JP7640351B2 - Liquid circulating device and liquid ejecting device - Google Patents

Description

Embodiments of the present invention relate to a liquid circulation device and a liquid ejection device.

There is a liquid circulation device that circulates liquid along a circulation path that includes a liquid ejection head. Liquid circulation devices are used in inkjet printers that record images by ejecting ink from a liquid ejection head onto a recording medium. The ink used in inkjet printers has a temperature range that is suitable for ejecting ink droplets. Therefore, a liquid circulation device is known in which a heater is installed in part of the circulation path, and the heating by the heater is controlled so that the ink flowing through the circulation path maintains a temperature within that temperature range.

Normally, this type of liquid circulation device performs heating control when a sufficient amount of ink is circulating through the circulation path. However, there are cases where heating control is performed even when ink is not circulating due to some reason. If heating control is performed when ink is not circulating, the heater temperature rises rapidly in a short period of time. If the heater overheats beyond its upper limit temperature, there is a risk that the temperature fuse will be activated or the heater will be damaged. In addition, the temperature of the ink near the heater will also rise rapidly, which may cause the composition of the ink to change.

JP 2017-105212 A

The problem that the embodiments of the present invention aim to solve is to provide a technology that prevents problems caused by overheating in a liquid circulation device that uses a heater to heat the circulating liquid or in a liquid ejection device that uses such a liquid circulation device.

In one embodiment, the liquid circulation device includes a liquid chamber, a pipeline, a heater, a first temperature sensor, a second temperature sensor, and a controller. The liquid chamber stores liquid to be supplied to the liquid ejection head. The pipeline circulates the liquid between the liquid chamber and the liquid ejection head. The heater heats the liquid circulating through the pipeline. The first temperature sensor detects the temperature of the heater. The second temperature sensor detects the temperature of the liquid circulating through the pipeline. The controller controls the output of the heater based on the temperature of the liquid detected by the second temperature sensor. The controller also monitors the temperature change of the heater detected by the first temperature sensor. Then, when a temperature change that satisfies a stop condition is detected, the controller stops the output of the heater. The controller monitors the slope of the temperature change per unit time, and stops the output of the heater when the slope exceeds a threshold value.

1 is a side view for illustrating an outline of an inkjet printer according to an embodiment. 2 is a schematic diagram for explaining the configuration of a liquid discharge head and a liquid circulation device of the liquid discharge device in the inkjet printer. FIG. 2 is a block diagram showing the main circuit configuration of an inkjet control device in the inkjet printer. 4 is a flowchart for explaining an ink heating control function of a processor of the inkjet control device. 4 is a flowchart for explaining an overheating monitoring control function of a processor of the inkjet control device. 6 is a diagram showing one aspect of a temperature change of a heater controlled by ink heating control and overheating monitoring control. FIG. 10 is a graph showing a correspondence relationship between the environmental temperature and a third threshold value. 10 is a graph showing the correspondence relationship between the ink flow rate and a third threshold value. 13 is a schematic diagram showing main memory areas formed in a RAM of an inkjet control device in a second embodiment; 13 is a flowchart illustrating a function of overheating monitoring control that the processor of the inkjet control device has in the second embodiment. 13 is a flowchart illustrating a function of overheating monitoring control that the processor of the inkjet control device has in the second embodiment.

Below, an embodiment of a liquid circulation device and a liquid ejection device will be described with reference to the drawings, using as an example an inkjet printer that ejects ink droplets from a circulation type liquid ejection head to form an image on a recording medium.

[First embodiment]
First, the first embodiment will be described with reference to FIGS. 1 to 8. FIG.
1 is a side view for explaining an outline of an inkjet printer 1. The inkjet printer 1 includes a plurality of liquid ejection devices 10, a head support mechanism 11, a head driving mechanism 12, a medium support mechanism 13, and a printer control device 14.

The head support mechanism 11 supports the multiple liquid ejection devices 10 in parallel in the direction of arrow A. The head drive mechanism 12 reciprocates the multiple liquid ejection devices 10 in the direction of arrow A, which are aligned in parallel by the head support mechanism 11. The medium support mechanism 13 supports the recording medium S in a position opposite the multiple liquid ejection devices 10 reciprocating in the direction of arrow A by the head drive mechanism 12, so that the recording medium S can be moved in a direction perpendicular to the direction of arrow A. The printer control device 14 controls the operation of the components of the inkjet printer 1, including the head drive mechanism 12.

The liquid ejection device 10 is equipped with a liquid ejection head 20 and a liquid circulation device 30. The liquid ejection device 10 ejects a liquid, such as ink I, from the liquid ejection head 20 while moving back and forth in the direction of arrow A by the head drive mechanism 12, thereby forming a desired image on a recording medium S supported by a medium support mechanism 13.

The multiple liquid ejection devices 10 eject ink of multiple colors, for example, cyan ink, magenta ink, yellow ink, black ink, and white ink. The multiple liquid ejection devices 10 have the same configuration but use different inks. The color or characteristics of the ink I used are not limited. For example, instead of white ink, transparent glossy ink, special ink that changes color when exposed to infrared or ultraviolet light, etc. may be ejected.

Figure 2 is a schematic diagram for explaining the configuration of the liquid ejection head 20 and the liquid circulation device 30 of the liquid ejection device 10. The liquid ejection head 20 has an ink supply port 21 and an ink discharge port 22. The liquid ejection head 20 forms an ink flow path inside the liquid ejection head 20 so that ink supplied from the ink supply port 21 is discharged from the ink discharge port.

The liquid ejection head 20 has multiple pressure chambers arranged in the middle of the ink flow path. The liquid ejection head 20 supplies ink to each pressure chamber through the ink flow path. The liquid ejection head 20 has a nozzle and an actuator for each pressure chamber. The nozzle communicates with the corresponding pressure chamber. The actuator displaces the volume of the corresponding pressure chamber. In the liquid ejection head 20, the ink I in the pressure chamber is ejected from the nozzle communicating with that pressure chamber by displacing the volume of the pressure chamber through the action of the actuator. The liquid ejection head 20 ejects ink from each pressure chamber that has not been ejected from the nozzle through the outlet 22.

