JP2008036903A - Recording head and positional deviation correcting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a recording head including a constitution capable of controlling flying characteristics in the main scanning direction of ink droplets delivered from a nozzle in the recording head using piezoelectric converting elements for an ink droplet delivering means for delivering the ink droplets stored in a pressure room from the nozzle. <P>SOLUTION: Two piezoelectric converting elements 9a and 9b are approximately symmetrically arranged on both sides of the main scanning direction using the nozzle 16 as a center, and can be driven by individually applying electric voltages Va and Vb. Namely, by making Va>Vb, the delivering direction of the ink droplets 16 delivered from the nozzle 16 is made for example, into a direction toward one end side of the main scanning direction 7, and by making Vb>Va, it is made into a direction toward another end side of the main scanning direction 7, and in addition, by making Va=Vb, it is made into a direction toward just below arrangement of the nozzle. It is possible thereby to control hitting positions of the ink droplets 16 delivered on every nozzle on a recording paper 3 by making the applied electric voltages Va and Vb to be appropriate values containing an equal value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention reduces the landing accuracy of each nozzle of a line type recording head in a recording head using a piezoelectric conversion element as an ink droplet ejecting means for ejecting ink droplets contained in a pressure chamber from a nozzle, and a line type ink jet printer. The present invention relates to a misregistration correction apparatus that corrects the resulting misregistration of an image position.

  As is widely known, an ink jet printer uses ink on a recording head (also referred to as an ink jet head) that includes a nozzle and ink droplet ejection means (such as an electrothermal conversion means or a piezoelectric conversion element) that ejects ink droplets from the nozzle. And the ink droplet ejection means of the recording head is driven based on the input image information to eject ink from the recording head, and the ejected ink dots are scanned and adhered onto the recording paper. A printing apparatus for forming an ink dot pattern image.

  Specifically, in the image recording operation of this ink jet printer, first, various data and commands input from a host device such as a personal computer are analyzed, and a dot configuration and a pair of images to be printed are determined according to the analysis result. The print data which is bit image data corresponding to one is created, and the print data is stored in the print buffer in the memory. Next, the print data is read from the print buffer, and the recording head is driven based on the print data to eject ink dots onto the recording paper. Thus, the print data is printed and recorded as an image with an ink dot pattern on the recording paper.

  Such inkjet printers include a serial method and a line method. The serial method is a method in which printing is performed by moving one recording head in the width direction (main scanning direction) of the recording paper. The line method is a method in which printing for one line in the main scanning direction is performed in a lump, and is mainly used in industrial inkjet printers.

  Various techniques have been proposed for recording heads of ink jet printers. In the line system, a single recording head that covers the entire width of the recording paper is integrally formed of silicon wafer, glass, or the like. There are various problems such as yield, heat generation, and cost, which are not realistic. Therefore, in the line system, a long line type recording head having a length corresponding to the printing width by arranging a plurality of small recording heads side by side in the width direction (main scanning direction) of the recording paper. Are arranged side by side in the number of chromatic components required in the paper conveyance direction (sub-scanning direction), and printing is performed on recording paper by performing appropriate signal processing on each recording head in each line-type recording head. At this stage, batch recording over the entire width of the recording paper is made possible.

  As a method for manufacturing such a line type recording head, for example, (Patent Document 1) discloses a technique for forming a long line type recording head by modularizing a printer head and arranging a plurality of the head modules in series. ing. This method of arranging the head modules in the sub-scanning direction has an advantage that not only the line type recording head corresponding to various paper sizes can be manufactured but also the performance can be checked in units of modules. Further, if some of the modules are inconvenient when assembling the line-type recording head, only defective modules can be replaced, so that the production yield can be improved. Ink jet printers equipped with such a head do not require scanning by a carriage in the main scanning direction, so that the speed can be increased, and the market is expanding especially in the field of industrial on-demand printing.

  By the way, in this type of ink jet printer, high-quality image recording is required. Therefore, clarity of character reproduction and color reproducibility similar to a silver salt photograph are important issues. In the following, conventional techniques for dealing with this problem will be outlined.

  Factors that reduce the clarity of character reproduction include the shaggy feeling and fluctuations at the edges, and the color reproducibility is mainly due to the graininess, color shift, and texture of the photographic image. The essential cause of these image defects is that the dot positions printed on the recording paper are shifted from the normal positions. If the factor analysis is further advanced with respect to the positional deviation, it can be seen that this is a result of overlapping the fluctuation in the pitch of the sub-scanning drive for conveying the sheet, so-called sub-scanning unevenness, and the variation in the landing accuracy of the recording head itself.

  Sub-scan pitch fluctuations are caused by complex factors such as mechanical transmission characteristics, so-called gear accuracy, transport roller center axis deviation, and drive control system transmission characteristics are not optimized. is doing. In addition, in a single recording head, since the deviation and direction of the coaxiality due to the processing accuracy of the discharge nozzles vary, the discharge direction cannot be determined in a fixed direction. Furthermore, since the amount of displacement of actuators such as piezo elements, which are piezoelectric conversion elements mounted in the recording head, varies naturally among the nozzles, the components in both the main and sub-scan directions are different. As a result, the landing positions of sub-scanning vary.

