Prism-Based Light Grid Sensor Stray Light Reduction
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Solution Overview
Problem
Existing optoelectronic sensors face issues with scattered light interference and the need for precise alignment, leading to increased size and complexity, as well as challenges in meeting safety standards due to stray light and beam crosstalk.
Innovation Solution
The use of a prism with a refractive index greater than 1.4, positioned close to the transmitting or receiving elements, for total reflection of light beams, combined with apertures to control beam angles and prevent crosstalk, allows for efficient separation of useful and stray light, reducing the need for light traps and enhancing assembly tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a prism with refractive index greater than 1.4 is used for total reflection, then stray light is effectively filtered and measurement precision is improved, but device complexity increases due to precise positioning requirements
Solution Approach 1:
The patent changes the refractive index parameter of the prism material to greater than 1.4, which fundamentally alters the critical angle for total internal reflection. This parameter change enables the prism to effectively filter stray light while maintaining a compact design, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The prism acts as an intermediary optical element positioned between the light source and the detection area. It mediates the light paths by reflecting useful beams while allowing stray light to pass through or be absorbed by the printed circuit board, thereby improving measurement precision without requiring complex additional components.
2Reliability
If the optical axis is routed parallel to the printed circuit board, then the sensor meets safety standards and reduces stray light interference, but the transmitter and receiver must protrude from the board increasing device size
Solution Approach 1:
The patent routes the optical axis parallel to the printed circuit board plane rather than perpendicular to it. This dimensional change in the optical path arrangement allows the system to meet safety standards for stray light reduction while keeping the transmitter and receiver within the housing footprint, eliminating the need for protruding components and reducing overall device volume.
Solution Approach 2:
The optical components (transmitter, receiver, and prism) are merged into a compact arrangement where the optical axis runs parallel to the circuit board. This integration allows all components to be housed within the same envelope space, eliminating protrusions and reducing the overall sensor housing volume while maintaining safety compliance.
3Manufacturing precision
If all light is deflected by total reflection, then beam direction control is improved, but obliquely incident light still reaches the receiving element causing interference
Solution Approach 1:
The patent applies total internal reflection locally at the prism interface with specific geometric angles, while other regions (the printed circuit board and housing interior) serve as absorption zones for stray light. This local differentiation in optical properties allows useful beams to be precisely directed while stray light is absorbed, resolving the contradiction between beam alignment precision and stray light 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 configuration minimizes stray light interference, allows for a more compact design, and meets safety standards by effectively filtering out unwanted light, reducing assembly complexity and production costs while maintaining high precision.
Implementation Method 1
The transmitted light beams and received light beams are totally reflected at a first interface of the prism running at an angle of 45° to the plane of the front pane
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The optoelectronic sensor (1) has a housing (20,20') and a prism (2,2') arranged as detour unit for received or transmitted rays of light around ninety degrees due to total reflection, at a distance of zero millimeter to three millimeter before a transmission or receipt element. The prism has a refractive index more then 1.4, and is made of polymethyl metacrylate, polycarbonate or glass.