Image forming apparatus

Abstract: A mode for sorting sheets having two sides, on which images have been printed, is performed such that sheets each having one printed side are stacked in an automatic double side device, and the sheets stacked in the automatic double side device are sequentially extracted and conveyed. If a jam takes place (ST13) during extraction and conveyance of the sheets, the position, at which the jam has taken place, is displayed (ST14) on an LCD display unit (116). After the jammed sheet has been removed, the printing operation is caused to restart. If the sheets stacked in the automatic double side device lack (ST17) before the printing operation is completed, a copy key (121) is depressed to perform control (ST12) to again perform the printing operation.

Description: The present invention relates to an image forming apparatus, such as a digital copying machine, having functions of compressing and expanding an image, storing images and automatically copying images on the two sides of sheets, and to a method of forming an image. Hitherto, a digital copying machine, serving as the image forming apparatus, has been provided with a so-called memory edition and copying function capable of combining a plurality of original-document images with one another to form an image for one sheet so as to print (form) the image. Moreover, the copying machine of the foregoing type has been provided with an electronic sorting and copying function for compressing images read by a scanner and supplied from the same to store the compressed images in a page memory having file areas sectioned into areas for respective pages and then expanding and printing image data stored in the page memory. The digital copying machine of a type having a stapler is enabled to have a staple sorting mode which is set for the purpose of stapling sheets printed and discharged due to the electronic sorting and copying function to form one or more copies of sheets. An automatic double side device (ADD) adaptable to the digital copying machine enables double side copying to be performed such that images are printed on the two sides of the sheets by the following steps of: temporarily stacking, onto a tray, sheets having one sides (for example, reverse sides), on which images have been printed; and sequentially taking out the sheets stacked on the tray to print images on the residual sides (for example, the right sides). In general, if a jam (a problem) takes place during the double side printing operation in a sorting mode in which a plurality of original-document sheets are printed to obtain a plurality of copies and they are divided into each copy, a user is required to remove the sheets which encountered the jam and to instruct the apparatus to restart the printing operation. Thus, the apparatus again prints the images for the pages, on which the image could not be printed due to the jam, to new sheets so that the printing operation is continued. However, the number of the jammed sheets which have been removed by the user and the number counted and estimated by the apparatus sometimes do not coincide with each other, thus resulting in pages being sometimes lacked. Job recovery methods in double side printing mode are e.g. known from US-A-4 163 897. If a jam takes place during the double side printing operation in a group mode in which an original document consisting of a plurality of sheets is printed to obtain a plurality of copies and the printed sheets are divided into groups of the same page, also the user is required to remove the sheets which encountered the jam and to instruct the apparatus to restart the printing operation so that the apparatus again prints the pages lacked due to the jam and continues the printing operation. However, the number of the jammed sheets which have been removed by the user and the number counted and estimated by the apparatus sometimes do not coincide with each other, thus resulting in pages being sometimes lacked. Accordingly, an object of the present invention is to provide'an image forming apparatus and an image forming method capable of compensating lacking in the printed pages after a user has removed a jammed sheet and instructed to restart the printing operation if a jam takes place during a double side printing operation in a sorting mode or a group mode. The above object is achieved by an image forming apparatus according to claim 1 and a method according to claim 8. Further developments of the invention are given in the dependent claims. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a cross sectional view showing an image forming apparatus according to an embodiment of the present invention; FIG. 2 is a diagram showing the system structure of the image forming apparatus; FIG. 3 is a block diagram showing the structure of a basic CPU; FIG. 4 is a block diagram showing the structure of a scanner portion; FIG. 5 is a block diagram showing the structure of a printer portion; FIG. 6 is a control block diagram showing an electronic sorting function of the image forming apparatus; FIG. 7 is a diagram showing a storage region of a page memory; FIGS. 8A to 8C are diagrams showing an operation to be performed when an original document consisting of four sheets, each having one side on which an image has been formed, is double side printed by using an automatic double side device in a sorting mode; FIGS. 9A and 9B show a flow chart of an operation to be performed when a jam takes place during a double side printing operation in a sorting mode for obtaining double side printed sheets; FIG. 10 is a diagram showing occurrence of a jam during the double side printing operation; FIGS. 11A and 11B are diagrams showing a jam taking place due to double supply of sheets from a tray of the automatic double side device; FIGS. 12A to 12C are diagrams showing the double side printing operation using the automatic double side device; FIGS. 13A and 13B show a flow chart of an operation to be performed when a jam takes place during a double side printing operation in a group mode; FIGS. 14A and 14B are diagrams showing control to be performed when a copying operation