Abstract: In an optical recording apparatus, a detecting section detects disk identification information of an optical disk for selecting a constant which relates to the detected disk identification information. A test OPC section performs test writing operation for OPC at a predetermined linear velocity prior to recording of data so as to obtain a test value. A formulating section formulates an equation expressing a target value in function of a recording linear velocity based on the constant, the predetermined linear velocity and the test value. A running OPC section performs running operation of OPC by monitoring an actual value while irradiating a laser beam for the recording of data at the recording linear velocity. A controlling section controls the power of the laser beam such that the monitored actual value coincides with the target value which is determined by the equation with respect to the recording linear velocity.

Abstract: A semiconductor laser device comprises a semiconductor laser, a photo-diode, a first input terminal and a second input terminal. A sample hold circuit, having a first switch and a capacitor, is provided between the first input terminal and the semiconductor laser. A second switch is provided between the second input terminal and the semiconductor laser. A drive current is supplied to the semiconductor laser based on a light radiation level command signal input to the first input terminal. A constant current is generated based on a signal input through the second input terminal. In a sampling mode, the first and second switches are turned ON, and thus, a control current, which is obtained by subtracting the constant current from the drive current, is sampled by the sample hold circuit. In a holding mode, one of a bias current, obtained based on the control current and the constant current, or the drive current are supplied to the semiconductor laser, in accordance with ON/OFF of the second switch.

Abstract: In an image recording apparatus 1 which records an image on a recording medium 9 by moving an optical head 10 while rotating the recording medium 9 held by a holding drum 7, a photodetector 2 having a plurality of photodetector elements 21 is provided in a range of movement of the optical head 10. In correcting beam intensity, the optical head 10 is positioned so precisely that the photodetector 2 can receive the signal light beams. This constitution makes it possible to detect signal light beams from the light modulator with high S/N ratio as compared with a conventional case where one photodetector element sequentially receives the signal light beams, and therefore possible to correct the beam intensities with high accuracy.

Abstract: A laser driving apparatus which includes a plurality of laser emitting elements, a light receiving element for monitoring amounts of light from the plurality of laser emitting elements, and a current-voltage converter for converting a light amount monitor current outputted from the light receiving element to a light amount monitor voltage. The laser driving apparatus also includes a control circuit for controlling a drive current of each of the plurality of laser emitting elements, based on the light amount monitor voltage outputted from the current-voltage converter. The current-voltage converter includes a common resistor and a plurality of non-common resistors, wherein the common resistor is connected to said light receiving element, and each of the plurality of non-common resistors is connectable to the common resistor through a respective switch and is connected to the control circuit.

Abstract: A system for printing on a print media. The device comprises at least one high energy emitting device and a parameter estimation device. The parameter estimation device is coupled to the high energy emitting device and is adapted to classify the print media and quantify an amount of energy per time to be emitted by the high energy emitting device during printing.

Abstract: An intensity correction circuit adjusts the intensity of the pixel data which modulates the light beam of a raster output scanner to compensate for facet to facet reflectivity intensity differences of the rotating polygon mirror used to scan the modulated light beam on a photosensitive medium.

Abstract: A calibration station (34) for a printhead (20) adapted to provide a beam of electromagnetic radiation from a variable electromagnetic energy source onto a sensitive radiation medium, the calibration station (34), incorporates a sensor (26) disposed for sensing the beam (16) provided by the printhead (20), wherein the sensor (26) provides an output sensor signal indicative of the sensed power of the beam (16). A control circuit is adapted to accept the output sensor signal from the sensor and adjusts the variable electromagnetic energy source. A filter is disposed in the path of the beam (16) between the printhead (20) and sensor (26), adapted to transmit to the sensor (26) a portion of incident electromagnetic radiation over a predefined range of wavelengths, dependent upon a measured response characteristic of the radiation-sensitive medium.

Abstract: In a solid scanning optical writing device that writes images on a photoreceptor by turning ON/OFF many light shutter elements aligned in an alternating fashion in two rows in the main scanning direction, single-row illumination and double-row illumination of the light shutter elements are alternately performed on a time sharing basis prior to the image writing in order to perform high-quality light amount correction. The positions of the light shutter elements are identified from the light amount data obtained from single-row illumination, and the transmitted light amount for each light shutter element during double-row illumination is sought from the light amount data obtained from double-row illumination. Calculation for shading correction is then performed from these sets of data.

Abstract: Methods and apparatus for determining the optimal adjustment of imaging systems used to prepare lithographic printing surfaces for a printing press are described. A series of test patterns are imaged while varying a particular imaging parameter. This is followed, if necessary, by processing the plate in processing line. The plate is then returned to the digital imaging system where the reflectivity of the imaged test patterns is measured using a radiation source and detector, to determine the optimal setting for the parameter.

Abstract: A laser modulating device is provided with a monitoring system that outputs a detection voltage signal corresponding to the output power, a minimum output level setting system that outputs a minimum level voltage signal, a modulating voltage signal generating system, a first adder that outputs a reference voltage signal corresponding to a sum of the minimum level voltage signal and the modulating voltage signal, a comparing system that outputs a driving voltage signal corresponding to a difference between the reference voltage signal and the detection voltage signal, a first V/I converting system that converts the driving voltage signal to a first driving current, the first driving current being supplied to the laser diode, a second V/I converting system, and a circuit that directly supplies the modulating voltage signal from the modulating voltage signal generating system to the second voltage to current converting system, the second voltage to current converting system converting the modulating voltage sign

Abstract: In a light power modulating system for modulating output power of a laser diode, an output power of the laser diode is monitored and a voltage signal corresponding to the detected output power is output. An image signal output system is provided to form an image signal representative of a thickness density of an image to be formed, and a modifying system modifies the image signal such that a changing rate of the image signal between a lower value and a higher value is lowered. A differential amplifier outputs an amplified difference between the modified image signal and the voltage signal, and a driving current to be supplied to the laser diode is generated based on the amplified difference output by the differential amplifier.

Abstract: A method and apparatus for reducing image unevenness due to light emission of a transfer element. Namely, when a printing speed is changed to 1/2n (n is a positive integer), a SLED head controller repeats a cycle to perform exposure control for one line and then stops the exposure control for the lines corresponding to 1/2n speed. For example, in the 1/2 speed (i.e., n=1), transfer and light emission driving are performed at an initially set maximum speed, and the cycle when the exposure control for one line is stopped after the one-line exposure control is repeated. The printing speed is changed on the basis of the type or kind of recording medium used.

Abstract: An optical write head which drives a plurality of light shutter elements arranged in a main scanning direction individually to write a multi-tone image on a recording medium. Prior to the image writing, while the light shutter elements are driven for reproduction of tone levels of 0, 48, 160 and 240, the quantities of light outputted from each of the elements are measured with a sensor, and from the measured values, an approximate expression indicating the output characteristic of each of the elements is calculated. The difference between the recording medium and the sensor in spectral sensitivity is made up, for example, by changing the intensity of light of each of the three primary colors emitted from a lamp by switching the voltage applied to the lamp between at the time of measurement and at the time of exposure or by changing the sensitivity of the sensor in receiving each of the three primary colors by switching the accelerating voltage applied to the sensor.

Abstract: There is provided an image recorder which allows easy malfunction detection in a light modulator and can previously prevent the occurrence of fogging of a photosensitive material, a fire, or the like.

Abstract: A device for spotwise imaging printing surfaces includes a laser light source producing at least one laser beam movable relative to a printing surface, the laser beam defining an image spot on the printing surface, the laser beam having a laser power. A laser control varies the laser power or an exposure time as a function of a distance of the laser light source from the image spot.

