Robotic system for moving a payload with minimal payload sway and increased positioning accuracy

Patent metadata

Field	Value
Publication number	US-12005583-B2
Application number	US-202217666699-A
Country	US
Kind code	B2
Filing date	Feb 8, 2022
Priority date	Feb 8, 2022
Publication date	Jun 11, 2024
Grant date	Jun 11, 2024

Abstract

A robotic system for use with a payload includes a robot, a passive compliance mechanism, position sensors, and an electronic control unit (ECU). Actuated joints of the robot provide the robotic system with actuated degrees of freedom (DOF). The compliance mechanism is connected to the robot and payload, and has unactuated joints providing the robotic system with unactuated DOF. The sensors measure joint positions of the joints. The ECU has a trajectory generator block which generates a payload trajectory signal in response to dynamic control inputs, and an impedance control unit (ICU) applying damping and stiffness parameters to the payload trajectory signal to generate an initial velocity command. A stiction compensation block allows the robotic system to generate a velocity offset, and applies the velocity offset to the initial velocity command to produce a final velocity command for the robot.

First claim

What is claimed is:

1. A robotic system for use with a payload, comprising:
a robot having actuated joints collectively providing the robotic system with multiple actuated degrees of freedom (DOF);
a compliance mechanism coupled in series with the robot and connectable to the payload, the compliance mechanism having unactuated joints collectively providing the robotic system with multiple unactuated DOF;
a set of position sensors collectively configured to measure corresponding joint positions of the actuated joints and the unactuated joints; and
an electronic control unit (ECU) in communication with the robot and with the set of position sensors, wherein the ECU is programmed with:
a trajectory generator block operable for generating a payload trajectory signal in response to at least one dynamic control input, including a maximum permissible velocity and a maximum permissible acceleration of the payload and the robot;
an impedance control unit (ICU) configured to generate an initial velocity command in response to the payload trajectory signal that (i) increases a damping coefficient (b) until an overdamped behavior of the robot is achieved that eliminates sway of the payload, and (ii) decreases a stiffness coefficient (k) sufficiently to prevent overshoot of the maximum permissible velocity; and
a stiction compensation block configured to allow the robotic system to generate a velocity offset, and to apply the velocity offset to the initial velocity control signal from the ICU to produce a final velocity control signal, wherein the velocity offset is configured to minimize a position error of the robot and payload due to static friction, wherein the ECU is operable for transmitting the final velocity control signal to the robot to thereby cause the robot to move the payload without the sway of the payload.

2. The robotic system of claim 1 , wherein the ECU is configured to generate the payload trajectory signal such that an actual velocity of the payload and the robot does not exceed the maximum permissible velocity.

3. The robotic system of claim 1 , wherein the ECU is configured to generate the payload trajectory signal such that an actual acceleration of the payload and the robot does not exceed the maximum permissible acceleration.

4. The robotic system of claim 1 , wherein the stiction compensation block is configured to calculate the velocity offset as a function of a maximum displacement of the compliance mechanism.

5. The robotic system of claim 4 , wherein the stiction compensation block is configured to process the maximum displacement of the compliance mechanism through a saturation block, the saturation block being configured to apply maximum and minimum limits to the maximum displacement to generate a limited displacement value.

6. The robotic system of claim 5 , wherein the stiction compensation block includes a low-pass filter operable for receiving the limited displacement value and a cutoff frequency setting, and to generate the velocity offset using the limited displacement value and the cutoff frequency setting.

7. The robotic system of claim 1 , wherein the robot comprises a multi-axis industrial robot.

8. The robotic system of claim 1 , wherein the robot comprises an overhead rail system or trolley.

9. The robotic system of claim 1 , wherein the compliance mechanism includes multiple interconnected linkages, such that the compliance mechanism comprises an articulated compliance mechanism.

10. The robotic system of claim 1 , wherein the ICU is configured to provide the overdamped behavior, and to avoid a velocity overshoot of the robot and the payload via the overdamped behavior.

11. A method for controlling a robotic system for use with a payload, comprising:
connecting a compliance mechanism in series with a robot;
connecting the payload to the compliance mechanism, wherein the compliance mechanism has unactuated joints collectively providing the robotic system with multiple unactuated degrees of freedom (DOF), and wherein the robot includes actuated joints collectively providing the robotic system with multiple actuated DOF;
measuring corresponding joint positions of the actuated joints and the unactuated joints via a set of position sensors; and
via an electronic control unit (ECU) in communication with the robot and the set of position sensors:
receiving dynamic control inputs via a trajectory generator block of the ECU, including receiving a desired position command of the payload and the robot, a maximum permissible velocity of the payload and the robot, and a maximum permissible acceleration of the payload and the robot;
generating a payload trajectory signal in response to the dynamic control inputs using the trajectory generator block of the ECU;
generating an initial velocity command in response to the payload trajectory signal, including (i) increasing a damping coefficient (b) until an overdamped behavior of the robot is achieved that eliminates sway of the payload, and (ii) decreasing a stiffness coefficient (k) sufficiently to prevent overshoot of the maximum permissible velocity, via an impedance control unit (ICU) of the ECU;
generating a velocity offset using a stiction compensation block of the ECU, wherein the velocity offset is configured to minimize position error of the robot and payload due to static friction;
applying the velocity offset to the initial velocity control signal to produce a final velocity control signal; and
transmitting the final velocity control signal to the robot to thereby cause the robot to move the payload without the sway of the payload.

12. The method of claim 11 , further comprising:
generating the payload trajectory signal, such that corresponding actual velocities of the payload and the robot do not exceed the maximum permissible velocity.

13. The method of claim 11 , further comprising:
generating the payload trajectory signal, such that corresponding actual accelerations of the payload and the robot do not exceed the maximum permissible acceleration.

14. The method of claim 11 , further comprising: calculating the velocity offset via the stiction compensation block as a function of a maximum displacement of the compliance mechanism.

15. The method of claim 14 , further comprising: processing the maximum displacement of the compliance mechanism through a saturation block of the ECU, including applying maximum and minimum limits to the maximum displacement, thereby generating a limited displacement.

16. The method of claim 15 , further comprising:
receiving the limited displacement and a cutoff frequency setting via a low-pass filter of the stiction compensation block; and
generating the velocity offset via the stiction compensation block using the limited displacement and the cutoff frequency setting.

17. The method of claim 11 , wherein connecting the compliance mechanism to the robot includes connecting the compliance mechanism to an overhead rail system or trolley, or to a multi-axis serial robot.

18. The method of claim 11 , wherein the compliance mechanism comprises an articulated compliance mechanism having a plurality of linkages interconnected via the unactuated joints, and wherein connecting the compliance mechanism to the robot includes connecting the articulated compliance mechanism to the robot.

19. A non-transitory computer-readable storage medium on which is recorded instructions executable by a processor of an electronic control system of a robotic system, the robotic system having a compliance mechanism to a payload, wherein ex

Assignees

• Gm Global Tech Operations Llc

Inventors

• Abdallah Muhammad E

Classifications

• B25J9/1664

  characterised by motion, path, trajectory planning · CPC title

• B25J9/1633 Primary

  compliant, force, torque control, e.g. combined with position control · CPC title

• G05B2219/39338

  Impedance control, also mechanical · CPC title

• G05B2219/40272

  Manipulator on slide, track · CPC title

• G05B2219/40241

  Underactuated robot, has less actuators than number of DOF · CPC title