Laser Radar Frequency Modulation Control for Vibration Measurement
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Solution Overview
Problem
Conventional laser radar devices face challenges in accurately measuring target information due to performance limits in the demodulation band, particularly when the frequency of the return signal component from a target with accelerated motion or vibration falls outside the permissible demodulation band.
Innovation Solution
A laser radar device that includes a modulated light generator, optical splitter, optical combiner, photodetector, demodulation circuit, frequency-to-voltage converter, characteristic calculator, and parameter setting unit, which adjusts the control parameter to ensure the center frequency of the return signal component falls within the demodulation band, enabling high-accuracy measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional laser radar device uses a fixed demodulation band, then the device complexity is low, but the measurement precision deteriorates when the return signal frequency falls outside the demodulation band
Solution Approach 1:
The patent implements dynamic adjustment of the demodulation band by changing the center frequency and bandwidth parameters based on the detected frequency characteristics of the return signal. This allows the system to adapt to targets with different motion states (stationary, uniform motion, accelerated motion, vibration) and maintain high measurement precision without requiring an excessively complex fixed-wide-band system
Solution Approach 2:
The system changes the operational parameters (center frequency and bandwidth) of the demodulation band according to the measured frequency characteristics of the return signal. This parameter adaptation enables the system to handle various target motion scenarios while avoiding the need for a permanently complex high-bandwidth design
2Measurement precision
If the demodulation band is widened to cover all possible return signal frequencies, then the measurement precision is maintained, but the device complexity and cost increase
Solution Approach 1:
Rather than using a permanently wide demodulation band, the system dynamically adjusts the band width and center frequency to match the actual signal requirements. This dynamic approach achieves the same measurement precision as a wide-band system but with lower average complexity and cost
Solution Approach 2:
The system modifies the demodulation band parameters (center frequency and bandwidth) based on the detected signal characteristics, allowing a simpler demodulator to effectively handle the full range of possible signal frequencies through adaptive parameter changes
3Reliability
If the filter bandwidth is fixed to reject internally reflected light, then the device complexity is low, but the reliability deteriorates when return signal frequency shifts occur
Solution Approach 1:
The system implements dynamic adjustment of the demodulation band parameters to track the frequency shifts of the return signal caused by target motion. This ensures reliable measurement of target information even when frequency shifts occur, without requiring an overly complex fixed-wide-band system
Solution Approach 2:
The system uses feedback from the frequency-to-voltage converter and characteristic calculator to detect the center frequency of the return signal and automatically adjusts the demodulation band parameters accordingly, ensuring the system adapts to frequency shifts while maintaining measurement reliability
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 solution allows for accurate measurement of target information even when the demodulation band has performance limitations, effectively capturing vibration frequency and displacement of moving targets with high precision.
Implementation Method 1
a photodetector configured to detect the interference light and output an electrical signal
Implementation Method 2
an optical combiner configured to combine the received light and the local light to generate interference light
Implementation Method 3
a frequency-to-voltage converter configured to convert the electrical signal output from the photodetector into a voltage signal having a signal voltage corresponding to a frequency of the electrical signal
Data Source
AI summary
The laser radar device includes: a modulated light generator configured to generate modulated laser light using frequency modulation based on a control parameter; an optical combiner configured to combine the received light and the local light to generate interference light; a photodetector configured to detect the interference light and output an electrical signal; a frequency-to-voltage converter configured to convert the electrical signal into a voltage signal; a characteristic calculator configured to measure a characteristic value of the voltage signal; an evaluator configured to evaluate, on a basis of the characteristic value, whether a center frequency of a spectrum of a return signal component is within a range of a demodulation band of a demodulation circuit; and a parameter setting unit configured to change the control parameter when it is evaluated that the center frequency is not within the range of the demodulation band.