Self-Mixing Laser Sensor Velocity Correction
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Solution Overview
Problem
Conventional vehicle speed measurement devices require an independent reference speed for calibration, which is inaccurate due to indirect determination methods, and existing technologies like laser Doppler interferometry struggle with orientation changes and vibrations, leading to low measurement accuracy for speed-over-ground measurements.
Innovation Solution
A self-mixing laser sensor system that determines the orientation of the sensor relative to the reference surface and applies transformations to velocity data to correct for misalignments, using multiple laser beams with fixed angles to accurately measure forward and lateral velocities independently of sensor orientation changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement devices are used for vehicle speed, then calibration can be performed with reference speed, but the measurement accuracy is low due to indirect determination methods
Solution Approach 1:
The patent replaces conventional mechanical speed sensors and GPS-based indirect speed determination with a laser-based interferometric measurement system. This optical system directly measures the vehicle's speed over ground by detecting the Doppler shift of laser light reflected from the road surface, eliminating the need for mechanical reference systems and achieving higher measurement precision.
Solution Approach 2:
The laser sensor system performs self-calibration by automatically determining the orientation of the sensor relative to the road surface and applying transformations to correct for misalignments. The system uses its own measurements to adjust and validate its calibration parameters without requiring external reference equipment, making the calibration process autonomous and simplifying the overall system.
2Measurement precision
If laser Doppler interferometry is used for speed-over-ground measurement, then direct velocity measurement is achieved, but measurement accuracy deteriorates due to orientation changes and vibrations
Solution Approach 1:
The system performs preliminary calibration to determine the orientation of the laser sensor relative to the road surface before actual speed measurements are taken. By pre-determining the sensor's angular position and applying appropriate transformation matrices, the system compensates for orientation changes and vibrations during operation, maintaining measurement reliability under dynamic conditions.
Solution Approach 2:
The patent applies mathematical transformations to the measured velocity components based on the determined sensor orientation parameters. By changing the reference frame and adjusting the measurement parameters according to the sensor's actual angular position, the system compensates for orientation deviations and vibration effects, maintaining accurate speed-over-ground measurements despite environmental disturbances.
3Measurement precision
If sensor orientation is not corrected, then the system is simpler to operate, but measurement accuracy is compromised due to misalignment with reference surface
Solution Approach 1:
The laser sensor system automatically determines its own orientation relative to the road surface and performs self-calibration by applying transformations to correct for misalignments. This autonomous self-adjustment eliminates the need for manual orientation adjustments by operators, maintaining measurement precision while preserving ease of operation. The system serves itself by automatically compensating for installation errors and orientation changes.
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 system achieves enhanced accuracy in measuring vehicle velocity components by compensating for sensor misalignments and vibrations, providing direct and complete kinetic data for improved car safety systems.
Implementation Method 1
When the laser beam hits the road, it will be reflected in all directions. When the road moves with respect to the laser (i.e. the car with the laser mounted thereon moving with respect to the road), the frequency of the reflected light is slightly different from the frequency of the incident laser beam. This frequency shift is the so-called Doppler shift and proportional to the component of the velocity of the road into the direction of the laser beam.
Implementation Method 2
When a small portion of this reflected, Doppler-shifted laser light re-enters the laser cavity, it will mix with the 'undisturbed' laser cavity light leading to an interference pattern. This interference pattern will change periodically with again exactly the Doppler frequency.
Data Source
AI summary
The method is based on a determination of the orientation of the sensor to the surface moving with respect to the sensor and then acquiring data where the lateral velocity is small and the forward velocity is large. Then, the orientation of the sensor with respect to the direction of the forward velocity is determined and the velocity data subsequently measured are corrected using the measured orientation of the sensor with respect to the reference surface and the forward velocity direction.