Liquid discharge device

Abstract

To provide a liquid discharge device that is configured so that cleaning means for a liquid discharge head can be appropriately selected.SOLUTION: A liquid discharge device comprises a liquid discharge head that discharges liquid. The liquid discharge head is formed of a circuit substrate and a flow passage forming member which are joined to each other, where a liquid chamber which is filled with liquid is formed on the joined part. The circuit substrate is provided with a liquid supply port that supplies liquid to the liquid chamber. The flow passage forming member is provided with a nozzle for discharging liquid in the liquid chamber. The circuit substrate is further provided with a plurality of driving elements that are applied with voltages to produce heat and discharge liquid, a plurality of removing means which are provided with a plurality of temperature sensors and remove foreign matters in the liquid discharge head, and a control part that analyzes waveforms of signals outputted from the temperature sensors to select the removing means for removing the foreign matters.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a liquid ejection device. [Background technology]

[0002] Liquid ejection devices that eject liquid from nozzles are known. The liquid ejection device can be applied to inkjet recording type liquid ejection devices (recording devices) that eject ink as a liquid and attach it to a recording medium such as paper. Among such liquid ejection devices, there is a thermal inkjet type that ejects ink from a nozzle using thermal energy generated by a heater. There is a demand for such liquid ejection devices to achieve higher image quality and higher speeds.

[0003] In general, thermal inkjet recording devices generate bubbles in the nozzles by locally heating liquid such as ink with a micro-sized heater, and the bubbles cause the ink to be ejected from the nozzles and land on the printing target. In such thermal liquid ejection (recording head), the heat generating resistor elements that heat the ink are integrated on a semiconductor substrate together with logic circuits for driving the heat generating resistor elements. This meets the demands for higher image quality and higher speeds mentioned above, and enables high-speed driving by arranging the heat generating resistor elements in a high density.

[0004] Patent Document 1 discloses such a thermal inkjet recording device. This inkjet recording device has a liquid ejection head equipped with a plurality of temperature sensors corresponding to a plurality of heating resistor elements. It is proposed that the recording element substrate has a means for determining the ejection state of the nozzles based on the waveform of the temperature sensor and outputting the result to the outside, thereby determining whether the ejection is normal or defective. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-094878 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, when an abnormality appears in the ink ejection, the defective nozzle can often be restored to a normal state by performing maintenance such as cleaning on the head. For example, if a poorly soluble substance such as kogation is adsorbed on the heater, it is advisable to clean or remove the deposits on the heater. Also, if the viscosity of the liquid near the nozzle increases due to drying, it is advisable to replace it with a normal liquid by suction or circulation. Thus, most ejection defects are caused by foreign matter inside the liquid chamber, including above the heater, or around the nozzle corresponding to the liquid chamber, and ejection can be improved by properly removing the foreign matter. On the other hand, cleaning involves physical contact and chemical alteration, so depending on the removal method, it may damage the head, and the accumulation of the foreign matter may shorten the life of the liquid ejection head.

[0007] However, in Patent Document 1, only the normal / failure of the ejection is judged, and the cause of the failure is not identified, so the optimal cleaning method may not be selected. Also, since it is not possible to capture minute changes in the speed and amount of droplets within the range of normal ejection, there is a risk that the device will be used until it fails, which may result in the need for highly damaging cleaning.

[0008] The present invention has been made in view of the above problems, and provides a cleaning means for a liquid ejection head. It is an object of the present invention to provide a liquid ejection device that allows an appropriate selection. [Means for solving the problem]

[0009] The present invention employs the following configuration. In a liquid ejection device having a liquid ejection head for ejecting liquid, The liquid ejection head is formed by bonding a circuit board and a flow path forming member, a liquid chamber filled with liquid is provided at a portion where the circuit board and the flow path forming member are joined, a liquid supply port for supplying the liquid to the liquid chamber is provided on the circuit board; the flow passage forming member is provided with a nozzle for discharging the liquid in the liquid chamber, The circuit board is provided with a plurality of drive elements that generate heat when a voltage is applied to eject the liquid, and a plurality of temperature sensors; a plurality of removal means for removing foreign matter from within the liquid ejection head; a control unit that selects one of the plurality of removal units to remove the foreign matter based on a result of analyzing a waveform of a signal output from the temperature sensor; The liquid ejection device further comprises: Effect of the Invention

[0010] According to the present invention, it is possible to provide a liquid ejection apparatus that allows an appropriate selection of cleaning means for the liquid ejection head. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic perspective view of a recording element substrate for a liquid ejection head; [Diagram 2] FIG. 1 is a plan view showing a sensor arrangement according to a first embodiment; [Diagram 3] FIG. 1 is a cross-sectional view showing a sensor structure according to a first embodiment; [Figure 4] Block diagram according to the first embodiment [Diagram 5] Flowchart according to the first embodiment [Figure 6] Graph showing a waveform based on temperature change according to the first embodiment [Figure 7] Signal output from the state classification circuit according to the first embodiment [Figure 8] Example of output with classification and classification number associated with nozzle [Figure 9] Schematic diagram of a liquid ejection device to which the substrate of the present invention can be applied. [Figure 10] Schematic diagram of a liquid ejection head to which the substrate of the present invention can be applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A preferred embodiment of the present invention will be described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in the embodiment are not intended to limit the scope of the present invention to those alone. Furthermore, the materials, shapes, etc. of the members once described in the following description are the same as those described initially, unless otherwise specified. Well-known or publicly known technologies in the relevant technical field can be applied to configurations and processes not particularly shown or described. Furthermore, duplicated descriptions may be omitted.

[0013] <1. First embodiment> (1.1 Structure of the element substrate) 1 is a partially cutaway perspective view conceptually showing a recording element substrate for a liquid ejection head of this embodiment. The liquid ejection head substrate 1 (recording element substrate) of this embodiment is formed by bonding a flow path forming member 120 to a circuit board 100 for applying thermal energy to the liquid. This flow path forming member 120 has a plurality of nozzles 121 formed therein for ejecting liquid at positions facing drive elements 101, which are thermal action parts for heating the liquid. In addition, A liquid chamber 122 is formed which communicates with a nozzle 121 through an area above the driving element 101 from a liquid supply port 102 provided above the driving element 101. The circuit board 100 also includes a counter electrode 103 required for applying a voltage to electrochemically dissolve the protective film.

[0014] FIG. 2 is a plan view showing a schematic arrangement of the driving element 101 and the sensor 130 corresponding to the nozzle 121. FIG. 2 is a plan view seen from the top surface of the substrate, and is a perspective view, so that the underlying patterns can be seen through the various components. Note that a protective film is formed over the entire surface, and is therefore not shown in FIG. 2. One or more driving elements 101 that generate heat when a current flows are arranged on the circuit substrate 100. As shown in FIG. 1, the circuit substrate 100 and the flow path forming portion A liquid chamber 122 is provided at the joint of the members 120, and ink is filled into the liquid chamber 122 from a liquid supply port 102 which is a part of a liquid flow path.

[0015] When a current is passed from the power supply to the driving element 101, heat is generated, and the liquid that receives the thermal energy from the generated heat bubbles, causing the liquid to be ejected. In Fig. 2, the driving element 101 is rectangular in plan view, but the shape is not limited to this as long as it can pass a current.

[0016] A sensor 130 is provided under the driving element 101 to detect temperature changes from changes in resistance and capacitance. In FIG. 2, nine sensors 130 are arranged in an area corresponding to one driving element 101, but the position and number are not limited to this. The shape of the driving element 101 is desirably designed according to the temperature change to be detected, and is not limited to a rectangle. Regarding the position of the sensor 130, at least a part of the sensors 130 is desirably arranged at a position overlapping the liquid chamber 122 when viewed from above in order to detect the size of bubbles and the position of bubble destruction. However, this is not limited, and depending on the design, the sensor 130 can be arranged at a position not overlapping the liquid chamber 122 to detect changes in environmental information such as temperature. In order to detect a steep temperature change, it is preferable to arrange the sensor 130 in a position close to the liquid. For example, if the sensor 130 is located above the driving element 101 or on the surface or inside of the flow path forming member 120, the temperature change can be detected sensitively. The sensor 130 may be arranged in the same layer as the driving element 101. However, even if the sensor 130 is disposed below the driving element 101, there is no problem as long as the desired detection performance is obtained.

[0017] It is desirable that the center of the nozzle 121 coincides with or is close to the center of the driving element 101 in a plan view. However, as long as it is possible to eject liquid by bubbling, the center positions do not have to coincide. In addition, the nozzle shape is not limited to a circle.

[0018] 3 is a cross-sectional view showing a schematic arrangement of the driving element 101 and the sensor 130 corresponding to the nozzle 121. As shown in the figure, a liquid chamber 122 formed in a portion where the flow path forming member 120 and the circuit board 100 are joined receives liquid from a liquid supply port 102 and communicates with the nozzle 121, and supplies liquid to the nozzle 121 when the liquid is ejected. The driving element 101 is covered with a lower protective film 141 and an upper protective film 142. These films each have their own role, with the lower protective film insulating the driving element 101 and the upper protective film protecting the driving element 101 from physical and chemical erosion by liquid and the like. Therefore, as long as the driving element 101 is sufficiently protected, the number of layers of the protective film is not limited to two.

[0019] The upper protective film 142 comes into contact with the liquid in the liquid chamber 122. When the driving element 101 is supplied with power from the connection wiring 151 to generate heat, the temperature instantly rises to several hundred degrees and then drops within a few milliseconds. When the liquid foams due to boiling, it may generate vacuum microbubbles called cavitation when the bubbles disappear, and when the bubbles collapse, a large impact pressure is applied to the protective film. In order to adequately protect the driving element 101 from such a harsh environment, it is desirable for at least a part of the protective film to contain a physically and chemically stable material, and a film containing a platinum group element such as palladium, iridium, or platinum is preferable. In this embodiment, the upper protective film 142 is formed to a thickness of 100 nm. The iridium film and the lower protective film 141 were made of a silicon nitride film having a thickness of 100 nm.

