E-STOP Circuit - will this cause any problems?

I have a 3-axis CNC kit from Zapp which consists of 3Nm steppers, M542 drives, 50V PSU and a PCPPS V3 interface board. Bought it some time ago but only just getting on with it. You know what these projects are like... :distracted:

For the E-Stop circuits, I'm going to use a Telemecanique contactor with a latching circuit and a reset button. Obviously all the stop buttons will be wired in series with dual N.C. contacts on each. I was planning to maintain a constant 24V DC supply for the safety circuit and then drop all remaining AC supplies which would be the Milling machine I'm converting, the 50V PSU and the PC. The PCPPS board would still be powered as it will be connected to the 24V DC supply. Will this setup cause any problems or risk buggering any of the components? I can probably cut the 24V to the PCPPS as well but may not have a N.O. aux available on the contactor.

Yes this will work fine and using relays it's basicly how I do all my control boxs. It's very Safe and much better at handling noise.

Leave the PCPPS powered, Don't kill the PC power and if your using a VFD for spindle then Keep the VFD powered but kill the Run signal.

Is K1 going to be the emergency stop contacts?
If so why are you killing power to the pc. If you do this you wont be able to restart any jobs after an estop activation. You would need to home the machine again.

You DON'T run mains voltage through an E Stop circuit!

Right enough Andy, I missed that bit but the drawing is not complete and I just assumed that he would be using a 24VDC coil and usin the maintained 24VDC supply for the estop circuit and switching the 240V AC.

Andy, there's nothing wrong with wiring the mains through the estop. Pro's like Strike CNC have been doing it for years! Lol

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Originally Posted by Web Goblin

Right enough Andy, I missed that bit but the drawing is not complete and I just assumed that he would be using a 24VDC coil and usin the maintained 24VDC supply for the estop circuit and switching the 240V AC.

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Yes you are right it's not complete, I have assumed that K1 and K2 are the E Stop N/C contacts, no doubt birchy will be along shortly to clarify.

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Originally Posted by Shinobiwan

Andy, there's nothing wrong with wiring the mains through the estop. Pro's like Strike CNC have been doing it for years! Lol

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It makes me cringe to think how many of their machines are out there still being used and a potential death trap!

K1 is the 24V DC contactor. All the safety stuff will be run from the 24V DC supply, so the E-Stops will be 24V and NOT 240V. I've not yet drawn the latching circuit. The above drawing is only for the AC side of things and doesn't show any E-Stops. I do have a Pilz safety relay but am limited on space due to its height, so will use a contactor instead.

240VAC can be used for estops but its not very common on machine controls these days. Most pro companies machinery that I have worked on always use 24VDC for control circuits.

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Originally Posted by birchy

K1 is the 24V DC contactor. All the safety stuff will be run from the 24V DC supply, so the E-Stops will be 24V and NOT 240V. I've not yet drawn the latching circuit. The above drawing is only for the AC side of things and doesn't show any E-Stops.

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Ok I will let you off this time :beer:

Birchy thats the safest way to do it especially if you are going to have a hand held control box at any time.

Damn Andy beat me. Need to type faster.

FWIW, I work in engineering and have built many machine control panels over the years, so am familiar with standard conventions. However, CNC conversions are new territory and I'm a little concerned that I might blow a drive card or something if I break the wrong circuits on an E-Stop.

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Originally Posted by audioandy

Yes you are right it's not complete, I have assumed that K1 and K2 are the E Stop N/C contacts, no doubt birchy will be along shortly to clarify.

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I didn't think anybody would be that Stupid Andy and also like GOBY presumed it incomplete.!! . . But suppose I should know better Esp after Seeing first hand the Strike time Bomb.!!

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Originally Posted by audioandy

Yes you are right it's not complete, I have assumed that K1 and K2 are the E Stop N/C contacts, no doubt birchy will be along shortly to clarify.

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As I said previously, K1 is the contactor. Terminals (1) and (2) are N.O. contacts that will switch the L and N when the contactor is latched following a reset. The latching circuit will obviously drop out if an E-Stop is active. BTW, there aren't any N.C. contacts on the drawing I posted...

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Originally Posted by birchy

As I said previously, K1 is the contactor. Terminals (1) and (2) are N.O. contacts that will switch the L and N when the contactor is latched following a reset. The latching circuit will obviously drop out if an E-Stop is active. BTW, there aren't any N.C. contacts on the drawing I posted...

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No but you mention them in your post, my fault for assuming!

Birchy I take it that your control pcb does not have estop contacts?

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Originally Posted by Web Goblin

Birchy I take it that your control pcb does not have estop contacts?

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It's a PCPPS V3.0 board. Doesn't appear to have any E-Stop contacts on it. My thinking is that if I kill all the AC devices, then the 50V supply to the steppers will also be killed which should be as safe as it can get?

