(Click here to view article in digital edition)A series of light beams that protect workers form dangerous moving equipment: we could argue that safety light curtains are the guardian angels of the modern factory. Light curtains are a common safety device in today’s manufacturing plants. A sub category of Electro Sensitive Protective Equipment (ESPE), they protect the personnel that interact with automated machinery, such as hydraulic presses, palletisers, and conveyors with a manual infeed or outfeed. Light curtains consist of a transmitting head and a receiving head: the transmitter projects an array of infrared light beams to the receiver, and when something – such as an operator’s hand – interrupts the beams’ flow, the curtain sends a stop signal to the guarded machine. This stops the machine, preventing injuries. The light beams emitted by the transmitter are pulsed at a specific frequency and the receiver is designed to only accept the pulse and frequency of its transmitter: this ensures that the curtain does not consider any spurious infrared light sources. This is the same way the wireless doorbell in your house works; when someone presses the button, it doesn’t set off every doorbell in the street, just the one whose frequency it is attuned to. Light curtains can be set up at different resolutions – that is, the distance between successive beams – depending on the kind of protection they provide. Resolutions between 300 and 400mm detect only full body access, 30mm detects a hand intrusion, and 14mm detects a finger. The most common resolutions on the market are 30mm and 14mm.Testing stop timeIt is important to test light curtains regularly to make sure that they fulfil their safety functions. In the manufacturing industry, it is very common to set up light curtains using theoretical calculations only, but safety engineers warn against this practice and recommend field testing instead. The first thing that needs to be assessed is the appropriate distance between the curtain and the guarded machine, which can be established by a stop-time performance test. The goal is to determine how long it will take for the machine to stop after an intrusion has been detected by the light curtain. It is essential that the plant manager or machine operator perform this test regularly. A machine’s speed can fluctuate or be adjusted over time to suit new production needs, and this can impact its stopping time. It is important to make sure that the machine will stop in time to prevent dangerous contact with the operator. If the user fails to perform this test regularly and an accident occurs, the company can incur criminal charges for breaking the Provision and Use of Work Equipment Regulations 1998 (PUWER).Testing resistancePrior to installation, other tests can be performed to make sure that light curtains withstand even the harshest plant environments. The first of these is the impact test, also called a durability or shock test. This is usually performed by dropping a weight, such as an iron ball, on the curtain’s heads to see if they still operate after the impact. It is particularly important to test all four surfaces of the curtain’s heads, especially the ones where the lenses are positioned. It is preferable to use curtains with recessed lenses, because they are less prone to breakage.Other tests include the water submersion test and oil resistance test, which assess the curtain’s resistance to humidity and exposure to greasy substances, respectively. These tests are performed by simply immersing the curtain’s heads in water or in an oil-based solution for a set period and checking whether they are still operational afterwards. Our guardian angels of the factory clearly fulfil an essential purpose in factory environments, both protecting machine operators and keeping business owners on the right side of the Provision and Use of Work Equipment Regulations 1998 (PUWER). So, next time your doorbell rings, remember how similar technology is keeping people safe in plants across the globe. About the author:Jonathan Wilkins is the marketing director of industrial automation components supplier, EU Automation. A professional brand advocate and commercial marketing strategist, Jon focuses on delivering growth via a multi-channel approach that has a significant positive impact on business. He has been part of the EU Automation team since its humble beginning ten years ago and has over a decade of experience in marketing.
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