JP2012045797A - Driving device and driving method of ink jet head, and ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form dots regardless of size of dots formed when the sizes of dots formed are controlled by the number of liquid droplets ejected from nozzles.SOLUTION: The ink jet head includes: a waveform generating means which generates a reference driving waveform that includes a plurality of ejection waveform elements for ejecting liquid droplets from nozzles and that forms dots on an object by uniting a plurality of liquid droplets ejected by a plurality of ejection waveform elements in the reference driving waveform during flying; a data acquiring means which acquires size data of dots formed; a waveform selecting means which selects ejection waveform elements sequentially from the last among the plurality of ejection waveform elements in the reference driving waveform according to the size data; and a driving means which causes the selected ejection waveform element to eject liquid droplets from the nozzles. The waveform generating means generates the reference driving waveform so that an amplitude of the later ejection waveform element is smaller.

Description

  The present invention relates to an inkjet head driving apparatus and driving method, and an inkjet recording apparatus, and more particularly to an inkjet ejection technique for forming dots of a plurality of sizes.

  In an ink jet recording apparatus that forms a desired image on a recording medium using an ink jet method, when forming a plurality of sizes of dots, a common drive waveform having a plurality of drive waveforms is selected according to the desired dot size. There is known a driving method in which one or more driving waveforms are selected and a driving element such as a piezoelectric element is operated.

  Patent Document 1 discloses a first pulse for ejecting ink droplets in an ink jet recording apparatus that ejects a plurality of ink droplets within one printing cycle and combines these ink droplets during flight and then landed on a recording paper. , A technique using a drive signal in which the interval between the second pulse and the third pulse is arranged so as to gradually approach the reference resonance period is disclosed.

JP 2003-175601 A

  When the pulse interval is gradually brought closer to the reference resonance period as in Patent Document 1, the difference in droplet speed between the ink droplet ejected by one pulse and the ink droplet ejected by a plurality of pulses becomes large. For this reason, the landing positions of the ink droplets ejected by one pulse and the ink droplets ejected by a plurality of pulses are different, and there is a problem that the image quality is deteriorated.

  The present invention has been made in view of such circumstances, and when forming dots of a plurality of sizes on an object, an inkjet head drive device that stably forms dots without depending on the dot size to be formed And a driving method and an ink jet recording apparatus.

  In order to achieve the above object, the ink jet head drive device according to claim 1 is characterized in that a nozzle for discharging droplets, a liquid chamber communicating with the nozzle, and a liquid chamber when a predetermined drive signal is supplied. And an actuator for pressurizing the liquid in the inkjet head driving apparatus, wherein the reference driving waveform includes a plurality of ejection waveform elements for ejecting droplets from the nozzle, and the plurality of ejections within the reference driving waveform. Waveform generation means for generating a reference driving waveform for forming a dot on an object by uniting a plurality of droplets ejected by a waveform element during flight, and size data of dots to be formed on the object Data acquisition means for acquiring, waveform selection means for sequentially selecting discharge waveform elements from the plurality of discharge waveform elements in the reference drive waveform according to the size data, and Drive means for discharging droplets from the nozzles by the selected discharge waveform element, and the waveform generation means generates a reference drive waveform having a smaller amplitude as the discharge waveform element is later in time. To do.

  According to the first aspect of the present invention, the reference driving waveform includes a plurality of ejection waveform elements for ejecting one droplet from the nozzle, and the plurality of droplets ejected by the plurality of ejection waveform elements fly. Generate a reference drive waveform that forms dots on the object by uniting them in, and select from the discharge waveform elements later in time according to the size of the dots to be formed on the object from the reference drive waveform When the droplet is ejected from the nozzle by the selected ejection waveform element, the waveform generating means generates a reference drive waveform having a smaller amplitude as the ejection waveform element is later in time, thereby contributing to the dot size to be formed. Dots can be formed stably, and the difference in the appropriate amount of liquid for each dot size can be increased.

  According to a second aspect of the present invention, in the inkjet head drive device according to the first aspect, the waveform generation unit generates the reference drive waveform having at least three ejection waveform elements, and the data acquisition unit includes at least 3 It is characterized by acquiring various types of size data.

  Thereby, dots of at least three types of sizes can be formed.

  According to a third aspect of the present invention, in the ink jet head drive device according to the second aspect, the waveform generation unit generates a reference drive waveform having three ejection waveform elements, and the waveform selection unit includes the data acquisition unit. Selects all the discharge waveform elements in the reference drive waveform when acquiring the large size data, and among the discharge waveform elements in the reference drive waveform when the data acquisition means acquires the medium size data The latter two waveform elements are selected, and when the data acquisition means acquires small size data, the last waveform element is selected from the ejection waveform elements in the reference drive waveform.

  Thereby, the dot of three types of sizes can be formed appropriately.

  According to a fourth aspect of the present invention, in the inkjet head drive device according to the second or third aspect, the intervals between the start ends of the plurality of ejection waveform elements are substantially the same.

  Thereby, a desired dot can be appropriately formed.

In the drive apparatus of an ink jet head according to claim 2 or 3 as shown in claim 5, the distance between the starting end of said plurality of ejection wave element is a Helmholtz period T _C obtained from the structure of the ink jet head Features.

  Thereby, a desired dot can be appropriately formed.

6. The ink jet head drive apparatus according to claim 2, wherein the interval between the start ends of the plurality of ejection waveform elements is a Helmholtz period T determined from the structure of the ink jet head as it comes later in time. It is characterized by approaching _C.

  Thereby, a desired dot can be appropriately formed.

  According to a seventh aspect of the present invention, in the inkjet head drive device according to any one of the second to sixth aspects, the plurality of ejection waveform elements have substantially the same width.

  Thereby, a desired dot can be appropriately formed.

According to an eighth aspect of the present invention, in the ink jet head driving apparatus according to the seventh aspect, the width of the plurality of ejection waveform elements is T _C / 2.

  Thereby, a desired dot can be appropriately formed.

  9. The ink jet head driving apparatus according to claim 2, wherein the width of the plurality of ejection waveform elements becomes smaller and approaches TC / 2 later in time. And

  Thereby, a desired dot can be appropriately formed.

  The inkjet head drive device according to any one of claims 1 to 9, wherein the waveform generation unit discharges from the nozzle regardless of the number of discharge waveform elements selected by the waveform selection unit. The reference drive waveform is generated so that the velocity of the droplets is substantially constant.

  Thereby, the landing position can be made constant regardless of the dot size to be formed.

  In order to achieve the above object, an ink jet recording apparatus according to an eleventh aspect is the ink jet head driving apparatus according to any one of the first to tenth aspects, a nozzle for discharging droplets, and a liquid communicating with the nozzle. An inkjet head having a chamber, and an actuator that pressurizes the liquid in the liquid chamber when a predetermined drive signal is supplied; and a moving unit that relatively moves the object and the inkjet head. It is characterized by.

  Accordingly, it is possible to provide an ink jet recording apparatus that can stably form dots regardless of the dot size to be formed, and can increase the difference in the appropriate amount of liquid for each dot size.

  In order to achieve the above object, a driving method of an ink jet head according to claim 12, wherein a nozzle that discharges droplets, a liquid chamber that communicates with the nozzle, and a predetermined driving signal are supplied to the liquid chamber. An inkjet head driving method comprising: an actuator for pressurizing liquid, wherein the reference driving waveform includes a plurality of ejection waveform elements for ejecting droplets from the nozzles, and the ejection waveform elements that are later in time A waveform generation step of generating a reference drive waveform having a smaller amplitude, a data acquisition step of acquiring size data of dots to be formed on the object, and a plurality of the reference drive waveforms in the reference drive waveform according to the size data A waveform selection step for selecting discharge waveform elements in order from the later among the discharge waveform elements, and a driving step for discharging droplets from the nozzles by the selected discharge waveform elements There are, characterized in that a drive process for coalescing a plurality of liquid droplets ejected by a plurality of ejection wave elements during flight.

  According to the present invention, it is possible to stably form dots without depending on the dot size formed on the object.

