Photoelectric Sensor Stray Light Shielding
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Solution Overview
Problem
Coaxial retro-reflective type photoelectric sensors face issues with detection accuracy due to stray light entering the light receiving element, as the light projection and reception paths are not physically separated, leading to degradation in detection performance.
Innovation Solution
A light shielding member is positioned between the optical-path separation portion and the light projecting or receiving unit, extending obliquely with respect to the optical axis, to prevent stray light from reaching the light receiving unit, and is preferably colored black to inhibit reflection, with the option of being integrated with the lens or support member to simplify the structure and reduce the number of components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a coaxial retro-reflective type photoelectric sensor is used to achieve compact structure and alignment ease, then the sensor size and installation complexity are reduced, but detection accuracy deteriorates due to stray light entering the light receiving element
Solution Approach 1:
A light shielding member is introduced as an intermediary component between the optical-path separation portion and the light projecting/receiving units. This mediator blocks stray light from reaching the light receiving element, resolving the contradiction between compact coaxial structure and detection accuracy by adding a targeted light-blocking element without changing the overall sensor configuration
Solution Approach 2:
The harmful stray light path is extracted and blocked separately from the main optical path. The light shielding member selectively removes the unwanted light component that would otherwise enter the light receiving element, allowing the coaxial structure to be maintained while eliminating the harmful effect
2Measurement precision
If a light shielding member is added to block stray light and improve detection accuracy, then detection accuracy is improved, but device complexity and number of components increase
Solution Approach 1:
The light shielding member is merged with existing structural components such as the lens or support members. By integrating the light-shielding function into already-present components rather than adding a completely separate part, the detection accuracy is improved while minimizing the increase in device complexity and component count
3Measurement precision
If the light shielding member is positioned close to the light projecting unit to effectively block stray light, then stray light blocking effectiveness is improved, but positioning precision requirements increase
Solution Approach 1:
The light shielding member serves as a mediator positioned at the optical-path separation portion, which is strategically located to block stray light effectively. By positioning it where the optical paths diverge rather than immediately near the light source, the component achieves high blocking effectiveness while allowing for more relaxed positioning tolerances during manufacturing and assembly
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 enhances detection accuracy by eliminating stray light and simplifying the sensor structure, allowing for improved object detection without the need for high positioning accuracy of the light shielding member.
Implementation Method 1
a light-emitting diode for generating detection light
Implementation Method 2
a half mirror for separating the optical path of the detection light from returned light
Implementation Method 3
a photodiode for receiving the returned light from the half mirror
Implementation Method 4
A light shielding member is positioned between the optical-path separation portion and the light projecting or receiving unit, extending obliquely with respect to the optical axis, to prevent stray light from reaching the light receiving unit
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
It is an object to provide a photoelectric sensor with excellent detection accuracy. A photoelectric sensor includes a light-emitting diode for generating detection light; a photodiode for receiving returned light induced by reflection of the detection light outside and returned thereto; a light projection/reception lens which is adapted to exit the detection light from the light-emitting diode to the outside, and further, is adapted such that the returned light from the outside enters there; a half mirror which is provided on an optical path between the light projection/reception lens and the light-emitting diode and the photodiode, and further, is adapted to separate the optical path of the detection light which proceeds toward the light projection/reception lens from the light-emitting diode, from the optical path of the returned light which proceeds toward the photodiode from the light projection/reception lens; and a light shielding member which is provided in such a way as to overlap the optical path of the detection light or the returned light at any position on the optical path between the light projection/reception lens and the light-emitting diode and the photodiode, and further, is adapted to partially intercept the detection light or the returned light.