Installation manual

Danaher Motion Kollmorgen 08/04 System Operation
SERVOSTAR S Installation M-SS-001-01 Rev. T 63
7.2.1 ANALOG INPUT (ANIN)
The position, velocity, or torque loop can receive its command from
an analog voltage source and is selectable through the OPMODE
variable. The analog input to the SERVO
STAR is differential. This
means that the signals received at the two inputs are subtracted
from each other to create a difference, which is then used to
command the rest of the system. This type of input has a high
degree of noise immunity and, in many cases, will allow for ground
isolation between systems. This analog input also has a low pass
filter (ANLPFHZ) to prevent high frequency noise from entering the
system.
The input voltage from the differential receiver is applied to a
precise 14-bit Analog-to-Digital (A/D) conversion system. The A/D
conversion system is read by the microprocessor every 500 µs for
the position loop modes, every 250 µs for the velocity loop mode,
and every 62.5 µs for the torque (current) loop mode of operation.
Encoder-based units come with the additional benefit of a Dual
Gain (ANDG) input. When enabled, the system uses two 14-bit A/D
inputs to read the user-supplied analog signal. One input is a direct
reading of the ± 10 V signal, while the other incorporates a 2x gain
term. When the input voltage is less than 4 V, the 2x channel is
used to determine the input voltage, which extends the resolution to
a 15-bit equivalent. Above 4 V, the system uses the straight 14-bit
conversion. Special software algorithms are used to minimize
crossover distortion and add 0.25 V of hysterisis.
Analog systems often require scaling and offset bias. The
SERVO
STAR adds an analog offset (ANOFF) variable to this
reading, performs an analog deadband (ANDB) adjustment, and
scales it through either the position loop input scaling (GEARI,
GEARO), velocity loop input scaling (VSCALE), or torque loop input
scaling (ISCALE) before passing the data to the selected control
loop. The analog input (ANIN) variable indicates the analog reading
after the offset (ANOFF) and the deadband (ANDB) adjustments
but before the loop scaling. The ANIN variable range is ± 22500
counts (or mV).
The SERVO
STAR also offers an automatic analog input zeroing
function. Invoking the ANZERO command while the drive is
enabled or disabled samples motor velocity over a 32 ms period
and updates ANOFF accordingly to the analog input offset. This
command also incorporates an internal offset mechanism that has
finer resolution than ANOFF is capable of providing.