The liquid circulation device 30 is integrally connected to the liquid ejection head 20 at the top of the liquid ejection head 20 by, for example, a metal connecting part. The liquid circulation device 30 includes an upstream tank 31, a downstream tank 32, a supply tank 33, a circulation pump 34, and a supply pump 35. The upstream tank 31, the downstream tank 32, and the supply tank 33 are for storing the same type of ink. The circulation pump 34 is for sending ink stored in the downstream tank 32 to the upstream tank 31. The supply pump 35 is for sending ink stored in the supply tank 33 to the upstream tank 31.

The liquid circulation device 30 has a first pipeline 361, a second pipeline 362, a third pipeline 363, and a fourth pipeline 364. The first pipeline 361 is a pipeline that connects the upstream tank 31 and the supply port 21 of the liquid ejection head 20. The second pipeline 362 is a pipeline that connects the exhaust port 22 of the liquid ejection head 20 and the downstream tank 32. The third pipeline 363 is a pipeline that connects the downstream tank 32 and the upstream tank 31. The fourth pipeline 364 is a pipeline that connects the supply tank 33 and the upstream tank 31.

The ink stored in the upstream tank 31 is sent through the first pipeline 361 to the supply port 21 of the liquid ejection head 20, and passes through an ink flow path formed inside the liquid ejection head 20. The ink discharged from the outlet 22 of the liquid ejection head 20 through the ink flow path is sent through the second pipeline 362 to the downstream tank 32, and is stored in the downstream tank 32. The ink stored in the downstream tank 32 is sent through the third pipeline 363 to the upstream tank 31 by the action of the circulation pump 34, and returns to the upstream tank 31.

In this way, the first pipeline 361, the second pipeline 362, and the third pipeline 363 constitute a pipeline that circulates the ink liquid between the upstream tank 31, which is a liquid chamber, and the liquid ejection head 20, which is a so-called circulation path 36.

The liquid ejection device 10 ejects ink circulating through the circulation path 36 from the liquid ejection head 20. As a result, the amount of ink stored in the upstream tank 31 decreases. When the ink becomes low, the ink stored in the supply tank 33 is sent to the upstream tank 31 through the fourth pipe 364 by the action of the supply pump 35, and is replenished to the upstream tank 31.

The liquid circulation device 30 has liquid level sensors 41, 42 provided inside the upstream tank 31 and the downstream tank 32, respectively. The liquid level sensor 41 detects the amount of ink in the upstream tank 31. The liquid level sensor 42 detects the amount of ink in the downstream tank 32. The printer control device 14 appropriately controls the supply pump 35 based on the detection results of the liquid level sensors 41, 42 to supply ink from the supply tank 33 to the upstream tank 31. By supplying ink from the supply tank 33 to the upstream tank 31, the printer control device 14 adjusts the amount of ink circulating through the circulation path 36 to an appropriate amount.

The liquid circulation device 30 is provided with pressure sensors 43, 44 in the upstream tank 31 and the downstream tank 32, respectively. The pressure sensor 43 detects the pressure in the upstream tank 31. The pressure sensor 44 detects the pressure in the downstream tank 32. The liquid circulation device 30 is equipped with a pressure adjustment mechanism 45. The pressure adjustment mechanism 45 opens the upstream tank 31 and the downstream tank 32 to the atmosphere, or pressurizes and depressurizes the downstream tank 32. The printer control device 14 controls the pressure adjustment mechanism 45 as appropriate based on the detection results of the pressure sensors 43, 44 to adjust the pressure in the circulation path 36. The printer control device 14 adjusts the ink pressure in the nozzles of the liquid ejection head 20 by adjusting the pressure in the circulation path 36.

The liquid circulation device 30 has a heater 51 in the middle of the first pipe 361. The heater 51 is for heating the ink flowing in the first pipe 361. The liquid circulation device 30 has a first temperature sensor 52 in the heater 51. The first temperature sensor 52 is for detecting the temperature of the heater 51. The liquid circulation device 30 also has a second temperature sensor 53 in the middle of the second pipe 362. The second temperature sensor 53 is for detecting the temperature of the ink flowing in the second pipe 362. The printer control device 14 controls the power supply to the heater 51 to be turned on and off based on the detection result of the second temperature sensor 53, and adjusts the temperature of the ink flowing in the circulation path 36 to an appropriate value. The printer control device 14 also prevents the heater 51 from overheating based on the detection result of the first temperature sensor 52.

Figure 3 is a block diagram showing the main circuit configuration of the printer control device 14. The printer control device 14 includes a processor 61, a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 63, a timer 64, an operation panel 65, a communication interface 66, a motor 67, and a liquid ejection device interface 68. The printer control device 14 connects the processor 61 with the ROM 62, the RAM 63, the timer 64, the operation panel 65, the communication interface 66, the motor 67, and the liquid ejection device interface 68 via a system bus 69. The system bus 69 includes an address bus, a data bus, etc.

The processor 61 controls each component to realize the various functions of the inkjet printer 1 according to the operating system and application programs.

The ROM 62 stores the operating system and application programs described above. The ROM 62 may also store data necessary for the processor 61 to execute processes for controlling each component.

RAM 63 stores data necessary for processor 61 to execute processing. RAM 63 is also used as a work area where information is rewritten by processor 61 as appropriate. The work area includes an image memory where print data is expanded.

The timer 64 measures the time.
The operation panel 65 has an operation section and a display section. The operation section has function keys such as a power key, an error reset key, etc. The display section can display various states of the inkjet printer 1.

The communication interface 66 receives print data from a client terminal connected via a network such as a LAN (Local Area Network). For example, when an error occurs in the inkjet printer 1, the communication interface 66 transmits a signal notifying the client terminal of the error.
The motor 67 is a drive source for the head support mechanism 11 and the medium support mechanism 13 .

The liquid ejection device interface 68 relays signals transmitted and received between the processor 61 and the multiple liquid ejection devices 10. Signals transmitted from the processor 61 to the liquid ejection devices 10 include signals for controlling the operation of the liquid ejection head 20, and signals for controlling the operation of the circulation pump 34, the supply pump 35, the pressure adjustment mechanism 45, and the heater 51 in the liquid circulation device 30. Signals transmitted from the liquid ejection devices 10 to the processor 61 include detection signals from the liquid level sensors 41, 42, the pressure sensors 43, 44, and the first and second temperature sensors 52, 53 in the liquid circulation device 30.

In this configuration, the processor 61 has at least the function of an ink heating control 611 and the function of an overheating monitoring control 612. These functions are provided for each liquid ejection device 10. These functions are realized by a program stored in the ROM 62.

Figure 4 is a flow diagram for explaining the function of the ink heating control 611 for one liquid ejection device 10. The function of the ink heating control 611 for other liquid ejection devices 10 is similar, so a description thereof will be omitted here. Note that the heater 51 and second temperature sensor 53 that appear in the following description are provided in the liquid circulation device 30 of the liquid ejection device 10 to be controlled.

When the processor 61 starts functioning as the ink heating control 611, it turns on the power to the heater 51 in ACT 1. Then, the processor 61 acquires the liquid temperature LT detected by the second temperature sensor 53 in ACT 2. The liquid temperature LT is the temperature of the ink flowing through the second pipeline 362.

The processor 61 checks whether the liquid temperature LT is equal to or higher than the first threshold value TSa in ACT 3. The first threshold value TSa is the upper limit temperature of the temperature range suitable for ejecting ink droplets. The optimal value of the first threshold value TSa is determined based on the type of ink used in the liquid ejection device 10, the ink flow rate, etc., and is set in the RAM 63.

If the liquid temperature LT is less than the first threshold value Sa, the processor 61 determines NO in ACT 3 and returns to ACT 2. The processor 61 repeatedly executes the processes in ACT 2 and ACT 3 until the liquid temperature LT becomes equal to or greater than the first threshold value TSa.

When the liquid temperature LT becomes equal to or higher than the first threshold value TSa, the processor 61 determines YES in ACT 3 and proceeds to ACT 4. The processor 61 turns off the power to the heater 51 in ACT 4. Then, the processor 61 obtains the liquid temperature LT detected by the second temperature sensor 53 in ACT 5.

The processor 61 checks whether the liquid temperature LT is less than the second threshold value TSb in ACT 6. The second threshold value TSb is the lower limit temperature of the temperature range suitable for ejecting ink droplets. The optimal value of the second threshold value TSb is determined based on the type of ink used in the liquid ejection device 10, the ink flow rate, etc., and is set in the RAM 63.

If the liquid temperature LT is equal to or higher than the second threshold value Sb, the processor 61 determines NO in ACT 6 and returns to ACT 5. The processor 61 repeatedly executes the processes in ACT 5 and ACT 6 until the liquid temperature LT becomes less than the second threshold value TSb.

When the liquid temperature LT becomes less than the second threshold value TSb, the processor 61 determines YES in ACT 6 and proceeds to ACT 1. The processor 61 turns on the power supply to the heater 51 in ACT 1. Thereafter, the processor 61 executes the processes from ACT 2 onwards in the same manner as described above.

In this way, the processor 61 appropriately controls the power supply to the heater 51 to be turned on or off so that the temperature of the ink flowing through the circulation path 36 falls within a temperature range suitable for ejecting ink droplets. Through this control, the temperature of the ink ejected from each liquid ejection device 10 is adjusted to fall within a temperature range suitable for ejecting ink droplets during normal use of the inkjet printer 1. As a result, high-quality printing is possible.

Here, the processor 61 having the function of ink heating control 611 constitutes a control unit that controls the output of the heater 51 based on the ink temperature detected by the second temperature sensor 53.

In the liquid circulation device 30, the ink heating control by the processor 61 is usually performed when a sufficient amount of ink is circulating through the circulation path 36. However, for example, if the circulation pump 34 breaks down or a bug occurs in the process that controls the circulation pump 34, the ink heating control may be performed without the ink circulating. If the ink heating control is performed without the ink circulating, the temperature of the heater 51 will rise rapidly in a short time. If the temperature of the heater 51 rises rapidly and overheating occurs beyond the upper limit temperature of the heater 51, there is a risk that the temperature fuse will be activated or the heater 51 will be broken. In addition, since the temperature of the ink near the heater 51 will rise rapidly, there is a risk that the composition of the ink will change. In order to prevent such malfunctions, the processor 61 has a function as an overheating monitoring control 612 for monitoring overheating of the heater 51.

Figure 5 is a flow chart for explaining the function of overheating monitoring control 612 for one liquid ejection device 10. The function of overheating monitoring control 612 for other liquid ejection devices 10 is similar, so a description thereof will be omitted here. Note that the heater 51 and first temperature sensor 52 that appear in the following description are provided in the liquid circulation device 30 in the liquid ejection device 10 to be controlled.

The processor 61 checks whether or not power is being supplied to the heater 51 in ACT 11. If power is not being supplied to the heater 51, the result in ACT 11 is NO. The processor 61 waits for power to be supplied to the heater 51 to be turned on.

In the function of the ink heating control 611 described with reference to FIG. 4, when power is turned on to the heater 51, the processor 61 determines YES in ACT 11 and proceeds to ACT 12. In ACT 12, the processor 61 acquires the heater temperature HT detected by the first temperature sensor 52. The heater temperature HT is the temperature of the heater 51. In ACT 13, the processor 61 stores the heater temperature HT in the work memory of the RAM 63 as the previous heater temperature HTa.

