Hitachi, Ltd.

Japan Science and Technology Agency

Hitachi Global Storage Technologies Japan, Ltd.

Jiro Abe

Yosuke Hamada

Hidehiko Numasato

Takenori Atsumi

Shinsuke Nakagawa

Iwao Oshimi

Kiyotada Ito

Yoichi Kobayashi

A method for authenticating a security mark containing a photochromic compound can provide higher security performance. The method comprises a process of irradiating a security mark containing a photochromic compound with excitation light, a process of acquiring first security information on a time-dependent change in the absorption spectrum and/or reflection spectrum of the security mark after the irradiation with excitation light, and a process of checking the acquired first security information against previously acquired first security information on the security mark. In this method, the security mark preferably contains two or more photochromic compounds different from one another in color development and/or in quenching rate after the color development in a photochromic reaction.

Security mark, authentication method therefor, authentication device and manufacturing method as well as security mark ink and manufacturing method therefor

A seek controller corresponds to a velocity control system which produces a target value based upon a target track, a present position, and a remaining distance from a commencement of a seek operation up to a time instant when a sign of an operating amount is changed; and the seek controller corresponds to a Two Degree of Freedom control system which sets an waveform by a function of time as a target value after the time instant when the sign of the operating amount is changed. The hard disk drives applies a velocity control system based upon a deviation of head positions as to a VCM voltage saturation and a uniform velocity mode, and also, applies a Two Degree of Freedom control system with employment of a function of time having a smooth locus in a decelerated velocity mode so as to suppress residual vibrations.

Magnetic disk apparatus

A magnetic disk drive that drives and positions an actuator using a voice coil motor, includes a current sensing resistor connected in series to a terminal on current input side of the voice coil motor, a first operational amplifier and a second operational amplifier. The magnetic disk drive further includes one of a third operational amplifier and a microcomputer.

Magnetic disk drive and voice coil motor drive circuit

Settling response characteristics after change-over from a speed controller to a position controller is attained. Fluctuations in a time taken until change-over is made from the speed controller to the position controller are reduced to stabilize a moving time and to shorten an access time. To this end, a position controller generates a drive signal of a linear or primary function of time in such a manner that a position deviation signal responds to it with a ternary-order function of time which becomes zero in a desired finite settling time. Further, a feedforward signal generator is provided to reduce a follow-up error to a target position signal as an output of a target position signal generator. Furthermore, a switching judger is provided to start its judging operation after the position deviation signal reaches a predetermine position deviation and to perform switching operation from the speed controller to the position controller when the position deviation signal is not larger than a value corresponding to a proportional multiple of a speed signal.

Disk storage device and head positioning method

A magnetic disk drive uses a back electromotive force sensor that detects the back electromotive force produced in a VCM actuator without being affected by fast changes of current during a high-speed control sampling cycle, and that enables configuration of a fast, high-band speed control system. A back electromotive force sensor for disk drives has a first circuit that detests the coil terminal voltage of a voice coil motor and outputs that value as a band limited signal that is a constant multiple-of that value, a second circuit that detects a drive current in the voice coil motor and outputs a voltage signal proportional to that drive current, and a computation circuit that takes the difference between the output of said first circuit and the output of said second circuit.

Growing community of inventors

Sagamihara, Japan

Jiro Abe