Liquid circulating device and liquid ejecting device

Abstract

To prevent a failure due to overheating of a liquid circulation device which heats circulating liquid by a heater.SOLUTION: A liquid circulation device includes: a liquid chamber; a pipeline; a heater; a first temperature sensor; a second temperature sensor; and a control section. The liquid chamber stores liquid supplied to a liquid discharge head. The pipeline circulates liquid between the liquid chamber and the liquid discharge head. The heater heats liquid circulating in the pipeline. The first temperature sensor detects the temperature of the heater. The second temperature sensor detects the temperature of liquid circulating in the pipeline. The control section controls an output of the heater on the basis of the temperature of the liquid detected by the second temperature sensor. The control section monitors a temperature change of the heater detected by the first temperature sensor. The control section stops the output of the heater when the temperature change satisfying a stop condition is detected.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE The present invention relates to a liquid circulation device and a liquid ejection device. [Background technology]

[0002] 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 heating by the heater is controlled so that the ink flowing through the circulation path is maintained at a temperature within that temperature range.

[0003] Typically, 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. When heating control is performed when ink is not circulating, the heater temperature rises rapidly in a short period of time. If overheating occurs that exceeds the upper limit temperature of the heater, 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-105212 A Summary of the Invention [Problem to be solved by the invention]

[0005] The problem that an embodiment of the present invention aims to solve is to provide technology that prevents malfunctions caused by overheating in a liquid circulation device that uses a heater to warm the circulating liquid, or in a liquid ejection device that uses such a liquid circulation device. [Means for solving the problem]

[0006] 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 control unit. 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 control unit controls the output of the heater based on the temperature of the liquid detected by the second temperature sensor. The control unit also monitors temperature changes of the heater detected by the first temperature sensor. Then, when a temperature change that satisfies a stop condition is detected, the control unit stops the output of the heater. The control unit monitors the slope of the temperature change per unit time, and when the slope exceeds a threshold value, stops the output of the heater. [Brief description of the drawings]

[0007] [Figure 1] 1 is a side view for illustrating an outline of an inkjet printer according to an embodiment. [Diagram 2] 2 is a schematic diagram for explaining the configuration of a liquid ejection head and a liquid circulation device of the liquid ejection device in the inkjet printer. [Diagram 3] FIG. 2 is a block diagram showing the main circuit configuration of an inkjet control device in the inkjet printer. [Figure 4] 4 is a flowchart for explaining an ink heating control function of a processor of the inkjet control device. [Diagram 5] 4 is a flowchart for explaining an overheating monitoring control function of a processor of the inkjet control device. [Figure 6] 6 is a diagram showing one aspect of a temperature change of a heater controlled by ink heating control and overheating monitoring control. FIG. [Figure 7] 10 is a graph showing the correspondence relationship between the environmental temperature and the third threshold value. [Figure 8] 10 is a graph showing the correspondence relationship between the ink flow rate and a third threshold value. [Figure 9] FIG. 11 is a schematic diagram showing main memory areas formed in a RAM of the inkjet control device in the second embodiment. [Figure 10] 13 is a flowchart illustrating an overheating monitoring control function of a processor of the inkjet control device in the second embodiment. [Figure 11] 13 is a flowchart illustrating an overheating monitoring control function of a processor of the inkjet control device in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of a liquid circulation device and a liquid ejection device will be described with reference to the drawings, taking 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.

[0009] [First embodiment] First, the first embodiment will be described with reference to FIGS. 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.

[0010] The head support mechanism 11 supports the multiple liquid ejectors 10 in parallel in the direction of arrow A. The head drive mechanism 12 reciprocates the multiple liquid ejectors 10, which are aligned in parallel in the direction of arrow A by the head support mechanism 11, in the direction of arrow A. The medium support mechanism 13 supports a recording medium S at a position facing the multiple liquid ejectors 10 reciprocating in the direction of arrow A by the head drive mechanism 12, so as to be movable in a direction perpendicular to the direction of arrow A. The printer control device 14 controls the operations of the components of the inkjet printer 1, including the head drive mechanism 12.