[0020] The sensor 130 is disposed below the driving element 101. The temperature sensor is preferably located near the liquid chamber 122 or the liquid supply port 102 to capture temperature changes caused by the movement of the liquid. In this embodiment, the sensor is disposed below the driving element 101, but the sensor may be located above the driving element 101, on the surface or inside of the flow path forming member 120, or in the same layer as the driving element 101 or the driving element 101 itself. The temperature characteristic of the sensor is represented by TCR (Temperature Coefficient of Resistance), and it is desirable that the change in resistance value per unit temperature change is large. Specifically, it is preferable that the sensor is formed of a material containing at least one element selected from platinum, iridium, tungsten, zirconium, copper, nickel, zinc, titanium, silicon, aluminum, and the like. In this embodiment, an alloy film containing titanium is assumed.

[0021] (1.2 Specific examples of foreign objects and how to remove them) In this case, the term "foreign matter" refers to any substance that is in contact with the liquid and prevents normal foaming. A typical example of foreign matter is solid burnt matter in contact with the film that protects the driving element 101. Other examples of foreign matter include solid matter derived from liquid or high-viscosity liquid that is retained or attached to the nozzle 121 or to a position close to the nozzle 121 on the air-side surface (the surface opposite to the liquid chamber side) of the flow path forming member 120. Other examples of foreign matter include dust and bubbles that are clogged in the liquid supply port 102. These foreign matters can have an effect on the flow path resistance during foaming, disrupt the balance between hydrophilicity and hydrophobicity of the flow path forming member 120, and make the foaming itself uneven, thereby causing problems in the speed, amount, and ejection angle of the droplets.

[0022] In this embodiment, the foreign matter is removed by the following method. For example, it is effective to wipe off the foreign matter (such as liquid-derived solidified matter or highly viscous liquid) on the air-side surface of the flow path forming member 120 with a wiper made of a highly flexible material. In addition, foreign matter around the nozzle or inside the nozzle can be removed by sucking the liquid from the nozzle 121 with a suction means such as a suction tube using air pressure. Wiping and suction may be performed simultaneously. However, in order to discharge the foreign matter in the direction of droplet ejection, such as wiping or suction, it is often necessary to prepare a mechanical device separate from the liquid ejection head. Therefore, the downtime increases due to the time required for installation and removal. Furthermore, this leads to an increase in cost and an increase in size of the device due to the need for installation space.

[0023] Therefore, if possible, it is desirable to discharge foreign matter in the direction of the flow path, such as the liquid supply port 102. For example, foreign matter around the nozzle 121 can be discharged in the direction of the flow path by pumping and circulating the liquid with one end of the liquid supply port 102 as an inlet and the other end as an outlet. In addition, by foaming the liquid with the driving element 101, it is possible to push and peel off not only foreign matter around the nozzle 121, but also solid foreign matter in contact with the film that protects the driving element 101, by the foaming pressure and defoaming pressure of the liquid. In this case, the driving element that pushes and peels off the foreign matter does not need to be the same as the driving element 101 that ejects droplets for printing, and the driving element and the flow path may be designed separately so that the pushing and peeling force is appropriately applied.

[0024] In addition, if the kogation generated by exposing the liquid to high temperatures accumulates, it becomes relatively difficult to remove it by any of the above methods. Therefore, for example, the foreign matter on the upper protective film 142 can be removed by electrochemically dissolving the upper protective film 142. Specifically, the upper protective film 142 can be made a conductive film containing a platinum group element such as palladium, iridium, or platinum, and the film can be dissolved by applying a voltage to the anode. However, as long as the film can be dissolved by voltage, the film material is not limited to a platinum group element. In addition, the applied potential is not limited to a positive potential. The amount of dissolution can be controlled with high precision by managing the amount of current. On the other hand, the film thickness that can be dissolved is limited to the film thickness of the protective film created, so the removal operation is difficult. This also has the side effect of shortening the life of the liquid ejection head.

[0025] FIG. 4 is a block diagram showing an example of a hardware and software configuration when the waveform obtained from the sensor 130 is fed back to the head cleaning means. The components related to the sensor waveform processing are shown, and some hardware and software are not shown. For example, an interface for inputting print data to the liquid ejection device is not shown. Each function shown in the software configuration can be realized by an information processing device such as a computer or a control circuit having computational resources such as a processor and memory operating in response to program instructions or user input. FIG. 4 shows a recording element unit 501 including the above-mentioned circuit board and the like, a state classification unit 502 for determining classification of foreign matter, and a device main body unit 503 corresponding to the main body of the liquid ejection device (recording device). However, this does not necessarily indicate a physical division. For example, the function of the state classification unit 502 may be executed by an information processing device included in the main body of the liquid ejection device. In addition, various information processing may be executed by an external information processing device capable of communicating with the liquid ejection device. In the present invention, regardless of which block acquires and analyzes the waveform output from the sensor 130, determines whether there is a foreign object, and selects a removal method, these blocks together can be considered to be a control unit.

