Laser Scanner Pseudo-Random Code Correlation Distance Measurement
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Solution Overview
Problem
Optoelectronic sensors, particularly laser scanners, face challenges in achieving high range and measurement accuracy while maintaining angular resolution, due to limitations in manufacturing costs, eye protection requirements, and the need for high-priced components to achieve millimeter resolution in distance determination.
Innovation Solution
The use of a pseudo-random code sequence for the scanning beam, with a detuned time grid for coding and sampling, allows for improved interference immunity and time resolution, enabling better signal-to-noise ratio and range without requiring expensive components, by broadening the correlation maximum on the time axis at the cost of peak height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ultra-short pulses with high peak powers and complete digitization are used, then measurement precision and time resolution are improved, but manufacturing costs increase significantly
Solution Approach 1:
The patent changes the time scale parameter by using longer pulse durations (nanosecond range instead of picoseconds) and lower peak powers, while achieving comparable measurement precision through statistical averaging of multiple pulses. This parameter transformation allows the use of less expensive components while maintaining measurement accuracy.
Solution Approach 2:
The invention employs periodic transmission of multiple light pulses and statistical averaging of the received signals. By repeating the measurement process multiple times and averaging the results, the system achieves high signal-to-noise ratio and measurement precision without requiring ultra-short single pulses, thus avoiding the need for expensive high-speed components.
2Reliability
If a large number of pulses are transmitted for statistical averaging, then signal-to-noise ratio is improved, but measurement time increases
Solution Approach 1:
The patent applies preliminary time-of-flight filtering by only evaluating photons that arrive within an expected time window based on the maximum measurement range. This preliminary filtering reduces the number of photons that need to be processed and averaged, thereby reducing measurement time while maintaining signal-to-noise ratio.
3Reliability
If the time grid of pseudo-random code sequence and sampling are synchronized, then correlation peak height is maximized, but time resolution is degraded due to subsampling
Solution Approach 1:
The patent intentionally introduces asymmetry by detuning the sampling frequency from the chip rate of the pseudo-random code sequence. This deliberate mismatch prevents regular sampling patterns and enables more accurate time-of-flight estimation through correlation analysis, improving time resolution beyond what would be achievable with synchronized sampling.
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 results in a significantly better time resolution and increased range with the square root of the number of pulses, rather than the fourth root, while maintaining high measurement accuracy and allowing detection of objects under disturbed conditions, such as through glass or in adverse weather.
Implementation Method 1
a light transmitter (12) for generating transmitted light pulses
Implementation Method 2
method for detecting and determining the distance of objects using a time-of-flight method
Implementation Method 3
coding the scanning beam with a pseudo-random code according to a frequency spread method
Implementation Method 4
a correlation unit (40) for correlating the received signal with the pseudo-random code sequence used for modulation of the transmitted light beam (16)
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5d
AI summary
An optoelectronic sensor (10), in particular a laser scanner, for detecting and determining the distance of objects in a monitoring area (20) is described, comprising a light transmitter (12) for emitting a transmitted light beam (16) modulated with a pseudorandom code sequence at a transmission time, a deflection unit (18) for periodically deflecting the transmitted light beam (16) into the monitoring area (20), a light receiver (26) for generating a received signal from the transmitted light (22) remitted or reflected by objects in the monitoring area (20), an A/D converter (36) for sampling the received signal, a correlation unit (40) for generating a correlation signal (62, 64, 66) by correlating the sampled received signal with the pseudorandom code sequence, and an evaluation unit (32) configured to derive a correlation maximum from the correlation signal (62, 64,66) to determine a reception time and, based on the transmission time, to determine a measured value for the object distance via the light travel time from the sensor (10) to an object. A first time grid of the code elements of the pseudorandom sequence and a second time grid of the sampling of the received signal are detuned relative to each other.