Abstract: A disk drive is disclosed comprising a head disk assembly (HDA) filled with a gas, the HDA comprising a head actuated over a disk, and an electrical heating element. A pressure inside the HDA is measured, and the electrical heating element is heated for a first heating time. A rate of temperature change of the electrical heating element is measured, and the gas leaking from the HDA is detected in response to the pressure and the rate of temperature change.

Abstract: A data storage device (DSD) is disclosed comprising a non-volatile memory (NVM), such as a disk or non-volatile semiconductor memory, and control circuitry for detecting a power failure condition. A frequency range of a supply voltage from a first frequency to a second frequency is extracted, wherein the first frequency is greater than ten hertz, the second frequency is higher than the first frequency, and the second frequency is less than one megahertz. The power failure condition is detected in response to the extracted frequency range of the supply voltage.

Abstract: A magnetically activated switch assembly is provided. The magnetically activated switch assembly includes a magnet and a magnetic circuit. The magnetic circuit includes a magnetically activated switch, a first set of flux conductors, and a second set of flux conductors. The first set of flux conductors has first flux conductor flanges adapted to conduct flux from ends of the magnet. The second set of flux conductors is slidingly positioned relative to the first set of flux conductors and is adapted to conduct flux from the first set of flux conductors to the magnetically activated switch. The first set of flux conductors are adapted to rotate clockwise or counter-clockwise and to tilt up or down. The first magnetic circuit is adapted to conduct flux to activate the magnetically activated switch only when the first flux conductor flanges are rotationally aligned with ends of the magnet and tilted to an operational position.

Abstract: An apparatus for sensing relative positions of mechanically coupled devices. The apparatus includes a magnetically actuated switch connected to a set of flux conductors to form a switch assembly. A permanent magnet is affixed to a set of flux conductors to form a magnet assembly. The flux conductors are positioned adjacently to conduct flux from the permanent magnet to the magnetically actuated switch. Movement of either assembly results in the reduction of flux conduction between the magnet and the magnetically actuated switch. The apparatus can be integrated into a helmet mount for night vision goggles to sense the relative position of the helmet mount for controlling the operation of the night vision goggle.

Abstract: A magnetically activated switch assembly is provided. The magnetically activated switch assembly includes a magnet and a magnetic circuit. The magnetic circuit includes a magnetically activated switch, a first set of flux conductors, and a second set of flux conductors. The first set of flux conductors has first flux conductor flanges adapted to conduct flux from ends of the magnet. The second set of flux conductors is slidingly positioned relative to the first set of flux conductors and is adapted to conduct flux from the first set of flux conductors to the magnetically activated switch. The first set of flux conductors are adapted to rotate clockwise or counter-clockwise and to tilt up or down. The first magnetic circuit is adapted to conduct flux to activate the magnetically activated switch only when the first flux conductor flanges are rotationally aligned with ends of the magnet and tilted to an operational position.

Abstract: A disk drive is disclosed comprising an interface for receiving a primary supply voltage and a secondary supply voltage from a host computer. The primary supply voltage is applied to the windings of a multi-phase spindle motor in a commutation sequence, and the secondary supply voltage is connectable to a center tap of the windings.

Abstract: A disk drive is disclosed comprising an interface for receiving a supply voltage from a host computer and control circuitry for controlling at least one operation of the disk drive. The supply voltage is applied to the windings of a multi-phase spindle motor in a commutation sequence during a normal operating mode, and a secondary voltage supplied by a center tap of the windings is used to power the control circuitry during the normal operating mode.

Abstract: A split actuator comprising two spring coupled actuators that share a common pivot bearing. The two reduced inertia actuators permit overlapping motions during a seek operation thereby reducing dead times in transfer of data between disk and transducers disposed on the actuators. A spring member that spring couples the two actuators boosts relative motions by storing and releasing spring potential energy selectively. The spring member is also configured so as to substantially restrict the relative motions of the two actuators to rotational motions about a common axis of the common pivot bearing. Rigidity of the spring member to non-rotational relative motions, as well as tuning of the spring member to provide a rigid response to selected frequencies, the spring member in conjunction with the common pivot bearing result in mechanical disturbance being substantially common to the two actuators, thereby allowing predictable and manageable disturbance corrections.

Abstract: A disk drive is disclosed comprising a velocity extraction circuit for extracting a velocity of an actuator arm from a back EMF voltage across a voice coil of a voice coil motor when embedded servo information is unavailable. The velocity extraction circuit comprises a dual slope integrator for integrating a voltage representing a current flowing through the voice coil and the voltage across the voice coil. The sum of the integrations cancels the resistance of the voice coil from the back EMF measurement. In one embodiment, the dual slop integrator also integrates the reverse polarity of the voltage representing the current flowing through the voice coil and the reverse polarity of the voltage across the voice coil in order to cancel the inductance (L·di/dt) of the voice coil from the back EMF measurement.