1 is a block diagram of an inkjet discharge apparatus according to an embodiment of the present invention. Sectional drawing which shows the structural example of the inkjet head shown in FIG. The figure explaining the drive waveform at the time of small size dot discharge concerning a 1st embodiment. The figure explaining the drive waveform at the time of medium size dot discharge concerning a 1st embodiment The figure explaining the drive waveform at the time of the large sized dot discharge which concerns on 1st Embodiment. The figure which shows the relationship between the dot size which concerns on 1st Embodiment, and the speed of a droplet The figure which shows the relationship between the dot size and drop amount concerning 1st Embodiment The figure which shows the waveform of the comparative example shown in FIG. 6, FIG. The figure explaining the drive waveform which concerns on 2nd Embodiment The figure which shows the relationship between the dot size which concerns on 2nd Embodiment, and the speed of a droplet The figure which shows the relationship between the dot size and droplet amount concerning 2nd Embodiment The figure which shows the waveform of the comparative example shown in FIG. 10, FIG. The figure explaining the drive waveform which concerns on 3rd Embodiment The figure which shows the relationship between the dot size which concerns on 3rd Embodiment, and the speed of a droplet The figure which shows the relationship between the dot size and drop amount concerning 3rd Embodiment The figure which shows the waveform of the comparative example shown in FIG. 14, FIG. 1 is an overall configuration diagram of an inkjet recording apparatus to which an inkjet ejection apparatus according to the present invention is applied. Plane perspective view of an ink jet head applied to the ink jet recording apparatus shown in FIG. Partial enlarged view of FIG. The figure explaining the nozzle arrangement of the inkjet head shown in FIG. FIG. 17 is a block diagram showing a schematic configuration of a control system of the ink jet recording apparatus shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Description of inkjet discharge device]
FIG. 1 is a block diagram of an inkjet discharge apparatus according to an embodiment of the present invention. An inkjet discharge apparatus 10 shown in this example includes an inkjet head 12 that discharges droplet-like liquid (droplet) by an inkjet method, and a drive apparatus that operates the inkjet head 12 by supplying a predetermined drive signal to the inkjet head 12. 14.

  The inkjet head 12 is provided with a piezoelectric actuator 16 serving as a pressurizing source when ejecting droplets. The piezoelectric actuator 16 operates in accordance with a drive signal supplied from the driving device 14 to eject droplets. The piezoelectric method is applied. Although details will be described later (see FIG. 2), the ink jet head 12 communicates with a nozzle serving as a droplet discharge port, a pressure chamber pressurized by a piezoelectric actuator 16 and the pressure chamber. Configurations such as a liquid flow path are provided.

  The drive device 14 includes a waveform generation unit 18 that generates a reference drive waveform including a plurality of waveform elements, and a waveform selection unit that generates a waveform selection signal for selecting a waveform element corresponding to the dot size from the reference drive waveform. 20 based on a drive waveform comprising a nozzle selection unit 22 that generates a nozzle selection signal for selecting a nozzle from which droplets are ejected based on ejection data, and a waveform element selected by the waveform selection unit 20. And a head drive unit 24 that generates a drive signal and supplies the drive signal to the piezoelectric actuator 16 corresponding to the nozzle selected by the nozzle selection unit 22.

  The ink jet ejection apparatus 10 shown in the present embodiment is configured to be able to eject three types of dot sizes, large droplets, medium droplets, and small droplets, onto a droplet ejection object. That is, when a large dot is formed on the droplet ejection target, a large drop driving waveform is output, and when a medium size dot is formed, a medium droplet driving waveform is output. In the case of forming a dot, a drive waveform for a droplet is output.

  Further, in the inkjet discharge device 10 shown in this example, a common drive signal is supplied to the piezoelectric actuator 16 provided in each of the plurality of nozzles, and the nozzles that are discharged by the nozzle selection signal sent from the nozzle selection unit 22 are provided. A method in which a drive signal is applied only to the piezoelectric actuator 16 corresponding to the nozzle selected and selected by the nozzle selection signal is applied.

  In addition, the inkjet head 12 and the drive device 14 may be connected separately using a wiring member such as a flexible substrate, or the inkjet head 12 and the drive device 14 may be integrated.

[Configuration of inkjet head]
Next, a structural example of the inkjet head 12 shown in FIG. 1 will be described.

  FIG. 2 is a cross-sectional view showing an example of the three-dimensional structure of the inkjet head 12, and illustrates one channel of droplet discharge elements serving as recording element units.

  The ink jet head 12 shown in FIG. 1 operates a piezoelectric element 27 provided on the ceiling surface of the pressure chamber 26 to pressurize the liquid in the pressure chamber 26 and eject droplets from a nozzle 28 communicating with the pressure chamber 26. It is configured to let you. When droplets are ejected from the nozzle 28, the liquid is supplied from a tank (not shown) serving as a liquid supply source to the pressure chamber 26 via the common flow path 32 via a supply port 30 communicating with the pressure chamber 26. Filled.

  2 includes a nozzle plate 36 in which nozzles 28 are formed on a nozzle surface 34, a flow path plate 38 in which flow paths such as a pressure chamber 26, a supply port 30, and a common flow path 32 are formed. It has a laminated structure. The nozzle plate 36 forms a nozzle surface 34 of the inkjet head 12, and a plurality of nozzles 28 communicating with the pressure chambers 26 are arranged in a predetermined arrangement pattern.

  The flow path plate 38 constitutes a side wall portion of the pressure chamber 26 and a flow in which a supply port 30 is formed as a constricted portion (most narrowed portion) of an individual supply path that guides liquid from the common flow path 32 to the pressure chamber 26. It is a path forming member. For convenience of explanation, the flow path plate 38 has a structure in which one or a plurality of substrates are stacked, although it is illustrated schematically in FIG. The nozzle plate 36 and the flow path plate 38 can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  The diaphragm 40 constituting a part of the pressure chamber 26 (the ceiling surface in FIG. 2) is provided with an upper electrode (individual electrode) 42 and a lower electrode 44, and a piezoelectric element is interposed between the upper electrode 42 and the lower electrode 44. A piezoelectric element (piezo element) 27 having a structure in which a body 46 is sandwiched is joined. When the diaphragm 40 is made of a metal thin film or a metal oxide film, it functions as a common electrode corresponding to the lower electrode 44 of the piezoelectric element 27. In the aspect in which the diaphragm is formed of a non-conductive material such as resin, a lower electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member.

  By applying a driving voltage to the upper electrode 42, the piezoelectric element 27 is deformed and the diaphragm 40 is deformed to change the volume of the pressure chamber 26, and a droplet is ejected from the nozzle 28 due to the pressure change accompanying this. The piezoelectric actuator 16 shown in FIG. 1 includes the piezoelectric element 27 and the diaphragm 40 shown in FIG. 2, and serves as a pressure generation source that generates a liquid discharge pressure in accordance with a drive signal. Note that the piezoelectric actuator 16 may have a mode in which the diaphragm 40 illustrated in FIG. 2 is omitted (for example, a bimorph structure in which two piezoelectric elements are stacked).

[Description of Drive Signal: First Embodiment]
Next, the drive signal according to the first embodiment of the present invention will be described. FIG. 3A is a diagram schematically showing one ejection cycle of the reference drive waveform 100 generated by the waveform generator 18, where the horizontal axis represents time and the vertical axis represents voltage. The rising part of the drive waveform shown in this example operates the piezoelectric element so as to draw the meniscus into the nozzle (pulling operation), and the falling part operates the piezoelectric element so as to push the meniscus out of the nozzle (pushing). Operation).

  The reference drive waveform 100 shown in the figure has the same number of ejection pulses (ejection waveform elements) 102 as the maximum number of ejections per dot (3 times in this example), and the first ejection pulse 102-1, The second ejection pulse 102-2 and the third ejection pulse 102-3 are provided in this order at predetermined time intervals.

  Here, the “ejection pulse” is a waveform for ejecting a predetermined amount of droplets from the nozzle 28 by operating the piezoelectric element 27 (see FIG. 2).

Each ejection pulse 102 has a trapezoidal shape, and the pulse width (the time from the center of the rising portion of the ejection pulse 102 to the center of the falling portion) is a Helmholtz period determined from the structure of the inkjet head 12 shown in FIG. it is 1/2 of T _C. In the present embodiment, the Helmholtz period _{T C} is 10 [mu] s.

  Further, the amplitude (voltage) of each ejection pulse 102 is set so as to become smaller in time with respect to the reference drive waveform 100 (the amplitude becomes smaller than the amplitude of the previous ejection pulse 102 in terms of time). Here, the amplitude of the first ejection pulse 102-1 is 50V, the amplitude of the second ejection pulse 102-2 is 48V, and the amplitude of the third ejection pulse 103-3 is 42V.

In addition, the time interval from the beginning of the first ejection pulse 102-1 to the beginning of the second ejection pulse 102-2 and the beginning of the second ejection pulse 102-2 to the beginning of the third ejection pulse 102-3. time interval between (the output period of each ejection pulse 102) is an integral multiple of the Helmholtz period T _C (in FIG. 3 1x).

  FIG. 3B shows a waveform selection signal 110 output from the waveform selection unit 20 when a small applied drive waveform is output. The horizontal axis represents time, and the vertical axis represents voltage. The waveform selection signal 110 is a negative logic pulse signal in which the H level 110H means “not selected” and the L level 110L means “selected”.

  When the logical sum of the waveform selection signal 110 shown in FIG. 3B and the reference drive waveform 100 shown in FIG. 3A is taken, the third ejection pulse 102-3 is selected, and the first ejection pulse 102 is selected. -1 and the second ejection pulse 102-2 are removed.

