Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Application No. 2004-5366, filed Jan. 28, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having an optimized driving mechanism and a method of driving the same.  
         [0004]     2. Description of the Related Art  
         [0005]     As generally known in the art, an image forming apparatus refers to a printing machine, such as a photocopier, a printer or a facsimile machine, to output image data onto a printing medium such as a paper. The image forming apparatus includes a housing, a printer engine mounted within the housing to develop an image onto a paper, a variety of rollers mounted along a predetermined paper path within the housing, and a driving mechanism to drive the printer engine.  
         [0006]     The driving mechanism includes a driving source and a power transfer unit to transfer power generated from the driving source to the printer engine and the variety of rollers.  
         [0007]     In general, the number and type of a driving source or driving sources used for an image forming apparatus vary depending on the size of the image forming apparatus and the number of components of the apparatus. For example, a small-sized image forming apparatus can drive a printer engine and a plurality of rollers using a single driving source. Such a small apparatus can reduce the manufacturing cost by adopting a low-output motor. On the other hand, an image forming apparatus having a printer engine with a greater driving load and a relatively large number of rollers generally uses two or more motors having a high output.  
         [0008]     It is a current trend that the number of components provided in an image forming apparatus is increasing to implement various functions, such as duplex-printing and color-printing, thereby resulting in an increase of the driving load of the image forming apparatus. Accordingly, studies are under progress to provide an optimized driving mechanism by disposing a plurality of motors, including a high-output motor with low control capability and a low-output motor with high control capability, in proper positions within an image forming apparatus.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, it is an aspect of the present invention to solve at least the above problems and/or disadvantages and to provide at least the advantages described below.  
         [0010]     It is another aspect of the present invention to provide an image forming apparatus using both a motor with a high output characteristic and a motor with a high control capability to realize an optimized driving mechanism, and a method of driving the same.  
         [0011]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
         [0012]     The foregoing and/or other aspects are achieved by providing an image forming apparatus including a first driving section having a feed mechanism and a printer engine, a second driving section having a delivery mechanism, a first motor, a second motor, and a controller. The first and second motors drive the first and second driving sections, respectively. The power applied to one of the first and second motors having a higher output is cut off earlier by a predetermined compensation time as compared to a power applied to the other motor having a lower output.  
         [0013]     In the image forming apparatus having the structure as explained above, the compensation time should be equal to or shorter than the difference |T 1 −T 2 | between a first stop time T 1  required to actually stop the first motor after cut-off of the power supplied to the first motor and a second stop time T 2  required to actually stop the second motor after cut-off of the power supplied to the second motor. The first motor has a higher output than the second motor.  
         [0014]     A BLDC motor is used as the first motor, and a stepping motor is used as the second motor. The printer engine includes a photoconductive drum, a developing roller and a transfer roller. The second driving section may additionally include a fusing roller.  
         [0015]     The foregoing and/or other aspects are also achieved by providing a method of driving an image forming apparatus, characterized in that the driving of the image forming apparatus is stopped by cutting off a power supplied to a motor having a higher output earlier by a predetermined compensation time as compared to a power supplied to a motor having a lower output. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0017]      FIG. 1  is a cross-sectional side view showing the structure of an image forming apparatus according to an embodiment of the present invention;  
         [0018]      FIG. 2  is a schematic view showing the structure of the image forming apparatus of  FIG. 1 ;  
         [0019]      FIG. 3  is a block diagram showing the structure of the image forming apparatus of  FIG. 1 ; and  
         [0020]      FIG. 4  illustrates graphs showing a process of controlling the driving of an image forming apparatus according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Reference will now be made in detail to the embodiment of the present invention, an example of which is illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiment is described below to explain the present invention by referring to the figures.  
         [0022]     Referring to FIGS.  1  to  3 , an image forming apparatus  100  according to an embodiment of the present invention includes a first driving section  110 , a second driving section  140 , a first motor  150 , a second motor  160 , a power supplier  170 , a sensor  180  and a controller  190 .  
         [0023]     A housing  101  forms the exterior structure of the image forming apparatus  100 . A paper cassette  102  to load a plurality of paper sheets is removably mounted at the lower part of the housing  101 . Also, a paper path P to feed the paper sheets loaded in the paper cassette  102  one by one to delivery rollers  147  and  148  is provided within the housing  101 .  
