Geometric Error Determination Using Variable Laser Beam
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Solution Overview
Problem
Existing methods for determining geometric errors in machine tools require precise and costly laser tracers capable of continuous interferometric measurements, introducing additional unknowns such as the dead path of the interferometer and complex tracking requirements.
Innovation Solution
A method using a variable laser beam with two degrees of rotational freedom, combined with a kinematic model and feedback control, allows for interferometric measurement of a back-reflector's position, simplifying the determination of geometric errors by aligning measurement points along a single direction and using a straightforward device without high angular aiming precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a precise laser tracer capable of continuous interferometric measurements is used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The measurement process is segmented into discrete positional measurements rather than continuous tracking. The laser beam is directed to measure points sequentially at different positions along the axis, rather than requiring continuous angular tracking. This segmentation allows using simpler interferometer positioning mechanisms instead of complex continuous tracking systems.
Solution Approach 2:
The measurement is performed through periodic positioning of the laser beam at discrete points along the measurement axis. The interferometer is periodically repositioned to each measurement point rather than continuously tracking moving targets. This periodic action simplifies the interferometer design while maintaining measurement precision through systematic sampling.
2Measurement precision
If continuous interferometric tracking of a moving back-reflector is performed, then measurement precision is improved, but the introduction of additional unknowns (dead path and tracer position) increases device complexity
Solution Approach 1:
The back-reflector is extracted from continuous motion and positioned discretely at predetermined points. Instead of tracking a moving back-reflector, the system measures at fixed positions where the back-reflector is sequentially placed or passed through. This extraction eliminates the need to track and compensate for continuous positional changes of the reflector.
Solution Approach 2:
The positions of the back-reflector are predetermined and prepared in advance along the measurement axis. The measurement system is configured with pre-calculated measurement points, eliminating the need for real-time determination of tracer position and dead path compensation during the measurement process.
3Adaptability or versatility
If multiple laser tracer positions are used to cover the measuring volume, then measurement completeness is improved, but the number of additional unknowns increases
Solution Approach 1:
A single interferometer is designed to perform multiple measurement functions by positioning itself at different predetermined locations along the measurement axis. The same interferometer measures geometric errors at multiple positions rather than requiring multiple specialized tracers, reducing the number of unknown parameters while maintaining measurement completeness.
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 reduces the complexity and cost of error determination, simplifies the alignment of measurement points, and eliminates the need to determine the interferometer's position and dead path, providing accurate geometric error parameters with improved precision.
Implementation Method 1
an interferometer measuring device, i.e. an instrument capable of generating and orienting a laser beam along a direction that is variable with two degrees of rotational freedom (azimuth and elevation), and for interferometrically determining the abscissa
Implementation Method 2
The reflector is tracked by an optical tracking device or 'laser tracer' located on the machine bed and comprising an interferometer
Data Source
Figure 1~2
AI summary
A method of determining geometric errors in a machine tool or measuring machine having a mobile unit for moving a target within a measuring volume, the method including the steps of determining a first direction within the measuring volume; moving the target into a number of points along the direction by means of the mobile unit; measuring, by means of a measuring device, the abscissa of each of the points from an origin located along the first direction; acquiring the coordinates of each of the points by means of the machine; repeating the foregoing steps for a number of directions within the measuring volume; and determining error parameters of the machine on the basis of the abscissas measured by the measuring device, and the coordinates of the points acquired by the machine.