  That is, the droplet driving waveform 120 shown in FIG. 3C is composed of ejection pulses 102-3 of the ejection pulses 102 of the reference driving waveform 100. Small droplets are formed on the droplet ejection target by the droplets ejected by the small droplet driving waveform 120.

  4A shows a reference drive waveform 100 that is the same as the reference drive waveform shown in FIG. 3A, and FIG. 4B shows a waveform selection in the case of outputting a medium drop drive waveform. Signal 112 is shown. The waveform selection signal 112 is a negative logic pulse signal having an H level 112H and an L level 112L, similarly to the waveform selection signal 110 illustrated in FIG. When the logical sum of the waveform selection signal 112 shown in FIG. 4B and the reference drive waveform 100 shown in FIG. 4A is taken, the second ejection pulse 102-2 and the third ejection pulse 102-3 are obtained. Selected, the first ejection pulse 102-1 is removed.

  That is, the drive waveform 122 for medium droplets shown in FIG. 4C is composed of the second ejection pulse 102-2 and the third ejection pulse 102-3 among the ejection pulses 102 of the reference drive waveform 100. The

  When the drive waveform 122 for medium droplets is applied to the piezoelectric actuator 16, two droplets are ejected by the second ejection pulse 102-2 and the third ejection pulse 102-3.

As described above, the time interval from the beginning of the second ejection pulse 102-2 to start end of the third ejection pulse 102-3, has a Helmholtz period T _C. That is, the third ejection pulse 102-3 is applied in the same phase with respect to the meniscus vibration after ejection by the second ejection pulse 102-2.

  Therefore, the droplet ejected by the third ejection pulse 102-3 has a higher speed than the droplet ejected by the second ejection pulse 102-2 because the meniscus vibration is amplified. As a result, the two droplets are united in the air during flight to form one droplet, and one medium-sized dot is formed on the droplet ejection object.

  5A shows a reference drive waveform 100 that is the same as the reference drive waveform shown in FIGS. 3A and 4A, and FIG. 5B shows a drive waveform for a large droplet. A waveform selection signal 114 for output is shown. The waveform selection signal 114 is a negative logic pulse signal having an H level 114H and an L level 114L. When the logical sum of the waveform selection signal 114 shown in FIG. 5B and the reference drive waveform 100 shown in FIG. 5A is taken, the first ejection pulse 102-1, the second ejection pulse 102-2, The third ejection pulse 102-3 is selected.

  That is, the large droplet driving waveform 124 shown in FIG. 5C includes the first ejection pulse 102-1, the second ejection pulse 102-2, and the second ejection pulse 102-2 of the ejection pulses 102 of the reference driving waveform 100. 3 ejection pulses 102-3.

  When this large droplet driving waveform 124 is applied to the piezoelectric actuator 16, three droplets are generated by the first ejection pulse 102-1, the second ejection pulse 102-2, and the third ejection pulse 102-3. Is discharged.

As described above, the time interval from the beginning of the first ejection pulse 102-1 starting end of the second ejection pulse 102-2, has a Helmholtz period T _C. That is, the second ejection pulse 102-2 is applied in the same phase with respect to the meniscus vibration after ejection by the first ejection pulse 102-1.

  Accordingly, the droplet ejected by the second ejection pulse 102-2 has a higher speed than the droplet ejected by the first ejection pulse 102-1 because the meniscus vibration is amplified. As a result, the two droplets are united in the air during flight to form one droplet.

  Further, the third ejection pulse 102-3 is applied in the same phase with respect to the vibration of the meniscus after ejection by the second ejection pulse 102-2. Therefore, the meniscus vibration is amplified, and the droplet ejected by the third ejection pulse 102-3 has a higher speed than the droplet ejected by the second ejection pulse 102-2. As a result, the previously merged droplet and the droplet ejected by the third ejection pulse 102-3 are merged in the air to form one droplet, and one large size dot is formed on the droplet ejection object. Form.

  When dots are not formed on the droplet ejection object, that is, when droplet ejection is not performed, all waveforms of the reference drive waveform 100 are not selected by keeping the waveform selection signal at the H level, The drive signal may be maintained at the L level. From the viewpoint of preventing the liquid from drying near the nozzle 28, the meniscus may be shaken to the extent that the liquid is not discharged from the nozzle 28.

  As described above, the waveform selection signal output from the waveform selection unit 20 is temporally later among the plurality of ejection pulses 102 of the reference drive waveform 100 according to the size of the dots to be formed on the droplet ejection target. The discharge pulses 102 are selected in order.

  FIG. 6 shows the relationship between the number of pulses (dot size) and the droplet velocity in this embodiment, and FIG. 7 shows the relationship between the dot size and the droplet amount. These data are obtained under the condition that the number of ejection nozzles is 256 and the ejection frequency is 2 kHz. 6 and 7 simultaneously show the speed and appropriate amount of droplets of each dot size when the same control is performed using the waveform shown in FIG. 8 for comparison.

As shown in FIG. 8A, the reference drive waveform 100 ′ of the comparative example includes a first ejection pulse 102-1 ′, a second ejection pulse 102-2 ′, and a third ejection pulse 102-3 ′. Are trapezoidal with a pulse width T _C / 2 and an amplitude of 50 V, the time interval from the start of the first discharge pulse 102-1 ′ to the start of the second discharge pulse 102-2 ′, and the second discharge time interval from the beginning of the pulse 102-2' to 'start end of the third ejection pulse 102-3 is in the _{T C.} That is, it differs from the reference drive waveform 100 of this embodiment shown in FIG. 3 in that the voltage of each ejection pulse 102 is constant.

  Using this reference drive waveform 100 ′, a waveform selection signal (not shown) is used to drive a small drop drive waveform 120 ′ shown in FIG. 8B, a medium drop drive waveform 122 ′ shown in FIG. A driving waveform 124 ′ for a large droplet shown in FIG. 8D was generated, and the velocity and appropriate amount of each droplet size were obtained.

  As shown in FIG. 6, when the reference driving waveform 100 ′ having a constant voltage is used, the droplet speed increases as the dot size increases. Thus, if there is a difference in the speed of the liquid droplets, the position on the droplet hitting target object varies depending on the dot size, and the image quality deteriorates.

  On the other hand, when the reference drive waveform 100 of the present embodiment is used, the speeds of the small, medium, and large droplets can be made constant at about 6.5 m / sec. As described above, regardless of the dot size to be formed, the position error on the droplet hitting object on which the droplets land can be reduced, and a high quality image can be obtained.

  The permissible range of the droplet velocity is also related to the distance between the inkjet head 12 and the droplet ejection object (droplet flight distance) and the relative movement speed between the inkjet head 12 and the droplet ejection object. The error is preferably within 5%.

  Further, as shown in FIG. 7, when the reference drive waveform 100 ′ is used, the dot size (number of pulses) and the droplet volume are proportional. On the other hand, when the reference drive waveform 100 of the present embodiment is used, the difference between the drop amount of the small droplet and the drop amount of the large drop becomes large. Therefore, it is possible to achieve both the recording of the portion requiring high coverage in the image and the recording of the portion requiring high definition image quality, and high definition image quality can be realized while maintaining high productivity.

  In this way, the amplitude of each ejection pulse in ejection control in which dots of different sizes are formed on the droplet ejection object by removing the pulses according to the dot size from the head of the reference drive waveform consisting of a plurality of ejection pulses. By generating a reference drive waveform so that the amplitude (voltage) is smaller than the amplitude of the previous ejection pulse in time, the speed of the ejected droplet can be made constant regardless of the dot size The difference between the droplet volume of small droplets and the volume of large droplets can be increased.

  In this embodiment, the voltage of each ejection pulse 102 is set to 50 V, 48 V, and 42 V. However, the voltage value may be appropriately determined according to the composition of the ink, and the ejection pulse 102 has an amplitude that is temporally previous. It only needs to be smaller than the amplitude of. Further, the shape of each ejection pulse 102 may be appropriately changed in parameters such as pulse width and slope (rise time, fall time). Furthermore, the shape is not limited to a trapezoidal shape, and a rectangular wave, a triangular wave, or the like can be applied.

In addition, here, the time interval from the beginning of the first ejection pulse 102-1 to the beginning of the second ejection pulse 102-2 and the third ejection pulse 102-3 from the beginning of the second ejection pulse 102-2. of it is set to both T _C the time interval between the start end, this time interval is not limited to T _C, droplets it is sufficient coalescence droplets ejected previously discharged later.

  Furthermore, in the present embodiment, an example in which only one ejection pulse is selected when forming a droplet having the minimum dot size is illustrated, but a plurality of ejection pulses are selected when forming a droplet. Embodiments are also possible. In this example, an example in which three types of dot sizes can be selected is illustrated, but two types of dot sizes may be used, or four or more types may be used.

