LIDAR Surface Normal Detection Using Probe Pulse Stretching
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Solution Overview
Problem
Existing LIDAR systems face challenges in accurately determining surface orientations and resolving measurement ambiguities, particularly in scenes with complex surfaces, due to limitations in pulse width measurement and cross-talk between laser emissions.
Innovation Solution
A LIDAR system with a rotatable chassis and multiple laser emitters and sensor elements, where the processing unit compares the width of emitted pulses to return pulses to determine surface orientations, and employs techniques like cross-correlation and pulse stretching to differentiate between reflections from different surfaces, while varying pulse spacing to reduce cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse width measurement is used to determine surface orientation, then surface normal information can be obtained, but measurement precision deteriorates due to pulse stretching and cross-talk between laser emissions
Solution Approach 1:
The patent segments the laser emission into multiple distinct pulses with varying time spacing, and segments the detection into separate time windows for each pulse. This allows individual pulse width measurements without overlap from other pulses, eliminating cross-talk and enabling accurate surface orientation determination from each reflected pulse's width.
Solution Approach 2:
The patent applies preliminary pulse stretching to the emitted laser pulses before they reach the target surface. By pre-stretching the pulses to a known extent, the system creates a reference pulse width that can be compared against the reflected pulse width to accurately determine surface orientation, compensating for additional stretching that occurs during reflection.
2Productivity
If multiple laser emitters are used to measure multiple surface points, then productivity increases, but cross-talk between emissions causes measurement errors
Solution Approach 1:
The patent employs periodic emission of laser pulses from multiple laser emitters in a time-multiplexed manner. Each emitter fires at specific time intervals with controlled spacing, creating a periodic measurement pattern that allows the sensor to distinguish between reflections from different emitters based on their temporal separation, thus enabling high productivity without cross-talk interference.
Solution Approach 2:
The patent dynamically adjusts the time spacing between pulses from different laser emitters based on the scan position and surface distance. By varying the pulse spacing dynamically, the system optimizes the measurement window for each pulse, ensuring that reflected pulses from multiple emitters do not overlap in time, thereby maintaining measurement precision while achieving high productivity.
3Device complexity
If fixed pulse spacing is used between laser emissions, then device complexity is reduced, but cross-talk occurs between reflections from different surfaces
Solution Approach 1:
The patent applies preliminary pulse stretching to each emitted pulse before it leaves the laser emitter. This pre-stretching creates a known, controlled pulse width that serves as a reference. By comparing the stretched reference pulse width with the width of the reflected pulse, the system can identify the reflection source and distinguish between different surfaces, preventing cross-talk without requiring complex dynamic pulse spacing control.
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 enables accurate determination of surface orientations and reduces measurement ambiguities, allowing for the generation of precise 3D point clouds and improved obstacle detection in autonomous vehicles and other applications.
Implementation Method 1
the system may measure the propagation time of a light signal as it travels from the laser emitter, to the surface, and back to the sensor element
Implementation Method 2
measuring properties of the reflections of the light
Implementation Method 3
The sensor element may comprise a photodetector such as a photomultiplier or avalanche photodiode (APD) that converts light intensity to a corresponding electrical signal
Data Source
AI summary
A LIDAR system includes a laser emitter configured to emit a laser pulse in a sample direction of a sample area of a scene. A sensor element of the LIDAR system is configured to sense a return pulse, which is a reflection from the sample area corresponding to the emitted laser pulse. The LIDAR system may compare a width of the emitted laser pulse to a width of the return pulse in the time-domain. The comparison of the width of the emitted pulse to the width of the return pulse may be used to determine an orientation or surface normal of the sample area relative to the sample direction. Such a comparison leads to a measurement of the change of pulse width, referred to as pulse broadening or pulse stretching, from the emitted pulse to the return pulse.