Patent Publication Number: US-6905186-B2

Title: Image recording apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image recording apparatus which reduces deviation in the feeding distance or feeding speed of a recording material and the movement of a printing head. 
     2. Background Arts 
     Various printers such as an inkjet printer, a thermal printer and the like are generally used for recording an image on recording paper. When some malfunction occurs in a recording device of the printer, image quality of the recorded image becomes inferior. Taking a case of the inkjet printer, for example, a nozzle for ejecting ink is sometimes clogged with the ink. The clogging causes imperfection in ink ejection, since an ejection amount is decreased. Imperfection in ink ejection causes streaky color unevenness and density unevenness which appear on the recorded image. 
     When color unevenness or density unevenness happens, the printer is switched over a head cleaning mode to correct imperfection in ink ejection of the recording device. Since color unevenness or density unevenness causes waste of the ink and the recording paper, some business-use printers automatically print test patterns to correct imperfection in ink ejection at regular time intervals. (for example, United States Patent Publication No. 2001/0004284 and Japanese Patent Laid-Open Publication No. 11-198358.) U.S. Pat. No. 6,412,902 also discloses a printer which prints test patterns on a margin between images, in order to reduce the waste of recording paper. 
     The cleaning of the printing head, as described above, can correct print imperfection caused by the recording device. The streaky unevenness, however, still appears, since it is caused by deviation in the feeding distance of the recording paper and the movement of the printing head. 
     These days, various types of recording paper having different texture, thickness, width and the like have been used. The friction between the recording paper and a pair of feed rollers is changed depending on the type of recording paper, so that the feeding distance or feeding speed of the recording paper deviates. The friction between the recording paper and the feed roller pair slightly varies in accordance with the variation in environment temperature and humidity. The diameter of the feed roller also varies in accordance with the variation in environment temperature. Therefore, there is a problem that the deviation in the feeding distance or feeding speed of the recording paper causes a white streak appearing in an unprinted area, or a black streak appearing in an area where adjacent print lines are overlapped. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image recording apparatus which reduces deviation in the feeding distance or feeding speed of recording paper and the movement of a printing head, in order to prevent streaky unevenness and the like caused thereby. 
     Another object of the present invention is to provide an image recording apparatus which efficiently detects a faulty recording device. 
     To achieve the above objects, an image recording apparatus according to the present invention comprises a recording head for recording an image, a detection means, a test pattern analyzer, and a correction means. The recording head, having plural neatly arranged recording devices, records a test pattern in a margin of the image. The detection means detects the recorded test pattern. The test pattern analyzer analyzes signals from the detection means, to calculate deviation in relative movement or relative speed of the recording paper or the recording head. Then, the correction means corrects the relative movement or relative speed on the basis of the deviation. 
     The test pattern may include first check pattern. The first check pattern comprises plural first check lines which are recorded by the same recording device driven at predetermined time intervals on the basis of predetermined drive signals, while the recording material is relatively moved to the recording head. The test pattern analyzer measures distance between the first check lines to determine deviation in the relative movement or relative speed. 
     The test pattern may include second check pattern. The second check pattern comprises plural second check lines which are recorded by the same recording device for predetermined elapsed time on the basis of predetermined drive signals, while the recording material is relatively moved to the recording head. The test pattern analyzer measures the length of the second check line to determine deviation in the relative movement or relative speed. 
     The test pattern may include at least one of a faulty recording device check pattern, a calibration pattern, and a solid fill check pattern. 