[Second Embodiment]
Next, drive signals according to the second embodiment of the present invention will be described. FIG. 9A is a diagram schematically illustrating one ejection cycle of the reference drive waveform 200 according to the present embodiment, where the horizontal axis represents time and the vertical axis represents voltage.

  The reference driving waveform 200 shown in the figure is provided at predetermined time intervals in the order of the first ejection pulse 202-1, the second ejection pulse 202-2, and the third ejection pulse 202-3. .

Each ejection pulse 202 has a trapezoidal shape, the pulse width is 1/2 of the Helmholtz period T _C.

  Further, the amplitude of each ejection pulse 202 is set so as to become smaller after the reference drive waveform 200. Here, the amplitude of the first ejection pulse 202-1 is 50V, the amplitude of the second ejection pulse 202-2 is 45V, and the amplitude of the third ejection pulse 202-2 is 40V.

Further, the time interval from the start of the first discharge pulse 202-1 to the start of the second discharge pulse 202-1 and from the start of the second discharge pulse 202-2 to the start of the third discharge pulse 202-3. time interval, the more becomes after the reference driving waveform 200 is set so as to approach the Helmholtz period T _C.

Here, 0.8 times the time interval from the beginning of the first ejection pulse 202-1 starting end of the second ejection pulse 202-2 Helmholtz period _{T C,} from the beginning of the second ejection pulse 202-2 the time interval between the beginning of the third ejection pulse 202-3 is set to 0.9 times the Helmholtz period _{T C.}

  Similarly to the first embodiment, among the plurality of ejection pulses 202 of the reference drive waveform 200, the ejection pulses 202 are removed by the number corresponding to the dot size in order from the previous pulse in time by a waveform selection signal (not shown). Thus, a drive waveform for each dot size is generated. FIGS. 9B to 9D show a small droplet driving waveform 220, a medium droplet driving waveform 222, and a large droplet driving waveform 224 generated from the reference driving waveform 200, respectively. .

  When dots are not formed on the droplet ejection object, not all waveforms of the reference drive waveform 200 are selected by the waveform selection signal, and the drive signal is maintained at the L level.

  FIG. 10 shows the relationship between the number of pulses (dot size) and the droplet velocity in this embodiment, and FIG. 11 shows the relationship between the dot size and the droplet amount. These data are obtained under the conditions that the number of ejection nozzles is 256 and the ejection frequency is 2 kHz, as in the case of FIGS.

  10 and 11 simultaneously show the velocity and appropriate amount of each dot size droplet when the same control is performed using the waveform shown in FIG. 12 for comparison.

As shown in FIG. 12A, the reference drive waveform 200 ′ of the comparative example includes a first ejection pulse 202-1 ′, a second ejection pulse 202-2 ′, and a third ejection pulse 202-3 ′. Are trapezoidal with a pulse width T _C / 2 and an amplitude of 50 V, and the time interval from the beginning of the first ejection pulse 202-1 ′ to the beginning of the second ejection pulse 202-2 ′ is T _C × 0. 8. The time interval from the beginning of the second ejection pulse 202-2 ′ to the beginning of the third ejection pulse 202-2 is T _C × 0.9. That is, it differs from the reference drive waveform 200 of the present embodiment shown in FIG. 9 in that the voltage of each ejection pulse 202 is constant.

  Using the reference drive waveform 200 ', a waveform selection signal (not shown) is used to drive a small drop drive waveform 220' shown in FIG. 12B, a medium drop drive waveform 222 'shown in FIG. A driving waveform 224 ′ for a large droplet shown in FIG. 12D was generated, and the velocity and appropriate amount of each droplet size were obtained.

  As shown in FIG. 10, when the reference driving waveform 200 of the present embodiment is used, the speeds of small droplets, medium droplets, and large droplets can be made constant at about 6.5 m / sec. It was.

  Further, as shown in FIG. 11, when the reference drive waveform 200 of the present embodiment is used, compared to the case where the reference drive waveform 200 ′ of the comparative example is used, the droplet amount of the small droplet and the medium droplet are reduced. The difference between the drop amount and the difference between the medium drop amount and the large drop amount can be increased.

Thus, it is possible by such increasingly closer to T _C as the spacing of the ejection pulse go after the reference driving waveform, who droplets discharged later is discharged efficiently by utilizing the meniscus vibration . Therefore, since the liquid droplets discharged later can be discharged at a low voltage, the volume (liquid amount) of the liquid droplets can be reduced. As a result, it is possible to increase the difference in the drop amount between the large droplet and the small droplet.

In this embodiment, the time interval from the beginning of the first ejection pulse 202-1 to the beginning of the second ejection pulse 202-1 is 0.8 times _TC , and from the beginning of the second ejection pulse 202-2. Although the time interval between the beginning of the third ejection pulse 202-3 was 0.9 times the T _C, the ratio may be changed as appropriate. It is also possible to approach the Helmholtz period T _C while becoming smaller as made after the reference driving waveform 200.

For example, the time interval from the beginning of the first ejection pulse 202-1 starting end of the second ejection pulse 202-2 is 1.2 times the Helmholtz period _{T C,} the starting end of the second ejection pulse 202-2 time interval between the beginning of the third ejection pulse 202-3 may be 1.1 times the Helmholtz period _{T C} from.

Furthermore, the time interval from the beginning of the first ejection pulse 202-1 starting end of the second ejection pulse 202-2 is 1.2 times the Helmholtz period _{T C,} the starting end of the second ejection pulse 202-2 time interval between the beginning of the third ejection pulse 202-3 may also be 0.9 times the Helmholtz period T _C from the second ejection pulse from the beginning of the first ejection pulse 202-1 time interval between the beginning of 202-2 is 0.8 times the Helmholtz period _{T C,} the third Helmholtz period is the time interval until the beginning of the discharge pulse 202-3 from the beginning of the second ejection pulse 202-2 it may be 1.1 times the T _C.

[Third Embodiment]
Next, drive signals according to the third embodiment of the present invention will be described. FIG. 13A is a diagram schematically showing one discharge cycle of the reference drive waveform 240 according to the present embodiment, where the horizontal axis represents time and the vertical axis represents voltage.

  The reference drive waveform 240 shown in the figure is provided at predetermined time intervals in the order of the first ejection pulse 242-1, the second ejection pulse 242-2, and the third ejection pulse 242-2. .

Each ejection pulse 242 has a trapezoidal shape, and its pulse width is set so as to become smaller after the reference drive waveform 200 and is set closer to the Helmholtz period T _C / 2. Here, the pulse width of the first ejection pulse 242-1 is T _C /1.8, the pulse width of the second ejection pulse 242-2 is T _C /1.9, and the third ejection pulse 242-2 is The pulse width is T _C / 2.

  Further, the amplitude of each ejection pulse 242 is set so as to become smaller after the reference drive waveform 240. Here, the amplitude of the first ejection pulse 242-1 is 50V, the amplitude of the second ejection pulse 242-2 is 45V, and the amplitude of the third ejection pulse 242-2 is 40V.

Further, the time interval from the beginning of the first ejection pulse 242-1 to the beginning of the second ejection pulse 242-2, and the beginning of the second ejection pulse 242-2 to the beginning of the third ejection pulse 242-2. time interval of the past, are both the Helmholtz period T _C.

  As in the past, each dot is removed from the plurality of ejection pulses 242 of the reference drive waveform 240 by the waveform selection signal (not shown) in order according to the dot size in order from the previous ejection pulse 242 in terms of time. Generate a drive waveform for size. FIGS. 13B to 13D show a small droplet driving waveform 260, a medium droplet driving waveform 262, and a large droplet driving waveform 264 generated from the reference driving waveform 240, respectively. .

  When dots are not formed on the droplet ejection object, not all waveforms of the reference drive waveform 240 are selected by the waveform selection signal, and the drive signal is maintained at the L level.

  FIG. 14 shows the relationship between the number of pulses (dot size) and the droplet velocity in this embodiment, and FIG. 15 shows the relationship between the dot size and the droplet amount. These data are obtained under the conditions that the number of ejection nozzles is 256 and the ejection frequency is 2 kHz, as in the case of FIGS.

  FIGS. 14 and 15 simultaneously show the velocity and appropriate amount of droplets of each dot size when the same control is performed using the waveform shown in FIG. 16 for comparison.

As shown in FIG. 16A, the reference drive waveform 240 ′ of the comparative example includes a first ejection pulse 242-1 ′, a second ejection pulse 242-2 ′, and a third ejection pulse 242-2 ′. There is a trapezoidal shape of both the amplitude 50 V, which is respectively the pulse width _{T C /1.8,T C /1.9,T C / 2} .

Further, the time interval from the beginning of the first ejection pulse 242-1 'to the beginning of the second ejection pulse 242-2', and the third ejection pulse 242-2 from the beginning of the second ejection pulse 242-2 '. time interval of up to three of the 'beginning is both a T _C. That is, it differs from the reference drive waveform 240 of this embodiment shown in FIG. 13 in that the voltage of each ejection pulse 242 is constant.