  In order to improve the processing accuracy and assembly accuracy of the recording head alone in response to the problems mentioned above, the production cost decreases due to the prolonged work time in the process and the cost of equipment increases due to the introduction of expensive mass production equipment. Invite you. In addition, piezo elements that function as actuators in recording heads are said to be technically difficult to achieve uniform material composition and physical properties at the mass production level and to achieve zero variations in displacement. I don't get it. For the purpose of overcoming these problems, technical proposals have been conventionally made in the direction of correction on the premise of the positional deviation resulting from the variation in physical characteristics (for example, Patent Documents 2 and 3).

  That is, in (Patent Document 2), each color ink can be ejected from each color nozzle group of C (cyan), M (magenta), Y (yellow), and K (black) at a timing shifted by a predetermined offset value from the reference ejection timing. In an inkjet printer, first, an ink discharge timing from each color nozzle group is changed according to a plurality of different offset values to create sample images with different printing positions for each color to create alignment patterns, and refer to the alignment patterns. To determine the offset value. Thereafter, a technique is disclosed in which a final offset value is determined with reference to a plurality of gray patterns created when the timing of ejecting ink from each color nozzle group is changed according to a plurality of different offset values.

  Further, in (Patent Document 3), for the purpose of correcting the variation between the nozzles, a misregistration detection pattern is created on the recording paper, the misalignment amount with respect to the target landing position is obtained, and the method shown in FIG. A technique for updating a map of an image memory in accordance with the shift amount is disclosed. FIG. 9 is a conceptual diagram (test pattern on recording paper) for explaining the operation of correcting the image position shift in the sub-scanning direction in the serial inkjet head.

  In summary, in this (Patent Document 3), if the actual printing resolution is an ink jet printer with 600 dpi, when a test pattern is printed, it is executed at a scanning resolution of 1200 dpi in order to increase the correction accuracy. A test pattern is printed based on the memory map (FIG. 9), and the print dot shift of each nozzle is calculated by the shift detection operation. According to the numerical value, an address conversion table (address of the image memory) in the RAM (not shown) is calculated. The content of updating the reference table instructing the content of change is described.

  Next, in recent industrial inkjet printers, when the above-mentioned demand for high image quality is required, in particular, color misregistration in single colors and color misregistration when each color is superimposed are further increased as the printing density is increased. It is a particularly important issue.

  In line type recording heads used in industrial inkjet printers, landing accuracy from the nozzles in the head module is important, and shading of character portions and color images appear as color shifts. However, the technique disclosed in (Patent Document 3) is a technique for correcting landing position deviation in the sub-scanning direction of the serial type ink jet head, and landing in the main scanning direction from all nozzles in the line type ink jet head. Misalignment cannot be dealt with. For this reason, in a line-type inkjet head that uses a piezoelectric conversion element as an ink droplet ejection means for ejecting ink droplets from a nozzle, an operator adjusts the landing variation of each line head manually by using a jig or the like in the manufacturing process. The method is used.

  Regarding the landing position control in this line type ink jet head, a thermal type line type recording head using an electrothermal conversion means as an ink drop discharge means for discharging ink drops from nozzles has been proposed (for example, Patent Document 4). ). Hereinafter, the outline will be described with reference to FIG.

FIG. 10 shows the internal configuration of a thermal printer head chip used for landing position control. That is, in (Patent Document 4), a liquid chamber 32 that stores liquid to be discharged, a heating resistor 33 that is disposed in the liquid chamber 32 and generates bubbles in the liquid in the liquid chamber 32 by supplying energy, In a liquid ejection apparatus including a head 31 in which a plurality of liquid ejection units including nozzles 38 for ejecting liquid in the liquid chamber 32 in association with the generation of bubbles by the heat generation resistor 33 are arranged in a specific direction. 33 is divided into two in one liquid chamber 32, supplying energy to two heat generating resistors 33 in one liquid chamber 32, and one heat generating resistor 33 and the other heat generating resistor 33. A technique is disclosed in which a difference is provided in how energy is supplied when energy is supplied to and the flight characteristics of the liquid ejected from the nozzle 38 are controlled based on the difference.
JP 2002-86695 A JP-A-9-99566 JP 2003-205607 A JP 2004-1364 A

  However, in the technique described in (Patent Document 4), the heating resistor requires a considerably large current for generating bubbles, and is, for example, 2 to 10 times that when the piezoelectric conversion element is driven to eject ink. Current consumption. As a result, the drive circuit is increased in size and cost.

  In addition, the amount of ink droplets discharged from the nozzle generally does not increase monotonously with an increase in power applied to the heating resistor, but tends to increase rapidly when a predetermined power value is exceeded. Bubble generation is also rapid. Therefore, it is difficult to finely control the flight direction with high resolution by simply adjusting the balance of the current values of the plurality of heating resistors.

