Abstract: An improved servo demodulator channel employing a transconductance balanced modulator as a polarity switch, an AGC amplifier and a signal separation circuit. A transconductance balanced modulator comprises two amplification transistors and four output transistors which together form two signal channels, each comprised of an amplification transistor connected in parallel to two output transistors. In a specific embodiment, the transistors are n-p-n transistors, the emitters of the two output transistors associated with a given channel being connected to the collector of the amplification transistor. The transconductance balanced modulator is configured so that the two amplification transistors are interconnected as a differential amplifier, and the base electrode of an output transistor in one signal channel is connected to the base electrode of an output transistor in the other signal channel, the base electrodes of the other two output transistors also being interconnected.

Abstract: A velocity sensing method and apparatus to be used in conjunction with a linear motor having a moveable voice coil. More particularly, an apparatus is disclosed whereby a velocity sensing loop is positioned on a surface defined by wire windings of a linear motor voice coil. The velocity sensing loop is configured so that an end portion is perpendicular to the longitudinal axis of the voice coil and two side portions are parallel to the longitudinal axis of the voice coil. As the end portion of the velocity sensing loop traverses a magnetic field with which the voice coil reacts for positioning thereof, a voltage is induced within the velocity sensing loop which is proportional to the velocity of the loop as it passes through the magnetic field.

Abstract: An improved servo demodulator channel employing a transconductance balanced modulator as a polarity switch, an AGC amplifier and a signal separation circuit. A transconductance balanced modulator comprises two amplification transistors and four output transistors which together form two signal channels, each comprised of an amplification transistor connected in parallel to two output transistors. In a specific embodiment, the transistors are n-p-n transistors, the emitters of the two output transistors associated with a given channel being connected to the collector of the amplification transistor. The transconductance balanced modulator is configured so that the two amplification transistors are interconnected as a differential amplifier, and the base electrode of an output transistor in one signal channel is connected to the base electrode of an output transistor in the other signal channel, the base electrodes of the other two output transistors also being interconnected.

Abstract: A simple flexible magnetic disk memory system is provided which enables precise positioning of a read/write head to follow a data track, despite non-uniform expansion or contraction of the disk. Several positioning sectors of the disk are formed which have positioning tracks recorded thereon, and several corresponding holes are punched in the disk to enable an optical sensor to determine the sector locations. Although a step motor positions a head at the approximate middle of a selected data track, an analog circuit repeatedly adjusts the head location as each positioning sector passes the head. Four positioning sectors can be used which are each aligned with or angled by 90.degree. from the direction of machining of the sheet material of which the disk was made, to minimize track run-out in each data region that lies between positioning sectors.

Abstract: A digital phase lock loop system used in conjunction with a flexible disk drive controller for recovering data information from either single density or double density serially encoded data. More specifically, a phase lock system is disclosed in which data bit windows and clock bit windows are defined by a plurality of phase clock cycles. A circuit is provided for determining during which phase clock cycle a bit occurs, an adjustment being made to the duration of its corresponding bit window and thus to the initiation time of a subsequent bit window which will tend to position the window so that it will be centered about its corresponding bit. In a specific embodiment for double density encoded data, a circuit is provided whereby the subsequent bit window is positioned in accordance with the position of the current bit within its corresponding window and the position of a preceding bit within its corresponding bit window.

Abstract: An improved servo demodulator channel employing a transconductance balanced modulator as a polarity switch, an AGC amplifier and a signal separation circuit. A transconductance balanced modulator comprises two amplification transistors and four output transistors which together form two signal channels, each comprised of an amplification transistor connected in parallel to two output transistors. In a specific embodiment, the transistors are n-p-n- transistors, the emitters of the two output transistors associated with a given channel being connected to the collector of the amplification transistor. The transconductance balanced modulator is configured so that the two amplification transistors are interconnected as a differential amplifier, and the base electrode of an output transistor in one signal channel is connected to the base electrode of an output transistor in the other signal channel, the base electrodes of the other two output transistors also being interconnected.

Abstract: Apparatus for aligning a printed circuit board (PCB) relative to a datum line defined between two pins fixed to a supporting member. One pin is cylindrically shaped and the other is shaped in the form of a frustum of a cone. Two aligning holes are provided on the PCB spaced apart by a distance slightly different from the spacing between the pins so that with one hole over the cylindrical pin, the edge of the other hole rests on the sloped side of the other pin. As the PCB is pressed against the supporting member between the two pins by securing means, the PCB is sprung, and the stored force of the sprung PCB presses the edges of the PCB holes against the pins for precise alignment relative to the datum line between the two pins.