in the group mode is performed; FIGS. 15A and 15B are diagrams showing a jam taken place due to double supply of sheets from the tray of the automatic double side device; FIGS. 16A to 16C are diagrams showing a jam taken place due to double supply of sheets from the tray of the automatic double side device; and FIGS. 17A and 17B are diagrams showing a double side printing operation using the automatic double side device. A preferred embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall structure of an electronic copying machine which is an image forming apparatus according to the present invention. The apparatus has an original-document scanning portion 140 and an image forming portion 160. An automatic original-document supply unit 200 is mounted on an upper portion of the electronic copying machine. The automatic original-document supply unit 200 has a cover body 21 serving as the frame and having a rear end which is fastened to the rear end of the upper portion of the body of the apparatus by a hinge unit (not shown) so that the cover body 21 can be opened and closed as required. Thus, the overall body of the automatic original-document supply unit 200 can be rotated and displaced to open the upper portion of an original-document retainer 2. An original-document supply frame 22 capable of collectively holding a plurality of original-document sheets is disposed at a somewhat leftward position of the upper surface of the cover body 21. A supply means 23 for, one by one, extracting the plural original-document sheets to supply the sheets to an end (the left end of FIG. 1) of the original-document retainer 2 is disposed at an end of the apparatus. The supply means 23 has pickup rollers 27 for extracting the original document, a weight plate 28 for pressing the original document against the pickup rollers 27 and an empty sensor 29 serving as an original-document detection sensor for detecting a state where the original document is set to the original-document supply frame 22. In a direction in which the pickup rollers 27 extract the original document, sheet supply rollers 32 are disposed so that the original document sheets are sequentially supplied. An original-document conveying belt 37 covering the upper surface of the original-document retainer 2 is arranged on the upper surface of the original-document retainer 2. The original-document conveying belt 37 comprises a wide endless belt arranged between a pair of belt rollers 40 and having a white outer surface, the original-document conveying belt 37 being moved forwards or rearwards by a belt drive mechanism (not shown). On the reverse side of the inside portion of the original-document conveying belt 37, there are disposed a plurality of belt holding rollers 41 for pressing the surface of the original-document conveying belt 37 against the original-document retainer 2 and a set switch (not shown) for detecting a state where the automatic original-document supply unit 200 is opened or closed. The original document supplied by the supply means 23 is conveyed from an end (the left end) of the original-document retainer 2 to another end (the right end) of the same. A sheet-discharge means 38 is disposed in the right-hand portion of the apparatus. The sheet-discharge means 38 has conveying rollers 44, pinch rollers 45 for pressing the original document against the conveying rollers 44, a sheet discharge sensor 46 serving as an original-document detection means for detecting the rear end of the original document which is moved in a direction in which the original document is discharged. Sheet discharge rollers 48 are disposed downstream from the passage for discharging the original document. The original document discharge passage has a gate 82 for introducing the original document into the original-document retainer 2 while reversing the original document. As a result, images can be copied onto the two sides of the original document. The original-document scanning portion 140 consists of an exposure lamp 6 serving as a light source; a first carriage 7 having a mirror 15; a second carriage 9 having mirrors 8a and 8b for warping the optical path; a lens 10; a photoelectric conversion portion 11 for receiving reflected light; a drive system (not shown) for changing the positions of the foregoing elements; and an A/D conversion portion (not shown) for converting an output from the photoelectric conversion portion 11, that is, image data from analog data to digital data. The first and second carriages 7 and 9 are connected to each other by a timing belt (not shown) and arranged in such a manner that the second carriage 9 is moved in the same direction as that of the movement of the first carriage 7 at a speed which is the half of that of the first carriage 7. As a result, scanning can be performed in such a manner that the length of the optical path to the lens 10 is made to be constant. The lens 10 has a fixed focal length and arranged to be moved in the direction of the optical axis when the magnification is changed. The photoelectric conversion portion 11 photoelectrically convert light reflected by the original document, the photoelectric conversion portion 11 being mainly composed of, for example, a CCD line image sensor. In this case, one pixel of the original document corresponds to one element of the CCD sensor. An output from the photoelectric conversion portion 11 is transmitted to the A/D conversion portion. The movement of each of the first and second carriages 7 and 9 and the mirrors 8a and 8b is performed by a stepping motor (not shown). The first and second carriages 7 and 9 are moved in accordance with the operation of a timing belt (not shown) arranged between a drive pulley (not shown) connected to a rotational shaft of the stepping motor and an idle pulley (not shown). The lens 10 is moved in the direction of the optical axis due to spiral operation of a spiral shaft (not shown) rotated by a corresponding stepping motor (not shown). Reference numeral 60 represents an electrooptic conversion portion (a semiconductor laser unit). A collimator lens 62, a polygonal mirror (polyhedron reflecting mirror) 64, a