Spread Spectrum ToF Camera Interference Reduction
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Solution Overview
Problem
Multiple depth sensing cameras in the same environment experience interference in their operations, leading to erroneous depth sensing due to synchronized light pulse emissions and gate operations, resulting in interference and electromagnetic noise.
Innovation Solution
Implementing a spread spectrum technique that varies the cyclical operations of pulsed light sources and gated image sensors pseudo-randomly, ensuring that light pulses from one camera arrive at another's open gate with random time delays, effectively broadening the frequency of operation and reducing interference by integrating these delays into a signal mimicking ambient light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple ToF cameras operate simultaneously in the same environment with synchronized light pulse emissions and gate operations, then depth sensing can be performed by each camera, but interference occurs between cameras leading to erroneous depth measurements
Solution Approach 1:
The patent implements periodic light pulse emissions and gate operations with pseudo-randomly varied periods. Each camera emits light pulses and opens its gate in cyclical sequences, but the periods of these sequences are varied pseudo-randomly. This periodic action with randomized timing allows multiple cameras to operate simultaneously while distributing interference evenly across the depth range, preventing systematic measurement errors.
Solution Approach 2:
The patent changes the temporal parameters of light pulse emission and gate operation by introducing pseudo-random variations in the periods between consecutive pulses and gate openings. Instead of fixed periodic intervals, the system dynamically adjusts these parameters according to pseudo-random sequences, thereby spreading the spectral content and reducing coherent interference between multiple cameras.
2Measurement precision
If multiple ToF cameras use fixed frequency light pulse emissions and gate operations, then depth measurements can be obtained, but electromagnetic interference noise increases
Solution Approach 1:
The patent applies parameter changes by modulating the frequency and timing of light pulse emissions and gate operations using pseudo-random sequences. This spreads the electromagnetic energy across a broader frequency spectrum rather than concentrating it at a single frequency, thereby reducing peak electromagnetic interference noise levels while maintaining depth measurement capability.
Solution Approach 2:
The system transitions from static, fixed-frequency operation to dynamic, time-varying operation. The periods of light pulse emissions and gate openings are continuously varied according to pseudo-random sequences, making the system adaptive and reducing coherent electromagnetic interference that would occur with fixed-frequency operation.
3Ease of operation
If ToF cameras operate with synchronized cycles, then simple timing coordination is maintained, but light pulses from one camera arrive at another's open gate causing interference
Solution Approach 1:
The patent maintains periodic operation for ease of implementation while introducing pseudo-random variations in the periods. Each camera continues to operate in cyclical sequences of light pulse emission and gate opening, which preserves the simplicity of timing coordination. However, the pseudo-random variation in periods ensures that cameras are not perfectly synchronized, causing light pulses from one camera to arrive at another's gate with random time delays that integrate into ambient light rather than structured interference.
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 reduces interference among cameras and decreases electromagnetic interference noise, allowing multiple time-of-flight cameras to operate simultaneously with improved accuracy in depth measurements.
Implementation Method 1
measure distances to features of an imaged scene in three dimensions (3D)
Implementation Method 2
pulsed light source such as a laser or light emitting diode (LED)
Data Source
AI summary
Reduction in interference between different time of flight (ToF) cameras used for depth measurements and operating in the same application environment is achieved using a spread spectrum technique in which the cyclical operations of a pulsed light source such as a laser or light emitting diode (LED) and gated image sensor are varied in a pseudo-random manner in each camera. In an alternative embodiment, spread spectrum logic is applied in a ToF camera that employs phase modulation techniques.