The present disclosure relates to a liquid ejection apparatus configured to eject a liquid and a determination method for determining an ejection state.
An inkjet recording apparatus (a liquid ejection apparatus) records various information such as an image on a recording material such as paper by ejecting ink (liquid) from a small nozzle (an ejection port). A thermal inkjet method is known as one of recording methods for an inkjet recording apparatus. In the thermal inkjet method, ink is ejected from an ejection port by film-boiling ink with heat energy generated in a heater (an electrothermal conversion element).
In the inkjet recording apparatus, an image formation problem occurs when a failure of ejecting ink occurs. In a full-line type recording apparatus, a huge number of nozzles are arranged on a line with a length corresponding to the entire width of a recording medium, which enables high-speed printing. An occurrence of an ejection failure is likely to cause an adverse effect on an image, and thus it is necessary to perform a recovery operation of a recording head. The recovery operation has following two types: wiping a nozzle surface while sucking; and wiping the nozzle surface without sucking. Both types cause downtime to occur. When the recovery operation includes sucking, wasting of ink occurs. For the inkjet recording apparatus, it is desirable to have as little downtime and wasting of ink as possible. Therefore, it is important to quickly identify what type of ejection failure is occurring in which one of the huge number of nozzles to make it possible to perform an adequate recovery operation at an adequate timing.
The ejection failure is roughly classified into two cases: a first case where an ejection failure occurs when there is ink on the heater; and a second case where an ejection failure occurs when there is no ink on the heater. A first type of the ejection failure in the first case is an external-dust ejection failure which occurs, for example, when the ejection is hindered by a foreign material such as paper dust adhering to the nozzle surface. A second type of the ejection failure in the first case is a wet ejection failure which occurs when ink adheres to the nozzle surface due to a satellite droplet or mist which hinders ejection. A third type of the ejection failure in the first case is a thickened ink ejection failure which is an ejection failure due to thickening of ink caused by moisture evaporation from the ejection port. A fourth type of the ejection failure in the first case is an internal-dust ejection failure which occurs when a foreign material intrudes into the inside of the nozzle and the ejection is hindered by the foreign material. An example of an ejection failure in the second case is an air bubble ejection failure which occurs when an air bubble intrudes into the inside of a nozzle and the ejection is hindered by the air bubble. When an ejection failure occurs, which type of ejection failure is dominant depends on the head structure and the nozzle structure.
Conventionally, to detect such an ejection failure in a thermal inkjet recording apparatus, it is known to check a change in temperature with time which occurs when a heater is driven to eject ink. An apparatus has been proposed which uses the method of determining the type of the ejection failure.
Japanese Patent Laid-Open No. 2007-331354 discloses a method of identifying a state of an ejection failure by measuring temperature at a predetermined timing and comparing the measured temperature with a plurality of threshold values.
Although Japanese Patent Laid-Open No. 2007-331354 discloses the technique of determining the state of the ejection failure by making comparisons with a plurality of threshold values at one timing, this technique does not allow it to provide a large determination range for each state determination because it is necessary to make the comparisons with the plurality of threshold values. Therefore, there is a possibility that it is difficult to maintain high determination reliability including the robustness against variations of the ink and the nozzle. Japanese Patent Laid-Open No. 2007-331354 also describes a technique of performing determination by making a comparison with one threshold value at each of a plurality of timings. However, to identify the ejection failure state, the determination process is performed three or more times, which makes it difficult to achieve high-speed determination.
To handle the above situation, the present disclosure provides a method of determining a state of an ejection failure with a high determination reliability in a short time by making a comparison with one threshold value at each of two timings.
The present disclosure provides a method of determining, in a liquid ejection apparatus, a state of a liquid ejection from an ejection port, the liquid ejection apparatus including the ejection port configured to eject a liquid, a substrate comprising an electrothermal conversion element configured to generate heat for ejecting the liquid from the ejection port, and a temperature detection unit configured to detect temperature information on the substrate, the method including performing a first comparison process to compare the temperature information on the substrate detected at a first timing by the temperature detection unit with a first threshold value, and performing a second comparison process to compare the temperature information on the substrate detected at a second timing by the temperature detection unit with a second threshold value.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present disclosure are described in detail below.
Sensor
A configuration of an inkjet recording apparatus is described below to which the present disclosure is applicable.
