Servo Problems

Problem:

Servo system appears normal, but servos do not move.

Possible Cause:

Either the acceleration value or the velocity value is currently set to 0. This will cause the LM628 to signal a completed move, but not move the servos. This problem typically arises when the acceleration value is loaded before the velocity value during initialization. When the system is started, the LM628 comes up with both the velocity and acceleration set to 0. By loading the acceleration first, the requirement that the acceleration value be less than the velocity value is violated and the acceleration is left at it's current value, 0. Another possible cause is that the axis amplifiers are shut off, or that the front panel Manual/Auto switch is in the Manual position. Inspection of the ZY Status Word will show if one of these is indeed the cause of the problem.

Remedial Action:

Place the ABV command before the ABA command during initialization. Use the AXIS command to turn on the servo amplifiers. Ensure that the Auto/Manual front panel switch is on.

Problem:

Servo move takes a long time to complete, or do not complete at all.

Possible Cause:

The servo system is not properly tuned, causing the servo motors to oscillate about their destination. This problem usually occurs during operations that require the servo to settle on target, such as FHM, CWT, WAI, VHM or SCN.

Remedial Action:

Tune the servos.

Problem:

Some high level commands fail with the message ``axis n not homed''.

Possible Cause:

The servo axis n is not homed. Coordinates used on this axis will be invalid, so operations that require absolute servo coordinates will fail.

Remedial Action:

Execute FHM for that axis