JP4860296B2 - Liquid ejection device and pressure detection method - Google Patents

Description

  The present invention relates to a liquid ejection apparatus and a pressure detection method, and more particularly to ejection detection in a liquid ejection apparatus that forms an image or the like on a medium by ejecting liquid from a nozzle.

  In an inkjet system in which ink droplets are ejected by pressurizing ink in a pressure chamber, a method has been proposed in which the pressure in the pressure chamber is detected by a pressure sensor to grasp the ejection state of the ink droplets. For example, the peak value or frequency (period) of the pressure in the pressure chamber is obtained based on the detection signal obtained from the pressure sensor, and the change in physical properties of the ink or the presence or absence of bubbles in the pressure chamber can be determined from these values. it can.

  The invention described in Patent Document 1 applies a measurement pulse to a piezo element prior to a printing operation, detects a pressure fluctuation in the pressure chamber by the piezo element and a detection circuit, and generates a drive waveform based on the pressure fluctuation. When calculating and printing, a drive voltage waveform is applied to the piezo element based on the calculated drive waveform.

  The invention described in Patent Document 2 is configured to detect the displacement state of the vibrator that changes the volume in the ink chamber, and to detect the displacement state of the vibrator with respect to the electrical signal applied to the vibrator.

The invention described in Patent Document 3 includes a multi-pulse driving method in which a piezo element is deformed a plurality of times in a short time to gradually eject ink in an ink chamber to form one ink droplet with the ink. Discloses a technique for detecting a pressure fluctuation in the ink chamber and controlling the driving means so as to generate a subsequent pulse to a predetermined pulse based on the detection result.
JP 7-132592 A Japanese Patent Laid-Open No. 55-118878 JP-A-6-155733

  However, when the inkjet head is formed at a high density, a wiring for transmitting a detection signal obtained from the pressure sensor and a wiring for transmitting a detection signal obtained from a drive signal or another sensor are arranged close to each other, and there is a wiring between the wirings. Capacity will exist. Due to the presence of such wiring capacitance, other signal components (noise components) are superimposed on the detection signal, making it difficult to perform accurate pressure detection. In particular, in a system in which driving and detection are performed almost simultaneously, a component of the driving signal is easily superimposed on the detection signal, and there is a concern that the accuracy of pressure detection is reduced.

  In the inventions described in Patent Documents 1 to 3, the wiring capacity existing between the wiring for transmitting the detection signal and the other wiring is not considered, and the existence of such wiring capacity is described. Not.

  The present invention has been made in view of such circumstances, and provides a liquid ejection apparatus and a pressure detection method in which preferable pressure detection is performed in consideration of a wiring capacity existing between wirings of a detection signal and other signals. The purpose is to do.

To achieve the above Symbol purpose, a liquid ejection apparatus according to the present invention comprises a pressure chamber for accommodating a liquid to be ejected from the nozzle, and a pressure generating element that gives an ejection force to the liquid contained in the pressure chamber, said pressure a pressure detecting element Ru generates a detection signal corresponding to the pressure chamber, and a liquid ejection head and a drive signal generator for generating a drive signal supplied to the pressure generating element, the pressure from the driving signal generating unit a drive signal line for transmitting a driving signal to the generating element, a pressure detection unit for detecting the pressure of the pressure chamber on the basis of the detection signal obtained from the previous SL pressure sensing element, said pressure detection portion from said pressure detection element transmitting a detection signal to a position where noise is superimposed due to the change of the drive signal to the detection signal the transmission, and a detection signal line at least partially disposed, the driving signal lines and before The detection signal the detection signal of the pressure detector and the electrostatic capacitance value C of the wiring capacitance between the detection signal lines is represented by the product C × R of the resistance value R of the input resistor provided in an input unit that is input The attenuation time of the noise component is set such that the attenuation time of the noise component superimposed on the pressure chamber is longer than the resonance period of the pressure chamber.

  According to the present invention, the resistance value R of the input resistance of the pressure detection unit is set so that the decay time of the noise component superimposed on the detection signal is longer than the resonance period of the pressure chamber. A preferable pressure detection is performed without being affected by noise components such as noise superimposed on the detection signal from the drive signal via the wiring capacitance between the detection signal wiring and the detection signal wiring.

  As the detection element, a fluororesin piezoelectric element such as PVDF (polyvinylidene fluoride) is preferably used. A ceramic piezoelectric element such as PZT may be used.

  As the pressure generating element, a ceramic piezoelectric element (piezoelectric actuator) such as PZT (lead zirconate titanate) is preferably used. The pressure generating element may also serve as the detecting element.

  In the aspect including a plurality of piezoelectric elements as the detection element and the pressure generating element, an aspect in which a piezoelectric body is integrally formed with respect to the plurality of pressure chambers and electrodes are provided in portions corresponding to the pressure chambers may be applied. A mode in which a piezoelectric body is formed for each pressure chamber and an electrode is provided on each piezoelectric body may be applied.

  The pressure detection unit may include signal processing means for performing predetermined signal processing such as amplification and noise removal on the detection signal obtained from the detection element.

  The liquid discharge head has a line-type head having an ejection hole array having a length corresponding to the entire width of the recording medium (image forming width of the recording medium) and an ejection hole array having a length less than the entire width of the recording medium. There is a serial type head that scans a short head in the width direction of the recording medium.

  Line-type liquid ejection heads can be combined with short heads with short ejection hole arrays that are less than the length corresponding to the full width of the recording medium in a linear or zigzag pattern and connected to support the full width of the recording medium It may be the length to be.

  The invention according to claim 2 relates to an aspect of the liquid ejection apparatus according to claim 1, wherein the pressure detection unit measures at least one of a maximum value and a minimum value of the detection signal. And a period calculation unit that calculates the period of the detection signal from the time interval between the maximum value and the minimum value of the detection signal.

  According to the second aspect of the invention, the period (period fluctuation) of the pressure waveform generated in the pressure chamber is accurately determined from the period of the detection signal. Note that the frequency of the detection signal may be obtained.

  In general, it is possible to grasp the state of the pressure chamber such as the generation of bubbles in the pressure chamber and the change in the viscosity of the liquid in the pressure chamber from the period of the pressure waveform. For example, when the pressure chamber is pressurized at a predetermined frequency (resonance frequency of the pressure chamber), a pressure having the predetermined frequency (cycle) is generated in the pressure chamber. If bubbles are generated in the pressure chamber or if the physical properties (viscosity, temperature) of the liquid in the pressure chamber change, the cycle of this pressure waveform will fluctuate. Judgment can be made.

  For example, there is a mode in which a time interval between the first minimum value appearing first in the pressure waveform and the second minimum value appearing next is obtained, and this time interval is set as the period of the pressure waveform. Of course, a mode in which the frequency of the pressure waveform that is the reciprocal of the period is obtained is also possible.

  A third aspect of the present invention relates to the liquid ejection device according to the first aspect, wherein a threshold value setting unit that sets a voltage threshold value of the detection signal, and the detection signal is the voltage threshold value. And a cycle calculating unit that calculates the cycle of the detection signal from the timing of crossing with.

  The voltage threshold value of the detection signal is set between an extreme value that appears first (for example, a minimum value) and an extreme value that appears next (a maximum value when the first extreme value appears as a minimum value). That is, the voltage threshold value is determined so that there are three or more timings of crossing the detection signal.

