Ready Steady Eddy

My breakout board has a charge pump output that I'm currently not using. Mach3 is using it but I think I will look at incorporating it into the hardware stop circuit as your drawing shows.
Also, and this is very important but open to interpretation, I am not removing power from the spindle inverter during emergency stop, I mentioned this is another post. The reason is that the inverter can stop the spindle faster than it will stop on it's own, it does this by applying dynamic braking. Other options for bringing the spindle to a timely halt would be a spring loaded mechanical brake or as in the case of my table saw, a DC injection braking system. Removing power to the inverter via a contactor is the obvious emergency stop strategy and it could be said that removing power from the inverter under load will damage it, that might be true but better to have a damaged inverter than a damaged limb. According to the machinery Regs. which won't apply in a private houshold situation, the spindle should stop within 10 seconds, now I've not had my spindle up to speed yet so time will tell how long it takes to stop on it's own.

Quote:

---

Originally Posted by EddyCurrent

Also, and this is very important but open to interpretation, I am not removing power from the spindle inverter during emergency stop, I mentioned this is another post. The reason is that the inverter can stop the spindle faster than it will stop on it's own, it does this by applying dynamic braking. Other options for bringing the spindle to a timely halt would be a spring loaded mechanical brake or as in the case of my table saw, a DC injection braking system. Removing power to the inverter via a contactor is the obvious emergency stop strategy and it could be said that removing power from the inverter under load will damage it, that might be true but better to have a damaged inverter than a damaged limb. According to the machinery Regs. which won't apply in a private houshold situation, the spindle should stop within 10 seconds, now I've not had my spindle up to speed yet so time will tell how long it takes to stop on it's own.

---

Good info, thanks.
If I had your VFD rather than my cheap Chinese one, I might be more inclined to trust it to stop the spindle during an Estop as well. :courage:

Quote:

---

Originally Posted by EddyCurrent

Removing power to the inverter via a contactor is the obvious emergency stop strategy and it could be said that removing power from the inverter under load will damage it, that might be true but better to have a damaged inverter than a damaged limb.

---

Why would the inverter be damaged in this situation? Is it because once the power is cut to the inverter the spindle acts as a generator and this generated current can damage the inverter?

I would like to have a safety system that does not compromise at all on safety but has the best chance on leaving the equipment undamaged (also how do you test an estop circuit if testing it may damage the equipment?!?).

I'm not that keen on the mechanical breaking solution, so that leaves the following:-

EStop

• Dynamic/Rheostatic braking
  Cut cables from inverter to spindle and attach spindle to a bank of breaking resisters to apply dynamic breaking (is this even how it works!?!). At same time cut the run cable to the inverter.
• DC injection braking system
  Same as above but DC injection brake cuts the link from inverter to spindle and applies DC to the spindle to stop it.

I like the idea of the DC injection braking system but they seem pretty expensive (RS DC Injection Brake @ ~£160 with VAT!). I wonder how easy/cheap it would be to do dynamic braking (without the vfd)?

edit - Just noticed my Huanyang vfd has terminals to add a braking resistor. If power is removed from the inverter would this still be used/effective? would it cause damage to the inverter?

Some reading.

LPC Siemens Micromaster440
HMK Direct High Performance Drives and Positioning Systems
Motor drives & safety interlock circuits: AC Drives: FAQ (part 3)
Variable Speed Drives - E-stop

My conclusion is that when someone hits the emergency stop button the drive control signals must instantly tell the drive to stop and after a short delay the power is removed from the drive input via a suitable contactor. A braking resistor would be used to slow down the load as quickly as possible but as far as I'm aware it would only be operational if the drive was powered up.
As it happens the ABB drive I'm using has the STO function built in. I'll add a new drawing ASAP.

Ok lets have a reality check.!!

The spindle is a low powered affair, even at 2.2Kw and if the shit hit's the fan then reality is the situation will be one of just few things gone wrong.
E-stop is hit due to Limit or some other none spindle related condition then doesn't really matter how long spindle takes to slow down and coasting to a stop isn't long or problem.
E-stop is hit due to tool sticking etc then bloody thing will have stopped anyway or will grind to a halt dam quick.!!
E-stop is hit because you have been stupid enough to stick a hand or some other bodily part in the spindle then Yes you'll want the Spindle to stop quick has possibly but again your flesh or clothing will do a good job of acting has a braking and the spindle isn't powerful and doesn't have massive torque so will stall.!! . . So what I'm saying is the VFD's built in DC braking will be enough no resistor required.

