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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Pneumatic or electric controls?
I have some air circuits that are controlled by cams that actuate manual air
valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves or air piloted valves to control air valves. Which is more reliable? I do have really clean, dry air. Bill's post made me think of this. |
#2
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Pneumatic or electric controls?
On Jul 1, 5:20*pm, "Buerste" wrote:
I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam.. Would I be better off with electric limit switches on the cams and use electric air valves? *The cam rotates at 120 rpm. *The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves *or air piloted valves to control air valves. *Which is more reliable? *I do have really clean, dry air. Bill's post made me think of this. I will have to guess, but, since electrical relays bounce when making a transfer, the air valves will be more reliable. Paul |
#3
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Pneumatic or electric controls?
Buerste wrote:
I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. Why don't you replace the cams with discs with notches (the existing cams might actually still work) and use optical sensors to sense the up/down of the cam? This will have no wear at all except the shaft bearings of the cam. The sensors can then drive a single transistor to control DC solenoid valves. Some of the better valves can operate for millions of cycles. And, if they wear out, you don't have to adjust the cam timing when you replace them. I have salvaged sensors from old floppy drives and used them for a bunch of projects. Jon |
#4
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Pneumatic or electric controls?
Jon Elson wrote:
Buerste wrote: I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. Why don't you replace the cams with discs with notches (the existing cams might actually still work) and use optical sensors to sense the up/down of the cam? This will have no wear at all except the shaft bearings of the cam. The sensors can then drive a single transistor to control DC solenoid valves. Some of the better valves can operate for millions of cycles. And, if they wear out, you don't have to adjust the cam timing when you replace them. I have salvaged sensors from old floppy drives and used them for a bunch of projects. Jon Dust problems? Optical isn't reliable long term in a dusty environment. -- Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED) ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL: |
#5
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Pneumatic or electric controls?
"Jon Elson" wrote in message ... Buerste wrote: I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. Why don't you replace the cams with discs with notches (the existing cams might actually still work) and use optical sensors to sense the up/down of the cam? This will have no wear at all except the shaft bearings of the cam. The sensors can then drive a single transistor to control DC solenoid valves. Some of the better valves can operate for millions of cycles. And, if they wear out, you don't have to adjust the cam timing when you replace them. I have salvaged sensors from old floppy drives and used them for a bunch of projects. Jon WAY dusty atmosphere and I don't want to complicate a simple function. A mechanic can replace an air switch in 5 minutes. The time to troubleshoot anything more complex would cost $7/min in lost production. |
#6
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Pneumatic or electric controls?
On Jul 2, 6:26 am, "Buerste" wrote:
"Jon Elson" wrote in message ... Buerste wrote: I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. Why don't you replace the cams with discs with notches (the existing cams might actually still work) and use optical sensors to sense the up/down of the cam? This will have no wear at all except the shaft bearings of the cam. The sensors can then drive a single transistor to control DC solenoid valves. Some of the better valves can operate for millions of cycles. And, if they wear out, you don't have to adjust the cam timing when you replace them. I have salvaged sensors from old floppy drives and used them for a bunch of projects. Jon WAY dusty atmosphere and I don't want to complicate a simple function. A mechanic can replace an air switch in 5 minutes. The time to troubleshoot anything more complex would cost $7/min in lost production. As an Electrical Engineer I always think that electrical is the best solution. In a dusty environment magnetic sensing of the cam will be pretty reliable, think anti lock brakes. Magnetize the cam, Hall effect senor driving a transistor, driving an air solenoid. Add a couple of LEDs for trouble shooting. Output of hall not blinking replace the hall, output of the transistor not blinking replace the transistor, else replace solenoid. The solenoid will be 90 % of the reliability issues. The hall effect sensor and transistor are reliable if the design is good. CarlBoyd |
#7
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Pneumatic or electric controls?
As an Electrical Engineer I always think that electrical is the best
solution. CLIP As a pneumatics guy most of the day, I was thinking that his set-up is pretty reliable now with a 2 year replacement schedule... Just schedule in a swap out of the switch every 1.5 years. However, what about a reed switch-like device that senses the cam? Do they respond quickly enough to make it work? -- Regards, Joe Agro, Jr. (800) 871-5022 01.908.542.0244 Automatic / Pneumatic Drills: http://www.AutoDrill.com Multiple Spindle Drills: http://www.Multi-Drill.com Flagship Site: http://www.Drill-N-Tap.com VIDEOS: http://www.youtube.com/user/autodrill V8013-R |
#8
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Pneumatic or electric controls?
On Jul 1, 5:20*pm, "Buerste" wrote:
I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam.. Would I be better off with electric limit switches on the cams and use electric air valves? *The cam rotates at 120 rpm. *The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves *or air piloted valves to control air valves. *Which is more reliable? *I do have really clean, dry air. Use electrical. It's far easier to service and you should get at least 5 years (probably more) out of the cams/micro-switches. This was a standard Honeywell method and I always found it worked well, was easy to adjust, and fault finding with a meter was easy. Don't screw around with optical / position sensors - you'll spend more time fixing those. |
#9
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Pneumatic or electric controls?
On Wed, 1 Jul 2009 20:20:10 -0400, "Buerste" wrote:
I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. One difference between the approaches is that the cams operate the mechanical switches gradually compared to switches and electric air valves, so changing to electric might introduce some "hammer" when they abruptly open and/or close. The difference may also affect system timing, but once set up right it would tend to survive repairs involving replacement of switches and/or valves. |
#10
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Pneumatic or electric controls?
On Thu, 02 Jul 2009 09:47:54 -0500, the infamous Don Foreman
scrawled the following: On Wed, 1 Jul 2009 20:20:10 -0400, "Buerste" wrote: I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. One difference between the approaches is that the cams operate the mechanical switches gradually compared to switches and electric air valves, so changing to electric might introduce some "hammer" when they abruptly open and/or close. The difference may also affect system timing, but once set up right it would tend to survive repairs involving replacement of switches and/or valves. I've seen air-damped solenoids, so I know they're available in at least some form factors, FWIW. Only the curious will learn and only the resolute overcome the obstacles to learning. The quest quotient has always excited me more than the intelligence quotient. -- Eugene S. Wilson |
#11
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Pneumatic or electric controls?
On Jul 1, 8:20*pm, "Buerste" wrote:
I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam.. Would I be better off with electric limit switches on the cams and use electric air valves? *The cam rotates at 120 rpm. *The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves *or air piloted valves to control air valves. *Which is more reliable? *I do have really clean, dry air. Bill's post made me think of this. This doesn't help on the switch end but they are some neat air operated valve actuators for retrofit on hermetic type valves, Asco, Skinner etc. see: www.pneumagnetic.com |
#12
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Pneumatic or electric controls?
On Thu, 02 Jul 2009 13:38:46 -0700, Larry Jaques
wrote: On Thu, 02 Jul 2009 09:47:54 -0500, the infamous Don Foreman scrawled the following: On Wed, 1 Jul 2009 20:20:10 -0400, "Buerste" wrote: I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. One difference between the approaches is that the cams operate the mechanical switches gradually compared to switches and electric air valves, so changing to electric might introduce some "hammer" when they abruptly open and/or close. The difference may also affect system timing, but once set up right it would tend to survive repairs involving replacement of switches and/or valves. I've seen air-damped solenoids, so I know they're available in at least some form factors, FWIW. Solenoids or solenoid valves? |
#13
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Pneumatic or electric controls?
Don Foreman wrote:
One difference between the approaches is that the cams operate the mechanical switches gradually compared to switches and electric air valves, so changing to electric might introduce some "hammer" when they abruptly open and/or close. The difference may also affect system timing, but once set up right it would tend to survive repairs involving replacement of switches and/or valves. No, these MicroSwitch pneumatic valves are snap-action, just like an electrical MicroSwitch. I have some of them in my pick and place machine, and they definitely do not respond slowly. Jon |
#14
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Pneumatic or electric controls?
"Buerste" wrote in message ... I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves or air piloted valves to control air valves. Which is more reliable? I do have really clean, dry air. Bill's post made me think of this. Have you carefully considered the profile of your cam? Adjusting things for minimum movement, and ramp angles the minimize the speed of the roller arms could help. How many cycles do you make in two years? What is the pressure and diameter of the air line. I would think a roller tip micro switch and a quality relay should last for millions of cycles. |
#15
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Pneumatic or electric controls?
"Tim" wrote in message ... "Buerste" wrote in message ... I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves or air piloted valves to control air valves. Which is more reliable? I do have really clean, dry air. Bill's post made me think of this. Have you carefully considered the profile of your cam? Adjusting things for minimum movement, and ramp angles the minimize the speed of the roller arms could help. How many cycles do you make in two years? What is the pressure and diameter of the air line. I would think a roller tip micro switch and a quality relay should last for millions of cycles. Hmmm, I'd say an average of 28,800,000 in 2 years. Air line is 1/4" Nylon at @100 psi. |
#16
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Pneumatic or electric controls?
On Fri, 03 Jul 2009 12:39:45 -0500, Jon Elson
wrote: Don Foreman wrote: One difference between the approaches is that the cams operate the mechanical switches gradually compared to switches and electric air valves, so changing to electric might introduce some "hammer" when they abruptly open and/or close. The difference may also affect system timing, but once set up right it would tend to survive repairs involving replacement of switches and/or valves. No, these MicroSwitch pneumatic valves are snap-action, just like an electrical MicroSwitch. I have some of them in my pick and place machine, and they definitely do not respond slowly. Jon Right. They may be noticably quicker than mechanical valves operated by cams. |
#17
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Pneumatic or electric controls?
In article ,
"Buerste" wrote: "Tim" wrote in message ... "Buerste" wrote in message ... I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves or air piloted valves to control air valves. Which is more reliable? I do have really clean, dry air. Bill's post made me think of this. Have you carefully considered the profile of your cam? Adjusting things for minimum movement, and ramp angles the minimize the speed of the roller arms could help. How many cycles do you make in two years? What is the pressure and diameter of the air line. I would think a roller tip micro switch and a quality relay should last for millions of cycles. Hmmm, I'd say an average of 28,800,000 in 2 years. Air line is 1/4" Nylon at @100 psi. How accurate and repeatable does the trip point need to be? I'd be tempted to use an aluminum cam sensed by an electromagnetic non-contact proximity sensor of some kind. This will work through most kinds of dust and dirt, and can be hosed down as needed. What is the dust and dirt mainly made of? Joe Gwinn |
#18
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Pneumatic or electric controls?
On Jul 2, 5:26*am, "Buerste" wrote:
"Jon Elson" wrote in message ... Buerste wrote: I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? *The cam rotates at 120 rpm. *The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. Why don't you replace the cams with discs with notches (the existing cams might actually still work) and use optical sensors to sense the up/down of the cam? This will have no wear at all except the shaft bearings of the cam. *The sensors can then drive a single transistor to control DC solenoid valves. Some of the better valves can operate for millions of cycles. *And, if they wear out, you don't have to adjust the cam timing when you replace them. *I have salvaged sensors from old floppy drives and used them for a bunch of projects. Jon WAY dusty atmosphere and I don't want to complicate a simple function. *A mechanic can replace an air switch in 5 minutes. *The time to troubleshoot anything more complex would cost $7/min in lost production. There is your answer. Stay with air. Check the quality of the air switch...there are different levels of quality=number of activations. You may get the desired result by using a better air switch. TMT |
#19
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Pneumatic or electric controls?
On Jul 2, 9:47*am, Don Foreman wrote:
On Wed, 1 Jul 2009 20:20:10 -0400, "Buerste" wrote: I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? *The cam rotates at 120 rpm. *The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. One difference between the approaches is that the cams operate the mechanical switches gradually compared to switches and electric air valves, *so changing to electric might introduce some "hammer" when they abruptly open and/or close. *The difference may also affect system timing, but once set up right it would tend to survive repairs involving replacement of switches and/or valves. Don is correct on this...you have a working system (that you apparently depend on now). Sometimes the answer is "don't mess with it". If you do, change over a low priority section and see what the results are. I predict that you will stay with air. TMT |
#20
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Pneumatic or electric controls?
Replace the valves with proximity switches and solenoid valves. I've done
it a number of times on packaging machines and it has gotten rid of the reliability problems completely |
#21
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Pneumatic or electric controls?
"Joseph Gwinn" wrote in message ... In article , "Buerste" wrote: "Tim" wrote in message ... "Buerste" wrote in message ... I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves or air piloted valves to control air valves. Which is more reliable? I do have really clean, dry air. Bill's post made me think of this. Have you carefully considered the profile of your cam? Adjusting things for minimum movement, and ramp angles the minimize the speed of the roller arms could help. How many cycles do you make in two years? What is the pressure and diameter of the air line. I would think a roller tip micro switch and a quality relay should last for millions of cycles. Hmmm, I'd say an average of 28,800,000 in 2 years. Air line is 1/4" Nylon at @100 psi. How accurate and repeatable does the trip point need to be? I'd be tempted to use an aluminum cam sensed by an electromagnetic non-contact proximity sensor of some kind. This will work through most kinds of dust and dirt, and can be hosed down as needed. What is the dust and dirt mainly made of? Joe Gwinn Dust is wood dust from drilling one 9/32" x 1/2" deep hole in Beech every rotation. The cam is "soft" activation and the trip point is +/- 10 deg or so. |
#22
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Pneumatic or electric controls?
In article ,
"Buerste" wrote: "Joseph Gwinn" wrote in message ... In article , "Buerste" wrote: "Tim" wrote in message ... "Buerste" wrote in message ... I have some air circuits that are controlled by cams that actuate manual air valves that look like limit switches with roller arms that follow the cam. Would I be better off with electric limit switches on the cams and use electric air valves? The cam rotates at 120 rpm. The dwell on the switch is 45 degrees. I do have to replace the air switches every 2 years or so. I will NOT install a PLC or anything more complex. I have a similar application coming up and will need to use electric relays to control air valves or air piloted valves to control air valves. Which is more reliable? I do have really clean, dry air. Bill's post made me think of this. Have you carefully considered the profile of your cam? Adjusting things for minimum movement, and ramp angles the minimize the speed of the roller arms could help. How many cycles do you make in two years? What is the pressure and diameter of the air line. I would think a roller tip micro switch and a quality relay should last for millions of cycles. Hmmm, I'd say an average of 28,800,000 in 2 years. Air line is 1/4" Nylon at @100 psi. How accurate and repeatable does the trip point need to be? I'd be tempted to use an aluminum cam sensed by an electromagnetic non-contact proximity sensor of some kind. This will work through most kinds of dust and dirt, and can be hosed down as needed. What is the dust and dirt mainly made of? Joe Gwinn Dust is wood dust from drilling one 9/32" x 1/2" deep hole in Beech every rotation. The cam is "soft" activation and the trip point is +/- 10 deg or so. This ought to be easy. Wood dust will not affect an electromagnetic prox sensor at all. A cam with sharp ramps will easily manage ten degrees. The absence of contact means that the cam profile need not be that gentle. A cam made of aluminum with some kind of adjustable collet lock on the shaft ought to work just dandy with a prox sensor with circuit closure output. One can buy adjustable ready-made cams where one can set the duty cycle by adjustment of the cam halves. Perhaps one of these will suffice. Failing that, one can always cut a cam with a scroll saw. As there is no physical contact, the surfaces need not be smooth. Joe Gwinn |
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