[0026] Usually, information such as an image to be printed and driving conditions of the driving elements is transmitted from the data transmission unit 441 to the data reception unit 401 of the recording element unit 501 mounted on the liquid ejection head by a command from the application unit 451. Based on the information, the driving element unit 402 of the recording element unit 501 selects the ejection nozzle and inputs the driving conditions. In addition, at the same time as driving the driving element, the temperature sensor unit 403 of the recording element unit 501 acquires a temperature waveform by the sensor 130. The temperature sensor 403 unit may be considered as the sensor 130 itself, or as a combination of the sensor 130 and a control block that processes its output. Since the sensor waveform is acquired during printing or between printings separately from printing, the information transmitted from the data transmission unit 441 may be dedicated data for acquiring the sensor waveform. The temperature waveform acquired by the temperature sensor unit 403 is transmitted to the waveform collection unit 411 of the state classification unit 502.

[0027] The waveform information received by the waveform collecting unit 411 of the state classification unit 502 is used in the feature extracting unit 412 and the state determining unit 413 to extract the waveform features and to determine and classify the state. Usually, there are multiple nozzles 121 for ejection, and there may be multiple temperature sensors for each nozzle. Therefore, in order to improve the printing speed, it is necessary to process the determination of multiple waveforms at high speed. Therefore, it is preferable that at least a part of the circuit constituting the state classification unit is configured to be able to process a large amount of sensor waveforms at high speed. More preferably, it is preferable that the circuit is arranged in the liquid ejection head. Even more preferably, it is preferable that the circuit is configured on the same element substrate as the recording element unit mounted on the liquid ejection head. Similarly, it is preferable that the information output from the state classification unit 502 is a digital signal that can be output at high speed. On the other hand, depending on the amount and frequency of data of the sensor waveform to be acquired, the state classification unit 502 may be incorporated in the device main body, and the mounting location is not limited. The classification and determination result information is output from the determination output unit 414 and transmitted to the determination recording unit 421 of the device main body unit 503.

[0028] The judgment recording unit 421 stores all judgment records of the liquid ejection heads used in the device. Since it is necessary to retain past information even when the storage head is replaced, it is desirable for the judgment recording unit 421 to be provided in the liquid ejection device body. The inference unit 422 uses the judgment records of each nozzle of the liquid ejection head, as well as information on other liquid ejection devices and the latest inference model based on that information, as judgment materials to determine the optimal processing flow. Next, the means selection unit 423 feeds back the selection of the cleaning method and whether it is necessary to perform cleaning to the application unit 451. In this embodiment, the cleaning means are A, B, and C (reference numerals 431 to 433). Three types of configurations are shown as examples, but the number of cleaning means is not limited. Also, even for the same cleaning, it is possible to change the target range and strength. The inference unit 422 also considers optimal cleaning conditions. This makes it possible to perform effective cleaning with a minimum of downtime.

[0029] FIG. 5 is a flow chart showing an example of a sensor waveform processing procedure during printing by the liquid ejection device. In step S601, a voltage is applied to the driving element 101 at a predetermined position based on image information, and ink droplets are ejected to record an image on a recording medium. The sensor 130 detects a temperature change due to this image recording (printing), and outputs a sensor waveform in step S602. Note that the sensor waveform output and the determination process are not necessarily performed all the time. Considering the information processing cost, it is desirable to perform these processes at a timing when it is effective to perform cleaning required for removing foreign matter. The flow in FIG. 5 describes a case where the sensor waveform is output, and a case where it is not output is omitted. The determination process shown in step S603 is performed based on the output waveform, and the necessity of cleaning the liquid ejection head is determined based on the result of the determination. The sensor waveform is typically output at a timing when the device is started up, after a predetermined number of images are recorded, at a predetermined time interval, during maintenance of the device, or the like. However, it may be performed all the time after each image recording.

[0030] If it is determined in step S604 that cleaning is necessary, in many cases it is necessary to stop printing as shown in step S605. However, depending on the type of foreign matter and the contents of cleaning, some can be performed during printing. In that case, printing does not need to be stopped. For example, if there is only a small amount of dust in the liquid chamber, it is possible to remove the dust in parallel with printing by making only the nozzle 121 corresponding to the position of the dust bubble. Also, if there is only a slight amount of ink adhesion near the nozzle 121, it is possible to eliminate the adhesion in parallel with printing by applying a stronger pulse to the driving element 101 as a heat application unit.