The CPU 400 includes a ROM 401 and a RAM 402, and performs control such that a proper recording condition is given for input information and the recording head 412 is driven so as to record the input information according to the recording condition. A program for executing a recovery procedure to recover the recording head is stored in the RAM 402 in advance, and recovery conditions such as a preliminary ejection condition are given to the recovery processing control circuit 407, the recording head, etc.
A recovery processing motor 408 drives the recording head, a blade (a cleaning blade) 409 provided facing the recording head, a cap 410, and a suction pump 411.
A recording head drive control circuit 414 drives the heater 3, which is an electrothermal conversion element of the recording head 412, according to a driving condition given by the CPU 400, and causes the recording head to perform preliminary ejection and recording ink ejection.
Determination Based on Change in Temperature with Time
In
Referring to
In
There is a large difference in the thermal conductivity between the gas and the liquid, and thus rapid cooling occurs as a result of the replacement of the gas with the liquid. In
In
In the external-dust ejection failure state, the bubble disappearing time is longer than in the normal ejection state, and the temperature of the heater decreases gradually with passage of time, which causes the difference in temperate between the heater and ink to become small. Therefore, the temperature change which occurs in the external-dust ejection failure state is smaller than that which occurs in the normal ejection state.
The change in the cross section of the nozzle part with time which occurs in the external-dust ejection failure state, which is one of the ink-presence ejection failure states, has been described above with reference to
a wet ejection failure which occurs when ink adheres to the nozzle surface due to a satellite droplet or mist and ejection is hindered by the adhering ink; a thickened ink ejection failure which occurs when the viscosity of ink is increased (thickened) by moisture evaporation from the ejection port and ejection is hindered by the increased viscosity; and an internal-dust ejection failure which occurs when a foreign material intrudes into the inside of the nozzle and the ejection is hindered by the foreign material. Also in these types of ink-presence ejection failure states, a characteristic point appears later than in the case of the normal ejection state. However, there is a slight difference in the degree of delay of the advent of the characteristic point depending on the type and degree of the ejection failure.
This is because the flow resistance on the ejection port side and the flow resistance on the ink supply flow path side in the nozzle part vary depending on the type and degree of ejection failure, and thus a difference occurs in the process of the growth and the disappearance.
In
In this specific example, the nozzle has a nozzle height h1=26 μm and a flow path height h2=20 μm. Under the conditions in the present embodiment, the characteristic point appears 5 μsec after the drive voltage is applied in the case of the normal ejection state, and the characteristic point appears 9 μsec after the drive voltage is applied in the case of the external-dust ejection failure state which is one of the ink-presence ejection failure states. In these cases, the characteristic points are based on the bubble disappearance time. The time at which the characteristic point occurs in the normal ejection state is determined by various factors including the driving conditions such as the drive voltage pulse condition, the nozzle dimensions such as the ejection port shape, the nozzle height, and the like, the physical ink properties such as the viscosity and temperature of the ink, and the like. On the other hand, in the ink-presence ejection failure state, the characteristic point occurs always later than in the normal ejection state because the flow resistance in the nozzle part is higher than that in the normal ejection. The fact that the characteristic point occurs in both the normal ejection state and the ink-presence ejection failure state, and the fact that the characteristic point in the ink-presence ejection failure state occurs later than in the normal ejection state always hold regardless of the details of the conditions. Therefore, it is always possible to determine the normal ejection and the ink-presence ejection failure.
First, in step S1, a head drive condition applied to the heater 3 is referred to, and a first detection timing 34 and a second detection timing 35 are set in advance such that the first detection timing 34 occurs between a characteristic point in the normal ejection state and a characteristic point in the ink-presence ejection failure state, and the second detection timing 35 occurs after the characteristic point in the ink-presence ejection failure state.
Since a temperature difference occurs depending on whether a characteristic point occurs or not, it is possible to set temperature threshold values in advance. In step S2, a threshold value at the first detection timing 34 is set to T(1_normal ejection). In step S3, a threshold value at the second detection timing 35 is set to T(2_ink-presence ejection failure). The threshold values may be set to predicted values in advance before shipment, or may be set based on the normal ejection state and the ink-presence ejection failure state experimentally generated by changing the conditions of the drive voltage pulse.
Then, in step S4, the temperature is output from the temperature sensor at the first and second detection timings as the drive control is performed. Then, in step S5, the temperature T(1) at the first detection timing (the first timing) 34 is acquired, and in step S6, the temperature T(2) at the second detection timing (the second timing) 35 is acquired.
In step S7, the detected temperature acquired in steps S4 are compared with the threshold value set in step S2, and in step S9, the detected temperature acquired in step S5 are compared with the threshold value set in step S3. In a case where it is determined in step S7 that T(1)≥T(1_normal ejection), the process proceeds to step S8 in which it is determined that the nozzle is in the normal ejection state. On the other hand, in a case where it is determined in step S7 that T(1)<T(1_normal ejection), the process proceeds to step S9. That is, at the first timing 34, it can be determined whether a liquid is ejected from the ejection port normally or abnormally. In a case where it is determined in step S9 that T(2)≥T(2_ink-presence ejection failure), the process proceeds to step S10 in which it is determined that the nozzle is in the ink-presence ejection failure state. In this case, the process further proceeds to step S11 in which a warning is displayed or a recovery operation is performed. In a case where it is determined in step S9 that T(2)<T(2_ink-presence ejection failure), the process proceeds to step S12 in which it is determined that the nozzle is in the no-ink ejection failure state. In this case, the process further proceeds to step S13 in which a warning is displayed or a recovery operation is performed. That is, when it is determined at the first timing 34 that the liquid ejection from the ejection port is abnormal, it is possible to determine, at the second timing 35, the type (the cause) of the abnormality. In the present embodiment, in steps S7 and S9, the detected temperature detected at the first and second detection timings are each compared with the corresponding one threshold value. This is important because each threshold value can be set within a large range, and thus it becomes possible to achieve more reliable determination result. That is, this makes it possible to enhance the robustness against the manufacturing variation of the nozzle size and the variation of the ink physical properties due to the change with time.
According to the first embodiment described above, a determination is made twice as to whether a temperature reduction related to a characteristic point occurs such that the determination is made once at one of the two detection timings based on the normal ejection state, and the determination is made once at the other one of the two detection timings based on the ink-presence ejection failure state. This makes it possible to determine whether the ejection failure is of the ink-presence ejection failure type or the no-ink ejection failure type.
In other words, the state of liquid ejection from the ejection port can be determined.
In the first embodiment described above, the state of the ejection failure is determined from the detections at the two detection timings based on characteristic points in the change in the sensor temperature with time. In a second embodiment described below, using the fact that a sudden temperature reduction occurs at a characteristic point, the detected temperate is first-order differentiated over the entire range of the temperature reduction process thereby emphasizing the temperature change at the characteristic point. Variations of ink and nozzles are often occur as high-frequency noise, and thus the influence of such variations on the result of the emphasizing process can be reduced by using a filter circuit. Therefore, from the viewpoint of detecting whether there is a characteristic point, the second embodiment provides a better method than the above-described first embodiment based on a change in temperate. In the present embodiment, the first-order differentiation is used in the emphasizing process, but second-order differentiation, frequency analysis, or other methods may be used to achieve the emphasizing process.
First, in step S21, a head drive condition applied to the heater 3 is referred to, and a first detection timing 34 and a second detection timing 35 are set in advance such that the first detection timing 34 is located near a peak based on a characteristic point in the normal ejection state, and the second detection timing 35 is located near a peak based on a characteristic point in the ink-presence ejection failure state.
Depending on whether there is a characteristic point or not, a peak occurs and the value thereof changes, and thus it is possible to set a threshold value in advance.
In step S22, a threshold value at the first detection timing 34 is set to D(1_normal ejection). In step S23, a threshold value at the second detection timing 35 is set to D(2_ink-presence ejection failure). Also in this case, the threshold values may be set to predicted values in advance before shipment, or may be set based on the normal ejection state and the ink-presence ejection failure state experimentally generated by changing the conditions of the drive voltage pulse.
Then, in step S24, the temperature sensed by the temperature sensor is first-order differentiated at the first and second detection timings as the drive control is performed, and the resultant derivatives are output. In step S25, the derivative D(1) at the first detection timing 34 is acquired, and in step S26, the derivative D(2) at the second detection timing 35 is acquired.
In step S27, the derivative acquired in steps S24 is compared with the threshold value set in step S22, and in step S29, the derivative acquired in step S25 is compared with the threshold value set in step S23. In a case where it is determined in step S27 that D(1)≤D(1_normal ejection), the process proceeds to step S28 in which it is determined that the nozzle is in the normal ejection state. On the other hand, in a case where it is determined in step S27 that D(1)>T(1_normal ejection), the process proceeds to step S29. In a case where it is determined in step S29 that D(2)≤D(2_ink-presence ejection failure), the process proceeds to step S30 in which it is determined that the nozzle is in the ink-presence ejection failure state. In this case, the process further proceeds to step S31 in which a warning is displayed or a recovery operation is performed. In a case where it is determined in step S29 that D(2)>D(2_ink-presence ejection failure), the process proceeds to step S32 in which it is determined that the nozzle is in the no-ink ejection failure state. In this case, the process further proceeds to step S33 in which a warning is displayed or a recovery operation is performed.
