Patent Description:
Conventionally, a printing apparatus having a sheet stacking apparatus for stacking printed sheets discharged from the apparatus housing is known. In <CIT>, it is disclosed that a grip unit for holding the stacked sheet bundle is provided at predetermined intervals on a conveyor which is a sheet stacking unit. Further, it discloses that in order to improve visibility of a stacked sheet bundle, a sheet bundle for each job is held by a grip unit and the conveyor is moved by a predetermined amount. <CIT> relates to a printing apparatus for sorting printing paper in each of a plurality of printing paper groups, without causing irregularities in a stacked state, even if printing papers of different sizes coexist in the same group.

The present invention in its first aspect provides a sheet stacking apparatus as specified in claims <NUM> to <NUM>.

The present invention in its second aspect provides a printing apparatus as specified in claim <NUM>.

The present invention in its third aspect provides a control method as specified in claims <NUM> to <NUM>.

The present invention in its fourth aspect provides a computer program as specified in claim <NUM>.

In the above prior art, since the distance between the grip units is fixed, when the discharged sheets are shorter than the distance between the grip units, the distance between adjacent sheet bundles is larger, and the number of sheets that can be stacked on the stacking unit is lower. On the other hand, when the discharged sheets are longer than the interval between the grip units, adjacent sheet bundles overlap with each other, and the workability of retrieving the sheet bundles may suffer.

Embodiments of the present invention provide a technique by which it is possible to stack a larger number of sheets while reducing diminished workability in retrieval of sheet bundles.

Note, the following embodiments are not intended to limit the scope of the claimed invention, which is solely defined by the appended claims.

In this specification, the term "printing" (sometimes referred to as "recording") is not limited to the case of forming meaningful information such as characters, graphics, and the like, and also may be the case of forming meaningless information. Furthermore, "print" broadly encompasses cases in which an image or pattern is formed on a print medium irrespective of whether or not it is something that a person can visually perceive, and cases in which a medium is processed.

In addition, the "print medium" is not limited to paper used in a general printing apparatus, but broadly represents something that can receive ink such as cloth, plastic film, metal plate, glass, ceramics, wood, leather, and the like.

In addition, "ink" (sometimes referred to as "liquid") should be construed broadly similarly to the above definition for "printing". Accordingly, "ink" encompasses liquids that by being applied to a print medium can be supplied in the forming of images, patterns or the like, processing of print mediums, or processing of ink (for example, insolubilization or freezing of a colorant in ink applied to a print medium).

Furthermore, unless otherwise specified, the term "nozzle" generally refers to an ejection port or a liquid path communicating therewith, and an element for generating energy used for ink ejection.

<FIG> is a diagram schematically illustrating the internal structure of a printing system SY according to an embodiment. The printing system SY of the present embodiment is a high-speed ink jet type line printer which uses a continuous sheet wound in a roll shape and supports both single-sided printing and double-sided printing. The printing system SY can be used in the field of large-volume printing in a photo printing lab, for example, or the like.

The printing system SY includes a printing apparatus <NUM> and a sheet stacking apparatus <NUM>. The printing apparatus <NUM> includes a sheet supply unit <NUM>, a curl correction unit <NUM>, a skew correction unit <NUM>, a printing unit <NUM>, an inspection unit <NUM>, a cutter unit <NUM>, an information printing unit <NUM>, a drying unit <NUM>, a winding unit <NUM>, a discharge unit <NUM>, and a control unit <NUM>. The sheet is conveyed by a conveyance mechanism including a roller pair, a belt, and a motor for driving the rollers along a sheet conveyance path indicated by a solid line in the drawing, and processing is performed by each unit.

The sheet supply unit <NUM> is a unit for accommodating the continuous sheet wound in a roll shape (roll sheet) as well as supplying to the conveyance path by pulling out the stored continuous sheet. In the present embodiment, the sheet supply unit <NUM> can accommodate two rolls R1 and R2, and is configured to alternatively draw out and supply a sheet. It should be noted that the number of rolls that the sheet supply unit <NUM> can accommodate is not limited to two, and a configuration in which the sheet supply unit <NUM> accommodates one roll, or three or more rolls can be adopted.

The curl correction unit <NUM> is a unit for reducing the curl (warpage) of a sheet supplied from the sheet supply unit <NUM>. In the present embodiment, the curl correction unit <NUM> reduces curl by bending the sheet so as to curve in the opposite direction of the curl and squeeze it by using two pinch rollers with respect to one driving roller.

