Multi-Frequency AM Rangefinder Phase Ambiguity Resolution
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Solution Overview
Problem
Existing rangefinders using the AM method face challenges in measuring accurate distances when phase delay exceeds one period of the modulation frequency, and the TOF method has low detection accuracy and difficulty in achieving high-accuracy rangefinding required for applications like robotics, while also struggling to meet safety standards for laser emission.
Innovation Solution
A rangefinder that employs an AD conversion unit to convert analog reflection signals into digital signals synchronized with the modulation signal, uses Fourier transformation to detect phase differences, and calculates wave position based on differential calculus of average waveforms to correct wavenumber errors and improve measurement accuracy, while also determining the presence of disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the AM method is used for distance measurement, then multiple measuring points can be set up for averaging processing to improve measurement accuracy, but it becomes impossible to measure accurate distance when the phase delay exceeds one period of the modulation frequency
Solution Approach 1:
The patent segments the distance measurement process into multiple frequency components by using three different modulation frequencies. Each frequency provides a different unambiguous measurement range, and by combining the results from all three frequencies, the system achieves both high precision (from the highest frequency) and extended reliable range (from the lower frequencies that can resolve larger phase delays).
Solution Approach 2:
The patent transitions from a single-frequency measurement approach to a multi-frequency approach, adding the dimension of frequency variation. This allows the system to resolve the ambiguity of phase delay exceeding one period by using the complementary information from multiple frequency domains, where each frequency contributes to different aspects of the distance measurement.
2Reliability
If the TOF method is used to measure long distances while satisfying Class 1 safety standards, then emission intensity can be set high with short pulse width, but detection accuracy is low because only a rising edge point is used for measurement
Solution Approach 1:
The patent merges the advantages of both AM and TOF methods. It uses the AM modulation technique with multiple frequencies to achieve high detection accuracy through multiple measuring points and averaging processing, while simultaneously maintaining compliance with Class 1 safety standards by controlling the overall emission duration and average power, rather than relying on high-intensity short pulses characteristic of TOF methods.
3Measurement precision
If measuring beams modulated with three kinds of frequencies are used to measure one point, then correct distance can be determined, but emission duration is lengthened and it becomes difficult to satisfy Class 1 safety standards
Solution Approach 1:
The patent employs periodic modulation at three different frequencies, where each frequency component is activated in a structured sequence. By using periodic action with carefully selected frequencies and duty cycles, the system achieves accurate distance measurement through multi-frequency analysis while controlling the total emission duration to comply with Class 1 safety standards, as the periodic structure allows for efficient use of emission time.
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 solution enables accurate distance measurement beyond one wavelength of the modulation signal, enhances detection accuracy to 7.5 mm for a 10 m range, and meets Class 1 safety standards for laser emission, improving the reliability and precision of rangefinding.
Implementation Method 1
a light source for outputting a measuring beam
Implementation Method 2
an AM modulation unit for AM modulating the measuring beam with a modulation signal consisting of a sinusoidal wave
Implementation Method 3
the measuring beam being AM modulated with a sinusoidal wave and its reflected beam are subjected to photoelectric exchange
Data Source
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AI summary
The present invention provides a rangefinder that has a light source 3a for outputting a measuring beam, an AM modulation unit 3b for AM modulating the measuring beam with a modulation signal consisting of a sinusoidal wave, a light receiving unit 5 for detecting a reflected beam that is part of the measuring beam modulated by the AM modulation unit 3b and reflected by a measurement object X, a phase difference detection unit 91 for finding a phase difference between the measuring beam and the reflected beam, a distance arithmetic unit 93 for calculating a distance to the measurement object X based on the phase difference detected by the phase difference detection unit 91, a burst drive unit 3b for pulse-driving the light source 3a to operate in burst emission, and a wave position detection unit 92 for detecting a wave position of the sinusoidal wave based on a delay time from output of the measuring beam to detection of the reflected beam, wherein the distance arithmetic unit 93 calculates the distance to the measurement object X based on the wave position detected by the wave position detection unit 92 and the phase difference detected by the phase difference detection unit 91.