JP2018008451A - Liquid discharge unit, liquid discharge device, drive voltage correction method, and drive voltage correction program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a positional deviation of a droplet due to aged deterioration of characteristics in a liquid discharge unit. A liquid discharge unit that discharges liquid from a nozzle opening that communicates with a pressure chamber due to fluctuations in a piezoelectric element, a drive voltage application unit that applies a drive voltage to a piezoelectric element that applies pressure to the pressure chamber, and a liquid discharge The liquid arrival detection unit that is arranged first and detects the liquid arrival timing, the distance measurement unit that measures the distance from the nozzle opening to the liquid discharge destination, and the time until the liquid reaches the discharge destination from the nozzle opening. A time calculation unit to calculate, a speed calculation unit to calculate the velocity of the liquid based on the distance and time, a correction value calculation unit to calculate a correction value of the drive voltage based on the calculated velocity, and a correction value And a drive voltage correction unit that corrects the drive voltage. [Selection] Figure 8

Description

  The present invention relates to a liquid discharge unit, a liquid discharge apparatus, a drive voltage correction method, and a drive voltage correction program.

  2. Description of the Related Art Liquid ejecting apparatuses that eject liquid and form images in printers, facsimiles, copiers, and image forming apparatuses that are multi-function machines having a plurality of these functions are known. Such a liquid ejecting apparatus is also called an ink jet recording apparatus. An ink jet recording apparatus is an apparatus that discharges liquid from an ink jet recording head and forms an image of liquid droplets on a recording medium such as paper or OHP.

  As an ink jet recording head mounted on an ink jet recording apparatus, a piezoelectric type using a piezoelectric element as a pressure generating element for pressurizing a liquid in a flow path is known. The piezoelectric type has a configuration in which a diaphragm that forms the wall surface of the flow path is vibrated by a piezoelectric element. By the vibration of the piezoelectric element, the volume in the flow path is changed and the liquid is ejected as droplets.

  When the characteristics deteriorate due to the aging of the ink jet recording head, the performance is inferior to the original characteristics of the ink jet recording head, and the normal operation becomes difficult. For example, changes occur such as a decrease in the liquid discharge speed, an increase in the viscosity of the liquid, and a decrease in the liquid discharge speed. When the liquid discharge speed is slow in the ink jet recording head, the position where the liquid droplet reaches is shifted.

  As a technology to solve the positional deviation of the droplet arrival position, a distance measuring sensor that can detect the distance between the droplet ejection opening and the droplet arrival position in the inkjet recording head is provided, and droplet ejection is performed according to the detected distance. One that adjusts timing is known (see, for example, Patent Document 1). Japanese Patent Laid-Open No. 2004-228561 describes the droplet movement from the droplet movement angle acquired from the position correction information and the distance obtained from the distance and the main scanning speed of the carriage that moves the recording head in the main scanning direction. A technique for preventing thickening is also disclosed.

  When the technique disclosed in Patent Document 1 is used, an image of a test pattern is formed in order to correct a printing misalignment that occurs when the ejection speed of the liquid droplets decreases due to the aging of the ink jet recording head. That is, according to the technique disclosed in Patent Document 1, in order to correct a positional deviation (printing deviation) or a thickened state of a droplet, a test pattern image is formed and recorded. It must be output on a medium (eg paper). Therefore, conventionally, correction for positional deviation and thickened state could not be made unless a recording medium and a large amount of liquid (ink, etc.) were consumed.

  The present invention has been made in view of the above-described problems, and an object thereof is to correct a positional deviation of liquid droplets in a liquid discharge unit.

  In order to solve the above-described problem, an aspect of the present invention is to drive a liquid discharge unit that discharges liquid from a nozzle opening that communicates with a pressure chamber due to fluctuations in the piezoelectric element, and the piezoelectric element that applies pressure to the pressure chamber. A driving voltage applying unit that applies a voltage; a liquid arrival detecting unit that is disposed at the liquid discharge destination and detects the arrival timing of the liquid; and a distance measurement that measures a distance from the nozzle opening to the liquid discharge destination A time calculation unit that calculates time until the liquid reaches the discharge destination from the nozzle opening, and a speed calculation unit that calculates the speed of the liquid based on the distance and the time. A correction value calculation unit that calculates a correction value of the drive voltage based on the speed, and a drive voltage correction unit that corrects the drive voltage based on the correction value.

  According to the present invention, it is possible to correct a positional deviation of a droplet due to aged deterioration of characteristics in a liquid discharge unit.

FIG. 2 is a configuration diagram schematically illustrating configurations of a liquid ejection unit according to an embodiment of the present invention, which is a (a) serial head type and (b) line head type. It is a longitudinal cross-sectional view which shows the structure of the liquid discharge head in this embodiment. It is a graph explaining the tendency of aged deterioration of the liquid discharge unit in this embodiment. It is a graph which illustrates the relationship between the liquid discharge speed and liquid flight distance in this embodiment. It is a figure explaining the platen gap in this embodiment. It is a longitudinal cross-sectional view which shows the adjustment mechanism of the platen gap in this embodiment. It is a figure explaining the droplet detection principle of the electrostatic capacitance sensor in this embodiment. It is a functional block diagram which shows the function structure of the control part with which the liquid discharge apparatus in this embodiment is provided. It is a block diagram explaining the structure of the liquid discharge head in this embodiment. It is a graph which shows the relationship between the platen gap in this embodiment, and a liquid discharge speed. It is a figure which shows the example of correction | amendment of the drive voltage in this embodiment. It is a longitudinal cross-sectional view which shows the structure of the liquid discharge head in another embodiment of this invention. It is a graph which shows the relationship between the viscosity of the liquid and liquid discharge speed in this embodiment. It is a flowchart which shows the flow of the drive voltage correction process in this embodiment. It is a flowchart which shows the detailed flow of the drive voltage correction process in this embodiment. It is a flowchart which shows another detailed flow of the drive voltage correction process in this embodiment. It is a flowchart which shows the detailed flow of the thickening correction process in this embodiment.

