Printer

This application claims priority from Japanese Patent Application No. 2017-072098 filed on Mar. 31, 2017, the content of which is incorporated herein by reference in its entirety.

The present invention relates to a printer.

There is known a printer that determines conveyance error of a sheet by forming test patterns on the sheet. A test pattern forming method is known in which a first pattern is formed on the sheet, the sheet is minutely conveyed and a second pattern is formed on the sheet, which is repeatedly performed. Conveyance error is determined based on overlapping of the second pattern formed each time minute conveying is performed, and the first pattern.

In a well-known printer, power from a motor is transmitted to rollers, and the sheet is conveyed by rotation of the rollers. Multiple gears are included in a power transmission mechanism from the motor to the rollers, and there is backlash between adjacent gears.

Although determination of conveyance error of the sheet based on test patterns intends to determine conveyance error primarily due to roller structure, the conveyance error of the sheet during minute-distance conveyance due to this backlash makes the conveyance error due to roller structure difficult to discern. Examples of conveyance error due to roller structure include conveyance error due to roller eccentricity and conveyance error due to outer shapes of rollers.

It has been found desirable to provide a technology that suppresses influence of play in the power transmission mechanism, and enables sheet conveyance error due to roller structure to be determined by test patterns with high accuracy.

A printer according to an aspect of the present disclosure includes a first roller, a second roller, and a motor configured to drive the first roller and the second roller to convey a sheet in a conveyance direction from the first roller toward the second roller. The printer includes a head disposed between the first roller and the second roller in the conveyance direction, the head comprising a plurality of nozzles aligned in the conveyance direction, the plurality of nozzles comprising a first nozzle and a second nozzle positioned in a downstream side from the first nozzle in the conveyance direction and a controller configured to control the head and the motor to print a first pattern comprising a plurality of first pattern elements on the sheet by alternately repeating, ejecting a liquid droplet from the first nozzle toward the sheet to print one of the first pattern elements on the sheet, and conveying the sheet in the conveyance direction by a first distance. The controller is configured to, after printing the first pattern on the sheet, control the motor to convey the sheet in the conveyance direction by a second distance where one of the first pattern elements of the first pattern faces the second nozzle during ejecting the liquid droplet toward the sheet and control the head to eject the liquid droplet from the second nozzle toward the sheet to print a second pattern on the sheet without conveying the sheet, a respective first pattern element and a corresponding second pattern element being disposed at a same location in a direction orthogonal to the conveyance direction.

Influence of play in the power transmission mechanism readily occurs at the initial stage of operations of repeatedly performing slight distance conveyance of the sheet. By performing slight distance conveyance once or multiple times, free spinning of the motor due to the play in the power transmission mechanism is resolved, so in subsequent slight distance conveyance, conveyance error due to play in the power transmission mechanism does not readily occur. Accordingly, performing formation of an image involving slight distance conveyance first, and subsequently performing formation of an image that does not involve slight distance conveyance, enables the influence of play in the power transmission mechanism to be suppressed, and a test pattern can be formed where conveyance error of the sheet due to the roller structure can be detected with high accuracy.

FIG. 1 is a block diagram illustrating a schematic configuration of an image forming system.

FIG. 2 is a diagram illustrating a schematic configuration of a sheet conveyance mechanism.

FIG. 3 is a diagram describing the relationship between overlaying pattern elements and conveyance error.

FIG. 4 is a flowchart illustrating text printing processing that is executed by a main controller.

FIG. 5 is a flowchart illustrating test printing processing that is executed by the main controller.

FIG. 6 is a diagram describing a test pattern formation form.

FIG. 7 is a flowchart illustrating test pattern formation processing according to a first embodiment.

FIG. 8 is a diagram describing change in a test pattern due to conveyance error.

FIG. 9 is a diagram relating to function fitting.

FIG. 10 is a diagram illustrating information to be stored.

FIG. 11 is a flowchart illustrating image formation processing based on input image data.

FIG. 12 is a diagram describing the effects of conveyance error in a case where minute-distance conveyance is executed beforehand.

FIG. 13 is a diagram describing the effects of conveyance error in a case where minute-distance conveyance is executed afterwards.

FIG. 14 is an explanatory diagram relating to conveyance sections.

FIG. 15 is a flowchart illustrating test pattern formation processing according to a second embodiment.

FIG. 16 is a diagram describing a test pattern formation form according to the second embodiment.

FIG. 17 is a flowchart illustrating test pattern formation processing according to a third embodiment.

FIG. 18 is a diagram describing a test pattern formation form according to the third embodiment.

Exemplary embodiments will be described with reference to the drawings.

First Embodiment

An image forming system 1 according to a first embodiment illustrated in FIG. 1 is configured as a digital multi-function printer. This image forming system 1 includes a main controller 10 , a printer unit 20 , a scanner unit 70 , and a user interface 90 . The main controller 10 centrally controls the overall image forming system 1 . The main controller 10 includes a central processing unit (CPU) 11 , read-only memory (ROM) 13 , random access memory (RAM) 15 , and non-volatile RAM (NVRAM) 17 .

The CPU 11 executes processing in accordance with programs stored in the ROM 13 . The RAM 15 is used as a work region when the CPU 11 executes programs. The NVRAM 17 is non-volatile memory capable of electrically rewriting data. Examples of the NVRAM 17 include flash memory and electrically erasable programmable ROM (EEPROM). The main controller 10 further includes a communication interface (omitted from illustration) that is communicable with an external device 3 . An example of the external device 3 is a personal computer.