lens 66, reflecting mirrors 68 and 70 and a lens 51 are disposed to correspond to the electrooptic conversion portion 60. Thus, a photosensitive drum 50 is irradiated with a laser beam transmitted from an exposure unit 52. The image forming portion 160 is formed by combining, for example, a laser optical system and an electrophotographic method capable of forming an image on transfer paper. That is, the image forming portion 160 has the photosensitive drum 50 serving as an image carrier rotatively supported at substantially the central portion of the apparatus. The exposure unit 52, a development unit 54, a transference charger 55, a separation charger 56, a cleaning charger 57, a destaticizing charger 58 and a charger 59 are disposed in this sequential order around the photosensitive drum 50. The photosensitive drum 50 is uniformly charged by the charger 59. Moreover, a laser beam emitted from the original-document scanning portion 140 causes the image of the original document to be formed on the photosensitive drum 50 so that an electrostatic latent image is formed. The electrostatic latent image formed on the photosensitive drum 50 is developed by the development unit 54. The developed image is transferred to copying paper P supplied, by the transference charger 55, from a sheet supply cassette 30 serving as a paper supply means to be described later through the resist controllers 20. The copy paper P having the image transferred by the transference charger 55 is separated by the separation charger 56 due to AC corona discharge, and then conveyed to a fixing unit 72 by the conveyance belt. The copy paper P having the developed image, which has been melted and fixed by the fixing unit 72, is discharged onto a discharge tray 74 through a sorter 80 by a pair of discharge rollers 73. The sorter 80 has a stapler 76 for stapling each set of copied sheets in a staple sorting mode. Developer retained on the photosensitive drum 50, from which the developed image has been transferred and separated to the copy paper P, is cleaned by the cleaning charger 57. Then, the destaticizing charger 58 makes the potential of the surface of the photosensitive drum 50 to be lower than a predetermined level to enable a next copying operation to be performed. When the double side copying operation for printing images on the two sides of the copy paper P is performed, the copy paper P having the developed image, which has been melted and fixed by the fixing unit 72, is conveyed through a conveyance passage 75a, and then stacked on a tray 75b. The copy paper P, each having one side on which the image has been printed, is conveyed to the transference charger 55 through a conveyance passage 75c so that developed images are transferred to the residual sides, on which no image has been printed. A light-reflecting type paper sensor 75d is disposed in the lower portion of the tray 75b to detect whether or not paper sheets have been stacked on the tray 75b. The conveyance passage 75a, the tray 75b, the conveyance passage 75c and the paper sensor 75d form an automatic double side device (ADD) 75 serving as an automatic double side reversing mechanism. Reference numeral 30 represents each of a plurality of sheet supply cassettes mounted vertically and serving as a sheet supply means mounted detachably from the front portion of an apparatus body 1. The sheet supply cassette 30 is in the form of a cassette case 31 which is a box accommodating the copy paper P. An extraction end of the cassette case 31 is inclined with respect to a direction in which the copy paper P is extracted. The copy paper P accommodated in the cassette case 31 of the sheet supply cassette 30 is, by pickup rollers 81, picked up and extracted in the downward direction such that the uppermost sheet is picked up first. The copy paper P, extracted by the pickup rollers 81 and conveyed to the extraction end of the cassette case 31, is separated one by one in a sheet separation portion consisting of sheet supply rollers 84 and separation rollers (or a separation pad) 85 disposed on the inside portion of an upper portion of the cassette case 31 so as to be conveyed to the image forming portion 160. Referring to FIGS. 2 to 5, a control circuit for the image forming apparatus will now be described. FIG. 2 is a schematic block diagram of the image forming apparatus such as a digital copying machine control system according to the embodiment of the present invention. FIG. 3 shows a CPU portion, FIG. 4 shows a scanner portion and FIG. 5 shows a printer portion. As shown in FIG. 2, the digital copying machine control system is composed of two blocks consisting of a basic portion 301 and a page memory portion 302. In the basic portion 301, an image processing portion 314 is connected between a scanner 313 and a printer 315 so that the digital copying machine is formed. The page memory portion 302 realizes memory copy by receiving and storing image data from the basic portion 301 and by again transferring the stored image data items to the basic portion 301. The basic portion 301 and the page memory portion 302 are connected to each other by a basic-portion system interface 316 for communicating control data and a basic-portion image interface 317 for communicating image data. The basic portion 301 consists of the scanner 313, the printer 315, the image processing portion 314 and a basic control portion 311 for controlling the foregoing units. As shown in FIG. 3, a ROM 102, a RAM 104, an image memory 106, a timer memory 108, a password code memory 110, a timer 112, an internal interface 122 and an external interface 124 are connected to a main CPU 100 of the basic control portion 311. An operation panel 114 is connected to the internal interface 122. The operation panel 114 has an LCD display unit 116, a ten-key pad 118, a job password mode button 120, a copy key 121 and the like. The external interface 124 is connected to the sorter 80 and an external unit 138. A sheet-discharge tray 74 of the sorter 80 is driven by a tray drive portion 79. In the structure formed as described above, image information is stored and read by the main CPU 100. In a case