Abstract:
There is provided a process and an image formation apparatus for enhancing the image quality of an image forming apparatus such as a printer, a facsimile and a complex machine employing an electrophotographic technique, capable of obtaining a good image quality even though the image is formed on a thick paper such as an envelope. The process includes the steps of: storing image data to be printed at a memory if a print demand is received; detecting the kind of paper selected by a user; editing by reducing the number of pixels of the image data at a certain rate if the detected paper is a thick; and transmitting the edited image data to the LSU and performing the printing work for the edited image data.

Description:
CLAIM OF PRIORITY 
   This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application METHOD FOR ENHANCING THE IMAGE QUALITY OF AN IMAGE FORMING APPARATUS for earlier filed in the Korean Industrial Property Office on the 7th day of the month of July 1999, and there duly assigned Serial No. 27215/1999. 
   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to image formation process and apparatus generally, and, more particularly, to image formation process and apparatus for enhancing the image quality of images printed on thicker, albeit narrower paper while employing an electrophotographic developing technique. 
   2. Description of the Related Art 
   In general, an image forming apparatus that employs an electrophotographic developing technique such as a facsimile, a printer and a complex machine, is equipped with an electrification roller, a photosensitive drum, a transfer roller, a developing roller, a toner supply roller, a fixer and a laser scanning unit (i.e., a “LSU”) for printing images onto a printable media such as a cut sheet of paper. I have noticed deficiencies in the pre-transfer system of image forming processes and apparatus. By way of example, if the user intends to form an image on a printable material that is relatively thicker than the standard grade of xerographic paper such as an envelope, the toner coated on the photosensitive drum is not transferred onto the paper and the remaining toner on the photosensitive drum is transferred onto the next piece of printable material that passes along the path conveying the printable material through the apparatus, thereby causing a mis-transfer which is referred to as “ghost phenomenon”, because the transfer electric field cannot transmit the thick paper. Moreover, when a thick envelope having a relatively narrower width in comparison to a sheet of A4 or 8½″ by 11″ paper is used in a transfer system using a conductive roller, in a state wherein a high voltage required for the transfer is applied to the transfer roller, the conductive layer of the photosensitive drum is broken. This defect is frequently referred to as a “pin hole”, and occurs in the region (either on the right, the left, or possibly on both sides of the sheet of the printable media) where the transfer roller and the photosensitive drum come into direct contact with each other due to the absence of any intermediate printable media, thereby causing fatal and unrepairable damage to the photosensitive exterior circumferential surface of the drum. 
   SUMMARY OF THE INVENTION 
   It is, therefore, a primary object of the present invention to provide an improved image formation process and apparatus. 
   It is another object to provide an image formation process and apparatus demonstrating an enhancement of image quality of the images formed by the process and the apparatus. 
   It is still another object to provide an image formation process and apparatus capable of improving transfer efficiency. 
   It is yet another object to provide an image formation process and apparatus capable of forming a high quality of image on a thicker paper. 
   It is still yet another object to provide an image formation process and apparatus capable of minimizing damage to the photosensitive drum while printing images upon media that have a width less than the axial length of the photosensitive drum. 
   It is a further object to provide an image formation process and apparatus capable of for enhancing the image quality of printed images while preventing damage of the photosensitive drum although a transfer roller directly contacts the photosensitive drum in case an image is formed on a thick envelope with a narrow width. 
   These and other objects may be attained according to the principles of the present invention, with an image formation process and apparatus using either a reduced number of pixels of light emitted from a laser scanning unit, a decreased amount of light or an increased level of developing voltage by faintly treating the image signals generated by a controller. 