     According to the present invention, the deviation in the relative moving distance of the recording paper or the recording head is corrected based on the analysis result of the test pattern. Accordingly, it is possible to prevent the occurrence of print imperfection, such as streaky unevenness and the like, caused by the deviation thereof. If both of check patterns for detecting the faulty nozzle and for calculating the deviation are used at the same time, it is possible to prevent the occurrence of general print imperfection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become apparent from the following detailed descriptions of the preferred embodiments when read in association with the accompanying drawings, which are given by way of illustration only and thus do not limit the present invention. In the drawings, the same reference numerals designate like or corresponding parts throughout the several views, and wherein: 
         FIG. 1  is a schematic view a serial print type inkjet printer according to the present invention; 
         FIG. 2  is a plan view of a printing device and a test pattern imaging device in the printer of  FIG. 1 ; 
         FIG. 3  is an enlarged front view of an inkjet head; 
         FIG. 4  is a flow chart showing the processes of the inkjet printer; 
         FIG. 5  is an explanatory view showing an example of a test pattern; 
         FIG. 6  is an explanatory view showing another example of the test pattern; 
         FIG. 7  is an explanatory view showing an example of a paper feeding distance check pattern; 
         FIG. 8  is an explanatory view showing an example of a head movement check pattern; 
         FIG. 9  is an explanatory view showing an example of a faulty recording device check pattern; 
         FIG. 10  is an explanatory view showing an example of a density check pattern; 
         FIG. 11  is an explanatory view showing an example of a solid fill check pattern; 
         FIG. 12  is a schematic view of a line print type of an inkjet printer; 
         FIG. 13  is a plan view of a printing device and a test pattern imaging device in the printer of  FIG. 12 ; 
         FIG. 14  is an explanatory view showing an example of a paper feeding distance check pattern in the printer of  FIG. 12 ; and 
         FIG. 15  is an explanatory view showing another example of the paper feeding distance check pattern in the printer of FIG.  12 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the present invention will be hereinafter described with taking a serial print type inkjet printer (a serial printer) as an example. Referring to  FIGS. 1 and 2 , an inkjet printer  92  is provided with a paper supply unit  93 , a printing device  94 , a paper cutter  95 , a test pattern imaging device  96 , a test pattern analyzer  97 , a tray  98  and the like. A recording paper roll  10  is set in the paper supply unit  93 . The recording paper roll  10  drawn out by feeder rollers (not illustrated) is fed into the printing device  94  as recording paper  11 . 
     The printing device  94  comprises a platen roller  12 , a set of pinch rollers  13  and  14 , an inkjet head  15 , and a head carriage  16  as head carrying means to move the inkjet head  15  in a main scan direction. The pinch rollers  13  and  14  disposed above the platen roller  12  press the recording paper  11  against the platen roller  12  in order to prevent the recording paper  11  from sagging. 
     Referring to  FIG. 3 , the inkjet head  15  has yellow (Y) nozzles  21 , magenta (M) nozzles  22 , cyan (C) nozzles  23 , and black (K) nozzles  24 . The nozzles  21  to  24  of each color are neatly aligned in a sub scan direction. In the inkjet head  15 , as is well known, piezoelectric elements are provided in an ink flowing path near each nozzle  21  to  24 . When the piezoelectric elements constrict and release the ink flowing path, ink is discharged or supplied. 
     The head carriage  16  carries the inkjet head  15  in the main scan direction, as shown in  FIG. 2 , so that a full color image of one line is printed along the main scan direction. The head carriage  16  includes a carriage body  16   a , a carrying mechanism  16   b , a guide shaft  16   c  and the like. The platen roller  12  rotated by a pulse motor  17  feeds the recording paper  11  by one line in the sub scan direction, whenever the image of one line is printed. A system controller  30  controls the pulse motor  17  via a driver  17   a . The platen roller  12  and the pulse motor  17  compose recording paper feeding means in the sub scan direction. 
     A head driver  25 , as shown in  FIG. 1 , controls each piezoelectric element of the ink jet head  15 . The head driver  25  connected to the system controller  30  provides each piezoelectric element with drive signals based on image data. The system controller  30  is connected to a frame memory  31 , a key input section  32 , a display panel  33  and the like. Image data read by an image reader and the like is stored in the frame memory  31 . The system controller  30  calculates drive amount of the piezoelectric elements of each color nozzle  21  to  24  on the basis of image data, and sends it to the head driver  25 . The head driver  25  drives each piezoelectric element in synchronization with the operation of the head carriage  16 . Accordingly, ink droplets the size of which correspond to image data are ejected onto the recording paper  11 , so that the color inks of Y, M, C and K adhere to the recording paper  11 . The inkjet head  15  records the image of one line while moving in the main scan direction. Upon completion of one line image recording in the main scan direction, the pulse motor  17  rotates to feed the recording paper  11  by one line in the sub scan direction. The recording paper  11  may be so fed as to complement the space between dots recorded in the main scan direction. Repeating the foregoing operations, the full-color image of a single picture frame is recorded on the recording paper  11 . To achieve high image quality, one or plural gradient expressions such as dot diameter control, dot density control and the like are adopted in recording the image. 
