Variable-Stiffness Cable Actuator for Safe Robot Arm Torsion
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Solution Overview
Problem
Robot arm actuators face safety concerns due to high stiffness, which can lead to damage when encountering unwanted objects, and existing solutions that reduce stiffness compromise torsion capabilities.
Innovation Solution
An actuator design that includes a casing, output disc, transmission component, cable, and tension adjustment assembly, allowing for adjustable stiffness by varying the tension of the cable through a lever, elastic component, and slidable component, enabling responsive stiffness adjustments to operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stiffness between the motor and the arm is limited to make the arm more elastically reacting to objects, then safety is improved, but the arm loses sufficient torsion capability
Solution Approach 1:
The patent applies a variable stiffness mechanism that dynamically adjusts the stiffness between the motor and arm based on operational requirements. The mechanism includes a spring element and a tensioning device that can modify the pre-tension force on the cable, allowing the system to transition between high stiffness (for torsion capability) and low stiffness (for safety and elastic reaction) states. This dynamic adjustment resolves the contradiction by making stiffness a variable parameter rather than a fixed property.
Solution Approach 2:
The invention changes the stiffness parameter of the transmission system by adjusting the tension in the cable through the tensioning device. By varying the pre-tension force applied to the spring-cable assembly, the effective stiffness between the motor output and the arm can be modified. This parameter change allows the system to optimize between safety (lower stiffness) and torsion capability (higher stiffness) depending on the operational context.
2Force
If high stiffness is maintained in the motor-arm connection, then torsion capability is improved, but safety deteriorates due to potential damage from unwanted objects
Solution Approach 1:
The variable stiffness mechanism enables the system to switch between high and low stiffness states dynamically. During normal operation requiring high torque, the system maintains high stiffness for sufficient torsion capability. When safety is a concern or during collision detection, the stiffness is reduced to allow elastic reaction, preventing damage to the motor and arm. This dynamic switching resolves the contradiction between torsion capability and safety.
Solution Approach 2:
The spring element in the cable-tensioning mechanism serves as a pre-configured cushioning element. The spring is pre-compressed or pre-tensioned to provide a baseline compliance that can absorb impact energy from unwanted objects before they reach the motor. This beforehand cushioning protects the motor while still allowing the system to maintain sufficient stiffness for normal torsional loads through the tensioning device.
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 actuator provides adjustable stiffness and torsion to robot arm members, enhancing safety by allowing for responsive reactions to external forces while maintaining sufficient mechanical capability.
Implementation Method 1
The elastic component is connected to the casing and the second end of the lever
Implementation Method 2
The tension of the cable can be adjusted by adjusting the ratio of the effort arm of the cable to the resistance arm of the elastic component
Data Source
AI summary
An actuator includes a casing, an output disc, a transmission component, a cable, a power source, and a tension adjustment assembly. The output disc and the transmission component are rotatably disposed on the casing. The cable is disposed through the transmission component and connected to the output disc. The power source can drive the transmission component. The tension adjustment assembly includes a lever, an elastic component, and a slidable component. The lever has a first end and a second end opposite to each other. The first end is connected to the cable. The elastic component is connected to the casing and the second end of the lever. The slidable component is in contact with a portion of the lever located between the first end and the second end, and is slidable along the lever to change its position to adjust a tension of the cable.