In ACT 14, the processor 61 waits for one second to be counted by the timer 64. When one second has been counted, the processor 61 determines YES in ACT 14 and proceeds to ACT 15. In ACT 15, the processor 61 obtains the heater temperature HT detected by the first temperature sensor 52.

In ACT 16, the processor 61 subtracts the previous heater temperature HTa stored in the work memory from the heater temperature HT to calculate the temperature rise width HTx per second. Then, in ACT 17, the processor 61 checks whether the temperature rise width HTx is equal to or greater than the third threshold value TSc.

The third threshold value TSc is a value that is suitable for determining that the temperature rise HTx per second, i.e., the slope of the temperature change per unit time, is at risk of overheating the heater 51. For example, if the temperature of the heater 51 rises by about 2°C per second, it is considered that there is a risk of overheating the heater 51. In this case, the third threshold value TSc is set to "2°C."

In ACT 17, if the temperature increase amount HTx is less than the third threshold value TSc, the processor 61 determines NO in ACT 17 and returns to ACT 13. In ACT 13, the processor 61 overwrites the heater temperature HT obtained in the process of ACT 15 as the previous heater temperature HTa in the work memory of the RAM 63. After that, the processor 61 executes the processes from ACT 14 onwards in the same manner as described above.

In ACT 17, if the temperature increase amount HTx is equal to or greater than the third threshold value TSc, the processor 61 determines YES in ACT 17 and proceeds to ACT 18. In ACT 18, the processor 61 turns off the power supply to the heater 51. With this, the processor 61 ends the control of the procedure shown in the flowchart of FIG. 5.

In this way, the processor 61 monitors the heater temperature HT detected by the second temperature sensor 53 when the heater 51 is energized. The processor 61 then turns off the heater 51 when the temperature rise rate HTx of the heater temperature HT per second becomes equal to or greater than the third threshold value TSc. When the temperature rise rate HTx of the heater temperature HT per second becomes equal to or greater than the third threshold value TSc, there is a risk of overheating by the heater 51. When overheating occurs, there is a risk that the temperature fuse will be activated or the heater 51 will be damaged. In addition, the temperature of the ink near the heater 51 will rise rapidly, which may cause the composition of the ink to change.

In this embodiment, when the temperature rise rate HTx per second of the heater temperature HT becomes equal to or greater than the third threshold value TSc, the power supply to the heater 51 is turned off. This makes it possible to prevent the heater 51 from overheating. As a result, there is no risk of the temperature fuse activating or the heater 51 being damaged by overheating. In addition, the composition of the ink is not changed by overheating.

Here, the processor 61 having the function of overheating monitoring control 612 constitutes a control unit that monitors the temperature change of the heater 51 detected by the first temperature sensor 52, and stops the output of the heater 51 when a temperature change that satisfies the stop condition is detected.

Figure 6 is a diagram showing one aspect of the temperature change of the heater 51 controlled by the ink heating control 611 and the overheating monitoring control 612. In Figure 6, the vertical axis represents the temperature HT (°C) of the heater 51, and the horizontal axis represents time t (seconds).

In FIG. 6, the time t is "0" when power to the heater 51 is turned on in ACT1 of the ink heating control 611. When power to the heater 51 is turned on, the temperature HT of the heater 51 rises over time t, as shown in section Wa. However, the slope of the temperature change per unit time in this section Wa never exceeds the slope set by the third threshold value TSc.

In FIG. 6, the time t is "ta" when the power supply to the heater 51 is turned off in ACT 4 of the ink heating control 611. When the power supply to the heater 51 is turned off, the temperature HT of the heater 51 decreases with the passage of time t, as shown by the section Wb.

In FIG. 6, the point in time t at "tb" is the point in time when the ink in the supply tank 33 is supplied to the upstream tank 31 by driving the supply pump 35. As the ink is replenished, the temperature of the ink circulating through the circulation path 36 drops, and power is turned on to the heater 51. As a result, the temperature HT of the heater 51 rises over time t, as shown in the section Wc. However, the slope of the temperature change per unit time in this section Wc never exceeds the slope set by the third threshold value TSc.

In FIG. 6, the time t is "tc" when the power supply to the heater 51 is turned off in ACT 4 of the ink heating control 611. When the power supply to the heater 51 is turned off, the temperature HT of the heater 51 decreases with the passage of time t, as shown by the section Wd.

In FIG. 6, the time t is "td" when ink stops circulating through the circulation path 36. When ink stops circulating through the circulation path 36, the temperature HT of the heater 51 rises rapidly in a short period of time, as shown in section We. The slope of the temperature change per unit time in this section We is equal to or greater than the slope set by the third threshold value TSc. If this state of temperature rise in the heater 51 is allowed to continue, the temperature HT of the heater 51 will exceed the upper limit temperature, for example 150°C, as shown at time te. When the temperature HT of the heater 51 exceeds the upper limit temperature, the thermal fuse will activate. Alternatively, the heater 51 will break down. Also, the composition of the ink will change due to overheating.

In this embodiment, when a sudden rise in heater temperature HT as shown in section We is detected, power to the heater 51 is turned off at an early stage in the section We. This makes it possible to prevent overheating of the heater 51, which would cause the temperature of the heater 51 to exceed the upper limit temperature. As a result, there is no risk of the temperature fuse activating or the heater 51 breaking down. In addition, there is no risk of the ink composition changing due to overheating.

The above describes the first embodiment of the liquid circulation device 30 and the liquid ejection device 10, but the first embodiment is not limited to this.

For example, in the first embodiment, the third threshold value TSc that is compared with the slope of the temperature change per unit time is a fixed value. The third threshold value TSc may be variably set depending on the temperature of the environment in which the liquid circulation device 30 is placed.