  A fourth aspect of the invention relates to an aspect of the liquid ejecting apparatus according to the third aspect of the invention, further comprising a noise component detection unit that detects a noise component superimposed on the detection signal, and the threshold value setting unit includes: The voltage threshold is set based on a noise component detected by the noise component detector.

  According to the fourth aspect of the present invention, it is possible to eliminate the influence of the noise component superimposed on the detection signal, and to perform preferable pressure detection.

  There is a mode in which the detection signal when the pressure generating element in the pressure chamber in the liquid-unfilled state is driven is a noise component superimposed on the detection signal at the time of pressure detection. A mode provided with storage means for storing the detected noise component is preferable.

  The invention according to claim 5 relates to an aspect of the liquid ejecting apparatus according to claim 4, wherein the threshold value setting unit is configured to use the voltage threshold value based on a noise component detected by the noise component detection unit. The shift amount is calculated, and the shift amount is shifted from the initial value of the preset voltage threshold by the shift amount.

  Since the shift amount of the voltage threshold is determined based on the noise component detected by the noise component detector, further improvement in detection accuracy is expected.

A method invention is provided to achieve the above object. That is, the pressure detection method according to claim 6 is in accordance with the pressure chamber for storing the liquid to be discharged from the nozzle, the pressure generating element for applying a discharge force to the liquid stored in the pressure chamber, and the pressure in the pressure chamber. A pressure detection method for a liquid discharge apparatus having a liquid discharge head including a pressure detection element that sends a detection signal, from a drive signal generation unit that generates a drive signal applied to the pressure generation element to the pressure generation element drive signal line for transmitting the driving signal, and the transmit detect signal obtained from the pressure sensing element from the pressure sensing element to the pressure detection unit for detecting the pressure of the pressure chamber on the basis of the detection signal, the said transmission a position noise due to the change of the drive signal to the detection signal is superimposed that, the capacitance value C of the wiring capacitance between the detection signal lines at least partially disposed, prior to the pre Ki圧 force detector It is larger than the resonance period of the decay time of the noise component superimposed on the detection signal the detection signal is expressed by the product C × R of the resistance value R of the input resistor provided in an input unit to be inputted the pressure chamber Thus, the decay time of the noise component is set as described above.

  A seventh aspect of the invention relates to an aspect of the pressure detection method of the sixth aspect, wherein the noise component is detected, the noise component is stored, and the period of the detection signal is obtained from the noise component. Obtaining a shift value of a threshold value to be used, obtaining a period of the detection signal based on the threshold value shifted by the shift value, and determining a pressure abnormality in the pressure chamber based on the period of the detection signal. To do.

  According to the seventh aspect of the present invention, it is possible to detect the presence or absence of bubbles generated in the pressure chamber and the size of the bubbles. It is preferable to perform a recovery process on the nozzle communicating with the pressure chamber based on the pressure detection result.

  According to the present invention, since the resistance value R of the input resistance of the pressure detection unit is set so that the decay time of the detection signal is longer than the resonance period of the pressure chamber, the wiring between the drive signal wiring and the detection signal wiring Even if noise is superimposed on the detection signal from the drive signal via the capacitor, preferable pressure detection is performed without being affected by the noise. In addition, since the state of the pressure chamber is determined based on the period of the pressure wave generated in the pressure chamber, it is possible to accurately detect the generation of bubbles in the pressure chamber.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus (liquid ejection apparatus) according to an embodiment of the present invention. As shown in FIG. 1, the inkjet recording apparatus 10 includes a plurality of inkjet heads (liquids) provided corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. (Discharge head, hereinafter referred to as a head)) A printing unit 12 having 12K, 12C, 12M, and 12Y, an ink storage / loading unit 14 that stores ink to be supplied to each of the heads 12K, 12C, 12M, and 12Y, and recording A paper feeding unit 18 that supplies recording paper 16 serving as a medium, a decurling unit 20 that removes curling of the recording paper 16, and a nozzle surface (ink ejection surface) of the printing unit 12 are arranged to face the recording paper 16. A suction belt conveyance unit 22 that conveys the recording paper 16 while maintaining the flatness of the recording medium, and a paper discharge unit 26 that discharges the recorded recording paper (printed material) to the outside.

  The ink storage / loading unit 14 has an ink supply tank that stores ink of a color corresponding to each of the heads 12K, 12C, 12M, and 12Y, and each tank has the heads 12K, 12C, 12M, and the like via a required pipe line. 12Y is communicated. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When a plurality of types of recording paper 16 are configured to be usable, an information recording body such as a barcode or a wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reading device. Thus, it is preferable to automatically determine the type (media type) of the recording paper 16 to be used and perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 forms a horizontal surface (flat surface). Has been.

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the printing unit 12 inside the belt 33 spanned between the rollers 31 and 32, and the suction chamber 34 is connected to the fan 35. The recording paper 16 is sucked and held on the belt 33 by suctioning to negative pressure.

  The power of the motor (reference numeral 88 in FIG. 5) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The held recording paper 16 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 12K, 12C, 12M, and 12Y of the printing unit 12 has a length corresponding to the maximum paper width of the recording paper 16 targeted by the inkjet recording apparatus 10, and the recording paper 16 of the maximum size is provided on the nozzle surface. This is a full-line head in which a plurality of nozzles for ejecting ink are arranged over a length exceeding at least one side (the full width of the drawable range) (see FIG. 2).

  The heads 12K, 12C, 12M, and 12Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction (paper feeding direction) of the recording paper 16. The heads 12K, 12C, 12M, and 12Y are fixedly installed so as to extend along a direction substantially orthogonal to the paper transport direction.

  A color image can be formed on the recording paper 16 by discharging different color inks from the heads 12K, 12C, 12M, and 12Y while transporting the recording paper 16 by the suction belt transporting section 22.

  As described above, according to the configuration in which the full-line heads 12K, 12C, 12M, and 12Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 16 and the printing unit in the paper feeding direction (sub-scanning direction). The image can be recorded on the entire surface of the recording paper 16 by performing the operation of relatively moving the 12 only once (that is, by one sub-scanning). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

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

  A post-drying unit 42 is provided following the printing unit 12. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Configuration of liquid discharge head]
Next, the structure of the inkjet head will be described. Since the structures of the respective heads 12K, 12C, 12M, and 12Y for each color are common, the heads are represented by the reference numeral 50 in the following.

  FIG. 3A is a plan perspective view showing an example of the structure of the head 50, and FIG. 3B is an enlarged view of a part thereof. 3C is a perspective plan view showing another example of the structure of the head 50, and FIG. 4 is a sectional view showing a three-dimensional configuration of the ink chamber unit (4-4 in FIGS. 3A and 3B). It is sectional drawing which follows a line.

  In order to increase the dot pitch printed on the recording paper 16, it is necessary to increase the nozzle pitch in the head 50. As shown in FIGS. 3A to 3C, the head 50 of this example includes a plurality of ink chamber units each including a nozzle 51 serving as an ink droplet ejection hole, a pressure chamber 52 corresponding to each nozzle 51, and the like. 53 is arranged in a zigzag matrix (two-dimensionally), so that it is projected substantially in a line along the longitudinal direction of the head (main scanning direction orthogonal to the paper feed direction). High density of nozzle spacing (projection nozzle pitch) is achieved.

