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RE: step-motor controller/driver connection
Responding to Tim Mooneys signal list:
I would suggest to use a DB 25 connector. The 15 pins are cutting it really
tight.
I think you should provide for the possibility to add the following signals:
1. amplifier fault
2. overtravel
3. CW limit N/O (in addition to the CW limit N/C signal)
4. CCW limit N/O (in addition to the CCW limit N/C signal)
5. a second home signal or second index pulse
Function of signals:
overtravel:
shuts off the power to the stepper driver (or the output to a DC-motor) if the
motor travels past the limits i.e. controller does not receive or disregards
limit signals or other malfunction.
CW (CCW) limit N/O:
At X9 NSLS we found that when you drive very slowly into a limit switch it is
possible to get a transient limit signal (=switch opened). As a response the
controller stopped the motion. But by that time the limit signal was gone (=
switch was closed again) and no limit indication light was on. You scratch your
head and ask why did the motion stop?
To cure this little problem we used a R/S-latch and a DTSP switch to create a
stable limit signal plus get some hysteresis. The R/S-latch goes up (= limit)
when the N/C contact of the limit switch closes for the first time. It stays
this way until one drives back enough so that the N/C contact closes again.
Then the latch goes down (= no limit). Spurious openeing of either contact does
not change the state of the latch.
At X9 we had the R/S-latch together with a buffer driver for the encoder
signals on a small PC-board on the device. Then we had only 2 limit signals to
transmit. But if someone want to do the latching on the distribution panel you
may need 4 limit signals.
second home signal / index pulse:
The encoder index comes once per turn. So your home signal has to be precise to
about 1/2 turn in order to identify 'home' in combination with the index pulse.
In a highly reduced drive or a high resolution drive one encoder turn may only
be 20 micrometer drive travel which is too small for a reliable home switch.
You may need another signal, once per turn, at a less reduced place of your
drive and have to combine 'home', 'index2' and 'index1' (from encoder) for
homing.
Responding to Mark Rivers' concern about the tiny, flaky fasteners for DB-
connectors:
You can get spring clip latches for DB-connector shells. Also, make sure you
get shells with sturdy metal strain reliefs for cables. Not the shells with the
flimsy plastic wedges or the one screw which is driven into the mantel of the
cable from the side. Those don't work, they always rip out.