Patent Publication Number: US-8111420-B2

Title: Printer control apparatus and method of controlling the same, printer and method of controlling the same, reader and method of controlling the same, and image forming system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation application of and claims priority from U.S. patent application Ser. No. 11/748,449, filed May 14, 2007, which is a divisional application of U.S. patent application Ser. No. 10/254,453 filed Sep. 25, 2002, now U.S. Pat. No. 7,233,410 which claims priority from Japanese Patent Application 2001-301047 filed Sep. 28, 2001 the content of each of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printer control apparatus having a controller for use in exchanging data between a reader and a printer thereof, and a method of controlling the same, a printer and a method of controlling the same, a reader and a method of controlling the same, and an image forming system. 
     2. Description of the Related Art 
     Conventionally, an image forming apparatus has been proposed, which is comprised of a reader section that reads an image, a printer that prints image data, and an image controller that performs image processing, stores images, and controls image data. The reader, the printer, and the image controller are configured as an integral unit. 
     Many of image forming apparatuses of this kind are digital copying machines that are comprised of a reader and a printer which perform processing at the same processing speed. In the case where the processing speeds of the reader and the printer are equal, the timing for starting scanning an original by the reader and the timing for starting printing by the printer are uniquely defined such that the printer starts printing data on the sheet and the reader starts scanning the original at the same time, when a sheet is fed to a print-enabling position. 
     In recent years, however, digital copying machines have been developed which are additionally provided with multiple functions such as a facsimile function and a PDL printing function. Some of such digital copying machines have a page memory that temporarily stores image data on a page-by-page basis, and some of such digital copying machines are called image servers and are capable of storing image data compressed in advance. Further, multifunction digital copying machines with increased productivity have been developed, and they have realized a considerable increase in the processing speed at which a reader scans an original and the processing speed at which a printer carries out printing operation. 
     Under the circumstances, digital copying machines have been proposed which enable efficient printing by absorbing a speed difference in the case where there is a difference in processing speed between a reader and a printer thereof. 
     Specifically, the data transfer speed of photoelectric conversion means such as a CCD which converts an optical image into electric image data after scanning of an original by the reader is usually higher than the data transfer speed of exposure means such as a laser which forms an image as an electrophotograph by the printer. Since thus there is a difference in the processing speed between the reader and the printer, the digital copying machines are configured to temporarily store image data from the reader in the above-mentioned page memory and then transmit the image data from the page memory to the printer in timing calculated according to a predetermined equation to absorb the difference in the processing speed. 
     With this arrangement, image data can be efficiently printed in such timing that transmission of image data to the printer never outpaces writing of an image by the reader. 
     With the trend of multi-functioning, however, digital copying machines have been developed which are comprised of a reader that reads an original and converts the read image into image data, a printer that receives the image data and prints the same on a sheet or the like, and a controller that executes an image data processing function, image data storage function, PDL function, network function, and others. These component parts are configured in separate bodies, and the controller controls respective engines of the reader and the printer via an interface common to them. With this arrangement, a plurality of readers that perform processing at different processing speeds and a plurality of printers that perform processing at different processing speeds can be connected to one controller. 
     In order to efficiently transfer image data from the reader to the printer via the page memory of the controller in the above described image forming apparatus, there is the necessity of acquiring respective processing speeds of a plurality of readers and a plurality of printers and calculating the timing for transmitting image data to the printers according to configurations of the readers and the printers. This requirement, however, cannot be satisfied according to the prior art. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a printer control apparatus and a method of controlling the same, a printer and a method of controlling the same, a reader and a method of controlling the same, and an image forming system, which can be applied to an image forming apparatus in which a plurality of types of readers and a plurality of types of printers can be connected to a single controller, and which enable efficient transfer of image data from the reader to the printer via an image memory of the controller. 
     To attain the above object, in a first aspect of the present invention, there is provided a printer control apparatus that receives image data from a reader, stores the image data in a memory, and transmits the stored image data from the memory to a printer, comprising first acquiring means for acquiring reader information related to the reader from the reader, second acquiring means for acquiring printer information related to the printer from the printer, and a controller that, while image data received from the reader is being written to the memory, determines timing for transmitting the image data written in the memory to the printer according to the reader information acquired by the first acquiring means and the printer information acquired by the second acquiring means. 
     Preferably, in the printer control apparatus according to the first aspect, the controller determines the timing according to the reader information acquired by the first acquiring means, the printer information acquired by the second acquiring means, and a sub-scan size of the image data. 
     To attain the above object, in a second aspect of the present invention, there is provided a printer control apparatus that receives image data from a reader, stores the image data in a memory, and transmits the stored image data from the memory to a printer, comprising first acquiring means for acquiring a reader processing speed, at which the reader reads image data in a sub-scanning direction, from the reader, second acquiring means for acquiring a printer processing speed, at which the printer prints image data in the sub-scanning direction, from the printer, and a controller that, while image data of a predetermined size received from the reader is being written to the memory, determines timing for transmitting the image data written in the memory to the printer according to the reader processing speed acquired by the first acquiring means, the printer processing speed acquired by the second acquiring means, and a sub-scan size of the image data. 
     Preferably, in the printer control apparatus according to the second aspect, the controller determines the timing according to a difference between the reader processing speed acquired by the first acquiring means and the printer processing speed acquired by the second acquiring means, and the sub-scan size of the image data. 
     To attain the above object, in a third aspect of the present invention, there is provided a printer control apparatus that receives image data from a reader, stores the image data in a memory, and transmits the stored image data from the memory to a printer, comprising first acquiring means for acquiring a reader ID representing a type of the reader from the reader, second acquiring means for acquiring a printer ID representing a type of the printer from the printer, a reader processing speed table showing a relationship between a reader processing speed, at which the reader reads image data in a sub-scanning direction, and the reader ID, a printer processing speed table showing a relationship between a printer processing speed, at which the printer prints image data in the sub-scanning direction, and the printer ID, and a controller that, while image data of a predetermined size received from the reader is being written to the memory, determines timing for transmitting the image data written in the memory to the printer according to the reader processing speed acquired by referring to the reader processing speed table with the reader ID, the printer processing speed acquired by referring to the printer processing speed table with the printer ID, and a sub-scanning size of the image data. 
     Preferably, in the printer control apparatus according to the third aspect, the controller determines the timing according to a difference between the reader processing speed acquired from the reader processing speed table and the printer processing speed acquired from the printer processing speed table, and the sub-scan size of the image data. 
     To attain the above object, in a fourth aspect of the present invention, there is provided a printer control apparatus that receives image data from a reader, stores the image data in a memory, and transmits the stored image data from the memory to a printer, comprising first acquiring means for acquiring a number of copies read by the reader per unit time from the reader, second acquiring means for acquiring a number of copies printed by the printer per unit time from the printer, a reader processing speed table showing a relationship between a reader processing speed, at which the reader reads image data in a sub-scanning direction, and the number of copies read by the reader per unit time, a printer processing speed table showing a relationship between a printer processing speed, at which the printer prints image data in the sub-scanning direction, and the number of copies printed by the printer per unit time, and a controller that, while image data of a predetermined size received from the reader is being written to the memory, determines timing for transmitting the image data written in the memory to the printer according to the reader processing speed acquired by referring to the reader processing speed table with the number of copies read by the reader per unit time, the printer processing speed acquired by referring to the printer processing speed table with the number of copies read by the printer per unit time, and a sub-scanning size of the image data. 
     Preferably, in the printer control apparatus according to the fourth aspect, the controller determines the timing according to a difference between the reader processing speed and the printer processing speed, and the sub-scan size of the image data. 