   In accordance with one aspect of the present invention, the process contemplates storing image data to be printed at a memory if a print demand is received; detecting the kind of paper selected by a user; editing by reducing the number of pixels of the image data at a certain rate if the detected paper is a thick; and transmitting the edited image data to the LSU and performing the printing work for the edited image data. The editing step may include equally splitting the pixels of the light scanned into an integer number of pixels in order to represent one pixel of the image data, and editing by using Econo (economy) mode at which only a certain number of pixels among the equally split pixels of the light are scanned. In addition, the editing step may include splitting the print area into a plurality of small areas, and editing by using Ret (resolution enhancement technology) mode at which some pixels among the total pixels for the resolution included in the respective split small areas are removed. 
   In accordance with another aspect of the present invention, the process contemplates storing image data to be printed at a memory if a print demand is received; detecting the kind of paper selected by a user; transmitting the image data to the laser scanning unit if the detected paper is thick; and decreasing the amount of the light emitted from the laser scanning unit at a predetermined rate and performing the printing work. 
   In accordance with another aspect of the present invention, the process contemplates storing image data to be printed at a memory if a print demand is received; detecting the kind of paper selected by a user; transmitting the image data to the laser scanning unit if the detected paper is thick; and increasing a developing voltage applied to the developing machine to a predetermined voltage level and then performing the printing work. The predetermined voltage level is equal to or less than −250 volts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
       FIG. 1  schematically shows an image forming apparatus employing an electrophotographic developing technique; 
       FIG. 2  is a schematic block diagram of an image forming apparatus constructed according to the principles of the present invention; 
       FIG. 3  is a flow chart showing the first embodiment of a process for enhancing the image quality of the image forming apparatus according to the principles of the present invention; 
       FIG. 4  is a flow chart showing the second embodiment of a process for enhancing the image quality of the image forming apparatus according to the principles of the present invention; and 
       FIG. 5  is a flow chart showing the third embodiment of a process for enhancing the image quality of the image forming apparatus according to the principles of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning now to the drawings,  FIG. 1  shows an image forming apparatus  100  such as a facsimile, a printer and a complex machine, employing a electrophotographic developing technique. Image forming apparatus  100  may be constructed with a pick-up roller  101 , an electrification roller  102 , a photosensitive drum  103 , a transfer roller  104 , a developing roller  105 , a supply roller  106 , a fixer  107  and a laser scanning unit (“LSU”)  108  for printing certain image data onto a recording medium such as a cut sheet of paper that is withdrawn by pick-up roller  101  from the top side of a stack of cut sheets stored within paper cassette  109 , and propelled along a path of conveyance  120  through apparatus  100 . During the printing process, the electrification roller  102  uniformly electrifies the photosensitive substance coated on the external surface of the photosensitive drum  103  while rotating, and the light generated from LSU  108  forms an electrostatic latent image that is to be printed, on the electrified photosensitive drum  103 . Then, there is a voltage difference between the supply roller  106  to which a higher supply voltage is applied and the developing roller  105  to which a lower voltage is applied. Therefore, negative charges move from the supply roller  106  to the developing roller  105 . In this way, toner supplied to the developing roller  105  is coated on the electrostatic latent image formed on the exterior circumferential surface of photosensitive drum  104  to form a visible image. The high voltage of transfer roller  104  causes the visible image formed by the toner coating the surface of the photosensitive drum  103  to be transferred to the recording paper  109  delivered along path  120 . After the transfer of the visible image onto the recording paper  109  is fixed on the recording paper  109  by the high temperature and high pressure of a heating roller  110  and the pressure exerted by pressing roller  111  mounted within fixer  107  to engage opposite sides of the recording media, thereby finishing the printing process and discharging a sheet of paper bearing toner particles that form a visible image. This sequence of supplying sheets of paper, developing, transfer and application of electrification voltages is continuously applied to the supply roller  106 , the developing roller  105 , the transfer roller  104  and the electrification roller  102 , respectively until the printing process is completed for each job. The heating roller  110  in the fixer  107  is maintained in a turned-on state until the printing process has been completed. 