Although the first-order derivative makes it possible to indicate a characteristic point by a peak, when a slight shift between the detection timing and the peak occurs due to a variation in ink or the nozzle, the slight shift can cause a significant influence on the values. To handle the above situation, instead of setting the detection timing near the peak, it may be better to set a detection range with a time width around the peak and output a minimum value thereof. Especially when an analog circuit is used, this method is very suitable because it is easy for the analog circuit to provide an output in such a manner.
In the second embodiment, as described above, a determination is made twice as to whether a peak related to a characteristic point occurs in the first-order derivative in the temperature reduction process such that the determination is made once at a detection timing based on the normal ejection state, and the determination is made once at a detection timing based on the ink-presence ejection failure state. This makes it possible to determine whether the ejection failure type is the ink-presence ejection failure or the no-ink ejection failure. Thus, it is possible to display an optimum warning and/or perform an optimum recovery operation depending on the type of the ejection failure. In this second embodiment as in the first embodiment, in each of comparison steps S27 and S29 at the first and second detection timings, the comparison is made with one threshold value. This is important because each threshold value can be set within a large range, and thus it becomes possible to achieve more reliable determination result. That is, this makes it possible to enhance the robustness against the manufacturing variation of the nozzle size and the variation of the ink physical properties due to the change with time.
Application to Supplying Ink from One Side
In the examples described above, ink is supplied to the nozzle from both sides. Assuming this nozzle structure, the ejection failure state is determined based on the fact that a characteristic point occurs due to bubble disappearance in the normal ejection state and the ink-present ejection failure state, and the fact that the characteristic point occurs in the ink-presence ejection failure statue later than in the normal ejection state. This feature also occurs in the case where the nozzle is configured such that ink is supplied from one side, and thus it is possible to perform a determination process in a similar manner to the case where ink is supplied from both sides.
In the above description according to the present embodiment, it has been assumed that the bubble generated in the nozzle disappears without communicating with the atmosphere. However, depending on the nozzle dimensions, the generated bubble may communicate with the atmosphere. In this case, the bubble may behave as follows. The bubble pressure with a negative pressure tries to become equal to the atmospheric pressure, but a tail part of an ejected droplet is torn off by the negative pressure of the bubble and crashes down to the heater surface (hereinafter, this will be referred to as a tail tear-off crash). Such a nozzle may have dimensions of, for example, h1=22 μm and h2=16 μm. As a result of the tail tear-off crash, the bubble on the heater surface is replaced with ink, that is, gas covering the heater surface is replaced with a liquid and thus quick cooling occurs, which causes a characteristic point to occur. Also in such a nozzle, in the normal ejection state, re-contacting of ink with the heater surface causes quick cooling. Therefore, also in this type of nozzle, as with the nozzle that does not communicate with the atmosphere according to the first or second embodiment, a characteristic point occurs in the ink-presence ejection failure state later than in the normal ejection state. That is, the temperature changes with time in a similar manner to that in the previous embodiments, and it is possible to detect an ejection failure by performing a determination process in a similar manner.
There is a possibility that depending on the nozzle dimensions, after the bubble gets to communicate with the atmosphere, all ink on the heater surface is ejected without tail tear-off crash onto the heater surface. Such a nozzle may have dimensions of, for example, h1=9.5 μm and h2=5.0 μm. Such a nozzle may have temperature changes with time as shown in
Second Detection Timing
In the present embodiment, based on the fact that in the ink-presence ejection failure state, the characteristic point occurs earlier than in the normal ejection state, the first and second detection timings corresponding to the respective characteristic points are set fixedly. In the normal ejection state, the characteristic point occurs at the fixed point of time when the ink and nozzle conditions are the same. On the other hand, in the ink-presence ejection failure state, the characteristic point occurs at different points of time depending on the details of the ejection failure, or, even for the same type of ejection failure, depending on the degree of the ejection failure.
