HP 13255 Technical Information page 32

132~5
Cartridge Tape MOdule
13255-91032/30
~ev AUG-01-16
filter. The filter integrates the pulses of the one-shot to help re-
duce the ripple on the feedbacK signal.
80th
tach feedbaCK polarities
are ted to the main 2-pole minimum phase Chebychev filter (2 poles at
200 HZ). This output is the servo FeedbacK Voltage (FDRK VOLTAGE).
The
fp.edbac~
Voltage waveform looks liKe the ramp command waveform with
extra ripple riding on it. This is risldual digital tach ripple that
is not filtered out
by
the 2-pole filter, but instead is filtered out
by the mechanical pole of the motor drive.
3.1.9 CTU DRlVE CIRCUITS - READ/wRITE PCA.
3.1.9.1 The CTU drive
circ~its
use the error voltage generated at the summing
junction as an input to the power amplifier determined by the selected
CTU fransport driving the motor for that transport.
3.1.9.2
A
2-drive tape system has two dc servo motors which must be selectively
driven. The selection of the motor to be driven is done at the low
signal level using junction field effect transistors. EaCh power amp
has two FFTs associated with it. The first
FET (Q6
or Ql0) switches
3.1.10
a power amp to the power amp summing junction. The R55 speed adjust
potentiometer and
~25
convert the Ramp Voltages (RAMP
VOLTAG~)
to
command currents into the power amp summing junction. In addition,
FDBK
VOLTAGE is changed to a feedback current by
R24
into the power amp
summing junction. The second
FET (05
or
Q9)
clamps the unused power
amp off so that leakage currents cannot cause the non-selected motor
to turn. The power amps are op-amps (U9) with high gain bipolar
emitter followers (07 and Q8 or Uti and Q12). The buffer power tran-
sistors are mounted on an aluminum heat sink.
the outputs of the power amplifiers are fed to the drive motors. The
return side of the motors come through a current sensing resistor
(R31). The motor current produces a voltage across this resistor which
drives current limit detector transistors Q13 and
Q14.
They clamp the
power amp through diode bridge CR8. C32 and C33 stabilize the current
limit feedback loop. The current sense voltaqe also is used for com-
pensation of the velocity feedback loop by locally characterizing the
response of the power amp through R29, R28, C34 and C35 back to the
power amp summing junction. This compensation gives the servo velocity
loop a 55-hertz bandwidth (With typically 45 degrees phase margin and
12 dB gain mdrgin).
CARTRIDG~
DETECT CIRCUIT - READ/WRITE PCA.
3.1.10.1 The cartridge detect circuit delays the CI signal from the CTU Trans-
port allowing time for the CIU Transport to mechanically stabilize
after a cartridge is inserted.