  In addition, since the relationship between the electric energy of the heating resistor and the generated bubble volume is non-linear, it is vulnerable to electrical and physical disturbances and the reproducibility of the flight direction for a predetermined electric energy is poor. Therefore, there is also a problem that the landing position variation probability increases.

  In short, with the technique described in (Patent Document 4), it is unavoidable that high-resolution landing position control based on bubble shape balance by energization control of a plurality of heating resistors is difficult. In addition, a line-type recording head using a heating resistor is inferior in production efficiency because it is necessary for an operator to set its correction current ratio by measuring its misalignment characteristics using a jig at the time of manufacture. In addition, since the correction value once set cannot be updated, it is not possible to cope with changes in landing position deviation due to environmental fluctuations and changes with time in the market.

  The present invention has been made in view of the above, and an ink droplet ejected from a nozzle in a recording head using a piezoelectric conversion element as an ink droplet ejecting means for ejecting an ink droplet accommodated in a pressure chamber from the nozzle. An object of the present invention is to obtain a recording head having a configuration capable of controlling the flight characteristics in the main scanning direction.

  According to the present invention, each module of the line type recording head in the line type ink jet printer is configured by the recording head according to the above invention, and the landing accuracy at each nozzle of the line type recording head among the positional deviations in the ink jet recording. It is an object of the present invention to provide a misregistration correction apparatus capable of preventing printing defects such as misregistration and color misregistration.

  In order to achieve the above-described object, the present invention provides a recording head using a piezoelectric conversion element as an ink droplet discharge means for discharging an ink droplet stored in a pressure chamber from a nozzle. Is composed of at least two piezoelectric transducer elements arranged so as to be capable of driving control by individually applying a driving voltage on both sides in the main scanning direction with respect to the nozzle position.

  According to the present invention, the two piezoelectric conversion elements can be driven by individually applying the voltages Va and Vb. Therefore, by setting the discharge direction of the ink droplets discharged from the nozzles to Va> Vb, for example, the direction toward one end in the main scanning direction can be set, and by setting Vb> Va, the main scanning direction. The direction can be the direction toward the other end of the nozzle, and by setting Va = Vb, the direction can be the direction directly below the nozzle arrangement. Thus, the flight characteristics of the ink droplets ejected from the nozzles in the main scanning direction can be controlled to desired characteristics, and the landing position on the recording paper can be controlled for each nozzle.

  According to the recording head using the piezoelectric conversion element as the ink droplet ejection means for ejecting the ink droplet accommodated in the pressure chamber from the nozzle according to the present invention, the flying characteristic of the ink droplet ejected from the nozzle in the main scanning direction is improved. This has the effect that the landing position on the recording paper can be controlled for each nozzle.

  Exemplary embodiments of a recording head and a misregistration correction apparatus according to the present invention are explained in detail below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a line-type inkjet printer equipped with a recording head and a positional deviation correction device according to an embodiment of the present invention. FIG. 2 is a conceptual diagram showing the configuration of each line type recording head shown in FIG. FIG. 3 is a diagram showing a main configuration of the present invention in the head module shown in FIG.

  In FIG. 1, a line type recording head 2 for each color component of C (cyan), M (magenta), Y (yellow), and K (black) is conveyed to a frame 1 of the ink jet printer main body. It is fixedly arranged on the frames 1 on both sides in the width direction of the recording paper 3 so as to straddle the recording paper 3 in the width direction (main scanning direction) along the direction (sub-scanning direction) 4. For the sake of simplicity, two line recording heads 2-k for K printing and two line recording heads 2-c for C printing are shown.

  As shown in FIG. 2, each line type recording head 2 has a plurality of head modules 6 (6-1 to 6 -m), which are small recording heads, arranged so that the ends thereof are connected in the main scanning direction 7. This is a configuration in which the necessary number of color components are arranged in the paper conveyance direction (sub-scanning direction).

  Each head module 6 has a plurality of nozzle rows 6a in the sub-scanning direction in which a large number of nozzles are arranged at regular intervals along the main scanning direction 7 on the surface facing the recording paper 3 (two rows are illustrated in FIG. 2). ) Provided at regular intervals.

  In addition, as shown in FIG. 3, a pressure chamber 8 that stores ink liquid to be ejected is provided in a one-to-one relationship with one nozzle in each nozzle row 6 a. In each embodiment, each pressure chamber 8 is provided with two piezoelectric conversion elements 9a and 9b as ink droplet ejection means. The two piezoelectric transducer elements 9a and 9b are arranged almost symmetrically on both sides in the main scanning direction 7 with one nozzle interposed therebetween (see FIG. 4).

