Time-of-Flight Sensor Cover Reflection Separation at Close Range
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Solution Overview
Problem
Time of flight sensors face challenges in accurately determining target distances due to optical crosstalk from light reflections off the sensor cover or contamination, which can overlap with target reflections, especially at close ranges.
Innovation Solution
A method for time of flight sensors that involves emitting a series of light pulses, analyzing photon detection distributions to distinguish between cover reflections and target reflections, and measuring the separation between peaks to calculate distances, using a transparent cover and photodetectors to minimize optical crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single transparent cover is used to enclose the emitter and detector, then the device structure is simplified, but optical crosstalk from light reflections off the cover increases
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before actual distance measurements to characterize and store reference profiles of cover reflections. This allows the system to pre-compensate for optical crosstalk effects without adding physical structural complexity. The reference profiles are obtained by measuring photon detection distributions with no target present, capturing the characteristic timing and intensity patterns of light reflecting off the cover.
Solution Approach 2:
The patent introduces an intermediary approach by using software-based signal processing and reference profile comparison to separate cover reflections from target reflections. Instead of physically blocking reflections with additional covers, the system uses computational methods to identify and subtract the harmful optical crosstalk signals, effectively mediating between the simplified physical structure and the need for accurate measurement.
2Object-generated harmful factors
If the emitter and detector are located in separate adjacent cavities covered by separate transparent covers, then optical crosstalk from cover reflections is reduced, but the device structure becomes more complex
Solution Approach 1:
The patent performs calibration measurements in advance to capture reference profiles of optical crosstalk characteristics. By measuring photon detection distributions with no target present, the system stores reference data that characterizes the timing and intensity patterns of reflected light from the cover. This preliminary characterization enables subsequent measurements to distinguish between cover reflections and actual target reflections through pattern matching and subtraction algorithms.
Solution Approach 2:
The patent creates a computational copy or model of the cover reflection patterns through reference profile measurement. Instead of physically eliminating optical crosstalk through complex multi-cover structures, the system creates a digital representation of the reflection characteristics and uses this model to subtract harmful signals from measurements, achieving the same effect with simpler hardware.
3Device complexity
If light reflections from the cover are not accounted for, then the measurement system is simpler, but distance measurement accuracy deteriorates especially at close ranges
Solution Approach 1:
The patent implements feedback by continuously comparing measured photon detection distributions against stored reference profiles during actual measurements. The system uses the reference profiles (obtained during calibration) to identify and correct for cover reflection effects in real-time, adjusting the distance calculations to compensate for optical crosstalk. This feedback mechanism maintains high measurement accuracy without requiring complex real-time physical modifications.
Solution Approach 2:
The patent performs preliminary calibration measurements to establish reference profiles of optical crosstalk characteristics before actual distance measurements are taken. During calibration, the system measures photon detection distributions with no target present, capturing the characteristic timing and intensity patterns of light reflecting off the cover. These reference profiles are stored and then used during normal operation to identify and subtract harmful optical crosstalk signals, ensuring accurate distance measurements even at close ranges where cover reflections would otherwise dominate the signal.
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
Enables accurate distance measurement to targets close to the sensor by distinguishing and measuring reflections, even when they overlap with cover reflections, thereby improving the sensor's accuracy and range.
Implementation Method 1
emitting a series of pulses of light from the light emitter
Implementation Method 2
detecting reflections of the light from the target
Implementation Method 3
using the one or more photodetectors to obtain a distribution of times at which at least one photodetector detected photons
Implementation Method 4
light from the emitter which is reflected off the cover
Implementation Method 5
light from the emitter may be totally internally reflected within the cover to reach the emitter
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A method of measuring a distance using a time of flight sensor comprising a substantially transparent cover covering a light emitter and one or more photodetectors. The method comprises emitting a series of pulses of light from the light emitter; and using the one or more photodetectors to obtain a distribution of times at which at least one photodetector of the one or more photodetectors detected photons after each emission of the series of pulses of light. If the distribution of times comprises only a single peak, the method further comprises analysing the single peak to determine if the single peak includes counts of photons reflected from a target. If the single peak includes counts of photons reflected from a target, the method further comprises measuring the separation between a reference time and a point of the single peak.