Correction method of feeding amount of conveyance belt and inkjet recording apparatus using the method

An inkjet recording apparatus includes: a control device that controls feeding of the conveyance belt so that a recording medium is conveyed at a pitch of a prescribed feeding amount in a feeding direction, and establishes an origin on the recording medium based on a detection of a starting point arranged on the conveyance belt, and controls driving of the inkjet head so that test dots of an amount equivalent to one round of the conveyance belt are printed on the recording medium at the pitch, from the origin; and a correction device that corrects the feeding amount of the conveyance belt to a corrected feeding amount corresponding to a feeding position of the conveyance belt based on the measurement results for an inputted printing space, wherein the control device causes an ink droplet to jet to the recording medium according to the corrected feeding amount.

This application is based on Japanese Patent Application No. 2009-112221 filed on May 1, 2009, which is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a correction method of a feeding amount of a conveyance belt and to an inkjet recording apparatus employing the correction method of a feeding amount of a conveyance belt.

As an inkjet recording apparatus wherein ink drops are jetted from an ink jet head on a recording medium to be printed, there has been known one wherein a recording medium is conveyed by a conveyance belt of an endless type that is trained about plural rollers.

This conveyance belt is usually formed to be in an endless form by combining both ends of a belt-shaped belt member to be in a serrated form, so that both ends may be aced and spliced. In this thermal fusion splicing, both end portions of the belt member are pressed while they are fused. Therefore, the spliced portion thus spliced receives heat and pressure in the case of splicing, and its physical properties are changed, resulting in the phenomena where hardness and thickness of the spliced portion are different from those of other potions of the conveyance belt.

When a recording medium is conveyed by the conveyance belt having this spliced portion, when the spliced portion touches a roller, a difference of an amount of elongation from other portions of the belt is caused, and therefore, a feeding amount of the conveyance belt is fluctuated, resulting in troubles that an amount of conveyance for a recording medium is fluctuated.

Incidentally, it is also possible to manufacture a conveyance belt in an endless type, which, however, is not preferable because the manufacturing cost is high.

As a method for solving the aforesaid troubles, there have been suggested a method to detect the spliced portion to avoid sending of a recording medium and image forming in the spliced portion (for example, see Unexamined Japanese Patent Application Publication No. 2004-115176) and a method to detect a speed of the conveyance belt from rotation of a roller and to control speed fluctuation of the conveyance belt in the case of image forming by correcting image forming timing in the case when a reference position on the conveyance belt passes through the bottom part of an inkjet head, based on the aforesaid detection (for example, see Unexamined Japanese Patent Publication No. 2005-305919). In addition, there have been suggested methods to detect sheet-feeding errors of the conveyance belt and to control sheet-feeding errors by correcting encoder pulse to drive motor based on the results of the aforesaid detection by detecting an amount of conveyance for a recording medium from rotations of a roller and by confirming banding (white streaks and black streaks) by printing of plural-colored test patterns (for example, see Unexamined Japanese Patent Application Publication No. 2003-11345 and Japanese Patent Application Publication No. 3876654).

However, in the method described in Unexamined Japanese Patent Application Publication No. 2004-115176, it was impossible to print on a recording medium, because a fluctuation of a feeding amount of a conveyance belt in the case when the spliced portion touches the upper portion of the roller has not been controlled. Further, in the case of the methods described in Unexamined Japanese Patent Publication Nos. 2005-305919 and 2003-11345, and Japanese Patent Publication No. 3876654, fluctuations of feeding amount caused by a difference of an amount of elongation of the aforesaid conveyance belt cannot be detected by rotation of the roller, although speed fluctuations of the conveyance belt or sheet feeding errors are controlled based on the detection of rotations of the roller. In other words, fluctuations of feeding amount caused by distributions of hardness and thicknesses represented by the spliced portion and the other portions have not been controlled, because a feeding amount of the conveyance belt and an amount of rotation of the roller are not necessarily the same.

The present invention has been achieved in view of the aforesaid situation, and its objective is to provide a method of correcting a feeding amount of the conveyance belt that can control fluctuations of a feeding amount caused by distributions of hardness and thickness of the conveyance belt, and to provide an inkjet recording apparatus.

SUMMARY OF THE INVENTION

An aspect of the invention is as follows.