     The paper cutter  95  comprises a fixed blade  40 , a rotatable blade  41 , a blade carrying mechanism  42 , and a shift guide  43 . The long fixed blade  40  is disposed along the width direction of the recording paper  11 . Since the blade carrying mechanism  42  carries the rotatable blade  41  along the fixed blade  40 , the recording paper  11  is cut in its width direction between adjacent image frames. 
     The shift guide  43  is movable between a guide position illustrated by a chain double-dashed line and an evacuated position illustrated by a solid line. When the shift guide  43  is at the guide position, the recording paper  11  on which test patterns  50  and  51  are recorded is guided to a waste paper box  44 . Then, the recording paper  11  is cut as a sheet of waste paper  48 . When the shift guide  43  is at the evacuated position, the recording paper  11  is guided to the tray  98  to be cut as a print sheet  18 . Only a part of the print sheet  18  on which the test patterns  50  and  51  are recorded may be cut and guided to the waste paper box  44  as the waste paper. 
     The test pattern imaging device  96  comprises a camera  46  and a camera carrying mechanism  47  (refer to  FIG. 2 ) for carrying the camera  46  in the width direction of the recording paper  11 . The test pattern imaging device  96  takes the image of the test patterns recorded on the recording paper  11  to obtain image data. In a case where the test patterns are recorded across plural picture frames, the borderline of picture frames is detected by a pattern matching process. Image data merged with respect to the borderline becomes continuous test pattern image data. Image data is sent to the pattern analyzer  97 . On the basis of test pattern image data, the pattern analyzer  97  judges if print imperfection appears. The result of judgment is sent to the system controller  30 . 
     The system controller  30  has a normal print mode and a test print mode. In the normal print mode, as shown in  FIG. 4 , the system controller  30  controls each part to record an image on the recording paper  11 . Then, as long as there is another image to be recorded, the system controller  30  continues recording operation. Upon completing the record of all images, the inkjet printer  92  ends the recording operation. In the test print mode, the system controller  30  records the test patterns  50  and  51  (refer to FIGS.  5  and  6 ). Then, the test patterns  50  and  51  are taken in the test pattern imaging device  96 , and image data is sent to the test pattern analyzer  97 . On the basis of image data of the test patterns  50  and  51 , the test pattern analyzer  97  judges if print imperfection happens. If the feeding imperfection of the recording paper  11  is detected from image data, for example, a feeding distance correction section  30   b  (refer to  FIG. 1 ) corrects the feeding distance of the recording paper  11 . If the clogging of the nozzle is detected, a nozzle wiping process, an ink discharge process, an ink suction process and the like are carried out. If the density of each color deviates from predetermined standard density, a density correction section  30   c  (refer to  FIG. 1 ) adjusts the size of ink droplets by changing applied voltage to the piezoelectric elements, for example. When the print imperfection occurs, the system controller  30  may display a warning massage on the display panel  33 , in order to inform a user of the occurrence of print imperfection. Otherwise, the system controller  30  may generate an alarm for the same purpose. 
     The test pattern  50  shown in  FIG. 5  is recorded in a margin  53  between image areas  90 . The test pattern  51  shown in  FIG. 6  is recorded in a margin  54  between an image area  52  and one side edge of the recording paper  11 . A test pattern may be recorded in a L-shaped margin (not illustrated) which is a combination of the margin  53  of FIG.  5  and the margin  54  of FIG.  6 . The user can select the print position, format and the like of the test patterns  50  and  51  by operating the key input section  32 . Since the margins  53  and  54  are efficiently used for recording the test patterns  50  and  51 , it is possible to reduce the waste of recording paper  11 . In a case of  FIG. 6 , the image area  52  adjacent to the margin  54  is narrower than the other image areas  90  in width. In other words, the sizes of the image areas  52  and  90  are different from each other. 
