On Friday, May 27, 2016 at 6:59:46 AM UTC-4, Jim Wilkins wrote:
"rangerssuck" wrote in message
...
A customer has a very large, very old (and pretty dirty) machine that
needs some help. It is a multi station drilling and tapping machine.
The production items sit on 4" square pallets spaced roughly 8" center
to center. There is a microswitch that is activated by contact with
the leading edge of a pallet. The switch causes the drive motor to
stop, and the drilling & tapping to begin.

Their problem is that the stopping point is somewhat variable, and
they thought that if I replace the microswitch with a prox sensor, all
would be well. So, I went down there and had a look, and found a good
place to mount the prox sensor and a brush to sweep off whatever
debris was there (and maybe an air jet for good luck). Then, I had a
talk with the plant electrician.

The electrician, who really knows his stuff, pointed out that the
controls stop the motor, but it's really a hydraulic motor that drives
the system, and maybe it coasts a little when the electric motor is
shut off. Also, he pointed out, that the offset changes during the
day, maybe as a result of the fluid heating up. So, my not-at-all
educated in hydraulic motors mind started thinking, what if, instead
of shutting of the pump, what if we installed, right at the motor, the
hydraulic equivalent of a DPDT relay that would disconnect the motor
from the pump and put a short across the motor?

Does that make sense, would it (as would a DC motor) stop on a dime? I
have googled a bit and I believe I have seen such circuits, but I'm
really pretty much in the dark about such stuff. If it DOES work, do I
have to worry about overpressure in the lines? I haven't seen the
machine run, but I'm told that a) it doesn't move fast and b) it
doesn't move far.

The pump motor is 3-phase, so I suppose I could install a VFD (they
probably have extras on site) and use a second prox sensor to cause
the speed to ramp down, but it would be better if I could just stop
the motor. And, there really isn't a good place to mount a magnetic
brake.

As always, all thoughts (especially kind ones) are welcome.

======================
https://www.toro.com/~/media/Files/T...9sl.ashx?la=en

--jsw

Though I think this problem is pretty much solved (ask me again in a week or so when I install the controls), this is a GREAT read. I will print it out and keep it in my reference library. It's much more clear than others I've seen, with illustrations of actual parts along with schematic symbols.

Thanks for the pointer.