Distance Sensor Noise Suppression via Dual-Threshold Digitization
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Solution Overview
Problem
Conventional distance-measuring sensors are sensitive to interference signals, particularly in noisy environments, which can lead to inaccurate measurements due to the inability to distinguish between weak echoes from objects and interference, such as those caused by external light or contaminants.
Innovation Solution
A distance-measuring sensor employing a pair of comparator units with different thresholds to digitize and weight signal sections, allowing for the suppression of noise and interference echoes in the histogram, thereby improving the signal-to-noise ratio and reducing sensitivity to interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional single-threshold digitization is used, then the system is simple to operate, but the sensor becomes sensitive to small analog noise and interference echoes
Solution Approach 1:
The signal evaluation is segmented into multiple threshold levels (first threshold and second threshold) that divide the received signal into different sections. Each section is evaluated separately and weighted differently in the histogram, allowing discrimination between noise and useful echoes based on their amplitude characteristics
Solution Approach 2:
Different weighting factors are applied to different signal sections based on their amplitude characteristics. The first section (below first threshold) receives one weighting, the second section (between thresholds) receives another weighting, and the third section (above second threshold) receives a third weighting, optimizing the evaluation for each local signal characteristic
2Device complexity
If conventional histogram evaluation is used, then the device complexity is low, but the measurement precision deteriorates in noisy environments
Solution Approach 1:
The histogram evaluation is segmented by introducing multiple threshold levels that create distinct signal sections. Each section contributes differently to the histogram based on its amplitude characteristics, improving the ability to distinguish useful echoes from noise without requiring complex evaluation electronics
Solution Approach 2:
The evaluation parameters are changed by introducing weighting factors that modify how different signal sections contribute to the histogram. This parameter change allows the system to prioritize certain signal amplitude ranges over others, improving measurement precision in noisy environments
3Reliability
If signal distance is increased to suppress noise, then the robustness improves, but the device complexity increases due to additional construction measures
Solution Approach 1:
Instead of increasing physical signal distance through complex optical constructions, the invention changes the evaluation parameters by introducing multiple threshold levels and weighting factors. This software-based parameter change achieves noise suppression without adding complex optical or electronic hardware
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 sensor becomes less sensitive to small analog noise and interference echoes, enhancing the resolution of distance measurements and reducing incorrect shut-downs in safety-critical applications by effectively filtering out noise and improving the robustness of the system.
Implementation Method 1
a time of flight process is known from EP 1 972 961 A1 or EP 2 469 296 A1, which carries out a plurality of individual measurements with a respective one transmitted pulse
Implementation Method 2
light signals are transmitted and the time up to the reception of the light signals remitted or reflected at objects is measured
Data Source
AI summary
A distance-measuring sensor (10) is provided for detecting and determining the distance of objects (18) in a monitored zone comprising a transmitter (12) for transmitting transmitted pulses; a receiver (20) for generating a received signal from the transmitted pulses remitted in the monitored zone; a first comparator unit (36a) for digitizing the received signal with reference to a first threshold; and a control and evaluation unit (30) which is configured to transmit a plurality of transmitted pulses via the transmitter (12), to collect the received signals thereupon generated by the receiver (20) in a histogram and to determine a received time point from the histogram and thus to determine a measured value for the signal transit time from the sensor (10) to the object (18). In this respect, a second comparator unit (36b) is provided for digitizing the received signal with reference to a second threshold, wherein the first comparator unit (36a), the second comparator unit (36b) and the control and evaluation unit (30) are configured to acquire three digital states of a respective section of the received signal with reference to the first threshold and to weight the contributions of the section to the histogram in dependence on the digital state.