Abstract: The object of the present invention is to precisely correct the luminous energy of a laser beam on a scanned surface which varies according to scanning and varies according to an angle of incidence with the scanned surface when a laser beam emitted from a semiconductor laser for emitting a laser beam having luminous energy according to supply current is scanned on the scanned surface via a scanning optical system.

Abstract: An electric photograph system for improving non-linearities of an exposing light intensity and an operating current at a low exposing level when performing analog printing operation. A range (saturable absorber) having a saturable absorbing characteristic is provided in a part of an optical path including a semiconductor laser as light source to improve the non-linearity of the operating current when the light intensity is weak. The saturable absorber may be made in the form of a non current injected area provided in a part of the semiconductor laser as the light source or a thin film layer provided partly in films coated on a facet of the semiconductor laser. Due to the provision of the saturable absorber, the light output power characteristic can exhibit its linearity in its low optical power range, the size of a printing dot can be arithmetically changed, and thus fine laser printing can be realized.

Abstract: A light beam scanner unit includes a light beam generating unit for generating light beams at a fixed power, a polygon mirror for reflecting light beams generated from the light beam generating means toward a surface to be scanned, thereby scanning it, and a light beam power sensing unit for sensing light beam power for scanning a surface to be scanned with the polygon mirror. This light beam scanner unit further has a mirror contamination sensing unit for sensing contamination of the polygon mirror by comparing a sensing result obtained from the light beam power sensing unit when light beams are emitted by the light beam generating unit with a preset reference value.

Abstract: In a photographic printer using a laser scanning unit for exposing a latent image corresponding to an image data on a sensitized surface of a photographic paper, intensities of the laser beams exposing the photographic paper is adjusted corresponding to a variation of an actual sensitivity of the photographic paper and deterioration of a developer with respect to nominal values of them. At least the intensities directly emitted from laser light sources, or values of optical modulation data for modulating the laser beams corresponding to the image data are varied. Alternatively, transmittances of optical elements such as polarizing beam splitters provided on optical paths are varied for adjusting the intensities of the laser beams.

Abstract: A solid scanning optical writing device has multiple optical elements which are aligned in a zigzag fashion to form two lines in a main scanning direction. Each of the optical elements is turned ON/OFF in accordance with image data to write an image. In the solid scanning optical writing device, the amount of light output from each of optical elements is corrected based on correction data. The correction data is obtained by detecting light amount distribution of each of the two lines and obtaining ridge light amount and trough light amount from the detected light amount distributions.

Abstract: An image recording apparatus includes a PLZT head. The PLZT head performs an interval exposure based on an interval exposure data between exposures of photosensitive material. Further, exposure data of a predetermined number of lines already used in an N-th and preceding exposures may be maintained in a RAM as a basis of correction to an exposure data for an N+1-th print. The PLZT head performs an exposure for an exposure time given by the corrected exposure data.

Abstract: In a laser beam scanner of used for exposing a latent image on a photographic paper, intensities of the laser beams are maintained in predetermined range by compensating amplitude of driving signals supplied to acousto-optic modulators when intensities of the laser beams emitted from laser light sources are varied. The intensities of the laser beams passing through the modulators are sensed by photo sensors and compared with predetermined standard value. When any of the intensity of the laser beam is discrepant from the standard value, a difference between them is calculated and an optical modulation data for controlling the amplitude of the driving signal is compensated by subtracting the difference value from the standard value. Thereby, the amplitude of the driving signal of the modulator is compensated.

Abstract: A method of testing light-emitting condition of a vacuum florescent print head is disclosed. The print head is of a type having a plurality of luminous elements disposed along a main scanning direction for forming dots in the form of a linear column on a print paper, and the print head is movable in a sub-scanning direction relative to the print paper. The method includes a first step of exposing and forming on a print paper a plurality of linear dot columns, each column consisting of a plurality of dots arranged along a main scanning direction with a predetermined space therebetween, the plurality of dot columns being juxtaposed with each other with a predetermined space therebetween; a second step of determining density of each dot formed and exposed by the first step one column after another by using a scanner; and a third step of outputting the determined densities of the respective dots as light-emitting amounts of a plurality of luminous elements forming the linear dot column.