  The configuration in which one or more nozzle rows are configured over a length corresponding to the entire width of the recording paper 16 in a direction substantially orthogonal to the feeding direction of the recording paper 16 is not limited to this example. For example, instead of the configuration of FIG. 3 (a), short head blocks 50 ′ in which a plurality of nozzles 51 are two-dimensionally arranged are arranged in a staggered manner and connected as shown in FIG. 3 (c). A line head having a nozzle row having a length corresponding to the entire width of the recording paper 16 may be configured.

  In this example, the planar shape of the pressure chamber 52 is a substantially square shape, but the planar shape of the pressure chamber 52 is not limited to a substantially square shape, and may be a substantially circular shape, a substantially elliptical shape, or a substantially parallelogram ( Various shapes such as diamonds can be applied. Further, the arrangement of the nozzles 51 and the supply ports 54 is not limited to the arrangement shown in FIG. 3, and the nozzles 51 may be arranged at substantially the center of the pressure chamber 52, or the supply ports 54 are provided on the side walls of the pressure chamber 52. You may arrange.

  As shown in FIG. 3 (b), a large number of arrays are arranged in a lattice pattern with a constant array pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle θ not orthogonal to the main scanning direction. By doing so, the high-density nozzle head of this example is realized.

  That is, with a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example, and various nozzle arrangement structures such as an arrangement structure having one nozzle row in the sub-scanning direction can be applied.

  FIG. 4 is a cross-sectional view showing a three-dimensional configuration of the ink chamber unit 53. As shown in the figure, a piezoelectric actuator 58 (pressure generating element) having individual electrodes 57 is joined to a diaphragm 56 that constitutes the top surface of the pressure chamber 52 and also serves as a common electrode.

  Further, a pressure sensor 59 (provided with an extraction electrode (common electrode) 100 on the outside of the pressure chamber 52 on the bottom surface of the pressure chamber 52 and an extraction electrode (individual electrode) 102 on the surface opposite to the pressure chamber 52). Further, a space 104 is formed on the side of the pressure sensor 59 opposite to the pressure chamber 52, and a deformation region is secured so as not to prevent deformation when the pressure sensor 59 receives pressure. ing.

  In the configuration shown in FIG. 4, when a drive voltage (drive signal) is applied to the individual electrode 57 of the piezoelectric actuator 58, the piezoelectric actuator 58 is deformed and ink is ejected from the nozzle 51. When ink is ejected, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  The drive signal applied to the piezoelectric actuator 58 is transmitted to the individual electrode 57 via the horizontal wiring 105 (drive signal wiring) formed on the surface of the diaphragm 56 where the piezoelectric actuator is provided. In other words, the individual electrode 57 has a wiring structure that is electrically connected to the horizontal wiring 105 formed on the surface of the diaphragm 56 where the piezoelectric actuator 58 is provided. In addition, at least a region where the horizontal wiring 105 is formed on the surface of the diaphragm 56 where the piezoelectric actuator 58 is provided is insulated so that the diaphragm 56 and the horizontal wiring 105 are not conductive.

  In a mode in which a block (head driver 84, see FIG. 5) for generating a drive signal is provided outside the head 50, the horizontal wiring 105 is drawn out to the outside of the head 50 via a flexible substrate (not shown).

  Further, when pressure (pressure fluctuation) is generated in the pressure chamber 52 due to ink ejection or refilling, a distortion (stress) corresponding to the pressure is generated in the pressure sensor 59, and this distortion is generated from the extraction electrode 102 of the pressure sensor 59. A corresponding detection signal can be obtained. That is, a detection signal (waveform) corresponding to the pressure generated in the pressure chamber 52 by the pressure sensor 59 can be obtained.

  Although details will be described later, in the inkjet recording apparatus 10, the pressure in the pressure chamber 52 is detected based on the detection signal obtained from the pressure sensor 59, and the discharge state (absence of discharge abnormality) and the state inside the pressure chamber 52 are detected. Detecting the state of the meniscus.

  As shown in FIG. 4, the head 50 shown in this example has a laminated structure in which a plurality of cavity plates are laminated. That is, the head 50 includes a nozzle plate 110 in which the nozzle 51 is formed, a flow path plate 114 in which a part of the discharge side flow path 112 that connects the nozzle 51 and the pressure chamber 52 is formed, and the pressure chamber 52 and the discharge. A pressure chamber plate 116 in which a part of the side flow path 112 is formed, a flow path plate 118 in which a part of the discharge side flow path 112 and a part of the supply port 54 are formed, and a part of the discharge side flow path 112 The flow path plate 120 in which a part of the supply port 54 and the space 104 are formed, the flow path plate 122 that forms the bottom surface of the pressure chamber 52 and to which the pressure sensor 59 is joined, and the pressure at which the pressure chamber 52 is formed. The chamber plate 124 and the diaphragm 56 that forms the top surface of the pressure chamber 52 and is joined to the piezoelectric actuator 58 are sequentially laminated.

  For joining between the plates constituting the laminated structure, a joining method according to the material and shape of the plate is appropriately used. This joining method includes joining by a joining member, joining by pressurization, joining by heating, and joining combining these.

  The extraction electrode 100 on the flow path plate 122 side (pressure chamber 52 side) of the pressure sensor 59 is a common electrode common to each pressure sensor 59, and the extraction electrode 102 on the flow path plate 118 side (opposite side of the pressure chamber) is Each pressure sensor 59 is an individual electrode.

  The extraction electrode 100 common to each sensor is formed so as to conduct on the surface on which the pressure sensor 59 is disposed (sensor disposed surface). For example, there is an aspect in which the extraction electrode 100 is integrally formed on the sensor arrangement surface of the flow path plate 122.

  The extraction electrode (individual electrode) 102 is drawn out to the sensor arrangement surface and is electrically connected to the horizontal wiring 130 formed on the sensor arrangement surface of the flow path plate 118. The horizontal wiring 130 is electrically connected to the vertical wiring 132 formed so as to penetrate the flow path plate 122 and the pressure chamber plate 124, and is further electrically connected to the horizontal wiring 134 formed on the diaphragm 56 side of the pressure chamber plate 124. It has a wiring structure. In the embodiment in which insulation processing is performed between the diaphragm 56 and the horizontal wiring 134 and the extraction electrode 100 is integrally formed on the sensor mounting surface of the flow path plate 122, the extraction electrode 100 and the horizontal wiring 130 are formed. A predetermined insulation treatment is performed between the two.

In the aspect in which the detection signal processing block (pressure detection unit 85, see FIG. 5) is provided outside the head 50, the horizontal wiring 134 is joined to a wiring pattern formed on a flexible substrate (not shown) , It is pulled out of the head 50. The vertical wiring 132 may be formed so as to penetrate the diaphragm 56 and the horizontal wiring 134 may be formed on the surface of the diaphragm 56 where the piezoelectric actuator is provided. The wiring structure described above is an example, and horizontal wirings 130 and 134 and vertical wirings 132 are appropriately provided on each plate, and a detection signal obtained from the pressure sensor 59 is drawn out of the head 50 through these wirings.

  The extraction electrode 100 and the extraction electrode 102 are provided separately for each sensor, and a floating output type sensor that outputs a detection signal obtained from the extraction electrode 100 and an inverted signal obtained by inverting the detection signal obtained from the extraction electrode 102. May be applied to the pressure sensor 59.

