Time of Flight Camera Harmonic Error Cancellation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Time of flight range imaging systems face errors due to high-order harmonic frequencies present in square wave modulation signals, which are commonly used, leading to inaccuracies in phase measurements.
Innovation Solution
A method that generates a set of phase-separated output signals with specific phase offset values to cancel harmonic components, allowing the camera system to calculate and correct for harmonic errors using cancellation phase values, thereby improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If square wave modulation signals are used to drive the modulation of light source and imaging transducer, then the number of harmonic components is minimized and ease of manufacture is improved, but measurement precision deteriorates due to harmonic errors in phase measurements
Solution Approach 1:
The patent converts the harmful harmonic components of square wave signals into beneficial cancellation effects. By introducing additional phase-shifted measurement signals specifically designed to counteract harmonic distortions, the method transforms the harmful square wave harmonics into correctable error patterns, enabling precise sinusoidal-like measurements despite using simple square wave generation hardware.
Solution Approach 2:
The patent changes the parameter of phase offset values used in modulation. Instead of using standard equal phase offsets, the method employs specifically calculated non-equal phase offsets that create measurement patterns capable of separating and canceling harmonic components. This parameter modification allows the system to maintain measurement precision while continuing to use simple square wave signals.
2Measurement precision
If custom camera with changing modulation signal capacity is used to cancel harmonic components, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses copying by creating multiple copies of the measurement process with different phase offsets. Instead of modifying the physical modulation signal generation hardware, the method creates virtual copies of the measurement at different phase conditions through software processing. These copied measurements are then combined mathematically to cancel harmonics, achieving high precision without additional hardware complexity.
Solution Approach 2:
The patent applies preliminary action by pre-calculating the specific phase offset values needed for harmonic cancellation before the actual measurement process. The method determines the appropriate phase shifts in advance and programs them into the measurement sequence, allowing the camera system to execute simple, predetermined operations rather than dynamically adjusting modulation signals during acquisition.
3Ease of operation
If equal size increases of phase offsets are applied to light source, then ease of operation is improved, but measurement precision deteriorates due to inability to cancel harmonic errors
Solution Approach 1:
The patent introduces asymmetry by using non-equal phase offset values in the modulation process. Instead of symmetric equal phase increments, the method employs asymmetric phase offsets that create unequal measurement patterns. This asymmetry is specifically designed to break the symmetry of harmonic distortion patterns, enabling their separation and cancellation from the fundamental signal through mathematical processing.
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
In one aspect the invention provides a time of flight camera system which includes a time of flight transmitter arranged to transmit modulated radiation at a target, and a phase adjustment element configured to adjust the phase of a source modulation signal used to modulate the radiation transmitted at the target. This phase adjustment element provides a set of phase separated output signals, each output signal provided having one of a set phase offsets values applied, where at least one of these phase offset values is the cancellation phase value of another member of the set of phase offset values. The camera system also includes an image sensor modulated with the source modulation signal and configured to measure radiation reflected from a target, and a processor arranged to receive the image sensor measurements and being programmed to resolve range information from the measurements received by the image sensor.