[0011] The liquid ejection device 10 integrally includes a liquid ejection head 20 and a liquid circulation device 30. The liquid ejection device 10 ejects a liquid, for example, ink I, from the liquid ejection head 20 while moving back and forth in the direction of arrow A by a head driving mechanism 12, thereby forming a desired image on a recording medium S supported by a medium support mechanism 13.

[0012] The liquid ejection devices 10 eject ink of a plurality of colors, for example, cyan ink, magenta ink, yellow ink, black ink, and white ink. The 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 irradiated with infrared or ultraviolet light, etc. may be ejected.

[0013] 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 includes 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 22.

[0014] The liquid ejection head 20 has a plurality of pressure chambers disposed 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 volume of the pressure chamber is displaced by the action of the actuator, whereby ink I in that pressure chamber is ejected from the nozzle communicating with that pressure chamber. The liquid ejection head 20 ejects ink in each pressure chamber that has not been ejected from the nozzle from an outlet 22.

[0015] The liquid circulation device 30 is integrally connected to the liquid ejection head 20 at an upper portion 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.

[0016] 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 discharge 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.

[0017] 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.

[0018] In this manner, the first pipe 361, the second pipe 362, and the third pipe 363 constitute a pipe for circulating the ink, which is a liquid, between the upstream tank 31, which is a liquid chamber, and the liquid ejection head 20, which is a so-called circulation pipe .

[0019] The liquid ejection device 10 ejects the 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 the ink is replenished to the upstream tank 31.

[0020] 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.

[0021] 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.

[0022] The liquid circulation device 30 has a heater 51 provided in the middle of the first pipe 361. The heater 51 is for heating the ink flowing through the first pipe 361. The liquid circulation device 30 has a first temperature sensor 52 provided 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 provided in the middle of the second pipe 362. The second temperature sensor 53 is for detecting the temperature of the ink flowing through 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, thereby adjusting the temperature of the ink flowing through 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.

[0023] 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.

[0024] The processor 61 controls each unit to realize various functions of the inkjet printer 1 in accordance with an operating system and application programs.

[0025] The ROM 62 stores the above-mentioned operating system and application programs, and may also store data necessary for the processor 61 to execute processes for controlling each unit.

[0026] The RAM 63 stores data necessary for the processor 61 to execute processes. The RAM 63 is also used as a work area where information is appropriately rewritten by the processor 61. The work area includes an image memory where print data is expanded.

[0027] The timer 64 counts 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.

[0028] 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 .

[0029] 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 a signal for controlling the drive of the liquid ejection head 20, and signals for controlling the drive 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 of 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.

[0030] In this configuration, the processor 61 has at least a function as an ink heating control 611 and a function as 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.

[0031] 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 the other liquid ejection devices 10 is similar to this, so a description thereof will be omitted here. Note that the heater 51 and the second temperature sensor 53 that appear in the following description are provided in the liquid circulation device 30 in the liquid ejection device 10 to be controlled.

[0032] When the processor 61 starts functioning as the ink heating control 611, it turns on the power supply to the heater 51 as ACT1. Then, the processor 61 acquires the liquid temperature LT detected by the second temperature sensor 53 as ACT2. The liquid temperature LT is the temperature of the ink flowing through the second pipe 362.

[0033] The processor 61 checks whether the liquid temperature LT is equal to or higher than a first threshold value TSa as ACT3. The first threshold value TSa is the upper limit temperature of a 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.

[0034] If the liquid temperature LT is less than the first threshold value Sa, the processor 61 determines NO in ACT3 and returns to ACT2. The processor 61 repeatedly executes the processes of ACT2 and ACT3 until the liquid temperature LT becomes equal to or higher than the first threshold value TSa.

[0035] When the liquid temperature LT becomes equal to or higher than the first threshold value TSa, the processor 61 determines YES in ACT3 and proceeds to ACT4. The processor 61 turns off the power supply to the heater 51 in ACT4. Then, the processor 61 acquires the liquid temperature LT detected by the second temperature sensor 53 in ACT5.

[0036] The processor 61 checks whether the liquid temperature LT is less than a second threshold value TSb as ACT6. The second threshold value TSb is the lower limit temperature of a 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.

[0037] 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 of ACT 5 and ACT 6 until the liquid temperature LT becomes lower than the second threshold value TSb.