A feeding amount correction method for the conveyance belt in an inkjet recording apparatus that jets an ink droplet to a recording medium from an inkjet head while conveying the recording medium supported on the conveyance belt by feeding of an endless conveyance belt for conducting printing, wherein there are provided a test printing process to print test dots equivalent in terms of an amount to one round of the conveyance belt at a pitch of the prescribed feeding amount, from an origin on the recording medium to be established when a starting point arranged on the conveyance belt is detected, while causing the conveyance belt to convey the recording medium in the feeding direction of the conveyance belt at the pitch of the prescribed feeding amount, a process of measuring an amount of conveyance that measures a printing space for the test dots printed in the test printing process, a correction process that corrects a feeding amount of the conveyance belt to the corrected feeding amount corresponding to the conveyance position of the conveyance belt, based on results of the measurement in the aforesaid process of measuring an amount of conveyance, and an ordinary printing process that conducts printing on the recording medium, while feeding the conveyance belt with the aforesaid corrected feeding amount that results from the correction in the aforesaid correction process.

Another aspect of the invention is as follows.

An inkjet recording apparatus that conducts printing by discharging an ink droplet to the aforesaid recording medium from an inkjet head while causing an endless conveyance belt to convey the recording medium supported on the conveyance belt, wherein there are provided a control device that controls feeding of the conveyance belt so that the aforesaid recording medium may be conveyed at a pitch of the prescribed feeding amount in the direction of feeding the conveyance belt, and establishes an origin on the recording medium based on the detection of a starting point arranged on the conveyance belt, and controls driving of the inkjet head so that print test dots equivalent in terms of an amount to one round of the conveyance belt may be printed on the recording medium at the pitch of the prescribed feeding amount, from the origin, an input device where results of the measurement for the aforesaid printing space for the test dots are inputted, and a correction device that corrects a feeding amount of the conveyance belt to a corrected feeding amount corresponding to the position of feeding the conveyance belt, based on results of the measurement for the inputted printing space, and the control device causes an ink droplet to break out to the recording medium from the inkjet head while feeding the conveyance belt according to the corrected feeding amount corrected by the correction device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention will be explained as follows, referring to the drawings.

FIG. 1is a perspective view of inkjet recording apparatus100relating to the invention.

As is shown in this diagram, the inlet recording apparatus100is equipped with printer main body1, control PC4and with test dots measuring section5(seeFIG. 6). Among these items, the printer main body1is equipped with main scanning section2, conveyance section3and printer section6(seeFIG. 6).

Among these items, the main scanning section2and the conveyance section3will be explained first.

The main scanning section2is provided to be straddling the conveyance section3, and inside of the main scanning section2, there are provided cylindrical guide rails21and21which are extended in the direction of arrow X (hereinafter referred to as main scanning direction X) above the conveyance section3. On these guide rails21and21, carriage22that is mostly in a shape of a casing is supported to be capable of reciprocating freely in main scanning direction X.

FIG. 2Ais a front elevation of carriage22andFIG. 2Bis a bottom view of carriage22.

On the carriage22, there are mounted a plurality of recording heads220as shown inFIG. 2AandFIG. 2B, and in the present embodiment, there are mounted total 24 recording heads in total (8 colors×3 sets) wherein a row of only one set and a row having two sets arranged in the direction of arrow Y (hereinafter referred to as sub-scanning direction Y) are arranged reciprocally in the main scanning direction X to be in quantity of 16 rows. A bottom surface of the recording head220is exposed from carriage22, and on the bottom surface, plural nozzles221each breaking out ink droplet I for each color of yellow (Y), magenta M, cyan (C) and black (K) are arranged in the sub-scanning direction Y.

Further, head driver222(seeFIG. 6) that drives each recording head220for causing ink droplet I to jet from nozzle221is mounted on carriage22, and carriage motor23(seeFIG. 6) that causes the carriage22to scan in the main scanning direction X is connected to the carriage22.

As shown inFIG. 1, endless conveyance belt31that conveys the recording medium in the direction of arrow Z (hereinafter referred to as feeding direction Z) by its feeding while supporting the unillustrated recording medium from the rear side, is arranged on the upper portion of the conveyance section3. On both ends of the conveyance belt31in the main scanning direction, there are provided side plates311. As a recording medium, it is possible to use a resin film and metals, in addition to a sheet and cloth, and there is no limitation in particular.

FIG. 3is a perspective view showing the surroundings of conveyance belt31in conveyance section3. Incidentally, inFIG. 3, illustration of side plate311is omitted.