[0031] The sensor waveform is analyzed to see how the foaming, discharging, and defoaming movements deviate from normal, and the position and state of the foreign matter causing the defect are estimated, and an effective cleaning method is selected in step S606. For example, cleanings A to C can be selected, and if any one of them is determined to be effective, the selected cleaning process is performed and then the process ends.

[0032] On the other hand, if it is determined that there is no effective cleaning means prepared (determined as "none" in S606), cleaning is not performed unnecessarily, and the process proceeds to determining whether head replacement is necessary in step S607. The selection of a cleaning means involves choosing an effective one from multiple means, and may involve a combination of multiple means or the same means being performed multiple times. Note that even if it is determined in step S604 that cleaning is not necessary, the process proceeds to step S607 to determine whether head replacement is necessary. Head replacement is necessary, for example, when there is a nozzle that does not provide normal ejection characteristics (ejection speed, ejection amount, ejection angle, etc.) even after various cleaning processes, and there is no nozzle with normal characteristics to complement that nozzle. In order to determine the need for replacement, a measurement process of the ejection characteristics may be performed after the cleaning process.

[0033] If head replacement is required, the process moves to a replacement sequence. Replacement may be performed automatically, or the user may be notified of the need for replacement and performed manually. If head replacement is not required, a determination is made in step S607 as to whether the print job has ended. If the print job has not ended, printing is resumed.

[0034] In this embodiment, a configuration having three types of cleaning, A, B, and C, is illustrated, but the number of cleaning means is not limited. The process may be performed in parallel with the ejection of droplets from the nozzle, or the judgment process shown in S603 may be configured to make a judgment by combining the waveform outputs from multiple sensors. By performing the above-mentioned process, it is possible to select the most suitable and effective removal means for the foreign matter that has occurred in the liquid ejection head through feedback, and it is possible to minimize downtime and damage to the head.

[0035] (1.3 Analysis of sensor waveforms) FIG. 6(a) is a part of an analog waveform of a signal (pressure) that can be acquired by a temperature sensor as the sensor 130. The horizontal axis indicates time [s], and the vertical axis indicates the sensor output voltage [V]. A constant current is passed through the sensor 130, and the change in voltage value when the temperature changes is read, and a waveform like the one shown in the figure is output. Here, since the alloy film containing titanium has a negative TCR value, the resistance value decreases when the temperature rises. In other words, the voltage value decreases with an increase in temperature. Therefore, the minimum peak (1) of the waveform in FIG. 6(a) can be read as the point where the temperature is the highest. In the liquid chamber 122, motion and phase change appear in a short time due to the thermal energy from the driving element 101. The liquid boils due to the thermal energy, and high-pressure bubbles are generated. At this moment, the fluid in contact with the upper protective film 142 changes from liquid to gas. After foaming, the volume of the bubbles increases, but the pressure of the bubbles instantly decreases to negative pressure, so it is inertia that makes the bubbles larger. After that, the bubble volume reaches its maximum and then starts to shrink, and the liquid attracted by the negative pressure reaches the protective film on the drive element 101. During this time, depending on the size of the liquid chamber 122 and the size of the bubble, the liquid film around the bubble may break, allowing room temperature air to flow into the bubble.

[0036] The waveform of the sensor 130 includes information on the phase state and temperature change of the fluid in the complicated liquid chamber 122. When the fluid in the liquid chamber moves or undergoes a phase change, a temperature change inevitably occurs due to contact between materials with different thermal conductivities. It is possible to capture the movement of the fluid by determining the presence or absence of this temperature change from the sensor waveform. In addition, it is essential to analyze the time of the temperature change. For example, just as it is easy to estimate the movement of the fluid by analyzing the time from the time when bubbles appear to the time when bubbles disappear, the movement of the fluid can be accurately captured by analyzing the time and duration of the change point in addition to the position of the sensor and the amount of temperature change. This makes it possible to accurately determine the occurrence and state of foreign matter. On the other hand, in the case of a sudden change, such as the moment when the fluid in contact with the protective film changes into a liquid, if the temperature time profile is known to some extent, the time of the change point can be measured by the amount of temperature change, so it is not necessary to have a circuit that directly analyzes the time.

[0037] In order to capture the change point as a signal on an electric circuit, one of the effective means is to convert the temperature change into a peak. FIG. 6(b) shows a waveform processed so that the change point to be obtained becomes a peak. The horizontal axis indicates time [s], and the vertical axis indicates the voltage change [dV / dt]. At the moment of bubbling, the fluid in contact with the protective film changes from liquid to gas, and the heat release from the circuit board 100 to the liquid weakens. In FIG. 6(a), there is a moment when the voltage decrease accelerates from the beginning of the waveform toward the negative extreme value, and this is the change point caused by bubbling. FIG. 6(b) shows a waveform obtained by converting the waveform of FIG. 6(a) using a band pass filter to convert this change point into a peak. The point (2) where the negative extreme value appears in FIG. 6(b) can be obtained as the time of bubbling. In this embodiment, the change point is peaked using a band pass filter, but a method such as differential processing or frequency analysis may be used as long as it is possible to emphasize and output the change point.

[0038] An example of a method for converting waveform time information into droplet ejection speed information is shown below. By using the waveform conversion shown in Figure 6(b), it is possible to convert the time at which bubbling occurs (first time) shown in (2) into the time of the minimum value, and the time at which the liquid comes into contact with the protective film on the drive element again (second time) shown in (3) into the time of the maximum value. Then, by outputting the times showing the maximum and minimum peaks, or the times of these two points from the circuit, it is possible to calculate the interval time from bubbling to the time at which the liquid comes into contact with the liquid again. In Figure 6(b), the interval time is shown as the time from (1) to (2). This time and the droplet ejection speed have a correlation depending on the design of the nozzle and the liquid chamber, so as shown in Figure 7, The horizontal axis of Fig. 7 shows the speed [m / s], and the vertical axis shows the interval time [μs].

[0039] Therefore, the characteristics specific to the nozzle and flow path design shown in FIG. 7 are obtained in advance, and the interval time obtained from the sensor waveform is compared to obtain the droplet velocity from the time information of the waveform. For example, if the interval time is 4.0 μs, the discharge velocity can be converted to 6.8 m / s. Since the characteristics may shift due to changes over time, the discharge velocity range may be converted by taking the characteristic shift into account in advance. In the case of FIG. 7, the initial conversion coefficient is shown by a solid line, and the conversion coefficient after a certain time has passed is shown by a dashed line. Therefore, the predicted range of the discharge velocity when the interval is 4.0 μm is 6.8 to 7.1 m / s. In this example, we focused on the time of bubbling and re-contact with the liquid, but there are other change times that affect the discharge velocity, such as the release of bubble pressure due to communication with the atmosphere and refilling of liquid from the flow path direction. Therefore, by focusing on these, it is possible to convert to the discharge velocity and discharge amount.

[0040] (Cleaning Method Selection) An example of a method for selecting a cleaning method from information on the discharge speed, which is one of the droplet characteristics, is explained below. As shown in Figure 7, by continuously acquiring information on the discharge speed of a certain droplet and capturing the change over time, it is possible to effectively select a cleaning method. For example, if a slight decrease in speed is observed over time, it is highly likely that a poorly soluble substance, such as kogation, has adhered to the protective film. In that case, the discharge speed can be effectively restored by applying a voltage to the protective film on which the kogation has adhered and chemically dissolving it.

[0041] Also, if the ejection speed repeatedly drops significantly and then recovers, there is a high possibility that proper filling and circulation of the liquid is being hindered due to foreign matter clogging the flow path, etc. In that case, the ejection speed can be effectively restored by using a liquid delivery pump or filter to flush the foreign matter toward the flow path, or by using a vacuum pump to suck the foreign matter out of the head from within the liquid chamber.

[0042] In this way, by capturing various change points and their changes over time, the position and state of the foreign object can be appropriately determined. However, the conversion process shown in this embodiment is only an example, and other forms are acceptable as long as the state of the foreign object can be appropriately determined. For example, the foreign object may be determined by deep learning using a part or all of the analog output waveform in FIG. 6(a) as input data, in which case a dedicated processing circuit is incorporated in the feature extraction unit 412, state determination unit 413, inference unit 422, etc.

[0043] Using FIG. 8, an example of classification by numbers output from the state classification unit 502 and an example of classification numbers being output in association with each nozzle in each row will be described. Here, the discharge amount accuracy and discharge angle can be calculated by applying the obtained waveform to a trained model that indicates the relationship between a previously created waveform, the discharge amount accuracy, and the discharge angle. The discharge speed and discharge amount are obtained as values ​​(scalars), and an index that combines the discharge speed and the discharge amount can be called the discharge amount accuracy. Here, the accuracy of the discharge speed and the discharge amount is divided into four stages, "S", "A", "B", and "ND (abnormal)", in order of best to worst. That is, "S" indicates that there is no problem with both the discharge speed and the discharge amount, "A" indicates that there is a change in either one, and "B" indicates that there is a change in both. In addition, the magnitude of the discharge angle (ejection angle) is divided into three stages, small, medium, and large. Then, as shown in FIG. 8(a), classification numbers are assigned to the positions of the matrix. When the accuracy is "ND", the same classification number (9) is assigned regardless of the discharge angle.

[0044] For some or all of the nozzles, the classification based on the classification number is determined from the waveform and output as a digital signal. Figure 8(b) is a table showing an example of classification. It is assumed that there are nozzles 121 from 1 to 500 in each row (row1, row2). In this table, one of the above-mentioned classification numbers 0 to 9 is recorded for each nozzle 121. The device main body unit 503, which has recorded the classification, selects an appropriate foreign matter removal means and cleans the recording element unit 501 based on the information on the distribution of the classification and changes over time.

