linear machine control

need help. machine has ab slc(5/03 16k), spectrum high speed counter(8 channel with two quadurature scales and one quadurature rotary), accurite scales. travel of 100" at approx 3"/sec. hydraulic motor driving ballscrew. 640 counts per inch.

1. every time i reset machine it adds approx 10 counts. (it resets against a limit switch)

2. small impacts to the machine in any direction adds about 5 counts.

3. stop points are +/- 1/2", need more accuracy.

where do i look....scale wiring? counter card? slc speed? scale? program? should i abandon slc and go to pc? should i abandon hyd motor and go to servo or stepper?

Have you checked for mechanical backlash in the system? You won't get reliable positioning if the coupling on the ball screw is loose.

Aside from that, you don't provide any information about the hydraulic motor, or the load that's being driven. How much mass are we talkin' here? A light-weight load will be more susceptible to "bumps" than a heavier one.

Any motor can move a load from point A to point B, but what you seem to want is the ability to hold that position, and that says "servo". A stepper can provide some holding torque, but is limited by the strength of it's magnets.

Perhaps you need a brake or clamping mechanism on the load, so the rotor of the hyd-motor is held stationary when no movement is taking place.

Good luck!

TM