The printer unit 20 is controlled by the main controller 10 to form images on a sheet Q. The printer unit 20 is configured as an ink-jet printer. The printer unit 20 forms images on the sheet Q based on data received from the external device 3 , and image data representing images of documents read by the scanner unit 70 , for example. The printer unit 20 further is controlled by the main controller 10 to form test patterns on the sheet Q to determine conveyance error of the sheet Q.

The scanner unit 70 is controlled by the main controller 10 to optically read documents placed on a document table, and input image data representing the images read from the documents to the main controller 10 . The user interface 90 has a display that displays various types of information of the user, and an input device for accepting instructions from the user.

In detail, the printer unit 20 includes a print controller 30 , a recording head 40 , a carriage conveying mechanism 51 , a carriage (CR) motor 53 , a linear encoder 55 , a sheet conveying mechanism 61 , a paper feed (PF) motor 63 , and a rotary encoder 65 .

The print controller 30 is configured to control discharge of ink droplets from the recording head 40 , conveyance control of a carriage 52 (see FIG. 2 ), and conveyance control of the sheet Q, in accordance with instructions from the main controller 10 .

The recording head 40 is controlled by the print controller 30 to discharge ink droplets and form images on the sheet Q. The recording head 40 has a discharge nozzle group N 0 of ink droplet discharge nozzles arrayed in a sub-scanning direction, provided on a lower face thereof facing the sheet Q. The sub-scanning direction corresponds to the conveyance direction of the sheet Q, and corresponds to the Y-axis direction in FIG. 2 . A main scanning direction corresponds to a direction orthogonal to the sub-scanning direction, and corresponds to the conveyance direction of the carriage 52 (the normal direction of the plane of view, i.e., the X-axis direction, in FIG. 2 ). The nozzle group N 0 of discharge nozzles provided to the recording head 40 will hereinafter be referred to as “nozzle group N 0 ”.

The carriage conveying mechanism 51 has the carriage 52 to which the recording head 40 is mounted, and is configured to convey the carriage 52 in the main scanning direction. The CR motor 53 is the driving source of the carriage conveying mechanism 51 , and is configured of a DC motor. The CR motor 53 is controlled by the print controller 30 . The conveyance control of the carriage 52 is realized by the print controller 30 controlling rotations of the CR motor 53 .

The linear encoder 55 inputs pulse signals, corresponding to displacement of the carriage 52 in the main scanning direction, to the print controller 30 as encoder signals. The print controller 30 detects the position and speed of the carriage 52 in the main scanning direction based on the encoder signals input from the linear encoder 55 , and performs feedback control of the position and speed of the carriage 52 . The print controller 30 controls the recording head 40 in conjunction with the movement of the carriage 52 , and causes the recording head 40 to intermittently discharge ink droplets, thereby forming the intended image on the sheet Q.

The sheet conveying mechanism 61 is configured to convey sheet Q from a sheet feed tray (omitted from illustration) to a discharge tray (omitted from illustration). FIG. 2 illustrates one example of a configuration around the recording head 40 . In FIG. 2 , a lead edge of the sheet Q has past the discharge roller 617 . The sheet conveying mechanism 61 has a platen 611 below the recording head 40 , as illustrated in FIG. 2 . The sheet conveying mechanism 61 also includes a conveyance roller 613 and pinch roller 614 disposed facing each other, upstream from the platen 611 in the sheet conveyance direction, and a discharge roller 617 and a spur roller 618 disposed facing each other, downstream from the platen 611 in the sheet conveyance direction.

The conveyance roller 613 and discharge roller 617 are linked to the PF motor 63 via a power transmission mechanism 62 , and rotate synchronously under power received from the PF motor 63 . The PF motor 63 is the driving source of the sheet conveying mechanism 61 , and is configured of a DC motor. The power transmission mechanism 62 includes a gear mechanism on the power transmission path between the PF motor 63 and conveyance roller 613 .

The sheet conveying mechanism 61 separates the sheet Q loaded on the sheet feed tray one sheet at a time by rotation of a sheet feed roller (omitted from illustration), and provides the separated sheet Q to the nip of the conveyance roller 613 and pinch roller 614 . The conveyance roller 613 is rotationally driven by the PF motor 63 , and thus conveys the sheet Q supplied from the sheet feed tray downstream in the sheet conveyance direction indicated by the dashed-line arrow in FIG. 2 . The conveyance roller 613 conveys the sheet Q downstream by rotation, in a state where each sheet Q is nipped between the conveyance roller 613 and pinch roller 614 .

The sheet Q conveyed downstream by rotation of the conveyance roller 613 pass through a recording region R 0 while being supported by the platen 611 . The recording region R 0 corresponds to a region below the nozzle group N 0 of the recording head 40 , within the conveyance path of the sheet Q. The sheet Q that has passed through the recording region R 0 are nipped between the discharge roller 617 and spur roller 618 and conveyed downstream by rotation of the discharge roller 617 . The sheet Q that has passed the discharge roller 617 are finally discharged to the discharge tray.

The rotary encoder 65 is provided on a rotation shaft of the PF motor 63 , and inputs pulse signals corresponding to rotations of the conveyance roller 613 to the print controller 30 as encoder signals. The print controller 30 detects the rotation amount, rotation speed, and rotation phase ϕ of the conveyance roller 613 , based on encoder signals from the rotary encoder 65 . The rotation phase ϕ corresponds to the rotation angle ϕ of the conveyance roller 613 .

The main controller 10 stores a control parameter group corresponding to the individual variance of the printer unit 20 in the NVRAM 17 . The main controller 10 appropriately controls the printer unit 20 based on this control parameter group. Specifically, the main controller 10 sets to the print controller 30 a parameter group regulating operations of the print controller 30 based on the control parameter group stored in the NVRAM 17 , and causes the print controller 30 to operate, thereby appropriately controlling the printer unit 20 such that the operations of the print controller 30 match the individual variability.

The print controller 30 executes control of the CR motor 53 and PF motor 63 based on the parameter group set by the main controller 10 , based on encoder signals from the linear encoder 55 and the rotary encoder 65 . This collaboration between the main controller 10 and print controller 30 realizes discharge control of ink droplets from the recording head 40 , conveyance control of the carriage 52 on which is mounted the recording head 40 , and conveyance control of the sheet Q, in the present disclosure.

In an aspect of the disclosure, the control parameter group that the NVRAM 17 stores includes correction parameter groups for correcting the rotation amount of the conveyance roller 613 in a direction of suppressing conveyance error of the sheet Q. The main controller 10 references these correction parameter groups to calculate a target rotation amount LS for the conveyance roller 613 that corresponds to the target sheet conveyance amount, and sets to the print controller 30 a parameter that represents the target rotation amount LS of the conveyance roller 613 that has been calculated. Sheet conveyance by the conveyance roller 613 is realized with conveyance error due to eccentricity and the outer shape and so forth of the conveyance roller 613 suppressed, due to this setting. At least part of the correction parameter groups is updated to values corresponding to the individual variance, based on test pattern formation results.

A test pattern is realized by, for example, forming a first pattern element PE 1 at an upstream portion R 1 of the recording region R 0 using a first nozzle group N 1 of the recording head 40 , and forming a second pattern element PE 2 at a downstream portion R 2 of the recording region R 0 using a second nozzle group N 2 of the recording head 40 , as illustrated in FIGS. 2 and 3 .

Of the nozzle group N 0 that the recording head 40 has, the first nozzle group N 1 corresponds to a nozzle group situated at the upstream side in the sheet conveyance direction, as illustrated in FIG. 2 . The upstream portion R 1 of the recording region R 0 corresponds to a region in the recording region R 0 where image formation can be performed by the first nozzle group N 1 . Of the nozzle group N 0 , the second nozzle group N 2 corresponds to a nozzle group situated at further on the downstream side in the sheet conveyance direction than the first nozzle group N 1 . The downstream portion R 2 of the recording region R 0 corresponds to a region in the recording region R 0 where image formation can be performed by the second nozzle group N 2 .

In a case where the distance between the first nozzle group N 1 and second nozzle group N 2 is a distance L 0 , the distance between the upstream portion R 1 and downstream portion R 2 in the recording region R 0 is the distance L 0 , which is a fixed distance that is geometrically determined.

Accordingly, in a case of forming the first pattern element PE 1 on a sheet Q, as illustrated at the top in FIG. 3 , and then conveying the sheet Q correctly by the distance L 0 and forming the second pattern element PE 2 on the sheet Q, the second pattern element PE 2 is formed completely overlaying the first pattern element PE 1 as illustrated at the middle in FIG. 3 . On the other hand, in a case where the sheet Q is conveyed further than the distance L 0 by a distance D regardless the PF motor 63 being controlled so as to convey the sheet Q by the distance L 0 , the second pattern element PE 2 is formed on the sheet Q deviated from the first pattern element PE 1 , as illustrated at the bottom in FIG. 3 . Conveyance error of the sheet Q is determined in the present embodiment from test patterns using this phenomenon.

Specifically, upon receiving input of a test pattern print command from the user interface 90 or external device 3 , the main controller 10 executes the test printing processing illustrated in FIGS. 4 and 5 in accordance with a program stored in the ROM 13 . For example, a user using the image forming system 1 , or a worker at the manufacturer of the image forming system 1 before shipping, operates the user interface 90 or external device 3 to input the test pattern printing instruction.

When the test printing processing illustrated in FIG. 4 is started, the main controller 10 executes registration processing (S 110 ). In the registration processing, the main controller 10 controls the PF motor 63 such that the sheet Q is conveyed by a predetermined amount by rotation of the conveyance roller 613 and discharge roller 617 , and the sheet Q is situated in the recording region R 0 below the recording head 40 (S 110 ). Accordingly, the sheet Q is situated at a position for forming a test pattern.

It should be understood in the following description that references to the main controller 10 controlling or driving the recording head 40 , CR motor 53 , and/or PF motor 63 , should be understood to mean that the main controller 10 controls or drives the recording head 40 , CR motor 53 , and/or PF motor 63 through the print controller 30 . Controlling and driving through the print controller 30 is realized by the main controller 10 inputting a command to the print controller 30 for realizing this controlling and driving. Instructing operations include parameter setting operations performed with regard to the print controller 30 .

Upon ending the processing in S 110 , the main controller 10 executes test pattern formation processing (S 120 ). In the test pattern formation processing, the main controller 10 controls the recording head 40 , CR motor 53 , and PF motor 63 , such that a test pattern PA illustrated below in FIG. 6 is formed on the sheet Q.

The test pattern PA (below in FIG. 6 ) is an overlaid image of a first pattern image P 1 and a second pattern image P 2 . The first pattern image P 1 is indicated by hatching with lines slanting from the upper right to the lower left in FIG. 6 , while the second pattern image P 2 is indicated by hatching with lines slanting from the upper left to the lower right. It should be understood that these images are illustrated in this manner simply for illustrative purposes, and that the actual first and second pattern images P 1 and P 2 are solid monochrome images. In the test pattern formation processing (S 120 ), the first pattern image P 1 is formed using the first nozzle group N 1 (see above in FIG. 6 ), and thereafter the second pattern image P 2 is formed using the second nozzle group N 2 (see below in FIG. 6 ).

