Time-of-Flight Camera Error Compensation via Internal Reference Path
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Solution Overview
Problem
Time-of-flight (ToF) camera systems face inaccuracies due to cyclic and offset errors, which affect the precision of distance measurements by introducing phase wrapping and harmonic components in the laser modulation signals.
Innovation Solution
Incorporating a secondary image sensor to detect errors and modify the light emission control signals, adjusting timing, phase, and duty cycle to compensate for cyclic and offset errors, and using multiple secondary image sensors to enhance error detection and compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If modulated light is emitted at multiple frequencies to resolve phase wrapping, then distance measurement range is improved, but measurement precision deteriorates due to cyclic and offset errors
Solution Approach 1:
The patent applies preliminary action by measuring and characterizing cyclic and offset errors using an internal optical path before actual distance measurements are performed. The controller determines error characteristics by comparing phase differences between the internal path (known distance) and external path, then uses these pre-determined error characteristics to correct subsequent measurements, thereby maintaining precision across extended measurement ranges.
Solution Approach 2:
The patent implements feedback by continuously monitoring phase differences through the internal optical path and using this information to correct measurements from the external optical path. The controller uses the known distance of the internal path as a reference to detect cyclic and offset errors, then applies corrections to compensate for these errors in the actual distance measurements, creating a closed-loop error correction system.
2Measurement precision
If a single frequency is used for modulation, then measurement precision is improved, but distance measurement range deteriorates due to phase wrapping
Solution Approach 1:
The patent characterizes cyclic and offset errors at the operating frequency before measurements are taken. By pre-measuring the error characteristics using the internal optical path and storing these error profiles, the system can apply corrections to maintain precision even when operating at frequencies that extend the measurement range beyond the single-frequency phase-wrapping limit.
Solution Approach 2:
The system uses the internal optical path as a continuous reference to detect and correct frequency-dependent errors. By comparing phase measurements from the internal path (known distance) with expected values, the controller identifies cyclic and offset errors and applies real-time corrections to extend the accurate measurement range beyond what would be possible with a single frequency alone.
3Measurement precision
If multiple secondary image sensors are used to detect errors, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent makes the image sensor multi-functional by using it for both capturing external scene information and detecting internal reference light from the internal optical path. The same image sensor alternates between measuring external objects at different frequencies and measuring the internal reference path to characterize errors, eliminating the need for separate sensors and reducing system complexity while maintaining precision.
Solution Approach 2:
The patent combines the external measurement function and internal reference measurement function into a single integrated system. The image sensor, optical path, and controller work together to perform both external distance measurements and internal error characterization, merging what could have been separate subsystems into one unified apparatus that reduces overall system complexity.
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 significantly improves the accuracy of distance measurements by reducing errors and phase wrapping, allowing for more precise depth mapping and reducing the impact of harmonics in the ToF system.
Implementation Method 1
determine, based on charge accumulated by the image sensor, an error of the ToF system... determine a first phase difference between the emitted light and reflected light
Data Source
AI summary
The present disclosure provides an improved time-of-flight system. The ToF system includes an image sensor, a controller and a light source. The controller is configured to determine at least one of a cyclic error or an offset error of the ToF system. The ToF system modifies the operation of the light source to reduce the cyclic or offset error.