Abstract:
An imaging device is enabled to stabilize toner mass usage by implementing a closed loop feedback system. Actual toner mass per area used is compared with a target mass per area reference to produce an error signal for modifying toner consumption in the imaging device. A method for stabilizing toner mass consumption in an imaging device includes calculating first indicia indicative of an actual mass per area of toner consumed in the imaging device, comparing the first indicia with second indicia indicative of a target mass per area of toner consumed, and modifying toner consumption in the imaging device based on the comparing. In a preferred embodiment, a toner level sensed is compared to an original toner reference amount to produce a toner mass used. Pixels rendered are tracked to calculate a total area imaged relative to a time frame established in association with the original toner reference amount. The total mass used is divided by the total area imaged to produce the actual mass per area used. Toner consumption is modified using laser pulse width modulation or pixel masking such that subsequent actual mass per area of toner consumed approaches the target mass per area.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation in part of co-pending U.S. application Ser. No. 09/014,296 filed Jan. 27, 1998.  
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates in general to image forming devices and, more particularly, to controlling toner consumption in electrophotographic imaging devices.  
         BACKGROUND OF THE INVENTION  
         [0003]    In electrophotographic (EP) printing, such as in laser printers and copiers, a pattern of electrostatic charges corresponding to a print image is developed on an optical photoconductor (OPC) using radiated energy, either visible spectrum light or optical energy outside the visible light spectrum. Conventionally, near infrared laser light is used to develop an electrostatic image on the OPC. The OPC is usually a continuous surface such as a drum or belt.  
           [0004]    The laser light scans across the charged surface of photosensitive material on the OPC in a succession of scan lines. Each scan line is logically divided into picture element (pixel) areas and the laser beam is modulated such that selected pixel areas are exposed to light. Pixel size (or pixel space) is defined by a given dot pitch, scan velocity and spot size of the printer. The exposure to light results in the reduction of voltage on the OPC at those select pixel locations forming a latent image pattern. Subsequently, toner is applied (deposited) onto those pixel locations to form a visible image and this image is then transferred to a print media (typically a sheet of paper).  
           [0005]    The toner transferred onto the sheet media appears in a pattern of dots (or spots), with each dot corresponding to a pixel (or combination of pixels for developing tones). While dots are usually associated with the image on the sheet media and pixels are usually associated with the corresponding electronic image, the one-to-one correspondence of dots to pixels commonly results in the terms being used interchangeably.  
           [0006]    For any given print engine, toner consumption depends upon the discharge voltage level on the OPC. Although pixel development may be controlled by modulation of the laser power, operation of the laser diode in a non-saturated mode is often not desirable because there are too many environmental factors that are difficult to control and that tend to cause less stable overall pixel development. For example, laser modulation is very sensitive to parameters such as aging of the laser diode and temperature conditions. However, a similar effect is accomplished by turning the laser full on (saturated mode) and full off for periods of time shorter than what is needed or budgeted for developing the full pixel (dot) size for a given dot pitch and scan velocity. This is known as pulse width modulation (PWM) of the laser diode. Specifically, PWM is the modification of the duty cycle of the video (laser) signal wave form within a unit amount of time and has the effect of changing the level of exposure intensity. The duty cycle is the percent of time the signal is in an active state (for exposing a pixel space) within the specified unit amount of time. In essence, PWM permits a sub-sized pixel (or portion of a pixel) to be developed on an OPC. Thus, if the laser beam is modulated (using PWM), the resultant variations in voltage on the OPC will ultimately be translated to proportionate amounts of toner mass being developed onto the OPC and then transferred onto a sheet of media. PWM is commonly used in applications such as gray scaling, halftoning, and color imaging (i.e., for precise mixing of colors as well as control of the intensity of the colors).  
           [0007]    Regardless of whether a full laser diode pulse is applied to develop a full sized pixel, or whether the laser is modulated using PWM to develop a sub pixel, the amount of toner mass that is applied to the exposed area is critical to the quality of the resultant image that is transferred to media. Additionally, excessive toner that is unnecessarily developed onto the pixel or sub pixel is wasted. For example, too much developed toner mass tends to cause toner scatter, which is a dusting or blurring of the resultant image by the excess/wasted toner. This occurs in both monochrome and color imaging systems. This problem is magnified when the print engine utilizes an intermediate transfer belt. Print quality degradation is especially noticeable when printing text and fine detail because a cloud of toner surrounds the characters making them unclear. Additionally, toner scatter is exaggerated in connection with media that moves slower through the fusing system, such as with glossy paper.  
