Indirect Time of Flight Multipath Error Compensation
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Solution Overview
Problem
Indirect Time of Flight (iToF) range calculation systems face multipath error issues due to multiple reflections and propagation paths, which affect distance measurement accuracy and are exacerbated by the need for high modulation frequencies, limiting the unambiguous measurement range and frame rate.
Innovation Solution
A method and apparatus that utilize an unstructured light source and a structured light source concurrently to illuminate a scene, generating sets of signals with an array of photodetectors, and derive an error estimate by calculating differences between signal measurements from selected and subsequent time frames, allowing for multipath error compensation without reducing the distance frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high modulation frequencies are used in iToF systems to achieve low stochastic distance measurement errors, then measurement precision is improved, but the unambiguous measurement range is reduced
Solution Approach 1:
The patent segments the measurement process into multiple time frames, using structured light illumination only during selected frames while using unstructured light during other frames. This temporal segmentation allows the system to collect multipath error data during unstructured illumination frames and apply compensation during structured illumination frames, resolving the contradiction between measurement precision and unambiguous range by enabling error compensation without requiring continuous high-frequency modulation
2Measurement precision
If structured light patterns are used for multipath error compensation, then measurement accuracy is improved, but the distance frame rate is reduced
Solution Approach 1:
The patent implements periodic action by alternating between structured light illumination and unstructured light illumination across consecutive time frames. The structured light source illuminates during predetermined frames (e.g., every other frame), while the unstructured light source illuminates during other frames. This periodic switching enables multipath error compensation to be performed intermittently without continuously reducing the frame rate, thereby maintaining productivity while improving measurement accuracy
Solution Approach 2:
The patent applies preliminary action by deriving multipath error estimates during unstructured illumination frames before applying compensation during structured illumination frames. The error characteristics are pre-characterized during frames when structured light is not present, and these pre-derived error estimates are then used to compensate measurements from frames with structured light illumination, enabling accurate compensation without slowing down the overall measurement process
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 multipath errors in iToF systems while maintaining the frame rate, enhancing the accuracy of distance measurements and reducing the impact of multiple reflections and propagation paths.
Implementation Method 1
Light reflected from the object in the scene is received by the detection device and converted to an electrical signal
Implementation Method 2
a phase angle between illumination and reflection can be determined, and the determined phase angle can be used to determine a distance to the reflecting feature of the scene
Data Source
AI summary
A method for multipath error compensation comprises an unstructured light source (142) illuminating a scene during a plurality of consecutive time frames. A structured light source (144) illuminates the scene concurrently, the illumination by the structured source (144) occurring during predetermined frames of the plurality of consecutive time frames. An array of photodetectors (102) each generate a set of signals in response to irradiation with light reflected from the scene according to an indirect time of flight calculation technique to yield a plurality of sets of signals. An error estimate is derived (130) from the plurality of sets of signals generated during a selected time frame of the plurality of consecutive time frames when structured illumination takes place and another time frame temporally about the selected time frame when both structured and unstructured illumination takes place. The error estimate is applied in a range calculation with respect to the scene.