The skew correction unit <NUM> is a unit for correcting skew (inclination with respect to the original traveling direction) of the sheet passing through the curl correction unit <NUM>. For example, skew correction unit <NUM> corrects a skewed sheet by pressing, against a guide member, one end, which is to serve as a reference, of the two sheet ends in the width direction that intersects the sheet conveyance direction.

The printing unit <NUM> is a unit for printing an image on a conveyed sheet. For example, the printing unit <NUM> includes a print head unit <NUM> and a plurality conveyance rollers which are conveyance members for conveying sheets.

The print head unit <NUM> of the present embodiment includes a plurality of print heads, and each print head is formed with an ink-jet nozzle row in a range covering the maximum width of sheet to be used. In this embodiment, a plurality of print heads are arranged in parallel along the conveyance direction. As an example, the print head unit <NUM> includes seven print heads corresponding to seven colors of C (cyan), M (magenta), Y (yellow), LC (light cyan), LM (light magenta), G (gray), and K (black). The number of colors of ink and the number of print heads are not limited to seven, and may be changed as appropriate.

As the method by which the print head ejects ink, a method using a heating element, a method using a piezo element, a method using an electrostatic element, a method using a MEMS element, or the like can be adopted. The inks of the respective colors are supplied from, for example, ink tanks to the print head unit <NUM> via ink tubes.

The inspection unit <NUM> is a unit for inspecting the state of the nozzle of the print head, the sheet conveyance state, the image position, and the like by optically reading the inspection pattern or the image printed on the sheet by the printing unit <NUM>. The cutter unit <NUM> is a unit provided with a mechanical cutter for cutting the sheet after printing to a predetermined length. The information printing unit <NUM> is a unit that prints printing information such as a serial number and a date of printing on the back side of the cut sheet. The drying unit <NUM> is a unit which heats the sheet printed by the printing unit <NUM> to dry the imparted ink in a short time. Each of the inspection unit <NUM>, the cutter unit <NUM>, the information printing unit <NUM>, and the drying unit <NUM> may include a conveyance belt or a conveyance roller for feeding the sheet to the next process.

The winding unit <NUM> is a unit that temporarily winds up a continuous sheet on which front-side printing is finished when the double-sided printing is performed. The winding unit <NUM> is provided with a rotating take-up drum for winding the sheet. The specific operation of the winding unit <NUM> at the time of double-sided printing will be described later.

The discharge unit <NUM> is a unit for conveying the sheet cut by the cutter unit <NUM> and dried by the drying unit <NUM>, discharging the sheet from the printing apparatus <NUM>, and transferring the sheet to the sheet stacking apparatus <NUM>. The specific configuration of the discharge unit <NUM> will be described later.

The control unit <NUM> is a unit that controls each unit of the printing apparatus <NUM>. The control unit <NUM> may include, for example, a processor represented by a CPU, a RAM, a memory such as a ROM, a controller <NUM> including various interfaces such as an I/O interface or a communication interface, and a power supply.

The controller <NUM> controls the operation of the printing apparatus <NUM> based on the received instruction. For example, the controller <NUM> acquires an instruction from a user received by an operation unit such as an operation panel provided in a housing of the printing apparatus <NUM> via an I/O interface, and controls the operation of the printing apparatus <NUM> based on the content thereof. For example, the controller <NUM> is controlled based on an instruction received from an external device <NUM> such as a host computer connected via a communication interface.

The sheet stacking apparatus <NUM> stacks sheets discharged from the discharge unit <NUM> of the printing apparatus <NUM>. The sheet stacking apparatus <NUM> may be configured to be detachable from the printing apparatus <NUM>. For example, the sheet discharge tray provided in the printing apparatus <NUM> may be removed, and the sheet stacking apparatus <NUM> may be added to the discharge unit <NUM>. The specific configuration of the sheet stacking apparatus <NUM> will be described later.

Next, the basic operation of the printing system SY at the time of printing will be described. Hereinafter, operations of single-sided printing and double-sided printing will be described respectively.