           [0008]    Clearly, the EP printing process is inherently unstable with respect to toner mass development per unit area. In addition to image quality issues, this leads to difficulty in estimating toner cartridge life (toner usage) and some uncertainty in predicting the cost per page for a given print platform. If toner mass per unit area developed by the EP printing process were stable, the amount of toner consumed in printing a given page could be predicted from knowing how many of the possible dots on the page were actually printed. Although pixel (or dot) counting is conventional in the art, the accuracy of pixel counting varies from platform to platform in about the 15-25% range because of the uncertainty of actual toner mass development per unit area.  
           [0009]    Although recent technologies have enabled more accurate toner level sensing in a toner cartridge for predicting the cartridge life (toner usage), the actual toner usage and cost per page predictability still varies from platform to platform because, again, of the uncertainty of actual toner mass development per unit area.  
           [0010]    Accordingly, an object of the present invention is to assist in the stabilization of toner consumption for improving the estimating of toner usage and cost per page for a given print platform.  
         SUMMARY OF THE INVENTION  
         [0011]    According to principles of the present invention in a preferred embodiment, an imaging device is enabled to stabilize toner mass development by implementing a closed loop feedback system. Actual toner mass used is compared with a target mass reference to produce an error signal for modifying toner consumption in the imaging device.  
           [0012]    A method for stabilizing toner mass used in an imaging device includes calculating first indicia indicative of an actual mass per area of toner consumed in the imaging device, comparing the first indicia with second indicia indicative of a target mass per area of toner consumed, and modifying toner consumption in the imaging device based on the comparing.  
           [0013]    Also in a preferred embodiment, a toner level sensed is compared to an original toner reference amount to produce a toner mass used. Pixels rendered are tracked to calculate a total area imaged relative to a time frame established in association with the original toner reference amount. The total mass used is divided by the total area imaged to produce the actual mass per area used. Toner consumption is modified using laser pulse width modulation or pixel masking such that subsequent actual mass per area of toner consumed approaches the target mass per unit area.  
           [0014]    Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is high level block diagram of a page printer incorporating the present invention apparatus and method for stabilizing toner consumption.  
         [0016]    [0016]FIG. 2 is a schematic block diagram depicting a preferred embodiment of the present invention for stabilizing toner consumption in the printer of FIG. 1.  
         [0017]    [0017]FIG. 3 is a flow chart depicting a preferred method of the present invention.  
         [0018]    [0018]FIG. 4 is a timing diagram depicting three signals representing exemplary clock pulses for modifying pixel development under the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]FIG. 1 is a high level block diagram of a page printer  10  incorporating the present invention apparatus and method for stabilizing toner consumption for improving the estimating of toner usage and cost per page within the printer. Page printer  10  is controlled by a microprocessor  15  which communicates with other elements of the system via bus  20 . A print engine controller  30  and associated print engine  35  connect to bus  20  and provide the print output capability for the page printer. For purposes of this disclosure, print engine  35  is a laser printer that employs an electrophotographic drum and imaging system utilizing discharge area development that is well known in the art. However, as will be obvious to those of ordinary skill in the art, the present invention is similarly applicable to other types of printers and/or imaging devices including, for example, facsimile machines, digital copiers, or the like.  
         [0020]    An input/output (I/O) port  40  provides communications between the page printer  10  and a host computer  45  and receives page descriptions (or raster data) from the host for processing within the page printer. A dynamic random access memory (DRAM)  50  provides a main memory for the page printer for storing and processing a print job data stream received from host  45 . A read only memory (ROM)  55  holds firmware which controls the operation of microprocessor  15  and page printer  10 . Code procedures stored in ROM  55  include, for example, a page converter, rasterizer, compression code, page print scheduler, print engine manager, and/or other image processing procedures (not shown) for generating an image from a print job data stream. The page converter firmware converts a page description received from the host to a display command list, with each display command defining an object to be printed on the page. The rasterizer firmware converts each display command to an appropriate bit map (rasterized strip or band) and distributes the bit map into memory  50 . The compression firmware compresses the rasterized strips as specified or in the event insufficient memory exists in memory  50  for holding the rasterized strips.  
