E-STOP Circuit - will this cause any problems?

[JAZZCNC]

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 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.

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.

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.

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.

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.

[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.

[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.

[birchy]

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!

[camhguh]

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!


[/QUOTE]

[birchy]

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?

[JAZZCNC]

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?

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.!

[Web Goblin]

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.

[birchy]

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.

[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!