JP7835129B2 - Image forming apparatus, method for estimating the state change of phase transition ink, and program for estimating the state change of phase transition ink. - Google Patents

Description

This invention relates to an image forming apparatus, a method for estimating the state change of a phase transition ink, and a program for estimating the state change of a phase transition ink.

Inkjet image forming apparatuses (hereinafter referred to as inkjet image forming apparatuses) are known that eject ink onto recording media such as paper to form images on the recording media. In inkjet image forming apparatuses, the ink ejected from the inkjet head (hereinafter referred to as the head) includes gel ink (phase-transition ink) containing a gel component that undergoes a reversible sol-gel phase transition due to temperature changes.

Ink, such as gel ink, can undergo changes in its state (for example, an increase in gel concentration in the case of gel ink) at various points along the flow path within the apparatus. For instance, uneven temperature distribution within the flow path—specifically, areas with lower temperatures—can cause gel component precipitation at those points, resulting in a gel concentration in the gel ink exceeding the predetermined concentration (e.g., the appropriate concentration).

When gel ink with a high gel concentration is supplied to the print head, and the gel ink is ejected from the head to form an image, the gel ink droplets that land on the recording medium do not spread sufficiently. Therefore, an image defect occurs where the dot diameter formed by these droplets is smaller than the predetermined dot diameter (e.g., the appropriate dot diameter). In particular, when forming pattern images such as halftone images, an image defect occurs where the image density is lower than the appropriate image density.

To prevent the image defects described above, the gel ink in the print head is refreshed by ejecting the gel ink with a high gel concentration and supplying new gel ink to the head. This maintains the gel concentration of the gel ink within the print head at a predetermined level. For example, in Patent Document 1 below, the ink in the print head is ejected by methods such as ink suction purging (which sucks out the ink) or ink pressure purging (which applies pressure from the ink supply side).

Japanese Patent Publication No. 2003-127430

Incidentally, inkjet image forming machines typically consist of multiple ink tanks and multiple print heads connected downstream of each of these ink tanks. Therefore, if a change in the state of the gel ink occurs within the print head, it's possible that a similar change is also occurring in the ink tanks upstream of the print head.

However, in conventional inkjet image forming apparatuses, such as the one shown in Patent Document 1, the state of the ink within the print head is determined based on the ink droplets ejected from the head, and the ink within that head is ejected accordingly. In other words, the ink state is determined and ejected on a per-head basis, and the state of the ink upstream of the head, i.e., the state of the ink in the ink tank, is not determined.

Therefore, even if only the gel ink in the print head is emptied, if the gel ink in the upstream ink tank has undergone a state change, the changed gel ink will be supplied to the print head, and the image defect problem will not be resolved. As a result, it becomes necessary to empty the gel ink from the print head again, and repeating this process increases the downtime of the equipment and reduces the productivity of image formation.

Furthermore, the aforementioned gel ink discharge affects the running costs of the equipment. Therefore, it is desirable to identify the locations where gel ink discharge is necessary and to discharge only the necessary amount of gel ink, thereby reducing gel ink consumption. Thus, it is desirable to discharge the gel ink only after confirming the location where a change in the gel ink's state has occurred.

The object of the present invention is to provide an image forming apparatus capable of estimating the occurrence of a phase transition ink state change upstream of an inkjet head, a method for estimating the phase transition ink state change, and a program for estimating the phase transition ink state change.

The image forming apparatus according to the present invention is
Multiple inkjet heads that eject phase transition ink, supplied and stored in corresponding storage units from the upstream side of the ink supply path, onto a recording medium,
A first estimation unit estimates the occurrence of a state change in the phase transition ink on an inkjet head basis, based on the first reading result of the pattern image formed by the plurality of inkjet heads,
A second estimation unit estimates the occurrence of the state change on the upstream side based on the occurrence status of the state change in two or more inkjet heads among the plurality of inkjet heads,
It is equipped with.

The method for estimating the state change of a phase transition ink according to the present invention is:
Phase transition ink, supplied and stored in the corresponding storage section from the upstream side of the ink supply path, is ejected from multiple inkjet heads to form a pattern image on the recording medium.
Based on the first reading result of the pattern image formed by the plurality of inkjet heads, the occurrence of a state change in the phase transition ink is estimated on an inkjet head basis.
Based on the occurrence of the state change in two or more of the plurality of inkjet heads, the occurrence of the state change on the upstream side is estimated.

The phase transition ink state change estimation program according to the present invention is
On the computer,
A process of forming a pattern image on a recording medium by ejecting phase-transition ink, which is supplied and stored in a corresponding storage unit from the upstream side of the ink supply path, from multiple inkjet heads,
A process to estimate the occurrence of a state change in the phase transition ink on an inkjet head basis, based on the first reading result of the pattern image formed by the plurality of inkjet heads,
A process for estimating the occurrence of the state change on the upstream side based on the occurrence status of the state change in two or more inkjet heads among the plurality of inkjet heads,
Make it run.

According to this invention, it is possible to estimate the occurrence of a phase transition ink state change upstream of the inkjet head.

This figure shows a schematic configuration of an image forming apparatus according to an embodiment of the present invention. This block diagram shows the main parts of the control system of the image forming apparatus shown in Figure 1. This is a flowchart illustrating the method for estimating the state change of the phase transition ink performed in the image forming apparatus shown in Figure 1. Figure 3 is a diagram illustrating a method for estimating the state change of the phase transition ink, and shows an example of a location where the state change occurs. Figure 3 is a diagram illustrating a method for estimating the state change of the phase transition ink, and shows another example of the location where the state change occurs. This diagram illustrates how ink droplets ejected from an inkjet head change when the number of ejections (degree of deterioration) of the inkjet head differs. This graph shows the relationship between the number of ink ejections and the optimal voltage applied to the piezoelectric element of the inkjet head. This diagram illustrates how ink droplets ejected from an inkjet head change when the concentration of the gel component in the ink differs. This graph shows the relationship between the number of ink ejections and the optimal voltage applied to the piezoelectric element of the inkjet head, for inks containing an appropriate concentration of gel component and inks containing a high concentration of gel component. This flowchart illustrates a modified version of the method for estimating the state change of the phase transition ink shown in Figure 3. This flowchart illustrates a modified version of the method for estimating the state change of the phase transition ink shown in Figure 3. Figures 10A and 10B are flowcharts illustrating modified examples of the method for estimating the state change of the phase transition ink. This diagram illustrates ink droplets ejected from an inkjet head onto a recording medium at room temperature and a recording medium at a temperature above the phase transition temperature, using ink containing an appropriate concentration of gel component and ink containing a high concentration of gel component.

The embodiments of the present invention will be described in detail below with reference to the drawings.

[Image forming apparatus]
Figure 1 is a diagram showing the schematic configuration of an inkjet printer 100 (image forming apparatus in the present invention) according to this embodiment. Figure 2 is a block diagram showing the main parts of the control system of the inkjet printer 100.

As shown in Figures 1 and 2, the inkjet printer 100 includes a transport unit 10, a supply unit 20, an ejection unit 30, an ink supply unit 40, an image forming unit 50, a reading unit 60, an operation display unit 70, an input/output interface 80, a control unit 90, and the like.

The transport unit 10 has multiple transport components, including a transport belt 11, a drive roller 12, and a driven roller 13. The transport unit 10 transports the recording medium M through the transport operation of these components. Specifically, in the transport unit 10, the transport belt 11 is stretched over the drive roller 12 and the driven roller 13, and is driven by rotating the drive roller 12. As a result, the recording medium M supplied from the supply unit 20 is transported to the image forming unit 50 while placed on the transport surface 11a of the transport belt 11. After image formation (printing) in the image forming unit 50, it is transported to the discharge unit 30.

The recording medium M can be any medium capable of fixing the ink ejected from the inkjet head 55. For example, the recording medium M may be a sheet of paper, cloth, or resin. However, the recording medium M is not limited to a sheet; it may also be a roll of paper, cloth, resin, or other material.

Furthermore, while this example illustrates a transport unit 10 that transports the recording medium M using a transport belt 11, the transport unit 10 is not limited to a transport belt 11; it may also be configured to transport the recording medium M using drums or rollers.

The supply unit 20 includes a supply stacking unit 21 for stacking and storing multiple recording media M, and a supply transport unit 22 for transporting and supplying the recording media M from the supply stacking unit 21 to the transport unit 10. The supply stacking unit 21 is configured to be vertically movable. When the topmost recording media M is transported to the transport unit 10 by the supply transport unit 22, the supply stacking unit 21 rises so that the recording media M that becomes the topmost after transport can be transported to the supply transport unit 22.

The discharge unit 30 includes a discharge loading unit 31 for loading and storing multiple recording media M, and a discharge transport unit 32 for transporting the recording media M discharged from the transport unit 10 to the discharge loading unit 31. The discharge loading unit 31 is configured to be vertically movable, and when the recording media M are transported from the discharge transport unit 32 to the discharge loading unit 31, the discharge loading unit 31 lowers.

The supply and transport unit 22 and the discharge and transport unit 32, for example, have multiple rollers, and the recording medium M is transported by rotating the rollers. The supply and transport unit 22 and the discharge and transport unit 32 are not limited to rollers; they may also be composed of belts, or a combination of rollers and belts.

Furthermore, when a roll-shaped medium is used as the recording medium M, instead of the supply and loading section 21 and the discharge and loading section 31, an unwinding roller that stores the roll-shaped medium in a wound state and a winding roller that winds up the roll-shaped medium are used. The roll-shaped medium is transported to the transport section 10 by rotating the unwinding roller, and wound onto the winding roller by rotating the winding roller.

Furthermore, a post-processing device for performing post-processing on the recording medium M, which has an image formed in the image forming unit 50, may be provided between the transport unit 10 and the discharge unit 30. One such post-processing device is a fixing device for fixing ink to the recording medium M. For example, when using ultraviolet-curable ink, a fixing device is used that irradiates the recording medium M with ultraviolet light to fix the ink. Alternatively, when using water-based or solvent-based ink, a fixing device is used that fixes the ink to the recording medium M by drying or other methods. In addition, other devices besides a fixing device may be used as post-processing devices, such as a cutting device for cutting the recording medium M to a desired length.

The ink supply unit 40 is a device that supplies ink to the first sub-tank 52a of the image forming unit 50, which will be described later. The ink supply unit 40 includes a main tank 41 and components related to ink supply (e.g., a pump and valves, etc.) which are not shown. The main tank 41 stores the ink to be supplied to the first sub-tank 52a at room temperature. The ink supply unit 40 uses a pump or the like (not shown) to supply ink from the main tank 41 to the first sub-tank 52a via a flow path 42 (the ink supply path in this invention).

In this embodiment, a gel ink (phase transition ink) containing wax, which is a gel component that undergoes a reversible sol-gel phase transition due to temperature changes, is used as the ink. For example, an energy-ray curable gel ink (such as an ultraviolet-curable gel ink) that is gel-like at room temperature, sol-like at temperatures above the phase transition temperature, and hardens upon irradiation with energy rays can be used.

The image forming unit 50 includes a carriage 51, a first sub-tank 52a, a second sub-tank 52b, flow channels 53a, 53b, 53c, a head drive unit 54, an inkjet head (hereinafter simply referred to as the head) 55, etc. (See Figures 1 and 2).

Note that in Figure 1, for the sake of simplicity, only one ink supply unit 40 and image forming unit 50 are shown. However, the arrangement of the ink supply unit 40 and image forming unit 50 depends on the number of colors used. For example, when using four colors—yellow (Y), magenta (M), cyan (C), and black (K)—four ink supply units 40 and image forming units 50 are arranged, and the image forming units 50 are positioned at predetermined intervals along the transport direction T.

Furthermore, the second sub-tank 52b and the inkjet head 55 are connected in a tree-like configuration downstream of the first sub-tank 52a, as shown in Figures 4 and 5 described later. However, in Figure 1, for the sake of simplicity, only one of each is shown.

The carriage 51 is a housing that internally holds the first sub-tank 52a, the second sub-tank 52b, the flow channels 53a, 53b, and 53c, the head drive unit 54, the head 55, and other equipment and components necessary for image formation. Although not shown in the figures, the carriage 51 also includes an ink heating unit that heats and maintains the gel ink within the carriage 51 at a temperature above the phase transition temperature of the gel component of the gel ink.

The first sub-tank 52a is connected downstream of the main tank 41. The first sub-tank 52a stores the gel ink supplied from the main tank 41 within the carriage 51. The gel ink in sub-tank 52 is supplied to the second sub-tank 52b via a flow path 53a (ink supply path in this invention) using a pump or the like (not shown) within the carriage 51.

Multiple second sub-tanks 52b are connected downstream of the first sub-tank 52a (see Figures 4 and 5). The second sub-tanks 52b store the gel ink supplied from the first sub-tank 52a within the carriage 51. The gel ink in the second sub-tanks 52b is supplied to the manifold 56 of the head 55 (described later) via a flow path 53b (the ink supply path in this invention) using a pump or the like (not shown) within the carriage 51. The gel ink supplied to the manifold 56 is then recirculated back to the second sub-tank 52b via flow path 53c. In other words, flow paths 53b and 53c form a circulation path for the gel ink between the second sub-tank 52b and the manifold 56.

The head drive unit 54, based on the control of the control unit 90 (described later), outputs a drive voltage corresponding to the image data of the image to be formed to the piezoelectric element 58 of the head 55 (described later). The drive voltage from the head drive unit 54 drives the piezoelectric element 58, causing it to eject an amount of gel ink corresponding to the image data from the nozzle 59 of the head 55 (described later).

Multiple heads 55 are connected to the downstream side of each of the multiple second sub-tanks 52b (see Figures 4 and 5). In other words, the second sub-tanks 52b and heads 55 are connected in a tree-like structure downstream of the first sub-tank 52a.

The head 55 includes a manifold 56 (storage section in this invention), a pressure chamber 57, a piezoelectric element 58, nozzles 59, etc. The head 55 has multiple nozzles 59, and the number of pressure chambers 57 and piezoelectric elements 58 is provided according to the number of nozzles 59.

The manifold 56 communicates with multiple pressure chambers 57, and the gel ink supplied to the manifold 56 is supplied to the pressure chambers 57. The pressure chambers 57 are spaces where the discharged gel ink is stored, and piezoelectric elements 58 are provided on their walls. The nozzle 59 has one end communicating with the pressure chamber 57 and the other end is an open end.

A drive voltage from the head drive unit 54 is applied to the piezoelectric element 58. When the drive voltage from the head drive unit 54 is applied to the piezoelectric element 58, the piezoelectric element 58 deforms in accordance with the applied drive voltage, causing the pressure chamber 57 to deform. This deformation of the pressure chamber 57 imparts a pressure change to the gel ink in the pressure chamber 57 that is supplied to the nozzle 59.

Therefore, when the drive voltage from the head drive unit 54 is applied to the piezoelectric element 58, the piezoelectric element 58 and the pressure chamber 57 deform, causing a pressure change in the gel ink within the pressure chamber 57. As a result, the gel ink in the pressure chamber 57 is ejected from the nozzle 59. In this way, by ejecting the gel ink from the nozzle 59, an image can be formed on the transported recording medium M.

In the carriage 51, the head 55 may be configured to perform image formation in a single pass (one-pass) method, or it may be configured to perform image formation in multiple passes (multi-pass) method. In the single-pass method, the carriage 51 has a number of heads 55 equal to the image formation width in the width direction of the recording medium M (the direction perpendicular to the transport direction T of the recording medium M).

The reading unit 60 is positioned downstream of the image forming unit 50 in the transport direction T of the recording medium M, and reads the image (for example, a predetermined pattern image) formed on the recording medium M as it is transported by the transport belt 11. The reading unit 60 outputs the reading result of the predetermined pattern image to the control unit 90. Based on the reading result, the control unit 90 changes the image formation conditions, such as the image formation position and the drive conditions of the head 55.

Although not shown in the diagram, the inkjet printer 100 is equipped with a maintenance unit for performing maintenance such as cleaning the print head 55.

