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| Machine Safeguarding Applications & Solutions |
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| Initiating Motion with a Light Curtain |
I am an OEM who built a hydraulically powered rotor trimmer to trim tubing for a customer. The trimmer was originally designed for two-hand start (not two-hand tie down) even though the trimmer is protected by a light curtain. Previously, the customer altered it to be a one-hand start. I had no problem with that since the machine was protected by a light curtain anyway.
During a recent visit to the customer's facility I stopped to look at this trimmer and noticed it was being started simply by blocking then clearing the light curtain. The person in charge told me OSHA approves this type of operation. I would never build a machine like this and it does not appear to be safe. Is it ok to operate like this? It only runs 300 parts per hour. There really is no need to do this just to save a few ms of time. It already runs faster than the press that feeds it.
Omron STI Response: This is a great question, and I am afraid the answer is not necessarily going to make you happy, nor completely clear up the matter.
First, OSHA does not "approve" this kind of operation specifically, but neither is there a prohibition against it for this kind of machine. The type of operation you describe is called PSDI, Presence Sensing Device Initiation, and OSHA addresses it in 1910.217. In this section, which regulates mechanical power presses, OSHA defines the requirements for PSDI and requires that any such operation be certified by an independent third party. For other machinery, like your trimmer, OSHA is mute.
As you suspect, the use of PSDI is generally applied as a productivity enhancer, but there can also be ergonomic issues that make its use attractive as well. There are currently products on the market that are safety certified to perform the PSDI function. Whether your customer has properly employed one of these devices and correctly configured his machine control system to interface with it is the key as to whether this application is safe.
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