Cushion Control - Siemens SIMATIC 505 User & Programmers Manual

5.6

Cushion Control

Cushion control is an attempt to maintain a consistent end-of-inject
position. Its goal is to eliminate rejects due to short shots.
The cushion control loop retains an actual screw position at the end of
injection profile and compares it with the required value (location V136 in
the download table). Any deviation is then added to or subtracted from the
shot-size setpoint. (i.e., the last step of the plasticate profile) on the next
shot. As long as the cushion control bit is enabled (bit 6 of constant 10 is set
to 1), the cushion control process keeps track of the deviation from one cycle
to the next. To start out with a new deviation or to disable the cushion
control feature, set the cushion control bit to 0.
The cushion control loop also includes the following features:
Correction gain (location V137 in the download table) — allows the
control loop to make corrections as a percentage of the deviation. This
allows making corrections in incremental steps rather than in one large
step. Correction gain resolution is from 0.01% to 320%.
Cushion values report — allows data collection for various applications,
such as safety checking for leaky ring, checking for lack of material,
SPC/SQC, etc. Cushion values are found in the Upload table in location
V57 for the adjusted cushion value and V58 for the adjusted last step of
plasticate profile position step-data.
Selected Functions 5-13