The operation display unit 70 is, for example, a flat panel display such as a liquid crystal display (LCD) or an organic EL (Electro-Luminescence) display with a touch panel. The operation display unit 70 displays operation menus for the user, information related to image data, and various statuses of the inkjet printer 100. The operation display unit 70 also has multiple keys to accept various user input operations.

The input/output interface 80 mediates the transmission and reception of data between the external device 200 and the control unit 90. The input/output interface 80 is composed of, for example, various serial interfaces, various parallel interfaces, or a combination thereof.

The external device 200 is, for example, a personal computer or a facsimile machine, and supplies print jobs, image data, etc., to the control unit 90 via the input/output interface 80.

The control unit 90 includes a CPU (Central Processing Unit) 91, RAM (Random Access Memory) 92, ROM (Read Only Memory) 93, and a storage unit 94.

The CPU 91 reads various control programs and setting data stored in the ROM 93, stores them in the RAM 92, and executes the programs to perform various calculations. For example, the control unit 90 generates a drive signal for the image to be formed based on the image data received from the input/output interface 80 and outputs it to the head 55.

RAM 92 provides the CPU 91 with a working memory space and stores temporary data. RAM 92 may also include non-volatile memory.

ROM 93 stores various control programs and configuration data executed by the CPU 91. Alternatively, rewritable non-volatile memory such as EEPROM (Electrically Erasable Programmable Read Only Memory) or flash memory may be used instead of ROM 93.

The storage unit 94 stores print jobs and image data related to print jobs that are input from the external device 200 via the input/output interface 80. For example, the storage unit 94 may use a non-volatile semiconductor memory (so-called flash memory) or an HDD (Hard Disk Drive), and DRAM (Dynamic Random Access Memory) may also be used in combination.

The control unit 90 is connected to the transport unit 10, supply unit 20, discharge unit 30, ink supply unit 40, image forming unit 50, reading unit 60, operation display unit 70, input/output interface 80, etc. The control unit 90 provides overall control of the inkjet printer 100. The transport unit 10, supply unit 20, discharge unit 30, ink supply unit 40, image forming unit 50, reading unit 60, operation display unit 70, input/output interface 80, etc., are controlled by the control unit 90 to perform predetermined processes.

The inkjet printer 100, having the above configuration, supplies the recording medium M from the supply unit 20 to the transport unit 10 under the control of the control unit 90. The image forming unit 50 forms an image on the recording medium M transported to the transport unit 10, and the image-formed recording medium M is then transported to the discharge unit 30.

Incidentally, inkjet image forming machines typically consist of multiple ink tanks and multiple print heads connected downstream of each of these ink tanks. Therefore, if a change in the gel ink state (e.g., a change in gel concentration) occurs within the print head, it's possible that a similar change is also occurring in the ink tanks upstream of the print head.

However, in conventional inkjet image forming apparatuses, such as the one shown in Patent Document 1, the state of the ink within the print head is determined based on the ink droplets ejected from the head, and the ink within that head is ejected accordingly. In other words, the ink state is determined and ejected on a per-print head basis, and the state of the ink in the ink tank is not determined.

Therefore, even if only the gel ink in the print head is emptied, if the gel ink in the upstream ink tank has undergone a state change, the changed gel ink will be supplied to the print head, and the image defect problem will not be resolved. As a result, it becomes necessary to empty the gel ink from the print head again, and repeating this process increases the downtime of the equipment and reduces the productivity of image formation.

Furthermore, the aforementioned gel ink discharge affects the running costs of the equipment. Therefore, it is desirable to identify the locations where gel ink discharge is necessary and to discharge only the necessary amount of gel ink, thereby reducing gel ink consumption. Thus, it is desirable to discharge the gel ink only after confirming the location where a change in the gel ink's state has occurred.

Therefore, in this embodiment, the inkjet printer 100 includes a first estimation unit and a second estimation unit, as described below. The first and second estimation units are provided as functions of the control unit 90, and are, for example, provided as programs executed by the control unit 90.

The first estimation unit estimates the occurrence of a change in the state of the gel ink on a per-head 55 basis, based on the first reading result of the pattern image formed by the multiple heads 55. The second estimation unit estimates the occurrence of a change in the state of the gel ink upstream, based on the occurrence status of the change in the state of the gel ink in two or more of the multiple heads 55.

The location where the gel ink state changes may occur is sometimes only the print head 55, as described below. Alternatively, it may include multiple print heads 55 along with the upstream second sub-tank 52b to which these multiple print heads 55 are commonly connected. Furthermore, it may include multiple print heads 55 and multiple second sub-tanks 52b along with the upstream first sub-tank 52a to which these multiple second sub-tanks 52b are commonly connected.

Here, a method for estimating the occurrence of a change in the state of the gel ink upstream of the print head 55 will be explained with reference to Figures 3 to 5. Figure 3 is a flowchart illustrating the method for estimating the state change of the gel ink implemented in the inkjet printer 100. The method for estimating the state change of the gel ink shown in Figure 3 is executed as a program in the control unit 90, which is a computer.

Figure 4 illustrates the method for estimating the state change of the gel ink shown in Figure 3, and shows an example of a location where the state change occurs. Figure 5 also illustrates the method for estimating the state change of the gel ink shown in Figure 3, and shows another example of a location where the state change occurs. In Figures 4 and 5, the locations where the gel ink state change occurs are indicated by thick lines.

(Step S11)
The control unit 90 controls the image forming unit 50 to form pattern images on the recording medium M using each head 55 (see pattern images P1 to P8 shown in Figures 4 and 5). As the pattern image, a halftone image dot pattern or the like is used so that the reading unit 60 can measure the image density and dot diameter.

(Step S12)
The control unit 90 uses the reading unit 60 to read the pattern images P1 to P8 formed on the recording medium M and obtains a first reading result (image density, dot diameter, etc.).

(Step S13)
The control unit 90 determines, based on the acquired first reading result, whether there are image defects in the pattern images P1 to P8 caused by gel ink ejection failure. For example, if the image density or dot diameter of the dot pattern cannot be properly acquired, it is determined that there are image defects caused by gel ink ejection failure. If it is determined that there are image defects (YES), the process proceeds to step S14; if it is determined that there are no image defects (NO), the process proceeds to step S15A.

(Step S14)
The control unit 90 uses the maintenance unit to clean the head 55. After cleaning the head 55, the system returns to step S11 and repeats steps S11 to S13. If cleaning is to be performed a predetermined number of times (for example, three times) consecutively, the control unit 90 may, for example, notify the operation display unit 70 of an error via a message or sound.

(Step S15A)
The control unit 90 determines, based on the acquired first reading result, whether the image density of pattern images P1 to P8 is equal to or greater than a specified value. If it is determined that the image density of all pattern images P1 to P8 is equal to or greater than a specified value (YES), the series of processes is terminated. If it is determined that the image density of any of the pattern images P1 to P8 is less than a specified value (NO), the process proceeds to step S16.

As described above, if the gel concentration of the gel ink is higher than a predetermined concentration (e.g., the appropriate concentration), the image density of the pattern image, for example, the image density of the dot pattern in a halftone image, will be lower than the appropriate image density. Therefore, a default value is set, for example, the appropriate image density of the pattern image. This allows the control unit 90 to estimate that a state change has occurred in the gel ink in the manifold 56 of the head 55 corresponding to the pattern images P1 to P8, where the image density is below the default value.

(Step S16)
The control unit 90 selects the gel ink in the manifold 56 of the head 55 that corresponds to the pattern image P1 to P8 whose image density is less than a specified value as the target for refreshing.

For example, Figure 4 shows an example where the image density of pattern images P1, P3, P4, P7, and P8 is above the specified value, while the image density of pattern images P2, P5, and P6 is below the specified value. In this case, the gel ink in the manifold 56 of heads 55-2, 55-5, and 55-6 corresponding to pattern images P2, P5, and P6, which have image densities below the specified value, is subject to refresh. The refresh process in this case will be explained in step S21.

(Step S17)
The control unit 90 checks whether there is a second sub-tank 52b that is subject to refreshing all downstream heads 55. If there is a second sub-tank 52b that is subject to refreshing all downstream heads 55 (YES), the process proceeds to step S18. If there is no second sub-tank 52b that is subject to refreshing all downstream heads 55 (NO), the process proceeds to step S21.

