Print control method and print apparatus

A reference mark is recorded in an area between one image and the next image sequentially printed on a first surface of a continuous sheet. In a print on a second surface of the sheet, the recorded reference mark is read, and a print position of the image on a second surface of the sheet is set. A plurality of images are sequentially printed on the second surface on the basis of this setting.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a print apparatus and a print control method using a continuous sheet.

2. Description of the Related Art

Japanese Patent Laid-Open NO. 2008-126530 discloses a print apparatus that performs a duplex printing on front and rear faces of a sheet in an inkjet system by using a lengthy continuous sheet wound into a roll. In this apparatus, while an image of a leading edge of the sheet fed from a sheet feeding unit is picked up, print positions for a plurality of subsequent images are set by using this positional information as a reference, and the sheet is cut by a cutter for each image after a print.

As the sheet used in the print apparatus is longer, an accumulation of sheet conveyance errors is larger. Also, in the print apparatus using liquid such as ink, the sheet length itself changes in some cases because of infiltration of moisture into the sheet, evaporation, or heat at the time of drying. As in Japanese Patent Laid-Open NO. 2008-126530, according to a method of picking up an image of a leading edge of the sheet first and using this as a reference for setting a subsequent print position, it is possible to obtain a high accuracy for the print position of the image in the vicinity of the leading edge. However, as being further away from the leading end, an influence of the conveyance error and sheet expansion and contraction is received, and the print displacement becomes larger as the sheet is longer.

In particular, when a plurality of images are disposed and printed sequentially on both faces of a continuous sheet, it is necessary to accurately match the print positions of the images on both the faces to each other, and relative errors of front and rear faces need to be smaller. However, a surface state of the sheet changed upon ink application. In a front face print and a rear face print, the sheet conveyance states are different from each other, and the relative errors tend to be increased. According to the system of Japanese Patent Laid-Open NO. 2008-126530, even when an alignment of the images on the front and rear sides in the vicinity of the leading edge attains a high accuracy, as being further away from the leading end, the influence of the conveyance error and sheet expansion and contraction is received, and an accuracy degradation in the alignment of the image on the front face and the image on the rear side of the sheet is expanded. In other words, as the sheet used in the one-time duplex printing is longer, the displacement of the image on the front face and the image on the rear side tends to be conspicuous.

The present invention has been made on the basis of a recognition of the above-mentioned problems. The present invention provides a print control method and a print apparatus with which when the duplex printing is performed on the continuous sheet, no matter how much the sheet used in the one-time duplex printing is longer, it is possible to suppress the print displacement of the images on the front face and the rear face.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, there is provided a method of performing duplex printing, the method comprising, printing a plurality of images on a first surface of a sheet that is continuous, recording a reference mark in an area between one image and the next image sequentially printed on the first surface, reversing the sheet where the plurality of images are printed on the first surface, reading the reference mark recorded on the first surface of the reversed sheet, setting a position to be printed of an image on a second surface which is a back of the first surface, on the basis of the reading of the reference mark, and printing a plurality of images on the second surface.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a description will be provided of a print apparatus using an inkjet system according to an embodiment. The print apparatus of the present example is a high speed line printer that uses a lengthy continuous sheet (long continuous sheet which is longer than a length of a repetitive print unit in a conveying direction (which is referred to as one page or unit image)) and deals with both a simplex printing and a duplex printing. For example, this is suitable to a field of a large amount of prints in a print laboratory or the like. It is noted that according to the present specification, even when a plurality of small images, characters, and spaces are mixed in an area of one print unit (one page), the components included in the relevant area are collectively referred as one unit image. In other words, the unit image means one print unit (one page) in a case where a plurality of pages are sequentially printed on the continuous sheet. It is noted that this may simply be referred to as image instead of unit image in some cases. A length of the unit image varies in accordance with a size of an image to be printed. For example, for a photograph of L-plate size, the length in a sheet conveying direction is 135 mm, and for A4 size, the length in the sheet conveying direction is 297 mm.

The present invention can widely be applied to print apparatuses such as a printer, a printer multi-function device, a copier, a facsimile apparatus, and a manufacturing apparatus for various devices. A print processing may adopt any system such as the inkjet system, an electrophotography system, a thermal transfer system, a dot impact system, and a liquid development system. Also, the present invention can also be applied to a sheet processing apparatus that performs not only the print processing but also various processings on a roll sheet (such as recording, process, application, irradiation, reading, and inspection).

