EP-4739468-A1 - CONTINUAL ACCELERATION DETECTION AND COMPENSATION OF ROBOT ARM

Abstract

Disclosed is a robot system comprising a robot base and a plurality of robot joints, each robot joint comprising a joint motor; a robot controller configured to control operation of the robot arm based on a robot control program; and an inertial measuring unit; wherein the robot controller is configured to control each joint motor by providing a motor control signal to the joint motor based on a dynamic model configured to generate motor control signals based on an input received from the inertial measuring unit, the input received from the inertial measuring unit defining an operational condition of the robot arm in the dynamic model; wherein the input received from the inertial measuring unit represents at least one of the following: a cartesian acceleration provided by the inertial measuring unit, or an angular acceleration provided by the inertial measuring unit.

Inventors

• TINGSKOV, CARSTEN NOMMENSEN
• SØE-KNUDSEN, Rune

Assignees

• Universal Robots A/S

Dates

Publication Date

20260513

Application Date

20240701

Claims (20)

1. 1. A robot system comprising: a robot arm comprising a robot base and a plurality of robot joints, each robot joint of said plurality of joints comprising a joint motor; a robot controller configured to control operation of said robot arm based on a robot control program; and an inertial measuring unit; wherein said robot controller is configured to control each joint motor of said plurality of robot joints by providing a motor control signal to said joint motor based on a dynamic model, wherein said dynamic model is configured to generate motor control signals based on an input received from said inertial measuring unit, said input received from said inertial measuring unit defining an operational condition of said robot arm in said dynamic model; wherein said input received from said inertial measuring unit represents at least one of the following accelerations: a cartesian acceleration provided by said inertial measuring unit, or an angular acceleration provided by said inertial measuring unit.
2. 2. A robot system according to claim 1, wherein said operational condition is modifiable and arranged to be modified on the basis of input received from said inertial measuring unit.
3. 3. A robot system according to claim 1 or 2, wherein said dynamic model is configured to determine a torque to be generated by a joint motor of a robot joint of said plurality of robot joints based on one or more torque contributing factors.
4. 4. A robot system according to claim 3, wherein said dynamic model is configured to generate said motor control signals based on said torque determined by said dynamic model.
5. 5. A robot system according to claim 3 or 4, wherein said input received from said inertial measuring unit is used as a parameter of at least one torque contributing factor of said one or more torque contributing factors of said dynamic model.
6. 6. A robot system according to any of the claims 3-5, wherein said one or more torque contributing factors comprises a factor relating to moment of inertia of said robot arm.
7. 7. A robot system according to any of the claims 3-6, wherein said one or more torque contributing factors comprises a factor relating to Coriolis effect and centripetal torque.
8. 8. A robot system according to any of the claims 3-7, wherein said one or more torque contributing factors comprises a factor relating to gravity.
9. 9. A robot system according to claim 8, wherein said factor relating to gravity is arranged to take as input argument a cartesian acceleration of said robot base and/or an angular acceleration of said robot base.
10. 10. A robot system according to any of the claims 3-9, wherein said one or more torque contributing factors comprises a factor relating to friction.
11. 11. A robot system according to any of the claims 3-10, wherein said one or more torque contributing factors comprises a factor relating to an external torque applied to said robot arm.
12. 12. A robot system according to any of the preceding claims, wherein said robot controller comprises a memory storing thereon said dynamic model.
13. 13. A robot system according to any of the preceding claims, wherein said dynamic model is configured to take as input a target motion provided by said robot control program.
14. 14. A robot system according to any of the preceding claims, wherein said dynamic model is a matrix implemented model.
15. 15. A robot system according to any of the preceding claims, wherein said cartesian acceleration is a cartesian acceleration of said robot base, and wherein said angular acceleration is an angular acceleration of said robot base.
16. 16. A robot system according to any of the preceding claims, wherein said cartesian acceleration of said robot base is an acceleration of a base reference point in relation to a reference coordinate system, and wherein said angular acceleration is an angular acceleration of said base reference point in relation to said reference coordinate system.
17. 17. A robot system according to any of the preceding claims, wherein said robot system comprises a safety system associated with a plurality of safety parameter ranges defining allowable operations of said robot arm when controlled by said robot controller, wherein said safety system is arranged to monitor one or more safety parameters relating to control of said robot arm and to evaluate said one or more safety parameters with respect to one or more safety parameter ranges of said plurality of safety parameter ranges to determine whether said monitored one or more safety parameters are within said one or more safety parameter ranges, and wherein one or more safety parameters of said plurality of safety parameter ranges are at least partly calculated based on input received from said inertial measuring unit.
18. 18. A robot system according to claim 17, wherein said safety system comprises a protective stop system implemented in said robot controller, said protective stop system being associated with a first set of safety parameter ranges of said plurality of safety parameter ranges, wherein said protective stop system is arranged to monitor one or more safety parameters relating to control of said robot arm and to suspend execution of said robot control program when at least one safety parameter of said one or more safety parameters is outside a corresponding safety parameter range of said first set of safety parameter ranges.
19. 19. A robot system according to any of the claims 17-18, wherein said safety system comprises an auxiliary system controller associated with a second set of safety parameter ranges of said plurality of safety parameter ranges, wherein said auxiliary system controller is configured to monitor one or more safety parameters relating to control of said robot arm and to perform an emergency stop of said robot system when at least one safety parameter of said one or more safety parameters is outside a corresponding safety parameter range of said second set of safety parameter ranges.
20. 20. A robot system according to any of the preceding claims, wherein said robot system is configured to receive input by a user of said robot system, said input defining a target motion of said robot arm.

