PMDX 126 REV C, setup with AM882 Fault Detection

[dachopper]

Hi guys,
I am in the process of upgrading my mill to both the PMDX 126RevC, and changing to digital AM882 leadshine drivers. I am wanting to integrate the 882 ability for Alarm, to halt the machine and software.
From what I understand in the 126 manual, can I run from the FAULT, to ALM+ driver1, out ALM-, into ALM+ driver 2 , out ALM- etc, out the last driver ALM- into J13 GND pin, and set all the Drivers to fault active low condition ( so they are in series, with active low - to match the 126 fault active low - fault pin.

Question 1 - where is the fault signal coming from ( does the Fault PIN - have it's own + signal ) that is grounded by ALM+/_ switch if a drive detects fault?

or

I noticed in the AM882 schematic which only shows a single drive, in Common Anode they have linked the Pul+ to VCC, Dir +, ENA + and ALM + all in parallel linked together.    Or in the other schematic they have Pul + with ALM +, and all the PUL/DIR/ALM- linked to go to GND together. I get the impression if I want to hook up 5 drives to signal a fault condition, this is not going to work.

So is it possible to just hook up the ALM + / _ in series, coming from the fault pin, and into a GND pin, or do I need to attatch the first drive Pul + signal before the ALM+ termninal?

Should I ground the PUL- and DIR- on the J13 GND as in the AM882 guide along with the ALRM-, or run these seperately to their respective J3/J4 plug GND ( Ie keep the ALM -going to  GND in the J13 area, and the Pul/Dir GND in their respective plug areas ( not a common GND? ) If the GND is common, is there a problem with me daisy chaining all the PUL-/DIR- together between 5 different drives, running to the same J13 GND? )

Or should I be using ther ERR+ and ERR- on J13 somehow?

So confused!

Still!

Nick

[Steve Stallings]

Because the ALARM outputs of these drivers are optically isolated, you
can use either the Fault input or the ERR+ and ERR- inputs to the
PMDX-126. Both will result in an Emergency Stop signal going to the
Mach software. In either case the drives should be configured for the
Alarm signals to be configured as LOW active and should all be
wired in parallel, not series. Trying to use several of this style of
isolated ALARM outputs in series results in too much voltage drop
and erratic operation.

The Fault input of the PMDX-126 has an internal pull up to 5 volts.
You would connect the ALARM+ from the drives to the Fault input
of the PMDX-126 and the ALARM- from the drives to the GND next
to the Fault input on J13 of the PMDX-126.

The ERR+ and ERR- inputs require you to supply the external
power source and allow you to wire it so that it acts on a High
or on a Low signal. It provides isolation and can be used with
24 volt control signals. It is recommend for drivers which do not
provide isolated Alarm outputs, such as the ERR/Res outputs of
a Gecko servo driver.

You should be aware that some drivers will output an ALARM if
they are not enabled. Trying to use a signal from the PMDX-126
to provide the enable signal from the PMDX-126 in such cases
may result in a "deadly embrace" where the ALARM will not go
away because the drive is not enabled, and the Enable will not
activate until the ALARM is removed. When using the isolated
ALARM signal from these drivers there are no ground loop
issues to consider because they can be entirely separate circuits.
The wiring of the Step and Direction signals is not dictated by the
ALARM wiring and it is OK to have the GND for the ALARM signal
be the isolated machine side GND while the Step and Direction
signals are referenced to the PC+5 or PCgnd system. Indeed,
this is how it should be done with these drivers.

You can wire the Step (Pulse) and Direction signals to use a
common PC+5 to the + inputs of the driver or a common PCgnd
to the - inputs of the driver. The active edge of the step pulse
will be affected by your choice. While it is acceptable to have
multiple drive sharing the connection to PC+5 or PCgnd, it is
often desirable to run them individually so that it is easier to
disconnect one driver without affecting the others.

[dachopper]

Thanks Steve - this is contrary to the AM882 schematic - in all of those pictures, the ALM+ is also connected to the  PUL+ signal before the fault pin.

Are you saying effectively the Fault pin provides the signal, so no connection to the PUL+ signal is required ? If we have 5 cards wired in parallel, how does the PDMX know that one of them is fault low, when the other 4 aren't? Ie - won't the signal go to ground, as much as bypass that driver and still go to board ground? Where as series the signal is cut?

Sorry for all the questions.

nick

[Steve Stallings]

The diagram in the AM882 manual makes assumptions that are not
true for the PMDX-126, specifically that the input of the breakout
board does not contain an internal pull-up, which in fact it does.

The ALARM output of the AM882 is an opto-coupler whose two
output connections on ALARM+ and ALARM- are totally isolated
from everything else until you connect them somewhere.

With the 5 ALARM signals in parallel, any one of the becoming
active will provide a ground to the Fault input of the PMDX-126.
This is because the  ALARM+ signal is an "open collector" output
which can pull to ground but does not supply any voltage output
to take the signal high. It acts somewhat like a mechanical
switch. The PMDX-126 will see the Fault signal go to ground if
any one of the drivers activates its Fault output, but will not
know which one did it.

[dachopper]

Thanks Steve, that makes sense to me know.

Regarding the Common +5V_gnd or Common PC_gnd, I didn't really find any literature talking about the pro's or cons of each - just that either can be setup for the AM882. Is there one I should be using over the other for my setup? and do I need to change any software config - based on which way I setup the driver connectors like active edge rising or falling, or has O/C or PNP got nothing to do with the pulse edge timing or any other setting?

Also - do the connectors on J12 ( pin 11 to 15 ) also have pullup resistors, so that for example, I run the X axis limit switch( NC ) from pin 9 - through the NCswitch and back to pin 10 on J12 to complete the circuit, and just setup in the software pin 15 port 1 = X limit active low?

thanks for the advice,
Nick

[Steve Stallings]

Most motor drivers including the AM882 units describe their signal
response in terms of rising or falling current flow into the optocoupler.

For Mach configuration you should leave it set to a red X in the active low
column in the configuration chart, and wire the output signal from the
PMDX-126 to the PUL+ and PCgnd to PUL- so that a signal transitioning
from a logic low to a logic high will result in rising current into the optocoupler.
This corresponds to Common PC_gnd. Other methods will also work, but I
chose to explain this one because it is least confusing.

The input signals on J12 do have pull-up resistors to +5 volts. You can connect
your signals from a normally closed switch from the input to Gnd and leave
the Mach configuration at the default red X for Active Low (meaning active high).

[NoellEagan]

Hi...i am a new user here. As per my knowledge the Fault input of the PMDX-126 has an internal pull up to 5 volts.You would connect the ALARM+ from the drives to the Fault input of the PMDX-126 and the ALARM- from the drives to the GND next to the Fault input on J13 of the PMDX-126.