Patent Publication Number: US-6704540-B2

Title: Cleaning device of image forming machine

Description:
FIELD OF THE INVENTION 
     This invention relates to a cleaning device which is applied to an image forming machine, such as an electrostatic copier, a laser printer, or a facsimile, especially, an image forming machine equipped with an a-Si-based (amorphous silicon-based) photoconductor drum. 
     DESCRIPTION OF THE PRIOR ART 
     Image forming machines, for example, printers, using an a-Si-based photoconductor drum have been put to practical use. An a-Si material as a photoconductor is characterized by relative hardness and a long life, but after long-term use, is prone to leakage of electric charges, causing a disturbance to a toner image. To prevent this disturbance in the toner image, a cleaning roller is disposed in a cleaning device, and is in constant contact under pressure with the surface of a photoconductor drum to polish the surface of the photoconductor drum. The cleaning roller is formed from foamed synthetic rubber. A cleaning device provided with such a cleaning roller is disclosed, for example, in Japanese Unexamined Patent Publication No. 2000-112309. The cleaning device disclosed in this publication comprises a pair of arm members each having an intermediate portion pivotable about a support shaft, a cleaning roller rotatably supported between the front ends of the arm members via a shaft, helical tension springs for urging the other ends of the arm members so as to bring the cleaning roller into contact under pressure with the surface of an a-Si-based photoconductor drum, a drive gear integral with the photoconductor drum, and a driven gear integral with the cleaning roller and in mesh with the drive gear. A straight line connecting the support shaft (fulcrum) in each of the arm members and the shaft (point of action) of the cleaning roller is placed on a line nearly parallel to the line of action at the point of engagement between the drive gear and the driven gear (i.e., the line of action in the direction of transmission of force). A configuration in which the position of this support shaft (fulcrum) is slightly displaced from the parallel line is also disclosed in the publication. 
     In a printer having the cleaning device disclosed in the above-mentioned publication, a sheet transport passage extending through a transfer zone of the photoconductor drum may be disposed so as to extend substantially in an up-and-down direction in the transfer zone. In this case, the printing time from the start of printing to the completion of printing can be shortened, because the total length of the sheet transport passage is smaller than when the sheet transport passage is disposed so as to extend substantially in a lateral direction (horizontal direction) in the transfer zone. As a result, the long life and high speed of the printer can both be achieved. However, if the sheet transport passage is disposed in the cleaning device so as to extend substantially in the up-and-down direction in the transfer zone, the cleaning device is placed above the photoconductor drum. The support shaft (fulcrum) in each of the arm members, the other end of each of the arm members, and the helical tension springs urging the other ends are arranged downstream, in the direction of rotation of the photoconductor drum, from the position of the photoconductor drum in contact under pressure with the cleaning roller. Thus, they interfere with toner transport means disposed in the same region. To avoid this drawback, the support shaft (fulcrum) in each of the arm members has been placed upstream, in the direction of rotation of the photoconductor drum, from the position of the photoconductor drum in contact under pressure with the cleaning roller. In this case, it has been confirmed that an irregular drive due to a driving force by the drive gear occurs. Thus, a further improvement has been demanded. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a novel cleaning device of an image forming machine, which prevents the occurrence of the irregular drive and permits compactness of the structure. 
     Another object of the present invention is to provide a novel cleaning device of an image forming machine, which prevents the occurrence of the irregular drive, permits compactness of the structure, and achieves both of the long life and high speed of the image forming machine. 
     According to the present invention, there is provided a cleaning device of an image forming machine, comprising: 
     a pair of arm members each having one end portion pivotable about a support shaft; 
     a cleaning roller rotatably supported between front end portions of the arm members via a shaft; 
     spring means for urging each of the arm members so as to bring the cleaning roller into contact under pressure with a surface of a photoconductor drum; 
     a drive gear integral with the photoconductor drum; and 
     a driven gear integral with the shaft of the cleaning roller and in mesh with the drive gear, and wherein 
     each of the arm members is disposed axially outwardly of the photoconductor drum, and 
     a center of the support shaft of each of the arm members is either placed on an extension of a line of action passing a point of engagement between the drive gear and the driven gear, or placed on an extension of a straight line passing the point of engagement, the straight line being within an angular range of some angle to the line of action. 
     Preferably, the center of the support shaft of each of the arm members is placed on the extension of the straight line passing the point of engagement, the straight line being within the angular range of ±10° to the line of action. 
