Correlation Analysis and Compensation

This section describes how to perform correlation analysis and compensation.

Correlation reflects the absolute accuracy of the measurement system itself, indicating how closely results match the true value. Even if the repeatability of an inline measurement system is very good, the results still cannot meet requirements if correlation is poor. Therefore, correlation analysis and compensation must be carried out so that inline measurement results and coordinate measuring machine (CMM) results stay within the agreed range and meet measurement requirements.

Phase Goal

The goal of this phase is to evaluate the consistency between inline measurement results and CMM results, and configure compensation when necessary so the results meet project agreement requirements.

Entry Criteria

Before starting correlation analysis and compensation, it is recommended that the following conditions have been met:

  • The system has passed repeatability validation.

  • Parts for analysis and corresponding CMM reports are prepared.

  • Current output of the inline measurement system is stable and suitable for comparative analysis.

Correlation

Correlation refers to the degree of consistency between the measurement results of two different measurement devices when measuring the same dimension of the same part.

Correlation analysis and compensation

Correlation analysis and compensation refer to analyzing the relationship between the measurement results of two different measuring devices, followed by compensating the results of one device to improve the reliability of the device.

CMM Measurement Report

A CMM measurement report refers to a report generated by a coordinate measuring machine (CMM) that records, summarizes, and presents the measurement results of part dimensions and geometric features. Reports usually contain information about the part to be measured, measurement items, nominal values, measured values, deviations, and judgment results. In correlation analysis scenarios, CMM measurement reports are often used as a benchmark for consistency analysis with inline measurement results.

Principle of Correlation Compensation

  1. Select 5 parts. Measure each part 3 times using CMM and 10 times using the inline measurement system.

  2. For each measurement point, calculate "CMM value - Mech-Metrics value" to obtain the deviation.

  3. Calculate deviations for the 5 parts separately, remove outliers, and use the average as the compensation value.

  4. Add the compensation value to the Mech-Metrics measurement value so that inline measurement results at each point stay within the agreed range relative to CMM results.

Before performing correlation analysis and compensation, you must first verify the repeatability of the inline measurement system.

Correlation Compensation Methods

There are two main methods for correlation compensation:

  • Manual compensation

    For dimension cards in Mech-Metrics, the measurement value (output value) = raw measurement value + compensation value + offset value.

    • Compensation value: Calculated by comparing with CMM measurement values.

    • Offset value: Manually adjusted according to process requirements.

    Only administrators can view and modify this setting.

  • Compensation using the correlation compensation tool

    Mech-Metrics provides a correlation compensation tool that automatically calculates compensation values and applies them to measurement results without manual adjustment. For details, refer to Analyze correlation and perform correlation compensation.

Completion Criteria

After this phase is completed, the following conditions should be met:

  • Correlation results of key measurement points have been analyzed.

  • If a systematic deviation exists, compensation values have been calculated and configured.

  • Inline measurement results after compensation stay within the agreed range relative to CMM results.

  • The system is ready to enter go-live operation and continuous analysis.

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