Laser Rangefinder Digital Counting to Eliminate Timing Walk Error
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Solution Overview
Problem
Conventional laser rangefinders suffer from systematic timing walk errors and inaccuracies in measuring target distances due to variations in reflected signal amplitude and target characteristics, despite employing techniques like leading edge timing, zero crossing timing, and constant fraction timing.
Innovation Solution
A digital counting and display system for laser rangefinders, comprising a pulsed Nd:YAG laser, an afocal Gallilean telescope, a silicon avalanche photodetector, a low noise multistage amplifier, and an analog-to-digital converter, which generates digital voltage signals for a digital counting and display circuit to accurately measure time differences and calculate distances with reduced cross walk error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional timing methods (leading edge timing, zero crossing timing, constant fraction timing) are used to measure target distance, then the measurement can be performed, but systematic timing walk errors occur due to variations in reflected signal amplitude and target characteristics
Solution Approach 1:
The patent changes the measurement parameter from amplitude-based timing (which suffers from timing walk error when signal amplitude varies) to time-based counting. By using a clock signal to generate fixed-duration gates and counting the number of gates between transmitted and reflected pulses, the system achieves timing measurement that is independent of signal amplitude variations, thereby eliminating timing walk error while maintaining measurement precision
Solution Approach 2:
The patent replaces the conventional analog timing measurement system (which uses voltage comparison and timing circuits susceptible to amplitude variations) with a digital counting system. The digital counter counts fixed-duration clock gates, substituting mechanical/analog timing mechanisms with digital logic that is inherently more stable and immune to signal amplitude fluctuations, thus improving reliability while maintaining precision
2Length of stationary object
If the laser wavelength is set to 1.06 μm for atmospheric transmission, then the measurement range is extended, but the laser pulses become invisible and may damage eyes requiring safety precautions
Solution Approach 1:
The patent changes the laser wavelength from the conventional 1.06 μm (infrared, invisible, potentially harmful) to 532 nm (green visible light). This color/wavelength change makes the laser pulses visible for safety and alignment purposes while reducing the risk of undetected eye damage. The 532 nm wavelength is within the visible spectrum, allowing operators to see the laser beam and target illumination, thereby maintaining measurement range capability while mitigating harmful effects
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 provides accurate distance measurements with a resolution of at least 5 meters, an accuracy of 1.5 meters, and a maximum range of 15 kilometers, while minimizing timing walk errors and enhancing detection sensitivity and resolution.
Implementation Method 1
A pulsed laser is configured to emit a pulsed laser beam
Implementation Method 2
an afocal Gallilean telescope configured to receive backscattered laser pulses and generate a series of focused backscattered laser pulses
Implementation Method 3
a silicon avalanche photodetector connected to the afocal Gallilean telescope, wherein the silicon avalanche photodetector is configured to generate series of current signals proportional to the series of focused backscattered laser pulses
Implementation Method 4
a low noise multistage amplifier connected to the silicon avalanche photodetector, wherein the multistage amplifier is configured to generate a series of linearly changing amplified voltage signals from the series of current signals
Implementation Method 5
an analog-to-digital, A/D, converter connected to the low noise multistage amplifier, wherein the A/D converter is configured to convert the series of linearly changing amplified voltage signals to a series of digital voltage signals
Implementation Method 6
The digital counting and display circuit is configured to count each of the digital voltage signals, generate a total count and display the total count on a display
Data Source
AI summary
A digital counting and display system and methods for use with a laser rangefinder that counts backscattered laser beams and displays a distance between a laser and a target. The laser rangefinder includes a laser configured to emit a pulsed laser beam, an afocal Gallilean telescope configured to receive backscattered laser pulses and generate a series of focused backscattered laser pulses, a silicon avalanche photodetector connected to the afocal Gallilean telescope, configured to generate a series of currents signal proportional to the series of focused backscattered laser pulses, a low noise, multistage amplifier connected to the silicon avalanche photodetector, configured to generate a series of linearly changing amplified voltage signals from the series of current signals, an analog-to-digital converter configured to convert the series of linearly changing amplified voltage signals to a series of digital voltage signals, and a digital counting and display circuit connected to the analog-digital converter.