   I have noticed deficiencies in the pre-transfer system of image forming processes and apparatus. By way of example, if the user intends to form an image on a printable material that is relatively thicker than the standard grade of xerographic paper such as an envelope, the toner coated on the photosensitive drum is not transferred onto the paper and the remaining toner on the photosensitive drum is transferred onto the next piece of printable material that passes along path  120 , thereby causing a mis-transfer which is referred to as “ghost development”, because the transfer electric field cannot transmit the thick paper. Moreover, when a thick envelope having a relatively narrower width in comparison to a sheet of A4 or 8½″ by 11″ paper is used in a transfer system using a conductive roller, in a state wherein a high voltage required for the transfer is applied to the transfer roller, the conductive layer of the photosensitive drum is broken. This defect is frequently referred to as a “pin hole”, and occurs in the region (either on the right, the left, or possibly on both sides of the sheet of the printable media) where the transfer roller and the photosensitive drum come into direct contact with each other due to the absence of any intermediate printable media, thereby causing fatal and unrepairable damage to the photosensitive exterior circumferential surface of drum  103 . 
   Referring now to  FIG. 2 , a preferred embodiment of the present invention may be implemented with an image forming apparatus  200  constructed with a central processing unit (“CPU”)  201  for controlling the image forming apparatus pursuant to a given operational program as a whole. In particular, central processing unit  201  controls the function block in the image forming apparatus in accordance with the particular kind of paper selected by a user of apparatus  200 , thereby enhancing the image quality. In other words, central processing unit  201  attenuates, or “faints” the image information derived from image data received from an external source such as a computer, a document scanner, or a telephone wire, and applies the image information to a laser scanning unit (“LSU”)  202  faintly by either reducing the number of pixels of light emitted from the LSU  202 , or by increasing the magnitude of the developing voltage when the user selects a thick paper, thereby enhancing the transfer efficiency. Power convertor  203  receives the common household line voltage, i.e., either 110 volts or 220 volts, transforms the line voltage to a voltage level required at each function block in the image forming apparatus, and then supplies the transformed voltage to each function block under the control of central processing unit  201 . 
   Developing voltage controller  204  controls the developing voltage applied to developing roller  205  under the control of central processing unit  201 . That is, developing voltage controller  204  increases the developing voltage level applied to the developing roller  205  from −300 volts to −250 volts or more under the control of central processing unit  201 , in accordance with the kind of printable medium (e.g., a cut sheet of xerographic grade paper) detected by central processing unit  201 , in response to either a manual input by a user or a signal supplied by a sensor (e.g., a sensor deployed to detect passage of paper through a bypass tray or a paper thickness sensor) located along the path  220  of conveyance through apparatus  200 . 
   A memory  206  stores various operational programs for controlling image forming apparatus  200  through the central processing unit  201  as well as the image data to be printed by the image forming apparatus  200 . Laser scanning unit (“LSU”)  202  scans signals of light corresponding to the image data selected by the user to be printed onto the printable medium, in order to form electrostatic latent images on the exterior circumferential surface of photosensitive drum  207 . Electrification roller  208  electrifies the surface of the photosensitive drum  207  at a constant potential with a high electrification voltage (−1.4 kilo-volts) drawn from power convertor  203 . The supply roller  210  supplies the particles of toner drawn from the hopper of a toner container to developing roller  205  while rotating in contact with developing roller  205 . A developing roller  205  applies the toner supplied by supply roller  210  to the electrostatic latent image on the photosensitive drum  207  while contacting the photosensitive drum at a constant pressure to form a visible image on the photosensitive exterior circumferential surface of drum  207 . Transfer roller  209  is electrified with a high transfer voltage (+1.5 kilovolts) drawn from power convertor  203 , and transfers the toner coated onto the photosensitive exterior circumferential surface of drum  207  to the printable medium delivered paper along path  220  while rotating in contact with the photosensitive drum  207  at a constant pressure. 
   The operation of each of the several embodiments according to the practice of the principles of the present invention including such an arrangement will now be described. 
