Magnetic Parallel-Elastic Actuator for Backdrivable Pose Holding
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Solution Overview
Problem
Existing electric motors used in robotics face challenges such as high gear ratios leading to backlash, stick-slip friction, lack of compliance, and inefficiency, while direct-drive motors are weak for their size and weight, and traditional actuators struggle with being backdrivable and holding a pose under load without consuming power.
Innovation Solution
A magnetic cogging parallel-elastic actuator (MC-PEA) that combines a motor with a cogging-torque element, featuring alternating polarity magnets on a stator and rotor, allowing torques to sum in parallel, providing compliance, backdrivability, and the ability to hold a pose without power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high gear ratios are used to increase torque and reduce speed, then torque output is improved, but backlash and stick-slip friction are introduced reducing efficiency
Solution Approach 1:
The patent extracts and eliminates the gear train from the motor system, using a direct-drive motor configuration. This removes the source of backlash and stick-slip friction while maintaining high torque output through motor design optimization rather than mechanical multiplication.
Solution Approach 2:
The patent replaces the mechanical gear transmission system with an electromagnetic field-based direct-drive system. The motor generates high torque directly through electromagnetic interaction between stator and rotor magnets, eliminating mechanical gear interfaces and their associated losses.
2Force
If high gear ratios are used to increase torque and reduce speed, then torque output is improved, but compliance decreases becoming infinite impedance
Solution Approach 1:
The patent removes the rigid gear train that provides high gear ratios, replacing it with a direct-drive system that inherently provides compliance through the motor's electrical characteristics and control capabilities, eliminating the infinite impedance problem.
Solution Approach 2:
The patent changes the system parameters by using a direct-drive motor with optimized magnetic field interactions, allowing the motor to operate at lower speeds with high torque output while maintaining electrical compliance through control system adjustments rather than mechanical gearing.
3Ease of operation
If direct-drive motors are used to eliminate gears, then compliance and backdrivability are improved, but torque strength decreases for the size
Solution Approach 1:
The patent merges the stator and rotor magnetic field systems in a direct-drive configuration, optimizing the interaction between alternating polarity magnets to generate high torque directly at the motor shaft without mechanical multiplication, thereby achieving both compliance and torque strength.
Solution Approach 2:
The patent uses composite magnetic field structures with alternating polarity magnets arranged in specific patterns on both stator and rotor, creating a composite electromagnetic system that maximizes torque density while maintaining direct-drive compliance and backdrivability.
4Stability of the object's composition
If brakes are added to achieve holding torque, then pose holding capability is improved, but backdrivability is lost
Solution Approach 1:
The patent replaces the mechanical brake system with an electromagnetic field-based holding mechanism. The alternating polarity magnets create magnetic springs that provide passive elastic holding torque, allowing the system to maintain pose while remaining backdrivable through the magnetic field interaction.
Solution Approach 2:
The patent implements a self-holding mechanism where the magnetic spring system automatically maintains pose through its elastic energy storage capability. The system serves itself by using the magnetic field configuration to provide both motion control and position holding without external braking components.
5Stability of the object's composition
If series clutch actuators are used to achieve holding torque, then pose holding capability is improved, but nonlinearities are introduced
Solution Approach 1:
The patent replaces the friction-based series clutch mechanism with an electromagnetic magnetic spring system. This substitution eliminates the nonlinear friction characteristics of clutch actuators while providing smooth, predictable elastic holding torque through magnetic field interactions.
Solution Approach 2:
The magnetic spring system provides automatic pose holding through its inherent elastic properties, eliminating the need for complex clutch control mechanisms and their associated nonlinearities. The system self-regulates through magnetic field strength and configuration.
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 MC-PEA achieves higher torque and lower speed efficiently, with multiple stable equilibria for holding loads, reducing energy consumption and heat generation, and enabling backdrivability without nonlinearities or additional components.
Implementation Method 1
a plurality of stator magnet elements disposed radially about the stator and a plurality of rotor magnet elements radially positioned about the rotor
Implementation Method 2
cogging-torque element can include a stator that is stationary relative to the motor and a rotor that is rotatable relative to the stator
Data Source
AI summary
A magnetic cogging parallel-elastic actuator (100) can include a motor (102) having an output shaft (104). The actuator (100) can further include a cogging-torque element (106). The cogging-torque element (106) can include a stator that is stationary relative to the motor (102) and a rotor that is rotatable relative to the stator and comprises an output shaft (104). A plurality of stator magnet elements can be disposed radially about the stator and a plurality of rotor magnet elements can be radially positioned about the rotor. The output shaft (108) of the rotor of the cogging-torque element (106) can be connected in parallel with the output shaft (104) of the motor (102) such that an output torque of the actuator (100) is a sum of a torque of the cogging-torque element (106) and a torque of the motor (102).