TOF Distance Sensing With Adaptive Modulation for Aliasing Control
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Solution Overview
Problem
Existing time-of-flight (TOF) cameras face challenges in measuring distances with high precision and wide dynamic range due to aliasing and dynamic range limitations when objects with different reflectance ratios are present in the same scene.
Innovation Solution
A distance-measuring apparatus employs a pair of modes: high-frequency and low-frequency modulation, performing multiple measurements with varying exposure times or light intensities to reduce aliasing and increase dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the modulation frequency is increased to reduce aliasing and improve measurement precision, then the measurement precision is improved, but the dynamic range is reduced when objects with different reflectance ratios are present
Solution Approach 1:
The system dynamically switches between high-frequency and low-frequency modulation modes based on the measurement scene. The controller determines which mode to use by evaluating the reflected light intensity and phase detection results, allowing the modulation frequency to adapt rather than remain fixed. This resolves the contradiction by using high frequency when needed for precision and low frequency when needed for dynamic range.
Solution Approach 2:
The system changes the modulation frequency parameter between two distinct states (high-frequency mode and low-frequency mode). By switching the modulation frequency parameter based on scene conditions, the system can achieve both high measurement precision (when aliasing is a concern) and wide dynamic range (when reflectance variations are present).
2Measurement precision
If multiple measurements are performed at high modulation frequency to reduce aliasing, then aliasing is reduced, but the measurement time increases
Solution Approach 1:
The system dynamically adjusts the number and frequency of measurements based on the detected scene conditions. When aliasing is detected or the scene requires high precision, the system performs multiple measurements at high frequency. When the scene is simple or reflectance variations are present, the system uses fewer measurements at lower frequency, thereby reducing measurement time while maintaining sufficient precision.
Solution Approach 2:
The system performs the minimum necessary number of measurements to achieve adequate precision rather than always performing maximum measurements. By evaluating phase detection results and reflected light intensity, the system determines whether additional measurements are needed, avoiding excessive measurements when they provide diminishing returns and increase time consumption.
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
The solution achieves both reduction in aliasing and expansion of the dynamic range, enabling precise distance measurements across varying reflectance ratios and distances.
Implementation Method 1
As a method of measuring the distance between a distance-measuring apparatus and an object, technologies to irradiate an object with light to calculate the distance to the object based on the time difference between the emitted light and the light reflected by the object, which are called time-of-flight (TOF) method, are known in the art.
Implementation Method 2
a light receiver configured to receive the light that is emitted from the light emitter and returns as reflected by the object
Data Source
AI summary
A distance-measuring apparatus includes a light emitter to emit light with modulated frequency to an object, a light receiver to receive the light that is emitted from the light emitter and returns as reflected by the object, and a controller to measure, based on radiation intensity of received light by the light receiver, a length of time between a time at which the light is emitted by the light emitter and a time at which the light is received by the light receiver to obtain a distance to the object. The controller performs a first measurement in which the light emitter emits the light at a first modulation frequency to measure the length of time by the time at which the light is received by the light receiver a first plurality of times.