Laser Tracking Interferometer Robustness Against Runout
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Solution Overview
Problem
Existing laser tracking interferometers are susceptible to runout of the rotational mechanism, flaws, and dust particles on the reference sphere, and often require expensive and hard-to-find high-precision spheres, leading to accuracy issues and high costs.
Innovation Solution
A laser tracking interferometer design that uses a reference sphere with a displacement gage on both sides to measure relative displacement, employing a Michelson interferometer and position-sensitive detectors to track the retroreflector's displacement, and control mechanisms to maintain beam alignment, making it robust to rotational runout and surface imperfections, and allowing the use of inexpensive metal spheres.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-precision reference sphere is used to improve measurement accuracy, then measurement precision is improved, but the cost increases and the sphere becomes hard to find
Solution Approach 1:
The patent uses a position-sensitive detector to detect the position of the laser beam reflected from the reference sphere, creating an optical copy of the sphere's surface position information. This allows measurement of sphere position and orientation without requiring the sphere itself to be extremely precise, as long as the laser reflection point is detectable.
Solution Approach 2:
The patent replaces mechanical measurement methods with optical methods. Instead of using mechanical contact or complex mechanical positioning systems, the invention uses laser beams and position-sensitive detectors to measure the reference sphere's position and orientation, thereby avoiding the need for expensive high-precision mechanical spheres.
2Measurement precision
If the laser beam is focused on the center of the reference sphere to improve measurement accuracy, then measurement precision is improved, but the system becomes susceptible to runout of the rotational mechanism
Solution Approach 1:
The patent introduces a position-sensitive detector as an intermediary between the laser beam and the measurement system. This detector captures the position of the reflected laser beam, allowing the system to measure both the reference sphere's position and orientation simultaneously, thereby compensating for rotational runout effects.
Solution Approach 2:
The laser beam serves multiple functions: it measures both the position and orientation of the reference sphere. By using the same laser beam for dual measurement purposes, the system can cross-validate measurements and compensate for rotational runout, improving reliability without sacrificing precision.
3Measurement precision
If the laser beam is focused on the surface of the reference sphere to improve measurement accuracy, then measurement precision is improved, but the system becomes susceptible to flaws and dust particles on the surface
Solution Approach 1:
The position-sensitive detector acts as an intermediary that captures information about the laser beam's reflection point on the reference sphere. By detecting the position of the reflected beam rather than directly measuring surface properties, the system avoids being affected by surface flaws and dust particles.
4Measurement precision
If a position-sensitive detector is used to detect beam deviation and improve tracking accuracy, then measurement precision is improved, but the device complexity increases
Solution Approach 1:
The position-sensitive detector performs multiple functions: it detects both the position and orientation of the reference sphere using the same device. This multi-functionality reduces the need for separate sensors and simplifies the overall system architecture, offsetting the added complexity of the detector itself.
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
The design provides high accuracy and robustness against rotational runout and surface flaws, reducing costs by using commercially available metal spheres and minimizing susceptibility to temperature fluctuations and optical axis deviations.
Implementation Method 1
sense a displacement of the retroreflector using the interference with a laser beam back reflected from the retroreflector
Implementation Method 2
track the retroreflector using a change in position of the optical axis of the laser beam
Data Source
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AI summary
A laser tracking interferometer directs a laser beam to a retroreflector serving as an object to be measured to sense a displacement of the retroreflector using interference with a laser beam back reflected from the retroreflector as well as to track the retroreflector using a change in position of the optical axis of the laser beam. The laser tracking interferometer includes: a reference sphere disposed at a fixed location; a carriage configured to rotate about a center of the reference sphere; a laser interferometer for providing a displacement signal corresponding to a displacement of the retroreflector, and a displacement gage for providing a displacement signal corresponding to a relative displacement between the reference sphere and the displacement gage, the laser interferometer and the displacement gage being disposed on the carriage; a data processing apparatus for computing a displacement of the retroreflector with respect to the reference sphere in accordance with the displacement signal provided by the displacement gage and the displacement signal provided by the laser interferometer; a position sensitive detector for providing a position signal corresponding to the amount of deviation of a laser beam when the laser beam is reflected off the retroreflector back into the laser interferometer and deviated in a direction orthogonal to its optical axis; and a controller for controlling rotation of the carriage based on the position signal from the position detector so that the amount of deviation becomes zero. This makes the laser tracking interferometer is robust to the runout of the rotational mechanism. The laser tracking interferometer is less susceptible to flaws and dust particles on the surface of the reference sphere, and is capable of employing a relatively inexpensive reference sphere.