Now regards the Kill power or Kill signal to VFD then I used to be Kill Signal guy but I'm now I Kill all power. Reason being what happens if the signal breaks or Even the VFD goes faulty.? Kill power and all doubt is removed. In practice the reality is the spindle will be jammed, either in material or flesh or in a situation where doesn't affect safety and the DC braking allowed without need for a resistor is more than enough.

For DIY use then it's more than good enough to just kill power and Let the spindle coast.

Dean, you are correct in that every situation has to be risk assessed on it's own.
I also think the braking resistor is not required because of the fairly low inertia of the load.
I agree that for DIY either strategy is fine but maybe not everyone reading this is in a DIY situation, in which case they should be referring to the relevant regulations.
The main aim of this is to get a good emergency stop system using the gear we've got.

It would be useful if we could define some scenarios and strategies for stopping a cnc machine, your input is valuable here.

I've listed some ways to stop the machine and the strategy to adopt, I'm not saying it's comprehensive so please add or amend as you think.

*emergency stop button pressed - strategy 1 or 2
*limit switch activated (not home limits) - strategy 2
*spindle over temperature switch activated - strategy 3
*Stepper driver alarm relay activated (e.g. AM882) - strategy 3
*'Stop' button pressed - strategy 4
*Charge Pump error - strategy 1 or 2

Strategy 1
----------
* remove power to all devices immediately

Strategy 2
----------
* remove power to stepper drives immediately
* remove power to ancillary devices immediately e.g. air, water, dust extraction
* issue stop command to VFD then after delay remove power to VFD

Strategy 3
----------
* issue audio visual alarm before taking action (with time delay)
* controlled stopping of all machine actuators and ancillary devices
* leave power supply on to VFD

Strategy 4
----------
* controlled stopping of all machine actuators and ancillary devices
* leave power supply on to VFD

Quote:

---

Originally Posted by EddyCurrent

Removing power to the inverter via a contactor is the obvious emergency stop strategy and it could be said that removing power from the inverter under load will damage it, that might be true but better to have a damaged inverter than a damaged limb.

---

Unlikely to cause significant damage to your limbs due to spindle's low inertia, so personally I'd rather it damaged the limb as that'll get fixed for free on the NHS, unlike the VFD.

Quote:

---

Originally Posted by cncJim

Why would the inverter be damaged in this situation? Is it because once the power is cut to the inverter the spindle acts as a generator and this generated current can damage the inverter?

---

Vaguely.

Quote:

---

Originally Posted by cncJim

Just noticed my Huanyang vfd has terminals to add a braking resistor. If power is removed from the inverter would this still be used/effective? would it cause damage to the inverter?

---

If you remove the power, the inverter can't do anything as it will only remain switched on for less than 1/10th of a second before the capacitors discharge. So no, it wont apply the brake.

Quote:

---

Originally Posted by cncJim

I would like to have a safety system that does not compromise at all on safety but has the best chance on leaving the equipment undamaged

---

In that case you need to separate 'fault conditions' from safety concerns - e.g hitting a limit switch or stepper driver fault signals do not pose safety hazards, so treat them as such and wire it so the machine just pauses. The only one that warrants fast and complete shutdown is pressing the e-stop, as that's what you can supposedly do if you're about to get hurt.

Quote:

---

Originally Posted by JAZZCNC

Now regards the Kill power or Kill signal to VFD then I used to be Kill Signal guy but I'm now I Kill all power. Reason being what happens if the signal breaks or Even the VFD goes faulty.?

---

The signal should be wired such that if the wire's broken or otherwise interfered with the signal changes state and the system stops. The VFD going faulty sounds exceptionally unlikely, but if you're worried about that then just have a timed relay to switch the VFD power off a couple of seconds after the signal (as mentioned earlier), since by that point the spindle will have stopped so you wont damage the VFD by cutting the power, and if it's not stopped then the VFD has gone faulty so you probably don't care about risking damage to it by cutting the power.

