ROBOT, DRIVE UNIT FOR A ROBOT AND POSITIONING METHOD

Abstract

A drive unit for a robot, having an input shaft, an input shaft drive motor and a strain wave gear mechanism for transmission to an output shaft. The strain wave gear mechanism has a wave generator which is operatively connected to the input shaft, a flexible ring and a toothed ring are connectable to the output shaft, a first sensor for detecting an angular position of the input shaft and a second sensor for detecting the angular position of the output shaft. In order to allow the drive unit to precisely adjust the angular position of the output shaft to each setpoint angular position, the drive unit has a third sensor for detecting an expansion of the flexible ring. A robot having such a drive unit and a method for precisely adjusting the angular position of the output shaft are also provided.

Claims

1. A drive unit for a robot, the drive unit comprising: a drive shaft; a drive motor for driving the drive shaft; a strain wave gear mechanism for transmission from the drive shaft to an output shaft, the strain wave gear mechanism having a wave generator operatively connected to the drive shaft, a flexible ring, and a toothed ring that is connectable to the output shaft; a first sensor for detecting an angular position of the drive shaft; a second sensor for detecting an angular position of the output shaft; and a third sensor for detecting an expansion of the flexible ring.

2. The drive unit according to claim 1, wherein the flexible ring has a radially extending collar, and the third sensor is arranged on the collar.

3. The drive unit according to claim 1, wherein the second sensor is arranged on the toothed ring.

4. A robot comprising at least one of the drive units according to claim 1.

5. A method for adjusting an angular position of an output shaft positioned by a drive motor via a drive shaft and a strain wave gear mechanism in of a drive unit, the method comprising: providing the drive unit having the strain wave gear mechanism for transmission from the drive shaft to the output shaft, the strain wave gear mechanism having a wave generator operatively connected to the drive shaft, a flexible ring, and a toothed ring that is connectable to the output shaft, a first sensor for detecting an angular position of the drive shaft, a second sensor for detecting an angular position of the output shaft, and a third sensor for detecting an expansion of the flexible ring; using a calibration method for determining angular distances of the drive shaft and the output shaft by the first, the second, and the third sensors at an acceleration over which there is a non-linear relationship between the angular position of the drive shaft and the angular position of the output shaft due to the expansion of the flexible ring; and using a positioning method and adjusting the angular position of the output shaft from an actual angular position to a target angular position with the second sensor as an actual value generator, and checking whether there is at least the determined angular distance of the output shaft between the actual angular position and the target angular position, and if this is not the case, rotating the output shaft until the actual angular position is spaced apart from the target angular position by at least the determined angular distance of the output shaft, and then adjusting the actual angular position to the target angular position using the second sensor.

6. The method according to claim 5, further comprising, in the calibration process, first, setting the expansion of the flexible ring to 0% and as the first angular positions, the angular position of the drive shaft is detected by the first sensor and the angular position of the output shaft is detected by the second sensor, then accelerating the output shaft in a defined manner in a first direction of rotation to a first speed, wherein the angular position of the drive shaft is detected by the first sensor and the angular position of the output shaft is detected as the second angular positions by the second sensor as soon as the third sensor detects the continuous expansion of the flexible ring; and defining the distance between the first detected angular position and the second detected angular position as codirectional angular distances.

7. The method according to claim 6, further comprising, subsequently, stopping the output shaft and detecting the third angular positions and the angular position of the drive shaft by means of the first sensor and detecting the angular position of the output shaft by the second sensor; then rotating the output shaft in a second direction of rotation and again stopping the output shaft as soon as the third sensor detects the expansion of the flexible ring of 0%, wherein at rest, the angular position of the drive shaft is detected as the fourth angular positions by the first sensor and the angular position of the output shaft is detected by the second sensor; then accelerating the output shaft in a defined manner in the second direction, wherein the angular position of the drive shaft is detected by the first sensor and the angular position of the output shaft is detected by the second sensor as the fifth angular positions as soon as the third sensor detects an unchanged expansion of the flexible ring; and, defining the distance between the third detected angular position and the fifth detected angular position as opposed angular distances.

