Replacing a Manual Pulse Generator with a PLC.

I am working on a project that will likely incorporate a small CNC mill system as an X/Y/Z motion system carrying a camera rather than a Spindle motor.
My intention is to take digital images of samples over time. These samples will be arranged on a grid. The observation period will be will be hours, if not days, with multiple sets of photos taken.
With this in mind I am thinking that we would mount a camera in place of the spindle on an inexpensive CNC router system and create a plc program that would move the camera some number mm in the X/Y/ and maybe Z axis some number of times and the return to the original starting point and wait for some amount of time and then do it again. I can program the camera to image and store a series of photos each time. However I am not familiar with servo control.
I believe I can create a circuit that will pass the MPG to the router OR I could pull specific lines high or low to emulate the physical MPG controller using a PLC.
My question is how I reverse the servo for the return trip.
I see plus and minus on the MPG depending of direction of knob rotation. But I do not know what is happening with clockwise vs counter clockwise. Is there a plus movement signal wire vs a minus movement signal wire? Is the polarity of the pulse inverted or maybe there is possibly a directional bit?
Not looking to you for a tutorial, but can someone point me to a good tutorial that’s relevant to my question?

Thank you for taking the time tore read my question.

Specfic task. You need to prevent control system against entering energy saving mode.
I would try just a part program. Movement and dwell, no spiindle rotation.
Speaking about manual control knob most likely it is sin - cos sequence, two meanders. It is simpliest solution at least.

Forget the MPG, not needed. There are 2 inputs on each stepper driver: 1 Step bit, and 2 Direction bit. Both are digital inputs. You can run these with 6 outputs from the PLC for 3 axes.

If you have more questions we'll be here.