Quote:

---

Originally Posted by JAZZCNC

E-stop is hit due to Limit or some other none spindle related condition then doesn't really matter how long spindle takes to slow down and coasting to a stop isn't long or problem.

---

My new spindle takes 107 seconds to stop from full speed if left to coast. I tend to agree that it's not really a problem though.

Quote:

---

Originally Posted by EddyCurrent

*emergency stop button pressed - strategy 1 or 2

---

Two, see above. You could take advantage of the enable signal on the stepper drivers to disable them, then link cutting the power to the delay associated with the VFD.

Quote:

---

Originally Posted by EddyCurrent

I also think the braking resistor is not required because of the fairly low inertia of the load.

---

Yes - the internal resistor is sufficient to stop the 2.2kW spindles in less than a second, so you can easily implement the above method.

(3000th post... :moody:)

Quote:

---

Originally Posted by EddyCurrent

I agree that for DIY either strategy is fine but maybe not everyone reading this is in a DIY situation, in which case they should be referring to the relevant regulations.
The main aim of this is to get a good emergency stop system using the gear we've got.

It would be useful if we could define some scenarios and strategies for stopping a cnc machine, your input is valuable here.

---

Yes Agree in industrial situation then machine needs to be safe and Regs followed to keep the HSE police happy but mostly folks here are DIY and there's world of difference between Reg compliant and being used safely in a shed.!! . . . Practical common sense is all that's needed IMO.

Regards Strategy's then here's my take.!! (which has changed over the years.! I used to kill everything regardless)

E-stop means Foooooooking Hell EVERYTHING STOP NOW.!! . . . So Strategy 1 only.!

Limit/s trip means machine is outside it's working parameters so do something about it.!! . . So disable the drives using the drives enable signal, Not killing power to drives so maintaining holding torque. At same time inform the Control software so it's halts program execution.
Send Stop signal to Spindle/VFD again leave power on has it's not an emergency, it's a machine position error so we just need it to come to a controlled stop.
Along side this you could if wanted turn off other things like vacuum etc either by informing control software or by locally controlling on/off thru Relays but all this should just be on the Limit circuit NOT The E-stop.
Same regards the Fault signals from drives, It's a machine Error not an emergency so same applies just stop the machine in a controlled manner.

If any of the above happens then it should be wired in such away that some form of Latch is dropped and not allowed to re-latch until fault is cleared and then only with Push of a Momentary button not Reset switch.

The E-stop should have ultimate control and Kill power to everything in the event of an emergency so all Latches are dropped and won't reset or start again without some input. Ie Pushing Reset momentary button.

Charge pump and over Temp etc are again machine errors not emergency conditions so just bring machine to stop in controlled manner.

Personally I wouldn't have Temperature control anything over than alert the user thru audible or Visual means. Problem comes from the manner in how the machine is stopped.? To safely stop the machine and not wreck the work piece or lose position requires a Feed hold not a Stop command.! If you stop the machine while it's moving, either thru E-stop, limit trip/machine error or just pushing Stop button on control screen then you MUST presume you have lost position thru inertia pushing, THE ONLY SAFE WAY to bring the machine to stop and not lose position is to use Feed hold and allow the control software to do a controlled stop.
Problem with this is it's doesn't do it instantly so there's always some delay until look ahead buffer is cleared or it's finished the current move. If you have an overtemp problem you won't want to wreck the job so a controlled stop is required so feed hold must be used.
It is possible to use an input and have Mach watch it then use an OEM trigger to activate the Feedhold if the state changes but personally I wouldn't and just have a Spindle siren scream at me.!!

This also answers your "Stop Button" option.! . .Pressing stop will only stop the machine and other attached devices in a semi controlled manner but it won't be controlled and can't reliably be resumed from without first homing the machine to get back into position.

Also noted you said Home limit's.? Home switches are not limits of any kind neither are they part of any system, e-stop or limit etc. They solely define the Machine coordinate Zero position and are purely input's to the Control system and nothing else..!! . . . .(Eddy I know you probably know this but others may not)

Looks like we're all largely saying the same things now.