     Preferably, the drive gear is disposed at one end in the axial direction of the photoconductor drum, one of the arm members is disposed axially outwardly of the drive gear, and the driven gear is disposed in a region in the shaft of the cleaning roller which is located between the one arm member and one end in the axial direction of the cleaning roller. 
     Preferably, the spring means comprise a pair of helical compression springs, and each of the helical compression springs is disposed so as to act on a region in the corresponding arm member which is located between the support shaft and the shaft of the cleaning roller. 
     Preferably, a sheet transport passage passing through a transfer zone of the photoconductor drum extends substantially in an up-and-down direction in the transfer zone, the shaft of the cleaning roller is disposed downstream from the transfer zone of the photoconductor drum and above the photoconductor drum, toner transport means is disposed downstream, in the direction of rotation of the photoconductor drum, from a position of the photoconductor drum in contact under pressure with the cleaning roller, and is disposed above the photoconductor drum, and the support shaft of each of the arm members is disposed upstream, in the direction of rotation of the photoconductor drum, from the position of the photoconductor drum in contact under pressure with the cleaning roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional front view of the configuration of a laser printer equipped with an embodiment of a cleaning device according to the present invention; 
     FIG. 2 is an enlarged sectional view of the cleaning device shown in FIG. 1, illustrated together with a photoconductor drum; 
     FIG. 3 is a perspective view, partly omitted, of a drum unit; 
     FIG. 4 is a perspective view showing one end portion of the drum unit; 
     FIG. 5 is a side view of the drum unit shown in FIG. 4, as viewed in the axial direction of the photoconductor drum; 
     FIG. 6 is a perspective view partially showing the photoconductor drum and a support mechanism for a cleaning roller; 
     FIG. 7 is a schematic view showing the configuration of the support mechanism for the cleaning roller; and 
     FIG. 8 is a schematic view showing the positional relationship between the center of a support shaft of an arm member and a line of action passing a point of engagement between a drive gear and a driven gear in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of a cleaning device of a laser printer, which is an image forming machine, constituted in accordance with the present invention will now be described in detail with reference to the accompanying drawings. With reference to FIG. 1, a laser printer entirely indicated at the numeral  200  has a printer body  200   a  of a nearly rectangular parallelopipedal shape. When the printer body  200   a  is viewed from front, an a-Si-based photoconductor drum  201  is disposed at a position close to one end in a right-and-left direction within the printer body  200   a , namely, at a position close to the left end in FIG. 1, and at a position above the center in an up-and-down direction within the printer body  200   a . Around the photoconductor drum  201  within the printer body  200   a , there are disposed a main charger  202  for uniformly charging the surface of the photoconductor drum  201  to a predetermined polarity, a laser scanning unit LSU for scanning the uniformly charged surface of the photoconductor drum  201  with laser light corresponding to image information to form an electrostatic latent image, a developing device  203  for developing the electrostatic latent image formed on the surface of the photoconductor drum  201  to a toner image, a transfer roller  204  as transfer means for transferring the toner image developed on the surface of the photoconductor drum  201  to paper such as plain paper, and a cleaning device  100  to be described in detail later. The developing device  203  has a development housing  203   a , and a toner container  205 , etc. for feeding a developer into the development housing  203   a . A sheet transport passage  206  is disposed within the printer body  200   a . The sheet transport passage  206  passes through a transfer zone formed on the surface of the photoconductor drum  201  in cooperation with the transfer roller  204 , and extends substantially in the up-and-down direction at least in the transfer zone. 
     The laser scanning unit LSU, which converts image information into laser light and irradiates the circumferential surface of the photoconductor drum  201  with the laser light, is disposed parallel to the development housing  203   a  at a position on the opposite side of the development housing  203   a  from the photoconductor drum  201  (i.e., at a position to the right of the development housing  203   a ), and at a position on practically the same height as the development housing  203   a . The toner container  205  is disposed above, and spaced from, the laser scanning unit LSU. A partial region of the toner container  205  (concretely, the region where a toner outlet portion (not shown) is disposed) is located so as to be present above a partial region of the development housing  203   a . A manual sheet feed tray  210  is disposed at a position immediately below the laser scanning unit LSU, and in a right end portion in FIG. 1 within the printer body  200   a . A feeder portion of the manual sheet feed tray  210  is connected to the sheet transport passage  206  via a manual sheet feed transport passage  212  extending nearly horizontally at a position immediately below the development housing  203   a  and the laser scanning unit LSU. Sheet feeding cassettes  214  and  216  are arranged, one above the other and parallel to each other, at a position below the manual sheet feed tray  210  and the manual sheet feed transport passage  212 . Feeder portions of the sheet feeding cassettes  214  and  216  are connected to the sheet transport passage  206 . A delivery tray  218  is disposed above the toner container  205 . A fixing device  220  and a delivery roller pair  222  are disposed in a downstream end portion of the sheet transport passage  206  disposed so as to extend in a nearly vertical direction. 
