Friction Wheel Encoder Position Error Compensation

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Solution Overview

Problem

Existing methods for compensating accumulated position error in synchronous motors, particularly in high pole count permanent magnet motors used for elevator control, are ineffective below one-third of rated speed due to reliance on electrical signals prone to noise, and the physical construction of these motors makes traditional encoder mounting challenging, leading to errors in angular position determination.

Innovation Solution

A system that includes a friction wheel encoder engaging a rotating surface of the motor, a non-contact sensor detecting a target on the motor, and a controller that uses both the encoder signal and sensor pulse to determine and correct the angular position of the motor, compensating for errors caused by slippage and diameter ratios.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a friction wheel encoder is used to engage the rotating surface, then the motor can be mounted in the elevator shaft with reduced footprint, but position error accumulates due to slippage and diameter ratio imprecision

Engineering Contradiction:

Improvemotor footprintVSAvoidangular position accuracy

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The system uses feedback from a non-contact sensor detecting a target on the rotor to continuously monitor and correct the angular position. The controller compares the sensor signal with the encoder signal and applies correction to compensate for accumulated position errors, thereby maintaining measurement precision while using the space-saving friction wheel encoder configuration.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces the traditional mechanical contact-based encoder mounting with a non-contact sensor system. The non-contact sensor uses optical or electromagnetic fields to detect the target on the rotor, eliminating mechanical contact and associated errors while maintaining the friction wheel encoder's space-efficient design.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If sensorless techniques are used to determine angular position, then device complexity is reduced, but position error compensation fails below one-third of rated speed due to electrical noise

Engineering Contradiction:

Improveposition sensing system complexityVSAvoidposition error compensation reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The system introduces a target attached to the rotor as an intermediary element that the non-contact sensor can detect. This target serves as a reliable reference marker that generates a distinct signal independent of electrical noise, enabling accurate position detection and error compensation across the full speed range including low speeds where sensorless techniques fail.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If a shaft-mounted encoder is used for direct angular position measurement, then position accuracy is maintained, but the motor axial length increases protruding further into the elevator shaft

Engineering Contradiction:

Improveangular position accuracyVSAvoidmotor axial length

Core Design Contradiction:

Measurement precisionVSLength of moving object

Solution Approach 1:

The patent replaces the mechanical shaft-mounted encoder configuration with a friction wheel encoder combined with non-contact sensing. The friction wheel engages the rotor's external surface radially, and the non-contact sensor detects the target without mechanical connection, eliminating the need for an axial shaft extension while maintaining position measurement capability through signal processing and error compensation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 system effectively compensates for position errors across the full operating range of the motor, improving accuracy and reducing the need for direct shaft mounting, thus enhancing the motor's efficiency and reducing physical footprint.

Implementation Method 1

a non-contact sensor mounted to the PM motor. The non-contact sensor is configured to generate a signal corresponding to the target being located within a detection distance from the non-contact sensor

Methodology Applied

Scientific EffectNon-contact detection:

Implementation Method 2

an encoder with a friction wheel engages a rotating surface of the motor. The friction wheel is spun by the rotation of the motor

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentEP2824825B1Method and apparatus for determining position for a permanent magnet elevator motor

Publication Date: 2022.09.14 MAGNETEK INC

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AI summary

A system for determining the angular position of a synchronous motor includes an encoder with a friction wheel engaging a rotating surface of the motor. The friction wheel is spun by the rotation of the motor, and the encoder generates a signal corresponding to the angular position of the friction wheel. An independent sensor is provided to generate a pulse once per revolution of the motor. The independent sensor detects the presence of a target on the rotating surface of the motor and generates the pulse when the target is proximate to the sensor. A controller receives the signal corresponding to the angular position of the friction wheel as well as the pulse generated by the independent sensor to determine the angular position of the motor. The controller compensates the angular position of the motor each time the pulse is generated, correcting accumulated position error.