Confocal Aperture Plate Linear Scanning Mechanism
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Solution Overview
Problem
Existing three-dimensional shape measuring techniques using confocal optical systems face challenges in linearly scanning surfaces due to variations in scanning speed and rotational deflection caused by Nipkow disk rotation, leading to inaccuracies and vibrations.
Innovation Solution
A three-dimensional shape measuring apparatus employing a confocal optical system with a two-dimensionally arranged aperture plate, a focus position changing unit with parallel plate members, and a photo-detector group, which allows for linear scanning and discrete position changes to optimize exposure timing and movement speed, ensuring consistent scanning and improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a Nipkow disk is used to scan spots on the measurement object, then high-speed scanning is achieved, but scanning speed variation and rotational deflection occur due to different aperture curvatures and eccentricity
Solution Approach 1:
The patent extracts and eliminates the Nipkow disk from the optical system, replacing it with a stationary aperture plate. This removes the source of rotational deflection and scanning speed variation, allowing for precise linear scanning without the curvature and eccentricity problems inherent in rotating disk systems.
Solution Approach 2:
Instead of rotating the aperture plate (as in Nipkow disk systems), the patent inverts the approach by keeping the aperture plate stationary and moving it linearly in the scanning direction. This fundamental reversal of the scanning mechanism eliminates rotational deflection while maintaining high-speed scanning capability.
2Measurement precision
If the aperture plate is moved at constant speed, then linear scanning is achieved, but exposure timing must be precisely coordinated with movement to ensure measurement accuracy
Solution Approach 1:
The patent incorporates feedback control where the imaging control unit monitors the position of the aperture plate and the rotation position of the focus position changing unit, and adjusts exposure timing accordingly. This ensures that exposure occurs at the correct focal depth for each scanned position, maintaining measurement accuracy while coordinating multiple moving parts.
Solution Approach 2:
The system pre-coordinates exposure timing with the known constant speed movement of the aperture plate and the predetermined rotation speed of the focus position changing unit. By calculating and setting exposure moments in advance based on these controlled movements, the system achieves precise measurement without requiring complex real-time adjustments.
3Measurement precision
If multiple parallel plate members with different refractive indices and thicknesses are used for focus position changing, then discrete focus positions are achieved, but the device structure becomes more complex
Solution Approach 1:
The focus position changing unit is segmented into multiple discrete parallel plate members, each with specific refractive index and thickness characteristics. This segmentation allows the system to achieve multiple discrete focus positions by rotating to different plate members, providing precise focal control while keeping each individual component relatively simple.
Solution Approach 2:
The rotating body with multiple parallel plate members serves multiple functions: it acts as both a focus position changing mechanism and a depth of field control device. By selecting different plate members with varying optical properties, the system can adjust focus depth and scanning range, making this single component multi-functional and reducing the need for separate focus adjustment mechanisms.
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 apparatus achieves high-resolution, linear scanning with reduced measurement errors, enabling precise three-dimensional shape measurement by controlling the aperture plate's movement and focus position changes, thereby improving scanning speed and accuracy.
Implementation Method 1
The focus position changing unit includes a rotating body provided thereon with a plurality of parallel plate type members different from each other at least in one of refractive index and thickness and arranged along a rotation direction so as to cross an optical axis of the objective lens
Implementation Method 2
The objective lens converge each of the light beams having passed through the plurality of confocal apertures, at an object side focused point, and again converge each of reflected light beams formed by reflection of converged light beams at a measurement object, at respectively corresponding confocal apertures
Implementation Method 3
The photo-detector group includes a plurality of photo-detectors each of which outputs a signal corresponding to an intensity of a reflected light beam having again passed through the confocal aperture
Data Source
AI summary
According to one embodiment, a three-dimensional shape measuring apparatus includes at least an aperture plate that is provided with a plurality of confocal apertures which are two-dimensionally arranged to have a predetermined arrangement period, and an aperture plate displacement portion that displaces the aperture plate at a constant speed in a predetermined direction perpendicular to the optical axis direction. Further, the aperture plate is provided with a cover member which is moved integrally with the aperture plate and which includes a transparent body allowing the light beams from the light source to pass therethrough and to be irradiated to the plurality of confocal apertures, and protects the plurality of confocal apertures from dust. Further, an imaging optical system, by which each of reflected light beams is guided to a photo-detector, is designed in consideration of optical properties of the whole optical system including the transparent body of the cover member.