Abstract: Circuit means for use in a moving head type magnetic disk drive for unloading the heads under emergency conditions, such as power loss, to avoid loss of data and head or disk damage. The circuit means include a dynamic brake circuit which responds to an emergency condition to electrically short a positioner coil to thereby reduce the head support structure radial velocity to substantially zero. After a short delay, a velocity control circuit is activated, first in a low current mode to move the support structure at a controlled velocity toward the disk outer edge and then in a high current mode to enable the support structure to climb an unload ramp to move the heads axially away from the disk surface. The dynamic brake and velocity control circuits are powered by a capacitor which is charged during normal operation.

Abstract: A transient temperature compensation system for use in a magnetic disk drive comprised of both fixed and removable disks. The system includes first and second thermistors respectively mounted immediately adjacent the fixed and removable disks. The second thermistor is preferably mounted for movement between an operative position and an inoperative position. In the operative position, the thermistor is positioned in very close proximity to the disk. In the inoperative position, the thermistor is spaced from the disk to permit sufficient clearance to enable the disk to be removed from the drive. The outputs of the two thermistors are used to develop a signal representing the temperature differential between the two discs which signal is supplied to the disk drive head positioning system. This signal is used to modify the positioning of the heads relative to the fixed disk to compensate for differences in the radial positions of corresponding tracks on the fixed and removable disks.

Abstract: A disk assembly which is normally fixed on a disk drive, but which can be removed in the field from the disk drive spindle and replaced on the spindle with extreme precision so that pre-recorded tracks are concentric with the axis of the spindle within extremely small tolerances. The disk assembly includes a mounting ring which fits around the drive spindle, the ring having three resilient centering flexures extending slightly radially inwardly of the rest of the ring to engage the drive spindle, and all being outwardly deflected substantially the same amount to center the ring on the spindle.

Abstract: Mounting means for removably securing a circuit board in a fixed spaced relationship to a base plate. The mounting means includes one or more fasteners, each comprised of a spacer member and a latch member. The spacer member includes a disk-like portion having a first flat surface for securement against the base plate and a second flat surface on which the circuit board is supported. A post extends from the disk-like portion second flat surface through an opening in the circuit board. The latch member is mounted for movement on the post between a first position which allows it to pass through the circuit board opening and a second position in which it is locked against one surface of the circuit board forcing the opposite circuit board surface against the disk-like portion second flat surface.

Abstract: An opto-electronic transducer for determining position and/or velocity of one member with respect to another member is provided with light amplitude control. The transducer is comprised of a scale with a transmission grating on a first track and an indexing bar near each end of a second track adjacent the first, and a reticle with two sections of the same grating, one section being offset spatially one quarter cycle with respect to the other section for producing quadrature signals through two photosensors opposite the first track from which relative position and/or velocity between the reticle and the scale can be determined. A slit is provided in the reticle in order to provide information for determining position relative to the indexing bars. A single photosensor opposite the second track is used both to detect the indexing bars and to provide a feedback control signal to maintain the amplitude of light illuminating the scale and reticle constant.

Abstract: A synthesizer for multiphase waveforms is disclosed which is useful, for example, in open and closed loop control of a two-phase induction motor, such as for a magnetic recording disk spindle, utilizing a plurality of bistable elements, two for each phase, to control output power drivers. A single clock pulse counter is employed to time the setting and resetting of each bistable element according to some predetermined pattern controlled by combinational logic which presets the counter to proper values at appropriate times in response to external stimuli, such as speed feedback control and start-stop control.

Abstract: A phase-locked loop is provided with a phase detector capable of providing phase error magnitude and direction information for synchronizing a voltage controlled oscillator with a train of data pulses spaced apart in integral multiples of a fundamental clock period using an edge-triggered flip-flop and simple digital logic gates.

Abstract: The spindle motor for a flexible recording disk is connected to a disk with an annular track of optical markings which are scanned to derive therefrom a train of reset pulses for a counter counting higher frequency clock pulses. Reaching of a particular count state is ascertained for each reset cycle to obtain a train of pulses of constant duration with pauses inbetween, varying with motor speed. A steady signal linearly varying with motor speed is derived from that train, compared with a reference and used to controlthe motor.

Abstract: A flexible magnetic disk drive system including a read/write head carried by a carriage that is threadably engaged with a lead screw, but with the head carriage being free to pivot a fraction of a turn about the axis of the lead screw to move the head against and away from the disk.

Abstract: In a rotating magnetic memory, a phase-locked loop tracks pulses derived from sector marks on means mechanically connected to rotate with the memory. The output frequency of the phase-locked loop, which is significantly higher by a factor of N than the frequency of the sector mark pulses, is cyclically counted down to divide each revolution of the memory into M equally time spaced sectors. Third and fourth order filtering in the phase-locked loop assures a high degree of precision and consistency in the sectoring.