Encoder Eccentricity Calibration via Software Correction

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Solution Overview

Problem

Surface measurement instruments with rotary encoders face measurement errors due to eccentricity between the encoder's measurement axis and the turntable's rotation axis, requiring costly mechanical adjustments or additional read heads for correction.

Innovation Solution

A method and apparatus to characterize and correct for encoder eccentricity by measuring an artefact's undulating profile at multiple rotational positions, processing data to extract parameters describing the eccentricity, and using software to calculate corresponding angles, allowing for calibration without physical modifications.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If mechanical adjustment means are employed to correct encoder eccentricity, then measurement precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidinstrument complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces mechanical adjustment means with a software-based solution. The system uses a processor to calculate correction parameters based on measured data from the eccentric rotary encoder, then applies software corrections to compensate for eccentricity effects, eliminating the need for mechanical adjustment mechanisms.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operational parameters of the rotary encoder by allowing it to operate with eccentricity rather than requiring perfect alignment. The system measures the actual eccentric parameters and uses these measured parameters to calculate and apply correction factors, transforming the problem from one of mechanical precision to one of computational correction.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If a second read head spaced 180° apart is used to correct eccentricity, then measurement precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidencoder complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the hardware solution of adding a second read head with a software-based correction approach. The single read head collects data that includes eccentricity effects, and the processor subsequently removes these effects through computational algorithms, avoiding the need for additional hardware components.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent creates a computational model or representation of the eccentricity effects based on measured data, then uses this model to generate correction parameters. This virtual copy of the eccentricity behavior allows the system to compensate for errors without physically duplicating the read head hardware.

Inventive Principle:

Principle #26Copying

3Measurement precision

If mechanical adjustment means are provided for encoder positioning, then measurement precision is improved, but ease of operation and calibration time worsen

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidcalibration time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent replaces time-consuming mechanical adjustment and calibration procedures with automated software-based calibration. The system automatically measures eccentricity parameters during operation and calculates correction factors without requiring manual mechanical adjustments or repeated measurement-correction cycles.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent performs preliminary measurement of the eccentricity parameters during the initial setup or operation, then uses these pre-measured parameters to calculate correction factors that are applied continuously. This eliminates the need for repeated measurement-correction cycles and establishes the correction parameters in advance.

Inventive Principle:

Principle #10Preliminary action

4Measurement precision

If existing instruments are retro-corrected with additional hardware, then measurement precision is improved, but ease of manufacture and cost worsen

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidretrofit cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent replaces hardware-based retro-correction solutions with a software update approach. Existing instruments can be retro-fitted with the eccentricity correction capability simply by updating the firmware or software and loading the measured correction parameters, avoiding the need for expensive mechanical modifications or additional hardware installation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP2542853B1Surface measurement instrument and calibration thereof

Publication Date: 2017.09.20 TAYLOR-HOBSON

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AI summary

A method of calibrating a surface measurement instrument comprises: rotating a work piece having an undulating surface on a turntable of a metrological apparatus; measuring the surface of the work piece at a plurality of rotational positions; analysing the results of the measurement to determine parameters describing an error causing characteristic of the metrological apparatus; and using the determined parameters to correct measurement data for the error causing characteristic of the metrological apparatus.