Reference Module Error Compensation for Coordinate Measuring Machines
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Solution Overview
Problem
Coordinate measuring machines face challenges in accurately compensating for errors caused by dynamic movements and external influences, leading to measurement uncertainties and increased calibration complexity, especially with weight reduction efforts aiming for faster positioning but resulting in increased vibrations and deformations.
Innovation Solution
A modular reference module with a sensing unit and reference element, allowing for pre-calibration and compensation of up to six degrees of freedom without full assembly, enabling precise coordinate determination and reduced calibration efforts by using a look-up table and dynamic modeling to account for deformations and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the frame structure is made heavier to increase stiffness and reduce vibrations, then measurement precision is improved, but acceleration capability and productivity deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the reference module outside the CMM using a laser interferometer to establish accurate position data before use. This pre-calibration stores correction information that compensates for dynamic errors during actual measurement, allowing the system to achieve high precision without requiring excessive mass for stiffness
Solution Approach 2:
The patent replaces the traditional mechanical approach of increasing frame mass for stiffness with a sensor-based measurement and calculation system. The reference module with laser interferometer and evaluation unit substitutes mechanical rigidity requirements with electronic measurement and computational correction, enabling lightweight design while maintaining precision
2Productivity
If weight reduction is implemented to improve acceleration and productivity, then productivity is improved, but vibrations and deformations increase leading to worsened measurement precision
Solution Approach 1:
The patent implements feedback by continuously monitoring the position of the reference module relative to the CMM structure using the laser interferometer. The evaluation unit processes this feedback data and applies corrections based on pre-calibrated compensation values, allowing the system to maintain precision despite vibrations from rapid positioning movements
Solution Approach 2:
The system performs preliminary calibration of the reference module to establish accurate position data and compensation values before dynamic measurements. This pre-established reference framework enables real-time correction of vibration-induced errors during fast positioning operations
3Measurement precision
If a reference module is integrated into the CMM to improve measurement precision through error compensation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by separating the reference module as an independent, modular component that can be attached to or removed from the CMM. This modular design isolates the complexity of the laser interferometer and calibration system into a discrete unit, making the overall system more manageable and easier to calibrate without affecting the entire CMM structure
4Measurement precision
If dynamic errors are compensated through detailed modeling and calibration, then measurement precision is improved, but calibration time and complexity increase
Solution Approach 1:
The patent significantly reduces calibration time by performing the complex laser interferometer calibration and compensation value generation as a preliminary action outside the CMM. The reference module is pre-calibrated against absolute standards before being attached to the CMM, eliminating the need for time-consuming in-situ calibration of the entire measurement system
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the calibration and compensation process, enhances measurement precision, and reduces the complexity and time required for calibration, while allowing for more robust and cost-effective coordinate measurement systems.
Implementation Method 1
a stand-alone reference module with a reference element and a sensor unit, in particular with a laser interferometer, for determining a position of the reference module relative to the CMM structure
Data Source
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AI summary
The invention pertains to methods of compensating errors in a coordinate measuring machine (2) which is adapted for determination of at least one spatial coordinate of a measurement point on an object to be measured, the coordinate measuring machine (2) comprising a base (11), a probe head (15) for approaching the measurement point, a machine structure for linking the probe head (15) to the base (11), comprising at least a first structural component (12',12'') and at least one drive mechanism moveably linking the base (11) and the first structural component (12',12'') for provision of movability of the probe head (15) relative to the base (11), a reference module comprising at least a first mechanical reference element (21,21') and at least a first sensor unit (22,22') assigned to the first reference element (21,21') and a controlling and processing unit adapted for execution of a modelling functionality. The method comprises measuring a distance from the first reference element (21',21'') to the first structural component (12',12''), wherein the measured distance indicates a displacement or a deformation of the first structural component (12',12''), defining a dynamic model with a first set of state variables, the state variables being related to a set of physical properties of the reference module and representing an actual state of the reference module, deriving the actual state of the reference module by a calculation based on the dynamic model, and deducing compensation parameters based on the actual state.