JP2010253943A - Liquid discharge apparatus, and apparatus and method for controlling liquid viscosity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control an actual flow rate to be closer to the ideal one by a simple constitution, and to reduced a size and cost of a device. <P>SOLUTION: An ink viscosity controlling apparatus 24 is equipped with: flow passages 110; heaters 58 for heating liquids flowing in the passages 110 at predetermined heating points P; temperature sensors 62 arranged at temperature detecting points Q positioned downstream of the flow passages 110 from the heating points P, and detecting temperatures of the liquids when the liquids heated by the heaters 58 reach the temperature detecting points Q; a flow rate measuring apparatus 22 for measuring flow rates of the liquids flowing in the flow passages 110 by using outputs of the temperature sensors 62: and a heater controlling apparatus 22 for controlling outputs of the heaters 58 so that the measured flow rates measured by the flow rate measuring apparatus 22 become closer to the ideal ones to discharge the liquids from nozzles 68. A method for controlling the liquid viscosity is executed by the ink viscosity controlling apparatus 24. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus, a liquid viscosity control apparatus, and a control method for controlling the viscosity of a liquid ejected from a nozzle.

  For example, an ink jet printer is well known as a liquid ejecting apparatus that ejects liquid from a nozzle. A general ink jet printer includes an ink tank that stores ink, an ejection head having a nozzle that ejects ink, and an ink tube that supplies ink in the ink tank to the ejection head. The discharge head includes a flow path unit having a nozzle and a pressure chamber communicating with the nozzle, and a drive unit having a drive unit that applies discharge pressure to the ink in the pressure chamber, and is applied to the drive unit. Ink is ejected from the nozzles based on the voltage.

  In such an ink jet printer, there is a suitable ink flow rate (that is, an ideal flow rate) that is determined according to “type of ink”, “printing duty”, and the like in order to form a desired image on paper. When the temperature of the ink fluctuates under the environment, the viscosity of the ink also fluctuates, so that it is not easy to stably obtain the ideal flow rate. For example, when a high viscosity ink such as an ultraviolet curable ink is used, it is necessary to reduce the viscosity of the ink by heating the ink in order to stabilize the image quality. In this case, the “print duty” is high. Then, since the cooling of the discharge head is promoted and the temperature of the ink is lowered, there is a problem that the viscosity of the ink is increased and the ink flow rate is undesirably reduced.

  As means for solving this problem, Patent Document 1 discloses an ink jet printer in which the ink flow rate is controlled to be substantially constant by controlling the temperature of the ink in the ejection head within a set range. . This ink jet printer uses the “temperature difference information” relating to the temperature difference between the temperature of the ink in the ejection head and the temperature of the ink supplied to the ejection head, and the “ink amount relating to the ink amount required for recording calculated from the image data. Based on the “information”, “information about the heating temperature” such as “how much the recording head is cooled or heated” is acquired, and the electric power supplied to the heater is controlled based on the “information about the heating temperature” Thus, the ink temperature is controlled within a set range (see paragraph [0022] of Cited Document 1).

JP 2006-334967 A

  In the prior art described in Patent Document 1, although the ink viscosity can be controlled within a certain range by controlling the temperature of the ink, the temperature control of the ink is performed based on “information on the heating temperature”. Therefore, the actual ink flow rate cannot be reflected in the ink viscosity control, and it is still difficult to bring the actual ink flow rate close to the ideal flow rate. In addition, since it is necessary to use at least two heaters in order to obtain “temperature difference information”, there is a problem that the entire apparatus is increased in size and the manufacturing cost of the apparatus is increased.

  The present invention has been made to solve the above-mentioned problems, and the flow rate of the actual liquid can be brought close to the ideal flow rate with a simple configuration, and the size and cost of the apparatus can be reduced. An object of the present invention is to provide a liquid ejection device, a liquid viscosity control device, and a control method.

  In order to solve the above problems, a liquid viscosity control device according to the present invention is a liquid viscosity control device that controls the viscosity of a liquid discharged from a nozzle, and includes a flow path that guides the liquid to the nozzle, A heater that heats the liquid flowing through the flow path at a predetermined heating point, and a temperature detection point located downstream of the flow path from the heating point, and the liquid heated by the heater reaches the temperature detection point A temperature sensor that detects the temperature of the liquid, a flow rate measuring device that measures a flow rate of the liquid flowing through the flow path using an output of the temperature sensor, and a measured flow rate measured by the flow rate measuring device is the A heater control device that controls the output of the heater so as to approach an ideal flow rate for discharging liquid from the nozzle.

  In this configuration, when the liquid viscosity control operation is started, the liquid flowing through the flow path is heated by the heater at the heating point, and when the heated liquid reaches the temperature detection point located downstream from the heating point. The temperature of the liquid is detected by a temperature sensor. Then, the output of the temperature sensor is given to the flow measuring device, and the flow rate of the liquid is measured by the flow measuring device. The flow rate of the liquid can be obtained by, for example, integrating the “liquid flow velocity” and the “cross-sectional area of the flow path”, and the output of the temperature sensor is necessary for calculating the “liquid flow velocity”, for example. It is used to acquire "time information". Then, the flow rate of the measured liquid is fed back to the heater control device, and the output of the heater is controlled by the heater control device so that the measured flow rate approaches the ideal flow rate. That is, the liquid is heated by the heater so that the measured flow rate approaches the ideal flow rate, and thereby the viscosity of the liquid is appropriately controlled. Note that the ideal flow rate is a suitable flow rate determined according to “type of liquid”, “printing duty”, and the like as described above.