     Accordingly, it is preferable that an image unsusceptible to difference in size, like an index image  55 , is recorded in the image area  52  adjacent to the margin  54 . 
       FIGS. 7  to  10  show check patterns composing the test patterns  50  and  51 . Referring to  FIG. 7 , a paper feeding distance check pattern  60  checks deviation in the feeding distance of the recording paper  11  in the sub scan direction. In recording the paper feeding distance check pattern  60 , the system controller  30  provides the pulse motor  17  with drive pulses the number of which corresponds to feeding the recording paper  11  by one line or for predetermined time. The check pattern  60  includes plural paper feeding distance check lines  61   a  to  61   c  which are recorded by the same recording devices, for example, first, tenth and twentieth nozzles, whenever the recording paper  11  is fed by one line or predetermined time. 
     Measuring distance L 1  between the check lines  61   a  recorded by the first nozzle, for example, makes it possible to detect deviation in the feeding distance in the sub scan direction on the basis of difference between the measurement value of L 1  and its design value. A correction value of the feeding distance is obtained on the basis of the amount of deviation. It is preferable to record approximately ten check lines  61   a  to  61   c , for accurate correction. It is preferable that the correction value of the feeding distance is determined by the average of the amounts of deviation obtained by each of the check lines  61   a  to  61   c . Instead of obtaining the correction value from one of three types of check lines  61   a  to  61   c , the correction value may be determined by the average of deviations obtained by all the three types of check lines  61   a  to  61   c.    
       FIG. 8  shows a head movement check pattern  62 . The check pattern  62  includes head carrying distance check lines  63  which are recorded by nozzle line of one color, a cyan nozzle line  23  for instance, in the sub scan direction. The head movement check line  63  is recorded whenever the head carriage  16  carries the inkjet head  15  by the predetermined number of pulses. Measuring distance L 2  between the check lines  63  in the main scan direction makes it possible to obtain the deviation in the carrying distance of the head carriage  16 , on the basis of difference between the measurement value of L 2  and its design value. A correction value of the carrying distance is obtained from the amount of deviation. Corrected movement of the inkjet head  15  is the sum of actual movement and the correction value. In a case where the distance L 2  varies in the main scan direction, the correction value may be determined on the basis of the distribution thereof. 
       FIG. 9  is a faulty recording device check pattern  65  for detecting a nozzle malfunction due to clogging and the like. The faulty recording device check pattern  65  includes faulty recording device check lines  66  in the main scan direction recorded by each nozzle. For instance, check lines  66  of a predetermined length are recorded by use of first, tenth, and nineteenth nozzles. Then, similar check lines  66  are recorded by use of second, eleventh, and twentieth nozzles. The other nozzles also record the check lines  66  in the same way. The length of the check lines  66  in the main scan direction, and the interval thereof in the sub scan direction are properly decided based on the size of a check pattern. It is possible to detect the malfunction of the nozzle by checking if the corresponding check line  66  is faded. For example, the malfunction of the nozzle may be detected when the measured length L 3  of the check line  66  does not reach a predetermined value. Deviation in the movement of the recording head may be detected on the basis of difference between the measurement value of L 3  and its design value. 
     In  FIGS. 7  to  9 , first check pattern is defined as check pattern recorded by the same recording device driven at predetermined time intervals, and second check pattern is defined as check pattern recorded by the same recording device driven for predetermined elapsed time. Then, the paper feeding distance check patterns  60  shown in FIG.  7  and the head movement check patterns  62  shown in  FIG. 8  correspond to the first check patterns. The faulty recording device check pattern  65  shown in  FIG. 9 , as described above, can be used as head movement check pattern which corresponds to the second check pattern. 
