Installation manual

Danaher Motion Kollmorgen 08/04 Wiring
SERVOSTAR S Installation M-SS-001-01 Rev. T 37
4.9.3.2. Cable Lengths
The recommended cable length when using the SERVOSTAR to
source the encoder is no longer than 50 ft. (15 m). Long encoder
cables tend to have high DC resistance that may create significant
loading effects in the supply lines to the encoder. Please consider
this carefully when designing the system. An option that would
allow the use of longer lengths implements a separate supply
located at the motor to source the encoder. Quadrature signals
returned to the drive are differentially connected which normally
does not constitute a problem with longer cable lengths.
4.9.3.3. Resolution and Accuracy
A SERVOSTAR encoder-based system typically exhibits minimal
inaccuracies outside of the encoder itself. To get an approximate
total value the customer need only look to the specifications listed
for the encoder being used.
4.9.4 SINE ENCODER
The SERVOSTAR can receive an analog (or sine) encoder
feedback device to monitor the motor shaft position. As opposed to
a digital encoder, which generates incremental square-wave
signals, a sine encoder outputs analog differential sinusoidal
signals. These sine signals are quadrature-decoded and passed to
an interpolation circuit that breaks each 360° cycle into 256 parts
before passing it to the drive’s control board. Thus, the resolution
seen by the drive is 256 times the fundamental sinusoidal track on
the motor’s encoder. The advantage of this approach is the ability
to obtain much high encoder resolution while maintaining a
relatively low input frequency through the cable and into the
SERVO
STAR. The encoder interface includes three groups of
wires:
1. A/B (and complements) lines make up the encoder quadrature
signals. The signals are received differentially at 1 V peak-to-
peak amplitudes before being processed by the interpolation
circuitry.
2. The narrow Index pulse normally appears once per mechanical
revolution and indicates a known physical position of the shaft.
This pulse is received differentially through an op amp before
being squared up and sent to the control board.
3. Upon power up, commutation signals are used to communicate
coarse position information. The first three signal types give
approximate position information so the drive can commutate
the motor forward until the index pulse is found (There are
situations where the index signal is not available. Course
position information is used to commutate the motor
indefinitely). The fourth gives absolute information bypassing
the need for the index signal. They are: