Abstract: An oscillation sensing device includes a magnetised member mounted on a substrate. A magneto-electrical material is mounted on the substrate such that the magneto-electrical material is subjected to the magnetic field generated by the magnetised member. A movable member is mounted for oscillation in response to an oscillating force. Oscillation of the movable member causes a change in the magnetic field experienced by the magneto-electrical material and an electrical property of the electro-electrical material changes in response to changes in the magnetic field experienced by the magneto-electrical material due to oscillation of the movable member.

Abstract: A motor constant Km of a sled mechanism of an optical disc drive is to be measured. To this end, a parameter measurement device 1 for the sled mechanism includes an oscilloscope 8 for detecting the back-electromotive force Eb of a sled motor 5, a laser Doppler meter 7 for detecting the movement velocity v0 of the pickup 4 and a computer 9. The computer calculates an equation Eb=KmRmv0, where Rm is the resistance of a motor, to find the motor constant Km.

Abstract: A device for measuring focusing characteristics of an optical pickup and/or an optical disc capable of measuring characteristics of focusing states with high accuracy by a simplified circuit. An arithmetic-logic unit 12d controls an offset supplying circuit 23 for applying an offset voltage to a focusing servo control signal. This arithmetic-logic unit 12d detects an error rate of the playback data in such a state in which the focusing position of the laser light is deviated by a pre-set offset amount. The arithmetic-logic unit 12d sequentially varies the offset voltage to repeat the above processing for detecting the error rate. The arithmetic-logic unit 12d approximates the relationship of the error rate to the offset amount by a quadratic curve based on detected data. The offset amount which minimizes the error rate is found from this equation of approximation.

Abstract: A device for measuring characteristics of an optical pickup and/or an optical disc by which characteristics of tracking signals can be measured accurately in a noise-free manner. The measurement device 1 has a sample-and-hold circuit 8 and an analog-to-digital converter 10 for directly sampling an output of an optical pickup 2 as signals A to F in order to store the resulting digital data in a second memory 11. An arithmetic-logic unit 12d measures tracking error signals based on the digital data stored in the second memory 11. The arithmetic-logic unit 12d eliminates unstable portions of the tracking signals generated responsive to rotational eccentricity of the optical disc to find data.

Abstract: A device for measuring characteristic values of an optical pickup and/or an optical disc capable of detecting tracking signals for measuring characteristic values even if optical disc rotation is not subjected to eccentricity. The device for measuring characteristic values of an optical pickup and/or an optical disc 1 samples outputs of photodetectors of an optical pickup 2 as signals A to F directly by a sample-and-hold circuit 8 and an analog-to-digital converter 10 to store the resulting digital data in a second memory 11. An arithmetic-logic unit 12d measures tracking error signals based on the digital data stored in the second memory 11. A signal generating circuit 25 then sends a sine wave signal to a tracking coil 2b for moving the laser light illuminated on the optical disc along the radius of the disc.