive period, the drive is stopped and an error message is output. On the other hand, if a change in angle is detected as expected at the end of the drive period, the control system transitions to controlling the drive with the actual value of the first sensor as long as rotation is in the second direction.

[0015] In a further preferred embodiment, the actuation period is determined based on the first torque only if the first torque is outside a limit range. The detected torque is then assumed to be on the second path, which allows the torsion of the flexible ring to be determined in a sufficient manner. The limit range is determined in particular so as to be defined by a hysteresis curve between the point passing through the zero line of the torsion of the first path and the point passing through the zero line of the torsion of the second path.

[0016] In a further preferred embodiment, if the first torque is within a limit range, the actuation period is determined based on the first torque and based on a hysteresis error of the flexible ring. In this regard, the fact that the correlation between the twist and torque of the flexible ring is unknown within the limit range is circumvented by the circumstance that it is known that the correlation must be found within a certain range, i.e., between the first path and the second path. This range, known as the hysteresis error, is defined for each torque detected within the limit range, so that the known hysteresis error can be used to estimate the correlation between twist and torque.

[0017] In a preferred embodiment, the drive period is determined as the number of drive pulses. Such drive pulses are defined in particular with respect to a control signal of the drive device, particularly preferably a digital control signal. A linear correlation exists between the drive pulses and the angular distance the drive device rotates during the drive pulse. Thus, the number of drive pulses corresponds to the predetermined angular distance traveled by the drive device. Particularly advantageously, such drive pulses can directly correspond to pulses in a signal from a sensor, particularly the first sensor. In this regard, the first sensor is preferably configured as an incremental rotary encoder. The drive period as the number of drive pulses can be particularly easily derived from the detected torque and can be monitored by simply counting the drive device during operation over the drive period.

[0018] A further aspect of the invention relates to a drive unit for a robot having a drive shaft, a drive for driving the drive shaft, and a strain wave gear for transmission from the drive shaft to an output shaft, the strain wave gear having a wave generator operatively connected to the drive shaft, a flexible ring, and a toothed ring connected to the output shaft, the strain wave gear comprising a first sensor for detecting the angular position of the output shaft and a second sensor for detecting the torque transmitted by the flexible ring, the drive unit being configured to perform the method described above. The drive unit has the advantages described above for the method, in particular it can be configured without a sensor on the drive shaft, thereby making the drive unit simple, inexpensive and compact.

[0019] In one embodiment, the first and second sensors are connected to each other in a signal-enabled manner. In this way, the signals can be pre-combined in the sensors, and the combined signal is then transmitted to the control device via a single signal connection. In particular, the second sensor has corresponding data processing means, e.g., on a printed circuit board, for receiving the signals detected by the first and second sensors and, in particular, formatting them into suitable control signals before transmitting them to the control unit. In this way, the parallel connection of the first sensor with the control device and the parallel connection of the second sensor with the control device can also be omitted, thereby simplifying the drive unit. This is particularly advantageous when the control device is located in the drive unit away from the strain wave gear, e.g., at the opposite end.

[0020] In a further preferred embodiment, the first sensor is configured as an incremental rotary encoder. This allows the angular position of the output shaft to be reliably detected, and the sensor has a compact configuration. For example, the encoder can resolve to 16 bits.

[0021] In yet another preferred embodiment, the second sensor is arranged on the collar of the flexible ring, and the torque transmitted through the flexible ring can be acquired in a particularly advantageous manner at the collar, with the second sensor being arranged in particular as a printed circuit board on the collar, thus also having a compact configuration.

[0022] According to yet another aspect, the invention relates to a robot having a drive unit as described above, in which the method described above can be carried out with the advantages described above, allowing safe and precise positioning of the moving parts of the robot, while the robot is of simple, cheap and compact construction.

[0023] Further ways of improving the invention are illustrated below with the aid of the figures and in conjunction with the description of preferred exemplary embodiments of the invention. [Brief explanation of the drawings]

[0024] [Figure 1] 2 shows a cross section of a drive unit in the first embodiment. [Figure 2] 1 illustrates the correlation between the twist of a flexible ring and the torque transmitted by the flexible ring. [Figure 3] 1 shows a highly simplified representation of a flexible ring in several torsional states. [Figure 4] 1 shows the correlation between drive rotation and output shaft rotation. [Figure 5] 1 shows a diagram illustrating the sequence of a method according to an aspect of the invention; DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows a cross-sectional view of a drive unit 100, with a housing 2 defining the drive unit 100 on the outside. All components are rotationally symmetrical about an axis AX. In particular, the housing 2 is configured as a cylindrical sleeve. A drive shaft 4 is mounted inside the housing 2 by means of ball bearings 3.1 and 3.2 and can be driven by a drive unit 5 configured as an electric machine. The drive unit 5 is configured as an axial-flux motor and is formed by a rotor 5.1 located inside in the axial direction A and pressed onto the drive shaft 4, and two stators 5.2 and 5.3 located outside in the axial direction A. The stators 5.2 and 5.3 are pressed into a motor housing 5.4, which is pressed into the housing 2. Thus, the rotor 5.1 is non-rotatably connected to the drive shaft 4, and the stators 5.2 and 5.3 are non-rotatably connected to the housing 2.

