CALIBRATION OF AN IMPEDANCE CONTROL OF A ROBOT MANIPULATOR

Abstract

A method of calibrating an impedance control of a robot manipulator, the method including: deflecting a reference point of the robot manipulator from a zero position to a deflected position, wherein the robot manipulator applies a counterforce dependent on a spring constant of the impedance control and on a first determined deflection, wherein the first determined deflection is determined based on joint angles detected by joint angle sensors of the robot manipulator; detecting a second determined deflection by an external position measuring unit; and adapting the spring constant of the impedance control in such a way that the counterforce applied by the robot manipulator corresponds to a predetermined counterforce of the robot manipulator based on the second determined deflection.

Claims

1. A method of calibrating an impedance control of a robot manipulator, wherein the robot manipulator comprises a plurality of links connected to one another by joints, the method comprising: deflecting a reference point of the robot manipulator from a zero position to a deflected position, wherein the robot manipulator applies a counterforce dependent on a spring constant of the impedance control and on a first determined deflection of the reference point of the robot manipulator, wherein the first determined deflection is determined based on joint angles detected by means of joint angle sensors of the robot manipulator; detecting a second determined deflection of the reference point of the robot manipulator in its deflected position by an external position measuring unit; and adapting the spring constant of the impedance control in such a way that the counterforce applied by the robot manipulator corresponds to a predetermined counterforce of the robot manipulator based on the second determined deflection.

2. The method according to claim 1, wherein after deflection of the reference point of the robot manipulator from the zero position to the deflected position, the method comprises: holding the reference point of the robot manipulator in the deflected position; detecting the second determined deflection while the reference point of the robot manipulator is being held in the deflected position; and adapting the spring constant of the impedance control in such a way that the counterforce applied by the robot manipulator corresponds to a stationary counterforce of the robot manipulator based on the second determined deflection.

3. The method according to claim 1, wherein the method further comprises: determining a speed of the reference point of the robot manipulator at at least one location of deflection of the reference point by an external speed measuring unit, and adapting a damping constant of the impedance control in such a way that the counterforce applied by the robot manipulator corresponds to the predetermined counterforce of the robot manipulator based on the second determined deflection and based on the speed of the reference point as determined.

4. The method according to claim 1, wherein the spring constant is constant over the deflection of the reference point between its zero position and its deflected position.

5. The method according to claim 1, wherein the spring constant is dependent on a current deflection of the reference point of the robot manipulator.

6. The method according to claim 1, wherein adaptation of the spring constant of the impedance control takes place in modal coordinates.

7. The method according to claim 1, wherein the reference point of the robot manipulator is deflected from the zero position to the deflected position by manual guiding of the robot manipulator by a user.

8. The method according to claim 1, wherein the reference point of the robot manipulator is deflected from the zero position to the deflected position by corresponding activation of actuators of the robot manipulator.

9. The method according to claim 1, wherein the method comprises repeating the deflecting the reference point of the robot manipulator, detecting the second determined deflection, and adapting the spring constant of the impedance control for a plurality of different deflection ranges and/or in different deflection directions of the reference point of the robot manipulator, wherein the spring constant is adapted in dependence on a respective deflection range and/or a respective deflection direction.

10. A robot system comprising: a robot manipulator; and a control unit configured to carry out an impedance control of the robot manipulator, wherein the impedance control is calibrated by the control unit configured; deflect a reference point of the robot manipulator from a zero position to a deflected position, wherein the robot manipulator applies a counterforce dependent on a spring constant of the impedance control and on a first determined deflection of the reference point of the robot manipulator, wherein the first determined deflection is determined based on joint angles detected by joint angle sensors of the robot manipulator; detect a second determined deflection of the reference point of the robot manipulator in its deflected position by an external position measuring unit, and adapt the spring constant of the impedance control in such a way that the counterforce applied by the robot manipulator corresponds to a predetermined counterforce of the robot manipulator based on the second determined deflection.

11. The robot system according to claim 10, wherein after deflection of the reference point of the robot manipulator from the zero position to the deflected position, the control unit is configured to: hold the reference point of the robot manipulator in the deflected position; detect the second determined deflection while the reference point of the robot manipulator is being held in the deflected position; and adapt the spring constant of the impedance control in such a way that the counterforce applied by the robot manipulator corresponds to a stationary counterforce of the robot manipulator based on the second determined deflection.

12. The robot system according to claim 10, wherein the control unit is configured to: determine a speed of the reference point of the robot manipulator at at least one location of deflection of the reference point by an external speed measuring unit, and adapt a damping constant of the impedance control in such a way that the counterforce applied by the robot manipulator corresponds to the predetermined counterforce of the robot manipulator based on the second determined deflection and based on the speed of the reference point as determined.

13. The robot system according to claim 10, wherein the spring constant is constant over deflection of the reference point between its zero position and its deflected position.

14. The robot system according to claim 10, wherein the spring constant is dependent on a current deflection of the reference point of the robot manipulator.

15. The robot system according to claim 10, wherein adaptation of the spring constant of the impedance control takes place in modal coordinates.

16. The robot system according to claim 1, wherein the reference point of the robot manipulator is deflected from the zero position to the deflected position by manual guiding of the robot manipulator by a user.