<FIG> is a diagram for explaining an operation of the printing system SY during single-sided printing. In <FIG>, the sheet on the conveyance path is illustrated by a thick solid line. Sheets fed from the sheet supply unit <NUM> on the conveyance path and processed by the curl correction unit <NUM> and the skew correction unit <NUM> respectively are printed on the front side in the printing unit <NUM>. After passing through the inspection unit <NUM>, the sheet printed by the printing unit <NUM> is cut by the cutter unit <NUM> for each predetermined unit length which is set in advance. Next, in the information printing unit <NUM>, the printing information is printed on the back side of the cut sheet as necessary. Then, cut sheets are conveyed one by one to the drying unit <NUM> to dry the ink. Thereafter, the sheets are discharged from the discharge unit <NUM> to outside of the printing apparatus <NUM> and are sequentially stacked on the sheet stacking apparatus <NUM>.

<FIG> is a diagram for explaining an operation of the printing system SY during double-sided printing. In double-sided printing, a back side printing sequence is performed following the front side printing sequence. In <FIG>, a continuous sheet conveyed to the winding unit <NUM> by the front side printing sequence is illustrated by a thick solid line.

In a first front side printing sequence, the operation in each unit from the sheet supply unit <NUM> to the inspection unit <NUM> is the same as the operation of the above-described single-sided printing, but in the cutter unit <NUM>, the cutting operation is not performed and the continuous sheet is conveyed to the drying unit <NUM> as is. After the ink on the front side dries in the drying unit <NUM>, the continuous sheet is introduced into the path on the side of the winding unit <NUM>, rather than the path on the side of the discharge unit <NUM>. The introduced sheet is wound on the take-up drum of the winding unit <NUM> which rotates in the forward direction (counterclockwise direction in the drawing). When the printing of all scheduled front sides is finished in the printing unit <NUM>, the trailing end of the printing area of the continuous sheet is cut in the cutter unit <NUM>. With reference to the cutting position, the continuous sheet on the downstream side in the conveyance direction (the side on which printing has been performed) passes through the drying unit <NUM> and is completely wound up to the trailing end (the cutting position) of the sheet by the winding unit <NUM>. Meanwhile, the continuous sheet upstream of the cutting position in the conveyance direction is rewound to the sheet supply unit <NUM> so that the leading end (cutting position) of the sheet does not remain in the curl correction unit <NUM>.

Back side printing sequence is performed following the foregoing front side printing sequence. In <FIG>, a portion of the conveyance path of the continuous sheet at the time of the back side printing sequence from the winding unit <NUM> to the curl correction unit <NUM> is illustrated by a thick broken line. The take-up drum of the winding unit <NUM> rotates in the opposite direction (clockwise direction in the drawing) to the time of winding. Then, the end of the wound sheet is fed into the curl correction unit <NUM> in a state in which the front and back of the continuous sheet is inverted. Incidentally, the leading end of the sheet fed into curl correction unit <NUM> at this time is the trailing end of the sheet at the time of winding. That is, the leading end and the trailing end of the sheet are switched between the time of front-side printing and the time of the back-side printing. In the curl correction unit <NUM>, straightening a curl in the opposite direction is performed at the time of front-side printing. This is because a sheet wound on a take-up drum is wound so as to be front/back inverted with the roll in the sheet supply unit <NUM>, and is curled in the opposite direction. Thereafter, printing is performed on the back side of the continuous sheet by the printing unit <NUM> through the skew correction unit <NUM>. After passing through the inspection unit <NUM>, the printed sheet is cut by the cutter unit <NUM> for each predetermined unit length which is set in advance. Since the cut sheet is printed on both sides, printing by the information printing unit <NUM> is not performed. Cut sheets are conveyed one by one to the drying unit <NUM>, discharged to the outside of the printing apparatus <NUM>, and sequentially stacked onto the sheet stacking apparatus <NUM> from the discharge unit <NUM>.

<FIG> is a diagram illustrating a configuration around the discharge unit <NUM> and the sheet stacking apparatus <NUM>.

The discharge unit <NUM> includes a discharge roller <NUM> at the most downstream in the conveyance direction. The discharge roller <NUM> is rotated by, for example, a motor (not illustrated). The discharge roller <NUM> discharges the sheet from a discharge opening <NUM> formed in the casing of the printing apparatus <NUM>.

The sheet stacking apparatus <NUM> includes a conveyor unit <NUM>, a sheet detection sensor <NUM> and a conveyor control unit <NUM>.

The conveyor unit <NUM> carries out the stacking of sheets discharged from the discharge unit <NUM> of the printing apparatus <NUM> and the conveying of the stacked sheets. The conveyor unit <NUM> is provided below the discharge opening <NUM> of the discharge unit <NUM> (-Z direction). The conveyor unit <NUM> includes a conveyor belt <NUM> and a conveyor driving roller <NUM>.

The conveyor belt <NUM> is an endless belt forming a sheet stacking surface. In the present embodiment, the sheet stacking surface is formed so as to extend from a position close to the printing apparatus <NUM> below the discharge opening <NUM> in the X direction and the Z direction. In other words, the sheet stacking surface formed by the conveyor belt <NUM> is inclined upward downstream in the direction in which sheets stacked on the conveyor belt <NUM> are conveyed. This inclination is provided so that the sheets stacked on the conveyor belt <NUM> are caused to be aligned by the aligning unit <NUM>, as will be described later. Incidentally, the inclination may be set, for example, at an angle of <NUM> to <NUM> degrees in consideration of the performance of sheet stacking alignment by the aligning unit <NUM> and the performance of sheet stacking alignment when a later-described feeding operation is performed.

Further, the length of the sheet stacking surface formed by the conveyor belt <NUM> in the conveyance direction may be set to be longer than the maximum sheet length that the printing apparatus <NUM> can discharge, for example.

Here, in the present embodiment, a part of an exterior member of the printing apparatus <NUM> functions as the aligning unit <NUM> to align the sheets stacked on the conveyor unit <NUM>. Specifically, sheets discharged from the printing apparatus <NUM> are moved to the printing apparatus <NUM> side by the inclination of the sheet stacking surface, and the sheets stacked on the conveyor unit <NUM> are aligned by the end that is upstream in the direction in which sheets are discharged abutting the aligning unit <NUM>. However, the aligning unit <NUM> may be a member provided separately from the exterior member of the printing apparatus <NUM>. For example, the sheet stacking apparatus <NUM> may include a member that regulates the movement of the sheet by the inclination of the sheet stacking surface.

The sheet detection sensor <NUM> detects whether or not the printing apparatus <NUM> is currently discharging a sheet. In the present embodiment, the sheet detection sensor <NUM> is positioned downstream of the discharge roller <NUM> in the discharging direction. In the present embodiment, the sheet detection sensor <NUM> turns on when a sheet discharged from the discharge roller <NUM> is present at the detection position of the sheet detection sensor <NUM>, and turns off when the sheet is not present at the detection position. That is, when the sheet is nipped in the discharge roller <NUM> and is being discharged, the sensor turns on, and when the sheet is not being discharged and is away from the nip of the discharge roller <NUM>, the sensor turns off. As the sheet detection sensor <NUM>, a well-known sensor such as a photoelectric sensor, a laser sensor, an ultrasonic sensor, or a capacitance sensor can be employed as appropriate.

The conveyor driving roller <NUM> drives the conveyor belt <NUM> in accordance with a conveyor driving motor (not illustrated).

The conveyor control unit <NUM>, by controlling the driving of the conveyor driving roller <NUM>, controls a feeding operation of the conveyor unit <NUM>. For example, the conveyor control unit <NUM> may include a processor as typified by a CPU, a RAM, a memory such as a ROM, a controller including various interfaces such as an I/O interface or a communication interface, and a power supply.

The conveyor control unit <NUM> controls the driving of the conveyor driving roller <NUM> based on speed information of the sheet discharged from the discharge unit <NUM>, discharge interval information for sheets of the same print job discharged from the discharge unit <NUM>, or information from the sheet detection sensor <NUM>. For example, the conveyor control unit <NUM> acquires the sheet speed information and the sheet discharge interval information by receiving input from a user through an operation unit (not illustrated) provided on the sheet stacking apparatus <NUM>. Further, for example, the conveyor control unit <NUM> acquires the sheet speed information and the sheet discharge interval information by receiving them from the control unit <NUM> of the printing apparatus <NUM>. The sheet speed information received by the conveyor control unit <NUM> from the printing apparatus <NUM> may be a set value or may be a value measured by an encoder or the like provided on the discharge roller <NUM>.

Further, the print job may be, for example, data including instructions, image data, setting information, and the like for causing the printing apparatus <NUM> to execute print processing. The printing apparatus <NUM> can discharge one or more cut sheets from the discharge unit <NUM> based on the same print job.