Description

CONTINUAL ACCELERATION DETECTION AND COMPENSATION OF ROBOT ARM FIELD OF THE INVENTION [0001] The present invention relates to a robot system, a method of controlling a robot arm of a robot system, and a computer program product. BACKGROUND OF THE INVENTION [0002] Robot arms comprising a plurality of robot joints and links where motors can rotate the joints in relation to each other are known in the field of robotics. Typically, the robot arm comprises a robot base which serves as a mounting base for the robot arm and a robot tool flange where to various tools can be attached. A robot controller is configured to control the robot joints to move the robot tool flange in relation to the base. For instance, in order to instruct the robot arm to carry out a number of working instructions. [0003] Typically, the robot controller is configured to control the robot joints based on a dynamic model of the robot arm, where the dynamic model defines a relationship between the forces acting on the robot arm and the resulting accelerations of the robot arm. Often, the dynamic model comprises a kinematic model of the robot arm, knowledge about inertia of the robot arm and other parameters influencing the movements of the robot arm. The kinematic model defines a geometric relationship between the different parts of the robot arm and may comprise information of the robot arm such as, length, size of the joints and links and can for instance be described by Denavit-Hartenberg parameters or the like. The dynamic model makes it possible for the controller to determine which torques the joint motors shall provide in order to move the robot joints for instance at specified velocity, acceleration or in order to hold the robot arm in a static posture. [0004] On many robot arms it is possible to attach various end effectors to the robot tool flange, such as grippers, vacuum grippers, magnetic grippers, screwing machines, welding equipment, dispensing systems, visual systems etc. [0005] In some robots the robot joint comprises a joint motor having a motor axle configured to rotate an output axle via a robot joint gear. Typically, the output axle is connected to and configured to rotate parts of the robot arm in relation to each other. The complicity of such robot control is typically increased when the robot is to operate under challenging operational conditions such as not mounted on a fixed and stationary platform. [0006] US 2013/0245825 Al discloses a safety device for the safe use of industrial robots. Inertial sensor means are attached to a part of a robot arm, and the inertial sensor means operate independently of the movement means in order to make additional measurements of kinematic state values of the robot arm and are functionally associated with at least one safety module. [0007] US 2021/0008710 Al discloses a mobile robot including a movable platform including wheels, a manipulator having a base supported by the movable platform, and an arm attached to the base. The movable platform comprises internal sensors including an inertial sensor. The sensor data provided by the sensors is used by a first control circuit controlling movement actuators of the movable platform. [0008] WO 2020/228978 Al discloses a robot with an actuated robot manipulator comprising a number of rigid body links connected via joints. The robot comprises an inertial measuring unit configured to determine an angular velocity information of a given link. [0009] None of the above documents describe ways of controlling individual robot joints to take account of challenging operational conditions, and accordingly there is a need in the art for more advanced control schemes of robot arms. SUMMARY OF THE INVENTION [0010] The objective of the present invention is to address the abovedescribed limitations with the prior art or other problems of the prior art. This is achieved by a robot system comprising: a robot arm comprising a robot base and a plurality of robot joints, each robot joint of said plurality of joints comprising a joint motor; a robot controller configured to control operation of said robot arm based on a robot control program; and an inertial measuring unit; wherein said robot controller is configured to control each joint motor of said plurality of robot joints by providing a motor control signal to said joint motor based on a dynamic model, wherein said dynamic model is configured to generate motor control signals based on an input received from said inertial measuring unit, said input received from said inertial measuring unit defining an operational condition of said robot arm in said dynamic model; wherein said input received from said inertial measuring unit represents at least one of the following accelerations: a cartesian acceleration provided by said inertial measuring unit, or an angular acceleration provided by said inertial measuring unit. [0011] Thereby is provided an advantageous robot system capable of operating under chall