Laser Tracking Interferometer Thermal Expansion Compensation
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Solution Overview
Problem
Conventional laser tracking interferometers experience measurement errors due to thermal expansion of the housing and carriage, which affect the accuracy of distance change measurements.
Innovation Solution
A laser tracking interferometer design that includes a reference sphere, a carriage with displacement gauges, and a data processor to calculate the displacement of a retroreflector by combining signals from multiple displacement gauges and a laser interferometer, while also using a position detector to correct misalignment and thermal expansion errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser interferometer is fixated to a carriage for measuring distance changes, then measurement capability is improved, but thermal expansion of the carriage causes measurement errors
Solution Approach 1:
A retroreflector is introduced as an intermediary component attached to the carriage. The laser beam reflects off this retroreflector to reach the laser interferometer, which remains stationary on the base. This intermediary setup allows the measurement system to track the carriage's position without being physically attached to it, thereby eliminating measurement errors caused by carriage thermal expansion.
Solution Approach 2:
The measurement system is segmented into two independent parts: the laser interferometer remains fixed on the base while the retroreflector moves with the carriage. This segmentation separates the measurement device from the moving component, allowing independent thermal management and preventing thermal expansion of the carriage from affecting measurement accuracy.
2Adaptability or versatility
If the laser interferometer housing undergoes thermal expansion, then the distance from connection point to reference point changes, but this causes measurement errors even when the measured object is stationary
Solution Approach 1:
The retroreflector serves as a stable intermediary reference point attached to the carriage. By reflecting the laser beam back to the stationary interferometer, it creates a measurement path that is independent of the interferometer housing's thermal expansion, maintaining measurement precision under varying temperature conditions.
Solution Approach 2:
The system uses the reflected laser beam from the retroreflector as feedback to continuously monitor and track the position of the carriage. This feedback mechanism allows the system to compensate for any changes in the measurement path caused by thermal expansion of the interferometer housing, maintaining accurate measurements.
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
Enables highly accurate measurement of distance changes even under thermal expansion conditions, reducing measurement errors and allowing for the use of less expensive materials for the interferometer components.
Implementation Method 1
detecting a displacement of a first retroreflector by utilizing interference of a laser beam emitted toward the first retroreflector as a measured body and reflected by the first retroreflector in a return direction
Implementation Method 2
when a housing of the laser interferometer undergoes thermal expansion due to a change in surrounding temperature or the like, an amount of change ΔL4 is generated in a distance L4 from the connection point P to the reference point P1
Data Source
AI summary
A laser tracking interferometer has a carriage provided with a first displacement gauge outputting a displacement signal associated with a relative displacement from a reference sphere; a second retroreflector provided to the carriage; a laser interferometer provided to the carriage and outputting a displacement signal associated with a relative displacement between the first retroreflector and the second retroreflector; and a data processor calculating a displacement of the first retroreflector with reference to the reference sphere based on the displacement signal output from the first displacement gauge and the displacement signal output from the laser interferometer.