         [0024]     The first driving section  110  includes a feed mechanism  120  and a printer engine  130 . The feed mechanism  120  feeds a paper sheet to the printer engine  130  ( FIG. 3 ) and includes a pickup roller  121  and feed rollers  122  to  125 . The pickup roller  121  picks up the paper sheets loaded in the paper cassette  102  one by one. The feed rollers  122  to  125  convey the picked-up sheets to the printer engine  130 . The printer engine  130  includes a developing unit  131  and a transfer roller  136 . The developing unit  131  contains a toner therein and includes a photoconductive drum  132 , a charging roller  133 , a developing roller  134 , and a supply roller  135 . The photoconductive drum  132 , charging roller  133 , developing roller  134  and supply roller  135  are driven together in mesh by the engagement of gear teeth and their overall driving torque varies depending on the driving hours. In other words, the developing unit  131  is replaced when the toner contained therein is completely consumed. The driving torque of the developing unit  131  is highest immediately after replacement and is gradually reduced with the reduction of the residual toner amount.  
         [0025]     As generally known in the art, a laser beam generated from an exposure unit  105  is emitted to the photoconductive drum  132  to form an electrostatic latent image. The charging roller  133  applies a uniform electric charge to the surface of the photoconductive drum  132 . The developing roller  134  attaches toner to the photoconductive drum  132  to develop the electrostatic latent image, thereby producing a visible developed toner image. The supply roller  135  supplies the toner to the developing roller  134 . The transfer roller  136  transfers the toner image formed on the photoconductive drum  132  onto a paper.  
         [0026]     The second driving section  140  includes a fusing unit  141  and a delivery mechanism  144  including a plurality of delivery rollers  145  to  148 . The toner image is fused and stuck onto the paper passing through the printer engine  130  by the heat and pressure applied from the fusing unit  141 . The fusing unit  141  includes a heating roller  142  and a pressure roller  143 . The delivery rollers  145  to  148 , which are positioned at the rear of the fusing unit  141  on the paper path P, discharge the paper to the outside of the housing  101  of the image forming apparatus  100 .  
         [0027]     The first motor  150  drives the first driving section  110 . Since the first motor  150  should drive the pickup roller  121 , feed rollers  122  to  125 , photoconductive drum  132 , charging roller  133 , developing roller  134 , supply roller  135  and transfer roller  136  of the first driving section  110 , a brushless DC (BLDC) motor having a small size and a high output is employed as the first motor.  
         [0028]     The second motor  160  drives the second driving section  140 . As the second motor to drive the heating roller  142 , pressure roller  143  and delivery rollers  145  to  148  of the second driving section  140 , a stepping motor having a lower output and a superior control characteristic is employed.  
         [0029]     The power supplier  170  supplies electric power to the first and second driving motors  150  and  160 .  
         [0030]     The sensor  180  positioned on the paper path P detects a jam of a paper being fed along the paper path P and sends a corresponding signal to the controller  190 .  
         [0031]     The controller  190  controls the power supplied to the first and second motors  150  and  160  from the power supplier  170  according to the signal received from the sensor  180 . Since the first and second motors  150  and  160  have different outputs, they are stopped at different points in time when the powers supplied to the two motors  150  and  160  are cut off simultaneously.  
         [0032]     As shown in  FIG. 4 , if the powers supplied to the first and second motors  150  and  160  are cut off at time T 1 , the second motor  160  having a low output and little inertial force will stop immediately at T 1  (see  FIG. 4 , part (a)), while the first motor  150  having a high output and great inertial force will slowly reduce its driving speed and stop at time T 2  (see  FIG. 4 , part (b)). Accordingly, there will be a time difference T A  between T 2  at which the first motor  150  stops and T 1  at which the second motor  160  stops. The paper passing along the paper path P may be wrinkled (see W in  FIG. 2 ) when it contacts both the printer engine  130  and the fusing unit  141 . In such an event, the toner image transferred onto the paper is blurred, thereby deteriorating the printing quality.  
         [0033]     In order to solve this problem, the controller  190  controls the power supplied to the first motor  150  to be cut off earlier than the power supplied to the second motor  160 . As shown in  FIG. 4 , part (c), the power supplied to the first motor  150  is cut off earlier by the compensation time T A  than the cut-off time T 1  of the power supplied to the second motor  160 . Consequently, the first and second motors  150  and  160  can be stopped concurrently at T 1 .  
