3D Time-of-Flight Camera Reference Channel for Safety Diagnostics
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Solution Overview
Problem
Conventional 3D time-of-flight cameras lack robust safety features and efficient diagnostic capabilities, particularly in safety-critical applications, due to limitations in measurement accuracy, sensitivity to extraneous light, and the need for extensive testing procedures that compromise response time and reliability.
Innovation Solution
A 3D time-of-flight camera system with a reference channel for internal function testing, where reference part measurements are distributed over multiple distance measurements, allowing for continuous operation and high-repetition-rate function tests without affecting the actual recording time, and utilizing a control and evaluation unit to manage partial and reference partial measurements for precise distance calculation and error detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple partial measurements are performed to compensate for pixel asymmetries and account for background light, then measurement accuracy and reliability are improved, but acquisition time increases and frame rate decreases
Solution Approach 1:
The patent divides the image sensor pixels into different groups, where each group performs a different number of partial measurements. Some pixels perform more measurements for higher accuracy while others perform fewer measurements for faster acquisition, allowing the system to achieve both high reliability and high productivity simultaneously through heterogeneous measurement strategies.
2Reliability
If the number of charge storage units in pixels is increased to determine background light, then robustness against ambient light is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent makes the number of partial measurements a variable parameter that can be adjusted based on application requirements. The same pixel structure can adaptively perform different numbers of measurements (e.g., 2, 3, 4, or more) depending on whether the application prioritizes speed or accuracy, eliminating the need for fixed hardware configurations for different measurement robustness levels.
3Reliability
If extensive testing procedures are implemented to meet safety standards, then safety and reliability are improved, but response time increases and productivity decreases
Solution Approach 1:
The patent incorporates reference measurements that are performed in advance or interspersed with actual distance measurements. These reference measurements establish baseline data for safety diagnostics before critical failures occur, enabling the system to meet safety standards through proactive monitoring rather than reactive testing, thus minimizing response time while maintaining high reliability.
4Measurement precision
If more samples are acquired per frame, then measurement precision and accuracy are improved, but acquisition time increases and motion artifacts increase
Solution Approach 1:
The patent introduces dynamic adaptability where the number of partial measurements per pixel can be adjusted based on real-time conditions such as scene complexity, required accuracy, and motion detection. This dynamic configuration allows the system to optimize the balance between measurement precision and acquisition time, reducing motion artifacts by minimizing measurements when motion is detected while maintaining high precision when the scene is static.
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 enables the camera to meet high safety standards, such as SIL 2 or PL d, by ensuring reliable operation and rapid fault detection, while maintaining a high frame rate and reducing power consumption and thermal load, thus enhancing its applicability in safety-critical environments.
Implementation Method 1
An illumination unit generates transmitted light, which is modulated with a first modulation frequency
Implementation Method 2
The transmitted light reflected by objects in the detection area, superimposed with ambient or background light, falls onto an image sensor with a plurality of receiving elements or pixels, which generate a corresponding received signal
Implementation Method 3
A multitude of demodulation units, using a lock-in method, extract a sample value from the received signal by demodulating it with a signal at the first modulation frequency. The propagation-related absolute phase shift between the transmitted and received signals is proportional to the object distance in the scene
Implementation Method 4
A reference illumination unit emits reference light, also modulated at the first modulation frequency, which illuminates the image sensor
Data Source
Figure 1~2
Figure 3~4b
Figure 4c~4f
AI summary
A camera (10) for capturing three-dimensional image data from a capture area (18) is specified, comprising an illumination unit (12) for emitting transmit light (16) modulated with at least a first modulation frequency, an image sensor (26) with a plurality of receiving elements (26a) for generating a respective received signal, a plurality of demodulation units (32) for demodulating the received signals with the first modulation frequency to obtain sample values, a reference illumination unit (38) for emitting reference light (42) modulated with the first modulation frequency and directed onto the image sensor (26) within the camera (10), and a control and evaluation unit (34) configured toFor distance measurement, the illumination unit (12) and/or the demodulation units (32) are controlled for a first number of partial measurements, each with a different phase shift between the first modulation frequency for the transmitted light (16) and the first modulation frequency for demodulation, and a distance value is determined from the sampled values obtained by the partial measurements for each receiving element (26a). For a functional test, the reference illumination unit (38) and/or the demodulation units (32) are controlled for a second number of reference partial measurements, each with a different phase shift between the first modulation frequency for the reference light (42) and the first modulation frequency for demodulation, and a reference distance value is determined from the sampled values obtained by the reference partial measurements for each receiving element (26a). The control and evaluation unit (34) is further configured toto distribute the reference measurements for a functional test over several distance measurements.