Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Patent
1995-04-07
1997-09-09
Dinh, Tan
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
360114, 360 46, G11B 1100
Patent
active
056663331
ABSTRACT:
There is disclosed an apparatus for controlling the strength of a magnetic field, comprising a first controller, a second controller, a digital-to-analog converter, a current driver, and a bias coil. The first controller determines the position of the focal point of a lens and passes it to the second controller, which provides a digital signal related to the position. The digital-to-analog converter converts the digital signal to a driver voltage and passes the driver voltage to a current driver, which provides to the bias coil a bias current related to the driver voltage. The bias coil produces a magnetic field having a strength related to the bias current. The second controller accounts for stray magnetic fields in creating the digital signal. The stray magnetic fields may be constant or may vary in strength based on position of the objective lens, circumferential velocity of the storage medium, or longitudinal velocity of the storage medium. Furthermore, the apparatus may comprise a current sensor for measuring the bias current, and a feedback device for providing to the current driver a feedback voltage related to the bias current. A method is also disclosed for controlling the strength of a magnetic field, comprising the steps of determining the position of a focal point of a lens, calculating a digital signal related to the position, generating a driver voltage related to the digital signal, generating a bias current related to the driver voltage, and producing a magnetic field having strength related to the bias current. The method accounts for stray magnetic fields in calculating the digital signal. The stray magnetic fields may be constant or may vary in strength based on position of the objective lens, circumferential velocity of the storage medium, or longitudinal velocity of the storage medium. Furthermore, the method may measure the bias current and provide to the current driver a feedback voltage related to the bias current.
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Clark Ronald J.
Dinh Tan
Discovision Associates
Gaetje Clay E.
Thyfault Paul M.
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