Siemens SIMATIC FM 453, Руководство пользователя

Страница: 258 / 380

9-58
FM 453 Servo Drive / Step Drive Positioning Module
C79000-G7076-C453-01
Machine data item MD9 defines the value by which the FM 453 recognizes
the end of the rotary axis.
This value is the theoretical maximum that the actual value can reach. At this
value, display of the actual value switches back to 0.
The theoretical maximum, however, is never displayed, because it is physi-
cally located in the same position as the start of the rotary axis (i.e., 0).
Example:
The following example in Figure 9-4 illustrates the behavior of the axis.
Assume you specify a value of 10,000 for the end of the rotary axis.
The value 10,000 will never be displayed. The display always rolls over from
9,999 to 0.
If the direction of rotation is negative, the display rolls over from 0 to 9,999.
Rotary axes are subject to certain restrictions in the choice of encoder/gear-
box/motor, as shown in Figure 9-5. These restrictions arise from the need to
reproduce the actual position accurately over several revolutions when refer-
encing (with incremental encoders or on POWER OFF/ON with absolute
encoders). See also “Dependencies”, Section 5.3.1).
Encoder type?
Incremental encoder
Absolute encoder
Type of
reference point approach?
Single-turn or
multi–turn encoder?
MD18
w
4
MD18 < 4 Single–turn
Multi–turn
Any rotary axis
cycle Condition:
Condition:
Condition:
S
RA
= n S
GZ
n = 1, 2, 3
S
GZ
= 2
n
S
RA
n = 0, 1, 2
S
GZ
= 2
n
S
RA
n = ...–2, –1, 0, 1, 2, ...
Examples:
Rotary axis cycle S
RA
Encoder cycle S
GZ
or or
e.g.: 2 rev
e.g.: 4 rev
Fig. 9-5 Encoders on rotary axes
Rotary Axis End
Encoders on
Rotary Axes
Description of Functions