Patent Publication Number: US-2022234851-A1

Title: Sheet transport device including gear train having movable gear with helical gear, and leaf spring that buffers movement of movable gear in one direction, and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application claims priority to Japanese Patent Application No. 2021-011685 filed on Jan. 28, 2021, the entire contents of which are incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to a sheet transport device including a gear train that transmits rotating force from a motor to a transport roller that transports a sheet, and to an image forming apparatus. 
     Existing image forming apparatuses generally include a transport roller pair that transports recording sheets. The transport roller pair include a drive roller, and a follower roller made to rotate by the rotation of the drive roller. The drive roller is connected to a motor, via a gear train. The drive roller is made to rotate by rotating force transmitted from the motor through the gear train 
     In case a paper jam occurs during an image forming operation, the sheet may remain caught by the transport roller pair. Accordingly, a technique to solve the paper jam is known, including allowing one of the gears constituting the gear train to move between a normal position, where transmission of the rotating force to the drive roller is enabled, and a disengaged position where the transmission of the rotating force to the drive roller is interrupted. When the gear is moved to the disengaged position to fix the paper jam, the drive roller can freely rotate, and therefore the jammed paper can be removed from the transport roller pair, without significant difficulty 
     For example, the existing image forming apparatuses include a planetary gear mechanism (gear train) provided between the drive motor and the paper feed roller (drive roller). The planetary gear mechanism includes a sun gear, a planetary gear meshed with the sun gear, and a first-stage gear meshed with the planetary gear. When a paper jam occurs, the drive motor is made to rotate reversely for a predetermined time, to reversely rotate the sun gear and disengage the planetary gear from the first-stage gear. In this way, the existing image forming apparatuses interrupt the transmission of the rotating force, from the drive motor to the paper feed roller. 
     SUMMARY 
     The disclosure proposes further improvement of the foregoing technique. In an aspect, the disclosure provides a sheet transport device including a transport roller, a drive source, and a gear train The transport roller transports a sheet. The gear train transmits rotating force from the drive source to the transport roller. The gear train includes a movable gear and a leaf spring. The movable gear is configured to move between a normal position where transmission of the rotating force to the transport roller is enabled, and a disengaged position where the transmission of the rotating force to the transport roller is interrupted, and also to move in an axial direction, and includes a helical gear that generates force to axially move in one direction, when the movable gear moves from the normal position to the disengaged position. The leaf spring buffers the movement of the movable gear in the one direction. 
     In another aspect, the disclosure provides an image forming apparatus including the foregoing sheet transport device, and an image forming device. The image forming device forms an image on a sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view showing an image forming apparatus, with its outer cover removed; 
         FIG. 2  is a side view showing the image forming apparatus, with its outer cover and cover plate removed; 
         FIG. 3  is a perspective view showing a movable gear and a leaf spring; 
         FIG. 4A  is a side view of the movable gear located at a normal position; 
         FIG. 4B  is a side view of the movable gear located at a disengaged position; 
         FIG. 5  is a perspective view showing the leaf spring; 
         FIG. 6A  is a side view of the movable gear and the leaf spring, located at the normal position; and 
         FIG. 6B  is a side view of the movable gear and the leaf spring, located at the disengaged position. 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, an image forming apparatus according to an embodiment of the disclosure will be described, with reference to the accompanying drawings. 
     Referring first to  FIG. 1  and  FIG. 2 , the image forming apparatus  1  will be described.  FIG. 1  is a side view showing the image forming apparatus  1 , with its outer cover removed.  FIG. 2  is a side view showing the image forming apparatus  1 , with its outer cover and cover plate  5  removed. Reference codes Fr, Rr, L, and R in the drawings indicate the front side, the rear side, the left side, and the right side of the image forming apparatus  1 , respectively. 
     The image forming apparatus  1  includes a casing  3  having an internal space of a generally rectangular parallelepiped shape. Inside the casing  3 , a paper feeding device that feeds sheets, an image forming device  100  that forms a toner image on the sheet, a fixing device that fixes the toner image onto the sheet, and a delivery device that delivers the sheet, are accommodated. Inside the casing  3 , also a transport route of the sheet is provided, from the paper feeding device to the delivery device through the image forming device  100  and the fixing device. A resist roller pair and a transport roller pair are provided, at predetermined positions on the transport route. These roller pairs serve to transport the sheet from the paper feeding device to the delivery device, along the transport route. On the upper face of the casing  3 , an output tray is provided. 
     The paper feeding device includes a feed roller. The feed roller delivers, by rotating, the sheet placed on a paper cassette or a manual bypass tray to the transport route. The image forming device  100  includes an exposure device, a photoconductor drum, a charging device, a developing device, a cleaning device, and a toner container. The image forming device  100  forms a toner image by means of electrophotography, on the sheet delivered from the paper feeding device. The fixing device includes a heat roller and a pressure roller, and fixes the toner image onto the sheet while transporting the sheet, by causing the mentioned rollers to rotate. The delivery device includes a delivery roller pair, and delivers, by causing the delivery roller pair to rotate, the sheet on which the toner image has been fixed, to the output tray. 
     The plurality of rotating bodies, such as the transport roller pair, the feed roller, the heat roller, the pressure roller, and the photoconductor drum are driven to rotate by a drive mechanism  10  shown in  FIG. 2 . The drive mechanism  10  includes a bidirectionally rotatable, brushed DC motor  11 , and a gear train  13  including drive gears fixed to the rotary shaft of the respective rotating bodies. When the rotating force of the motor  11  is transmitted to each of the plurality of rotating bodies via the gear train  13 , each of the rotating bodies is made to rotate in a predetermined direction, at a predetermined rotation speed. The motor  11  according to this embodiment exemplifies the drive source in the disclosure. The plurality of rotating bodies, the drive mechanism  10 , and the gear train  13  act as a sheet transport device  101  according to the disclosure. 
     As shown in  FIG. 2 , an end portion (left end portion) of an output shaft  11 A of the motor  11  is penetrating through a side plate  3 L (left side plate) of the casing  3 . To the end portion of the output shaft  11 A protruding from the side plate  3 L, an output gear  21  is fixed. An end portion (left end portion) of the rotary shaft of each of the rotating bodies is also penetrating through the side plate  3 L of the casing  3 . To the end portion of each of the rotary shafts protruding from the side plate  3 L, a drive gear is fixed. As shown in  FIG. 1 , most of the drive gears are covered with the cover plate  5 . In other words, most of the drive gears are located in the space between the side plate  3 L and the cover plate  5 . 
     Referring to  FIG. 2 , a gear train  13 X, provided between the motor  11  and the transport roller pair, will be described hereunder. The transport roller pair is located on the transport route, at a position between the image forming device  100  and the fixing device, and includes a transport drive roller  15  and a follower roller made to rotate by the rotation of the transport drive roller  15 . In this embodiment, the transport drive roller  15  exemplifies the transport roller in the disclosure. As described above, an end portion (left end portion) of the rotary shaft of the transport drive roller  15  is penetrating through the side plate  3 L of the casing  3 . To the end portion of the rotary shaft protruding from the side plate  3 L, a transport drive gear  23  is fixed. Here, description of the drive gears other than the gear train  13 X will be skipped. 
     The gear train  13 X includes the output gear  21 , a first to fourth drive gears  25 ,  27 ,  29 , and  31 , a movable gear  33 , and the transport drive gear  23 . The output gear  21  is meshed with the first drive gear  25 . The first drive gear  25  is meshed with the second drive gear  27 . The second drive gear  27  is meshed with the third drive gear  29 . The third drive gear  29  is meshed with the fourth drive gear  31 . The fourth drive gear  31  is meshed with the transport drive gear  23 , via the movable gear  33 . 
     The movable gear  33  is set to move between a normal position where the movable gear  33  is meshed with the transport drive gear  23 , and a disengaged position where the movable gear  33  is disengaged from the transport drive gear  23 . When the movable gear  33  is located at the normal position, the transmission of the rotating force from the fourth drive gear  31  to the transport drive gear  23  is enabled, via the movable gear  33 . When the movable gear  33  moves to the disengaged position, the transmission of the rotating force from the fourth drive gear  31  to the transport drive gear  23  is interrupted. 