  In order to solve the above problems, a liquid ejection apparatus according to the present invention includes a plurality of nozzles that eject liquid, a plurality of pressure chambers individually connected to the plurality of nozzles, and a plurality of pressure chambers. A flow path unit having a manifold communicated in common with each other, a drive unit having a plurality of drive units for individually applying discharge pressure to the liquid in the plurality of pressure chambers, and a liquid supplied to the flow path unit An ink tank containing the ink tank, an ink tube communicating the ink tank and the manifold, and the liquid viscosity control device described above, and at least the ink tube, the manifold, and the plurality of pressure chambers. A flow path for guiding the liquid is configured, and in the manifold, the cross-sectional area of the flow path is expanded toward the downstream side, and the heating point Fine the temperature detection point is located on the upstream side of the manifold.

  In order to solve the above problems, a liquid viscosity control method according to the present invention is a liquid viscosity control method for controlling the viscosity of a liquid discharged from a nozzle provided at an end of a flow path, a) heating the liquid flowing through the flow path by a heater at a predetermined heating point; and (b) the liquid heated at the heating point reaching a temperature detection point located downstream of the flow path from the heating point. A step of detecting by a temperature sensor, (c) a step of measuring the flow rate of the liquid flowing through the flow path using the output of the temperature sensor, and (d) the measured flow rate discharges the liquid from the nozzle. A step of adjusting the degree of heating of the liquid by the heater so as to approach an ideal flow rate.

  The present invention has been made to solve the above problems, and controls the viscosity of the liquid by controlling the output of the heater so that the measured flow rate measured by the flow rate measuring device approaches the ideal flow rate. Therefore, the viscosity control for obtaining the ideal flow rate can be directly performed based on the actual flow rate, and the responsiveness of the viscosity control can be enhanced. In addition, since the "heater that heats the liquid to measure the flow rate" and the "heater that heats the liquid to control the viscosity" are shared, the configuration of the control device can be simplified, The manufacturing cost of the control device can be reduced. Further, since the flow rate of the liquid is measured in the flow path that guides the liquid to the nozzle, the viscosity of the liquid can be appropriately controlled in real time during the operation of discharging the liquid.

1 is a plan view showing an overall configuration of a liquid ejection apparatus (inkjet printer) according to an embodiment. 1 is a block diagram illustrating an electrical configuration of a liquid ejection apparatus (inkjet printer) according to an embodiment. It is sectional drawing which shows the structure of a discharge head. It is a block diagram which shows typically the structure of the control apparatus of the liquid viscosity which concerns on embodiment. It is a flowchart which shows the process of the control method (1st control aspect) of the liquid viscosity which concerns on embodiment. It is a flowchart which shows the process of the 2nd control aspect in a viscosity control process. It is a flowchart which shows the process of the 3rd control aspect in a viscosity control process. It is a flowchart which shows the process of the 4th control aspect in a viscosity control process.

  Hereinafter, a “liquid ejection device”, a “liquid viscosity control device”, and a “liquid viscosity control method” according to a preferred embodiment of the present invention will be described with reference to the drawings. In the following embodiments, the present invention is applied to an “inkjet printer” that ejects ink using an “actuator”. However, the present invention uses pressure when heated by a “heating element”. Other “liquid ejecting devices” such as “inkjet printers” that eject ink, “colored liquid ejecting devices” that eject colored liquids, “conductive liquid ejecting devices” that eject conductive liquids, etc. Applicable. When the present invention is applied to a “colored liquid ejecting apparatus” or “conductive liquid ejecting apparatus” or the like, “ink” used in the following description is read as “colored liquid” or “conductive liquid” or the like. “Color” shall be read as “Liquid type”. Further, “lower” used in the following description means the direction in which ink is ejected, and “upper” means the opposite direction.

[Overall configuration of inkjet printer]
FIG. 1 is a plan view showing an overall configuration of an inkjet printer 10 as a “liquid ejection device”, and FIG. 2 is a block diagram showing an electrical configuration of the inkjet printer 10.

  As shown in FIG. 1, the inkjet printer 10 forms an image on the surface of the paper 12 by ejecting ink as “liquid” onto the paper 12, and includes an ejection head 14 that ejects ink, An ink supply unit 16 for supplying ink to the ejection head 14, a scanning unit 18 for reciprocating scanning of the ejection head 14, a transport device 20 for transporting the paper 12 to the scanning area A of the ejection head 14, and an image forming unit A control device 22 that executes various controls, an ink viscosity control device 24 (FIG. 4) as a “liquid viscosity control device” that controls the viscosity of ink, and a left side of a conveyance region B where the paper 12 is conveyed Flushing foam 39.