[0045] In this embodiment, as an example, the classification number is set based on the droplet discharge state, but the present invention is not limited to this. For example, the information output from the state classification unit 502 may directly specify the type and conditions of the removal means. Alternatively, information indicating the state and position of the foreign matter may be output, and in this case, the inference unit 422 will also consider the optimal removal means.

[0046] (Device configuration) 9 and 10 are schematic diagrams showing the configuration of the main parts of an inkjet type liquid ejection device (recording device) to which the present invention can be applied. FIG. 9 is an overall view showing the overall configuration of a liquid ejection device 150. FIG. 10 is a perspective view showing a liquid ejection head 110, which is a component of the liquid ejection device. Here, the liquid ejection head 110 records an image on a recording medium 125 by ejecting ink droplets from ejection openings corresponding to the nozzles. The liquid ejection head 110 includes a recording element substrate 135 having a plurality of nozzle rows in which a plurality of nozzles are arranged.

[0047] By applying the present invention to such a liquid ejection head 110 and liquid ejection device 150, it is possible to select an optimal cleaning method and reduce the occurrence of ejection defects, thereby enabling good image recording with image defects suppressed.

[0048] As described above, the present invention can provide a liquid ejection device including a liquid ejection head (recording head) that can effectively maintain high print quality, thereby reducing downtime due to cleaning or replacement, and maximizing the lifespan of the liquid ejection head, thereby reducing running costs.

[0049] [Configuration 1] In a liquid ejection device having a liquid ejection head for ejecting liquid, The liquid ejection head is formed by bonding a circuit board and a flow path forming member, a liquid chamber filled with liquid is provided at a portion where the circuit board and the flow path forming member are joined, a liquid supply port for supplying the liquid to the liquid chamber is provided on the circuit board; the flow passage forming member is provided with a nozzle for discharging the liquid in the liquid chamber, The circuit board is provided with a plurality of drive elements that generate heat when a voltage is applied to eject the liquid, and a plurality of temperature sensors; a plurality of removal means for removing foreign matter from within the liquid ejection head; a control unit that selects one of the plurality of removal units to remove the foreign matter based on a result of analyzing a waveform of a signal output from the temperature sensor; The liquid ejection device further comprises: [Configuration 2] The control unit analyzes the waveform to determine the type of the foreign matter, and selects the removal means according to the type of the foreign matter. 2. The liquid ejection device according to configuration 1, [Configuration 3] The control unit determines a position of the foreign matter based on waveforms of the respective temperature sensors, and selects the removal means according to the position of the foreign matter. 3. The liquid ejection device according to configuration 1 or 2. [Configuration 4] At least some of the temperature sensors are disposed at positions overlapping with the liquid chambers when the liquid ejection head is viewed from above. 4. The liquid ejection device according to any one of configurations 1 to 3. [Configuration 5] a protective film is provided on the circuit board between the drive element and the liquid chamber; the foreign matter is kogane attached to the protective film, The removing means is a means for removing the kogation by applying a voltage to the protective film to dissolve the protective film. 2. The liquid ejection device according to claim 1, [Configuration 6] The protective film is a conductive film containing a platinum group element. 6. The liquid ejection device according to configuration 5. [Configuration 7] The foreign matter is a solidified matter or a highly viscous liquid derived from the liquid. 7. The liquid ejection device according to any one of configurations 1 to 6, [Configuration 8] the foreign matter is attached to a surface of the flow passage forming member opposite to the liquid chamber side, The removing means is a wiper that wipes the opposite surface. 8. The liquid ejection device according to configuration 7. [Configuration 9] The removing means is a means for expelling the foreign matter by pressurizing and circulating the liquid in the liquid chamber. 9. The liquid ejection device according to configuration 7 or 8. [Configuration 10] The removing means is a means for discharging the foreign matter by applying a voltage to the driving element to cause the liquid in the liquid chamber to bubble. 10. The liquid ejection device according to any one of configurations 7 to 9. [Configuration 11] The foreign matter is adhered to or retained inside the nozzle. 11. The liquid ejection device according to any one of configurations 7 to 10. [Configuration 12] The removing means is a means for sucking the foreign matter from a surface of the flow path forming member opposite to the liquid chamber side. 12. The liquid ejection device according to claim 11, [Configuration 13] The control unit determines the state of the foreign matter by analyzing a phase state of the liquid in the liquid chamber and a change in temperature from a waveform of a signal output from the temperature sensor. 13. The liquid ejection device according to any one of configurations 1 to 12. [Configuration 14] a protective film is provided on the circuit board between the drive element and the liquid chamber; the control unit calculates, based on a waveform of the signal, a first time when the liquid bubbles due to heat generated by the driving element and a second time when the liquid comes into contact with the protective film again; The state of the foreign matter is determined by calculating a discharge speed of the liquid based on an interval time from a first time to the second time. 14. The liquid ejection device according to claim 13, [Configuration 15] The control unit determines that the foreign matter is kogation adhered to the protective film when the discharge speed decreases over time. 15. The liquid ejection device according to configuration 14. [Configuration 16] The control unit determines that the foreign matter is clogged in the flow path when the discharge speed repeatedly decreases and recovers. 15. The liquid ejection device according to configuration 14. [Configuration 17] The temperature sensor is formed of a material containing at least one element selected from the group consisting of platinum, iridium, tungsten, zirconium, copper, nickel, zinc, titanium, silicon, and aluminum. 17. The liquid ejection device according to any one of configurations 1 to 16, [Configuration 18] The control unit determines whether or not the liquid ejection head needs to be replaced based on a waveform of a signal output from the temperature sensor. 18. The liquid ejection device according to any one of configurations 1 to 17. [Explanation of symbols]