  Although not shown in FIG. 4, a mode in which a wiring member (for example, a flexible substrate) in which a wiring pattern (not shown) for transmitting a drive signal and a detection signal is formed on the opposite side of the diaphragm 56 of the piezoelectric actuator 58 is disposed. There is.

  In the above-described aspect, a space is provided between the flexible substrate and the diaphragm 56 so as not to hinder the deformation of the piezoelectric actuator 58, and the support member supports the flexible substrate from the lower side (the diaphragm 56 side). Is provided.

  The flexible substrate here has a structure in which a conductor layer such as copper is formed on a support layer (insulating layer) made of a resin member such as epoxy or polyimide. In an aspect in which the head 50 includes a large number of piezoelectric actuators 58 and pressure sensors 59, a flexible substrate having a multilayer structure in which three or more conductor layers and a plurality of support layers are alternately stacked is preferably used.

A piezoelectric element using a ceramic material such as PZT (Pb (Zr · Ti) O ₃ , lead zirconate titanate) is preferably used for the piezoelectric actuator 58 shown in FIG. 4, and PVDF (Polyvinylidene) is used for the pressure sensor 59. A piezoelectric element using a fluororesin material such as fluoride or polyvinylidene fluoride) or PVDF-TrFE (polyvinylidene fluoride trifluoride ethylene copolymer) is preferably used. Of course, a fluororesin piezoelectric element may be applied to the piezoelectric actuator 58, and a ceramic piezoelectric element such as PZT may be applied to the pressure sensor 59.

In general, a piezoelectric element having a large absolute value of an equivalent piezoelectric constant (d constant, electromechanical conversion constant, piezoelectric strain constant) and excellent driving characteristics is preferable for an actuator that generates pressure, and a piezoelectric output coefficient for a sensor that detects pressure. A piezoelectric element having a large (g constant, electromechanical conversion constant, piezoelectric stress constant) and excellent detection characteristics is preferable. That is, a ceramic material such as PZT is suitable for a piezoelectric element having excellent driving characteristics, and a fluorinated resin material such as PVDF or PVDF-TrFE is suitable for a piezoelectric element having excellent detection characteristics. Ceramic materials include lead zirconate titanate (Pb (Zr · Ti) O ₃ ), and the basic composition is ferroelectric lead titanate (PbTiO ₃ ) and antiferroelectric lead zirconate (PbZrO ₃ ). By changing the mixing ratio of these two components, various characteristics such as piezoelectricity, dielectricity, and elasticity can be controlled.

  The arrangement of the piezoelectric actuator 58 that applies ejection force to the ink in the pressure chamber 52 and the pressure sensor 59 that detects the pressure in the pressure chamber 52 is not limited to the arrangement shown in FIG. Or may be provided on different wall surfaces. A mode in which the piezoelectric actuator 58 and the pressure sensor 59 are provided inside the pressure chamber 52 is also possible. In the aspect in which the piezoelectric actuator 58 and the pressure sensor 59 are provided in the pressure chamber 52, a predetermined ink-resistant process (insulation process) is performed on the portions of the piezoelectric actuator 58 and the pressure sensor 59 that come into contact with ink.

  It is also possible to use the piezoelectric actuator 58 and the pressure sensor 59 as the pressure sensor 59 after the piezoelectric actuator 58 is driven by driving the piezoelectric actuator 58 together. For example, a signal switching means such as a switch element is provided in a wiring that is electrically connected to the individual electrode 57 of the piezoelectric actuator 58, and is electrically connected to a wiring that transmits a drive signal when used as a piezoelectric actuator, and is detected when used as a pressure sensor. You may comprise so that it may become conductive with the wiring in which a signal is transmitted.

  Although not shown, the head 50 can be applied with the structure described below. A common flow path (common liquid chamber) 55 common to the pressure chambers 52 is provided on the opposite side of the pressure chambers 52 to the diaphragm 56, and the pressure chambers 52 and the common flow paths are formed via supply ports 54 formed in the diaphragm 56. Communicate with 55. Further, a vertical wiring member is formed so as to rise in a vertical direction from the piezoelectric actuator placement surface of the diaphragm 56 so as to penetrate at least a part of the common flow channel 55, and the individual electrodes 57 and The extraction electrode 102 of the pressure sensor 59 is configured to be electrically connected to the wiring pattern of the flexible substrate provided on the upper surface (the side opposite to the diaphragm 56) of the common flow channel 55.

  By applying such a structure, even if the arrangement of the ink chamber units 53 is increased in density, the volume of the common flow channel 55 can be increased as compared with the structure shown in FIG. The flow path resistance on the supply side can be reduced, and the refill characteristics can be improved. The piezoelectric actuator 58 is provided with a cover so as not to come into contact with the ink in the common flow channel 55, and the surface of the vertical wiring member disposed in the common flow channel 55 that comes into contact with the ink has a predetermined ink resistance treatment. (Insulation treatment) is performed.

[Description of maintenance unit]
The inkjet recording apparatus 10 includes a maintenance unit such as a cap (not shown) as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade (not shown) as a means for cleaning the nozzle surface. (Not shown) is provided.

  The maintenance unit including the cap, the cleaning blade, and the like can be moved relative to the head 50 by a moving mechanism (not shown), and is moved from a predetermined retraction position to a maintenance position below the head 50 as necessary.

  The cap is displaced up and down relatively with respect to the head 50 by an elevating mechanism. When the power is turned off or during printing standby, the cap is raised to a predetermined raised position and brought into close contact with the head 50, thereby covering the nozzle surface with the cap.

  During printing or standby, if the frequency of use of a specific nozzle 51 is reduced and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. In such a state, ink cannot be ejected from the nozzle 51 even if the piezoelectric actuator 58 is operated.

  Before such a state is reached (within the range of viscosity that can be discharged by the operation of the piezoelectric actuator 58), the piezoelectric actuator 58 is operated to cap the deteriorated ink (ink in the vicinity of the nozzle whose viscosity has increased) to be discharged. Preliminary ejection (purging, idle ejection, brim ejection, dummy ejection) is performed toward (ink receiving).

  In addition, when bubbles are mixed in the ink in the head 50 (in the pressure chamber 52), the ink cannot be ejected from the nozzle even if the piezoelectric actuator 58 is operated. In such a case, a cap is applied to the head 50, the ink in the pressure chamber 52 (ink mixed with bubbles) is removed by suction with a suction device such as a suction pump, and the suctioned and removed ink is sent to the recovery tank. .

  In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time. Since the suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption increases. Therefore, it is preferable to perform preliminary ejection when the increase in ink viscosity is small.

  In the inkjet recording apparatus 10 shown in this example, when it is determined that bubbles are generated in the pressure chamber 52, the above-described maintenance process (recovery process) such as suction is performed. In this example, as an example of the bubble removal process, the cap is brought into close contact with the head 50 and the ink in the head 50 is sucked from each nozzle. Of course, the bubbles in the pressure chamber 52 are removed by a process other than the suction. May be.

  The cleaning blade is made of an elastic member such as rubber, and can slide on the ink discharge surface (nozzle plate surface) of the head 50 by a blade moving mechanism (wiper) (not shown). When ink droplets or foreign matter adheres to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade on the nozzle plate to clean the nozzle plate surface. It should be noted that when the ink ejection surface is cleaned by the blade mechanism, preliminary ejection is performed in order to prevent foreign matter from being mixed into the nozzle 51 by the blade.

