Patent Publication Number: US-7224920-B2

Title: Sheet processing apparatus and control method thereof

Description:
FIELD OF THE INVENTION 
   The present invention relates to a sheet processing apparatus and a control method thereof and, more particularly, to execution control of processes in a sheet processing apparatus which is connected to an image forming apparatus, applies a predetermined process for a plurality of sheets that have undergone image formation as a unit, and has a power storage means which can store electric power required to execute the process. 
   BACKGROUND OF THE INVENTION 
   Currently, apparatuses which form images according to an electrophotography system have been prevalently used. For example, laser beam printers which form (print) images on cut sheets, OHP sheets, and the like on the basis of an image signal sent from a host apparatus such as a computer or the like have prevailed, and some models of such printers have a staple function of stapling a set (bundle) of sheets (recording media) on which images are formed. 
   Such staple function is normally provided by a sheet processing apparatus which is connected to an image processing apparatus upon use, and Japanese Patent Laid-Open No. 11-322181 describes such sheet processing apparatus. 
   A conventional image forming apparatus and a conventional sheet processing apparatus will be described below with reference to  FIGS. 10 to 15 .  FIG. 10  is a schematic sectional view showing the structure of an image forming apparatus,  FIG. 11  is a view for explaining a scanner unit,  FIG. 12  is a schematic sectional view showing the structure of a sheet processing apparatus,  FIG. 13  is a top view of the sheet processing apparatus,  FIG. 14  is a block diagram showing electrical connections between the image forming apparatus and sheet processing apparatus, and  FIG. 15  is a graph schematically showing a change in consumption current in the sheet processing apparatus. 
   The image forming operation of an image forming apparatus  301  of this prior art will be described below mainly with reference to  FIGS. 10 and 11 . Reference numeral  101  denotes an image signal (VDO signal), which is input to a laser unit  102 . Reference numeral  103  denotes a laser beam which is ON/OFF-modulated by the laser unit  102 . Reference numeral  104  denotes a scanner motor, which steadily rotates a rotary polygonal mirror  105 . Reference numeral  106  denotes an imaging lens which forms a focal point of a laser beam  107  deflected by the polygonal mirror on a photosensitive drum  108  as a surface to be scanned. 
   Therefore, the laser beam  107  modulated based on the image signal  101  is horizontally scanned (in the main scan direction) on the photosensitive drum  108 . Reference numeral  109  denotes a beam detection port which fetches the beam via a slit-like entrance port. The laser beam which has entered via this entrance port is guided to a photoelectric conversion element  111  via an optical fiber  110 . The laser beam which is converted into an electrical signal by the photoelectric conversion element  111  is amplified by an amplifier circuit (not shown) to obtain a horizontal sync signal. 
   A latent image formed on the photosensitive drum  108  is visualized by a developer  123  to obtain a toner image, which is transferred onto a transfer sheet  112  by a transfer roller  120 . 
   Reference numeral  131  denotes a paper cassette which feeds one type of standard-size transfer sheets of a size selected from an A4 size, LETTER size, and the like. 
   A single-sided print operation on the transfer sheet  112  fed from the paper cassette  131  will be explained below. 
   When a pickup roller  132  makes one revolution, one of transfer sheets  112  on the multi-tray (paper cassette)  131  is fed to paper feed rollers  134 . The transfer sheet  112  is fed to registration rollers  135  upon rotation of the paper feed rollers  134 , and stands by for synchronization with an image forming unit. 
   A registration sensor  137  as a combination of a photointerrupter (light transmitting sensor) and flag processing is arranged in the vicinity of the registration rollers  135 , and detects that the leading end of the transfer sheet  112  arrives the registration roller  135 . 
   An image forming apparatus control circuit  402  ( FIG. 14 ) that controls the image forming unit detects the arrival timing of the leading end of the transfer sheet  112  to the registration rollers  135  on the basis of the detection result of the registration sensor  137 , starts image formation on the photosensitive drum  108  and controls the temperature of a halogen heater (not shown) of a fixing unit  121  to a predetermined value. 
   The transfer sheet  112  which stands by at the position of the registration rollers  135  is conveyed in synchronism with the timing of the detection result of the registration sensor  137  and the image forming process, and a toner image formed on the photosensitive drum  108  is transferred onto the transfer sheet  112  by a transfer roller  120 . The transfer sheet  112  on which the toner image has been transferred is fixed by the fixing unit  121  which incorporates a halogen heater, and is guided to an discharge unit  122  as the upper portion of the image forming apparatus via discharge rollers  140  and a flapper  141  set at the a side, and is discharged from the discharge unit  122  by discharge rollers  156 . 
   On the other hand, a sheet processing apparatus  302  is connected as an option to the image forming apparatus  301 , and the following control is made to discharge a sheet to the sheet processing apparatus  302 . 
   When the sheet processing apparatus  302  is connected to the image forming apparatus  301  and a connected host computer or the like (not shown) issues an discharge instruction to the sheet processing apparatus, the image forming apparatus control circuit  402  sets the flapper  141  to the b side, and conveys the transfer sheet  112  into the sheet processing apparatus  302  by the discharge rollers  140  after the printed transfer sheet  112  has passed the fixing unit  121 . The transfer sheet  112  that has undergone image formation by the image forming apparatus main body  301  is passed to the sheet processing apparatus  302  connected as an option with its obverse surface facing up (face up). 
   As shown in  FIG. 14 , a sheet processing apparatus control circuit  409  in the sheet processing apparatus  302  is connected to the image forming apparatus control circuit  402  in the image forming apparatus main body to communicate with each other. When the image forming apparatus control circuit  402  issues a staple instruction for stapling a set of a plurality of transfer sheets, the sheet processing apparatus control circuit  409  conveys the transfer sheet  112  to a stack tray used to staple it intact or while being reversed by a reverse mechanism in a stacker. The transfer sheet  112  conveyed to the stack tray is aligned in the convey direction and widthwise direction by an aligning plate until a predetermined number of transfer sheets  112  are conveyed. When a set of a predetermined number of transfer sheets is formed, a shutter is closed to fix and staple the set of transfer sheets. 
   The set of transfer sheets  112  stapled by the stapler is discharged onto the discharge tray by driving discharge rollers. 
   The staple operation in the sheet processing apparatus  302  will be described below mainly with reference to  FIGS. 12 to 14 . 
   Reference numeral  303  denotes an entrance sensor which detects the transfer sheet  112  fed from the image forming apparatus main body  301 . The detection information of the transfer sheet  112  by the entrance sensor  303  is input to the sheet processing apparatus control circuit  409 . Upon reception of this information, the sheet processing apparatus control circuit  409  drives a transfer sheet convey motor (not shown). When the transfer sheet convey motor is driven, entrance rollers  304 , reverse rollers  310 , a slip roller  306 , and a pair of set convey rollers (set convey means)  305  are simultaneously driven. 
   The reverse rollers  309  are initially rotated to convey the transfer sheet  112  in the feed direction. However, when a reverse solenoid works in response to a signal output from the sheet processing apparatus control circuit  409 , the rotation direction of the rollers  309  is reversed to convey the transfer sheet  112  in the reverse direction. Reference numeral  308  denotes a flapper which is controlled by the sheet processing apparatus control circuit  409 . When a flapper solenoid (not shown) operates, the transfer sheet  112  is fed into the convey rollers  310  facing up, and forms a transfer sheet set  112   a  on a stack tray (stack means)  318 . 
   The pair of convey rollers  305  normally contact the convey path surface. When a set convey roller solenoid (not shown) controlled by the sheet processing apparatus control circuit  409  is driven, the upper roller of the rollers  305  moves upward to a set convey roller upper position  305   a  where that roller does not contact the convey path surface. While the set convey roller solenoid is driven, a shutter  307  is closed. 
   When the transfer sheets  112  are stacked on the stack tray  318  to staple the transfer sheet set  112   a , the set convey roller solenoid is driven to move the upper one of the set convey rollers to the position  305   a , and to close the shutter  307 . 
   The slip roller  306  has a very weak convey force. The roller  306  conveys the sheet until the leading end of the sheet contacts the shutter  307 , and slips on the sheet so as to align the sheet leading end and to hold the sheet position after the sheet leading end contacts the shutter  307 . When the transfer sheet  112  begins to be stacked, a stack tray sheet sensor  313  detects the sheet and inputs a detection signal to the sheet processing apparatus control circuit  409 . An alignment means that aligns the leading end portions of the transfer sheets  112  is formed. 
   When the transfer sheets  112  are to be stacked at the position of the shutter  307 , aligning plates R  402  and L  403  are moved in the widthwise direction in correspondence with the size of the transfer sheets  112 . The aligning plates R  402  and L  403  are controlled by the sheet processing apparatus control circuit  409  via an aligning plate motor drive circuit (not shown) and are driven by aligning plate R and L motors (neither are shown). 
   The moving positions of the aligning plates R  402  and L  403  are controlled by determining moving amounts from aligning plate R and L home position sensors (not shown) by the sheet processing apparatus control circuit  409  on the basis of the transfer sheet size which is sent from the image forming apparatus control circuit  402  via a communication line. 
   When a predetermined number of transfer sheets  112  are stacked, the image forming apparatus control circuit  402  issues a staple designation to the sheet processing apparatus control circuit  409 . Upon reception of the staple designation, the sheet processing apparatus control circuit  409  moves a staple unit  312  in the widthwise direction indicated by the double-headed arrows, and drives a staple motor (not shown) in a staple drive unit  410 , thus stapling the transfer sheet set  112   a . The staple unit  312  is moved by driving a stapler moving motor (not shown) controlled by the sheet processing apparatus control circuit  409 . The moving amount of the staple unit  312  is controlled by the sheet processing apparatus control circuit  409  on the basis of the moving distance from a stapler unit home position sensor (not shown). 
   Whether or not the operation of a stapler  312   a  of the staple unit  312  normally ends can be confirmed when a staple cam returns to the position of the staple home position sensor a predetermined period of time after the sheet processing apparatus control circuit  409  begins to drive the staple motor. When the shutter  307  is opened before the transfer sheet set  112   a  is stapled, and the transfer sheet set  112   a  is stapled after it is conveyed by a predetermined distance, the transfer sheet set  112   a  can be stapled at an arbitrary position in the convey direction. 
   A pair of discharge rollers (set discharge means) R  406  and L  407  are arranged near downstream of the shutter  307 . Reference numeral  317  denotes an discharge sensor which is equipped on an discharge tray (sheet set stack means)  316 , and inputs a sensor signal to the sheet processing apparatus control circuit  409 . 
   In the conventional image forming apparatus  301  and sheet processing apparatus  302  as an option, a power supply circuit  401  for the image forming apparatus and a power supply circuit  415  for the sheet processing apparatus are independently provided, and are connected to a commercial power supply via AC plugs  411  and  414 , thus operating the image forming apparatus  301  and sheet processing apparatus  302 . 
   The reason why commercial power is supplied to the respective power supply circuits is that the sheet processing apparatus  302  requires large power in the staple operation, as shown in  FIG. 15 , and it is not practical to design the power supply circuit  401  for the image forming apparatus main body  301  as a large-capacity power supply circuit in consideration of the load on the sheet processing apparatus  302 . 
   In  FIG. 15 , a current Is 1  that requires normal operations such as a sheet convey operation and the like of the sheet processing apparatus is as relatively small as about 24 V/1 A. However, when the staple operation is done, a maximum current Is 3  as high as 5 A flows for about 100 msec. In order to supply electric power from the image forming apparatus to the sheet processing apparatus in consideration of electric power based on this maximum current Is 3 , the output electric power of the power supply for the image forming apparatus must be set as high as about 120 W(=24 V×5 A). As a result, a large-scale, expensive power supply circuit is required, resulting in an increase in price which is unnecessary for users who use only the image forming apparatus (does not require any sheet processing apparatus). 
   For this reason, conventionally, since the power supply circuit  401  for the image forming apparatus  301  and the power supply circuit  415  for the sheet processing apparatus  302  are independently provided, minimum required portions (e.g., a communication interface and the like) are provided to the image forming apparatus main body for the sheet processing apparatus as an option, thus suppressing an increase in cost. 
   On the other hand, as one of reasons why the power supply circuits are independently provided, an image forming apparatus that requires a sheet processing apparatus is normally limited to a large-scale, high value-added image forming apparatus such as a monochrome high-speed printing machine, a high image quality machine that can perform color print, and the like. 
   More specifically, the power supply circuits are independently provided for the following reasons: two AC plugs are agreeable in terms of design since a system formed by connecting the image forming apparatus to the sheet processing apparatus as an option is bulky; even when the total AC current that flows in the system of the image forming apparatus and sheet processing apparatus exceeds maximum allowable electric power (e.g., 1,500 W) of one commercial power supply system, since the system is installed by a service person, the service person need only connect the two AC plugs to different commercial power supply systems so as not to exceed the maximum allowable electric power of the commercial power supply; and so forth. 
   In recent years, along with the improvements of the technologies of image forming apparatuses, image forming apparatuses which belong to a category of middle-speed machines (middle-class machines) have been speeded up while their size and price reductions are achieved, and have gained a speed comparable to that of conventional high-speed machines. Based on such improvements, added values such as expandability of options, energy savings, and the like are demanded from the market more strongly. 
   Under such circumstances, a demand is increasing for an image forming apparatus which can improve its design upon mounting an option and allows the user to easily attach/detach an option by supplying electric power from the image forming apparatus to an option apparatus. 
   However, when electric power is supplied from the power supply in the image forming apparatus main body to the sheet processing apparatus such as a staple stacker or the like, the staple operation requires large electric power, as described above. For this reason, a large-capacity power supply circuit must be prepared in the image forming apparatus main body in consideration of consumption power in the sheet processing apparatus. However, this arrangement results in an increase in price unnecessary for users who use only the image forming apparatus. In order to meet such conflicting requisites, it is demanded to reduce electric power to be supplied to the sheet processing apparatus and to minimize an increase in cost of the image forming apparatus main body. 
   In a large-scale, high value-added image forming apparatus such as a monochrome high-speed printing machine, a high image quality machine that can perform color print, and the like, i.e., in a so-called high-speed machine (high-class machine), more functions are required, and consumption power tends to increase although energy-saving measures are taken. One indication of the upper limit of electric power consumed by these apparatuses is the maximum electric power (e.g., 1,500 W=100 V×15 A if the commercial power supply voltage is 100 V) that can be supplied by the commercial power supply. 
   In general, the image forming apparatus main body is normally designed so that the maximum electric power of the apparatus does not exceed that of the commercial power supply. Therefore, when an option such as the sheet processing apparatus that consumes relatively large electric power or the like is connected to the image forming apparatus whose maximum electric power is approximate to that of the commercial power supply, it is recommended that a power supply circuit is independently provided to the sheet processing apparatus, and is connected to a commercial power supply system different from the main body using an AC plug different from the image forming apparatus main body. 
   However, the AC plugs of the image forming apparatus main body and sheet processing apparatus are often connected to the same commercial power supply system unless they are connected by a service person or the like in consideration of the maximum consumption power. Therefore, it is demanded to reduce the maximum electric power of each of the image forming apparatus and sheet processing apparatus so as to prevent protection means such as the circuit breaker of the commercial power supply from operating even when the two AC plugs are connected to the same commercial power supply system, and to prevent the maximum electric power of the system from exceeding the maximum electric power that can be supplied by one commercial power supply system. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to reduce the peak of consumption power in a sheet processing apparatus and to reduce cost as a whole. 
   In order to achieve the above object, according to one aspect of the present invention, there is provided a sheet processing apparatus, which is connected to an image forming apparatus, and applies a predetermined process to a plurality of sheets that have undergone image formation as a unit, comprising: power storage means capable of storing electric power required to execute the process; a charge circuit for charging the power storage means with electric power; a detection circuit for detecting an output voltage of the power storage means; and a control circuit for, when the voltage detected by the detection circuit exceeds a predetermined value, controlling the process to be executed by using the electric power stored in the power storage means in accordance with an instruction from the image forming apparatus. 
   In order to achieve the above object, according to another aspect of the present invention, there is provided a method of controlling a sheet processing apparatus, which is connected to an image forming apparatus, applies a predetermined process to a plurality of sheets that have undergone image formation as a unit, and has power storage means capable of storing electric power required to execute the process, comprising: a charge step of charging the power storage means with electric power; a detection step of detecting an output voltage of the power storage means; and a control step of controlling, when the voltage detected in the detection step exceeds a predetermined value, the process to be executed by using the electric power stored in the power storage means in accordance with an instruction from the image forming apparatus. 
   That is, in the sheet processing apparatus which is connected to the image forming apparatus, applies a predetermined process for a plurality of sheets that have undergone image formation as a unit, and has a power storage means which can store electric power required to execute the process, the power storage means is charged with electric power, the output voltage of the power storage means is detected, and when the detected voltage exceeds a predetermined value in accordance with an instruction from the image forming apparatus, the process is executed using electric power stored in the power storage means. 
   In this way, since the process is executed using electric power supplied from the power storage means, consumption power can be prevented from temporarily increasing upon executing the process. 
   Therefore, the peak of consumption power of the sheet processing apparatus can be reduced, and installation of a system including the image processing apparatus and sheet processing apparatus is facilitated. In addition, the capacity of the power supply provided to the sheet processing apparatus or image processing apparatus can be reduced, and the cost of the overall system including the sheet processing apparatus or the image processing apparatus can be reduced. 
   The charge circuit may be configured to charge the power storage means with electric power supplied from the image forming apparatus. 
   The charge circuit may further comprises a power supply circuit for generating internally required electric power from a commercial power supply, and the charge circuit may be configured to charge the power storage means with electric power supplied from the power supply circuit. 
   The control circuit may control a route of electric power supplied from the power storage means so as to prevent the charge process on the power storage means by the charge circuit, and execution of the process from being made at the same time. 
   When the voltage detected by the detection is not greater than the predetermined value, the control circuit may instruct the image forming apparatus to pause an image forming operation without executing the process. 
   Otherwise, when the voltage detected by the detection circuit is not greater than the predetermined value, and when the detected voltage exceeds a second predetermined value less than the predetermined value and the number of sheets as the unit exceeds a predetermined value, the control circuit may execute the process. 
   In this case, when the voltage detected by the detection circuit is not greater than the predetermined value, and when the detected voltage exceeds a second predetermined value less than the predetermined value or the number of sheets as the unit is not greater than a predetermined value, the control circuit may instruct the image forming apparatus to pause an image forming operation, and then execute the process using the electric power supplied to the charge circuit. Otherwise, when the voltage detected by the detection circuit is not greater than the predetermined value, and when the detected voltage exceeds a second predetermined value less than the predetermined value and the number of sheets as the unit is not greater than a predetermined value, the control circuit may instruct the image forming apparatus to delay an image forming operation, and then execute the process. 
   The process may be one of a staple process for stapling the plurality of sheets, a trimming process for trimming the plurality of sheets, and a booklet process for bookbinding the plurality of sheets. 
   The power storage means may comprise a capacitor or a secondary battery, and the capacitor may be an electric double layer capacitor. 
   Note that the above object is also achieved by an image forming system including the aforementioned sheet processing apparatus and image forming apparatus, a computer program that makes a computer apparatus execute the method of controlling the sheet processing apparatus, and a storage medium storing that computer program. 
   Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a block diagram showing the electrical arrangement of an image forming apparatus and sheet processing apparatus according to the first embodiment of the present invention; 
       FIG. 2  is a graph showing an example of a change in output voltage of a power storage means; 
       FIG. 3  is a flowchart of a staple process of the first embodiment; 
       FIG. 4  is a block diagram showing the arrangement of a modification of the first embodiment; 
       FIG. 5  is a block diagram showing the arrangement of another modification of the first embodiment; 
       FIG. 6  is a block diagram showing the arrangement of still another modification of the first embodiment; 
       FIG. 7  is a flowchart of a staple process of the second embodiment; 
       FIG. 8  is a flowchart of a staple process of the third embodiment; 
       FIG. 9  is a block diagram showing the electrical arrangement of an image forming apparatus and sheet processing apparatus according to the fourth embodiment of the present invention; 
       FIG. 10  is a schematic sectional view showing the structure of a general image forming apparatus; 
       FIG. 11  is a view for explaining the arrangement of a scanner unit of the image forming apparatus shown in  FIG. 10 ; 
       FIG. 12  is a schematic sectional view showing the structure of a general sheet processing apparatus; 
       FIG. 13  is a top view of the sheet processing apparatus shown in  FIG. 12 ; 
       FIG. 14  is a block diagram showing an example of the electrical arrangement of the image forming apparatus and sheet processing apparatus; and 
       FIG. 15  is a graph showing a change in consumption current of the sheet processing apparatus. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. Note that each element in the following elements is not intended to limit the scope of the invention, but is described only as an example. 
   First Embodiment 
   The first embodiment according to the present invention will be described in detail hereinafter with reference to  FIGS. 1 to 6 . 
     FIG. 1  is a block diagram showing the electrical control arrangement of an image forming apparatus and sheet processing apparatus,  FIG. 2  is a graph showing a change in output voltage of a power storage means,  FIG. 3  is a flowchart showing the operation of the first embodiment, and  FIGS. 4 to 6  are block diagrams showing other arrangements of the first embodiment. 
   The image forming operation of the image forming apparatus, and the operation of the sheet processing apparatus are the same as those in the prior art mentioned above, and a description thereof will be omitted. Also, the same reference numerals denote the same parts as in the prior art, and a detailed description thereof will be omitted. 
   A power supply circuit  401  is provided to an image forming apparatus  301  to supply a predetermined voltage to an image forming apparatus control circuit  402  that controls image formation, and to supply a predetermined voltage Va to a sheet processing apparatus  302  set as an option via a connector. The image forming apparatus control circuit  402  communicates, via a connector, with a sheet processing apparatus control circuit  409 , which is arranged in the sheet processing apparatus  302 , and controls the convey and staple operations of transfer sheets in the sheet processing apparatus, thus making timing control so that the convey and staple operations of transfer sheets  112  conveyed from the image forming apparatus  301  can be made smoothly. 
   Reference numeral  406  denotes a charge circuit, which receives the voltage Va supplied from the power supply circuit  401  of the image forming apparatus, supplies a predetermined voltage Vb(Va&lt;Vb) to a power storage means  405  including a plurality of electric double layer capacitors in accordance with a charge command from the sheet processing apparatus control circuit  409 , and changes until the output voltage of the power storage means reaches a predetermined voltage Vc(≈Vb). The electric double layer capacitor has received a lot of attention in many fields in recent years, since it has a capacitance as large as several F or more, higher charge efficiency than a secondary battery, and a long life. 
   A power storage means voltage detection circuit  407  detects the charge voltage of the power storage means  405 , and transmits the detection result to an A/D port of a CPU (not shown) in the sheet processing apparatus control circuit  409  as, e.g., an analog signal. According to this voltage detection result of the power storage means, the sheet processing apparatus control circuit  409  supplies a charge instruction to the charge circuit  406 . A constant voltage control circuit  408  controls the charge voltage Vc of the power storage means  405  to be equal to or higher than a voltage Vs(Vs≈Va−Vf, Vs&lt;Vc, Vf=forward voltage of a diode  403 : about 0.6 V), and supplies the voltage Vs to a staple drive unit  410  via a switch  413 , thereby driving a staple unit  312 . 
   As the switch  413 , a semiconductor switch such as a FET or the like is preferably used in terms of durability of ON/OFF operations. However, a mechanical switch such as a relay or the like may be used if it does not pose any problem in a service life such as ON/OFF counts and the like. A diode  403  is provided to prevent the output from the power supply circuit  401  of the image forming apparatus from being supplied to the staple drive circuit  410 , while the voltage Vs is supplied from the power storage means  405  via the constant voltage control circuit  408 . 
   Therefore, the diode  403  may be replaced by a switch  423 , as shown in  FIG. 4 , and the switch  413  may be controlled to be OFF when the switch  413  is ON; it may be controlled to be ON when the switch  413  is OFF, thus obtaining the same effect. 
   Furthermore, when the switch  413  is replaced by a diode  404 , as shown in  FIG. 5 , power supply from the power storage means  405  to the staple drive unit  410  and that from the power supply  401  of the image forming apparatus  401  can be automatically switched in accordance with the charge voltage Vc of the power storage means  405 . 
   Also, if the image forming apparatus main body  301  can directly supply a voltage Vbo which satisfies Vbo&gt;Va and Vbo≈Vb, as shown in  FIG. 6 , the power supply  401  of the main body may supply the voltage Vbo to the sheet processing apparatus. When the voltage Vbo is supplied to the power storage means  405  via the charge circuit  406  to charge it, the number of connectors (contacts) for power supply between the main body  301  and sheet processing apparatus  302  increases, but the charge circuit  406  need not boost the voltage Va to Vb(Vbo≈Vb), thus forming a low-cost charge circuit. 
   The process upon executing the staple operation by power supply from the power storage means will be described below with reference to the flowchart of  FIG. 3 . 
   When N transfer sheets, which are set in advance, are stacked on a stack tray  318 , the sheet processing apparatus  302  starts the staple operation on the basis of the following flow. The sheet processing apparatus control circuit  409  monitors the charge voltage Vc of the power storage means  405  (step S 701 ), and confirms if the charge voltage falls within a predetermined range (Vc 1 &gt;Vc&gt;Vc 2 ) between a maximum charge voltage Vc 1  and charge operation start voltage Vc 2  shown in  FIG. 2  (step S 702 ). If the charge circuit  406  is configured to set Vc to be lower than Vc, only Vc&gt;Vc 2  may be confirmed, as shown in  FIG. 3 . 
   If it is confirmed that Vc falls within the predetermined range, the sheet processing apparatus control circuit  409  turns on the switch  413  in synchronism with the timing of the image forming operation to supply the voltage Vs to the staple drive unit  410  (step S 703 ) and to drive the staple unit  312  via the staple drive unit  410 , thus stapling a transfer sheet set  112   a  (step S 704 ). 
   In this embodiment, since the staple operation is executed by energy (electric power) stored in the power storage means  405 , a maximum current (consumption current of the sheet processing apparatus) supplied from the power supply circuit  401  of the image forming apparatus to the sheet processing apparatus  302  in the staple operation can be reduced to be lower than the conventional value (Is 3  in  FIG. 15 ; about 5 A). For this reason, the consumption current of the sheet processing apparatus of this embodiment assumes a value as the sum of a current Is 1  required for normal operations, and a current required to charge, and can be roughly reduced to a current value Is 2  indicated by the broken line in  FIG. 15 . This means that the maximum current (maximum consumption current) that flows in the sheet processing apparatus is reduced, and the maximum consumption current of the system including the sheet processing apparatus and image forming apparatus is also reduced. 
   Upon completion of the staple operation, the switch  413  is turned off (step S 705 ), and it is checked if a job is complete (step S 706 ). If the job is not complete yet, the power storage means  405  is charged to prepare for the next staple operation (step S 707 ); otherwise, the process ends. 
   If it is determined in step S 706  that the job is not complete yet, and if the charge voltage Vc falls within the predetermined range (Vc 1 &gt;Vc&gt;Vc 2 ), the power storage means need not always be charged, and the switch  413  need not always be turned off in step S 705 . That is, if the charge voltage Vc becomes lower than the charge operation start voltage Vc 2 , the switch  413  can be turned off to start charge. 
   On the other hand, if the charge voltage Vc is lower than the charge operation start voltage Vc 2  in step S 702 , the voltage Vs required for the operation is unlikely to be supplied to the staple drive unit  410 , i.e., the staple operation is unlikely to be executed depending on the conditions, e.g., the print speed, the number of sheets to be stapled, and the like. In such case, the image forming operation is paused (step S 708 ), and the power storage means  405  is charged until its output voltage reaches the maximum voltage Vc 1  (step S 707 ). 
   Since the image forming operation is paused in step S 708 , consumption power of the voltage Va(≈Vs+Vf) internally consumed by the image forming apparatus is reduced. Since this reduction of consumption power can produce a margin in supply performance at the output voltage Va of the power supply  401  of the image forming apparatus, when that margin can supply electric power required for the staple operation, the image forming operation may be paused, and electric power may be supplied to the staple drive unit  410  via the diode  403  to execute the staple operation. 
   This embodiment has exemplified the arrangement in which the charge circuit  406  boosts the output voltage Va from the power supply  401  of the image forming apparatus to the charge circuit output voltage Vb to charge the power storage means  405 , and the output voltage Vc of the power storage means  405  is stepped down to Vs by the constant voltage control circuit  408  to supply that voltage to the staple drive unit  410 . However, other arrangements may be adopted. 
   For example, when the charge circuit  406  is replaced by a simple switch circuit, the output voltage Va from the power supply  401  of the main body may be set to be nearly equal to the output voltage Vb of the charge circuit  406  to charge the power storage means  405 , and the output voltage Vc of the power storage means  405  may be boosted to Vs by the constant voltage control circuit  408  so as to be supplied to the staple drive unit  410 , thus implementing the same control as in this embodiment. 
   As described above, according to this embodiment, in the system in which the power supply of the image forming apparatus supplies electric power to the sheet processing apparatus, the sheet processing apparatus includes the power storage means, and the staple operation is executed using electric power supplied from the power storage means. Hence, power supply to be supplied from the power supply of the main body can be reduced upon execution of the staple operation. An increase in cost of the image forming apparatus itself can be minimized, and an inexpensive image forming apparatus can be provided to users who do not require any sheet processing apparatus. 
   Second Embodiment 
   The second embodiment according to the present invention will be described below. The second embodiment is directed to the system including the image forming apparatus and sheet processing apparatus as in the first embodiment. In the following description, a description of the same part as in the first embodiment will be omitted, and a characteristic part of this embodiment will be mainly explained. 
   In the first embodiment, when the set number of transfer sheets to be stapled changes, the operation remains the same. However, this embodiment is characterized in that whether or not the staple operation is feasible is checked in accordance with the set number of transfer sheets to be stapled and the charge voltage. 
   The process executed upon performing the staple operation using electric power supplied from the power storage means in this embodiment will be described below with reference to  FIG. 7 . 
   When N transfer sheets, which are set in advance, are stacked on a stack tray  318 , the sheet processing apparatus  302  starts the staple operation on the basis of the following flow. The sheet processing apparatus control circuit  409  monitors the charge voltage Vc of the power storage means (step S 601 ), and confirms if the charge voltage falls within a predetermined range (Vc 1 &gt;Vc&gt;Vc 2 ) between a maximum charge voltage Vc 1  and charge operation start voltage Vc 2  shown in  FIG. 2  (step S 602 ). If the charge circuit  406  is configured to set Vc to be lower than Vc, only Vc&gt;Vc 2  may be confirmed, as shown in  FIG. 7 . 
   If it is confirmed that Vc falls within the predetermined range, the sheet processing apparatus control circuit  409  turns on the switch  413  in synchronism with the timing of the image forming operation to supply the voltage Vs to the staple drive unit  410  (step S 603 ) and to drive the staple unit  312  via the staple drive unit  410 , thus stapling a transfer sheet set  112   a  (step S 604 ). 
   In this embodiment, since the staple operation is executed by energy (electric power) stored in the power storage means  405 , a maximum current (consumption current of the sheet processing apparatus) supplied from the power supply circuit  401  of the image forming apparatus to the sheet processing apparatus  302  in the staple operation can be reduced to be lower than the conventional value (Is 3  in  FIG. 15 ; about 5 A). For this reason, the consumption current of the sheet processing apparatus of this embodiment assumes a value as the sum of a current Is 1  required for normal operations, and a current required to charge, and can be roughly reduced to a current value Is 2  indicated by the broken line in  FIG. 15 . This means that the maximum current (maximum consumption current) that flows in the sheet processing apparatus is reduced, and the maximum consumption current of the system including the sheet processing apparatus and image forming apparatus is also reduced. 
   Upon completion of the staple operation, the switch  413  is turned off (step S 605 ), and it is checked if a job is complete (step S 606 ). If the job is not complete yet, the power storage means  405  is charged to prepare for the next staple operation (step S 607 ); otherwise, the process ends. 
   If it is determined in step S 606  that the job is not complete yet, and if the charge voltage Vc falls within the predetermined range (Vc 1 &gt;Vc&gt;Vc 2 ), the power storage means need not always be charged, and the switch  413  need not always be turned off in step S 605 . That is, if the charge voltage Vc becomes lower than the charge operation start voltage Vc 2 , the switch  413  can be turned off to start charge. 
   On the other hand, if the charge voltage Vc is lower than the charge operation start voltage Vc 2  in step S 602 , the voltage Vs required for the operation is unlikely to be supplied to the staple drive unit  410 , i.e., the staple operation is unlikely to be executed depending on the conditions, e.g., the print speed, the number of sheets to be stapled, and the like. In such case, it is checked if the charge voltage Vc exceeds a voltage Vc 3  (step S 608 ). 
   Note that the voltage Vc 3  assumes a value which is determined in advance in correspondence with the number N of sheets per set of the transfer sheet set  112   a . For example, when the number of sheets per set of the transfer sheet set  112   a  is Na, the voltage Vc 3  is determined so that the time required to stack Na transfer sheets, and the time required until the voltage starting to be charged from the Vc 3  reaches the charge start voltage Vc 2  or more become equal, as shown in  FIG. 2 . More specifically, if Vc&gt;Vc 3  and N&gt;Na, the voltage of the power storage means is charged to a value that exceeds Vc 2  between the two staple operations. 
   Hence, if Vc&gt;Vc 3 , it is checked if N&gt;Na (step S 609 ). If N&gt;Na, the flow advances to step S 603  to execute the subsequent processes in the same manner as described above. 
   On the other hand, if it is determined in step S 609  that N≦Na, this means that the voltage of the power storage means cannot be charged to a value that exceeds Vc 2  during the staple operation. Hence, since the staple operation is unlikely to be executed, the image forming operation is paused (step S 610 ) to reduce consumption power of the voltage Va(≈Vs+Vf) internally consumed by the image forming apparatus. Since this reduction of consumption power can produce a margin in supply performance at the output voltage Va of the power supply  401  of the image forming apparatus, the switch  413  is turned off (step S 611 ) to supply electric power required for the staple operation from the power supply  401  of the image forming apparatus to the staple drive unit  410  via the diode  403 , thus executing the staple operation (step S 612 ). 
   If it is determined in step S 608  that Vc≦Vc 3 , the flow jumps to step S 610  to pause the image forming operation, and to supply electric power required for the staple operation from the power supply  401  of the image forming apparatus to the staple drive unit  410  via the diode  403 , thus executing the staple operation. 
   As described above, according to this embodiment, in addition to the same effect as in the first embodiment, even when the charge voltage of the power storage means is insufficient, if the number of sheets to be stapled is less than a predetermined value, the staple operation by the sheet processing apparatus can be executed without pausing the image forming operation, thereby improving the system operating rate. 
   Third Embodiment 
   The third embodiment according to the present invention will be described below. The third embodiment is directed to the system including the image forming apparatus and sheet processing apparatus as in the first and second embodiments. In the following description, a description of the same part as in the first and second embodiments will be omitted, and a characteristic part of this embodiment will be mainly explained. 
   In this embodiment, whether or not the staple operation is feasible is checked in correspondence with the set number of transfer sheets to be stapled, and the charge voltage as in the second embodiment. However, this embodiment is characterized in that when the set number of transfer sheets to be stapled is small, and the time required to stack set sheets is shorter than the time required until the voltage of the power storage means reaches a predetermined voltage, the operation is slowed down without pausing the image forming operation. 
   The process executed upon performing the staple operation using electric power supplied from the power storage means in this embodiment will be described below with reference to  FIG. 8 . 
   When N transfer sheets, which are set in advance, are stacked on a stack tray  318 , the sheet processing apparatus  302  starts the staple operation on the basis of the following flow. The sheet processing apparatus control circuit  409  monitors the charge voltage Vc of the power storage means (step S 651 ), and confirms if the charge voltage falls within a predetermined range (Vc 1 &gt;Vc&gt;Vc 2 ) between a maximum charge voltage Vc 1  and charge operation start voltage Vc 2  shown in  FIG. 2  (step S 652 ). If the charge circuit  406  is configured to set Vc to be lower than Vc, only Vc&gt;Vc 2  may be confirmed, as shown in  FIG. 8 . 
   If it is confirmed that Vc falls within the predetermined range, the sheet processing apparatus control circuit  409  turns on the switch  413  in synchronism with the timing of the image forming operation to supply the voltage Vs to the staple drive unit  410  (step S 653 ) and to drive the staple unit  312  via the staple drive unit  410 , thus stapling a transfer sheet set  112   a  (step S 654 ). 
   In this embodiment, since the staple operation is executed by energy (electric power) stored in the power storage means  405 , a maximum current (consumption current of the sheet processing apparatus) supplied from the power supply circuit  401  of the image forming apparatus to the sheet processing apparatus  302  in the staple operation can be reduced to be lower than the conventional value (Is 3  in  FIG. 15 ; about 5 A). For this reason, the consumption current of the sheet processing apparatus of this embodiment assumes a value as the sum of a current Is 1  required for normal operations, and a current required to charge, and can be roughly reduced to a current value Is 2  indicated by the broken line in  FIG. 15 . This means that the maximum current (maximum consumption current) that flows in the sheet processing apparatus is reduced, and the maximum consumption current of the system including the sheet processing apparatus and image forming apparatus is also reduced. 
   Upon completion of the staple operation, the switch  413  is turned off (step S 655 ), and it is checked if a job is complete (step S 656 ). If the job is not complete yet, the power storage means  405  is charged to prepare for the next staple operation (step S 657 ); otherwise, the process ends. 
   If it is determined in step S 656  that the job is not complete yet, and if the charge voltage Vc falls within the predetermined range (Vc 1 &gt;Vc&gt;Vc 2 ), the power storage means need not always be charged, and the switch  413  need not always be turned off in step S 655 . That is, if the charge voltage Vc becomes lower than the charge operation start voltage Vc 2 , the switch  413  can be turned off to start charge. 
   On the other hand, if the charge voltage Vc is lower than the charge operation start voltage Vc 2  in step S 652 , the voltage Vs required for the operation is unlikely to be supplied to the staple drive unit  410 , i.e., the staple operation is unlikely to be executed depending on the conditions, e.g., the print speed, the number of sheets to be stapled, and the like. In such case, it is checked if the charge voltage Vc exceeds a voltage Vc 3  (step S 658 ). 
   Note that the voltage Vc 3  assumes a value which is determined in advance in correspondence with the number N of sheets per set of the transfer sheet set  112   a . For example, when the number of sheets per set of the transfer sheet set  112   a  is Na, the voltage Vc 3  is determined so that the time required to stack Na transfer sheets, and the time required until the voltage starting to be charged from the Vc 3  reaches the charge start voltage Vc 2  or more become equal, as shown in  FIG. 2 . More specifically, if Vc&gt;Vc 3  and N&gt;Na, the voltage of the power storage means is charged to a value that exceeds Vc 2  between the two staple operations. 
   Hence, if Vc&gt;Vc 3 , it is checked if N&gt;Na (step S 659 ). If N&gt;Na, the flow advances to step S 653  to execute the subsequent processes in the same manner as described above. 
   On the other hand, if it is determined in step S 659  that N≦Na, this means that the voltage of the power storage means cannot be charged to a value that exceeds Vc 2  during the staple operation. Hence, the image forming apparatus control circuit  402  controls to delay the image forming operation interval (step S 660 ) so as to broaden the time interval of transfer sheets  112  to be stacked on the stack tray  318 , thereby setting the time required to stack N transfer sheets, which are set in advance, to be longer than the time required until the power storage means is charged with a voltage that exceeds the charge start voltage Vc 2 . That is, the operation interval of the image forming operation is set so that the voltage is charged to a value that exceeds Vc 2  during the staple operation. After that, the flow advances to step S 653  to execute the staple operation in the same manner as described above. 
   If it is determined in step S 658  that Vc≦Vc 3 , the image forming operation is paused (step S 661 ), and the power storage means  405  is charged (step S 657 ). 
   As described above, according to this embodiment, in addition to the same effect as in the first embodiment, even when the charge voltage of the power storage means is insufficient, if the charge voltage of the power storage means is equal to or higher than a predetermined value, the staple operation by the sheet processing apparatus can be executed without pausing the image forming operation, thereby improving the system operating rate. 
   Fourth Embodiment 
   The fourth embodiment according to the present invention will be described below. The fourth embodiment is directed to the system including the image forming apparatus and sheet processing apparatus as in the first to third embodiments. In the following description, a description of the same part as in the first to third embodiments will be omitted, and a characteristic part of this embodiment will be mainly explained. 
   In the first to third embodiments, only the image forming apparatus comprises the power supply circuit, but the sheet processing apparatus does not comprise any power supply circuit. However, this embodiment is characterized in that both the image forming apparatus and sheet processing apparatus respectively have power supply circuits. 
   This embodiment will be explained below with reference the block diagram that shows the electrical arrangement of the image forming apparatus and sheet processing apparatus of this embodiment. 
   A power supply circuit  401  arranged in an image forming apparatus  301  supplies a predetermined voltage to an image forming apparatus control circuit  402  that controls image formation. The image forming apparatus control circuit  402  communicates, via a connector, with a sheet processing apparatus control circuit  409 , which is arranged in the sheet processing apparatus  302 , and controls the convey and staple operations of transfer sheets in the sheet processing apparatus, thus making timing control so that the convey and staple operations of transfer sheets  112  conveyed from the image forming apparatus  301  can be made smoothly. 
   On the other hand, a power supply circuit  415  is arranged in the sheet processing apparatus, and supplies electric power required for the convey and staple operations of transfer sheets in the sheet processing apparatus. Reference numeral  406  denotes a charge circuit, which receives a predetermined voltage Va supplied from the power supply circuit  415 , supplies a predetermined voltage Vb(Va&lt;Vb) to a power storage means  405  including a plurality of electric double layer capacitors in accordance with a charge command from the sheet processing apparatus control circuit  409 , and changes until the output voltage of the power storage means reaches a predetermined voltage Vc(≈Vb). The electric double layer capacitor has received a lot of attention in many fields in recent years, since it has a capacitance as large as several F or more, higher charge efficiency than a secondary battery, and a long life. 
