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US 2021/0260757 A1Published application
Dual mode free-drive of robot arm
AssigneeUniversal Robots A/S
InventorsOluf Skov NIELSEN, Andreas Rune FUGL, Anders Skovgaard KNUDSEN
Life of this patent
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Abstract
Method and robot arm, where the motor torques of the joint motors of a robot arm are controlled based on a static motor torque indicating the motor torque needed to maintain the robot arm in a static posture, where the static motor torque is adjusted in response to a change in posture of the robot arm caused by an external force different from gravity applied to the robot arm. Further the motor torque of the joint motors is controlled based on an additional motor torque obtained based on a force-torque provided to the robot tool flange, where the force-torque is obtained by a force-torque sensor integrated in the tool flange of the robot arm.
Claims20
A robot system comprising:
- a robotic arm comprising joints connecting a base of a robot to a tool flange, where the tool flange is configured for attachment to an end effector, and where each of the joints comprises:
- an output flange that is rotatable relative to a body of a corresponding joint;
- a motor that is configured to rotate the output flange relative to the body;
- and
- at least one sensor configured to provide a sensor signal indicative of at least one of an angular position of the output flange, an angular position of a shaft in the motor, or a current in the motor;
- at least one controller configured to control the joints by controlling torque provided by each motor based on a sensor signal from the at least one sensor, the at least one controller being switchable into a free-drive mode of operation in which the at least one controller is configured to perform operations comprising:
- maintaining the robotic arm in a static posture when an only force acting on the robotic arm is gravity, the robotic arm being maintained in the static posture by driving each motor to provide static motor torque to overcome gravity without moving one or more parts of the robotic arm, where the at least one controller is configured to obtain the static torque based on the posture of the robotic arm and a dynamic model of the robotic arm;
- and
- allowing a change in the posture of the robotic arm when an external force different from gravity is applied to the robotic arm and, in response to the change in posture, adjusting the static torque based on the change in posture and the dynamic model;
- and
- a force-torque sensor integrated into the tool flange, the force-torque sensor for providing a force signal indicative of a force-torque applied to the tool flange;
- wherein, in the free-drive mode of operation, the at least one controller is configured to control torque provided by each motor to the joints based on the force signal by controlling each motor to provide additional torque that is based on a current posture of the robotic arm, the dynamic model of the robotic arm, and the force-torque signal, and wherein the at least one controller is configured to control the joints by controlling the torque provided by each motor based on the additional torque and the static torque.
9 more elements
A method of changing a posture of a robot arm of a robot, where the robotic arm comprises joints connecting a base of the robot to a tool flange, where the tool flange is configured for attachment to an end effector, and where each of the joints comprises:
- an output flange that is rotatable relative to a body of a corresponding joint;
- a motor configured to rotate the output flange relative to the body;
- and
- at least one sensor configured to provide a sensor signal indicative of an angular position of the output flange;
- wherein the method comprises the steps of:
- obtaining a static torque for each motor based on the posture of the robotic arm and a dynamic model of the robotic arm, where the static torque comprises torque that each motor needs to provide in order to keep the robot arm in a static posture under influence of gravity;
- controlling the torque of each motor based on the static motor torque;
- and
- in response to a change in the posture of the arm caused by an external force that is applied to the arm and that is different from gravity:
- adjusting the static torque based on the change in the posture of the robotic arm and a dynamic model of the robotic arm, where an adjusted static torque corresponds to a torque that each motor needs to provide in order to keep the robotic arm at the change in the posture under influence of gravity;
- and
- controlling the torque of each motor based on an adjusted static torque;
- obtaining a force-torque on the tool flange based on a force-torque sensor integrated into the tool flange;
- and
- obtaining an additional torque based on the force-torque, the dynamic model, and the posture of the robotic arm;
- wherein controlling the torque of each motor is based on the additional torque.
13 more elements
A robot system comprising:
- a robotic arm comprising joints connecting a base of a robot to a tool flange, each of the joints comprising:
- an output flange that is rotatable relative to a corresponding joint;
- a motor configured to rotate the output flange;
- and
- at least one sensor configured to provide a sensor signal corresponding to at least one of an angular position of the output flange, an angular position of a shaft of the motor, or a current in the motor;
- at least one robot controller associated with the robot and configured to control the joints by controlling torque provided by each motor based on a corresponding sensor signal, the at least one controller being switchable into a free-drive mode of operation in which the at least one robot controller is configured to perform operations comprising:
- maintaining the robotic arm in a static posture when an only force acting on the robotic arm is gravity;
- and
- allowing a change in posture of the robotic arm when an external force that is different from gravity is applied to the robotic arm;
- and
- a force-torque sensor integrated into the tool flange, the force-torque sensor for providing a force signal representing a force-torque applied to the tool flange;
- wherein the at least one controller is configured to enter the free-drive mode of operation based on the force signal.
9 more elements
Dependencies are inferred from the claim text.