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.

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

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

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:

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.

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

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

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.

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.

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

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

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?

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

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.

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.

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.

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

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

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

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

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.

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