  Returning to FIG. 1, as a control system for correcting the misalignment by controlling the flight characteristics of the ink droplets ejected from the nozzles of such a line type recording head 2, a misalignment sensor 11 and a misalignment detection circuit are provided. 12, a control circuit 13, and a head drive circuit 14. Among them, the head drive circuit 14 corresponds to the nozzle ejection control means, the positional deviation sensor 11 and the deviation amount detection circuit 12 as a whole correspond to the positional deviation amount detection means, and the control circuit 13 corresponds to the positional deviation correction data collection means. ing.

  The misalignment sensor 11 is fixed to the frames 1 on both ends in the width direction of the recording paper 3 so as to be positioned above the recording paper 3 in a state parallel to the main scanning direction. The positional deviation sensor 11 includes a light source (for example, LED) that projects light onto the recording paper 3, a light receiving sensor (for example, CCD), and an optical system such as a rod lens array that guides reflected light from the recording paper 3 to the light receiving sensor. In the predetermined image reading sequence, each landing position from each nozzle in the test pattern image (line image) on the recording paper 3 passing below in the sub-scanning direction 4 is detected (FIGS. 5A and 5B). )reference).

  The displacement amount detection circuit 12 detects the displacement amount in the main scanning direction from the reference position of each landing position from the image level detected by the displacement sensor 11 (see FIGS. 5C, 6 and 7). ).

  The control circuit 13 obtains the ratio of the applied voltage levels to the two piezoelectric transducers 9a and 9b in each pressure chamber 8 based on the positional deviation amount detected by the deviation amount detection circuit 12 (see FIG. 8). Then, the “ratio of applied voltage levels to the two piezoelectric transducers 9a and 9b in each pressure chamber 8” obtained for each of the C, M, Y, and K line type recording heads 2 is used as correction data used during image formation. Accumulate in memory.

  A test pattern is input to the head drive circuit 14 from an external test pattern generation circuit (not shown) at the time of misalignment correction. A test pattern image (line image) printed on the recording paper 3 in accordance with this test pattern is a missing dot image obtained by repeating one-dot printing with two or more consecutive missing dots interposed therebetween. In this embodiment, the test pattern image (line image) is a two-dot missing dot image obtained by repeating one-dot printing with two consecutive missing dots interposed therebetween.

  The head drive circuit 14 alternately turns two piezoelectric conversion elements 9a and 9b provided in each pressure chamber 8 in the one-line recording head 2 to be corrected at the time of positional deviation for each line under a predetermined printing sequence. By driving (see FIGS. 4 and 6), the test pattern image, which is the above-described missing dot image, is printed on the recording paper 3. This is performed for each of the C, M, Y, and K line type recording heads 2. At the time of image formation, correction data is obtained from the control circuit 13 and the two piezoelectric conversion elements 9a and 9b are driven simultaneously.

  Hereinafter, the operations of the recording head and the misregistration correction apparatus according to this embodiment configured as described above will be described in detail with reference to FIGS. 4 is a cross-sectional view in the main scanning direction showing the relationship between the two piezoelectric transducers provided on the ceiling side of one pressure chamber shown in FIG. 3 and the nozzle provided on the floor surface, and ejection by the two piezoelectric transducers. It is a conceptual diagram explaining a control aspect. FIG. 5 is a conceptual diagram illustrating the configuration of the positional deviation sensor shown in FIG. 1 and the positional deviation detection operation in the deviation amount detection circuit. FIG. 6 is a conceptual diagram illustrating details of the misregistration detection operation shown in FIG. FIG. 7 is a relationship characteristic diagram between the detection level ratio of the misregistration sensor shown in FIG. 1 and the misregistration amount. FIG. 8 is a diagram for explaining the relationship between the optimum applied voltage ratio to the two piezoelectric transducer elements provided in one pressure chamber and the landing position by the control circuit shown in FIG.

  In FIG. 4, one nozzle 16 is provided on the floor surface of the pressure chamber 8. On the ceiling side of the pressure chamber 8, a diaphragm (for example, a chromium thin film) 17 common to all the pressure chambers and a lower electrode film (conductor thin film such as copper) 18 that is a common electrode are formed from the bottom to the top. Is done. The piezoelectric transducers 9a and 9b formed on the upper surface of the lower electrode film 18 using a ceramic material such as PZT are symmetrical with respect to the hole diameter center 19 of the nozzle 16 at an appropriate distance on both sides in the main scanning direction 7. The upper electrode films (conductor thin films such as platinum) 19a and 19b, which are individual electrodes, are laminated on the upper end surfaces of the piezoelectric conversion elements 9a and 9b, respectively. That is, one pressure chamber 8 includes two piezoelectric actuators.

  Now, the head drive circuit 14 applies the voltage Va for the piezoelectric conversion element 9 a between the upper electrode film 19 a and the lower electrode film 18, and applies the voltage Va for the piezoelectric conversion element 9 b between the upper electrode film 19 b and the lower electrode film 18. Assume that the voltage Vb is applied. For ease of explanation, it is assumed that the piezoelectric transducer elements 9a and 9b exhibit a piezoelectric effect in a longitudinal vibration mode that expands and contracts in the vertical direction in FIG. As a result, the diaphragm 17 which is the ceiling plate of the pressure chamber 8 is displaced in the vertical direction in FIG. 4 in the portion immediately below the position where the piezoelectric transducers 9a and 9b are arranged, increasing the volume (that is, pressure) in the pressure chamber 8. The ink droplet 20 is ejected from the nozzles 16 toward the recording paper 3 by decreasing.