[0038] When the liquid temperature LT becomes less than the second threshold value TSb, the processor 61 determines YES in ACT6 and proceeds to ACT1. In ACT1, the processor 61 turns on the power supply to the heater 51. Thereafter, the processor 61 executes the processes from ACT2 onwards in the same manner as described above.

[0039] 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.

[0040] Here, the processor 61 having the function of the ink heating control 611 constitutes a control unit that controls the output of the heater 51 based on the temperature of the ink detected by the second temperature sensor 53 .

[0041] In the liquid circulation device 30, the ink heating control is usually performed by the processor 61 when a sufficient amount of ink is circulating through the circulation path 36. However, for example, the circulation pump 34 breaks down, or a bug occurs in the process of controlling the circulation pump 34, and 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 rises 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 rises rapidly, there is a risk that the composition of the ink will change. In order to prevent such a malfunction, the processor 61 has a function as an overheating monitoring control 612 for monitoring overheating of the heater 51.

[0042] 5 is a flow chart for explaining the function of the overheating monitoring control 612 for one liquid ejection device 10. The function of the overheating monitoring control 612 for the other liquid ejection devices 10 is similar to this, so a description thereof will be omitted here. Note that the heater 51 and the first temperature sensor 52 appearing in the following description are provided in the liquid circulation device 30 in the liquid ejection device 10 to be controlled.

[0043] The processor 61 checks whether or not power is supplied to the heater 51 in ACT11. If power is not supplied to the heater 51, the processor 61 determines NO in ACT11. The processor 61 waits for power to be supplied to the heater 51 to be turned on.

[0044] 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 ACT11 and proceeds to ACT12. In ACT12, 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 ACT13, the processor 61 stores the heater temperature HT in the work memory of the RAM 63 as the previous heater temperature HTa.

[0045] 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. The processor 61 acquires the heater temperature HT detected by the first temperature sensor 52 in ACT 15.

[0046] The processor 61 calculates the temperature rise width HTx per second by subtracting the previous heater temperature HTa stored in the work memory from the heater temperature HT as ACT 16. Then, the processor 61 checks whether the temperature rise width HTx is equal to or greater than the third threshold value TSc as ACT 17.

[0047] The third threshold value TSc is a value suitable for determining that the temperature rise width HTx per second, i.e., the gradient 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."

[0048] In ACT17, if the temperature increase width HTx is less than the third threshold value TSc, the processor 61 judges NO in ACT17 and returns to ACT13. In ACT13, the processor 61 overwrites the heater temperature HT acquired in the process of ACT15 as the previous heater temperature HTa in the work memory of the RAM 63. Thereafter, the processor 61 executes the processes from ACT14 onwards in the same manner as described above.

[0049] In ACT 17, if the temperature increase width 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. The processor 61 turns off the power supply to the heater 51 in ACT 18. With this, the processor 61 ends the control of the procedure shown in the flowchart of FIG.

[0050] In this way, the processor 61 monitors the heater temperature HT detected by the second temperature sensor 53 while the heater 51 is energized. The processor 61 turns off the heater 51 when the temperature rise width HTx of the heater temperature HT per second becomes equal to or greater than the third threshold value TSc. When the temperature rise width 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 thermal 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.

[0051] In this embodiment, when the temperature rise width 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 overheating by the heater 51. As a result, there is no risk of the temperature fuse activating or the heater 51 breaking due to overheating. Furthermore, the composition of the ink is not changed due to overheating.

[0052] 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.

[0053] Fig. 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 Fig. 6, the vertical axis represents the temperature HT (°C) of the heater 51, and the horizontal axis represents time t (seconds).

[0054] 6, the time t is "0" when the power supply to the heater 51 is turned on in ACT1 of the ink heating control 611. When the power supply to the heater 51 is turned on, the temperature HT of the heater 51 rises with the passage of time t, as shown in the section Wa. However, the slope of the temperature change per unit time in this section Wa does not exceed the slope set by the third threshold value TSc.

[0055] 6, the time t is "ta" when the power supply to the heater 51 is turned off in ACT4 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.

[0056] 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 with the passage of time t, as shown in section Wc. However, the gradient of the temperature change per unit time in this section Wc does not exceed the gradient set by the third threshold value TSc.