     An optical path L of laser light directed from the laser scanning unit LSU onto the circumferential surface of the photoconductor drum  201  via reflectors, such as polygon mirrors, disposed inside is formed so as to pass through a gap between the upper surface of the development housing  203   a  and the lower surfaces of the toner container  205  and the main charger  202 . In the embodiment, the optical path L is set to extend in a slightly upwardly inclined manner, relative to a horizontal line, toward the circumferential surface of the photoconductor drum  201 . Image information supplied from the outside to the laser scanning unit LSU is converted to laser light, and directed onto the circumferential surface of the photoconductor drum  201  to form an electrostatic latent image on the circumferential surface. This electrostatic latent image is developed to a toner image by the developing device  203 . The developed toner image is transferred, in the transfer zone, to a sheet fed and transported, for example, from the sheet feeding cassette  214  through the sheet transport passage  206 . The toner image transferred onto the sheet is fixed at the fixing device  220 , and the sheet having the toner image fixed thereon is delivered onto the delivery tray  218  by the delivery roller pair  222 . In roughly the above-described manner, a printing action by the printer  200  is performed repeatedly to produce prints. In the machine of the configuration shown in FIG. 1, a document feeder may be provided on the upper surface of the body, an image reader may be provided within an upper end portion of the printer body  200   a  in correspondence with the document feeder so that the image of the document fed by the document feeder is read by the image reader, and the laser scanning unit LSU may be actuated based on the image information read. In this case, the machine can be utilized as an electrostatic copier. 
     Next, the cleaning device  100  according to the present invention, which is installed in the printer  200 , will be described. With reference to FIGS. 2 and 3, the cleaning device  100  and the photoconductor drum  201  are mounted on a framework  102 . The framework  102  has a pair of side frames  104  opposed to each other with spacing, and a connecting frame (not shown) extending between the side frames  104  so as to connect the side frames  104  integrally. The photoconductor drum  201  is rotatably supported between the side frames  104 . The cleaning device  100  has a cleaning roller  110 , a toner transport member  120  as toner transport means, and a cleaning blade  130 . The framework  102 , the cleaning device  100 , and the photoconductor drum  201  constitute a wholly integral drum unit. 
     With reference to FIGS. 3 to  6 , the photoconductor drum  201  is rotatably supported on the side frames  104  via bearings  105 . A drive gear  201   a  (see FIG. 6) is integrally disposed at one end in the axial direction of the photoconductor drum  201 . A pair of arm members  111  are disposed on external sides in the axial direction of the side frames  104 . Each of the arm members  111  has one end supported so as to be pivotable about a support shaft  112  protruding laterally outwardly from the side frame  104 . The cleaning roller  110  is rotatably supported between the other ends (front ends) of the arm members  111  via a shaft  113 . The cleaning roller  110 , comprising foamed synthetic rubber, for example, a foam of EPDM, is integrally mounted on the shaft  113 , and the shaft  113  is rotatably supported by the opposite ends of the arm members  111  via bearings (not shown). Each of the arm members  111  is disposed axially outwardly of the photoconductor drum  201 , and one of the arm members  111  is disposed axially outwardly of the drive gear  201   a  of the photoconductor drum  201 . A driven gear  114  is integrally connected to one end portion of the shaft  113  of the cleaning roller  110 . The driven gear  114  is disposed in that region in the shaft  113  of the cleaning roller  110  which lies between the one arm member  111  (the arm member  111  disposed on the right in FIG. 6) and one end  110   a  (see FIG. 6) in the axial direction of the cleaning roller  110 . 
     Helical compression springs  115  as spring means are disposed between each of the arm members  111  and the flange portions  104   a  formed in the side frames  104 . Each of the flange portions  104   a  protrudes laterally outwardly from one side edge of the corresponding side frame  104 . Each of the helical compression springs  115  is disposed such that one end thereof acts on that region in the corresponding arm member  111  which is present between the support shaft  112  and the shaft  113  of the cleaning roller  110 . Each of the arm members  111  is urged by the corresponding helical compression spring  115  so as to turn clockwise about the support shaft  112  in FIGS. 3 to  6 . Thus, the surface of the cleaning roller  110  is contacted under pressure with the surface of the photoconductor drum  201 . Simultaneously, the driven gear  114  of the cleaning roller  110  is meshed with the drive gear  201   a  of the photoconductor drum  210 . 
     With reference to FIGS. 6 to  8 , when the cleaning device  100  is viewed in the axial direction of the photoconductor drum  201 , the center O of the support shaft  112  of each of the arm members  111  is placed on an extension of a line of action, L 1 , passing a point of engagement (pitch point), P, between the driven gear  114  of the cleaning roller  110  and the drive gear  201   a  of the photoconductor drum  210 . In FIGS. 7 and 8, the symbol L 3  denotes a straight line passing the axial center O 1  of the driven gear  114  and the axial center O 2  of the drive gear  201   a . The symbol L 2  denotes a straight line intersecting the straight line L 3  at right angles, and a tangent to the pitch circles of the driven gear  114  and the drive gear  201   a . An angle α formed by the intersection of the line of action L 1  [a normal to the point of contact, P, (i.e., pitch point) of the tooth flanks of the driven gear  114  and the drive gear  201   a  in mesh] and the tangent L 2  constitutes a pressure angle. In FIGS. 6 and 8, the direction of rotation of the drive gear  201   a  of the photoconductor drum  210  is clockwise, so that the direction of rotation of the driven gear  114  of the cleaning roller  110  is counterclockwise. Thus, a driving force acts in the direction in which the driving pressure of the drive gear  201   a  works, namely, in the direction of the line of action L 1  (the direction of an arrow along the line of action L 1  in FIGS.  7  and  8 ). As stated earlier, the center O of the support shaft  112  of each of the arm members  111  is placed on an extension of the line of action L 1  at the point of engagement P between the driven gear  114  of the cleaning roller  110  and the drive gear  201   a  of the photoconductor drum  210  (in the embodiment, an extension of L 1  in the direction directly opposite to the direction of the driving force of the drive gear  201   a ). Thus, the turning moment about the support shaft  112  of each of the arm members  111  produced by the helical compression spring  115  is prevented from fluctuating under the influence of the driving force of the drive gear  201   a . As a result, the occurrence of an irregular drive is reliably prevented. Thus, the stable polishing of the surface of the photoconductor drum  201  by the cleaning roller  110  is ensured, making it possible to form the image stably and prolong the life of the photoconductor drum. Furthermore, each of the arm members  111  is disposed axially outwardly of the photoconductor drum  201 . Hence, the entire structure is compact, although the center O of the support shaft  112  of each of the arm members  111  is placed on the extension of the line of action L 1  at the point of engagement P between the driven gear  114  of the cleaning roller  110  and the drive gear  201   a  of the photoconductor drum  210 . Besides, the length of each of the arm members  111  can be shortened. 
     As described earlier, moreover, the drive gear  201   a  of the photoconductor drum  201  is disposed at one end in the axial direction of the photoconductor drum  201 , one of the arm members  111  is disposed axially outwardly of the drive gear  201   a , and the driven gear  114  of the cleaning roller  110  is disposed in that region in the shaft  113  of the cleaning roller  110  which lies between the one arm member  111  and one end in the axial direction of the cleaning roller  110  (see FIG.  6 ). Thus, the support for the driven gear  114  is not in a cantilevered state, so that vibrations of the driven gear  114  and the cleaning roller  110  are suppressed, and an irregular drive due to the vibrations can be prevented. 
     As described above, each of the helical compression springs  115  is disposed so as to act on that region in the corresponding arm member  111  which is located between the support shaft  112  and the shaft  113  of the cleaning roller  110 . Thus, the length of the arm member  111  can be shortened, and the space in the direction of this length can be decreased, thus achieving a compact entire configuration. 
     In the embodiment shown in FIG. 1, the sheet transport passage  206  passing through the transfer zone of the a-Si-based photoconductor drum  201  extends substantially in the up-and-down direction in the transfer zone. As shown in FIG. 7, moreover, the shaft  113  of the cleaning roller  110  is disposed downstream from the transfer zone of the photoconductor drum  201 , and above the photoconductor drum  201 . A toner transport member  120 , comprising a shaft and a helical blade, is disposed downstream, in the direction of rotation of the photoconductor drum  201 , from a position of the photoconductor drum  201  in contact under pressure with the cleaning roller  110 , and above the photoconductor drum  201 . The support shaft  112  of each of the arm members  111  is disposed upstream, in the direction of rotation of the photoconductor drum  201 , from a position of the photoconductor drum  201  in contact under pressure with the cleaning roller  110 . In the above embodiment, the use of the a-Si-based photoconductor drum  201  and the employment of the sheet vertical transport system make it possible to prevent the occurrence of the aforementioned irregular drive, make the configuration compact, and achieve the long life and high speed of the printer. 