     To attain the above object, in a fifth aspect of the present invention, there is provided a printer control apparatus that receives image data from a reader, stores the image data in a memory, and transmits the stored image data from the memory to a printer, comprising first acquiring means for acquiring a reader ID representing a type of the printer from the reader, second acquiring means for acquiring a printer ID representing a type of the printer from the printer, a timing table showing an image data readout timing generation ratio corresponding to the reader ID and the printer ID, and a controller that, while image data of a predetermined size received from the reader is being written to the memory, determines timing for transmitting the image data written in the memory to the printer according to the image data readout timing generation ratio acquired by referring to the timing table with the reader ID and the printer ID, and a sub-scan size of the image data. 
     To attain the above object, in a sixth aspect of the present invention, there is provided a printer control apparatus that receives image data from a reader, stores the image data in a memory, and transmits the stored image data from the memory to a printer, comprising first acquiring means for acquiring a number of copies read by the reader per unit time from the reader, second acquiring means for acquiring a number of copies printed by the printer per unit time from the printer, a timing table showing an image data readout timing generation ratio corresponding to the number of copies read by the reader per unit time and the number of copies printed by the printer per unit time, and a controller that, while image data of a predetermined size received from the reader is being written to the memory, determines timing for transmitting the image data written in the memory to the printer according to the image data readout timing generation ratio acquired by referring to the timing table with the number of copies read by the reader per unit time and the number of copies printed by the printer per unit time, and a sub-scanning size of the image data. 
     To attain the above object, in a seventh aspect of the present invention, there is provided a printer that receives image data from a reader that reads an original, and prints the image data on a sheet, comprising a memory that stores the image data received from the reader, receiving means for receiving reader information related to the reader from the reader, and a controller that, while image data received from the reader is being written to the memory, determines timing for reading out the image data written in the memory according to the reader information received by the receiving means and printer information related to the printer. 
     Preferably, in the printer according to the seventh aspect, the controller determines the timing according to the reader information received by the receiving means, the printer information, and a sub-scan size of the image data. 
     To attain the above object, in an eighth aspect of the present invention, there is provided a reader that reads image data on an original and transmits the read image data to a printer, comprising a memory that stores the read image data, receiving means for receiving printer information related to the printer from the printer, and a controller that, while the read image data is being written to the memory, determines timing for reading out the image data written in the memory according to the printer information received by the receiving means and reader information related to the reader. 
     Preferably, in the reader according to the eighth aspect, the controller determines the timing according to the printer information received by the receiving means, the reader information, and a sub-scan size of the image data. 
     To attain the above object, in a ninth aspect of the present invention, there is provided a method of controlling a printer control apparatus that receives image data from a reader that reads an original, stores the image data in a memory, and transmits the stored image data from the memory to a printer, the method comprising the steps of receiving reader information related to the reader from the reader and printer information related to the printer from the printer, determining, while image data received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the reader information received from the reader and the printer information received from the printer, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in a tenth aspect of the present invention, there is provided a method of controlling a printer control apparatus that receives image data from a reader that reads an original, stores the image data in a memory, and transmits the stored image data from the memory to a printer, the method comprising the steps of receiving a reader processing speed, at which the reader reads image data in a sub-scanning direction, from the reader, and a printer processing speed, at which the printer prints image data in the sub-scanning direction, from the printer, determining, while image data of a predetermined size received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the reader processing speed received from the reader and the printer processing speed received from the printer, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in an eleventh aspect of the present invention, there is provided a method of controlling a printer control apparatus that receives image data from a reader that reads an original, stores the image data in a memory, and transmits the stored image data from the memory to the printer, the method comprising the steps of receiving a reader ID representing a type of the reader from the reader and a printer ID representing a type of the printer from the printer, determining a reader processing speed, at which the reader reads image data in a sub-scanning direction, according to the reader ID received from the reader, and determining a printer processing speed, at which the printer prints image data in the sub-scanning direction according to the printer ID received from the printer, determining, while image data of a predetermined size received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the reader processing speed corresponding to the reader ID, the printer processing speed corresponding to the printer ID, and a sub-scanning size of the image data, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in a twelfth aspect of the present invention, there is provided a method of controlling a printer control apparatus that receives image data from a reader that reads an original, stores the image data in a memory, and transmits the stored image data from the memory to a printer, the method comprising the steps of receiving a number of copies read by the reader per unit time from the reader and a number of copies printed by the printer per unit time from the printer, determining a reader processing speed, at which the reader reads image data in a sub-scanning direction, according to the number of copies read by the reader per unit time, and determining a printer processing speed, at which the printer prints image data in the sub-scanning direction according to the number of copies printed by the printer per unit time, determining, while image data of a predetermined size received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the reader processing speed corresponding to the number of copies read by the reader per unit time, the printer processing speed corresponding to the number of copies printed by the printer per unit time, and a sub-scanning size of the image data, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in a thirteenth aspect of the present invention, there is provided a method of controlling a printer control apparatus that receives image data from a reader that reads an original, stores the image data in a memory, and transmits the stored image data from the memory to a printer, the method comprising the steps of receiving a reader ID representing a type of the printer from the reader and a printer ID representing a type of the printer from the printer, determining an image data readout timing generation ratio corresponding to the reader ID received from the reader and the printer ID received from the printer, determining, while image data of a predetermined size received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the image data readout timing generation ratio corresponding to the reader ID and the printer ID, and a sub-scanning size of the image data, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in a fourteenth aspect of the present invention, there is provided a method of controlling a printer control apparatus that receives image data from a reader that reads an original, stores the image data in a memory, and transmits the stored image data from the memory to a printer, the method comprising the steps of receiving a number of copies read by the reader per unit time from the reader and a number of copies printed by the printer per unit time from the printer, determining an image data readout timing generation ratio corresponding to the number of copies read by the reader per unit time, received from the reader, and the number of copies printed by the printer per unit time, received from the printer, determining, while image data of a predetermined size received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the image data readout timing generation ratio corresponding to the number of copies read by the reader per unit time and the number of copies printed by the printer per unit time, and a sub-scanning size of the image data, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in a fifteenth aspect of the present invention, there is provided a method of controlling a printer that receives image data from a reader that reads an original, stores the received image data in a memory, and prints the image data on a sheet, the method comprising the steps of receiving reader information related to the reader from the reader, receiving printer information related to the printer from the printer, determining, while image data of a predetermined size received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the reader information received from the reader and the printer information received from the printer, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in a sixteenth aspect of the present invention, there is provided a method of controlling a reader that reads and stores image data in a memory, and transmits the stored image data to a printer, the method comprising the steps of receiving a reader information related to the reader from the reader, receiving printer information related to the printer from the printer, determining, while image data received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the reader information received from the reader and the printer information received from the printer, causing the reader to start reading the original, and transmitting the written image data from the memory to the printer in the determined timing. 
