JP2006247840A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when the number of driving signals included in a driving waveform becomes larger than the number of gradations which can be specified by gradation data, the dimension of a droplet is remarkably changed to the change in gradation, and on the other hand, when the number of bits of the gradation data is increased, cost increases. <P>SOLUTION: The image forming apparatus is equipped with a liquid delivering head 11 for delivering droplets of a recording liquid, a driving waveform generating part 301 for generating a driving waveform containing a plurality of driving signals within one printing period, and a head driver 208 for inputting gradation data, selecting a required driving signal through a switching means opening and closing in accordance with the gradation data among the driving waveforms, and applying it on the liquid delivering head. A data transferring part 302 for transferring the gradation data composed of a plurality of bits per one channel to the head driver 208 for a plurality of times within one printing period, is also installed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a liquid discharge head that discharges droplets of a recording liquid.

  As various image forming apparatuses such as printers, facsimiles, copying machines, plotters, printer / fax / copier multifunction machines, etc., recording heads (printing heads) constituted by droplet discharging heads that discharge recording liquid (for example, ink) droplets are used. ) Is mounted on a carriage, and the carriage is a recording medium (hereinafter referred to as “paper”, but the material is not limited to paper, and is also referred to as recording medium, recording paper, transfer material, etc.). In addition to serial scanning in a direction orthogonal to the conveyance direction, the recording medium is intermittently conveyed according to the recording width, and an image is formed on the recording medium by repeating conveyance and recording (recording, printing, Printing and printing are also used synonymously.) There is a serial type image forming apparatus or a line type image forming apparatus equipped with a line type recording head.

In order to perform gradation printing (gradation printing) in an image forming apparatus using such a liquid ejection head, for example, Patent Document 1 discloses a first technique for ejecting a first ink droplet within one printing cycle. And the second driving pulse for ejecting the second ink droplet having a different size from the first ink droplet, the first and second driving waveforms are used. An apparatus is described that selectively forms dots of four gradations or more by combining drive pulses.
Japanese Patent No. 3264422

  In the apparatus described in Patent Document 1, print data of 1 channel (CH) 1 bit (1 bit / CH) is transferred to the head driver for each drive pulse constituting the drive waveform. One channel corresponds to one nozzle, a liquid chamber corresponding to the nozzle, and pressure generating means.

  This data transfer method will be described with reference to FIG. 20. Print data is serially transferred by a clock, set in a shift register, and latched by a latch signal (LAT) at a timing corresponding to a drive pulse delimiter. Thus, ON / OFF of the analog switch (switch means) corresponding to each channel is determined. That is, the previous print data (if it is a medium drop, the data transferred at the time of a large drop) is reflected. Thereby, a part of the common drive waveform is applied to the pressure generating means (piezoelectric element), and droplets having different sizes are ejected.

However, in such a driving method, data transfer must be completed in the cycle of the driving pulse with the shortest pulse width that needs to be switched ON / OFF. This makes it impossible to transfer data, for example, the clock frequency of data transfer must be increased. In addition, in order to increase the printing speed, the number of channels of the head tends to increase. For this reason, the pulse width of the driving pulse also tends to be shortened, so that the data transfer time becomes the rate limiting of the printing speed. However, with this data transfer method, ON / OFF can be selected for each drive pulse, so that in principle, the gradation can be increased to 2 ⁿ (n = 1 the number of drive pulses within one printing cycle).

In Patent Document 2, a storage means (shift register) and a translation means are provided from a common drive waveform consisting of a plurality of drive pulses within one print cycle, and the operation of the switch means is controlled based on the decoded print data. Thus, it is described that the data transfer within one printing cycle is 2 bits / CH (in the case of 4 gradations) once and the translation amount is provided to reduce the data transfer amount and the number of signal lines. .
Japanese Patent No. 3219241

  In this data transfer method, data transfer can be performed once per printing cycle regardless of the drive pulse interval, so that data transfer corresponding to the number of channels and the printing speed can be performed. The burden is also reduced. However, only 2 gradations (large, medium, small, and none) can be obtained with 2 bits / CH. In this case, the number of gradations can be increased by increasing the number of bits (for example, 8 gradations for 3 bits / CH), but the number of circuit elements in the head driver increases, leading to an increase in cost. Increasing the number of bits also increases the amount of data transferred.

Further, Patent Document 3 describes a method of transferring gradation data and selecting a part of the common drive waveform with a control signal corresponding to the gradation.
JP 2003-1817 A

  This data transfer system will be described with reference to FIG. 21. Two bits of gradation signals 0 and 1 are transferred by another line, set in a shift register, and each latch signal at the beginning of one printing cycle Determine the tone of the channel (large, medium, small, no). Each gradation determines ON / OFF of the analog switch based on the respective control signal. Specifically, in the channel in which the gradation of the large droplet (1, 1) is set, ON / OFF of the analog switch is determined based on the large droplet line signal of the control signal.

  This method is the same as that described with reference to FIG. 21 except that different waveforms are selected for each of the large droplet / medium droplet / small droplet, but the required time for the medium droplet is the data transfer time. There is an advantage that the waveform selection can be switched even if it is shorter than that, and the data transfer amount can be reduced.

  Although these Patent Documents 2 and 3 differ in the method of switching the analog switch ON / OFF for each gradation, gradation data is transferred once within one printing cycle, and based on this, the common drive waveform The selection of the waveform to be applied is the same.

  By the way, in the image forming apparatus, there are non-interlaced and one-pass printing as printing modes for performing high-speed printing. In this print mode, an image is formed by one scan, so high-speed printing can be performed.

  In this non-interlaced printing, the resolution in the sub-scanning direction is the same as the nozzle pitch of the head. Therefore, in order to be able to print a solid image, the size of the largest droplet (large droplet) is an ejection that fills the solid. It is necessary to have a drop volume.

  However, particularly in a head using an electromechanical transducer (piezoelectric element), the machining accuracy becomes the limit of the nozzle pitch, so the resolution cannot be increased so much. Currently, there is a limit of about 360 dpi in a single-row 180 dpi, 2-row staggered arrangement. In this case, in order to fill the solid in one scan, an ejection droplet amount of 30 to 50 pl is required depending on the paper type / ink type.

  On the other hand, from the pursuit of high image quality, smaller droplets (small droplets) used in the high image quality mode are required to be smaller. The discharge amount may exceed 2 pl, reach 1.5 pl, and possibly 1 pl in the future.

  As described above, in an image forming apparatus using a recording liquid, there is an increasing demand for changing the droplet amount in a wider range.

  However, when changing the discharge amount over a wide range, it is very difficult to realize by simply controlling the discharge of one drop, and in many cases, a large drop is formed by discharging a plurality of drops. . In addition, with the expansion of the range in which the discharge amount must be varied, the discharge amount Mj per droplet tends to be decreased and the number of discharged droplets further increased. In order to make it easy to fill the sub-scanning direction, it is effective to merge the droplets before landing on the paper so as to spread in the sub-scanning direction, rather than simply ejecting the number of droplets.

  However, increasing the number of droplets in one printing cycle shortens the discharge interval (pulse interval), and as a result, as described above, print data is transferred for each drive pulse (Patent Document 1). However, it is preferable to transfer gradation data of 2 bits or more and provide translation means, selection means, etc. (Patent Documents 2 and 3).

  However, even the methods described in Patent Documents 2 and 3 have the following problems. That is, when the number of drive pulses (= number of ejected droplets) generated within one printing cycle is larger than the number of gradations, the size of the droplets changes significantly due to the change in gradation.

  For example, the example shown in FIG. 23 is an example of 4 gradations (2 bits) and a drive waveform of 4 pulses (described as first, second,... From the first drive pulse, and so on). However, in this case, a gradation that increases with one set of two pulses (two drops) always occurs. In this example, the first droplet is selected for the small droplet, the first and second pulses are selected for the middle droplet, and the first to fourth pulses are selected for the large droplet. Will change.