<Summary of the present invention>
SUMMARY OF THE INVENTION The present invention is directed to correcting the liquid discharge speed based on the arrival speed when the liquid discharged from the liquid discharge unit reaches the arrival target as a liquid droplet, thereby preventing the arrival position deviation of the liquid droplet. One of them. More specifically, when the liquid discharge unit in the present invention has deteriorated over time, the arrival speed of the droplet is calculated using a potential fluctuation detection sensor arranged at the position where the droplet related to the liquid discharged from the discharge head reaches. To do. Based on the arrival speed, the liquid discharge speed in the liquid discharge unit is controlled by correcting the drive voltage for the discharge head.

<Configuration of liquid ejection device>
First, a liquid discharge apparatus and a liquid discharge unit according to the present invention will be described. FIG. 1A is a plan view schematically showing a configuration of an ink jet recording apparatus 100 which is an embodiment of a liquid ejection apparatus according to the present invention. FIG. 1B is a perspective view schematically showing a configuration of an ink jet recording unit 101 which is an embodiment of the liquid discharge unit.

  An ink jet recording apparatus 100 shown in FIG. 1A includes a serial head type liquid discharge unit. An inkjet recording unit 101 shown in FIG. 1A includes a carriage unit 5, a main scanning motor 8, a gear 9, a pressure roller 10, a timing belt 11, a guide rod 12, a platen 22, an electrostatic device. A capacitance sensor 126.

  The carriage unit 5 is equipped with a liquid ejection mechanism 15 that is a liquid ejection head that ejects liquid such as ink. The liquid discharge mechanism 15 is divided according to the color of the ink. The yellow liquid discharge mechanism 6y discharges yellow (Y) ink, the cyan liquid discharge mechanism 6c discharges cyan (C) ink, and magenta (M) ink. A magenta liquid discharge mechanism 6m and a black liquid discharge mechanism 6k for discharging black (Bk) are included. That is, the inkjet recording unit 101 can be applied to the formation of a color image. The liquid ejection mechanism 15 constitutes a liquid ejection unit.

  The ink jet recording unit 101 is configured such that the driving force of the main scanning motor 8 is transmitted to the carriage unit 5 by the gear 9, the pressure roller 10, and the timing belt 11. The carriage unit 5 is attached to the guide rod 12 so as to be slidable in the main scanning direction. Therefore, the main scanning motor 8 can be reciprocated in the main scanning direction by the driving force. The main scanning direction is the direction indicated by the arrow A in FIG.

  The platen 22 corresponds to a part of a medium transport unit that is used when transporting the medium 16 that is a target to be reached in the liquid droplets ejected from the liquid ejection mechanism 15. Here, the medium 16 is a sheet-like material, and is generally paper (plain paper). The medium 16 according to the present embodiment is not limited to paper (plain paper) but also includes sheet-like members such as coated paper, cardboard, OHP, plastic film, prepreg, and copper foil. The thickness dimension of the medium 16 is very small compared to the distance from the liquid ejection mechanism 15 to the platen 22. Therefore, in the following description, correction of the liquid discharge speed will be described based on the distance (platen gap) between the liquid discharge mechanism 15 and the platen.

  The electrostatic capacity sensor 126 is a sensor whose potential changes when the liquid discharged from the liquid discharge mechanism 15 arrives. The capacitance sensor 126 is disposed outside the platen 22 in the main scanning direction of the platen 22. The position where the capacitance sensor 126 is disposed is a position where the ink jet recording unit 101 moves and stops when the operation starts or stops, and corresponds to the home position 501 of the carriage unit 5. The distance between the liquid ejection mechanism 15 and the platen 22 at the home position 501 is equal to the distance between the liquid ejection mechanism 15 and the capacitance sensor 126.

  The carriage unit 5 is provided with an encoder sensor 41. The encoder sensor 41 can detect the moving position of the carriage unit 5 by reading the encoder sheet 40 provided along the moving direction (main scanning direction) of the carriage unit 5.

  As the carriage unit 5 reciprocates in the main scanning direction, the liquid ejection mechanism 15 ejects ink droplets of an appropriate color toward the medium 16 at an appropriate timing, whereby an image is formed on the medium 16.

  The medium 16 is sent from the paper feed unit to the transport unit by a paper feed motor. Further, the medium 16 sent to the transport unit drives a transport roller by a transport motor, is transported in the direction of arrow B (sub-scanning direction) orthogonal to the main scanning direction, and is transported to the platen 22.

  When the inkjet recording apparatus 100 starts operating, for example, when the operation power is turned on, the carriage unit 5 is placed at the home position 501.

  FIG. 1B is another example of a liquid discharge unit provided in the inkjet recording apparatus 100. The ink jet recording unit 101a shown in FIG. 1B is a line head type.

  As shown in FIG. 1B, the ink jet recording unit 101a includes a liquid ejection mechanism 15a, a drive control board 18, a flat cable 19, and an adjuster plate 25, and these are configured as main components. .

  The drive control board 18 is a rigid board having a circuit for generating a drive waveform for driving a piezoelectric element included in the liquid ejection mechanism 15a and a circuit for generating an image data signal. The flat cable 19 is for electrically connecting the drive control board 18 and the liquid ejection mechanism 15a. The adjuster plate 25 is for fixing and fixing a plurality of liquid ejection mechanisms 15a with high accuracy.

  Similar to the liquid ejection mechanism 15, the liquid ejection mechanism 15 a has a built-in piezoelectric element, drives the piezoelectric element based on a drive waveform and an image data signal transmitted from the drive control board 18, and drops droplets on the medium 16. Is discharged.

  The ink jet recording unit 101a is a line head type in which the liquid ejection mechanisms 15a are arranged in the entire printing width, and color printing is performed by each of the black, cyan, magenta, and yellow line heads. The nozzle surface 122 (see FIG. 7) of each line head is supported with a predetermined gap from the medium 16.

