Aspheric Field Mirror Optical Testing Device Height Reduction
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Solution Overview
Problem
Existing optical testing devices employing telecentric optical trains are bulky, expensive, and suffer from chromatic aberration and astigmatism, particularly when used with polychromatic light, and have undesirably large heights that can be a challenge in space-constrained environments.
Innovation Solution
A compact device using an aspheric field mirror with a short focal length and a semitransparent mirror to image light onto the camera's entrance pupil, combined with a ground glass or semiconductor light source for bright-field illumination, minimizing height and employing a beam splitter to reduce stray light, and allowing for adjustable light sources and configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a field lens is employed in a telecentric optical train, then imaging of the surface zone is achieved, but the height of the arrangement exceeds the focal length of the field lens by more than the overall length of camera and lens
Solution Approach 1:
A planar beam-deflecting mirror is introduced as an intermediary component between the field lens and the camera lens. This mirror redirects the optical path, allowing the camera to be positioned laterally rather than axially, thereby reducing the overall height of the arrangement while maintaining the telecentric imaging function and image fidelity
Solution Approach 2:
The optical path is redirected from a vertical arrangement to a lateral arrangement using the beam-deflecting mirror. This changes the dimension in which the camera is positioned, moving it from the optical axis direction to a perpendicular direction, thus reducing the height of the arrangement without compromising imaging quality
2Length of moving object
If field lenses with short focal lengths are employed to reduce height, then chromatic aberration occurs when polychromatic light is used
Solution Approach 1:
The planar beam-deflecting mirror serves as an intermediary that allows the use of short focal length field lenses without suffering from chromatic aberration. By redirecting the optical path, the system can accommodate polychromatic light while maintaining image fidelity, as the mirror does not introduce additional chromatic effects
3Illumination intensity
If a semitransparent mirror is used for bright-field illumination, then illumination is provided, but astigmatism occurs that reduces image fidelity
Solution Approach 1:
The harmful astigmatism effect is extracted and eliminated by removing the semitransparent mirror from the optical path. The illumination system is reconfigured to provide bright-field illumination through alternative means that do not introduce astigmatism, thereby maintaining image fidelity while still providing adequate illumination
4Measurement precision
If telecentric optical trains are employed for imaging, then accurate surface imaging is achieved, but the overall height of the arrangement is undesirably large
Solution Approach 1:
A planar beam-deflecting mirror is introduced as a mediator to redirect the optical path of the telecentric arrangement. This allows the camera to be positioned perpendicular to the optical axis, maintaining the telecentric imaging accuracy while significantly reducing the overall height of the arrangement
Solution Approach 2:
The camera positioning is changed from the optical axis direction to a perpendicular direction using the beam-deflecting mirror. This dimensional change allows the telecentric optical train to maintain its imaging accuracy while occupying less vertical space, making the arrangement more compact
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 provides a compact, cost-effective optical testing device capable of imaging with various wavelengths, minimizing height and reducing imaging errors, while maintaining high image fidelity and flexibility in light source configurations.
Implementation Method 1
an aspheric field mirror (4) having a short focal length to image light emanating from the zone (3) of the surface (2) under investigation onto the entrance pupil (13) of the lens (12)
Implementation Method 2
light from the light sources for illuminating surfaces is reflected normal to the camera's optical axis by a semitransparent mirror
Implementation Method 3
the beam path transits the semitransparent-mirror's plane-parallel plate
Implementation Method 4
an aspheric field mirror (4) having a short focal length to image light emanating from the zone (3) of the surface (2) under investigation onto the entrance pupil (13) of the lens (12)
Implementation Method 5
a ground glass plate irradiated by a monochromatic, or polychromatic, semiconductor light source
Data Source
AI summary
The invention generally relates to a compact, inexpensive-to-manufacture device consisting of few components for optically testing a surface. The zone on the surface that is to be investigated is illuminated by a semitransparent mirror and an aspheric field mirror, employing a telecentric optical train, and at least part of the light reflected or scattered by the surface is imaged onto the entrance pupil of the lens of an electronic camera by the field mirror, via the semitransparent mirror. Images recorded by the camera are analyzed using known image-processing methods.