Robot Wheel Motor Encoder Layout for Magnetic Field Balance

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Solution Overview

Problem

Existing robot wheel driving apparatuses using inverter motors face issues with magnetic encoder accuracy due to magnetic field leakage and imbalance caused by components like bearings, leading to reduced control precision, increased torque ripple, and motor vibration.

Innovation Solution

The apparatus optimally designs the relative positions and distances of the encoder sensor, sensor magnet, and magnetic parts (such as bearings) to maintain precise magnetic flux density, enhancing the accuracy of the magnetic encoder and reducing torque ripple.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If magnetic parts (bearings, washers) are positioned around the encoder sensor and sensor magnet, then the motor structure is compact and support is stable, but magnetic field leakage and imbalance occur, reducing encoder accuracy

Engineering Contradiction:

Improveencoder accuracyVSAvoidmagnetic field leakage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A non-magnetic spacer is introduced as an intermediary component between the magnetic parts (bearings, washers) and the encoder components (sensor magnet, encoder sensor). This spacer acts as a magnetic field barrier that prevents magnetic field leakage and imbalance, thereby maintaining encoder accuracy while allowing the motor structure to remain compact.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The motor structure is segmented into distinct zones: a magnetic component zone containing bearings and washers, and an encoder zone containing the sensor magnet and encoder sensor. The non-magnetic spacer creates physical separation between these zones, preventing magnetic interference while maintaining structural integrity.

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If the distance between sensor magnet and encoder sensor is reduced, then the magnetic flux density increases and detection sensitivity improves, but magnetic field imbalance increases due to nearby magnetic parts

Engineering Contradiction:

Improverotation angle detection precisionVSAvoidmagnetic field balance

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The non-magnetic spacer serves as a protective intermediary that shields the encoder sensor and sensor magnet from magnetic field distortion caused by nearby magnetic parts. This allows the components to be positioned close together for high detection sensitivity while the spacer maintains magnetic field balance.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The spacer provides localized magnetic field protection specifically in the encoder detection zone, allowing different parts of the motor to have different magnetic properties - the encoder zone maintains balanced magnetic fields while other zones can use magnetic parts for structural support.

Inventive Principle:

Principle #3Local quality

3Device complexity

If magnetic parts are assembled close to the encoder components, then assembly is simplified and device complexity is reduced, but torque ripple and vibration increase due to magnetic field imbalance

Engineering Contradiction:

Improveassembly complexityVSAvoidtorque ripple

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The non-magnetic spacer is a simple component that does not complicate the assembly process. It can be easily positioned and fixed between magnetic parts and encoder components, providing magnetic field protection without adding significant assembly complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The spacer converts the potentially harmful effect of being close to magnetic parts into a benefit by using the spacer itself as a magnetic field barrier. The close positioning that would normally cause torque ripple is now advantageous because it reduces the overall motor size while the spacer prevents magnetic interference.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 design improves motor control precision, increases torque, and decreases torque ripple, resulting in more stable and accurate motor operation.

Implementation Method 1

The encoder sensor receives a change in the magnetic field (or a magnetic flux density) at each angle generated while the sensor magnet rotates to determine a rotation angle of the rotor

Methodology Applied

Scientific EffectMagnetic field detection: Magnetic Field

Implementation Method 2

The sensor magnet is connected to a rotor of the motor and rotates with the rotor. The encoder sensor receives a change in the magnetic field (or a magnetic flux density) at each angle generated while the sensor magnet rotates

Methodology Applied

Scientific EffectMagnetic field generation: Magnetism

Data Source

PatentUS12556068B2Robot wheel driving apparatus

Publication Date: 2026.02.17 LG ELECTRONICS INC

AI summary

A robot wheel driving apparatus includes a wheel configured to rotate to drive a robot, a motor housing positioned inside the wheel, a motor including a stator and a rotor configured to rotate about the stator to transmit a rotating force to the wheel, a sensor magnet connected to the rotor, and an encoder sensor configured to receive a change in a magnetic field caused by rotation of the sensor magnet to detect a rotation angle of the rotor. A first set distance is maintained between the sensor magnet and the encoder sensor.