Time-of-Flight Distance Measurement with Dynamic Histogram Evaluation
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Solution Overview
Problem
Current time-of-flight measurement methods for determining distances between a measuring device and objects are prone to measurement errors due to dark or poorly reflective surfaces, environmental influences like fog, and high reflection properties of objects, which lead to inaccurate detection and false triggering, especially when multiple objects are present or when objects are at varying distances.
Innovation Solution
The method involves emitting a large number of light pulses with a constant increase in the start time of the time measurement, using a mathematical sequence (ts + nΔt), and storing the measured values in a histogram to evaluate light intensities and distances, allowing for reliable distance determination regardless of the number of objects and environmental influences, by adjusting the sensitivity and ignoring background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of individual APD diode pixels are used in the receiving diode to detect reflected light pulses, then the sensitivity for detecting distant objects with dark surfaces is improved, but the susceptibility to scattered light and false triggering increases
Solution Approach 1:
The receiving diode is divided into a large number of individual APD diode pixels arranged in a grid, where each pixel operates independently in Geiger mode. This segmentation allows the system to detect single photons while maintaining high sensitivity for distant objects with dark surfaces.
Solution Approach 2:
The evaluation system uses a histogram method that continuously monitors measurement results and distinguishes between genuine reflected light pulses and false triggering from scattered light. By analyzing the distribution of measurement values and comparing against background noise levels, the system can filter out false signals while preserving genuine detections.
2Device complexity
If the start time of time measurement is fixed for all light pulses, then the measurement process is simple, but multiple objects at different distances cannot be reliably distinguished
Solution Approach 1:
The start time of the time measurement is dynamically adjusted for each light pulse according to a mathematical sequence (ts + nΔt). This dynamic timing allows the histogram evaluation to distinguish between multiple objects at different distances by analyzing the distribution of time measurement results across multiple pulses with different start times.
3Measurement precision
If a histogram method is used to evaluate measurement results and filter false triggering, then measurement accuracy is improved, but the measurement process becomes more complex and time-consuming
Solution Approach 1:
The system performs multiple rapid time-of-flight measurements with dynamically adjusted start times and accumulates the results in a histogram before final evaluation. This preliminary accumulation of data allows for efficient filtering of false triggering through statistical analysis, improving measurement accuracy without requiring complex real-time processing for each individual pulse.
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 precise detection of multiple objects at different distances while minimizing the impact of environmental factors like fog and transparent objects, reducing measurement errors and enhancing sensitivity for distant objects, thereby providing reliable distance measurements.
Implementation Method 1
calculates the distance s according to the physical formula s=c×t when the time span t required by light waves between the measuring device and the object is measured
Implementation Method 2
The receiving diode is, for example, an APD (Photon Avalanche Diode) with a so-called avalanche effect
Implementation Method 3
an APD (Photon Avalanche Diode) with a so-called avalanche effect, i. H. the APD photodiode has an internal gain that is adjustable across the operating voltage and can be increased up to a maximum factor of 100
Data Source
Figure 1
Figure 2~3
AI summary
In a method for determining a distance (D) between a measuring device (1) and an object (2) by means of time-of-flight measurement, wherein the method comprises the following steps: - emitting a light pulse (5) by a transmitting diode (4), - receiving a light pulse (7) reflected by the object (5) by a receiving diode (6), - creating a histogram into which a plurality of measurement cycles are read, which are recorded by the receiving diode (6) within a specified time interval, the distances D of several objects (2) that are immersed in the monitoring area (3) are to be determined without measurement errors, and environmental influences, for example fog or transparent objects, for example glass plates, arranged in the beam path (of the light pulses (5)), are to be compensated for.the measurement signals are not affected. This is achieved by the following process steps: - Emitting a plurality of light pulses (5) with a constant increase in the respective start time (ts) of the time measurement in a time-to-digital converter (10) according to the mathematical sequence ts + nx Δt, where ts is the time of emission of the light pulse (5), n is a natural number starting at zero up to a predetermined end value of at least 4, and Δt is the amount of time delay by which the start time of the time measurement of the converter (10) is delayed in each instance, wherein for each number n a plurality of light pulses (5) are emitted and the received pulse (7) captures the time measurement result of the converter (10), which is changed by the missing time amount nx Δt, - or by reversing the sequence of the time delays,- Storing the measured values obtained from such a measurement cycle in the histogram and - Evaluating the histogram after the completed measurement cycle in the histogram as a function of the light intensities, intensity and/or number of light pixels of the receiving diode (6) that were activated by the received light and/or the distance (D) between the start time (ts) of the emitted light pulses (5) and their measurement times at the receiving diode (6).