If there is a second sub-tank 52b that is subject to refreshment for all downstream heads 55 (if the answer in step S17 is YES), then not only the heads 55 but also the upstream second sub-tank 52b will be subject to refreshment. On the other hand, if there is no second sub-tank 52b that is subject to refreshment for all downstream heads 55 (if the answer in step S17 is NO), then only the heads 55 will be subject to refreshment.

(Step S18)
The control unit 90 checks whether all second sub-tanks 52b are subject to refresh. If all second sub-tanks 52b are subject to refresh (YES), the process proceeds to step S20. If none of the second sub-tanks 52b are subject to refresh (NO), the process proceeds to step S19.

If all second sub-tanks 52b are subject to refresh (if the answer is YES in step S18), then not only all heads 55 and second sub-tanks 52b, but also the upstream first sub-tank 52a will be subject to refresh. On the other hand, if not all second sub-tanks 52b are subject to refresh (if the answer is NO in step S17), then some heads 55 and second sub-tanks 52b will be subject to refresh.

(Step S19)
The control unit 90 determines that the gel ink in the second sub-tank 52b, which is subject to refreshment for all downstream heads 55, is the target of refreshment.

For example, in Figure 4, heads 55-5 and 55-6 corresponding to pattern images P5 and P6, whose image density is below the specified value, are subject to refresh. Therefore, all heads 55-5 and 55-6 downstream of the second sub-tank 52b-3 are subject to refresh. Consequently, the gel ink in the second sub-tank 52b-3 is also subject to refresh. This refresh process will be explained in step S21.

(Step S20)
The control unit 90 determines that the gel ink in the first sub-tank 52a is to be refreshed.

Steps S15A to S20 described above correspond to the processes performed by the first estimation unit and the second estimation unit in the present invention.

(Step S21)
The control unit 90 refreshes the gel ink in the target area. Refreshing involves performing a discharge operation to eject the gel ink in the target area where a change in state is presumed to have occurred, and supplying new gel ink to that target area.

For example, in Figure 4, since head 55-2 is the target for refresh, the gel ink is discharged from the manifold 56 of head 55-2, and new gel ink is supplied from the second sub-tank 52b-1 into the manifold 56 of head 55-2.

Furthermore, in Figure 4, the print heads 55-5, 55-6, and the second sub-tank 52b-3 are also subject to refresh. In this case, the gel ink is discharged from the manifold 56 of print heads 55-5 and 55-6 and from the second sub-tank 52b-3, and new gel ink is supplied from the first sub-tank 52a to the second sub-tank 52b-3 and to the manifold 56 of print heads 55-5 and 55-6.

Furthermore, Figure 5 shows an example where the image density of all pattern images P1 to P8 is below the specified value, and all heads 55-1 to 55-8, all second sub-tanks 52b-1 to 52b-4, and the first sub-tank 52a are also subject to refresh. In this case, gel ink is discharged from the manifold 56 of heads 55-1 to 55-8, the second sub-tanks 52b-1 to 52b-4, and the first sub-tank 52a. Then, new gel ink is supplied from the main tank 41 (see Figure 1) to the first sub-tank 52a, the second sub-tanks 52b-1 to 52b-4, and the manifold 56 of heads 55-1 to 55-8.

In any case of the area to be refreshed, the control unit 90 controls the head 55 (head drive unit 54) to perform a discharge operation, ejecting the gel ink from the nozzle 59 of the head 55 within the target area. At this time, the gel ink discharged from the nozzle 59 is collected, for example, in a recovery tank in the maintenance unit.

Then, the gel ink in the target area is discharged, and gel ink is supplied to the target area from the upstream main tank 41, the first sub-tank 52a, or the second sub-tank 52b, so the gel ink in the target area is automatically refreshed (reset).

(Step S22)
After refreshing the gel ink in the target area, the control unit 90 controls the image forming unit 50 to form a pattern image on the recording medium M using each head 55. As described above, a dot pattern of a halftone image is used as the pattern image.

(Step S23)
The control unit 90 uses the reading unit 60 to read the pattern images P1 to P8 formed on the recording medium M and obtains a first reading result (image density and dot diameter).

(Step S24A)
The control unit 90 determines, based on the acquired first reading result, whether the image density of pattern images P1 to P8 is equal to or greater than a specified value. If it is determined that the image density of all pattern images P1 to P8 is equal to or greater than a specified value (YES), the series of processes is terminated. If it is determined that the image density of any of the pattern images P1 to P8 is less than a specified value (NO), the process returns to step S16.

Returning to step S16, the control unit 90 executes steps S16 to S23 again. If steps S16 to S23 are executed consecutively a predetermined number of times (for example, three times), the control unit 90 may, for example, notify the operation display unit 70 of an error via a message or sound.

As described above, in this embodiment, the inkjet printer 100 includes a first estimation unit and a second estimation unit. The first estimation unit estimates the occurrence of gel ink state changes on a per-head 55 basis, based on the first reading result of the pattern image formed by the multiple heads 55. The second estimation unit estimates the occurrence of gel ink state changes upstream, based on the occurrence status of gel ink state changes in two or more of the multiple heads 55.

According to this embodiment, based on the occurrence of state changes in the gel ink within the manifold 56 of the multiple heads 55, it is possible to estimate the location upstream of the head 55 where a state change in the gel ink is occurring. Since the location of the state change in the gel ink can be estimated in this way, only the gel ink within the location of the change can be discharged from the first sub-tank 52a, the second sub-tank 52b, and the head 55. In other words, discharge of gel ink from locations other than the location of the change can be avoided.

As a result, unlike conventional methods, the gel ink in the head 55 is not repeatedly discharged, reducing downtime and improving the productivity of image formation. Furthermore, since only the gel ink within the generated area is discharged, the amount of gel ink discharged is limited to the minimum necessary, reducing gel ink consumption and thus lowering the running costs of the device.

<Variation 1>
In the embodiment described above, the first estimation unit estimates whether or not a change in state has occurred in the gel ink in each manifold 56, based on the first reading result of the pattern image formed by each head 55. This estimation can be performed without any problems if there is no change in the head 55 over time.

However, changes may occur in the print head 55 over time, in which case the quality of the formed image will change. Specifically, the piezoelectric element 58 of the print head 55 may deteriorate over time, in which case the amount of gel ink ejected decreases, and the quality (density) of the formed image deteriorates. Therefore, it is desirable for the first estimation unit to estimate whether or not a change in the state of the gel ink has occurred, taking into account the deterioration of the print head 55 over time.

The inkjet printer 100 has a function (described below as a drive condition modification unit) that adjusts the drive conditions of the print head 55 so that the gel ink is ejected at an appropriate rate, in order to maintain the quality of the image formed even if the print head 55 deteriorates over time.

As will be explained in detail later, in this modified example, the first estimation unit estimates whether or not a change in state has occurred in the gel ink within the manifold 56 of each head 55, based on the adjusted drive conditions of the head 55 and the usage history of the head 55. By performing such estimation, it is possible to estimate whether or not a change in state has occurred in the gel ink, taking into account the deterioration of the head 55 over time.

First, referring to Figures 6 to 9, we will explain the driving conditions for the head 55, specifically the adjustment of the driving voltage applied to the piezoelectric element 58.

Figure 6 illustrates the changes in gel ink droplets ejected from the print head 55 when the number of ejections (degree of deterioration) of the print head 55 differs. Figure 7 is a graph showing the relationship between the number of gel ink ejections and the optimal driving voltage applied to the piezoelectric element 58 of the print head 55.

The print head 55 deteriorates over time, causing changes in the quality of the resulting image. For example, as the piezoelectric element 58 deteriorates with the number of ejection cycles, the amount of gel ink ejected from the print head 55 decreases, the gel ink droplets become smaller (see droplets D1→D2 in Figure 6), and the quality (density) of the resulting image decreases.

To address this deterioration over time, the inkjet printer 100 is equipped with a drive condition modification unit. This unit is provided as a function of the control unit 90, and is, for example, provided as a program executed by the control unit 90.

