Exoskeleton Joint Actuator Using Ball Screw and Cam Force Transmission
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Solution Overview
Problem
Current exoskeletons face challenges in applying bidirectional force to joints efficiently, as existing actuators are bulkier, prone to failure, and limited in mechanical advantage, especially when located near joints, which affects maneuverability and safety.
Innovation Solution
The use of a ball screw-driven joint cam actuator system with a load cell, where a yoke translates axially along a ball screw to rotate a joint cam, allowing bidirectional movement and force application, and is integrated with a load cell for precise force sensing, reducing bulk and eliminating failure-prone components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If actuators are located near joints to apply force directly, then force transmission efficiency is improved, but device bulk and complexity increase
Solution Approach 1:
The actuator system is divided into separate functional components: a motor unit, a ball screw mechanism, and a joint cam. This segmentation allows the motor to be positioned away from the joint while the compact ball screw and cam mechanism are located near the joint, achieving both efficient force transmission and reduced bulk at the joint location.
Solution Approach 2:
The ball screw mechanism acts as an intermediary between the motor and the joint cam. It converts rotational motion from the motor into linear motion that actuates the joint cam, enabling efficient force transmission over a distance while keeping the joint-mounted components compact.
2Force
If traditional actuator mechanisms are used, then force application is achieved, but reliability decreases due to failure-prone components
Solution Approach 1:
The invention replaces traditional belt-driven or gear-driven mechanisms with a ball screw mechanism. The ball screw provides direct mechanical coupling between the motor and the joint cam, eliminating failure-prone components like belts and gears while maintaining reliable force application through its self-lubricating, wear-resistant threaded interface.
3Force
If mechanical advantage is increased to improve force multiplication, then force output is improved, but device complexity and bulk increase
Solution Approach 1:
The ball screw mechanism provides mechanical advantage through its threaded geometry, where the pitch of the threads determines the force multiplication ratio. By adjusting the thread pitch parameter, the system achieves variable mechanical advantage without adding complexity, as the same ball screw mechanism adapts to different force requirements through parameter selection rather than structural modification.
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
This solution enables efficient bidirectional force transmission with reduced bulk, improved safety, and precise control of joint movement, enhancing exoskeleton mobility and usability in various environments.
Implementation Method 1
a ball screw-driven joint cam actuator system with a load cell, where a yoke translates axially along a ball screw to rotate a joint cam
Data Source
AI summary
An exoskeleton includes a first support, a second support, and a joint connecting the first and second supports. An actuator causes relative rotation between the first and second supports at the joint. The actuator includes a motor, a ball screw, a ball nut, and a yoke. The motor causes translation of the yoke via the ball screw and the ball nut. In some embodiments, the actuator further includes a roller and a joint cam having a track. Translation of the yoke causes movement of the roller within the track, and movement of the roller within the track causes rotation of the joint cam. In other embodiments, the actuator further includes a linkage and a joint crank. Translation of the yoke causes movement of the linkage, and movement of the linkage causes rotation of the joint crank. Rotation of the joint cam or the joint crank causes relative rotation between the first and second supports.