Rotary Encoder Angle Compensation for Scale Misalignment Errors

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Solution Overview

Problem

Conventional rotary encoders face challenges in accurately detecting rotation angles due to misalignment and deformation of the rotary scale, leading to errors in angle calculation, which are compounded by the need for multiple sensor heads to improve accuracy, complicating the structure and increasing costs.

Innovation Solution

A rotary encoder system that includes a rotary scale with a cylindrical surface and relative angle track, a sensor head to detect the track with varying signals, a first angle calculator, an angle error storage, and an angle compensator to compensate for errors based on stored angle errors, allowing accurate angle detection without increasing the number of sensor heads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple sensor heads are used to improve detection accuracy, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvedetection accuracyVSAvoidstructure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent creates a lookup table storing angle error compensation values in advance during system initialization or calibration. During normal operation, the microcontroller simply retrieves pre-calculated compensation values from the table based on the current rotation angle, eliminating the need for complex real-time calculations or multiple sensor heads.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses a software-based lookup table that copies and stores pre-calculated angle error compensation data. This virtual copy of the correction information allows the system to compensate for eccentricity and deformation errors without requiring additional physical sensor heads, thus reducing hardware complexity while maintaining high measurement precision.

Inventive Principle:

Principle #26Copying

2Measurement precision

If multiple sensor heads are used to compensate for eccentricity errors, then measurement precision is improved, but manufacturing cost increases

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent replaces the mechanical approach of using multiple physical sensor heads with a software-based error compensation system. The lookup table stores pre-calculated correction values that are applied through software processing, substituting complex hardware configurations with simpler software algorithms that achieve the same error compensation effect.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If the rotary scale is coupled with high precision to the rotating shaft, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improverotation angle detection accuracyVSAvoidcoupling precision requirement

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent accepts the inevitable eccentricity and deformation errors introduced during rotary scale coupling and converts them into beneficial correction data. By measuring the actual error characteristics during calibration and storing them in the lookup table, the system transforms what would be harmful misalignment errors into useful compensation information that improves overall measurement accuracy.

Inventive Principle:

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

Solution Approach 2:

The patent performs error characterization and lookup table creation during system initialization or calibration before normal operation begins. This preliminary action captures the specific error characteristics of the installed rotary scale configuration, allowing the system to compensate for coupling imperfections without requiring high-precision mechanical coupling in the first place.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS12467731B2Rotary encoder, rotary encoder system, and rotation angle detection method using rotary encoder

Publication Date: 2025.11.11 MAGNESCALE

AI summary

A rotary encoder 1 includes a rotary scale 2 having a cylindrical surface 2a as a detected surface and having a relative angle track 2b formed circumferentially on the cylindrical surface 2a, a sensor head 3 arranged with an interval from the cylindrical surface 2a and detecting the relative angle track 2b and outputting a detection signal, and a first angle calculator 4 calculating a rotation angle of the rotary scale 2 based on the detection signal from the sensor head 3. The rotary encoder 1 includes an angle error storage 7 storing an angle error corresponding to the size of the interval at each rotation angle calculated based on the detection signal from the sensor head 3, and an angle compensator 8 compensating the rotation angle calculated by the first angle calculator 4 based on the angle error at each rotation angle stored in the angle error storage 7.