culmulative error in x axis

[multiplex]

some background..

i have 4 viper 95 drives. 2 for the y axis, that are slaved. 1 for x, 1 for z.

I'm using mach3, with a simple BOB to drive the drives

i'm running a program that does a large pocket (20" x 10" x .6"). I'm stepping down by .09" in z each time. I'm stepping over in x, y by .375"

At each Z increment point, you can see that the X axis is getting off by approx .008" in the positive direction.

The Y axis however is dead on.

What are some possibilities? All drives have the same parameters, rapid speeds and acceleration.

For the moment, i'm resetting my x position from the limit switch on each step. Thats fine for now, but i'd like to find a better solution

I'm using single ended US digital encoders, but I would suspect more error if it was due to noise.

[Larken]

You are loosing steps in the Encoder or Step input. Most likely the encoder

Zero the drive (turn off power then on) and Zero mach. Make a mark on the motor shaft.
Run your program, then tell the machine to go back to zero.

Read the drive's M command and it will show Encode and Step input counters.

( The M and S are going to be close since the drive is trying to make the zero)

If the S setting isn't zero then you are loosing step input pulses between the BOB and drive.

If the S is zero and the motor shaft is off, then you are loosing encoder counts.

Is it a single ended or differential encoder ? Are you using twisted pair cable
?

Larry K