E-stop Wiring

[bill south]

I'm in the process of designing my mill control system and have a general type wiring question for those with experience in this area. I'm installing a mushroom button on the mill itself for estop purposes. I started with the idea of installing relays which would disable the high voltage to the motors. But, instead of working on the motor side of the power supply, how about breaking the voltage to the single torrodial supplying the high voltage. This would greatly simplify the installation. And, I think e-stop should stop all movement in the axis and ultimately, even the spindle motion. I'm not going to control the spindle initially. So, to make the question short, is there a problem with a estop cicruit which consists of a button controlling an isolation relay which controls the supply voltage to the high voltage transformer???? Almost too simple?????
Thanks in advance.
billyjack

[mjc117]

Hi Billyjack

I used the e-stop button to kill power to my servo transformer utilizing a relay and have not had any problems. Actually the way it is wired the limits, e-stop, mach3 charge pump are all in the e-stop circuit. I haven't had any problems with doing it this way.

Mike

[beone]

E-stop should stop all motion, deenergize all high voltage and make the machine "safe". it is to turn it off NOW. No orderd shutdown, no bit protection,just stop now. Kill it!
beone

[Al_The_Man]

One problem with just main power e-stop is the amplifiers power supply is still charged and the voltage has to decay allowing motor operation in some cases, if you go this route, it pays to also open the enable on the motor amplifiers, which hopefully have this option.
This is the way it is often done on commercial systems.
Al.

[mjc117]

Good point Al

On my system I have 2 taps on the transformer, one for the Servo 110vdc side and one for the 110vac circuit that powers my 24vdc control circuit. So when I kill power to my transformer (E-stop) it also kills the 24vdc to my Rutex drives, spindle relay, and mist cooler. This stops everything immediately. I think I have it right

Mike

[bill south]

Wow Guys;
All good points! How about a relay on the AC in to the entire system that opens on estop and kills everything with maybe the exception of a fault or e-stop lamp wired on the normally closed contacts. This would make sure nothing happens until reset. Of course the relay would be energized anytime the system is hot. Any thoughts. Seems quite simple!
billyjack

[Zippi]

Yep, kill power at the source AND kill "enable" lines for any and all other devices (controllers, spindle, etc). That residual power in capacitors may allow your machine to go a hair farther than you meant when you slam that stop button. If you have any braking devices, enable them, too!

[Bear]

Hi All,
Seems to me Estop should be just that,whats with the powering down
of servos/steppers? Isnt this an emergency? The machine is going to
shut down,the tool is usually scattered,as well as the part and or machine elements.While it is good to incorperate as many "safety" factors as one can dream of isnt it safe to just stop "stuff"?
Bear

[Al_The_Man]

I know most hobby CNC'rs have no legal obligation or code conformance, but this is the definitive 'legal' definition, in N. America anyway it is as follows, you can pick out of it what you want.
There are three categories of Emergency stop.
Category 0:
Stopping by immediate removal of power to the machine actuators . An uncontrolled stop: 'The stopping of machine motion by removing power to the machine actuators, all brakes or other mechanical stopping devices be actuated'.
Category 1:
A controlled stop: The stopping of machine motion by reducing the command to zero, but retaining power to the machine actuators during the stopping process. And then removal of power when the stop is achieved.
Category 2:
A controlled stop with power left available to the machine actuators.
Each machine to be equipped with a category 0 stop.
Category 1 and/or category2 stops shall be provided where demanded by safety and functional requirements of the machine.
Category 0 and 1 shall be in place and take priority.
In other words when you remove power to a machine and the servo's are still capable of moving by virtue of charged capacitors, power to the control can be left in place in order to achieve a controlled stop.
Also, it may be desirable to leave power to a spindle drive in order to stop it with dynamic braking, whereas just cutting the power, causes it to freewheel to a stop.
The general wording is that an estop shall be done in a manner to prevent Harm to an operator and damage to machinery.
Al.

[Allyd]

If you have a machine with a servo controller on it you will probably find that it has an E-stop input on the servo. Drop the voltage to that input and the servo will stop in whatever manner the manufacturer deemed appropriate ( normally in accordance with regulations) and then enter it's own estop conditions. You should also find a set of volt free contacts for dropping out the machines e-stop if the sero has a fatal error. I don't know about anywhere else but in the UK all machinery has to conform to the regs when it is sold. Not sure about the situation when you build one from parts or retrofit for domestic use.

[Haydn]

On my machine I have an estop on my control box and on machine frame. I designed mine so when I hit the switch power is lost to everything except the breakout board (Campbell). The breakout board has an e stop relay built on it and sends the signal to mach 3, this is done by effectively shorting two pins. I put a NO relay across these pins which is controlled from e stop relays in the supply I built. When the stop is hit the high potential is drained from the supply and the motors very quickly through a high wattage bleed resistor. Power to the spindle and extractor is also cut. If I can find my circuit schematic i'll put it up.

[Al_The_Man]

I think there is still some illusion here that some believe that killing the main power will stop all motion, not always so.
A case in point, If I am using say AMC servo amplifiers, these derive their power from one source, the High voltage DC power supply, the internal low level drive logic etc also is powered from this supply, now if I use an e-stop to remove power to the primary of the HV DC power supply, the transformer is off immediatly, but the DC supply is taking time to decay, still powering, to some extent the servo's, now the controller has been shut off at the same time as the AC to the Txfmr. So now the control input signal to the drives, is unpredictable, because they still are under part power, they are still capable of moving (trust me they do).
This is why it is neccessary in many case to also shut the enable off on the drives at e-stop time.
Al.