Robot Lead-Through Control Switching for Precise Teaching
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Solution Overview
Problem
Existing robot systems face challenges in lead-through mode, where maintaining joint 'tonus' and overcoming internal friction make it difficult to achieve precise and effortless movement teaching, especially for large industrial robots, as impedance-based control struggles with precise positioning due to static friction and requires significant user effort.
Innovation Solution
A robot system with a controller that switches between impedance-based and admittance-based control modes, allowing for efficient long-haul movements under impedance control and precise short-haul movements under admittance control, using switches, sensors, and torque feedback to adapt control modes based on user input and movement intent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If impedance-based control is used for lead-through mode, then fast and far-flung movements can be taught without effort, but precise positioning becomes difficult due to static friction causing jerking
Solution Approach 1:
The system dynamically switches between impedance-based control and admittance-based control modes based on the operational phase. During long-haul movements, impedance-based control is used for effortless operation. When approaching the target position, the system transitions to admittance-based control to overcome static friction and achieve precise positioning, eliminating jerking effects.
Solution Approach 2:
The control parameters are changed by switching between two distinct control modes: impedance-based control (with virtual stiffness and damping) for coarse positioning, and admittance-based control (with force-to-position mapping) for fine positioning. This parameter change allows the system to optimize performance for each phase of the movement.
2Manufacturing precision
If admittance-based control is used for lead-through mode, then precise positioning can be achieved, but significant user force is required throughout the movement
Solution Approach 1:
The movement is segmented into two phases: long-haul movement and short-haul positioning. During the long-haul phase, impedance-based control requires minimal user force. During the short-haul phase near the target, admittance-based control is engaged to achieve precise positioning with reduced user exertion since the movement distance is small.
Solution Approach 2:
Admittance-based control is applied partially only during the final positioning phase rather than throughout the entire movement. This partial application of admittance control provides precise positioning when needed while avoiding the continuous user force requirement during the longer travel portions of the movement.
3Stability of the object's composition
If the manipulator maintains sufficient tonus to retain pose, then joint stability is improved, but internal friction increases making movement difficult
Solution Approach 1:
The controller dynamically adjusts the level of tonus and friction compensation based on the operational mode. During impedance-based control, higher tonus is maintained for stability during long-haul movements. During admittance-based control near the target, the controller reduces tonus and friction to enable precise, effortless positioning, resolving the contradiction between stability and ease of manipulation.
Solution Approach 2:
The controller parameters including gravity compensation and friction compensation are adjusted based on the control mode. In impedance mode, full gravity and friction compensation is applied for stability. In admittance mode, reduced compensation is applied to minimize resistance during fine positioning, allowing the system to adapt between stability and ease of operation.
Data Source
AI summary
A robot system comprises a manipulator and a controller therefore, wherein the controller supports impedance-based control of a lead-through operation mode, characterized in that the controller is switchable between impedance-based and admittance-based control of the lead-through mode.