CMM Frame Error Compensation via Reference Sensors
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Solution Overview
Problem
Coordinate measuring machines (CMMs) face errors due to dynamic effects, weak structures, and external influences like temperature and vibration, which current calibration methods struggle to accurately compensate for, especially at high speeds and with dynamic deflections.
Innovation Solution
The implementation of a CMM with mechanical or optical reference elements and displacement sensors to measure and compensate for frame structure displacements and deformations in real-time, eliminating the need for lengthy pre-calibration procedures and accounting for both static and dynamic errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration methods are used to correct geometrical errors, then measurement accuracy is improved for static conditions, but the calibration process becomes lengthy and invalidates when the machine settles or operates at different speeds
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements at multiple predetermined speeds during the calibration phase. The system stores speed-specific calibration data in lookup tables, so that when the machine operates at any of these predetermined speeds, the appropriate calibration data is already available for immediate application, eliminating the need for recalibration when speed changes occur.
Solution Approach 2:
The patent changes the parameter of calibration speed by performing calibration at multiple different speeds (not just one speed). This creates a set of calibration data corresponding to different speed parameters, allowing the system to select and apply the appropriate calibration data based on the current operating speed, thereby maintaining accuracy across varying speeds without time-consuming recalibration.
2Productivity
If calibration is performed at high speeds to meet productivity demands, then measurement throughput is improved, but dynamic deflections and vibrations cause larger measurement errors
Solution Approach 1:
The system performs preliminary calibration measurements at multiple predetermined speeds including high speeds. During this preliminary phase, the calibration data capturing the actual dynamic deflection and vibration characteristics at each speed is stored. During actual measurement operations, the pre-captured calibration data corresponding to the current speed is applied to compensate for dynamic errors, enabling high-speed measurement without sacrificing accuracy.
Solution Approach 2:
The system uses feedback by comparing the measured position with the pre-captured calibration data obtained at the same speed. The calibration data, which contains information about dynamic deflections and vibrations at each speed, is used to compensate for these effects in real-time during measurement operations, thereby maintaining measurement accuracy even at high speeds.
3Measurement precision
If the frame structure is made more rigid to reduce dynamic deflections, then measurement accuracy is improved, but the machine becomes more complex and expensive to manufacture
Solution Approach 1:
The patent replaces the mechanical approach of making the frame structure more rigid with a computational approach. Instead of increasing structural rigidity (which would add complexity and cost), the system uses software-based error compensation by capturing calibration data that includes dynamic deflection characteristics and applying this data to correct measurements. This substitutes mechanical reinforcement with intelligent software compensation.
Solution Approach 2:
The patent changes the approach from modifying physical parameters (frame rigidity) to modifying computational parameters (calibration data). By capturing and applying calibration data that accounts for dynamic deflections at different speeds, the system achieves measurement accuracy without needing to physically strengthen the frame structure, thereby avoiding the complexity and cost associated with a more rigid mechanical design.
4Productivity
If acceleration of the probe is increased to improve inspection speed, then productivity is improved, but dynamic structural deflections of the frame structure increase causing inaccurate position reporting
Solution Approach 1:
The system performs preliminary calibration measurements at multiple predetermined speeds that correspond to different acceleration levels. The calibration data captured includes the dynamic structural deflections that occur at each speed level. During actual inspection operations, when the probe moves at any of these predetermined speeds, the corresponding pre-captured calibration data is applied to compensate for the dynamic deflections, enabling high-speed inspection while maintaining position accuracy.
Solution Approach 2:
The system uses feedback by comparing the current operating speed with the predetermined speeds and selecting the appropriate calibration data. The calibration data, which contains information about dynamic structural deflections at each speed, is applied to compensate for these deflections in real-time during high-speed inspection operations, thereby maintaining accurate position reporting even when the probe accelerates at high rates.
Data Source
AI summary
A coordinate measuring machine for determination of at least one spatial coordinate of a measurement point on an object to be measured. The coordinate measuring machine comprises a stationary base, a probe head for approaching the measurement point and a frame structure for linking the probe head to the base. At least a first mechanical reference element extending along a first part of the frame structure is fastened fixedly to the frame structure in a substantially unloaded way, and at least one displacement sensor is assigned to the first reference element, wherein the first reference element and the displacement sensor are designed and arranged in such a way, that a distance from the first reference element to the frame structure in the region of the first part is measurable, the distance indicating a displacement and/or deformation of the frame structure in the region of the first part.