Robotic Joint Actuator Backlash Reduction

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Solution Overview

Problem

Existing robotic joint actuators struggle to provide high torque at low speeds without significant backlash, which is essential for forming precise and human-like movements in humanoid robots.

Innovation Solution

The development of an actuator that includes a motor with a stator and rotor, an output shaft, and a gear reducer, such as a strain wave gear, which couples the rotational motion of the rotor to the output shaft, along with rotary encoders to measure rotational parameters, enabling high torque and low-speed operation with minimal backlash.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If a gear reducer is used to provide high torque at low speed, then torque output is improved, but backlash increases

Engineering Contradiction:

Improvetorque outputVSAvoidbacklash

Core Design Contradiction:

ForceVSManufacturing precision

Solution Approach 1:

The patent replaces traditional mechanical gear reducers with a direct-drive motor system that uses electromagnetic fields to generate torque directly at the output shaft. This eliminates the mechanical gear train entirely, providing high torque without any backlash while maintaining low-speed operation capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a magnetic field as an intermediary between the motor and the load. The magnetic field couples the rotor to the stator, enabling torque transmission without physical mechanical contact or gear mechanisms, thus achieving backlash-free torque delivery.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If a motor is used to provide rotational motion, then speed is improved, but torque at low speed decreases

Engineering Contradiction:

Improverotational speedVSAvoidtorque at low speed

Core Design Contradiction:

SpeedVSForce

Solution Approach 1:

The patent changes the operating parameters of the motor by designing it with high pole count and optimized magnetic field distribution, enabling the motor to deliver high torque even at low rotational speeds. The motor control system also dynamically adjusts current and voltage parameters to maintain optimal torque-speed characteristics.

Inventive Principle:

Principle #35Parameter changes

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

This actuator effectively provides rotational motion with high torque and low speed, suitable for forming robotic joints with multiple degrees of freedom, enabling precise and human-like movements in humanoid robots.

Implementation Method 1

The motor includes a stator rotationally fixed relative to the actuator housing and a rotor rotatable relative to the stator and the actuator housing

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

A first rotary encoder is coupled to the rotor and measures at least one parameter of the rotational motion of the rotor

Methodology Applied

Scientific EffectMagnetic field detection: Magnetic Field

Data Source

PatentUS12240111B2Robotic joint actuator

Publication Date: 2025.03.04 SANCTUARY COGNITIVE SYST CORP

AI summary

An actuator for a robotic joint includes an actuator housing. A motor is disposed within the actuator housing. The motor includes a stator that is rotationally fixed relative to the actuator housing and a rotor that is rotatable relative to the stator and actuator housing. An output shaft is coupled to a rotational motion of the rotor by a gear reducer. A first rotary encoder is coupled to the rotor to measure one or more parameters of the rotational motion of the rotor. A second rotary encoder is coupled to the output shaft to measure one or more parameters of a rotational motion of the output shaft.