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Offline comet

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electro-pneumatic slide lock
« on: July 03, 2009, 11:29:21 AM »
Hi,
   I would like to make some pneumatic slide locks for my  mill.
What I'm thinking is a tap off the step line to a transistor then to a small 5V pcb type relay finally to a 24V solenoid and an air cylinder.
 I would like it to open or release instantly upon sensing the first step ( within reasonable workable boundaries) then lock again when the pulse stream stops I would like a delay on re-lock of about 0.5 second.
  How can I achieve this? can I use a cap/resistor delay or a 555 timer? or is it a job for a PIC ?
Any help or circuit suggestions would be welcome.
    Tony
« Last Edit: July 03, 2009, 11:32:27 AM by comet »
Re: electro-pneumatic slide lock
« Reply #1 on: July 03, 2009, 12:21:26 PM »
Hi,
   I would like to make some pneumatic slide locks for my  mill.
What I'm thinking is a tap off the step line to a transistor then to a small 5V pcb type relay finally to a 24V solenoid and an air cylinder.
 I would like it to open or release instantly upon sensing the first step ( within reasonable workable boundaries) then lock again when the pulse stream stops I would like a delay on re-lock of about 0.5 second.
  How can I achieve this? can I use a cap/resistor delay or a 555 timer? or is it a job for a PIC ?
Any help or circuit suggestions would be welcome.
    Tony

I'm not sure why you'd want to do that, but you'd stand an excellent chance of losing a step every time you start a move, because relays and air cylinders are slooooooow, so you will be preventing the axis from making one (or more) step(s) it wants to make until both relays and the air cylinder have done their thing.  That arrangement should not be necessary, unless there's a problem with your machine.  What problem are you trying to solve? 

Regards,
Ray L.
Regards,
Ray L.

Offline comet

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Re: electro-pneumatic slide lock
« Reply #2 on: July 03, 2009, 12:29:10 PM »
Ray,
 My machine has normal lead screws,so there is always a touch of back lash.
I am not fussed about the step loss you mentioned as I use servo's and they make up the "lost"
steps of there own accord.
   Tony
Re: electro-pneumatic slide lock
« Reply #3 on: July 03, 2009, 01:33:43 PM »
Ray,
 My machine has normal lead screws,so there is always a touch of back lash.
I am not fussed about the step loss you mentioned as I use servo's and they make up the "lost"
steps of there own accord.
   Tony

OK, in that case, a 555 timer will do exactly what you want - assert the output the instant a step pulse occurs, and sometime after the last pulse,  the output will be de-asserted.   As long as the period of the step pulses is longer than the 555 time-constant (I guess 0.5 second in your case), the output will remain continuously asserted. You want the monostable mode, as shown here:

http://en.wikipedia.org/wiki/555_timer_IC

The output of a 555 can sink or source up to 200mA, which should be enough to drive a relay coil directly - just remember to use a protection diode so the back-EMF from the coil doesn't fry it.  You might want to use a solid-state relay, to get faster response - connections are the same as a mechanical relay.

Regards,
Ray L.
Regards,
Ray L.

Offline comet

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Re: electro-pneumatic slide lock
« Reply #4 on: July 03, 2009, 07:08:44 PM »
Cheers Ray,
Sounds good, any suggestions of a circuit I could try? I have built 555 based PWM circuits so I am reasonably familiar with them.
the thing that I was wondering was would the tap on the pulse stream short it or interfere at all?
I dont mind experimenting if pointed in the right direction!!
 tony
Re: electro-pneumatic slide lock
« Reply #5 on: July 03, 2009, 07:58:35 PM »
Cheers Ray,
Sounds good, any suggestions of a circuit I could try? I have built 555 based PWM circuits so I am reasonably familiar with them.
the thing that I was wondering was would the tap on the pulse stream short it or interfere at all?
I dont mind experimenting if pointed in the right direction!!
 tony

The monostable circuit on the Wiki page is exactly what you need.  The TRIG input is the step signal.  OUT drives the relay coil, or SSR control input.  The only thing you may need to add is an inverter on the TRIG , if your step line is active high.  You just need to decide how long you want it to remain active after the steps stop, and calculate the R and C values using the equation on the Wiki page.

Regards,
Ray L.
Regards,
Ray L.

vmax549

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Re: electro-pneumatic slide lock
« Reply #6 on: July 05, 2009, 12:19:39 PM »
Would it not be easier to just fiox the backlash??  The brake is GOING to severly LAG way behind MACH everytime. AND how do yoou tell the brake to apply itself. There is NO end of line data  in the pulse stream to use as indicators to start and stop the brake. You will LOOSE steps and the servo CANNOT make up the steps it will falt out.

Just a thought (;-) TP

Offline comet

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Re: electro-pneumatic slide lock
« Reply #7 on: July 05, 2009, 12:44:48 PM »
vmax,
 when the pulses start the brake releases when the pulses stop the brake locks after a 1/2 second delay.Its that simple.
The pulses themselves trigger the 555 timer which inturn triggers the brake.
the cylinder is a single sided with a light spring holding it continuosly against the lock pad,it unlocks in a fraction of a second as there
is only a few microns of movement to release.
I would concede however that a stepper setup might lose steps that it will never make up but thats always the problem with steppers!.
The Idea is to use it on a Z quill lock. The delay on lock will keep the lock off during rapid direction changes when peck drilling.

I have built the 555 circuit and it all works fine.

 Fixing the backlash is a very expensive option on this machine.Or any knee type machine that has the quill rack and pinion motorised,
because the only option you have is to bolt a ballscrew on the side ala anilam. And even then when using a big milling cutter
it can draw the cutter in.
 I used to have a Beaver knee CNC which used a auto quill lock and it was a far better machine than the bridgeport type.

     Tony

vmax549

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Re: electro-pneumatic slide lock
« Reply #8 on: July 05, 2009, 06:06:07 PM »
TOny the numbers don't add up. In that fraction of a second 1000s of pulses have gone by. More than enough to trip a servo drive. AND the brake does have to move more than a MICRON to release (;-). IN that .5 sec of delay to lock the damage of the loose quill has already been done(;-)

BUT let us know how it works out. I could be wrong (;-)

PS: Fixin the backlash is not as hard as it sounds.

Just a thought, (;-) TP