     Now, in case a paper jam occurs while the sheet is being transported along the transport route, the transport roller pair suspends the rotation, and therefore the sheet may remain caught by the transport roller pair. Although one tries to draw out the sheet caught by the transport roller pair, it is difficult to draw out the sheet owing to the friction between the transport drive roller  15  and the sheet, because the transport drive roller  15  has stopped rotating. To fix the paper jam, therefore, the movable gear  33  is moved to the disengaged position, to interrupt the transmission of the rotating force from the motor  11  to the transport drive roller  15 , so that the transport drive roller  15  is allowed to freely rotate. As result, the jammed sheet can be removed, without significant difficulty. 
     The configuration of the movable gear  33  will be described, with reference to  FIG. 3 ,  FIG. 4A , and  FIG. 4B .  FIG. 3  is a perspective view showing the movable gear and a leaf spring.  FIG. 4A  and  FIG. 4B  illustrate the movable gear before and after the position change. In  FIG. 3 , the side plate  3 L is not shown. 
     As shown in  FIG. 3 , the movable gear  33  includes a gear portion  41  and a rotary shaft  43 . The end portions of the rotary shaft  43  are respectively supported by the side plate  3 L (see  FIG. 1  and  FIG. 2 ) and the cover plate  5 . The gear portion  41  of the movable gear  33  includes a large-diameter helical gear  41 A meshed with the fourth drive gear  31 , and a small-diameter plain gear  41 B meshed with the transport drive gear  23 . 
     The side plate  3 L and the cover plate  5  each include a slot  51 , formed along the circumferential direction of a circle centered at the axial center of the movable gear  33  ( FIG. 3  only shows the slot  51  of the cover plate  5 ). An end portion of the rotary shaft  43  of the movable gear  33  is inserted in the slot  51  of the side plate  3 L, and the other end portion is inserted in the slot  51  of the cover plate  5 . Thus, the end portions of the rotary shaft  43  are supported rotatably, and also movably along the circumferential direction of the circle centered at the axial center of the movable gear  33 . In this embodiment, the side plate  3 L exemplifies the second plate in the disclosure, and the cover plate  5  exemplifies the first plate. 
     Referring to  FIG. 4A  and  FIG. 4B , when the fourth drive gear  31  rotates clockwise, the movable gear  33  moves clockwise along the slot  51 , while rotating counterclockwise. The movable gear  33  thus moves until the end portion of the rotary shaft  43  abuts against an end (rear end) of the slot  51  (see  FIG. 4A ). At this position, the plain gear  41 B of the movable gear  33  (see  FIG. 3 ) is meshed with the transport drive gear  23 . In other words, the position where the end portion of the rotary shaft  43  of the movable gear  33  abuts against the rear end of the slot  51  corresponds to the normal position. 
     On the other hand, when the fourth drive gear  31  rotates counterclockwise, the movable gear  33  moves counterclockwise along the slot  51 , while rotating counterclockwise. The movable gear  33  thus moves until the end portion of the rotary shaft  43  abuts against the other end (front end) of the slot  51  (see  FIG. 4B ). At this position, the plain gear  41 B of the movable gear  33  is disengaged from the transport drive gear  23 . In other words, the position where the end portion of the rotary shaft  43  of the movable gear  33  abuts against the front end of the slot  51  corresponds to the disengaged position. 
     As shown in  FIG. 1  and  FIG. 3 , in the vicinity of the slot  51  of the cover plate  5 , a hook portion  53  formed by cutting away a portion of the side edge of the cover plate  5 , and a rectangular opening  55  (see  FIG. 1 ) are located close to each other. On the inner face of the cover plate  5 , a boss  57  (see  FIG. 3 ) is formed so as to protrude, between the hook portion  53  and the opening  55 . 
     In general, a helical gear is subjected, depending on the rotation direction, to a force exerted in the axial direction of the rotary shaft (thrust load). In this embodiment, when the movable gear  33  moves to the disengaged position, a force is exerted on the helical gear  41 A along the axial direction, from the side plate  3 L toward the cover plate  5 . Such a force may cause an end portion of the rotary shaft  43  to come off from the slot  51  of the side plate  3 L, or make the engagement between the movable gear  33  and the fourth drive gear  31  imperfect. Accordingly, the gear train  13 X includes a leaf spring  61  that buffers the movement of the movable gear  33  in the axial direction. 