Further, in the present embodiment, the conveyor control unit <NUM> manages the execution state (job status) of the print job based on the detection result of the sheet detection sensor <NUM> as the information from the sheet detection sensor <NUM>. For example, the CPU of the conveyor control unit <NUM> determines the job status from the detection result of the sheet detection sensor <NUM>, and stores the determination result in the memory of the conveyor control unit <NUM> as the job status. In the present embodiment, according to the flowchart of <FIG>, which will be described later, it is determined whether the job status is "continuing" indicating that the print job is being executed or "finished" indicating that the print job is not being executed. The job status managed by the conveyor control unit <NUM> is determined by the conveyor control unit <NUM> only based on the detection result of the sheet detection sensor <NUM>, and it is possible that it does not coincide with the execution state of the print job in the processing performed by the control unit <NUM> of the printing apparatus <NUM>.

Next, the behavior of a sheet when the sheet is stacked on the sheet stacking apparatus <NUM> will be described.

A sheet discharged from the discharge roller <NUM> falls onto the conveyor belt <NUM> due to gravity. The sheet that has fallen onto the conveyor belt <NUM> moves toward the printing apparatus <NUM> due to the inclination of the sheet stacking surface of the conveyor belt <NUM>, the end of the sheet hits the aligning unit <NUM>, and the movement stops. In such a movement, a sheet discharged from the discharge roller <NUM> is aligned and stacked on the conveyor belt <NUM> in sequence before the conveyor unit <NUM> is operated by the conveyor control unit <NUM>.

The conveyor control unit <NUM> executes a feeding operation of the conveyor unit <NUM> when the discharging of a sheet from the printing apparatus <NUM> based on, for example, the same print job is finished. At this time, the conveyor control unit <NUM> controls the acceleration of the conveyor belt <NUM> to perform the feeding operation so as not to ruin the performance of stacking alignment for a sheet bundle stacked on the conveyor belt <NUM>. By this feeding operation, it is possible to ensure a sheet stacking space when a sheet is discharged from the printing apparatus <NUM> based on the next print job. Then, since sheets discharged based on the next print job are stacked on the conveyor belt <NUM>, a plurality of sheet bundles are aligned and stacked on the conveyor belt <NUM> (see <FIG>).

Incidentally, in the feeding operation of the conveyor unit <NUM> described above, if the feed amount is larger than the length of the sheet discharged from the printing apparatus <NUM> next, the spacing between the sheet bundles may increase, and the number of sheets that the sheet stacking apparatus <NUM> can stack may be lower. On the other hand, if the feed amount is smaller than the length of the sheet to be next discharged from the printing apparatus <NUM>, adjacent sheet bundles will overlap with each other, and the workability of taking out the sheet bundles may suffer. Therefore, in the present embodiment, the conveyor control unit <NUM>, by the following control, controls the feed amount of the conveyor unit <NUM>.

<FIG> is a flowchart illustrating a control example of the sheet stacking apparatus <NUM>. This flowchart is realized, for example, by the CPU of the conveyor control unit <NUM> reading a program stored in the ROM into the RAM and executing the program.

Further, <FIG> is a diagram illustrating an operation example of the sheet stacking apparatus <NUM>, and illustrates an operation example for when the flowchart of <FIG> is executed. <FIG> illustrates an example of operation of the sheet stacking apparatus <NUM> when subsequent sheet SH1 and sheet SH2 are discharged from the printing apparatus <NUM> in a state in which two sheet bundles are already stacked on the conveyor unit <NUM>. In the following explanation, it is assumed that the sheet SH1 and the sheet SH2 are sheets which are to be discharged based on a print job subsequent to the print job when the sheet bundle on the left as illustrated in state ST1 or the like of <FIG> which is stacked on the conveyor unit <NUM> has been discharged. Therefore, in the state ST1 of <FIG>, the job status is "finished".

In step S1, the conveyor control unit <NUM> confirms the job status, and proceeds to step S2 if the job status is "finished", and proceeds to S3 if the job status is "continuing". For example, the conveyor control unit <NUM> reads out information about the job status stored in the memory and performs confirmation. In the case of <FIG>, since the job status in the status ST1 is "finished" as described above, the conveyor control unit <NUM> proceeds to S2.