Quote:

---

Originally Posted by JAZZCNC

This also answers your "Stop Button" option.! . .Pressing stop will only stop the machine and other attached devices in a semi controlled manner but it won't be controlled and can't reliably be resumed from without first homing the machine to get back into position.

---

For the non-emergency stop button, you could just wire it to an input set to activate the feed hold, so the machine does in a controlled manner. It's still likely to leave a mark on the work, but prevent something worse.

Quote:

---

Originally Posted by Jonathan

The VFD going faulty sounds exceptionally unlikely

---

Not that unlikely really has I've got one here that did just that in that it wouldn't turn off thru a signal or the control panel. Turned out to be faulty panel and was replaced by ABB but the fact was it stayed bloody on so no signal would have turned it off.!!

Quote:

---

Originally Posted by JAZZCNC

Not that unlikely really has I've got one here that did just that in that it wouldn't turn off thru a signal or the control panel. Turned out to be faulty panel and was replaced by ABB but the fact was it stayed bloody on so no signal would have turned it off.!!

---

What's your point? The timed switch off mentioned twice (now three times) in this thread would have turned it off. Also you can't judge how likely something is with such a small sample size.

A couple of months ago I got a 15kW ABB VFD. Wired it up correctly and 5 minutes later the input rectifier blew up leaving my ears ringing for about half an hour!

Quote:

---

Originally Posted by Jonathan

Looks like we're all largely saying the same things now.

---

Didn't see your post until after I'd posted that.

Quote:

---

Originally Posted by Jonathan

For the non-emergency stop button, you could just wire it to an input set to activate the feed hold, so the machine does in a controlled manner. It's still likely to leave a mark on the work, but prevent something worse.

---

Erm.!! . . . Well that would just be a Feed hold so why not Call it Feed Hold.??

Quote:

---

Originally Posted by Jonathan

What's your point? The timed switch off mentioned twice (now three times) in this thread would have turned it off. Also you can't judge how likely something is with such a small sample size.

---

Point is that it does happen and equally you can't say it's unlikely because it has happened.!! . . . . . Agree thou it's irrelevant has it will be safe eventually if power cutoff is just delayed. ( I was more meaning it's unsafe if just relying on Signals.)

E-stop systems are always a good cause for debate.
Ultimately they should stop movement likely to cause personal injury, and how that can be acheived depends on the machine.

We've got some quite expensive lorries at work with external equipment where some will kill everything including the lorry engine when an E-stop is pressed, whereas others will only kill the external equipment. There are pros and cons to both.
The key requirement is they should be fail safe, and periodically checked.

One question for everybody is, when did you last check all your limits and E-stop buttons worked?

Quote:

---

Originally Posted by m_c

One question for everybody is, when did you last check all your limits and E-stop buttons worked?

---

Don't have limits but I must hit the Oh shite button at least ounce per day. . .Lol

Quote:

---

Originally Posted by EddyCurrent

.....
The main aim of this is to get a good emergency stop system using the gear we've got.

It would be useful if we could define some scenarios and strategies for stopping a cnc machine, your input is valuable here.

I've listed some ways to stop the machine and the strategy to adopt, I'm not saying it's comprehensive so please add or amend as you think.
.....

---

This is a great idea Eddy, great for noobs like me. Might be nice to add example circuits for each strategy (might be getting carried away now...:emmersed:)?
I have made some changes based on some of the feedback and tried to make clear which things should be done in hardware and software, hope that's ok. Maybe it could make a good sticky?

List of scenarios and possible strategies for dealing with them.