  Since FIG. 4 shows the case of Va> Vb, the diaphragm displacement 21a immediately below the position where the piezoelectric transducer 9a is disposed is larger than the diaphragm displacement 21b immediately below the position where the piezoelectric transducer 9b is disposed. In this case, in the pressure chamber 8, the rate of increase in pressure immediately below the position where the piezoelectric conversion element 9 a is disposed becomes large, and thus the ink droplet 20 ejected from the nozzle 16 toward the recording paper 3 is shown in FIG. 4. In this way, a flight trajectory landing at a position x1 on the recording paper 3 that is shifted by Δx from the hole diameter center 19 of the nozzle 16 to one end side (right side in the figure) in the main scanning direction 7 is drawn.

  On the other hand, when Va <Vb, the reverse phenomenon occurs, and the diaphragm displacement 22b immediately below the piezoelectric transducer 9b is positioned more than the diaphragm displacement 22a just below the piezoelectric transducer 9a. Although not shown, the ink droplets 20 ejected from the nozzles 16 toward the recording paper 3 are moved from the hole diameter center 19 of the nozzles 16 to the other end side (left side in the figure) in the main scanning direction 7. A flight trajectory that lands on a position on the recording paper 3 that is shifted by a predetermined amount is drawn.

  As can be understood from the above description, when Va = Vb, the diaphragm displacement amount immediately below the piezoelectric transducer element 9a is equal to the diaphragm displacement amount just below the piezoelectric transducer element 9b. Therefore, the ink droplet 20 ejected from the nozzle 16 toward the recording paper 3 draws a flight trajectory that lands on the position x0 on the recording paper 3 that coincides with the hole diameter center 19 of the nozzle 16.

  Since the displacement amount of the piezoelectric transducer changes substantially linearly with respect to the applied voltage level, in the example shown in FIG. 4, when changing from Va = Vb to Va> Vb, the above-described displacement amount. Δx shows a monotone increasing tendency with respect to an increase in Va / Vb. Therefore, by changing the ratio of the applied voltages Va and Vb, it is possible to control the ejection direction (flying direction) of the ink droplet 20 on both sides in the main scanning direction. This is the content of the correction data required by the control circuit 13.

  Next, the configuration and operation of the positional deviation sensor 11 and the deviation amount detection circuit 12 will be described with reference to FIG. As shown in FIGS. 5A and 5B, the positional deviation sensor 11 receives light reflected on the recording paper 3 and reflected light from the recording paper 3 through an optical system (not shown) on the recording paper 3. And a light receiving sensor 11b for detecting a line image (dot image) 3a. The light receiving sensor 11b includes the same number of light receiving elements as the number of nozzles of the line recording type head 2 in the same arrangement mode, and can detect a line image (dot image) 3a on the recording paper 3 in units of one dot. ing.

  FIG. 5C shows the operation of the deviation amount detection circuit 12. As described above, the one-line missing dot image printed by the head driving circuit 14 according to this embodiment according to the test pattern is two dots obtained by repeating one dot printing with two consecutive missing dots in the main scanning direction. Since it is a missing dot image, as shown in FIG. 5C, the shift amount detection circuit 12 detects the detection signals of the dot images (A), (B), and (C) detected every two dots. Is entered.

  In FIG. 5C, a dot image (A) is a dot image that is completely detected by one light receiving element without straddling two adjacent light receiving elements of the light receiving sensor 11b, and its detection level (light receiving sensor 11b). It is shown that the sensor analog output of FIG.

  The subsequent dot image (2) after missing two dots shows the case where the light is detected by two light receiving elements adjacent to the light receiving sensor 11b. Most of the dots are detected by one light receiving element, and the remaining small parts are detected. It shows that it was detected by the other light receiving element. In this case, it is shown that the detection level V2 of the one light receiving element that detects the most part is considerably higher than the detection level V1 of the other light receiving element that detects the remaining small part.

  The subsequent dot image (c) after missing two dots shows a case where two adjacent light receiving elements of the light receiving sensor 11b detect equally. In this case, the detection levels V3 and V4 of both light receiving elements are equal.

  As described above, the two detection voltages when detected by two light receiving elements are smaller than the detection voltages when both can be completely detected by one light receiving element. When two light receiving elements can detect the two detection voltages, there are a case where they are equal and a case where they are not equal. When the values are not equal, it can be determined from the magnitude relationship how much the main scanning direction is shifted to what side.

  Since the head drive circuit 14 switches the piezoelectric transducer to be used in the second line image printing, the displacement amount of the print dot position with respect to each nozzle is detected as in the first line image described above.