Abstract: A raster output scanner in which both the start-of-scan and the beam intensity of a laser beam are determined using a single photodetector. The raster output scanner has a laser source for generating a laser beam; a rotating polygon for sweeping the laser beam along a scan line plane, an optical fiber with a light receiving end positioned at a known position in the scan line plane and which intercepts at least a portion of the sweeping laser beam, and a photodetector for converting the intercepted laser beam into a beam current. The raster output scanner further includes both a scan detection circuit for producing a star-of-scan signal from the beam current and a beam intensity circuit for producing an electrical output which depends upon the magnitude of the beam current.

Abstract: Double clad fiber gain medium systems particularly adapted for marking indicia on surfaces of articles are disclosed. These systems provide a modulated output from a pump or seed semiconductor laser source to a double clad fiber gain medium which provides an amplified marking output scanned over the article surface with an optical scanner forming a plurality of strokes, the completion of which results in the indicia.

Abstract: At least two light beam detection units are spaced at a predetermined distance and provided in the scanning direction of a surface to be scanned. A light beam is emitted to the light beam detection unit provided on a scanning start side, by lighting a light beam source which is employed to scan the surface linearly during a scanning period equivalent to 1 dot during scanning. A light beam is emitted to the light beam detection unit provided on a scanning end side, by lighting the light beam source during the scanning period after elapse of a light-off period computed from a previously designed scanning speed and the predetermined distance. Based on a detection result of the light beam detection unit provided on the scanning start side and a detection result of the light beam detection unit provided on the scanning end side, scanning characteristics required of the light beam are evaluated.

Abstract: An image forming apparatus, including a driving circuit for a multichip laser chip, which can limit or interrupt emission of laser light sources in accordance with a result of comparison of an optical output of each laser light source with a limiting value during time-division control is provided. The apparatus includes a plurality of laser light source, a light-amount control device for controlling an optical output of a laser beam from each of the plurality of laser light sources to a constant amount of light by performing time division processing, and a light detection device for detecting optical outputs of the plurality of laser light sources. The light detection device includes sensor units whose number is smaller than the number of the plurality of laser light sources.

Abstract: A method and apparatus for a fault tolerant recording system using a pair of laser diode arrays is disclosed. Two monolithic laser diode arrays made of individually addressable diodes are used to record parallel tracks on a recording surface. A pair diodes, (one diode from each array) are assigned to each track, but only one diode (the primary diode) is activated. In the case where the primary diode fails, the secondary diode is activated. Digital delays are employed to synchronize the data from the two diode arrays in order to align the written marks on the recording surface.

Abstract: At least two light beam detection units are spaced at a predetermined distance and provided in the scanning direction of a surface to be scanned. A light beam is emitted to the light beam detection unit provided on a scanning start side, by lighting a light beam source which is employed to scan the surface linearly during a scanning period equivalent to 1 dot during scanning. A light beam is emitted to the light beam detection unit provided on a scanning end side, by lighting the light beam source during the scanning period after elapse of a light-off period computed from a previously designed scanning speed and the predetermined distance. Based on a detection result of the light beam detection unit provided on the scanning start side and a detection result of the light beam detection unit provided on the scanning end side, scanning characteristics required of the light beam are evaluated.

Abstract: In an image recording apparatus, exposure light amounts measured by a sensor immediately after a PLZT head performs an exposure with exposure light amounts corrected first by a controller using an original scanner or the like are stored in a memory as correction reference exposure light amounts. Thereafter, the controller performs an exposure correction such that the exposure light amounts measured by the sensor agree with the correction reference exposure light amounts. At this time, since the correction reference exposure light amounts are set according to the precision of the sensor, a shortage of the exposure light amount can be easily recognized by comparing both exposure light amounts even if the precision of the sensor is not high. As a result, the exposure correction can be reliably performed. Accordingly, the exposure light amounts can be accurately corrected even when using a sensor having a relatively large scanning displacement.

