Patent Publication Number: US-6219500-B1

Title: Developer liquid squeegee apparatus for liquid electrophotographic printer

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 my application DEVELOPER LIQUID SQUEEGEE APPARATUS FOR LIQUID ELECTROPHOTOGRAPHIC PRINTER filed with the Korean Industrial Property Office on Feb. 6, 1999 and there duly assigned Ser. No. 4096/1999. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a liquid electrophotographic printer and, more particularly, to a developer liquid squeegee apparatus for removing excess developer liquid sticking to and wrapped around the recording surface of a photosensitive medium. 
     2. Related Art 
     A liquid electrophotographic printer develops a latent electrostatic image formed on a photosensitive medium using a developer liquid and prints a desired image. 
     In such a printer, a development region having substantially the same width as that of a development roller of the printer is formed on a photoreceptor belt. Developer liquid sticking to the development region is compressed by a squeegee roller, and only the developer liquid required for development of the latent electrostatic image remains thereon, with excess developer liquid being removed. 
     However, a problem arises in that the excess developer liquid tends to be pushed outside the development region of the photoreceptor belt by a wrap-around phenomenon in which the excess developer liquid moves to both edges of the squeegee roller along a gap between the squeegee roller and the photoreceptor belt. In that case, an air nozzle can be used to spray air toward the wrap-around developer liquid, thereby preventing the wrap-around developer liquid from flowing outside the development region of the photoreceptor belt. 
     However, a further problem arises in that, if the air is not properly sprayed or the air spraying force is weak due to clogging of the air nozzle or malfunction of a pump associated therewith, the wrap-around developer liquid flows toward both edges of the development region of the photoreceptor belt. Thus, the wrap-around developer liquid results in developer liquid contamination and degrading of print quality in the printed image. In particular, in the case of a color printer, discoloration of the printed image may occur due to mingling of differently colored inks. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an object of the present invention to provide a developer liquid squeegee apparatus for a liquid electrophotographic printer having enhanced print quality by additionally providing an arrangement for cleaning developer liquid wrap-around outside the development region of a photoreceptor belt. 
     In order to achieve the above object, there is provided a developer liquid squeegee apparatus for a liquid electrophotographic printer comprising a first squeegee roller for squeegeeing developer liquid supplied to a development region of a photoreceptor belt and removing excess developer liquid, a pair of air nozzles for spraying air toward both edges of the first squeegee roller to prevent the wrap-around developer liquid from being induced thereto, a heating roller for drying the developer liquid on an image developed on the development region of the photoreceptor belt; and a wrap-around developer liquid removing arrangement provided between the first squeegee roller and the heating roller. 
     According to the present invention, the wrap-around developer liquid removing arrangement includes a detector provided directly under both edges of the development region of the. photoreceptor belt for detecting the presence of the wrap-around developer liquid sticking to both edges of the development region of the photoreceptor belt, a second squeegee roller for removing the wrap-around developer liquid sticking to both edges of the development region of the photoreceptor belt while selectively contacting the photoreceptor belt and rotating according to a signal transmitted from an optical sensor module and indicative of the detection result, and a driving unit for driving the second squeegee roller to selectively contact the photoreceptor belt. 
     In addition, a ring-shaped cleaning member which is brought into contact with both edges of the development region of the photoreceptor belt to remove the developer liquid thereon may be provided at both ends of the second squeegee roller. 