[Explanation of control system]
FIG. 5 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, a memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, a pressure detection unit 85, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. For the communication interface 70, a serial interface such as USB (Universal serial bus), IEEE 1394, Ethernet (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 image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the memory 74.

  The memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 72 controls each part such as the communication interface 70, the memory 74, the motor driver 76, the heater driver 78, etc., performs communication control with the host computer 86, read / write control of the memory 74, etc. A control signal is generated to control a motor 88 such as the motor No. 88 and a heater 89 such as a heater of the post-drying section 42.

  The memory 74 stores programs executed by the CPU of the system controller 72 and various data necessary for control. Note that the memory 74 may be a non-rewritable storage means or a rewritable storage means such as an EEPROM. The memory 74 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives a heater 89 such as a temperature adjustment heater in the post-drying unit 42, the inkjet recording apparatus 10, and the head 50 in accordance with an instruction from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the memory 74 in accordance with the control of the system controller 72, and the generated print It is a control unit that supplies data (dot data) to the head driver 84. Necessary signal processing is performed in the print control unit 80, and the ejection amount and ejection timing of the ink droplets of the head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  The head driver 84 drives the piezoelectric actuator 58 of the head 50 of each color based on the print data given from the print control unit 80. That is, the head driver 84 generates a drive signal to be supplied to the piezoelectric actuator 58 based on the dot data obtained from the print control 80, and the drive signal is transmitted to each piezoelectric actuator 58 via a predetermined circuit and wiring. Supplied to. The head driver 84 may include a feedback control system for keeping the head driving condition constant.

  That is, image data to be printed is input from the outside via the communication interface 70 and stored in the memory 74. At this stage, RGB image data is stored in the memory 74.

  The image data stored in the memory 74 is sent to the print controller 80 via the system controller 72, and is converted into dot data for each ink color by the print controller 80. That is, the print control unit 80 performs processing for converting the input RGB image data into dot data of four colors of KCMY. The dot data generated by the print controller 80 is stored in the image buffer memory 82.

  The head driver 84 generates a drive control signal for the head 50 based on the dot data stored in the image buffer memory 82. By applying the drive control signal generated by the head driver 84 to the head 50, ink is ejected from the head 50. An image is formed on the recording paper 16 by controlling the ink ejection from the head 50 in synchronization with the conveyance speed of the recording paper 16.

  The pressure detection unit 85 performs predetermined signal processing on the detection signal obtained from the pressure sensor 59 shown in FIG. 4, detects the pressure generated in the pressure chamber 52, and sends the pressure information to the print control unit 80. The print control unit 80 determines whether or not bubbles are generated in the nozzles 51 and the pressure chambers 52 (ink chamber units 53) based on the pressure information, and the nozzles determined as bubbles are generated. A control signal is sent to each part such as the system controller 72 so as to execute a predetermined recovery process for the pressure chamber 51 and the pressure chamber 52.

  For example, when the nozzle 51 and the pressure chamber 52 in which bubbles are generated are present, the print control unit 80 sends the information (signal) to the system controller 72 so that the above-described cap is brought into close contact with the nozzle formation surface of the head 50. The cap moving mechanism is operated, the suction pump is operated, and the bubble removal processing in the head 50 (nozzle 51 and pressure chamber 52) is executed from the nozzle 51 side. Details of the configuration of the pressure detector 85 and the pressure detection control will be described later.

  Various control programs are stored in the program storage unit 90 of FIG. 5, and the control programs are read and executed in accordance with instructions from the system controller 72. The program storage unit 90 may use a semiconductor memory such as a ROM or an EEPROM, or may use a magnetic disk or the like. An external interface may be provided and a memory card or PC card may be used. Of course, you may provide multiple types of storage media among these storage media. The program storage unit 90 may also be used as a storage unit (not shown) for operating parameters and the like.

  In this example, the system controller 72, the memory 74, the print control unit 80, and the like are illustrated as individual blocks as functional blocks, but these may be integrated and configured as one processor. Further, a part of the function of the system controller 72 and a part of the function of the print control unit 80 can be realized as one processor.

[Description of pressure detector]
Next, details of the pressure detector 85 shown in FIG. 5 will be described. FIG. 6 is a block diagram showing a schematic configuration of the pressure detection unit 85 and its periphery.

  As shown in FIG. 6, the pressure detection unit 85 includes a voltage measurement unit 140 that measures the voltage of the detection signal obtained from the pressure sensor 59, and a frequency calculation unit 142 that measures the frequency (cycle) of the detection signal. It consists of Although not shown in FIG. 6, there is an aspect in which the pressure detection unit 85 includes a circuit block such as an amplifier circuit that amplifies the detection signal.

  Although only one pressure sensor 59 is illustrated in FIG. 6, the same number of pressure sensors 59 as the number of ink chamber units 53 provided in the head 50 are provided. For example, in an aspect including N pressure sensors 59, the pressure sensor 59 that acquires the detection signal is selectively switched by a switch array (multiplexer circuit) having N switch elements corresponding to each of the pressure sensors 59. With this configuration, a circuit block that performs predetermined signal processing on the detection signal can be shared, and the configuration of the pressure detection unit 85 can be simplified.

Reference numeral 144 illustrated in FIG. 6 indicates detection signal wiring from the pressure sensor 59 to the pressure detection unit 85 including the horizontal wiring 130, the vertical wiring 132, and the horizontal wiring 134 illustrated in FIG. The detection signal wiring 144 includes a wiring pattern for transmitting a detection signal formed in the flexible substrate. Reference numeral 146 denotes a drive signal wiring from the head driver (drive circuit) 84 including the horizontal wiring 105 shown in FIG. 4 to the piezoelectric actuator 58. Similarly to the detection signal wiring 144, the driving signal wiring 146 includes a wiring pattern for transmitting a driving signal formed on the flexible substrate.

  Between the detection signal wiring 144 and the drive signal wiring 146 described above, there is a wiring capacitance (floating capacitance) illustrated by reference numeral 148 in FIG. Although one wiring capacitor 148 is schematically illustrated in FIG. 6, the wiring capacitor 148 actually exists over the entire region where the detection signal wiring 144 and the drive signal wiring 146 are disposed.

  For example, in FIG. 4, the wiring capacitance 148 also exists in the portion where the horizontal wiring 134 (detection signal wiring 144) and the horizontal wiring 105 (drive signal wiring 146) are formed across the diaphragm 56.

  FIG. 7 shows a schematic equivalent circuit diagram of the detection signal system 180 including the pressure sensor 59 and the detection signal wiring 144, and the drive signal system 182 including the piezoelectric actuator 58 and the drive signal wiring 146.

  As shown in FIG. 7, wiring resistances indicated by reference numerals 150, 152, and 154 exist in the detection signal wiring 144 that transmits the detection signal. The resistance values of the wiring resistors 150, 152, and 154 are each about several Ω to 100 Ω.

  The voltage measurement unit 140 of the pressure detection unit 85 includes an input resistor 156, and a detection signal transmitted from the pressure sensor 59 via the input resistor 156 is acquired. The pressure sensor 59 is represented as a capacitor in the equivalent circuit shown in FIG.