The drive condition changing unit adjusts the drive conditions of each head 55 so that the gel ink is ejected at an appropriate rate, based on the first reading result of the pattern image formed by each head 55, in order to maintain the quality of the formed image. For example, based on the first reading result, which is the image density and droplet dot diameter, the drive voltage to the piezoelectric element 58, which is a drive condition of the head 55, is adjusted to obtain the optimal voltage so that the gel ink ejection rate is such that the formed pattern image matches the reference pattern image.

Furthermore, if the drive conditions of the print head 55 meet predetermined conditions, for example, as shown in Figure 7, if the optimal drive voltage of the piezoelectric element 58 exceeds the upper voltage limit, adjusting the drive voltage of the piezoelectric element 58 will no longer allow the gel ink to be ejected at the appropriate rate. In this case, it is determined that the print head 55 has reached the end of its lifespan, and it is replaced with a new print head 55.

When using gel ink as the ink, as described above, the concentration of the gel component in the gel ink stored in the first sub-tank 52a, the second sub-tank 52b, and the manifold 56 of the head 55 may become high.

Figure 8 illustrates the changes in the gel ink droplets ejected from the print head 55 when the concentration of the gel component in the gel ink differs. Figure 9 is a graph showing the relationship between the number of gel ink ejections and the optimal driving voltage applied to the piezoelectric element 58 of the print head 55, for gel ink containing an appropriate concentration of gel component and gel ink containing a high concentration (>appropriate concentration) of gel component.

When the concentration of the gel component in the gel ink increases, its pinning properties increase, preventing the gel ink droplets ejected from the head 55 from expanding to the specified dot diameter (see droplets D3→D4 in Figure 8).

Therefore, it is necessary to adjust the driving conditions of the head 55 to maintain the quality of the formed image. Specifically, as described above, the driving conditions of the head 55 (for example, the driving voltage to the piezoelectric element 58) are adjusted based on the first reading result (image density, droplet dot diameter) so that the gel ink is ejected at an appropriate rate.

Thus, even when the drive conditions of the print head 55 (the drive voltage of the piezoelectric element 58) are adjusted due to a change in the concentration of the gel component of the gel ink, the lifespan of the print head will be predicted and judged based on the change in the drive conditions of the print head 55, as shown in Figure 9. Therefore, there is a risk of mistakenly determining that the print head has reached the end of its lifespan, even though it has not actually reached the end of its life, due to a change in the drive conditions of the print head 55 caused by a change in the concentration of the gel component of the gel ink. If this determination is made, the print head 55 will be unnecessarily replaced with a new one, even though it has not actually reached the end of its life, resulting in increased costs.

Therefore, in this modified example, the first estimation unit estimates the occurrence of a change in the state of the gel ink in the sub-tank 52 when the driving conditions of the head 55 satisfy predetermined conditions.

The first estimation unit estimates the occurrence of a change in the state of the gel ink in the sub-tank 52 when the driving conditions of the head 55 meet predetermined conditions, specifically when the optimal voltage of the piezoelectric element 58 exceeds the voltage upper limit. The estimation of the occurrence of a change in the state of the gel ink in the sub-tank 52 is based on the usage history of the head 55 (the period of use of the head 55 and the number of times ink has been ejected by the head 55), determining whether a change in the concentration of the gel component of the gel ink has occurred.

In addition, in this modified configuration, the inkjet printer 100 includes a determination unit described below. The determination unit determines whether the print head 55 has reached the end of its lifespan, depending on whether or not a change in state has been estimated. The determination unit is provided as a function of the control unit 90, and is, for example, provided as a program executed by the control unit 90.

The determination unit determines whether the print head 55 has reached the end of its lifespan, based on whether the first estimation unit has estimated the occurrence of a state change, that is, based on whether a change in the concentration of the gel component of the gel ink has occurred. Even if the optimal voltage of the piezoelectric element 58 exceeds the voltage upper limit, if a change in the concentration of the gel component of the gel ink has occurred, the determination unit determines that the print head 55 has not reached the end of its lifespan.

Next, the method for estimating the state change of the gel ink in this modified example will be explained with reference to Figures 10A and 10B. Figures 10A and 10B are flowcharts illustrating a modified example of the gel ink state change estimation method shown in Figure 3. The gel ink state change estimation method shown in Figures 10A and 10B is also executed as a program in the control unit 90, which is a computer.

Here, the method for estimating the state change of the gel ink in this modified example is the same as the method for estimating the state change of the gel ink shown in Figure 3, except for steps S15B and S24B. Therefore, Figure 10A shows step S15B instead of step S15A, and Figure 10B shows step S24B instead of step S24A. The illustrations of steps S11-S14 and S16-S23 are omitted. Furthermore, steps S11-S14 and S16-S23 are the same processes as those described in Figure 3, so their explanations are also omitted.

In this modified example, after performing steps S11 to S14 shown in Figure 3, the control unit 90 performs step S15B.

(Step S15B-1)
The control unit 90 adjusts the driving conditions of the head 55 (the driving voltage of the piezoelectric element 58) based on the acquired first reading result (image density and dot diameter). Specifically, based on the image density and dot diameter, it adjusts the driving voltage of the piezoelectric element 58 so that the amount of gel ink ejected becomes the amount of the reference pattern image when the formed pattern image is obtained. In this case, for example, if the image density is lower than the reference, the driving voltage is adjusted to increase the ejection amount, and if the image density is higher than the reference, the driving voltage is adjusted to decrease the ejection amount.

(Step S15B-2)
The control unit 90 checks whether the drive voltage of the adjusted piezoelectric element 58 is less than a predetermined voltage. For example, as shown in Figure 9, it checks whether the drive voltage of the adjusted piezoelectric element 58 is less than the voltage upper limit, which is a predetermined voltage.

If the drive voltage of the adjusted piezoelectric element 58 is below a predetermined voltage (YES), it can be determined that the head 55 has not reached the end of its lifespan, and the series of processes is terminated. On the other hand, if the drive voltage of the adjusted piezoelectric element 58 is not below a predetermined voltage (NO), that is, if the drive voltage is above the predetermined voltage, the head 55 may have reached the end of its lifespan, and the process proceeds to step S15B-3.

(Step S15B-3)
The control unit 90 checks whether the numerical values related to the usage history of the print head 55 are equal to or greater than a predetermined value. For example, the control unit 90 stores the usage period and the number of ink ejections of the print head 55 in, for example, the storage unit 94. At this time, it is desirable that the usage period and the number of ejections of inks other than gel ink be included when inks other than gel ink are used. If the drive voltage of the adjusted piezoelectric element 58 is equal to or greater than a predetermined voltage (if NO in step S15B-2), then in step S15B-3, the control unit 90 checks the usage period and the number of ink ejections of the print head 55 by referring to the storage unit 94.

If the numerical value related to the usage history of the print head 55 is equal to or greater than the predetermined value (YES), it can be determined that the print head 55 has reached the end of its lifespan, and the process proceeds to step S15B-4. On the other hand, if the numerical value related to the usage history of the print head 55 is not equal to or greater than the predetermined value (NO), that is, if the value is less than the predetermined value, it is possible that the drive voltage exceeded the predetermined voltage due to the concentration of the gel component in the gel ink, and the process proceeds to step S16.

For example, if the usage period of the print head 55 exceeds a predetermined period, or if the number of ink ejections exceeds a predetermined number, it can be determined that the print head 55 has reached the end of its lifespan, and the process proceeds to step S15B-4. On the other hand, if the usage period of the print head 55 is less than the predetermined period, or if the number of ink ejections is less than the predetermined number, it is possible that the drive voltage exceeded the predetermined voltage due to the concentration of the gel component in the gel ink, and the process proceeds to step S16.

In this way, the control unit 90 estimates the occurrence of a change in the state of the gel ink by checking whether the numerical value related to the usage history of the print head 55 is equal to or greater than a predetermined value.

(Step S15B-4)
The control unit 90 notifies the operation display unit 70 of the head 55 replacement with a message or sound, and then terminates the series of processes. In this case, upon receiving notification of the head 55 replacement, the operator will perform the head 55 replacement work.

