Variable-Stiffness Robotic Link With Adjustable Lever Arm
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Solution Overview
Problem
There is a need for improvements in variable-stiffness links to enhance robotic interactions and payload handling, particularly in making the actuator package compact while maintaining a meaningful stiffness adjustment range.
Innovation Solution
A variable stiffness link mechanism utilizing an actively changing lever arm with a spring-loaded carriage and a belt drive system to adjust stiffness without increasing the actuator's size, allowing for decoupled stiffness adjustment from rotational load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable-stiffness actuators use traditional designs with sufficient lever length for meaningful stiffness adjustment range, then stiffness adjustment range is improved, but actuator package size increases
Solution Approach 1:
The carriage is positioned inside the actuator housing, with the spring mechanism nested within the carriage structure. The lever arm is integrated into the housing itself rather than being a separate external component. This nesting arrangement allows the stiffness adjustment mechanism to fit within a compact actuator package while maintaining a sufficient lever arm length for meaningful stiffness adjustment range.
Solution Approach 2:
The carriage is made movable along the lever arm through a belt-driven mechanism, allowing the effective lever length to be dynamically adjusted. This dynamic reconfiguration enables the actuator to vary stiffness by changing the carriage position relative to the rotation axis, achieving a wide stiffness adjustment range without requiring a large fixed lever arm that would increase package size.
2Adaptability or versatility
If variable-stiffness mechanisms use long lever arms for meaningful stiffness adjustment, then stiffness adjustment range is improved, but device complexity increases
Solution Approach 1:
The lever arm serves multiple functions: it acts as both the structural element that transmits rotational force and the guide rail for the carriage movement. The belt mechanism that moves the carriage also serves to adjust the stiffness characteristic. This multi-functionality reduces the number of separate components needed, simplifying the overall mechanism while maintaining a meaningful stiffness adjustment range.
3Reliability
If stiffness adjustment is coupled with rotational load in variable-stiffness actuators, then actuator performance is improved, but actuator package size increases
Solution Approach 1:
The actuator is segmented into distinct functional modules: the motor module that generates rotational torque, the carriage module that positions the spring, and the spring module that provides the stiffness element. This segmentation allows the stiffness adjustment function to be decoupled from the rotational load path, enabling a more compact actuator package since the stiffness adjustment mechanism does not need to be oversized to handle full rotational loads.
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 mechanism provides a simple, inexpensive, and effective way to vary stiffness, ensuring safe robotic interactions and preventing damage during payload handling by decoupling stiffness adjustment from rotational load, thus enabling compact and efficient actuator packaging.
Implementation Method 1
a spring may be slidably and/or translationally coupled (e.g., via a carriage in some embodiments) to one of the first and second elongate arms such that the spring rides along one arm and is in contact with the other arm such that a spring force (e.g., determined by an amount of compression or tension of the spring
Data Source
AI summary
A variable stiffness mechanism for robotic applications. A robotic arm segment comprising two bodies pivotably coupled together at one end and having a generally elongate form factor. A spring-loaded carriage moves longitudinally along one of the two bodies and is in contact with the other body, such that the effective rotational stiffness of the pin joint is equal to the stiffness of the carriage spring multiplied by the distance between the pin joint and the spring. The distance between the pin joint and the spring can be varied using a motor and belt drive arrangement. A stopper may be coupled to the belt drive to lock the relative motion of the two bodies.