ToF Object Tracking via Modulo Distance Unwrapping
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Solution Overview
Problem
Existing ToF distance sensing technologies face challenges in accurately tracking objects beyond the unambiguous range without additional hardware, leading to limitations in range estimation and object tracking, especially for high-speed objects.
Innovation Solution
The proposed solution involves treating ToF measurements as modulo samples and employing systems and methods that unwrap these modulo measurements using continuity constraints, allowing for continuous trajectory estimation of objects beyond the unambiguous range without requiring additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the pulse period is increased to measure distance over a range longer than the maximum unambiguous range, then the measurable distance range is extended, but the rate of light detection decreases
Solution Approach 1:
The patent segments the distance measurement problem into two components: (1) modulo distance measurement within the unambiguous range using standard pulsed ToF, and (2) integer multiple determination using continuity constraints across multiple measurement frames. This segmentation allows the system to maintain high pulse repetition rates for accurate modulo measurement while reconstructing absolute distances beyond the unambiguous range through temporal continuity analysis.
Solution Approach 2:
The patent performs preliminary modulo distance measurements at high pulse repetition rates to capture continuous trajectory data points. These preliminary measurements establish a temporal sequence that enables subsequent unwrapping to determine integer multiples, thereby extending the measurable range without sacrificing detection rate.
2Length of stationary object
If non-periodic pulse sequences or multiple repetition rates are used to avoid the unambiguous range limitation, then the measurable distance range is extended, but the hardware complexity increases
Solution Approach 1:
The patent changes the parameter being measured from absolute distance to modulo distance, which naturally fits within the unambiguous range. By measuring modulo distance at high pulse repetition rates and then unwrapping the results using continuity constraints, the system extends the measurable range while maintaining simple periodic pulse emission hardware.
Solution Approach 2:
The patent introduces continuity constraints as an intermediary mechanism to bridge the gap between modulo distance measurements and absolute distance determination. The continuity constraint acts as a mathematical mediator that uses temporal coherence across multiple frames to resolve integer ambiguities without requiring complex hardware modifications.
3Length of stationary object
If non-periodic pulse sequences or multiple repetition rates are used to avoid the unambiguous range limitation, then the measurable distance range is extended, but the photon detection efficiency decreases
Solution Approach 1:
The patent segments the measurement into high-rate modulo distance acquisition and low-rate integer multiple determination. The majority of energy is spent on rapid modulo measurements that capture trajectory continuity, while minimal additional energy is required for the unwrapping process, thereby maintaining high overall photon detection efficiency.
Solution Approach 2:
The patent maintains continuous high-rate pulse emission to capture modulo distance measurements throughout the trajectory, ensuring no useful photon detection opportunities are missed. The continuity of this useful action allows the system to reconstruct absolute distances later without requiring reduced pulse rates during critical measurement phases.
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 enables accurate range estimation and tracking of objects beyond the unambiguous range of the sensing system, maintaining high precision and efficiency without the need for extra hardware, thus being suitable for applications like autonomous driving.
Implementation Method 1
The sensor emits short pulses of infrared light towards the target. The emitted light reflects off the target surface and travels back to the sensor.
Implementation Method 2
The sensor measures the time it takes for the light to make this round trip. Using the known speed of light, the sensor calculates the distance to the target by multiplying the time of flight by the speed of light
Data Source
AI summary
A system for tracking positions of a target object comprises circuitry configured to control an illumination source to periodically emit illumination pulses for illuminating the target object. The illumination reflected from the target object is detected to estimate a sequence of modulo distances to the target object wrapped by a pulse repetition period. The circuitry unwraps the sequence of modulo distances subject to one or more continuity constraints to output a continuous trajectory of the target object.