Step S15B described above is performed for each head 55, and it is estimated whether or not a state change has occurred in the gel ink at each head 55.

In this modified example, the control unit 90 executes steps S16 to S21 shown in Figure 3. During steps S16 to S21, based on the status of gel ink state changes in the multiple heads 55 obtained in step S15B, the control unit estimates the locations where state changes are occurring in the gel ink and refreshes (resets) the gel ink within those locations.

In this modified example, the control unit 90 executes step S24B after performing steps S22 and S23 as shown in Figure 3.

(Step S24B-1)
The control unit 90 adjusts the driving conditions of the head 55 (driving voltage of the piezoelectric element 58) based on the acquired first reading results (image density and dot diameter).

(Step S24B-2)
The control unit 90 checks whether the drive voltage of the adjusted piezoelectric element 58 is less than a predetermined voltage. For example, as shown in Figure 9, it checks whether the drive voltage of the adjusted piezoelectric element 58 is less than the voltage upper limit, which is a predetermined voltage.

If the drive voltage of the adjusted piezoelectric element 58 is below a predetermined voltage (YES), it can be determined that the head 55 has not reached the end of its lifespan, and the series of processes is terminated. On the other hand, if the drive voltage of the adjusted piezoelectric element 58 is not below a predetermined voltage (NO), that is, if the drive voltage is above the predetermined voltage, it can be determined that the head 55 has reached the end of its lifespan, and the process proceeds to step 24B-3.

(Step S24B-3)
The control unit 90 notifies the operation display unit 70 of the head 55 replacement with a message or sound, and then terminates the series of processes. Upon receiving notification of the head 55 replacement, the operator proceeds with the head 55 replacement work.

As described above, in this modified example, the inkjet printer 100 includes a drive condition changing unit that changes the drive conditions for ejecting gel ink from each head 55 based on the first reading result. The first estimation unit, if there is a head 55 whose drive conditions changed by the drive condition changing unit satisfy predetermined conditions, estimates whether a change in state has occurred in the gel ink within the manifold 56 of that head 55, based on the usage history of that head 55.

According to this modified configuration, the system estimates whether or not a change in the state of the gel ink in the manifold 56 of each head 55 has occurred, based on the drive conditions changed by the drive condition change unit and the usage history of the head 55. This allows for the estimation of whether or not a change in the state of the gel ink in the manifold 56 of the head 55 has occurred, taking into account the deterioration of the head 55 over time.

Furthermore, similar to the embodiment described above, based on the occurrence of state changes in the gel ink within the manifold 56 of the multiple heads 55, the location upstream of the head 55 where a state change in the gel ink is occurring can be estimated. In this way, since the location where a state change in the gel ink is occurring can be estimated, only the gel ink within that location can be discharged.

As a result, similar to the above embodiment, it is possible to suppress the downtime of the device and improve the productivity of image formation, and to reduce the running costs of the device by reducing the consumption of gel ink.

Furthermore, as explained above, in this modified example, the inkjet printer 100 includes a determination unit that determines whether the print head 55 has reached the end of its lifespan, depending on whether or not a change in state has been estimated.

According to this modified configuration, even if the optimal voltage of the piezoelectric element 58 exceeds the voltage limit, the lifespan of the head 55 is determined based on the usage history of the head 55 to determine whether a change in the concentration of the gel component of the gel ink has occurred.

Conventional inkjet image forming machines do not take into account changes in the state of the gel ink, which can lead to errors in determining the lifespan of the print head 55. In contrast, this modified version considers changes in the state of the gel ink (changes in the concentration of the gel component) to determine the lifespan of the print head 55, allowing for accurate determination of its lifespan. As a result, the machine can appropriately notify the system of the appropriate replacement timing for the print head 55, preventing unnecessary replacements and thus preventing increased costs.

<Modified Example 2>
The modified inkjet printer 100 will be described with reference to Figures 1 and 2. In addition to the configuration described in the above embodiment, the modified inkjet printer 100 further includes a heating unit 110, as shown by the long dotted lines in Figures 1 and 2.

The heating unit 110 is positioned upstream of the image forming unit 50 in the transport direction T of the recording medium M, and heats the recording medium M, which is transported by the transport belt 11, to a predetermined temperature. The heating unit 110 is connected to the control unit 90 (see Figure 2) and controlled by the control unit 90.

For example, the heating unit 110 has an infrared heater, etc., and power is supplied to the infrared heater based on a control signal supplied from the control unit 90, causing the infrared heater to generate heat and heat the recording medium M to a predetermined temperature. In this modified example, the predetermined temperature is a temperature above the phase transition temperature of the gel component of the gel ink.

In this example, the heating unit 110 is positioned on the upper side of the conveyor belt 11. However, instead of (or in addition to) the heating unit 110, a heating unit may be provided on the lower side of the conveyor belt 11 to heat the conveyor belt 11 and thereby heat the recording medium M.

Next, the method for estimating the state change of the gel ink in this modified example will be explained with reference to Figure 11. Figure 11 is a flowchart illustrating a modified example of the gel ink state change estimation method shown in Figure 10A. The gel ink state change estimation method shown in Figure 11 is also executed as a program in the control unit 90, which is a computer.

Here, the method for estimating the state change of the gel ink in this modified example is the same as the method for estimating the state change of the gel ink described in Modified Example 1, except for step S15C. In other words, in this modified example, in the method for estimating the state change of the gel ink shown in Figure 3, step S15C shown in Figure 11 is used instead of step S15A, and step S24B shown in Figure 10B is used instead of step S24A.

Therefore, the illustrations of steps S11-S14 and S16-S24B, other than step S15C shown in Figure 11, are omitted. Furthermore, since steps S11-S14 and S16-S24B are the same processes as those explained in Figures 3, 10A, and 10B, their explanations are also omitted.

In this modified example, after performing steps S11 to S14 shown in Figure 3, the control unit 90 performs step S15C.

As described above, in step S15B shown in Figure 10A, the control unit 90 estimates the occurrence of a change in the state of the gel ink by checking whether the numerical value related to the usage history of the head 55 is equal to or greater than a predetermined value.

On the other hand, in step S15C of this modified example, the control unit 90 estimates the occurrence of a state change in the gel ink based on the second reading result of the pattern image formed on the recording medium M, which has been heated to a temperature above the phase transition temperature of the gel component, as described below.

(Step S15C-1)
The control unit 90 adjusts the driving conditions of the head 55 (driving voltage of the piezoelectric element 58) based on the acquired first reading results (image density and dot diameter). Since this step S15C-1 is the same as step S15B-1 described above, a detailed explanation is omitted.

(Step S15C-2)
The control unit 90 checks whether the drive voltage of the adjusted piezoelectric element 58 is less than a predetermined voltage. If the drive voltage of the adjusted piezoelectric element 58 is less than the predetermined voltage (YES), the series of processes is terminated. On the other hand, if the drive voltage of the adjusted piezoelectric element 58 is not less than the predetermined voltage (NO), the process proceeds to step S15C-3. Step S15C-2 is the same as step S15B-2 described above, so a detailed explanation is omitted.

(Step S15C-3)
The control unit 90 controls the heating unit 110 to heat the recording medium M to a temperature above the phase transition temperature of the gel component.

(Step S15C-4)
The control unit 90 controls the image forming unit 50, causing the head 55 to form a pattern image on the recording medium M. As described above, a dot pattern of a halftone image is used as the pattern image.

(Step S15C-5)
The control unit 90 uses the reading unit 60 to read the pattern image formed on the recording medium M and obtains a second reading result.

(Step S15C-6)
The control unit 90 checks whether the numerical value related to the second reading result is greater than or equal to a predetermined value. In this modified example, the numerical value related to the second reading result is, for example, the dot diameter of the gel ink droplet when the gel ink is ejected under predetermined driving conditions.

Here, the numerical values related to the second reading result will be explained using the dot diameter of the gel ink droplet as an example, with reference to Figure 12. Figure 12 illustrates the gel ink droplets ejected from the head 55 onto a recording medium M at room temperature and a recording medium M at a temperature above the phase transition temperature, for gel ink containing an appropriate concentration of gel component and gel ink containing a high concentration of gel component.