It would stop the machine but you would lose position and not be able to restart the job from the same position easily. I dont have any experience with this pcb but I would think that one of the inputs would be able to be configured as a estop sense so that the software can recognise an estop signal.

Must admit I hadn't really considered maintaining position in order to restart as I assumed that an E-Stop would be in emergencies only because something had gone drastically wrong. Would it not be more accurate to re-zero the tool because it would most likely overrun slightly when the E-Stop is activated? Plus a tool breakage would probably require manual movement of the Z-axis in order to replace it.

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Originally Posted by birchy

It's a PCPPS V3.0 board. Doesn't appear to have any E-Stop contacts on it. My thinking is that if I kill all the AC devices, then the 50V supply to the steppers will also be killed which should be as safe as it can get?

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It does but it's not shown has E-stop and is just an input. Any input can be used for E-stop and just setup in control software to watch this pin.

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Originally Posted by Web Goblin

It would stop the machine but you would lose position and not be able to restart the job from the same position easily. I dont have any experience with this pcb but I would think that one of the inputs would be able to be configured as a estop sense so that the software can recognise an estop signal.

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After any E-stop It should be Assumed that your out of position due to inertia pushing.!! That's why home switchs make it easy to get back in position.

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Originally Posted by birchy

Must admit I hadn't really considered maintaining position in order to restart as I assumed that an E-Stop would be in emergencies only because something had gone drastically wrong. Would it not be more accurate to re-zero the tool because it would most likely overrun slightly when the E-Stop is activated? Plus a tool breakage would probably require manual movement of the Z-axis in order to replace it.

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Yes exactly what should be done after any E-stop which has occurred at anything other than very low feeds.

What you should really be doing is Mechanicly killing either signals or Electrical connections to devices and not relying on software to do it.

So thru relay contacts either kill the Enabel signal to drives or the power.? If you just kill the enable signal then the drives will stop but remain powered so keep there holding Torque. (Position will still have been lost.!) Personaly I kill the power to the transformer has I want the power shut down just to be extra safe.
Then at the same this happens the control software should be informed thru the input used for E-stop telling it to stop the code.

The BOB and PC should be left powered and out side the e-stop circuit.

Any other Powered Devices like spindle, Coolant pump or Vacuum should be shut down thru killing power Via Relay contacts. Again signalling to control software thru inputs.
Any device powered by VFD should be left powered but stopped by breaking Run signal thru a relay contact.

I would much prefer to kill the power and re-zero rather than rely on software. At the end of the day, it's a safety circuit. I'm not going to add spindle speed control at this stage, however I may add it in the future if I need to replace the motor and/or upgrade to an inverter drive. Latest drawing is attached. Please let me know if you see any mistakes or can suggest improvements!


Attachment 7653

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Originally Posted by JAZZCNC

I didn't think anybody would be that Stupid Andy and also like GOBY presumed it incomplete.!! . . But suppose I should know better Esp after Seeing first hand the Strike time Bomb.!!

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I didnt think I had said anything that required being called "Goby" but never mind.

Birchy the estop input is not relying on the software to stop the machine but rather informing it that an estop has occurred but I think youve got that now.
I would still leave the pc on a seperate supply though but thats a personal opinion. I would not like a fault on the machine control side to trip the mcb and dump the pc at the same time.

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Originally Posted by Web Goblin

I didnt think I had said anything that required being called "Goby" but never mind.

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Didn't say anything wrong and No offence ment Mr was just being lazy.!!

Don't see any limit switch's. . . Are you not using them.?

If you do plan to use wire them in series with E-stop. Which then you'll need a limit override momentary button to back off.!

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Originally Posted by Web Goblin

I would not like a fault on the machine control side to trip the mcb and dump the pc at the same time.

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Fair point and easy to change.

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Originally Posted by JAZZCNC

Don't see any limit switch's. . . Are you not using them.?

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Ermmmm...good question! I presume you mean limit switches to prevent the X, Y, Z from trying to drive beyond their physical stops? Although I've considered them, I was thinking that the stops can be set within the software, and if something went wrong, the drives would trip on overcurrent protection? Should limit switches REALLY be wired into the Safety Circuit? It seems wrong to me as they should be part of the machine functionality rather than an Emergency or Safety device?

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Originally Posted by birchy

Ermmmm...good question! I presume you mean limit switches to prevent the X, Y, Z from trying to drive beyond their physical stops? Although I've considered them, I was thinking that the stops can be set within the software, and if something went wrong, the drives would trip on overcurrent protection? Should limit switches REALLY be wired into the Safety Circuit? It seems wrong to me as they should be part of the machine functionality rather than an Emergency or Safety device?

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Not wrong very correct and right.!! . . . They are safety limits so should be part of the E-stop system and again the software should just be informed not left in charge.!!

Edit:

The other beauty of running 24v thru limit switch's(And E-stop) is better noise immunity which can affect the standard 5V signal from Parallel port. The 5v signal is just used to inform software so the wire run is tiny just coming from BOB (+) input passing thru relay contact and back to (-) input so far less chance of picking up noise.!