FIG. 1is a schematic diagram of a cross section illustrating an internal configuration of the print apparatus. The print apparatus according to the present embodiment can perform the duplex printing on a first surface of the sheet and a second surface on a back side of the first surface by using the sheet wound into a roll. In the print apparatus, roughly, respective units including a sheet feeding unit1, a decurling unit2, a skew correction unit3, a print unit4, an inspection unit5, a cutter unit6, an information recording unit7, a drying unit8, a reverse unit9, a discharge conveyance unit10, a sorter unit11, a discharge unit12, and a control unit13are provided. The sheet is conveyed by a conveyance mechanism composed of a roller pair and a belt along a sheet conveyance path represented in the solid line in the drawing and processed in the respective units. The sheet is conveyed downstream along the sheet conveyance path while printing. At an arbitrary position in the sheet conveyance path where the sheet is conveyed from feeding means to discharging means, a side toward the feeding means is referred to as “the upstream side”, and the opposite side toward the discharging means is referred to as “the downstream side”.

The sheet feeding unit1is a unit for holding and feeding the continuous sheet wound into the roll. The sheet feeding unit can accommodate two rolls R1and R2and has a configuration of alternatively pulling out the sheet to be fed. It is noted that the number of rolls that can be accommodated is not limited to two, and the sheet feeding unit may accommodate one roll or three or more rolls. Also, as long as the sheet is a continuous sheet, the sheet is not limited to the sheet wound into the roll. For example, the continuous sheet may be provided with a perforation for every unit length and folded for each perforation to be stacked and accommodated in the sheet feeding unit1.

The decurling unit2is a unit that suppresses a curl (warping) of the sheet fed from the sheet feeding unit1. In the decurling unit2, by using two pinch rollers for one driving roller, the sheet is bent and allowed to pass so that a warping in a reverse way to the curl is provided, and a decurling force is affected to suppress the curl.

The skew correction unit3is a unit that corrects a skew of the sheet passing through the decurling unit2(inclination with respect to the original travelling direction). By pressing a sheet end part on a side serving as the reference against a guide member, the skew of the sheet is corrected.

The print unit4is a sheet processing unit that performs a print processing on a sheet by a print head14with respect to the conveyed sheet to form an image. In other words, the print unit4is a processing unit that performs a predetermined processing on the sheet. The print unit4is also provided with a plurality of conveying rollers for conveying the sheet. The print head14has a line-type print head in which an inkjet system nozzle array is formed in a range covering a maximum width of a sheet expected to be used. In the print head14, a plurality of print heads are disposed in parallel in the conveying direction. In the present example, seven print heads corresponding to seven colors including C (cyan), M (magenta), Y (yellow), LC (light cyan), LM (light magenta), G (gray), and K (black) are provided. It is noted that the number of colors and the number of print heads are not limited to seven. For the inkjet system, a system using a heater element, a system using a piezoelectric element, a system using an electrostatic element, a system using an MEMS element, or the like can be adopted. Ink of the respective colors is supplied from an ink tank via respective ink tubes to the print head14.

The inspection unit5is a unit for optically reading an inspection pattern or an image printed by the print unit4on the sheet by using a scanner and inspecting a nozzle state of the print head, a sheet conveyance state, an image position, or the like to determine whether the image is correctly printed. The scanner has a CCD image sensor or a CMOS image sensor.

The cutter unit6is a unit provided with a mechanical cutter20for cutting the sheet after the print at a predetermined length. The cutter unit6is further provided with a cut mark sensor19that optically detects the cut mark recorded on the sheet and a plurality of conveying rollers for sending out the sheet to the next step. In the vicinity of the cutter unit6, a dust bin17is provided. The dust bin17is designed to accommodate small sheet scraps generated while the margin areas are cut off by the cutter unit6and discharged as litter. The cutter unit6is provided with a sorting mechanism for deciding whether the cut sheet is discharged into the dust bin17or shifted to the original conveyance path.

The information recording unit7is a unit that records print information (unique information) such as a serial number for the print or a date in a non-print area of the cut sheet. The recording is carried out by printing a character or a code on the basis of the inkjet system, the thermal transfer system, or the like. On the upstream of the information recording unit7and also on the downstream of the cutter unit6, an edge sensor21that detects the leading end edge of the cut sheet is provided. In other words, regarding the edge sensor21, on the basis of the detection timing for the edge sensor21that detects the end part of the sheet between the recording positions by the cutter unit6and the information recording unit7, the timing for the information recording unit7to perform the information recording is controlled.

The drying unit8is a unit for drying the applied ink in a short period of time by heating the sheet printed by the print unit4. Inside the drying unit8, heated air is blown to the passing sheet at least from a lower face to dry the ink applied face. It is noted that the drying system is not limited to the system of blowing the heated air but may also be a system of irradiating the sheet surface with electromagnetic waves (ultraviolet rays, ultrared rays, or the like).

The above-mentioned sheet conveyance path from the sheet feeding unit1to the drying unit8is referred to as first path. The first path has a U-turn shape between the print unit4and the drying unit8, and the cutter unit6is located in the midcourse of the U-turn shape.

The reverse unit9is a unit for temporarily rolling up the continuous sheet whose front face print is ended when the duplex printing is to be carried out to reverse the front and rear sides. The reverse unit9is provided in the midcourse of a path starting from the drying unit8via the decurling unit2to reach the print unit4(loop path) (which will be referred to as second path) for feeding the sheet passing through the drying unit8to the print unit4again. The reverse unit9is provided with a winding rotary member (drum) rotating so as to roll up the sheep. The uncut continuous sheet where the print is performed on the front face is temporarily rolled up by the winding rotary member. When the rolling-up is ended, the winding rotary member inversely rotates, and the wound sheet is sent out in reverse to the rolling-up to be fed to the decurling unit2and fed to the print unit4. The sides of this sheet are reversed, and it is possible to carry out the print on the rear face by the print unit4. A more specific operation of the duplex printing will be described below.

The discharge conveyance unit10is a unit that conveys the sheet cut by the cutter unit6and dried by the drying unit8to be delivered to the sorter unit11. The discharge conveyance unit10is provided on a path (which will be referred to as third path) which is different from the second path where the reverse unit9is provided. In order that the sheet conveyed through the first path is selectively guided to one of the second path and the third path, a path switching mechanism having a movable flapper is provided at a blanching position of the path.

The sorter unit11and the discharge unit12are provided on a side end of the sheet feeding unit1and also on a tail end of the third path. The sorter unit11is a unit for sorting the printed sheets when necessary for each group. The sorted sheets are discharged into the discharge unit12composed of a plurality of trays. In this manner, the third path has such a layout that the sheet passes below the sheet feeding unit1to be discharged on the opposite side to the print unit4and the drying unit8while sandwiching the sheet feeding unit1.

As described above, the sheet feeding unit1to the drying unit8are sequentially provided in the first path. A section after the drying unit8is blanched to the second path and the third path. In the midcourse of the second path, the reverse unit9is provided, and a section after the reverse unit9is merged into the first path. The discharge unit12is provided at the tail end of the third path.

The control unit13is a unit that governs the control on the respective units of the entire print apparatus. The control unit13has a CPU, a storage apparatus, a controller provided with various control units, an external interface, and an operation unit15through which a user performs the input and output. An operation of the print apparatus is controlled on the basis of an instruction from a host apparatus16such as a controller or a host computer connected via the external interface to the controller.

A mark reader18is provided between the skew correction unit3and the print unit4. The mark reader18is a reflective optical sensor that optically reads the reference mark recorded on the first surface of the sheet conveyed from the reverse unit9from the opposite side to the side where the print is carried out. The mark reader18is a light source that illuminates the sheet face (for example, white LED) and a photo diode or the photoreceiver such as an image sensor that detects the light from the illuminated sheet face for each RGB component. The mark can be read on the basis of a change in a signal level of the photoreceiver or an image analysis on image pickup data. As will be described below, by using a detection timing of a reference pattern by the mark reader18as a trigger, positions for printing the images on the rear face are set, and recording positions for the cut marks serving as the reference for finally cutting the sheet by the cutter for each unit image are set.

FIG. 2is a block diagram illustrating a concept of the control unit13. A controller (range surrounded by a broken line) included in the control unit13is composed of a CPU201, a ROM202, a RAM203, an HDD204, an image processing unit207, an engine control unit208, and an individual unit control unit209. The CPU201(central processing unit) integrally controls the operations of the respective units in the print apparatus. The ROM202stores a program executed by the CPU201and fixed data used for various operations of the print apparatus. The RAM203is used as a work area for the CPU201, used as a temporary storage area for various pieces of reception data, and configured to store various pieces of setting data. The HDD204(hard disc drive) can store and read the program executed by the CPU201, print data, and setting information used for various operations of the print apparatus. The operation unit15is an input and output interface with the user and includes an input unit such as a hard key or a touch panel and an output unit such as a display for presenting the information or an audio generator.

With regard to a unit required to perform a high speed data processing, a dedicated-use processing unit is provided. The image processing unit207performs an image processing on the print data dealt with by the print apparatus. A color space of the input image data (for example, YCbCr) is converted into a standard RGB color space (for example, sRGB). Also, various image processings such as a resolution conversion, an image analysis, and an image compensation are applied on the image data as needed. The print data obtained through these image processings is stored in the RAM203or the HDD204. On the basis of a control command received from the CPU201or the like, in accordance with the print data, the engine control unit208performs a drive control on the print head14of the print unit4. The engine control unit208further performs a control of the conveyance mechanism of the respective units in the print apparatus. The individual unit control unit209is a sub controller for individually controlling the respective units of the sheet feeding unit1, the decurling unit2, the skew correction unit3, the inspection unit5, the cutter unit6, the information recording unit7, the drying unit8, the reverse unit9, the discharge conveyance unit10, the sorter unit11, and the discharge unit12. The operations of the respective units are controlled by the individual unit control unit209on the basis of the instruction of the CPU201. An external interface205is an interface (I/F) for connecting the controller to the host apparatus16, which is a local I/F or a network I/F. The above-mentioned components are connected via a system bus210.

The host apparatus16is an apparatus functioning as a supply source for the image data to be printed by the print apparatus. The host apparatus16may be composed of a general-use or dedicated-use computer or also a dedicated-use image device such as an image capture having an image reader, a digital camera, or a photo storage. In a case where the host apparatus16is composed of a computer, an OS, application software for generating image data, and a printer driver for the print apparatus are installed in the storage apparatus included in the computer. It is noted that all of the above-mentioned processings may not be realized by the software, and a part or all of the above-mentioned processings may also be realized by hardware.

Next, a description will be provided of a basic operation at the time of the print. The print has different operations in the simplex printing mode and the duplex printing mode, and therefore each of the print modes will be described.

FIG. 3Ais an explanatory diagram for describing the operation in the simplex printing mode. The sheet fed from the sheet feeding unit1and processed by the decurling unit2, the skew correction unit3the print unit4is subjected to the print on the front face (first surface). On the lengthy continuous sheet, the image having a predetermined unit length in the conveying direction (unit image) is sequentially printed, and a plurality of images are disposed and formed. Herein, a margin area is provided between a certain image and the next image, and a cut mark is recorded in the margin area by the print unit4. The printed sheet passes through the inspection unit5and is cut by the cutter20for each unit image on the basis of the detection of the cut mark by the cut mark sensor19in the cutter unit6. On the cut sheet thus cut, as needed, the print information is recorded on the rear face of the sheet by the information recording unit7. Then, the cut sheet is conveyed one by one to the drying unit8for performing the drying. After that, the sheet passes through the discharge conveyance unit10and is sequentially discharged into the discharge unit12of the sorter unit11to be stacked. On the other hand, the sheet remaining on the side of the print unit4after the cut of the last unit image is fed back to the sheet feeding unit1, and the sheet is rolled up by the roll R1or R2.

In this manner, in the simplex printing, the sheet passes through the first path and the third path to be processed but does not pass through the second path. To elaborate, in the simplex printing mode, under the control of the control unit13, the following sequence of (1) to (6) is executed:(1) the sheet is fed out from the sheet feeding unit1to be fed to the print unit4;(2) the print of the unit image and the cut mark on the first surface of the fed sheet is repeatedly performed by the print unit4;(3) the cut of the sheet is repeatedly performed by the cutter unit6for each unit image printed on the first surface;(4) the cut sheet is caused to pass through the drying unit8one by one for each unit image;(5) the sheet passing through the drying unit8one by one is caused to pass through the third path to be discharged into the discharge unit12; and(6) the last unit image is cut, and the sheet remaining on the side of the print unit4is fed beck to the sheet feeding unit1.

FIG. 3Bis an explanatory diagram for describing the operation in the duplex printing mode. In the duplex printing, following the front face (the first surface) print sequence, the rear face (the second surface) print sequence is executed. In the first front face print sequence, the operations of the respective units from the sheet feeding unit1to the inspection unit5are the same as the above-mentioned operations in the simplex printing. In the cutter unit6, the cutting operation is not carried out, and the sheet is conveyed to the drying unit8as the continuous sheet. After drying the ink on the front face by the drying unit8, the sheet is guided to the path on the side of the reverse unit9(the second path) instead of the path on the side of the discharge conveyance unit10(the third path). On the second path, the sheet is rolled up by the winding rotary member of the reverse unit9that rotates in a forward direction (in the drawing, a counterclockwise direction). In the print unit4, when the planed front face prints are all ended, the rear end of the print area of the continuous sheet is cut by the cutter unit6. While the cut position is set as the reference, the continuous sheet on the downstream side in the conveying direction (the printed side) passes through the drying unit8and is rolled up by the reverse unit9up to the sheet trailing end (cut position). On the other hand, at the same time as this rolling-up, the continuous sheet remaining on the upstream side in the conveying direction with respect to the cut position (on the side of the print unit4) is rewound to the sheet feeding unit1so that the sheet leading end (cut position) does not remain in the decurling unit2, and the sheet is rolled up to the roll R1or R2. By this rewinding, the collision with the sheet fed again in the following rear face print sequence is avoided.

