On/Off switch with a difference

[Dave, I can't do that]

Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

 

[Lord Garth]

"Dave, I can't do that" <davenpete@gmail.com> wrote in message
news:17996318-361f-439a-9b4e-e1812c46b80b@a29g2000pra.googlegroups.com...

Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

A retriggerable monostable can do the job. Set the time delay for 3
seconds.
As long as the home switch is held active, the time out continues. As the
home
switch is released, your delay interval begins, the end of which, the
coolant
will start. I'm assuming your cutting head doesn't instantly engage as home
is
released.

If the cutter needs coolant instantly, you'll need another switch to force a
reset
to the monostable.

 

[Tim Wescott]

Dave, I can't do that wrote:

Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

Does your CNC system support auxiliary outputs? I've never, ever
programmed for CNC so I could be blowing smoke, but I understand that
the language supports coolant on-off commands.

Perhaps a quick go-through of the manual is in order, to make sure you
aren't reinventing the wheel.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[WW]

"Dave, I can't do that" <davenpete@gmail.com> wrote in message
news:17996318-361f-439a-9b4e-e1812c46b80b@a29g2000pra.googlegroups.com...

Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

How about a micro switch with a long flexible arm.??

Switch
xxxxxxx
\
\
arm\

This would depress switch to shut off but allow arm pressure to release
somewhat with out turning on.

 

[Jamie]

Dave, I can't do that wrote:

Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave
Get your self a Time Delay relay for the coolant.

Time Delay on..
http://www.drillspot.com/products/46713/Icm_ICM102_Time_Delay_Relay

I suppose you could make one but it would cost you more than that
relay..
Using a 555 timer would do it.



http://webpages.charter.net/jamie_5"

 

[Tim Wescott]

WW wrote:

"Dave, I can't do that" <davenpete@gmail.com> wrote in message
news:17996318-361f-439a-9b4e-e1812c46b80b@a29g2000pra.googlegroups.com...
Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

How about a micro switch with a long flexible arm.??

Switch
xxxxxxx
\
\
arm\

This would depress switch to shut off but allow arm pressure to release
somewhat with out turning on.


Or your flexible arm, but with a magnet on it (assuming it works against

something ferrous). Then the "make" will happen when the thing is quite
close to home, but it'll have to pull well away from home before it
"breaks".

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[ehsjr]

Dave, I can't do that wrote:

Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

You can use this general circuit:

+12 ---+-------------+
| | Ry1 N/O
+---- N/O [Ry1] |<|
+---^ SW | | |
| | | +--- to sprayer
[470] | +----- to sprayer
| /c
+------+----| NPN
| |+ \e
[POT] [C1] |
| | |
Gnd ---+------+------+

When you start the machine, it leaves the home position and the
NO limit switch closes, energizing the relay through the NPN.
When the machine returns to home, the switch opens, but the
charge on C1 keeps the relay energized. C1 discharges through
the NPN and relay and also through the pot, which is used to
adjust how long the relay stays energized. The amount of time
depends upon the relay coil and transistor gain as well as the
RC timing of C1 and the pot. 100K for the pot and 100uF for the
cap should work for you. The 470 ohm resistor limits the current
to protect transistor base and the supply and switch, in case
the pot is erroneously set to 0 ohms.

Ed

 

[Dave, I can't do that]

On Nov 9, 4:26 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Hi Jamie and others,

Thank you all for the replies.

Get your self a Time Delay relay for the coolant.

Jamie:
That is exactly what I am looking for and under 20-bucks delivered it
will do fine as I can get it to control the existing coolant pump
relay.

WW:
I had tried the long arm but it worked only some of the time as the
first home bounce is quite fast.

Tim:
I didn't think of the magnet idea but that is quite clever.

Tim:
It is an older machine and does not have M-codes for coolant, but
thanks for thinking of that.

Ed:
That looks exactly what I need. Thanks for going to the trouble to lay
that out. I do appreciate you taking the time to do the design and
ASCII art though.

I will go with the time delay relay as it is a plug 'n' play thing.
You guys are gooood! <grin>

Dave

 

[Paul E. Schoen]

"ehsjr" <ehsjr@NOSPAMverizon.net> wrote in message
news:OAPRk.520$U5.218@nwrddc01.gnilink.net...

