Multi-Axis Machine Calibration for Rotary Positioning Accuracy

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Solution Overview

Problem

CNC machines with multiple rotation axes face inaccuracies due to imperfections in the movement mechanisms, leading to discontinuities in machining precision as the position and orientation of the second rotation axis can vary relative to the component at different angular positions, causing offsets and disorientations during machining.

Innovation Solution

A method involving the measurement of tridimensional positions of a reference feature at multiple angular positions around both rotation axes, allowing for the determination and calibration of two coordinate systems, which are used to adjust the machine's operation to account for the actual position and orientation of the axes, rather than relying on mathematical rotations, thereby reducing inaccuracies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If mathematical rotations are used to control the component around multiple axes, then the machine can operate with multiple rotation axes, but mechanical imperfections cause discontinuities and offsets in positioning accuracy at different angular positions

Engineering Contradiction:

Improvemulti-axis rotation capabilityVSAvoidpositioning accuracy

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by pre-determining coordinate systems at multiple reference angular positions around the second rotation axis. Instead of relying on mathematical rotations that accumulate errors, the system performs measurements and establishes accurate coordinate systems in advance at discrete angular positions (e.g., 0°, 90°, 180°, 270°). This allows the machine to switch between pre-calibrated coordinate systems based on the current angular position, eliminating the need for continuous mathematical rotation calculations and their associated errors.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements dynamics by making the coordinate system adaptive and changeable based on the angular position of the component. Rather than using a single fixed coordinate system or continuous mathematical transformations, the system dynamically selects from multiple discrete coordinate systems that have been predetermined at different angular positions. This dynamic switching allows the machine to maintain high positioning accuracy throughout the full range of motion around the second rotation axis.

Inventive Principle:

Principle #15Dynamics

2Ease of operation

If a single reference coordinate system is used for all angular positions, then the machine operation is simplified, but positioning accuracy deteriorates due to offsets and disorientations at different angular positions

Engineering Contradiction:

Improvecoordinate system managementVSAvoidmachining accuracy

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The patent applies segmentation by dividing the continuous rotation around the second axis into discrete angular segments, each with its own predetermined coordinate system. Instead of using a single coordinate system for all positions, the system creates multiple coordinate systems at specific reference angular positions (e.g., four positions at 90° intervals). This segmentation allows each coordinate system to be optimized for its specific angular range, maintaining high accuracy while keeping the complexity manageable through systematic organization.

Inventive Principle:

Principle #1Segmentation

3Manufacturing precision

If coordinate systems are predetermined at multiple reference angular positions, then positioning accuracy is improved across all angular positions, but the calibration process and device complexity increase

Engineering Contradiction:

Improvepositioning accuracyVSAvoidcalibration system complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies universality by using a single measuring device that can measure the position of reference features at multiple angular positions around the second rotation axis. The same measuring device and reference feature setup are used repeatedly at each angular position, rather than requiring different measurement systems for each position. This multi-functional approach allows the system to gather all necessary data using the same hardware, reducing overall device complexity while still achieving high positioning accuracy through multiple coordinate systems.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11487268B2Method of calibrating a machine having at least two rotation axes

Publication Date: 2022.11.01 PRATT & WHITNEY CANADA CORP

AI summary

The method can include measuring the tridimensional positions of a reference feature for a first at least three different angular positions of the reference feature around the first rotation axis and a same first reference angular position around the second rotation axis, the reference feature being fixed relative to the component; and measuring the tridimensional positions of the reference feature for a second at least three different angular positions of the reference feature around the first rotation axis and a same second reference angular position around the second rotation axis.