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Thread: Emergency stop function

  1. #1
    Project Engineer
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    Emergency stop function

    Hi folks

    I have an update to do on some older equipment. on this unit it had behind the safety doors an arm that swings with an air cylinder. it weights about 3 lbs and is about 20" long, it's not accessible by people without a door opening. in the original design the machine just shut off and dumped the air. at one point in it's cycle this arm is suspended by the air cylinder but when the air dumps off the cylinder slowly drops. This movement ha been deemed unsafe because it happens after an E-stop signal from a door opening for example and I suppose someone could get in there quick enough to be touched by this thing. There is no pinch or entrapment issue with it, it's free in the air,

    I suggested that we make the arm a balanced unit with a friction disc on it so when the air dumps the unit would stop in whatever orientation it's in, but it still might move a little with some of it's momentum. I'm not sure if this is a good approach or putting an actual brake on it or the cylinder which seems a little silly as there is such little risk of injury here.

  2. #2
    Lead Engineer Cake of Doom's Avatar
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    The first idea I had for this would be a delayed lock on the door, so the air has time to dump and the arm can come fully to rest before access can be gained. Is this something you've already looked at and dismissed, or would this cause operator issues?

    Not knowing the machines purpose; this is my best guess. Perhaps do a little feasibility study on each of you're ideas and see which one would cause you the least amount of headaches

  3. #3
    Project Engineer
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    Well I've just been resisting going whole hog on the safety of this machine. The problem is their competition are not doing anything different with the same parts. If I threw the proverbial book at it all the guards would have to be extended,we'd have monitored E-stops and locked doors like you suggest. this is almost the whole cost of the machine again and it would be the only one in the market. There is a tricky sales opportunity in that actually but I don't think this particular client is up to it.

  4. #4
    Lead Engineer Cake of Doom's Avatar
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    Is there no way around this issue with just a risk assessment and/or probability study? That way, the client can get nice health and safety compliance stickers without impacting the cost of the machinery too much.

    Is the client looking for international sales to countries (like the UK) with ridiculous health and safety legislation, or are they just wanting to be different to the competition?

    From your posts, it sounds like your judgement is telling you "if it ain't broke; don't fix it".

  5. #5
    Project Engineer
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    Yes this is mainly for Europe.... It's always Europe. Had to stop nickle plating too. for this they chose to leave the machine pressurized in an E-stop condition. Wouldn't have been my choice.

  6. #6
    Lead Engineer Cake of Doom's Avatar
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    Wouldn't have been my choice either. I think you was on the right track by adding a brake but client knows best eh?

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