Abstract: A disk drive that includes a base, a magnetic disk, a rotary actuator that carries a head for reading and writing data from the disk in a track-following mode under the control of a servo control system, and at least two sensors—one fixed sensor rigidly coupled to the overall disk drive and one mobile sensor mounted to the rotating actuator—for differentially detecting accelerations of the rotary actuator relative to the overall disk drive and its disk. The disk drive detects and actively compensates for accelerations imparted to a balanced actuator that has an effective imbalance. The fixed sensor is preferably mounted to a PCBA that is secured to the base. The mobile sensor is preferably mounted to an actuator arm of the rotary actuator, as far outboard as possible, and so as to align with the fixed sensor as the rotary actuator swings through its range of travel. The preferred sensors are linear accelerometers.

Abstract: A disk drive includes a head disk assembly having a housing including a first surface area, and a strain transducer for producing a strain signal representing strain in the first surface area due to a mechanical shock on the disk drive. The strain transducer includes a first electrode, a second electrode, and a volume of piezosensitive material defining a second surface area. The piezosensitive material is disposed between the first electrode and the second electrode. The first surface area overlaps the second surface area. The strain transducer further includes means for securing the first electrode and the piezosensitive material to the first surface area such that the strain in the first surface area is replicated in the piezosensitive material. The disk drive includes means responsive to the strain signal for controlling a write operation in the disk drive.

Abstract: A disk drive controller having a microprocessor and a sampled signal head positioning system measures and stores the relative rotational offsets between heads arranged in a stacked relationship and respective servo wedges on different disk surfaces. The offsets are stored in a table and subsequently applied to a servo wedge detection circuit to ensure that a next sequential wedge is detected after a head switch.

Abstract: A digital-to-analog converter (DAC) is preferably employed to receive a digital input word and provide an analog output signal to a motor driver in a disk drive servo. The digital input word has a plurality of bit positions for establishing a resolution for the DAC. These bit positions define first and second groups of bits. The DAC comprises circuitry responsive to the first group of bits for producing a pair of analog signals defining a common-mode magnitude and a differential magnitude. The common-mode magnitude is a function of the value of the first set of bits and the differential magnitude is a function of the number of bit positions in the first group of bits.

Abstract: A disk drive for operating in an environment in which the drive is subject to physical shock includes a circuit which senses movement of a transducer head support arm which result from a shock's rotational component. The rotational shock is detected as a residual BEMF signal in the drive's VCM coil winding. The residual signal is extracted from much larger position control signals that are applied to the VCM winding during normal system operation by providing circuits that simulate the VCM winding voltage caused by the position control signal and subtracting the outputs of the simulation circuits from the actual VCM coil winding voltage. This eliminates the normal operating components and leaves a residual signal that represents only the small portion of the VCM BEMF signal that results from the rotational shock. A threshold circuit compares the shock BEMF signal to a predetermined threshold. If the BEMF signal exceeds the threshold, disk drive write operations are aborted.

Abstract: A method for controlling a programmable source of a plurality of string of clock signals, a program is stored with a plurality of different indications of desired frequencies, each indication corresponding to one of the strings of clock signals. The frequency of each of a plurality of oscillator is controlled by the memory content of a separate memory for each oscillator. The content of each memory is adjusted in accordance with the actual frequency of each string, the frequency indicated by the corresponding indication of a desired frequency and a reference.

Abstract: A switchable termination module for use with addressable devices on a communication bus has a terminator for each signal transmission path, a signal source, for example a switch for signalling whether termination is desired and a terminator control circuit for engaging and disengaging the terminators in response to the signal from the signal source. The control circuit has a transistor between the source of potential and the terminators to couple the terminators to the transmission paths when termination is desired. The switch which signals whether termination is desired may also be used to select the address for the device.

Abstract: A mounting system for mounting an expansion card inside a computer chassis includes a mounting bracket having a combination board mounting clip and chassis mounting tab formed as an integral unit in which the bracket releasebly fastens to a corner of the expansion card. The expansion card has a bottom edge connector for plugging into an expansion card socket at the base of the computer chassis inside the expansion slot. The computer chassis also has a removeable cover plate on a panel of the chassis for shielding the expansion slot. The board mounting clip releasably fastens to the expansion card by engaging the opposite faces of the board in a continuous frictional means of attachment without the use of external fastening means.

Abstract: An apparatus and automated process to improve the accuracy and reduce the time, cost, and effort necessary to prepare reproduction artwork for charts is disclosed. A numerically or computer controlled imaging system is used to expose photographic film or emulsion with specially prepared halftone pattern symbols. This allows a computer to be used to select both the symbol and location, instead of slow and costly manual methods. Greatest benefits accrue when the final chart is to be in color. One sheet of film per primary color is exposed using a few basic symbols, which are then combined to yield a wide range of color in the symbols of the final chart. Typically, the final product of this process is one or more sheets of monochromatic film used as masters for a color printing or color key process. Further, a method is described to avoid erroneous density (and resultant color) changes where halftone symbols overlap, as well as various other methods to improve legibility and produceability of the charts.