In step S2, the conveyor control unit <NUM> executes a conveyor feed process. In the case where the job status is "finished", the print job when the sheets stacked on the conveyor belt <NUM> are discharged is finished, and therefore, the next sheet to be discharged from the discharge unit <NUM> will be the first sheet based on the next print job. On the other hand, when the job status is "continuing", the next sheet to be discharged from the discharge unit <NUM> will be the second sheet or a later sheet based on the currently ongoing print job. Therefore, in the present embodiment, by the branching in step S1, a conveyor feed process is executed to discharge the first sheet of a print job, but the conveyor feed process is not executed for the discharge of the second and subsequent sheets of the same print job.

<FIG> is a flowchart illustrating an example of control of the sheet stacking apparatus <NUM> and illustrates a specific processing example of step S2 in <FIG>.

In step S201, the conveyor control unit <NUM> confirms whether the discharge of the sheet from the discharge unit <NUM> has started; if it is started, the conveyor control unit <NUM> proceeds to step S202, and if it is not started, the conveyor control unit <NUM> returns to step S201. For example, since the state ST1 of <FIG> is a state prior to the sheet SH1 being detected by the sheet detection sensor <NUM>, the conveyor control unit <NUM> determines that the sheet discharge is not started (step S201: No). On the other hand, when the conveyance of the sheet by the discharge roller <NUM> progresses to the state ST2 of <FIG>, since the leading end of the sheet SH1 is detected by the sheet detection sensor <NUM>, the conveyor control unit <NUM> determines that sheet discharging is started (step S201: Yes).

In step S202, the conveyor control unit <NUM> updates the job status stored in a memory of the conveyor control unit <NUM> to "continuing". In step S203, the conveyor control unit <NUM> starts a feeding operation of the conveyor unit <NUM>. Specifically, the conveyor control unit <NUM> drives the conveyor belt <NUM> by the conveyor driving roller <NUM>. Thus, the bundle of sheets SH stacked on the conveyor belt <NUM> moves downstream in the conveyance direction of the conveyor belt <NUM> (to the left in <FIG>). Therefore, the stacking space of the sheet SH2 being discharged is formed in a region close to the printing apparatus <NUM> of the conveyor belt <NUM> (the state ST3 of <FIG>).

Here, acceleration of the conveyor unit <NUM> may be set to a value at which alignment performance of the sheet bundle stacked on the conveyor unit <NUM> is not ruined. Further, the conveying speed of the conveyor unit <NUM> can be set correspondingly to the sheet discharge speed of the discharge unit <NUM>. For example, the conveying speed of the conveyor unit <NUM> may be the same speed as the sheet discharge speed of the discharge unit <NUM>. Further, for example, the conveying speed of the conveyor unit <NUM> may be set to be a value within the sheet discharge speed ± <NUM> to <NUM>% of the discharge unit <NUM>. In other words, the conveying speed of the conveyor unit <NUM> may be set to a value close to the discharging speed of the sheet from the printing apparatus <NUM>. Thus, when the conveyor unit <NUM> is operated correspondingly to the sheet discharging period from the printing apparatus <NUM>, the feed amount of the conveyor unit <NUM> can be made close to the length of the discharged sheet.

In step S204, the conveyor control unit <NUM> confirms whether or not the sheet discharge has finished; the conveyor control unit <NUM> proceeds to step S205 if it has finished, and returns to step S204 if the sheet discharging has not finished, that is, discharging continues. The conveyor control unit <NUM> may determine that sheet discharging has finished based on the result of detection by the sheet detection sensor <NUM> switching from on to off.

The conveyor control unit <NUM>, after waiting for a predetermined time in step S205, terminates the feeding operation of the conveyor unit <NUM> in step S206, and terminates the flowchart of <FIG>. Here, deceleration of the conveyor unit <NUM> may be set to a value at which alignment performance of the sheet bundle stacked on the conveyor unit <NUM> is not ruined.