[0057] 6, the time t is "tc" when the power supply to the heater 51 is turned off in ACT4 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.

[0058] 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 by section We. The gradient of the temperature change per unit time in this section We is equal to or greater than the gradient set by the third threshold value TSc. If this state of temperature rise of 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 by time te. When the temperature HT of the heater 51 exceeds the upper limit temperature, the thermal fuse will be activated. Alternatively, the heater 51 will be broken. Also, the composition of the ink will change due to overheating.

[0059] In this embodiment, when a sudden rise in the heater temperature HT as shown in section We is detected, power to the heater 51 is turned off at an early stage of 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. In addition, there is no risk of the ink components changing due to overheating.

[0060] Although the first embodiment of the liquid circulation device 30 and the liquid ejection device 10 has been described above, the first embodiment is not limited to this.

[0061] For example, in the first embodiment, the third threshold value TSc to be compared with the gradient 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 circulating apparatus 30 is placed.

[0062] FIG. 7 is a graph showing the correspondence between the environmental temperature and the third threshold value TSc. In FIG. 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 difficult to increase. Therefore, the third threshold value TSc is made smaller. That is, the slope of the temperature change per unit time is made gentler. By doing so, even when the temperature of the heater 51 is difficult to increase, it is possible to predict in advance an event in which overheating occurs such that the temperature of the heater 51 exceeds the upper limit temperature. Therefore, even when the environmental temperature is low, overheating of the heater 51 can be reliably prevented.

[0063] Conversely, when the environmental temperature is 25° C. or higher, the third threshold value TSc is increased. When the environmental temperature becomes high, the temperature of the heater 51 tends to rise. Therefore, the third threshold value TSc is increased. In other words, the gradient of the temperature change per unit time is made steeper. By doing so, even when the temperature of the heater 51 tends to rise, 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 high, overheating of the heater 51 can be reliably prevented.

[0064] FIG. 8 is a graph showing the correspondence relationship between the ink flow rate in the circulation path 36 and the third threshold value TSc. In FIG. 8, the vertical axis represents the third threshold value TSc, and the horizontal axis represents the ink flow rate. The third threshold value TSc is set to 2° C. when the ink flow rate is 25 ml / min, for example. 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. That is, the slope of the temperature change per unit time is made gentle. By doing so, even if the ink flow rate increases, it is possible to predict in advance the occurrence of an overheating event in which the temperature of the heater 51 exceeds the upper limit temperature. Therefore, even if the environmental temperature is low, it is possible to reliably prevent the heater 51 from overheating.

[0065] Conversely, when the ink flow rate is 25 ml / min or less, the third threshold value TSc is increased. For example, when a large amount of air bubbles are entrained in the ink flowing through the circulation path 36, even a small amount of ink circulates and therefore heat is lost, 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, it is possible to reliably prevent overheating of the heater 51.

[0066] In the first embodiment, the unit time for monitoring the gradient of the temperature change 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.

[0067] [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 the superheating monitoring control 612. Since the rest is common to the first embodiment, Figs. 1 to 4 are also applied to the second embodiment as they are, and detailed description thereof will be omitted.

[0068] 9 is a schematic diagram showing main memory areas formed in the RAM 63. In the second embodiment, some of the memory areas of the RAM 63 are 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.

[0069] 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 a 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 a heater temperature HTn. The temperature difference memory 634 stores a 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 a differential temperature HTd.

[0070] The first shift register 635 includes 60 data storage areas SRa=1 to 60, from the first to the 60th. The first shift register 635 sequentially shifts data stored in the first to the 59th data storage areas SRa=1 to 59 to the second to the 60th data storage areas SRa=2 to 60 in accordance with the timing of the data shift, and stores new data in the first data storage area SRa=1, which is now empty. The second shift register 636 includes five data storage areas SRb=1 to 5, from the first to the fifth. The second shift register 636 sequentially shifts data stored in the first to the fourth data storage areas SRb=1 to 4 to the second to the fifth data storage areas SRb=2 to 5 in accordance with the timing of the data shift, and stores new data in the first data storage area SRb=1, which is now empty.

