Eastman-Kodak Company

Stuart D Perry

Roger A Hajjar

Joseph F Revelli, Jr

Mark A Barton

Jasper S Chandler

Douglas G Stinson

An apparatus for compensating for radial and vertical runout of an optical disc using an actuator having a lens for focus of a laser beam and wherein the focus and tracking currents control the position of the lens in the vertical and radial directions is disclosed. The apparatus focuses the actuator lens along at least one revolution of a track on an optical disc and producing lens position signals. Structures provided which responds to the lens position signals to produce the frequency content of surface height and track deviations of the optical disc using a frequency transform technique. The surface height and track deviations frequency content are stored and a signal representing the focusing and tracking actuator currents and in response to the focusing and tracking actuator current signals and the stored surface height and track deviation frequencies the lens position is controlled thereby reducing focusing and tracking errors.

Compensation apparatus for radial and vertical runout of an optical disc

A digital compensator controls a servomechanism, such as the focus servo of an optical disk drive. The compensator waits one full sample period before applying the correction that was calculated for the proceeding sample. The compensator does not use the present input sample in its calculation of the present output sample. The method for operating the digital compensator comprises the steps of receiving a first input sample at time t.sub.1, receiving a second input sample at time t.sub.2, and computing a first output in response to the first input sample at time t.sub.2. The method does not require a present input sample to calculate a present output.

Digital compensator for controlling a servo to correct the value of a

A method and apparatus for controlling the relative states between a rotating load member driven by a motor via a transmission where the velocity and position of the rotating load member are determined and the velocity and position of the motor are determined. The information concerning the velocity and position of the load and motor are used by a controller to generate a torque signal for controlling the velocity and position of the motor such that there is increased relative damping and relative stiffness between the rotating load member and the motor.

Controlling the speed of an image-bearing member using relative states

A power efficient amplifier uses two stages, a low voltage stage and a high voltage stage. The low voltage stage supplies a nominal operating current to a load from a low voltage low power output when the requirements are small, and the high voltage stage supplies a desired output current to the load exceeding the nominal operating current when the load requires such. Switching to the high voltage output stage in response to sensing current to the load exceeding the nominal operating current conserves energy and increases operational efficiency. The amplifier circuitry produces a power efficient voltage-to-current transformation. The circuitry includes an operational amplifier that receives a signal proportional to the current flowing to the load and, an input signal which represents the desired load current. When the output increases above a certain level, it turns off the low voltage stage and turns on the high voltage stage causing the available output power to increase. A power efficient amplifier is obtained by operating with the lowest required output power.

Power efficient voltage to current coverter

A circuit for driving a focus actuator of the 'double-solenoid' (i.e. twin-coil) variety comprises circuit means for selectively supplying current to one or the other of the actuator's coils in such a manner as to eliminate any dead-band discontinuity in the actuator response while current-switching between the coils. Such circuitry comprises a current source and/or amplifier for selectively providing current to the actuator coils, means for detecting the difference in current flowing in the coils, an a differential amplifier, connected in a feedback loop, for comparing the output of the detecting means with a signal indicating the focal position of a focusing lens. The output of the differential amplifier is used to control the output of the current source, controlling which of the two actuator coils receives current and how much.

Driving circuit for double solenoid focus actuator

Disclosed herein are an improved method and apparatus for optically reading pre-recorded magnetic information on a magneto-optic recording element. The invention addresses the technical problem of minimizing the adverse effect of unpredictable variations in the state of polarization of the beam of radiation used for read-out. Such variations may be produced, for example, by birefringence variations in a transparent layer or substrate through which the recorded information is recovered. According to the invention, the undesired polarization variations are sensed from the system's output signal, and an error signal representative of such variations is produced. Such error signal is used to adjust the state of polarization of the read-out beam prior to detection by the system's detector elements. Preferably, the read beam is directed through the combination of a quarterwave plate and a Faraday rotator, and the error signal is used to control the magnetic field of the Faraday rotator. In effect, the combination of the quarterwave plate and Faraday rotator behaves like a variable phase retardation plate as far as the resultant output signal is measured by differential detection is concerned.

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Rochester, NY, United States of America

Stuart D Perry