  As described above, when the change in the size of the droplet with respect to the gradation change is large, it is clearly disadvantageous in terms of smoothly connecting the image density, and the granularity of the large droplet is conspicuous in the halftone processing. Such a problem also occurs.

  This tendency becomes more prominent as the smaller droplets are smaller and the number of droplets required for larger droplets is increased. For example, the example shown in FIG. 24 is an example of 4 gradations (2 bits) and a driving waveform of 6 pulses. In this example, the small droplet is the first pulse, the medium droplet is the first to third pulses, For the large droplet, the first to sixth pulses are selected, and the size of the small droplet and the medium droplet is changed by 2 droplets, and the size of the medium droplet and the large droplet is changed by 3 droplets.

  In this case, it is sufficient to increase the number of gradations and finely control the droplet amount. However, as described above, increasing the number of gradations, that is, increasing the number of bits increases the cost. In other words, although the fine drop amount can be controlled by increasing the number of drops, the fine drop amount cannot be controlled substantially due to the restriction by the number of gradations.

  On the other hand, a method is known in which the resolution of main scanning is different from the resolution of sub scanning, for example, an image is formed at 600 dpi for main scanning and 300 dpi for sub scanning. In other words, when the nozzle arrangement direction is the sub-scanning direction in the serial type, the sub-scanning resolution is defined by the nozzle pitch, but the main-scanning resolution is determined by the carriage speed and printing cycle, so adjust the carriage speed. Can be changed relatively easily, and only the main scanning resolution can be increased.

  For example, as shown in FIG. 25, an image is normally formed with main scanning resolution × sub-scanning resolution = 300 dpi × 300 dpi, whereas, as shown in FIG. 26, only the main scanning resolution is increased to 600 dpi. An image is formed at × 300 dpi.

  As described above, if only the main scanning resolution is increased, the discharge amount of large droplets can be reduced. However, in a solid image, the sub-scanning direction must be filled with ink, so the main scanning resolution is doubled. However, the required discharge volume for large drops is not halved. In order to keep the printing speed the same, the drive frequency of the head must be doubled. For example, a 20 pl droplet is driven at 20 kHz rather than a droplet with a droplet volume of 40 pl is ejected at a drive frequency of 10 kHz. It is difficult in terms of control to discharge at a frequency.

  That is, FIG. 27 shows an increase in the amount of droplets when the number of droplets is increased, and the amount of droplets discharged by each drive pulse is calculated based on the difference. As shown in the figure, when the number of drive pulses is increased (the number of droplets), the total droplet amount Mj per droplet can be changed linearly to some extent. The droplet amount (each pulse Mj) of the droplets ejected by the drive pulse (single droplet before joining) increases as the droplets are ejected later.

  This phenomenon occurs because when a large number of droplets are ejected, the meniscus rises due to the ejection of the preceding droplet. For example, in FIG. 27, one drop of about 37 pl is formed by combining six drops, but the total of three drops ejected by each of the first to third driving pulses in this drop is about It is about 40% of the whole at 15 pl.

  Further, in the method in which the resolution is different between the main scanning direction and the sub-scanning direction as described with reference to FIG. 26 (for example, 600 dpi × 300 dpi), it is necessary to fill the sub-scanning. Even if it is doubled, the discharge amount is not half, so that the required droplet amount becomes large and the control becomes more difficult.

  However, by increasing the resolution even in the main scan alone, the gradation is smoothly connected, and only the large droplets are clearly recognized and the graininess is impaired, as represented by the widening of the density range that can be expressed only by small droplets. Less. In addition, there is an advantage that it is effective in correcting jaggies of characters and the like, and the backlash of lines can be suppressed.

  In addition, in order to form a large droplet that fills the solid, it is necessary to strictly control the droplet ejection interval as the number of droplets ejected within one printing cycle is increased. When the number of ejected droplets increases, it is impossible to wait for the pressure in the liquid chamber of the head to sufficiently attenuate before ejecting the next droplet. For this purpose, it is necessary to efficiently eject droplets in accordance with the pressure vibration of the liquid chamber and to control the pressure so that the pressure vibration does not run away. For these reasons, the time and voltage of the driving waveform that forms a large droplet must be controlled.

  The present invention has been made in view of the above problems, and provides an image forming apparatus capable of high-quality and high-speed printing by increasing the number of gradations that can be expressed without increasing the number of bits of gradation data. With the goal.

  In order to solve the above problems, an image forming apparatus according to the present invention includes means for transferring the gradation data composed of a plurality of bits per channel to the driving means a plurality of times within one printing cycle. It was set as the composition.

  Here, when the liquid ejection head is driven with gradation data for ejecting a plurality of droplets, it is preferable that the droplets are combined to form a single droplet before landing.

  In addition, it is preferable that the number of droplets ejected by a plurality of driving signals included in one printing cycle is equal to or greater than the number of gradations of the gradation data. In this case, the plurality of driving signals included in one printing cycle The number of ejected droplets to be ejected is preferably 4 or more.

  Further, it is preferable that the timing for transferring the gradation data a plurality of times within one printing cycle can be changed. Further, it is preferable to be able to switch between a mode in which gradation data is transferred a plurality of times within one printing cycle and a mode in which gradation data is transferred once within a printing cycle.

  In addition, at least one of the drive signals for ejecting a plurality of droplets that form a large droplet among the plurality of drive signals constituting the drive waveform is not a large droplet for the plurality of gradation data. It is preferable to use it as a drive signal for discharging a droplet forming a droplet.

  Further, the drive waveform preferably includes two drive signals for ejecting droplets of substantially the same size at least twice based on gradation data transferred a plurality of times within one printing cycle. The two drive signals for ejecting the same size droplet at least twice may be configured not to be used for ejecting other size droplets, or the substantially same size droplet may be ejected at least twice. One drive signal may be configured to be used to eject droplets of other sizes.

  The image forming apparatus according to the present invention includes a mode in which only a relatively large droplet is ejected in accordance with the sub-scanning resolution in the main scanning direction when an image having a higher main scanning resolution than the sub-scanning resolution is formed. It was.

  Here, via drive waveform generating means for generating a drive waveform including a plurality of drive signals within one printing cycle, and switch means for inputting gradation data and opening / closing according to the gradation data from the drive waveform. A driving unit that selects a required driving signal and applies the selected driving signal to the liquid ejection head; and a unit that transfers gradation data including a plurality of bits per channel to the driving unit a plurality of times within one printing cycle; When forming a large drop with a plurality of drops, the plurality of drops forming the large drop are ejected based on a reference signal corresponding to the position of the carriage, and a plurality of gradation data at a settable time from this reference signal It is preferable to transfer.

  In addition, at least one drive signal of the drive signal for ejecting a plurality of droplets that form a large droplet among the plurality of drive signals constituting the drive waveform is not a large droplet for the plurality of gradation data. It is preferable to use it as a drive signal for discharging a droplet forming a droplet.

  In a mode in which only large droplets are ejected in accordance with the sub-scanning resolution in the main scanning direction, it is preferable to form an image by a non-interlace method.

  According to the image forming apparatus of the present invention, the gradation data composed of a plurality of bits per channel is provided with means for transferring the gradation data to the driving means a plurality of times within one printing cycle. The number of gradations can be substantially increased without increasing the number of bits of gradation data, and a high-quality image can be printed at high speed.

  The image forming apparatus according to the present invention has a mode in which, when forming a higher resolution image in the main scanning than in the sub-scanning, only relatively large droplets are ejected in accordance with the sub-scanning resolution in the main scanning direction. The sub-scanning direction can be easily filled, the resolution of the small droplets in the main scanning direction can be increased, the image quality can be improved, and high-speed printing can be performed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall structure of the mechanism section of the image forming apparatus, and FIG. 2 is a plan view for explaining the mechanism section.

  In this image forming apparatus, a carriage 4 is slidably held in a main scanning direction by a guide rod 2 and a stay 3 which are guide members horizontally mounted on left and right side plates 1A and 1B constituting a frame 1, and a main scanning motor. 5 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG. 2 via the timing belt 7 spanned between the driving pulley 6A and the driven pulley 6B.

