Method for determining a weight and a center of gravity of a robot manipulator load

Patent metadata

Field	Value
Publication number	US-12311538-B2
Application number	US-202017420017-A
Country	US
Kind code	B2
Filing date	Jan 22, 2020
Priority date	Jan 23, 2019
Publication date	May 27, 2025
Grant date	May 27, 2025

Abstract

A method of determining a weight and a center of gravity of a load for a robot manipulator, the method including: gripping the load using an end effector; moving the load into a number n of distinct static poses; determining an external wrench wrench F ext for each of the n static poses; determining, in a base coordinate system, at least components of each external wrench F ext that indicate the external forces; determining a particular estimation of the weight of the load from a particular component pointing in a direction of a gravity vector from among the components of each external wrench F ext that indicate the external forces in the base coordinate system, and from a magnitude of the gravity vector; determining the weight of the load by averaging respective estimations of the weight of the load; determining estimations of coordinates of the center of gravity of the load for each of the n static poses based on the weight of the load or the particular estimation of the weight of the load determined for a particular static pose and based on the components of the external wrench F ext that indicate externally acting torques; and determining the center of gravity of the load by averaging respective estimations of coordinates of the center of gravity.

First claim

The invention claimed is:

1. A method of determining a weight and a center of gravity of a load for a robot manipulator, wherein the robot manipulator is arranged on a base and comprises a plurality of links, the links connected to one another by joints and movable or rotatable relative to one another by actuators on the joints, wherein the robot manipulator further comprises an end effector to grip the load, the method comprising:
gripping the load by the end effector,
moving the load into a number n of distinct static poses, wherein the load is moved into the number n of distinct static poses only by controlling a number k of actuators, with k≤n, wherein the number k is a predefined quantity and the k actuators are arranged on or assigned to k joints that are closest to the end effector;
determining an external wrench F ext for each of the n static poses, wherein a respective external wrench Fest indicates external forces and torques acting on the robot manipulator;
determining, in a base coordinate system, at least components of each external wrench F ext that indicate the external forces, wherein the base coordinate system is a Cartesian coordinate system and arranged in a body-fixed manner on the base of the robot manipulator, and an axis of the base coordinate system is parallel to a gravity vector;
determining a particular estimation of the weight of the load from a particular component pointing in a direction of the gravity vector from among the components of each external wrench F ext that indicate the external forces in the base coordinate system, and from the magnitude of the gravity vector;
determining the weight of the load by averaging respective estimations of the weight of the load for the n static poses;
determining estimations of coordinates of the center of gravity of the load for each of the n static poses based on the weight of the load as averaged and based on the components of the external wrench F ext that indicate the externally acting torques; and
determining coordinates of the center of gravity of the load by averaging respective estimations of coordinates of the center of gravity.

2. The method according to claim 1 , wherein the external wrench F ext is determined by torque sensors in the joints.

3. The method according to claim 1 , wherein the external wrench F ext is determined by strain gauges on the joints or on the links.

4. The method according to claim 1 , wherein the load is moved several times from distinct directions into a number m of the n static poses, with m≤n.

5. The method according to claim 1 , wherein n=8.

6. The method according to claim 1 , wherein the external wrench F ext is determined for each of the n static poses in an end effector coordinate system that is body-fixed to the end effector, and for determining at least the components of each external wrench F ext that indicate the forces, a system transformation takes place in the base coordinate system between the end effector coordinate system and the base coordinate system.

7. The method according to claim 1 , wherein estimations for coordinates of the center of gravity of the load are determined for each of the n static poses in an end effector coordinate system that is body-fixed to the end effector.

8. The method according to claim 1 , wherein the center of gravity of the load is determined by arithmetic averaging of the respective estimations of coordinates of the center of gravity of the load.

9. The method according to claim 1 , wherein the weight of the load is determined by arithmetic averaging of the respective estimations of the weight of the load.

10. A system to determine a weight and a center of gravity of a load for a robot manipulator, wherein the robot manipulator is arranged on a base and comprises a plurality of links, the links connected to one another by joints and rotatable relative to one another by actuators arranged on the joints, wherein the robot manipulator further comprises:
an end effector designed to grip the load;
a control unit designed to control the actuators arranged on the joints for moving the load into a number n of distinct static poses, wherein the load is moved into the number n of distinct static poses only by controlling a number k of actuators, with k≤n, wherein the number k is a predefined quantity and the k actuators are arranged on or assigned to k joints that are closest to the end effector:
a processing unit; and
a memory storing instructions that, when executed by the processing unit, cause the processing unit to perform operations comprising:
determining an external wrench F ext for each of the n static poses, wherein the respective external wrench F ext indicates external forces and torques acting on the robot manipulator;
determining, in a base coordinate system, at least components of each external wrench F ext that indicate the external forces, wherein the base coordinate system is a Cartesian coordinate system and arranged in a body-fixed manner on the base of the robot manipulator, and an axis of the base coordinate system is parallel to a gravity vector;
determining a particular estimation of the weight of the load from a particular component pointing in a direction of the gravity vector from among the components of each external wrench F ext that indicate the external forces in the base coordinate system, and from the magnitude of the gravity vector;
determining the weight of the load by averaging respective estimations of the weight of the load for the n static poses;
determining estimations of coordinates of the center of gravity of the load for each of the n static poses based on the weight of the load as averaged and based on the components of the external wrench F ext that indicate the externally acting torques; and
determining coordinates of the center of gravity of the load by averaging respective estimations of coordinates of the center of gravity.

11. The system according to claim 10 , wherein the robot manipulator comprises torque sensors in the joints, the torque sensors designed to determine the external wrench F ext .

12. The system according to claim 10 , wherein the robot manipulator comprises strain gauges on the joints or on the links, the strain gauges designed to determine the external wrench F ext .

13. The system according to claim 10 , wherein the load is moved several times from distinct directions into a number m of the n static poses, with m≤n.

14. The system according to claim 10 , wherein n=8.

15. The system according to claim 10 , wherein the external wrench F ext is determined for each of the n static poses in an end effector coordinate system that is body-fixed to the end effector, and for determining at least the components of each external wrench F ext that indicate the forces, a system transformation takes place in the base coordinate system between the end effector coordinate system and the base coordinate system.

16. The system according to claim 10 , wherein estimations for coordinates of the center of gravity of the load are determined for each of the n static poses in an end effector coordinate system that is body-fixed to the end effector.

17. The system according to claim 10 , wherein the center of gravity of the load is determined by arithmetic averaging of the respective estimations of coordinates of the center of gravity of the load.

18. The system according to claim 10 , wherein the weight of the load is determined by arithmetic averaging of the respective estimations of the weight of the load.

19. The method

Assignees

• Franka Emika Gmbh

Inventors

• Spenninger Andreas
• Streitel Fangyi

Classifications

• G01M1/122

  Determining position of centre of gravity · CPC title

• G01G19/52

  Weighing apparatus combined with other objects, e.g. furniture (with walking sticks A45B3/08) · CPC title

• B25J9/1638 Primary

  compensation for arm bending/inertia, pay load weight/inertia · CPC title

• G05B2219/39194

  Compensation gravity · CPC title

• B25J9/1653

  parameters identification, estimation, stiffness, accuracy, error analysis · CPC title