Siemens SIMATIC FM 453, Manual

Page: 259 / 380

9-59
FM 453 Servo Drive / Step Drive Positioning Module
C79000-G7076-C453-01
9.6 Encoders
One of the following encoders must be connected to the measuring-system
interface of the FM 453 (see Fig. 1-1).
S
Incremental encoder
S
Absolute encoder (SSI)
Paths and positions are displayed in 10
–3
mm, 10
–4
inches or 10
–4
degrees, as
selected with machine data item MD7.
The path resolutionof the machine axis obtained by the encoder is calculated
within the FM from machine data MD11 to MD13.
The prerequisite for achieving a given positioning accuracy is an n-fold im-
provement in path resolution by the encoder.
Recommended Values for n
Minimum Optimum Maximum
2 4 10
For that reason, when configuring a given specific application, select an en-
coder that meets the desired positioning accuracy requirements.
The known design data for the machine axis and the desired measurement
resolution A:
A =
1
n
Positioning accuracy (mm), (inches), (degrees)
yield a calculation of the necessary pulse number per encoder revolution ac-
cording to the following relationship (taking a metric measuring system as an
example):
Incremental Encoder Absolute Encoder (SSI) Stepper Motor without
Encoder
I
G
=
S (mm)
4 i
GS
A (mm)
S
G
=
S (mm)
i
GS
A (mm)
S
S
=
S (mm)
i
GS
A (mm)
Overview
Encoder Selection
Description of Functions