     Preferably, the driving unit includes a frame having one end rotated by the driving of the actuator and which rotatably supports both ends of the second squeegee roller, and a controller for driving the actuator according to the signal transmitted from the detector, the second squeegee roller selectively contacting the photoreceptor belt or the heating roller according to the signal transmitted from the detector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation ofthe invention, and may ofthe 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 is a schematic diagram illustrating essential parts of a liquid electrophotographic printer; 
     FIG. 2 is a plan view schematically illustrating essential parts of a developer liquid squeegee apparatus for the liquid electrophotographic printer shown in FIG. 1; 
     FIG. 3 illustrates a state in which developer liquid is wrapped around the squeegee apparatus in the liquid electrophotographic printer shown in FIG. 1; 
     FIG. 4 is a schematic diagram illustrating essential parts of a developer liquid squeegee apparatus for a liquid electrophotographic printer according to the present invention; 
     FIG. 5 is an extracted view schematically showing essential parts of the developer liquid squeegee apparatus shown in FIG. 4; and 
     FIG. 6 is a partially exploded perspective view illustrating a second squeegee roller shown in FIGS. 4 and 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic diagram illustrating essential parts of a liquid electrophotographic printer. As shown in FIG. 1, a liquid electrophotographic printer includes a photoreceptor belt  100  circulating on an endless track around a plurality of rotation rollers  101  and  102 , laser scanning units (LSUs)  120  installed in the vicinity of the photoreceptor belt  100 , a development unit  110 , a drying unit  130  and a printing unit  140 . 
     The LSUs  120  form latent electrostatic images on a transfer surface ofthe photoreceptor belt  100  by irradiating laser beams. The development unit  110  supplies developer liquid to the latent electrostatic image and develops the same. An image formed by the developer liquid on the latent electrostatic image of the photoreceptor belt  100  is dried by a drying roller  131  and heating rollers  132  of the dry unit  130  and then transferred to a recording sheet  10  as an image by a transfer roller  141  and a pressing roller  142  of the printing unit  140 . 
     The development unit  110  includes a developer liquid supplier  116  for supplying developer liquid  111 , a development roller  112 , a cleaning roller  113 , a squeegee roller  114 , an air nozzle  115  and a blade B. 
     The developer liquid supplier  116  supplies developer liquid  111  between the development roller  112  and the photoreceptor belt  100 , and the cleaning roller  113  removes developer liquid  111  remaining on the surface of the development roller  112 . The squeegee roller  114  removes excess developer liquid from the latent electrostatic image formed on the photoreceptor belt  100 . The blade B removes developer liquid from the surface of the squeegee roller  114 . 
     FIG. 2 is a plan view schematically illustrating essential parts of a developer liquid squeegee apparatus for the liquid electrophotographic printer shown in FIG. 1, and FIG. 3 illustrates a state in which developer liquid is wrapped around the squeegee apparatus in the liquid electrophotographic printer shown in FIG.  1 . 
     As shown in FIG. 2, a development region  100   a  having substantially the same width as that of the development roller  112  is formed on the photoreceptor belt  100 . Developer liquid  111  sticking to the development region  100   a  is compressed by the squeegee roller  114 , and only the developer liquid required for development of the latent electrostatic image remains thereon, with excess developer liquid being removed. 
     The excess developer liquid tends to be pushed outside the development region  100   a  of the photoreceptor belt  100  by a wrap-around phenomenon in which the excess developer liquid moves to both edges of the squeegee roller  114  along the gap between the squeegee roller  114  and the photoreceptor belt  100 . The air nozzle  115  sprays air toward the wrap-around developer liquid W, thereby preventing the wrap-around developer liquid W from flowing outside the development region  100   a  of the photoreceptor belt  100 . 
     However, in the case where the air is not properly sprayed or the air spraying force is weak due to clogging of the air nozzle  115  or malfunction of a pump P, as shown in FIG. 3, the wrap-around developer liquid  111 ′ flows toward both edges of the development region  100   a  of the photoreceptor belt  100 . Thus, the wrap-around developer liquid  111 ′ results in developer liquid contamination, degrading print quality in the printed image. In particular, in the case of a color printer, discoloration of the printed image may occur due to mingling of differently colored inks. 
     FIG. 4 is a schematic diagram illustrating essential parts of a developer liquid squeegee apparatus for a liquid electrophotographic printer according to the present invention, and FIG. 5 is an extracted view schematically showing essential parts of the developer liquid squeegee apparatus shown in FIG.  4 . 
     Referring to FIGS. 4 and 5, a developer liquid squeegee apparatus for a liquid electrophotographic printer according to the present invention includes a first squeegee roller  114  for squeegeeing developer liquid supplied to a development region  100   a  of a photoreceptor belt  100  and removing excess developer liquid, an air nozzle  115  for spraying air toward both edges of the first squeegee roller  114 , a heating roller  132  for drying developer liquid on an image developed on the development region  100   a  of the photoreceptor belt  100 , and a wrap-around developer liquid removing arrangement  200  provided between the first squeegee roller  114  and the heating roller  132 . In FIG. 4, the same reference numerals as those used in FIGS. 1 thru  3  are used to denote identical elements. 
