3D Sensor Lighting Pattern Optimization for Low Contrast
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Solution Overview
Problem
Existing 3D sensors face challenges in accurately measuring objects with low contrast and optical interference, particularly in industrial settings, due to limitations in pixel resolution, phase superimposition errors, and the need for expensive and hazardous light sources, which can lead to incorrect measurements and system failures.
Innovation Solution
A method using a 3D sensor with a two-dimensional, inhomogeneous, aperiodic, and self-unsimilar illumination pattern generated by a lighting unit, which enhances image contrast and allows for reliable triangulation of depth information, even in low-contrast scenarios, using cameras with overlapping solid angles and a control unit for image evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If propagation-time-based methods with modulated light pulses are used, then depth information can be obtained, but the sensor requires special photomixing detector chips with limited pixel resolution (maximum 160x120 pixels)
Solution Approach 1:
The patent replaces the complex photomixing detector chip (electronic/optical demodulation system) with a simpler directly readable optoelectronic sensor. Instead of using modulated light pulses requiring demodulation, the system uses directly detectable light pulses with the sensor, eliminating the need for special sensor chips while maintaining depth measurement capability through time-resolved detection of backscattered pulses
Solution Approach 2:
The patent extracts and removes the complex demodulation function from the sensor chip itself. By using directly readable optoelectronic sensors instead of photomixing detectors, the system separates the modulation function (performed by the light source) from the detection function (performed by the simple sensor), thereby simplifying the sensor chip while preserving depth measurement capability
2Measurement precision
If very short light pulses with shutter times of 30ns to 100ns are used, then time resolution is improved, but very powerful and expensive laser light sources are required which also entail considerable eye safety problems
Solution Approach 1:
The patent changes the parameters of the light source by using LED-based light sources with pulse durations in the microsecond to millisecond range instead of nanosecond laser pulses. This parameter change maintains sufficient time resolution for depth measurement while dramatically reducing the power and hazard level of the light source, thereby eliminating eye safety concerns and the need for expensive laser equipment
Solution Approach 2:
The patent replaces expensive, hazardous laser light sources with inexpensive, safe LED light sources. LEDs are much cheaper, have longer operational life, and do not require special safety measures, making the system more practical for industrial applications while maintaining the necessary measurement capabilities through appropriate pulse timing
3Reliability
If stereoscopy principle is used, then system robustness is improved, but low-contrast images lead to incorrect measurements and system failure
Solution Approach 1:
The patent uses periodic illumination with coded light patterns (such as pseudo-random sequences) that are projected onto the object and captured by the sensor. This periodic, structured illumination enhances the contrast and detectability of object features, allowing reliable depth measurement even for low-contrast objects while maintaining the robustness of the stereoscopic approach
Solution Approach 2:
The patent employs coded light patterns with varying intensities and temporal structures (analogous to color changes in spectral domain) to illuminate the object. These structured light patterns create artificial contrast on low-contrast objects, enabling the stereoscopic system to reliably detect and measure depth information that would otherwise be indistinguishable
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 and reliable depth measurement in low-contrast environments, reducing the influence of noise and random effects, and ensures system reliability, particularly in safety-critical applications, by using LED or laser light sources and diffractive optical elements for high resolution and adaptability.
Implementation Method 1
the propagation time of the light pulse being determined by determining the phase difference of the modulated light
Implementation Method 2
the backscattered light pulses arriving at the sensor at different times due to the different distances to different locations. To measure the distance, a time window is opened that is smaller than or equal to the length of the emitted light pulses
Implementation Method 3
an image of an object is recorded in a stereo camera with two camera systems, each consisting of an image sensor and associated imaging optics, for example, and whose optical axes are spaced apart by a basic length L. Knowing the focal length f of the imaging optics and a measure a+b of the displacement of the object on the two images, the desired distance or depth information R can then be printed out calculate
Data Source
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AI summary
The method involves optimizing a lighting pattern by recording an image of an object (15) without lighting. A contrast distribution and/or spatial frequencies of contrast of the image without lighting is determined as a contrast data record. The contrast data record obtained from the image without lighting is compared with a predetermined optimal contrast data record, which is different for different setups of three dimensional sensors (10). The lighting pattern, whose structure supplies optimal contrast data record filtered by real characteristics of the object, is determined. An independent claim is also included for a three dimensional sensor comprising a camera.