I've built a machine from scratch for my own personal use that will be used for a book binding process. There has been some castIng, lots of milling, drilling, tapping and turning involved and I'm about 100 hours into it. I'm not sure it would be prudent to show it on an open forum or not so for the time being I would just like to present my question. The machine is driven by a double acting pneumatic cylinder which is controlled by 5 port 4/2 solenoid. Since I am only using electricity for switching I will be using a 12v solenoid powered by a wall wart. The machine will be covered by sheetmetal side covers and interlocked so it can't be operated with the covers off but there will still be a pinch hazard because of the basic function of the machine. So the switching will need to be of the two-button variety. It is simple enough to run the two switches in series but I would really like to have the added safety of the buttons having to be pressed simultaneously so there's never any chance of one of the buttons just being taped down. Obviously there would need to be a bit of slack in "simultaneously" (500 milliseconds max). There are a couple of scenarios: 1) Both buttons are pressed simultaneously. If either button is released breaking the circuit, the mechanism returns to home position. (My simplistic selonoid/air manifold won't allow the mechanism to freeze in position). 2) Both buttons are pressed, not necessarily simultaneously, but both must be pressed to activate the solenoid. If one of the buttons is released, the solenoid remains activated until the second button is released. I have a factory built paper cutter that is electrically driven that functions like scenario 1 with the addition of a safety light curtain but that machine has an absolutely massive amount of circuitry onboard which is not in the cards here. I also have a hydraulically run paper cutter that works like scenario 2, but that is a function of the hydraulic valve(s) which is also not an option. I guess I'm looking for a canned circuit option that I can program, plug, and play that won't take up much space and allow everyone to keep all of their digits. Any help, suggestions, or re-directs would be appreciated. Pete
What little factory experience I have suggests both buttons simultaneously, it makes it harder for the truly challenged to get their fingers severed....though I am sure some will manage.
There was some discussion of something similar on Practical Machinist forum where a worker operated one switch out of two with their foot to get a compensation payout for an injured hand. A light curtain to detect any outside limbs going into the unit to disable the machine would make it safer. It's going to be hard to duplicate the exact function with just logic circuits and timers, while an Arduino could be programmed to give exactly what you want they are not intended for use in life support or potentially hazardous situations as they are not considered fully predicable in function. Some kind of light beam over the openings will prevent the person from operating both buttons with their foot inside the machine. Also the light beam can prevent the machine from operating and have a second solenoid to "jam" the mechanism with a steel bar or something so that it's dual fail safe. That way it protects two ways in case a relay gets stuck or similar.
If there is nothing in place to stop Bert sticking his fingers in while Ernie presses both buttons you are screwed. Trust me, I've worked with idiots that do crazy things! I think a light curtain is the way to go. There are self contained modules that don't require huge amounts of wiring or external controls. We had a guy running an auger chain drive whilst oiling the chain as it spun, his finger lost the battle with a 7.5HP motor geared down to the sprocket on the final drive (He reached for a piece of fluff that was stuck to the chain....it was just too tempting to leave it there as it went round and round in front of him!)
I've been doing machine safety in various forms for many years now, and every time we think we've got something idiot-proofed.... God just laughs at us and sends in a bigger and better idiot. Some of the crap we've had to guard over the years didn't really make any sense, but orders is orders. You say it's for your own use, but it almost sounds like you are trying to build the widget for sale. If it's for your own use you really don't have to do anything. If you are gonna let somebody else use it that opens up a whole 'nuther can of worms. You've got a pinch point, is there any way that you can mechanically guard that point to keep digits, and idjits, out of it? If you can't reach it, it can't hurt you. That option is a HELLUVA lot easier, and cheaper than trying to guard it electrically. I haven't looked recently, but I'm sure there are resources on-line that will tell you that if you have an opening of X, then your guarding must be at least Y from the pinch point. If you REALLY want to guard it electrically, and you are building it for sale, then I would recommend hiring a pro to design the safety circuit for you. It might cost you a couple of grand, but consider your liability in this compared to the cost of the service. We have built a very litigious society, and lawyers just LOVE to sue people. At least if you hire professionals when Joe Blow sues you because he lost his pinkie finger to your widget because he was running one button with one hand, the other button with a foot, and reaching in to hold a sloppily inserted part with his other hand - well... It just might look better in court that you hired competent professionals to design your safety circuit - and possibly keep you from losing everything you've got, everything you'll ever make, and your home. Don
LOL, along those same lines, I heard or read this many years ago,"If you call something idiot-proof, it just means you have met the right idiot, yet!" I wish I knew whom to give attribution but, I can't remember where that's from.
Yes, yes, no (not selling it), yes, and yes. It occurred to me as I was searching light curtains that I could just as easily configure the guarding to eliminate most of the hazard. I bought 2 sheets of 18ga (.050") cold rolled today, 48x48" so I'm off to the chinese toy store to buy their $44 bender.
Petee716: Were you successful in getting your Widget guarded? Or are you busy trying to guard the $44 Chinese toy store bender? (Lots of pinch points in those guys.) Don
I bought the 30" bender for about 65 bucks. It's worth it although it needed some modification. I'll take some pictures when I go out to the shed. Yes indeed I've guarded it. I'm not quite finished mounting the cover kill switches yet, but the covers are done. Admittedly I've taken the last week or so off for cold weather considerations. I'm really glad you chimed in on the project though. I have to confess to being a "I've got a picture in my mind" sort of a guy, often to my detriment, and input from others snaps me out of it (sometimes). Elimination of the immediate hazard was really the way to go here. Hopefully I wont meet that idiot Rocco mentioned above. Pete
Who did those welds on the top of that thing? ZAP???? Slick idea for the switches. Someone wont try to slice a ham sandwich in that thing this way.
His welding has gotten pretty good so I dont know if your question is good or bad (lol), but those welds look a helluva lot better after grinding and filling with JB Weld! Pete
I have spent most of my life in stamping plants. Stamping press requires a floor T stand with two palm buttons at the top of the T separated by 24 inches. The palm buttons and stand should be located at a safe distance that no other body part can reach a pinch location. The palm buttons were timed with a variable of half a second and had to be held continuously for the entire stroke. In cases that there was more than one operator, operator had to have his or her own T stand. Light curtains (or shadow curtains) became a norm during the 90s. In the late 90s I started working in a automotive sub assembly plant. We were allowed to move the palm button is closer to the machine, but they still had to be 24 inches apart. The way we were allowed to do this was with a pneumatic Lexan curtain that dropped and contacted two mechanical buttons that were timed with a two second delay on the cycle. The Lexan curtain had a force of less than two or three psi. Some of the assembly stations ran a fully pneumatic, some of them had DC transformers and some of them ran on 120VAC. I still have some of the palm button timers (maybe 10 years old). These particular ones are 85-265 VAC or 5 VDC. Two of them are required for each T stand (or one per home button). I think these circuit boards can be had for seven dollars now. Technically your set up would be totally fine if you prevented and guarded the pinch point from the pneumatic cylinder. The only other thing I can suggest is encourage employees not to be wearing any rings, jewellery, watches, Long sleeves or loose clothing while using the machine.