  Therefore, the deviation amount detection circuit 12 can detect the dot image of the ink droplet ejected from the nozzle located at one end of one target line-type recording head 2 with the corresponding one light receiving element. Based on the detection level (analog output level of the light receiving sensor 11b), the “deviation amount and its direction” are detected. At the subsequent two-dot missing position, one of the two adjacent light receiving elements is used as a reference. The direction is detected.

  With reference to FIG. 6, the operation of the deviation amount detection circuit 12 will be described more specifically. In FIG. 6, (a) the nozzle position of the target line type recording head 2, (b) the dot landing position on the recording paper 3, and (c) the analog output of the light receiving sensor 11 b that is input to the deviation amount detection circuit 12. The relationship between the level and (d) the light receiving position of the light receiving sensor 11b with respect to each nozzle position is shown.

  The detection of the amount of misalignment is performed using two line images. In the example shown in FIG. 6, the discharge control at each nozzle is performed using two line images using nozzles # 1, # 4, and # 7. Formation, two line image formation using nozzles # 2, # 5, and # 8, and so on are performed in this order. Here, a case where two line images using nozzles # 1, # 4, and # 7 are used will be described.

  In the first line image formation, of the voltages Vpl and Vpr applied to the two piezoelectric conversion elements in each nozzle, for example, the voltage Vpl is applied to the piezoelectric conversion element disposed on one end side (left side in the figure) in the main scanning direction. Apply. It is assumed that ink droplets are ejected from nozzles # 1, # 4, and # 7 in the direction indicated by solid arrows (the direction toward the other end side in the main scanning direction).

  Since the landing position Xl of the ink droplet ejected from the nozzle # 1 extends over the sensor positions N + 2 and N + 3, the detection voltage V1 is obtained at the sensor position N + 2, and the detection voltage V2 is obtained at the sensor position N + 3. In this case, most of the landing position Xl is located on the sensor position N + 2 side and the remaining little part is located on the sensor position N + 3 side. Therefore, the detection voltage V1 at the sensor position N + 2 is the detection voltage at the sensor position N + 3. Greater than V2. The ratio “V2 / V1” of the detection voltages V1 and V2 at this time indicates that the landing position Xl is shifted from the center of the sensor position N + 2 by a predetermined amount Δxl toward the other end side in the main scanning direction.

  In the second line image formation, the voltage Vpr is applied to the piezoelectric transducer arranged on the other end side (right side in the figure) in the main scanning direction. Assume that ink droplets are ejected from nozzles # 1, # 4, and # 7 in the direction indicated by the broken-line arrows (the direction toward one end in the main scanning direction).

  Since the landing position Xr of the ink droplet ejected from the nozzle # 1 extends over the sensor positions N + 1 and N + 2, the detection voltage V1 ′ is obtained at the sensor position N + 1, and the detection voltage V2 ′ is obtained at the sensor position N + 2. . In this case, most of the landing position Xr is located on the sensor position N + 1 side and the remaining little part is located on the sensor position N + 2 side. Therefore, the detection voltage V1 ′ at the sensor position N + 1 is detected by the sensor position N + 2. It is larger than the voltage V2 ′. The ratio “V1 ′ / V2 ′” of the detection voltages V1 ′ and V2 ′ at this time indicates that the landing position Xr is shifted from the center of the sensor position N + 2 by a predetermined amount Δxr toward one end side in the main scanning direction.

  Similarly, for the nozzle # 4, the positional deviation amount is detected with reference to the sensor position N + 5, and for the nozzle # 7, the positional deviation amount is detected with reference to the sensor position N + 8. The value of the positional deviation amount Δxl with respect to the ratio “V2 / V1” and the value of the positional deviation amount Δxr with respect to the ratio “V1 ′ / V2 ′” are obtained with reference to, for example, the conversion table shown in FIG.

  FIG. 7 shows the relationship between the ratio “V2 / V1” at the nozzle # 1 and the positional deviation amount X in the first line image. This is a plot of changes in the ratio “V2 / V1” while actually shifting the landing position Xl, and has a monotonically increasing characteristic. The positional deviation amount X in the case of V2 / V1 = 1 indicates that there is a deviation of ½ dot from the center of the light receiving position N + 2 of the light receiving sensor 11b to the other end side in the main scanning direction. If the nozzle density is 600 dpi, the light receiving sensor 11b has the same number of 600 dpi, but the pixel pitch is 42 μm, so that the ½ dot in this case is 21 μm.

  Similarly, the value of the positional deviation amount Δxr with respect to the ratio “V1 ′ / V2 ′” can be actually measured and prepared. That is, the shift amount detection circuit 12 stores in the memory the conversion table shown in FIG. 7 for the first line image and the conversion table corresponding to FIG. 7 for the second line image. Then, the positional deviation amount Δxl is obtained from the obtained ratio “V2 / V1”, the positional deviation amount Δxr is obtained from the obtained ratio “V1 ′ / V2 ′”, and each is supplied to the control circuit 13.

