Abstract:
A duplex printing method performed by a printing apparatus, the method comprising the steps of: feeding in a first sheet; transporting the first sheet along a sheet-circulating path; forming an image on a front side of the first sheet; feeding in a second sheet; detecting a sheet-feeding error; inhibiting an entry of the second sheet into the sheet-circulating path; forming an image on a back side of the first sheet; and ejecting the first sheet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention is a divisional application of the co-pending U.S. application Ser. No. 13/934,966, filed on Jul. 3, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a printing apparatus and a duplex printing method, and especially relates to the printing apparatus which continues carrying out an ongoing image-forming process even in the event of a multi-feed, paper jam or misfeed, and the duplex printing method performed by such printing apparatus. 
         [0004]    2. Description of the Prior Art 
         [0005]    A conventional printer would terminate a print job right away in the event of a multi-feed, paper jam or misfeed, and generate an alert to the user requesting the user to remove the sheet remained in the machine, and finally automatically restart the print job after the clearance. The page in the middle of the printing process at the moment the error occurs would be considered an unfinished document and reprinted after the error has been cleared, resulting in a waste of time, toner and paper. 
         [0006]    Therefore, the present invention provides a printing apparatus and a duplex printing method to solve the above problems. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, an object of the present invention is to provide a printing apparatus which utilizes a sheet-controlling device and two independent driving systems to complete the print process which will not be interrupted by the occurrence of the multi-feed, paper jam or misfeed, and a duplex printing method performed by such printing apparatus. 
         [0008]    In one embodiment, the present invention relates to a printing apparatus. The printing apparatus comprises an image forming system, a sheet-feeding system, a sheet-transporting system, a sheet-controlling device, a sheet-detection device, a first driving system, a second driving system and a controller. The sheet-transporting system, comprising a sheet-circulating path and a transporting mechanism, receives a recording medium from the sheet-feeding system and transports the recording medium through an image forming system. The transporting mechanism moves the recording medium along the sheet-circulating path. The image forming system, in the sheet-circulating path, forms an image on the recording medium. The sheet-controlling device and the sheet-detection device are disposed between the sheet-feeding system and the sheet-transporting system. The sheet-controlling device controls an entry of a sheet into the sheet-transporting system. The first driving system drives the sheet-controlling device, and the second driving system drives the transporting mechanism. The controller upon receiving an error signal from the sheet-detection device signals the sheet-controlling device to inhibit the entry of the sheet into the sheet-transporting system and signals the transporting mechanism to continue its operation. 
         [0009]    Further, in another embodiment, the present invention relates to a duplex printing method performed by a printing apparatus. The duplex printing method comprises the following steps: feeding in a first sheet; transporting the first sheet along a sheet-circulating path; forming an image on a front side of the first sheet; feeding in a second sheet; detecting a sheet-feeding error; inhibiting an entry of the second sheet into the sheet-circulating path; forming an image on a back side of the first sheet; and ejecting the first sheet. 
         [0010]    The printing apparatus of the present invention when detecting any paper feeding error would instruct the sheet-controlling device to stop the advancing of a paper sheet in front of the sheet-transporting system and continue the ongoing image-forming process for the paper sheet(s) already inside the sheet-transporting system until the print data designated for the sheet(s) are completely printed thereon. The duplex printing method of the present invention improves the efficiency of a printing process, where the printing apparatus would prioritize the ongoing image-forming process over the clearance of paper feeding error and finish the printing of the data onto the sheets inside the sheet-transporting system. After the error is cleared, the printing apparatus would start from printing of the data for the sheet being stopped by the sheet-controlling device. 
         [0011]    These and other objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1 and 1B  are elevation views of printing apparatuses according to preferred embodiments of the present invention. 
           [0013]      FIGS. 2A ,  2 B,  2 C,  2 D,  2 E,  2 F and  2 G are explanatory views of the sheet conveyance operation when a sheet-feeding error occurs when a second sheet is being fed in. 
