Inkjet printing apparatus and method for controlling the inkjet printing apparatus

Abstract

To reduce generation risk of a scatter, achieve a desired character height, and improve printing quality, even in printing by ink having different density.SOLUTION: An ink jet recording device includes a printing head which has an ink nozzle for generating an ink droplet, a charge electrode for charging the ink droplet, a deflection electrode for deflecting the ink droplet after charging, and a gutter for collecting the ink droplet which is not used for printing. The ink jet recording device further includes a control section for controlling the charge voltage for charging the ink droplet. The control section determines a reference charge voltage range to be given to the ink droplet on the basis of ink density of ink to be used, and controls the charge electrode on the basis of the determined reference charge voltage.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an inkjet printing apparatus and a method for controlling the inkjet printing apparatus. [Background technology]

[0002] A continuous-ejection, charge-controlled inkjet recording apparatus (hereinafter referred to as an inkjet recording apparatus) forms ink into droplets (particles), imparts an electric charge to the ink droplets (ink particles) corresponding to the characters to be printed, and deflects the charged ink droplets to fly toward a print target, thereby printing dots. In such inkjet recording apparatuses, it is necessary to optimize the amount of charge applied to the ink droplets in order to improve print quality. To achieve this goal, a technology is known, for example, as described in JP-A-2014-504974 (Patent Document 1).

[0003] In this patent document, the fluctuation of the charge amount of the droplets is monitored by an electrostatic detector, and the objective is to obtain a stable operation and a controlled print quality. As a means for this purpose, this patent document discloses a method for determining inkjet ejection quality, which includes: a) generating a first series of N1 droplets, all of which are charged by a charging means with the same voltage V1; b) subsequently generating at least one droplet G1 charged by the charging means with a second voltage (VG1), where the droplet G1 is followed by at least one droplet G2 charged by the charging means with a third voltage (VG2) lower than V1; c) subsequently generating a second series of N2 droplets, all of which are charged by the charging means with the same voltage V2; and d) measuring, via an electrostatic detector, the charge fluctuations in a jet of undeflected droplets, which includes droplets of the first series and droplets of the second series spaced apart by the droplets G1 and G2, before the jet passes in front of the electrostatic detector. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2014-504974 Summary of the Invention [Problem to be solved by the invention]

[0005] Continuous-jet charge-controlled inkjet recording devices print by ejecting tens of thousands of ink droplets per second, enabling high-speed printing. To print using an inkjet recording device, users must perform complex and careful adjustments to achieve high-quality printing with the intended print size and precise print dot placement.

[0006] Patent Document 1 describes a control method that uses an electrostatic detector to measure minute charge fluctuations in ink droplets not used in printing and detects the generation of tiny ink droplets called satellites from those charge fluctuations. This control adjusts the excitation voltage for forming ink droplets and the charging voltage for charging the ink droplets, enabling stable droplet formation and maintaining the desired amount of charge within the droplets. However, the method described in Patent Document 1 has the problem of not taking into account the adverse effects that differences in ink physical properties, such as ink density, have on print quality. The adverse effect on print quality that should be considered here is scatter. Scatter is a phenomenon in which multiple charged droplets approach each other due to differences in their air drag, causing Coulomb forces to be generated between the droplets, resulting in repulsion. This results in deviations in the droplet flight trajectory, reducing controllability of the landing position of the print dots formed by the droplets and reducing print visibility. Here, given the same charging voltage, the risk of scatter is higher with lighter inks, i.e., inks with lower density. In Patent Document 1, even when the physical properties of the ink change, the reference charging voltage is not changed, and only whether the desired charge amount is maintained in the droplets is determined. Therefore, when printing using low-density ink, although droplet formation itself is stable, the risk of scattering increases.

[0007] In view of this situation, an object of the present invention is to provide an inkjet recording device and a control method for an inkjet recording device that can achieve high-quality printing, i.e., reduce the risk of the above-mentioned scatter occurring, and achieve the desired character height, even when changing to ink of a different density. [Means for solving the problem]

[0008] One example of the present invention is an inkjet recording apparatus having a print head including an ink nozzle that ejects supplied ink as ink droplets, a charging electrode that applies a charging voltage to the ink droplets to charge them, a deflection electrode that deflects the ink droplets, and a gutter that collects the ink droplets that are not used for printing, and a control unit that controls the charging electrode to charge the ink droplets, wherein the control unit determines a reference charging voltage range that defines the range of the charging voltage to be applied to the ink droplets based on the ink density of the ink used, and controls the charging electrode based on the reference charging voltage range.