The first pattern image P 1 is made up of multiple first pattern elements PE 1 . The multiple first pattern elements PE 1 in the first pattern image P 1 are arrayed in a staggered manner slanted as to the main scanning direction, i.e., the X-axis direction. The second pattern image P 2 is made up of multiple second pattern elements PE 2 . The multiple second pattern elements PE 2 in the second pattern image P 2 are arrayed in parallel as to the main scanning direction.

Details of the test pattern formation processing executed in S 120 are illustrated in FIG. 7 . In this test pattern formation processing, the main controller 10 controls the recording head 40 , CR motor 53 , and PF motor 63 , so that the first pattern image P 1 is formed on the sheet Q, by repeatedly executing the processing of S 310 through S 330 .

In S 310 , the main controller 10 controls the recording head 40 and CR motor 53 so that one first pattern element PE 1 is formed on the stationary sheet Q by discharge of ink droplets from the first nozzle group N 1 . In S 330 , the PF motor 63 is driven such that the sheet Q is conveyed downstream by a minute distance L 1 .

The main controller 10 repeatedly executes the processing of S 310 and S 330 until a predetermined number of first pattern elements PE 1 are formed on the sheet Q, thereby forming the first pattern image P 1 on the sheet Q. It can thus be understood from the contents of the processing described above that the first pattern image P 1 is formed by repeatedly alternating the operation of forming one first pattern element PE 1 on the sheet Q and the operation of conveying the sheet Q by the minute distance L 1 .

Upon formation of the first pattern image P 1 illustrated above in FIG. 6 being completed by forming a predetermined number of first pattern elements PE 1 (Yes in S 320 ), the main controller 10 transitions the flow to S 340 .

In S 340 , the main controller 10 controls the PF motor 63 so that the sheet Q is conveyed downstream by a predetermined distance L (S 340 ). The predetermined distance L is the distance of one of the multiple first pattern elements PE 1 being conveyed to a position facing the second nozzle group N 2 at the downstream side of the recording head 40 .

Specifically, in a case assuming that there is no conveyance error of the sheet Q, the predetermined distance L is a distance L where the first pattern element PE 1 positioned at the center of the first pattern image P 1 is completely overlaid by the second pattern element PE 2 . In a case where the number of first pattern elements PE 1 in the first pattern image P 1 is

2×M+1,

the predetermined distance L corresponds to distance

L0−M×L1.

Hereinafter, conveying of the sheet Q by the predetermined distance L described above will be referred to as “long-distance conveyance” of the sheet Q.

After performing long-distance conveyance of the sheet Q by controlling the PF motor 63 , the main controller 10 controls the recording head 40 and CR motor 53 so that the second pattern image P 2 is formed on the stationary sheet Q (S 350 ).

In the processing in S 350 , the PF motor 63 is not rotated, and the sheet Q is maintained in a stopped state. While conveying the carriage 52 in the main scanning direction by control through the print controller 30 , the main controller 10 causes liquid droplets to be discharged from the second nozzle group N 2 of the recording head 40 so as to form the second pattern elements PE 2 at positions in the main scanning direction at which the first pattern elements PE 1 have each been formed. According to this control, the second pattern image P 2 made up of the second pattern elements PE 2 arrayed in a single row in the main scanning direction is formed on the sheet Q, thereby completing the test pattern PA.

Once the test pattern PA is formed in this way, the main controller 10 judges whether or not formation of all test patterns PA has been completed (S 130 ). Test patterns PA are formed at multiple positions on the sheet Q in the test printing processing according to the present embodiment, in order to determine conveyance error of the sheet Q at each rotation phase ϕ of the conveyance roller 613 . Thus, a predetermined number of test patterns PA are formed on the sheet Q.

In a case where the predetermined number of test patterns PA have been formed, the main controller 10 returns a positive judgement in S 130 and advances the flow to S 190 . In a case where the predetermined number of test patterns PA have not been formed, the main controller 10 returns a negative judgement in S 130 and advances the flow to S 140 .

In S 140 , the main controller 10 drives the PF motor 63 to convey the sheet Q to the next text pattern formation position. Then in S 150 , test pattern formation processing is performed in the same way as with the processing in S 120 , and the flow transitions to S 130 . Thus, the processing of S 130 through S 150 is repeatedly executed until the predetermined number of test patterns PA are formed. Once the predetermined number of test patterns PA have been formed, the flow advances to S 190 .

In S 190 , the main controller 10 executes control through the print controller 30 to discharge the sheet Q, on which the test patterns PA have been formed, to the discharge tray, thereby ending the test printing processing. Thereafter, the flow transitions to S 210 (see FIG. 5 ).

In S 210 , the main controller 10 displays, on the display of the user interface 90 , a message prompting the user to place the sheet Q on which the test patterns have been printed on the document table of the scanner unit 70 and to input a scan instruction. The flow then stands by until the scan instruction is input via the user interface 90 (S 220 ).

Upon the scan instruction being input, the main controller 10 controls the scanner unit 70 to read the sheet Q on which the test patterns have been printed, and acquires read image data of the read image from the scanner unit 70 (S 230 ).

Based on the read image data acquired from the scanner unit 70 , the main controller 10 identifies a positional deviation E between the first pattern image P 1 and second pattern image P 2 in each test pattern PA formed on the sheet Q (S 240 ). The positional deviation E here corresponds to an amount of positional deviation of the first pattern image P 1 as to the second pattern image P 2 in the sub-scanning direction, with the positional relationship between the first pattern image P 1 and second pattern image P 2 when the conveyance error of the sheet Q is zero as a reference.

The test pattern PA above in FIG. 8 is a test pattern in a case where the conveyance error of the sheet Q is zero, the same as the test pattern PA below in FIG. 6 . It can be seen from the example illustrated above in FIG. 8 that the first pattern element PE 1 situated at the middle perfectly matches the position of the second pattern element PE 2 . The positional deviation E in this case is zero.

In comparison with this, the test pattern PA below in FIG. 8 exhibits conveyance error of the sheet Q of an amount equal to distance L 1 . That is to say, this is a test pattern where the positional deviation E=L 1 . In this test pattern PA, the first pattern element PE 1 at the middle of the first pattern image P 1 , and the second pattern element PE 2 at the middle of the second pattern image P 2 , are offset by distance L 1 . Instead, the first pattern element PE 1 adjacent to the first pattern element PE 1 at the middle perfectly matches the second pattern element PE 2 .

In S 240 , the main controller 10 uses the above-described phenomenon to search for a combination of a first pattern element PE 1 and second pattern element PE 2 that are most fully overlapping, for each test pattern PA in the read image data, and can thus calculate the positional deviation E based on a position H in the main scanning direction of the combination most fully overlapping. The position H here corresponds to a position in the main scanning direction as to a point of origin O set at the center of the first pattern image P 1 .

Alternatively, the main controller 10 may calculate a distance W in the sub-scanning direction (see upper side in FIG. 8 ) between first pattern elements PE 1 and corresponding second pattern elements PE 2 , for each first pattern element PE 1 . The main controller 10 then may identify the position H in the main scanning direction where the distance W is the smallest as illustrated in FIG. 9 by function fitting as to the distribution of these distances W, thereby identifying the positional deviation E.

Thus, the main controller 10 identifies the positional deviation E for each test pattern PA formed on the sheet Q, and determines the identified positional deviation E to be the conveyance error of the sheet Q. The main controller 10 subsequently updates the correction parameter group stored in the NVRAM 17 , so that the conveyance error determined for each test pattern PA is set as a correction amount C 1 for a target conveyance amount at a corresponding rotation phase ϕ of the conveyance roller 613 (S 250 ). The correction parameter groups stored in the NVRAM 17 include a correction amount C 1 for each rotation phase ϕ, as illustrated in FIG. 10 . The main controller 10 updates the correction amount C 1 to the positional deviation E identified in S 240 .

When image data to be printed is input from outside or from the scanner unit 70 , the main controller 10 executes processing to form this image data on the sheet Q in accordance with the printing conditions input along with the image data. Specifically, as illustrated in FIG. 11 , the main controller 10 forms an image based on the image data to be printed on the sheet Q by alternately repeating processing of controlling the PF motor 63 to convey the sheet Q (S 410 ) and processing of controlling the recording head 40 and CR motor 53 to form, on the sheet Q, part of the image based on the image data to be printed (S 420 ).

In S 410 , the main controller 10 executes processing of reading out the correction amount C 1 corresponding to the rotation phase ϕ of the conveyance roller 613 from the NVRAM 17 (S 411 ), and processing of reading out a correction amount C 2 from the NVRAM 17 that corresponds to conveyance conditions (S 412 ).

The main controller 10 further executes processing of correcting a target conveyance amount LP of the sheet Q by the correction amount C 1 and correction amount C 2 that have been read out (S 413 ), and processing of setting a target rotation amount LS for the conveyance roller 613 in accordance with the corrected target conveyance amount (LP−C 1 −C 2 ) (S 414 ). The main controller 10 executes processing of controlling the PF motor 63 so as to rotate the conveyance roller 613 by an amount equal to the target rotation amount LS set above (S 415 ), thereby controlling the PF motor 63 to convey the sheet Q by an amount equal to the target conveyance amount LP.

The correction amount C 2 read out in S 412 is a correction amount determined beforehand by conveyance conditions such as the type of the sheet Q, the sheet conveyance amount immediately prior, the conveyance speed, and so forth. The NVRAM 17 stores the correction amount C 2 for each of the conveyance conditions, as illustrated in FIG. 10 . The correction amount C 2 may be understood to be a correction amount for correcting conveyance error due to factors other than conveyance error of the sheet Q due to the structure of the conveyance roller 613 .

In S 412 , the main controller 10 reads out the correction amount C 2 for the conveyance conditions identified from the printing conditions. The printing conditions include conditions relating to printing mode, for example. Conveyance conditions such as the type of sheet Q, conveyance speeds, and so forth, differ in different printing modes, a fact that is commonly known.

According to the image forming system 1 of the present embodiment described above, when forming a test pattern PA, a first pattern image P 1 involving minute-distance conveyance of the sheet Q is first formed, and thereafter long-distance conveyance of the sheet Q is performed, and a second pattern image P 2 is formed. This formation method of the test pattern PA including these procedures enables the test pattern to be formed on the sheet Q with less influence of play of the power transmission mechanism 62 , as compared to a conventional test pattern formation method where formation of a pattern image involving minute-distance conveyance is performed after the long-distance conveyance. As a result, influence of play of the power transmission mechanism 62 can be suppressed, and the correction parameter (C 1 ) of conveyance error due to the structure of the conveyance roller 613 such as eccentricity and outer form, for example, can be updated with high accuracy.

Play of the power transmission mechanism 62 , i.e., formation error in test patterns due to backlash among gears according to the present embodiment, is readily manifested immediately after the long-distance conveyance, which is to say at the early stages of minute-distance conveyance. The PF motor 63 is rotated by an amount smaller than the backlash in minute-distance conveyance, so there are cases where the PF motor 63 spins free at the early stages of minute-distance conveyance that is repeatedly performed.