           [0014]      FIGS. 3A ,  3 B,  3 C,  3 D,  3 E,  3 F,  3 G,  3 H and  3 I are explanatory views of the sheet conveyance operation when a sheet-feeding error occurs when a third sheet is being fed in. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIGS. 1A and 1B  are elevation views of printing apparatuses  1  according to preferred embodiments of the present invention. As shown in  FIG. 1A , the printing apparatus  1  comprises an image forming system  10 , a sheet-feeding system  20 , a sheet-transporting system  30 , a sheet-controlling device  40 , a sheet-detection device  50 , a first driving system  60 , a second driving system  70  and a controller  80 . The image forming system  10  forms an image on a recording medium, for example a sheet of paper. The printing apparatus  1  in this embodiment is an electro-photographic printer, where the image forming system  10  comprises at least a photosensitive drum  12 , an image transfer roller  14  and a fusing device  16 . 
         [0016]    The sheet-feeding system  20  comprises a paper cassette  22  or a manual paper feeding entrance, a feeding roller  24 , a separation roller  26  and a retard roller  28 . The feeding roller  24  picks up a sheet S from the paper cassette  22 , or the manual paper feeding entrance, and transports to the separation roller  26  and the retard roller  28 . The separation roller  26  and the retard roller  28  separate the sheet S from other sheets to make sure that only one sheet at one time will pass through the image forming system  10 . The sheet-transporting system  30  comprises a sheet-circulating path  32 , a transporting mechanism  34  and a sheet outlet  38 . The sheet-transporting system  30  receives the sheet S from the sheet-feeding system  20  and transports the sheet S through the image forming system  10 . The transporting mechanism  34  moves the sheet S along the sheet-circulating path  32 . When the sheet S is transported through the image forming system  10 , the image forming system  10  forms an image on the sheet S. To print images on both sides of the sheet S, the transporting mechanism  34  moves the sheet S through the image forming system  10  twice along the sheet-circulating path  32 . The transporting mechanism  34  comprises at least a transfer roller pair  34   a  and a switching roller pair  34   b.  The sheet-controlling device  40  and the sheet-detection device  50  are disposed between the sheet-feeding system  20  and the sheet-transporting system  30 . As shown in  FIG. 1A , the sheet-detection device  50  is disposed at a position upstream of the sheet-controlling device  40  in a sheet conveyance direction. The sheet S passes the sheet-detection device  50  before reaching the sheet-controlling device  40 . Alternatively, the sheet-detection device  50  may be disposed at a position downstream of the sheet-controlling device, as shown in  FIG. 1B . The sheet-controlling device  40  controls an entry of the sheet S into the sheet-transporting system  30 . The sheet-detection device  50  detects the feeding states of the sheet S. The sheet-detection device can be a thickness sensor which utilizes ultra-sonic technology. Once a sheet-feeding error is detected the sheet-detection device sends an error signal to the controller  80 . 
         [0017]    The first driving system  60  drives the sheet-controlling device  40 . The second driving system  70  drives the transporting mechanism  34 . The first driving system  60  and the second driving system  70  are independent of each other and may consist of power generating components such as motors and solenoid vales. In this embodiment, the sheet-controlling device  40  includes an entrance roller pair  42  driven by a motor and selectively rotated. However, the sheet-controlling device  40  may be a stopper board selectively blocking the passage to the sheet-transporting system  30 . The stopper board can be driven to extend and retract by a motor or a solenoid valve. 
         [0018]    The controller  80  controls the operations of the printing apparatus  1 . Upon receiving the error signal from the sheet-detection device  50 , the controller  80  signals the sheet-controlling device  40  to inhibit the entry of the sheet S into the sheet-transporting system  30 . The controller  80  further signals the transporting mechanism  34  to continue the operation of the transporting mechanism  34 , particularly when a recording medium is already in the sheet-circulating path  32  and in the middle of the image forming process. In this embodiment, the controller  80  upon receiving the error signal from the sheet-detection device  50  discontinues rotation of the entrance roller pair  42  to stop the sheet S from being conveyed into the sheet-circulating path  32 . The sheet-controlling device  40  may otherwise be composed of another type of transport component, such as a belt conveyor or a vacuum force creating unit which draws the sheet to move or maintain it at the same position. 