Dave, I can't do that wrote:
Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

You can use this general circuit:

+12 ---+-------------+
| | Ry1 N/O
+---- N/O [Ry1] |<|
+---^ SW | | |
| | | +--- to sprayer
[470] | +----- to sprayer
| /c
+------+--R-| NPN
| |+ \e
[POT] [C1] |
| | |
Gnd ---+------+------+

When you start the machine, it leaves the home position and the
NO limit switch closes, energizing the relay through the NPN.
When the machine returns to home, the switch opens, but the
charge on C1 keeps the relay energized. C1 discharges through
the NPN and relay and also through the pot, which is used to
adjust how long the relay stays energized. The amount of time
depends upon the relay coil and transistor gain as well as the
RC timing of C1 and the pot. 100K for the pot and 100uF for the
cap should work for you. The 470 ohm resistor limits the current
to protect transistor base and the supply and switch, in case
the pot is erroneously set to 0 ohms.

You might need a resistor in series with the base as indicated by the "R" I
added above. But even better would be to use an n-channel MOSFET. The
problem with a BJT is that the B-E junction is like a diode, and it does
not take much voltage change to go from full on to full off. A MOSFET will
turn on fully at the 12 volts, and will stay on until the voltage drops to
about 3 volts. Your time constant will be about 2RC, so 10 uF and 100k will
give you about 2 seconds max, and adjustable down to about 100 mSec when
the pot is at 5k.

Also don't forget to add a commutating diode across the relay coil.

Good luck,

Paul

 

[ehsjr]

Paul E. Schoen wrote:

"ehsjr" <ehsjr@NOSPAMverizon.net> wrote in message
news:OAPRk.520$U5.218@nwrddc01.gnilink.net...

Dave, I can't do that wrote:

Hi all,

I have a machine that I'd like it to turn the coolant system off when
it has finished a job as it sprays crap everywhere on a stopped
cutter.

The cutting head always returns to a "home" position at the end of the
work so I put a cherry switch there. It sort of works but it does not
go cleanly "home"

It hits a limit switch then backs off a little then advances slowly to
the home position. During this little dance, it seems to encourage the
coolant system to spray crap even further as the coolant turns off and
on rapidly.

The homing tales about 3 seconds so I'd like a switch that will delay
until it has reached the home position or a few seconds after that
then shuts down the coolant.

I would like it to turn the coolant on when it leaves the "home"
position to begin a new job. Fortunately that is a straight turn on
with no delay required.

Can anyone suggest something that will do this?

Thanks.

Dave

You can use this general circuit:

+12 ---+-------------+
| | Ry1 N/O
+---- N/O [Ry1] |<|
+---^ SW | | |
| | | +--- to sprayer
[470] | +----- to sprayer
| /c
+------+--R-| NPN
| |+ \e
[POT] [C1] |
| | |
Gnd ---+------+------+

When you start the machine, it leaves the home position and the
NO limit switch closes, energizing the relay through the NPN.
When the machine returns to home, the switch opens, but the
charge on C1 keeps the relay energized. C1 discharges through
the NPN and relay and also through the pot, which is used to
adjust how long the relay stays energized. The amount of time
depends upon the relay coil and transistor gain as well as the
RC timing of C1 and the pot. 100K for the pot and 100uF for the
cap should work for you. The 470 ohm resistor limits the current
to protect transistor base and the supply and switch, in case
the pot is erroneously set to 0 ohms.


You might need a resistor in series with the base as indicated by the "R" I
added above. But even better would be to use an n-channel MOSFET. The
problem with a BJT is that the B-E junction is like a diode, and it does
not take much voltage change to go from full on to full off. A MOSFET will
turn on fully at the 12 volts, and will stay on until the voltage drops to
about 3 volts. Your time constant will be about 2RC, so 10 uF and 100k will
give you about 2 seconds max, and adjustable down to about 100 mSec when
the pot is at 5k.

Also don't forget to add a commutating diode across the relay coil.

Good luck,

Paul

Good points.
Right on the base resistor - it needs to be there. And it has
to be a fairly high value. Also, the transistor needs to be
high gain - a darlington would be good. I should have said
that. So I'll redo as a specific rather than a general
schematic, add the missing base resistor, and use a darlington:

+12 ---+---------------------+
| | Ry1 N/O
+---- N/O [Ry1] |<|
+---^ SW | | |
| | | +--- to sprayer
[470] | +----- to sprayer
| /c
+------+---[100K]---| 2N5308
| |+ \e
/ [100uF] | Ry1 = Omron G5LE-1-G-DC12
100K \ | |
/<--+ | |
\ | | |
| | | |
Gnd ---+---+--+--------------+


A commutating diode can be added, but is not needed.
As the charge on the 100 uF decreases, the current
through the transistor decreases, so you do not get
a large di at shut off.

I like your idea of using a Mosfet.

Ed

 

[Dave, I can't do that]

On Nov 13, 9:02 am,

ehsjr wrote:

Paul E. Schoen wrote:

You guys are good, thanks to both of you.