   A power storage means voltage detection circuit  407  detects the charge voltage of the power storage means  405 , and transmits the detection result to an A/D port of a CPU (not shown) in the sheet processing apparatus control circuit  409  as, e.g., an analog signal. According to this voltage detection result of the power storage means, the sheet processing apparatus control circuit  409  supplies a charge instruction to the charge circuit  406 . A constant voltage control circuit  408  controls the charge voltage Vc of the power storage means  405  to be equal to or higher than a voltage Vs(Vs≈Va−Vf, Vs&lt;Vc, Vf=forward voltage of a diode  403 : about 0.6 V), and supplies the voltage Vs to a staple drive unit  410  via a switch  413 , thereby driving a staple unit  312 . 
   As the switch  413 , a semiconductor switch such as a FET or the like is preferably used in terms of durability of ON/OFF operations. However, a mechanical switch such as a relay or the like may be used if it does not pose any problem in a service life such as ON/OFF counts and the like. The diode  403  is provided to prevent the output from the power supply circuit  415  from being supplied to the staple drive circuit  410  while the voltage Vs is supplied from the power storage means  405  via the constant voltage control circuit  408 . 
   The sheet processing apparatus executes the staple operation on the basis of the flow shown in  FIG. 3 , that has been explained in association with the first embodiment. That is, electric power stored in the power storage means is supplied to the staple unit to execute the staple operation, thereby reducing peak electric power to be supplied from the power supply circuit  415  in the sheet processing apparatus upon execution of the staple operation. 
   Since the maximum output power of the power supply circuit  415  of the sheet processing apparatus is nearly proportional to electric power supplied from the commercial power supply via an AC plug connected to the power supply circuit  415 , the maximum consumption power of the sheet processing apparatus can be reduced. As a result, the maximum consumption power of the system including the image forming apparatus and sheet processing apparatus can be reduced. 
   As described above, according to this embodiment, since the maximum consumption power of the sheet processing apparatus can be reduced, no problem is posed even when the AC plugs of the image forming apparatus main body and sheet processing apparatus are connected to the same commercial power supply system. Hence, no expert such as a service person or the like who has special knowledge is required, and system installation is facilitated. In addition, when electric power that can be supplied from the commercial power supply has a margin for the maximum consumption power of the system by reducing the maximum consumption power of the sheet processing apparatus, electric power to be supplied to the image forming apparatus can be further increased to be effectively utilized in improvement of specifications, thus allowing design changes. 
   Other Embodiments 
   In the first to fourth embodiments, the electric double layer capacitors are used as an example of the power storage means. Alternatively, a plurality of electrolytic capacitors such as large-capacity aluminum electrolytic capacitors or a secondary battery such as a nickel-metal-hydride battery, lithium battery, and the like may be used as the power storage means by limiting the use conditions or in consideration of a sequence and the like. However, when the secondary battery is used as the power storage means, since the secondary battery normally suffers a short life time (e.g., a charge/discharge count or the like), it must be arranged as an exchangeable part which can be detached from the sheet processing apparatus. 
   In the above embodiments, the apparatus that applies the staple process as a post-process to printed sheets (that have undergone image formation) has been exemplified as the sheet processing apparatus. However, the present invention can be applied to sheet processing apparatuses that apply other post-processes. As other post-processes, for example, a trimming process, booklet process, and the like of sheets may be used. In this case, if execution of such post-process instantaneously requires large electric power, the same effects as those in the above embodiments can be obtained. 
   The present invention may be applied to a system including a plurality of apparatuses (image forming apparatus and sheet processing apparatus), or an apparatus consisting of a single device such as a sheet processing apparatus, an apparatus that integrates an image forming apparatus and sheet processing apparatus, an image processing apparatus having a function of a sheet processing apparatus, and the like. 
   Furthermore, the invention can be implemented by supplying a software program, which implements the functions of the foregoing embodiments, directly or indirectly to a system or apparatus, reading the supplied program code with a computer of the system or apparatus, and then executing the program code. In this case, so long as the system or apparatus has the functions of the program, the mode of implementation need not rely upon a program. 
   Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the claims of the present invention also cover a computer program for the purpose of implementing the functions of the present invention. 
   In this case, so long as the system or apparatus has the functions of the program, the program may be executed in any form, such as an object code, a program executed by an interpreter, or scrip data supplied to an operating system. 
   Example of storage media that can be used for supplying the program are a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a magnetic tape, a non-volatile type memory card, a ROM, and a DVD (DVD-ROM and a DVD-R). 
   As for the method of supplying the program, a client computer can be connected to a website on the Internet using a browser of the client computer, and the computer program of the present invention or an automatically-installable compressed file of the program can be downloaded to a recording medium such as a hard disk. Further, the program of the present invention can be supplied by dividing the program code constituting the program into a plurality of files and downloading the files from different websites. In other words, a WWW (World Wide Web) server that downloads, to multiple users, the program files that implement the functions of the present invention by computer is also covered by the claims of the present invention. 
   It is also possible to encrypt and store the program of the present invention on a storage medium such as a CD-ROM, distribute the storage medium to users, allow users who meet certain requirements to download decryption key information from a website via the Internet, and allow these users to decrypt the encrypted program by using the key information, whereby the program is installed in the user computer. 
   Besides the cases where the aforementioned functions according to the embodiments are implemented by executing the read program by computer, an operating system or the like running on the computer may perform all or a part of the actual processing so that the functions of the foregoing embodiments can be implemented by this processing. 
   Furthermore, after the program read from the storage medium is written to a function expansion board inserted into the computer or to a memory provided in a function expansion unit connected to the computer, a CPU or the like mounted on the function expansion board or function expansion unit performs all or a part of the actual processing so that the functions of the foregoing embodiments can be implemented by this processing. 
   If the present invention is realized as a storage medium, program codes corresponding to at least one of the above mentioned flowcharts ( FIGS. 3 ,  7  and  8 ) is to be stored in the storage medium. 
   As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the claims. 
   CLAIM OF PRIORITY 
   This application claims priority from Japanese Patent Application No. 2004-031403 filed on Feb. 6, 2004, which is hereby incorporated by reference herein.