As is shown inFIG. 3, the conveyance belt31is trained about drive roller32and driven roller33in the feeding direction, and belt motor34for driving the drive roller32to rotate is connected to the side of one end of the chive roller32in the main scanning direction. The conveyance belt31is constructed so that it is sent in the feeding direction Z when the drive roller32is caused by the belt motor34to rotate. On the belt motor34, there is fixed rotary encoder (hereinafter referred to as encoder)341that detects rotation phase of an unillustrated motor axis, and AC servo motor amplifier (hereinafter referred to as motor amplifier)35(seeFIG. 6) that drives the belt motor34is connected to the belt motor34. The encoder341is arranged to output encoder pulse corresponding to rotation phase of the detected motor axis to motor amplifier35.

Further, on one end portion of the conveyance belt31in the main scanning direction X which does not support a recording medium, there is pierced hole31athat stipulates a position (also referred to as a starting point) for feeding conveyance belt31in the feeding direction Z. In addition, on the conveyance belt31, there is formed spliced portion31bwhen the conveyance belt31is formed in an endless form to be extended in the main scanning direction X as a prescribed length, and in this spliced portion31b, hardness and thickness are different from those on other portions.

Below the upper portion of conveyance belt31, there is arranged platen36in a shape of a rectangular plate that is extended in the main scanning direction X, and on both ends of platen36in the main scanning direction X, there are arranged holding plates37for preventing violent behavior of the conveyance belt31. These platen36and holding plate37are arranged so that carriage22may scan the upper portion of the platen36and the holding plate37.

On the portion that is over the conveyance belt31and is on the one end side of the conveyance belt, detection sensor38for detecting hole31aof the conveyance belt is fixed on the side plate311through sensor clamping plate39(seeFIGS. 5A and 5B). Specifically, a position for arrangement of detection sensor38in the main scanning direction X is a position through which the hole31apasses the lower portion in the case of feeding of the conveyance belt31. Further, a position of arrangement of detection sensor38in the sub-scanning direction Y is a position where the hole31acan be detected when the spliced portion31bof the conveyance belt31is in the vicinity of drive roller32and is at the upstream side of the drive roller32in the feeding direction Z, in other words, when the spliced portion31bis entering the drive roller32when the conveyance belt31is advanced. However, a position of arrangement of detection sensor38in the sub-scanning direction Y may also be a position where the hole31acan be detected, when the spliced portion31bis in the vicinity of driven roller33in place of the drive roller32and is at the upstream side of the driven roller33in the feeding direction Z.

Further, the detection sensor38is an optical sensor of a reflection type and it irradiates rays of light for detection downward in detecting operations. Therefor, the detection sensor38detects reflection of the rays of light for detection when a portion of conveyance belt31other than the hole31ais positioned to be in the lower part as is shown inFIG. 5A, while, the detection sensor38cannot detect reflection of the rays of light for detection when the hole31ais positioned to be in the lower part as is shown inFIG. 5B. In other words, the detection sensor38is arranged to be capable of detecting that the hole31ais positioned to be in a lower part, as an occasion to be impossible to detect reflection of the rays of light for detection. Then, when the detection sensor38detects the hole31a, the detection signals are outputted to interruption controller66(seeFIG. 6) which will be explained later.

Further, the conveyance belt31is connected to belt regular rotation switch71and to belt reverse rotation switch72(seeFIG. 6), and a user can advance the conveyance belt31manually in the regular direction (feeding direction Z) or in the reverse direction (direction opposite to the feeding direction Z), by pressing down the belt regular rotation switch71or the belt reverse rotation switch72.

Next, a structure of control for the inkjet recording apparatus100will be explained as follows referring toFIG. 6.FIG. 6is a block diagram showing the structure of control for the inkjet recording apparatus100.

As is shown in the drawing, the inkjet recording apparatus100is equipped with control PC4, test dots measuring section5and with printer control section6.

Among them, the control PC4is an operation device through which a user operates the inkjet recording apparatus100, and the printer control section6is controlled based on contents of the operations. In a concrete form, the control PC4outputs control command and image data of printing image. As this control command, there are a command of correction for feeding amount which will be explained later and a command of test printing for confirming an accuracy of conveyance for the conveyance belt31. In addition, the control PC4is constructed so that results of measurement for printing spaces of test dots may be inputted from test dots measuring section5to be outputted to printer control section6.

