Thermal Variable Impedance Actuator Using Polycaprolactone
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Solution Overview
Problem
Existing variable impedance actuators (VIAs) are bulky and heavy due to added mechanisms for impedance adjustment, limiting their suitability in physical human-robot interaction applications, particularly in bipedal locomotion and manipulation, where energy efficiency and safety are critical.
Innovation Solution
A thermal-based variable impedance actuator using polycaprolactone, a thermoplastic polymer with temperature-dependent viscoelastic properties, controlled by embedded Peltiers to adjust stiffness and damping, offering a lightweight and compact design suitable for off-line impedance adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If dedicated mechanisms are added to adjust impedance parameters, then impedance regulation capability is improved, but actuator weight and volume increase
Solution Approach 1:
The patent replaces traditional mechanical impedance adjustment mechanisms with a thermal field-based approach. By using thermal actuators that expand or contract in response to temperature changes, the system achieves impedance regulation without bulky mechanical components, directly resolving the contradiction between regulation capability and weight.
Solution Approach 2:
The invention changes the physical state of the actuator material through temperature variation. By controlling the thermal parameters of the material (such as phase transition temperature or thermal expansion coefficient), the impedance characteristics are adjusted dynamically, eliminating the need for heavy mechanical adjustment mechanisms.
2Adaptability or versatility
If dedicated mechanisms are added to adjust impedance parameters, then impedance regulation capability is improved, but actuator complexity increases
Solution Approach 1:
The patent substitutes complex mechanical adjustment systems with a simpler thermal control system. The thermal actuator responds directly to temperature changes, eliminating the need for multiple mechanical components, linkages, and control mechanisms, thereby reducing overall device complexity while maintaining impedance regulation capability.
Solution Approach 2:
The invention utilizes phase transition phenomena in materials to achieve impedance adjustment. By controlling temperature to induce phase transitions (such as solid-liquid or crystalline-amorphous transitions), the material's mechanical properties change dramatically, providing impedance regulation through a simple thermal trigger rather than complex mechanical means.
3Measurement precision
If multiple independent motors are used to control damping and stiffness, then impedance control precision is improved, but device complexity and weight increase
Solution Approach 1:
The patent employs a single thermal actuator that performs multiple functions simultaneously. By controlling different aspects of the thermal field (such as temperature magnitude and heating rate), the system can independently regulate both stiffness and damping characteristics, eliminating the need for separate motors and reducing overall complexity.
Solution Approach 2:
The invention utilizes composite material structures with specific thermal-mechanical properties. These composite materials exhibit coupled thermo-mechanical behavior where temperature changes simultaneously affect both elastic and viscous properties, enabling precise control of multiple impedance parameters through a single thermal control channel.
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 achieves efficient impedance regulation with scalable design, enhancing safety and energy efficiency by leveraging temperature-dependent viscoelastic properties of polycaprolactone, while maintaining compactness and reducing inertia, thus improving performance in human-robot interaction tasks.
Implementation Method 1
controlled by embedded Peltiers to adjust stiffness and damping
Implementation Method 2
polycaprolactone, a thermoplastic polymer with temperature-dependent viscoelastic properties
Data Source
AI summary
An actuator includes an output link; an input member, wherein the output link and the input member are rotatable about an axis of rotation; an elastic member disposed between the output link and the input member and configured to allow transmission of torque between the output link and the input member about the axis of rotation, and to allow at the same time, as a result of elastic deformation of the elastic member, a relative rotation between the output link and input member about the axis of rotation; and a thermo-active module comprising one or more thermoplastic inserts, wherein the thermoplastic inserts are configured to apply a variable resistance between the output link and the input member and provide an adjustable damping between the output link and the input member.