Robot End-Effector Force Control Under Uncertain Contact Geometry
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Solution Overview
Problem
Current robotic systems face challenges in precisely controlling contact forces during physical interactions with environments, especially when environmental geometry is uncertain, leading to inaccuracies and limitations in force control, particularly in hybrid task directions.
Innovation Solution
The implementation of an extended Cartesian impedance control method that combines hybrid impedance-force control, allowing compliant behavior in free movement directions and direct force control in restricted directions, with dynamic effects considered, enabling precise force tracking and motion control during rapid movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If indirect force control through impedance control is used, then compliant behavior is achieved, but force control precision deteriorates due to environmental model inaccuracies
Solution Approach 1:
The task space is segmented into free directions and restricted directions. Impedance control is applied in free directions to maintain compliant behavior, while direct force control is applied in restricted directions to achieve precise force control. This segmentation resolves the contradiction by applying different control strategies to different spatial dimensions.
Solution Approach 2:
Different control characteristics are applied locally to different directions: compliant impedance control in free directions and precise direct force control in restricted directions. This local differentiation allows the system to simultaneously achieve both compliant behavior and force control precision where needed.
2Measurement precision
If direct force control is used, then force control precision is improved, but compliant behavior deteriorates in task directions requiring adaptability
Solution Approach 1:
The control space is segmented into restricted directions (where precision is prioritized) and free directions (where adaptability is prioritized). This allows direct force control to be applied only where needed while maintaining impedance control for adaptive behavior in other directions.
Solution Approach 2:
Different control qualities are applied locally: direct force control provides precise force regulation in restricted directions, while impedance control provides adaptive compliant behavior in free directions. This local quality differentiation resolves the contradiction between precision and adaptability.
3Measurement precision
If environmental geometry is known with high accuracy, then force control precision is improved, but system complexity and measurement requirements worsen
Solution Approach 1:
The environmental interaction space is segmented into restricted directions (where force control is needed) and free directions. In restricted directions, the system uses direct force control that is less sensitive to environmental geometry inaccuracies, reducing the need for complex environmental models while maintaining force control precision.
Solution Approach 2:
The control strategy changes from indirect impedance control (sensitive to environmental model accuracy) to direct force control in restricted directions. This parameter change in control approach reduces dependence on precise environmental geometry knowledge while maintaining force control accuracy.
4Productivity
If robot moves rapidly, then productivity is improved, but force control accuracy deteriorates due to dynamic effects
Solution Approach 1:
The control system dynamically adapts based on movement characteristics. During rapid movements, the hybrid controller maintains direct force control in restricted directions with dynamic compensation, allowing high-speed operation while preserving force control accuracy despite dynamic effects.
Solution Approach 2:
The direct force control component uses real-time force feedback in restricted directions to compensate for dynamic effects during rapid movements. This feedback mechanism maintains force control accuracy even at high speeds by continuously correcting for inertial and dynamic disturbances.
Data Source
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AI summary
In a method for controlling a robot device with an end effector, wherein the robot device is controlled by means of a robot control device, it is provided that the robot control device controls the robot device by means of an extended Cartesian impedance control in which a hybrid impedance-force control is carried out, wherein a compliant behavior by means of impedance control is implemented in at least one free direction of movement and a direct force control is implemented in at least one restricted direction, wherein the dynamic effects that occur due to the movement of the end effector are taken into account in the direct force control.