Rotary Table Error Mapping for Accurate CMM Calibration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Coordinate Measuring Machines (CMMs) face challenges in achieving high accuracy and robustness due to errors induced by rotary tables, particularly dynamic thermal and mechanical stress, humidity changes, and human input, which are costly to mitigate and require frequent recalibration.
Innovation Solution
A method and system for autonomously calibrating rotary tables in CMMs by generating error maps through measuring deviations in 6 degrees of freedom pose at various angles, allowing for accurate coordinate transformation between part and CMM coordinate systems, enabling error correction and reducing the need for high-precision bearings, thus improving measuring accuracy and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-precision bearings and frequent recalibration are used to maintain measuring accuracy, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent transforms the rotary table error characteristics by changing the parameter representation from physical bearing precision to software-based error maps. Error maps store correction values for different angular positions, allowing the system to compensate for mechanical imperfections through parameter transformation rather than relying on high-precision physical components.
Solution Approach 2:
The patent replaces the mechanical precision requirement with a software-based correction system. Instead of relying on high-precision mechanical bearings, the system uses computing units to generate and apply error maps that mathematically compensate for mechanical errors, substituting mechanical precision with computational correction.
2Measurement precision
If high-precision bearings are used to reduce errors, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent employs lower-cost, lower-precision bearings that can be easily replaced, substituting them with software-based error compensation. The error maps serve as a virtual replacement for expensive precision bearings, allowing the use of cheaper mechanical components while maintaining measurement accuracy through computational correction.
Solution Approach 2:
The patent changes the approach from improving mechanical parameters (bearing precision) to optimizing software parameters (error map accuracy). This parameter transformation allows the system to achieve high measurement precision through data processing rather than expensive mechanical components.
3Reliability
If rotary tables are constructed to be long-term stable, then reliability is improved, but manufacturing cost increases
Solution Approach 1:
The patent performs preliminary error characterization by measuring and storing error maps at different angular positions before actual measurement tasks. This preliminary action captures mechanical imperfections and thermal drift characteristics, allowing the system to compensate for these errors during operation without requiring the mechanical structure to be inherently more stable or expensive.
Solution Approach 2:
The system implements feedback through error maps that provide correction values based on measured deviations. The computing unit uses this feedback information to adjust measurements, compensating for thermal drift and mechanical instability without requiring the rotary table to be constructed with expensive long-term stable materials.
4Measurement precision
If factory calibration is performed to correct errors, then measurement precision is improved, but loss of time occurs due to frequent recalibration needs
Solution Approach 1:
The patent performs preliminary error characterization by generating comprehensive error maps that cover the full range of angular positions and thermal conditions. This preliminary action creates a lookup table of correction values that can be quickly applied during measurement tasks, eliminating the need for frequent time-consuming recalibration procedures.
Solution Approach 2:
The error map system dynamically adapts to changing conditions by storing correction values for different angular positions and thermal states. This dynamic approach allows the system to select appropriate correction values based on current operating conditions, maintaining accuracy without requiring frequent manual recalibration.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention discloses a Coordinate Measuring Machine (CMM) system comprising a CMM, a rotary table, and a rotation arrangement, wherein the CMM system is configured to be calibrated by determining the 6 dof pose of a jig, and to a method for calibrating a CMM system. The jig can e.g. be mounted to the rotary table or to at least one component of the rotation arrangement, such that a current pose of the jig is associated with a current pose of the rotary table with respect to the CMM. The rotary table can be moved into multiple poses, and the 6 dof pose of the jig is measured for each of the multiple poses of the rotary table. An error map is generated, based on the angles associated with the poses of the rotary table, and is used to generate a coordinate transformation from the CMM coordinate system to the part coordinate system, which is associated with the rotary table, based on the error map. The present invention further relates to a computer program product comprising program code, which is stored on a machine-readable medium, or being embodied by an electromagnetic wave comprising a program code segment, and has computer-executable instructions for performing, particularly when run on a Coordinate Measuring Machine (CMM) according to the inventive CMM system or according to an inventive method.