Figure 7 is a graph showing the correspondence between the environmental temperature and the third threshold value TSc. In Figure 7, the vertical axis represents the third threshold value TSc, and the horizontal axis represents the environmental temperature. For example, when the environmental temperature is 25°C, the third threshold value TSc is set to 2°C. When the environmental temperature is 25°C or lower, the third threshold value TSc is made smaller. When the environmental temperature is low, the temperature of the heater 51 is unlikely to increase. Therefore, the third threshold value TSc is made smaller. In other words, the slope of the temperature change per unit time is made gentler. By doing so, even when the temperature of the heater 51 is unlikely to increase, it is possible to predict in advance an event in which overheating occurs, such as the temperature of the heater 51 exceeding the upper limit temperature. Therefore, even when the environmental temperature is low, overheating of the heater 51 can be reliably prevented.

Conversely, when the environmental temperature is 25°C or higher, the third threshold value TSc is increased. When the environmental temperature rises, the temperature of the heater 51 is likely to rise. Therefore, the third threshold value TSc is increased. In other words, the slope of the temperature change per unit time is made steeper. By doing so, even when the temperature of the heater 51 is likely to rise, it is possible to predict in advance an event in which overheating occurs, causing the temperature of the heater 51 to exceed the upper limit temperature. Therefore, even when the environmental temperature is high, overheating of the heater 51 can be reliably prevented.

Figure 8 is a graph showing the correspondence between the ink flow rate in the circulation path 36 and the third threshold value TSc. In Figure 8, the vertical axis represents the third threshold value TSc, and the horizontal axis represents the ink flow rate. For example, the third threshold value TSc is set to 2°C when the ink flow rate is 25 ml/min. When the ink flow rate is 25 ml/min or more, the third threshold value TSc is reduced. When the ink flow rate increases, the temperature of the heater 51 does not easily increase. Therefore, the third threshold value TSc is reduced. In other words, the slope of the temperature change per unit time is made gentler. By doing so, even if the ink flow rate increases, it is possible to predict in advance the occurrence of overheating in which the temperature of the heater 51 exceeds the upper limit temperature. Therefore, even if the environmental temperature is low, overheating of the heater 51 can be reliably prevented.

Conversely, if the ink flow rate is 25 ml/min or less, the third threshold value TSc is increased. For example, if the ink flowing through the circulation path 36 entrains a large amount of air bubbles, even a small amount of circulation will take away heat, causing the temperature of the heater 51 to rise more rapidly. Therefore, the third threshold value TSc is increased. In other words, the slope of the temperature change per unit time is made steeper. By doing so, even if the temperature of the heater 51 rises rapidly, it is possible to predict in advance the occurrence of overheating, in which the temperature of the heater 51 exceeds the upper limit temperature. Therefore, even if the environmental temperature is high, overheating of the heater 51 can be reliably prevented.

In the first embodiment, the unit time for monitoring the temperature change slope is set to 1 second. The unit time is not limited to 1 second. The unit time may be a time longer than 1 second or a time shorter than 1 second.

Second Embodiment
Next, a second embodiment will be described with reference to FIGS.
The second embodiment differs from the first embodiment in the function of the processor 61 as an overheating monitoring control 612. Since the rest is common to the first embodiment, Figures 1 to 4 are also applied to the second embodiment as they are, and detailed description thereof will be omitted.

Figure 9 is a schematic diagram showing the main memory areas formed in the RAM 63. In the second embodiment, part of the memory area of the RAM 63 is used as an area for a timer counter 631, an area for a first temperature memory 632, an area for a second temperature memory 633, an area for a temperature difference memory 634, an area for a first shift register 635, and an area for a second shift register 636. The areas for the timer counter 631, the first temperature memory 632, the second temperature memory 633, the temperature difference memory 634, the first shift register 635, and the second shift register 636 are formed for each liquid ejection device 10.

The timer counter 631 counts the time t in synchronization with the timer 64. The first temperature memory 632 stores the temperature of the heater 51 detected by the first temperature sensor 52. Hereinafter, the temperature data stored in the first temperature memory 632 is referred to as heater temperature HTm. The second temperature memory 633 stores the temperature of the heater 51 previously stored in the first temperature memory 632. Hereinafter, the temperature data stored in the second temperature memory 633 is referred to as heater temperature HTn. The temperature difference memory 634 stores the difference value between the heater temperature HTm stored in the first temperature memory 632 and the heater temperature HTn stored in the second temperature memory 633. Hereinafter, the temperature data of the difference value stored in the temperature difference memory 634 is referred to as differential temperature HTd.

The first shift register 635 includes 60 data storage areas SRa=1-60, from the first to the 60th. The first shift register 635 shifts the data stored in each of the first to 59th data storage areas SRa=1-59 in sequence to the second to 60th data storage areas SRa=2-60 in response to the timing of the data shift, and stores new data in the empty first data storage area SRa=1. The second shift register 636 includes five data storage areas SRb=1-5, from the first to the fifth. The second shift register 636 shifts the data stored in each of the first to the fourth data storage areas SRb=1-4 in sequence to the second to the fifth data storage areas SRb=2-5 in response to the timing of the data shift, and stores new data in the empty first data storage area SRb=1.

Figures 10 and 11 are flow charts for explaining the function of overheating monitoring control 612 for one liquid ejection device 10 in the second embodiment. The function of overheating monitoring control 612 for other liquid ejection devices 10 is similar, so the explanation here is omitted. Note that the heater 51, first temperature sensor 52, and second temperature sensor 53 that appear in the following explanation are provided in the liquid circulation device 30 in the liquid ejection device 10 to be controlled. Also, the timer counter 631, first temperature memory 632, second temperature memory 633, temperature difference memory 634, first shift register 635, and second shift register 636 are areas formed in RAM 63 for the liquid ejection device 10 to be controlled.

In ACT 21, the processor 61 waits for the power to the heater 51 to be turned on. As described above, in ACT 1 of FIG. 4, the power to the heater 51 is turned on. When the processor 61 detects that the power to the heater 51 has been turned on, the processor 61 judges that the result is YES in ACT 21 and proceeds to ACT 22. In ACT 22, the processor 61 resets the time t of the timer counter 631 to "0".