     To attain the above object, in a seventeenth aspect of the present invention, there is provided an image forming system comprising a reader that reads an original as image data, a printer that forms image data as an image on a sheet, a controller that receives the image data from the reader, stores the received image data in a memory, and transmits the stored image data from the memory to the printer first notifying means for supplying the controller with reader information related to the reader, and second notifying means for supplying the controller with printer information related to the printer, the controller determines, while image data received from the reader is being written to the memory, timing for transmitting the image data written in the memory to the printer according to the reader information supplied by the first notifying means and the printer information supplied by the second notifying means. 
     The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing the construction of an image forming apparatus to which is applied a printer control apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a schematic block diagram showing the arrangement of various controllers of the image forming apparatus of  FIG. 1 ; 
         FIG. 3  is a block diagram showing the construction of an image controller section  203  in  FIG. 2 ; 
         FIG. 4A  is a view showing a reader processing speed table; 
         FIG. 4B  is a view showing a printer processing speed table; 
         FIG. 4C  shows equations; 
         FIG. 5A  is a timing chart showing clocks; 
         FIG. 5B  is a timing chart showing horizontal synchronization signals; 
         FIG. 6  is a conceptual diagram showing an image forming method; 
         FIG. 7  is a conceptual diagram showing timing for writing (inputting) and reading out (outputting) an image into and from an image memory; 
         FIG. 8  is a conceptual diagram showing a state in which the image data is written into and read out from the image memory at the same time; 
         FIG. 9  is a conceptual diagram showing a state immediately after writing and reading of the image data have been completed; 
         FIG. 10  is a flow chart showing an ID acquiring process in initialization; 
         FIG. 11  is a flow chart showing the procedure for controlling the image memory during copying; 
         FIG. 12A  is a view showing a reader processing speed table used in a second embodiment of the present invention; 
         FIG. 12B  is a view showing a printer processing speed table used in the second embodiment; 
         FIG. 12C  shows equations used in the second embodiment; 
         FIG. 13  is a flow chart showing a number information acquiring process according to the second embodiment; 
         FIG. 14  is a flow chart showing the procedure for controlling an image memory during copying according to the second embodiment; 
         FIG. 15A  is a view showing a timing table used in a fourth embodiment of the present invention; 
         FIG. 15B  shows equations used in the fourth embodiment; 
         FIG. 16  is a flow chart showing the procedure for controlling an image memory during copying according to the fourth embodiment; 
         FIG. 17A  is a view showing a timing table used in a fifth embodiment of the present invention; 
         FIG. 17B  shows equations used in the fifth embodiment; 
         FIG. 18  is a flow chart showing the procedure for controlling an image memory during copying according to the fifth embodiment; 
         FIG. 19A  is a schematic view showing the arrangement of an image forming apparatus including a reader according to a sixth embodiment of the present invention; and 
         FIG. 19B  is a schematic view showing the arrangement of an image forming apparatus including a printer according to a seventh embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described below with reference to the accompanying drawings showing preferred embodiments thereof. 
     First Embodiment 
       FIG. 1  is a sectional view showing the construction of an image forming apparatus to which is applied a printer control apparatus according to a first embodiment of the present invention. 
     The image forming apparatus is comprised of a reader  102 , a printer  100 , an original feeder or document feeder (DF)  180 , and a post-processing device  190 . The post-processing device  190  is comprised of a sheet discharging device  191 , a Z-folding machine  192 , and a binding machine  197 . It should be noted that the image forming apparatus may be a system that is comprised of a reader and a printer, which are configured in separate bodies and are connected to each other via a cable. 
     Reference numeral  101  denotes a platen glass that is comprised of an original radiation lamp  103 , a scanning mirror  104 , and the like. A motor, not shown, causes a scanner, not shown, to scan an original while moving back and forth in a predetermined direction. Light reflected on the original is transmitted through a lens  107  via scanning mirrors  104  to  106 , and is formed on a CCD sensor in an image sensor section  108 . The image sensor section  108  converts the reflected light into an electric signal. 
     Reference numeral  119  denotes a laser section, which irradiates laser light, which has been modulated based on an image signal obtained by performing predetermined image processing on the electric signal converted by the image sensor section  108 , as described later, upon a photosensitive drum  111 . 
     A primary electrifier  112 , a developer  113 , a transfer electrifier  116 , a pre-exposure lamp  114 , and a cleaning device  115  are disposed around the photosensitive drum  111 . 
     In an image forming section  110 , a motor, not shown, causes the photosensitive drum  111  to rotate in a direction indicated by an arrow in  FIG. 1 . After the photosensitive drum  111  is electrified by the primary electrifier  112  to a desired potential, the laser light from the laser section  119  is irradiated on the photosensitive drum  111  to form an electrostatic latent image thereon. The electrostatic latent image formed on the photosensitive drum  111  is developed by the developer  113  so that it can be made visible as a toner image. 
     On the other hand, a transfer sheet fed from a right cassette deck  121 , a left cassette deck  122 , an upper cassette deck  123  or a lower cassette deck  124  by the corresponding pickup roller  125 ,  126 ,  127 , or  128  is conveyed to the main body of a printer  100  by the corresponding sheet feeding roller  129 ,  130 ,  131 , or  132 . The transfer sheet is then fed to a transfer belt  134  by a resist roller  133 , and the toner image made visible is transferred on the transfer sheet by the transfer electrifier  116 . 
     After the transfer, the cleaning device  115  removes residual toner from the photosensitive drum  111 , and the pre-exposure lamp  114  erases residual electric charge. The transfer sheet on which has been transferred the toner image is separated from the photosensitive drum  111  by a separation electrifier  117 , and is conveyed to a fixing device  135  by the transfer belt  134 . The fixing device  135  fixes the toner image on the transfer sheet by pressurizing and heating, and the transfer sheet is then discharged from the printer  100  by a discharge roller  136 . 
     The printer  100  is equipped with a deck  150  that is capable of storing four thousand transfer sheets, for example. A lifter  151  of the deck  150  moves up according to the volume of transfer sheets so that the transfer sheet can be constantly in contact with a pickup roller  152 . Each transfer sheet is conveyed to the main body of the printer  100  by a sheet feed roller  153 . The printer  100  is also equipped with a multiple manual feed tray  154  that is capable of storing one hundred transfer sheets. 
     Further, in  FIG. 1 , reference numeral  137  denotes a sheet discharge flapper that switches the path between a transfer path  138  and a discharge path  143 . Reference numeral  140  denotes a lower transfer path that turns upside down the transfer sheet conveyed from the discharge roller  136  via an inversion path  139  to a sheet refeed path  141 . A transfer sheet fed from the left cassette deck  122  by the sheet feed roller  130  is also conveyed to the sheet refeed path  141 . Reference numeral  142  denotes a sheet refeed roller that refeeds the transfer sheet to the image forming section  110 . 
     Reference numeral  144  denotes a discharge roller that is disposed in the vicinity of the sheet discharge flapper  137  and discharges a transfer sheet, whose path has been switched to the discharge path  143  by the sheet discharge flapper  137 , from the apparatus (the printer  100 ). 
     To carry out double-sided recording (double-sided printing), the sheet discharge flapper  137  is moved upward, so that a transfer sheet, on which has been printed an image, is conveyed to the sheet refeed path  141  via the transfer path  138 , the inversion path  139 , and the lower transfer path  140 . On this occasion, an inversion roller  145  draws the transfer sheet into the inversion path  139  up to a such a position that the rear end of the transfer sheet completely moves out of the transfer path  138  and is caught by the inversion roller  145 . The inversion roller  145  is then reversed to feed the transfer sheet to the transfer path  140 . 
     To invert and discharge a transfer sheet from the main body of the printer  100 , the sheet discharge flapper  137  is moved up to draw the transfer sheet into the inversion path  139 , and the inversion roller  145  draws the transfer sheet into the inversion path  139  up to a such a position that the rear end of the transfer sheet remains on the transfer path  138 . The inversion roller  145  is then reversed to feed the transfer sheet turned upside down toward the discharge roller  144 . 
     The sheet discharging device  191  aligns and binds transfer sheets discharged from the printer  100 . The sheet discharging device  191  stacks transfer sheets discharged on a sheet-by-sheet basis on a processing tray  193 , and aligns the transfer sheets. If part of transfer sheets on which images have been formed has been discharged, the sheet discharging device  191  staples the transfer sheets in a bundle and discharges the bundle of the transfer sheets onto the processing tray  193  or a sheet discharge tray  194 . The sheet discharging tray  194  is controlled to move up and down by a motor, not shown, so that it can be moved to a discharging position before the start of image formation. 
     Reference numeral  196  denotes a sheet tray on which are stacked interleaved sheets to be inserted between transfer sheets discharged onto the processing tray  193 . The Z-folding machine  192  folds the discharged transfer sheets in Z-form. The binding machine  197  performs booking by folding one set of discharged transfer sheets in the middle and then stapling them. A bundle of the stapled transfer sheets is discharged onto a discharge tray  198 . 
       FIG. 2  is a schematic block diagram showing the arrangement of respective control sections for the original feeder, reader, image controller section, printer, and post-processing device in the image forming apparatus of  FIG. 1 . 
     Reference numeral  201  denotes an original feeder control section that controls the original feeder  180  in  FIG. 1 . Reference numeral  202  denotes a reader control section that controls component parts such as the original radiation lamp  103 , scanning mirror  104 , and image sensor section  108  of the reader  102  in  FIG. 1 . The original feeder control section  201  and the reader control section  202  exchange data via a cable  200  so that information on feeding and replacement of originals can be transmitted from the reader  102  and information on completion of placement of an original and the size of an original can be transmitted from the original feeder  180 . 
     Reference numeral  203  denotes an image controller section that captures image data photoelectrically converted by the image sensor section  108  of the reader  102  into the image controller section  203  via a reader image data bus  209  in synchronism with a clock that drives the CCD sensor, performs predetermined image processing on the captured image data, makes settings as to storage of the image data, and controls the entire image data. 
     The reader control section  202  and the image controller section  203  exchange control data via a cable  206  so that the reader control section  202  can notify the image control section  203  of a reader ID representing the type of the reader and the size of an original to be fed by the original feeder  180 , which has been detected by the original feeder control section  201 . The image controller section  203  in turn gives the reader  102  an instruction or command for scanning an original and an instruction or command for stopping feeding an original. 
     Reference numeral  204  denotes a printer control section that controls the printer  100  to provide control related to image formation, such as control of the image forming section  110 , control of the laser section  119  for exposing image data, and control for feeding sheets from the respective sheet feeding cassettes  121 ,  122 ,  123 ,  124 ,  150 ,  154 , and others and conveying the sheets to the post-processing device  190 . 
     The image controller section  203  and the printer control section  204  exchange control data via a cable  207  so that the printer control section  204  can notify the image controller section  203  information on of a printer ID representing the type of the printer and give the section  203  information on completion of feeding, completion of image formation, discharging, and the like. 
     The image controller section  203  also gives the printer control section  204  a sequence of instructions, such as a sheet feeding instruction for printing image data and an instruction for causing the image forming section  110  to start image formation, so as to form image data as an image on a sheet based on image data, and carries an instruction for causing the post-processing device  190  to carry out post-processing of sheets on which images have been formed by the post-processing device  190 . 
     On this occasion, the image controller section  203  transfers the image data from the image memory therein to the printer control section  204  via a printer clock synchronous image data bus  210  in synchronism with a clock that drives the laser section  119  of the printer  100 . 
     Reference numeral  205  denotes a post-processing device control section that receives an instruction given to the post-processing device  190  according to the post-processing instruction received from the image controller section  203 , the timing for forming an image onto a sheet by the printer control section  204 , and an instruction given to the post-processing device  190  according to the conveyance of a sheet described with reference to  FIG. 1  from the printer control section  204  to control the sheet discharging device  191 , Z-folding machine  192 , binding machine  197 , and the like. 
     The post-processing device control section  205  and the printer control section  204  exchange control data via a cable  208  so that the post-processing device control section  205  gives the printer control section  204  information on the configuration of the post-processing device  190  such as the sheet discharging device  191 , Z-folding machine  192 , and binding machine  197 , and information on the condition of the post-processing device  190 , e.g. whether the post-processing has been completed or not. On the other hand, the printer control section  204  gives the post-processing device control section  205  an instruction for providing control related to discharge of a sheet on which an image has been formed according to the post-processing instruction received from the image controller section  203  as mentioned above. 
       FIG. 3  is a block diagram showing the construction of the image controller section  203  in  FIG. 2 . In  FIG. 3 , reference numeral  302  denotes a job control section of the image controller section  203 . The job control section  302  analyzes copy mode settings inputted via an operating section, not shown, and controls execution of jobs such as a copy job in response to an instruction for executing a job such as an instruction for starting a copy job inputted via the operating section. In the case where the image controller  203  is provided with a PDL (Page Description Language) system, the job control section  302  is capable of controlling execution of a PDL job. 
     Reference numeral  301  denotes a reader control communication I/F as a sending and receiving section in the cable or communication line  206  between the image controller section  203  and the reader control section  202 . The reader control communication I/F  301  enables the job control section  302  to transmit control data for controlling the reader  102  and the original feeder  180  and acquire original size information and information as to whether there is any original or not from the reader control section  202 . 
     Reference numeral  303  denotes a printer control communication I/F as a sending and receiving section in the cable or communication line  207  between the image controller section  203  and the printer control section  204 . This enables the job control section  302  to send control data for controlling the printer  100  and the after-treatment device  190  and acquire information on a sheet conveyance condition, printing condition, after-treatment condition, and so forth from the printer control section  204 . 
     Reference numeral  304  denotes an image control section that makes settings as to reading of image data according to the copy mode settings analyzed by the job control section  302 . For example, if the magnification/reduction ratio for copying is designated via the operating section, the image control section  304  calculates the image size according to the magnification/reduction ratio and the determined size of an original notified from the reader control section  202 . 
     Reference numeral  305  denotes an image memory control section that secures an image data area in the image memory  307  according to the image size calculated by the image control section  304  and sets a start address of image data and the like. 
     A reader image I/F  306  as a receiving section that receives reader clock synchronous image data inputted from the reader control section  202  to the image controller section  203  via the reader clock synchronous image data bus  209  is connected to the image memory  307  via a reader image clock synchronous image data bus  309  of the image controller section  203 , so that an image read by the reader  102  can be written into the image memory  307 . 
     Further, in order that the printer control section  204  reads out image data from the image memory  307 , the image controller section  203  transfers an image to the printer clock synchronous image data bus  210  through the printer image I/F  308  via a printer clock synchronous image data bus  310  according to a printer clock supplied from the printer control section  204 . Then, the laser section  119  of the printer  100  exposes the image data onto the photosensitive drum  111 . 
     As described above, by transferring image data received from the reader control section  202  to the printer control section  204  via the image memory  307 , the image controller section  203  converts the transfer speed of the image data from the speed synchronous with the reader clock into the speed synchronous with the printer clock inside the image controller section  203 . 
     A description will now be given of how reading and writing image data from and into the image memory  307  is carried out. 
       FIG. 4A  is a reader processing speed table used in the first embodiment, and shows the relationship between IDs of a plurality of types of readers having an image sensor such as a CCD with different image transfer clocks and processing speeds of the readers. 
     In  FIG. 4A , the processing speed is 100 mm/sec if the reader ID is “1”, the processing speed is 150 mm/sec if the reader ID is “2”, the processing speed is 250 mm/sec if the reader ID is “3”, and the processing speed is 300 mm/sec if the reader ID is “4”. 
       FIG. 4B  is a view of a printer processing speed table used in the first embodiment and showing the relationship between IDs of a plurality of types of readers having an exposure device such as a laser with different image transfer clocks and processing speeds of the printers. 
     In  FIG. 4B , the processing speed is 300 mm/sec if the printer ID is “1”, the processing speed is 350 mm/sec if the printer ID is “2”, the processing speed is 400 mm/sec if the printer ID is “3”, and the processing speed is 450 mm/sec if the printer ID is “4”. 
       FIG. 4C  shows equations for use in calculating the timing for reading out printer clock synchronous image data by the image controller section  203  in the case where a reader having the reader ID “2” in the reader processing speed table and a printer having the printer ID “1” in the printer processing speed table are used in combination. 
     If the job control section  302  having received the reader ID and the printer ID notifies the image control section  304  of these IDs, the image control section  304  performs calculation according to the equations of  FIG. 4C . The image control section  304  notifies the image memory control section  305  of printer clock readout timing as the result of the calculation to set the timing for reading out image data from the image memory  307 . 
     Where the sub-scan size of the image size calculated by the image control section  304  is designated by ImgV, the reader processing speed is designated by R, and the printer processing speed is designated by P, the timing T for reading out the printer clock synchronous image data is calculated according to the following equation:
 
 T =Img V ×( P−R )/ P  
 
     If the reader processing speed R is 150 mm/sec as in the example of  FIG. 4A  and the printer processing speed P is 300 mm/sec as in the example of  FIG. 4B , the printer clock synchronous image data readout timing T is represented by the following expression: 
                   T   =     Img   ⁢           ⁢   V   ×       (     300   -   150     )     /   300                   =     Img   ⁢           ⁢   V   ×   0.5                 
As is clear from this expression, half of the image size corresponds to the printer clock synchronous image data readout timing.
 
       FIG. 5A  is a timing chart showing the timing relationship between a reader clock as an image transfer clock of the image sensor section  108  and a printer clock as an image transfer clock of the exposure device such as the laser section  119  in the case where the reader processing speed R is 150 mm/sec as in the example of  FIG. 4A  and the printer processing speed P is 300 mm/sec as in the example of  FIG. 4B . 
     Since the reader processing speed R is 150 mm/sec and the printer processing speed P is 300 mm/sec, one cycle of the reader clock is twice as long as that of the printer clock. 
       FIG. 5B  is a timing chart showing the timing relationship between a reader HSYNC as a horizontal synchronization signal representing the sub-scanning side image writing timing of the reader and a printer HSYNC as a horizontal synchronization signal representing the sub-scanning side image writing timing of the printer. These signals are generated by a circuit, not shown, based on the reader clock and the printer clock, and one cycle of the reader HSYNC is twice as long as that of the printer HSYNC as is the case with the relationship between the reader clock and the printer clock. 
       FIG. 6  is a conceptual diagram showing how an image is actually written onto the image memory  307 . The main scan size and sub-scan size of an image in a copy job calculated by the image control section  304  are designated by ImageH and ImageV, respectively, and an image area specified by ImageH and ImageV is secured on the image memory  307 . The starting point of the secured image area is taken as an address on the image memory  307 , and corresponds to an image input/output starting point in  FIG. 6 . 
     The reader clock synchronous image data transferred through the reader image I/F  306  is written in the secured image area in the main scanning direction on a line-by-line basis in synchronism with the reader HSYNC, i.e. in directions indicated by arrows. 
     The starting points of the arrows correspond to the leading ends of the image data in the main scanning direction depending on an image effective interval signal, not shown, set by the memory control section  305  based on the size corresponding to ImageH from the starting point of the reader HSYNC, and the ending points of the arrows correspond to the trailing ends of the image data in the main scanning direction depending on the image effective interval signal. 
     The sub-scan size ImageV of the image in the copy job calculated by the image control section  304  is determined by an effective interval signal, not shown, set by the image memory control section  305 , and the reader clock synchronous image data is written a number of times synchronous with the reader HSYNC. 
     In this way, the reader clock synchronous image data is written onto the image memory  307 . Likewise, the printer clock synchronous image data is read from the image area specified by ImageH and ImageV on the image memory  307  starting with the image input/output starting point thereof and transferred to the printer image I/F  308  in synchronism with the printer clock and the printer HSYNC. 
       FIG. 7  is a conceptual diagram showing the timing for writing (inputting) and reading out (outputting) an image into and from the image memory  307  in the case where the respective processing speeds are set as in the examples of  FIGS. 4A  and  FIG. 4B . 
     Since the printer image readout timing corresponds to half of the sub scan image size ImageV as is clear from the result of calculation according to the equation in  FIG. 4C , the readout of the printer clock synchronous image data is started (“start of image output” in  FIG. 7 ) in timing in which the writing of the reader clock synchronous reader image is half completed (“end of ½ image input” in  FIG. 7 ). 
       FIG. 8  is a conceptual diagram showing a state in which the reader clock synchronous image data is written into the image memory  307  and the printer clock synchronous image data is read out from the image memory  307  at the same time. 
     In  FIG. 8 , lines with both ends thereof indicated by black circles are main scan lines for which the readout of the image data has been completed, and lines with trailing ends thereof indicated by arrows are main scan lines for which the writing of the image data has been completed but the readout of the image data has not been completed. In the state shown in  FIG. 8 , ¾ of the image data has been inputted and ½ of the image data has been read out. 
       FIG. 9  is a conceptual diagram showing a state immediately after the writing and reading of the image data have been completed. In the example of  FIG. 9 , all of the image data in the image area specified by ImageH and ImageV has been written into the image memory  307 , and all of the image data has been outputted. 
     As described above, the image data can be efficiently written into and read out from the image memory  307  based on the reader and printer processing speeds in the examples of  FIG. 4A  and  FIG. 4B  and the image readout timing calculated according to the equation of  FIG. 4C . 
     Referring to a flow chart of  FIG. 10 , a description will now be given of the procedure for acquiring IDs which are used in acquiring the reader processing speed corresponding to the reader ID and the printer processing speed corresponding to the printer ID as exemplified in  FIGS. 4A and 4B . 
     Power is applied to the image forming apparatus in  FIG. 1  in a step S 101 , and the image controller section  203  starts initializations in a step S 102 . In the step S 102 , the image controller section  203  makes settings of registers of circuits, not shown, that control the image memory  307 , and carries out initialization of communication with the reader control section  202  and the printer control section  204 , and others. 
     After completion of the initializations, the image controller section  203  determines in a step S 103  whether or not the printer control section  204  is connected to the image controller section  203  through the printer control communication I/F  303 . If it is determined that the printer control section  204  is not connected to the image controller  203 , the image controller section  203  waits until the printer control section  204  is connected thereto. Upon detection of the connection, the image controller section  203  acquires a printer ID from the printer control section  204 , and causes the job control section  302  to store the ID in a step S 104 . 
     After acquiring the printer ID, the image controller section  203  determines in a step S 105  whether the reader control section  202  is connected to the image controller  203  through the reader control communication I/F  301 . If it is determined that the reader control section  202  is not connected to the image controller  203 , the image controller section  203  waits until the reader control section  202  is connected thereto. Upon detection of the connection, the image controller section  203  acquires a reader ID from the reader control section  202 , and causes the job control section  302  to store the ID in a step S 106 , and terminates the initialization in a step S 107 . In this way, the reader ID and the printer ID are acquired. 
       FIG. 11  is a flow chart showing the procedure for controlling the image memory during copying, and shows a process for determining the image readout timing in the actual copy job and actually forming an original image on a sheet, with reference to the reader ID and the printer ID acquired according to the procedure of  FIG. 10 . 
     First, in a step S 111 , the job control section  301  starts a copy job in response to an instruction for starting copy inputted through the operating section, not shown. 
     In the next step S 112 , the job control section  302  determines copy mode settings based on settings made through the operating section, not shown, such as the magnification. Further, in a step S 113 , the job control section  302  determines the size of an original, which is detected by the reader control section  202  and acquired via the reader control communication I/F  301 , as the original size. The job control section  302  selects a sheet from those stacked on the feeding cassettes  121 ,  122 ,  123 ,  124 ,  150 , and  154  according to the determined copy mode settings and the determined original size, and then determines the sheet to be fed. 
     In the next step S 114 , the job control section  302  notifies the image control section  304  of the original size, the sheet size, and the like determined in the step S 113 , and the image control section  304  determines the image size. The image control section  304  then notifies the image memory control section  305  of the image size, and the image memory control section  305  secures an image area for the image data on the image memory  307 . 
     In a step S 115 , the reader and printer processing speeds are acquired with reference to the respective processing speed tables of  FIG. 4A  and  FIG. 4B  based on the reader ID and the printer ID notified from the job control section  302 . 
     In a step S 116 , by calculation according to the equation of  FIG. 4C , the image control section  304  determines the print image data readout timing, and notifies the image memory control section  305  of the timing and sets the actual print image data readout timing in the image memory  307 . 
     In a step S 117 , scanning of the original is started to start inputting image data to the image memory  307 . In a step S 118 , the image memory control section  305  waits until the print image data readout timing. Upon the print image data readout timing being reached, the image memory control section  305  sets an image readout starting position in the image memory  307  to start printing the print image data to be read out and printed in a step S 119 . 
     In a step S 120 , the image memory control section  305  waits until readout of the image is completed. In this case, the completion of the readout of the image means that the input of the image is completed at the same time according to the equation of  FIG. 4C . 
     In a step S 121 , the job control section  302  determines whether or not there is the next original on the original feeder  180  or whether or not the original is to be read again by the reader  102 . If it is determined in the step S 121  that there is the next original or the original is to be read again, the process returns to the step S 113  to determine the original size again and perform the subsequent processing to prepare for copying. 
     If it is determined in the step S 121  that there is no next original or the original is not to be read again, the process proceeds to a step S 122  to end copying. 
     The above described process makes it possible to input an image of an original to the image memory  307  and output the image to be printed on a sheet from the image memory  307  in an efficient manner. 
     Second Embodiment 
     Although in the first embodiment described above, the respective processing speeds are acquired based on the reader ID and the printer ID, the respective processing speeds are acquired based on the number of copies read by a reader and the number of copies printed by a printer according to a second embodiment of the present invention. 
       FIG. 12A  shows a reader processing speed table used in the second embodiment, and shows the relationship between the number of copies read by a plurality of types of readers, which read different numbers of copies per unit time (one minute), and the reader processing speeds of the readers. 
     In  FIG. 12A , the reader processing speed is 100 mm/sec if the number of copies read by a reader is “20”, the reader processing speed is 150 mm/sec if the number of copies read by a reader is “30”, the reader processing speed is 250 mm/sec if the number of copies read by a reader is “40”, and the reader processing speed is 300 mm/sec if the number of copies read by a reader is “60”. 
       FIG. 12B  is a view of a printer processing speed table used in the second embodiment and showing the relationship between the number of copies printed by a plurality of types of printers, which output different numbers of copies per unit time (one minute), and the printer processing speeds of the printers. 
     In  FIG. 12B , the printer processing speed is 300 mm/sec if the number of copies printed by a printer is “30”, the printer processing speed is 350 mm/sec if the number of copies printed by a printer is “40”, the printer processing speed is 400 mm/sec if the number of copies printed by a printer is “60”, and the printer processing speed is 450 mm/sec if the number of copies printed by a printer is “80”. 
       FIG. 12C  shows equations for use in calculating the timing for reading out printer clock synchronous image data by the image controller section  203  in the case where the number of copies read by a reader is “30” in the reader processing speed table and the number of copies printed by a printer is “30” in the printer processing speed table. 
     Calculations according to the equations of  FIG. 12C  are executed by the image control section  304  when the job control section  302  having received the number of copies read by the reader and the number of copies printed by the printer notifies the image control section  304  of the respective numbers of copies. The image control section  304  notifies the image memory control section  305  of printer clock readout timing as the result of the calculations to set the timing for reading out image data from the image memory  307 . 
     Where the sub-scan size of the image size calculated by the image control section  304  is designated by ImgV, the reader processing speed is designated by R, and the printer processing speed is designated by P, the timing T for reading out the printer clock synchronous image data is calculated according to the following equation:
 
 T =Img V ×( P−R )/ P  
 
     If the reader processing speed R is 150 mm/sec as in the example of  FIG. 12A  and the printer processing speed P is 300 mm/sec as in the example of  FIG. 12B , the printer clock synchronous image data readout timing T is represented by the following expression: 
                   T   =     Img   ⁢           ⁢   V   ×       (     300   -   150     )     /   300                   =     Img   ⁢           ⁢   V   ×   0.5                 
As is clear from this expression, half of the image size corresponds to the printer clock synchronous image data readout timing.
 
