SIEMENS
11/7
Siemens D 21.4 · 2017
Motion Control Encoder measuring systems
Built-on optoelectronic rotary encoders
Absolute encoders
11
■
Function
Absolute encoders with SSI/EnDat and PROFIBUS DP (top), and
DRIVE-CLiQ and PROFINET IO (bottom)
Absolute encoders output an absolute angular position between
0° and 360°. They operate on the same scanning principle as
incremental encoders, but have a greater number of tracks. For
example, if there are 13
tracks, then 2
13
=
8192 steps are coded
in the case of single-turn encoders. The code used is a one-step
code (gray code). This prevents any scanning errors from occur-
ring. After switching on the machine, the position value is trans-
ferred immediately to the controller, travel to a reference point is
not necessary.
All absolute encoders are available in single-turn and multi-turn
versions.
Single-turn encoders
Single-turn encoders divide one rotation (360 degrees mechan-
ical) into a specific number of steps, e.g. 8192. A unique code
word is assigned to each position. After 360° the position values
are repeated.
Multi-turn encoders
Multi-turn encoders record the number of revolutions in addition
to the absolute position within one revolution. To do this, further
code discs which are coupled via gear steps with the encoder
shaft are scanned. When evaluating 12 additional tracks, this
means that an additional 2
12
= 4096 revolutions can be coded.
Interfaces
The following interfaces are supported by the absolute encoders:
Data transfer for absolute encoders with SSI interface
n
=
data word length (13 bits for single-turn and 25 bits for multi-turn)
T
=
1 ... 10 μs
t
cal
=
≤
5 μs
t
1
=
≤
0.4 μs (without cable)
t
2
=
17 ... 20 μs
Interface
Benefits
DRIVE-CLiQ
• Very high data transfer rates possible
• Advantages in time-critical applications
• Simple and quick automatic configuration using
electronic rating plates
• Fast and easy diagnostics with a single tool
• One interface for connecting drives as well as indirect
and direct measurement systems to the CNC.
SSI
• Advantages in time-critical applications
EnDat 2.1
• High data transfer rate, bidirectional
• Advantages in time-critical applications
• Incremental encoder sin/cos 1 V
pp
• Connection via SINAMICS Sensor Modules SMC/SME
PROFIBUS DP-V2
• Parameterizable built-on encoder
• Reduced wiring overhead in plants with a large
number of encoders
• Isochronous operation and direct data exchange
PROFINET IO
• Parameterizable built-on encoder
• Reduced wiring overhead in plants with a large
number of encoders
• Supports RT and IRT operating modes
• IRT (isochronous mode)
• 2 ports
n
×
T
t
2
t
1
t
cal
T
MSB
n
n
-1
n
-2
2
1
LSB
G_NC01_XX_00630
© Siemens AG 2017