We are driving a Gantry system with two X axes and a Y crossbeam.
The system is a 7344 motion card, Parker Trilogy Linear motors, and Accelus amplifiers.
We are using linear encoders with a 0.5 micron resolution.
One X-axis is on Axis1 of the 7344, the other X axis on on Axis2 and the Y axis is Axis3.
We have been driving the two X Axis using the master/slave function with the gearing VI's and a gearing ratio of 1:1.
Master/Slave is selectable in that either can be master and the other is slave.
For the past two months we have been having anomolous readings in the final positions of the slave axis.
We had thought that it was our lack of experience with these systems.
As it turns out, we are now convinced that there is a problem with the system that may be a bug in the driver (or elsewhere in the motion code).
For reference, X' is Axis1 on the 7344 and X is Axis2.
The typical configuration was for X to be master and X' to be slave.
For any motion (although most noticeable with longer than 20 inches)
With X as master, X' was ALWAYS (between 1.5 and 2.0 *10-5 * distance counts) behind X.
With X' as master, X was ALWAYS (between 1.5 and 2.0 *10-5 * distance counts) ahead of X'.
That is a count of 30 inches (1,524,000) would lose (or gain) approximately 25 counts.
Although this only amounts to 0.0005 inches (1/2 of 1/1000),this error was cumulative in that the next move would also add that error.
This may warrant some investigation on the part of NI.
