Xerox Corporation

Palo Alto Research Center Inc.

Robert P Kowalski

David L Hecht

Robert Arthur Sprague

Eric J Shrader

Richard N Ellson

Robert L Thornton

Dan S Bloomberg

Babur B Hadimioglu

William D Turner

Uma Srinivasan

Sven E Karlsson

Thanh D Truong

Robert Matusiak

David L Steinmetz

Mark S Bernstein

Carol A Hankins

David E Kizer

A beam position control system controls a position of a beam directed from a beam source. The beam position control system includes a beam position sensing system that generates one or more satellite beams which are used to determine the position of a main beam. A beam offset computation block determines a relative position of the main beam with respect to a desired main beam position and provides beam offset information to a controller that generates a compensation signal used to adjust the main beam position to the desired main beam position via a beam actuation system.

Optical beam position active sensing and control using satellite beams

An active controller is provided to control operation of an acoustic printhead in which impedance of the printhead changes with both the active printing row and the distribution of active ejectors in the row. The active controller varies the input power to the printhead in response to active ejectors. Power requirements are insured while also reducing power consumption and maintaining print quality. The determination of RF power is based on the active row, how many ink ejectors are to be switched on, and their position within a row. Look-up tables used to determine proper attenuation or power values are provided in a cascaded fashion.

Methods and apparatuses for operating a variable impedance acoustic ink printhead

A substantially vertical contact scanning assembly records both sides of a document in a memory. In one embodiment, the vertical contact imaging assembly is a pair of two-dimensional sensor arrays. The document is fed between the pair of two-dimensional sensor arrays when they are space apart from each other using gravity. A registration stop positioned under the vertical contact imaging assembly aligns one edge of the document with an edge of the pair of two-dimensional sensor arrays. Once properly registered, the pair of two-dimensional sensor arrays are brought into contact with the document. After recording an electronic representation of both sides of the document, the two-dimensional sensor arrays are spaced apart from each other. Subsequently, the document is released into an output tray using gravity by lowering one edge of the registration stop.

Document scanner with gravitational registration

An apparatus for imaging books or other bound documents with minimal stress being applied to the book structure, and for successively imaging and turning pages of a book without the need for manual intervention. The book imager includes a support, for placement of a book in an open position, an imager having opposed imaging surfaces capable of simultaneously imaging the entire exposed, facing adjacent pages of the book in a distortion preventing manner, and a page turner. The support and the imager are relatively movable toward and away from one another, from a first position in which imaging is effected, to a second position in which page turning is effected.

Bound document imager with page turner

A simple technique for determining and indicating, in real times as an image is scanned, the presence of halftones within a page. in brief, the technique contemplates monitoring a pixel stream, typically on a line basis, determining the proportion of pixel transitions (relative to the overall number of pixel intervals), and controlling the process based on this information. In one embodiment, a numerical value representing such a proportion is compared to a threshold, and a value in excess of the threshold is taken to signify the presence of halftone regions. Based on this, special processing for halftones is enabled or special processing for non-halftone regions is disabled. In a specific hardware embodiment, the pixel monitoring circuitry includes a transition detector (50), an up/down activity counter (52), a threshold selector (55), and a counter controller (57).

High speed halftone detection technique

A technique for producing pixel patterns at different selected wavelengths. A diode laser is repeatedly pulsed and has its temperature changed from pulse to pulse, which causes the output wavelength to change. This allows pixel patterns to be interlaced by the use of dispersive elements such as prisms in the optical train. A temperature shift of about 15.degree. C. provides a wavelength shift of about 30 angstroms, which is usable. A temperature shift of 20.degree. C.-30.degree. C. or more is preferable. The temperature shifts may be accomplished by supplying specific currents below threshold and above threshold. For two-wavelength operation, the laser is driven at a first bias current below threshold for a first non-illumination interval, at a first pulse current above threshold for a first illumination interval, at a second bias current below threshold for a second non-illumination interval, and a second pulse current above threshold for a second illumination interval. The bias currents are sufficiently different so as to establish different operating temperatures for the illumination intervals. The temperature shifts may also be accomplished at least in part by use of an auxiliary heater.

Temperature controlled light source for interlaced printer

In accordance with the present invention, correction factors for dynamically equalizing the optical channels of a multichannel optical imaging system, individually or on a group-by-group basis, are recursively computed while the imaging system is idle (i.e., not printing) through the use of an iterative process comprising the steps of: measuring the output intensities of the respective sets of channels, sequentially comparing the measured channel intensities against a system calibrated reference intensity level, and adjusting the correction factor for each set of channels that is found to be operating at an intensity level deviating from the reference intensity level in the direction that is required to reduce the magnitude of the deviation (unless the correction factor value already is at the limit of its dynamic range in that direction). Preferably, the correction factor adjustments are made by incrementing and decrementing their least significant values, thereby maximizing the sensitivity of each iteration of the process to the affect of the immediately preceding iteration on the amount of crosstalk occurring between neighboring sets of channels. For example, the correction factors suitably are multi-bit binary values which are adjusted by incrementing and decrementing their least significant bits (LSB's). The reference intensity level typically is calibrated by measuring the uncorrected output intensities of the respective sets of channels and by then selecting the intensity of the set of channels which is determined to be operating at the lowest valid intensity level for use as the reference intensity. Advantageously, this calibration procedure is repeated on a predetermined schedule for recalibrating the reference level from time-to-time to correct for gradual drift in the optical characteristics of the imaging system.

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Campbell, CA, United States of America

Robert P Kowalski