[0071] 10 and 11 are flow charts for explaining the function of the overheating monitoring control 612 for one liquid ejection device 10 in the second embodiment. The function of the overheating monitoring control 612 for other liquid ejection devices 10 is similar to that described above, and therefore will not be described here. The heater 51, the first temperature sensor 52, and the second temperature sensor 53 appearing in the following description are provided in the liquid circulation device 30 in the liquid ejection device 10 to be controlled. 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 areas formed in the RAM 63 for the liquid ejection device 10 to be controlled.

[0072] In ACT21, the processor 61 waits for the power supply to the heater 51 to be turned on. As described above, in ACT1 of Fig. 4, the power supply to the heater 51 is turned on. When the processor 61 detects that the power supply to the heater 51 has been turned on, the processor 61 judges that the result is YES in ACT21 and proceeds to ACT22. In ACT22, the processor 61 resets the time t of the timer counter 631 to "0".

[0073] Next, the processor 61 starts the timer 64 in ACT23. Then, the processor 61 waits for one second to be counted by the timer 64 in ACT24. When one second has been counted, the processor 61 determines YES in ACT24 and proceeds to ACT25. The processor 61 counts up the time t of the timer counter 631 by "1" in ACT25.

[0074] The processor 61 acquires the liquid temperature LT detected by the second temperature sensor 53 as ACT26. 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 as ACT27. 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 a 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 set in advance 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.

[0075] When the power supply to the heater 51 is initially turned on, the liquid temperature LT is lower than the target temperature TSt. The processor 61 judges NO in ACT27 and returns to ACT24. The processor 61 executes the processes from ACT24 onwards in the same manner as described above. That is, the processor 61 obtains the liquid temperature LT every second counted by the timer 64, and waits for the liquid temperature LT to rise to the target temperature TSt.

[0076] When the liquid temperature LT reaches the target temperature TSt, the processor 61 determines YES in ACT27 and proceeds to ACT28. The processor 61 resets the time t of the timer counter 631 to "0" in ACT28. The processor 61 also acquires the heater temperature HT detected by the first temperature sensor 52 in ACT29. 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 in ACT30. After that, the processor 61 proceeds to ACT31 in FIG. 11.

[0077] 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".

[0078] The processor 61 acquires the heater temperature HT detected by the first temperature sensor 52 in ACT33. 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 ACT34. The processor 61 then rewrites the temperature HTm in the first temperature memory 632 to the heater temperature HT acquired in ACT33 in ACT35. The processes of ACT33 and ACT34 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, and then 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.

[0079] The processor 61 calculates the difference value between the temperature HTn in the second temperature memory 633 and the temperature HTm in the first temperature memory 632 as ACT36, and rewrites the difference temperature HTd in the temperature difference memory 634 to that 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 is a negative value if it has fallen.

[0080] 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 as ACT37 to the second to 60th data storage areas SRa=2 to 60. Then, 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 as ACT38.

[0081] The processor 61 checks whether the time t of the timer counter 631 has counted "60" in ACT39. If the time t of the timer counter 631 has not counted "60", the processor 61 judges NO in ACT39 and returns to ACT31. The processor 61 executes the process from ACT31 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 differential temperature HTd from the heater temperature HT (temperature HTn) immediately before one second ago, and repeats the process of writing the differential 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 differential temperature HTd for the past one minute, i.e., the amount of change in 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.

[0082] The processor 61 calculates the fourth threshold value TSd based on each differential temperature HTd in the first shift register 635 as ACT40. Specifically, the processor 61 acquires all the positive values ​​of the differential temperatures HTd in the past minute, that is, the differential temperatures HTd when the heater temperature HT rose in one second. The processor 61 then calculates the average value of all the acquired differential temperatures HTd, and sets the fourth threshold value TSd to 1.5 times the average value.

[0083] The processor 61 shifts the data stored in the first to fourth data storage areas SRb=1 to 4 of the second shift register 636 in sequence to the second to fifth data storage areas SRb=2 to 5 as ACT61. The processor 61 also checks whether the temperature difference HTd in the temperature difference memory 634 is equal to or greater than the fourth threshold value TSd as ACT42.

