Time of Flight Camera Multi-Frequency Phase Measurement
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Solution Overview
Problem
Time of flight (TOF) camera systems face limitations in distance measurement accuracy and uniqueness range due to interference and parasitic effects, such as fixed pattern noise and background light, which affect the reliability of distance determination.
Innovation Solution
The TOF camera system operates with at least three modulation frequencies, determining phase shifts in multiple cycles and calculating distance deviations to ensure that only valid distance values within a tolerance limit are output, thereby increasing the uniqueness range and reducing interference between systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single modulation frequency is used for distance measurement, then the measurement process is simple and fast, but the uniqueness range is limited and interference between multiple TOF systems occurs
Solution Approach 1:
The patent applies periodic action by using multiple modulation frequencies in cyclic measurement sequences. The system performs phase measurement cycles at different modulation frequencies (e.g., f1, f2, f3) in a repeating pattern, allowing distance values to be determined through comparison across cycles. This periodic multi-frequency approach extends the uniqueness range while maintaining systematic measurement control.
Solution Approach 2:
The patent implements parameter changes by varying the modulation frequency across different measurement cycles. Instead of using a fixed modulation frequency, the system changes the modulation frequency parameter (f1, f2, f3) in successive cycles, which enables extended uniqueness range and reduced interference. The evaluation unit compares distance values obtained at different frequency parameters to determine valid distances.
2Measurement precision
If multiple phase measurement cycles are implemented to improve distance determination, then the accuracy increases, but the effective frame rate is reduced
Solution Approach 1:
The patent applies partial action by performing phase measurements at multiple modulation frequencies but only outputting distance values when specific conditions are met. The evaluation unit determines validity by comparing distance values from successive cycles, and only outputs distances when they fall within tolerance limits. This partial output approach maintains accuracy while preserving frame rate by avoiding unnecessary re-measurements.
Solution Approach 2:
The patent implements feedback through the evaluation unit that compares distance values from successive measurement cycles and determines validity based on tolerance limits. The system uses feedback from previous cycle results to decide whether to output a distance value or continue measuring, thereby optimizing the balance between accuracy and frame rate without requiring complete re-measurement sequences.
3Reliability
If tolerance limits are set strictly to filter distance mismatches, then measurement reliability improves, but more valid distance values may be incorrectly rejected
Solution Approach 1:
The patent applies dynamics by adaptively determining tolerance limits based on the specific application requirements and measurement conditions. Rather than using fixed strict thresholds, the system can adjust tolerance values dynamically to balance reliability and information retention. The evaluation unit compares distance values against these tolerance limits to determine validity, allowing flexible optimization between rejecting mismatches and preserving valid measurements.
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 enhances the accuracy and reliability of distance measurements by increasing the uniqueness range and reducing interference, while maintaining an effective frame rate and effectively filtering out noise and motion-related deviations.
Implementation Method 1
the modulator is operable with at least three modulation frequencies
Implementation Method 2
the reflected light is mixed with the modulating signal in the PMD sensor
Implementation Method 3
Time of flight (TOF) camera systems that determine distances directly from the time of flight
Data Source
AI summary
A light transit time camera system and method for operating such a system which can be operated with at least three modulation frequencies, having the steps a) determining a phase shift (φi) of an emitted signal (Sp1) and a received signal (Sp2) for a modulation frequency (f1, f2, f3) in a phase-measuring cycle (PM1, PM2, . . . ), b) carrying out a plurality of phase-measuring cycles (PM1, PM2, . . . ), c) determining a distance value (dn,n+1) on the basis of the phase shifts (φn, φn+1) determined in two successive phase-measuring cycles (PMn, PMn+1), in a distance-measuring cycle (M1, M2, . . . ), d) carrying out a plurality of distance-measuring cycles (M1, M2, . . . ), e) determining a distance deviation (Δd) between the distance values of successive distance-measuring cycles, f) outputting of a distance value (dn,n+1) as a valid distance value if the distance deviation (Δd) is within a tolerance limit (Δdtol) is provided.