Thus, the conveyor control unit <NUM> continues the feeding operation of the conveyor unit <NUM> while the sheet SH1 continues to be detected by the sheet detection sensor <NUM>, that is, during the discharging of the sheet from the printing apparatus <NUM>. On the other hand, the conveyor control unit <NUM>, in response to the sheet SH1 no longer being detected by the sheet detection sensor <NUM>, that is, in response to the printing apparatus <NUM> having finished discharging the sheet, terminates the feeding operation of the conveyor unit <NUM>. In other words, the feeding operation of the conveyor unit <NUM> is executed corresponding to a time period over which the sheet detection sensor <NUM> detects that the printing apparatus <NUM> is discharging the sheet. Thus, the stacking space of the sheet discharged from the printing apparatus <NUM> is secured on the stacking surface (on the conveyor unit) of the sheet of the conveyor belt <NUM> corresponding to the period in which the sheet detection sensor <NUM> detects that the printing apparatus <NUM> is discharging the sheet.

Returning to <FIG>. In step S3, the conveyor control unit <NUM> executes a job status determination process. <FIG> is a flowchart illustrating an example of control of the sheet stacking apparatus <NUM> and illustrates a specific processing example of step S3.

In step S301, the conveyor control unit <NUM> proceeds to step S302 if a period over which no sheet is discharged by the discharge unit <NUM> if the threshold value or more, and terminates the flowchart if it is less than the threshold value. Further, the conveyor control unit <NUM>, if the sheet is being discharged by the discharge unit <NUM> or if the elapsed time since the completion of the discharge of the last discharged sheet is less than the threshold value, terminates the flowchart.

Here, <FIG> schematically illustrates an operation example of sheet conveyance when a plurality of jobs are executed in the discharge unit <NUM>. In job <NUM>, a plurality of sheets of the same size are sequentially conveyed with a predetermined gap A therebetween. In job <NUM>, sheets of the same size but different to the sheet size of job <NUM>, are sequentially conveyed with a predetermined gap A therebetween. The last sheet in the print process based on the job <NUM> and the first sheet in the print process based on the job <NUM> are conveyed with a gap B therebetween. In the present embodiment, the relationship is set such that sheet gap B between different jobs > sheet gap A in the same job. Therefore, the off time of the sheet detection sensor <NUM>, that is, the period over which no sheet is discharged by the discharge unit <NUM> is longer between sheets of different jobs than between sheets in the same job. Therefore, the conveyor control unit <NUM> can determine whether or not the job is continuing or has finished from the period over which no sheet is discharged based on the sheet detection sensor <NUM>.

Returning to <FIG>. For example, when the period over which no sheet is discharged in the case where the gap between the sheets is the gap A is the period TA [sec], and the period over which no sheet is discharged in the case where the gap between the sheets is the gap B is the period TB [sec], the threshold value of step S301 may be set to a value between the period TA and the period TB.

In step S302, the conveyor control unit <NUM> updates the job status stored in the memory to "finished", and ends the flowchart of <FIG>.

Returning to <FIG>. In step S4, the conveyor control unit <NUM> confirms the job status, and if the job status is "finished", the process proceeds to step S5, and if the job status is "continuing", the flowchart is ended. For example, the conveyor control unit <NUM> reads out information about the job status stored in the memory and performs confirmation.

In step S5, the conveyor control unit <NUM> executes a discontinuous conveyor feed. Specifically, the conveyor control unit <NUM> drives the conveyor belt <NUM> by the conveyor driving roller <NUM> by a predetermined amount so that the sheet stacked on the conveyor unit <NUM> is conveyed by a predetermined amount. This operation is performed, for example, to provide a buffer between sheet bundles of different jobs (state ST5 of <FIG>).

As described above, according to the present embodiment, the feeding operation of the conveyor unit <NUM> is executed correspondingly to the period in which the sheet detection sensor <NUM> detects that the printing apparatus <NUM> is discharging the sheet (step S201 to step S206). Therefore, a stacking space corresponding to the sheet length of the sheet to be detected is secured on the conveyor belt <NUM>. Therefore, it is possible to suppress the workability of retrieval suffering due to overlapping of the sheet bundles. In addition, even when jobs in which sheets having different sheet lengths are discharged are performed successively, it is possible to appropriately control between the sheet bundles. Therefore, more sheet bundles of different sheet lengths can be stacked on the conveyor belt <NUM>.

