Hi,
you are correct the manual I'm using has slightly different page numbers.
I'm using the line driver input pairs (37,39 and 41,43) but NOT the HighSpeed inputs (36,38 and 40,42).
The line driver inputs allow 500kHz signaling and yet I require 417kHz for my machine, so the 'plain' line driver inputs
are sufficient.
I have made circuit boards to interface between my BoB and the servo drives. I'll post a picture at a later date, I'm at home now and my machine
(under construction) is at work.
The wiring of CN1-11 and CN1-17 becomes clear in circuit diagram C9 on page 3-33. VDD (pin 17) is hooked to COM+ (pin 11) by a jumper in the plug.
All the digital inputs (DI's) become active low, per the example depicted in C9. In that particular case SON (servo on) is the DI depicted and if
pin 9 is pulled low (that is to COM-) then the servo is turned on. I'm using a transistor in my adaptor board to pull the input low.
Note that once you have wired pins 11 and 17 like this ALL DI's assume the same character. Thus the alarm reset signal, ARST, needs to be pulled
low, hence another transistor.
The two inputs, SON and ARST, in effect require three wires, one for each input, but also the COM- which establishes the 0V of the BoB/adaptor board
as the same potential as COM-.
But SON & ARST, on my machine nothing is connected and it works(?)
Yes, you can either hardwire SON to be permanently on, or program it to be permanently on, OR have a signal to it.....which is what I have done.
Its the norm in industrial practice to have a enable signal to each servo, and I have followed that practice, but its not strictly required.
If the servo never faults then you don't ever need to reset it and therefore ARST is not required. If the servo does fault and you need to reset it
in absence of a ARST signal you'll have to de-power then re-power the servo. I have elected to have a dedicated signal. On my Mach4 screen
I will have three LEDs indicating the fault status of each servo and a button to reset all of them.
Note that my controller has only one SON output and that enables ALL three servos. Also my controller has only one ARST signal an I'm applying
that to ALL three servos.
Each servo has its own fault signal however. If a servo faults I want to know which axis faulted, therefore combining all the fault signals together
would thwart that.
As far as the DO signal outputs. I have elected to wire CN1-27 to COM- CN1-14 and have just on wire attached to CN1-28 travelling back to my adaptor/BoB/
controller combination. You could as you say have two wires and therefore the transistor in the drive is isolated....but why? The transistor has
NO current limiting whether its isolated or not so the precaution about supplying external current limiting applies in either case. I elected a wiring scheme
that requires just one wire in the control cable rather than two, but that just a matter of preference. My scheme means that the DO is active low
which is symmetrical and 'philosophically' identical to my DIs, which is again my preference or 'style' if you will, rather than essential.
I was running a heavy roughing operation but within parameters that ran fine before - 6061-T6, 1/2" roughing mill, .2 RDOC, .5 ADOC, 20K RPM, forget exact chipload but it was reasonable, maybe .002". My theory is a servo alarmed, but the servos being improperly connected to the cnc controller by the manufacturer caused it to continue feed instead of estop retracting and this greatly compounded the problem. So sorry if I'm more than a little paranoid here.
A couple of things to consider here:
1) Limits. As you know the limits can be direct connected to the drive, and the drive is smart enough to stop but also prevent you from jogging even further
out of bounds to get the axis back. The drive could, if you program it, report the limit fault back to Mach and Mach could stop the other servos.
The other alternative, which seems simpler to me, and certainly more 'philosophically' familiar to me, is have the limit switches connected to Mach via the
BoB per normal and allow Mach to EStop all the servos.
2) Estop. You may have noticed there is a programmable DI called EMGS (CN1-30 by default) that if asserted will emergency stop the servo. You could wire your
machine such that if one EMGS is asserted it would stop ALL servos. I have not done so, for any particular reason, I'm quite happy with Machs EStop
arrangement as is. All my limit switches, the EStop panic button, the three servo alarm signals can individually set an EStop and the whole machine stops.
With regards the crash you had.....how have you setup the 'Following Error Window'?
A servo has a number of conditions where it faults, over-voltage, over-current and over-heat are usually immediate EStop conditions....but there are others
which are not immediate. Following Error is one. You can program the drive to fault if the actual servo position deviates from its commanded
position by a certain amount, called Following Error. If the actual position deviates from commanded position then you will at least have an inaccurate
part but worse may be that one axis lags the other two and you end up with a crash.
When the drive comes from the factory the Following Error parameter is set very wide so that when you are tuning and setting up you do not get whole
bunch of nuisance trips. It is intended that you will narrow the window when you have tuned up. Have you done so? What may happen is that an axis
can lag 1/2 a revolution or so BEFORE an alarm condition is generated, but 1/2 a revolution could also mean CRASH.
Craig