The term “spins free” as used here means that the conveyance roller 613 or discharge roller 617 is not moving, i.e., the sheet is not moving, despite the PF motor 63 rotating. The “+L 1 ” in FIG. 12 indicates that minute-distance conveyance is being performed by an amount equal to the distance L 1 . At the upper left in FIG. 12 , the sheet Q is not moving due to the influence of backlash, even though minute-distance conveyance of “+L 1 ” is performed, so adjacent first pattern elements PE 1 are formed at generally the same position in the sub-scanning direction (Y-axis direction). The rectangles in FIG. 12 drawn using dotted lines indicate the positions of the first pattern elements PE 1 in a case where there is no free spinning of the PF motor 63 due to backlash, while the hatched rectangular blocks in FIG. 12 indicate the positions of the first pattern elements PE 1 influenced by free spinning.

A distance J indicated by an arrow in FIG. 12 represents a conveyance amount J of the sheet Q that occurs for each first pattern element PE 1 , from formation of the first pattern element PE 1 until formation of the second pattern element PE 2 corresponding to that first pattern element PE 1 .

Formation of each first pattern element PE 1 included in the first pattern image P 1 is performed including the influence of conveyance error δ of the sheet Q due to free spinning at the initial stage of minute-distance conveyance. In a case where long-distance conveyance is performed after the minute-distance conveyance, such as in the present embodiment, the influence of the conveyance error δ of the sheet Q due to the free spinning that has occurred at the initial stage of the minute-distance conveyance remains without change when forming the second pattern elements PE 2 . That is to say, each of the second pattern elements PE 2 is also formed on the sheet Q including the influence of conveyance error δ due to free spinning at the initial stage of the minute-distance conveyance, and the degree thereof is the same as that of the first pattern elements PE 1 .

Accordingly, the conveyance amount J of the sheet Q from the first pattern elements PE 1 being formed until the second pattern elements PE 2 are formed does not include the conveyance error δ due to free spinning, except for the combination of the first pattern element PE 1 formed first or at the initial stage of minute-distance conveyance and the corresponding second pattern element PE 2 (the combination illustrated to the far left side in FIG. 12 ).

In contrast with this, in the conventional test pattern formation method where formation of the pattern image involving minute-distance conveyance after the long-distance conveyance, the conveyance error δ due to free spinning in minute-distance conveyance occurs after the long-distance conveyance, so almost the entire test pattern is influenced by the conveyance error δ, as illustrated in FIG. 13 .

The example illustrated in FIG. 13 shows a third pattern image P 3 including multiple third pattern elements PE 3 being formed without involving minute-distance conveyance in the same way as the second pattern image P 2 , and thereafter a fourth pattern image P 4 including multiple fourth pattern elements PE 4 being formed involving minute-distance conveyance in the same way as the first pattern image P 1 .

It can be seen from FIG. 13 that, with regard to each of the third pattern elements PE 3 , a conveyance amount J 1 of the sheet Q from formation of the third pattern element PE 3 to the formation of the fourth pattern element PE 4 includes the conveyance error δ due to free spinning in all combinations of third pattern elements PE 3 and fourth pattern elements PE 4 , with the exception of the combination of the third pattern element PE 3 and fourth pattern element PE 4 formed first without involving minute-distance conveyance.

Accordingly, the conveyance error of the sheet Q can only be identified from the test patterns in a way that includes the influence of backlash in the conventional test pattern formation method. On the other hand, the conveyance error of the sheet Q due to the structure of the conveyance roller 613 can be identified from test patterns in the present embodiment, with the influence of backlash suppressed as described above.

Thus, according to the present embodiment, the target conveyance amount LP can be corrected more appropriately than the conventional method when correcting the target conveyance amount LP using the correction amounts C 1 and C 2 for each factor. As a result, the quality of the image formed on the sheet Q can be improved.

Moreover, the combination of the first pattern element PE 1 and second pattern element PE 2 formed by minute-distance conveyance in the initial stage include the influence of conveyance error due to backlash, so the main controller 10 may operate to identify the positional deviation E while deeming this one combination to not exist in the test pattern PA.

That is to say, in S 240 (see FIG. 5 ) the main controller 10 may calculate the distribution of distances W based on the layout of all first pattern elements PE 1 included in the test pattern PA where the first pattern image P 1 and the second pattern image P 2 are overlaid, excluding a predetermined number of first pattern elements PE 1 from the first pattern element PE 1 first formed on the sheet Q, and the layout of second pattern elements PE 2 corresponding thereto. The main controller 10 then may perform function fitting with regard to these distributions, and thereby identify the positional deviation E between the first pattern image P 1 and second pattern image P 2 .

Setting and updating the correction amount C 1 based on the positional deviation E identified in this way enables the target rotation amount LS to be corrected to reduce the conveyance error of the sheet Q with higher precision, whereby the quality of the image formed on the sheet Q can be improved.

Second Embodiment

The image forming system 1 according to a second embodiment forms test patterns according to the conventional technique in the first test pattern formation processing (S 120 ). That is to say, formation of a pattern image involving minute-distance conveyance is performed after a pattern image not involving minute-distance conveyance is formed and long-distance conveyance is performed. The image forming system 1 according to the second embodiment is configured in the same way as the image forming system 1 according to the first embodiment except for the points described below.

The first test pattern formation processing (S 120 ) according to the present embodiment is executed in a conveyance section regarding the sheet Q, where there is change from a state in which the leading edge of the sheet Q is situated further upstream from the discharge roller 617 , illustrated above in FIG. 14 , to a state in which the leading edge of the sheet Q passes the discharge roller 617 and is conveyed under force acting thereupon from both the conveyance roller 613 and the discharge roller 617 , illustrated below in FIG. 14 .

