Calibration Artefact for CMM Error Compensation

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Solution Overview

Problem

Coordinate measuring machines (CMMs) face challenges with long-term errors due to thermal, humidity, and mechanical influences, leading to inaccuracies and increased downtimes during calibration processes, which are time-consuming and disruptive to production.

Innovation Solution

A calibration artefact with defined touching regions is used to provide exact positional information, allowing for precise calibration by synchronizing machine coordinates with a nominal calibration position, enabling efficient error handling and reduced downtimes through simultaneous contact with touch tools, thereby deriving actual machine states and generating global error maps.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If calibration is performed frequently to maintain accuracy, then measurement precision is improved, but productivity deteriorates due to increased downtimes

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidproduction output

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The calibration artefact is pre-configured with multiple touching regions at precisely defined positions, allowing the calibration process to proceed directly without requiring complex setup or measurement procedures during calibration events

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The calibration artefact is designed to be self-calibrating through its geometric features, where the touching regions inherently define reference positions that the CMM can automatically detect and use for calibration, reducing the need for operator intervention and calibration complexity

Inventive Principle:

Principle #25Self-service

2Productivity

If calibration process is simplified to reduce downtime, then productivity is improved, but measurement precision deteriorates

Engineering Contradiction:

Improvecalibration speedVSAvoidcalibration accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The calibration artefact is segmented into multiple distinct touching regions, each serving as an independent reference point that can be quickly and accurately measured, allowing comprehensive calibration to be achieved through multiple simple measurements rather than one complex procedure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The calibration artefact utilizes geometric features with distinct visual characteristics (analogous to color changes) that enable rapid optical detection and verification of touching region contact, ensuring measurement accuracy while maintaining fast calibration speed

Inventive Principle:

Principle #32Color changes

3Measurement precision

If frame structure is made heavier for stability, then measurement precision is improved, but productivity worsens due to slower positioning

Engineering Contradiction:

Improvemeasurement stabilityVSAvoidpositioning speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent replaces reliance on heavy mechanical frame structures with a calibration artefact-based error compensation system that uses geometric reference features and computational methods to achieve and maintain measurement accuracy, allowing the use of lighter, faster-positioning frames

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Productivity

If frame structure is made lighter for faster positioning, then productivity is improved, but measurement precision deteriorates due to increased vibrations

Engineering Contradiction:

Improvepositioning speedVSAvoidmeasurement accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The calibration artefact serves as an intermediary reference object that mediates between the CMM measurement system and the workpiece, providing stable geometric references that compensate for vibrations and instabilities in lighter frame structures, enabling accurate measurements despite reduced mechanical rigidity

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP3470777B1System, method and computer program product for determining a state of a tool positioning machine

Publication Date: 2021.09.29 HEXAGON TECH CENT GMBH

Figure 1~2
Figure 3a~3c
Figure 4a~5

AI summary

System for providing state information for at least a part of a tool positioning machine (5) embodied as manipulating machine or as coordinate measuring machine. The system comprises the tool positioning machine (5) defining a machine coordinate system and having a base (31) and a machine structure. The structure comprises a tool head and structural components (32-34) for linking the tool head to the base, at least one drive mechanism for providing movability of the machine structure relative to the base (31), a position determining system for deriving at least one coordinate of the machine structure in the machine coordinate system and a controlling unit adapted for controlling movement of the machine structure. The system comprises a calibration setup comprising at least two calibration components which are provided by a touch tool (35) and a calibration artefact (11,11'). One of the at least two calibration components is mounted on the machine structure and defines a moveable reference point, another one of the at least two calibration components is arranged with defined spatial relation to the base (31) and provides a nominal calibration position (13). The calibration artefact (11,11') comprises at least two touching regions which are aligned transverse to one another and the calibration artefact (11,11') and the touch tool (35) are arranged so and moveable by the machine structure relative to each other so that simultaneous contact of the touch tool (35) with the at least two touching regions is providable.