<Ink supply unit>
As shown in FIG. 1, the ink supply unit 16 includes four ink tanks 26 a to 26 d that store four color inks of black (BK), yellow (Y), cyan (C), and magenta (M), and discharge. The damper device 28 includes a damper device 28 that reduces pressure fluctuations of ink supplied to the head 14, and four ink tubes 30 a to 30 d that supply the ink in the ink tanks 26 a to 26 d to the damper device 28. 28 is disposed above the ejection head 14, and each of the ink tanks 26 a to 26 d is disposed at a predetermined position below the ejection head 14. When ink is supplied to the ejection head 14, the ink in the ink tanks 26 a to 26 d is supplied to the damper device 28 via the ink tubes 30 a to 30 d, and is provided for each color inside the damper device 28. After the ink pressure fluctuations are alleviated in the damper chambers 28a to 28d (FIG. 4), the ink is supplied to the corresponding ink flow paths N1 to N4 (FIG. 4) of the ejection head 14.

<Scanning part>
As shown in FIG. 1, the scanning unit 18 includes a carriage 32 that holds the ejection head 14 and the damper device 28, two long plate-shaped guide rails 34a and 34b that guide the carriage 32, two pulleys 36a, An endless belt 38 stretched between 36 b and a scanning motor 40 for applying a rotational force to one pulley 36 a are provided, and the carriage 32 is fixed to the endless belt 38. Therefore, when the pulley 36a is rotated by the scanning motor 40, the endless belt 38 is rotated, and the carriage 32 fixed to the endless belt 38 is linearly reciprocated along the guide rails 34a and 34b. In the following description, the direction in which the carriage 32 is scanned is referred to as “main scanning direction X”, and the direction orthogonal to “main scanning direction X” is referred to as “sub-scanning direction Y”.

<Conveyor>
The transport device 20 includes a paper transport path B that transports the paper 12 in the sub-scanning direction Y, an upstream transport roller 42 a disposed upstream of the scanning area A in the paper transport path B, and a scan in the paper transport path B. It has a downstream conveyance roller 42b disposed downstream of the area A, and a conveyance motor 44 that rotates the conveyance rollers 42a and 42b at a predetermined timing. The conveyance motor 44 rotates the conveyance rollers 42a and 42b. As a result, the paper 12 is conveyed to the scanning area A.

<Flushing foam>
As shown in FIG. 1, the flushing foam 39 is arranged on the left side of the transport area B where the paper 12 is transported, and when the ejection head 14 is positioned on the left side of the transport area B by the carriage 32, the flushing foam 39. And the ejection head 14 face each other. The flushing form 39 is for receiving the ink discharged from the nozzle 68 during the flushing operation in which the ink is discharged from the nozzle 68 of the ejection head 14 and the nozzle 68 is recovered before printing. The flushing foam 39 includes a porous absorber, and the absorber holds ink ejected from the nozzles 69.

<Control device>
The control device 22 comprehensively controls the operation of the inkjet printer 10, and as shown in FIG. 2, a CPU (Central Processing Unit) 50 that executes various arithmetic processes, various programs, and ideal flow rates. A ROM (Read Only Memory) 52 for storing information, a RAM (Random Access Memory) 54 for temporarily storing various information, a control circuit 56 for controlling the ejection head 14, and a scanning motor for driving the scanning motor 40 Drive circuit 40a, transport motor drive circuit 44a for driving transport motor 44, a plurality of heater drive circuits 58a for driving a plurality of heaters 58 to be described later, and a plurality of auxiliary heater drives for driving a plurality of auxiliary heaters 60 to be described later Circuit 60a. The discharge head 14, the scanning motor 40, the transport motor 44, the plurality of heaters 58, and the plurality of auxiliary heaters 60 are connected to the control device 22, and a plurality of temperature sensors 62, which will be described later, and various commands are input. An operation panel 64 and an image memory 66 for storing image information are connected. The control operation of the control device 22 will be described later. The control circuit 56 that controls the ejection head 14 so as to perform the flushing operation described above is an example of the “recovery device” in the present invention.

<Discharge head>
FIG. 3 is a cross-sectional view showing the configuration of the ejection head 14 used in the inkjet printer 10. As shown in FIGS. 1 and 3, the ejection head 14 uses four colors of ink of black (BK), yellow (Y), cyan (C), and magenta (M) supplied from the ink tanks 26 a to 26 d. Based on various control signals given from the control device 22, the nozzles 68 are selectively ejected toward the paper 12 from the plurality of nozzles 68. The flow path unit 70, the actuator unit 72, and the flexible wiring board 74 are provided. Have.

  As shown in FIG. 3, the flow path unit 70 is configured by stacking five plates 76 a to 76 e, and “concave portions” or “through holes” formed in these plates 76 a to 76 e are mutually connected. By communicating with each other, a manifold 80 that stores ink, an ink supply port (not shown) that supplies ink to the manifold 80, a plurality of nozzles 68 that discharge ink in the manifold 80 to the outside, a manifold 80, and a plurality of A plurality of individual flow paths 82 communicating with the nozzles 68 are configured for each ink color. Each of the plurality of individual flow paths 82 includes a pressure chamber 84 that communicates with the nozzle 68 individually.