  Using this reference drive waveform 240 ', a small waveform drive waveform 260' shown in FIG. 16B, a medium drop drive waveform 262 'shown in FIG. A driving waveform 264 ′ for a large droplet shown in FIG. 16D was generated, and the velocity and appropriate amount of each droplet size were acquired.

  As shown in FIG. 14, when the reference drive waveform 240 of the present embodiment is used, the speeds of the small, medium, and large droplets can be made constant at about 6.5 m / sec. did it.

  Further, as shown in FIG. 15, when the reference drive waveform 240 of the present embodiment is used, compared to the case where the reference drive waveform 240 ′ of the comparative example is used, the droplet amount of the small droplet and the medium droplet are reduced. The difference between the drop amount and the difference between the medium drop amount and the large drop amount can be increased.

In this manner, the size of the liquid droplet ejected earlier can be increased by making the width of the ejection pulse approach _TC / 2 while decreasing the width after the reference drive waveform. Therefore, it is possible to increase the volume of a droplet that uses a previously ejected droplet such as a large droplet. As a result, the difference in the appropriate amount between the large droplet and the small droplet can be increased.

[Application example to inkjet system]
Next, the case where the above-described inkjet discharge apparatus is applied to an on-demand inkjet recording apparatus (on-demand inkjet system) will be described.

(Description of overall configuration of inkjet recording apparatus)
FIG. 17 is a configuration diagram showing the overall configuration of the ink jet recording apparatus according to the present embodiment. The ink jet recording apparatus 310 shown in the figure forms an image on a recording surface of a recording medium 314 based on predetermined image data using an ink containing a color material and an aggregating treatment liquid having a function of aggregating the ink. This is a two-liquid aggregation type recording apparatus.

  The ink jet recording apparatus 310 mainly includes a paper feeding unit 320, a processing liquid application unit 330, a drawing unit 340, a drying processing unit 350, a fixing processing unit 360, and a discharge unit 370. Transfer cylinders 332, 342, 352, and 362 are provided as means for delivering the recording medium 314 conveyed upstream of the processing liquid application unit 330, the drawing unit 340, the drying processing unit 350, and the fixing processing unit 360. As means for conveying the recording medium 314 while holding it in the coating unit 330, the drawing unit 340, the drying processing unit 350, and the fixing processing unit 360, impression cylinders 334, 344, 354, and 364 having drum shapes are provided. .

  The transfer cylinders 332, 342, 352, 362 and the impression cylinders 334, 344, 354, 364 are provided with grippers 380 A, 380 B that hold the front end (or rear end) of the recording medium 314 at predetermined positions on the outer peripheral surface. It has been. The structure for holding the tip of the recording medium 314 in the gripper 380A and the gripper 380B and the structure for transferring the recording medium 314 between the other impression cylinder or the gripper provided in the transfer cylinder are the same, and The gripper 380 </ b> A and the gripper 380 </ b> B are arranged at symmetrical positions that are moved 180 ° in the rotation direction of the pressure drum 334 on the outer peripheral surface of the pressure drum 334.

  When the transfer cylinders 332, 342, 352, 362 and the impression cylinders 334, 344, 354, 364 are rotated in a predetermined direction with the gripper 380 A, 380 B holding the leading end of the recording medium 314, the transfer cylinders 332, 342 are rotated. , 352, 362 and the impression cylinders 334, 344, 354, 364, the recording medium 314 is rotated and conveyed along the outer peripheral surface.

  In FIG. 17, only the grippers 380 </ b> A and 380 </ b> B provided on the pressure drum 334 are denoted by reference numerals, and the other gripper and transfer cylinder grippers are omitted.

  When the recording medium (sheet) 314 stored in the paper feeding unit 320 is fed to the processing liquid application unit 330, the aggregation process is performed on the recording surface of the recording medium 314 held on the outer peripheral surface of the impression cylinder 334. A liquid (hereinafter simply referred to as “treatment liquid”) is applied. The “recording surface of the recording medium 314” is an outer surface in a state where the impression cylinders 334, 344, 354, and 364 are held, and is a surface opposite to a surface held by the impression cylinders 334, 344, 354, and 364. It is.

  Thereafter, the recording medium 314 to which the aggregation processing liquid has been applied is sent to the drawing unit 340, and color ink is applied to the area of the recording surface to which the aggregation processing liquid has been applied, thereby forming a desired image.

  Further, the recording medium 314 on which the image of the color ink is formed is sent to the drying processing unit 350, where the drying processing unit 350 performs the drying process, and after the drying process, the recording medium 314 is sent to the fixing processing unit 360 to perform the fixing process. Applied. By performing the drying process and the fixing process, the image formed on the recording medium 314 is hardened. In this manner, a desired image is formed on the recording surface of the recording medium 314. After the image is fixed on the recording surface of the recording medium 314, the image is conveyed from the discharge unit 370 to the outside of the apparatus.

  Hereinafter, each part (the paper feed unit 320, the processing liquid application unit 330, the drawing unit 340, the drying processing unit 350, the fixing processing unit 360, and the discharge unit 370) of the ink jet recording apparatus 310 will be described in detail.

(Paper Feeder)
The paper feed unit 320 is provided with a paper feed tray 322 and a feed mechanism (not shown), and the recording medium 314 is configured to be fed from the paper feed tray 322 one by one. The recording medium 314 sent out from the paper feed tray 322 is positioned by a guide member (not shown) so that the leading end is positioned at a gripper (not shown) of the transfer drum (paper feed drum) 332 and temporarily stops.

(Processing liquid application part)
The processing liquid coating unit 330 includes a pressure drum (processing liquid drum) 334 that holds the recording medium 314 delivered from the paper feed cylinder 332 on the outer peripheral surface and transports the recording medium 314 in a predetermined transport direction, and a processing liquid drum. And a processing liquid coating device 336 that applies the processing liquid to the recording surface of the recording medium 314 held on the outer peripheral surface of 334. When the processing liquid drum 334 is rotated counterclockwise in FIG. 17, the recording medium 314 is rotated and conveyed in the counterclockwise direction along the outer peripheral surface of the processing liquid drum 334.

  The processing liquid coating device 336 shown in FIG. 17 is provided at a position facing the outer peripheral surface (recording medium holding surface) of the processing liquid drum 334. As a configuration example of the processing liquid coating device 336, a processing liquid container in which the processing liquid is stored, a pumping roller that is partially immersed in the processing liquid in the processing liquid container, and pumps up the processing liquid in the processing liquid container, and a pumping roller An embodiment including an application roller (rubber roller) that moves the pumped processing liquid onto the recording medium 314 is exemplified.

  In addition, there is provided an application roller moving mechanism that moves the application roller in the vertical direction (the normal direction of the outer peripheral surface of the treatment liquid drum 334), and a configuration in which collision between the application roller and the grippers 380A and 380B can be avoided. preferable.

  The treatment liquid applied to the recording medium 314 by the treatment liquid application unit 330 contains a color material flocculant that aggregates the color material (pigment) in the ink applied by the drawing unit 340, and the treatment liquid is applied on the recording medium 314. And the ink come into contact with each other, the separation of the color material and the solvent in the ink is promoted.

  The treatment liquid application device 336 is preferably applied while measuring the amount of the treatment liquid applied to the recording medium 314, and the film thickness of the treatment liquid on the recording medium 314 is determined by the ink droplets ejected from the drawing unit 340. It is preferable to make it sufficiently smaller than the diameter.

(Drawing part)
The drawing unit 340 holds an impression cylinder (drawing drum) 344 that holds and conveys the recording medium 314, a sheet pressing roller 346 for bringing the recording medium 314 into close contact with the drawing drum 344, and an inkjet that applies ink to the recording medium 314. Heads 348M, 348K, 348C, and 348Y are provided. The basic structure of the drawing drum 344 is the same as that of the processing liquid drum 334 described above, and a description thereof is omitted here.

  The sheet pressing roller 346 is a guide member for bringing the recording medium 314 into close contact with the outer peripheral surface of the drawing drum 344, faces the outer peripheral surface of the drawing drum 344, and delivers the recording medium 314 between the transfer drum 342 and the drawing drum 344. The recording medium 314 is disposed on the downstream side in the conveyance direction of the recording medium 314 from the position, and further on the upstream side in the conveyance direction of the recording medium 314 than the inkjet heads 348M, 348K, 348C, and 348Y.

  The recording medium 314 transferred from the transfer drum 342 to the drawing drum 344 is pressed by the sheet pressing roller 346 when being rotated and conveyed with the leading end held by a gripper (reference number omitted), and the outer periphery of the drawing drum 344. Adhere to the surface. After the recording medium 314 is brought into close contact with the outer peripheral surface of the drawing drum 344 in this way, the recording medium 314 is sent to the print area immediately below the ink jet heads 348M, 348K, 348C, 348Y without being lifted from the outer peripheral surface of the drawing drum 344. It is done.