Scenarios

• Emergency stop button pressed - Strategy 1, 2 or 2.5
• Limit switch activated (not home limits) - Strategy 2 or 2.5
• Spindle over temperature switch activated - Strategy 3 or 3.5
• Stepper driver alarm relay activated (e.g. AM882) - Strategy 3 or 3.5
• 'Stop' button pressed - Strategy 4
• Charge Pump error - Strategy 1, 2 or 2.5

Strategy 1

• remove power to all devices immediately (Hardware)
• Inform control software of Estop condition (Software)

Strategy 2

• remove power to stepper drives immediately (Hardware)
• remove power to ancillary devices immediately e.g. air, water, dust extraction (Hardware)
• issue stop command to VFD then after delay remove power to VFD (Hardware)
• Inform control software of Estop condition (Software)

Strategy 2.5

• Issue stop to stepper drives then after delay remove power to stepper drives (Hardware)
• issue stop command to VFD then after delay remove power to VFD (Hardware)
• remove power to ancillary devices immediately e.g. air, water, dust extraction (Hardware)
• Inform control software of Estop condition (Software)

Strategy 3

• issue audio visual alarm before taking action (with time delay) (Hardware/Software)
  After delay:-
• Stopping of all machine actuators and ancillary devices (Software - "Stop" Command)
• leave power supply on to VFD

Strategy 3.5

• issue audio visual alarm before taking action (with time delay) (Hardware/Software)
  After delay:-
• inform control software to activate Feedhold (Software)
• Move to safe Z (Software)
• Issue stop command to spindle (Software)
• leave power supply on to everything

Strategy 4

• Stopping of all machine actuators and ancillary devices (Software - "Stop" Command)
• leave power supply on to VFD

Thanks to all who contributed it's been very rewarding I think and thanks to Dean and Jim for pointing out the FeedHold function of Mach3. With all of this each individual will have to make their own judgement, this is just mine.
After going through the available information I decided to list the 'stopping methods' for each of the major components, i.e. VFD, stepper motors, Mach3, ancillary equipment.
I decided that cutting power directly to the VFD was not for me so will implemented method 1 below.
Also I decided that control of the ancillary equipment was currently outside the scope of my control cabinet but if later on it does fall within the scope changes will have to made.

VFD stopping methods
---------------------------------
1. immediately issue 'emergency stop' command and after delay remove power to input ('e/stop' command can be set to stop drive faster than 'stop')
2. immediately issue 'stop' command and leave power to input
3. use STO function if available to prevent restart (this is not a stopping function)

Stepper Drivers stopping methods
-----------------------------------------------
4. immediately remove power to stepper drivers
5. immediately activate 'enable' signal (breakout board also uses charge pump signal to disable outputs to stepper drivers (not using 'enable' signal)

Ancillary equipment stopping methods
-----------------------------------------------------
6. immediately issue stop command (varies according to equipment)

Mach3 stopping methods
-----------------------------------
8. immediately issue Feed Hold command to Mach3
9. immediately issue Stop command to Mach3

Other stopping methods
---------------------------------
7. immediately issue audio visual signal

Next I looked at the stopping scenarios, developed strategies and assigned 'stopping methods' to them, I felt it was important to minimise the number of strategies so carried out some mental boolean algebra and Karnough mapping.

Only strategy 1 will be considered Safety related, it also aligns with the suggested drawing in Mach3 documentation.
Emergency stop is obvious, for me limit switch activation may lead to a dangerous situation, charge pump activation means Mach3 has lost control so anything could happen.

*emergency stop button pressed - strategy 1
*limit switch activated (NOT home limits) - strategy 1
*Charge Pump error - strategy 1
*'Stop' button pressed - strategy 2
*spindle over temperature switch activated - strategy 5 (assumes someone is in attendance otherwise use strategy 4)
*Stepper driver alarm relay activated (e.g. AM882) - strategy 3

Strategy 1 ( 1,4,9 )
Strategy 2 ( 2,5,9 )
Strategy 3 ( 2,4,9 )
Strategy 4 ( 2,5,8 )
Strategy 5 ( 7 )

Next up will be some updated drawings to implement this.

In the interest of practicality I'm proposing these changes

*emergency stop button pressed - strategy 1
*limit switch activated (NOT home limits) - strategy 1
*Charge Pump error - strategy 1
*'Stop' button pressed - strategy 2 or strategy 4
*spindle over temperature switch activated - strategy 5
*Stepper driver alarm relay activated (e.g. AM882) - strategy 2

The reasons being,
* If the spindle is overtemp then sound an alarm and let the operator take action at the Mach3 screen or otherwise.
* If the stepper driver alarm relay operates then it should be sufficient to issue the 'enable' signal, if not then the emergency stop can be operated.

