Abstract: The present invention is a method and apparatus for digitally controlling the output of multiple laser diodes in a system that forms a plurality of scan lines in a Raster Output Scanning (ROS) system. Output of the laser diodes is digitally controlled by monitoring and controlling the bias and run level power for each of the laser diodes. The system employs predetermined, controllable biasing currents to increase the resolution of the exposure current and thereby accurately control the output power of each of the multiple laser diodes, and to provide a fixed exposure level that is detectable by a low-cost start-of-scan detector.

Abstract: An image bar printing system, which, in a preferred embodiment, utilizes a plurality of LED arrays to provide a plurality of color images. The print bars are used in conjunction with a plurality of gradient index lens arrays which optically couple and focus the LED outputs onto a photosensitive surface. In order to maintain image-to-image registration, out of spec deviations in active write length of the image bar and scan line bow are identified and compensated for by selective deformation of one or more lens arrays in a specified manner. The lens deformation serves to reorient the position of certain of the lens elements, redirecting the transmitted LED outputs so as to shorten or lengthen the active write length, or to eliminate bow in the scan line.

Abstract: The present invention discloses a dynamic control of a drive circuit to a diode laser used in a raster output scanning system. In the prior art, the binary serial stream input to a diode laser operates on the laser to pulse the laser on when a "one" input is applied, the laser staying on when the first one input is immediately followed by successive one inputs. The first on pixel creates an exposure at an image plane which is less than uniform due to the characteristics of the drive circuit due to the overshoot or undershoot characteristics of the drive circuit. The second and succeeding pixels following the first pixel turned on will be at a maximum exposure value and hence will have an undesirable exposure contrast with the first pixel.

Abstract: The present invention provides a means and method for efficiently and automatically monitoring and adjusting the power output of either a single or a dual beam laser diode array used to provide the scanning beams in a ROS system. Collimated light outputs from a collimator lens assembly following either a single or dual beam laser are reflected along an optical path to impinge on one or two photodiodes positioned so as to intercept the reflected light. The photodiode output is proportional to the power output of the laser diode associated with the photodiode. In one multi-beam embodiment, polarization of the laser diode output is controlled so as to ensure that only outputs from an associated laser diode is sensed by an associated photodiode. In another embodiment, a half wave plate is used to rotate the polarization of one of the laser diodes.

Abstract: A print bar color printing system wherein exposure occurs through previously deposited color toner is compensated for light absorption in the previously deposited toner by selectively increasing the output of the print bar during a pixel time interval. Each time interval is divided into sublines which are available for applying image data. One subline transmits image data corresponding to the color of the image to be exposed at the photoreceptor surface, while the second subline carries information as to previously exposed and developed color images which overlap the subsequent image. The print bar is then selectively addressed to form the main color image with a pulse of relatively long duration, or duty cycle, followed by a pulse having a relatively short duty cycle. The second or third pulses represent the additional exposure level needed to compensate for light absorbed by previous color toners formed on the belt during the earlier development process.

Abstract: Output copy quality in a ROS electrophotographic printer is maintained by a method and apparatus designed to selectively vary the beam intensity level of a laser beam scan in response to changed conditions within the scanning or xerographic output subsystems. A test pattern video data input is periodically applied to a laser creating an exposure of the test pattern at the photoreceptor. The resulting print has a plurality of horizontal bands with each band associated with a specific beam intensity correction signal. The test pattern band which appears to provide optimum density is identified. The corresponding digital beam intensity correction signal in the ESS memory is enabled and replaces the previous beam intensity signal controlling the laseer output level.