[0026] Furthermore, a strain wave gear 6 is arranged on the first side 1.1 of the drive unit 100. The strain wave gear 6 converts the rotational movement of the drive shaft 4 into a slower rotational movement of an output shaft (not shown). The strain wave gear 6 comprises a wave generator 6.1, a flexible ring 6.3 (flexspline) mounted opposite the wave generator 6.1 via a ball bearing 6.2, and a toothed ring 6.4 (circular spline). The wave generator 6.1 is formed directly on the drive shaft 4, and the toothed ring 6.4 forms the output part of the strain wave gear 6 and is connected or can be connected to the output shaft (not shown). The toothed ring 6.4 is movably mounted relative to a first component fixed to the housing 2.1 by means of a rolling bearing 6.6 (shown only diagrammatically). The flexible ring 6.3 has a collar 6.5 and is thereby fixed between a first component fixed to the housing 2.1 and a second component fixed to the housing 2.2. The second component fixed to the housing 2.2 also holds the first ball bearing 3.1. The first component 2.1 and the second component 2.2 fixed to the housing 2 are each part of a strain wave gear 6 and are press-fit into the housing 2.

[0027] On a second side 1.2 of the drive unit 100 opposite the strain wave gear 6 in the axial direction A, adjacent to the drive 5, a bearing wall 8 is held in the housing 2, which holds a second ball bearing 3.2. Adjacent to the bearing wall 8 in the axial direction A, a control unit 10 is held on the bearing wall 8. The control unit 10 is configured rotationally symmetrical on the outside and is arranged coaxially with the drive shaft 4.

[0028] The strain wave gear 6 further includes a first sensor 11.1, which is arranged on a first component fixed to the housing 2.1 and interacts with a sensor target 11.2 arranged on the toothed ring 6.4. The sensor 11.1 is configured as an incremental rotary encoder and detects the angular position of the toothed ring 6.4 and, therefore, the angular position of the output shaft. The strain wave gear 6 further includes a second sensor 12, which is arranged on a collar 6.5 of the flexible ring 6.3 and extends between the collar 6.5 and a second component fixed to the housing 2.2. The second sensor 12 detects the torque applied to the flexible ring 6.3. The first sensor 11.1 is connected to the second sensor 12 by a first signal line 13.1, and the second sensor 12 is connected to the control unit 10 via a second signal line 13.2 extending through the housing 2, whereby signals containing information detected by the sensors 11.1, 12 are transmitted to the control unit 10 via the first signal line 13.1 and the second signal line 13.2.

[0029] FIG. 2 shows the correlation between the torsion of the flexible ring 6.3 and the torque transmitted by the flexible ring 6.3. Here, torque applied in the negative range of the X-axis corresponds to rotation of the drive unit 100 in a first direction, and torque applied in the positive range of the X-axis corresponds to rotation of the drive unit 100 in a second direction. In this context, maximum torsion occurs in both directions from a given torque and is referred to as the first transmitted torsion 14.1 or the second transmitted torsion 14.2. As shown in FIG. 2, when there is a change in direction between the first and second directions, the correlation follows a hysteresis curve. Thus, starting from a rotation in the first direction, the correlation follows a first path 15.1, and starting from a rotation in the second direction, the correlation follows a second path 15.2.

[0030] During a change of direction, e.g., from a first direction to a second direction, if the first torsional transmission 14.1 is fully formed, e.g., if a drive in the first direction occurs immediately before the change of direction, the correlation follows the first path and is always defined. The correlation is defined at the beginning and end of the change of direction when the first torsional transmission 14.1 is not fully formed, but a drive in the first direction nevertheless occurs immediately before the change of direction. The progression of the correlation during such a change of direction is shown by several circles starting from the first starting point 9.1. In this regard, the correlation passes through an undefined range to reach the first path 15.1 from the second path 15.2. The correlation is not defined at the beginning of the change of direction if no torque is applied, e.g., if no rotation occurs before the change of direction. The correlation is then found within the limit range 16. However, within this limit range 16, it is known that the actual twist is found only between the first path 15.1 and the second path 15.2. The distance between these two paths 15.1, 15.2 for a given torque is defined as the hysteresis error 17 and used to determine the drive period when detecting torque. The progression of this correlation during such a change in direction is shown by several squares beginning at the second starting point 9.2. In particular, part of the drive period is calculated to overcome the maximum hysteresis error, and part is calculated to arrive at the transmitted twist 14.2 from the hysteresis error; the two parts are then added together to form the actual drive period.

[0031] FIG. 3 shows, very diagrammatically, several representations of the torsion of the flexible ring 6.3 during a change of direction. In the first representation, a first transmission torsion 14.1 is formed. Starting from this state, a change of direction causes the torsion to first decrease through the second representation to the third representation, as shown in the fourth and fifth representations, and then build up to a second transmission torsion 14.2. Here, only the input side 18.1 of the flexible ring 6.3 rotates, while the output side 18.2 does not. Only when the second transmission torsion 14.2 is achieved in the fifth representation do the input side 18.1 and the output side 18.2 rotate synchronously again, as shown in the sixth representation.

[0032] Figure 4 shows the progression of the angular position of the drive shaft 4 in a first graph 19.1 and the progression of the angular position of the output shaft in a second graph 19.2, in each case showing the progression over time during a change of direction as shown in Figure 3. Here, the change in angular position of the drive shaft 4 corresponds to the rotation of the input side 18.1 of the flexible ring 6.3, and the angular position of the output shaft corresponds to the rotation of the output side 18.2 of the flexible ring 6.3. In this respect, the second graph 19.2 lags the first graph 19.1 by one phase 20.

[0033] FIG. 5 illustrates a sequence of a method 200 according to one embodiment of the present invention. In a first method step 21.1, the drive 5 receives a control signal for driving the drive shaft 4. This is followed by a second method step 21.2, which determines whether the direction of this drive is different from the previous drive or rotation. If so, there is a change in direction. In a third method step 21.3, the torque transmitted by the flexible ring 6.3 is then detected by the second sensor 12. In a fourth method step 21.4, it is then determined whether the detected torque is within or outside the limit range 16. If it is within the limit range 16, in a fifth method step 21.5, the number of drive pulses of the drive 5 is calculated as the drive period, which is derived from the number of drive pulses required to overcome the hysteresis error 17 and the number of drive pulses required to achieve the transmission torsion 14.1, 14.2 after overcoming the hysteresis error 17. Thereafter, in a sixth method step 21.6, driving of the drive unit 5 for a drive period is initiated. In a seventh method step 21.7, a drive period signal is generated indicating that the drive period is not yet complete. The drive period signal is deactivated after the drive period has elapsed. In an eighth method step 21.8, a change in the angular position of the output shaft is detected by the first sensor 11.1. If such an angular change exists, the drive period signal is terminated in a ninth step 21.9, after which control of the drive unit 5 based on the first sensor 11.1 is initiated in a tenth step 21.10, particularly using a control method, and in an eleventh method step 21.11, the output shaft is moved to a target position based on this control. In a twelfth method step 21.12, the method 200 ends.

[0034] If it is determined in eighth method step 21.8 that no change in angular position has been detected, a thirteenth method step 22.1 checks whether the drive period signal is still present. If this is the case, method 200 continues with seventh method step 21.7. If this is not the case, in fourteenth method step 22.2, the torque applied to flexible ring 6.3 is again detected. If a significant change is detected here compared to the torque detected immediately during the change in direction, method 200 continues with seventh method step 21.7. If no change in torque is detected, an error signal is generated in fifteenth method step 22.3, which causes drive unit 5 to be stopped in sixteenth method step 22.4, and method 200 then ends.

[0035] If in the fourth method step 21.4 it is detected that the detected torque is outside the limit range 16, in a seventeenth method step 23.1 the torsion present on the flexible ring 6.3 is determined from the detected torque based on the correlation shown in Figure 2, and in an eighteenth method step 23.2 the drive period is calculated from this torsion, after which the method 200 continues from the sixth method step 21.6. Furthermore, if in the second method step 21.2 a constant drive direction compared to the previous rotation is detected, the method 200 continues from the tenth method step 21.10. [Explanation of symbols]