After the above-mentioned front face print sequence, the sequence is switched to the rear face print sequence. The winding rotary member of the reverse unit9rotates in a direction reverse to the direction at the time of the rolling up (in the drawing, the clockwise direction). The end part of the wound sheet (the sheet trailing end at the time of the rolling-up becomes the sheet leading end at the time of the feeding-out) is fed into the decurling unit2along the path represented by the broken line in the drawing. In the decurling unit2, the correction on the curl applied by the winding rotary member is carried out. In other words, the decurling unit2is provided between the sheet feeding unit1and the print unit4in the first path and also between the reverse unit9and the print unit4in the second path and becomes a common unit functioning as the decurling in any of the paths. The sheet whose front and rear sides are reversed passes through the skew correction unit3and is fed to the print unit4where the print of the unit image and the cut mark on the rear face of the sheet is carried out. The printed sheet passes through the inspection unit5and is cut at a predetermined unit length which is set in advance in the cutter unit6. As the print is carried out on both the sides of the cut sheet has, the recording is not performed by the information recording unit7. The cut sheet is conveyed one by one to the drying unit8and passes through the discharge conveyance unit10to be sequentially discharged into the discharge unit12of the sorter unit11and stacked.

In this manner, in the duplex printing, the sheet passes through the first path, the second path, the first path, and the third path in the stated order to be processed. To elaborate, in the duplex printing mode, under the control of the control unit13, the following sequence of (1) to (11) is executed:(1) the sheet is fed out from the sheet feeding unit1to be fed to the print unit4;(2) the print of the unit image is repeatedly performed by the print unit4on the first surface of the fed sheet;(3) the sheet where the print is performed on the first surface is caused to pass through the drying unit8;(4) the sheet passing through the drying unit8is guided to the second path and rolled up by the winding rotary member provided to the reverse unit9;(5) when the repetitive print on the first surface is ended, the sheet is cut by the cutter unit6after the lastly printed unit image;(6) the sheet is rolled up to the winding rotary member until the end part of the cut sheet passes through the drying unit8to reach the winding rotary member. Together with this, the sheet cut and left on the side of the print unit4is fed back to the sheet feeding unit1;(7) after the rolling-up is ended, the winding rotary member is inverted rotated, and the sheet is fed from the second path to the print unit4again;(8) the print of the unit image and the cut mark is repeatedly performed on the second surface of the sheet fed from the second path in the print unit4;(9) the cut of the sheet is repeatedly performed in the cutter unit6for each unit image where the print is performed on the second surface;(10) the cut sheet is caused to pass through the drying unit8one by one for each unit image; and(11) the sheet passing through the drying unit8is caused to pass through the third path one by one to be discharged into the discharge unit12.

Next, in the print apparatus having the above-mentioned configuration, the print control method with which it is possible to suppress the print displacement of the front face and the rear face at the time of the duplex printing will be described in more detail.

FIG. 4is an explanatory diagram for describing a print order of a plurality of images (pages) in the duplex printing mode according to a second embodiment. While following the control of the control unit13, first, by the print head14of the print unit4, on the front face (first surface) of the sheet, a plurality of images100are sequentially printed every two pages also in the page ascending order (odd-numbered pages P1, P3, . . . , P9, P11) in succession. At that time, a reference mark120is recorded in each margin area101between a certain one image100and the next image100by the print head14. In other words, the continuous sequential print of the plurality of images mentioned herein means continuous image print including the recording in the margin area in one face of the sheet.

The reference mark120has a color and a shape which can be clearly identified by the mark reader18.FIG. 5illustrates an example of a specific shape of the reference mark. The reference mark120is formed in the margin area101between one certain image100(n-th page: n is an odd number) and the next image100((n+2)-th page). One reference mark120is composed of a line segment120aformed along the direction of the sheet width and two line segments120bwhich are formed along the sheet conveying direction at both ends of the line segment120aand which are shorter than the line segment120a. The mark reader18obtains the position information in the sheet conveying direction through the detection of the line segment120a. Furthermore, when the line segment120ais detected at a plurality of positions in the sheet width direction, it is possible to obtain information on an inclination of the sheet (skew component). On the other hand, through the detection of the two line segments120b, it is possible to obtain information on the sheet expansion and contraction in the sheet width direction or the displacement from the interval and the positions thereof. It is noted that the reference mark may omit the line segments120bas long as at least the line segment120aexists because a main aim is to obtain the position information in the sheet conveying direction.