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


Also a section in this

http://www.bara.org.uk/info/safety/A...pplication.pdf

Kill all power, no doubt.

Here is how i have my CNC working:

-the PC id surge protected and connected to a 1500w UPS. Also the CNC is conected there
-the VFD enables the BOB
-the charge pump enables the BOB and the VFD

Typical everyday scenarios:

Power interruption from outside of the house. It happens a lot here in Spain. Or a fuse trip. I have a lot of stuff at that fuse :-)
-the VFD stops and stops Mach3. I go and see which line the process is. I write it down on a piece of paper. If power comes for the next half hour , i just continue from there. If not, i stop the PC and when i have power again, simp[ly continue from the line.

My mistake
-Spindle digs, VFD trips, Mach3 stops, Usually reset, lift the Spindle, check Z0, usually that is the mistake, Z0 and voilaaa

Mach3 goes down and decides some crazy movement. Happens rarely but happens.
-the bit digs, spindle stops and trip signal stops the process. if nothing is damaged, i check the xyz0 and if ok i continue from there, if not, i throw in the garbage and do it again

PC stops, restarts alone or whatever similar.
-VFD stops

I hit the EStop
-no power to the drives, no power to the BOB, VFD stops

I greatly recommend a pause button also on the machine. Sometimes when not sure what is happening if nothing crashes is better to just pause the process and contemplate. Though an extra second is lost meanwhile

Quote:

---

Originally Posted by silyavski

I greatly recommend a pause button also on the machine. Sometimes when not sure what is happening if nothing crashes is better to just pause the process and contemplate. Though an extra second is lost meanwhile

---

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 ?

Quote:

---

Originally Posted by EddyCurrent

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.

Quote:

---

Originally Posted by EddyCurrent

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.

---

Quote:

---

Originally Posted by EddyCurrent

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.

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.

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

Attachment 10806Attachment 10807Attachment 10808Attachment 10809

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

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.

Attachment 10822

Quote:

---

Originally Posted by 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.

Attachment 10822

---

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...

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)

Attachment 10832

Quote:

---

Originally Posted by EddyCurrent

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?

Quote:

---

Originally Posted by EddyCurrent

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:-
Attachment 10833
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?

Quote:

---

Originally Posted by 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)

Attachment 10832

---

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

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:
Attachment 10834

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

Quote:

---

Originally Posted by 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.

Attachment 10822

---

Quote:

---

Originally Posted by 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)

Attachment 10832

---

Quote:

---

Originally Posted by irving2008

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

R needse 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

---

Please forgive my ignorance but could someone explain how this will work in basic terms? Why is Eddy's first circuit not fail safe and how does the next circuit achieve that?

Sorry, I've not had a lot of sleep over the past few nights (babies all have colds....) and I think my brain may be turning to mush.

Quote:

---

Originally Posted by cncJim

Please forgive my ignorance but could someone explain how this will work in basic terms? Why is Eddy's first circuit not fail safe and how does the next circuit achieve that?

---

The transistor is used as a switch. When positive current is applied to the base of an NPN it switches on. In the original circuit, the transistor is simply connected in series with the relay, so when the current is applied the transistor switches on and so does the relay. The problem is, if the signal to the base is broken (e.g. wire accidently cut), the transistor and thus the relay will switch on. We want the relay to be off in this situation, so another transistor is used to invert the signal. When the current is applied to 'new' transistor, it switches on so connects the base of the second transistor to ground, which in turn switches it off - hence the signal is inverted.

Quote:

---

Originally Posted by Jonathan

The transistor is used as a switch. When positive current is applied to the base of an NPN it switches on. In the original circuit, the transistor is simply connected in series with the relay, so when the current is applied the transistor switches on and so does the relay. The problem is, if the signal to the base is broken (e.g. wire accidently cut), the transistor and thus the relay will switch on. We want the relay to be off in this situation, so another transistor is used to invert the signal. When the current is applied to 'new' transistor, it switches on so connects the base of the second transistor to ground, which in turn switches it off - hence the signal is inverted.

---

Thanks for taking the time to reply Jonathan. Very helpful. I was also having hard time understanding/visualising the "active low" part of the puzzle.

This also helped me understand:-
Attachment 10837
"If the input signal is high there will flow current through R2 and the transistor's base-emitter junction (base, not gate). This current will be amplified, and the collector current through R1 will cause a voltage drop so that the output will be low. Input high, output low.
If the input signal is low there won't be any base current, and no collector current. No current through R1 means no voltage drop, so that the output will be at +V. Input low, output high."

Quote:

---

Originally Posted by cncJim

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?

---

Yes that's what the Charge Pump relay is doing. The BOB is turning a 12khz signal from Mach3 into a 0 or 5vdc output, on my particular BOB the output of ENA is 0v when Mach3 is healthy and +5v dc when it stops.

Quote:

---

Originally Posted by cncJim

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:-
Attachment 10833
Finder TYPE 55.34
The 5A rating, is that for the entire relay or for each contact?

---

Those look just right, I looked on Farnell and they appear to be 4 pole Change Over which is what you need if using my diagram, the 5A rating is for each contact.

Quote:

---

Originally Posted by irving2008

BD679 is fine as output transistor if a bit of an overkill.

---

Thank's for info on component sizes.
That is correct, it's just that I have some and they have a high gain because I need to keep the load on ENA as low as possible as it's also supplying 4 x stepper drivers.

Quote:

---

Originally Posted by EddyCurrent

Yes that's what the Charge Pump relay is doing. The BOB is turning a 12khz signal from Mach3 into a 0 or 5vdc output, on my particular BOB the output of ENA is 0v when Mach3 is healthy and +5v dc when it stops.

---

Of course, what a spanner! sorry that makes perfect sense now.

Quote:

---

Originally Posted by 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:
Attachment 10834

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

---

That would be a sensible solution Jonathan and one that I shall test, thank you

The breakout board I'm using is this one SYSTEM1
I emailed Roy regarding the charge pump relay and he obviously suggested a transistor buffer but more interestingly the board has 'spare' 12v and 5v outputs and his suggestion was to connect a small 5v reed type relay between +5v and ENA. This has the advantage that when Mach3 is healthy ENA is at 0v therefore a potential of 5v exists between +5v and ENA making it fail safe plus it would share the load better with the 4 connected AM882's. This might be the way to go other than the reed relay does not sound too appealing although in practice one of those encapsulated type that look like a chip with about 8 legs have proved to be reliable in industrial situations.

Quote:

---

Originally Posted by cncJim

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

---

With electrical systems there are generally two main circuits, the 'control circuit' and the 'power circuit'. Contactors are regarded as components of the power circuit whereas relays belong to the control circuit, it's mostly to do with the current carrying capacity and the ability to break that circuit without arcing or at least controlling the arcing. There are relays with positive guided contacts and these are for use in safety circuits, I have not come across equivalent contactors but that's not to say they don't exist. I'm not 100% on this but I think relays originated in communications areas such as telephone exchanges. Contactors can have auxilliary contacts fitted which in essence are relay equivalents and are used in the control circuits for those contactors.

Just to clarify Jonathan's answer, the BOB ENable signal is Active Low i.e. enabled = 0v, disabled = 5v. In Eddy's original circuit the relay would be OFF when the BOB says Enabled and ON when disabled. But a BOB failure, a supply voltage failure, or burn out of the transistor would all turn the relay OFF, an enabled state, so not fail safe. As J says, the addition of the second transistor inverts the logic so relay is ON only when system is enabled and voltages are present.

J's later solution achieves the same result by using a PNP transistor to invert the logic.

[edit] typed this ages ago but forgot to hit submit.... :roll: and now its out of date lol

Quote:

---

Originally Posted by Jonathan

The transistor is used as a switch. When positive current is applied to the base of an NPN it switches on. In the original circuit, the transistor is simply connected in series with the relay, so when the current is applied the transistor switches on and so does the relay. The problem is, if the signal to the base is broken (e.g. wire accidently cut), the transistor and thus the relay will switch on. We want the relay to be off in this situation, so another transistor is used to invert the signal. When the current is applied to 'new' transistor, it switches on so connects the base of the second transistor to ground, which in turn switches it off - hence the signal is inverted.

---