Hi,
The need is to use a bipolar + & - 10v analog signal from two Mach4 DRO axes to tell the servos to move.
Why do you need analogue voltages?
Most modern servos can still be driven by an analogue voltage but that requires a feedback capable motion controller.
In this setup the encoder is still hooked to the servo drive, as I explained earlier the encoder is required by the drive
to compose it output. The encoder, or some derived signal from it, is outputted to the controller. The controller
closes the loop. The controller outputs a precision analogue voltage and the servo turns at a speed determined by the
voltage. The servo is in velocity mode.
The same servo could be in position mode. In this set up the position is commanded by Mach4/Galill as a series of
step/direction pulses. The servo drive accumulates those pulses and therefore knows where is it supposed to be.
It compares where it supposed to be to where it actually is (by the encoder) and drives the servo accordingly.
The PID tuning is done entirely within the servo drive. The controller has no need of the encoder signal at all.
If Mach4 decides that it needs to drive an axis 100mm in the +direction it will plan the trajectory as a series of
P(osition)V(elocity)over T(ime) data packets in 1 ms slices. The motion controller will convert the PVT data to step/direction
pluses for all servos.
At the beginning of the move Mach will plan to accelerate the axis smoothly before reaching it ultimate speed. The servo
and drive are assumed to be capable of the acceleration and ultimate speed required. If the servo can't keep up with the
planned trajectory then the drive will fault 'following error'.
In this way Mach4/Gallil are an open loop controller only. It provides the trajectory which is converted to step direction pulses
and the servo just goes there. If it can't it will signal that with a following error fault. This is a more modern control setup. It means
that the motion controller does not have to be feedback capable. The only feedback capable controllers that work with Mach4
(Gallil, Hicon Integra, CSMIO/A) are all expensive, the cheapest is 600Euro. By comparison the plain open loop step/direction
motion controllers (Ethernet SmoothStepper, UC300, UC00, UC100,57CNC, 57CNCdb25,PMDX-411, PMDX-242) range from
$120 to $250.
The Ethercat solution which is being developed for Mach4 requires two pieces of software for your PC only. RTX64 by
Interval Zero provides a realtime core capability to your non-realtime Windows PC and KingStar provide the plugin
that makes Mach4 an Ethercat Master. The servo drives (all Ethercat slaves) are connected by a daisy chain of Ethernet
cables.......and that's it. No expensive hardware controller required!
You may have noticed that you can hook limit switches to your drive, you don't have to hook them to the controller at all.
The servo drive is smart enough to handle that. It is in fact a required feature that any servo drive must be able to do
if it is ever to be Ethercat slave capable. That is to say that the servo can act autonomously.
Craig