When gel ink is ejected onto the recording medium M under predetermined driving conditions, the dot diameter of the ejected gel ink droplets changes depending on the concentration of the gel component of the gel ink, the temperature of the recording medium M, and other factors.

When the gel component concentration of the gel ink is at an appropriate concentration and the temperature of the recording medium M is at room temperature, the dot diameter of the gel ink droplet D11 when the gel ink is ejected under predetermined driving conditions is defined as d11. Furthermore, when the gel component concentration of the gel ink is at an appropriate concentration and the temperature of the recording medium M is above the phase transition temperature of the gel component, the dot diameter of the gel ink droplet D12 when the gel ink is ejected under predetermined driving conditions is defined as d12.

When the temperature of the recording medium M is above the phase transition temperature of the gel component, the gel ink droplet D12 expands to a dot diameter equivalent to that of ink without the gel component. In other words, the dot diameter d12 of droplet D12 becomes larger than the dot diameter d11 of droplet D11.

Furthermore, when the gel component concentration of the gel ink is high (> appropriate concentration) and the temperature of the recording medium M is room temperature, the dot diameter of the gel ink droplet D13 when the gel ink is ejected under predetermined driving conditions is defined as d13. Also, when the gel component concentration of the gel ink is high and the temperature of the recording medium M is above the phase transition temperature of the gel component, the dot diameter of the gel ink droplet D14 when the gel ink is ejected under predetermined driving conditions is defined as d14.

When the gel component concentration of gel ink is high, the pinning properties increase compared to when the gel component concentration is at an appropriate level. As a result, the dot diameter d13 of the gel ink droplet D13 does not expand to the dot diameter d11 of the gel ink droplet D11. In other words, the dot diameter d13 of droplet D13 becomes smaller than the dot diameter d11 of droplet D11.

Furthermore, even when the gel component concentration of the gel ink is high, if the temperature of the recording medium M is above the phase transition temperature of the gel component, the gel ink droplet D14 expands to a dot diameter equivalent to that of ink without a gel component. In other words, the dot diameter d14 of droplet D14 is larger than the dot diameter d13 of droplet D13, and also larger than the dot diameter d11 of droplet D11.

On the other hand, if the head 55 is degraded (the piezoelectric element 58 is degraded), even if gel ink is ejected under predetermined driving conditions, the actual ejection amount will be small. Therefore, even when the temperature of the recording medium M is above the phase transition temperature of the gel component, the dot diameter of the ejected gel ink droplets will not be as large as droplets D12 and D14 shown in Figure 12. In this modified example, this point is taken into consideration, and the occurrence of a change in the state of the gel ink is estimated by comparing the dot diameter of the pattern image acquired in step S15C-5 with, for example, the dot diameter d11 of droplet D11. Specifically, if the dot diameter of the pattern image acquired in step S15C-5 is greater than or equal to the dot diameter d11 of droplet D11, the occurrence of a change in the state of the gel ink (increased concentration of the gel component) can be estimated.

Therefore, when the gel component concentration of the gel ink is at the appropriate concentration and the temperature of the recording medium M is at room temperature, the dot diameter d11 of the gel ink droplet D11 when a predetermined amount of gel ink is ejected is measured in advance. The measured dot diameter d11 is then stored as a predetermined value in the storage unit 94.

Furthermore, the dot diameter d11 of the gel ink droplet D11 when different amounts of gel ink are dispensed may be measured in advance, and the correspondence between the dispensed amount and the dot diameter d11 may be stored as a table in the storage unit 94.

Then, in step S15C-6 described above, when checking whether the numerical value related to the second reading result is greater than or equal to a predetermined value, the control unit 90 compares the dot diameter of the pattern image acquired in step S15C-5 with the dot diameter d11 stored in the storage unit 94. The control unit 90 checks whether the dot diameter of the pattern image acquired in step S15C-5 is greater than or equal to the dot diameter d11 stored in the storage unit 94.

Then, if the dot diameter of the pattern image acquired in step S15C-5 is greater than or equal to the dot diameter d11 stored in the storage unit 94 (YES), the control unit 90 proceeds to step S16. In other words, it is possible that the drive voltage exceeded the predetermined voltage due to the concentration of the gel component in the gel ink, so the process proceeds to step S16. On the other hand, if the dot diameter of the pattern image acquired in step S15C-5 is not greater than or equal to the dot diameter d11 stored in the storage unit 94 (NO), it can be determined that the head 55 has reached the end of its lifespan, and the process proceeds to step S15C-7.

(Step S15C-7)
The control unit 90 notifies the operation display unit 70 of the head 55 replacement with a message or sound, and then terminates the series of processes. In this case, upon receiving notification of the head 55 replacement, the operator will perform the head 55 replacement work.

Thus, the control unit 90 estimates the occurrence of a change in the gel ink state by checking whether the dot diameter of the pattern image acquired in step S15C-5 is greater than or equal to the dot diameter d11 stored in the storage unit 94.

Step S15C described above is also performed for each head 55, and it is estimated whether or not a state change has occurred in the gel ink at each head 55.

In this modified example, the control unit 90 executes steps S16 to S23 shown in Figure 3 and step S24B shown in Figure 10B. During steps S16 to S21, based on the occurrence of state changes in the gel ink in the multiple heads 55 obtained in step S15C, the control unit estimates the locations where state changes are occurring in the gel ink and refreshes (resets) the gel ink within those locations.

In this explanation, the dot diameter of the gel ink droplet was used as an example of the numerical value related to the second reading result. However, image density may also be used as the numerical value related to the second reading result. Even when using image density as the numerical value related to the second reading result, it is possible to estimate the occurrence of a change in the state of the gel ink in the same manner as with the dot diameter.

As explained above, in this modified example, the first estimation unit estimates the occurrence of a state change in the gel ink based on the second reading result of the pattern image formed by the head 55 on the recording medium M heated to a temperature above the phase transition temperature of the gel ink.

According to this modified configuration, even if the optimal voltage of the piezoelectric element 58 exceeds the voltage upper limit, it is possible to determine whether a change in the concentration of the gel component of the gel ink has occurred based on the second reading result of the pattern image.

Therefore, similar to the above embodiment, based on the occurrence of state changes in the gel ink within the manifold 56 of the multiple heads 55, it is possible to estimate the location upstream of the head 55 where a state change in the gel ink is occurring. Since the location where the state change in the gel ink is occurring can be estimated, only the gel ink within that location can be discharged.

As a result, similar to the above embodiment, it is possible to suppress the downtime of the device and improve the productivity of image formation, and to reduce the running costs of the device by reducing the consumption of gel ink.

Furthermore, according to this modified version, based on the second reading result of the pattern image, it is determined whether a change in the concentration of the gel component of the gel ink has occurred, and then the lifespan of the print head 55 is determined. In this way, the lifespan of the print head 55 is determined by considering the change in the state of the gel ink (change in the concentration of the gel component), allowing for accurate determination of the print head 55's lifespan. As a result, the timing for replacing the print head 55 can be appropriately notified, eliminating the need to unnecessarily replace the print head 55 with a new one, thus preventing increased costs.

<Other variations>
In the above embodiments and modified examples 1 and 2, in step S21, the gel ink is ejected simultaneously (at the same time) from the parts of the first sub-tank 52a, the second sub-tank 52b, and the head 55 that are to be refreshed. Alternatively, the gel ink may be ejected sequentially from the downstream side while checking the pattern image.

For example, if there is a second sub-tank 52b where a change in the gel ink is presumed to be occurring, the multiple heads 55 connected to the second sub-tank 52b will discharge the gel ink in their manifolds 56. After discharging the gel ink, the multiple heads 55 will re-form the pattern image on the recording medium M. The formation of the pattern image may be the same as in step S11 described above.

Subsequently, the control unit 90 reads the pattern image using the reading unit 60, similar to step S12 described above, and obtains a first reading result. After obtaining the first reading result, the control unit 90 estimates, based on the first reading result of the newly formed pattern image, whether or not a change in state has occurred in the gel ink within the manifold 56 of the multiple heads 55.