  The inkjet heads 348M, 348K, 348C, and 348Y correspond to inks of four colors, magenta (M), black (K), cyan (C), and yellow (Y), respectively, and the rotation direction of the drawing drum 344 (see FIG. 17 (counterclockwise direction in FIG. 17) are arranged in order from the upstream side, and the ink discharge surfaces (nozzle surfaces, indicated by reference numeral 114A in FIG. 5) of the ink jet heads 348M, 348K, 348C, and 348Y are illustrated in the drawing drum. It is arranged so as to face the recording surface of the recording medium 314 held by 344. The “ink ejection surface (nozzle surface)” is a surface of the ink jet heads 348M, 348K, 348C, and 348Y that faces the recording surface of the recording medium 314. This is a surface on which is formed.

  In addition, the inkjet heads 348M, 348K, 348C, and 348Y shown in FIG. In such a manner, it is arranged to be inclined with respect to the horizontal plane.

  The inkjet heads 348M, 348K, 348C, and 348Y are full-line heads having a length corresponding to the maximum width of the image forming area in the recording medium 314 (the length in the direction orthogonal to the conveyance direction of the recording medium 314). The recording medium 314 is fixedly installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 314.

  On the nozzle surfaces of the inkjet heads 348M, 348K, 348C, and 348Y, nozzles for ejecting ink are formed in a matrix arrangement over the entire width of the image forming area of the recording medium 314.

  When the recording medium 314 is transported to the printing area immediately below the inkjet heads 348M, 348K, 348C, 348Y, the image data is converted into the area where the aggregation processing liquid of the recording medium 314 is applied from the inkjet heads 348M, 348K, 348C, 348Y. Based on this, ink of each color is ejected (droplet ejection).

  When ink droplets of the corresponding color ink are ejected from the inkjet heads 348M, 348K, 348C, 348Y toward the recording surface of the recording medium 314 held on the outer peripheral surface of the drawing drum 344, processing is performed on the recording medium 314. The liquid and the ink come into contact with each other, and an aggregation reaction of the color material (pigment-based color material) dispersed in the ink or the color material (dye-based color material) to be insolubilized appears, and a color material aggregate is formed. As a result, movement of the color material in the image formed on the recording medium 314 (dot misalignment, dot color unevenness) is prevented.

  Further, since the drawing drum 344 of the drawing unit 340 is structurally separated from the processing liquid drum 334 of the processing liquid application unit 330, the processing liquid does not adhere to the inkjet heads 348M, 348K, 348C, and 348Y. In addition, the cause of abnormal ink ejection can be reduced.

  In this example, the configuration of CMYK standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special colors are used as necessary. Ink may be added. For example, it is possible to add an inkjet head that discharges light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

  The ink jet ejection apparatus 10 described with reference to FIGS. 1 to 16 is applied to the drawing unit 340 in the ink jet recording apparatus illustrated in FIG.

(Dry processing part)
A drying processing unit 350 holds a recording medium 314 after image formation and conveys a pressure drum (drying drum) 354, and a solvent drying device 356 that performs a drying process for evaporating water (liquid component) on the recording medium 314. It has. The basic structure of the drying drum 354 is the same as that of the processing liquid drum 334 and the drawing drum 344 described above, and a description thereof is omitted here.

  The solvent drying device 356 is a processing unit that is disposed at a position facing the outer peripheral surface of the drying drum 354 and evaporates moisture present in the recording medium 314. When ink is applied to the recording medium 314 by the drawing unit 340, the liquid component (solvent component) of the ink and the liquid component (solvent component) of the processing liquid separated by the aggregation reaction between the processing liquid and the ink are placed on the recording medium 314. Since it remains, it is necessary to remove such a liquid component.

  The solvent drying device 356 performs a drying process for evaporating the liquid component existing on the recording medium 314 by heating with a heater, blowing with a fan, or a combination thereof, and a process for removing the liquid component on the recording medium 314. Part. The amount of heating and the amount of air supplied to the recording medium 314 are appropriately set according to parameters such as the amount of moisture remaining on the recording medium 314, the type of the recording medium 314, and the conveyance speed (interference processing time) of the recording medium 314. Is done.

  When the drying process is performed by the solvent drying device 356, the drying drum 354 of the drying processing unit 350 is structurally separated from the drawing drum 344 of the drawing unit 340. Therefore, the inkjet heads 348M, 348K, 348C, and 348Y. In this case, it is possible to reduce the cause of abnormal ink ejection due to drying of the head meniscus by heat or air blowing.

  In order to exhibit the cockling correction effect of the recording medium 314, the curvature of the drying drum 354 is preferably 0.002 (1 / mm) or more. In order to prevent the recording medium from being curved (curled) after the drying process, the curvature of the drying drum 354 is preferably set to 0.0033 (1 / mm) or less.

  In addition, a means (for example, a built-in heater) for adjusting the surface temperature of the drying drum 354 may be provided, and the surface temperature may be adjusted to 50 ° C. or higher. By performing heat treatment from the back surface of the recording medium 314, drying is promoted and image destruction during the subsequent fixing process is prevented. In such an embodiment, it is more effective to provide means for bringing the recording medium 314 into close contact with the outer peripheral surface of the drying drum 354. As an example of means for closely attaching the recording medium 314, vacuum adsorption, electrostatic adsorption, and the like can be given.

  The upper limit of the surface temperature of the drying drum 354 is not particularly limited, but from the viewpoint of safety of maintenance work such as cleaning ink adhering to the surface of the drying drum 354 (preventing burns due to high temperatures). It is preferably set to 75 ° C. or lower (more preferably 60 ° C. or lower).

  The recording medium 314 is held on the outer peripheral surface of the drying drum 354 configured as described above so that the recording surface of the recording medium 314 faces outward (that is, in a state where the recording surface of the recording medium 314 is convex). By performing the drying process while rotating and transporting, drying unevenness due to wrinkling and floating of the recording medium 314 is surely prevented.

(Fixing processing part)
The fixing processing unit 360 includes a pressure drum (fixing drum) 364 that holds and conveys the recording medium 314, a heater 366 that heats the recording medium 314 that has been subjected to image formation and from which the liquid has been removed, and the recording And a fixing roller 368 that presses the medium 314 from the recording surface side. The basic structure of the fixing drum 364 is the same as that of the processing liquid drum 334, the drawing drum 344, and the drying drum 354, and a description thereof is omitted here. The heater 366 and the fixing roller 368 are disposed at a position facing the outer peripheral surface of the fixing drum 364, and are sequentially disposed from the upstream side in the rotation direction of the fixing drum 364 (counterclockwise direction in FIG. 17).

  In the fixing processing unit 360, the recording surface of the recording medium 314 is subjected to preliminary heating processing by the heater 366 and fixing processing by the fixing roller 368. The heating temperature of the heater 366 is appropriately set according to the type of recording medium, the type of ink (the type of polymer fine particles contained in the ink), and the like. For example, a mode in which the glass transition temperature and the minimum film forming temperature of the polymer fine particles contained in the ink are considered.

  The fixing roller 368 is a roller member for heating and pressurizing the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the recording medium 314. The Specifically, the fixing roller 368 is disposed so as to be in pressure contact with the fixing drum 364 and constitutes a nip roller with the fixing drum 364. As a result, the recording medium 314 is sandwiched between the fixing roller 368 and the fixing drum 364 and nipped at a predetermined nip pressure, and the fixing process is performed.

  As an example of the configuration of the fixing roller 368, there is an embodiment in which the fixing roller 368 is configured by a heating roller in which a halogen lamp is incorporated in a metal pipe such as aluminum having good thermal conductivity. By heating the recording medium 314 with such a heating roller, when thermal energy equal to or higher than the glass transition temperature of the polymer fine particles contained in the ink is applied, the polymer fine particles are melted to form a transparent film on the surface of the image. Is done.

  When pressure is applied to the recording surface of the recording medium 314 in this state, the polymer fine particles melted into the unevenness of the recording medium 314 are pressed and fixed, and the unevenness of the image surface is leveled, so that preferable glossiness can be obtained. A configuration in which a plurality of fixing rollers 368 are provided in accordance with the thickness of the image layer and the glass transition temperature characteristics of the polymer particles is also preferable.

  The surface hardness of the fixing roller 368 is preferably 71 ° or less. By making the surface of the fixing roller 368 softer, a follow-up effect can be expected with respect to the unevenness of the recording medium 314 caused by cockling, and uneven fixing due to the unevenness of the recording medium 314 can be more effectively prevented. .

  In the ink jet recording apparatus 310 shown in FIG. 17, an inline sensor 382 is provided at a subsequent stage (downstream side in the recording medium conveyance direction) of the processing area of the fixing processing unit 360. The inline sensor 382 is a sensor for reading an image formed on the recording medium 314 (or a check pattern formed in a blank area of the recording medium 314), and a CCD line sensor is preferably used.