  The carriage 4 includes, for example, four droplet ejection heads 11k, 11c, 11m, and 11y that eject ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). The recording head 11 is mounted with the nozzle row of the nozzle surface 11a on which a plurality of ink discharge ports (nozzles) are formed arranged in a direction (sub-scanning direction) orthogonal to the main scanning direction, and the ink discharging direction is directed downward. . Although an independent droplet discharge head is used here, a configuration in which one or a plurality of heads having a plurality of nozzle rows that discharge droplets of recording liquid of each color can be used. Further, the number of colors and the arrangement order are not limited to this.

  Here, as described above, the recording head 11 is composed of four separate heads 11k, 11c, 11m, and 11y that discharge droplets of the respective colors, and the heads 11k, 11c, 11m, and 11y are shown in FIG. As described above, the nozzle array is formed by arranging two nozzles n for discharging droplets side by side (each nozzle array is referred to as nozzle arrays NA and NB). Not limited to this, as shown in FIG. 4, two nozzle rows 11 kA, 11 kB, 11 cA, 11 cB, 11 mA, 11 mB, 11 yA, and 11 yB that discharge droplets of each color are arranged in one recording head 11. It can also be constituted by a head having one or a plurality of nozzle rows that eject black ink and a head having one or a plurality of nozzle rows for each color that ejects color ink.

  As the ink jet head constituting the recording head 11, a head provided with a piezoelectric actuator such as a piezoelectric element as pressure generating means (actuator means) for generating a pressure for discharging a droplet is used as will be described later. .

  A driver IC is mounted on the recording head 11 and connected to a control unit (not shown) via a harness (flexible print cable: FPC cable) 12.

  In addition, the carriage 4 is equipped with a sub tank 15 for each color for supplying ink of each color to the recording head 11. Each color sub-tank 15 is supplementarily supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 9 via the ink supply tube 16 of each color. The cartridge loading 9 is provided with a supply pump unit 17 for feeding ink in the ink cartridge 10, and the ink supply tube 16 is engaged with the rear plate 1C constituting the frame 1 in the middle of turning. It is held by a stop member 18.

  On the other hand, as a paper feed unit for feeding the paper 22 stacked on the paper stacking unit (pressure plate) 21 of the paper feed tray 20, a half-moon roller (feed) that separates and feeds the paper 22 one by one from the paper stacking unit 21. A separation pad 24 made of a material having a large friction coefficient is provided opposite to the sheet roller 23 and the sheet feeding roller 23, and the separation pad 24 is biased toward the sheet feeding roller 23 side.

  In order to feed the paper 22 fed from the paper feeding unit to the lower side of the recording head 11, a guide member 25 for guiding the paper 22, a counter roller 26, a conveyance guide member 27, and a tip pressure roller. And a holding belt 28 as a conveying means for electrostatically attracting the fed paper 22 and conveying it at a position facing the recording head 11.

  The conveyance belt 31 is an endless belt, is configured to wrap around the conveyance roller 32 and the tension roller 33 and circulate in the belt conveyance direction (sub-scanning direction). 34 is charged (charged).

  The transport belt 31 may be a single-layer belt or a multi-layer (two or more layers) belt. In the case of the conveyance belt 31 having a one-layer structure, the entire layer is formed of an insulating material because it contacts the paper 32 and the charging row 34. In the case of the transport belt 31 having a multi-layer structure, the side that contacts the paper 22 and the charging roller 34 is preferably formed of an insulating layer, and the side that does not contact the paper 22 and the charging roller 34 is preferably formed of a conductive layer. .

As an insulating material for forming the transport belt 31 having a single layer structure and an insulating material for forming the insulating layer of the transport belt 31 having a multi-layer structure, for example, a conductive material such as PET, PEI, PVDF, PC, ETFE, or PTFE is used. It is preferable that the material does not contain a control material, and the volume resistivity is 10 ¹² Ωcm or more, preferably 10 ¹⁵ Ωcm. In addition, as a material for forming the conductive layer of the transport belt 31 having a multilayer structure, it is preferable that the resin or elastomer contains carbon and has a volume resistivity of 10 ⁵ to 10 ⁷ Ωcm.

The charging roller 34 is arranged so as to come into contact with an insulating layer (in the case of a multilayer belt) forming the surface layer of the transport belt 31 and to rotate following the rotation of the transport belt 31, and to apply pressure to both ends of the shaft. It is over. The charging roller 34 is formed of a conductive member having a volume resistivity of 10 ⁶ to 10 ⁹ Ω / □. As will be described later, for example, 2 kV positive and negative AC bias (high voltage) is applied to the charging roller 34 from an AC bias supply unit (high voltage power supply). The AC bias may be a sine wave or a triangular wave, but a square wave is more preferable.

  In addition, a guide member 35 is disposed on the back side of the conveyance belt 31 so as to correspond to a printing area by the recording head 11. The guide member 35 has an upper surface that protrudes toward the recording head 11 from the tangent line of the two rollers (the conveyance roller 32 and the tension roller 33) that support the conveyance belt 31, thereby maintaining high-precision flatness of the conveyance belt 31. Like to do.

  The transport belt 31 rotates in the belt transport direction of FIG. 2 when the transport roller 32 is rotationally driven by the sub-scanning motor 36 via the drive belt 37 and the timing roller 38. Although not shown, an encoder wheel having a slit is attached to the shaft of the conveying roller 32, and a transmission type photosensor for detecting the slit of the encoder wheel is provided, and the wheel encoder is configured by the encoder wheel and the photosensor. It is composed.

  Further, as a paper discharge unit for discharging the paper 22 recorded by the recording head 11 to the paper discharge tray 40, a separation claw 41 for separating the paper 22 from the transport belt 31, a paper discharge roller 42, and paper discharge The roller 43 is provided.

  A duplex unit 51 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 51 takes in the paper 22 returned by the reverse rotation of the transport belt 31, reverses it, and feeds it again between the counter roller 26 and the transport belt 31. The upper surface of the duplex unit 51 is a manual feed tray 52.

  Further, a maintenance / recovery mechanism 61 for maintaining and recovering the state of the nozzles of the recording head 11 is disposed in a non-printing area on one side in the scanning direction of the carriage 4. The maintenance / recovery mechanism 61 includes cap members (hereinafter referred to as “caps”) 62 a to 62 d (hereinafter referred to as “caps 62” when not distinguished) and nozzles for capping the nozzle surfaces 11 a of the recording head 11. A wiper blade 63 that is a blade member for wiping the surface 11a, an empty discharge receiver 64 that receives liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid, and the like It has. Here, the cap 62a is a suction and moisture retention cap, and the other caps 62b to 62d are moisture retention caps.

  Further, in the non-printing area on the other side of the carriage 4 in the scanning direction, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 68 is disposed, and the idle discharge receiver 68 is provided with an opening 69 along the nozzle row direction of the recording head 11.

  Further, as shown in FIG. 1, a density sensor 71 including an infrared sensor (a type of sensor is not limited to the infrared sensor) which is a medium detecting unit for detecting the presence or absence of the paper 22 in the carriage 4. Is provided. The density sensor 71 is provided on the recording area (image forming area) side (conveying belt 31 side) side of the carriage 4 at the home position and upstream of the recording head 11 in the paper conveying direction. .

  Further, an encoder scale 72 having slits is provided on the front side of the carriage 4 along the main scanning direction, and an encoder sensor 73 including a transmission type photosensor for detecting the slits of the encoder scale 72 is provided on the front side of the carriage 4. These components constitute a linear encoder 74 for detecting the position of the carriage 4 in the main scanning direction.

