Bi-telecentric Magnifying Optical System for Interference Fringe Projection
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Solution Overview
Problem
The contrast of interference fringes projected onto an object surface decreases at the periphery, leading to reduced measurement accuracy in shape measurement apparatuses due to unequal intensity overlap of light beams separated by birefringent and polarizing components.
Innovation Solution
A bi-telecentric magnifying optical system with a focal length ratio f1/f2 > 3, where f1 is the focal length of the incident-side lens group and f2 is the focal length of the exit-side lens group, maintains equal amplitudes of light beams and minimizes optical axis shifts, ensuring high contrast and accurate shape measurement across the object surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a single projection lens is used to magnify and project the interference fringe, then the device size can be reduced, but the contrast of interference fringes decreases at the periphery due to unequal intensity overlap of light beams
Solution Approach 1:
The single projection lens is divided into two separate lens groups: an incident-side lens group and an exit-side lens group. This segmentation allows independent optimization of each group's function, enabling the incident-side group to focus on beam convergence while the exit-side group handles beam parallelization, thereby maintaining fringe contrast across the entire projection area while achieving compact device dimensions.
Solution Approach 2:
The patent transitions from a single-lens configuration to a two-group lens system arranged in a telecentric optical path. This dimensional reorganization of the optical system creates separate functional zones for beam convergence and parallelization, resolving the contradiction between compact size and peripheral fringe contrast by distributing optical functions across different spatial dimensions.
2Device complexity
If the focal length ratio f1/f2 is not optimized (f1/f2 ≤ 3), then the optical system is simpler, but the contrast of interference fringes at the periphery decreases due to optical axis shifts and unequal intensity overlap
Solution Approach 1:
The patent establishes a specific parameter threshold for the focal length ratio (f1/f2 > 3) of the two lens groups. This parameter optimization ensures that the incident-side lens group adequately converges light beams while the exit-side lens group effectively parallelizes them, maintaining equal amplitude overlap across the projection area and preserving high fringe contrast without requiring complex additional components.
3Ease of manufacture
If the magnifying optical system does not maintain equal amplitudes of light beams, then the system is easier to assemble, but the contrast of interference fringes decreases at the periphery
Solution Approach 1:
The patent designs the incident-side and exit-side lens groups to create equipotential optical conditions where light beams from both polarization components maintain equal amplitudes throughout the projection area. This equipotential design ensures that the optical path lengths and beam intensities are balanced, resulting in high fringe contrast across the entire field of view while using standard optical components that are easy to assemble.
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 solution maintains high contrast and accuracy of interference fringes over a wide range on the object surface, reducing eccentric sensitivity and facilitating assembly, while minimizing the impact of optical axis shifts on intensity distribution.
Implementation Method 1
is subsequently incident on the birefringent plate 117, and is separated into a light beam with two polarization components
Implementation Method 2
are further incident on the polarizing plate 118. Only the coherent components are extracted from among the two polarization components
Implementation Method 3
Only the coherent components are extracted from among the two polarization components to generate an interference fringe
Implementation Method 4
The interference fringe is magnified by the projection lens 131 and projected onto the object surface
Data Source
AI summary
An interference fringe generating optical system generates an interference fringe, and a magnifying optical system magnifies the interference fringe and projects the interference fringe on an object surface. The magnifying optical system includes an incident-side lens group on the side where a light beam forming the interference fringe is incident and an exit-side lens group on the side where the light beam is emitted and the interference fringe is projected towards the object surface. The expression f1/f2>3 holds, where f1 is the focal length of the incident-side lens group, and f2 is the focal length of the exit-side lens group. The incident-side and exit-side lens groups each have a positive refractive power. The expression xd/(f1+f2)<2 is satisfied, where xd is the distance from the exit-side principal point of the incident-side lens group to the incident-side principal point of the exit-side lens group.