Concerning test dots to be explained later which are printed when a command of test printing is outputted to printer control section6from the control PC4, the test dots measuring section5measures printing spaces in the feeding direction Z, and outputs the results of the measurement to the control PC4. For the test dots measuring section5of this kind, heretofore known measuring instruments such as a scanner and a measuring microscope can be used. However, when a scanner is used, it is preferable to use one having a high resolution that is, for example, 2400 dpi (dot per inch) or higher.

The printer control section6is one to control respective sections of the printer main body1, and it is equipped with total control section60, image data processing section61, carriage control section62and with conveyance control section63.

Among the aforesaid items, the total control section60receives control commands coming from the control PC4, and controls image data processing section61, carriage control section62and conveyance control section63. In addition, the total control section60stores printing spaces for test dots outputted from the control PC4in memory for measured values68.

The image data processing section61is controlled by the total control section60to store image data inputted from the control PC4in image memory69, then, to process the image data to generate ink jetted data. And it outputs the ink jetted data thus generated to head driver222of carriage22. The head driver222in which the ink jetted data have been inputted causes a droplet of ink I to jet from each of nozzles221of each recording head220based on the ink jetted data.

The carriage control section62is controlled by the total control section60to control driving of carriage motor23of carriage22.

The conveyance control section63is one that is controlled by the total control section60to control feeding of the conveyance belt31, and it is equipped with belt control section64, pulse generator65, interruption controller66and with belt position memory67.

The belt control section64outputs drive signals for feeding the conveyance belt31at a certain feeding amount to the pulse generator65, and reads out an encoder count which was calculated by pulse generator65and will be explained later, to detect a feeding amount for the conveyance belt31. Further, when interruption signals coming from the interruption controller66explained later are inputted, the belt control section64outputs reset signals for resetting the encoder count to the pulse generator65. The belt control section64calculates a total feeding amount of the conveyance belt31from detection of hole31a, namely, a feeding position of the conveyance belt31whose reference is hole31a, by calculating the total sum of feeding amount in drive signals after inputting of interruption signals coming from interruption controller66, and outputs the calculated position in belt position memory67. However, when the conveyance belt31is fed manually by the belt regular rotation switch71or the belt reverse rotation switch72, feeding position of the conveyance belt31whose reference is hole31ais calculated by an encoder count after input of interruption signals.

Further, the belt control section64is connected to the belt regular rotation switch71and to the belt reverse rotation switch72, and it keeps outputting drive signals for the feeding amount established in advance to the pulse generator65during the period when the belt regular rotation switch71or the belt reverse rotation switch72is pressed down.

The pulse generator65receives drive signals coming from the belt control section64, and generates chive pulses corresponding to the feeding amount of the conveyance belt31in this chive signals, to output them to motor amplifier35, and to count encoder pulses from encoder341inputted through motor amplifier35as an encoder count. Meanwhile, in the present embodiment, one pulse of each of drive pulses and encoder pulses corresponds to a feeding amount of conveyance belt31of about 0.6 μm.

When detection signals from detection sensor38are inputted in interruption controller66, the interruption controller66outputs interruption signals to belt control section64.

The belt position memory67stores a feeding position for the conveyance belt31on which a reference is hole31ainputted from the belt control section64.

Next, a correction method of feeding amount of conveyance belt31will be explained as follows, referring mainly toFIGS. 7 to 9.

Each ofFIGS. 7 to 9is a flow chart of a correction method of feeding amount of conveyance belt31.

First, as shown inFIG. 7, a user operates the control PC4to turn off an instruction of feed amount correction (step S1). This instruction of feed amount correction is a control command for feeding the conveyance belt31at a corrected feed amount LMODwhich will be explained later.

Next, test printing is conducted for confirming an accuracy of conveyance for the conveyance belt31(step S2). This test printing is carried out when a user operates the control PC4to cause an instruction of test printing to be outputted. Incidentally, when a state of jetting of ink droplet I from plural nozzles221is not excellent, it is preferable to conduct cleaning of plural recording heads220in advance.

After this test printing has been carried out, printer control section6controls first head driver222to conduct a purge of ink in nozzle221for improving jetting properties, as shown inFIG. 8(step S21). In this case, ink droplets I in quantity of about 150 shots are caused to jet from nozzle221.

Next, the printer control section6drives belt motor34to convey a recording medium by feeding the conveyance belt31by a feeding amount that is double the pitch LCOMfor the prescribed feeding amount which will be explained later (step S22).

Incidentally, a nozzle purge and belt feeding in step S21and step S22do not need to be conducted, if there is no problem in jetting properties for ink droplets I from a plurality of nozzles221.