While a plurality of images are printed on the first surface, the sheet area after the print is rolled up by the reverse unit9. When the last image expected to be printed on the first surface is printed, the print head14records a last cut mark121in an area after the last image. In the cutter unit6, the cut mark sensor19built in as described above detects the last cut mark121, and the sheet is cut. The reverse unit9rolls up all the cut sheets.

Subsequently, the rear face print is started. In the rear face print, the sheet passes through the print unit4in a direction opposite to the direction at the time of the front face print. Thus, on the second surface, a plurality of images110are sequentially printed every two pages also in the descending order (even-numbered pages P12, P10, . . . , P4, P2) in succession. The margin area111is provided between the respective the images110, and a cut mark122is formed in the margin area111.

FIG. 7is a flow chart for an operation sequence in a rear face print. These operations are executed by the control of the control unit13. In step S10, the reverse unit9inversely rotates to feed the sheet to be fed to the print unit4again. In step S11, the reference mark120on the first surface of the sheet where the front and rear faces are reversed is read by the mark reader18located on the upstream with respect to the print position of the print unit4. That is, at a faster timing than the start of the print, the reference mark120is read. A sheet conveyance speed for the sheets in the print unit4is constant, and therefore a time from the reading timing for the reference mark120to the start of the print of the corresponding cut mark and image becomes a predetermined time. The following computations in step S12and step S13are performed within this predetermined period of time.

In step S12, on the basis of the reading timing of the reference mark120in step S11, the image print position for the second surface is computed and set. To be more specific, a print start position for starting the print of the image on the second surface corresponding to the image on the first surface is set. If the image on the first surface and the image to be printed on its rear face have the same size, the image print position on the second surface is at the position precisely matched with the image on the first surface on the front and rear faces.

In step S13, on the basis of the reading timing for the reference mark in step S11, a recording position for the cut mark122that should be recorded in the margin area111between the one image110and the next image110on the second surface is computed and set. It is noted that the order of step S12and step S13may be swapped. The cut mark122has a color and a shape which can be clearly identified by the cut mark sensor19. The recording position for the cut mark122is a position matched on the front and rear faces with the reference mark120recorded on the first surface in the sheet conveying direction. It is noted that the reference mark120may not necessarily be matched with the cut mark122on the front and rear faces, and a slight displacement may be accepted.

In step S14, the cut mark122is recorded at the set recording position following the image print in step S13. In step S15, at the set image print position on the second surface, the image corresponding to the image on the first surface is printed. These recording and print are performed while on the basis of the detection signal of the encoder provided to the conveying roller of the print unit4, at a timing at which the cut mark recording position and the image print position on the sheet passes through the print head14, the ink is ejected from the print head14.

In step S16, the cut mark122recorded in step S14on the second surface is detected by the cut mark sensor19. In step S17, on the basis of the timing at which the cut mark122is detected in step S16, the sheet is cut for each unit image. The sheet of the cut unit image (cut sheet) passes through the drying unit8and is discharged as the finished product. The margin area is cut off through the cut, and the sheet scrap is discharged as litter. This sheet scrap is discharged into the dust bin17provided in the vicinity of the cutter unit6.

Herein, a technique for a sheet cut by the cutter unit6for each unit image will be described below.FIG. 6illustrates the cut mark122recorded in the margin area111between one image110(m-th page: m is an even number)) and the next image110((m+2)-th page) in the rear face print. It is noted that inFIG. 6, for convenience of the description, the arrangement order of the images in the rear face print is left-right reversal to that ofFIG. 4. The cut mark122is detected by the cut mark sensor19built in the cutter unit6, and the control unit13sets the cut position of the sheet on the basis of the detection result to perform a control so that the image printed on the second surface is cut for each unit image.