Abstract: A laser imaging system having a diode laser for producing a laser beam; a beamsplitter for splitting the laser beam into a laser writing portion and a feedback portion; a photodetector for detecting the feedback portion; a photodetector amplifier for amplifying the output of the photodetector; a sample and hold coupled to the photodetector amplifier; an integrator adder; an integrator for integrating the outputs of the photodetector amplifier and the sample and hold processed by the integrator adder; and a laser input circuit including a laser amplifier, a linear power signal provider, a threshold power signal provider, and a laser input adder for adding the laser power signal, the linear power signal, and the output of the integrator.

Abstract: The magnification of an image in the main scanning direction thereof is altered by making the frequency of the image clock variable. At this time, if the pre-SOS lighting signal and the APC signal are output synchronously with the frequency of the image clock, then an SOS signal may not be output from the SOS sensor and control of the amount of light of a light beam may not be accurately executed. Therefore, the timings of the outputs of the pre-SOS lighting signal and the APC signal are controlled so as to normally be output at a uniform timing (i.e. the periods from the input of the SOS signal until the outputs of each signal are made uniform).

Abstract: A method and apparatus for determining a line start writing position of a scanning light beam in a scanning light beam writing system. A first detector and a second detector are positioned in the scan path of the scanning light beam for detection of the scanning light beam. The information obtained from the detector is used to determine the line start for commencing writing on a media and for monitoring and controlling the power level of the scanning light beam.

Abstract: A method for measuring the quantity of light emitted from an optical write head which drives an array of light shutter elements extending in a main scanning direction individually in accordance with image data. In order to measure the quantity of light outputted from each of the light shutter elements, a photosensor is moved in the main scanning direction at a constant speed while the light shutter elements are driven in such a way that adjacent elements are not driven at a time. While light shutter elements which are in odd numbers in the array are driven, the photosensor is moved forward to measure the quantities of light outputted therefrom, and while light shutter elements which are in even numbers in the array are driven, the photosensor is moved backward to measure the quantities of light outputted therefrom.

Abstract: A first embodiment of an adjustment circuit for a laser diode output power compensator includes a feedback circuit for adjusting the laser diode output power compensator so that the output power of the laser diode is substantially constant. The feedback circuit includes a photodiode for measuring the output power of a VCSEL diode. The signal from the photodiode is coupled to a first amplifier. The difference between the signal from the photodiode and a first reference value is amplified and coupled through electronic switches to selectively charge one of multiple capacitors. The multiple capacitors are each coupled to one of a drive current source, a compensation current source, and a voltage controlled resistor, each of which are voltage controlled. A second amplifier is used for amplifying the difference between the signal from the photodiode and a second reference value to charge a capacitor coupled to a voltage controlled bias current source.

Abstract: A highlight raster output scanner is disclosed which utilizes an amplitude modulation with its reference level being placed at its white level. Having the reference level at the white level provides the possibility of utilizing two independent power drivers to generate modulation pulses. One power driver generates color pulses (above the white level) and the second power driver generates black pulses (bellow the white level). Since an independent power driver is generating the color pulses, the color level can be raised to saturation to prevent the nonuniformity of the intensity of the light beam for color. Also, any intensity variation of the white level can be adjusted by comparing the white level against the reference level. Finally, the black level is kept at ground potential in the same manner as the prior art.

Abstract: In a method of correcting output light quantities of a plurality of optical output media aligned in one direction in an optical writing apparatus that activates and deactivates the optical output media in multi-gradation to thereby perform optical writing onto an object onto which writing is to be performed, the quantity of light outputted from each of the optical output media is measured, and a variation in the output light quantities of the optical output media is corrected based on a result of the measurement. In performing the correction, in a specific gradation range, correction is performed so that the output light quantities of the optical output media are not made uniform.