Next, the processor 61 starts the timer 64 in ACT 23. Then, the processor 61 waits for the timer 64 to count one second in ACT 24. When one second has been counted, the processor 61 judges as YES in ACT 24 and proceeds to ACT 25. The processor 61 counts up the time t of the timer counter 631 by "1" in ACT 25.

The processor 61 acquires the liquid temperature LT detected by the second temperature sensor 53 in ACT 26. The liquid temperature LT is the temperature of the ink flowing through the second pipe 362. The processor 61 checks whether the liquid temperature LT has reached the target temperature TSt in ACT 27. The target temperature TSt is any temperature that is equal to or higher than the second threshold value TSb, which is the lower limit temperature of the temperature range suitable for ejecting ink droplets, and equal to or lower than the first threshold value TSa, which is the upper limit temperature of the same temperature range. The target temperature TSt is preset within the range of equal to or higher than the second threshold value TSb and equal to or lower than the first threshold value TSa described above.

When the power supply to the heater 51 is first turned on, the liquid temperature LT is lower than the target temperature TSt. The processor 61 determines NO in ACT 27 and returns to ACT 24. The processor 61 executes the process from ACT 24 onwards in the same manner as described above. That is, the processor 61 obtains the liquid temperature LT every time one second is counted by the timer 64, and waits for the liquid temperature LT to rise to the target temperature TSt.

When the liquid temperature LT reaches the target temperature TSt, the processor 61 determines YES in ACT 27 and proceeds to ACT 28. In ACT 28, the processor 61 resets the time t of the timer counter 631 to "0". In ACT 29, the processor 61 also acquires the heater temperature HT detected by the first temperature sensor 52. In ACT 30, the processor 61 rewrites the heater temperature HTm in the first temperature memory 632 to the heater temperature HT detected by the first temperature sensor 52. After that, the processor 61 proceeds to ACT 31 in FIG. 11.

In ACT 31, the processor 61 waits for one second to be counted by the timer 64. When one second has been counted, the processor 61 determines YES in ACT 31 and proceeds to ACT 32. In ACT 32, the processor 61 counts up the time t of the timer counter 631 by "1".

The processor 61 acquires the heater temperature HT detected by the first temperature sensor 52 in ACT 33. The processor 61 also rewrites the temperature HTn in the second temperature memory 633 to the temperature HTm in the first temperature memory 632 in ACT 34. The processor 61 then rewrites the temperature HTm in the first temperature memory 632 to the heater temperature HT acquired in ACT 33 in ACT 35. The processes in ACT 33 and ACT 34 may be reversed. That is, the temperature HTn in the second temperature memory 633 may be rewritten to the temperature HTm in the first temperature memory 632, the heater temperature HT detected by the first temperature sensor 52 may be acquired, and the temperature HTm in the first temperature memory 632 may be rewritten to that heater temperature HT.

In ACT 36, the processor 61 calculates the difference between the temperature HTn in the second temperature memory 633 and the temperature HTm in the first temperature memory 632, and rewrites the difference temperature HTd in the temperature difference memory 634 to this difference value. That is, the processor 61 writes the amount of change in the heater temperature HT in the most recent second as the difference temperature HTd in the temperature difference memory 634. Incidentally, the difference temperature HTd is a positive value if the heater temperature HT has risen in the most recent second, and a negative value if it has fallen.

In ACT 37, the processor 61 sequentially shifts the data stored in the first to 59th data storage areas SRa = 1 to 59 of the first shift register 635 to the second to 60th data storage areas SRa = 2 to 60. Then, in ACT 38, the processor 61 writes the differential temperature HTd of the temperature difference memory 634 to the first data storage area SRa = 1 that has been vacated by the data shift.

In ACT 39, the processor 61 checks whether the time t of the timer counter 631 has counted "60". If the time t of the timer counter 631 has not counted "60", the processor 61 judges NO in ACT 39 and returns to ACT 31. The processor 61 executes the process from ACT 31 onwards in the same manner as described above. That is, the processor 61 acquires the heater temperature HT (temperature HTm) every time one second is counted by the timer 64, calculates the difference temperature HTd from the heater temperature HT (temperature HTn) one second ago, and repeats the process of writing the difference temperature HTd while shifting it sequentially to the first shift register 635. Thus, when the time t of the timer counter 631 counts "60", the difference temperature HTd for the past minute, i.e., the change amount of the heater temperature HT per second, is stored in chronological order in all data storage areas SRa = 1 to 60 from the 1st to 60th data storage areas SRa = 1 to 60 of the first shift register 635.

In ACT 40, the processor 61 calculates the fourth threshold value TSd based on each differential temperature HTd in the first shift register 635. Specifically, the processor 61 acquires all of the differential temperatures HTd over the past minute that are positive values, in other words, all differential temperatures HTd when the heater temperature HT rose over one second. The processor 61 then calculates the average value of all the acquired differential temperatures HTd, and sets 1.5 times the average value as the fourth threshold value TSd.

In ACT 61, the processor 61 sequentially shifts the data stored in the first to fourth data storage areas SRb = 1 to 4 of the second shift register 636 to the second to fifth data storage areas SRb = 2 to 5. In ACT 42, the processor 61 checks whether the differential temperature HTd in the temperature difference memory 634 is equal to or greater than the fourth threshold value TSd.

When the differential temperature HTd is less than the fourth threshold value TSd, it is acceptable to determine that the slope of the temperature change per unit time of the heater 51 is such that there is no risk of the heater 51 overheating. However, when the differential temperature HTd is equal to or greater than the fourth threshold value TSd, there is a risk of the heater 51 overheating.

If the differential temperature HTd is less than the fourth threshold value TSd, the processor 61 determines NO in ACT 42 and proceeds to ACT 43. In ACT 43, the processor 61 writes data "0" to the first data storage area SRb=1 of the second shift register 636 that has been vacated by the data shift. The data "0" is data indicating that the differential temperature HTd is less than the fourth threshold value TSd.