where a password code and image information are stored for example, image information read by the scanner portion under control of a scanner CPU 160 is stored in the image memory 106 to follow an instruction issued from the main CPU 100. The mode of the instruction from the main CPU 100 is determined in accordance with input (input using keys) from the operation portion. Referring to FIG. 4, the detailed structure of the scanner portion 313 will now be described. The scanner CPU 160 of the scanner portion 313 is connected to a lamp control portion 164 for controlling an irradiation lamp 6, a motor driver 168 for controlling a scanning motor 166, an original-document size detection sensor 169 and an operation portion 172 for operating and controlling variable sensors, switches and solenoids 170 so as to control the connected elements. The scanner CPU 160 is also connected to an A/D conversion circuit 174 for processing image information supplied from the photoelectric conversion element 11, a resolution conversion circuit 178, a shading correction circuit 176, an image quality improving circuit 180 and a binary-coding circuit 182 so as to control the connected elements. Referring to FIG. 5, the printer 315 will now be described in detail. In the printer 315, a printer CPU 190 is connected to a main motor driver 194 for rotating a main motor 192, a sheet-size detection sensor 195, an operation portion 198 for controlling sensors, switches and solenoids 196, a fixing-lamp control portion 202 for controlling a fixing lamp 200, a high-voltage output control portion 212 for controlling a charger 204, a transference charger 206, a separation charger 208 and a PCC charger 210, a destaticizing lamp control portion 216 for controlling a destaticizing lamp 214, a sheet supply control portion 224 for controlling a sheet supply motor 222 for rotating sheet supply rollers 218 and pickup rollers 220 and a modulation circuit 232 for controlling a laser operation circuit 230 for the electrooptic conversion portion (a laser diode) 60 and a polygonal-mirror motor 228. The page memory portion 302 will now be described in detail with reference to FIG. 2. The structure of a bus line 310 connected to a system bus 318 of the basic portion 301 is converted into a bus line 329 by a bus conversion portion 330. A page memory 323 temporarily stores image data, while an address control portion 306 generates address for the page memory 323. An image bus 320 is a bus line for transferring data between devices in the page memory portion 302. A data control portion 307 controls data transference when data is transferred between the page memory 323 and the other device through the image bus 320. An image data I/F 308 interfaces image data when image data is transferred to and from the basic portion 301 through the basic-portion image interface 317. A resolution conversion/binary rotation portion 325 converts the resolution of image data to the resolution of another unit when image data is transmitted to the unit having the different resolution, converts image data received from a unit having a different resolution to the resolution of the printer 315 of the basic portion 301 and rotates binary-coded image data by an angular degree of 90 degrees. A compression/expansion portion 324 compresses supplied image data for the devices for performing facsimile transmission or optical disc storage which compresses and transmits image data and expands image data in the compressed form to be visualized through the printer 315. A multi-value rotation memory 309 is connected to the image data I/F means 308 and operated to rotate image data by an angular degree of 90 degrees or - 90 degrees so as to transmit the rotated image data when the image data is transmitted to the printer 315. FIG. 6 is a functional block diagram showing an electronic sorting function of the image forming apparatus according to the present invention. Referring to the functional block diagram shown in FIG. 6, a portion for controlling reading an original document and enlargement/contraction portion 351 corresponds to, for example, the scanner 313 and the image processing portion 314, an image compression control portion 352 and an image expansion control portion/development position control portion 354 correspond to the compression/expansion portion 324, an image printing control portion 355 corresponds to the printer 315 and a file control portion 353 corresponds to the data control portion 307 and the like. The portion for controlling reading an original document of the portion for controlling reading of an original document and enlargement/contraction portion 351 quantizes image data supplied from the scanner portion 313 to write the same on the page memory 323. If an original document has been set to the automatic original-document supply apparatus 200, the portion for controlling reading of an original document causes the original document to be supplied from the automatic original-document supply apparatus 200 and reads the original document correspondently. The original document set to the automatic original-document supply apparatus 200 is read such that the final page is read first. If a double side original document has been instructed, the original document is read in such a manner that the reverse side of the final page is read first, the right side of the same is read and then the right side of the leading pages read last. The enlargement/contraction portion of the portion for controlling reading of an original document and enlargement/contraction portion 351 is a sub-module of the portion for controlling reading of an original document and arranged to determine the reduction or the enlargement ratio (hereinafter called as a "magnification") in accordance with the relationship between the sheet and the size of the original document, determines the number of longitudinal and horizontal pixels of an image to be copied and processes, that is, enlarges or reduces image data supplied from the scanner portion 313. In the image compression control portion 352 and the file control portion 353, image data on the page memory 323 is compressed and, in a file form, written on a region to be controlled. FIG. 7 shows the structure of the storage region of the page memory 323 which is sectioned into page buffer region M1 on which image data of the original document read by the scanner portion 313 is written as it is and a file area M2 on which data formed by compressing the image data above is written and which is sectioned into regions for corresponding pages. The leading address of each page of the file area M2 is stored in leading address storage region M3 for storing page data in each file area in the address control portion 306. Note that the file may be formed on a volatile memory, such as a RAM, or a large capacity non-volatile memory, such as a hard disk. When an operator has set an original document to, for example, the automatic original-document supply apparatus 200 and depressed the copy key 121 to copy the original document, the portion for controlling reading of an original document and enlargement/ contraction portion 351 causes the original document to be supplied and enlarges or contracts image data obtained by reading the supplied original document. The file control portion 353 writes the image data on the page memory 323. The image compression control portion 352 compresses written image data for each page and causes the same to be stored in the file area M2 sectioned into corresponding pages. The foregoing process is performed until all of the original document sheets set to the automatic original-document supply apparatus 200 are supplied. After data of all of the original document sheets has been stored in the page memory 323, the control is performed by the image expansion control portion/development position control portion 354. The image expansion control portion/development position control portion 354 sequentially reads, from the file area M2, the compressed images of the original document to expand the image in units of one side (the page to be output) to be output (printed), the image expansion control portion/development position control portion 354 then transferring the expanded image to the image printing control portion 355. The foregoing process is performed until all of the original document images are read. The sequential order of the operations of reading the compressed image data items are determined to correspond to the original document page numbers to be described later. The images are printed in the determined order, and then the printed sheets are stacked on the tray 75b of the automatic double side unit 75. In the automatic double side unit 75, the sheets having the printed reverse sides are stacked on the tray 75b, and then the sheets are extracted from the tray 75b so that the right sides are printed. Then, the sheets having the two sides on which images have been printed are discharged onto the sheet-discharge tray 74. In a case where the original document has a plurality of sheets, the reverse side of each sheet is initially printed, and then all of the printed sheets having the printed reverse sides are stacked. Then, the right sides of the sheets are printed while being discharged from the automatic double side unit 75. Thus, the sheets having the printed two sides are discharged onto the sheet-discharge tray 74. FIG. 8 is a diagram showing an operation to be performed when four original document sheets having images on one side thereof are printed into sheets having two printed sides. As shown in FIG. 8A, compressed data of a second page and stored in the file area M2 of the page memory 323 is initially printed on the reverse side of a first sheet under control of the data control portion 307, and then the sheet is placed on the tray 75b of the automatic double side unit 75. Then, image data of a fourth page is printed on the reverse side of the second sheet, and then stacked on the tray 75b. Then, as shown in FIG. 8B, the sheet having the reverse side, on which the fourth page has been printed, is extracted from the tray 75b, followed by printing the third page on the right side of the sheet and discharging the same. Then, the sheet having the reverse side on which the second page has been printed is extracted from the tray 75b, followed by printing a first page on the right side of the sheet and discharging the same. When two or more copies are printed, the foregoing operation is repeated to obtain a required number of copies. If the number of sheets of the original document is not a multiple of two, the printing operation is performed in such a manner that each page is made to advance by one to cause the reverse side of the final page to be a white page. FIG. 8C shows a case where an original document having three sheets are printed out. An operation to be performed if the foregoing structure encounters a jam in a sorting mode of the double side printing operation, that is, in a mode of the double side printing operation in which an original document having a plurality of sheets is printed to obtain a plurality of copies so as to be sectioned into each copy will now be described with reference to a flow chart shown in FIGS. 9A and 9B. The description will now be described about an operation to be performed when an original document consisting of ten sheets each having one printed side is double side printed and a third sheet has encountered a jam during a process in which the same is stacked on the tray 75b of the automatic double side unit 75. When a menu has been selected due to an operation of the LCD display unit 116 performed by a user, the main CPU 100 causes a mode selection screen to be displayed on the LCD display unit 116 (ST1). When the sorting mode of double side printing displayed on the selection screen of the LCD display unit 116 has been selected and depressed, the main CPU 100 causes the LCD display unit 116 to display a requirement to set the number of required copies (ST2). After setting (for example, a required number of copies of three) has been performed by the operator (ST3), the main CPU 100 checks whether an original document exists on the automatic original-document supply apparatus 200 in accordance with a detection signal supplied from