Delta MMC120 - Manual (Page 69)

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dead band eliminator circuits that make tuning easier.
3. If you have a servo motor and a ball screw, is there any backlash? Backlash
produces a dead band when the axis changes direction, so the controller will tend to
oscillate around the dead band.
The axis oscillates
This problem could have several causes. The first items to check are:
1. Make sure that the DEAD BAND ELIMINATOR value is not too high.
2. Try reducing the PROPORTIONAL , INTEGRAL , or DIFFERENTIAL GAINS .
The axis does not finish moves or moves differently than expected
This can be caused by the P/C issuing unintended commands to the module. Use the
Command Log to monitor commands sent by the P/C to the module. Confirm that only
the expected commands are being sent.
Hydraulic System Problems
These hydraulic system problems can make system tuning difficult or impossible.
Nonlinear Valves
A valve is linear when the flow through it is directly proportional to the input signal over
the entire range of the input signal:
It is nonlinear when the output is not directly proportional to the input. You may find two
types of valve non-linearity:
Overlapped valves - Oil does not start to flow through these valves until the spool has
moved some distance. This causes a dead band in the system, where small amounts of
drive do not produce motion. Overlapped valves are designed for manual and on/off type
control and are not suited for servo control. These valves should be replaced with non-
overlapped valves.