Articulated Probe Head Calibration via Hybrid Model
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Solution Overview
Problem
Coordinate-measuring systems with articulated probe heads require extensive and time-consuming calibration for each configuration, leading to reduced machine availability and increased unproductive time due to the need for precise calibration across multiple orientations and to compensate for thermal drifts and tool tolerances.
Innovation Solution
A method involving a two-step calibration process: a first 'factory calibration' that defines a model of the articulated probe head across a large set of configurations, and a second 'additional calibration' that determines model parameters for the assembly with the coordinate probe, allowing for faster in-situ calibration with fewer configurations, using a hybrid approach that combines model-based and look-up table methods for improved precision and reduced calibration time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods are used for each configuration of the articulated probe head, then measurement accuracy is maintained, but calibration time increases significantly and machine availability decreases
Solution Approach 1:
The patent performs a comprehensive factory calibration that captures the motion of the articulated head across all possible configurations beforehand. This preliminary action stores calibration data in a look-up table, eliminating the need for time-consuming on-site calibration of each individual configuration. The factory calibration is performed once during manufacturing, and the results are reused during operation to maintain accuracy without repeated calibration time loss.
Solution Approach 2:
The patent creates a digital model (copy) of the articulated head's motion characteristics through factory calibration. Instead of physically recalibrating each configuration, the system uses the stored digital model and look-up table to replicate the calibration results for any given configuration. This copying approach maintains measurement precision while avoiding the time-consuming process of actual recalibration for each configuration.
2Measurement precision
If comprehensive calibration across all configurations is performed, then superior accuracy is achieved, but device complexity and calibration procedure complexity increase
Solution Approach 1:
The complex task of capturing the articulated head's motion across all configurations is performed once during factory calibration. The comprehensive calibration data is stored in a look-up table, simplifying the on-site procedure to merely retrieving the pre-computed calibration parameters for the current configuration. This preliminary action transfers the complexity from operation time to manufacturing time.
Solution Approach 2:
The patent replaces the mechanical/calibration procedure complexity with a computational solution. Instead of manually calibrating each configuration, the system uses a computer-implemented method with stored calibration data and look-up tables to automatically determine the correct calibration parameters. This substitution of computational procedures for manual calibration procedures reduces complexity during operation.
3Reliability
If frequent calibration is performed to compensate for thermal drifts and tool tolerances, then measurement reliability is improved, but productivity and machine availability deteriorate
Solution Approach 1:
The factory calibration performs the comprehensive accuracy compensation for thermal drifts and tool tolerances in advance. The calibration data captured during factory conditions is stored and reused during operation, maintaining measurement reliability without requiring frequent recalibration. This preliminary action ensures that the system is prepared to handle environmental variations without sacrificing productivity.
Solution Approach 2:
The system uses the pre-stored calibration data and look-up tables to self-correct for thermal drifts and tool tolerances during operation. Instead of requiring external calibration intervention, the system automatically applies the appropriate calibration parameters based on the current configuration, maintaining reliability while preserving machine availability and productivity.
Data Source
Figure 1~2
AI summary
A method of calibrating a coordinate measuring machine in which the immutable parameters of the articulated probe head are determine and stored at factory, while the connection parameters and other parameters dependent on the configuration of the system are determined in-situ, with a calibration artifact. The process builds a mathematical model that is the composition of an immutable factory-determined model with the in-situ model. The immutable model can be stored in a non-volatile memory physically provided in the articulated head. The method can fall back to a correction look up table for certain selected orientations of the probe where improved accuracy is needed.