  Next, an example of a droplet discharge head constituting the recording head in this image forming apparatus will be described with reference to FIGS. 5 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber of the head, and FIG. 6 is a cross-sectional explanatory view of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

  The droplet discharge head includes a flow channel plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by nickel electroforming, for example, bonded to the lower surface of the flow channel plate 101, and a flow plate. A nozzle plate 103 bonded to the upper surface of the path plate 101 is bonded and stacked, and a nozzle communication path 105, a liquid chamber 106, and a liquid chamber, which are channels through which the nozzles 104 that discharge liquid droplets (ink droplets) communicate with each other. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to 106 is formed.

  In addition, two rows (only one row is shown in FIG. 6) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing ink in the liquid chamber 106 by deforming the diaphragm 102. An element 121 and a base substrate 122 to which the piezoelectric element 121 is bonded and fixed are provided. Note that a column portion 123 is provided between the piezoelectric elements 121. This support portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the support portion 123 becomes a simple support.

  Further, an FPC cable 12 equipped with a drive circuit (drive IC) (not shown) is connected to the piezoelectric element 121.

  The peripheral edge of the diaphragm 102 is joined to a frame member 130, and the frame member 130 serves as a through-hole 131 and a common liquid chamber 108 that house an actuator unit composed of the piezoelectric element 121 and the base substrate 122. A recess and an ink supply hole 132 for supplying ink from the outside to the common liquid chamber 108 are formed. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  Here, the flow path plate 101 is formed by, for example, subjecting the single crystal silicon substrate having a crystal plane orientation (110) to anisotropic etching using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 105, Although a recess or a hole serving as the liquid chamber 106 is formed, the invention is not limited to a single crystal silicon substrate, and other stainless steel substrates, photosensitive resins, and the like can also be used.

  The vibration plate 102 is formed from a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Alternatively, a metal plate or a joining member between a metal and a resin plate may be used. it can. The piezoelectric element 121 and the support post 123 are bonded to the diaphragm 102 with an adhesive, and the frame member 130 is further bonded with an adhesive.

  The nozzle plate 103 forms a nozzle 104 having a diameter of 10 to 30 μm corresponding to each liquid chamber 106 and is bonded to the flow path plate 101 with an adhesive. The nozzle plate 103 is formed by forming a water repellent layer on the outermost surface of a nozzle forming member made of a metal member via a required layer. The surface of the nozzle plate 103 is the nozzle surface 34a described above.

  The piezoelectric element 121 is a stacked piezoelectric element (here, PZT) in which piezoelectric materials 151 and internal electrodes 152 are alternately stacked. An individual electrode 153 and a common electrode 154 are connected to each internal electrode 152 drawn out to different end faces of the piezoelectric element 121 alternately. In this embodiment, the ink in the liquid chamber 106 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric element 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric element 121. The ink in the liquid chamber 106 may be pressurized. Alternatively, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the droplet discharge head configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the vibration plate 102 descends to expand the volume of the liquid chamber 106. As a result, the ink flows into the liquid chamber 106, and then the voltage applied to the piezoelectric element 121 is increased to extend the piezoelectric element 121 in the stacking direction, and the diaphragm 102 is deformed in the direction of the nozzle 104 to change the volume of the liquid chamber 106. / By contracting the volume, the recording liquid in the liquid chamber 106 is pressurized, and droplets of the recording liquid are ejected (jetted) from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric element 121 to the reference potential, the diaphragm 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. The recording liquid is filled in 106. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (pulling-pushing), and it is also possible to perform striking or pushing depending on the direction to which the driving waveform is given.

  In the image forming apparatus configured as described above, the sheets 22 are separated and fed one by one from the sheet feeding unit, and the sheets 22 fed substantially vertically upward are guided by the guide 25, and the conveyance belt 31 and the counter roller 26, and the leading end is guided by a conveying guide 27 and pressed against the conveying belt 31 by a leading end pressing roller 29, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately and repeatedly applied to the charging roller 34 from an AC bias supply unit, which will be described later, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 31 alternates, that is, a loop In the sub-scanning direction, which is the direction, plus and minus are alternately charged in a band shape with a predetermined width. When the paper 32 is fed onto the conveying belt 31 that is alternately charged with plus and minus, the paper 22 is attracted to the conveying belt 31 by electrostatic force, and the paper 22 is conveyed in the sub-scanning direction by the circular movement of the conveying belt 31. Is done.

  Therefore, by driving the recording head 11 according to the image signal while moving the carriage 4, ink droplets are ejected onto the stopped paper 22 to record one line, and after the paper 22 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 22 has reached the recording area, the recording operation is finished and the paper 22 is discharged onto the paper discharge tray 40.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 32 is fed into the double-sided paper feeding unit 51 by rotating the conveyor belt 31 in reverse. The paper 22 is reversed (with the back surface being the printing surface), fed again between the counter roller 26 and the conveyor belt 31, controlled in timing, and conveyed by the conveyor bell 31 as described above. After recording on the back surface, the paper is discharged onto the paper discharge tray 40.

Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.
In the control unit 200, the CPU 211 that controls the entire apparatus, the ROM 202 that stores programs executed by the CPU 211 and other fixed data, the RAM 203 that temporarily stores image data and the like, and the power supply of the apparatus are cut off. A rewritable non-volatile memory 204 for holding data in between, an image processing for performing various signal processing and rearrangement on image data, and an ASIC 205 for processing input / output signals for controlling the entire apparatus. ing.

  The control unit 200 includes an I / F 206 for transmitting and receiving data and signals to and from the host side, a head drive control unit 207 including a data transfer unit for driving and controlling the recording head 11, and a carriage 4 side. A head driver (driver IC) 208, which is a head driving device for driving the provided recording head 11, a main scanning motor driving unit 210 for driving the main scanning motor 5, and a sub scanning motor 36 are driven. A sub-scanning motor drive unit 211, an AC bias supply unit 212 that supplies an AC bias to the charging roller 34, detection pulses from the linear encoder 74 and the wheel encoder 236, a detection signal from the temperature sensor 215 that detects the environmental temperature, and An I / O 213 for inputting detection signals from other various sensors is provided. The control unit 200 is connected to an operation panel 214 for inputting and displaying information necessary for the apparatus.

  Here, the control unit 200 transmits print data from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, etc. via an I / F 206 via a cable or a network. Receive.

  Then, the CPU 201 of the control unit 200 reads and analyzes the print data in the reception buffer included in the I / F 206, performs necessary image processing, data rearrangement processing, and the like in the ASIC 205, and this image data is head-driven. The data is transferred from the control unit 207 to the head driver 208. The dot pattern data for image output may be generated by storing font data in the ROM 202, for example, or the image data is developed into bitmap data by a host-side printer driver and transferred to this apparatus. You may do it.

  The head drive control unit 207 transfers the above-described image data as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transferring the image data and confirming the transfer to the head driver 208. Includes a drive waveform generation unit including a D / A converter and an amplifier that D / A converts drive pulse pattern data stored in the ROM 202 and read out by the CPU 201. One drive pulse or a plurality of drive pulses A drive waveform composed of (drive signal) is output to the head driver 208.

  The head driver 208 selectively selects the drive pulse constituting the drive waveform supplied from the head drive control 207 based on the image data corresponding to one line of the print head 11 inputted serially (actuator means of the print head 11 ( In the head configuration described above, the head 11 is driven by being applied to the piezoelectric element 121).

  The main scanning motor driving unit 210 calculates a control value based on a target value given from the CPU 201 side and a speed detection value obtained by sampling a detection pulse from the linear encoder 74, and performs main scanning via an internal motor driver. The motor 5 is driven.

  Similarly, the sub-scanning motor drive control unit 211 calculates a control value based on a target value given from the CPU 101 side and a speed detection value obtained by sampling a detection pulse from the wheel encoder 136 to determine an internal motor driver. And the sub-scanning motor 36 is driven.

Next, an example of the configuration of the head drive control unit 207 and the head driver 28 will be described with reference to FIG.
As described above, the head drive control unit 207 generates and outputs a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one printing cycle, and printing. A data transfer unit 302 that outputs 2-bit image data (tone signals 0 and 1) corresponding to an image, a clock signal, a latch signal (LAT), and a control signal is provided.