  The ink jet recording unit 101 a discharges ink droplets according to the conveyance speed of the medium 16, thereby forming a color image on the medium 16. In the case of the line head type, the capacitance sensor 126 is provided directly below the liquid ejection mechanism 15a.

  In the following description, the serial head type inkjet recording unit 101 shown in FIG. A line head type is also applicable as an embodiment of the liquid discharge unit according to the present invention.

<Configuration of recording head>
Next, the configuration of the liquid ejection mechanism 15 which is a recording head in the present embodiment will be described with reference to the cross-sectional view of FIG. The liquid discharge mechanism 15 includes a pressure chamber plate 21 that constitutes the individual pressure chamber 20 in which the liquid is held, a nozzle surface 122 disposed at one end of the pressure chamber plate 21, and the other of the pressure chamber plates 21. A diaphragm 24 disposed at the end, a driving piezoelectric element 311, and a support piezoelectric element 312 are provided.

  In the liquid ejection mechanism 15, driving piezoelectric elements 311 and support piezoelectric elements 312 are alternately arranged. The driving piezoelectric element 311 is connected to a position corresponding to the individual pressure chamber 20 constituted by the pressure chamber plate 21 via the diaphragm 24. The support piezoelectric element 312 is connected via a diaphragm 24 to a position corresponding to a partition wall of the individual pressure chamber 20 formed by the meat portion of the pressure chamber plate 21.

  When a driving voltage is applied to the driving piezoelectric element 311, the driving piezoelectric element 311 is deformed according to the driving voltage. The driving force due to this deformation is transmitted to the individual pressure chamber 20 via the diaphragm 24. As a result, the liquid held in the individual pressure chamber 20 is discharged as droplets from the nozzle 123 (nozzle opening) communicating with the individual pressure chamber 20. Accordingly, the liquid ejection speed is determined by the pressure applied to the individual pressure chamber 20 by the driving piezoelectric element 311 in accordance with the driving voltage.

  In addition, when the piezoelectric element 311 for driving and the piezoelectric element 312 for support | pillar are arrange | positioned alternately, when connecting a piezoelectric element (the driving piezoelectric element 311 and the piezoelectric element 312 for support | pillar) to the diaphragm 24, it is. Even if the position shift occurs, the characteristic variation is less likely to occur. This stabilizes the ejection characteristics of the liquid ejection mechanism 15.

<Aging deterioration of the liquid discharge mechanism 15>
Next, an example of the secular change that occurs in the liquid ejection mechanism 15 will be described with reference to FIG. The graph shown in FIG. 3 shows an example of the secular change of the liquid discharge speed Vj in the liquid discharge mechanism 15. As shown in FIG. 3, when the liquid discharge mechanism 15 is used for many years, for example, the adhesive used for joining the flow path unit and the actuator of the liquid discharge mechanism 15 deteriorates. Due to such deterioration, the structure of the actuator joint changes, and the capacitance of the piezoelectric element changes. When the capacitance changes, the load capacity of the liquid discharge mechanism 15 changes, which affects the droplet discharge characteristics (droplet discharge speed).

  For example, when the capacitance increases due to aging of the liquid discharge mechanism 15, the drive waveform for driving the liquid discharge mechanism 15 is lost. When the driving waveform is rounded, the liquid discharge speed Vj in the liquid discharge mechanism 15 decreases, so that the liquid discharge speed Vj decreases with time as shown in FIG. The liquid discharge speed Vj is an important factor for causing the liquid droplets to reach an appropriate position with respect to the medium 16 that is a recording sheet. Accordingly, when the liquid discharge speed Vj is slowed, the position of the droplet reaching the medium 16 is shifted. When the arrival position of the liquid droplet is shifted, the image formed on the medium 16 is disturbed.

<Description of Liquid Discharge Speed Vj>
Next, the relationship between the liquid discharge speed Vj in the liquid discharge mechanism 15 and the flight distance until the discharged liquid reaches the arrival position will be described. As shown in FIG. 4, the liquid discharged from the liquid discharge mechanism 15 reaches the reaching position while receiving air resistance. When this reaching position is the platen 22, the flight distance becomes longer as the platen gap, which is the distance from the nozzle surface 122 to the platen 22, becomes longer. Therefore, the longer the platen gap, the lower the arrival speed Va at the arrival position even if the liquid discharge speed Vj from the nozzle surface 122 is the same.

  As shown in FIG. 4A, when the nozzle surface 122 is at the position where the platen gap is L1, the arrival speed Va of the liquid discharged from the liquid discharge mechanism 15 is defined as the arrival speed Va1. Further, as shown in FIG. 4B, when the platen gap is at the position where the platen gap is L2, the arrival speed Va of the liquid ejected from the liquid ejection mechanism 15 is defined as the arrival speed Va2. Here, if L1 <L2 (L1 is shorter than L2), the reaching speed Va1> the reaching speed Va2 is established. That is, the arrival speed Va2 is slower than the arrival speed Va1 due to air resistance.

<Platen gap>
Here, the platen gap will be described in more detail. FIG. 5 is a graph for explaining the platen gap of the platen 22 in the main scanning direction. As shown in FIG. 5, the value of the platen gap is not constant in the main scanning direction due to component variations of the platen 22, assembly variations of the platen 22, and the like. As described with reference to FIG. 4, the platen gap corresponds to the flight distance of the liquid. Therefore, if the platen gap is not constant, the arrival speed at the platen 22 is not constant in the main scanning direction due to the influence of air resistance. In the case of the serial head type liquid ejection mechanism 15, the speed of the reciprocating movement of the carriage unit 5 in the main scanning direction is kept constant. When liquid is ejected during this reciprocation, the platen gap varies depending on the position of the liquid ejection mechanism 15 in the main scanning direction, so that the liquid arrival speed varies. As a result, the position where the liquid reaches the platen 22 (or the medium 16) is shifted.