         [0021]    Additionally, ROM  55  includes Pixel Counter  80  for counting pixels rendered by print engine  35 . Pixel Counter  80  is any conventional pixel counting routine in the art, such as, for example, any one or more of the methods and/or apparatus taught in U.S. Pat. Nos. 5,802,420, 5,797,061, 5,794,094, 5,754,708, 5,754,312, 5,636,032, 5,572,292, 5,349,377, and 5,204,698, each of which is incorporated in full herein by reference.  
         [0022]    ROM  55  further includes Toner Consumption Controller  82  for controlling, generally, toner consumption (toner usage in pixel development) in printer  10 . In a preferred embodiment, Toner Consumption Controller  82  controls toner deposition for an image being processed in printer  10  by means of modifying laser pulse width modulations as will be discussed more fully herein. Alternatively, other conventional routines in the art capable of controlling toner usage/deposition are similarly feasible. For example, the methods and/or apparatus taught in U.S. Pat. No. 5,483,625, incorporated in full herein by reference, may be used. In any case, it should be noted that although Pixel Counter  80  and Toner Consumption Controller  82  are depicted as firmware, it will be obvious that hardware specific implementations (i.e., in an ASIC) are also feasible, depending on the overall design criteria of printer  10 .  
         [0023]    Importantly, under principles of the present invention, ROM  55  also includes Toner Stabilization Manager  85 . Toner Stabilization Manager  85  includes routines, tables and/or other data structures necessary for managing and stabilizing toner consumption by printer  10  as will be discussed more fully herein.  
         [0024]    In general, the operation of page printer  10  commences when it receives a page description from host computer  45  via I/O port  40  in the form of a print job data stream. The page description is placed in DRAM  50  and/or a cache memory associated with microprocessor  15 . Microprocessor  15  accesses the page description, line by line, and builds a display command list using the page converter firmware in ROM  55 . As the display command list is being produced, the display commands are sorted by location on the page and allocated to page strips in memory  50 . When all page strips have been evaluated, rasterized, compressed, etc. for processing by print engine  35 , the page is closed and the rasterized strips are passed to print engine  35  by print engine controller  30 , thereby enabling the generation of an image (i.e., text/graphics etc). The page print scheduler controls the sequencing and transferring of page strips to print engine controller  30 . The print engine manager controls the operation of print engine controller  30  and, in turn, print engine  35 .  
         [0025]    Processor  15  feeds to a video controller  60  a raster image of binary values which represent the image to be imprinted on a page. The video controller, in response, feeds a series of binary data signals to a laser driver  65  which, in turn, modulates laser  70  in accordance with the binary data signals.  
         [0026]    As conventional in the art, the modulated beam from laser  70  is directed at a rotating, faceted mirror which scans the beam across an imaging lens which directs the scanned beam to a mirror which redirects the scanned beam onto a moving OPC  75 . The laser beam is scanned across the OPC to cause selective discharge thereof in accordance with the modulation of the beam. At the termination of each scan action, the laser beam is incident on a photodetector which outputs a beam detect signal that is used to synchronize the actions of video controller  60  and processor  15 . Subsequent to the selective discharge of OPC  75 , toner is applied (deposited) from toner cartridge  90  onto the discharged pixel locations to form a visible image. The visible image is then transferred to a print media such as a sheet of paper that is passed through printer  10 . Toner usage amounts out of toner cartridge  90  are monitored with toner level sensor  95 . Toner level sensor  95  is any conventional sensor in the art capable of detecting with a reasonable degree of accuracy the amount of toner remaining in cartridge  95 . Examples of such sensor technologies include, for example, any one or more of the apparatus and/or methods taught in U.S. Pat. Nos. 5,587,770, 5,557,368, 5,465,619, 5,499,077, 5,214,475, 4,786,869, 4,397,265, 4,314,242, and 4,313,343, each of which is incorporated in full herein by reference.  
         [0027]    Further to the operation of printer  10  and according to principles of the present invention, Toner Stabilization Manager  85 : (i) determines an actual mass per area of toner deposited onto OPC  75  (based on toner level readings from sensor  95  and based on Pixel Counter  80 ), (ii) calculates a mass per area error signal relative to a target mass per area signal, and (iii) modifies Toner Consumption Controller algorithm  82  for stabilizing toner consumption in printer  10 .  
         [0028]    Referring now to FIG. 2, a schematic block diagram depicts a preferred embodiment of the present invention for stabilizing toner consumption in printer  10 . First, when a toner cartridge  90  is installed in printer  10 , a toner mass reference amount  205  is determined that identifies how much toner exists in the cartridge  90 . This reference amount is detected by toner sensor  95  (or other detection scheme known in the art) and is communicated to Toner Stabilization Manager  85  and stored for reference purposes. As print engine  35  proceeds with imaging operations, toner sensor  95  continues to monitor  210  the toner level in cartridge  90 . The toner level sensed  210  by sensor  95  during operation of printer  10  (i.e., during usage of cartridge  90 ) is summed  215  (or differenced) with the reference amount  205 , the difference being a value or signal indicative of the amount of toner used, or in other words, the toner Mass Printed  220 . Preferably, a change in toner level sensed  210  during operation of printer  10  is detectable by sensor  95  over a minimal number of pages printed by print engine  35 . In this context, the more finely accurate the toner level sense reading  210 , then the quicker and more responsive the present invention becomes for stabilizing toner consumption relative to the number of pages printed.  
         [0029]    Additionally, during operation of print engine  35 , Pixel Counter  80  continually counts pixels rendered and tracks the sum (or integral)  225  of such pixels to produce a value or signal indicative of a total Area Printed by the rendered pixels. The total Area Printed is determined based on a reference in time that corresponds to when the toner mass reference amount  205  was determined. Consequently,  235 , for this referenced operation interval or time frame, Toner Stabilization Manager  85  divides the Mass Printed  220  by the Area Printed  230  to produce a value or signal indicative of an Actual Mass/Area  240  amount of toner utilized by printer  10 .  
         [0030]    Importantly, now, Toner Stabilization Manager  85  compares  245  the Actual Mass/Area  240  with a Target Mass/Area  250 . The Target Mass/Area is a value or signal indicative of a desired amount of toner mass/area to be used by printer  10 . The Target Mass/Area is established by one or more factors that affect one or more operational parameters of printer  10 , such as image quality or cost per page. For example, if a slightly less quality image is an acceptable factor (i.e., by using/developing less toner on the image), then the Target Mass/Area is set to a lower value and, consequently, the cost per page is reduced. On the other hand, if image quality is of prime importance, then the Target Mass/Area is set to an increased value and, consequently, the cost per page is increased. In any case, the Target Mass/Area may be set independent of current operational settings/results of printer  10  or, alternatively, relative to the current operational settings/results of printer  10 . Additionally, the Target Mass/Area signal or value is input to printer  10  from an external source by conventional means such as software (i.e., print driver) in communication with printer  10 , or a control panel of printer  10  in communication with firmware in ROM  55 .  
         [0031]    The comparison  245  of the Actual Mass/Area  240  and the Target Mass/Area  250  produces a Mass/Area Error Signal (value)  255 . The Mass/Area Error Signal is then introduced into the Toner Consumption Controller procedure  82  to modify toner consumption accordingly in print engine  35 . For example, if the Mass/Area Error Signal is indicative of a need to reduce the Actual Mass/Area of toner to approach the Target Mass/Area (i.e., to reduce toner consumption and cost), then Toner Consumption Controller  82  responds to the Error Signal and modifies pixel development  260  accordingly for print engine  35 . For example, in a preferred embodiment, if toner consumption is to be reduced, pixel development is modified by varying the laser&#39;s  70  pulse width modulation (PWM) signals for print engine  35 . Alternatively, reduced pixel development occurs by using a checkerboard development pattern (mask), a draft/economy print mode, or other reduced print quality or toner saving modes conventional in the art.  