Further, according to the present embodiment, the conveyance period of the conveyor unit <NUM> is determined correspondingly to a period in which it is detected that the sheet is being discharged from the printing apparatus <NUM> by the sheet detection sensor <NUM>. Further, the conveying speed of the conveyor unit <NUM> can be set correspondingly to the sheet discharge speed of the discharge unit <NUM>. Therefore, the feed amount of the conveyor unit <NUM> is set based on the sheet discharge period and the sheet discharge speed of the discharge unit <NUM>. Therefore, the feed amount of the conveyor unit <NUM> can be an amount corresponding to the length of the sheet to be discharged. More specifically, since the feed amount of the conveyor unit <NUM> is set based on the discharge period (time) from the sheet printing apparatus <NUM> × the sheet discharge speed, the feed amount of the conveyor unit <NUM> can be made close to the length of the sheet. Therefore, it is possible to close the distance between the sheet bundles stacked on the conveyor unit <NUM>, and it is possible to increase the number of stacked sheets on the conveyor unit <NUM>.

Further, according to the present embodiment, the conveyor control unit <NUM>, based on the detection result of the sheet detection sensor <NUM>, secures sheet stacking space corresponding to the sheet length. Therefore, when the sheet stacking apparatus <NUM> is added to the printing apparatus <NUM>, the conveyor control unit <NUM> does not need to receive information such as the length of the sheet from the control unit <NUM> of the printing apparatus <NUM>. Therefore, the conveyor control unit <NUM> can control the operation of the conveyor unit <NUM> in a simpler manner.

In the above embodiment, the sheet detection sensor <NUM> detects whether or not the printing apparatus <NUM> is discharging a sheet, but whether or not the printing apparatus <NUM> is discharging a sheet may be detected in other manners. For example, whether or not the printing apparatus <NUM> is discharging the sheet may be detected based on the driving information of the discharge roller <NUM> of the discharge unit <NUM>. The driving information of the discharge roller <NUM> may be a driving current value of the discharge roller <NUM> or a detection result of an encoder capable of measuring a rotational speed of the discharge roller <NUM>. For example, the conveyor control unit <NUM> may acquire the driving information of the discharge roller <NUM> from the control unit <NUM> and control the feeding operation of the conveyor unit <NUM> in correspondence with a period in which the discharge roller <NUM> is being driven, that is, a period in which the printing apparatus <NUM> is discharging the sheet.

In the above embodiment, the printing system SY is configured by the printing apparatus <NUM> and the sheet stacking apparatus <NUM>, but a sheet stacking apparatus may be provided as a part of the printing apparatus. In this case, configuration may be such that the conveyor control unit <NUM> is not provided, and the control unit <NUM> of the printing apparatus <NUM> may control the operation of the conveyor unit <NUM>.

In the description of the above embodiment, a combination of one printing apparatus <NUM> and one sheet stacking apparatus <NUM> has been described, but when there is a plurality of discharge units <NUM> in one printing apparatus <NUM>, a plurality of sheet stacking apparatuses <NUM> may be provided. In this case, it is possible to align and stack the sheets in a plurality of sheet stacking apparatuses <NUM>.

In the description of the above embodiment, a combination of one printing apparatus <NUM> and one sheet stacking apparatus <NUM> has been described, but a plurality of printing apparatuses <NUM> and a plurality of sheet stacking apparatuses <NUM> may be provided. In this case, conveyors may be extended for the plurality of sheet stacking apparatuses <NUM>, and a plurality of sheet stacking apparatus <NUM> may be disposed so as to collect the end points of the conveyors in one place. Thus, the sheets stacked in an aligned manner will be collected in one place. As a result, sheets discharged from the plurality of printing apparatuses <NUM> can be easily advanced to post-processing.

The invention may also be realized in a process in which a program for implementing a function of one or more of the above described embodiments is supplied to a system or device via a network or storage medium, and one or more processors in the computer of the system or device read and execute the program. It can also be implemented by circuits (e.g., ASIC) that implement one or more functions.

The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the scope of the invention. Accordingly, the claims are appended hereto in order to make the scope of the invention public.

Claim 1:
A sheet stacking apparatus (<NUM>) comprising:
a conveyor means (<NUM>) for performing stacking of sheets discharged from a printing apparatus (<NUM>) and conveying of stacked sheets; and
a detection means (<NUM>) for detecting whether or not the printing apparatus (<NUM>) is currently discharging a sheet;
characterised by further comprising:
a control means (<NUM>) for, so as to secure a stacking space for the sheet discharged from the printing apparatus (<NUM>) on the conveyor means (<NUM>), executing a feeding operation of the conveyor means (<NUM>) during a period of time over which the detection means (<NUM>) detects that the printing apparatus (<NUM>) is discharging the sheet.