Light Barrier Beam-Shaping Element for Stray Light Rejection
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Solution Overview
Problem
Conventional light barriers are limited by their sensitivity to reflections and stray light, which can lead to false detection issues, especially in environments with reflective surfaces, and they struggle to achieve a compact size while maintaining high sensitivity.
Innovation Solution
The use of a beam-shaping element that employs total internal reflection to create a large aperture with a short effective focal length, allowing for a compact design with reduced sensitivity to reflections and stray light, achieved through the design of first and second beam-shaping structures that deflect light and guide it towards the receiver, minimizing the impact of oblique light and reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the aperture of the beam-shaping element is increased to achieve higher sensitivity, then the sensitivity of the light barrier is improved, but the overall height of the receiver unit must be increased, resulting in a larger aspect ratio and less compact design
Solution Approach 1:
The beam-shaping element employs curved optical surfaces, specifically a concave entry surface and a convex exit surface, to focus and direct light onto the photodetector. This curvature enables efficient light collection and focusing within a compact axial distance, achieving high sensitivity without increasing the overall height of the receiver unit.
Solution Approach 2:
The patent optimizes specific geometric parameters of the beam-shaping element, including the aperture diameter (5.5mm), the thickness (3mm), and the radii of curvature of the entry and exit surfaces. By carefully controlling these parameters, the design achieves a compact aspect ratio of 2.4 while maintaining high light collection efficiency and sensitivity.
2Reliability
If a conventional converging lens is used with a large aperture to maximize sensitivity, then light collection is improved, but the device becomes more susceptible to reflections and stray light from reflective surfaces in the environment
Solution Approach 1:
The curved optical surfaces of the beam-shaping element are designed with specific radii of curvature that focus light from the light-emitting diode onto the photodetector while inherently rejecting oblique incident light. This geometric configuration creates an angular sensitivity profile that accepts light from the intended source direction while rejecting reflections and stray light from other angles.
Solution Approach 2:
The beam-shaping element has non-uniform optical properties across its aperture, with the curved surfaces creating different light paths for different incident angles. Light from the intended source follows a specific path through the curved surfaces to the photodetector, while reflected light and stray light from other directions are directed away from the detector, creating localized optical quality control.
3Length of stationary object
If the overall height of the light barrier is reduced to achieve a more compact design, then the aspect ratio is improved, but it becomes difficult to maintain a large aperture for the beam-shaping element, reducing sensitivity
Solution Approach 1:
The curved optical surfaces enable the beam-shaping element to achieve a large aperture (5.5mm) within a small axial thickness (3mm). The concave entry surface and convex exit surface create an efficient light collection geometry that focuses light onto the photodetector without requiring a long optical path, thus maintaining high sensitivity in a compact form factor with aspect ratio 2.4.
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 results in a compact light barrier with enhanced sensitivity and reduced false detection due to reflections and stray light, enabling a greater range between transmitter and receiver while maintaining high reliability.
Implementation Method 1
The beam-shaping element has at least one first beam-shaping structure which is designed to direct light entering the first beam-shaping structure at least partially once or to reflect several times at a respective inner boundary surface of the first beam-shaping structure, so that the exit angle of the light emerging from the first beam-shaping structure differs from the entrance angle
Data Source
Figure 1a~1b
Figure 2~3
Figure 4~5
AI summary
The present invention relates to a light barrier with at least one light transmitter for emitting light in a monitoring area, with at least one light receiver for receiving light from the monitoring area, and at least one beam-shaping element associated with the light receiver, which is designed to focus light from the monitoring area onto the light receiver. The beam-shaping element has at least one first beam-shaping structure, which is designed to reflect light entering the first beam-shaping structure at least partially once or several times at a respective inner interface of the first beam-shaping structure, depending on its angle of incidence, such that the exit angle of the light exiting the first beam-shaping structure differs from the angle of incidence.