     Referring to  FIG. 10  a density check pattern  70  includes calibration patterns  71  to  74  in which the density of each color is varied step by step. It is possible to detect the density imperfection by comparing the density of each area of the calibration patterns  71  to  74  with standard density. When the density imperfection is detected, a calibration correction, such as the change of the size of ink droplets and the like, is carried out to achieve proper density. The calibration correction can decrease deviation in density caused by some reasons, such as increase in temperature of the inkjet head  15  and ink, and deterioration in the ink. 
     Referring to  FIG. 11 , a solid fill check pattern  75  includes solid fill patterns  76  to  79  of each color. The occurrence of density deviation is detected by the solid fill patterns  76  to  79 . It is also possible to detect the faulty recording device and deviation in the feeding distance of the recording paper  11 , by the appearance of a black or white streak in the solid fills  76  to  79 . Only the solid fill patterns  76  to  79  make it difficult, however, to judge that which of the faulty nozzle or the feeding distance deviation causes the black or white streak. Therefore, it is preferable to use either of the paper feeding distance check pattern  60  and the faulty recording device check pattern  65  with the solid fill check pattern  75 . According to the present invention, it is possible to reduce the streak caused by deviation in the feeding distance of the recording paper  11  or in the movement of the inkjet head  15 . 
     The check patterns  60 ,  65 ,  70  and  75  described above are just examples. The shape, location and the like thereof are properly changed. The test patterns  50  and  51  are a combination of the check patterns  60 ,  65 ,  70  and  75 . The combination of the check patterns  60 ,  65 ,  70  and  75  are properly changed on the basis of frequency in the use of each check pattern. For example, deviation in density is relatively small, so the density check pattern  70  and the solid fill check pattern  75  may be used less often than the paper feeding distance check pattern  60  and the faulty recording device check pattern  65 . Using other check patterns with the check patterns  60 ,  65 ,  70  and  75  makes it possible to prevent general print imperfection. 
     When the test print mode is selected, the camera  46  takes the image of the printed test pattern  50 . Then, image data of the test pattern  50  is sent to the test pattern analyzer  97 . The test pattern analyzer  97  judges the occurrence of print imperfection from image data. In a case where the print imperfection is detected, various correction processes are carried out. If a nozzle malfunction is detected, for example, the faulty nozzle is subject to various cleaning processes, such as a nozzle wiping process, an ink suction process, a discharge process and the like. In the nozzle wiping process referred to as blading or wiping, an elastic member wipes out ink dust and paper dust adhering to a nozzle hole. In the suction process referred to as pumping, the ink is forcefully sucked from the nozzle hole. In the discharge process referred to as purging, a certain amount of ink is discharged from all or a part of nozzles. 
     If the print imperfection is still detected after the cleaning, a warning message is displayed on the display panel  33  to inform the user of ink clogging. Then, the user sets the inkjet printer  92  in a cleaning mode, to further clean the faulty nozzle. In the cleaning mode, the ink in the nozzle is heated by a heating element (not illustrated) and powerfully discharged therefrom, so that the faulty nozzle is effectively cleaned up. 
     The camera  46  of the test pattern imaging device  96  requires higher resolution than the accuracy of image recording. In a case of carrying a measurement system for measuring the feeding distance of the recording paper  11 , the camera carrying mechanism  47  differs from a recording paper feeding mechanism. The camera carrying mechanism  47  must have higher accuracy than the recording paper feeding mechanism. In this embodiment, each test pattern is checked with the use of the camera  46 , but a line sensor or an area sensor may be used instead. 
     In the shuttle scan system of a serial printer, a streak extending to the sub scan distance appears in the solid fill check pattern  75 , when the feeding distance of the recording paper  11  deviates from a standard value. In a line printer, as described later, the length of a recorded image is varied in the feeding direction of the recording paper  11 . Variation in the length of the recorded image becomes variation in the density thereof. In other words, when the image is compressed due to the short feeding distance, the density becomes high. When the image is stretched due to the long feeding distance, on the other hand, the density becomes low. The deviation in the feeding distance of the recording paper  11  is detected by variation in the density of the recorded image and in the width of the streak. 