     Referring also to  FIG. 5 , in addition to  FIG. 3 , the leaf spring  61  will be described hereunder.  FIG. 5  is a perspective view showing the leaf spring  61 . 
     As shown in  FIG. 5 , the leaf spring  61  is made from a sheet metal. The leaf spring  61  includes a mounting portion  63  to be attached to the cover plate  5  (see  FIG. 3 ), a pressing portion  65  bent so as to define an acute angle with respect to the mounting portion  63 , and a distal end portion  67  bent from the pressing portion  65 . 
     The mounting portion  63  includes a generally rectangular base portion  69 , and a pair of hook portions  71  formed on the respective side edges of the base portion  69  opposed to each other. A circular opening  69 A is formed in the vicinity of the center of the base portion  69 . The pair of hook portions  71  are bent generally at right angle in the same direction, from the respective side edges of the base portion  69  opposed to each other, and further bent generally at right angle in opposite directions to each other. The pressing portion  65  has an elongate plate shape. The pressing portion  65  is arcuately bent generally in  180  degrees in the direction opposite to the bending direction of the pair of hook portions  71 , from a portion of another side edge of the base portion  69 , and extends further ahead with respect to the base portion  69 . Thus, the pressing portion  65  is bent so as to define an acute angle with respect to the mounting portion  63 . The pressing portion  65  is wider in the portion on the side of the base portion  69 , and narrower in the portion on the side of the distal end portion  67 . The distal end portion  67  is bent generally at right angle toward the mounting portion  63 , from the tip portion of the pressing portion  65 . The leading end of the distal end portion  67  is formed in an arcuate shape. In a free posture of the leaf spring  61 , with no compressive force applied thereto, the leading end of the distal end portion  67  does not reach the plane that includes the base portion  69 . 
     The cover plate  5  is located on the downstream side in the direction from the side plate  3 L to the cover plate  5 , and the side plate  3 L is located on the upstream side, in the same direction. As shown in  FIG. 3 , the leaf spring  61  is attached to the cover plate  5 , by fitting the boss  57  of the cover plate  5  in the opening  69 A of the base portion  69 , and respectively engaging the pair of hook portions  71  with the hook portion  53  and the opening  55  (see  FIG. 1 ) of the cover plate  5 . The pressing portion  65  abuts against the helical gear  41 A of the gear portion  41 , with a predetermined pressure applied in the direction from the cover plate  5  toward the side plate  3 L. A clearance C is defined between the leading end of the distal end portion  67  and the cover plate  5 . The clearance C is determined so as to keep the end portion of the rotary shaft  43  from coming off from the opening of the side plate  3 L, when the movable gear  33  has moved in the direction from the side plate  3 L toward the cover plate  5  until the distal end portion  67  abuts against the cover plate  5 , in other words so as to keep the end portion of the rotary shaft  43  supported by the side plate  3 L. The clearance C may be set, for example, to 0.4 mm. 
     The working of the gear train  13 X, when a paper jam is fixed in the image forming apparatus  1  configured as above, will be described hereunder, with reference to  FIG. 6A  and  FIG. 6B , in addition to  FIG. 2 ,  FIG. 3 ,  FIG. 4A , and  FIG. 4B .  FIG. 6A  and  FIG. 6B  illustrate the movable gear  33  and the leaf spring  61 , before and after the position change. 
     First, the working of the gear train  13 X in the normal operation will be described. When the motor  11  rotates in one direction in the normal operation, the output gear  21  fixed to the output shaft  11 A of the motor  11  rotates clockwise in  FIG. 2 . Then the fourth drive gear  31  rotates clockwise, via the first to third drive gears  25 ,  27 , and  29 . The rotation of the fourth drive gear  31  causes the movable gear  33  to move clockwise, while rotating counterclockwise. The movable gear  33  moves until reaching the normal position, and continues to rotate counterclockwise, at the normal position (see  FIG. 4A  and  FIG. 6A ). When the movable gear  33  is thus located at the normal position, the rotating force of the motor  11  is transmitted to the transport drive gear  23 , so that the transport drive roller  15  is made to rotate and transports the sheet. 