Next, there is conducted the finding of reference point of conveyance belt31(step S23). In this case, the printer control section6drives belt motor34to keep feeding the conveyance belt31in the feeding direction until the moment when the hole31ais detected by detection sensor38. Then, when the hole31ais detected, the printer control section6causes the conveyance belt31to stop, and resets the encoder count counted by pulse generator65. Further, the printer control section6establishes a position on a recording medium on which test dots are printed in the following step as an origin in the feeding direction Z for the test dots printed intermittently in the feeding direction Z.

Meanwhile, the finding of reference point for the conveyance belt31in the step S23may also be conducted before a nozzle purge and belt feeding in steps S21and S22. However, in that case, it is preferable to make the origin established on the recording medium to remain unchanged, by putting the conveyance belt31back in the direction opposite to the feeding direction Z by a feeding amount that is double the pitch LCOMfor the prescribed feeding amount fed in the feeding direction Z in step S22.

Next, the printer control section6drives carriage motor23to cause carriage22to move to a recording position (step S24). This recording position has only to be above the recording medium that is set on the conveyance belt31in advance. Incidentally, the recording medium used in this case can be anything provided that it is one in at least a length equivalent to one round of the conveyance belt31in the feeding direction, and it is preferable that the recording medium used in this case is a sheet of paper.

Next, the printer control section6controls head driver222to cause ink droplets I to jet from plural nozzles221, and causes test dots to be printed on the recording medium n (step S25). In this case, ink droplets I in quantity of 15 shots are caused to jet as test dots.

Next, the printer control section6drives belt motor34to feed the conveyance belt31by a length of a pitch LCOMfor the prescribed feeding amount in the feeding direction Z, to cause the recording medium to be conveyed (step S26). In this case, pitch LCOMfor prescribed feeding amount is a typical feeding amount selected in advance among plural feeding amounts of the conveyance belt31. This pitch LCOMfor prescribed feeding amount is 54.1867 mm in the present embodiment, and it is set as follows.

Since nozzles221in quantity of 512 per head are arranged at 180 npi (nozzle per inch) in the sub-scanning direction Yin recording head220, length W of this nozzle row in the sub-scanning direction Y is 25.4/180×512 which is nearly equal to 72.2489 mm (seeFIG. 2B). Further, three recording heads220per one color are provided so that each row does not overlap in the sub-scanning direction. Y, thus, the total length of the nozzle rows in these three recording heads220is 722489×3=216.7467 mm. For conducting printing by these recording heads220at 720 dpi in sub-scanning direction Y (feeding direction Z) as a typical printing mode in the inkjet recording apparatus100in the present embodiment, feeding operations in 720/180=4 times are needed. Therefore, for realizing this operation with even feeding of the conveyance belt31, it is necessary to make a pitch of feeding amount to be 216.7467/4=54.1867 mm.

Next, the printer control section6judges whether the total feeding amount of the conveyance belt31from the origin on the recording medium established in step23arrives at a length equivalent to one round of the conveyance belt31in the feeding direction Z or not (step S27), and when the total feeding amount has not arrived (step S27; No), a flow returns to step S25to repeat printing operations of test dots.

Further, when the total feeding amount of the conveyance belt31from the origin on the recording medium has not arrived at a length equivalent to one round of the conveyance belt31in the feeding direction Z in step S27(step S27; Yes), the printer control section6drives carriage motor23to cause carriage22to move to the prescribed position for standing by (step S28), and test printing is terminated. In the present embodiment, since a length equivalent to one round of the conveyance belt31in the feeding direction Z is about 2980 mm, the total number N of test dots in the feeding direction Z is 2980/54.1867 which is nearly equal to 55 points, excluding on point at the origin.

After termination of test printing, a space of printing for test dots, namely, actual amount of conveyance for the recording medium is measured by test dot measuring section5, as shown inFIG. 7(step S3). Then, the space of printing for test dots thus measured is read into control PC4to be outputted to printer control section6, and is stored in memory for measured values68.

When difference ΔL between each printing space of measured test dots and pitch LCOMwhich represents a command value of the space of printing for test dots for the prescribed feeding amount is represented graphically concerning an amount of conveyance of the recording medium, it becomes like one shown inFIG. 10A. From this graph, it is understood that, when spliced section31bof the conveyance belt31touches drive roller32or drive roller33, ΔL grows greater, namely, an accuracy of conveyance is lowered. This is caused by that hardness and a thickness of the spliced section31bare different from those of the other portion of the conveyance belt31.

