Charge pump - do I need this on?

[zeeway]

Trying to figure out the charge pump signal on Gecko 540 with Mach 3. My understanding is that the charge pump signal from Mach 3 to Gecko, tells the Gecko that the computer is alive. And apparently this is very important on metal cutting machines that typically have a coolant pump...am I close?

So my machine is a headed to becoming a wood/MDF cutting router - no coolant pumps anywhere. And my Gecko 540 has the little external switch that allows me to turn off the charge pump.

So, can I just turn off the charge pump switch on the Gecko and forget about the XML files and setting pin 16 in Mach 3 and all the rest of that jazz?

Is there any reason for me to have the charge pump signal active? I think if my computer dies, it will be pretty dang obvious.

Would one of you electronic guys enlighten me? Thank you kindly.

[Al_The_Man]

Historically processor controlled systems, which includes PC based systems, have used something called a watchdog timer, this essentially is used to produce the same result as a charge pump, it is just another method of using the 12.5khz signal.
I believe the original intention of Mach was to indicate when the system was either booting up or closing down and motion can be inhibited during this period.
My experience has always been to use any watchdog timer/charge pump signal output in the E-STOP string, this inhibits or shuts off any power devices, motors, drives etc.
This allows for the eventuality of a PC crash or shut down and when powering up/down to disable the rest of the system.
Obviously there is no point in drives obliviously controlling motors when the brain (PC) is dead.
Especially in such systems as Mach where the controll loop is either open (steppers) or not closed back to the servo controller.
Al.

[ger21]

The charge pump in Mach3 was created to keep relays from turning on and off, and the machine from moving, when Mach3 was not running.

[zeeway]

So, if i understand this correctly, the watch dog/charge pump function acts as a safety device to keep the muscles (drive/motors) from doing something bad when the brain (PC) suddenly dies? Okay, sounds like I need it to be active. Thanks, guys.

[ger21]

You shouldn't rely on the Charge Pump alone for safety.

If you only turn your drives on and off while Mach3 is running, then the charge pump won't really do anything for you, unless Mach3 crashes, or you lose power.

[Al_The_Man]

A hardware E-stop string can be wired to take care of all eventualities, so if the W.D./C.P signal is part of it, then you do not have to worry about using it in individual cases.
There is a snag, as if you monitor the E-stop by input to Mach to indicate an external E-stop has taken place, Mach turns off the 12.5khz signal on E_stop, so it becomes a catch 22.
The answer would be to use the E-stop reset P.B. to momentarily turn off the E-stop enable input.
Al.

[zeeway]

Sorry to be so dense...but I am getting confused. I thought the drive could not send a pulse to the motor unless Mach told it to. Hence in my understanding, the drive cannot give a move signal unless Mach is on...unless we are talking about the nanosecond where Mach has told the drive to pulse the motor...and the drive is executing that..and Mach crashes in the meanwhile...?

Hope I am not coming across as a smart aXXX, but I truly do not understand this stuff.

[Larken]

When a PC is booting up the steppers could jump around when windows is doing Plug and Play. (if the controller was on)
But the most serious thing would be if the spindle turned on randomly (and some one was changing a tool).

Like AL says, If Mach drops the CP signal when you hit the Estop, its good and bad. Its possible to loose machine steps when you enable/disable the Step/Dir driver.

Its a wasted line when you use the CP signal, but its your call.

Larry K

[phomann]

So, if i understand this correctly, the watch dog/charge pump function acts as a safety device to keep the muscles (drive/motors) from doing something bad when the brain (PC) suddenly dies? Okay, sounds like I need it to be active. Thanks, guys.

No. This is completely wrong. The original purpose of the Chargepump enable was to overcome the problem of PC's twiddling some of the parallel port output pins when the PC boots.

Depending on what is connected to these pins, you may end up with a spindle temporary turning on and/or spurious step signals being send to you drives. This means that the machine is no longer is the same position that it was when powered down.

The 12.5KHz signal was chosen as at the time Mach1 had a kernel speed of 25KHz, so the 12.5KHz was very easy to generate. The signal was generated whenever mach3 is running.

Later on some people wanted it tied to the Mach3 'Reset' State. In this case, the chargepump enable is now only generated when Mach3 is not in a 'Reset' state. Some people then assumed that this was a signal to use in an EStop situation. They have an EStop button connected to the parallel port via a BOB and have Mach3 stop the Chargepump and disable the drives, spindle etc.

This results in an extremely dangerous setup. The reason you press the estop may be because Mach3 is malfunctioning. When you press it Mach3 may ignore the input, not remove the estop and the drives and spindle keep running.

There is a config option in Mach3's general config tab that allows the Chargepump enable to be present all the time regardless of the 'Reset' State.

I recommend that people configure Mach3 to have the Chargepump signal present all the time Mach3 is running and have a proper EStop circuit that removes power from the drives and spindle when pressed.

If you want, you can have your Estop circuitry inform Mach3 that an EStop condition has occurred, so it also stops. But do not rely on software to execute an Estop.

Cheers,

Peter.

[zeeway]

Aha - now maybe I understand. So, when the computer is booting up or crashing, it may generate some spurious signals through the parallel port. If the drive is on during these events, these spurious signals may be interpreted by the drive as signals to turn on the spindle or move an axis a few bumps. The result could be dangerous or inconvenient depending on your setup. So, my understanding is now when the charge pump/watchdog timer signal is present, the drive knows that the computer is fully booted and giving it intentional (not spurious) commands.

So while having the charge pump/watch dog function is optional, it is a good idea to avoid some undesirable effects.

Thanks for all the help... (hope I got it right this time).

[Al_The_Man]

Watchdog timers and charge pumps have been used for decades and they were not intended as a primary source of E-Stop but were commonly used in the HARDWIRED e-stop string.
If an E-stop occurs it is customary to cut power to all powered devices and advise the controller that an E-stop has occurred, there is no reason it cannot be done safely.
At some point in time the W.D./C.P. signal has to be detected by hardware, it may as well be in the E-stop.
Al.

[phomann]

Watchdog timers and charge pumps have been used for decades and they were not intended as a primary source of E-Stop but were commonly used in the HARDWIRED e-stop string.
If an E-stop occurs it is customary to cut power to all powered devices and advise the controller that an E-stop has occurred, there is no reason it cannot be done safely.
At some point in time the W.D./C.P. signal has to be detected by hardware, it may as well be in the E-stop.
Al.

Al,

The watchdog timers and chargepumps you talk about have always been generated via independent hardware/software from the system they are monitoring.

The 12.5KHz signal Mach3 is generating does not fall into the Chargepump category that you described above. It has been incorrectly labelled 'chargepump', that's all.It is in fact an Enable output.

It is the same as the Mach3 input signal in the ports and pins config that has been incorrectly labelled as 'EStop'.

Cheers,

Peter.