     The cleaning device  100  of the present invention can be applied to an image forming machine adopting the lateral transport system for sheets, namely, an image forming machine of a configuration in which the sheet transport passage passing through the transfer zone of the photoconductor drum  201  extends substantially laterally (horizontally) in the transfer zone. In the illustrated embodiment, the center O of the support shaft  112  of each of the arm members  111  is placed on the extension of the line of action L 1  at the point of engagement P (pitch point) between the drive gear  201   a  and the driven gear  114 , and is also placed on the line of action L 1  in the direction directly opposite to the direction in which the driving force acts at the point of engagement P (see the arrow directed in an obliquely upper right direction in FIGS.  7  and  8 ). However, there may be an embodiment in which the center O is placed on the line of action L 1  in the direction in which the driving force acts at the point of engagement P. In this embodiment, the toner transport member  120  needs to be disposed at a position where the toner transport member  120  does not interfere with each of the arm members  111  and/or the support shaft  112 , the helical compression spring  115  or the like. This embodiment can obtain, at least, the effect that the occurrence of an irregular drive is reliably prevented. In the embodiment, moreover, the center O of the support shaft  112  of each of the arm members  111  is placed on the extension of the line of action L 1  passing the point of engagement P between the driven gear  114  of the cleaning roller  110  and the drive gear  201   a  of the photoconductor drum  210 . However, other embodiments in which the center O is not placed on the extension of the line of action L 1  also hold. That is, there holds other embodiment in which the center O of the support shaft  112  of each of the arm members  111  is placed on an extension of a straight line passing the point of engagement P between the driven gear  114  of the cleaning roller  110  and the drive gear  201   a  of the photoconductor drum  210 , the straight line being within an angular range at ±10° to the line of action L 1  (see FIG.  8 ). In FIG. 8, straight lines indicated by two-dot chain lines L 1   a  and L 1   b  correspond to such straight line forming angles of +10° and −10°, respectively, to the line of action L 1 . This embodiment, practically, is capable of achieving the effect that the turning moment about the support shaft  112  of each of the arm members  111  produced by the helical compression spring  115  is prevented from fluctuating under the influence of the driving force of the drive gear  201   a . As a result, the occurrence of an irregular drive is prevented without causing problems to practical use. Thus, the stable polishing of the surface of the photoconductor drum  201  by the cleaning roller  110  is ensured, making it possible to form the image stably and prolong the life of the photoconductor drum. 
     That is, the center O of the support shaft  112  of each of the arm members  111  is either placed on the extension of the line of action L 1  passing the point of engagement P between the drive gear  201   a  and the driven gear  114 , or placed on an extension of a straight line passing the point of engagement P, the straight line falling within an angular range of some angle to the line of action L 1 . The expression “angular range of some angle”, needless to say, refers to an angular range within which the occurrence of an irregular drive is prevented to a practically unproblematic level. According to the inventors&#39; experience, the “angular range of some angle” may be an angular range of ±10°, as stated above. The cleaning device of the present invention is applied to an image forming machine equipped with an a-Si-based photoconductor drum as described earlier. However, this cleaning device can be used in an image forming machine having an OPC (Organic Photoconductor) drum. 
     With the aforementioned drum unit being mounted within the printer body  200   a , the drive gear  201   a  of the photoconductor drum  201  is drivingly connected to an electric motor, a drive source, via other intermediate gears (not shown) disposed within the printer body  200   a . With reference to FIGS. 2,  7  and  8 , when the drive gear  201   a  is rotationally driven by the electric motor, the photoconductor drum  201  is rotationally driven clockwise in the drawings. The cleaning roller  110  is rotationally driven counterclockwise in the drawings via the driven gear  114 . The cleaning roller  110  is brought into contact under pressure with the surface of the photoconductor drum  201  by the helical compression springs  115 , and is set to have a slightly higher peripheral speed than does the photoconductor drum  201 . Thus, the surface of the photoconductor drum  201  is constantly polished. The cleaning blade  130  scrapes toner, remaining on the surface of the photoconductor drum  201 , from this surface. The toner transport member  120  transports the toner, scraped off the surface of the photoconductor drum  201 , into a recovery container (not shown).