After the space of printing of test dots is measured in step S3, printer control section6makes the correction of feeding amount to be effective (step S4). In other words, the printer control section6establishes to feed the conveyance belt31by the corrected feeding amount which will be explained later.

Next, the printer control section6conducts image printing (step S5). In this case, the printer control section6corrects a feeding amount of the conveyance belt31to the corrected feeding amount corresponding to the position of feeding for the conveyance belt31based on the results of measurement of test dots measured in step S3(correction process), then, it controls head driver222to cause ink droplet I to jet recording medium from nozzle221of recording head220while feeding the conveyance belt31in the corrected feeding amount by driving belt motor34, thus, inputted image data are printed (ordinary printing process).

In this image printing, the printer control section6first calculates mean value LAVEof the measured spaces of printing for one round of the conveyance belt31and total amount of conveyance LSUMof a recording medium from the origin to the position of feeding for the conveyance belt31to be calculated (step S51). The position of feeding for the conveyance belt31in this case means a position of the conveyance belt31on which optional test dots are printed. Further, the total amount of conveyance LSUMis calculated as LSUM=i×LCOM(where, i=1 to N) in the case of ithtest dot from the origin, for example, by using pitch LCOMfor the prescribed feeding amount.

Next, the printer control section6calculates, by using the following expression (1), the ordinal number n of the space of printing for test dots in the direction opposite to the feeding direction Z from the origin (step S52).
n=int(LSUM/LAVE)  (1)

In the expression above, int A is an integer that does not exceed A.

Next, the printer control section6judges whether the ordinal number n calculated in step S52is smaller than the total number of test dots or not (step S53), and if the number n is smaller than the total number N (step S53; Yes), the printer control section6calculates corrected feeding amount LMODrepresenting corrected pitch LCOMfor the prescribed feeding amount with the following expressions (2) to (4), by using measured nthprinting space Lnand (n+1)thprinting space Ln+1(step S54)
LRE=LSUMmod LAVE(2)
LPOS=Ln+LRE×{(Ln+1−Ln)/LAVE}(3)
LMOD=LCOM×LAVE/LPOS(4)

In the expressions above, AmodB is a residue of A/B.

The aforesaid calculation of corrected feeding amount LMODby the expressions (1) to (4) will be explained.

First, in expression (1), with respect to optional total amount of conveyance LSUMfrom the origin, the nearest one among test dots through which the LSUMpassed is calculated to be n. Then, in expression (2), a length by which the LSUMexceeds an amount of conveyance up to nthtest dot is calculated as LRE. Next, in expression (3), imaginary feeding amount LPOSat the position that is apart from Lnby LREis calculated by interpolating Lnand Ln+1linearly. Finally, corrected feeding amount LMODis calculated from LPOSby expression (4). A conceptual diagram for the above calculation is shown inFIG. 11. An example of the results of calculation is shown in the following Table 1.

Further, in step S54, the printer control section6predicts corrected feeding amount L′MODabout another feeding amount L′COMother than pitch for the prescribed feeding amount LCOM, based on results of measurement for printing space for test dots printed at pitch LCOMfor the prescribed feeding amount.

Specifically, when a value of feeding amount L′COMis smaller than pitch LCOMfor the prescribed feeding amount, L′MODis calculated by the following expression (5) that uses L′COMin place of LCOMin the expression (4).
L′MOD=L′COM×LAVE/LPOS(5)

On the other hand, when feeding amount L′COMtakes a value that exceeds pitch LCOMfor the prescribed feeding amount, L′MODis calculated by the following expressions (6) to (9), after L′SUM=i×L′COM(where, i=1 to N×LCOM/L′COM) is calculated concerning test dots from the origin to ithtest dot to be calculated.

When the number n calculated in step S52exceeds the total number N of test dots in step S53(step S53; No), the printer control section6judges whether printing operations are possible or not (step S55). In this case, there is a fear that belt motor34, detection sensor38or conveyance control section63is problematic, or mechanical portions are abnormal, or the conveyance belt31is slipping. Therefore, the printing operations are confirmed whether they are possible or not, and when they are judged to be possible (step S55; Yes), the printer control section6moves to step S56to conduct printing operations without correcting a feeding amount of the conveyance belt31. On the other hand, when the printing operations are judged to be impossible (step S55; No), the printer control section6indicates errors to a user, and stops operations of the inkjet recording apparatus100.

When corrected feeding amount LMODis calculated in step S54, the printer control section6conducts desired printing by causing ink droplets I to jet from nozzle221of recording head220, while feeding the conveyance belt31by using corrected feeding amount LMODin place of pitch LCOMfor the prescribed feeding amount LCOM(step S56). However, when feeding the conveyance belt31with another feeding amount L′COMother than pitch LCOMfor prescribed feeding amount, the printer control section6conducts printing while feeding the conveyance belt31by using corrected feeding amount L′MODin place of another feeding amount L′COM.

With respect to calculation or judgment in the aforesaid steps S51to S54, it is carried out each time feeding of the conveyance belt31is instructed as driving signals from belt control section64, for an amount of the feeding. In other words, the printer control section6conducts printing in step S56, while calculating the corrected feeding amount for each feeding of the conveyance belt31.

By conducting printing by using corrected feeding amount LMODas stated above, a feeding amount is corrected based on an amount of conveyance for a recording medium corresponding to a position of feeding of the conveyance belt31. Therefore, as is shown inFIG. 10B, it is possible to control a decline of an accuracy of conveyance in the case where the spliced portion31bof the conveyance belt31touches drive roller32or driven roller33, compared withFIG. 10Abefore the correction.

In the printing that employs this corrected feeding amount, the printer control section6causes starting point hole31ato be detected by detection sensor38, and resets a position of feeding conveyance belt31calculated by belt control section64, for each detection of the starting point hole31afollowing the feeding of the conveyance belt31. Then, the printer control section6controls conveyance control section63so that the conveyance belt31may be fed with a corrected amount of conveyance that corresponds to the new position of feeding the conveyance belt31that is sent after the resetting.

Further, in the printing that employs this corrected feeding amount, the position of feeding the conveyance belt31calculated by the belt control section64is stored in belt position memory67. Therefore, even when the conveyance belt31is fed manually by belt regular rotation switch71or belt reverse rotation switch72, the feeding position does not become unclear, and a feeding amount can be controlled properly.

In the correction method of feeding amount for conveyance belt31in the present embodiment, the feeding amount is connected based on an amount of conveyance of a recording medium corresponding to the position of feeding for the conveyance belt31as is stated above. Therefore, it is possible to control a decline of an accuracy of conveyance in the case where the spliced portion31bof the conveyance belt31touches drive roller32or driven roller33. Namely, it is possible to control fluctuations of a feeding amount caused by distribution of hardness and a thickness which are peculiar to the conveyance belt31.

Further, the starting point hole31aof the conveyance belt31is detected when spliced portion31bof the conveyance belt31is in the vicinity of drive roller32or driven roller33and it is at the upstream side of the drive roller32or of driven roller33in the feeding direction Z. Therefore, the spliced portion31btouches either one of the rollers immediately after the starting point hole31ais detected. In other words, the spliced portion31btouches either one of the rollers immediately after the printing of test dots is started. Therefore, entering of the spliced portion31binto either one of the rollers that causes greatest changes for the worse for accuracy of conveyance can be conducted in the initial stage of test printing where accumulation of errors is less. Accordingly, printing spaces at a position where the greatest change for the worse is caused can be measured at higher accuracy, resulting in possibility of correction at higher accuracy.

Further, since the starting point hole31ais arranged on a portion that is one end portion of the conveyance belt31in the main scanning direction X and does not support a recording medium, no harmful influence is exerted on printing operations on the recording medium. Further, since the starting point hole31ais a hole portion, there is no possibility of erroneous detection caused by adhesion of ink droplet I and by sliding of a marker itself, and it can be formed at low cost, which is different from an occasion where a marker is pasted on a surface of the conveyance belt31.

It is further possible to control accumulated errors for the feeding amount caused by microscopic slip of the conveyance belt31, because a position of feeding for the conveyance belt31is reset for each detection of the starting point hole31a.

Further, since the position of feeding the conveyance belt31having a reference of starting point hole31ais stored, even when the conveyance belt31is fed manually by belt regular rotation switch71or by belt reverse rotation switch72, the feeding position does not become unclear, and a feeding amount can be controlled properly.