     Referring to a flow chart of  FIG. 13 , a description will now be given of the procedure for acquiring information on the number of copies, which is used in acquiring the reader processing speed corresponding to the number of copies read by a reader per unit time and the printer processing speed corresponding to the number of copies printed by a printer as shown in  FIG. 12A  and  FIG. 12B . 
     First, after carrying out initialization as in the same manner as in the initialization in the steps S 101  to S 103  according to the first embodiment described with reference to  FIG. 10 , in a step S 201 , the number of copies printed by a printer per unit time (one minute) is acquired from the printer control section  204 , and the job control section  302  stores information on the number of copies printed by the printer. 
     Further, after the same process as in the step S 105  described with reference to  FIG. 10  is carried out, in a step S 202 , the number of copies read by a reader per unit time (one minute) is acquired from the reader control section  202 , and the job control section  302  stores information on the number of copies read by the reader. The initialization is then terminated in the step S 107  described with reference to  FIG. 10 . 
     In this way, the numbers of copies read by a reader and outputted by a printer per unit time (one minute) are acquired. 
       FIG. 14  is a flow chart showing the procedure for controlling the image memory during copying according to the second embodiment, and shows a process for determining the image readout timing in the actual copy job and actually forming an original image on a sheet with reference to information on the number of copies read by a reader and the number of copies printed by a printer acquired according to the procedure of  FIG. 13 . 
     First, after carrying out the same process as in the process of the steps S 111  to S 114  according to the first embodiment described with reference to  FIG. 11 , the respective processing speeds are acquired in a step S 301  by referring to the respective processing speed tables of  FIG. 12A  and  FIG. 12B  based on the information on the number of copies read by a reader and the number of copies read by a printer notified from the job control section  302 . 
     In the next step S 302 , by calculation according to the equation of  FIG. 12C , the image control section  304  determines print image data readout timing, and notifies the image memory control section  305  of the timing and sets the actual print image data readout timing in the image memory  307 . 
     Subsequently, the same process as the process of the steps S 117  to S 122  described with reference to  FIG. 11  is carried out, and the process is terminated. 
     The above described process makes it possible to input an image of an original to the image memory  307  and output the image to be printed on a sheet from the image memory  307  in an efficient manner. 
     Third Embodiment 
     Although in the first and second embodiments described above, the printer processing speed and the reader processing speed are acquired using the tables, the printer processing speed and the reader processing speed are acquired directly from a printer and a reader according to a third embodiment of the present invention. 
     Specifically, the reader control section  202  and the image controller section  203  carry out communication with each other to exchange control data via the cable  206 , so that the reader control section  202  notifies the image control section  203  of the reader processing speed as the image data transfer speed of the image sensor section  108 . 
     Further, the image controller section  203  and the printer section  204  carry out communication with each other to exchange control data via the cable  206 , so that the printer control section  204  notifies the image controller section  203  of the printer processing speed as the image data transfer speed of the laser section  119  at which image data stored in the image controller section  203  is transferred. 
     Therefore, as is the case with the first and second embodiments, the third embodiment enables efficient input of an image read from an original to the image memory  307  and efficient output of the image to be printed on a sheet from the image memory  307 . 
     Fourth Embodiment 
     Although in the first embodiment, the respective processing speeds for use in determining the timing for reading out data from the image memory  307  are acquired based on the reader ID and the printer ID, a timing generation ratio for determining the timing for reading out data from the image memory  307  is acquired based on the reader ID and the printer ID according to a fourth embodiment of the present invention. 
       FIG. 15A  is a view of a timing table used in the fourth embodiment and showing the relationship between IDs of a plurality of types of readers and printers and the timing generation ratio. 
     According to the table of  FIG. 15A , the timing generation ratio is 0.66 if the reader ID is “1” and the printer ID is“1”, the timing generation ratio is 0.5 if the reader ID is “2” and the printer ID is “1”, the timing generation ratio is 0.17 if the reader ID is “3” and the printer ID is “1”, and the timing generation ratio is 0 if the reader ID is “4” and the printer ID is “1”. 
     Further, the timing generation ratio is 0.71 if the reader ID is “1” and the printer ID is “2”, the timing generation ratio is 0.57 if the reader ID is “2” and the printer ID is “2”, the timing generation ratio is 0.28 if the reader ID is “3” and the printer ID is “2”, and the timing generation ratio is 0.14 if the reader ID is “4” and the printer ID is “2”. 
     Further, the timing generation ratio is 0.75 if the reader ID is “1” and the printer ID is “3”, the timing generation ratio is 0.63 if the reader ID is “2” and the printer ID is “3”, the timing generation ratio is 0.25 if the reader ID is “3” and the printer ID is “3”, and the timing generation ratio is 0.25 if the reader ID is “4” and the printer ID is “3”. 
     Further, the timing generation ratio is 0.78 if the reader ID is “1” and the printer ID is “4”, the timing generation ratio is 0.67 if the reader ID is “2” and the printer ID is “4”, the timing generation ratio is 0.44 if the reader ID is “3” and the printer ID is “4”, and the timing generation ratio is 0.33 if the reader ID is “4” and the printer ID is “4”. 
       FIG. 15B  shows equations for use in calculating the timing for reading out printer clock synchronous image data by the image controller section  203  in the case where a reader with the reader ID “2” and a printer with the printer ID “1” in the table are used in combination, and in the case where the a reader with the reader ID “4” and a printer with the printer ID “1” in the table are used in combination. 
     Calculations according to the above equations are executed by the image control section  304  when the job control section  302  having received the reader ID and the printer ID notifies the image control section  304  of the respective IDs. The image control section  304  notifies the image memory control section  305  of printer clock readout timing as the result of the calculation to set the timing for reading out image data from the image memory  307 . 
     Where the sub-scan size of the image size calculated by the image control section  304  is designated by ImgV and the timing generation ratio is designated by TGR, the timing T for reading out the printer clock synchronous image data is calculated according to the following equation:
 
 T =Img V ×TGR
 
     If a reader with the reader ID “2” and a printer with the printer ID “1” are used in combination and the timing generation ratio TGR is 0.5, the printer clock synchronous image data readout timing T is represented by the following expression:
 
 T =Img V× 0.5
 
As is clear from this expression, half of the image size corresponds to the printer clock synchronous image data readout timing.
 
     If a reader with the reader ID “4” and a printer with the printer ID “1” are used in combination and the timing generation ratio TGR is 0, the printer clock synchronous image data readout timing T is represented by the following expression:
 
 T =Img V× 0=0
 
As is clear from this expression, the input of an image from the reader and the readout of image data to the printer are started at the same time.
 