[0050] 100: circuit board, 101: driving element, 102: liquid supply port, 120: flow path forming member, 121: nozzle, 122: liquid chamber, 130: temperature sensor, 141: lower protective film, 142: upper protective film, 411: waveform collecting unit, 412: feature extracting unit, 413: state determining unit, 414: determination output unit, 421: determination recording unit, 422: inference unit, 423: means selecting unit

Claims

1. In a liquid ejection device having a liquid ejection head for ejecting liquid, The liquid ejection head is formed by bonding a circuit board and a flow path forming member, a liquid chamber filled with liquid is provided at a portion where the circuit board and the flow path forming member are joined, a liquid supply port for supplying the liquid to the liquid chamber is provided on the circuit board; the flow passage forming member is provided with a nozzle for discharging the liquid in the liquid chamber, The circuit board is provided with a plurality of drive elements that generate heat when a voltage is applied to eject the liquid, and a plurality of temperature sensors; a plurality of removal means for removing foreign matter from within the liquid ejection head; a control unit that selects one of the plurality of removal units to remove the foreign matter based on a result of analyzing a waveform of a signal output from the temperature sensor; The liquid ejection device further comprises:

2. The control unit analyzes the waveform to determine the type of the foreign matter, and selects the removal means according to the type of the foreign matter.

2. The liquid ejection device according to claim 1 .

3. The control unit determines a position of the foreign matter based on waveforms of the respective temperature sensors, and selects the removal means according to the position of the foreign matter.

2. The liquid ejection device according to claim 1,

4. At least some of the temperature sensors are disposed at positions overlapping with the liquid chambers when the liquid ejection head is viewed from above. The liquid ejection device according to claim 1 .

5. a protective film is provided on the circuit board between the drive element and the liquid chamber; the foreign matter is kogane attached to the protective film, The removing means is a means for removing the kogation by applying a voltage to the protective film to dissolve the protective film. The liquid ejection device according to claim 1 .

6. The protective film is a conductive film containing a platinum group element.

6. The liquid ejection device according to claim 5.

7. The foreign matter is a solidified matter or a highly viscous liquid derived from the liquid. The liquid ejection device according to claim 1 .

8. the foreign matter is attached to a surface of the flow passage forming member opposite to the liquid chamber side, The removing means is a wiper that wipes the opposite surface.

8. The liquid ejection device according to claim 7.

9. The removing means is a means for expelling the foreign matter by pressurizing and circulating the liquid in the liquid chamber.

8. The liquid ejection device according to claim 7.

10. The removing means is a means for discharging the foreign matter by applying a voltage to the driving element to cause the liquid in the liquid chamber to bubble.

8. The liquid ejection device according to claim 7.

11. The foreign matter is adhered to or retained inside the nozzle.

8. The liquid ejection device according to claim 7.

12. The removing means is a means for sucking the foreign matter from a surface of the flow path forming member opposite to the liquid chamber side. The liquid ejection device according to claim 11 .

13. The control unit determines the state of the foreign matter by analyzing a phase state and a temperature change of the liquid in the liquid chamber from a waveform of a signal output from the temperature sensor. The liquid ejection device according to claim 1 .

14. a protective film is provided on the circuit board between the drive element and the liquid chamber; the control unit calculates, based on a waveform of the signal, a first time when the liquid bubbles due to heat generated by the driving element and a second time when the liquid comes into contact with the protective film again; The state of the foreign matter is determined by calculating a discharge speed of the liquid based on an interval time from a first time to the second time. The liquid ejection device according to claim 13 .

15. The control unit determines that the foreign matter is kogation adhered to the protective film when the discharge speed decreases over time. The liquid ejection device according to claim 14 .

16. The control unit determines that the foreign matter is clogged in the flow path when the discharge speed repeatedly decreases and recovers. The liquid ejection device according to claim 14 .

17. The temperature sensor is formed of a material containing at least one element selected from the group consisting of platinum, iridium, tungsten, zirconium, copper, nickel, zinc, titanium, silicon, and aluminum.

13. The liquid ejection device according to claim 1,

18. The control unit determines whether or not the liquid ejection head needs to be replaced based on a waveform of a signal output from the temperature sensor.

13. The liquid ejection device according to claim 1,

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