<Gap adjustment mechanism>
Next, a gap adjusting mechanism that can adjust the platen gap will be described. FIG. 6 is a view of a longitudinal section of the gap adjusting mechanism as viewed from the right. The gap adjusting mechanism includes a reference shaft member 71, a slave reference shaft member 75, and an intermediate member 74. The intermediate member 74 is a member for raising and lowering between the reference shaft member 71 and the slave reference shaft member 75. The reference shaft member 71 and the intermediate member 74 are in contact with each other so that the reference shaft member 71 and the intermediate member 74 are in contact with each other. Two push-up surfaces are provided on the upper portion of the intermediate member 74, and the push-up surfaces are brought into contact with the reference shaft member 71.

  When the raising / lowering cam member 112 fixed to the secondary reference shaft member 75 is rotated, the intermediate member 74 is thereby lifted. When the intermediate member 74 is lifted, the reference shaft member 71 is lifted by the intermediate member 74, so that the platen gap is changed by raising the carriage unit 5. The elevating cam member 112 is an eccentric cam and is elliptical in FIG. 6, but may have other cross-sectional shapes.

  The contact surface 54 with the slave reference shaft member 75 in the carriage portion 5 has a width in the height direction, and the reference shaft member 71 and the contact surface 54 are in contact with each other even when the carriage portion 5 is raised. The state is to be kept.

  The drive source for rotating the secondary reference shaft member 75 and the drive source for rotating the elevating cam member 112 are not mounted on the carriage unit 5 but are arranged on the main body side and drive the carriage unit 5 at a predetermined position. The secondary reference shaft member 75 is connected and rotated.

  The carriage unit 5 includes an optical distance measuring sensor 121. The distance measuring sensor 121 is disposed in a position parallel to the main scanning direction of the carriage unit 5 and facing the platen 22. The platen gap can be measured using the distance measuring sensor 121 while moving the carriage unit 5 in the main scanning direction. The platen gap information is generated by associating the measurement value of the distance measuring sensor 121 with the position of the carriage unit 5 in the main scanning direction, and stored in the control unit 300 (see FIG. 8) in advance. The distance measuring sensor 121 and a drive voltage correction program to be described later correspond to a “ranging unit” in the present embodiment.

<Capacitance sensor>
Next, the principle of droplet detection in the capacitance sensor 126 will be described with reference to FIG. As shown in FIG. 7A, the electrode plate 124 of the capacitance sensor 126 is disposed at a position facing the nozzle 123 provided on the nozzle surface 122 of the liquid ejection mechanism 15. Therefore, the electrode plate 124 corresponds to the “ejection destination” in the present embodiment. The capacitance sensor 126 is disposed at the home position 501 of the carriage unit 5 (see FIG. 1).

  Here, as shown in FIG. 7B, when a high voltage is applied to the electrode plate 124, a potential difference is generated between the electrode plate 124 and the liquid ejection mechanism 15. Since the potential of the electrode plate 124 is higher than the potential of the liquid discharge mechanism 15 at this time, a positive charge is generated on the electrode plate 124 and a negative charge is generated on the nozzle surface 122 of the liquid discharge mechanism 15.

  As shown in FIG. 7C, when the droplet 127 is ejected in a state where a high voltage is applied to the electrode plate 124, the droplet 127 is charged to the surface charge (minus) of the nozzle surface 122 of the liquid ejection mechanism 15. Moving toward the electrode plate 124. When the negatively charged droplet 127 approaches the electrode plate 124, the negative charge of the droplet 127 and the positive charge of the electrode plate 124 cancel each other.

  As a result, as shown in FIG. 7D, the positive charge of the electrode plate 124 is reduced by the amount of the negatively charged droplet 127 attached to the positively charged electrode plate 124. Therefore, as shown in FIG. 7E, the high voltage applied to the electrode plate 124 slightly changes in an attempt to replenish the positive charge that has been canceled out and reduced.

  In the control unit 300 (see FIG. 8) provided in the ink jet recording unit 101, a time when the potential of the electrode plate 124 slightly changes (arrival timing) and a time when the liquid ejection mechanism 15 ejects the droplet 127 (ejection) The difference from (timing) is calculated. Thereby, the moving time of the droplet 127 can be calculated. If the movement time of the droplet 127 can be calculated, the platen gap that is the flight distance of the droplet 127 is known in advance. Therefore, if the flight distance is divided by the movement time, the arrival speed of the droplet 127 to the electrode plate 124 is calculated. Is done. Since the distance from the nozzle surface 122 of the liquid ejection mechanism 15 to the electrode plate 124 and the distance from the nozzle surface 122 of the liquid ejection mechanism 15 to the platen 22 are the same distance, the arrival speed of the droplet 127 to the electrode plate 124 is The arrival speed of the droplet 127 with respect to the platen 22 is the same. Therefore, the ejection speed of the droplet 127 from the liquid ejection mechanism 15 to the platen 22 can be corrected based on the speed at which the droplet 127 reaches the electrode plate 124.

<Control block>
Next, a control system of the inkjet recording apparatus 100 according to the present embodiment will be described with reference to the drawings. As shown in FIG. 8, the ink jet recording apparatus 100 includes a control unit 300 and functional blocks whose operations are controlled by the control unit 300.

  The control unit 300 includes a CPU 301, a main control unit 310, an external I / F 319, a head drive control unit 322, a main scan drive unit 313, a sub-scan drive unit 314, a paper feed drive unit 315, and a paper discharge. A drive unit 316, a scanner control unit 317, and a capacitance sensor control unit 318 are provided.

  The main control unit 310 controls the overall operation of the inkjet recording apparatus 100, calculates the liquid discharge speed Vj based on the droplet arrival speed, corrects the waveform in the drive voltage that drives the liquid discharge mechanism 15, and the liquid to be discharged. Control related to prevention of thickening of the skin.

  The main control unit 310 includes a CPU (Central Processing Unit) 301, a ROM (Read Only Memory) 302, a RAM (Random Access Memory) 303, an NVRAM (Non-Volatile Memory) 304, and an ASIC (Application Specific 305). And FPGA (Field-Problemable Gate Array) 306.