8. The method according to claim 7, wherein a residual expansion is a difference between the distance between the third detected angular position and the fourth detected angular position of the drive shaft and a distance between the third detected angular position and the fourth detected angular position of the output shaft.

9. The method according to claim 5, wherein in the positioning process, the output shaft is rotated in a same direction of rotation as in an immediately preceding rotation, to space the actual angular position apart by at least the determined angular distance from a setpoint angular position.

10. The method according to claim 9, wherein in the positioning method, when checking the distance between the actual angular position and the target angular position, depending on the direction of rotation in a previous rotation of the output shaft, a codirectional or an opposite angular distance is taken as a basis.

11. A drive unit for a robot, the drive unit comprising: a drive motor having a drive shaft; a strain wave gear mechanism having a wave generator connected to the drive shaft, a toothed ring connected to an output shaft, and a flexible ring, between the wave generator and the toothed ring; a first sensor for detecting an angular position of the drive shaft; a second sensor for detecting an angular position of the output shaft; and a third sensor for detecting an expansion of the flexible ring.

12. The drive unit according to claim 11, wherein the first, second, and third sensors comprise rotary encoders.

13. The drive unit according to claim 11, wherein the flexible ring has a radially extending collar, and the third sensor is arranged on the collar.

14. The drive unit according to claim 11, wherein the second sensor is arranged on the toothed ring.

15. A robot comprising at least one of the drive units according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further measures to improve the disclosure are illustrated below together with the description of preferred exemplary embodiments of the disclosure using the figures. In the figures,

[0029] FIG. 1 shows a schematic cross-section of a drive unit according to the disclosure;

[0030] FIG. 2 shows a plot of output shaft angular position on the first y-axis versus drive shaft angular position on the x-axis and flex ring expansion on the second y-axis under acceleration;

[0031] FIG. 3 shows a plot of output shaft angular position on the first y-axis versus drive shaft angular position on the x-axis, and torque in the flexible ring on the second y-axis under acceleration;

[0032] FIG. 4 shows a schematic representation of a positioning method according to the disclosure for the output shaft with a sufficient distance between the actual angular position and the setpoint angular position with codirectional rotation;

[0033] FIG. 5 shows a schematic representation of a positioning method according to the disclosure for the output shaft when the distance between the actual angular position and the desired angular position is sufficient with rotation in the opposite direction;

[0034] FIG. 6 shows a schematic representation of a positioning method according to the invention for the output shaft when the distance between the actual angular position and the desired angular position is insufficient with codirectional rotation;

[0035] FIG. 7 shows a schematic representation of a positioning method according to the invention for the output shaft when the distance between the actual angular position and the desired angular position is insufficient with rotation in the opposite direction; and

[0036] FIG. 8 shows a greatly simplified representation of a robot arm with a drive unit according to the disclosure.

DETAILED DESCRIPTION

[0037] FIG. 1 shows a drive unit 1 having a housing 2 delimiting it on the outside. Within the housing 2, a drive shaft 3 is mounted by means of ball bearings 10a, 10b, which can be driven by a drive motor 4 with a stator 4a and a rotor 4b. Furthermore, a strain wave gear mechanism 5 is arranged on the drive shaft 3, which converts a rotational movement of the drive shaft 3 into a slower rotational movement of an output. The strain wave gear mechanism 5 has a high transmission ratio and rigidity. A first sensor 6a is also arranged on the drive shaft 3 and detects an angular position .sub.i of the drive shaft 3. The first sensor 6a is designed here as a rotary encoder. A brake 7 also acts on the drive shaft 3, by means of which the drive shaft 3 can be braked.

[0038] The strain wave gear mechanism 5 has a wave generator 5a, a flexible ring 5c mounted opposite the wave generator 5a by means of a ball bearing 5b, and a toothed ring 5d. The wave generator 5a is formed directly on the drive shaft 3, while the toothed ring 5d forms the output of the strain wave gear mechanism 5 and is connected or can be connected to an output shaft 11. A second sensor 6b is arranged on the toothed ring 5d, which sensor detects an angular position .sub.o of the toothed ring 5d, which is the angular position of the output shaft 11 at the same time. For this purpose, the second sensor 6b detects the angular position .sub.o of the toothed ring 5d in relation to a corresponding sensor part 6d on the stationary component 8 on the housing side. The flexible ring 5c has a collar 5e by means of which it is fixed to the housing 2. A third sensor 6c is arranged on the collar 5e, by means of which an expansion in the sense of a torsion of the flexible ring 5c is detected. For this purpose, a relative displacement of a measuring point on the flexible ring 5c in relation to the stationary component 9 on the housing side is detected.

[0039] FIGS. 2 and 3 show the course of the angular position .sub.i of the drive shaft 3 and the angular position .sub.o of the output shaft 11 (or the toothed ring 5d) as well as the course of the expansion of the flexible ring in FIG. 2 and the course of the torque T in the flexible ring 5c in FIG. 3 during acceleration. The torque T or the expansion w in the flexible ring 5c builds up during the acceleration up to a maximum expansion .sub.max and a maximum torque T.sub.max, wherein the angular position .sub.o of the output shaft 11 does not yet change or the angular position .sub.i follows the drive shaft 3. If the acceleration reaches a constant target speed, the torque T or the resulting expansion w decreases until it reaches continuous values .sub.k or T.sub.k. Up to this point there is a non-linear relationship between the angular position .sub.i of the drive shaft 3 and the angular position .sub.o of the output shaft 11, which makes it impossible to precisely adjust a positioning of the output shaft 11 using only the values of the second sensor 6b as the actual value generator. From this point there is again a linear relationship between the angular position .sub.i of the drive shaft 3 and the angular position .sub.o of the output shaft 11. All of the angular positions .sub.o of the output shaft 11 lying therebehind can be adjusted by means of the second sensor 6b as an actual value generator.

[0040] In the case of codirectional acceleration, there is an angular distance .sub.i,gl of the drive shaft 3 between the zero point and the point at which .sub.k or T.sub.k is reached, over which there is a non-linear relationship between the angular position .sub.i of the drive shaft and the angular position .sub.o of the output shaft 11 due to an expansion of the flexible ring 5c. For the output shaft 11, there is an angular distance .sub.o,gl between the zero point and the point at which .sub.k or T.sub.k is reached, over which there is a non-linear relationship between the angular position of the drive shaft and the angular position of the output shaft 11 due to an expansion of the flexible ring 5c.

[0041] In the case of an opposite acceleration, the residual expansion, which corresponds to the continuous expansion .sub.k, must also be reduced from the previous rotation. This then results in an angular distance .sub.i,ge of the drive shaft 3 between the point .sub.iv corresponding to the residual elongation and the point at which .sub.k is reached, over which there is a non-linear relationship between the angular position .sub.i of the drive shaft 3 and the angular position .sub.o of the output shaft 11 due to an expansion of the flexible ring 5c. For the output shaft 11, there is an angular distance .sub.o,ge between the point .sub.ov corresponding to the residual expansion and the point at which .sub.k is reached, over which there is a non-linear relationship between the angular position .sub.i of the drive shaft 3 and the angular position .sub.o of the output shaft 11 due to an expansion of the flexible ring 5c.

[0042] FIGS. 4 to 7 show positioning methods of the output shaft 11 for different cases depending on whether at least the angular distance .sub.o,gl, .sub.o,ge of the output shaft 11 lies between the actual angular position and the target angular position (FIGS. 4 and 5) or not (FIGS. 6 and 7). Furthermore, cases are considered depending on whether the target angular position is located in the same direction (FIGS. 4 and 6) or in the opposite direction (FIGS. 5 and 7) as seen from the actual angular position. The actual angular position is shown as a round dot and the target angular position as a square dot.