The second and subsequent test pattern formation processing (S 150 ) is executed in a section in which the sheet Q is conveyed under force acting thereupon from both the conveyance roller 613 and the discharge roller 617 , and a section in which the trailing edge of the sheet Q is situated further downstream from the conveyance roller 613 , and where the sheet Q is conveyed under force acting thereupon from the discharge roller 617 . In a certain time of test pattern formation processing (S 150 ) that is performed multiple times, the first pattern image P 1 is formed in a state where the sheet Q is conveyed under force acting thereupon from both the conveyance roller 613 and the discharge roller 617 , and the second pattern image P 2 is formed in a state where the trailing edge of the sheet Q has passed the conveyance roller 613 .

In the second and subsequent test pattern formation processing (S 150 ), the processing illustrated in FIG. 7 is executed in the same way as in the first embodiment. On the other hand, the processing illustrated in FIG. 15 is executed in the first test pattern formation processing (S 120 ), thereby forming a test pattern PB made up of an overlaid image of a third pattern image P 3 and a fourth pattern image P 4 , as illustrated in FIG. 16 .

In the test pattern formation processing in FIG. 15 , the main controller 10 controls the recording head 40 and CR motor 53 so that the third pattern image P 3 is formed on the stationary sheet Q (S 510 ). The third pattern image P 3 is formed using the first nozzle group N 1 in a state where the leading edge of the sheet Q is situated further upstream from the discharge roller 617 , as illustrated above in FIG. 14 . This processing forms the third pattern image P 3 exemplarily illustrated above in FIG. 16 on the sheet Q.

Thereafter, the main controller 10 controls the PF motor 63 so that the sheet Q is conveyed downstream by the predetermined distance L (S 520 ). The predetermined distance L is the distance of the third pattern image P 3 being conveyed to a position facing the second nozzle group N 2 at the downstream side of the recording head 40 . Specifically, if there is no conveyance error of the sheet Q, the predetermined distance L is a distance L where the third pattern element PE 3 positioned at the center of the third pattern image P 3 is completely overlaid by the fourth pattern element PE 4 positioned at the center of the fourth pattern image P 4 . In a case where the number of third pattern elements PE 3 in the third pattern image P 3 is

2×M+1,

this distance L corresponds to distance

L0−M×L1,

the same as in the first embodiment.

When the processing in S 520 ends, the leading edge of the sheet Q passes the discharge roller 617 , and the sheet Q is nipped at the nip of the conveyance roller 613 and discharge roller 617 , as illustrated below in FIG. 14 .

Thereafter, the main controller 10 repeatedly executes the processing of S 530 through S 550 , thereby controlling the recording head 40 , CR motor 53 , and PF motor 63 so that the fourth pattern image P 4 is formed on the sheet Q.

In S 530 , the main controller 10 controls the recording head 40 and CR motor 53 so that one fourth pattern element PE 4 is formed on the stationary sheet Q by discharge of ink droplets from the second nozzle group N 2 . In S 550 , the PF motor 63 is driven such that the sheet Q is conveyed downstream by a minute distance L 1 .

The main controller 10 repeatedly executes the processing of S 530 and S 550 until as many fourth pattern elements PE 4 as the number of third pattern elements PE 3 that the third pattern image P 3 has are formed on the sheet Q corresponding to the third pattern element PE 3 , thereby forming the fourth pattern image P 4 on the sheet Q. Upon formation of the fourth pattern image P 4 illustrated below in FIG. 16 being completed by forming a predetermined number of fourth pattern elements PE 4 (Yes in S 540 ), the main controller 10 ends the test pattern formation processing illustrated in FIG. 15 .

In the present embodiment, the test pattern formation processing illustrated in FIG. 7 and the test pattern formation processing illustrated in FIG. 15 are switched between and executed, in accordance with the conveyance section of the sheet Q. If the processing illustrated in FIG. 7 is executed in a state where the leading edge of the sheet Q has not passed the discharge roller 617 , there is a possibility that formation of the first pattern element PE 1 in each minute-distance conveyance may be performed in a state where the sheet Q is unstable due to the leading edge of the sheet Q being a free edge. This can be a factor that lowers the determination accuracy of conveyance error.

On the other hand, according to the test pattern formation processing illustrated in FIG. 15 , although there is conveyance error due to backlash included in the test pattern PB, conveyance error due to instability of the sheet Q is generally suppressed. Accordingly, test patterns PA and PB can be formed by methods appropriate for the conveyance sections of the sheet Q, correction of conveyance error can be appropriately performed, and good quality image formation can be performed on the sheet Q, according to the present embodiment.

Third Embodiment

In the image forming system 1 according to a third embodiment, the test pattern formation processing illustrated in FIG. 17 is executed at each of the test printing processing of S 120 and S 150 in FIG. 4 , instead of the processing in FIG. 7 . The image forming system 1 according to the third embodiment is configured in the same way as the image forming system 1 according to the first embodiment except for the points described below.

According to the present embodiment, a first integrated pattern image IP 1 (see above in FIG. 18 ), which is a combination of the first pattern image P 1 and third pattern image P 3 , is formed using the first nozzle group N 1 , by the main controller 10 executing the processing illustrated in FIG. 17 . Thereafter, long-distance conveyance of the sheet Q is performed. Further, a second integrated pattern image IP 2 (see below in FIG. 18 ), which is a combination of the second pattern image P 2 and fourth pattern image P 4 , is formed using the second nozzle group N 2 . This forms a test pattern PC that is an overlaid image of the first integrated pattern image IP 1 and the second integrated pattern image IP 2 on the sheet Q. The test pattern PC corresponds to a test pattern where the above-described test patterns PA and PB are integrated.

When the processing in FIG. 17 starts, the main controller 10 controls the recording head 40 , CR motor 53 , and PF motor 63 , so that the first pattern image P 1 is formed on the sheet Q by discharge of ink droplets from the first nozzle group N 1 , by repeatedly alternately executing processing the same as that of S 310 through S 330 in S 610 through S 630 .