  Here, in the ejection control by the nozzle # 1, the landing position when the two piezoelectric transducers are actually driven at the same voltage (Vpl = Vpr) at the same time is zero if Δxr = Δxl. However, here, since Δxr> Δxl, it is shifted to one end side (left side in the figure) in the main scanning direction.

  That is, the control circuit 13 obtains the optimum applied voltage ratio “Vpr / Vpl” from the positional deviation amount ratio “Δxl / Δxr” for each nozzle using the conversion table shown in FIG. Is stored in the memory. FIG. 8A shows an extracted detection state at the light receiving sensor position N + 2 regarding the nozzle # 1 shown in FIG. As described above, in the first line image, the landing position Xl when the voltage Vpl is applied with the voltage Vpr = 0 is from the center of the light receiving sensor position N + 2 to the other end side (right side in the drawing) in the main scanning direction. It is shifted by Δxl. In the second line image, the landing position Xr when the voltage Vpr = 0 and the voltage Vpr is applied is shifted by Δxr from the center of the light receiving sensor position N + 2 to one end side (left side in the figure) in the main scanning direction. Yes.

  In FIG. 8B, the vertical axis represents the positional deviation amount X, and the horizontal axis represents the ratio “Vpr / Vpl” of the voltages applied to the two piezoelectric transducers. When the ratio of applied voltages to the two piezoelectric transducers “Vpr / Vpl” is changed and the two piezoelectric transducers are driven simultaneously to perform the ejection operation, the landing position is generally as shown in FIG. Change. In FIG. 8B, the positional deviation amount X of the landing position at the applied voltage Vpr = 0 is Δxl. The positional deviation amount X of the landing position when the applied voltage Vpl = 0 is −Δxr. The positional deviation amount X of the landing position at the applied voltage Vpr = Vpl is an intermediate point of Δxl−Δxr. It can be seen that the ratio “Vpr / Vpl” for achieving the positional deviation amount X = 0 is the ratio “Δxl / Δxr”. With the above method, the control circuit 13 obtains the optimum applied voltage ratio of the two piezoelectric transducer elements for each nozzle, and stores it in the memory in a one-to-one relationship with the nozzle.

  By the way, the landing position of the head module 6 changes due to a change in ink viscosity characteristics caused by environmental changes. In preparation for this, a means for monitoring the environmental characteristics is provided in the ink jet printer, and the test pattern image for missing multiple dots is formed according to a predetermined temperature change / humidity change. The position deviation can be corrected according to the level.

  As for fluctuations in the landing position deviation with time, the head drive circuit 14 is activated at a predetermined time such as when the power is turned on to cause the position deviation sensor 11, the deviation amount detection circuit 12 and the control circuit 13 to perform respective operations. An operation program is provided to ensure that image quality without misalignment is always obtained.

  As described above, according to this embodiment, a recording head (line-type ink-jet head (line-type recording head)) that uses a piezoelectric conversion element for ink droplet discharge means for discharging ink droplets from nozzles is configured. In each head module), each pressure chamber is provided with two piezoelectric conversion elements arranged so as to be capable of driving control by individually applying a driving voltage on both sides in the main scanning direction with respect to the nozzle position. It is possible to control the flight characteristics of the ejected ink droplets in the main scanning direction.

  In an ink jet printer equipped with a line type recording head provided with two piezoelectric conversion elements in each pressure chamber, two test pattern line images using one and the other of the two piezoelectric conversion elements printed on the recording paper alternately 2 is provided for detecting the amount of displacement of the landing position for each nozzle and obtaining the optimum value of the voltage applied to the two piezoelectric transducers in each nozzle, and using the obtained optimum value, 2 for each nozzle. Since the two piezoelectric conversion elements are driven simultaneously, it is possible to prevent the landing positions from being shifted for each nozzle.

  Accordingly, it is not necessary for an operator to manually adjust the landing variation of each line type recording head by using a jig or the like in the manufacturing process as in the prior art, and the cost can be greatly reduced. In addition, when two piezoelectric transducers are used, it is possible to finely adjust the landing position as compared with the thermal method disclosed in (Patent Document 4), thereby improving character reproduction and reducing color misregistration. The improvement of color image quality can be expected.

  Furthermore, even in the case of environmental fluctuations and changes in the market, it is possible to easily take measures to automatically correct the landing position by providing a startup sequence that takes these factors into account. There is also an effect that the maintenance work of the service person becomes very easy even when the head module is replaced.

  As described above, the recording head according to the present invention is useful for controlling the landing characteristics on the recording paper for each nozzle by controlling the flight characteristics of the ink droplets ejected from the nozzle in the main scanning direction. Particularly, it is suitable as a head module of a line type recording head in which landing position deviation is a problem.

  The misregistration correction apparatus according to the present invention is useful for preventing misprinting such as misregistration and color misregistration due to poor landing accuracy of each nozzle of a line type recording head in a line type ink jet printer.

