EP-4739467-A1 - DYNAMIC TIPPING PREVENTION OF ROBOT MOUNTING SURFACES

EP4739467A1EP 4739467 A1EP4739467 A1EP 4739467A1EP-4739467-A1

Abstract

Disclosed is a method for controlling torque applied by a robotic arm about at least one tipping point, said robotic arm being mounted on a support structure, said method comprising the steps of: establishing a threshold torque about said at least one tipping point; calculating one or more torque contributions about said at least one tipping 5 point; calculating an available torque to be applied by said robotic arm, wherein said available torque is a difference between said threshold torque and a sum of said one or more torque contributions, and controlling said robotic arm such that a torque about said at least one tipping point resulting from a change of state of said robotic arm is at or below said available torque.10 A robotic arm system and a computer program product are further disclosed.

Inventors

RATH HANSEN, Mikkel
SØE-KNUDSEN, Rune
THOMSEN, DAN KIELSHOLM

Assignees

Universal Robots A/S

Dates

Publication Date: 20260513
Application Date: 20240701

Claims (20)

1. A method for controlling torque applied by a robotic arm about at least one tipping point, said robotic arm being mounted on a support structure, said method comprising the steps of: - establishing a threshold torque about said at least one tipping point, - calculating one or more torque contributions about said at least one tipping point, - calculating an available torque to be applied by said robotic arm, wherein said available torque is a difference between said threshold torque and a sum of said one or more torque contributions, and - controlling said robotic arm such that a torque around said at least one tipping point resulting from a change of state of said robotic arm is at or below said available torque.
2. The method according to claim 1, wherein said one or more torque contributions comprises one or more dynamic torque contributions.
3. The method according to claim 2, wherein said one or more dynamic torque contributions arises from a movement of said robotic arm and/or from a movement of said support structure.
4. The method according to any of the preceding claims, wherein said one or more torque contributions comprises one or more gravitational torque contributions.
5. The method according to any of the preceding claims, wherein said one or more torque contributions comprises a torque exerted through use of a robot tool of said robotic arm or a torque arising from said robotic arm moving a payload.
6. The method according to any of the preceding claims, wherein said support structure is a movable support structure, and wherein said one or more torque contributions comprises a torque contribution associated with an acceleration of said support structure, a torque contribution associated with a deceleration of said support structure, a torque contribution associated with said support structure performing a turning manoeuvre, or any combination thereof.
7. The method according to any of the preceding claims, wherein said support structure is a movable support structure, and wherein said one or more torque contributions comprises a torque contribution associated with an emergency stop of said movable support structure.
8. The method according to any of the preceding claims, wherein said method is carried out throughout a plurality of subsequent control cycles, each control cycle of said plurality of subsequent control cycles executing said steps of calculating one or more torque contributions, calculating an available torque and controlling said robotic arm.
9. The method according to claim 8, wherein each control cycle of the plurality of control cycles comprises the step of establishing a threshold torque.
10. The method according to any of the preceding claims, wherein said step of controlling said robotic arm comprises determining a movement of said robotic arm from a first configuration of said robotic arm to a second configuration of said robotic arm, and performing said movement of said robotic arm, wherein a torque about said at least one tipping point resulting from said movement is less than or equal to said available torque.
11. The method according to any of the preceding claims, wherein said establishing said threshold torque comprises calculating said threshold torque on the basis of one or more physical parameters relating to said support structure.
12. The method according to any of the preceding claims, wherein said calculating said threshold torque comprises applying a safety factor.
13. The method according to any of the preceding claims, wherein said method comprises a step of defining one or more physical parameters about said robotic arm and/or said support structure, wherein said one or more defined physical parameters are used in said step of calculating one or more torque contributions and in said step of establishing a threshold torque.
14. The method according to claim 13, wherein said one or more physical parameters comprises one or more parameters selected from support structure height, support structure width, support structure length, robotic arm mounting pose, support structure mass, robot base mass, robotic arm link mass, and robotic arm link length.
15. The method according to claim 13 or 14, wherein said step of defining physical parameters comprises a user inputting said physical parameters in a user interface of a robot controller.
16. The method according to any of the preceding claims, wherein said available torque is dynamic and depends at least on a relative position of a tool center point with respect to said surface.
17. The method according to any of the preceding claims, wherein said support structure is a movable support structure comprising transporting means for transporting said support structure.
18. The method according to claim 17, wherein said movable support structure and said robotic arm are controlled in such a way that at any point in time during controlling, one of said movable support structure and said robotic arm is moving while the other is stationary.
19. The method according to any of the preceding claims, wherein said support structure is a mobile robot.
20. The method according to any of the preceding claims, wherein said at least one tipping point is arranged on at least one tipping axis.