  In the ink jet recording apparatus 310 shown in this example, the presence or absence of ejection abnormality of the ink jet heads 348M, 348K, 348C, and 348Y is determined based on the reading result of the inline sensor 382 (details will be described later). Further, the inline sensor 382 may include a measuring unit for measuring a moisture amount, a surface temperature, a glossiness, and the like. In such an embodiment, parameters such as the processing temperature of the drying processing unit 350, the heating temperature of the fixing processing unit 360, and the pressurizing pressure are appropriately adjusted based on the moisture content, surface temperature, and gloss reading result, and the temperature inside the apparatus. The control parameter is adjusted as appropriate in accordance with the change and the temperature change of each part.

(Discharge part)
As shown in FIG. 17, a discharge unit 370 is provided following the fixing processing unit 360. The discharge unit 370 includes an endless conveyance belt 374 wound around the stretching rollers 372A and 372B, and a discharge tray 376 that stores the recording medium 314 after image formation.

  The recording medium 314 after the fixing process sent out from the fixing processing unit 360 is transported by the transport belt 374 and discharged to the discharge tray 376.

(Description of structure of inkjet head)
FIG. 18 is a schematic configuration diagram of an ink jet head applied to the present invention. FIG. 18 is a view of the recording surface of the recording medium as viewed from the ink jet head (a plan perspective view of the head). In addition, since the inkjet heads 348M, 348K, 348C, and 348Y illustrated in FIG. 17 have the same structure, in the following description, when it is not necessary to distinguish the inkjet heads 348M, 348K, 348C, and 348Y, these are described. Collectively, it is described as “inkjet head 348”.

  The ink-jet head 348 shown in the figure forms a multi-head by connecting n sub-heads 348-i (i is an integer from 1 to n) in a line. Each sub head 348-i is supported by head covers 349A and 349B from both sides of the inkjet head 348 in the short direction. It is also possible to configure a multi-head by arranging the sub-heads 348 in a staggered manner.

  As an application example of a multi-head configured by a plurality of sub-heads, a full-line head corresponding to the entire width of a recording medium can be given. The full-line head has a plurality of nozzles (corresponding to the length (width) in the main scanning direction of the recording medium along the direction (main scanning direction) orthogonal to the moving direction (sub-scanning direction) of the recording medium. In FIG. 20, a reference numeral 108 is attached for illustration. An image can be formed over the entire surface of the recording medium by a so-called single-pass image recording method in which the inkjet head 348 having such a structure and the recording medium are scanned only once relatively to perform image recording.

  FIG. 19 is a partially enlarged view of the inkjet head 348. As shown in the figure, the sub head 348 has a substantially parallelogram-shaped planar shape, and an overlap portion is provided between adjacent sub heads. The overlap portion is a connecting portion of the sub-heads, and dots formed adjacent to the sub-heads 348-i in the arrangement direction (left-right direction in FIG. 18, main scanning direction X shown in FIG. 19) belong to different sub-heads. The

  FIG. 20 is a plan view showing the nozzle arrangement of the sub head 348-i. As shown in the figure, each sub head 348-i has a structure in which nozzles 328 are arranged two-dimensionally, and a head including such a sub head 348-i is a so-called matrix head.

  In the sub head 348-i shown in FIG. 20, a large number of nozzles 328 are arranged along a column direction W that forms an angle α with respect to the sub-scanning direction Y and a row direction V that forms an angle β with respect to the main scanning direction X. The substantial nozzle arrangement density in the main scanning direction X is increased. In FIG. 20, nozzle groups (nozzle rows) arranged along the row direction V are denoted by reference numeral 328V, and nozzle groups (nozzle rows) arranged along the column direction W are denoted by reference numeral 328W. ing.

  In this matrix arrangement, when the interval between adjacent nozzles in the sub-scanning direction is Ls, in the main scanning direction, each nozzle 328 is substantially equivalent to a linear arrangement with a constant pitch P = Ls / tan θ. It can be handled.

  The ink jet head 348 having the structure shown in FIGS. 18 to 20 includes the droplet discharge element (recording element) shown in FIG. 2 in the row direction V and the sub-scan, which form an angle β with the main scanning direction X, as shown in FIG. The high-density nozzle head of this example is realized by arranging a large number in a grid pattern with a constant arrangement pattern along the row direction W that forms an angle α with respect to the direction Y.

(Description of control system)
FIG. 21 is a block diagram illustrating a system configuration of the inkjet recording apparatus 310. As shown in FIG. 21, the inkjet recording apparatus 310 includes a communication interface 440 and a system control unit 442, and overall control of each unit of the apparatus is performed by the system control unit 442.

  The communication interface 440 is an interface unit (image input unit) that receives image data sent from the host computer 454. As the communication interface 440, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  The system control unit 442 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 310 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. To do. Further, it generates control signals for controlling the conveyance control unit 444, the image processing unit 446, the head driving unit 448, and the like, and functions as a memory controller for the image memory 450 and the ROM 452.

  The image processing unit 446 is a processing block that performs predetermined processing on the image data, and includes a processor having an image processing function. The image data sent from the host computer 454 is taken into the inkjet recording apparatus 310 via the communication interface 440 and temporarily stored in the image memory 450. The image memory 450 is a storage unit that stores an image input via the communication interface 440, and data is read and written through the system control unit 442. The image memory 450 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The image memory 450 stores programs executed by the CPU of the system control unit 442 and various data necessary for control (including data for ejecting test charts, abnormal nozzle information, and the like). The image memory 450 may be a non-rewritable storage means or a rewritable storage means such as an EEPROM.

  A temporary storage unit (not shown) is used as a temporary storage area for image data and various data, and is also used as a program development area and a calculation work area for the CPU.

  The image processing unit 446 performs various processing and correction processes for generating a droplet ejection control signal from image data (multi-valued input image data) in the image memory, under the control of the system control unit 442. It functions as a signal processing means. A droplet ejection control signal (ink ejection data) generated by the image processing unit 446 is supplied to the head driving unit 448.

  That is, the image processing unit 446 includes functional blocks such as a density data generation unit, a correction processing unit, and an ink ejection data generation unit. Each of these functional blocks can be realized by ASIC, software, or an appropriate combination.

  The density data generation unit is a signal processing unit that generates initial density data for each ink color from input image data, and includes density conversion processing (including UCR processing and color conversion) and, if necessary, pixel number conversion processing. I do. The correction processing unit is a processing unit that performs density correction using the density correction coefficient, and performs unevenness correction processing.

  The ink ejection data generation unit is a signal processing unit including a halftoning processing unit that converts the corrected image data (density data) generated by the correction processing unit into binary or multivalued dot data. Multi-value processing is performed. Various known means such as an error diffusion method, a dither method, a threshold matrix method, and a density pattern method can be applied as the halftone processing means. In the halftone process, generally, gradation image data having an M value (M ≧ 3) is converted into binary or multi-value gradation image data smaller than M. In the simplest example, the image data is converted into binary (dot on / off) dot image data. However, in the halftone process, the dot size type (for example, large size, medium size, small size) is used as in the above embodiment. Multi-level quantization corresponding to three types such as size can be performed.

  The image processing unit 446 is provided with an image buffer memory (not shown), and image data, parameters, and other data are temporarily stored in the image buffer memory when the image processing unit 446 processes image data. Note that the image buffer memory may be attached to the image processing unit 446 or may be used as the image memory. Further, the image processing unit 446 may be integrated with the system control unit 442 and configured with one processor.

  The ink discharge data generated by the image processing unit 446 (ink discharge data generation unit) is given to the head drive unit 448, and the ink discharge operation of the inkjet head 348 is controlled.

  The head drive unit 448 functions as means for controlling the ejection drive of the inkjet head 348 and generates a drive signal waveform for driving the actuator (piezoelectric actuator 16 shown in FIG. 5) corresponding to each nozzle 328 of the inkjet head 348. A drive waveform generator for generating is included. The signal output from the drive waveform generator may be digital waveform data or an analog voltage signal. Such a drive waveform generator corresponds to the waveform generator 18 of FIG.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 440 and stored in an image memory. At this stage, for example, RGB multi-valued image data is stored in the image memory.

  In the ink jet recording apparatus 310, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory is sent to the image processing unit 446 via the system control unit 442, and is processed by the density data generation unit, the correction processing unit, and the ink ejection data generation unit. Converted to dot data for each ink color.

  That is, the image processing unit 446 performs processing for converting the input RGB image data into dot data of four colors of M, K, C, and Y. The dot data thus generated by the image processing unit 446 is stored in the image buffer memory. This dot data for each color is converted into MKCY droplet ejection data for ejecting ink from the nozzles of the inkjet head 348 and printed, ink ejection data (dot timing for each nozzle and the dot size for each drive timing ( Discharge amount)) is confirmed.

