Xerox Corporation

Other

Laserdrive Ltd.

Ian Turner

Thomas A Tacklind

Theodore D Rees

Carl J Clement

John L McChesney

Chi H Chung

Fred H Stengel

Thomas A Tackland

William L Harvey

An improved focus and tracking error detection circuit for an optical disk servo system. The circuit calculates the logarithm of the signal from each of at least a pair of photodetectors. The difference between two logarithmic signals is then determined to give an error signal. The invention takes advantage of the property of logarithms that the difference between two logarithmic signals is equivalent to the logarithm of the ratio of the two signals. Accordingly, the error signal is a ratio, rather than an absolute difference signal, and is thus insensitive to variations which affect both signals. In addition, the logarithmic circuits inherently minimize variations which affect the photodetectors unequally by performing an AGC-type function. The error signal is inhibited during a write pulse to the laser to prevent saturation of the amplifiers. An automatic, periodic offset adjustment is provided by turning off the laser and varying an offset voltage until the error signal is zero. Peak detectors are used to eliminate the effects of data signals.

Logarithmic servo error detection for optical disk drive

A system for storing and retrieving encoded data on an optical recording medium using pit edge detection is disclosed. The pit extension characteristics of a given medium are determined by first using laser beam test write pulses to form one or more pits on the medium and then detecting the time durational difference between the pulse width of the test write pulses and the duration of the leading edge transitions to trailing edge transitions of the corresponding pits formed on said medium. This difference value may be stored in a certification sector of the medium. Subsequent write pulses are modified in duration in an amount equal to this detected durational difference. For forming a pit that is longer than a predetermined minimum length, the corresponding write pulse is made non-continuous in order to minimize cumulative pit extension. The number of non-continuous pulses used to form a given pit is a function of the desired length, the on time of each pulse and the duration of the off time between adjacent write pulses, said off time being a predetermined length to cause pit extension overlap between the portions of the pit formed during the one time of each said write pulse, thereby forming a continuous pit.

Apparatus and method for detecting and compensating for pit extension in

Electrostatic printer/plotter

A spear head access mechanism in a liquid development system wherein a machine mounted manifold, bearing a flow-through spear head connects the developer delivery system to a storage bottle. The bottle has a self sealing closure through which the spear head is forced and is encircled in an air tight manner when the bottle is pushed into operational position. A suction tube within the bottle is entered by the spear head. Upon removal of the bottle from the machine the self sealing closure forms a liquid tight seal preventing spillage of any remaining contents.

Liquid developer spear head access mechanism

An electrographic recorder of modular construction within which are a liquid development system and various electrical elements. Electromechanical connections between the electrical components and a housed power supply are made via a power distribution card lying upon the floor of the machine. To prevent electrical faults caused by liquid developer contamination, compartments are formed within the machine housing for isolating all liquid developer storage and usage locations from the electrical components. The compartments are configured to allow cooling air to be drawn into and through the housing, within the electrical component zone.

Electrographic recorder

An electrographic recorder including a unitary writing, developing and driving assembly comprising a precisely machined frame member to which is secured in accurate alignment a writing head positioning block, a developing fountain and a drive motor and roller. The assembly is attached to a support chassis for storing and feeding a supply of record bearing material so that the mounted components are properly positioned when acting on the record bearing material.

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Sunnyvale, CA, United States of America

Ian Turner