Upper-Limb Exoskeleton Kinematic Chain for Remote Torsion Actuation
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Solution Overview
Problem
Existing exoskeleton systems for limb rehabilitation face challenges in kinematic coupling and wearability due to mechanical architecture, particularly in actuating torsion of longitudinal segments, leading to inefficiency, high encumbrance, and discomfort for users.
Innovation Solution
A kinematic chain that enables remote center actuation between cylindrical elements without aligned motors, using a configuration of pivot points and links that allow rotation about an orthogonal axis, reducing external encumbrance and internal friction, and adapting to different anthropometries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a motor aligned with the rotation axis is used to actuate torsion of a longitudinal segment, then the actuation is direct and simple, but the motor causes encumbrance and interference with other body segments
Solution Approach 1:
The motor is extracted from the rotation axis location and placed in a remote position. The actuation function is separated from the rotation point, allowing the motor to be positioned where it does not interfere with body segments while still providing the necessary rotational actuation through a transmission mechanism.
Solution Approach 2:
A transmission mechanism acts as an intermediary between the remotely positioned motor and the rotation axis. This intermediary transfers the actuation force from the motor to the longitudinal segment, enabling torsion actuation without requiring the motor to be aligned with or adjacent to the rotation axis.
2Volume of moving object
If a remote centers actuating system with cylindrical joints is used to actuate torsion, then the motor can be positioned remotely, but the system becomes expensive, unreliable, heavy, and bulky
Solution Approach 1:
The complex cylindrical joint components (concentric cylinders, interposed bearings, creeping elements, slides with circular rails) are extracted and replaced with a simpler transmission mechanism. This removes the multiple potential failure points while maintaining the remote actuation capability.
Solution Approach 2:
The complex mechanical cylindrical joint system is substituted with a simpler transmission mechanism that achieves the same functional result. This substitution reduces the number of mechanical components, thereby improving reliability and reducing weight and bulk.
3Loss of energy
If the length of the short side of the parallelogram linkages is increased to minimize reaction forces, then the efficiency improves, but the encumbrance with respect to the circumference increases
Solution Approach 1:
The solution moves the actuation point to a different dimensional location (remote center) rather than extending the parallelogram linkage dimensions. This allows for efficient load transmission through geometric configuration rather than through increased component size, maintaining low reaction forces without increasing encumbrance.
Data Source
AI summary
Exoskeleton kinematic chain arranged to pivotally connect a first element to a second element, said first element comprising two pivot points A1 and B1 located at a distance A1B1, said second element comprising two pivot points A2 and B2 located at a distance A2B2. The exoskeleton kinematic chain comprises a first external link pivotally connected to the first element at the pivot point A1 and a first end link pivotally connected to the first external link at a pivot point D1, said pivot point D1 being located at a distance A1D1 by the pivot point A1. The exoskeleton kinematic chain comprises then a second external link pivotally connected to the second element at the pivot point A2, and a second end link pivotally connected to the second external link at a pivot point D2, said pivot point D2 being located at a distance A2D2 by the pivot point A2. The exoskeleton kinematic chain also comprises a first intermediate link pivotally connected to the first element at the pivot point B1 and integrally connected to the second end link at a junction point C2, a second intermediate link pivotally connected to the second element at the pivot point B2 and integrally connected to the first end link at a junction point C1. The first and the second end link are pivotally connected to each other at a pivot point M. Defining ==θ, for any value of θ, the projections of the pivot points A1, B1, A2, B2 in a plane π, lay in a circumference K having center O and radius r=A1D1=A2D2=D1B2=MB2=D2B1=MB1, in such a way that decreasing the value of θ the first and the second element rotate with respect to each other about an axis z orthogonal to the plane π and passing through the center O in the direction for which the point A1 is overlapped to the point B2.