Zapi EPS-AC0 SWs&ENC - Fighting the Dither

AEMZP0EA - EPS-AC0 SWs&ENC - User Manual Page - 35/95
U It is strongly suggested to connect to the truck frame all the parts of the truck
that can get in touch with the operator (who is most of the time the source of
ESD). For example, we strongly suggest to connect the stepper motor frame
to the truck frame.
3) PREVENTION: Another important issue is the storing and handling of ESD-
sensitive electronic parts. Then, ensure the operator is grounded; test grounding
devices on a daily basis for correct functioning. This precaution is particularly
important during controller handling in the storing and installation phase.
Use anti-static containers when transferring ESD-sensitive material.
7.10 Fighting the dither
In Closed Loop application with potentiometers, the quantum nature of the Analog to
Digital conversion, in combination with the noise of the analog signal, generates
dither on the steered wheel. This is a continuous rolling of the steered wheel from a
little bit right to a little bit left around the commanded position. When encoder and
toggle switches are used as feedback sensors, only the potentiometer in the tiller
side (SP POT) have noise and contributes to the problem.
There are some countermeasures to reduce or neutralize the dither.
1) Use shielded cable for the connections of the potentiometer (SP POT). The
shielded cable reduces the noise in the wiper voltage. Connect the shield to a
GND pin of the eps-ac0 connectors. See also SET HI RESOL AD (11.4.5.3).
2) By using a FB ENC (instead of the FB POT) as feedback sensor for steady state
condition, no noise in the encoder counting occurs. When the Encoder is
stopped in a position, the Encoder counting is absolutely constant. Encoder is
not involved in the dither generation.
3) Reduce the gain of the Closed Loop. It means KP and POS. ACCURACY
parameters must be decreased. When the gain reduces, the modification of the
position error due to noise, are less amplified giving less dither; but less
accuracy is got in the final pursuing at the wished position.