Exoskeleton Joint Actuator Using Ball Screw and Cam for Bidirectional Force
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Solution Overview
Problem
Current exoskeletons face challenges in applying bidirectional force to joints without increasing bulk, efficiently transferring force from motors to joints, and ensuring safety by avoiding failure-prone components like tensile members.
Innovation Solution
The use of ball screw-driven joint cam and in-line slider crank linkage actuator devices, which incorporate load cells for force sensing and are designed to be low-profile, allowing bidirectional movement and force application away from the joint, with electric motor-driven mechanisms that minimize energy consumption and provide mechanical advantage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tensile members are used to transfer force from motor to joint, then force transfer is achieved, but system reliability deteriorates due to failure-prone components
Solution Approach 1:
The patent removes tensile members (belts, chains, cables) from the force transfer mechanism and replaces them with a rigid rod connected to a cam mechanism. This extraction of the failure-prone tensile member eliminates the primary source of system failures while maintaining the ability to transfer force bidirectionally from the motor to the joint.
Solution Approach 2:
Instead of using a tensile member that can only pull in one direction, the patent inverts the approach by using a rigid rod with a cam mechanism that can push and pull bidirectionally. The cam profile converts the motor's rotational motion into bidirectional linear motion of the rod, eliminating the need for tensile members while achieving bidirectional force application.
2Force
If actuators are located proximal to joints, then force application is direct, but device bulk increases at the joint
Solution Approach 1:
The actuator system is segmented into two functional parts: the motor and power transmission components remain at a distance from the joint (in the arm or leg structure), while only the compact cam and rod mechanism are positioned proximal to the joint. This segmentation allows direct force application at the joint while keeping the bulk of the actuator远离 the joint.
Solution Approach 2:
The patent introduces a cam mechanism as an intermediary between the distant motor and the joint. The cam converts rotational motion into linear motion of the rod, which then directly actuates the joint. This intermediary allows the motor to be positioned away from the joint while still achieving direct force application through the compact rod-cam assembly at the joint location.
3Ease of operation
If bidirectional force application is implemented, then joint movement control is improved, but device complexity increases
Solution Approach 1:
The patent achieves bidirectional force application not by adding complex dual-motor or dual-tensile-member systems, but by inverting the simple unidirectional tensile member approach. A single motor driving a cam mechanism naturally produces bidirectional motion through the cam profile, achieving bidirectional control with simpler mechanics than alternative approaches.
Solution Approach 2:
The cam profile geometry is designed to change parameters of force application - the cam shape determines the timing, magnitude, and direction of force throughout the rotation cycle. By modifying the cam profile parameters, the system achieves sophisticated bidirectional joint control without increasing mechanical complexity, as the entire bidirectional control function is embedded in the cam's geometric parameters.
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
These solutions enable efficient, bidirectional force application with reduced bulk, improved safety by eliminating failure-prone components, and precise control of joint movement and force, enhancing exoskeleton mobility and usability in various environments.
Implementation Method 1
ball screw-driven joint cam and in-line slider crank linkage actuator devices
Implementation Method 2
electric motor-driven mechanisms that minimize energy consumption and provide mechanical advantage
Implementation Method 3
incorporate load cells for force sensing
Data Source
Figure 1A
Figure 1B
Figure 1C
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.