Medium Optical Disk (RW551/RW552) Library
6–16
EK–MOL80–SV. B01
Also on the servo PCA are control electronics for the loader assembly. Included
are drivers for the loader and spindle (speed control) motors, sensor circuitry for
the cartridge loaded and write protect detectors, LED drivers for the control
panel LEDs, and control circuitry for the bias magnet subassembly of the loader
mechanism.
Read and Write Channel Electronics
Read channel electronics take analog data from the optical head and convert it
into digital "transitions." These transitions are decoded by the decoder
electronics on the controller PCA in order to extract data from format and error
correction features. The write channel electronics take the serial data stream
from the formatter/sequencer and convert the digital pulses into analog data. This
analog data is then sent to the optical head.
Mechanism Assembly
Loader Mechanism
The loader mechanism consists of two motors: a spindle motor for speed control
and a loader motor for loading and unloading of the cartridge. The loader motor
includes a gear train and rack-and-pinion system that allow the cartridge shuttle
to raise and lower the cartridge within the loader housing. The bias magnet
subassembly sits on top of the cartridge shuttle and provides the correct polarity
for erasing or writing data.
Optical Head
A major feature of the optical head is a "split optics" design. This design
physically separates the laser diode and its associated detectors from the
focus/fine position actuators. This design results in a significant seek time
performance advantage due to less mass on the moving portion of the optical
head.
There are several actuators in the optical head. The coarse position actuator
moves the focus/fine position actuators to the vicinity of the desired sector on the
optical disk. The fine actuator makes small corrections (+/-25 tracks) to center
the optical head on the desired sector. The focus actuator then moves up and
down to provide optimal focus on the light beam. All these actuators, and the
laser diode (and its detectors) are controlled by the servo PCA.
The laser diode and its associated detectors are part of a flex circuit on the
optical head assembly. On this flex circuit are analog electronics which further
condition the control signals for the laser diode, and pre-amplifiers for the servo
and data control signals that are returned to the servo PCA.