In the cut mark detection (step S16), in order to reduce the possibility that a part of the images printed before and after the margin area is misidentified as the cut mark, a search range for the detection in the cut mark sensor19is limited to a range between a detection start position406and a detection end position407. The detection start position406and the detection end position407are respectively represented by relative distances from the sheet leading end or an immediately before cut position200. These positions are set while taking into account the sheet conveyance error. From the information on the already detected one or earlier cut mark and the printed image size, a position where the cut mark is most likely located is obtained, and this position is preferably set as an intermediate position of the search range. An anterior cut position401and a posterior cut position405are cut positions by the cutter while the cut mark122is used as the reference. The respective positions are represented by relative distances from the position of the cut mark122(an anterior distance408and a posterior distance409). In a case where a frameless print is performed, the anterior cut position401is located to be slightly displaced on the upstream side from a rear end position402of the image110at the m-th page, and the posterior cut position405is located to be slightly displaced on the downstream side from a leading end position404of the image110at the (m+2)-th page. The respective parameters in the above-mentioned sheet cut are summarized in Table 1.

TABLE 1Detection search range inDetection start position (406)cut mark sensor (19)Detection end position (407)Cut position by cutterAnterior cut position (401)(20)Posterior cut position (401)

While referring back to the flow chart ofFIG. 4, in step S18, it is determined whether the print of a plurality of images on the second surface is completed by the expected number of pages (same as the number of pages on the first surface). In a case where a result of the determination is NO, the flow returns to step S11, and a similar operation is repeatedly performed. In a case where the result of the determination is YES, the print sequence is ended.

It is noted that according to the present embodiment, the detection of the cut mark is carried out by the cut mark sensor19provided to the cutter unit6, but the inspection unit5may detect the cut mark and the cutting by the cutter may be control from the detection timing.

Incidentally, in the above-mentioned operation sequence in the duplex printing, when the cut mark sensor19detects the cut mark, possibilities exist that the cut mark cannot be detected because of various factors, and therefore a recovery unit therefore is preferably provided. Two possibilities exist that either the last cut mark121at the rear end on the first surface or the plurality of cut marks122on the second surface cannot be detected. First, a case will be described in which the last cut mark121cannot be detected.

As an example of a factor causing the detection failure, due to running out of the ink in the print head14or temporary clogging of the nozzle, a case exists in which the record failure of the cut mark is caused. Also, due to a partial scratch or dirt on the sheet surface, a case exists in which the record failure of the cut mark is caused. Also, a case exists in which the cut mark sensor19receives electric or optical noise and has disconnecting to cause the detection failure.

In a case where the last cut mark121recorded at the last of the front face print cannot be detected, it is necessary to estimate the cut mark position in some way. As described with reference toFIG. 6, in the cut mark sensor19, the search for the cut mark is made in the limited range from the detection start position to the detection end position. In a case where the last cut mark121cannot be detected through the search in this range, it is estimated that the cut mark is detected at a certain position in the search range (for example, the intermediate position from the detection start position406to the detection end position407, or the detection end position407). Then, on the basis of this estimation, the cut position is set, and the sheet is cut by the cutter20. As the cutting is performed on the basis of the estimation, the end part of the sheet cut and rolled up by the reverse unit9(the margin after the last image in the front face print, and this becomes the margin before the leading image in the rear face print) may have a length different from the original length. However, this is the sheet end part where the image does not continue any longer, and no problem occurs.

In a case where the last cut mark121cannot be detected, this effect is displayed on the operation unit15to notify the user. The user viewing the display performs a maintenance as needed. Subsequently, the rear face print is started. The mark reader18reads the reference mark120recorded at the beginning of the sheet fed from the reverse unit9, and by using this as a trigger, the print of the rear face image and the recording of the cut mark are carried out. Therefore, even if the last cut mark121cannot be detected, it is possible to certainly perform the duplex printing without receiving the influence.

Next, a description will be provided of a recovery in a case where one of the plurality of cut marks122inFIG. 4cannot be detected. As an example of a factor causing the detection failure, due to running out of the ink in the print head14or temporary clogging of the nozzle, a case exists in which the record failure of the cut mark is caused. Also, due to a partial scratch or dirt on the sheet surface, a case exists in which the record failure of the cut mark is caused. Also, a case exists in which the cut mark sensor19receives electric or optical noise and has disconnecting to cause the detection failure. Furthermore, a case exists in which the mark reader18receives electric or optical noise and cannot obtain the trigger to record the cut mark so that the cut mark is not recorded.

