Robot Force Control via Actuator Trajectory Correction
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Solution Overview
Problem
Existing robot systems face challenges in maintaining consistent machining quality due to positioning errors and individual differences in workpieces, as compliance mechanisms and force control systems struggle with errors beyond their stroke range and are affected by robot mass and inertia, leading to decreased responsiveness and potential undue pressing forces.
Innovation Solution
A robot system equipped with an actuator and position sensor that adjusts the acting point of the machining tool or workpiece, using a control device with force detection, position detection, and position correction units to maintain a predetermined force and correct motion trajectories, ensuring consistent machining quality even with large errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a compliance mechanism is used to absorb positioning errors, then positioning error absorption capability is improved, but the mechanism is deformed due to gravity when oriented horizontally or inclined, causing loss of error absorption capability and potential undue pressing force
Solution Approach 1:
The control device continuously detects the actual pressing force between the machining tool and workpiece, compares it with the target pressing force, and automatically adjusts the robot's motion trajectory in real-time to compensate for deviations caused by compliance mechanism deformation under gravity, ensuring consistent error absorption capability
Solution Approach 2:
The system dynamically changes the robot's motion parameters (position, speed, trajectory) based on detected pressing force deviations, allowing the compliance mechanism to operate effectively under various gravitational conditions by adjusting operational parameters rather than relying solely on mechanical rigidity
2Device complexity
If the compliance mechanism stroke is limited, then device complexity is reduced, but it cannot absorb positioning errors larger than the stroke range
Solution Approach 1:
The system compensates for limited linear stroke of the compliance mechanism by adjusting the robot's motion trajectory in multiple dimensions (position, orientation, speed), effectively expanding the error absorption capability beyond the mechanical stroke limits through multi-dimensional motion correction
3Force
If force control is performed using robot body mass and inertia, then pressing force control is achieved, but responsiveness is decreased due to large mass and inertia
Solution Approach 1:
The system separates force control into two independent components: the robot provides positioning and motion control, while a dedicated actuator with one or more degrees of freedom mounted on the machining tool or workpiece provides force control, allowing each component to optimize its function without being constrained by the other's limitations
4Manufacturing precision
If a force control mechanism with actuator is used to maintain constant contact force, then force control precision is improved, but the actuator stroke range is limited, preventing absorption of large positioning errors
Solution Approach 1:
The system merges the advantages of both robot mobility and actuator force control by having the robot handle large positioning adjustments through trajectory correction while the actuator maintains precise force control within its limited stroke range, achieving both adaptability and precision simultaneously
Data Source
AI summary
A robot system includes a robot that operates to move a machining tool relative to a workpiece, an actuator that changes a position of the machining tool, and a control device that controls the robot. The control device includes a robot control unit that operates the robot along a predetermined motion trajectory, a force detection unit that detects force acting between the machining tool and the workpiece, a position detection unit that detects a current position of the machining tool, a force control unit that obtains a target position of the machining tool such that a detection value of the force detection unit approaches a predetermined value, and a position correction unit that calculates a position correction amount of a motion trajectory of the robot and a position correction amount of the actuator in response to the target position of the machining tool.