Relative positioning with the simple positioner

Hello all...

I'm trying to do some positioning with the relative positioning mode with my masterdrives MC inverters. Until now I've always used absolute positioning beacouse it was more convenient for my aplications so far. But now that I have a problem with not haveing enough outputs(for the inputs on the terminal strip) on my PLC to make an aplication for homeing. The reason for homeing is beacouse the actual position that the drives are in goes away after a reset or power down.
So I got this idea:
I'll store the actual positon in the PLC at all times. And if the machine operator will acedently turn of the power or if there will be an power outege he will use the homeing function on the operator panel and bring the whole machine in it's starting position. Here is where the relative positioning kicks in.I just multipy the stored actual position by -1 so that the drives will traverse backwards an go to the starting position. When they reach the starting
position the operator will have to turn of the whole machine and turn it back on.

But the problem is that even with the position setpoint being negative the traversing still goes fowrard.
I' ve read the manual an this is stated:
In the case of relative positioning, the sign of the position setpoint
determines the direction of movement.

Has any one had a similar problems?

Homing without a home sensor; Nice idea in theory but it does have some drawbacks. If the axis is moving during power failure, you'll loose precision due to: 1) latency of data transmission / storage and 2) over-run of the axis without power due to inertia. I would suggest that you need either a "home" sensor or an absolute encoder.

With regards to your other problem: If memory serves me, position is a DINT (?) ensure that your code uses *D and not *I when multiplying by -1 or even easier use NEGD. Also check the relationship between encoder counts and position units in the drive (sorry can't remember parameters, I normally do my positioning loops inside the PLC)

Nick