Robot Arm Free-Drive via Tool Flange Force-Torque Control
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Solution Overview
Problem
Existing free-drive modes for robot arms require manipulation of individual joints, which can be difficult in situations where parts of the arm are obstructed, and existing teaching apparatuses complicate user interaction.
Innovation Solution
The robot arm incorporates a force-torque sensor in the tool flange to control joint motors based on static and additional motor torques, allowing the user to change the robot's posture by pushing, pulling, or rotating the tool flange, while also enabling manipulation of individual joints if desired.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the robot controller controls motor torque based on individual joint manipulation in free-drive mode, then the robot arm can be held in static posture, but the operation becomes difficult when parts of the arm are obstructed
Solution Approach 1:
The patent introduces a force-torque sensor as an intermediary device mounted on the tool flange to detect external forces applied by the user. This sensor acts as a mediator between the user's manual manipulation and the robot controller, enabling the controller to respond to forces applied at the tool flange rather than requiring direct joint manipulation. The force-torque sensor converts mechanical forces into electrical signals that the controller can process to adjust motor torques accordingly.
Solution Approach 2:
The patent transitions from controlling the robot arm through individual joint angles (one-dimensional control per joint) to controlling through forces applied at the tool flange (three-dimensional force vector control). This dimensional shift allows the user to manipulate the robot arm intuitively by applying forces in any direction at the tool flange, rather than having to calculate and manipulate each joint angle separately, especially when joints are obstructed.
2Ease of operation
If a force-torque sensor is integrated in the tool flange to detect forces, then the user can move the tool flange without direct joint manipulation, but the device complexity increases
Solution Approach 1:
The force-torque sensor integrated in the tool flange serves multiple functions: it detects forces applied by the user during free-drive mode, provides feedback for controller adjustments, and can potentially be used for other operations such as payload measurement or contact force monitoring. This multi-functionality justifies the added complexity by providing versatile capabilities beyond just free-drive manipulation.
Solution Approach 2:
The patent merges the force-torque sensor directly into the tool flange structure, combining the sensing function with the existing mechanical interface. This integration approach reduces the number of separate components and simplifies the overall system architecture compared to having a separate sensing device attached to the tool flange.
3Reliability
If the robot controller applies motor torque based on joint angles and dynamic model, then the robot arm can maintain static posture, but the user cannot easily change posture when joints are obstructed
Solution Approach 1:
The patent implements a dynamic control mode where the robot controller continuously adjusts motor torques based on real-time force-torque sensor readings. Instead of maintaining a fixed static posture control, the system dynamically responds to user-applied forces, allowing smooth transitions between postures even when joints are obstructed. The controller calculates the required motor torques based on the detected forces and the robot's dynamic model, enabling adaptive posture changes.
Data Source
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AI summary
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.