17. The robot system according to claim 10, wherein the reference point of the robot manipulator is deflected from the zero position to the deflected position by corresponding activation of actuators of the robot manipulator.

18. The robot system according to claim 10, wherein the control unit is configured to repeat deflection of the reference point of the robot manipulator, detection of the second determined deflection, and adaptation of the spring constant of the impedance control for a plurality of different deflection ranges and/or in different deflection directions of the reference point of the robot manipulator, wherein the spring constant is adapted in dependence on a respective deflection range and/or a respective deflection direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the drawings:

[0033] FIG. 1 shows a method according to an example embodiment of the invention;

[0034] FIG. 2 shows a robot manipulator on which the method according to FIG. 1 is carried out; and

[0035] FIG. 3 shows a robot system having a robot arm according to a further example embodiment of the invention.

[0036] The illustrations in the figures are schematic and not to scale.

DETAILED DESCRIPTION

[0037] FIG. 1 shows a method for calibrating an impedance control of a robot manipulator 1, wherein the robot manipulator 1 has a plurality of links connected to one another by joints. In a step S1, a reference point 3 on an end effector of the robot manipulator 1 is deflected from a zero position into a deflected position. The robot manipulator 1 is guided manually, and the actuators 11 generate a counterforce against the deflection. Naturally, the reference point 3 remains at least briefly in a rest position before the robot manipulator 1 is released, without having a speed. In this rest position, the respective deflection is detected. The counterforce of the robot manipulator 1 is generated by an impedance control, which has a spring constant in the form of a diagonal matrix, and by the level of a first determined deflection of the reference point 3 of the robot manipulator. The first determined deflection is determined based on joint angles detected by joint angle sensors 5 of the robot manipulator 1. In step S2, the same deflection is additionally detected as the second determined deflection of the reference point 3 of the robot manipulator 1 in its deflected position. This is carried out using an external position measuring unit 7, which includes multiple cameras. Finally, in step S3, this is followed by adapting the spring constant of the impedance control in such a way that the counterforce applied by the robot manipulator 1 corresponds to a predetermined counterforce of the robot manipulator 1 based on the second determined deflection. The adapted spring constant is assigned to the position of the reference point 3 of the robot manipulator 1 in its zero position and stored with the assignment. Steps S1-S3 are repeated for various positions of the reference point 3 of the robot manipulator 1 in its zero position in each case, resulting in a three-dimensional grid of positions for the reference point 3 of the robot manipulator 1 in its respective zero position, wherein a separately adapted spring constant is available for each of the grid points. When the robot manipulator 1 is released, it moves back into its zero position in a damped movement due to the counterforce of the actuators 11. For the adaptation of the damping constant similarly to the spring constant, which is selected to achieve an aperiodic limiting case of the homogeneous solution of the impedance control formulated as a differential equation, a speed of the reference point 3 of the robot manipulator 1 is determined in step S4 at a location of the still deflected reference point 3 while it swings back into the zero position by the external speed measuring unit 9, which corresponds to the position measuring unit 7 and generates the time derivative of the measured position curve over time of the reference point 3 of the robot manipulator 1. This is followed by step S5 of adapting the damping constant of the impedance control in such a way that the counterforce applied by the robot manipulator 1 corresponds to a predetermined counterforce of the robot manipulator 1 based on the second determined deflection at the location while it swings back and based on the speed determined at this location.

[0038] FIG. 2 shows a robot manipulator 1 on which the method according to FIG. 1 is carried out. The steps of the method will therefore not be repeated, instead reference is made to the description of FIG. 1. The components and units shown are also explained therein.

[0039] FIG. 3 shows a robot system 100 having a robot arm 101 and having a control unit 102, wherein the control unit 102 is designed to carry out an impedance control of the robot arm 101, wherein the impedance control is calibrated according to the method according to FIG. 1 for the robot manipulator 1 according to FIG. 2. The user of the robot system 100 can optionally read in and use the data series of the calibrated spring constant assigned to the three-dimensional grid of positions for the reference point 3 and the calibrated damping constant on the control unit 102 of the robot arm 101. This is possible for a plurality of robot systems 100 having a respective robot arm 101 and having a respective control unit 102, but is shown as an example for only a single robot system 100 in FIG. 3.

[0040] Although the invention has been further illustrated and described in detail by way of preferred example embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a plurality of possible variations exists. It is also clear that embodiments mentioned by way of example actually only represent examples, which are not to be construed in any way as limiting the scope of protection, the possible applications, or the configuration of the invention. Rather, the preceding description and the description of the figures enable a person skilled in the art to implement the example embodiments, wherein a person skilled in the art, knowing the disclosed concept of the invention, can make various changes, for example, with respect to the function or arrangement of individual elements cited in an example embodiment, without leaving the scope of protection as defined by the claims and their legal equivalents, such as more extensive explanations in the description.

LIST OF REFERENCE NUMERALS

[0041] 1 robot manipulator [0042] 3 reference point [0043] 5 joint angle sensors [0044] 7 external position measuring unit [0045] 9 external speed measuring unit [0046] 11 actuators [0047] 100 robot system [0048] 101 robot arm [0049] 102 control unit [0050] S1 deflect [0051] S2 detect [0052] S3 adapt [0053] S4 determine [0054] S5 adapt