Laser Scanner Resonant Frequency Tracking for Timing Accuracy
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Solution Overview
Problem
Conventional laser scanners face challenges in accurately receiving laser light reflected from the same measurement point on a target object due to changes in the resonant frequency of the scanning mirror, caused by environmental factors like temperature and pressure.
Innovation Solution
A laser scanner that synchronizes the emission of laser light and photodetection signal sampling with the operation of the scanning mirror using a phase locked loop (PLL) circuit and amplitude controller, ensuring accurate timing even when the resonant frequency changes, and includes a mechanism to detect and respond to defective states by adjusting emission and oscillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the scanning mirror oscillates at a fixed resonant frequency, then the laser light can be scanned efficiently with maximum amplitude, but the resonant frequency changes due to environmental factors causing inaccurate timing for receiving reflected laser light
Solution Approach 1:
The patent employs a feedback mechanism where the actual resonant frequency of the scanning mirror is continuously monitored and used to adjust the timing of laser light emission and photodetection signal sampling. This closed-loop approach ensures that timing accuracy is maintained despite environmental changes affecting the resonant frequency.
Solution Approach 2:
The system transitions from a static fixed-frequency approach to a dynamic adaptive approach. The resonant frequency is no longer assumed constant but is continuously tracked and used to adjust system parameters in real-time, allowing the system to adapt to environmental changes while maintaining measurement accuracy.
2Measurement precision
If the resonant frequency of the scanning mirror changes due to environmental factors, then the deflection angle changes causing the laser light to miss the same measurement point, but increasing adaptability to environmental changes requires complex frequency tracking and adjustment mechanisms
Solution Approach 1:
The patent uses feedback from the actual resonant frequency measurement to adjust the timing of laser emission and signal sampling. This ensures that even when the resonant frequency shifts due to environmental changes, the system can still accurately measure the same measurement point by synchronizing with the new frequency.
Solution Approach 2:
The system performs self-adjustment by using its own resonant frequency characteristics to determine the appropriate timing parameters. The scanning mirror's actual resonant frequency directly informs the timing of laser emission and photodetection sampling, eliminating the need for external complex adjustment mechanisms.
3Productivity
If continuous laser light emission is used, then the scanning mirror can continuously scan the target object, but defective areas may be continuously illuminated causing potential damage or inaccurate measurements
Solution Approach 1:
The patent implements periodic action by controlling the laser light emission to occur only during specific time windows when the scanning mirror is at appropriate positions. This pulsed emission approach maintains continuous scanning capability while avoiding continuous illumination of potentially defective areas, as the laser is activated only when needed for valid measurements.
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
Ensures accurate reception of laser light from the same measurement point on the target object even when the resonant frequency of the scanning mirror changes, preventing continuous emission to a defective area and allowing for reliable detection of scanner defects.
Implementation Method 1
The scanning mirror scans the laser light emitted from the light source, toward the target object by oscillating about a predetermined axis at a resonant frequency. The resonant frequency is a frequency specific to the scanning mirror. As FIG. 6 illustrates, the gain characteristics of the scanning mirror are maximum at the resonant frequency. Accordingly, while the scanning mirror is oscillating at the resonant frequency, the amplitude of oscillation of the scanning mirror is maximum.
Implementation Method 2
A laser scanner that synchronizes the emission of laser light and photodetection signal sampling with the operation of the scanning mirror using a phase locked loop (PLL) circuit and amplitude controller, ensuring accurate timing even when the resonant frequency changes
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
A laser scanner includes: a light source (10); a scanning mirror (14) that scans laser light emitted from the light source (10), toward a target object (20) by oscillating about axis C; a photodetector (16) that generates a photodetection signal upon receiving the laser light reflected from the target object (20); a controller (40) that controls emission of the laser light by the light source (10), and that performs sampling on the photodetection signal; and a detector (18) that detects an amount of displacement of the scanning mirror (14), and calculates a resonant frequency of the scanning mirror (14) based on the amount of displacement detected. The controller (40) determines a time at which the laser light is emitted from the light source (10) and a time at which sampling is performed on the photodetection signal, based on the resonant frequency calculated.