     In this embodiment, the piezoelectric elements are disposed in the ink flowing path. A heating element for heating the ink, however, may be disposed instead of the piezoelectric element. In that case, air bubbles generated by heating the ink discharges the ink. In the above embodiment, the inkjet printer  92  is provided with the ink of four colors, namely yellow, magenta, cyan, and black. The ink of light magenta, light cyan, dark yellow and the like may be provided therein in addition to that. In the inkjet head  15  of the above embodiment, the nozzles of each color are arranged in a single line, but may be arranged in plural lines. 
     In the above embodiment, the printer  92  contains the test pattern imaging device  96 , but a test pattern imaging device may be independently provided. The test pattern imaging device having a flathead scanner, for example, may be used for detecting the faulty nozzle. The camera is used in the test pattern imaging device  96  in the above embodiment, but a relatively movable line sensor may be used for imaging the test pattern. Non-contact measurement methods such as a laser Doppler method, a laser speckle method and the like may be used for measuring the feeding distance of the recording paper  11 . 
     In the above embodiment, the image recording apparatus according to the present invention is installed in the serial printer. The image recording apparatus, however, may be installed in a line printer. Referring to  FIGS. 12 and 13 , a line printer  81  is provided with a line head  80  in which nozzles are neatly arranged in parallel with the width direction of the recording paper  11 . In  FIGS. 12 and 13 , the same reference numbers are applied to identical components to  FIGS. 1 and 2 , and the description thereof is omitted. 
     The line head  80  is disposed in the width direction of the recording paper  11  (the main scan direction). The line head  80  has yellow (Y) nozzles, magenta (M) nozzles, cyan (C) nozzles, and black (K) nozzles. The nozzles of each color are neatly aligned along the main scan direction. The line printer  81  may be provided with plural line heads each of which has nozzles of a single color. In this case, an ink dryer head is disposed between each of the line heads. The ink dryer head may be provided with an air blower for blowing air on the recording paper  11 , a heater disposed opposite to the recording paper  11 , or both of the air blower and the heater. 
     The line printer  81  sequentially drives the nozzles from one end of the line head  80  to print an image of one line in the main scan direction. The way to drive the nozzles is not limited to it, but the nozzles divided into some blocks may be sequentially driven on a block basis. All nozzles arranged in the line head  80  may be driven at the same time. 
     The platen roller  12  rotated by the pulse motor  17  feeds the recording paper by one line in the sub scan direction, whenever the line head  80  prints an image of one line in the main scan direction. Repeating or carrying out at the same time the above operations makes it possible to record an image of one picture frame. 
     There are various types of line heads such as an inkjet head, a thermal head, and a LED array head and the like. The LED array head is used in an optical recording (exposure) method. There are various types of the thermal heads, such as a sublimation type, a wax transfer type, and a direct thermal type. The sublimation type and wax transfer type of printers use an ink ribbon. The direct thermal type of a thermal printer, on the other hand, uses a direct thermal type of recording paper in which a thermosensitive cyan coloring layer, a thermosensitive magenta coloring layer, and a thermosensitive yellow coloring layer are formed atop another on one side of a base material. The three coloring layers have different heat-sensitivities from each other. Each coloring layer has an absorption spectrum whose peak wavelength is specific, and loses coloring ability when it is exposed to ultraviolet rays of this wavelength range. Accordingly, the upper coloring layers, i.e. the yellow and magenta coloring layers, are unaffected by heat applied to the coloring layer under them. In the optical recording method, a recording paper has to be developed after optical recording. As in the case of the line head, the inkjet head, the thermal head, the LED array head and the like may be used as the serial type of shuttle head. The serial type of shuttle head, however, is hardly used in the direct thermal method which needs a complex optical fixing mechanism. 
     In the line printer  81 , as shown in  FIG. 6 , the width L 4  of the margin  54  is shorter than the length L 5  of the line head  80  shown by double-dashed lines. In this case, the line head  80  is so carried in the main scan direction as to record the check patterns with using all nozzles. Also in a case of the margin  53  extending to the width direction of the recording paper  11 , as shown in  FIG. 5 , the line head  80  is moved in the width direction of the recording paper  11  to move the nozzles inside the check patterns  61 ,  65  and  70 . Therefore, the check patterns are recorded with the use of all nozzles. 