  The processing in the image processing unit 446 corresponds to the processing in the waveform selection unit 20 and the processing in the nozzle selection unit 22 in FIG. That is, the waveform selection unit 20 and the nozzle selection unit 22 in FIG. 1 in FIG. 1 correspond to one function of the image processing unit 446 in FIG.

  The head drive unit 448 outputs a drive signal for driving the actuator 132 corresponding to each nozzle 328 of the inkjet head 348 in accordance with the print content based on the ink ejection data and the drive signal (drive waveform). The head drive unit 448 may include a feedback control system for keeping the head drive conditions constant. The head driving unit 448 illustrated in FIG. 21 corresponds to the head driving unit 24 illustrated in FIG.

  In this way, the drive signal output from the head drive unit 448 is applied to the inkjet head 348, whereby ink is ejected from the corresponding nozzle 328. An image is formed on the recording medium 314 by controlling ink ejection from the inkjet head 348 in synchronization with the conveyance speed of the recording medium 314.

  As described above, based on the ink ejection data and the drive signal waveform generated through the required signal processing in the image processing unit 446, the ejection amount and ejection timing of the ink droplets from each nozzle via the head driving unit 448 are determined. Control is performed. Thereby, a desired dot size and dot arrangement are realized.

  The in-line detection unit 470 illustrated in FIG. 21 is a functional block that provides information regarding abnormal nozzles to the system control unit 442 through reading of nozzle detection patterns, processing of read data, and processing of abnormal nozzle determination. The inline detection unit 470 includes the inline sensor 382 illustrated in FIG.

  The system control unit 442 performs various corrections on the ink jet head 348 based on information on the abnormal nozzle obtained from the inline detection unit 470 and other information, and also performs cleaning operations such as preliminary ejection, suction, and wiping as necessary ( Nozzle recovery operation) is performed.

  Although not shown, a maintenance processing unit including members necessary for head maintenance such as an ink receiver, a suction cap, a suction pump, and a wiper blade is provided as means for executing the cleaning operation.

  In addition, an operation unit as a user interface is provided, and the operation unit includes an input device 468 and a display unit (display) 466 for an operator (user) to perform various inputs. The input device 468 can employ various forms such as a keyboard, a mouse, a touch panel, and buttons. By operating the input device 468, the operator can input printing conditions, select an image quality mode, input / edit attached information, search for information, etc. This can be confirmed through display on the display unit 466. The display unit 466 also functions as means for displaying a warning such as an error message.

  The ink jet recording apparatus 310 of the present embodiment has a plurality of image quality modes, and the image quality mode is set by a user's selection operation or by automatic selection by a program. The criterion for determining an abnormal nozzle is changed according to the output image quality level required in the set image quality mode. The higher the required quality, the more severe the criteria.

  Information relating to printing conditions in each image quality mode and abnormal nozzle determination criteria is stored in the image memory 450.

  The ink jet recording apparatus 310 described in this example performs image recording using small size dots in the high image quality mode, and performs image recording using medium size dots and large size dots in the normal mode and the high speed recording mode. It is configured to be executed. In other words, because high-quality image formation has small-sized dots arranged in high density, dot shape deformation due to satellite generation becomes a problem, and dot deformation due to satellite generation is suppressed by suppressing satellite generation after ejection. Is avoided, and high-definition dots are formed.

  On the other hand, in normal mode and high-speed mode, short cycle continuous discharge using medium-sized dots and large side dots is performed, so meniscus vibration after discharge becomes a problem. In such a high-speed (normal) mode, the meniscus vibration after ejection is quickly converged by the action of the meniscus stabilization waveform, and problems such as nozzle omission in continuous ejection in a short cycle are prevented.

  As a modification of the present example, the reference drive waveform is modified so that the satellite suppression waveform is applied after the ejection pulse corresponding to the medium-size dot, and in the ejection when the medium-size dot is formed, An aspect configured to suppress the occurrence is also possible.

[Example of application to other devices]
In the above embodiment, application to an inkjet recording apparatus for graphic printing has been described as an example, but the scope of application of the present invention is not limited to this example. For example, a wiring drawing device that draws a wiring pattern of an electronic circuit, a manufacturing device for various devices, a resist printing device that uses a resin liquid as a functional liquid for ejection, a color filter manufacturing device, and a material deposition material. The present invention can be widely applied to inkjet systems that obtain various shapes and patterns using a liquid functional material, such as a fine structure forming apparatus for forming a structure.

  DESCRIPTION OF SYMBOLS 10 ... Inkjet discharge device 12, 348, 348M, 348K, 348C, 348Y ... Inkjet head, 14 ... Drive device, 16 ... Piezoelectric actuator, 18 ... Waveform generator, 20 ... Waveform selector, 24, 448 ... Head drive , 27 ... Piezoelectric element, 28 ... Nozzle, 100, 200, 240 ... Reference drive waveform, 102, 202, 242 ... Ejection pulse, 310 ... Inkjet recording device, 442 ... System controller

Claims (12)

In an inkjet head drive device comprising: a nozzle that discharges liquid droplets; a liquid chamber that communicates with the nozzle; and an actuator that pressurizes the liquid in the liquid chamber when a predetermined drive signal is supplied.
A reference driving waveform including a plurality of ejection waveform elements for ejecting droplets from the nozzle, wherein a plurality of droplets ejected by the plurality of ejection waveform elements in the reference driving waveform are combined during flight. Waveform generating means for generating a reference driving waveform for forming dots on the object;
Data acquisition means for acquiring size data of dots to be formed on the object;
Waveform selection means for selecting the discharge waveform elements sequentially from the plurality of discharge waveform elements in the reference drive waveform according to the size data;
Driving means for discharging droplets from the nozzle by the selected discharge waveform element;
With
The inkjet head drive apparatus, wherein the waveform generation unit generates a reference drive waveform having a smaller amplitude as the ejection waveform element is later in time. The waveform generation means generates the reference drive waveform having at least three ejection waveform elements,
The ink-jet head drive device according to claim 1, wherein the data acquisition unit acquires at least three types of size data. The waveform generation means generates a reference drive waveform having three ejection waveform elements,
The waveform selection unit selects all ejection waveform elements in the reference drive waveform when the data acquisition unit acquires large size data, and the data selection unit acquires the medium size data when the data acquisition unit acquires medium size data. When the last two waveform elements are selected from the discharge waveform elements in the reference drive waveform, and the data acquisition means acquires small size data, the last waveform among the discharge waveform elements in the reference drive waveform 3. The ink jet head driving apparatus according to claim 2, wherein an element is selected.   The inkjet head driving device according to claim 2, wherein the intervals between the start ends of the plurality of ejection waveform elements are substantially the same. Intervals beginning of the plurality of ejection wave elements, the driving apparatus of an ink jet head according to claim 2 or 3, characterized in that a Helmholtz period T _C obtained from the structure of the ink jet head. The plurality of starting interval of ejection wave elements, the driving apparatus of an ink jet head according to claim 2 or 3, characterized in that approach the Helmholtz period T _C obtained from the structure of the ink jet head as will later time.   The inkjet head driving device according to claim 2, wherein the plurality of ejection waveform elements have substantially the same width. The inkjet head driving apparatus according to claim 7, wherein a width of the plurality of ejection waveform elements is T _C / 2. The inkjet head driving device according to claim 2, wherein widths of the plurality of ejection waveform elements are smaller as they are later in time and approach T _C / 2.   The waveform generation means generates a reference drive waveform so that a velocity of a droplet discharged from the nozzle is substantially constant regardless of the number of discharge waveform elements selected by the waveform selection means. Item 10. The ink jet head drive device according to any one of Items 1 to 9. A drive device for an inkjet head according to any one of claims 1 to 10,
An inkjet head comprising: a nozzle that discharges droplets; a liquid chamber that communicates with the nozzle; and an actuator that pressurizes the liquid in the liquid chamber when a predetermined drive signal is supplied;
Moving means for relatively moving the object and the inkjet head;
An ink jet recording apparatus comprising: A method for driving an inkjet head, comprising: a nozzle that discharges droplets; a liquid chamber that communicates with the nozzle; and an actuator that pressurizes the liquid in the liquid chamber when a predetermined drive signal is supplied.
A waveform generating step for generating a reference drive waveform including a plurality of discharge waveform elements for discharging droplets from the nozzle, the amplitude of which is smaller as the discharge waveform element is later in time, and
A data acquisition step of acquiring size data of dots to be formed on the object;
A waveform selection step of selecting a discharge waveform element in order from the plurality of discharge waveform elements in the reference drive waveform according to the size data; and
A driving step for discharging droplets from the nozzle by the selected discharge waveform element, and a driving step for uniting a plurality of droplets discharged by a plurality of discharge waveform elements during flight;
A method for driving an ink-jet head, comprising:

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