  As shown in FIG. 3, the actuator unit 72 constitutes the upper surface 84 a of the pressure chamber 84 in the flow path unit 70 and selectively applies ejection pressure to the ink existing in each of the plurality of pressure chambers 84. It has a diaphragm 86, a piezoelectric layer 88, and a plurality of individual electrodes 90. The diaphragm 86 is made of a conductive material, and is joined to the upper surface of the flow path unit 70 so as to cover the plurality of pressure chambers 84. The piezoelectric layer 88 is made of a piezoelectric material mainly composed of lead zirconate titanate (PZT), and is polarized in the thickness direction. Each of the plurality of individual electrodes 90 is formed of a conductive material, and is disposed at a position facing the pressure chamber 84 on the surface of the actuator unit 72. Therefore, in the actuator unit 72, a portion of the piezoelectric layer 88 sandwiched between the diaphragm 86 and the individual electrode 90 is a drive unit 92 that is driven by a drive voltage.

  The flexible wiring board 74 includes an insulating sheet portion 94 (FIG. 3) made of a flexible synthetic resin material, and a plurality of connection terminals 96 (see FIG. 3) disposed on the surface of the insulating sheet portion 94 so as to face the individual electrodes 90. 3), a driver IC 98 (FIG. 2) mounted on the surface of the insulating sheet portion 94, and an output wiring 100 that is formed on the surface of the insulating sheet portion 94 and electrically connects the plurality of connection terminals 96 to the driver IC 98. (FIG. 2) and a covering layer 102 (FIG. 3) covering the output wiring 100. An opening for exposing the connection terminal 96 is formed in a portion corresponding to each of the plurality of connection terminals 96 in the covering layer 102, and the surface of the connection terminal 96 is electrically conductive so as to protrude from the opening. The bump 104 is formed. As shown in FIG. 3, the plurality of connection terminals 96 and the individual electrodes 90 corresponding to the connection terminals 96 are electrically connected via bumps 104 formed on the surface of the connection terminal 96. The driver IC 98 shown in FIG. 2 generates a drive voltage for driving the actuator unit 72 based on the control signal output from the control circuit 56 of the control device 22, and is output from the driver IC 98 to the output wiring 100. The drive voltage thus applied is applied to the drive section 92 (FIG. 3) through the connection terminals 96, the bumps 104, and the individual electrodes 90, as shown in FIG. Therefore, when the drive voltage is generated, Joule heat is generated in the driver IC, and the heat is transmitted through the output wiring 100, the connection terminal 96, the bump 104, and the individual electrode to heat the actuator unit 72.

<Ink viscosity control device>
FIG. 4 is a block diagram schematically showing the configuration of the ink viscosity control device 24. The ink viscosity control device 24 controls the viscosity of ink ejected from the plurality of nozzles 68 for each ink color, and is configured for each ink color except for the control device 22. Accordingly, in the following, the configuration of the ink viscosity control device 24 will be described focusing on the configuration for controlling the viscosity of the black ink (BK), and the configuration corresponding to the inks of other colors (Y, C, M). Are omitted by making the reference numbers the same. In FIG. 4, one nozzle 68 and one individual electrode 90 are shown for each ink color, but in the present embodiment, as described above, a plurality of nozzles 68 and a plurality of nozzles are provided for each ink color. Individual electrodes 90 are present.

  As shown in FIG. 4, the ink viscosity control device 24 includes a flow path 110 that guides ink to a plurality of nozzles 68, a heater 58 that heats ink flowing through the flow path 110 at a predetermined heating point P, and a heating point P. Also, a temperature sensor 62 that detects the temperature of the ink at a temperature detection point Q located downstream of the flow path 110, an auxiliary heater 60 that heats the ink ejected from the plurality of nozzles 68 in the ejection head 14, and the output of the heater 58 A control device 22 as a “heater control device” for controlling the flow rate, a control device 22 as a “flow rate measurement device” for measuring the flow rate of ink flowing through the flow path 110, and an “auxiliary heater control” that controls the output of the auxiliary heater 60. The control device 22 as the “device” and the control device as the “discharge control device” for controlling the operation of the plurality of drive units 92 in the actuator unit 72 And a 2. Each of the “heater control device”, “flow rate measuring device”, “auxiliary heater control device”, and “discharge control device” may be realized by a plurality of control devices (not shown) that are independent from each other.

  As shown in FIG. 4, the flow path 110 includes an ink tank 26a, an ink tube 30a, a damper chamber 28a provided in the damper device 28, a manifold 80 provided in the discharge head 14, and a manifold. The plurality of individual flow paths 82 (including the pressure chambers 84) communicating the 80 and the plurality of nozzles 68 are configured. When the channel 110 is viewed from the upstream side of the manifold 80, the channel cross-sectional area is enlarged toward the downstream side in the manifold 80. Accordingly, the heated ink heated by the heater 58 described later is stirred in the manifold 80, and the temperature distribution and viscosity of the heated ink are made uniform. In such a channel 110, the total discharge amount of the plurality of nozzles 68 (FIG. 3) that discharge black ink (BK) is equal to the flow rate of ink flowing between the outlet of the ink tank 26a and the inlet of the manifold 80. Therefore, in this embodiment, the flow rate of ink flowing through the flow path 110 (that is, the volume flowing per unit time) is measured in the region (hereinafter referred to as “flow rate measurement region”) E during this period.