  The control signal is a 2-bit signal that instructs each drop to open and close an analog switch 317, which will be described later, of the head driver 208. The control signal is a waveform that should be selected in accordance with the print cycle of the common drive waveform. The state transitions to (ON), and when not selected, the state transitions to L level (OFF), a signal (1, 1) for selecting a large droplet, a signal (1,0) for selecting a medium droplet, and a small droplet are selected. There is a signal (0, 1) and a signal (0, 0) for selecting non-ejection.

  The head driver 208 receives a gradation signal 0 and a clock signal that are serially transferred to a transfer clock (shift clock) from the data transfer unit 302 and receives a gradation signal 1 and a clock signal from the data transfer unit 302. Shift register 312, latch circuit 313 that latches the register value of shift register 311 with latch signal LAT from data transfer unit 302, and latches register value of shift register 312 with latch signal LAT from data transfer unit 302 And a selector 315 that selects a control signal from the data transfer unit 302 based on the output value of the latch circuit 313 and the output value of the latch circuit 314 and outputs the control signal to the level conversion circuit (level shifter) 316. Analyzes the logic level voltage signal of the selector. Level switch 316 that converts the level of the switch 317 to an operable level, and analog switches AS1 to ASn that are turned on / off (opened / closed) by the output of the selector 315 that is given via the level shifter 315 (the analog switch AS And an analog switch array (switch means) 317 configured as described above.

  Each analog switch AS1 to ASn of this analog switch array 317 is connected to a selection electrode (individual electrode) 154 of each piezoelectric element 121, and a common drive waveform from the drive waveform generation unit 301 is input thereto. Therefore, when the analog switch AS is turned on in accordance with the control signal selected based on the serially transferred image data (gradation data 0, 1), the required drive signal constituting the common drive waveform passes. (Selected) and applied to the piezoelectric element 121.

The drive waveform and data transfer in the first embodiment of the present invention will be described with reference to FIGS.
Here, as shown in FIG. 9A, the drive waveform generator 301 generates a drive waveform composed of six drive pulses (first pulse P1 to sixth pulse P6) within one printing cycle. And output. Here, the first pulse P1 to the sixth pulse P6 are arranged at a time interval (2Tc) that is twice the natural vibration period Tc of the liquid chamber 106. Thereby, pressure resonance can be used effectively, the discharge efficiency can be improved, and the drive voltage can be lowered relatively. However, the conditions of the voltages of the pulses P1 to P6 are set in detail so that the pressure resonance does not become excessive and discharge becomes unstable.

  Each of the pulses P1 to P6 has a waveform that is held constant after falling from the reference potential V1, rises to a potential exceeding the reference potential V1, and further falls to the reference potential V after being held constant. The falling potential is different for each pulse P1 to P6.

  On the other hand, the data transfer unit 302 uses the transfer clock shown in FIG. 9B to output the gradation signal 0 and the gradation signal 1 twice within one printing cycle as shown in FIG. Forward. In this case, the timing of the latch signal shown in FIG. 5D that defines the rewriting of data must correspond to a flat period of the drive waveform. In other words, during data rewriting, ON / OFF of the analog switch AS of the driver IC 208 is unstable and cannot be guaranteed, so the latch timing is set to a preferable timing from the time required for data transfer and the drive waveform.

  Here, the first transfer of the gradation data (gradation signals 0, 1) twice within one printing cycle is referred to as “first half” and the second is referred to as “second half”. The gradation data sent in the first half is latched and used for selection in the drive pulses P4 to P6 of the drive waveform in the second half. The gradation data used in the first half is gradation data transferred in the second half of the previous printing cycle.

FIG. 10 shows the selection of the drive waveform (selecting the drive pulse to be used) in this embodiment, that is, the presence or absence of droplet discharge by each pulse P1 to P6.
Here, the control signal is set so that the number of droplets to be ejected increases one by one by sequentially increasing the drive pulses to be selected one by one.

  Specifically, in the first half, non-ejection for non-ejection, one drop by the first pulse P1 for small droplets, two drops by the first and second pulses P1 and P2 for medium drops, and the first for large drops. 1 to 3 pulses with 3rd pulse P1 to P3, 4 drops with 4th pulse P4 by adding 4th pulse P4 to 3 pulses of the first half with large droplets in the second half, and similarly, 4th and 5th pulses with medium drops 5 drops by adding P4 and P5, and 6 drops are discharged by adding 4th to 6th pulses P4 to P6 in the case of a large drop.

  As a result, substantially seven gradations (six types of droplets + non-ejection) can be realized.

  In this case, it is only necessary to transfer the gradation data twice within one printing cycle on the data transfer unit 302 side, and it is not necessary to change the configuration on the data driver IC 208 side, so that the number of bits of the gradation data is increased. In addition, the number of gradations that can be expressed can be increased without increasing the drive frequency. That is, since the drive waveform can handle 6 drive pulses as a set, a large droplet can be stably ejected. This is different from a system in which three driving pulses are set as a set and driven at twice the driving frequency.

  Here, in order to make it easy to understand that the gradation is increased, in this embodiment, a driving waveform composed of six driving pulses is used, but in particular, when the gradation data is 2 bits, the driving waveform is used. This is effective when the number includes four or more drive pulses (a maximum of four droplets can be discharged within one printing cycle).

  That is, in the case of 2-bit gradation data, in principle, only up to 4 gradations can be classified. If no discharge is included, the size of the discharged droplets is three types, and up to three drive pulses can be increased for each pulse (one droplet), but when the number of pulses exceeds four, two droplets will increase at the same time. According to this embodiment, the number of pulses can be further increased for each pulse (one drop).

  In this way, a plurality of gradation data composed of a plurality of bits per channel are transferred to the head driving means (head driver here) a plurality of times within one printing cycle, thereby forming a plurality of driving waveforms. Even if the interval between the drive signals is shortened, each drive signal can be selected for each individual droplet, and the number of actual gradations can be increased by transferring gradation data a plurality of times. As a result, both high image quality and high-speed printing can be achieved.

  The same applies to the case where the control signal is used as in this embodiment and the case where the decoding means is used, and the present invention can also be applied to a method using the decoding means.

  Furthermore, although the serial type image forming apparatus is described in this embodiment, the present invention can also be applied to an image forming apparatus equipped with a full line type line type head. Even in the case of the full line type, according to the present invention, the gradation data is transferred a plurality of times within one printing cycle from the relationship between the number of bits of gradation data to be actually transferred and the number of pulses for discharging droplets. The number of possible gradations can be increased.

  In particular, in a full-line type image forming apparatus in which a plurality of droplets that form large droplets are merged before being landed on a sheet (combined during flight) to easily fill the nozzle row direction, It is effective because it can be compatible with large drops.

  In this way, by transferring the gradation data a plurality of times within one printing cycle, the number of gradations can be increased and the halftone can be smoothly connected. By forming a large droplet by merging a plurality of droplets before landing on the paper, the ink easily spreads in the sub-scanning direction after landing on the paper, and an image is formed with a sufficient amount of ink. Can be reduced, and it can be reduced.

  In addition, as described above, the number of droplets that can be ejected included in one printing cycle, that is, the number of drive signals is equal to or greater than the number of gradations that can be expressed by gradation data (4 gradations if 2 bits). The variable range can be made large, and a substantial number of gradations can be taken without increasing the cost of the circuit system.

  Furthermore, by setting the number of ejectable droplets contained in one printing cycle to 4 or more, it is possible to further increase the variable range of the droplet amount, and the actual number of gradations without increasing the cost of the circuit system. Can take a lot.

Next, drive waveforms and data transfer in the second embodiment of the present invention will be described with reference to FIGS.
The drive waveform used here has a 6-pulse configuration (consisting of 6 drive pulses) as in the first embodiment, but different types of waveforms are combined.