         [0032]    Clearly, the present invention closed loop feedback drives the Actual Mass/Area  240  to match the Target Mass/Area  250  whereby stabilization of toner usage is achieved for improving the estimating of toner usage and cost per page for printer  10 .  
         [0033]    [0033]FIG. 3 is a flow chart depicting a preferred method of the present invention for toner stabilization in an imaging device (such as printer  10  of FIG. 1). First,  305 , an actual toner Mass Printed is determined. In a preferred embodiment, this includes taking the difference of an amount of toner level sensed in toner cartridge  90  with a toner mass reference amount. Next (or additionally), an actual Area Printed is determined  310 . In a preferred embodiment, this includes counting pixels rendered and integrating using a predetermined average pixel area or a more actual pixel area based on, for example, laser pulse width modulation signals. The number of pixels counted is relative to a time frame established by when the toner mass reference amount was set.  
         [0034]    Subsequently,  315 , an Actual Mass/Area of toner used is calculated by dividing the actual Mass Printed by the actual Area Printed. Then,  320 , the Actual Mass/Area is compared to a Target Mass/Area and an error value is generated  325 . The Target Mass/Area is input at a control panel of the imaging device or via a software driver configuration. The error value is used  330  by a toner consumption control procedure to modify pixel development in the imaging device such that the Actual Mass/Area of toner usage approaches the Target Mass/Area, thus stabilizing toner consumption to the Target Mass/Area. Again, pixel development modification is accomplished using pulse width modulation, pattern mask, draft/economy print mode, or other reduced print quality or toner saving modes.  
         [0035]    Referring now to FIG. 4, a timing diagram depicts three signals “A”, “B” and “C” representing exemplary clock pulses that may be applied to laser driver  65  for pulsing laser  70  as controlled by Toner Consumption Control procedure  82  for modifying pixel development  260  under the present invention. These signals represent a preferred method of using laser pulse width modulation (PWM) for modifying pixel development in order to stabilize toner consumption in response to the Mass/Area Error Signal  255 .  
         [0036]    Specifically, in this preferred embodiment, toner consumption control is achieved by pulse width modulating the laser such that the OPC  75  potential is decreased to allow varying amounts of developed toner mass onto the OPC. In other words, the developed toner mass is precisely controlled with a simple change to laser exposure pulse “on-time”. Pulse width modulation is applied to each individual color plane as necessary and is used to help improve/control the quality of the developed spots, line edges and images by controlling the exposure profiles and spot geometry.  
         [0037]    Thus, in reference now again to the exemplary varying PWM signals of FIG. 4, signal “A” represents a full 100% clock pulse signal for full pixel development (exposure) within a reference time frame  90 . Reference time frame  90  is based on a given dot pitch, scan velocity and spot size of printer  10 . Signal “B” represents a 50% centered clock pulse signal for a generally 50% centered pixel development. In contrast, signal “C” represents a 50% split clock pulse signal for split pixel development. Signal “C” represents a split pulse within the reference time frame  90 . Importantly, signal “C” depicts how split pulsing the clock signal includes pulsing the clock signal at least twice within the full pulse width reference time frame  90  such that the at least two pulses are not immediately adjacent to each other. This split pulsing depicted in signal “C” is referred to herein as split-subpixel modulation (SSM). Alternatively, split pulsing occurs in a super pixel (multi-cell) context. For example, if a super pixel is defined as a four by four cell pixel, then SSM occurs at any point within the reference frame of the four by four super pixel. Importantly, any one of the PWM signals “A”, “B” or “C”, or any other PWM signal or combination of PWM signals may be used for modifying pixel development in order to stabilize toner mass/unit consumption in response to the Mass/Area Error Signal  255  under the present invention. Further discussion of PWM is found in U.S. patent application Ser. No. 09/014,296, incorporated in full herein by reference.  
         [0038]    Finally, it will be obvious to one of ordinary skill in the art that the present invention is easily implemented utilizing any of a variety of components and tools existing in the art. Moreover, while the present invention has been described by reference to specific embodiments, it will be apparent that other alternative embodiments and methods of implementation or modification may be employed without departing from the true spirit and scope of the invention.