Cogging-Torque Actuator for Passive Load Holding in Robotics
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Solution Overview
Problem
Conventional robotic actuators face challenges such as high-speed rotation inefficiency, weak direct-drive motors, continuous power supply needs for position holding, and lack of compliance, which complicates control and safety in agile robotics applications.
Innovation Solution
The development of a cogging-torque actuator (CTA) with a permanent magnet rotor and ferromagnetic stator poles, optimized for non-continuous rotation, which maximizes cogging torque and incorporates a controller for impedance control and torque sensing, allowing for efficient, compliant, and energy-efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional electromagnetic motors are used for robotic actuation, then continuous smooth rotation and high-speed operation are achieved, but the motors require continuous power supply for position holding and lack inherent compliance
Solution Approach 1:
The patent inverts the conventional motor design approach by intentionally maximizing cogging torque instead of minimizing it. This inversion allows the actuator to hold position passively without continuous power supply, as the high cogging torque creates stable equilibrium positions that naturally resist movement. The ferromagnetic stator poles and permanent magnet rotor are specifically designed to generate strong cogging torque that enables passive load holding.
Solution Approach 2:
The patent converts the harmful effect of cogging torque (which causes torque ripple and position inaccuracies in conventional motors) into a beneficial feature. By designing the stator and rotor geometries to maximize cogging torque, the actuator gains the ability to passively hold loads and provide inherent compliance, transforming what was previously a parasitic element into a useful functional characteristic.
2Ease of operation
If direct-drive motors are used, then ease of control and simplicity are achieved, but the motors are weak for their size
Solution Approach 1:
The patent changes the key design parameters of the electromagnetic actuator, specifically the number and configuration of stator poles and rotor magnets, to optimize cogging torque generation. The ferromagnetic stator poles are arranged with specific spacing and dimensions, and the permanent magnet rotor uses alternating polarity arrangements, all designed to maximize the cogging torque effect while maintaining a compact direct-drive structure.
3Force
If heavily geared motors are used, then torque output is increased, but efficiency decreases and compliance is lost
Solution Approach 1:
The patent extracts and eliminates the gearbox component entirely by designing a direct-drive actuator that generates high torque through maximized cogging torque effects. This removes the efficiency losses associated with gear meshes and mechanical transmissions, while the inherent compliance of the high-cogging-torque design provides the safety and robustness previously offered by geared systems.
4Reliability
If brakes are added to achieve holding torque, then position holding capability is improved, but device complexity increases
Solution Approach 1:
The actuator serves itself by using its own electromagnetic structure to provide position holding capability. The high cogging torque generated by the interaction between permanent magnet rotor and ferromagnetic stator poles creates stable equilibrium positions that naturally hold loads without requiring external brake mechanisms. The system's own design features provide the holding function internally.
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 CTA enables efficient, compliant, and energy-efficient operation by maximizing cogging torque, allowing for passive load holding without continuous power supply and simplifying control, enhancing robotic agility and safety.
Implementation Method 1
Cogging torque is the rate change of the magnetic energy with the angular position with null rotor currents. Cogging torque is caused by the interaction of rotor magnets with stator slots (i.e., the space between stator poles).
Implementation Method 2
The ferromagnetic pole body can have at least four ferromagnetic stator poles each wrapped in a conductive wire to define a stator coil. These ferromagnetic stator poles are sized, and spaced radially from each other, so as to define a maximum cogging torque of the electromagnetic actuator.
Implementation Method 3
each wrapped in a conductive wire to define a stator coil
Data Source
AI summary
An electromagnetic actuator for non-continuous rotation (cogging-torque actuator (CTA)) (100) comprises a support structure (116), an output shaft (104) rotatable about and defining an axis of rotation (X), a permanent magnet rotor (106) comprising at least two magnetic poles (108a, 108b) attached to the output shaft (104), and a stator device (110) comprising a ferromagnetic pole body (112) attached to the support structure (116) and surrounding the at least two magnetic poles (108a, 108b). The ferromagnetic pole body (112) can have at least four ferromagnetic stator poles (112a-d) each wrapped in a conductive wire (114a-d) to define a stator coil. The at least four ferromagnetic stator poles (112a-d) are sized, and spaced radially from each other, so as to define a maximum cogging torque of the electromagnetic actuator (100). The CTA (100) can operate as an actuator, an elastic spring, a clutch, and/or a load support device.