Upon formation of a predetermined number of first pattern elements PE 1 (Yes in S 620 ), the main controller 10 controls the recording head 40 and CR motor 53 in a state where the sheet Q is stationary so that a group of third pattern elements PE 3 is formed by discharge of ink droplets from the first nozzle group N 1 , in a region U 2 adjacent to a region U 1 where one group of first pattern elements PE 1 has been formed in S 610 through S 630 (S 640 ).

Thereafter, the main controller 10 controls the PF motor 63 so that the sheet Q is conveyed downstream by the predetermined distance L (S 650 ). Further, the main controller 10 controls the recording head 40 and CR motor 53 so that the second pattern image P 2 corresponding to the first pattern image P 1 is formed on the stationary sheet Q (S 660 ). That is to say, the main controller 10 controls the recording head 40 and CR motor 53 so that the second pattern elements PE 2 corresponding to each of the first pattern elements PE 1 are formed on the sheet Q by discharge of ink droplets from the second nozzle group N 2 as to the sheet Q (S 660 ).

Further, the main controller 10 repeatedly executes S 670 through S 690 , in the same way as the processing of S 530 through S 550 . That is to say, the main controller 10 controls the recording head 40 , CR motor 53 , and PF motor 63 so that the fourth pattern image P 4 corresponding to the third pattern image P 3 is formed on the sheet Q by discharging ink droplets from the second nozzle group N 2 .

Upon formation of the fourth pattern image P 4 including the predetermined number of fourth pattern elements PE 4 being completed (Yes in S 680 ), the main controller 10 ends the test pattern formation processing illustrated in FIG. 17 .

In the present embodiment, the main controller 10 acquires read image data corresponding to the above-described test pattern PC that is an overlaid image of the first integrated pattern image IP 1 where the first pattern image P 1 and third pattern image P 3 have been integrated and the second integrated pattern image IP 2 where the second pattern image P 2 and fourth pattern image P 4 have been integrated (S 230 ). The main controller 10 analyzes this read image data, and identifies the positional deviation E between the first pattern image P 1 and second pattern image P 2 (E 1 ) and the positional deviation E between the third pattern image P 3 and fourth pattern image P 4 (E 2 ) for each test pattern PC.

A conveyance error K 1 of the sheet Q due to the structure of the conveyance roller 613 is determined to be E 1 , and a conveyance error K 2 of the sheet Q due to play (backlash) of the power transmission mechanism 62 is determined to be the difference between positional deviation E 1 and positional deviation E 2 , i.e., |E 1 −E 2 | (S 240 ).

As described above, the positional deviation E 1 identified from the test pattern PA where minute-distance conveyance is executed first basically does not include components of the play of the power transmission mechanism 62 . On the other hand, the positional deviation E 2 identified from the test pattern PB where minute-distance conveyance is performed later basically includes components of play. Accordingly, the conveyance error K 2 of the sheet Q due to play in the power transmission mechanism 62 can be determined from the difference between the positional deviations E 1 and E 2 .

The main controller 10 sets the conveyance error K 1 identified for each test pattern PC to the correction amount C 1 at the corresponding rotation phase ϕ, and sets a representative value of the conveyance error K 2 identified for each test pattern PC to the correction amount C 2 for the corresponding conveyance conditions, and thus updates the correction parameter groups stored in the NVRAM 17 (S 250 ). The representative value may be an average value or median value of the conveyance error K 2 acquired from each of the multiple test patterns PC.

The main controller 10 can execute test printing processing under each of multiple conveyance conditions (see FIG. 4 ), to set and update the correction amounts C 2 for each of the conveyance conditions stored in the NVRAM 17 based on the conveyance error K 2 from the test patterns PC.

According to the present embodiment, the test pattern PC having the features of the first pattern image P 1 , second pattern image P 2 , third pattern image P 3 , and fourth pattern image P 4 is formed on the sheet Q, whereby the conveyance error K 1 due to the structure of the conveyance roller 613 and the conveyance error K 2 due to play in the power transmission mechanism 62 are determined as conveyance error of the sheet Q, and the conveyance error of the sheet Q can be appropriately corrected based on these conveyance errors K 1 and K 2 . Thus, the image forming system 1 that is capable of controlling sheet conveyance with high accuracy can be constructed according to the present embodiment.

Other Embodiments

The present disclosure is not restricted to the above-described embodiments; rather, various embodiments may be made. The technology according to the present disclosure is applicable to systems that perform image formation using systems other than the ink-jet system. Test patterns are not restricted to the configurations illustrated in the drawings. The test patterns illustrated in the drawings are simplified and conceptual illustrations for description, and are not intended to restrict features such as numbers, layouts, colors, sizes, and so forth, whatsoever. The rotary encoder 65 may be provided to the rotation shaft of the conveyance roller 613 , or may be provided on the power transmission path from the PF motor 63 to the conveyance roller 613 . In a case where the rotary encoder 65 is provided to the rotation shaft of the conveyance roller 613 , the rotations of the conveyance roller 613 and the output of the rotary encoder 65 agree, but the rotations of the discharge roller 617 and the output of the rotary encoder 65 do not agree, so error relating to play in the power transmission mechanism is generated in the same way. The present disclosure can also suppress influence of such error as well.

Functions had by one component in the above embodiments may be distributed among multiple components. Functions had by multiple components may be integrated in one component. Part of the configurations in the above-described embodiments may be omitted. At least part of the configurations in the above-described embodiments may be added to or substituted in other configurations of the above-described embodiments. All forms included in the technical spirit specified in the language in the Claims are embodiments of the present disclosure.