  In other words, the first pulse P1 is a dedicated waveform (pulse) for ejecting a very small droplet. When the pulse is raised from the reference potential and then raised to the reference potential, the first pulse P1 is raised for the first time. This is a pulse in which droplets are sometimes ejected to generate and eject minute droplets, and droplets are not ejected at the start of the second stage.

  Further, the fourth pulse P4 also has a waveform element (shape) different from that of the second, third, fifth, and sixth, and rises up to the reference potential V. Further, the interval between the fifth pulse P5 and the sixth pulse P6, that is, the ejection interval of the fifth and sixth droplets is set to three times the liquid chamber natural vibration period Tc (3Tc), and is longer than the other ejection intervals. is doing. Note that the transfer of the gradation data (gradation signals 0, 1) is performed twice within one printing cycle, as in the above embodiment.

  In this embodiment, the presence or absence of droplet ejection by the pulses P1 to P6 when the pulses P1 to P6 of the drive waveform are selected by the control signal shown in FIG. 11E is as shown in FIG. Here, a pulse (droplet) that is not selected elsewhere, such as the first half droplet (0, 1), is provided.

  As described above, the present invention does not fix the method of selecting each drive pulse constituting the drive waveform. Further, the shape of the drive pulse constituting the drive waveform and the discharge interval (inter-pulse interval) are not limited, and the combinations can be variously set.

Next, drive waveforms and data transfer in the third embodiment of the present invention will be described with reference to FIGS.
In the drive waveform used here, a fine drive pulse for oscillating the meniscus is inserted between the fifth pulse P5 and the sixth pulse P6 in the drive waveform of the second embodiment. The fine driving pulse is to prevent the ink of the nozzles from being dried during printing and causing a discharge failure by vibrating the meniscus of the nozzle with a pressure that does not discharge the ink droplets. Further, the transfer of gradation data (gradation signals 0, 1) is performed twice within one printing cycle, as in the above embodiments.

  In this embodiment, the presence or absence of droplet ejection by the pulses P1 to P6 and the fine driving by the fine driving pulse when the pulses P1 to P6 of the driving waveform and the fine driving pulse are selected by the control signal shown in FIG. Is as shown in FIG.

  In this way, non-ejection gradation can be assigned to fine driving. Further, it is not always necessary to select drive pulses in a continuous range. In this embodiment, the analog switch AS is in an OFF state in a channel in which another gradation is set at the time of the fine driving pulse, and is not continuous.

Next, drive waveforms and data transfer according to the fourth embodiment of the present invention will be described with reference to FIGS.
The drive waveform here is the same as the drive waveform of the first embodiment. Further, the transfer of gradation data (gradation signals 0, 1) is performed twice within one printing cycle, as in the above embodiments.

In this embodiment, the presence or absence of droplet ejection by the pulses P1 to P6 when the pulses P1 to P6 of the drive waveform are selected by the control signal shown in FIG. 15E is as shown in FIG.
That is, here, in the first half, the first pulse P1 is selected with the small droplet (0, 1) and one droplet is ejected, and the first and second pulses P1, P2 are performed with the middle droplet (1, 0). Is selected and two drops are ejected. In the second half, the fifth pulse P5 is selected with a small drop (0,1) and one drop is ejected, and the fifth, P with a medium drop (1,0). The sixth pulse P5, P6 is selected to eject two drops, and for the large drop (1, 1), all pulses P1 to P6 are selected to eject six drops.

  As described above, the gradation data (gradation signals 0 and 1) is transferred twice (a plurality of times) within one printing cycle, so that independent driving pulses are separately provided in the first half and the second half with respect to the small droplet and the middle droplet. A droplet is ejected to form dots. Accordingly, it is possible to cope with a case where the main scanning direction resolution and the sub scanning direction resolution are different.

  In this case, at least one drive signal for ejecting a plurality of droplets that form a large droplet out of a plurality of drive signals constituting the drive waveform is not a large droplet for the plurality of gradation data. By using it as a drive signal for ejecting the droplets that form the droplets (in the above example, ejecting the middle droplets), the entire drive waveform time can be shortened and the printing cycle itself can be shortened. Therefore, higher speed can be achieved.

Here, the concept of dot formation of this embodiment will be described with reference to FIG.
The basic resolution for dot formation is 300 dpi. When an image is formed by a non-interlace method using a head in which two rows of nozzles having a nozzle pitch of 150 dpi are arranged, the resolution in the sub-scanning direction is 300 dpi.

  In the main scanning direction, a period in which ejection is performed at 300 dpi intervals in accordance with the resolution in the sub-scanning direction is defined as one printing period. At this time, as shown in FIG. 17A, when a large droplet is landed at a dot position of 300 dpi × 300 dpi, the amount of droplet is such that the image can be filled (a solid image can be formed). Specifically, as shown in FIG. 15, six droplets are ejected within one printing cycle, and each droplet is merged to form one large droplet before landing on the paper.

  On the other hand, as shown in FIG. 16, the droplets are ejected using the first pulse P1 in the first half and using the fifth pulse P5 in the second half. The middle droplet is ejected using the first and second pulses P1 and P2 in the first half and using the fifth and sixth pulses P5 and P6 in the second half.

  In other words, in the first to third embodiments, the number of gradations including the combination of the first half and second half gradation data is increased by transferring the gradation data twice within one printing cycle. In contrast, in the fourth embodiment, regarding the middle droplet and the small droplet, an image is created independently for the first half and the second half.

  As a result, since the small droplet and the medium droplet can be ejected (formed) twice within one printing cycle, the resolution in the main scanning direction is artificially double 300 dpi as shown in FIG. 17B. 600 dpi.

  As a result, the density range that can be expressed by small droplets and medium droplets is expanded, and in particular, the continuity of the density in the highlight portion is improved. In addition, the granularity can be reduced by expanding the density range that can be expressed without including large droplets.

  That is, only the droplets that form solids (large droplets) have a printing mode in which the resolution in the main scanning direction is matched to the sub-scanning, so that the sub-scanning direction is easily filled and small droplets (medium and small droplets in the case of four gradations). Can increase the resolution in the main scanning direction, so that gradation skip in the highlight area can be suppressed, and the drops (large drops) that form solids can be shifted to darker gradations, reducing graininess, and Quality is improved.

  Further, as shown in FIG. 18 (a), it is also effective to fill a level difference like a jaggy correction of characters with a medium drop and a small drop to make it gentle. For comparison, FIG. 18B shows the case where medium and small droplets are ejected at the same 300 dpi × 300 dpi as the large droplets, but it is understood that they are rougher than those in FIG. .

  On the other hand, large droplets can be filled with a small amount of droplets by adjusting to the resolution (300 dpi) in the sub-scanning direction. As shown in FIG. 26 described above, when the resolution of a large droplet is raised in the same way as a medium droplet and a small droplet (600 dpi), the sub-scanning direction needs to be filled and the droplet needs to be large.

  In addition, when the droplets are continuously ejected to form a large droplet by a plurality of droplets as in the present invention, the entire drive waveform must be strictly conditioned in terms of voltage and time in order to stably eject the droplets. However, in this embodiment, since one printing cycle is based on large droplets, stable ejection can be achieved. Furthermore, since the amount of ejected droplets can be earned with subsequent droplets (fourth to sixth droplets in this embodiment), large droplets can be formed efficiently.

  As described above, in this embodiment, large droplets are formed by merging a plurality of droplets before landing on the paper in order to facilitate filling in the sub-scanning direction, but it is not always necessary to merge them.

  In the present embodiment, as shown in FIG. 15, latching (rewriting of gradation data) is performed between the third pulse P3 and the fourth pulse P4. Is the fifth pulse P5, it is possible to latch (rewrite gradation data) between the fourth pulse P4 and the fifth pulse P5. In short, it is sufficient to set the timing to transfer the first half and second half gradation data in time.

  Further, in the case of the serial type image forming apparatus as in the present embodiment, a position reference such as a linear encoder is often provided also in the main scanning direction in order to correct the speed unevenness of the carriage on which the head is mounted (described above). Linear encoder 74).

  In this case, a drive waveform is generated by using a signal (position reference signal) from the linear encoder 74 as a trigger to eject a droplet, so that the printing is synchronized with the position reference signal, but one print corresponding to the carriage speed unevenness. The period is not constant. Although the time varies depending on the specification of the carriage speed unevenness, the drive waveform and gradation data transfer time must be within the fastest carriage speed.

  The hatched area in FIG. 15 represents the range of time to be shortened. In this case, as in the present embodiment, the drive pulses for generating large droplets can be controlled as a single unit, so that a margin time (wasted time) for dealing with the carriage speed unevenness can be relatively shortened. .

  For example, when printing at 600 × 300 dpi including normal large droplets, the position reference signal generated from the encoder 74 also has a time interval corresponding to 600 dpi. Even if the first half and the second half are each three pulses, a time difference with respect to the carriage speed unevenness occurs. Usually, in order to enable stable ejection, a sufficient time must be ensured between the drive waveforms. Therefore, the time for the carriage speed unevenness must be ensured in two times. On the other hand, in this embodiment, since the drive pulses for forming large droplets are 300 dpi as a unit, it is sufficient to secure a time for one-time carriage speed unevenness.

  In other words, the normal two drops of 600 dpi × 300 dpi and the formation of large drops with the six pulses of this embodiment are completely different. When discharging multiple drops in succession, it is important that the timing of overlapping is fixed to control the residual pressure in the pressurized liquid chamber to discharge stably and to increase the amount of drops. is there.

  On the other hand, for medium drops and small drops, the visibility of the dots is not high, so even if the landing position is slightly deviated (because of the large drop waveform priority, the latter half of the drops are selected. (There is a slight difference in the amount of drops.) Rather, as described above, the image quality of the medium droplet and the small droplet is remarkably improved by artificially increasing the resolution in the main scanning direction.

  In this way, relatively large droplets (large droplets) formed by a plurality of droplets are ejected based on the reference signal obtained from the carriage position signal (linear encoder), and can be set from the reference signal. By switching the tone data (by performing a plurality of times of data transfer), it is possible to suppress the positional deviation of the large droplets and improve the image quality.

Next, drive waveforms and data transfer according to the fifth embodiment of the present invention will be described with reference to FIGS.
Here, the drive waveform is composed of first to eighth pulses P1 to P8, and among these, the second pulse P2 and the sixth pulse P6 are pulses having the same waveform as pulses used only for droplet formation, The first pulse P1 and the fifth pulse P5 are pulses used for forming a medium droplet and a large droplet, and have the same waveform. Further, the transfer of the gradation data (gradation signals 0, 1) is performed twice within one printing cycle, as in the fourth embodiment.

  In this embodiment, the presence or absence of droplet ejection by the pulses P1 to P8 when the pulses P1 to P8 of the drive waveform are selected by the control signal shown in FIG. 19E is as shown in FIG. That is, as in the fourth embodiment, regarding the small droplets (pulses P2 and P6) and the medium droplets (pulses P1 and P5), dots are formed independently in the first half and the second half. Can form an image with 300 × 300 dpi, medium droplets and small droplets equivalent to 600 × 300 dpi.

  Here, the waveform for large droplet generation does not include the waveform for small droplets, the same waveform is used for the waveform for droplet generation in the first half and the latter half, and the waveform for medium droplet generation is the same as the waveform for large droplet generation. In part, the same waveform is used in the first half and the second half, which is different from the fourth embodiment. As a result, the amount of medium droplets and small droplets in the first half and the second half are the same, which facilitates image formation and further improves image quality.

  As for the image quality, it is preferable to use the same drive pulse so that the medium drops and the small drops have the same drop amount in the first half and the second half as in this embodiment. In addition, as long as it falls within one printing cycle, it is also possible to use an independent driving pulse different from that of a large droplet for a medium droplet as well as a small droplet.

  If a part of the large drop generation drive pulse is used in common and the same waveform is used for both the first half and the second half, as in the case of the medium drop generation drive pulse of this embodiment, the large drop generation drive is used. Since the restriction condition of the pulse waveform condition increases, it is preferable to sandwich the pulse waveform in the middle so that adjustment can be performed with the subsequent waveform (droplet).

  Here, since the fifth pulse P5 has the same waveform as the first pulse P1 to generate a medium droplet, the droplets ejected with the fifth pulse P5 at the time of large droplet generation have a slightly lower ejection speed. This is a waveform obtained by correcting the subsequent seventh and eighth pulses P7 and P8 (the fifth drop and the sixth drop in the case of a large drop) slightly stronger (faster drop discharge speed). .

  In addition, when it makes a large drop, the discharge speed of the drop by the 5th pulse P5 becomes slow because the meniscus is raised by discharging continuously before that. This is also the reason why the droplet amount can be increased, but originally it is necessary to increase the voltage by the amount corresponding to the large droplet amount to give the ejection energy. At the same voltage as the first drop where the meniscus is not raised, the speed is slightly reduced. Therefore, by inserting the middle droplet generating pulse in the middle of a plurality of large droplet generating pulses, the subsequent droplet can be corrected. The ejection timing is set to a timing for stabilizing the continuous ejection of large droplets.

  As described above, the drive waveform includes two drive signals for ejecting droplets of substantially the same size at least twice based on gradation data transferred a plurality of times within one printing cycle, thereby improving image quality. In this case, the two drive signals for ejecting droplets of approximately the same size at least twice are not used to eject droplets of other sizes, so that the size of the droplets can be improved. The two drive signals for ejecting droplets of approximately the same size at least twice can be used to eject droplets of other sizes, so that the time of the entire drive waveform can be obtained. It is possible to cope with a case where (one printing cycle) is shortened.

Next, a sixth embodiment of the present invention will be described.
In the present embodiment, the mode using the drive waveform and data transfer in the first embodiment (FIG. 9) and the mode using the drive waveform and data transfer in the fifth embodiment (FIG. 19) are switched according to the print mode. I am trying to do it.

  At this time, the latch timing for rewriting the gradation data is different between FIG. 9 and FIG. As described above, since the ON / OFF state of the analog switch AS is indefinite during the latching time, the latching needs to be performed at a timing when the driving waveform is flat, and the driving waveform differs between FIG. 9 and FIG. Because. Therefore, it is possible to set the rewriting timing of the gradation data of one printing cycle according to the difference in the driving waveform.

  For example, in the case of an ink jet recording apparatus, the spreading method of ink after landing differs greatly depending on the type of paper used, and therefore there are several printing modes (for example, “plain paper is fast”, “glossy paper”, etc.). Yes.

  In this case, the amount of droplets (large, medium, and small) required by the printing mode is different, and therefore the drive waveform is also different, so that the rewriting timing of gradation data in one printing cycle can be set as in this embodiment. By doing so, it is possible to cope with the conversion of the drop amount. If the rewriting timing is fixed, there is a great restriction on setting the drive waveform condition (waveform design), and it may be impossible to design a drive waveform for discharging a desired droplet amount.

Next, a seventh embodiment of the present invention will be described.
In this embodiment, according to the print mode, the mode using the drive waveform and data transfer in the first embodiment (FIG. 9) and the drive waveform and data transfer described in FIG. 22 (one gradation within one print cycle). The mode using the data transfer configuration) can be switched.

  As described above, the ink jet recording apparatus has several print modes. In order to form a high-quality image such as a photographic image quality, the nozzle pitch cannot be set to the resolution in the sub-scanning direction. Some printing modes require a method.

  In the case of such a high-quality print mode, a large droplet as in the first embodiment (FIG. 9) is not necessary. Since the number of interlaces is increased with small droplets, the number of gradations in one printing cycle is not necessary. Therefore, in such a case, as described with reference to FIG. 22, the gradation data may be transferred once in one printing cycle. Rather, as shown in FIG. 9 (first embodiment), if gradation data is to be transferred a plurality of times, it takes time to create transfer data and gradation data, resulting in a problem in printing speed.