[0036] 1.1 First Side 1.2 Second Side 2. Housing 2.1 First component fixed to the housing 2.2 Secondary component fixed to the housing 3.1 First ball bearing 3.2 Second Ball Bearing 4 drive shaft 5. Drive unit 5.1 Rotor 5.2 First Stator 5.3 Second Stator 5.4 Motor housing 6 Strain Wave Gear 6.1 Wave Generator 6.2 Ball bearings 6.3 Flexible Ring 6.4 Toothed ring 6.5 Color 6.6 Rolling bearings 8 Bearing wall 9.1 First Starting Point 9.2 Second Starting Point 10. Control Unit 11.1 First Sensor 11.2 Sensor Target 12 Second Sensor 13.1 First signal line 13.2 Second Signal Line 14.1 First Transmission Torsion 14.2 Secondary Torsion 15.1 First Path 15.2 Second Path 16 Restricted Range 17 Hysteresis Error 18.1 Flexible Ring Input Side 18.2 Flexible Ring Output Side 19.1 First graph 19.2 Second graph 20 Phase 21.1 First Method Step 21.2 Second Method Step 21.3 Third Method Step 21.4 Fourth Method Step 21.5 Fifth Method Step 21.6 Sixth Method Step 21.7 Seventh Method Step 21.8 Eighth Method Step 21.9 Ninth Method Step 21.10 Tenth Method Step 21.11 Eleventh Method Step 21.12 Twelfth Method Step 22.1 Thirteenth Method Step 22.2 Fourteenth Method Step 22.3 Fifteenth Method Step 22.4 Sixteenth Method Step 23.1 Seventeenth Method Step 23.2 18th method step 100 Drive Unit 200 ways AX axis

Claims

1. A method (200) for controlling the angular position of an output shaft in a drive unit (100), the drive unit (100) comprising a drive shaft (4), a drive device (5) for driving the drive shaft (4), and a strain wave gear (6) for transmission from the drive shaft (4) to the output shaft, the strain wave gear (6) comprising a wave generator (6.1) operatively connected to the drive shaft (4), a flexible ring (6.3), and a toothed ring (6.4) connected to the output shaft; The drive unit (100) further comprises a first sensor (11.1) for detecting the angular position of the output shaft, a second sensor (12) for detecting the torque transmitted by the flexible ring (6.3), and a control device for processing signals containing information detected by the first sensor (11.1) and the second sensor (12) and for sending control signals for controlling a drive (5), the method (200) comprising: - the control device sends a signal to change the direction of rotation of the drive (5) relative to a previous rotation; - detecting, by means of said second sensor (12), a first torque transmitted by said flexible ring (6.3) immediately after the signal for changing the direction of rotation is recognized; - the control device determines, based on the first torque, the duration of the drive of the drive unit (5) until a maximum twist (14.1, 14.2) is reached during a change of direction of rotation of the flexible ring (6.3); - driving the drive shaft (4) by means of the drive (5) by the control device during said driving period; - said first sensor (11.1) detecting the change in angular position of said output shaft immediately after the end of said driving period; - when a change in the angular position of the output shaft is detected by the first sensor (11.1) immediately after the end of the drive period, the control device controls the drive with the actual value of the first sensor (11.1); A method (200) comprising:

2. 2. A method (200) according to claim 1, characterized in that the drive (5) is stopped if there is no change in angular position after the end of the drive period.

3. 3. The method (200) of claim 1 or 2, characterized in that the drive period is determined based on the first torque only if the first torque is outside a limit range (16).

4. 2. The method (200) of claim 1, characterized in that the actuation period is determined based on the first torque and based on a hysteresis error (17) of the flexible ring (6.3) when the first torque is within a limit range (16).

5. 2. The method (200) of claim 1, wherein the drive period is determined as a number of drive pulses.

6. A drive unit (100) for a robot, comprising a drive shaft (4), a drive (5) for driving said drive shaft (4), and a strain wave gear (6) for transmission from said drive shaft (4) to an output shaft, said strain wave gear (6) comprising a wave generator (6.1) operatively connected to said drive shaft (4), a flexible ring (6.3), and a toothed ring (6.4) connected to said output shaft; The drive unit (100) further comprises a first sensor (11.1) for detecting the angular position of the output shaft, a second sensor (12) for detecting the torque transmitted by the flexible ring (6.3), and a control device for processing signals including information detected by the first sensor (11.1) and the second sensor (12) and for sending control signals for controlling a drive (5), wherein the drive unit (100) is configured to perform the method (200) of claim 1.

7. 7. A drive unit (100) according to claim 6, characterized in that the first sensor (11.1) and the second sensor (12) are connected to each other in a signal-effective manner.

8. 8. Drive unit (100) according to claim 6 or 7, characterized in that the first sensor (11.1) is configured as an incremental rotary encoder.

9. 7. A drive unit (100) according to claim 6, characterized in that the second sensor (12) is arranged on a collar (6.5) of the flexible ring (6.3).

10. A robot having a drive unit (100) according to claim 6.

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