the empty sensor 29 or checks whether an original document exists on the original-document retainer 2 in accordance with a detection signal supplied from a sensor (not shown) (ST5). If an original document exists, the main CPU 100 causes an instruction to depress the copy key 121 to be displayed on the LCD display unit 116 (ST7). An assumption is performed here that an original document exists on the automatic original-document supply apparatus 200. If the setting operation is not completed after a predetermined period time has elapsed in step ST3, or if an original document is not set after a predetermined period of time has elapsed in step ST5, the flow proceeds to step ST2. After the copy key 121 has been depressed by the operator (ST8), the main CPU 100 causes the automatic original-document supply apparatus 200 to start supplying the original document. The scanner 313 scans (reads) the supplied original document to temporarily store the same in the page buffer region M1 of the page memory 323. The compression/expansion portion 324 compresses image data in the page buffer region M1 to form the same into a file, and then stores the file in the file area M2 of the page memory 323 (ST10). After the compression/expansion means 324 has stored the image of the original document in the file area M2 of the page memory 323 (ST11), the compression/ expansion portion 324 expands compressed data of the original document formed into the file stored in the file area M2 of the page memory 323. Then, the double side printing operation by the printer 315 starts under control of the image processing portion 314 (ST12). If a jam takes place during a process in which a third sheet is stacked on the tray 75b of the automatic double side unit 75 in the case where the original document having ten sheets is double side printed, the sheet on which the sixth page of the original document has been printed encounters a jam, as shown in FIG. 10. Since the forward sheet (the sheet on which the fourth page has been printed) or the next sheet (a sheet on which the eighth page has been printed) is jammed on the sheet conveyance passage depending upon the jam generation timing, the user is required to remove the jammed sheets additionally. In general, a user is able to detect sheet jam positions in accordance with jam positions displayed on the LCD display unit 116 of the operation panel 114 and remove the non-required sheets (jammed sheets). Also the main CPU 100 is able to determine the sheets correctly stacked on the automatic double side unit 75 or the sheets discharged from the automatic double side unit 75 in accordance with information supplied from a sheet existence detection sensor (not shown) disposed on the sheet conveyance passage. Since a jam of a type, for example, in which two stacked sheets are unintentionally conveyed results in the user removing the two sheets, the actual number sometimes does not coincide with the number counted in accordance with the control program of the main CPU 100. FIG. 11A shows a case where a sheet, on which a sixth page has been printed, and a sheet, on which a fourth page has been printed, are jammed due to double supply of sheets from the tray 75b of the automatic double side unit 75. If a jam takes place (ST13), the main CPU 100 detects the position at which a jam of a sheet has taken place in accordance with information supplied from a detection sensor (not shown) and causes the LCD display unit 116 of the operation panel 114 to display the position of the jam (ST14). In this case, generation of the jam at a discharge port of the automatic double side unit 75 is displayed. Note that generation of a jam is detected such that sheets do not interrupt light detection to be performed by optical sensors disposed at predetermined positions. The user removes the two sheets in accordance with the display of a jam at the discharge port of the automatic double side unit 75 on the LCD display unit 116 (ST15). However, the main CPU 100 considers that only the sheet on which the sixth page of the original document has been printed is removed, and then restarts the double side printing operation (ST16). A state where the jam has been solved when the printing operation has been started is shown in FIG. 11B. Therefore, the main CPU 100, as shown in FIG. 12A, temporarily prints the sixth page, and then stacks the sixth page on the tray 75b of the automatic double side unit 75. Then, as shown in FIG. 12B, the main CPU 100 causes a sheet to be discharged from the tray 75b of the automatic double side unit 75 to print the right side of the sheet. Then, the main CPU 100 causes the fifth page and the third page of the original document to be printed. When a sheet is intended to be supplied from the automatic double side unit 75 to print the first page as shown in FIG. 12C, information indicating that no sheet exists is obtained from the paper sensor 75d (ST17). Thus, a determination can be performed that the first page cannot be printed correctly and, thus the printing operation is interrupted. If the stapling mode has been instructed, the sheets are not stapled, and then the sheets are discharged (ST18). Then, the main CPU 100 causes the LCD display unit 116 of the operation panel 114 to display "No sheet exists in the automatic double side unit" (ST19). When the user has depressed the copy key 121 to instruct continuation of the copying operation (ST20), the main CPU 100 causes the two sides of the first copy (consisting of five sheets) to be again printed and discharged (ST21). In a case where a plurality of copies are sort-printed, the residual copies successively are printed (ST22). If setting that three copies are required has been performed, the two residual copies are successively printed. If the user depresses a stop key (not shown) on the operation panel 114 in place of depressing the copy key 121, the main CPU 100 completes the printing operation and deletes compressed data of the original document stored in the file area M2 of the page memory 323. If the user depresses another key (not shown) except the stop key on the operation panel 114 in place of depressing the