   The First Embodiment 
     FIG. 3  shows in a flow chart, one of the processes for enhancing the image quality of the image forming apparatus according to the practice of the instant principles, as a first embodiment of the present invention. When a print work is selected by a user (step S 1 ), central processing unit  201  stores within memory  206  image data transmitted from a computer or other external equipment (step S 2 ), and detects the kind of paper selected by the user (step S 3 ). If the grade of paper selected by the user at step S 3  is determined to be a thicker stock of paper (step  4 ), central processing unit  201  performs an editing function to reduce the image data to be printed at a certain rate per each pixel (step S 5 ), and transmits the edited image data to the laser scanning unit  202  (step S 6 ) and performs the print work for the edited image data (step S 7 ) by creating the image corresponding to the image information onto the surface of the printable media. If the grade of paper selected at step S 3  is determined during step S 4  to not be a thicker type of paper, central processing unit performs a normal printing work (step S 8 ). Then, central processing unit  201  determines whether or not the printing work should be completed (step S 9 ), and if additional printing is determined by step S 9  to be required for that job, central processing unit  201  proceeds to repeat all of the process after step S 5 , or if step S 9  determines that the print job has been completed, central processing unit  201  finishes the printing process. 
   Although there are various processes for the editing work, only two representative cases, that are used in the printing work, are described herein. At a print mode, “Econo mode” and “Ret mode” are present in various setting functions. The “Econo mode” is a process wherein, in order to represent one pixel of the image data, the number of pixels of the light scanned is split into an integer number N by laser scanning unit  202 , and only certain areas among the number of pixels of light split uniformly are emitted, thereby reducing the overall number of pixels to be illuminated. This means that since the number of pixels of light emitted by light scanning unit  202  is less than the number of pixels of light to be emitted for printing actual data during a normal printing mode, the total amount of toner to be used during the printing is deceased and, therefore, the amount of toner coated onto the photosensitive exterior circumferential surface of drum  207  from the developing roller  205  is decreased. Accordingly, even though the transfer potential is low due to the reduced amount of the toner coated onto the photosensitive drum  207 , an adequate quantity of toner to define the image to be printed can be transferred on the paper. 
   On the other hand, the “Ret mode” is a process wherein the print areas are split into a plurality of small areas, and some of total pixels per each resolution in the respective split small areas are removed. This mode is substantially similar to the “econo mode” in terms of both the constitution and the effect. 
   The Second Embodiment 
     FIG. 4  shows a flow chart for a process of enhancing the image quality of printed images in accordance with the second embodiment of the present invention. In  FIG. 4 , for the convenience of explanation, illustrates some of the same steps as shown in  FIG. 3 . When a print work is selected by a user (step S 10 ), central processing unit  201  stores within memory  206  image data transmitted from a computer or other external equipment (step S 11 ), and detects the grade and type of paper selected by the user (step S 12 ). If the grade and type of paper selected by the user at step S 12  is a thicker paper (step  13 ), central processing unit transmits image data to be printed to the light scanning unit  202  (step S 14 ), and controls light scanning unit  202  to reduce the amount of the light emitted from light scanning unit  202  onto the photosensitive exterior circumferential surface of drum  103  at a certain rate (step S 15 ), and then performs the print work with the reduced amount of the light (step S 16 ). 
   If the kind of paper selected at step S 3  is not a thick paper, central processing unit performs a normal printing work (step S 17 ). Then, central processing unit  201  determines whether or not the printing work is completed (step  18 ), and if not, proceeds all the steps after step S 14 , or if completed, finishes the printing process. That is, since the amount of the light emitted from the light scanning unit  202  is less than the actual amount of the light to be emitted for printing data, the electrification potential of the photosensitive drum  207  is not sufficiently low. This means that the engagement force of the toner coated on the surface of the photosensitive drum  207  is lowered. Therefore, even though the transfer potential is low due to the low engagement force of the toner transmitted from the developing roller  205  and coated on the photosensitive drum  207 , sufficient toner is transferred onto the sheet of paper conveyed along path  220 . 
