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Author Topic: Z axis brake releases to quickly on reset.  (Read 5008 times)

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Z axis brake releases to quickly on reset.
« on: September 09, 2011, 09:33:12 AM »
Hey guys
I know someone has a simple solution for this problem. I have configured my controller in a very typical way. When the system is reset, on the screen, power is put to my amplifiers and at the same time power is put to my electro-magnetic brake on the z-axis to dissengage the brake. I have a heavy spindle thus the brake requirement when powered off. The problem is that the brake is dissengaging before the z-axis servo takes over holding the spindle up. How can I slow down the power to the brake by about 2 or 3 seconds to get some overlap? Can i use a thermister or a capacitor? Delay relay? I am putting power to the brake by switching on an 24vdc power supply that is only used for this brake. How are you guys solving this problem.
As always....thanks for any input.
Russ.

Offline BR549

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Re: Z axis brake releases to quickly on reset.
« Reply #1 on: September 09, 2011, 10:24:42 AM »
You could do a time delay relay on the brake circuit.

That would be the least trouble

Just a thought, (;-) TP
« Last Edit: September 09, 2011, 10:27:55 AM by BR549 »

Offline Hood

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Re: Z axis brake releases to quickly on reset.
« Reply #2 on: September 09, 2011, 02:07:46 PM »
You may be find having the supply energised all the time (with your control power) and switching it to the brake via a relay may be enough as it could be the supply is just taking slightly too long to energise the coil as it itself has to power up.

Ignore the above, thinking arse for t*t with the operation. What you could possibly try is using the 6th enable signal for the brake as I am sure there is a slight delay purposely between enables.

Or you could use a Brain or Macropump to activate an output a determined time after the enable signal is seen.

Hood
« Last Edit: September 09, 2011, 02:15:06 PM by Hood »
Re: Z axis brake releases to quickly on reset.
« Reply #3 on: September 10, 2011, 02:38:49 PM »
Ahhhh good thinking Hood. Those are the ideas i was looking for. I will try those.
Russ.

Offline BR549

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Re: Z axis brake releases to quickly on reset.
« Reply #4 on: September 10, 2011, 02:57:36 PM »
One problem with those is MACH is continously pinging the relay that takes up CPU time. 

(;-) TP

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Re: Z axis brake releases to quickly on reset.
« Reply #5 on: September 10, 2011, 06:33:16 PM »
Not really sure what you mean Terry, relay would only ever get operated or shut off with the enable signal. A macropump would constantly be looking at the enable state but dont think that would hog the CPU too much unless your macropump was already loaded with other stuff. Brains dont seem to take much CPU on any of my machines either, CPU regualarly sits at 2% and very rarely gets above 20% and thats on a Via Pico 1GHZ embedded mobo.


Hood

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Re: Z axis brake releases to quickly on reset.
« Reply #6 on: September 10, 2011, 06:49:33 PM »
You would  need a double comparitor, turn on/off a indicator led and a bypass loop I believe. THe TD relay is simple, set and forget and NO programming required.

Just a thought, (;-) TP

Offline Hood

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Re: Z axis brake releases to quickly on reset.
« Reply #7 on: September 10, 2011, 06:57:40 PM »
Dont know why, would the output not be shut off when in Reset?
Hood

Offline BR549

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Re: Z axis brake releases to quickly on reset.
« Reply #8 on: September 10, 2011, 07:51:49 PM »
Yes it would and still be continously pinging the pins at 10 times per sec. The actuall  pinging of the pins is what ties up cpu time.

with a bypass loop IF conditions were correct then the process just loops around the code. When conditions vwarrant it then the code sets the led and turns ON the relayy ONCE.  Then continous on bypassing until a change is needed again.

Without it it is possible to see the small jitter on some systems..

It is not hard to build the monitor code with the built in safety and time delay setting of the relay.  BUT the simple TD relay solves all the problems AND no CB code to boot.

Just my opinion, your milage may vary (;-) TP

Offline Hood

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Re: Z axis brake releases to quickly on reset.
« Reply #9 on: September 10, 2011, 07:59:25 PM »
Timing relays here are not that cheap so unless you have one at hand a brain is cheaper :)
Maybe it would affect some systems but if it did then I think its time to get a new computer as obviously its struggling but thats just my opinion.
The Enable 6 as mentioned above may provide enough delay, if it does then no hassle with anything :)
Hood