On the other hand, if the differential temperature HTd is equal to or greater than the fourth threshold value TSd, the processor 61 determines YES in ACT 42 and proceeds to ACT 44. In ACT 44, the processor 61 writes data "1" to the first data storage area SRb=1 of the second shift register 636 that has been vacated by the data shift. The data "0" is data indicating that the differential temperature HTd is equal to or greater than the fourth threshold value TSd.

After completing the process of ACT 43 or ACT 44, the processor 61 proceeds to ACT 45. In ACT 45, the processor 61 checks whether or not three or more pieces of data "1" are stored in the data storage area SRb = 1 to 5 of the second shift register 636. If there are two or fewer pieces of data "1", the processor 61 judges NO in ACT 45 and returns to ACT 30. That is, if the number of occurrences of a gradient of temperature change per unit time of the heater 51 that should be determined to be at risk of overheating the heater 51 during the past five seconds is two or less, the processor 61 continues monitoring using the overheating monitoring control 612. The processor 61 executes the processes from ACT 30 onwards in the same manner as described above.

On the other hand, if the data "1" is three or more, the processor 61 determines YES in ACT 45 and proceeds to ACT 46. The processor 61 turns off the power to the heater 51 in ACT 46. That is, when the number of occurrences of a temperature change gradient per unit time of the heater 51 that should be determined to be at risk of overheating the heater 51 reaches three in the past five seconds, the processor 61 stops the heater 51 and stops monitoring by the overheating monitoring control 612. With this, the processor 61 ends the control of the procedure shown in the flowcharts of Figures 10 and 11.

Here, the processor 61 functions as a recording unit by executing the processes of ACT 33 to ACT 38 in FIG. 11. That is, the processor 61 uses the first shift register 635 of the RAM 63 to record the temperature data of the heater 51 detected by the first temperature sensor 52. The temperature data is the differential temperature HTd, that is, the amount of temperature change of the heater 51 per unit time.

The processor 61 also functions as a determination unit by executing the process of ACT 40 in FIG. 11. That is, the processor 61 determines the fourth threshold value TSd based on the data recorded by the recording unit. Specifically, the processor 61 determines 1.5 times the average of the positive temperature change amount as the fourth threshold value TSd.

Furthermore, the processor 61 functions as a control unit by executing the processes of ACT 41 to ACT 46 in FIG. 11. That is, the processor 61 monitors the temperature change of the heater 51 using the data recorded in the recording unit, and controls the output of the heater 51 to be stopped when a temperature change that satisfies the stop condition is detected. Specifically, when the amount of temperature change per unit time of the heater 51 exceeds the fourth threshold value TSd three or more times within five seconds, the processor 61 determines that a temperature change that satisfies the stop condition has been detected, and stops the output of the heater 51.

In the second embodiment having such a configuration, when the risk of overheating of the heater 51 increases, the power supply to the heater 51 is automatically turned off. This makes it possible to prevent the thermal fuse from activating and the heater from breaking down. In addition, there is no risk of the temperature in the vicinity of the heater 51 rising suddenly, causing changes in the composition of the ink.
In the second embodiment, the temperature change per unit time calculated from the measured temperature of the heater 51 is recorded in the RAM 63. Then, overheating of the heater 51 is predicted from the number of occurrences of a gradient of the temperature change per unit time of the heater 51 that should be determined to be at risk of overheating of the heater 51. Therefore, overheating of the heater 51 can be prevented more reliably.

In the second embodiment, the processor 61 checks whether the liquid temperature LT has reached the target temperature TSt in ACT 27. This may be modified to check whether the time t of the timer counter 631 has reached a set time. The set time is an arbitrary time when it is assumed that the liquid temperature LT will reach the target temperature TSt. In this case, the processor 61 judges NO in ACT 27 until the time t of the timer counter 631 reaches the set temperature. When the time t reaches the set temperature, the processor 61 judges YES in ACT 27.

In the second embodiment, the processor 61 calculates the difference temperature HTd from the heater temperature HT one second ago, and records the difference temperature HTd in the first shift register 635. In this regard, it is also possible to calculate the difference temperature from the heater temperature HT two seconds ago, for example, and record the difference temperature in the first shift register 635.

The processor 61 also records the heater temperature HT measured, for example, every second, in the first shift register 635. The processor 61 then obtains the differential temperature HTd from the heater temperatures HT recorded in the adjacent data storage areas SRa to calculate the fourth threshold value TSd. The processor 61 also checks whether the differential temperature HTd between the heater temperature HT of the first data storage area SRa=1 and the heater temperature HT of the second data storage area SRa=2 is equal to or greater than the fourth threshold value TSd. In other words, the temperature data recorded by the recording unit may be the temperature HT of the heater 51.

In the second embodiment, the fourth threshold value TSd is calculated as 1.5 times the average of the positive temperature change amount. The method of calculating the fourth threshold value TSd is not limited to this. For example, instead of 1.5 times, the fourth threshold value TSd may be calculated as a multiple of the average of the positive temperature change amount, which is a value greater than 1.5 or less than 1.5. Alternatively, the fourth threshold value TSd may be a fixed value that is arbitrarily set.

In the second embodiment, the processor 61 continues monitoring using the overheating monitoring control 612 if the number of occurrences of the gradient of the temperature change per unit time of the heater 51 that should be determined to be a risk of overheating of the heater 51 in the past five seconds is two or less, and if the number of occurrences is three or more, the processor 61 stops the heater 51 and stops monitoring. The timing for stopping monitoring is not limited to this. For example, the processor 61 may continue monitoring if the number of occurrences is three or less, and stop starting it if the number of occurrences is four or more. Alternatively, the processor 61 may stop monitoring if the number of occurrences is two or more.

In the first or second embodiment, the heater 51 is disposed in the first pipeline 361 that connects the upstream tank 31 and the liquid ejection head 20. The location of the heater 51 is not limited to this. For example, the heater 51 may be disposed in the upstream tank 31.