Abstract: A laser marking system comprises a high power fiber laser consisting of a double clad fiber having a doped core surrounded by an inner pump cladding and providing an optical output for marking; a high power laser diode source for pumping the double clad fiber laser via an input into the inner pump cladding; an optical scanner coupled to receive the marking output from the double clad fiber laser to scan the output over a surface of an article to be marked by sweeping the marking output in one, two or three dimensions to form strokes, the completion of which comprises indicia to be marked the article surface; and a controller to control the operation of the scanner in synchronism with the modulation of the laser diode pump source to initiate the marking output and sweep and modulate the marking optical output in one, two or three dimensions to form strokes comprising the indicia. A main advantage of the fiber laser marking system over CO.sub.

Abstract: An apparatus for scanning with multiple beams emitted from a semiconductor laser by a polygonal mirror, wherein an image is written for each scanning line by each beam of the multiple beams. The apparatus includes an automatic light amount control circuit having: (i) a light amount detecting circuit to detect a light amount of each beam for each scanning line, and (ii) a sampling/holding circuit to sample and hold a control voltage corresponding to the detected light amount of each beam for each scanning line. The automatic light amount control circuit controls the semiconductor laser based on the control voltage held by the sampling/holding circuit so as to control the light amount of each beam to be a predetermined light amount for each scanning line. The apparatus also includes a synchronization control circuit having an index sensor and a light receiving section on which each beam passes.

Abstract: In a laser scanning apparatus having a polygonal mirror, the laser light reflected from the multiple reflecting surfaces of polygonal mirror is detected with a photosensor. The respective detection outputs are stored in associated storage media (sample and hold circuits). When a certain reflecting surface has been rotated to the next laser light scan position, the detection output for the previous laser light scan is read out of the storage medium. A correction voltage is generated on the basis of the thus read detection output and the reference voltage is corrected with the generated correction voltage. Since the emission output of laser diode is controlled on the basis of the corrected reference voltage, the photoreceptor can be scanned with laser light of constant optical intensity despite the variation in the reflectance of laser light among the multiple reflecting surfaces of the polygonal mirror.

Abstract: Electrophotographic printers having raster output scanners that correct for polygon facet phasing errors and photoreceptor position errors by aerial scan line adjustments. A photoreceptor position sensor senses the position of the photoreceptor and a facet position sensor senses the position of the polygon facets. A scan line position controller produces a position signal that depends upon the photoreceptor position sensor and the facet position sensor. A piezoelectric-actuated lens mover assembly receives the position signal and moves a pre-polygon lens to adjust the scan line plane to correct for any misregistration. The piezoelectric-actuated lens mover assembly includes a large displacement piezoelectric element and a flexible arm assembly that holds the pre-polygon lens.

Abstract: An image forming apparatus includes reading means for converting image light obtained by optically scanning an original into an electric signal. An image signal conversion table converts the image signal from the reading means in response to a property of the image forming system. An image signal generating device generates a reference image signal, and an image forming device forms an image on a recording sheet in response to the image signal. The image is formed on the recording sheet by the image forming device in response to the image signal generated by the image signal generating device, and image light obtained by optically scanning the recording sheet is converted into an image signal by the reading device, and the image signal conversion table is corrected on the basis of the image signal converted by the reading device.

Abstract: A method of controlling the intensity of scanning light in a color image forming apparatus in which a photosensitive member is scanned with light modulated according to an image signal, comprises: a first step of turning on a light source of scanning light in order to illuminate at least the whole of one main scanning line before image formation based on the first color component, and controlling the light source according to the intensity of scanning light; a second step of controlling the light source according to the intensity of scanning light during scanning of a non-image scanning area before the image formation based on the first color component and after the intensity control of the first step; and a third step of controlling the light source according to the intensity of scanning light during scanning of a non-image scanning area between two cycles of image formation based on a color component.