Furthermore, if it is estimated that a change in the state of the gel ink in the manifold 56 of the multiple heads 55 has occurred, the multiple heads 55 will discharge the gel ink, including from the second sub-tank 52b upstream of the multiple heads 55. In other words, if refreshing the gel ink in the manifold 56 of the multiple heads 55 does not improve the state of the gel ink, the gel ink in the upstream second sub-tank 52b will also be discharged in addition to the gel ink in the manifold 56 of the multiple heads 55.

In this way, the gel ink is discharged sequentially from the downstream side while the pattern image is being monitored. This reduces the downtime of the device, improves the productivity of image formation, and also reduces the running costs of the device by decreasing the amount of gel ink consumed.

Furthermore, in the above embodiments and modifications 1 and 2, the second sub-tanks 52b-1 to 52b-4 are connected downstream of the first sub-tank 52a in a single-stage configuration. However, multiple second sub-tanks 52b may be connected in a tree-like configuration from the upstream side in multiple stages.

For example, multiple second sub-tanks 52b may be connected downstream of each of the second sub-tanks 52b-1 to 52b-4, creating a multi-stage tree-like configuration from the upstream side. In this case, multiple heads 55 are connected to each of the downstream second sub-tanks 52b.

Even with this configuration, as described in the above embodiments and modified examples 1 and 2, it is possible to estimate which tanks are experiencing a state change in the gel ink based on the occurrence of state changes in the gel ink within the manifold 56 of the multiple heads 55.

In this case, if there is an upstream second sub-tank 52b to which multiple downstream second sub-tanks 52b where a state change in the gel ink is occurring are commonly connected, it is presumed that a state change in the gel ink is occurring in that upstream second sub-tank 52b.

Thus, even in a configuration where the second sub-tank 52b is connected in a tree-like, multi-stage manner, it is possible to estimate which tank is experiencing a state change in the gel ink.

The embodiments described above are merely examples of how the present invention can be implemented, and the technical scope of the invention should not be interpreted as being limited by these embodiments. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

10 Conveying unit 11 Conveying belt 11a Conveying surface 12 Driven roller 13 Driven roller 20 Supply unit 21 Supply loading unit 22 Supply conveying unit 30 Discharge unit 31 Discharge loading unit 32 Discharge conveying unit 40 Ink supply unit 41 Main tank 42 Flow path 50 Image forming unit 51 Carriage 52a First sub-tank 52b (52b-1 to 52b-4) Second sub-tank 53a, 53b, 53c Flow path 54 Head drive unit 55 (55-1 to 55-8) Inkjet head 56 Manifold 57 Pressure chamber 58 Piezoelectric element 59 Nozzle 60 Reading unit 70 Operation display unit 80 Input/output interface 90 Control unit 100 Inkjet printer 110 Heating unit 200 External device

Claims (20)

Multiple inkjet heads that eject phase transition ink, supplied and stored in corresponding storage units from the upstream side of the ink supply path, onto a recording medium,
A first estimation unit estimates the occurrence of a state change in the phase transition ink on an inkjet head basis, based on the first reading result of the pattern image formed by the plurality of inkjet heads,
A second estimation unit estimates the occurrence of the state change on the upstream side based on the occurrence status of the state change in two or more inkjet heads among the plurality of inkjet heads,
An image forming apparatus equipped with the following features. The system comprises multiple tanks into which the phase transition ink is supplied and stored.
Each of the multiple tanks is connected to a storage unit for a corresponding multiple inkjet head via the aforementioned ink supply path.
The image forming apparatus according to claim 1. The second estimation unit estimates the occurrence of the state change in a tank if there is a tank to which a plurality of inkjet heads, whose occurrence of the state change has been estimated, are commonly connected.
The image forming apparatus according to claim 2. It has multiple tanks connected in a tree-like structure from the upstream side, and each of the downstream tanks among these multiple tanks is connected to a corresponding set of inkjet heads.
The second estimation unit estimates the occurrence of the state change in the upstream tank if there is an upstream tank to which a plurality of tanks to which the occurrence of the state change has been estimated is commonly connected.
The image forming apparatus according to claim 3. If there is a tank in which the occurrence of the aforementioned state change is estimated, the plurality of inkjet heads connected to the tank perform a discharge operation to discharge the phase transition ink in the tank and the phase transition ink in the storage section of the plurality of inkjet heads.
The image forming apparatus according to claim 3. If there is a tank in which the occurrence of the aforementioned state change is estimated, the plurality of inkjet heads connected to the tank perform a discharge operation to eject the phase transition ink in the storage section of the plurality of inkjet heads, and then re-form the pattern image.
The first estimation unit estimates the occurrence of the state change in the plurality of inkjet heads based on the first reading result of the re-formed pattern image.
If the occurrence of the state change in the plurality of inkjet heads is again estimated, the plurality of inkjet heads perform a discharge operation to discharge the phase transition ink in the tank and the phase transition ink in the storage section of the plurality of inkjet heads.
The image forming apparatus according to claim 3. If there is no tank in which the occurrence of the aforementioned state change is estimated, the inkjet head in which the occurrence of the aforementioned state change is estimated performs a discharge operation to eject the phase-transition ink in the storage section of the inkjet head.
The image forming apparatus according to claim 3. The system includes a drive condition changing unit that changes the drive conditions for ejecting the phase transition ink in each of the inkjet heads based on the first reading result,
The first estimation unit estimates the occurrence of the state change in an inkjet head if there is an inkjet head whose drive conditions, changed by the drive condition changing unit, satisfy predetermined conditions.
The image forming apparatus according to claim 1. The system includes a determination unit that determines whether or not the inkjet head has reached the end of its lifespan in response to the estimation of the occurrence of the aforementioned change in state.
The image forming apparatus according to claim 8. The first estimation unit estimates the occurrence of the state change based on the usage history of the inkjet head.
The image forming apparatus according to claim 8. The first estimation unit estimates the occurrence of the state change based on the second reading result of the pattern image formed by the inkjet head on the recording medium heated to a temperature above the phase transition temperature of the phase transition ink.
The image forming apparatus according to claim 8. The first estimation unit estimates the occurrence of the state change if the numerical value related to the usage history is less than a predetermined value.
The image forming apparatus according to claim 10. The first estimation unit estimates the occurrence of the state change if the numerical value related to the second reading result is greater than or equal to a predetermined numerical value.
The image forming apparatus according to claim 11. The aforementioned pattern image is formed by a dot pattern.
The image forming apparatus according to any one of claims 1 to 13. The reading result is the density of the pattern image, or the dot diameter of the phase transition ink constituting the pattern image.
The image forming apparatus according to claim 14. The drive condition changing unit modifies the drive conditions based on the first reading result so that the pattern image formed by the inkjet head becomes a reference pattern image.
The image forming apparatus according to claim 8. The inkjet head includes a nozzle for ejecting the phase transition ink, and a piezoelectric element that deforms in accordance with the applied drive voltage and imparts a pressure change to the phase transition ink supplied to the nozzle.
The aforementioned driving condition is the driving voltage applied to the piezoelectric element.
The image forming apparatus according to claim 16. The aforementioned predetermined condition is that the drive voltage is equal to or greater than a predetermined voltage.
The image forming apparatus according to claim 17. Phase transition ink, supplied and stored in the corresponding storage section from the upstream side of the ink supply path, is ejected from multiple inkjet heads to form a pattern image on the recording medium.
Based on the first reading result of the pattern image formed by the plurality of inkjet heads, the occurrence of a state change in the phase transition ink is estimated on an inkjet head basis.
Based on the occurrence of the state change in two or more of the plurality of inkjet heads, the occurrence of the state change on the upstream side is estimated.
A method for estimating the state change of phase-transition ink. On the computer,
A process of forming a pattern image on a recording medium by ejecting phase-transition ink, which is supplied and stored in a corresponding storage unit from the upstream side of the ink supply path, from multiple inkjet heads,
A process to estimate the occurrence of a state change in the phase transition ink on an inkjet head basis, based on the first reading result of the pattern image formed by the plurality of inkjet heads,
A process for estimating the occurrence of the state change on the upstream side based on the occurrence status of the state change in two or more inkjet heads among the plurality of inkjet heads,
A program to estimate the state changes of phase transition ink, which is used to perform this operation.