Cogging-torque actuator
Inventors
Abbott, Jacob J • Roundy, Shad • Aman, Jacob
Assignees
University of Utah • University of Utah Research Foundation Inc
Publication Number
US-11967871-B2
Publication Date
2024-04-23
Expiration Date
2038-09-17
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Abstract
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.
Core Innovation
The invention is an electromagnetic actuator for non-continuous rotation referred to as a cogging-torque actuator (CTA). It comprises a support structure, an output shaft rotatable about an axis of rotation, a permanent magnet rotor with at least two magnetic poles attached to the output shaft, and a stator device with a ferromagnetic pole body and at least four ferromagnetic stator poles, each wrapped in a conductive wire to form stator coils. The stator poles are sized and spaced to define a maximum cogging torque, with the total actuator torque being within the same order of magnitude as this maximum cogging torque.
The problem addressed is that traditional motors for robotic actuators are designed to minimize cogging torque, which leads to inefficiency for applications requiring holding torque, compliance, and position holding under load. Existing solutions involve additional brakes or elastic elements, resulting in complex and inefficient systems. The invention instead deliberately maximizes cogging torque to create stable passive equilibria, enabling the actuator to function as a spring, clutch, brake, and load support device without the need for continuous electrical power or complex mechanisms.
The core innovation includes the ability of the actuator’s control system to implement motion primitives associated with rotational movement, such as mechanical impedance, point-to-point submovements, and oscillations. These allow the actuator to dynamically adjust its magnetic spring and damping characteristics, step between equilibrium positions, and oscillate efficiently, using the magnetic forces created by the permanent magnet rotor and stator geometry. The approach enables improved energy efficiency, inherent compliance, and simplified control for a wide range of actuator and joint applications.
Claims Coverage
There are two main independent inventive features claimed in this patent, forming the core of the inventive coverage.
Electromagnetic actuator for non-continuous rotation with maximum cogging torque
The actuator includes: - A support structure - An output shaft rotatable about an axis - A permanent magnet rotor with at least two magnetic poles attached to the output shaft - A stator device comprising a ferromagnetic pole body attached to the support structure and surrounding the magnetic poles, with at least four ferromagnetic stator poles, each wrapped in a conductive wire to form a stator coil The ferromagnetic stator poles are sized and spaced radially from each other to define a maximum cogging torque, and the total torque of the actuator is within the same order of magnitude as the maximum cogging torque, where the same order of magnitude is less than ten times.
System for controlling rotational movement of a joint using a cogging-torque actuator
The system includes: - First and second support members rotatably coupled to define a joint - An electromagnetic joint module comprising: - An input member coupled to the first support member - An output shaft coupled to the second support member, where the input and output member are rotatable about the axis, and at least two magnetic poles are attached to the output shaft - A ferromagnetic pole body attached to the input member, with a plurality of ferromagnetic stator poles each wrapped in a conductive wire to define a stator coil The system is configured such that the magnetic poles and stator poles define a maximum cogging torque, the total torque is within the same order of magnitude as the maximum cogging torque (less than ten times), and a controller is operably coupled to each stator coil to control non-continuous rotational movement of the joint.
In summary, the inventive features cover a cogging-torque actuator that maximizes cogging torque for non-continuous rotation, and a control system for joints utilizing such actuators, with torque relationships and stator/rotor designs specified to maintain the actuator's holding capabilities and energy efficiency.
Stated Advantages
Provides inherent holding torque and stable passive equilibria, enabling the actuator to support a load without continuous electrical power or additional brake mechanisms.
Maximizes energy efficiency by using passive magnetic forces to maintain position and resist torque, reducing power consumption compared to traditional motors.
Offers inherent compliance and a magnetic spring effect, reducing the need for mechanical springs or other elastic elements.
Simplifies actuator and joint module design by combining actuator, spring, clutch, brake, and load support functionalities in one compact device.
Facilitates direct implementation of motion primitives such as mechanical impedance, step movements, and oscillations, enabling improved agility and control in robotic applications.
Provides inherent torque sensing capability due to a known relationship between position, stiffness, and stator currents.
Increases safety factor for robotic systems through inherent compliance and limited passive holding torque.
Documented Applications
Robotic joints, including actuators for robotic arms and legs.
Exoskeleton joints, such as lower or upper body exoskeletons for human augmentation.
Prosthetic joints for use in artificial limbs.
Precision actuators in manufacturing automation equipment.
Haptic interfaces for providing force feedback in interactive devices.
Load support and stepper hinge applications, such as in window or door hinges, monitor supports, and lighting armatures.
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