Motors And Control Circuits; Figure 34. Alternate Azimuth Angles - Seagate STD124000N Product Manual

Chapter 8

Motors and Control Circuits

Page 76
The recorded tracks are written diagonally across the tape from bottom to top by
each write head. Because the head is wider than the track written, tracks overlap
with no tape space between them. In conventional recording, such overlap or even
proximity results in crosstalk (signals from adjacent tracks interfering with signals
from another track).
However, in helical scan recording, the heads are set at different azimuth angles so
that alternate tracks on the tape are written at alternate azimuth angles. (See Figure
34.) Because the read head is set to the same angle as its corresponding write
head, it picks up a stronger signal from data written in the same azimuth angle as
itself. So it reads the track with minimal crosstalk. At the same time, the head is
maintained centered in the track by the timing tracking hardware and firmware.
Figure 34 shows alternate tracks and alternate azimuth angles.
Write head B

Figure 34. Alternate Azimuth Angles

The Scorpion 24 drive uses four direct-drive, brushless motors—the capstan,
cylinder and two reel motors. Using these small, direct-drive motors provides
maximum reliability. The cylinder motor rotates the cylinder. The capstan motor
moves the tape. The mode motor loads and ejects the cartridge. The two reel
motors turn the tape reels.
Cylinder, capstan and reel servo is controlled by custom ASICs and the motor
control firmware.
The fifth motor in the mechanism is a brush-type mode motor. This motor controls
(selects) the mechanism mode. Because the mode motor is not frequently used, the
brush-type motor is best suited to this application. The mode motor performs the
mode changes as directed; for example, this motor conditions the mechanism to
eject the cartridge. The motor is controlled by a driver that receives instructions from
mode motor controller.
Theory of Operations
3 tape tracks
Write head A
20˚ head azimuth
DAT Drives