  The ROM 302 stores programs executed by the CPU 301 and other fixed data. The RAM 303 temporarily stores image data and the like. Since the NVRAM 304 is a non-volatile storage unit, it retains platen gap information, liquid discharge speed data for each platen gap, and the like while the operation power supply of the inkjet recording apparatus 100 is shut off. The ASIC 305 is a processing unit dedicated to image processing that performs various signal processing, rearrangement, and the like on image data. The FPGA 306 is a processing unit that processes input / output signals for controlling other devices as a whole.

  The external I / F 319 is an interface for transmitting and receiving data and signals between the host side and the main control unit 310. The head drive control unit 322 includes a head driver configured by an ASIC for head data generation array conversion for driving and controlling the liquid ejection mechanism 15. The main scanning drive unit 313 is a motor driver and controls driving of the main scanning motor 8 that moves and scans the carriage unit 5. The sub scanning drive unit 314 is a motor driver and controls the driving of the sub scanning motor 131. The paper feed drive unit 315 controls the drive of the paper feed motor 49. The paper discharge driving unit 316 controls driving of each roller of the paper discharge unit 7. The scanner control unit 317 controls the image reading unit 13.

  The head drive control unit 322 corresponds to the “drive voltage application unit” in the present embodiment. A drive voltage correction program and a head drive control unit 322, which will be described later, correspond to a “drive voltage correction unit”, a “correction value calculation unit”, and a “thickening correction unit” in the present embodiment. The head drive control unit 322, the capacitance sensor control unit 318, the capacitance sensor 126, and a drive voltage correction program described later correspond to a “speed calculation unit” in the present embodiment.

  The main scanning drive unit 313, the main scanning motor 8, the gear 9, the pressure roller 10, and the timing belt 11 correspond to the “carriage driving unit” in the present embodiment.

  The capacitance sensor control unit 318 supplies a high voltage power source to the capacitance sensor 126, and controls a minute change in the high voltage voltage such as amplification. The capacitance sensor control unit 318 and the capacitance sensor 126 correspond to the “liquid arrival detection unit” in the present embodiment. Further, the capacitance sensor control unit 318 and a drive voltage correction program described later correspond to a “time calculation unit” in the present embodiment.

  In addition, it drives a recovery drive unit for driving a maintenance recovery motor that drives a maintenance recovery mechanism that eliminates nozzle clogging at the home position, a solenoid drive unit that drives various solenoids, and electromagnetic cracks. A clutch drive unit.

  Note that a detection signal from the distance measuring sensor 121 that detects the platen gap is also input to the main control unit 310.

  Further, the main control unit 310 captures necessary key inputs and outputs display information with the operation / display unit 327 including various keys such as a numeric keypad and print start key provided in the inkjet recording apparatus 100 and various displays. Do. The main control unit 310 receives an output signal from the photo sensor that constitutes the encoder sensor 41 that detects the position of the carriage unit 5 described above, and drives the main scanning motor 8 via the main scanning drive unit 313. And the carriage unit 5 is reciprocated in the main scanning direction.

  The main control unit 310 also receives an output signal (pulse) from a photosensor (encoder sensor) constituting a rotary encoder that detects the amount of sub-scanning movement. The main control unit 310 controls the driving of the sub-scanning motor 131 via the sub-scanning driving unit 314 based on this output signal, thereby moving the recording medium via the conveyance roller.

  Further, the main control unit 310 calculates the difference between the time when the liquid is discharged from the liquid discharge mechanism 15 and the time when the voltage fluctuation is detected in the capacitance sensor control unit 318, and the platen gap information acquired by the distance measuring sensor 121. Is used to calculate the liquid discharge speed Vj.

<Head configuration>
Next, the configuration of the liquid ejection mechanism 15 in the inkjet recording apparatus 100 will be described with reference to FIG. FIG. 9 is a view of the liquid discharge mechanism 15 as viewed from the nozzle 123 side. As shown in FIG. 9, in the liquid ejection mechanism 15, the nozzles 123 are arranged in a plurality of rows, and the plurality of nozzles 123 are arranged in one row. For example, 192 nozzles 123 are arranged in a straight line. That is, a plurality of nozzles 123 are arranged. Note that the liquid ejection mechanism 15 illustrated in FIG. 9 has a two-row configuration.

  In the present embodiment, a liquid ejection unit and a drive voltage application unit configured by the liquid ejection mechanism 15 and the head drive control unit 322, a liquid arrival detection unit configured by the capacitance sensor 126 and the capacitance sensor control unit 318, a measurement A liquid discharge unit is configured by the distance measuring unit configured by the distance sensor 121 and the main control unit 310, and the time calculation unit, speed calculation unit, correction value calculation unit, and drive voltage correction unit configured by the drive voltage correction program. Is done.

  In this embodiment, the carriage unit 5, the main scanning driving unit 313, the main scanning motor 8, the gear 9, the pressure roller 10, and the timing belt 11, the carriage driving unit, and the medium conveying unit including the platen 22. These and the liquid discharge unit constitute a liquid discharge apparatus.

<Embodiment of Driving Voltage Correction Method>
Next, correction of the drive voltage waveform (drive waveform) in the liquid ejection mechanism 15 will be described. FIG. 10 is a graph illustrating the relationship of the liquid ejection speed Vj with respect to the platen gap, with the horizontal axis being the platen gap and the vertical axis being the liquid ejection speed Vj. In FIG. 10, when the distance of the platen gap is L1, the speed when the droplet 127 reaches is VjL1. Further, when the distance of the platen gap is L2, the speed when the droplet 127 reaches is VjL2. In FIG. 10, since distance L1 <distance L2, speed VjL1> speed VjL2. As shown in FIG. 10, the changes in the speed VjL1 and the speed VjL2 with respect to the platen gap are linear.

  Here, it is assumed that the liquid discharge speed Vj at the distance L1 when the characteristics of the liquid discharge mechanism 15 deteriorate over time is the speed VjL1 ', and the liquid discharge speed Vj at the distance L2 is the speed VjL2'. As shown in FIG. 10, when the characteristics of the liquid discharge mechanism 15 deteriorate with time, the speed VjL1 decreases to the speed VjL1 'and the speed VjL2 decreases to the speed VjL2' due to the deterioration over time. Hereinafter, a method for correcting the waveform of the drive voltage for the liquid discharge mechanism 15 (drive voltage correction method) will be described in order to correct the decrease in the liquid discharge speed Vj due to deterioration over time.

