Laser Scanning Sensor with Rotary Polygon Mirror Timing Control
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Solution Overview
Problem
Molded polygon mirrors used in laser scanning sensors suffer from surface precision issues due to molding conditions, leading to distortion and uneven precision, making them impractical for continuous pulse emission and alignment, especially when requiring a single surface composition, and are costly to improve with metal cutting for higher precision.
Innovation Solution
A laser scanning sensor with a rotary polygon mirror that includes a light-emitting element, a light-receiving element, a rotary polygon mirror, a driving part, a rotation detecting part, and a control/calculation part to set and adjust the start timing of pulse laser beam projection on each reflecting surface, allowing alignment even with uneven precision, using a delay time and pulse cycle adjustment for each surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If molded polygon mirrors are used to reduce cost and enable mass production, then manufacturing cost and productivity are improved, but surface precision and alignment accuracy deteriorate due to molding distortion
Solution Approach 1:
The invention changes the operational parameters by using ultra-short pulse lasers (picosecond or femtosecond level) instead of continuous wave lasers. This parameter change allows the system to tolerate surface imperfections in molded polygon mirrors while maintaining measurement accuracy, thereby enabling cost-effective mass production without sacrificing precision
Solution Approach 2:
The invention applies partial action by using extremely short pulse durations where the laser interaction time is so brief that thermal diffusion and other error-amplifying processes do not occur. This partial temporal action allows molded surfaces with minor imperfections to still achieve accurate measurements
2Productivity
If continuous pulse emission is used to improve scanning coverage, then productivity is improved, but alignment accuracy deteriorates due to cumulative distortion effects on molded surfaces
Solution Approach 1:
The invention uses periodic ultra-short pulse emission where each pulse is so brief that thermal and mechanical effects do not accumulate between pulses. The periodic timing is controlled precisely, allowing high productivity through rapid repetition while maintaining alignment accuracy because each pulse acts independently on the molded surface
Solution Approach 2:
The invention substitutes mechanical precision requirements with temporal precision control. Instead of relying on mechanically perfect molded surfaces, the system uses precisely timed ultra-short pulses where the timing control replaces the need for high mechanical surface precision
3Manufacturing precision
If metal cutting is used to improve polygon mirror surface precision, then manufacturing precision is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The invention effectively makes the polygon mirror surface requirements 'disposable' in terms of precision tolerance. By using ultra-short pulse lasers, the system can tolerate molded surface imperfections that would be unacceptable with continuous lasers, thereby accepting cheaper molded mirrors instead of expensive precision-cut mirrors
Solution Approach 2:
The invention changes the laser operational parameters to ultra-short pulses, which fundamentally alters how the laser interacts with the polygon mirror surface. This parameter change reduces sensitivity to surface precision, allowing molded mirrors to be used instead of precision-cut mirrors
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 ensures accurate alignment of pulse laser beams on the irradiation surface, compensating for surface irregularities and misalignment, enhancing the precision and practicality of molded polygon mirrors in laser scanning sensors without the high costs associated with metal cutting.
Implementation Method 1
a light-emitting element configured to emit a pulse laser beam
Implementation Method 2
acquire information on a distance to the object, per each pulse of the pulse laser beam, based on a time after the start of emission of the pulse laser beam before the return of the reflected beam to the light-receiving element
Implementation Method 3
a rotary polygon mirror having a plurality of reflecting surfaces configured to change a travelling direction of the pulse laser beam
Data Source
AI summary
A laser scanning sensor includes a laser light-emitting element to emit a pulse laser beam, a light-receiving element to receive a returned reflected beam, a rotary polygon mirror having a plurality of reflecting surfaces to change the travelling direction of the pulse laser beam, and a drive motor to rotate the rotary polygon mirror in a predetermined direction. The sensor also includes an encoder to detect the rotation status of the rotary polygon mirror and to generate a reference signal and trigger signals for the respective reflecting surfaces, and a control/calculation unit to produce a projection pulse train in a specific pulse cycle after a delay time from the generation of a trigger signal for each of the reflecting surfaces, and to acquire distance information per pulse, based on the time after the start of emission of the pulse laser beam before the return of the reflected beam.