  The heater 58 is provided at a predetermined heating point P located in the flow rate measurement region E, and heats the ink flowing through the flow path 110 at the heating point P. Specifically, the heater 58 is a heating wire, a halogen lamp, or an infrared ray. Etc. are used as the heater 58. The heater 58 is controlled by the control device 22 as a “heater control device”, thereby at least a function of intermittently heating the ink (intermittent heating function) and a function of adjusting the amount of heat for heating the ink (output adjustment function). ), And by exhibiting these functions, “heating of ink for measuring the flow rate of ink” or “heating of ink for controlling the viscosity of ink” is achieved. Is done. That is, “heating for flow rate measurement” and “heating for viscosity control” are performed using one heater 58.

  The temperature sensor 62 is provided at a temperature detection point Q located downstream of the flow path 110 with respect to the heating point P in the flow rate measurement region E, and ink heated by the heater 58 (hereinafter referred to as “heating ink”). When the temperature detection point Q is reached, a detection signal corresponding to the temperature of the heated ink is output. Specifically, a thermistor, a platinum resistance thermometer, a thermocouple, or the like is used as the temperature sensor 62. The output of the temperature sensor 62 is given to the control device 22 as a “flow rate measuring device”, and is used to calculate the ink flow velocity, as will be described later. That is, in the control device 22 as the “flow rate measuring device”, “V = D / T” is set based on the distance D from the heating point P to the temperature detection point Q and the time T during which the heated ink travels the distance D. The ink flow velocity V is obtained by the equation, but the output of the temperature sensor 62 is used to acquire time information for calculating the time T. For example, when the ink is instantaneously heated by the heater 58, a peak is generated in the temperature distribution of the heated ink, and the peak is a mark indicating that the ink is heated. Therefore, if the output of the temperature sensor 62 includes the peak, it means that the heated ink has moved the distance D and has reached the temperature detection point Q. The time t1 when the heater 58 heated the ink and the temperature sensor. The time T (T = t2−t1) can be obtained based on the time t2 when the peak 62 is detected.

  Here, if the heated ink is cooled while moving the distance D, the peak of the temperature distribution cannot be extracted from the output of the temperature sensor 62, and time information for calculating the time T is acquired. Can not do. Further, when the flow velocity of the ink passing through the heating point P is slow, the peak of the temperature distribution in the heated ink is blurred, so that the peak of the temperature distribution detected by the temperature sensor 62 becomes ambiguous, and the calculation accuracy of the time T is high. descend. Therefore, in the present embodiment, the positions of the heating point P and the temperature detection point Q are designed so that the distance D does not become too long, so that the peak of the temperature distribution can be reliably extracted. Further, at least a portion from the heating point P to the temperature detection point Q is formed thinner than the other portions (not shown), and the ink that passes through the heating point P in the portion (hereinafter referred to as “thin diameter portion”) 110a. The peak of the temperature distribution detected by the temperature sensor 62 is made sharper by increasing the flow rate of.

  In the present embodiment, only one temperature sensor 62 is used. However, for example, two temperature sensors 62 may be arranged at a distance D2 downstream from the heater 58. In this case, since the two temperature sensors 62 can detect the peaks of the temperature distribution, the ink is expressed by the equation “S2 = D2 / T2” based on the time difference T2 between the two time points when the peaks are detected. Can be obtained.

  The auxiliary heater 60 is provided on any one or more of the upper surface of the actuator unit 72, the piezoelectric layer 88 constituting the actuator unit 72, the diaphragm 86, and the like. More specifically, each electrode is heated evenly. Specifically, when an electrode is formed on the piezoelectric layer, a pattern is formed at the same time, and the auxiliary heater 60 is used by connecting to a heating wire, a halogen lamp or infrared rays. . The auxiliary heater 60 is configured to exhibit a function (auxiliary heating function) to supplementarily heat ink by being controlled by the control device 22 as an “auxiliary heater control device”. By doing so, the viscosity of the ink (i.e., the ink flow rate) is more quickly controlled.

  The “discharge control device” that controls the operation of the drive unit 92, the “heater control device” that controls the output of the heater 58, the “flow rate measurement device” that measures the flow rate of the ink flowing through the flow path 110, and the output of the auxiliary heater 60. The “auxiliary heater control device” to be controlled is specifically the control device 22 (FIG. 2), and does not have physical characteristics. Therefore, these functions will be described in detail in the following [Operation of Inkjet Printer] and [Control Method of Ink Viscosity].

[Operation of inkjet printer]
When the operation of the inkjet printer 10 is started, as shown in FIGS. 1 and 2, the transport motor 44 is driven by the control device 22, the paper 12 is taken out from the paper tray (not shown), and the ejection head 14 is scanned. It is conveyed to the area A at a predetermined timing. Further, a control signal corresponding to the image information stored in the image memory 66 is given to the driver IC 98 of the ejection head 14 from the control device 22 as the “ejection control device”. Then, in the driver IC 98, a driving voltage for driving the driving unit 92 (FIGS. 3 and 4) of the actuator unit 72 is generated, and the driving voltage output from the driver IC 98 to the output wiring 100 is as shown in FIG. The voltage is applied to the drive unit 92 through the connection terminals 96, the bumps 104 and the individual electrodes 90. The drive unit 92 to which the drive voltage is applied is contracted in a direction perpendicular to the thickness direction (that is, the polarization direction), and thereby the diaphragm 86 is deformed so as to protrude downward. At this time, since the lower surface of the diaphragm 86 constitutes the upper surface 84a of the pressure chamber 84, the lower surface is deformed so as to protrude to the inside of the pressure chamber 84, and the volume of the pressure chamber 84 is reduced. Therefore, the ink existing in the pressure chamber 84 is given a discharge pressure according to the application timing of the drive voltage, and the pressurized ink is discharged from the nozzle 68 onto the surface of the paper 12 for printing.