  FIG. 14 is a flowchart illustrating an embodiment of the drive voltage correction method according to the present embodiment. The drive voltage correction method described below is executed in a drive voltage correction program stored in the ROM 302 in the main control unit 310. As a premise, it is assumed that the characteristics of the liquid ejection mechanism 15 in a normal state before the characteristics of the inkjet recording apparatus 100 change due to aging are measured in advance and stored in the NVRAM 304.

  First, a determination process for determining whether or not a drive waveform correction process is necessary is executed by detecting whether or not a positional deviation has occurred at the position where the droplet 127 reaches the medium 16 (S1401). If it is determined that a positional deviation or the like has occurred and a correction process is necessary, the process proceeds to the next process (S1401: YES). If it is determined that correction of the drive waveform is unnecessary, such as no positional deviation has occurred, the processing of the drive voltage correction program is terminated (S1401: NO). As a determination method of whether or not correction is necessary in the determination process, for example, the operation time of the inkjet recording apparatus 100 is accumulated, and it is estimated that a positional deviation occurs when the accumulated operation time exceeds a predetermined reference value (threshold value). And the operation timing. Further, when the number of times of printing in the inkjet recording apparatus 100 exceeds a predetermined reference value, it is estimated that a positional deviation occurs.

  Note that the determination conditions used in the determination process (S1401) are not limited to those based on the cumulative operation time as described above. For example, when it is detected that the ink jet recording apparatus 100 is turned on, the following correction is necessary. You may transfer to a process (S1401: YES). Alternatively, when the process (printing process or the like) in the inkjet recording apparatus 100 is started or when the process (printing process or the like) ends, the process may be shifted to the next process (S1401: YES).

  Therefore, the execution timing of the drive voltage correction method may be selected from the optimal timing that the user wants to correct.

  Next, drive voltage correction processing (S1402) is executed. Details of the drive voltage correction process (S1402) will be described later. Next, a viscosity correction process (S1403) is performed. When the viscosity correction process (S1403) ends, the process of the drive voltage correction program ends. Details of the viscosity correction processing (S1403) will be described later.

<Details of Drive Voltage Correction Process 1>
Details of the drive voltage correction process (S1402) will be described step by step with reference to the flowchart of FIG. First, the carriage unit 5 is moved to the home position 501 (S1501). The movement of the carriage unit 5 to the home position 501 is detected by the encoder sensor 41 reading the encoder sheet 40. As a result, the nozzle 123 moves above the capacitance sensor 126 (see FIG. 1).

  After the nozzle 123 moves to the capacitance sensor 126, a drive waveform (drive voltage waveform) is applied to the liquid ejection mechanism 15 to eject the droplet 127 from the nozzle 123. The droplet 127 reaches the electrode plate 124 of the capacitance sensor 126. The difference between the time when the potential fluctuation in the electrode plate 124 occurs and the time when the drive waveform is applied to the liquid ejection mechanism 15 is calculated, and the speed VjL1 is based on the difference time and the platen gap information stored in the NVRAM 304. 'Is calculated (S1502).

  Next, a speed variation rate is calculated using the calculated speed VjL1 'and the speed VjL1 stored in the NVRAM 304 (S1503). The speed fluctuation rate refers to the rate of decrease of the speed VjL1 'with respect to the speed VjL1. This speed fluctuation rate corresponds to the “correction value” in the present embodiment.

  Next, as shown in FIG. 11, the drive waveform magnification correction is executed based on the speed fluctuation rate (S1504). It is assumed that the drive waveform shown in FIG. Here, when the speed fluctuation rate is 83%, the drive waveform is corrected to 1.2 times as shown in FIG. Here, when the magnification correction is performed, the intermediate potential is maintained, and other potentials are changed using a magnification corresponding to the speed fluctuation rate. As a result, the corrected drive waveform (see FIG. 11B) can be calculated by multiplying the whole of the intermediate potential around the intermediate potential without changing the intermediate potential.

<Details of drive voltage correction process 2>
Here, another embodiment of the drive voltage correction process (S1402) will be described with reference to the flowchart of FIG. As already described with reference to FIG. 4, when the platen gap widens (when the flight distance of the droplet 127 increases), the droplet 127 is easily affected by air resistance, so the liquid discharge speed Vj is the same. However, the speed at which the medium 16 is reached (arrival speed) is slow. When the arrival speed becomes slow, the positional deviation of the droplet 127 occurs.

  As a premise, the speed VjL1 and the speed VjL2 before the aged deterioration of the distances L1 and L2 which are platen gaps are stored in the NVRAM in advance.

  First, the carriage unit 5 is moved to the home position 501 (S1601). When the carriage unit 5 moves to the home position 501 and the nozzle 123 moves above the capacitance sensor 126, the droplet 127 is ejected from the nozzle 123 to calculate the velocity VjL1 ′ and velocity VjL2 ′ (S1602). .

  Next, using the calculated speed VjL1 ′ and speed VjL2 ′ and the speed VjL1 and speed VjL2 stored in the NVRAM 304, the speed fluctuation rate at the distance L1 and the speed fluctuation rate at the distance L2 are calculated (S1603). .

  Next, magnification correction of the drive waveform in each platen gap is executed based on each speed variation rate (S1604). As described above, according to the drive voltage correction method of the present embodiment, correction corresponding to each of the plurality of platen gaps can be performed on the drive waveform.

  Note that the effect of air resistance on the droplet 127 is inversely proportional to the distance. As shown in FIG. 10, changes in the speed VjL1 'corresponding to the distance L1 and the speed VjL2' corresponding to the distance L2 are linear.

  Accordingly, the speed VjL1 ′ and the speed VjL2 ′ are calculated by using the distance L1 and the distance L2 so that one is the maximum platen gap and the other is the minimum platen gap, and a linear equation based on these is calculated. To do. From this linear equation, the velocity VjLn ′ corresponding to each platen gap can be calculated. Therefore, the liquid arrival speed Vi corresponding to the two points can also be calculated.

  That is, the liquid arrival speed Vi corresponding to the maximum distance L1 and the minimum distance L2 can be calculated, and the speed fluctuation rate with respect to the entire platen gap can be calculated. It should be noted that any two points may be used without limiting the platen gap used for calculating the linear equation to the two points of the minimum value and the maximum value.

  By using the drive voltage correction process (S1402) described above, the drive waveform can be corrected and the positional deviation of the droplet 127 can be corrected without consuming the medium 16.

  Also, when correction is performed for each platen gap, the correction time can be shortened by calculating Vi between any two points or between the minimum / maximum two points.

<Details of thickening correction processing>
Next, details of the thickening correction process (S1403) will be described. First, the correlation between the change in liquid discharge speed over time and the liquid viscosity will be described. FIG. 13 is a graph in which the viscosity of the liquid is correlated in the relationship between the liquid discharge speed Vj and the elapsed time. As shown in FIG. 13, the liquid discharge speed Vj1 that is the lower limit of the normal state 1301 and the liquid discharge speed Vj2 that is the upper limit are stored in the NVRAM 304 in advance.

  When the liquid viscosity increases with time and reaches a thickened state 1302, the liquid discharge speed Vj decreases. For example, when the nozzle 123 in the liquid ejection mechanism 15 is dried over time, the viscosity of the liquid increases. Therefore, a decrease in the liquid discharge speed Vj can be determined by comparing the liquid arrival speed corresponding to the liquid discharge speed Vj and the liquid arrival speed corresponding to the liquid discharge speed Vj1, thereby increasing the viscosity of the liquid. Can be detected.

  On the other hand, when the viscosity of the liquid decreases with time and becomes a reduced viscosity state 1303, the liquid discharge speed Vj increases. For example, when the temperature around the liquid ejection mechanism 15 is high, when the driver IC of the liquid ejection mechanism 15 generates heat due to continuous liquid ejection and the temperature of the liquid ejection mechanism 15 is high, the viscosity of the liquid is low. Thus, the liquid discharge speed Vj increases. Therefore, by comparing the liquid arrival speed corresponding to the liquid discharge speed Vj and the liquid arrival speed corresponding to the liquid discharge speed Vj2, it is possible to determine an increase in the liquid discharge speed Vj, thereby reducing the viscosity of the liquid. Can be detected. In any case, the normal state 1301 is departed with the passage of time.

  Therefore, the viscosity correction process (S1403) is executed. FIG. 17 is a flowchart showing a detailed processing flow of the thickening correction processing (S1403). In the thickening correction process (S1403), first, it is assumed that the speed VjL1 before the aging deterioration of the distance L1 and the speed VjL2 of the distance L2 before the aging deterioration are stored in the NVRAM 304 in advance. Further, it is assumed that the distance L1 is the maximum value of the platen gap and the distance L2 is the minimum value of the platen gap.

  The speed VjL1 'calculated in the drive voltage correction process (S1402) is compared with the speed VjL1 and the speed VjL2 stored in the NVRAM 304 (S1701).

  If the speed VjL1 'is smaller than the speed VjL1, a thickening correction process is executed (S1702). In the thickening correction processing, the number of times the meniscus of the nozzle surface 122 is slightly vibrated is increased so that the viscosity of the liquid is increased and the speed VjL1 'returns to the normal state 1301. The number of microvibrations of the meniscus on the nozzle surface 122 corresponds to the number of times of the minute driving voltage applied to the liquid ejection mechanism 15 by the head drive controller 322.

  If the speed VjL1 'is greater than the speed VjL1, a viscosity reduction process is executed (S1703). In the thinning correction process, the number of times that the meniscus of the nozzle surface 122 is finely vibrated is decreased so that the viscosity of the liquid is decreased and the speed VjL1 'returns to the normal state 1301.

  As described above, the viscosity state of the liquid discharged from the liquid discharge mechanism 15 is detected by comparing the reference speed with the speed calculated based on the measurement. The number of slight vibrations of the meniscus is corrected with respect to the detected viscosity state of the liquid. Thereby, it is possible to correct the positional deviation of the vortex droplet 127 caused by the change of the liquid over time.

  Further, according to the liquid ejection mechanism 15 in the present embodiment, the droplet 127 is ejected immediately above the capacitance sensor 126, and based on this, a correction process such as a drive waveform is performed. Accordingly, correction is not performed while moving the carriage unit 5 in the main scanning direction. Therefore, the correction of the ejection speed of the droplet 127 and the correction of the viscosity of the liquid can be executed without being affected by the bending of the guide rod 12 that instructs the carriage unit 5 or the sliding property of the timing belt 11.

<Embodiment 2>
Next, another embodiment of the liquid ejection apparatus according to the present invention will be described. FIG. 12 is a cross-sectional view of the ejection head for explaining the present embodiment. As shown in FIG. 12, the nozzle 123b located at the end of the nozzle surface 122 of the ejection head has the support piezoelectric element 312 only on one side. Therefore, as compared with 123a having the supporting piezoelectric elements 312 on both sides, the influence of the adjacent piezoelectric elements is only received from one side when the droplet 127 is ejected. As a result, a predetermined discharge speed may not be achieved.

  Therefore, when ejecting the droplet 127, by selecting the nozzles 123a other than both ends, it is possible to suppress printing misalignment in a state where the influence of the adjacent piezoelectric element is taken into consideration. Further, after obtaining the liquid arrival speed of the nozzle 123a, the liquid arrival speed of the nozzle 123b may be obtained, and based on this, the nozzle 123b to be ejected may be selected.

  Even with this method, it is possible to suppress printing misalignment in a state where the influence of adjacent piezoelectric elements is taken into consideration. In addition to the above reasons, all nozzles may not always achieve the same discharge speed due to variations in the nozzle diameter of each nozzle 123 and the meniscus state of each nozzle 123. Therefore, when ejecting droplets from any nozzle 123, the liquid arrival speed corresponding to the liquid ejection speed from the first nozzle to the 192nd nozzle is calculated, and the average speed is used to minimize variations in the nozzle 123. It is possible to suppress printing misalignment.

DESCRIPTION OF SYMBOLS 5 Carriage part 10 Pressure roller 11 Timing belt 12 Guide rod 15 Liquid discharge mechanism 16 Medium 20 Individual pressure chamber 100 Inkjet recording device 101 Inkjet recording unit 121 Ranging sensor 122 Nozzle surface 123 Nozzle 124 Electrode plate 126 Electrostatic capacity sensor 127 Liquid Drop 300 Control unit 301 CPU
302 ROM
303 RAM
304 NVRAM
305 ASIC
306 FPGA
310 Main Control Unit 311 Driving Piezoelectric Element 312 Supporting Piezoelectric Element 313 Main Scanning Driving Unit 314 Sub-scanning Driving Unit 315 Paper Feeding Driving Unit 316 Paper Discharge Driving Unit 317 Scanner Control Unit 318 Capacitance Sensor Control Unit 319 External I / F
322 Head drive control unit 327 Display unit 501 Home position

JP 2004-314361 A

Claims (9)

A liquid ejecting section for ejecting liquid from a nozzle opening communicating with the pressure chamber due to fluctuations in the piezoelectric element;
A driving voltage applying unit that applies a driving voltage to the piezoelectric element that applies pressure to the pressure chamber;
A liquid arrival detection unit that is disposed at the liquid discharge destination and detects the arrival timing of the liquid;
A distance measuring unit for measuring a distance from the nozzle opening to the discharge destination;
A time calculation unit for calculating a time until the liquid reaches the discharge destination from the nozzle opening;
A speed calculator that calculates the speed of the liquid based on the distance and the time;
A correction value calculation unit that calculates a correction value of the drive voltage based on the calculated speed;
A drive voltage correction unit that corrects the drive voltage based on the correction value;
A liquid discharge unit comprising: A storage unit for storing the distance measured in the ranging unit;
The liquid discharge unit discharges the liquid while moving,
The distance measuring unit measures a plurality of the distances to the discharge destination while moving in parallel with a movement direction with the liquid discharge unit,
The storage unit stores a plurality of the distances measured by the ranging unit,
The correction value calculation unit calculates the correction value according to the position of the nozzle opening based on the plurality of speeds calculated based on the plurality of distances.
The liquid discharge unit according to claim 1. The drive voltage correction unit calculates a linear equation that linearly connects any two velocities included in the plurality of velocities, and calculates the correction value corresponding to an arbitrary position based on the linear equation.
The liquid discharge unit according to claim 2. The two arbitrary speeds are the speed corresponding to the position where the distance is the maximum and the speed corresponding to the position where the distance is the minimum.
The liquid discharge unit according to claim 3. Based on the calculated speed, the drive voltage application unit includes a thickening correction unit that controls the number of times the minute drive voltage is applied to the piezoelectric element.
The liquid discharge unit according to claim 1, wherein the liquid discharge unit is a liquid discharge unit. A plurality of the pressure chambers provided in the liquid discharge part are arranged linearly,
The drive voltage application unit applies the drive voltage so that the piezoelectric element to which the drive voltage is applied applies pressure to the pressure chambers at the ends of the array among the plurality of pressure chambers.
The liquid discharge unit according to claim 1, wherein the liquid discharge unit is a liquid discharge unit. A carriage unit for holding the liquid discharge head;
A carriage drive unit for driving the carriage unit in the main scanning direction;
A medium transport unit for transporting a medium in a direction orthogonal to the main scanning direction;
With
The liquid discharge head held by the carriage unit is the liquid discharge unit according to any one of claims 1 to 6.
A liquid discharge apparatus characterized by that. A liquid discharge unit that discharges liquid from a nozzle opening that communicates with the pressure chamber due to fluctuations in the piezoelectric element; a drive voltage application unit that applies a drive voltage to the piezoelectric element that applies pressure to the pressure chamber; and a discharge destination of the liquid A liquid arrival detection unit that detects the arrival timing of the liquid, a distance measurement unit that measures a distance from the nozzle opening to the discharge destination, and until the liquid reaches the discharge destination from the nozzle opening A time calculation unit for calculating the time of the liquid, a speed calculation unit for calculating the speed of the liquid based on the distance and the time, and a correction value for calculating the correction value of the drive voltage based on the calculated speed In a liquid ejection unit comprising: a calculation unit; and a drive voltage correction unit that corrects the drive voltage based on the correction value.
Moving the nozzle opening to the discharge destination at a predetermined operation timing;
Discharging the liquid to the discharge destination;
Calculating a movement time of the liquid based on a difference between the discharge timing of the liquid and the arrival timing of the liquid with respect to the discharge destination;
Calculating the speed based on the travel time and the distance;
Calculating the correction value of the drive voltage based on the speed;
Correcting the drive voltage based on the correction value;
The drive voltage correction method characterized by performing these.   A liquid discharge unit that discharges liquid from a nozzle opening that communicates with the pressure chamber due to fluctuations in the piezoelectric element; a drive voltage application unit that applies a drive voltage to the piezoelectric element that applies pressure to the pressure chamber; and a discharge destination of the liquid The liquid arrival detection unit that detects the arrival timing of the liquid, the distance measurement unit that measures the distance from the nozzle opening to the liquid discharge destination, and the liquid reaches the discharge destination from the nozzle opening A time calculation unit that calculates a time until completion, a speed calculation unit that calculates a speed of the liquid based on the distance and the time, and a correction value of the drive voltage based on the calculated speed. A drive voltage correction program that is executed in a control unit of a liquid ejection unit that includes a correction value calculation unit and a drive voltage correction unit that corrects the drive voltage based on the correction value. Lamb.