Fujitsu M2361A Customer Engineering Manual page 152

m. Target speed generator
The target speed generator, consisting of the DA converter,
non-linear circuit, and switching circuit, determines the carriage
traveling speed during seek or rezero operations.
(a) DA converter
The DA converter converts the digital positional difference
(held to 144 when the number of remaining cylinders is not less
than 144) stored in the difference register. The number of
cylinders over which the carriage is to be moved is set and is
decremented whenever the track crossing pulse is detected,
decreasing the analog stair step waveform as the carriage
approaches the desired cylinder.
The DA converter is also used in converting the offset amount
(3-bit digital amount) to the corresponding analog voltage at
offset operation.
(b) Non-linear circuit
The non-linear circuit combines the stair step signal sent from
the DA converter with the signal sent from the smoother to
smooth the waveform and, at the same time, generates the
deceleration curve which is optimum from viewpoints of
decelerating current and the access time. In addition, it
applies the output from the charge-discharge circuit, which is
controlled by the Acceleration signal (ACCEL), to prevent
excessive accelerating force from being applied to the carriage.
(c) Switching circuit
The switching circuit selects the target velocity for seek, and
rezero operations based on the reference voltage generated by
means of various logic signals derived from the servo logic
circuit.
Figure 4.6.22 is the timing chart of the signals during the rezero
operation.
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