In the first or second embodiment, the second temperature sensor 53 is disposed in the second pipeline 362 connecting the liquid ejection head 20 and the downstream tank 32. The location of the second temperature sensor 53 is not limited to this. For example, the sensor may be disposed in the middle of the first pipeline 361 or the third pipeline 363, or inside the upstream tank 31 or the downstream tank 32. Alternatively, the sensor may be disposed in the ink flow path of the liquid ejection head 20.

In the first and second embodiments, a liquid circulation device 30 and a liquid ejection device 10 that use ink as the liquid are exemplified. The liquid used in the liquid circulation device 30 and the liquid ejection device 10 is not limited to ink. The present invention can also be similarly applied to liquid circulation devices and liquid ejection devices that use liquids other than ink by setting the third threshold value TSc to an appropriate value.

Although several other embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope of the invention and the scope of the invention and its equivalents described in the claims.
In addition, the claims as originally filed of this application are set forth below.
[C1]
a liquid chamber that stores liquid to be supplied to the liquid ejection head;
a conduit for circulating the liquid between the liquid chamber and the liquid ejection head;
a heater for heating the liquid circulating through the pipeline;
a first temperature sensor that detects a temperature of the heater;
a second temperature sensor for detecting a temperature of the liquid circulating through the pipe;
a control unit that controls the output of the heater based on the temperature of the liquid detected by the second temperature sensor, monitors temperature changes of the heater detected by the first temperature sensor, and stops the output of the heater when a temperature change that satisfies a stop condition is detected.
[C2]
The liquid circulation device according to [C1], wherein the control unit monitors a slope of the temperature change per unit time, and stops output of the heater when the slope exceeds a threshold value.
[C3]
The liquid circulation device according to [C2], wherein the threshold value varies depending on the environmental temperature.
[C4]
The liquid circulation device according to [C2], wherein the threshold value varies depending on the flow rate of the liquid.
[C5]
a liquid chamber that stores liquid to be supplied to the liquid ejection head;
a conduit for circulating the liquid between the liquid chamber and the liquid ejection head;
a heater for heating the liquid circulating through the pipeline;
a first temperature sensor that detects a temperature of the heater;
a second temperature sensor for detecting a temperature of the liquid circulating through the pipe;
a control unit that controls the output of the heater based on the temperature of the liquid detected by the second temperature sensor, and monitors temperature changes of the heater based on the data recorded by the recording unit, and stops the output of the heater when a temperature change that satisfies a stop condition is detected.
[C6]
the data recorded by the recording unit is a temperature change amount of the heater per unit time,
The liquid circulation device described in [C5], wherein when the number of times the temperature change amount exceeds the threshold value reaches a predetermined number, the control unit determines that a temperature change that satisfies a stop condition has been detected and stops the output of the heater.
[C7]
a determination unit that determines the threshold value based on the data recorded by the recording unit;
The liquid circulating apparatus according to [C6], further comprising:
[C8]
A liquid circulation device according to any one of [C1] to [C7],
A liquid ejection head that ejects liquid;
A liquid ejection device comprising:

1... inkjet printer, 10... liquid ejection device, 11... head support mechanism, 12... head drive mechanism, 13... medium support mechanism, 20... liquid ejection head, 30... liquid circulation device, 31... upstream tank, 32... downstream tank, 33... supply tank, 34... circulation pump, 35... supply pump, 36... circulation path, 41, 42... liquid level sensor, 43, 44... pressure sensor, 45... pressure adjustment mechanism, 51... heater, 52... first temperature sensor, 53... second temperature sensor, 61... processor, 62... ROM, 63... RAM, 64... timer, 65... operation panel, 66... communication interface, 67... motor, 68... liquid ejection device interface, 631... timer counter, 632... first temperature memory, 633... second temperature memory, 634... temperature difference memory, 635... first shift register, 636... second shift register.

Claims (7)

a liquid chamber that stores liquid to be supplied to the liquid ejection head;
a conduit for circulating the liquid between the liquid chamber and the liquid ejection head;
a heater for heating the liquid circulating through the pipeline;
a first temperature sensor that detects a temperature of the heater;
a second temperature sensor for detecting a temperature of the liquid circulating through the pipe;
a control unit that controls an output of the heater based on a temperature of the liquid detected by the second temperature sensor, monitors a temperature change of the heater detected by the first temperature sensor, and stops the output of the heater when a temperature change that satisfies a stop condition is detected,
The control unit monitors a gradient of the temperature change per unit time, and stops output of the heater when the gradient exceeds a threshold value . The liquid circulation system of claim 1 , wherein the threshold value varies with an environmental temperature. The liquid circulation system according to claim 1 , wherein the threshold value varies depending on a flow rate of the liquid. a liquid chamber that stores liquid to be supplied to the liquid ejection head;
a conduit for circulating the liquid between the liquid chamber and the liquid ejection head;
a heater for heating the liquid circulating through the pipeline;
a first temperature sensor that detects a temperature of the heater;
a second temperature sensor for detecting a temperature of the liquid circulating through the pipe;
a recording unit that records data on the temperature of the heater detected by the first temperature sensor;
a control unit that controls the output of the heater based on the temperature of the liquid detected by the second temperature sensor, monitors temperature changes of the heater based on the data recorded in the recording unit, and stops the output of the heater when a temperature change that satisfies a stop condition is detected. the data recorded by the recording unit is a temperature change amount of the heater per unit time,
The liquid circulating device according to claim 4 , wherein the control unit stops output of the heater when the number of times the temperature change amount exceeds the threshold value reaches a predetermined number, assuming that a temperature change satisfying a stop condition has been detected. a determination unit that determines the threshold value based on the data recorded by the recording unit;
6. The liquid circulation system of claim 5 , further comprising: A liquid circulation device according to any one of claims 1 to 6 ,
A liquid ejection head that ejects liquid;
A liquid ejection device comprising: