Calibrating Portable Coordinate Measurement Machines Using Digital Reference Models
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing calibration methods for portable coordinate measurement machines (PCMMs) are costly, time-consuming, and limited by the use of precision-manufactured length artifacts that are prone to thermal expansion, resulting in incomplete and inaccurate calibration.
Innovation Solution
A method and system for calibrating PCMMs using a coordinate measurement machine (CMM) with multiple contact positions, where the PCMM's probe head contacts the CMM's probe tip at various orientations, generating a high number of data sets to improve accuracy and reliability, and utilizing a contact probe with spherical portions to facilitate multiple orientations and electrical synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If precision-manufactured length artifacts are used for calibration, then measurement accuracy is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent replaces expensive precision-manufactured length artifacts with inexpensive, easily manufactured calibration objects. The calibration object can be a simple assembly of spherical elements positioned at known coordinates, which can be manufactured using standard machining or even 3D printing, eliminating the need for costly precision artifacts while maintaining calibration effectiveness
Solution Approach 2:
Instead of using physical precision artifacts, the patent creates a digital model of the calibration object with precisely known coordinates stored in a database. The PCMM measures the physical object and compares measurements against the digital reference model, separating the precision requirement from physical manufacturing and placing it in the digital domain where it can be maintained perfectly
2Measurement precision
If manual manipulation of PCMM between various positions is performed, then calibration is achieved, but calibration time increases
Solution Approach 1:
The calibration system uses the PCMM's own measurement capabilities to perform self-calibration. The automated measurement sequence allows the system to collect calibration data without requiring manual repositioning and intervention, reducing calibration time while maintaining accuracy through systematic data collection at multiple predetermined positions
Solution Approach 2:
The calibration object is pre-configured with spherical elements positioned at precisely calculated coordinates that optimize calibration efficiency. The measurement sequence is pre-programmed to visit all necessary positions systematically, eliminating the need for manual positioning decisions and reducing overall calibration time
3Ease of operation
If a small number of position readings are taken during calibration, then calibration process is simplified, but calibration reliability decreases
Solution Approach 1:
The calibration process is segmented into multiple independent measurement positions, each contributing to the overall calibration. The system automatically moves the PCMM to a series of predetermined positions around the calibration object, collecting data at each position. This segmentation allows for comprehensive calibration data collection while maintaining procedural simplicity through automation
Solution Approach 2:
The system uses feedback from multiple measurement positions to iteratively improve calibration accuracy. Position data obtained by the PCMM is analyzed and used to adjust calibration parameters, with the process incorporating statistical analysis to ensure reliability. The feedback loop continues until calibration meets predetermined accuracy criteria
4Measurement precision
If precision-manufactured length artifacts are used, then initial calibration accuracy is improved, but thermal expansion causes measurement variation
Solution Approach 1:
The patent replaces thermally sensitive precision artifacts with calibration objects made from materials that are either thermally stable or whose thermal expansion is easily compensable. The calibration object can be a simple assembly of spherical elements whose positions are determined by coordinates rather than physical dimensions, eliminating thermal expansion issues entirely
Solution Approach 2:
The patent transfers the reference standard from the physical domain to the digital domain. Instead of relying on physical artifacts that expand with heat, the system uses a digital model with precisely known coordinates stored in a database. This digital reference is immune to thermal expansion, eliminating the source of measurement variation while maintaining high accuracy
Data Source
AI summary
An articulated arm portable coordinate measurement machine (PCMM) can be calibrated or recalibrated using a coordinate measurement machine (CMM). In one method for PCMM calibration, the CMM can be moved to one position, and the PCMM moved to a contact position where a probe head of the PCMM contacts a probe head of the PCMM. The PCMM and the CMM can be operatively coupled, for example, by a synchronizing cable such that position data from the PCMM and the CMM can be obtained at the contact position. The PCMM can be repositioned one or more times to obtain position data at multiple PCMM positions. The CMM can be repositioned as desired and additional contact position data sets obtained by subsequent positioning and repositioning of the PCMM. Various probe head types such as touch trigger probes, hard probes, and contact probes can be used in the calibration systems and methods.