     According to the present invention, in order to remove wrap-around developer liquid induced into both edges of the development region  100   a  of the photoreceptor belt  100  due to malfunction or abnormal operation of the air nozzle  115 , the wrap-around developer liquid removing arrangement  200  includes an optical sensor module  210 , a second squeegee roller  220  and a driving unit  230  for driving these elements. 
     The optical sensor module  210  includes a light emitting diode (not shown) and a light receiving diode (not shown), and is disposed directly under both edges of the development region  100   a  of the photoreceptor belt  100 . The optical sensor module  210  detects the presence of the wrap-around developer liquid sticking to both edges of the development region  100   a  of the photoreceptor belt  100 , and transmits a signal indicative of the detection result to the second squeegee roller  220  via a controller  240 . 
     The second squeegee roller  220  selectively contacts the photoreceptor belt  100  or the heating roller  132  according to the signal transmitted from the optical sensor module  210  via a controller  240 . 
     The driving unit  230  for driving the second squeegee roller  220  includes a holder  231  for rotatably supporting both ends of the second squeegee roller  220 , a frame  232  for rotatably supporting the holder  231 , an actuator  233  for selectively rotating the holder  231 , and a controller  240  for driving the actuator  233  according to the signal transmitted from the optical sensor module  210 . 
     According to the present invention a cylinder or a solenoid may be used as the actuator  233 . In this case, the driving shaft  233   a  of the cylinder or solenoid is connected to a protrusion  231   a  provided in the holder  231 , and the driving shaft  233   a  reciprocates linearly to interact with the protrusion  231   a , thereby rotating the holder  231 . The holder  231  is axially coupled to both ends of the second squeegee roller  220  to allow rotation of the second squeegee roller  220 , and holder  231  is hinged to the frame  232  so as to be rotated. 
     According to another aspect of the present invention, a cam mechanism connected to the driving shaft of a driving motor to be rotated may be used as the actuator  233 . According to this configuration, although not shown, the cam mechanism interferes with the protrusion  231   a  of the holder  231  by the driving of a driving motor (not shown) to thus rotate the holder  231 , thereby selectively bringing the second squeegee roller  220  into contact with the photoreceptor belt  100  or the heating roller  132 . 
     Therefore, in the present invention, the actuator  233  can be implemented by various means, known to those of skill in the art, which means can interact with the protrusion  231   a  of the holder  231  for rotation, and such means are not limited to specific embodiments described above. 
     FIG. 6 is a partially exploded perspective view illustrating a second squeegee roller shown in FIGS. 4 and 5. 
     According to the present invention, as shown in FIG. 6, a ring-shaped cleaning member  221  which surrounds the outer circumferential surface of the second squeegee roller  220  is provided at both ends of the second squeegee roller  220 . The cleaning member  221  has a double-layered structure comprised of an inner non-absorptive layer  221   a  making contact with the outer circumferential surface of the second squeegee roller  220 , and an outer absorptive layer  221   b  stacked on the non-absorptive layer  221   a . The non-absorptive layer  221   a  is preferably made of urethane rubber, and the absorptive layer  221   b  is preferably made of sponge or a foam material. 
     In the aforementioned developer liquid squeegee apparatus for a liquid electrophotographic printer, according to the present invention, in a situation where the developer liquid transferred to the photoreceptor belt  100  by the development roller  112  of the development unit  110  sticks to a development region  100   a  having the same width as that of the development roller  112 , only that volume of developer liquid required for development remains on the development region  100   a , and excess developer liquid is removed by the first squeegee roller  114 . Some of the excess developer liquid causes the wrap-around phenomenon or problem in which the developer liquid deviates from the development region  100   a  along the gap between the squeegee roller  114  and the photoreceptor belt  100 . In that case, the air nozzle  115  sprays air toward the wrap-around developer liquid, thereby preventing the developer liquid from flowing out of the development region  100   a  of the photoreceptor belt  100 . 