  In addition, wiring resistances indicated by reference numerals 160, 162, and 164 also exist in the driving signal wiring 146 that transmits the driving signal, and the resistance values thereof are about several Ω to 100 Ω, respectively. The piezoelectric actuator 58 is represented by a capacitor and a resistor connected in parallel in the equivalent circuit of FIG.

  In the equivalent circuit shown in FIG. 7, the head driver (drive circuit) 84 is schematically represented by an AC voltage source 166 and an internal resistor 168, and the wiring capacitor 148 shown in FIG. 6 includes the detection wiring 144 and the drive signal wiring 146. Expressed as a coupling capacitor.

[Explanation of pressure detection]
Next, pressure detection of the pressure chamber 52 (ink chamber unit 53) in the inkjet recording apparatus 10 will be described.

  FIG. 8 shows a waveform of a pressure (a detection signal obtained from the pressure sensor 59) generated in the pressure chamber 52 when the ink is ejected from the nozzle 51 by operating the piezoelectric actuator 58. The horizontal axis in FIG. 8 indicates time, and the vertical axis indicates the pressure in the pressure chamber 52.

  A pressure waveform 200 shown by a solid line in FIG. 8 is a pressure waveform in a normal discharge state, and a pressure waveform 202 and a pressure waveform 204 shown by a broken line are pressure waveforms in a discharge abnormal state, respectively. In the normal discharge state, the pressure waveform of the pressure chamber 52 is a damped oscillation waveform that has substantially the same frequency as the resonance period T of the pressure chamber 52 and converges to the static pressure.

  On the other hand, in the abnormal discharge state, the pressure waveform is a damped oscillation waveform having a period different from the resonance period T of the pressure chamber 52. In FIG. 8, the period of the pressure waveform 202 is T ′, and the period of the pressure waveform 204 is T ″.

The pressure waveforms 202 and 204 in the abnormal discharge state shown in FIG. 8 have substantially the same peak value P _{p as} that in the normal discharge state, but the peak value of the pressure waveform is normal in the abnormal discharge state. It may be different from the peak value of the pressure waveform.

  The pressure waveform 202 shown in FIG. 8 has a period smaller than that of the pressure waveform 200 during normal discharge (T ′ <T), and when such a pressure waveform is obtained, a large-sized bubble is formed in the pressure chamber 52. Can be determined to have occurred.

  The pressure waveform 204 has a longer period than the pressure waveform 200 during normal discharge (T ″> T), and when such a pressure waveform is obtained, small bubbles are generated in the pressure chamber 52. It can be determined that

That is, the period T ₁ (frequency f ₁ = 1 / T ₁ ) of the pressure waveform in the pressure chamber 52 is detected, the detected period T _{1 of the} pressure waveform is compared with the resonance period T of the pressure chamber 52, and the pressure The presence / absence of bubbles in the chamber 52 and the size of the bubbles can be determined.

  FIG. 9A shows a drive signal 220 when the piezoelectric actuator 58 makes a step response, and FIG. 9B shows a detection signal 222 obtained from the pressure sensor 59 when the piezoelectric actuator 58 makes a step response. . The drive signal 220 has a voltage of approximately 10V, and the detection signal 222 has a voltage of 5V to 10V. The voltage of the detection signal 222 can be amplified with a predetermined gain in the pressure detector 85 shown in FIG.

The detection signal 222 has a similar relationship to the pressure waveform generated in the pressure chamber 52 in an ideal state (for example, a state where no bubbles are generated in the pressure chamber 52). The same period as the resonance period T (the same frequency as the resonance frequency f). The period of the detection signal 222 from the timing t _p1 which is the first minimum value, and the time interval until the timing t _p2, which is the next minimum value and the period T ₁ of the detection signal 222.

Note that the frequency f _{1 of the} detection signal may be obtained instead of the cycle T ₁ of the detection signal. The frequency f ₁ of the detection signal can be obtained as the reciprocal of the period T ₁ of the detection signal (f ₁ = 1 / (t _p2 −t _p1 )).

A method of calculating the period T ₁ of the detection signal 222 using a predetermined voltage threshold V _th (see FIG. 9D) may be applied. The voltage threshold value V _th described above is such that the detection signal and the voltage threshold value V so that the first to at least second wave of the detection signal intersects the threshold value (a waveform for at least one period). _It is determined that there are three or more timings at which _th intersects.

When the period T ₁ of the detection signal 222 is obtained using the voltage threshold V _th , the pressure detection unit 85 shown in FIG. 6 includes a voltage threshold setting unit for setting the voltage threshold and the voltage threshold. Is stored.

FIG. 9C shows a noise component mixed in the detection wiring 144 (superimposed on the detection signal 222) via the wiring capacitance 148 shown in FIG. 6 when the piezoelectric actuator 58 makes a step response by the drive signal 220. 224 is shown. This noise component 224 is. It has a pulse-like waveform synchronized with the falling edge (leading edge) of the drive signal 220, and its peak value becomes | V _p '| (> | V _p |) at timing t _p1 ' (≠ t _p1 ). ing.

  FIG. 9D shows a detection signal 226 on which the noise component 224 shown in FIG. 9C is superimposed. In addition to the noise component 224 shown in FIG. 9 (c), various noise components are superimposed on the actually obtained detection signal. Here, the detection with the noise component 224 shown in FIG. 9 (c) superimposed is performed. The signal 226 will be described.

The peak value of the detection signal 226 becomes | V _p ′ | (> | V _p |) at the timing t _p1 ′ (≠ t _p1 ). If such noise component to calculate the period T ₂ of the detection signal 226 superimposed, the method using the peak value, the timing at which the first minimum value is shifted to t _{p1 'from} t _p1, 9 ( T ₂ is different from the period T ₁ of the detection signal 222 shown in b) (T ₂ > T _{1 in the} example shown in FIG. 9D).

Further, 'be calculated, timing _{t th1} detection signal 226 is initially crosses the voltage threshold _{V th} period of the detection signal 226 _{(T 2)'} using the voltage threshold _{V th} and the detection signal Since the timing t _{th1 at} which 222 first crosses the voltage threshold value V _th is different, there arises a problem that the period of the detection signal T ₂ cannot be accurately detected.

In this example, as shown in FIG. 10A, the decay time of the noise component 224 ′ of the drive signal superimposed on the detection signal (from the timing when the voltage peak value is reached until the voltage reaches 70% of the voltage peak value). (Time constant) By making T ₃ longer than the resonance period T of the pressure chamber (that is, T ₃ > T), the influence of the noise of the drive signal in the detection signal is eliminated, and the detection signal is accurately detected. it is possible to calculate the period T _1. Thereby, the state of the pressure chamber 52 (the presence of bubbles, the change in the viscosity of the ink in the pressure chamber 52, the change in temperature, etc.) can be accurately detected. Furthermore, it is possible to detect or detect the occurrence of ejection abnormalities (non-ejection etc.) and improve the printing quality.

FIG. 10B shows a detection signal 226 ′ on which a noise component 224 ′ by the drive signal having the waveform shown in FIG. A waveform indicated by a broken line in FIG. 10B is a detection signal 222 (see FIG. 9B) on which noise is not superimposed.

