Laser raster?

At long last.. finally managed to log in.

Right...
I too have been looking at the above link pondering just how little I know.

I have set up a cartesian movement with a laser diode and interfaced the laser on off signal to Z axis up down movement whihc is miniscule ( equivalent to one count of the encoder.

The idea works a treat but... the movement is not smooth across the length of stroke . Every time the laser turns on or offthe movement either accelerates or decelerates.

This is a real pain in the neck. Wastes time whihc is already protracted in terms of painting with the laser dot.

I have now purchased XY galvanometric movements with positional feedback as a part of the drivercard. I would like to bring out the positional signal( an analogue signal ) and present it to linuxCNC via a suitable interface. I would like to add I am presently using mesa 5I20 and 7I33TA cards whihc do ot offer an analogue IO capability to the best of my understanding.

I can use the galvanometric movement in a closed loop with a setpoint from the 5I20 but without 5I20 "knowing" anything about the galvo position.

Is anyone aware of an interface card akin to 5I20 which might offer analogue input capability for the positional signal feedback?

I generate the raster information by creating an outline of the area in question and then filling it in with either X or Y strokes and converting strokes of the pen to G code .