In a case where the cut mark122cannot be detected during the rear face print, it is necessary to estimate the position of the cut mark in some way. As described with reference toFIG. 6, in the cut mark sensor19, the cut mark is searched for in the limited range from the detection start position to the detection end position. In a case where the last cut mark121cannot be detected through the search in this range, it is estimated that the cut mark is detected at the intermediate position in the search range (intermediate position from the detection start position406to the detection end position407). The intermediate position in the search range is a most likely position where the cut mark is located that is obtained from the information on the already detected one or earlier cut mark and the printed image size. For that reason, as long as the plurality of cut marks122cannot be detected continuously (only one or a small number of the cut marks122cannot accidentally be detected in many cases), the estimation has a high reliability to a large degree. After the estimation is made in this manner, as described with reference toFIG. 6, the anterior cut position401and the posterior cut position405are set to cut the sheet.

To be more reliable, the anterior cut position401and the posterior cut position405are set in the following manner. The anterior cut position401is set at a position added with a predetermined distance on the downstream side as compared with the original configuration, and the posterior cut position405is set at a position added with a predetermined distance on the upstream side as compared with the original configuration. In other words, the area sandwiched by the anterior cut position401and the posterior cut position405(sheet scrap cut off as litter) is narrower as compared with the original configuration. According to this, even when an error exists in the estimation on the position of the cut mark122, it is possible to reduce the possibility that the end part is missing because of an excess cut of the adjacent images as compared with the original configuration. In this case, the cut sheet cut and discharged into the discharge unit12may be larger than another cut sheet in the size in the sheet conveying direction, and a possibility exists that the margin is left at the end part. In view of the above, this effect is displayed on the operation unit15to notify the user. To facilitate the visual check by the user, only the cut sheets in which the size may be different are sorted by the sorter unit11to be output to a different tray from the other sheets.

In the above, the recording and the detection of the cut mark in the rear face print in the duplex printing mode have been described, but in the simplex printing mode too, a similar operation sequence is performed. That is, in the simplex printing mode too, the cut mark is recorded in the area between one image and the next image to be printed, and when the cut mark is detected, the cut position of the sheet is set on the basis of a detection result. It is however noted that the reference mark is not recorded, but the cut mark is directly recorded. If the cut mark cannot be detected, on the basis of the information on the already detected cut mark, the cut mark position where the detection cannot be performed is estimated, and the cut position of the sheet is set on the basis of this estimation. Then, the sheet after the print is cut at the set cut position. Herein, the cut positions are set at two positions before and after the cut mark, and the area between one image and the next image to be printed is cut off.

According to the above-mentioned embodiment, when a plurality of images are sequentially printed on the first surface of the sheet in succession, the reference mark is recorded in the margin area between one image and the next image to be printed. Herein, the embodiment is not limited to the mode in which the reference marks are recorded in all the margin areas between the images on the first surface. The reference mark may also be recorded once in a predetermined number of images (2 or more). In this case, in the rear face print, on the basis of the one-time detection of the reference mark, across the several images until the next reference mark is detected, the image print positions on the second surface and the cut mark positions are respectively estimated.

Also, according to the above-mentioned embodiment, on the basis of the detection of the reference mark, the cut mark is recorded in the margin area between one image and the next image on the second surface to cut the sheet. Herein, the embodiment is not limited to the mode in which the cut marks are recorded while corresponding to all the detected reference marks. Each time when a predetermined number of the reference marks (2 or more) are detected, the recording of the cut mark may be performed once. In this case, on the basis of the one-time cut mark, the cut positions for a several images are estimated until the next cut mark is detected, and the sheet is cut by the cutter.

As described above, the print position of the image on the second surface is set on the basis of the detection of the reference mark recorded on the first surface, the positions of the images on the first surface and the second surface are accurately matched with each other. In addition, the plurality of reference marks are recorded while the plurality of images are sequentially printed on the first surface. Thus, no matter how much the sheet used in the one-time duplex printing is longer, the print displacement of the images on the front face and the rear face does not occur.

Also, the cut mark is recorded in the margin area between one image and the next image on the second surface on the basis of the detection of the reference mark, and the sheet cut position is set on the basis of the detection of the cut mark to cut the sheet. According to this, it is possible to particularly accurately carry out the sheet cut for each final unit image.

Also, the cut mark is recorded and detected and the cut position of the sheet is set, and even in a case where the cut mark cannot be detected, the cut position of the sheet is set through the estimation. Thus, the sheet cut can be carried out at the accurate position.

Also, on a downstream of the print position, the cut mark is detected by the sensor provided at the position even closer to the cut position. For that reason, even in a case in which the sheet is warped or bent to form a loop in a sheet conveyance path between the print position of the image and the cutter and the sheet lengths fluctuate, it is possible to perform the sheet cut at the accurate position.

This application claims the benefit of Japanese Patent Application No. 2010-042347 filed Feb. 26, 2010, which is hereby incorporated by reference herein in its entirety.