Ready Steady Eddy

[Boyan Silyavski]

What would you have it do ?

Stop the VFD
Send a FeedHold signal to Mach3 and let it control the stepper motors


Is it not just as easy to do it from the PC ?

Sometimes i am not sure what happens, so i just hit the pause / feedhold/ button, instead of the estop. Spindle still rotates and i check. if everything ok, i hit the "cycle start" button which is also at the machine, so everything continues, as if nothing have happened.
The keyboard is 2m away in my case, so its not easier.

I do this if i want to check if the material has loosened on the fixture, clean some bearings, remove sticks from the vacuum shoe and so, without further interrupting the process.

On next machine i will have flood and vacuum buttons also. Sometimes when i want to do something with the keyboard i accidentally touch the wrong buttons. last time somehow i zeroed the machine coordinates. So had to stop, go to home, zero again, get out of Mach3,save fixture, then again in, zero on the work piece and start again the job.

[cncJim]

finding a suitable off delay for the VFD contactor AT THE RIGHT PRICE is proving a challenge right now. There are some cheap ON delays which could be used but would not be fail safe.

This seems to be the document required, have not read it yet but the title is "Application Note
Interfacing AC Drives with Safety Relays"

http://www.ab.com/support/abdrives/p...lays_Rev04.pdf

Excellent doc eddy, spot on. Also very handy as it details hooking up a AB msr138dp which I have just bought on ebay for £30! After looking into the specs there are 10 different varieties (various voltages/delay ranges) and I think this is the right one/most useful (hope so, I've bought it now!) - 440R-M23143 (24v - 0.15 - 3 seconds delay)?

Also, I spoke to the guy and he said he has another which he is willing to sell for the same price. Let me know if you are interested eddy and I will pass on his number

Cheers.

[Boyan Silyavski]

Eddy,
what is this one: *spindle over temperature switch activated ?

Where did you find a cheap temperature sensor with digital display that has a contactor or signal at programmed temperature?

I have bought a cheap 7eur battery one with temperature alarm, and thought of using the alarm output ~3v to connect to the BOB, but forgot about this project.

Once i accidentally switched off the water pump and spindle worked all day before i touched it and saw it was hot. Nothing happened. Still works. Though was just V carving.

[EddyCurrent]

Good timing lads !

@silyavski, the temperature switch was already built into my spindle, it is closed normally and opens at high temperature.
@cncJim, see latest drawings

Here are my latest drawings



Features
---------
Strategy 1

* Emergency stop immediately signals VFD to stop and several seconds later (time to be assessed but possibly 6 seconds) delayed contacts of Guardmaster safety relay open to operate STO (Safe Torque Off) feature of VFD which disables control voltage and power semiconductors.
* Power removed from Stepper Drivers via Guardmaster safety relay and K1
* Stop command issued to Mach3 via K1 (even if Mach was still active the VFD and Stepper Drivers would still be disabled)

Strategy 2

* Stop signal sent to VFD via K3 relay
* Stop command issued to Mach3 via K3
* Enable (ENA) signal activated via Mach3 and BOB to disable stepper drivers

Strategy 3

Not implemented - same as Strategy 2

Strategy 4

* Stop signal sent to VFD via K4 relay
* FeedHold command issued to Mach3 via K4
* Enable (ENA) signal activated via Mach3 and BOB to disable stepper drivers

Strategy 5

Not implemented


Notes:

Strategy 3 could be implemented by incorporating a relay contact from K3 into K1 coil circuit however because all 4 contacts of K3 are being used another single contact relay would have to be connected in parallel with K3.
Strategy 5 could be implemented by removing the Pause push button and having only K4-4 contacts operational.

* A PAUSE push button has been added, this will stop the VFD and send a FeedHold signal to Mach3, to continue the ON (RESET) push button is pressed.
* A Charge Pump relay has been added to the Emergency Stop circuit this so the system can initiate an Emergency Stop if the software stops or communication is lost.
* If the Circuit Breaker for the Stepper Drivers trips then K1 will de-energise and send a STOP signal to Mach3.
* ENA signal now connected from BOB to all Stepper Drivers

( ** As yet I have not cobbled together the Charge Pump relay but I think a small 5v coil one will do the job as my BOB can source 20mA. **)

Relays K2,K3 and K4 are these
http://www.ebay.co.uk/itm/1set-Base-...item5d388b7d84

[EddyCurrent]

I'm thinking this is going to be my Charge Pump relay circuit. My BOB ENA signal is active low so the relay will be in the 'healthy' state when de-energised, this is not fail safe and I could have inverted the signal but it's going to do. The BOB is supplied by 24vdc and so GND is common to the 5v and the 24V.

[irving2008]

I'm thinking this is going to be my Charge Pump relay circuit. My BOB ENA signal is active low so the relay will be in the 'healthy' state when de-energised, this is not fail safe and I could have inverted the signal but it's going to do. The BOB is supplied by 24vdc and so GND is common to the 5v and the 24V.

You have C and E swapped over. Its an NPN so E is always to -ve rail.

with only 3 or 4 more components you could make it failsafe and i would...

[EddyCurrent]

Irving, you are right, I just threw the drawing together on Paint and I have indeed got e and c crossed over. What would your plan be to make it failsafe ?

Maybe this ? (sorry for poor drawing, no tools at hand on this pc)

[cncJim]

Good timing lads !

...

( ** As yet I have not cobbled together the Charge Pump relay but I think a small 5v coil one will do the job as my BOB can source 20mA. **)

Good stuff EddyCurrent, I'm still working my way through your diagrams trying to fully understand :) - Do you have any provision for activating your estop circuit from the controlling software? I suppose the argument could be made that its not needed unless the pc a distance from the machine?

Relays K2,K3 and K4 are these
1set Base+OMRON coil power relay 14pin 4NO 4NC MY4NJ MY4N-J 5A DC24V 4PDT | eBay

I have just acquired 10 of these from a control panel I stripped down (7x 24v and 3x 230v) which seem to be a similar spec to yours:-

Finder TYPE 55.34
The 5A rating, is that for the entire relay or for each contact?

There are also 4 contactors which I haven't taken out yet. Are there any practical/safety differences between a relay and a contactor?

[irving2008]

Irving, you are right, I just threw the drawing together on Paint and I have indeed got e and c crossed over. What would your plan be to make it failsafe ?

Maybe this ? (sorry for poor drawing, no tools at hand on this pc)

that'll do it. i'd put a series resistor between BOB and base of transistor, value depends on pull-up on BOB. If there is no pull-up (i.e. its an o/c output) use 10k to 5v rail.

R needs to be something like 2k7 0.5W rating if connected to 24v, or 470R 0.125W if connected to 5v rail.

BD679 is fine as output transistor if a bit of an overkill. Any small signal NPN with a gain >50, Vce >40v and Ic >200mA will do for the input transistor e.g 2N3904, BC337 or similar

[Jonathan]

If the breakout board output is open collector, why not reduce the component count by using a PNP transistor to invert the signal?

e.g:


Edit: Also don't forget the back-emf protection diode!