     When a paper jam occurs, the motor  11  rotates in the reverse direction. Then the fourth drive gear  31  rotates counterclockwise, via the first to the third drive gears  25 ,  27 , and  29 . Such rotation of the fourth drive gear  31  causes the movable gear  33  to move counterclockwise, while rotating clockwise. The movable gear  33  moves until reaching the disengaged position, and continues to rotate clockwise (reversely), at the disengaged position (see  FIG. 4B  and  FIG. 6B ). When the movable gear  33  is thus located at the disengaged position, the transmission of the rotating force of the motor  11  to the transport drive gear  23  is interrupted. 
     When the movable gear  33  rotates clockwise as above, the movable gear  33  is subjected to a force exerted along the axial direction, in the direction from the side plate  3 L toward the cover plate  5 . However, since the pressing portion  65  of the leaf spring  61  is in contact with the gear portion  41 , applying a force in the direction from the cover plate  5  toward the side plate  3 L as shown in  FIG. 3 , the movement of the movable gear  33  in the axial direction can be buffered. The movable gear  33  can move until the distal end portion  67  of the leaf spring  61  abuts against the cover plate  5 . The movable gear  33  moves from the normal position to the disengaged position, against the pressing force of the leaf spring  61 . 
     Thereafter, the user removes the sheet caught between the transport roller pair. Since the transport drive roller  15  is freely rotatable at this point, the user can remove the sheet from the transport roller pair, without significant difficulty 
     Now, the gear train of some of the existing image forming apparatuses includes a helical gear. In this case, when the motor rotates reversely, the helical gear is subjected to a force exerted along the axial direction. This may cause the helical gear to come off or be imperfectly engaged, and therefore a compression spring is employed in the existing image forming apparatuses, to delimit the movement of the helical gear in the axial direction. However, in the case of employing the compression spring, it is necessary to stably support the compression spring, while securing the space for locating the compression spring and also the compression margin. Therefore, the freedom in designing is reduced, and the assembly work becomes complicated. 
     According to the foregoing embodiment, in contrast, the leaf spring  61  is employed to buffer the movement of the movable gear  33  in the axial direction. Therefore, the space for locating the leaf spring  61  can be reduced, and the assembly work of the gear train can be simplified. To be more detailed, it suffices to fit the opening  69 A of the leaf spring  61  around the boss  57  of the cover plate  5 , and respectively engage the pair of hook portions  71  of the leaf spring  61 , with the opening  55  and the hook portion  53 . In addition, an appropriate space can be secured between the movable gear  33  and the cover plate  5 , because of the presence of the distal end portion  67  of the leaf spring  61 , the deformation of the leaf spring  61  can be prevented, in the assembly work thereof. 
     Further, a relatively large contact area can be secured between the pressing portion  65  of the leaf spring  61  and the gear portion  41  of the movable gear  33 , and therefore the pressing portion  65  can stably remain in contact with the movable gear  33 , while the movable gear  33  is moving. Accordingly, the leaf spring  61  can stably buffer the movement of the movable gear  33 . Consequently, though the movable gear  33  is made to rotate reversely when moving from the normal position to the disengaged position, the rotary shaft  43  of the movable gear  33  can be prevented from coming off from the side plate  3 L, and the helical gear  41 A of the movable gear  33  can be prevented from becoming imperfectly engaged with the fourth drive gear  31 . 
     Further, the movable gear  33  is located between the transport drive gear  23 , and the fourth drive gear  31  located upstream of the transport drive gear  23  in the transmission direction of the rotating force. Such a location of the movable gear  33  minimizes the number of parts of the gear train 
     In the foregoing embodiment, the transport drive roller  15  of the transport roller pair exemplifies the transport roller in the disclosure. However, the transport roller is not limited to the transport drive roller  15 . The transport roller may be any of the drive rollers that are driven to rotate, among the roller pairs that transport the sheet by rotating. For example, the transport roller may be whichever of the heat roller and the pressure roller of the fixing device that is driven to rotate, or one of the resist roller pair that is driven to rotate. 
     Although the disclosure has been described on the basis of the foregoing embodiment, the disclosure is not limited thereto. Those skilled in the art may modify the foregoing embodiment, within the scope and the spirit of the disclosure. 
     While the present disclosure has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art the various changes and modifications may be made therein within the scope defined by the appended claims.