Encoder Signal Interference for Motor Position Resolution

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Solution Overview

Problem

Existing methods for detecting the dynamic state of brushless, electronically commutated direct current small servomotors face challenges in achieving high-resolution position determination within one revolution, especially with small motors, due to signal interference and fabrication tolerances, which affect the accuracy of rotor position measurement.

Innovation Solution

A method using a highly interpolated encoder system that compares the time profile of systematically fluctuating signal interference in the current output signal with a reference signal sequence to determine the current initial rotational position, allowing for unambiguous determination of rotational positions within one revolution, robust against mechanical loading and fabrication tolerances, without the need for additional sensors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a highly interpolated encoder system is used to achieve high resolution position determination, then measurement precision is improved, but signal interference and fabrication tolerances worsen the reliability of position measurement

Engineering Contradiction:

Improveposition determination resolutionVSAvoidposition measurement accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent converts the harmful signal interference and systematic fluctuations into a useful reference signal. By capturing and storing the characteristic time profile of systematically fluctuating interference from a reference signal sequence, the system uses these previously harmful fluctuations as a basis for comparison and correction in current measurements, thereby improving reliability despite high interpolation.

Inventive Principle:

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

Solution Approach 2:

The system implements feedback by comparing the time profile of systematically fluctuating signal interference in current output signals with the stored reference time profile. This continuous comparison allows the system to detect deviations caused by fabrication tolerances and mechanical loading, and correct the position determination accordingly, maintaining both high precision and reliability.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If additional sensors are added to improve position determination accuracy, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improverotor position accuracyVSAvoidsensor system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent makes the existing encoder system self-correcting by using its own signal interference characteristics as a reference. The system extracts and stores the systematic fluctuation pattern from the encoder output signal itself, then uses this stored reference to correct future measurements, eliminating the need for additional sensors while maintaining high accuracy.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The reference signal sequence serves multiple functions: it characterizes the systematic interference pattern, provides a baseline for comparison, and enables correction of position measurements. This multi-functionality allows the system to achieve high precision without adding dedicated reference sensors, thereby avoiding increased device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If the number of increments per revolution is increased to achieve higher resolution, then measurement precision is improved, but the impact of signal interference and fabrication tolerances worsens

Engineering Contradiction:

Improveangular resolutionVSAvoidfabrication tolerance sensitivity

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent converts the harmful effects of fabrication tolerances and signal interference into a beneficial reference pattern. By capturing the characteristic time profile of systematically fluctuating interference from a reference signal sequence obtained during manufacturing or initial operation, the system creates a unique fingerprint that accounts for fabrication variations. This reference is then used to correct subsequent measurements, enabling high angular resolution without being limited by manufacturing precision.

Inventive Principle:

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

Data Source

PatentUS8836262B2Method and arrangement for determining the dynamic state of an electric motor

Publication Date: 2014.09.16 DR FRITZ FAULHABER GMBH & CO KG

AI summary

In a method for the determination of a current initial rotational position of a rotor and in an arrangement for carrying out same, an incremental position encoder outputs an output signal. The output signal is produced by superposition of a chronologically random and systematically fluctuating signal interference on a basic signal, and composed of at least two component signals which change periodically in accordance with the rotational position of the rotor and are in a fixed angular relationship to one another. To determine the position, the output signal is used exclusively. The current initial rotational position of the rotor relative to a reference initial rotational position is determined by comparing the time profile of the portion of the systematically fluctuating signal interference of a current measured value sequence of the signal and the measured values of a signal sequence acquired starting from the reference initial rotational position.