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TABLE 3-4.
SERVO CIRCUIT FUNCTIONS (CaNT 'D)
Circuit Element
Function
Position Converter
Summing Amplifier
Load Gate
RTZ Gate
Power Amplifier
Velocity Amplifier
Velocity Integrator
Fine Enable and
Fine FF
Bit 0 Address
Register and
FF Slope
3-44
Uses the output of the digital to analog converter to develop
the coarse position error signal.
Generates a control signal to drive the power amplifier.
Con-
trol signal based on algebraic summation of Position Error and
Velocity Amplifier signal causes power amplifier to accelerate
carriage.
When Velocity signal exceeds Position Error, carriage
decelerates.
Provides a constant positive input to the summing amplifier.
Thi,s causes forward velocity of 7 ips.
Provides a constant negative input to the summing amplifier.
This causes reverse velocity of 7 ips.
Responds to summing amplifier derived control signal to drive
carriage mounted voice coil positioner.
Current feedback is
used. to stabilize the gain of the power amplifier.
Amplifies signal of carriage mounted linear velocity transducer
to provide an indication of velocity to the servo circuit. The
associated amplifier disable forces amplifier gain to zero dur-
ing a Power Off sequence (unload heads).
This is required so
that coupling between the positioner field and the velocity
transducer does not cause oscillation durinq movement of the
retracted position.
Provides an integrated representation of velocity between each
of the
~ast
127 track pulses of a seek.
Integrator is clamped
off to gain of zero at all other times.
Inteqrator output is a
sawtooth waveform applied to input of desired velocity function
generator between each track pulse to fill in or smooth out the
stepped siqnal of the O/A converter (received via the position
converter) •
Fine enable monitors integrated velocity.
When difference
counter is 1022 and fine enable (Velocity integrator output)
exceeds 1.28v, it indicates that there is one-half track to go.
Fine FF sets to enable fine gate and clear coarse gate.
This
switches Position Error input to summing amplifier from desired
velocity (coarse gate) to fine servo (fine gate).
Fine also
has the following effects:
a. Turn on inteqrator clamp to switch off velocity integrator.
b. Enables on cylinder detection.
During load or RTZ sequences, both the fine and coarse latches
are cleared.
This disables both the fine and coarse gates so
that motion is under control of load gate or RTZ gate.
Used to select proper track servo signal phase for use as Fine
Servo signal (signal controllinq servo loop as last track is
approached and carriage is stopped).
If bit 0 is not set, the
seek destination is an even numbered track and the track servo
signal will be inverted for use in stopping the carriage.
If
bit 0 is set, an odd track is identified and track servo is not
invert~d.
Register bit content is placed in Slope FF which
performs actual gating.
93318200
A
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