Time-of-Flight Sensor Distance Accuracy via Multi-Frequency Mapping
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Solution Overview
Problem
Time-of-Flight (ToF) cameras face erroneous measurements due to light reflection from cover glasses, which mix with external light reflections, leading to inaccurate distance calculations.
Innovation Solution
Performing ToF measurements using multiple modulation frequencies and determining distance values based on these measurements using a mapping function, allowing for reduced measurement numbers and resolution of distance ambiguities, while compensating for errors such as fixed-pattern phase noise and optical errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ToF measurements are performed using a single modulation frequency, then the measurement process is simple and fast, but distance ambiguities cannot be resolved and measurement accuracy is degraded
Solution Approach 1:
The patent applies parameter changes by performing ToF measurements at multiple modulation frequencies (e.g., first and second frequencies). This changes the measurement parameters to resolve distance ambiguities and improve accuracy. The distance is determined by combining measurement results from different frequencies using a mapping function, which eliminates the ambiguity inherent in single-frequency measurements while maintaining practical system complexity.
2Reliability
If cover glass is used to protect the imager and illumination unit, then the sensor is protected from the outside world, but light reflection from the cover glass mixes with external light reflections causing erroneous measurements
Solution Approach 1:
The patent converts the harmful effect of cover glass reflections into a beneficial solution by using multi-frequency measurements. The cover glass creates a fixed optical path length that results in a consistent phase shift at a specific distance (the cover glass position). By measuring at multiple frequencies and analyzing the phase differences, the system can identify and compensate for this fixed reflection, thereby eliminating its harmful effect on measurement accuracy.
3Measurement precision
If multiple ToF measurements are performed to resolve distance ambiguities, then measurement accuracy is improved, but the number of measurements and processing time increase
Solution Approach 1:
The patent employs periodic action by performing ToF measurements at different modulation frequencies in a systematic sequence. Instead of performing multiple measurements at a single frequency, the system alternates between different frequencies (e.g., frequency 1, frequency 2, frequency 1, frequency 2), which resolves distance ambiguities more efficiently. This periodic multi-frequency approach reduces the total number of measurements required compared to single-frequency repeated measurements, thereby reducing processing time while maintaining accuracy.
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 effectively mitigates erroneous measurements caused by cover glasses and enhances the accuracy of distance calculations in ToF sensing by using a combination of measurements from different modulation frequencies and error corrections.
Implementation Method 1
Time-of-Flight (ToF) sensing
Data Source
AI summary
A method for time-of-flight sensing of a scene is provided. For at least one pixel position, the method includes performing at least one time-of-flight measurement using a first modulation frequency to obtain at least one first measurement value for the pixel position. Further, the method includes for the at least one pixel position performing at least one time-of-flight measurement using a second modulation frequency to obtain at least one second measurement value for the pixel position. The method additionally includes determining an estimate of a distance value of the pixel position based on the at least one first measurement value and the at least one second measurement value using a mapping function.