[Ink viscosity control method]
As shown in FIG. 4, when ink is ejected from the nozzle 68 of the ink flow path N1, the ink in the manifold 80 is drawn into the individual flow path 82 of the ink flow path N1, so that the manifold 80 has a plurality of nozzles. Ink of the same amount as the total amount of ink discharged from 68 is drawn from the flow rate measurement region E of the flow path 110, thereby causing an ink flow in the flow rate measurement region E. The ink viscosity control method of the present embodiment measures the ink flow rate from the ink flow in the flow rate measurement region E, and adjusts the ink flow rate so that the measured flow rate (hereinafter referred to as “measured flow rate”) approaches the ideal flow rate. The viscosity is controlled, and is executed using the ink viscosity control device 24 described above. In the following, the ink viscosity control method according to the present embodiment will be described separately for the “flow rate measuring step” and the “viscosity control step”.

  There are two types of ink, “a type in which the viscosity decreases as the temperature increases” and “a type in which the viscosity increases as the temperature increases”. The type of ink used in the “viscosity control step” depends on which type is used. Although the control operation is different, in the following explanation, a case where ink of “kind whose viscosity becomes lower as the temperature becomes higher” is used will be described.

<Flow measurement process>
When the control operation by the ink viscosity control device 24 is started, as shown in FIG. 5, first, in step S1, the heater 58 is driven by the control device 22 as a “heater control device”. That is, a pulse voltage is applied to the heater 58 from the heater drive circuit 58a of the control device 22 at regular time intervals, and the ink flowing through the flow path 110 is intermittently heated. Therefore, in the heated ink heated by the heater 58, a temperature distribution pattern having a sharp peak appears intermittently at regular time intervals, and the peak of the temperature distribution pattern is a mark that the ink is heated. .

  In the subsequent step S3, the temperature of the heated ink is detected by the temperature sensor 62 at the temperature detection point Q located downstream from the heating point P, and the output of the temperature sensor 62 is given to the control device 22 as a “flow rate measuring device”. It is done. In the control device 22 as the “flow rate measuring device”, a peak is extracted from the temperature distribution pattern of the heated ink, and the heated ink is transferred from the heating point P based on the time t1 when the ink is heated and the time t2 when the peak is detected. A time T (T = t2−t1) in which the distance D to the temperature detection point Q is moved is calculated. Further, based on the time T and the distance D, the flow velocity V (V = D / T) of the heated ink is calculated. Furthermore, the ink flow rate R (R = V × S) is obtained based on the flow velocity V of the heated ink and the cross-sectional area S of the flow path 110 (the small diameter portion 110a in this embodiment).

  In this embodiment, since the peak of the temperature distribution in the heated ink is intermittently extracted from the output of the temperature sensor 62, the flow velocity V can be calculated for each peak, and a plurality of peaks corresponding to a plurality of peaks can be calculated. By calculating the average value of the flow velocity V, the flow velocity V can be calculated accurately, and the measured flow rate R can be calculated with high accuracy. In addition, since the flow velocity V of the ink actually used can be continuously calculated in the flow path 110, the ink flow rate can be calculated in real time at any time during the operation of the inkjet printer 10.

  In such a flow rate measurement process, the ink is heated by the heater 58 and the air bubbles mixed in the ink expand, so that the air bubbles are in the damper chamber 28a of the damper device 28 or at the inlet of the ink flow path N1. It is easily captured by a provided filter (not shown). Therefore, the amount of saturated oxygen dissolved in the ink can be reduced, and the ink can be stably ejected from the nozzle 68 without being obstructed by bubbles.

<Viscosity control process>
In the viscosity control step, any one of the following four control modes is executed alone, or these control modes are executed in any combination. The selection of “one control mode” or “combination of a plurality of control modes” is performed by a program stored in the ROM 52 in this embodiment, but the selection is a command signal input from the operation panel 64. May be performed on the basis of

(First control mode)
The first control mode is a basic control mode in the viscosity control step. When the measured flow rate R is obtained by the above-described flow rate measurement process (steps S1 and S3), it is determined in step S5 whether or not the measured flow rate R is larger than the ideal flow rate stored in the ROM 52. If “YES (large)” is determined, the output of the heater 58 is decreased in step S7, and if “NO (not large)” is determined, the output of the heater 58 is increased in step S9.

