PMDX424 - Controling pneumatic Z-axis?

[beezerlm]

Posted this in the Mach4 forum but maybe this is a better place:

"I am in the process of re-retrofitting a Jig grinding machine I did a long time ago.  The machine is sort of a hybrid between the old control and Mach3.  Mach3 controls the X,Y and U (wheel outfeed) Axis.  The old control still handles the Z axis which is pneumatically driven with glass scale feedback.  I would like to take control of the Z in Mach.  This axis does not need to be precision controlled, I just need to be able to set and upper and lower limit so the Z axis will reciprocate between those limits.  I have done something similar in LinuxCNC using a Moog hydraulic servo valve with glass scale feedback to control the position of a hydraulic cylinder, but I have not done this in Mach3 or Mach4.

I am thinking I should take control of the relays that operate the pneumatic solenoid and use a script to monitor the position of the axis.  Once the position hits the upper or lower limit it would activate the relay to change direction.  Does this sound feasible? Is there a better way to do this?"

I understand that Mach4 only monitors the signals at 10Hz. The axis moves at a max of 250ipm. Would there be a better way to set this up with the PMDX424?

Here is a pic of the current control:

[Bob at PMDX]

Not possible using the glass scale and up/down solenoids.  Not reliably, anyway.  That kind of function belongs somewhere that can handle real-time events.  Windows is not that environment.

The only way to have Mach4 control this is to convert your Z axis to stepper motor control and have Mach4 control it that way.

Bob

[beezerlm]

Thanks Bob.  Is the PMDX424 capable of reading the encoder signal to display as a DRO in Mach 4?

[Bob at PMDX]

Yes, in the upcoming plug-in release which should be out in a day or two.  The PMDX-410/422 rev B or C and the PMDX-424 will support an encoder connected to the "InputA" and "InputB" inputs.  The encoder value can be displayed on a DRO.  It can also be used as an MPG to jog the machine (I realize that is not your intent here).  Additional Lua or screen editing is required to select the jog axis.  If the encoder has an index pulse, it can be used to measure spindle position and RPM.  Spindle RPM from encoders without index pulses will be supported in a future release.

Bob

[beezerlm]

Bob - Could you post on example on how to set up a DRO with these inputs when the new plugin is released?

[Bob at PMDX]

Yep.