Multi-Channel Interferometer for Surface Contour Measurement
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Solution Overview
Problem
Conventional interferometric surface measurement systems face challenges such as mechanical complexity, reduced accuracy due to component movement, limited measurement resolution, and noise interference from speckle patterns and shot noise, which affect the stability and precision of surface contour measurements.
Innovation Solution
A multiple channel interferometric surface contour measurement system with spatially separate optical axes, a translation stage for diffraction gratings, and a crossbar for improved orientation stability, along with a digital camera and processor for image acquisition and data processing, which reduces noise and increases measurement accuracy by averaging data from multiple channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple diffraction gratings are multiplexed into the beam path to project additional fringe patterns, then the measurement coverage and versatility are improved, but the mechanical complexity and system weight increase due to multiple moving components
Solution Approach 1:
The patent divides the measurement system into multiple independent interferometer channels, each with its own diffraction grating and optical path. This segmentation allows each channel to operate independently, reducing the mechanical complexity of moving multiple gratings while maintaining the ability to project multiple fringe patterns simultaneously on different regions of the object surface.
Solution Approach 2:
The patent transitions from sequential grating movement along a single beam path to spatial separation of multiple interferometer channels in different directions. Each channel projects fringes at different orientations (e.g., x-direction and y-direction), enabling comprehensive surface coverage without requiring multiple gratings to share the same optical path.
2Adaptability or versatility
If diffraction gratings are moved frequently to implement phase shifts and multiplexing, then the measurement flexibility is improved, but the measurement stability and accuracy deteriorate due to component movement
Solution Approach 1:
By segmenting the system into multiple fixed interferometer channels, each channel maintains a stable optical path without requiring frequent grating movement. The phase shifting is achieved through controlled movement of mirrors or other components within each stable channel, preserving both flexibility and stability.
Solution Approach 2:
The patent combines multiple interferometer channels into a single integrated measurement system, where each channel contributes to the overall measurement flexibility. This merging allows the system to achieve complex measurement tasks through the coordinated operation of stable, fixed channels rather than moving single components.
3Device complexity
If a single focusing objective and spatial filter are used for multiple gratings, then the device complexity is reduced, but the optical performance and measurement precision deteriorate as parameters cannot be optimized for individual gratings
Solution Approach 1:
Each interferometer channel is equipped with its own focusing objective and spatial filter, allowing these optical components to be optimized for the specific requirements of each channel. This segmentation ensures that each component operates at peak performance for its designated channel while maintaining manageable system complexity through modular architecture.
4Area of stationary object
If the camera depth of field is increased to capture the entire object surface, then the field of view is improved, but the measurement resolution deteriorates due to the limit on maximum spatial frequency
Solution Approach 1:
The patent projects fringe patterns in multiple orientations (different spatial directions) simultaneously using separate interferometer channels. This multi-dimensional approach allows the system to capture surface information across the entire field of view while maintaining high measurement resolution through the combined analysis of fringes from different directions, effectively overcoming the single-direction depth of field limitation.
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 system achieves improved stability, increased measurement accuracy, and reduced mechanical complexity, allowing for precise surface contour determination with reduced sensitivity to optical noise and enhanced reliability.
Implementation Method 1
a diffraction grating is positioned in the path of a laser beam to generate multiple coherent laser beams at various angles to the original beam path
Implementation Method 2
an objective in optical communication with the diffraction grating to focus coherent beams propagating from the diffraction grating
Implementation Method 3
a spatial filter disposed on the optical axis to receive the focused coherent beams and to transmit an ordered pair of coherent beams
Implementation Method 4
The ordered pair of coherent beams interfere to generate the projected fringe pattern
Data Source
AI summary
Described is a multiple channel interferometric surface contour measurement system. The measurement system includes a multiple channel interferometer projector, a digital camera and a processor. The projector includes two or more interferometer channels. Each channel has an optical axis spatially separate from the optical axes of the other channels. Each channel projects a fringe pattern onto the surface of an object to be measured. Image data for the fringe patterns projected on the object surface are acquired by the digital camera. The processor controls the projection of the fringe patterns of different spatial frequencies, adjusts the phase of each fringe pattern and generates surface contour data in response to the camera image data. The multiple channel interferometric surface contour measurement system provides numerous advantages over conventional single channel interferometric systems, including reduced sensitivity to optical noise, improved stability and increased measurement accuracy.