Four-Bar Linkage Transmission for Powered Augmentation
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Solution Overview
Problem
Powered augmentation devices, such as prosthetics and exoskeletons, face challenges in achieving a broad range of speed-torque operating points, leading to larger, heavier, and more expensive actuators due to the need for a broad operating range, which limits the mechanical advantage and efficiency.
Innovation Solution
A four-bar linkage transmission provides a highly variable mechanical advantage, allowing the actuator to be optimized for a narrower operating range by varying the transmission ratio based on joint position, reducing peak speed and torque while maintaining efficiency and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed-ratio transmission element is used, then the structure is simple, but the actuator must cover a broad operating range leading to larger size, heavier weight, and higher cost
Solution Approach 1:
The patent applies a four-bar linkage mechanism that dynamically varies the transmission ratio based on joint position. The linkage connects the actuator to the joint through multiple moving links, allowing the mechanical advantage to change continuously as the joint moves through its range of motion. This dynamic transmission ratio enables the actuator to operate at lower peak speeds and torques while still delivering the required performance across the full operating range, thereby reducing actuator size and weight.
2Speed
If the transmission ratio is altered to reduce peak speed, then peak torque increases, but the broad operating range is still required
Solution Approach 1:
The four-bar linkage creates a dynamic transmission ratio that varies with joint position. At positions where high speed is needed, the linkage provides a lower transmission ratio; at positions where high torque is needed, it provides a higher transmission ratio. This dynamic adjustment allows both peak speed and peak torque to be reduced compared to a fixed-ratio system, as the actuator never needs to be sized for the worst-case combination of both parameters simultaneously.
3Use of energy by moving object
If a varying mechanical advantage is provided, then actuator efficiency increases, but the device complexity increases
Solution Approach 1:
The four-bar linkage provides varying mechanical advantage through its dynamic geometry, optimizing actuator efficiency across different joint positions. The linkage is designed so that the mechanical advantage automatically adjusts to match the torque-speed requirements at each position, keeping the actuator operating in its efficient range. While this adds mechanical complexity, the linkage uses simple rigid links and pivots without requiring active control systems, sensors, or complex actuators, thus limiting the increase in overall device complexity.
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 four-bar linkage transmission optimizes actuator efficiency, reduces bulk and weight, and allows for a compact, lightweight design by consolidating the speed-torque operating range, enabling effective operation across a broad range of joint positions with reduced peak motor speed and torque.
Implementation Method 1
A four-bar linkage transmission provides a highly variable mechanical advantage, allowing the actuator to be optimized for a narrower operating range by varying the transmission ratio based on joint position
Data Source
AI summary
Exemplary embodiments herein relate to a unique 4-bar linkage transmission provided between two adjacent links of a powered augmentation device that provides a varying mechanical advantage. Due to the kinematics of the linkage, the mechanical advantage between the actuator and the augmented joint varies with the position of the linkage. Thus, a high mechanical advantage can be provided in positions at which relatively high joint torque is required, and low mechanical advantage in positions at which relatively high joint speed is required. Consequently, the speed-torque (or velocity-force) operating area of the actuator can be consolidated by mapping the widespread output regions onto a smaller input region. This allows the actuator to be optimized for a narrower range of usage.