Multi-bar linkage for polycentric knee exoskeleton
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Solution Overview
Problem
Conventional exoskeleton robots fail to accurately mimic the polycentric rotation of the human knee joint, leading to discomfort and inadequate response to user movement due to a fixed axis of rotation for the knee joint, which limits mobility and stability.
Innovation Solution
A multi-bar linkage system that adjusts the center of rotation based on the angle of rotation, incorporating a driving unit, links, and a controller to mimic human knee movement, allowing for polycentric rotation and repositioning of the driving unit to reduce the moment of inertia and enhance mechanical bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed axis of rotation is used for the knee joint, then the mechanical structure is simple, but the exoskeleton robot cannot accurately mimic human knee movement and provides poor comfort and stability
Solution Approach 1:
The patent implements a dynamic center of rotation mechanism where the knee joint's rotation center moves along a predetermined trajectory during flexion and extension, rather than remaining fixed. This is achieved through a linkage mechanism comprising a thigh link, shank link, and auxiliary links that coordinate to reproduce the polycentric rotation characteristics of human knee joints, thereby accurately mimicking natural knee movement patterns
Solution Approach 2:
The knee joint mechanism is divided into multiple independent links (thigh link, shank link, first auxiliary link, second auxiliary link) that work together to achieve the polycentric rotation effect. Each link has specific pivot points and connection relationships that collectively produce the desired movement trajectory, allowing the complex motion to be broken down into manageable mechanical components
2Speed
If the driving unit is positioned at the knee joint, then the rotation axis is fixed and结构简单, but the moment of inertia increases and mechanical bandwidth is limited
Solution Approach 1:
The driving unit (actuator/motor) is extracted from the knee joint location and repositioned to the thigh link. This extraction reduces the moment of inertia of the rotating mass at the knee joint, allowing for faster acceleration and higher mechanical bandwidth. The driving shaft is connected to the thigh link, and its rotation is transmitted through the linkage mechanism to control the knee joint movement, separating the power source from the high-inertia joint location
3Productivity
If a single fixed rotation axis is used for the knee joint, then the control system is simple, but the exoskeleton robot cannot rapidly respond to user movement and provides poor mobility
Solution Approach 1:
The controller monitors the rotation angle of the driving shaft and uses this feedback to calculate the required torque for the knee joint based on the predetermined relationship between driving shaft angle and knee joint angle. This closed-loop control enables rapid response to user movement by continuously adjusting the driving torque according to the actual joint position, achieving adaptive control that mimics natural knee behavior
Solution Approach 2:
The system dynamically changes the effective rotation center position of the knee joint by varying the linkage configuration as the joint moves through its range of motion. The controller adjusts the driving torque parameters based on the current angle, utilizing the predetermined mapping between driving shaft rotation and knee joint rotation to optimize performance across different movement phases
Data Source
AI summary
A multi-bar linkage includes a driving unit that is configured to supply torque to a driving shaft, where the driving shaft is provided on a first portion of a first link. A driving arm has one end fixed to the driving shaft and an opposite end being movable following rotation of the driving shaft. A first auxiliary link has one end pivotably connected to the opposite end of the driving arm. A second auxiliary link is pivotably connected to a first point of a second portion of the first link and to an opposite end of the first auxiliary link. A second link is disposed below the first link and pivotably connected to the second auxiliary link. A third auxiliary link has one end pivotably connected to a second point of the second portion of the first link, separated from the first point, and an opposite end pivotably connected to the second link.