ACTUATOR ASSEMBLY

FIRST SEEK INTERLOCK MOTOR

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READ/WRITE HEADS (19) :....-- TRACK SERVO

HEAD(I)

DRIVE MOTOR PULLEY

Figure 3-7. Deck Assembly

DISK PACK CANNISTER

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SPINDLE

GROUND SPRING

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or spindle motor power is applied, brake

A vertically free-floating lockshaft runs through the center of the spindle assembly.

The upper end of the lockshaft contains internal threads that engage the external threads of a stud projecting from the disk pack. When the .disk pack canister cover handle is rotated clockwise, the spring-loaded lockshaftis pulled upward and the improperly configured unit.

Actuator magnetic field existing around the magnet assembly. The reaction either draws the voice coil into the permanent magnet field or forces i t away. Signal polarity deter-mines the direction of motion, while signal amplitude controls the acceleration of the motion. Load-ing paragraph for detailed information on read/write head loading and unloading.) The positioning signal is derived in the

HEAD/ARM RECEIVER

ACTUATOR - CARRIAGE RETRACTED

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TRANSDUCER END CAP/SPRING

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ACTUATOR

Pt==f:::::i""'ll==::!..._ .... /HOUSING

PARTIAL HEAD COMPLEMENT

SHOWN

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Figure 3-9. Actuator Assembly Elements During any .Seek operation, the logic must be

informed of the current location and velocity of the carriage. This information is pro-vided by the velocity transducer in the magnet assembly and the lone track servo head installed on the head/arm receiver.

The transducer is a two-piece device, one piece stationary and the other movable. Refer to the Transducers paragraph for a complete description.

The actuator contains a stop mechanism to limit extremes in forward and reverse move-ment. The stop assembly is a rubber cylin-der sandwiched between two metal plates. If the carriage moves too far toward the disk pack, the stop rod heads contact the plate on the magnet-side of the rubber cylinder.

If the carriage is retracted far enough

3-14

away from the disk pack, the rear of the head/arm receiver contacts the stop assem-bly stud protruding through the stop plate.

Head Loading

The read/write heads must be loaded to the disk surfaces before exchanging data with the controller. The heads must be removed

(unloaded) from this position and driven clear of the disk pack either when power is removed from the unit or when the disk pack velocity falls below about 2700 rpm. The actuator components involved in these oper-ations are identified in Figure 3-10.

Head loading amounts to allowing spring pressure of the floating arm (part of head/

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FLOATING ARM

UNFLEXED PROFILE

~::::::;::;L-_..Iiiiiii:iiiiiii:=====~=:::::::a OF HEAD ASSEMBLY FIXED ARM

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II I HEAD FACE MOVES CLEAR

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:":'H:EA"!:"'D=""""'C~A~M SECUR ED TO "!:"'AC=:1:-:U~A:-::T=-=O-::::R"""!H~O=-:-U""=S~IN'=G

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..J MOVES READ/WRITE HEAD TOWARD DISK SURFAr.E UNTIL OPPOSING FORCE OF AIR LAYER CANCELS en-countered, it resists any further approach by the head. Spring pressure is designed to disk pack during automatic operation, load-ing occurs only after the disk pack is up to ap-proximately 15 seconds.

83313200 A actuator. housing bear against the floating arm cam surfaces. The cams support the opposing forces balance.

The heads loaded switch status reflects the

fully retracted, the switch st~te reflects the unloaded status of the heads". As the carriage moves forward during a Power On/ "

First Seek, the switch transfers at a point within about 0.1 to 0.2 inch forward of the retracted stop. This switch status remains unchanged until the carriage is retracted to the same position and, as such, does not precisely indicate the loaded/unloaded stabm of the heads. Precise status is determined its current location toward the retracted stop. (Either normal or emergency methods can be used. Refer to Power Off Sequence paragraph for additional information.) As the carriage retracts, the cam surfaces en-counter the head arms and each head rides vertically away from the related di~k sur-face. The carriage continues back to the retracted position and stops.

Head/Arm Assemblies

Twenty head/arm assemblies are mounted on the carriage. A read/write head/arm assanbly consists of a read/write head assembly the arm) tangentially and radially relative to a data track on the disk surface. Such motion is require.d to compensate for IX>ssible

irregularities in the disk surface.

The arm structure consists of a floating arm interchangeable disk packs. During head loading, each floating arm is driven off the

FACE SEPARATED-";E~ ^ROTATION

IS LOADED TO DISK ~ GIMBAL SPRIN8 MOTION ABOUT THIS AXIS CREATED BY PIVOTING ABOUT ® Head/Arm Assembly Motion

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countered by a move in the opposite direction by the gimballed head and/or floating arm.

As a result, flight height remains nearly constant.

Transducers

The deck assembly contains two transducers:

speed sensing transducer and velocity trans-ducer. These transducers provide signals that are used by the logic chassis and the controller to generally control the progres-sion of most machine operations.

Speed Sensing Transducer

The speed sensor (Figure 3-7 and 3-12) gen-erates a voltage output whenever a ferrous material (steel pin set in spindle pulley) enters the magnetic field surrounding the pole piece at the pickup end of the trans-ducer. The logic then shapes this signal into a 55 microsecond pulse. As long as the speed exceeds 3000 rpm, one of these pulses will be sensed at least once each 20 ms. A sensing circuit within the logic monitors the pulse repetition rate and provides an emergency retract capacitor. The heads immediately are unloaded to two-piece device consisting of a stationary tubular coil/housing and a movable magnetic core.

The magnetic core is connected via "the ex-tension rod to the rear surface of the head/

"arm receiver. All motion of the carriage is therefore duplicated by the magnetic core.

As the core moves, an emf is induced in the output drives an operational amplifier lo-cated in the logic chassis. This signal is used by the servo logic to control acceler-ation/deceleration of the carriage during Seek operations.

First Seek Interlock Assembly

The First Seek Interlock assembly provides a fixed time delay from the completion of revolves until the reset switch is encountered.

The switch then transfers and removes power presence of this elevated pressure results in an outward dispersion of air preventing ingestion of contaminated air. This air flow greatly reduces possible contamination and resulting damage to the disk surfaces