Laser Scanning Micrometer Collimated Beam Design
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Solution Overview
Problem
Existing laser micrometers face accuracy and repeatability issues due to the lack of a spatial filter, leading to detection of off-axis reflected and diffracted light, and the use of larger beam diameters results in reduced precision and increased errors, especially when measuring objects with different reflectivity characteristics.
Innovation Solution
The design incorporates a rotating scanner mirror with a wedge-shaped receiver mirror and two light detecting diodes positioned between the laser and the rotating mirror, which allows for precise detection of the collimated beam and minimizes off-axis light issues, while also using a Ronchi rule with multiple data points for improved calibration and error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a small spot diameter is used at the measurement area, then the device can measure smaller features, but the beam diverges to a larger diameter entering the receiver creating reduced accuracy and repeatability
Solution Approach 1:
The patent changes the beam parameters by using a collimated beam of larger diameter instead of a diverging beam. This maintains a constant beam diameter throughout the measurement field, allowing the use of a small focal length lens while avoiding the accuracy and repeatability issues associated with focusing a diverging beam. The collimated beam approach resolves the contradiction by decoupling the spot size at the measurement area from the beam diameter at the receiver.
2Object-affected harmful factors
If a collimated beam of larger diameter is used, then off-axis light issues are reduced, but the spot diameter becomes much larger making detection difficult and worsening accuracy
Solution Approach 1:
The patent resolves this contradiction by changing the beam parameter from diverging to collimated, which maintains a constant diameter. This allows the system to use a small focal length lens for easy detection while still benefiting from the off-axis light rejection capability of the collimated beam configuration.
3Device complexity
If a small focal length lens is used, then the device becomes more compact, but the beam focus becomes difficult to control reducing measurement precision
Solution Approach 1:
The patent resolves this contradiction by changing the beam from diverging to collimated. This parameter change allows the use of a small focal length lens without the associated focus control difficulties, as the collimated beam maintains a constant diameter and does not require precise focusing to maintain measurement accuracy.
4Measurement precision
If calibration is performed with a Ronchi rule, then optical errors can be corrected, but a much larger line and gap spacing is needed reducing the number of lookup table values
Solution Approach 1:
The patent resolves this contradiction by changing the beam parameter to collimated, which allows for a smaller spot diameter at the measurement area. This enables the use of finer line and gap spacing in the Ronchi rule calibration target, thereby increasing the number of lookup table values and improving optical error correction resolution.
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
This approach significantly enhances measurement accuracy across the measurement region, reduces errors, and allows for precise detection of small spot diameters, even in the presence of optical defects, thereby improving the overall performance of the laser micrometer.
Implementation Method 1
a laser shining a beam on a rotating scanner mirror
Implementation Method 2
the rotating scanner mirror scatters light which divides in an arc into a collimating lens
Implementation Method 3
creating a collimated scanning beam
Implementation Method 4
two light detecting diodes positioned between the laser and the rotating mirror
Data Source
AI summary
The present invention provides multiple improvements to optical-based laser scanning micrometers and providing a small handheld version laser scanning micrometer based on the these improvements. For added accuracy and reduction in unit size, a double sided coated mirror receiver reflects the beam back into the transmitter light source. For added accuracy, a Ronchi rule is repositioned one or more times to calibrate additional lookup table correction values. To compensate for barometric pressure change and temperature, two additional reference edges are added to be combined with the reference edges in the transmitter to generate to null out pressure and temperature at the passline measurement area. To minimize beam errors and for part locating, a third derivative is detected. Two or more parallel scanning beams are generated to null out cosine errors and to measure, taper and spherical parts.