Laser Tracker Calibration via Foucault Pendulum Oscillation
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Solution Overview
Problem
Laser trackers face challenges in calibration due to large working volumes and the inability to isolate and measure individual parametric errors, particularly cyclic errors, which are not adequately addressed by existing standards like ASME B89.4.19-2006, and require complex and costly procedures for performance evaluation.
Innovation Solution
A mechanical oscillator, such as a Foucault pendulum, is used to generate periodic motions that can be modeled with Fourier series, allowing for the detection of instrument errors and augmentation of calibration standards to improve sensitivity to cyclic errors and servo system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods using calibrated artifacts are used, then the laser tracker can be evaluated for point-to-point length measurements, but cyclic errors cannot be adequately detected and the calibration is not sensitive to this subtle source of error
Solution Approach 1:
The patent applies mechanical vibration by using a precision machine tool to generate controlled periodic motions (cyclic movements) of the laser tracker's measurement beam. This vibration approach transforms the static calibration into a dynamic one, where the periodic motion allows cyclic errors to manifest as measurable deviations from the expected sinusoidal pattern, thereby enabling detection of this subtle error type without requiring complex calibration artifacts.
Solution Approach 2:
The patent implements periodic action by employing repetitive cyclic motions of the laser tracker through controlled movement along predefined paths. These periodic actions create a rich set of measurement data that reveals cyclic errors through deviations from the expected periodic pattern. The method uses Fourier series analysis of these periodic measurements to identify and quantify cyclic errors, simplifying the calibration process while improving precision.
2Volume of moving object
If the laser beam is steered to cover a large working volume, then the measurement range is increased, but individual parametric errors cannot be isolated and measured individually
Solution Approach 1:
The patent applies segmentation by dividing the complex calibration problem into separate components through Fourier series analysis. The measurement data collected over the large working volume is decomposed into individual frequency components, allowing each parametric error (such as scale error, zero error, and cyclic error) to be isolated and measured individually. This mathematical segmentation enables error identification without restricting the laser beam's ability to cover the full working volume.
Solution Approach 2:
The patent employs dynamics by transitioning from static calibration points to dynamic, continuous motion of the laser beam through the working volume. The laser tracker measures positions along continuous trajectories rather than discrete points, and the resulting dynamic measurement data is analyzed using Fourier series to extract individual error parameters. This dynamic approach maintains full working volume coverage while enabling isolation of parametric errors through temporal and spatial variation.
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 method provides a simple and effective means to dynamically calibrate laser trackers, enhancing their accuracy and usability by generating a rich set of measurement data that can identify and correct for various sources of error, including cyclic errors, without the need for additional interferometers or precision rails.
Implementation Method 1
A mechanical oscillator, such as a Foucault pendulum, is used to generate periodic motions that can be modeled with Fourier series
Data Source
AI summary
A method is disclosed whereby a laser-based spherical coordinate measurement system is dynamically calibrated. A mechanical oscillator, such as, but not limited to, a Foucault pendulum is used to generate periodic motions which can be fitted to Fourier series models. The residuals between the experimental measurements and the model can provide information which can be used to calibrate the instrument. The calibration information is used to augment the ASME B89.4.19-2006 standard to improve sensitivity to cyclic errors and include the servo systems.