   The Third Embodiment 
     FIG. 5  shows a flow chart of a process for enhancing the image quality in accordance with the third embodiment of the present invention. In  FIG. 5 , for the convenience of explanation, some of the same steps employed in the processes of  FIGS. 3 and 4  are described. When a print work is selected by a user during step S 19 , central processing unit  201  stores within memory  206  image data transmitted from a computer, page or line scanner, telephone line, facsimile machine, or other external equipment (step S 20 ), and detects the weight, type, quality, grade, thickness or kind of paper selected by the user during step S 21 . If the grade of paper selected by the user at step S 21  is determined during step S 22  to be a thicker grade of paper stock, central processing unit transmits image data to be printed to the laser scanning unit  202  (step S 23 ), and controls the developing voltage controller  204  to increase the developing voltage by a certain level (step S 24 ), and in step S 25  performs the printing work with the toner transmitted to the photosensitive drum  207  according to the increased developing voltage. 
   If the grade of paper selected at step S 21  is determined during step S 22  to not be a thicker grade of paper, central processing unit  201  performs a normal printing job during step S 26 . Then, in step S 27 , central processing unit  201  determines whether or not the printing work is completed, and if not, repeats all the steps after step S 23 , or if completed, stops the process. 
   When in the normal state, the developing voltage is maintained at about −300 V, the potential of the surface of the photosensitive exterior circumferential surface of drum  207  illuminated by the light scanned from the laser scanning unit  202  is maintained at about −50 volts. At that time, there is generated a voltage difference of about −250 volts between the developing voltage of the developing roller  205  and the surface potential of photosensitive drum  207  so that a large amount of toner is transferred onto the photosensitive exterior circumferential surface of drum  207  from developing roller  205 . If central processing unit  201  determines during step S 22  that a thicker grade of paper has been selected by the user, when the developing voltage is increased below about −250 volts, if a voltage difference of about −200 volts or less is created between the developing voltage of developing roller  205  and the surface potential of the photosensitive drum  207 , the amount of the toner transmitted to the photosensitive drum  207  from the developing roller  205  is reduced to less than the amount of the toner transferred during normal printing jobs using a normal grade (e.g, 20 pound cut sheets) of paper. Accordingly, although the transfer voltage is low due to the reduction in the quantity of toner coated onto photosensitive drum  207 , the quantity of toner that is transferred is still sufficient to be transferred and form sharply defined images onto the paper selected by the user. 
   The process for enhancing the image quality of the image forming apparatus in accordance with the principles of the present invention endows image formation with notable advantages. That is, in case that the image forming work is performed for a thicker stock of paper, by reducing the number of pixels of the light emitted from laser scanning unit  202  and enabling a reduction in the quantity of toner to be coated onto the photosensitive surface of drum  207 , the transfer efficiency and hence the image quality are enhanced. Moreover, by decreasing the amount of the light emitted by laser scanning unit  202  and lowering the engagement force of the toner coated onto the photosensitive surface of drum  207 , the transfer efficiency and hence the image quality of the resulting printed item are enhanced. In addition, by increasing the developing voltage by a certain level and reducing the quantity of toner transferred from developing roller  205  and coated onto the photosensitive surface of drum  207 , the transfer efficiency and hence the image quality are enhanced. 
   Although the invention has been shown and described with respect to the preferred embodiments according to the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. Although specific components of the circuit are exemplified herein, it is apparent to those skilled in the art that it is not intended to limit the present invention and that the present invention may be practiced without the specific components. Further, the detailed explanations on the related known functions or constitutions, which may render the subject matter of the present invention vague or unclear, are omitted herein. Therefore, the present invention should not be limited to the described embodiments and is defined by the appended claims and the equivalent thereof.