     In a paper feeding distance check pattern  85  for the line printer  81 , as shown in  FIG. 14 , while a recording device records one check line  86  in the main scan direction, the recording paper  11  is fed for a fixed period of pulses or time in the sub scan direction. Then, the same recording device records another check line  86 . Comparing actual distance L 6  between the check lines  86  with a value set at the fixed period of pulses or time makes it possible to calculate a correction value. In the line printer which carries the line head instead of feeding the recording paper, various check patterns are recorded in a like manner. The print imperfection is detected by the analysis results of the check patterns, and various correction processes are carried out. 
     In the line printer  81 , it is possible to use a paper feeding distance check pattern  88  as shown in  FIG. 5  instead of the paper feeding distance check pattern  85  shown in FIG.  14 . The paper feeding distance check pattern  88  includes check lines  87  extending in the sub scan direction which are recorded by a predetermined recording devices driven for predetermined time. Measuring the length L 7  of the check line  87  makes it possible to obtain deviation in feeding distance of the recording paper, on the basis of difference between the measurement value of L 7  and its design value. The paper feeding distance check pattern  85  shown in  FIG. 14  corresponds to the first check pattern, and the paper feeding distance check pattern  88  shown in  FIG. 15  corresponds to the second check pattern. 
     The check patterns make it possible to detect deviation in the relative movement or relative speed between the recording paper and the recording head from the check patterns, and therefore it is possible to correct the relative speed on the basis of the detected deviation. The relative speed between the recording paper and the recording head may be corrected by changing the pulse rate of the pulse motor. 
     In the line printer, it is possible to reduce the deviation in the magnification of the image in the sub scan direction (longitudinal magnification). In the line printer, it is possible to record a high-definition image by adopting a pixel-offset method in which the line head is displaced by, for example, half-pixel in the main scan direction. The line head may move in the main scan direction to the margin between the image area and one side edge of the recording paper, for the purpose of recording words in the margin. Instead of the words, the image maybe recorded across from edge to edge of the recording paper in the main scan direction. The recording elements of the line head may be arranged in plural lines in a staggered configuration, besides in a single line in the main scan direction. 
     In the above embodiment, the inkjet printer can detect an ink clogging of each nozzle, a malfunction of a drive device of each nozzle, deviation in feeding distance of the recording paper and the like. The present invention may be applicable to other recording types of printer, such as a thermal recording type, an exposure recording type, to detect similar malfunctions. 
     The interval of the test patterns  50  and  51  are more than one picture frame. The test patterns  50  and  51  may be recorded when the printer is powered. The test patterns  50  and  51  maybe recorded, whenever the predetermined number of images, for example, ten or one hundred, are recorded. If the test patterns  50  and  51  are printed before shipment or for user maintenance, it is possible to manually adjust the feeding distance of the recording paper and the movement of the recording device. When the recording paper roll  10  is exchanged, the type, thickness and width of the recording paper  11  are detected by a bar code recorded on a shaft. In that case, it is possible to display a message of whether to record the test patterns based on detection result. The printer may automatically record the test patterns to carry out the various correction processes. 
     When it turns out that the correction processes are necessary after completing the record of images, the printer may predict an image in which print imperfection begins by use of a previous test pattern, and may automatically rerecord images after the predicted one. It is possible to set the predicted image as the one positioned at 70 percent between the prior test pattern and the present test pattern. The position of the predicted image is properly changeable. Instead of rerecording, the printer may display a warning message on the display panel  33 , so that the user can select the number of rerecording and execute it. 
     In the above embodiment, a roll type of recording paper is used. The present invention, however, is applicable to a printer using a cut sheet type recording paper. In this case, various check patterns recorded outside of an image print area may be cut out later with a cutter. The various check patterns may be recorded all over the sheet as a test print. 
     Although the present invention has been described with respect to the preferred embodiment, the preset invention is not to be limited to the above embodiment but, on the contrary, various modifications will be possible to those skilled in the art without departing from the scope of claims appended hereto.