copy key 121, the main CPU 100 makes the key depression to be invalid. An operation to be performed when a jam takes place during a double side printing operation in a group mode in which an original document having a plurality of pages is printed and the printed sheets are divided for each of the same pages will now be described with reference to a flow chart shown in FIGS. 13A and 13B. When a menu has been selected by a user who has operated the operation panel 114, the main CPU 100 causes the LCD display unit 116 to display the mode selection screen (ST31). When a group mode of the double side printing on the selection screen of the LCD display unit 116 has been selected and depressed, the main CPU 100 causes the LCD display unit 116 to display a requirement to set the number of required copies (ST32). After setting (for example, a required number of copies of three) has been performed by the operator (ST33), the main CPU 100 checks whether an original document exists on the automatic original-document supply apparatus 200 in accordance with a detection signal supplied from the original-document detection sensor 29 or checks whether an original document exists on the original-document retainer 2 in accordance with a detection signal supplied from a sensor (not shown) (ST35). If an original document exists, the main CPU 100 causes an instruction to depress the copy key 121 to be displayed on the LCD display unit 116 (ST37). An assumption is performed here that an original document exists on the automatic original-document supply apparatus 200. After the copy key 121 has been depressed by the user (ST38), the automatic original-document supply apparatus 200 starts supplying the original document. Then, the scanner 313 scans (reads) the supplied original document to temporarily store the same in the page buffer region M1 of the page memory 323. Then, the compression/expansion portion 324 compresses image data in the page buffer region M1 to form the same into a file, and then stores the file in the file area M2 of the page memory 323 (ST40). After the compression/expansion means 324 has stored the original document in the file area M2 of the page memory 323 (ST41), the compression/expansion means 324 expands compressed data of the original document formed into the file stored in the file area M2 of the page memory 323. Expanded data is supplied to the printer 315 through the image processing portion 314 so that the double side printing operation starts (ST42). FIG. 16 shows control to be performed in a case where a copying operation is performed in the group mode. In the group mode, the same image is repeatedly printed until instructed number of copies are obtained. In a case where an original document having two sheets is double side printed, the main CPU 100 causes the second page of the original document to be printed by the number of times corresponding to the instructed number of copies and causes the printed sheets to be stacked on the tray 75b of the automatic double side unit 75, as shown in FIG. 14A. After the stacking operation has been completed, the main CPU 100 causes the sheet, on which the second page has been printed, to be discharged from the conveyance passage 75a of the automatic double side unit 75 so that the first page is printed, as shown in FIG. 14B. Similarly to the sorting mode, in the group mode, the number of sheets removed by the user sometimes does not coincide with the number of sheets counted in accordance with the control program of the main CPU 100. FIG. 15A shows a case where a sheet, on which the third sheet of the original document supplied from the tray 75b of the automatic double side unit 75 has been printed, and a sheet, on which a fourth sheet of the same has been printed, have been jammed due to double supply of sheets. If a jam takes place (ST43), the main CPU 100 detects the position of the jam in accordance with information supplied from the detection sensor (not shown) and causes the LCD display unit 116 of the operation panel 114 to display the position of the jam (ST44). In this case, generation of the jam at the discharge port of the automatic double side unit 75 is displayed. The user confirms the display of the jam taken place at the discharge port of the automatic double side unit 75 and removes the two sheets (ST45). However, the main CPU 100 considers that only the sheet having the third sheet printed thereon has been removed, and restarts the following printing operation (ST46). A state where the jam has been solved when the printing operation is caused to restart is shown in FIG. 15B. Therefore, the main CPU 100 prints data for the third sheet, which has been temporarily removed, on a sheet and stacks the sheet on the tray 75b of the automatic double side unit 75, as shown in FIG. 16A. Then, the main CPU 100 discharges a sheet from the tray 75b of the automatic double side unit 75 and prints the first page, as shown in FIG. 16B. Then, the main CPU 100 prints the third and fourth sheets. When the main CPU 100 intends to supply a sheet from the automatic double side unit 75 to print the fifth sheet as shown in FIG. 16C, information indicating no sheet is obtained from the paper sensor 75d (ST47). Thus, the main CPU 100 determines that the sheet corresponding to the fifth sheet lacks. Accordingly, the main CPU 100 prints the omitted sheet (ST48). As shown in FIG. 17A, the second page is printed by one and stacked on the tray 75b of the automatic double side unit 75. Then, as shown in FIG. 17B, a sheet is successively discharged from the tray 75b and the first page is printed to compensate the omitted page. If the pages of the original document which have not been printed exist, the pages are printed in the group mode to obtain the copies by the instructed number (ST49). As described above, according to the embodiment of the present invention, copies can correctly be printed even if a user removes sheets supplied double in a case where a jam takes place during a double side printing operation in a sorting mode or a group mode using an automatic double side unit and/or if a jam takes place due to double supply of sheets.

