Optoelectronic Sensor Shadow Detection Homogeneous Illumination
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Solution Overview
Problem
Existing optoelectronic sensors struggle to reliably detect small or narrow moving objects, such as antennas on vehicles, due to interference patterns and inhomogeneous light, leading to high error rates and potential safety issues in environments like train traffic.
Innovation Solution
The use of a spatially resolving line or matrix-type image sensor with a lighting unit featuring multiple individual light sources and a diaphragm arrangement that creates a homogeneous partial beam, reducing coherence and interference patterns, and a high-speed camera for image evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a simple photodiode light barrier is used, then the device is simple and robust, but it cannot detect small or narrow objects reliably
Solution Approach 1:
The patent divides the light barrier into multiple spatially resolving detection elements (photodiodes arranged in lines or matrices) instead of using a single photodiode. This segmentation allows the system to detect spatial patterns and shadows cast by small objects, significantly improving detection capability while maintaining relative structural simplicity.
Solution Approach 2:
The patent transitions from a single-point detection (1D) to a spatially resolved detection system with multiple photodiodes arranged in lines or matrices (2D). This dimensional expansion enables the system to capture spatial information and shadow patterns, allowing reliable detection of small and narrow objects that would be invisible to a simple photodiode.
2Measurement precision
If a camera with laser diode is used to cast object shadows, then small objects can be detected, but interference patterns and inhomogeneous light reduce detection reliability
Solution Approach 1:
The patent uses multiple individual light sources (VCSELs) with carefully controlled spatial arrangement and optical properties to create a homogeneous illumination field. The superposition of multiple incoherent light sources eliminates interference patterns and speckle effects, providing uniform light distribution that significantly improves detection reliability and reduces false signals.
Solution Approach 2:
The patent creates multiple copies of light sources (array of VCSELs) instead of using a single laser diode. These multiple light sources produce overlapping light fields that average out interference patterns, effectively copying the illumination function across multiple independent sources to achieve both high precision and reliability.
3Use of energy by moving object
If conventional laser light sources are used, then the light beam is coherent and intense, but interference patterns such as speckle effects appear that can be mistaken for small objects
Solution Approach 1:
The patent converts the harmful interference patterns of coherent laser light into a beneficial homogeneous illumination by using multiple incoherent light sources. The individual VCSELs are arranged and timed such that their incoherent superposition eliminates speckle effects and interference patterns, transforming what would be a harmful artifact into a clean, uniform light field that improves detection accuracy.
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 solution significantly improves the detection accuracy of small objects by minimizing interference and ensuring robustness against weather and vibrations, enabling reliable detection of objects as small as 1-2 mm in diameter at high speeds.
Implementation Method 1
The lighting unit (18) has a large number of individual light sources (18a), in particular a VCSEL array
Implementation Method 2
The diaphragm arrangement (20) selects a central partial beam from the transmitted light beam (30a)
Implementation Method 3
its shadow moves through the image sequence of the high-speed camera (22)
Implementation Method 4
The individual light sources ensure a certain intermixing of their respective individual light beams, so that the transmitted light beam has no or at least significantly less coherence
Data Source
Figure 1~2
Figure 3a~3b
AI summary
An optoelectronic sensor (10) for detecting a moving object (16) in a monitoring area (28) is described. The sensor (10) comprises an illumination unit (18) and an image sensor (24) arranged opposite each other, with the monitoring area (28) between them, and an evaluation unit (26) configured to recognize the object (16) from image data of the image sensor (24) by means of a shadow cast by the object (16) onto the image sensor (24). The illumination unit (18) has a plurality of individual light sources (18a) for generating a transmitted light beam (30a) in which coherence is disrupted by the superposition of the individual light sources (18a), and an aperture arrangement (20) that allows only a homogeneous sub-area (30) of the transmitted light beam (30a) to pass through.