Wrist Attachment with Variable Mechanical Impedance

Solution Overview

Problem

Existing physical therapy devices, such as CPM machines, have high mechanical impedance and lack the ability to vary impedance, which restricts patients' ability to express movement independently during rehabilitation, hindering effective motor rehabilitation and recovery.

Innovation Solution

The development of wrist and upper extremity attachments with low mechanical impedance, featuring motors and linkages that apply torques across multiple axes (pronation/supination, flexion/extension, and abduction/adduction) to provide assistance, resistance, and perturbation, allowing for controlled and variable impedance training.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If CPM machines with high mechanical impedance are used, then the range of motion can be extended, but patients cannot express movement independently and impedance variation is not allowed

Engineering Contradiction:

Improverange of motionVSAvoidindependent movement expression

Core Design Contradiction:

Length of moving objectVSEase of operation

Solution Approach 1:

The robotic device implements dynamic impedance control that allows the mechanical impedance to vary in real-time based on patient needs and therapy phase. The controller adjusts impedance parameters dynamically during operation, enabling the system to transition between high-impedance modes for passive motion and low-impedance modes for active patient participation, thereby resolving the contradiction between extending range of motion and enabling independent movement expression

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the mechanical impedance parameter from fixed (high) in traditional CPM machines to variable and adjustable. The controller modifies impedance characteristics based on detected patient effort, therapy goals, and motion phase, allowing the same device to provide both passive range-of-motion extension and active independent movement expression by simply changing the impedance parameter

Inventive Principle:

Principle #35Parameter changes

2Length of moving object

If high mechanical impedance is used to move the patient passively, then the range of motion is extended, but the system does not allow for impedance variation

Engineering Contradiction:

Improverange of motionVSAvoidimpedance variation capability

Core Design Contradiction:

Length of moving objectVSAdaptability or versatility

Solution Approach 1:

The robotic device implements dynamic impedance control that allows the mechanical impedance to vary in real-time based on patient needs and therapy phase. The controller adjusts impedance parameters dynamically during operation, enabling the system to transition between high-impedance modes for passive motion and low-impedance modes for active patient participation, thereby resolving the contradiction between extending range of motion and enabling independent movement expression

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The device is designed to perform multiple functions by varying its impedance characteristics. It can operate in passive CPM mode for range-of-motion extension, in active assistance mode for patient-driven movement, and in variable impedance mode for different therapy intensities, all within a single unified system that adapts its mechanical properties based on operational requirements

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS7618381B2Wrist and upper extremity motion

Publication Date: 2009.11.17 MASSACHUSETTS INST OF TECH

AI summary

Wrist and upper extremity motion systems and method may include positioning a subject's wrist or upper extremity in a motion device, and actuating one or more motors associated with the device to provide at least one of assistance, perturbation, and resistance to a wrist or upper extremity motion.