In addition, pitch for the prescribed feeding amount LCOMis a typical feeding amount selected in advance among plural feeding amounts of the conveyance belt31, and corrected feeding amount about another feeding amount other than the typical feeding amount is predicted based on results of measurement for printing space of test dots printed with the typical feeding amount. Thus, it is possible to correct highly accurately the feeding amount that is used at the highest frequency, for example, as a typical feeding amount, and it is possible to obtain plural corrected feeding amounts easily without necessity of conducting correction of feeding amount for all of the plural feeding amounts.

Meanwhile, the invention should not be construed to be limited to the aforesaid embodiment, and the embodiment can naturally be varied and improved.

For example, in the aforesaid embodiment, the spliced portion31bof the conveyance belt31has been described to be one formed to be extended in the main scanning direction X. However, the spliced portion31bmay also be one formed to be oblique relative to the main scanning direction X. However, in the case of conveyance belt31that has the oblique spliced portion31bof this kind and has a thickness exceeding the prescribed value, aggravation of an accuracy of conveyance caused by spliced portion31btouching either one of the rollers becomes inconstant, resulting in a fear that an inhibition of this problem by control is difficult, which is not preferable.

Though a feeding amount for the conveyance belt31can be measured by using a contact sensor such as, for example, an encoder, when a surface of the conveyance belt31is caused to be a surface to be measured, there is a fear that adhesives for sticking a recording medium adhere to the sensor to cause erroneous operations, while, when the reverse side is caused to be a surface to be measured, there are fears including a fear that the aforesaid adhesives run over to the reverse side and a fear that erroneous operations are caused by scattered ink droplets I, which is not preferable.

Further, the detection sensor38may also be of a transmission type without being of a reflection type, but in the case of a sensor of a transmission type, there is a fear that smudges adhere to a light-emitting device or a light-receiving device to cause erroneous detection, which is not preferable.

Further, in image printing in the correction method of a feeding amount for the conveyance belt31, a calculation of the corrected feeding amount is not always needed for each feeding of the conveyance belt31, and corrected feeding amounts for all printing spaces can be calculated collectively.

In the embodiment of the invention, test dots are printed on a recording medium with a pitch for the prescribed feeding amount from the origin established on the recording medium based on the starting point on the conveyance belt, and the feeding amount for the conveyance belt is corrected to the corrected feeding amount corresponding to the position of feeding of the conveyance belt, based on results of the measurement of printing space of the aforesaid test dots. In other words, it is possible to control fluctuations of feeding amount caused by distribution of hardness and a thickness which are peculiar to the conveyance belt, because the feeding amount is corrected based on an amount of conveyance for the recording medium corresponding to the position of feeding for the conveyance belt.

In another embodiment, the starting point of the conveyance belt is detected when a spliced portion of the conveyance belt is in the vicinity of a drive roller and is at the upstream side of the roller in the feeding direction, therefore, the spliced portion touches the roller immediately after the starting point is detected. In other words, the spliced portion touches the roller immediately after the start of printing of test dots, therefore, entering of the spliced portion into the roller that causes greatest changes for the worse for accuracy of conveyance can be conducted in the initial stage of test printing where accumulation of errors is less. Accordingly, printing spaces at a position where the greatest change for the worse is caused can be measured at higher accuracy, resulting in possibility of correction at higher accuracy.

In further another embodiment, the starting point is arranged on a portion that is an end portion of the conveyance belt in its width direction and does not support a recording medium, therefore, no harmful influence is exerted on printing operations on the recording medium. Further, since the starting point is a hole portion, there is no possibility of erroneous detection caused by adhesion of ink droplets and by sliding of a marker itself, and it can be formed at low cost, which is different from an occasion where the marker is pasted on a surface of the conveyance belt.

In still another embodiment, it is possible to control accumulated errors for the feeding amount caused by microscopic slip of the conveyance belt, because a position of feeding for the conveyance belt is reset for each detection of the starting point.

In still another embodiment, even when the conveyance belt is fed manually, for example, the feeding position does not become unclear, and a feeding amount can be controlled properly, because the position of feeding the conveyance belt having a reference of starting point is stored.

In still another embodiment, a pitch for the prescribed feeding amount is a typical feeding amount selected in advance among plural feeding amounts of the conveyance belt, and corrected feeding amount about another feeding amount other than the typical feeding amount is predicted based on the corrected feeding amount obtained through correction of the typical feeding amount, thereby, it is possible to correct highly accurately the feeding amount that is used at the highest frequency, for example, as a typical feeding amount, and it is possible to obtain plural corrected feeding amounts easily without necessity of conducting correction of feeding amount for all of the plural feeding amounts.