[0084] When the temperature difference HTd is less than the fourth threshold value TSd, it is acceptable to determine that the gradient of the temperature change per unit time of the heater 51 is such that there is no risk of overheating of the heater 51. However, when the temperature difference HTd is equal to or greater than the fourth threshold value TSd, there is a risk of overheating of the heater 51.

[0085] If the temperature difference 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 temperature difference HTd is less than the fourth threshold value TSd.

[0086] On the other hand, if the temperature difference HTd is equal to or greater than the fourth threshold value TSd, the processor 61 determines YES in ACT42 and proceeds to ACT44. In ACT44, 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 temperature difference HTd is equal to or greater than the fourth threshold value TSd.

[0087] After completing the process of ACT43 or ACT44, the processor 61 proceeds to ACT45. In ACT45, 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 less pieces of data "1", the processor 61 judges NO in ACT45 and returns to ACT30. That is, if 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 causing overheating of the heater 51 in the past five seconds is two or less, the processor 61 continues monitoring by the overheating monitoring control 612. The processor 61 executes the processes from ACT30 onwards in the same manner as described above.

[0088] On the other hand, if the number of data "1"s is three or more, the processor 61 determines YES in ACT45 and proceeds to ACT46. The processor 61 turns off the power supply to the heater 51 in ACT46. That is, when 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 causing overheating of 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 FIGS. 10 and 11.

[0089] Here, the processor 61 functions as a recording unit by executing the processes of ACT33 to ACT38 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.

[0090] Moreover, the processor 61 functions as a determination unit by executing the process of ACT40 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.

[0091] Furthermore, the processor 61 functions as a control unit by executing the processes of ACT41 to ACT46 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 when a temperature change that satisfies the stop condition is detected, controls the stop of the output of the heater 51. 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.

[0092] 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 value 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 causing overheating of the heater 51. Therefore, overheating of the heater 51 can be prevented more reliably.

[0093] In the second embodiment, the processor 61 checks whether the liquid temperature LT has reached the target temperature TSt in ACT27. 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 ACT27 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 ACT27.

[0094] 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, the processor 61 may 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.

[0095] 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 a differential temperature HTd from the heater temperatures HT recorded in the adjacent data storage areas SRa to calculate a fourth threshold value TSd. The processor 61 also checks whether the differential temperature HTd between the heater temperature HT in the first data storage area SRa=1 and the heater temperature HT in the second data storage area SRa=2 is equal to or greater than the fourth threshold value TSd. That is, the temperature data recorded by the recording unit may be the temperature HT of the heater 51.

[0096] 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 larger than 1.5 or smaller than 1.5. Alternatively, the fourth threshold value TSd may be a fixed value that is arbitrarily set.

[0097] In the second embodiment, the processor 61 continues monitoring using the overheating monitoring control 612 when the number of occurrences of the gradient of the temperature change per unit time of the heater 51 that should be determined to be at risk of overheating the heater 51 in the past five seconds is two or less, and stops monitoring by stopping the heater 51 when the number of occurrences is three or more. The timing for stopping monitoring is not limited to this. For example, the processor 61 may continue monitoring when the number of occurrences is three or less, and stop starting it when the number of occurrences is four or more. Alternatively, the processor 61 may stop monitoring when the number of occurrences is two or more.

[0098] In the first or second embodiment, the heater 51 is disposed in the first pipe 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.

[0099] 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 second temperature sensor 53 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 second temperature sensor 53 may be disposed in the ink flow path of the liquid ejection head 20.

[0100] In the first and second embodiments, the liquid circulation device 30 and the 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.

[0101] 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 an 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 recording unit that records data on the temperature of the heater detected by the first temperature sensor; a control unit that controls an 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 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 circulating device according to any one of [C1] to [C7], A liquid ejection head that ejects liquid; A liquid ejection device comprising: [Explanation of symbols]

[0102] 1...inkjet printer, 10...liquid ejection device, 11...head support mechanism, 12...head driving 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

1. 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.

2. The liquid circulation system of claim 1 , wherein the threshold value varies with an environmental temperature.

3. The liquid circulation system according to claim 1 , wherein the threshold value varies depending on a flow rate of the liquid.

4. 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.

5. 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 is configured to stop 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.

6. 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:

7. 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:

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