         [0034]     The compensation time T A  can be determined by measuring the inertial force of the first motor  150 , which refers to additional rotation of the first motor  150  after power cut-off. The additional rotation of the first motor  150  depends on the driving load of the first driving section  110  which also depends on the driving torque of the developing unit  131 . Table 1 shows the additional rotation (mm) of the first motor  150  according to the driving torque of the developing unit  131  when a paper is conveyed along the paper path P at a speed of 120 mm/sec.  
                                                                           TABLE 1                                       Driving torque of developing unit (kgf/cm)                9   8   7   6   5                        Additional rotations (mm)   3.0   3.5   4.2   5.8   7.6                  
 
         [0035]     As is clear from Table 1, the additional rotation of the first motor  150  increases with the reduction of the driving torque of the developing unit  131 . The compensation time T A  is determined based on the additional rotation (3 mm) at the highest driving torque 9 kgf/cm. Therefore, the compensation time T A  is {fraction (3/120)} sec. The controller  190  controls the power supplied to the first motor  150  to be cut off earlier by T A  than the power supplied to the second motor  160  so that the first and second motors  150  and  160  can be stopped simultaneously.  
         [0036]     Hereinbelow, the functions of the image forming apparatus and the method of driving the apparatus will be explained in more detail. It is assumed that the printing process of the image forming apparatus is performed at a speed of 120 mm/sec.  
         [0037]     As shown in  FIG. 2 , when a command to print is input to the image forming apparatus, the charging roller  133  applies a uniform electric charge to the surface of the photoconductive drum  132 . Also, a laser beam generated from the exposure unit  105  (see  FIG. 1 ) is emitted to the surface of the photoconductive drum  132  to form an electrostatic latent image. The developing roller  134  attaches a toner to the photoconductive drum  132  to develop the electrostatic latent image, thereby producing a toner image. In addition, papers loaded in the paper cassette  102  (see  FIG. 1 ) are fed one by one to the developing unit  131  by the pickup roller  121  and the feed rollers  122  to  125 . When a paper passes between the photoconductive drum  132  and the transfer roller  136 , the toner image formed on the photoconductive drum  132  is transferred onto the paper. The paper with the transferred toner image passes through the fusing unit  141  and is finally discharged out by the delivery rollers  145  to  148 .  
         [0038]     When a paper jam occurs during the printing process, the sensor  180  (see  FIG. 3 ) detects the jam and sends a corresponding signal to the controller  190 . Upon receiving the signal, the controller  190  cuts off the power supplied to the first motor  150  earlier by {fraction (3/120)} sec than the power cut-off for the second motor  160 . If the driving torque of the developing unit  131  is 9 kgf/cm, the stop point of the first motor  150  will be the same as that of the second motor  160  as shown in.  FIG. 4 , part (c).  
         [0039]     If the driving torque of the developing unit  131  is reduced to  5  kgf/cm, the time to stop the first motor  150  will be delayed by T B . Consequently, the first motor  150  will stop at T 4  ( FIG. 4 , part (d)). If the power supplied to the first motor  150  is cut off earlier by T A  than the power supplied to the second motor  160 , the first motor  150  will stop at T 5  and the time difference between the stop point of the first motor  150  and that of the second motor  160  will be reduced to T C  as shown in  FIG. 4 , part (e). When the driving torque of the developing unit  131  is 5 kgf/cm, the first motor  150  additionally rotates by 7.6 mm. It is possible to reduce the additional rotation of the first motor  150  to 4.6 mm by cutting off the power supplied to the first motor  150  earlier by {fraction (3/120)} sec.  
         [0040]     As a result, the paper wrinkling W as shown in  FIG. 2  can be reduced, thereby improving the printing quality.  
         [0041]     The image forming apparatus as described above is a so-called electrophotographic image forming apparatus which develops an electrostatic latent image formed on the photoconductive drum  132  by a laser beam emitted from the exposure unit  105  to produce a toner image and transfers the toner image onto a printing paper. However, the present invention is not limited only to the above image forming apparatus. The present invention is also applicable to any image forming apparatus with various printing methods, such as ink-jet printing.  
         [0042]     The embodiment of the present invention as described above provides an image forming apparatus which realizes an optimized driving mechanism by adopting both a motor with a high output and a motor with a superior control characteristic and appropriately controlling the driving of the two motors.  
         [0043]     Although an embodiment of the present invention has been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Technology Category: 3