Siemens SIMATIC FM 452, Manual

Page: 22 / 210

Basics of Cam Control
2-8
FM 452 Electronic Cam Controller
C79000-G7076-C452-04
2.3 Hysteresis
Definition
Mechanical disturbances on the axis can cause changes in the actual position
value. If the actual position value fluctuates around the edge of a cam or within an
active cam with only one activation direction, this cam would be continuously
activated and deactivated. Hysteresis prevents this switching.
A hysteresis is dependent on the actual value and applies to all cams. It becomes
active as soon as a change of direction is detected. Hysteresis also takes effect
even if no cam is set at the current axis position.
Rules for the Hysteresis Range
The following rules apply to the hysteresis range:
•
Hysteresis is always activated when there is a change in direction.
•
Within the hysteresis, the indication of the actual value remains constant.
•
The direction is not changed within the hysteresis.
•
Within the hysteresis, a distance cam is neither activated nor deactivated.
•
Within the hysteresis, a time cam is not activated; an active time cam is
deactivated when the set activation time elapses (even within the hysteresis
range).
•
After leaving the hysteresis range, the FM 452 determines the following:
– the actual position value,
– The current direction of motion of the axis
– the current states of all cams
•
The hysteresis range applies to all cams.