As shown in FIG. 10 (b), in the detection signal 226 ′, the maximum value and the minimum value are different from the detection signal 222, but the timing when the maximum value and the minimum value become substantially the same as the detection signal 222. The period T _{4 of} 226 ′ is substantially the same as the period T ₁ of the detection signal 222 shown in FIG. 9B (that is, T ₄ = T ₁ ). Even if the frequency of the detection signal 226 ′ is calculated using the voltage threshold V _th , the cycle T ₄ of the detection signal 226 ′ is substantially the same as the cycle T ₁ of the detection signal 222.

10 decay time T ₃ of the noise component 224 'shown in (a), using the capacitance C of the wiring capacitance 148 shown in FIG. 8, the resistance value R of the input resistor 156 of the voltage measuring unit 140, a, It can be expressed as T ₃ = C × R. That is, the capacitance C of the wiring capacitor 148 and the resonance period T of the pressure chamber 52 are obtained in advance, and the resistance value R of the input resistor 156 that satisfies T ₃ > T may be obtained.

The capacitance C of the wiring capacitance 148 can be calculated by analyzing from the measured value of the entire system (or a part of the system) measured using a measuring instrument such as an LCR meter. Further, the resonance frequency f ₁ of the pressure chamber 52 is determined from the material and size of which design conditions.

Capacitance C of the wiring capacitance 148, and an example of the resistance value R of the input resistor 156, C = 1 pF, a R = 100Keiomega～5emuomega, decay time _{T 3} of the noise component 224 'at this time is 0.1μsec ~ 1 μsec. For example, when the resonance period T of the pressure chamber 52 is 200 kHz, the resistance value R of the input resistor 156 is 5 MΩ or more. Further, the capacitance of the piezoelectric actuator 58 is approximately 5 pF, and the capacitance of the pressure sensor 59 is approximately 0.2 pF.

  FIG. 11 shows a flowchart of pressure detection in the pressure chamber 52 of this example. The pressure detection in this example is performed in real time for the discharge operation. That is, each time the piezoelectric actuator 58 is driven, a detection signal is acquired from the pressure sensor 59 and the pressure generated in the pressure chamber 52 is detected.

As shown in FIG. 11, when the piezoelectric actuator 58 operates for ink ejection (start, step S10), the pressure detector 85 shown in FIG. 5 acquires a detection signal from the pressure sensor 59 (step S12). In the pressure detection unit 85, the voltage measurement unit 140 shown in FIG. 6 measures the voltage of the detection signal and stores it in a predetermined memory (for example, the image buffer memory 82 shown in FIG. 5) (step S14). Further, the period of the detection signal (detection period, for example, T _{4 in} FIG. 10B) is obtained by the frequency calculation unit 142 and stored in a predetermined memory (step S16).

The detection period T ₄ is compared with the resonance cycle T of the pressure chamber 52 (step S18), and detected when the period T ₄ is lower than the resonance cycle T of the pressure chamber 52 (YES judgment), the bubbles of a large size pressure It is determined that the pressure is generated in the chamber 52 (step 26), and the pressure chamber 52 (nozzle 51) is subjected to a recovery process (step 28). When the recovery process in step S28 ends, the process returns to step S12.

On the other hand, (NO determination) when the detected period _{T 4} in step S18 is greater than the resonant period T of the pressure chamber 52, the process proceeds to step S20, whether the detected period _{T 4} is greater than the resonant period T of the pressure chamber 52 not Is judged. If the detection period T ₄ is greater than the resonant period T of the pressure chamber 52 (YES judgment), the small size bubbles is determined occurring in the pressure chamber 52, the pressure chamber 52 proceeds to step S28 (nozzle 51) A recovery process is applied.

  As an example of the recovery process shown in step S28, in the recovery process corresponding to large-sized bubbles and the recovery process corresponding to medium-sized bubbles, the purge time is set according to the size of the bubbles. Specifically, when removing large-sized bubbles, the purge time is set longer than that for removing medium-sized bubbles. As described above, according to the control for changing the recovery processing time according to the bubble size, the recovery processing time can be shortened as compared with the conventional recovery control performed according to simple time management or printing interval.

Further, the (NO judgment) when the detected period _{T 4} in step S20 is substantially the same as the resonance period T of the pressure chamber 52, it is determined that the pressure chamber 52 does not bubbles are generated (step S22), and to step S12 Return.

In the inkjet recording apparatus 10 configured as described above, attenuation of noise superimposed on a detection signal determined by the resistance value R of the input resistor 156 and the capacitance C of the wiring capacitance 148 of the pressure detection unit 85 (voltage measurement unit 140). Since the relationship between the time T ₃ and the resonance period T of the pressure chamber 52 satisfies the relationship of T ₃ > T, the pressure generated in the pressure chamber 52 can be accurately detected, The impact can be accurately captured.

[Application example]
Next, an application example according to the embodiment of the present invention will be described. In this application example, in the aspect in which the frequency of the detection signal is obtained using the voltage threshold V _th , the voltage threshold is based on the detection signal when the liquid is not filled (that is, the noise component due to the drive signal of the detection signal). calculating a shift value [Delta] V _th of V _th and stores the correction voltage threshold _{V th} shifted by the shift value [Delta] V _th when calculating the frequency of the detection signal _{'(= V th} -ΔV _th) Is used. The shift value ΔV _th and the correction voltage threshold value V _th ′ are stored in a predetermined memory (for example, the image buffer memory 82 in FIG. 5 or a memory (not shown)).

  FIG. 12A shows a drive signal 300 applied when the piezoelectric actuator 58 is pulled and driven, and FIG. 12B shows a piezoelectric signal applied with the drive signal 300 shown in FIG. The noise component 302 by the drive signal which detected the pressure of the pressure chamber 52 at the time of the ink unfilling obtained by driving the actuator 58 is shown.

  As shown in FIG. 12 (a), the drive signal 300 includes a first drive element 300A corresponding to the pulling operation of the piezoelectric actuator 58 and a second drive that maintains the deformation amount of the piezoelectric actuator 58 constant for a predetermined period. An element 300B and a third drive element 300C corresponding to the pushing operation of the piezoelectric actuator 58 are configured.

That is, the drive signal 300 is a first drive element during a period from timing t ₁ to t ₂ , and is a second drive element during a period from timing t ₂ to timing t ₃ , and from timing t ₃ to timing t _4. The period up to is the third driving element.

12 the average value of the noise component 302 shown in (b) the shift value [Delta] V _th becomes (average voltage of the base portion 302A of the noise waveform in the period from the timing _{t 2} to time _{t 3),} the shift value [Delta] V _th is given Stored in memory. 'In (if the decay time is relatively short), the noise component 302' noise component 302 shown in FIG. 12 (d) Since the base portion 302A of the waveform of 'does not become a constant voltage, the period from the timing t ₂ to time t ₃ Is stored as a shift value ΔV _th in a predetermined memory. The timing _{t 2} is the peak timing of the first drive element 302A of the drive signal 300, the timing _{t 3} is the start timing of the third drive element 300C.

As shown in FIG. 12 (c), by causing this way the shift value [Delta] V _th shifted the voltage threshold V _th obtained, by eliminating the influence of the noise component due to the driving signals, accurate detection signal Period (frequency) can be obtained. A reference numeral 304 illustrated in FIG. 12C indicates a detection signal on which noise due to the drive signal 300 is superimposed, and a reference numeral 306 indicates a detection signal on which the noise component is not superimposed.