Examples of types of ejection failures in the ink-presence ejection failure state include the external-dust ejection failure, the wet ejection failure, the thickened ink ejection failure, and the internal-dust ejection failure. The flow resistance of the nozzle part on the ejection port side and the flow resistance of the ink supply flow path side are different depending on the types of ejection failures, and thus the characteristic point occurs at different timings depending on the types of ejection failures. The higher the flow resistance depending on the type of the ejection failure, the later the timing of the characteristic point. Therefore, by appropriately setting the detection timing, it is possible to detect the type of the ejection failure in the ink-presence ejection failure state.
In the external-dust ejection failure state, for example, the degree of ejection failure may be such that, as shown in
As can be seen from the above discussion, the essence of the present disclosure is in that the first detection timing is set in advance based on the characteristic point occurring in the normal ejection state depending on the nozzle, and the second detection timing is set based on the characteristic point depending on the state of the ejection failure. That is, the second detection timing is provided not necessarily to determine whether or not the nozzle has the ink-presence ejection failure, but to determine the type of ejection failure that is to be surely detected and the degree of the ejection failure.
According to the embodiment described above, it is possible to determine whether or not the nozzle has an ejection failure, and determine the type of the ejection failure such as the ink-presence ejection failure or the no-ink ejection failure. The determination is performed at two timings based on the characteristic points corresponding to the normal ejection state and the ink-presence ejection failure state such that the determination process is performed twice wherein the comparison with one threshold value is performed in each determination process. Since the determination process is performed only twice, the determination can be made at a high speed. In addition, since the comparison is performed with only one threshold value in each determination process, it is allowed to set the comparison range large, which make it possible to achieve high reliability in the determination. Furthermore, depending on the position where the second detection timing is set, it is possible to more finely determine the state of the ejection failure and the degree of the ejection failure.
When the determination result indicates the occurrence of the no-ink ejection failure, the air bubble ejection failure is assumed and the recovery operation is performed such that the nozzle surface is wiped while performing sucking. A specific example of such a recovery operation is vacuum wiping. In the case of the ink-presence ejection failure, the wet ejection failure or the external-dust ejection failure is assumed, and the recovery operation is performed such that the nozzle surface is wiped without performing sucking. A specific example of such a recovery operation is blade wiping.
One example of the ink-presence ejection failure is a thickened ink ejection failure which occurs when the viscosity of ink increases owing to moisture evaporation from an ejection port and the ejection is hindered by the increased viscosity. Another example is an internal-dust ejection failure which occurs when a foreign material intrudes into the inside of the nozzle and the ejection is hindered by the foreign material. When such an ejection failure occurs, it may be necessary to perform a recovery operation such that the nozzle surface is wiped while performing sucking as with the recovery operation for the no-ink ejection failure. However, in a case where a nozzle has a capability of recirculation using a differential pressure or the like, the increase in ink viscosity does not occur, and thus the ejection failure is not cased by the increase in ink viscosity. In most cases, the internal-dust ejection failure is caused by a foreign material which intrudes during a manufacturing process, and it is often difficult to remove such a foreign material by the recovery operation. In such a case, it may be sufficient only to identify whether the ejection failure is of the ink-presence ejection failure type or the no-ink ejection failure type at a high speed with high accuracy. In such a case, in accordance with the result of the determination as to whether the ejection failure is of the ink-presence ejection failure type or the no-ink ejection failure type, an optimum recovery operation may be performed thereby making it possible to reduce the downtime and the amount of waste ink. Therefore, depending on the position where the second detection timing is set, as required, it is possible to more finely determine the ejection failure state and the degree of the ejection failure.
According to the present disclosure, it is possible to determine whether or not ink is normally ejected and it is possible to determine the state of an ejection failure by performing the determination process twice using a comparison with one threshold value in each determination process. This makes it possible to increase the detection speed and enhance the detection reliability. Thus, it is possible to determine the state of the ejection failure, and more specifically, it is possible to determine whether the ejection failure occurs in the state where there is ink on the heater as typified in the case of the external-dust ejection failure or the wet ejection failure, or whether the ejection failure occurs in the state in which there is no ink on the heater as typified in the case of the air bubble ejection failure. According to the determined state of the ejection failure, it is possible to perform an appropriate process such as the recovery operation.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2021-135582 filed Aug. 23, 2021, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2021-135582 | Aug 2021 | JP | national |
Number | Name | Date | Kind |
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20070229566 | Takabayashi | Oct 2007 | A1 |
20070291068 | Aoki | Dec 2007 | A1 |
20100156982 | Sasagawa | Jun 2010 | A1 |
Number | Date | Country |
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2007331354 | Dec 2007 | JP |
Number | Date | Country | |
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20230054702 A1 | Feb 2023 | US |