Abstract: In a laser scan based recording apparatus, laser light from a measuring laser diode is directed to one reflecting surface of a polygonal mirror. The reflected light is detected with a measuring photodiode. The reflectance of laser light is calculated from the detection output of the measuring photodiode and a reference voltage is generated. When the reflecting surface has rotated to the position where the laser light from laser light source scans a photoreceptor drum, the emission output of the laser light source is controlled by a laser output control circuit on the basis of the generated reference voltage. Despite variation in reflectance among the multiple reflecting surfaces of the polygonal mirror, the photoreceptor is scanned with a constant optical intensity of laser light. Since automatic power control is performed at all times, overdriving of the laser diode is effectively prevented to protect it against breakdown, producing consistent and highly reliable laser power control.

Abstract: A method and apparatus to accurately control the size of the spots or dots produced by individual lasers within an array of lasers of an image scanning device is disclosed. The lasers are driven in accordance with image information indicating an image to be scanned onto the image bearing member. Output intensity feedback information from each of the lasers is obtained by monitoring an intensity output from each of the lasers. Using this feedback information, the driving energy values of the lasers are adjusted to overcome any unwanted nonuniformities or otherwise calibrated. The invention can also be implemented as an apparatus. Regardless of how the invention is implemented, an image scanning/forming apparatus utilizing the invention is able to scan or print with an array of lasers without being susceptible to streaks and other defects which otherwise occur during the printing or scanning of an image when all of the lasers do not function in a uniform and consistent manner.

Abstract: An image processing apparatus includes an input unit for inputting an image signal, a conversion unit for converting the image signal input by the input unit into a pulsewidth modulated signal, a driving unit for driving a beam emission device for forming an image in accordance with the pulsewidth modulated signal, a detection unit for detecting an intensity of a beam emitted from the beam emission device, and a setting unit for setting conversion conditions for the conversion unit in accordance with an output from the detection unit.

Abstract: A method and structure for a printing system for a laser printer is provided including a data storage area containing a plurality of separate waveform signals. A controller selects a particular waveform signal to modulate the signal input to the system laser diode switch element to generate a halftone cell or a resolution enhancing cell with desired gray scale pixels. The digital laser signal from the printer controller is passed through a digital-to-analog converter circuit to a comparator circuit. The particular waveform selected from the data storage area is also applied to the comparator circuit to modulate the output signal from the digital-to-analog converter. The analog modulated signal from the comparator circuit has an analog value that maintains the laser diode switch element "on" to provide sub-pixels for the particular pixel gray level that is desired.

Abstract: A system and method of calibrating pulsewidth modulation of a laser. The output power of the laser is determined and a signal indicative of the output power is provided to a printer system control computer. The control computer calibrates the pulsewidth modulated signal responsive to the signal indicative of the output power. In a preferred embodiment, the control computer includes a lookup table or a mathematical model. The control computer compensates for timing variations in the pulsewidth modulated signal induced by system components and environmental operating conditions.

Abstract: A system controls the laser-induced discharging of pixel-sized image areas on a photoreceptor in a multi-color xerographic printer where multiple layers of toner are placed on the photoreceptor surface. A light collector, disposed to collect light either reflected from or passing through the photoreceptor, detects conditions in which the laser must pass through one or more layers of previously-placed toner to discharge the photoreceptor. When such a condition is detected, the system increases either the intensity or exposure duration of the laser.

Abstract: The optical intensity of laser light from a laser diode of a laser scanning apparatus having a polygonal mirror is detected with a monitoring photodiode. The detected output is delivered to a first switching end of a selector. The optical intensity of laser light reflected from the polygonal mirror is detected with a photosensor and the detection output is delivered to a second switching end of the selector. The selector selects either one of the switching ends in accordance with the timing of a laser scan. The associated detection signal is fed to a comparator, where it is compared with a reference voltage to produce a comparison voltage, which in turn is fed to a laser drive circuit to control the emission output of the laser diode. Despite variation in the reflectance of laser light from each reflecting surface of the polygonal mirror, a constant optical intensity is obtained on the basis of the reference voltage.