Abstract: In a system for transporting film materials, rotation of the transported film caused by uneven stress across a width of the film is eliminated by providing a pinch roll drive in which the driven roll is a precision metal roll and the non-driven roll is a rubber roll, the outer cylindrical surface of which is defined by a plurality of axially-spaced annular ribs. Accumulated error is removed at regular intervals by braking the film to cause correction of slippage. Feed under uniform stress is achieved by forming a dancer roll film loop and correcting for differential alignment of the various transport rolls by displacing a portion of one side of the loop.

Abstract: A method and apparatus for precisely advancing film material between two rollers includes a driven roller having a medium hardness rubber surface and a non-driven hard surfaced roller which contacts precision surfaces at either end of the driven roller to accurately control the spacing between the two rollers. The non-driven roller is urged against the driven roller precision surfaces by a spring force, and causes the rubber of the driven roller to compress when film material is in an operative position between the roller pair.

Abstract: A method and apparatus for maintaining a controlled precise energy output level for a laser diode, particularly useful in a precision scanning environment, provide for a thermal stabilization current to be added to the normal bias exposure current of the diode The thermal stabilization current is modeled to account for the temperature variation of the laser diode junction which affects the light energy output as a function of current. The addition of the thermal stabilization current provides a substantially flat and constant, precise output energy from the laser diode during its "on" time as a function of an input exposure value.

Abstract: A method and apparatus for accurately controlling a hysteresis synchronous motor velocity eliminate low frequency hunting, which is characteristic of the motor. A nominal input phase current is modified by providing feedback information, thereby enabling a microprocessor control system to modify the phase of quadrature input current signal to the motor and thereby eliminating hunting of the motor. Accordingly, in a high resolution scanning application, speed variations which could cause disturbing artifacts to appear in an output image are eliminated.

Abstract: An apparatus for scanning documents combines digitizing circuitry with a scanning platen to achieve precise selection of image areas on large documents. A vacuum system holds the document in place against a perforated scanning surface during registration and scanning. The assembly of scanning surface, vacuum chamber, and digitizing circuitry move as a unit beneath a fixed scanning apparatus. The apparatus further has a mechanical structure which allows the table assembly to rotate about a pivot axis toward an operator to reduce parallax error in mapping image areas.

Abstract: In digital halftone color printing, low spatial frequency patterning can occur due to the interaction of the overlapping angled halftone screens. The moire patterning can be minimized by automatically constructing digital haltone angled screens from screen tiles which are designed to minimize the low spatial frequency patterning. The screen tile boundaries are generated in response to selected integers which, together with the number of screen dots along a side of the tile in the direction of screen pitch measurement, determine the a limit on the magnitude of screen angle error. Based upon these values, each pixel within the tile boundary is associated with one of the screen dots of the image. Typically, the pixels are added to potential candidate lists from which they can be selected for inclusion within a particular screen dot.

Abstract: An apparatus and method for synchronizing to a scanning galvanometer system provide for magnification changes on the order of one part in a thousand. The apparatus employs two phase locked loops connected in series with a digital counter divider. The combination of phase locked loop, digital divider, and phase locked loop provide a multiplication factor equal to a*c/b which enables the required precision in magnification step change to be achieved. Critical to operation of the circuitry is the provision for resetting the divider counter when the first phase locked loop is sufficiently synchronized to a ruled grating which is part of the scanning system.

Abstract: Improvements in apparatus for making a halftone reproduction of an original document, of the type having an optical system comprising a source of light and a deflecting member for providing deflecting scanning and recording beams, a drive for providing relative motion between the original document and the scanning beam in a direction transverse to the direction of deflection thereof so that the scanning beam will trace a succession of scan lines across the document respectively during a succession of scanning cycles, an electro-optical pickup operative during each scanning cycle to detect the light from the scanning beam after it has impinged upon the document and to thereby provide an electrical output representative of the tone density (including any variation thereof) of the document along the scan line traced during that scanning cycle, video circuitry connected to the pickup for converting the electrical output into a video signal, a source of a succession of dot reference signals representative of the d