I maintain and repair industrial machines daily (production machines...not CNC) and have never (yet) seen a safety circuit that protects anything other than the end user. Things like E-Stops, gate switches, door interlocks, break-beams, pressure mats, etc are always there to protect the operator and must be activated manually. Things like position sensors, limit switches, etc are always kept separate. I understand the need for limit and homing switches (and not relying on the software), however I disagree that they should be part of the Safety circuit. Run off 24V DC....YES. As part of the machine logic...YES. As part of the Safety circuit...NO.

My reasoning is that if a drive goes to the end of its travel and activates a limit switch, we don't want it to kill everything and have to carry out a manual reset. It's not an emergency or a safety issue. Even if the drive keeps going, the physical stops will prevent it going any further. It might be an inconvenience to the operator but not a safety hazard...unless the machine is badly designed mechanically. So my idea of a limit switch is that it should stop the drive and inform the software but NOT kill the whole machine. Would you not agree?

Jazz,
Sorry just checking. I thought maybe I had upset you and not realised it. Thanks for clearing it up.
Birchy I would seperate the supplies for the cooling fans and fit a seperate fuse or mcb for them. The amount of times I have seen fans sieze up and take out control circuits isnt real. What rating is MCB1 going to be? Just wondering about the descrimination between it and the fuse for the WM16, a fault here might bypass the fuse and take out the mcb.

We have collision switches (proximity switches)mounted on our cnc machines at work at the cutting head and printer head mounts. These switches are connected to the emergency stop circuits to protect the machine and not the user.

Its always best to refer to the electrical machinery regulations for the latest interpertation of good practice re estops and safety circuity.

I would paste the link but Im not quite In control of this tablet yet :)


Just google It


QUOTE=birchy;39536]I would much prefer to kill the power and re-zero rather than rely on software. At the end of the day, it's a safety circuit. I'm not going to add spindle speed control at this stage, however I may add it in the future if I need to replace the motor and/or upgrade to an inverter drive. Latest drawing is attached. Please let me know if you see any mistakes or can suggest improvements!


Attachment 7653[/QUOTE]

Yes, the regulations are 2006/42/EC. I know they make reference to machinery working within its limits but that is for lifting equipment where uncontrolled movement could be hazardous to the operator.

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Originally Posted by birchy

My reasoning is that if a drive goes to the end of its travel and activates a limit switch, we don't want it to kill everything and have to carry out a manual reset. It's not an emergency or a safety issue. Even if the drive keeps going, the physical stops will prevent it going any further. It might be an inconvenience to the operator but not a safety hazard...unless the machine is badly designed mechanically. So my idea of a limit switch is that it should stop the drive and inform the software but NOT kill the whole machine. Would you not agree?

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No don't agree at all. Course it's a safety issue it's just crashed for some reason how do you know what that reason may be.? To have the system restart with out a manual reset is plan dangerous.!! . . You wouldn't have the machine restart upon releasing E-stop so why would you a Safety limit switch.?

You'll be hard pushed to find any commercial CNC machine that doesn't throw the machine into a reset condition from a limit trip.!

Relaying on Physical stops is bad practice and unhealthy to any machine and relaying on drive over current protection is just plain asking for trouble.!


End of the day it's your machine and components so do it how you feel best.! . . . Me I'll stick with being safe and the slight inconvenience of a reset thank you very much.!

It seems that we have different opinions of what a LIMIT switch and a SAFETY switch are. Obviously safety switches should be dual circuit and fail-safe. A limit switch/sensor is usually a single switch that tells the PLC or machine computer its current position. So I guess the safest way is to have LIMIT switches near the end of travel and SAFETY switches just before the physical stops. I think we're both on the same wavelength, but not using the same terminology!

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Originally Posted by birchy

It seems that we have different opinions of what a LIMIT switch and a SAFETY switch are. Obviously safety switches should be dual circuit and fail-safe. A limit switch/sensor is usually a single switch that tells the PLC or machine computer its current position. So I guess the safest way is to have LIMIT switches near the end of travel and SAFETY switches just before the physical stops. I think we're both on the same wavelength, but not using the same terminology!

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I may be talking tosh but this was a question that I asked when I first started thinking/designing my first machine. I got confused about home switches and limit switches and safety switches and I ended up having several physical work areas on my machine, depending on the size of the piece/part I was making, so if my machine sailed out of the physical working area I had defined, there was a good reason for it and it activated an E-stop shutting the machine down via the software stopping the program in its tracks, these physical working areas were movable/definable the in software, and a manual restart would be required whatever the condition, there were also a switches at the physical ends of all the axis, that was more brutal and just shut the power of completely. I even went and purchased a multiple input/output card (pokeys55) to achieve this. However as JAZZ has said all unexpected movement of an axis would imply a safety condition exists and should shut down the machine until it can be fully investigated..Rick