> On Sunday 13 October 2019 19:46:55 Kenneth Lerman wrote:
>
> > Hello All -- especially Gene,
> >
> > I've seen many posts on the lists regarding breakout boards and
> > dealing with issues regarding slow opto-isolators. I have a question:
> >
> > Is anyone using: ISO776x
> > <http://www.ti.com/lit/ds/symlink/iso7760.pdf> devices?
>
> I've seen that pdf before, but in the cases where I've simply bypassed
> them, I had good solid, noise free sources to start with. If I use a
> BoB, its a Saintsmart, simply because there is not any opto's in their
> output path, and most outputs goto the input opto's of a stepper driver,
> which I've found is a bit faster than the average bear. A 2M542 for
> instance can, if the drive is good rail to rail stuff, be driven to
> about 375k steps a second before it miss-behaves! That will turn a
> nema-23 motor rated for 270 oz/in, to over 3000 rpms if the supply
> voltage is pushing the 2M542 at around 42 volts. Nearly 2000 revs at 28
> volts.
>
Hi Gene,
I think you have your units mixed up here. There is no way you will get a
stepper motor to turn at 3000 RPM with a 48V supply. They just can't do that
physically.
The Bergerda AC Servos run 3000 RPM and with a 2500 line quadrature encoder
(10,000 edges per second) means a 500,0000 hz step rate is needed to achieve
that.
But, the Bergerda AC Servo drive has a dual purpose stepping input that can be
wired as RS422 or as opto-isolated up to 24V. According to the Bergerda motor
manual the TTL opto isolated inputs are not suitable to that high a step rate
while the differential RS422 inputs that are good to that speed.
So regardless of what sort of PC based step/dir interface you are using, if you
want isolated 500kHz step rates then your BoB needs to have something like the
ISO7760 in front of the RS422 differential drivers. I don't know if the
Bergerda differential inputs are isolated from the high voltage inside the
driver.
The iso7760 is nice device. The ground on the input side can be connected to
the PC ground and the output ground to the low voltage CNC machine control
ground. Note the data sheet also lists that half the units inside the package
(7763) can be reversed so it makes an ideal single isolator package for
multiple RS485 or RS232 circuits or a BoB where you want to isolate the PC
parallel port. Had I known about this part I'd probably have used it instead
of the multiple devices below.
What I've used are HCPL2631 and initial testing shows they can handle the step
rates for the Bergerda AC Servo. This module can be configured with jumpers to
interface to either RS422 step/dir/enable and fault signals for the STMBL Servo
Drive or to RS422 step/dir and opto-isolated enable/fault for the Bergerda AC
Servo Drive. Additionally this little board also creates the 5V for the MESA
7i92H and two Open Collector signals to reset the HP_UHU DC servo drives in
case of a Fault from one of them. Those are simple, and very slow, 4N25
devices.
http://www.autoartisans.com/mill/StepDir2STMBL_SCH.pdf
I built 3 of them.
http://www.autoartisans.com/mill/StepDir2STMBL.jpg
Should be installed this week once I make up some cables. Too many projects.
Never enough time.
John
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