  Here, the output of the heater 58 means “amount of heat for heating the ink per unit time”, and increasing / decreasing the output of the heater 58 means “one time with a constant number of outputs per unit time”. It means both “increasing and decreasing the amount of heat output in the heating operation” and “increasing and decreasing the number of times of output per unit time while keeping the amount of heat output in one heating operation constant”. In step S7 and step S9, either one of these control operations may be selectively executed, or both control operations may be executed simultaneously. However, the ROM 52 determines which control operation is executed. It is determined based on a stored program or a command signal input from the operation panel 64.

  When the output of the heater 58 is decreased in step S7, the ink temperature decreases, the ink viscosity increases, the ink does not flow easily, the ink flow rate decreases, and the measured flow rate R approaches the ideal flow rate. become. On the other hand, if the output of the heater 58 is increased in step S9, the temperature of the ink increases, so that the viscosity of the ink decreases, the ink easily flows, the ink flow rate increases, and the measured flow rate R becomes the ideal flow rate. Get closer. In addition, when the ink of “kind whose viscosity increases as the temperature increases” is used, the control operations in steps S7 and S9 are reversed, but the description of this case is omitted.

  In the subsequent step S11, it is determined whether or not the ink viscosity control is to be terminated. If it is determined to be “YES (finished)”, the ink viscosity control is terminated and “NO (not terminated)” is determined. Then, it returns to step S1. The measured flow rate R is continuously calculated until it is determined “YES (finished)” in step S11. Therefore, the ink flow rate is appropriately controlled in real time at any time point during the operation of the inkjet printer 10. be able to. Further, since the measured flow rate R actually measured is fed back and controlled, high responsiveness can be obtained in the ink flow rate control.

(Second control mode)
In the second control mode, in step S <b> 1 (FIG. 5), the auxiliary heater 60 is driven together with the heater 58, and the actuator unit 72 is heated by the auxiliary heater 60. Further, as shown in FIG. 6, step S13 is executed subsequent to step S7, or step S15 is executed subsequent to step S9, and the output of the auxiliary heater 60 is controlled based on the determination in step S5.

  That is, in step S13, the temperature of the actuator unit 72 is lowered by reducing the output of the auxiliary heater 60 by the control device 22 as the “auxiliary heater control device”, and the ink existing in the flow path unit 70 is reduced. The temperature is lowered. Thereby, the viscosity of the ink existing inside the flow path unit 70 is increased, and the flow rate of the ink is decreased. On the other hand, in step S 15, the output of the auxiliary heater 60 is increased by the control device 22 as the “auxiliary heater control device”, whereby the temperature of the actuator unit 72 is increased and the ink present in the flow path unit 70 is removed. The temperature is raised. Thereby, the viscosity of the ink existing inside the flow path unit 70 is reduced, and the flow rate of the ink is increased.

  These operations assist the function of the heater 58 in step S7 or step S9. However, the change in the ink flow rate in the flow path unit 70 is immediately reflected in the flow rate of the ink flowing in the flow rate measurement region E. Therefore, in the subsequent “flow rate measuring step (steps S1 and S3)”, the ink flow rate is measured based on the control result of the auxiliary heater 60. Therefore, the ink flow rate can be brought closer to the ideal flow rate more quickly than in the case of the first control mode, and the control responsiveness can be further improved.

(Third control mode)
In the third control mode, as shown in FIG. 7, step S17 is executed subsequent to step S7, or step S19 is executed subsequent to step S9, and the number of operations of the drive unit 92 based on the determination in step S5. Is controlled. That is, in step S <b> 17, the number of operations of the drive unit 92 in the actuator unit 72 is reduced by the control device 22 as the “ejection control device”, and the amount of ink ejected from the nozzle 68 per unit time is reduced. On the other hand, in step S <b> 17, the number of operations of the drive unit 92 is increased by the control device 22 as the “discharge control device”, and the amount of ink discharged from the nozzle 68 per unit time is increased. Here, the number of operations of the drive unit 92 is determined by the waveform of the drive voltage generated in the driver IC 98. In this embodiment, the number of operations of the drive unit 92 is increased or decreased by changing the waveform of the drive voltage. The

  These operations assist the function of the heater 58 in step S7 or step S9, but the change in the discharge amount discharged from the nozzle 68 is immediately reflected in the flow rate of ink flowing in the flow rate measurement region E. In the subsequent “flow rate measuring step (steps S1 and S3)”, the ink flow rate is measured based on the control result in step S17 or step S19, and the control responsiveness can be further improved.

(Fourth control mode)
In the fourth control mode, as shown in FIG. 8, step S21 is executed subsequent to step S9, and the drive unit 92 is “idle driven” based on the determination in step S5. Here, “idle driving” means an operation for generating Joule heat in the driver IC 98, and in this embodiment, a driving voltage that is low enough not to eject ink from the nozzle 68 is repeatedly applied to the driving unit 92. Thus, “idle driving” is performed. Since the heat generated in the driver IC 98 is transmitted through the output wiring 100 and heats the actuator unit 72, the temperature of the ink existing in the flow path unit 70 is the same as that of the auxiliary heater 60 used in the “second control mode”. Can be increased, and the viscosity of the ink can be decreased and the flow rate of the ink can be increased.

(Fifth control mode)
In the fifth control mode, the above-described flow rate measurement step (steps S1 and S3) is performed when the ejection head 14 performs the above-described flushing operation. According to this, since the flow rate measurement process is performed during the flushing operation before printing, the viscosity of the ink can be calculated before printing. A viscosity control step may be performed simultaneously with the flow rate measurement step. Since the viscosity of the ink can be adjusted before printing, non-ejection due to increased viscosity of the ink is less likely to occur during printing. Further, not only when the flow measurement process and the viscosity control process are performed simultaneously with the flushing operation before printing, but also during the flushing operation during printing, the flow measurement process and the viscosity control process may be performed.

E ... Flow measurement region N1 to N4 ... Ink flow path P ... Heating point Q ... Temperature detection point D ... Distance V ... Flow rate T ... Time R ... Flow rate S ... Cross-sectional area 10 of the flow path ... Inkjet printer (liquid ejection device)
14 ... Discharge head 22 ... Control device (flow rate measuring device, heater control device, discharge control device, auxiliary heater control device)
24 ... Ink viscosity control devices 26a to 26d ... Ink tank 58 ... Heater 60 ... Auxiliary heater 62 ... Temperature sensor 64 ... Operation panel 68 ... Nozzle 70 ... Flow path unit 72 ... Actuator unit 80 ... Manifold 84 ... Pressure chamber 92 ... Drive unit 100 ... Output wiring 110 ... Channel 110a ... Small diameter part

Claims (10)

A liquid viscosity control device for controlling the viscosity of a liquid discharged from a nozzle,
A flow path for guiding liquid to the nozzle;
A heater for heating the liquid flowing through the flow path at a predetermined heating point;
A temperature sensor that is provided at a temperature detection point located downstream of the flow path from the heating point and detects the temperature of the liquid when the liquid heated by the heater reaches the temperature detection point;
A flow rate measuring device that measures the flow rate of the liquid flowing through the flow path using the output of the temperature sensor;
A liquid viscosity control device comprising: a heater control device that controls an output of the heater so that a measured flow rate measured by the flow rate measurement device approaches an ideal flow rate for discharging liquid from the nozzle.   2. The liquid viscosity control device according to claim 1, wherein at least a portion of the flow path from the heating point to the temperature detection point is formed to be narrower than other portions. An auxiliary heater for heating the liquid discharged from the nozzle;
The liquid viscosity control device according to claim 1, further comprising an auxiliary heater control device that controls an output of the auxiliary heater based on a measured flow rate measured by the flow rate measuring device.   4. The liquid viscosity according to claim 1, wherein the heater control device controls the output of the heater to intermittently heat the liquid while the liquid flows in the flow path. Control device. A flow path unit having a plurality of nozzles for discharging liquid, a plurality of pressure chambers individually communicated with each of the plurality of nozzles, and a manifold commonly communicated with each of the plurality of pressure chambers;
A drive unit having a plurality of drive units for individually applying discharge pressure to the liquid in the plurality of pressure chambers;
An ink tank for storing the liquid supplied to the flow path unit;
An ink tube communicating the ink tank and the manifold;
A liquid viscosity control device according to any one of claims 1 to 4,
At least the ink tube, the manifold, and the plurality of pressure chambers constitute a flow path that guides the liquid to the nozzle,
In the manifold, the cross-sectional area of the flow path is enlarged toward the downstream side,
The liquid ejection device, wherein the heating point and the temperature detection point of the liquid viscosity control device are arranged upstream of the manifold. A recovery device that performs a recovery operation of discharging the liquid from the nozzle and recovering the nozzle;
The liquid viscosity control device is configured such that when the recovery device performs the recovery operation, the flow rate measurement device measures the flow rate of the liquid, and the heater control device controls the output of the heater. 5. The liquid ejection device according to 5. A liquid viscosity control method for controlling the viscosity of a liquid discharged from a nozzle provided at an end of a flow path,
(A) a step of heating the liquid flowing through the flow path by a heater at a predetermined heating point; and (b) a liquid heated at the heating point at a temperature detection point located downstream of the flow path from the heating point. Detecting the arrival by a temperature sensor;
(C) measuring the flow rate of the liquid flowing through the flow path using the output of the temperature sensor;
(D) adjusting the degree of heating of the liquid by the heater so that the measured flow rate approaches the ideal flow rate for discharging the liquid from the nozzle. In the step (a), the liquid flowing through the flow path is intermittently heated,
In the step (c), time information is acquired from the output of the sensor to measure the flow velocity of the liquid, and the flow rate of the liquid is measured based on the flow velocity and the cross-sectional area of the flow path. The liquid viscosity control method as described.   The nozzle and a drive unit for discharging liquid from the nozzle are integrally incorporated in the discharge head. In the step (d), when the measured flow rate measured in the step (c) is smaller than the ideal flow rate The liquid viscosity control method according to claim 7 or 8, wherein the number of operations of the drive unit is increased. The nozzle and a drive unit that discharges liquid from the nozzle are integrally incorporated in an ejection head, and a driver IC that generates a drive voltage is electrically connected to the drive unit,
In the step (d), the driver IC is driven idle when the measured flow rate measured in the step (c) is smaller than the ideal flow rate, thereby generating heat for heating the liquid in the driver IC. The method for controlling a liquid viscosity according to any one of claims 7 to 9.

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