Flexure-Based RCM Joint for Predictable Exoskeleton Rotation
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Solution Overview
Problem
Current robotic exoskeletons for rehabilitation face challenges due to their requirement for extremely precise and expensive manufacturing techniques to ensure proper operation, leading to issues like overconstraint and unpredictable behavior, which affect their usability and force sensitivity.
Innovation Solution
Incorporation of flexures into the parallelogram-based remote center of motion (RCM) mechanisms to manage overconstraint by allowing independent displacement of redundant joints, thereby maintaining predictable rotation and reducing manufacturing tolerance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If parallelogram-based RCM mechanisms are used to generate rotation about a remote center point, then the desired rotational motion is achieved, but the mechanism becomes overconstrained and exhibits unpredictable behavior
Solution Approach 1:
The patent introduces flexures that change the kinematic parameters of the mechanism by allowing redundant joints to displace independently. This transforms the overconstrained parallelogram mechanism into a system with controlled degrees of freedom, enabling predictable rotation about the remote center while accommodating manufacturing tolerances.
Solution Approach 2:
The flexures introduce dynamic compliance into the previously rigid parallelogram mechanism. By allowing controlled movement and displacement at redundant joints through elastic deformation, the mechanism transitions from a statically overconstrained system to a dynamically adaptable system that maintains predictability.
2Manufacturing precision
If extreme manufacturing precision is required to ensure proper operation of RCM mechanisms, then operational accuracy is improved, but manufacturing cost and complexity increase significantly
Solution Approach 1:
The flexures modify the kinematic constraints of the mechanism, transforming it from a system requiring tight tolerance control to one that accommodates broader manufacturing variations. The elastic elements absorb dimensional deviations, maintaining operational accuracy without demanding extreme manufacturing precision.
Solution Approach 2:
The flexures act as pre-designed compliance elements that anticipate and compensate for manufacturing errors before they affect mechanism operation. By built-in elastic displacement capacity, the system cushions against tolerance violations, ensuring proper operation even with moderate manufacturing precision.
3Stability of the object's composition
If redundant joints are present in the parallelogram RCM mechanism, then structural stability is improved, but overconstraint occurs leading to binding and unpredictable behavior
Solution Approach 1:
The flexures change the degrees of freedom available at each joint by introducing elastic compliance. This transforms the rigid, overconstrained system into a compliant mechanism where redundant joints can displace independently through flexural deformation, eliminating binding while preserving structural stability.
Solution Approach 2:
The patent employs flexures—thin, elastic structural elements—that provide controlled flexibility within the mechanism. These flexible components allow redundant joints to move independently through small displacements, preventing overconstraint and binding while maintaining overall structural integrity and stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The integration of flexures in RCM mechanisms enhances the predictability and force sensitivity of robotic systems, enabling cost-effective and precise operation even with manufacturing errors, critical for applications like physical therapy.
Implementation Method 1
The first link includes a first flexure, the first flexure including a first degree of freedom in a first direction
Data Source
AI summary
An embodiment includes an exoskeleton robotic system comprising a parallelogram-based remote center of motion (RCM) joint. The RCM mechanism includes a first link that is coupled to a second link, a third link, and a fourth link. A motor is coupled to the third link. A first of the first, second, third, or fourth links includes a first flexure. The first flexure includes a first degree of freedom in a first direction. A second of the first, second, third, or fourth links includes a second flexure, the second flexure including a second degree of freedom in a second direction. The first direction is not parallel to the second direction.