  FIG. 13 is a flowchart showing an outline of print control of the inkjet recording apparatus 10. As shown in FIG. 13, when printing control is started or when the power is turned on or when returning from the power saving mode (step S100), a threshold value used for calculation of the detection frequency is set (step S102).

  FIG. 14 shows the flow of threshold setting. In the threshold setting shown in FIG. 14 (step S102), the noise component of the detection signal by the drive signal is measured (step S120), the average value of the noise component is calculated (step S122), and the average value of the noise component is calculated. Is stored in a predetermined storage element (step S124).

  The threshold value of the noise component stored in step S124 is added to the default voltage threshold value (step S126), the voltage threshold value is updated (step S128), and the threshold value setting ends (step S130).

In the threshold setting shown in FIG. 14, a shift value (for example, shown in FIG. 12B) with respect to a predetermined default voltage threshold (for example, the voltage threshold V _th shown in FIG. 12B). Although the mode of calculating the shift value ΔV _th ) has been shown, the noise component of the drive signal may be used as the voltage threshold without having the default voltage threshold.

  In step S102 of FIG. 13, when a voltage threshold value for calculating a detection cycle is set, printing (image recording) is executed based on predetermined print data, and the pressure of the pressure chamber 52 is detected in real time. Is performed (step S104).

  When the predetermined printing is completed (step 106), it is determined whether there is next print data (step S108).

  If there is next print data (YES determination), the process proceeds to step S104, and printing based on the print data is executed. If there is no next print data (NO determination), the print control is ended. . If there is no print data, the power saving mode (standby mode) may be entered.

According to this application example, the noise component due to the drive signal superimposed on the detection signal is measured, and the threshold value _Vth used when calculating the period of the detection signal (detection period) based on the noise component is shifted. Therefore, it is possible to accurately detect the frequency variation of the pressure in the pressure chamber 52 and accurately grasp the influence on the discharge.

  In the above embodiment, an inkjet recording apparatus using a page-wide full-line head having a nozzle row having a length corresponding to the entire width of the recording paper 16 has been described, but the scope of application of the present invention is not limited to this, The present invention can also be applied to an ink jet recording apparatus that uses a shuttle head that records an image while reciprocating a short recording head.

  In the above embodiment, an ink jet recording apparatus that forms an image on the recording paper 16 by ejecting ink from nozzles provided in the head has been described. However, the scope of application of the present invention is not limited to this, and other than ink such as resist. The present invention can be widely applied to an image forming apparatus that forms an image (three-dimensional shape) with a liquid, a liquid ejecting apparatus such as a dispenser that ejects a chemical solution, water, or the like from a nozzle (ejection hole).

1 is an overall configuration diagram of an ink jet recording apparatus according to the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. Plane perspective view showing structural example of head Sectional view showing the three-dimensional structure of the head 1 is a principal block diagram showing the system configuration of the ink jet recording apparatus shown in FIG. The block diagram which shows the detailed structure of the pressure detection part shown in FIG. Equivalent circuit diagram of drive signal system and detection signal system The figure explaining the frequency of a detection signal The figure explaining the detection signal obtained from the pressure sensor The figure explaining the water-reduction time of the noise component by a drive signal The flowchart which shows the flow of the pressure detection control of this invention The figure explaining the application example which concerns on this invention Flow chart showing the outline of the flow of printing control Threshold setting flowchart

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12K, 12C, 12M, 12Y, 50 ... Head, 51 ... Nozzle, 52 ... Pressure chamber, 58 ... Piezoelectric actuator, 59 ... Pressure sensor, 80 ... Print control part, 85 ... Pressure detection part, 140 ... Voltage measuring unit, 142 ... Frequency step S calculating unit, 105, 146 ... Drive signal wiring, 130, 132, 134, 144 ... Detection signal wiring, 148 ... Wiring capacitance, 156 ... Input resistance

Claims (7)

A pressure chamber containing liquid to be discharged from the nozzle;
A pressure generating element that applies a discharge force to the liquid contained in the pressure chamber;
A pressure detecting element Ru generates a detection signal according to the pressure of the pressure chamber,
A liquid ejection head comprising:
A drive signal generator for generating a drive signal to be applied to the pressure generating element;
A drive signal line for transmitting a driving signal from the driving signal generating unit to the pressure generating element,
A pressure detecting unit for detecting the pressure of the pressure chamber on the basis of the detection signal obtained from the previous SL pressure sensing element,
A detection signal wiring that transmits a detection signal from the pressure detection element to the pressure detection unit, and at least a part thereof is arranged at a position where noise due to a change in the drive signal is superimposed on the transmitted detection signal;
With
A product C × R of a capacitance value C of a wiring capacitance between the drive signal wiring and the detection signal wiring and a resistance value R of an input resistance provided in an input unit to which the detection signal of the pressure detection unit is input. The liquid ejection apparatus, wherein the decay time of the noise component is set so that the decay time of the noise component superimposed on the detection signal represented is greater than the resonance period of the pressure chamber. The pressure detection unit is an extreme value measurement unit that measures at least one of a maximum value and a minimum value of the detection signal;
A period calculation unit for calculating a period of the detection signal from a time interval of the maximum value or the minimum value of the detection signal;
The liquid ejection apparatus according to claim 1, further comprising: A threshold value setting unit for setting a voltage threshold value of the detection signal;
A period calculation unit that calculates a period of the detection signal from a timing at which the detection signal crosses the voltage threshold;
The liquid ejection apparatus according to claim 1, further comprising: A noise component detection unit for detecting a noise component superimposed on the detection signal;
The liquid ejection apparatus according to claim 3, wherein the threshold value setting unit sets the voltage threshold value based on a noise component detected by the noise component detection unit.   The threshold value setting unit calculates a shift amount of the voltage threshold value based on the noise component detected by the noise component detection unit, and only the shift amount is calculated from an initial value of a preset voltage threshold value. The liquid ejecting apparatus according to claim 4, wherein the liquid ejecting apparatus is shifted. A pressure chamber for storing a liquid to be discharged from a nozzle, a pressure generating element for applying a discharging force to the liquid stored in the pressure chamber, and a pressure detecting element for sending a detection signal corresponding to the pressure in the pressure chamber. A pressure detection method for a liquid discharge apparatus having a liquid discharge head comprising:
A drive signal wiring for transmitting the drive signal from a drive signal generating unit for generating a drive signal to be applied to the pressure generating element to the pressure generating element ; and a detection signal obtained from the pressure detecting element from the pressure detecting element. Between the detection signal wirings that are at least partially disposed at a position where noise due to a change in the drive signal is superimposed on the transmitted detection signal. of the capacitance value C of the wiring capacitance, the detection signal the detection signal before Ki圧 force detector is represented by the product C × R of the resistance value R of the input resistor provided in an input unit that is input A pressure detection method, wherein the decay time of the noise component is set so that the decay time of the superimposed noise component is longer than a resonance period of the pressure chamber.   Detecting the noise component, storing the noise component, obtaining a shift value of a threshold value used when obtaining a period of the detection signal from the noise component, and based on the threshold value shifted by the shift value The pressure detection method according to claim 6, wherein a period of the detection signal is obtained, and a pressure abnormality in the pressure chamber is determined based on the period of the detection signal.

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