Claims: An image forming apparatus comprising: image reading means (140) for reading image information of an original document; image forming means (160) for forming an image on an image forming medium in accordance with image information read by said image reading means; means for setting a double side printing mode; memory means (323) for storing the image information read by said image reading means; accumulating means (75a, 75b) for accumulating image forming mediums having first page images formed thereon when said double side printing mode is set; conveying means (75c) for conveying the image forming mediums from the accumulating means (75a, 75b) to said image forming means (160) to form the second page images and for discharging the image forming mediums; first detection means (100, ST13) for detecting occurrence of a jam during conveyance of the image forming medium performed by said conveying means; means (ST15) for interrupting the conveyance when said first detection means has detected occurrence of a jam, so as to enable the operator to remove jammed image forming mediums; second detection means (100, ST17) for detecting, when said double side printing mode is set and after restart of the image forming operation, that the number of second pages for which image information is in the memory means (323) is larger than the number of image forming mediums which can be conveyed from the accumulating means (75a, 75b); and means for displaying (ST19) a message indicating a lack of image forming mediums. The image forming apparatus according to claim 1, further comprising automatic setting means (ST12, ST48) for automatically setting, to said image forming means, lacking image information and the number of times of image forming, and instructing means for instructing said image forming means to start an operation based on said image information and said number of times of image forming set by said automatic setting means (ST21, ST48). The image forming apparatus according to claim 2, further comprising sorting mode setting means (100, ST2) for setting a sorting mode for printing copies of an original document consisting of a plurality of sheets and dividing printed sheets into the copies, and in which said automatic setting means includes means (ST21) for instructing said accumulating means, said conveying means and said image forming means to again perform respective operations for the corresponding copy in accordance with a result of detection performed. The image forming apparatus according to claim 2, further comprising group mode setting means (100, ST32) for setting a group mode for printing copies of an original document consisting of a plurality of sheets and dividing printed sheets into groups each consisting of sheets of the same page. The image forming apparatus according to claim 1, further comprising means for controlling said accumulating means, said conveying means and said image forming means in accordance with the number of removed mediums detected by said second detection means, so as to read, from said storage means, image information corresponding to the images formed on the image forming mediums removed excessively and thus lacking and so as to normally form images represented by the image information. An image forming apparatus according to claim 5, further comprising means (100, ST2, ST32) for selecting either of a sorting mode for printing an original document consisting of a plurality of sheets by a plurality of numbers and dividing the printed sheets into each copy or a group mode for dividing the same for each page, wherein said control means has means (100, ST21) for instructing said conveying means and said image forming means to again perform the respective operations for the corresponding copy in a case where said sorting mode has been selected by said selection means. An image forming apparatus according to claim 5, further comprising means (100, ST2, ST32) for selecting either of a sorting mode for printing an original document consisting of a plurality of sheets by a plurality of numbers and dividing the printed sheets into each copy or a group mode for dividing the same for each page; and means (100, ST42) for automatically setting, to said image forming means, lacking image information and the number of lacking sheets on which the images are required to be formed in a case where said group mode has been selected by said selection means. An image forming method comprising the steps of: setting a double side printing mode; reading image information of an original document; storing the image information read in said reading step in memory means (323); forming first page images on image forming mediums in accordance with corresponding image information read in said reading step; accumulating image forming mediums having first page images formed thereon in said double side printing mode in accumulating means (75a, 75b); conveying the image forming mediums from the accumulating means (75a, 75b) and forming second page images on the image forming mediums and discharging the image forming mediums; detecting occurrence of a jam during conveyance of the image forming mediums performed in said conveying step; interrupting the conveyance when the occurrence of a jam has been detected, so as to enable the operator to remove jammed image forming mediums; detecting, when said double side printing mode is set and after restart of the image forming operation, that the number of second pages for which image information is in the memory means (323) is larger than the number of image forming mediums which can be conveyed from the accumulating means (75a, 75b); and displaying (ST19) a message indicating a lack of image forming mediums.

Inventors: KONNO MIKI, SHIBAKI MASAKO, TAKAHASHI TOSHIHARU, KONNO, MIKI, SHIBAKI, MASAKO, TAKAHASHI, TOSHIHARU
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1996
Main classification: G03G15
IPC codes: G03G15, H04N1, G03G21