Reflection Light Barrier Sensor Polarization Management
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Solution Overview
Problem
Conventional reflective light barrier sensors using the autocollimation principle face challenges in achieving high detection reliability for reflective objects while being cost-effective, due to the need for low-stress glass lenses that are expensive and prone to depolarization, which affects the state of polarization of transmitted and received light.
Innovation Solution
The reflective light barrier sensor arrangement includes a transmitter unit, receiver unit, and beam splitter, with the transmission polarizer placed between the imaging element and the beam splitter, and the reception polarizer placed between the beam splitter and the reception imaging element, allowing the use of inexpensive plastic optics without influencing the polarization state, and incorporating a deflection mirror to align optical axes and reduce component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low-stress glass lenses are used to maintain polarization state, then detection reliability is improved, but manufacturing cost increases
Solution Approach 1:
The optical path is divided into separate transmission and reception segments with distinct imaging elements. The transmission imaging element and reception imaging element are positioned at different locations, allowing each to be optimized independently. This segmentation enables the use of cost-effective plastic optics in both positions without compromising the overall polarization maintenance, as each imaging element no longer needs to serve dual functions simultaneously.
Solution Approach 2:
A beam splitter is introduced as an intermediary component to separate the transmitted and received light paths. The beam splitter allows the transmitted light to pass through to the reflector while directing the reflected light to the reception imaging element. This intermediary enables the use of plastic imaging elements by decoupling the polarization-maintaining function from the imaging function, as the beam splitter handles the critical polarization separation.
2Device complexity
If combined transmission/reception optics are used, then device complexity is reduced, but polarization state is degraded due to depolarization
Solution Approach 1:
The combined transmission/reception optics are separated into distinct transmission and reception imaging elements positioned at different locations. The transmission imaging element focuses transmitted light while the reception imaging element focuses reflected light, with each element having its own optimal position. This segmentation eliminates the depolarization issue by preventing the single imaging element from being traversed multiple times by polarized light in different directions.
Solution Approach 2:
The optical design transitions from a single-axis combined optics arrangement to a multi-position segmented arrangement. By positioning the transmission and reception imaging elements at different spatial locations and using a beam splitter to manage light paths, the system adds dimensional separation to the optical design, allowing polarization integrity to be maintained while still achieving functional integration.
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 ensures high detection reliability for reflective objects using cost-effective plastic optics, minimizing depolarization effects and reducing manufacturing costs by allowing the use of plastic imaging elements and combining components on a common printed circuit board.
Implementation Method 1
a beam splitter (18) in the transmitted light path (4) and the received light path (6)
Implementation Method 2
The transmitted light beams are polarized in a defined direction of polarization by means of a transmitting polarizer (16)
Implementation Method 3
A receiving polarizer (22) on the receiving side, aligned orthogonally to the transmitting polarizer, acts as an analyzer and only allows rays in its polarization direction to pass through
Implementation Method 4
a suitable reflector, which rotates the plane of polarization by 90° during reflection, for example a retroreflector with triple prisms
Data Source
Figure 1
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AI summary
The sensor (10) has a sender unit (12) e.g. LED or infrared diode, sending transmission light (4) towards a retro-reflector (20). A receiver unit (26) receives received light (6) reflected by the reflector, and a beam splitter (18) is arranged in transmission and received light paths. A transmission polarizer (16) is arranged between a transmission imaging element (14) and the beam splitter. A receiving polarizer (22) is arranged between the beam splitter and a receiver imaging element (24) that is arranged adjacent to the beam splitter in a dispersion direction of the received light.