Abstract: The track follow gain control of an actuator controller is calibrated by injecting a sinusoidal signal into the position error signal during a servo burst interrupt. The injected signal is bandpass filtered to optimize the coherence of the measurement. A sine error signal is derived based on the filtered (sine actual) signal and a sine desired signal. The sine error signal is applied to the track follow gain control to adjust the amplitude of the control signal to the actuator based on the sine error signal. The sine error is derived by averaging the peaks of the filtered injected signal and subtracting the averaged signal from the desired signal which represents the expected error of the sinusoidal signal under ideal conditions. The recording surfaces may be segmented into a plurality of radial zones in which case a central track is identified in one zone on a selected disc surface.

Abstract: An apparatus for detecting an over-velocity error condition of a head actuator driven by a voice coil motor in a hard disk drive system includes an integrator for providing an integrated value of the current flowing through the voice coil motor and a detector for detecting when the integrated value exceeds a threshold value. In response to this detection, the supply of current through the voice coil motor is interrupted. To prevent false detections, the integrator is inhibited until the motor current reaches a level indicative of a track access operation.

Abstract: An n-phase DC motor is controlled by converting a motor speed command signal generated from a programmed CPU to a motor drive signal and using this motor drive signal to apply DC power to a selected phase of the motor, the amount of applied DC power being a function of the value of the motor speed command signal. Signals representing the position and/or speed of the motor are supplied to the CPU from which the CPU detects speed errors. The speed command signal then is modified to speed up or slow down the motor so as to reduce the detected errors.

Abstract: A low offset position demodulator that may be used in the positioning servo of a disk drive or similar device. A first stage of the demodulator circuit multiplies or switches a servo carrier signal, modulated with position information, with a synchronized gate signal. This first stage of the demodulator circuit includes a differential output and means for controlling the common mode operating point thereof with an external control voltage. A low pass filter, also having a differential output, is coupled to the differential output of the first stage of the demodulator. A differential-to-single-ended conversion stage is tied to the low pass filter output to provide a single position output signal. Also coupled to the low pass filter differential output is an averaging network that averages the signal appearing on one of the two differential signal lines with the signal appearing on the other differential signal line.

Abstract: A constant bandwidth automatic gain control (AGC) system is presented. The system is especially suitable for use in the positioning servo system of a magnetic disk storage system. The system includes a double balanced modulator circuit and a fixed gain video amplifier circuit. The double balanced modulator circuit functions as a variable gain element, and the gain thereof is set by a control voltage derived from an otherwise conventional AGC loop. The gain of the current steering stage of the double balanced modulator is limited to values no greater than 0.5.

Abstract: An improved automatic gain control circuit suitable for use in the servo loop controlling the position of magnetic read/write heads with respect to magnetic disk data storage media is disclosed. The AGC circuit features a fast loop and a slow loop each of which loops contain gain varying elements, which in the preferred embodiment comprise field effect transistors. By using a reference voltage to control the operating point of the variable gain element in the fast loop, the effects of mechanical resonances on the servo data can be substantially eliminated while the overall AGC system response exhibits a substantially constant bandwidth.

Abstract: A method of suppressing resonances in electro-mechanical servo systems is disclosed. The servo systems are of the type where first signals indicative of actual position of the servo system are differentiated and second signals indicative of the acceleration of the system are integrated. The differentiated signals are applied to the integrator in order to provide accurate initialization thereof. In modes of operation where the acceleration of the system is substantially zero, the differentiators are not used, thus decoupling the mechanical system from the electronic control system and eliminating resonance from the servo loop. The duty cycle of the differentiators is varied in differing modes of operation of the servo system so as to provide maximum bandwidth and speed to the system coupled with minimum errors in positioning. The system is described in connection with the servoing of magnetic read/write heads radially with respect to rotating magnetic disk data storage media.

Abstract: As an aid in counting servo tracks in a position servo system, a position window detector (30) which normally provides coarse and fine pulses to counting logic (53) also provides fine pulses to a reset switch (45) of a tachometer signal integrator means (33), resetting the integrator once for each track. In the event of position signal drop-out wherein coarse pulses are not properly generated, a threshold detection means (43) senses when the output of the integrator reaches a threshold level and produces a threshold reached signal which is transmitted to counting logic means (53) for incrementing a track counter (61).

Abstract: An electronic tachometer that includes an integrator for producing a speed signal by integrating a signal representative of acceleration of a body and a differentiator for producing a speed signal by differentiating a signal representative of the position of the body, the differentiator being formed by a passive RC circuit and operatively associated with circuitry for alternately supplying to the differentiator two signals representative of position, one of which is inverted so that signals of a single polarity are supplied to the differentiator, and further circuitry for connecting the differentiator output to the integrator feedback circuitry so as periodically to update or reset the speed signal produced by the integrator, which is formed by an operational amplifier having a capacitive feedback which is shunted by a resistor when the differentiator output is active to update the integrator.

Abstract: A timing circuit for a track following servo system wherein an odd servo track having a series of prerecorded odd dibits thereon and an adjacent even servo track having a series of even dibits prerecorded thereon are moved with respect to a servo head to induce in the servo head signals that vary with the occurrence of the dibits and have an amplitude representative of the lateral position of the servo head with respect to the servo tracks. The servo head and its associated preamplifier produce a first signal having portions from both odd and even servo tracks and a second signal that is the inverse of the first signal. The first and second signals are processed by parallel identical circuit paths to generate a clocking signal that times the remainder of the data storage system in synchronism with the spacing of dibits on the servo tracks.

Abstract: A servo system for accurately positioning a transducer relative to data paths on a recording medium by detecting sync and servo signals from two parallel abutting servo tracks sharing a common longitudinal boundary within circumferentially spaced sectors of the medium. Within each sector of the recording medium, two servo waveforms of different frequencies in two abutting servo tracks are preceded by a sync reference waveform of the same frequency in both servo tracks which is used as a reference for a phase locked oscillator, connected to the transducer, generating a pair of modulation signals that are to be mixed with transducer signals from both servo waveforms. A pair of servo channels are provided for receiving the pair of modulation signals and the servo signals for deriving an imbalance error signal representing deviation of the transducer from the center line of a data path, which is the projection from the sectors of the common longitudinal boundary between servo tracks.

Abstract: An electronic tachometer comprising an integrator having its output coupled to a variable gain amplifier and responsive to an input signal representative of the acceleration of a moveable load, such as a head assembly of a disk drive, for producing a coarse velocity signal at the output of the variable gain amplifier indicative of the load velocity, a tachometer gain correction circuit including another integrator coupled to receive the coarse velocity signal to produce a coarse distance signal indicative of distance traveled by the load and means for combining the coarse distance signal with a reference distance signal to produce a distance error signal which functions to adjust the gain of the variable gain amplifier so as to vary the coarse velocity signal to make the coarse distance signal equal to the reference distance signal, and accumulative error compensation means coupled to receive a gain indicative signal derived from the distance error signal to produce a signal input to the tachometer integrator

Abstract: A signal compensator for a position servo loop system to attenuate the position error signal and provide stability at a larger band width by limiting the position actuator current in selected frequency ranges.