     However, in the case where the air is not properly sprayed or the pressure of the sprayed air is weak due to clogging of the air nozzle  115  or malfunction of pump P, the wrap-around developer liquid flows toward both edges of the development region  100   a  of the photoreceptor belt  100  and sticks thereto. When the wrap-around developer liquid sticking to regions other than the development region  100   a  ofthe photoreceptor belt  100  migrates to the drying unit  130 , the presence of the wrap-around developer liquid is detected by the optical sensor module  210 . For example, the optical sensor module  210  can detect the presence ofthe wrap-around developer liquid by comparing light reflectivity for the case where the developer liquid does not stick to regions other than the development region  100   a  of the photoreceptor belt  100  with light reflectivity for the case where the developer liquid sticks to the development region  100   a.    
     When the presence of the wrap-around developer liquid is detected by the optical sensor module  210 , a signal indicative of the detection result is transmitted to the controller  240  of the driving unit  230  so as to control the actuator  233  to be driven. Then, the actuator  233  rotates the holder  231 , supporting both ends of the second squeegee roller  220 , so as to bring the second squeegee roller  220  into contact with the recording plane of the photoreceptor belt  100 . 
     When the second squeegee roller  220  rotates into contact with the recording plane of the photoreceptor belt  100 , it lightly presses the recording plane, and it removes the wrap-around developer liquid. Here, the absorptive layer  221   b  of the ring-shaped cleaning member  221 , provided at both ends of the second squeegee roller  220 , contacts both edges of the development region  100   a  of the photoreceptor belt  100  and absorbs the wrap-around developer liquid therefrom. The non-absorptive layer  221   a  prevents the developer liquid absorbed by the absorptive layer  221   b  from flowing downward to the surface of the second squeegee roller  220 . The removal of wrap-around developer liquid by the cleaning member  221  of the second squeegee roller  220  is continuously performed while the photoreceptor belt  100  travels. 
     According to the present invention, a reference absorption amount of wrap-around developer liquid which can be absorbed by the cleaning member  221  of the second squeegee roller  220  is measured in advance. For example, the reference absorption amount is calculated by measuring the traveling distance of the photoreceptor belt  100  or the number of revolutions ofthe second squeegee roller  220 , each of which corresponds to the reference absorption amount. Thus, while the cleaning member  221  of the second squeegee roller  220  performs the wrap-around developer liquid removal operation, a determination is made as to whether the traveling distance of the photoreceptor belt  100  or the number of revolutions of the second squeegee roller  220  reaches a reference absorption amount. Then, a signal indicative of the result of such determination is applied to the controller  240  so as to cause the actuator  233  to be driven. Accordingly, the actuator  233  rotates the holder  231 , supporting both ends of the second squeegee roller  220 , so as to bring the second squeegee roller  220  into contact with the heating roller  132 . At this point, one cycle of the wrap-around developer liquid removal operation by the cleaning member  221  of the second squeegee roller  220  is completed, and the cleaning member  221 , which is in contact with the heating roller  132 , is heated so that the wrap-around developer liquid absorbed by the absorptive layer  231   b  of the cleaning member  221  is evaporated for subsequent recovery. 
     As described above, in the developer liquid squeegee apparatus for a liquid electrophotographic printer according to the present invention, in the case of malfunction of an air nozzle for spraying air toward the wrap-around developer liquid on both edges of a squeegee roller provided in a development unit to avoid a wrap-around problem, or in the case of weak air pressure, the presence of the wrap-around developer liquid is detected by an optical sensor module, and the wrap-around developer liquid is removed by a second squeegee roller. Therefore, it is possible to enhance the recovery efficiency of the developer liquid and to prevent degradation in print quality due to mingling or contamination due to non-removal of the wrap-around developer liquid by the first squeegee roller and air nozzles. 
     It should be understood that the present invention is not limited to the particular embodiment disclosed herein as the best mode contemplated for carrying out the present invention, but rather that the present invention is not limited to the specific embodiments described in this specification except as defined in the appended claims.