Light Grid Self-Testing via SPAD and Retroreflector
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Solution Overview
Problem
Current safety light grids with separate transmitter and receiver housings face challenges in self-testing, especially with freely scanning systems, as they require direct optical paths and result in high cabling efforts and space requirements, limiting their ability to achieve high safety categories and integration.
Innovation Solution
A light grid utilizing the time of flight principle with a single photon avalanche diode (SPAD) receiver, which determines distance by measuring the time between transmitted and received light signals, allowing for compact design, high integration, and self-testing capabilities without direct optical connection between transmitter and receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If freely scanning light grids are used to reduce cabling and space requirements, then installation complexity is reduced, but self-testing capability is lost due to missing direct counter-side
Solution Approach 1:
A retroreflector is introduced as an intermediary element in the optical path. The retroreflector returns light signals to the transmitter, enabling the transmitter to act as both light source and receiver. This mediator allows freely scanning systems to perform self-testing without requiring direct optical connection to a separate receiver, thus resolving the contradiction between reduced installation complexity and maintained self-testing capability
Solution Approach 2:
The light transmitter is designed to perform multiple functions: emitting light signals, receiving reflected light signals, and performing self-testing. By integrating receiver functionality into the transmitter unit, the system achieves multi-functionality that enables self-testing in freely scanning configurations without requiring separate receiver housings, thus reducing device complexity while maintaining reliability
2Reliability
If separate transmitter and receiver housings are used, then self-testing capability is improved through direct optical path, but device complexity and space requirements increase
Solution Approach 1:
The transmitter and receiver housings are merged into a single integrated unit. The light transmitter and light receiver are combined in one housing, eliminating the need for separate transmitter and receiver housings. This merging reduces device complexity and space requirements while the retroreflector enables the integrated unit to maintain self-testing capability through the optical path
3Difficulty of detecting and measuring
If amplitude threshold-based detection is used, then detection capability is improved, but adaptability to freely scanning systems is reduced
Solution Approach 1:
The detection principle is changed from amplitude threshold-based detection to time-based detection using time-of-flight measurement. This parameter change enables the system to adapt to freely scanning configurations because it detects objects by measuring the time for light to travel to and from the object, rather than relying on direct optical path amplitude measurements that require fixed transmitter-receiver alignment
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
The solution enables comprehensive self-testing, reduces cabling and space needs, and achieves high safety categories with compact, cost-effective designs, while maintaining sensitivity to detect single photons, thus enhancing safety and flexibility in configuration.
Implementation Method 1
at least one light receiver (4) which receives the light signals reflected from the measured zone and supplies them in the form of received electrical signals
Implementation Method 2
determines a distance signal representative of the distance (8) of objects (6) from the light grid (1) from the time between the transmission and the reception of the light signal or signals while taking account of the speed of light
Data Source
AI summary
A light grid in accordance with the time of flight principle having at least one light transmitter (2) which transmits light signals (3) into a measured zone (5) and having at least one light receiver (4) which receives the light signals (3) reflected from the measured zone (5) and supplies them in the form of received electrical signals to a control and evaluation unit (7) which determines a distance signal representative of the distance (8) of objects (6) from the light grid (1) from the time between the transmission and the reception of the light signal (3) while taking account of the speed of light, with the light receiver (4) having at least one single photon avalanche diode (9).