[0043] In the case according to FIG. 4, in which the target angular position is rectified to the actual angular position, it is checked whether the actual angular position and the target angular position are spaced apart by at least the rectified angular distance .sub.o,gl of the output shaft 11. Since it is determined that this is the case, the output shaft 11 is immediately moved to the target angular position.

[0044] In the case according to FIG. 5, in which the target angular position is in the opposite direction to the actual angular position, it is checked whether the actual angular position and the target angular position are spaced apart from one another by at least the opposite angular distance .sub.o,ge of the output shaft 11. Since it is determined that this is the case, the output shaft 11 is immediately moved to the target angular position.

[0045] In the case according to FIG. 6, in which the target angular position is rectified to the actual angular position, it is checked whether the actual angular position and the target angular position are spaced apart by at least the rectified angular distance .sub.o,gl of the output shaft 11. Since it is established that this is not the case, the output shaft 11 is first moved in the codirectional direction of rotation to a new actual angular position which is spaced from the setpoint angular position by at least the opposite angular distance .sub.o,ge of the output shaft 11. The output shaft 11 is then moved to the desired angular position.

[0046] In the case according to FIG. 7, in which the target angular position is in the opposite direction to the actual angular position, it is checked whether the actual angular position and the target angular position are spaced apart from one another by at least the opposite angular distance .sub.o,ge of the output shaft 11. Since it is established that this is not the case, the output shaft 11 is first moved in the codirectional direction of rotation to a new actual angular position which is spaced apart from the setpoint angular position by at least the opposite angular distance .sub.o,ge of the output shaft 11. The output shaft 11 is then moved to the desired angular position.

[0047] FIG. 8 shows a robot 15 in the form of a robot arm having the drive unit 1 for driving the output shaft 11. A first further shaft 13a and a second further shaft 13b are connected to the drive unit 1 via a first joint 12a and a second joint 12b. By way of example, a gripping tool 14 is arranged on the second further shaft 13b. Further drive devices 1 according to the disclosure can be arranged in the joints 12a, 12b to control the further shafts 12a, 12b in each case.

LIST OF REFERENCE SYMBOLS

[0048] 1 Drive unit [0049] 2 Housing [0050] 3 Drive shaft [0051] 4 Drive motor [0052] 4a Stator [0053] 4a Rotor [0054] 5 Strain wave gear mechanism [0055] 5a Wave generator [0056] 5b Ball bearing [0057] 5c Flexible ring [0058] 5d Gear ring [0059] 5e Flexible ring collar [0060] 6a First sensor [0061] 6b Second sensor [0062] 6c Third sensor [0063] 6d Sensor part [0064] 7 Brake [0065] 8 Fixed housing-side component [0066] 9 Fixed housing-side component [0067] 10a Ball bearing [0068] 10b Ball bearing [0069] 11 Output shaft [0070] 12a First joint [0071] 12b Second joint [0072] 13a First further shaft [0073] 13b Second further shaft [0074] 14 Gripping tool [0075] 15 Robots [0076] .sub.i Angular positions of the drive shaft [0077] .sub.iv Point corresponding to residual expansion [0078] .sub.i,gl Codirectional angular distance of the drive shaft [0079] .sub.i,ge Opposing angular distance of the drive shaft [0080] .sub.o Angular positions of the output shaft [0081] .sub.ov Point corresponding to residual expansion [0082] .sub.o,gl Codirectional angular distance of the output shaft [0083] .sub.o,ge Opposite angular distance of the output shaft [0084] Expansion of the flexible ring [0085] .sub.max Maximum expansion of the flexible ring [0086] k Continuous expansion of the flexible ring [0087] T Torque in the flexible ring [0088] T.sub.max Maximum torque in the flexible ring [0089] Tk Continuous torque in flexible ring