1 is a block diagram showing a configuration of a line-type inkjet printer equipped with a recording head and a positional deviation correction device according to an embodiment of the present invention. 1 is a conceptual diagram showing the configuration of each line type recording head shown in FIG. The figure which shows the principal part structure of this invention in the head module shown in FIG. FIG. 3 is a cross-sectional view in the main scanning direction showing the relationship between two piezoelectric transducers provided on the ceiling side of one pressure chamber shown in FIG. 3 and a nozzle provided on the floor side, and a concept for explaining a discharge control mode by the two piezoelectric transducers. Figure FIG. 1 is a conceptual diagram illustrating the configuration of the misalignment sensor shown in FIG. 1 and the misalignment detection operation in the misalignment detection circuit. Conceptual diagram for explaining the details of the misalignment detection operation shown in FIG. FIG. 1 is a characteristic chart showing the relationship between the detection level ratio of the misregistration sensor and the misregistration amount shown in FIG. The figure explaining the operation | movement which the control circuit shown in FIG. 1 calculates | requires the optimal applied voltage ratio to the two piezoelectric transducers provided in one pressure chamber Conceptual diagram for explaining an operation for correcting image position shift in the sub-scanning direction in a serial type inkjet head according to a conventional technique (Patent Document 3). An exploded perspective view showing an internal configuration of a thermal type printer head chip used for landing position control according to a conventional technique (Patent Document 4)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Frame of apparatus main body 2 Line type recording head 2-k Line type recording head for K printing 2-c Line type recording head for C printing 3 Recording paper 3a Dot image 4 Paper transport direction (sub scanning direction)
6 (6-1 to 6-m) Head module 6a Nozzle array 7 Main scanning direction 8 Pressure chamber 9a, 9b Piezoelectric transducer 11 Position shift sensor 11a Light source 11b Light receiving sensor 12 Deviation amount detection circuit 13 Control circuit 14 Head drive circuit 16 Nozzle 17 Diaphragm 18 Lower electrode film (common electrode)
19a, 19b Upper electrode film (individual electrode)
20 Ink droplet 21a, 21b, 22a, 22b Vibration plate displacement

Claims (6)

In a recording head using a piezoelectric conversion element as ink droplet discharge means for discharging ink droplets stored in a pressure chamber from a nozzle,
The piezoelectric conversion element provided in each pressure chamber is composed of at least two piezoelectric conversion elements arranged so as to be capable of driving control by individually applying a drive voltage on both sides in the main scanning direction with respect to the nozzle position.
A recording head characterized by that. A misalignment correction apparatus that corrects misalignment in the main scanning direction in a line-type inkjet printer,
The line-type recording head is individually driven on both sides in the main scanning direction with respect to the nozzle position for each pressure chamber as a piezoelectric conversion element that is an ink droplet ejection means for ejecting ink droplets contained in the pressure chamber from the nozzles. Comprising at least two piezoelectric transducer elements arranged to be able to be driven and controlled by applying a voltage;
During normal image formation, the at least two piezoelectric transducers arranged on both sides in the main scanning direction are simultaneously driven to print and form one line image on recording paper, while when misalignment correction data is collected, one end in the main scanning direction is formed. Nozzle ejection for printing two line images on recording paper by alternately driving the at least one piezoelectric transducer arranged on the side and the at least one piezoelectric transducer arranged on the other end in the main scanning direction Control means;
A positional deviation amount detecting means for detecting a deviation amount of each landing position of the corresponding ink droplet in each of the two line images on the recording paper printed and formed when the positional deviation correction data is collected by the nozzle ejection control means;
An optimum driving voltage to be applied to each of the two piezoelectric transducers is obtained from the two positional deviation amounts of the respective landing positions detected by the deviation amount detection means, and is used for the nozzle ejection control means during normal image formation. Misalignment correction data collection means to be provided;
A misalignment correction apparatus comprising: The nozzle discharge control means repeats control for stopping discharge from two or more adjacent nozzles and discharging from the next one nozzle at the time of collecting the misregistration correction data, so that two dots are formed on the recording paper. The misalignment correction apparatus according to claim 2, wherein a missing dot image is formed by repeating 1-dot printing with the continuous missing dots interposed therebetween. The deviation amount detecting means is a light receiving means for receiving reflected light from a line image on a recording sheet, and is arranged in the same number and in the same manner as the number of nozzles provided in the line type recording head. The positional deviation correction apparatus according to claim 2, further comprising: a light receiving unit that detects a deviation amount of each landing position based on output levels of the plurality of light receiving units. The monitoring device according to claim 2, further comprising a monitoring unit that monitors environmental characteristics, wherein the nozzle discharge control unit performs an operation at the time of collecting the positional deviation correction data as necessary based on a monitoring result of the monitoring unit. Misalignment correction device. 3. An operation program for starting the nozzle discharge control unit at a predetermined time such as when the power is turned on and causing the shift amount detection unit and the misalignment correction data collection unit to perform respective operations. The positional deviation correction apparatus described in 1.

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