Paul shouldn't you be hammering nails instead of swanning around on a
newsgroup?? LOL

Dave

 

[Dave, I can't do that]

On Nov 12, 4:39 pm, "Paul E. Schoen" <pst...@smart.net> wrote:

Hi Paul,

I am vacillating about using the delay timer Jamie suggested as I will
still need to add in another relay. On checking, the coolant is
controlled by the motor on relay and I want the spindle motor to stay
running. I want the coolant off so I can get in and change parts
without getting wet.

Your time constant will be about 2RC, so 10 uF and 100k will
give you about 2 seconds max, and adjustable

With 2 seconds it will be marginal and 5 or 10 seconds would be
better . Would I just slip a MOSFET in place of the 2N5308 or would
there be other changes as well?

I don't care about the coolant running for 10 seconds or so, but I do
need to get past the 3-second homing sequence and you are suggesting
Ed's design will only give me around 2 seconds max.

Dave

 

[ehsjr]

Dave, I can't do that wrote:

On Nov 12, 4:39 pm, "Paul E. Schoen" <pst...@smart.net> wrote:

Hi Paul,

I am vacillating about using the delay timer Jamie suggested as I will
still need to add in another relay. On checking, the coolant is
controlled by the motor on relay and I want the spindle motor to stay
running. I want the coolant off so I can get in and change parts
without getting wet.


Your time constant will be about 2RC, so 10 uF and 100k will
give you about 2 seconds max, and adjustable


With 2 seconds it will be marginal and 5 or 10 seconds would be
better . Would I just slip a MOSFET in place of the 2N5308 or would
there be other changes as well?

I don't care about the coolant running for 10 seconds or so, but I do
need to get past the 3-second homing sequence and you are suggesting
Ed's design will only give me around 2 seconds max.

Dave

No - you should get at least 5 seconds with the darlington
circuit. (As I recall, Paul computed based on 100K and 10uF,
for the mosfet design.) The bipolar circuit uses 100 uF, and
the added R reduces the resistance to ~50K for RC computation.
So in rough terms, the base of the transistor will see about
4 volts after 5 seconds, and should still be able to conduct
plenty of current for the relay.

If you need a longer time, you can change the cap from 100 uF
to something bigger. For ~10 seconds, you can use a 220 uF,
for 15 seconds, a 330 uF, and so on. The times are approximate,
but the pot lets you refine that within a range. The exact
time depends a lot on the relay used in addition to the cap
and pot values. Also, I used an extremely conservative
computation (1 RC instead of 2 RC) to be sure to get at least
the minimum time. It is closer to use 2RC, but the darlington
can't be counted on to conduct for the full 2 RC, so I chose
1 RC for the minimum computation.

Ed

 

[Paul E. Schoen]

"Dave, I can't do that" <davenpete@gmail.com> wrote in message
news:db993407-eaa9-4454-96da-0d51fc328945@o40g2000prn.googlegroups.com...

On Nov 12, 4:39 pm, "Paul E. Schoen" <pst...@smart.net> wrote:

Hi Paul,

I am vacillating about using the delay timer Jamie suggested as I will
still need to add in another relay. On checking, the coolant is
controlled by the motor on relay and I want the spindle motor to stay
running. I want the coolant off so I can get in and change parts
without getting wet.

Your time constant will be about 2RC, so 10 uF and 100k will
give you about 2 seconds max, and adjustable

With 2 seconds it will be marginal and 5 or 10 seconds would be
better . Would I just slip a MOSFET in place of the 2N5308 or would
there be other changes as well?

I don't care about the coolant running for 10 seconds or so, but I do
need to get past the 3-second homing sequence and you are suggesting
Ed's design will only give me around 2 seconds max.

Ed's improved design will probably give about 10 seconds with 100k and 100
uF. It all depends on the RC time constant and the point at which the
transistor will turn off. It will also depend on the relay drop-out
characteristic. The MOSFET design takes less parts and should be reliable.
Best bet is to make a quick prototype and test it.

If the relay coil draws less than 100 mA or so, a 555 timer might be
better. It has well-defined turn-on and turn-off points of 1/3 and 2/3 Vcc.
It will also give a sharp output transition, which means you need a diode
across the coil.

Paul

 

[Dave, I can't do that]

Thanks Ed and Paul,

I will breadboard Ed's layout. The delay is not critical as long as it
is more than about 3 seconds. I timed it with a stop watch so my tired
old reaction time would have had some effect too. <grin>

I will guess a fixed value in place of the the pot as I really don't
need that degree of accuracy. It takes me about 20 seconds to remove
the splash shield and brush the crap away before I need to get hands
in there.

Dave