Description

DYNAMIC TIPPING PREVENTION OF ROBOT MOUNTING SURFACES Field of the invention [0001] The present invention relates to a method for controlling torque applied by a robotic arm about at least one tipping point. The invention further relates to a robotic arm system and a computer program product. Background of the invention [0002] Robotic arms are machines that are programmable to execute a specific task quickly, efficiently, accurately, and safely. They are most often used for the rapid, consistent performance of heavy and/or highly repetitive procedures over extended periods of time, and are especially valued in industrial production, manufacturing, machining and assembly sectors. [0003] A typical industrial robot arm includes a series of articulated joints working together to closely resemble the motion and functionality of a human arm - at least from a purely mechanical perspective. Many robotic arms used in countless industries and workplace applications today are benchtop mounted, and some robotic arms are even mounted on mobile robots facilitating movement of the robotic system as a whole (mobile robot and robotic arm) throughout a workplace. Such benchtops or mobile robotic systems represent unstable surfaces for mounting the robotic arm to. [0004] Until now, the stability of a robotic arm mounted on an unstable surface is ensured by limiting the joint accelerations (and thereby to some degree torques) for one, several, or all robotic arm motions. This limit has to be determined empirically by the programmer, to ensure that no robot motion in the complete program/cycle will make the system tip over. Alternatively, virtual safety planes can be used in the robot controller, restricting the cartesian space in which the robotic arm is allowed to move (the further from the tipping point the robot is moving, the easier it is to tip the system over). However, even when moving the robot arm close to the base, high joint accelerations/torques can be applied, resulting in the system tipping over. [0005] JP 2006150567 A discloses a stabilization control device for a robot having a manipulator mounted on a cart. A target change in ZMP (Zero Moment Point) is set by comparing an actual ZMP with a ZMP limit value at which the standing state of the cart becomes unstable. If the actual ZMP is within a stable region, such as within the four corners of the cart, the target change in ZMP is set to zero. On the other hand, if the ZMP deviates from the stable region, the robot becomes unstable and a correction for stabilization becomes necessary. [0006] US 2019/0118380 Al discloses a method for robot fall prediction which includes searching for a gravity center offset weighting value corresponding to a posture of a robot, correcting a gravity center offset of the robot based on the gravity center offset weighting value, correcting an acceleration of the robot based on a gravity center offset direction of the robot, and determining whether the robot will fall or not based on the corrected gravity center offset and the corrected acceleration. [0007] Thus, there exists a need of improving the stability of a robotic arm without unduly restricting movements of the robotic arm and accordingly methods of controlling robotic arms in a stable way which may accommodate rapid joint motions. Summary of the invention [0008] The inventors have identified the above-mentioned problems and challenges related to stability of a robotic arm, and subsequently made the below-described invention which may increase stability and usability of a robotic arm. [0009] An aspect of the present invention relates to a method for controlling torque applied by a robotic arm about at least one tipping point, said robotic arm being mounted on a support structure, said method comprising the steps of: - establishing a threshold torque about said at least one tipping point, - calculating one or more torque contributions about said at least one tipping point, - calculating an available torque to be applied by said robotic arm, wherein said available torque is a difference between said threshold torque and a sum of said one or more torque contributions, and - controlling said robotic arm such that a torque around said at least one tipping point resulting from a change of state of said robotic arm is at or below said available torque. [0010] Thereby is provided an advantageous method of controlling torque applied by a robotic arm to a support structure, which may improve stability and utilization of a robotic arm in multiple applications of use. The method is advantageous for a number of reasons. [0011] First, the method is advantageous in that it has the effect, that a torque applied from the robotic arm about at least one tipping point (torque applied through movement of the robotic arm or through a force applied by the robotic arm to an external object, such as payload or fixed obstacle) does not cause the robotic arm to tip around the at least one tipping po