         [0019]      FIGS. 2A ,  2 B,  2 C,  2 D,  2 E,  2 F and  2 G are explanatory views of the sheet conveyance operation when a sheet-feeding error occurs when a second sheet S 2  is being fed in. Referring to  FIG. 2A , the sheet-feeding system  20  first feeds in a first sheet S 1 . The first sheet S 1  is then transported past the sheet-detection device  50 ; if the sheet-detection device  50  detects no sheet-feeding error, the sheet-controlling device  40  transports the first sheet S 1  to the sheet-circulating path  32  and the image forming system  10  forms an image on the front side of the first sheet S 1 , as shown in  FIG. 2B . At this time, the sheet-feeding system  20  feeds in the second sheet S 2 . If the sheet-detection device  50  detects a sheet-feeding error when the second sheet S 2  passes, the sheet-controlling device  40  inhibits the entry of the second sheet S 2  into the sheet-circulating path  32 . As shown in  FIG. 2C , when the second sheet S 2  reaches the entrance roller pair  42 , the rotation of the entrance roller pair  42  is discontinued, and the second sheet S 2  is not transported by the entrance roller pair  42  to the sheet-circulating path  32 . Referring to  FIGS. 2C to 2G , the second sheet S 2  is stopped at the entrance roller pair  42  in front of the sheet-circulating path  32  during the period of time when the first sheet S 1  is returned by the switching roller pair  34   b  to the sheet-circulating path  32  and transported through the image forming system  10  which forms an image on a back side of the first sheet S 1 , and finally is ejected from the printing apparatus  1 . According to the duplex printing method of the present invention, despite the sheet-detection device  50  detects the sheet-feeding error caused by the second sheet S 2 , the transporting mechanism  34  and the image forming system  10  would not cease but finish the printing process for the first sheet S 1 . In this way, the user can remove the second sheet S 2  from the printing apparatus  1  without interrupting the printing process for the first sheet S 1 . 
         [0020]      FIGS. 3A ,  3 B,  3 C,  3 D,  3 E,  3 F,  3 G,  3 H and  3 I are explanatory views of the sheet conveyance operation when a sheet-feeding error occurs when a third sheet S 3  is being fed in. Referring to  FIGS. 3A to 3C , the sheet-feeding system  20  first feeds in a first sheet S 1 . If the sheet-detection device  50  detects no sheet-feeding error, the sheet-controlling device  40  transports the first sheet S 1  to the sheet-circulating path  32 . Next, the image forming system  10  forms an image on a front side of the first sheet S 1 , and the sheet-feeding system  20  feeds in a second sheet S 2 . If the sheet-detection device  50  detects no sheet-feeding error when the second sheet S 2  passes, the sheet-controlling device  40  transports the second sheet S 2  into the sheet-circulating path  32 . The image forming system  10  forms an image on a front side of the second sheet S 2 . Referring to  FIG. 3D , the first sheet S 1  is returned by the switching roller pair  34   b  to the sheet-circulating path  32  to have the image forming system  10  forming an image on a back side of the first sheet S 1 . The second sheet S 2  is transported to the switching roller pair  24   b  after the image is formed on its front side. At this time, the sheet-feeding system  20  feeds in the third sheet S 3  which is transported past the sheet-detection device  50  and then to the sheet-controlling device  40 . If the sheet-detection device  50  detects a sheet-feeding error when the third sheet S 3  passes, the sheet-controlling device  40  inhibits the entry of the third sheet S 3  into the sheet-circulating path  32 . As shown in  FIG. 3E , when the third sheet S 3  reaches the entrance roller pair  42 , the rotation of the entrance roller pair  42  is discontinued, and the third sheet S 3  is not transported by the entrance roller pair  42  to the sheet-circulating path  32 . Referring to  FIGS. 3F to 3I , the third sheet S 3  is stopped at the entrance roller pair  42  in front of the sheet-circulating path  32  during the period of time when the first sheet S 1  and the second sheet S 2  each are being transported for a second time through the image forming system  10  and have the images formed on their back side, and then are ejected from the printing apparatus  1 . According to the duplex printing method of the present invention, when two sheets of paper are circulated in the sheet-circulating path  32 , the third sheet S 3  which causes the sheet-feeding error would be retained at a position in front of the sheet-circulating path  32 ; and in the mean time, the printing apparatus  1  carries out the printing operation for the first two sheets until printing is completed. 
         [0021]    While the present invention has been described with respect to a limited number of embodiments, it is to be understood that the present invention is not limited to the disclosed exemplary embodiments. It is intended that the appended claims cover all modifications, equivalent structures and variations as fall within the true spirit and scope of this present invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.