       FIG. 16  is a flow chart showing the procedure for controlling the image memory during copying according to the fourth embodiment, and shows a process for determining the image readout timing in the actual copy job and actually forming an original image on a sheet with reference to the reader ID and the printer ID acquired according to the procedure of  FIG. 10 . 
     First, after carrying out the same process as in the process of the steps S 111  to S 114  according to the first embodiment described with reference to  FIG. 11 , the respective processing speeds are acquired in a step S 401  by referring to the timing table of  FIG. 15A  based on the reader ID and the printer ID notified from the job control section  302 . 
     In the next step S 402 , by calculation according to the equation of  FIG. 15B , the image control section  304  determines print image data readout timing, and notifies the image memory control section  305  of the timing and sets the actual print image data readout timing in the image memory  307 . 
     Subsequently, the same process as the process of the steps S 117  to S 122  described with reference to  FIG. 11  is carried out, and the process is terminated. 
     The above described process makes it possible to efficiently input an image of an original to the image memory  307  and efficiently output the image to be printed on a sheet from the image memory  307 . 
     Fifth Embodiment 
     Although in the above described fourth embodiment, the timing generation ratio is acquired based on the reader ID and the printer ID, the timing generation ratio is determined based on the number of copies read by a reader and the number of copies printed by a printer according to a fifth embodiment of the present invention. 
       FIG. 17A  is a view of a timing table according to the fifth embodiment and showing the relationship between the number of copies read by a plurality of types of readers per unit time (one minute) and the number of copies printed by a plurality of types of printers per unit time (one minute) and the timing generation ratio. 
     According to the timing table of  FIG. 17A , the timing generation ratio is 0.66 if the number of copies read by a reader is “20” and the number of copies printed by a printer is “30”, the timing generation ratio is 0.5 if the number of copies read by a reader is “30” and the number of copies printed by a printer is “30”, the timing generation ratio is 0.17 if the number of copies read by a reader is “40” and the number of copies printed by a printer is “30”, and the timing generation ratio is 0 if the number of copies read by a reader is “60” and the number of copies printed by a printer is “30”. 
     Further, the timing generation ratio is 0.71 if the number of copies read by a reader is “20” and the number of copies printed by a printer is “40”, the timing generation ratio is 0.57 if the number of copies read by a reader is “30” and the number of copies printed by a printer is “40”, the timing generation ratio is 0.28 if the number of copies read by a reader is “40” and the number of copies printed by a printer is “40”, and the timing generation ratio is 0.14 if the number of copies read by a reader is “60” and the number of copies printed by a printer is “40”. 
     Further, the timing generation ratio is 0.75 if the number of copies read by a reader is “20” and the number of copies printed by a printer is “60”, the timing generation ratio is 0.63 if the number of copies read by a reader is “30” and the number of copies printed by a printer is “60”, the timing generation ratio is 0.25 if the number of copies read by a reader is “40” and the number of copies printed by a printer is “60”, and the timing generation ratio is 0.25 if the number of copies read by a reader is “60” and the number of copies printed by a printer is “60”. 
     Further, the timing generation ratio is 0.78 if the number of copies read by a reader is “20” and the number of copies printed by a printer is “80”, the timing generation ratio is 0.67 if the number of copies read by a reader is “30” and the number of copies printed by a printer is “80”, the timing generation ratio is 0.44 if the number of copies read by a reader is “40” and the number of copies printed by a printer is “80”, and the timing generation ratio is 0.33 if the number of copies read by a reader is “60” and the number of copies printed by a printer is “80”. 
       FIG. 17B  shows equations for use in calculating the timing for reading out printer clock synchronous image data by the image controller section  203  in the case where a reader which reads “30” copies per unit time and a printer which prints “30” copies per unit time in the table are used in combination, and in the case where the a reader which reads “60” copies per unit time and a printer which prints “30” copies per unit time in the table are used in combination. 
     Calculations according to the above equations are executed by the image control section  304  when the job control section  302  having received the reader ID and the printer ID notifies the image control section  304  of the respective IDs. The image control section  304  notifies the image memory control section  305  of printer clock readout timing as the result of the calculation to thus set readout timing for reading out image data from the image memory  307 . 
     Where the sub-scan size of the image size calculated by the image control section  304  is designated by ImgV and the timing generation ratio is designated by TGR, the timing T for reading out the printer clock synchronous image data is calculated according to the following equation:
 
 T =Img V ×TGR
 
     If a reader which reads “30” copies per unit time and a printer which prints “30” copies per unit time are used in combination and the timing generation ratio TGR is 0.5, the printer clock synchronous image data readout timing T is represented by the following expression:
 
 T =Img V× 0.5
 
     As is clear from this expression, half of the image size corresponds to the printer clock synchronous image data readout timing. 
     If a reader which reads “60” copies per unit time and a printer which prints “30” copies per unit time are used in combination and the timing generation ratio TGR is 0, the printer clock synchronous image data readout timing T is represented by the following expression:
 
 T =Img V× 0=0
 
     As is clear from this expression, the input of an image from the reader and the readout of image data to the printer are started at the same time. 
       FIG. 18  is a flow chart showing the procedure for controlling the image memory during copying according to the fifth embodiment, and shows a process for determining the image readout timing in the actual copy job and actually forming an original image on a sheet with reference to the number of copies read by a reader and the number of copies printed by a printer acquired according to the procedure of  FIG. 13 . 
     First, after carrying out the same process as in the process of the steps S 111  to S 114  according to the first embodiment described with reference to  FIG. 11 , the respective processing speeds are acquired in a step S 501  by referring to the timing table of  FIG. 17A  based on the number of copies read by a reader and the number of copies printed by a printer notified from the job control section  302 . 
     In the next step S 502 , by calculation according to the equation of  FIG. 17B , the image control section  304  determines print image data readout timing, and notifies the image memory control section  305  of the timing and sets the actual print image data readout timing in the image memory  307 . 
     Subsequently, the same process as the process of the steps S 117  to S 122  described with reference to  FIG. 11  is carried out, and the process is terminated. 
     The above described process makes it possible to efficiently input an image of an original to the image memory  307  and efficiently output the image to be printed on a sheet from the image memory  307 . 
     Although in the above described embodiments, the reader  102  and the printer  100  are configured as an integral unit, the present invention may be applied to a separate-type image forming apparatus in which a reader and a printer are connected to each other via a cable. 
       FIG. 19A  is a schematic view showing the arrangement of an image forming apparatus including a reader according to a sixth embodiment of the present invention. 
     As shown in  FIG. 19A , an image controller section  203  is arranged inside the reader  102 . 
     It should be noted that the image controller section  203  and the reader  102  may be arranged in separate bodies from each other. 
     The reader  102  is connected to the printer  100  via a cable  230  for communication with each other. 
     The reader  102  has provided therein a memory, not shown, that stores image data read by the reader  102 , and a receiver section that receives printer information related to the printer  100  from the printer  100 . The controller  203  determines, while the read image data is being written to the memory, timing for reading out the image data written in the memory according to the printer information received by the receiver section and reader information related to the reader  102 . 
       FIG. 19B  is a schematic view showing the arrangement of an image forming apparatus including a printer according to a seventh embodiment of the present invention. 
     As shown in  FIG. 19B , an image controller section  203  is arranged inside the printer  100 . 
     It should be noted that the image controller section  203  and the printer  100  may be arranged in separate bodies from each other. 
     The printer  100  is connected to the reader  102  via a cable  230  for communication with each other. 
     The printer  100  has provided therein a memory, not shown, that receives image data from the reader  102  and stores the same, and a receiver section that receives reader information related to the reader  102  from the reader  102 . The controller  203  determines, while the image data received from the reader  102  is being written to the memory, timing for reading out the image data written in the memory according to the reader information received by the receiver section and printer information related to the printer  100 . 
     It should be noted that the above described control methods can be realized by storing programs conforming to the flow charts of  FIGS. 10 ,  11 ,  13 ,  14 ,  16 , and  18  in a storage of the image controller section  203  and executing the programs. 
     The present invention may be applied to a system composed of a plurality of apparatuses or to a single apparatus. 
     It is to be understood that the object of the present invention may also be accomplished by supplying a system or an apparatus with a storage medium in which a program code of software which realizes the functions of the above described embodiments is stored, and causing a computer (or CPU or MPU) of the system or apparatus to read out and execute the program code stored in the storage medium. 
     In this case, the program code itself read from the storage medium realizes the functions of the embodiments described above, and hence the storage medium on which the program code is stored constitutes the present invention. 
     Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, a DVD-RW, a DVD+RW, a magnetic tape, a nonvolatile memory card, and a ROM. 
     Further, it is to be understood that the functions of the above described embodiments may be accomplished not only executing a program code read out by a computer, but also by causing an OS (Operating System) or the like which operates on the computer to perform a part or all of the actual operations based on instructions of the program code. 
     Further, it is to be understood that the functions of the above described embodiments may be accomplished by writing a program code read out from the storage medium into an expansion board inserted into a computer or a memory provided in an expansion unit connected to the computer and then causing a CPU or the like provided in the expansion board or the expansion unit to perform a part or all of the actual operations based on instructions of the program code.