  Therefore, in this embodiment, it is possible to select whether to transfer the gradation data once or a plurality of times depending on the print mode. As a result, data transfer suitable for the print mode becomes possible, and pseudo high gradation (first to third embodiments) and pseudo resolution increase in the main scanning direction (fourth and fifth embodiments). As a result, it is possible to improve the efficiency of data transfer when it is not necessary.

  Since these are only differences in data transfer timing, latches, etc. on the device body side, they can be dealt with by simply changing the sequence on the device body side (the above-mentioned data transfer unit). The hardware on the side can be made common and can be easily realized.

  In each of these embodiments, the configuration of 2 bits / CH has been described. However, in the case of 3 bits / CH or more, the number of droplets ejected within one printing cycle is larger than the number of gradations. It is effective to apply the present invention in the same manner.

1 is an explanatory side view illustrating an overall configuration of a mechanism unit of an image forming apparatus according to the present invention. It is a plane explanatory view of the mechanism part. FIG. 3 is an explanatory diagram illustrating an example of a recording head configuration of the image forming apparatus. FIG. 6 is an explanatory diagram illustrating another example of the recording head configuration. FIG. 6 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber showing an example of a droplet discharge head that also constitutes a recording head. FIG. 5 is a cross-sectional explanatory view along the lateral direction of the liquid chamber showing an example of a droplet discharge head that also constitutes a recording head. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit in the image forming apparatus. FIG. 3 is a block explanatory diagram illustrating an example of a head drive control unit and a head driver in the control unit. It is explanatory drawing explaining the drive waveform and data transfer in 1st Embodiment of this invention. It is explanatory drawing with which it uses for description of the presence or absence of the control signal and droplet discharge in the embodiment. It is explanatory drawing explaining the drive waveform and data transfer in 2nd Embodiment of this invention. It is explanatory drawing with which it uses for description of the presence or absence of the control signal and droplet discharge in the embodiment. It is explanatory drawing explaining the drive waveform and data transfer in 3rd Embodiment of this invention. It is explanatory drawing with which it uses for description of the presence or absence of the control signal and droplet discharge in the embodiment. It is explanatory drawing explaining the drive waveform and data transfer in 4th Embodiment of this invention. It is explanatory drawing with which it uses for description of the presence or absence of the control signal and droplet discharge in the embodiment. It is explanatory drawing with which it uses for description of the relationship between the main scanning direction resolution and the dot (droplet size) of the embodiment. It is explanatory drawing with which it uses for description of the effect of the same embodiment. It is explanatory drawing explaining the drive waveform and data transfer in 5th Embodiment of this invention. It is explanatory drawing with which it uses for description of the presence or absence of the control signal and droplet discharge in the embodiment. It is explanatory drawing with which it uses for description of the system which transfers print data about each drive pulse. FIG. 6 is an explanatory diagram for explaining a method in which the number of drive pulses of a drive waveform is three and grayscale data is transferred once. Similarly, it is an explanatory diagram for explaining a system in which the number of drive pulses of the drive waveform is four and gradation data is transferred once. Similarly, it is an explanatory diagram for explaining a method in which the number of drive pulses of the drive waveform is 6 and the gradation data is transferred once. It is explanatory drawing with which it uses for description of the relationship of the magnitude | size and arrangement | positioning of a main scanning direction resolution and a subscanning direction resolution, and a droplet (dot). It is explanatory drawing with which it uses for description of the relationship between the magnitude | size and arrangement | positioning of a droplet (dot) when both the main scanning direction resolution and the sub-scanning direction resolution are doubled. It is explanatory drawing which shows an example of the measurement result of the relationship between a droplet volume and the volume of each droplet.

Explanation of symbols

4 ... Carriage 5 ... Main scanning motor 11 ... Recording head 22 ... Recording medium (paper)
DESCRIPTION OF SYMBOLS 31 ... Conveyance belt 32 ... Conveyance roller 36 ... Sub scanning motor 121 ... Piezoelectric element 200 ... Control part 207 ... Head drive control part 208 ... Head driver 301 ... Drive waveform generation part 302 ... Data transfer part

Claims (14)

  A liquid ejection head for ejecting recording liquid droplets; drive waveform generating means for generating a drive waveform including a plurality of drive signals within one printing cycle; and gradation data being input, and from the drive waveform, the level In the image forming apparatus comprising a driving unit that selects a required driving signal through a switch unit that opens and closes according to tone data and applies the selected driving signal to the liquid discharge head, the gradation composed of a plurality of bits per channel An image forming apparatus comprising: means for transferring data to the driving means a plurality of times within one printing cycle.   2. The image forming apparatus according to claim 1, wherein when the liquid ejection head is driven with gradation data for ejecting a plurality of droplets, the droplets are merged to form a single droplet before landing. Forming equipment.   The image forming apparatus according to claim 1, wherein the number of droplets ejected by a plurality of drive signals included in one printing cycle is equal to or greater than the number of gradations of the gradation data. apparatus.   4. The image forming apparatus according to claim 3, wherein the number of ejected droplets ejected by a plurality of drive signals included in the one printing cycle is four or more.   5. The image forming apparatus according to claim 1, wherein timing for transferring the gradation data a plurality of times within one printing cycle can be changed.   6. The image forming apparatus according to claim 1, wherein a mode in which the gradation data is transferred a plurality of times within one printing cycle and a mode in which the gradation data is transferred once within a printing cycle. An image forming apparatus that is switchable.   7. The image forming apparatus according to claim 1, wherein at least one drive of a drive signal for ejecting a plurality of droplets forming a large droplet among the plurality of drive signals constituting the drive waveform. The signal is used as a drive signal for discharging a droplet that forms a droplet other than a large droplet with respect to the gradation data for a plurality of times.   The image forming apparatus according to claim 1, wherein the driving waveform includes two drivings that eject droplets of substantially the same size at least twice based on the gradation data transferred a plurality of times within one printing cycle. An image forming apparatus including a signal.   9. The image forming apparatus according to claim 8, wherein the two drive signals for ejecting the droplets of substantially the same size at least twice are not used for ejecting droplets of other sizes. Forming equipment.   9. The image forming apparatus according to claim 8, wherein the two drive signals for ejecting the droplets of substantially the same size at least twice are also used for ejecting droplets of other sizes. Image forming apparatus.   A liquid discharge head for discharging liquid droplets of recording liquid is provided, and it is possible to express gradations of liquid droplets of different sizes from this liquid discharge head to one pixel, and the main scanning is higher than the resolution of sub-scanning. In a serial type image forming apparatus capable of forming an image with high scanning resolution, the image forming apparatus has a mode in which only a relatively large droplet is ejected in accordance with the sub-scanning resolution in the main scanning direction. .   12. The image forming apparatus according to claim 11, wherein drive waveform generating means for generating a drive waveform including a plurality of drive signals within one printing cycle and gradation data are input, and the gradation data is selected from the drive waveforms. The drive means for selecting a required drive signal via a switch means that opens and closes in response to the liquid discharge head and applying the drive signal to the liquid discharge head, and the gradation data composed of a plurality of bits per channel within one printing cycle, Means for transferring to the driving means a plurality of times, and when forming the large drop with a plurality of drops, the plurality of drops forming the large drop are ejected based on a reference signal corresponding to the position of the carriage, An image forming apparatus that transfers gradation data for a plurality of times in a time that can be set from a reference signal.   13. The image forming apparatus according to claim 12, wherein at least one drive signal of the drive signal for ejecting a plurality of droplets forming a large droplet of the plurality of drive signals constituting the drive waveform is a plurality of times. An image forming apparatus characterized in that the gradation data is used as a drive signal for discharging a droplet that forms a droplet other than a large droplet. 14. The image forming apparatus according to claim 11, wherein an image is formed by a non-interlace method in a mode in which only the large droplets are ejected in accordance with the sub-scanning resolution in the main scanning direction. .

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