Position Control Circuit - Siemens SIMATIC S7-300 Manual

Starting up the FM 354
7.3.4 Optimizing the position controller
Overview
In principle, the dynamic response of an axis is essentially determined by the
dynamic response of the variable-speed drive; there is not sufficient space to
discuss this topic here. But this latter dynamic response, in turn, is influenced
by the design characteristics of the machinery, such as friction, backlash, tor-
sion and the like. By feeding back the measured displacement, a position
controller generally closes the outermost loop of a controller cascade with the
following structure:
FM 354
Servo
Ref.
controller
position
Fig. 7-10 Position control circuit
Procedure
The following instructions are intended as an aid for practical situations.
Position controllers must meet a variety of requirements for various techno-
logical applications.
Assessment criteria for the quality of the positioning process can include:
In most applications, several of these criteria will be important, so that most
of the time the dynamic response of the controller can be optimized only with
a number of compromises.
Execute test movements as in Figure 7-11 during the optimization steps de-
scribed below.
7-18
Drive
Speed
Regulator
Good uniformity of traversing movement
Little or no overshoot at the target point for positioning
Short positioning time
A continuous acceleration (soft travel).
Motor and
Machine
Current
Regulator
Actual position
FM 354 Servo Drive Positioning Module
M
Tacho
Encoders