Rehab Robot End-Effector Control for Motion Restriction Accuracy
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Solution Overview
Problem
Existing end-effector rehabilitation robots face challenges in maintaining stability and accuracy due to position error accumulation from control discretization and motor acceleration limitations, particularly in non-backdrivable mechanisms, which affect user experience and engagement.
Innovation Solution
A robotic device with a non-backdrivable mechanism employs an implicit Euler velocity control (IEVC) mechanism to address position error accumulation by using a two-level control hierarchy and a motion restriction map, allowing for precise trajectory following and area restriction control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motor velocity control is used for area restriction control on non-backdrivable mechanism, then the robotic device can provide stable support and portability, but position error accumulation occurs due to control discretization and motor acceleration limitations
Solution Approach 1:
The patent implements a feedback mechanism where the current position of the end-effector is continuously monitored and compared with the desired position within the restricted area. The control system calculates the position error and adjusts the motor velocity accordingly to minimize this error, preventing accumulation over time. This closed-loop feedback approach resolves the contradiction by maintaining both stability and position accuracy.
Solution Approach 2:
The patent dynamically adjusts control parameters including velocity limits, acceleration rates, and position error thresholds based on the end-effector's current state and the restricted area boundaries. By changing these parameters adaptively, the system maintains stability while compensating for discretization errors and acceleration limitations to preserve position accuracy.
2Manufacturing precision
If control frequency is increased and higher quality motors are used to reduce position error, then position accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent applies partial action by using a moderate control frequency combined with intelligent velocity adjustment strategies. Instead of continuously maximizing control updates, the system applies corrections only when position errors exceed predefined thresholds or when approaching area boundaries. This approach achieves sufficient position accuracy without requiring excessively high control frequencies or premium motors, thereby reducing device complexity.
Solution Approach 2:
The control system performs preliminary calculations of desired velocity and acceleration limits based on the restricted area geometry and current position before actual movement occurs. By pre-computing safe velocity profiles and boundary constraints, the system prevents position errors from accumulating in the first place, reducing the need for complex real-time corrections and high-frequency control updates.
Data Source
AI summary
Robotic device control for assisting a user in performing upper limb rehabilitation is disclosed. A method controls a robotic device having a non-backdrivable end-effector including motor(s) and position sensor(s) by: receiving trajectory restriction(s); generating a motion restriction map based on the received trajectory restriction(s); receiving, through the position sensor(s) of the end-effector, a current position of the end-effector; obtaining a desired velocity for the motor(s) at a current time by modifying, based on the generated motion restriction map and the received current position, a calculated velocity obtained based on the desired velocity at a previous time to limit the end-effector to move inside a permitted area represented by the motion restriction map; providing a movement instruction including the obtained desired velocity at the current time; and controlling the end-effector to move according to the provided movement instruction