How to make an x-y table starts to move from the same position each time a program is run.

[HAT]

My controller hardware consists of the PCI-7344 with the MID 7604/7602 Power Drive. I am able to move the x-y table from the same starting position when I run the program and for repeated scans as long as the power to the Power Drive is switched on. When I switch the power off and start a new scan the x-y table starts moving from the position at which the x-y table stopped at in the previous move. I would like to start the motion from the same position at any time I start running the program. I would also like to start the movement from the same position even if the position of either arms of the x-y table is altered physically (moved by hand accidentally while the cleaner is doing her
job!) before running the program. How can I do that?

[Amaury]

First, switching the drive on and off should not have any effect (excecpt maybe a few stray encoder counts) switching the controller on and off is what will cause you to lose track of position.

One posible solution is to use an anolog feedback rather than an incremental quarature encoder. With analog feedback your postion is absolute rather than rleative.

The other solution is to move to a known location. This is done by using either a home or a limit switch. 

Regards,
Amaury
NI Applications Engineer