[0009] Another example of the present invention is a control method for an inkjet recording device having a print head including an ink nozzle that ejects supplied ink as ink droplets, a charging electrode that charges the ink droplets, a deflection electrode that deflects the ink droplets, and a gutter that collects the ink droplets that were not used for printing, and a control unit that controls a charging voltage for charging the ink droplets, the control method for an inkjet recording device determining a reference charging voltage range that defines a range of the charging voltage based on the ink density of the ink used for printing, and controlling the charging electrode based on the reference charging voltage range. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an inkjet recording device and a control method for an inkjet recording device that can reduce the risk of scatter and achieve printing of a predetermined desired character height, even when printing with inks of different densities. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an external view of an inkjet recording apparatus. [Figure 2] FIG. 1 is a schematic diagram illustrating the configuration of an inkjet recording apparatus. [Figure 3] FIG. 10 is a diagram illustrating the relationship between the charging voltage and the height of a printed character. [Figure 4] FIG. 10 is a diagram illustrating the relationship between charging voltage and ink density. [Figure 5] FIG. 10 is a diagram showing a correspondence table showing the correspondence between ink and ink density. [Figure 6] 1 is a diagram illustrating a configuration of an inkjet recording apparatus according to a first embodiment of the present invention. [Figure 7] 4 is a flowchart showing a control procedure at the start of printing in the first embodiment. [Figure 8] 10 is a flowchart showing a procedure for correcting a charging voltage during printing in the first embodiment. [Figure 9] FIG. 10 is a diagram illustrating the configuration of an inkjet recording apparatus according to a second embodiment of the present invention. [Figure 10] 10 is a flowchart showing a procedure for correcting a charging voltage during printing in a second embodiment. [Figure 11] FIG. 10 is a diagram showing the configuration of an inkjet recording apparatus according to a third embodiment of the present invention. [Figure 12] 11 is a flowchart showing a procedure for correcting the charging voltage during printing in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention should not be construed as being limited to the description of the embodiments described below. In other words, it will be readily understood by those skilled in the art that the configuration of the present invention can be modified within the scope of the technical idea or spirit of the present invention. In addition, in the configurations of the embodiments described below, the same reference numerals are used in common between different drawings for the same devices or parts having similar functions, and duplicated explanations may be omitted. Furthermore, in order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings do not represent the position, size, shape, range, etc. of the device configuration in an actual product. Therefore, the present invention is not limited to the position, size, shape, range, etc. of the component devices disclosed in the drawings.

[0013] [Example 1] Next, a first embodiment of the present invention will be described with reference to FIGS. 1 to 8. FIG. 1 is an external view of the entire inkjet recording apparatus. FIG. 2 is a diagram showing a schematic configuration of the inkjet recording apparatus. FIG. 3 is a diagram explaining the relationship between charging voltage and the height of printed characters. FIG. 4 is a diagram explaining the relationship between charging voltage and ink density. FIG. 5 is a diagram showing the correspondence between ink and ink density. FIG. 6 is a diagram showing the configuration of the inkjet recording apparatus in the first embodiment of the present invention. FIG. 7 is a flow chart showing the procedure for setting the charging voltage range at the start of printing in the first embodiment. FIG. 8 is a flow chart showing the procedure for correcting the charging voltage range when printing is performed in the first embodiment.

[0014] First, the schematic configuration and print control of an inkjet recording apparatus according to a first embodiment of the present invention will be described with reference to FIGS.

[0015] In FIG. 1, the inkjet recording device comprises a print head 2 that receives a supply of ink and performs printing, and a device main body 1 that supplies printing ink to the print head 2 and collects unused ink from the print head 2. A cable 5 connects the device main body 1 to the print head 2. The device main body 1 also comprises an internal control unit 3. This control unit 3 controls the ink supply to the device main body 1 and the printing (charge control) of the print head 2. An operation display unit 4 is provided on the front of the device main body 1 and has the function of displaying information related to the printing operation and inputting information necessary for printing characters and the like into the control unit 3. The operation display unit 4 may be, for example, a touch panel with display and data input functions.

[0016] The print head 2 performs predetermined printing on the print target 10 being transported by a transport device 6 such as a belt conveyor. The arrow in the figure indicates the movement (transport) direction of the print target 10. When the print target 10 reaches the printing position, the control unit 3 controls the print head 2, and the print head 2 performs printing on the print target 10.

[0017] Next, the printing control principle of the inkjet recording device will be explained with reference to Figure 2. In Figure 2, the same symbols (numbers) as in Figure 1 indicate the same devices. First, the device main body 1 is equipped with an ink tank 11 that stores (contains) ink 109, an ink supply pump 12 for supplying the ink 109 to the print head 2, and an ink recovery pump 13 for recovering ink collected by the gutter 25 of the print head 2 into the ink tank 11.

[0018] 2, the print head 2 has an ink nozzle 21 for forming droplets (ink particles) from the ink supplied from the device main body 1. The ink nozzle 21 has a piezoelectric element to which a periodic excitation voltage is applied. This excites the ink in the ink nozzle 21, and the ink is ejected (spurted) from the ink nozzle 21 as an ink column 110, generating ink droplets. The generated ink droplets travel in a straight line at high speed.

[0019] The print head 2 further includes a charging electrode 22, a deflection electrode (comprised of a positive deflection electrode 23 and a negative deflection electrode 24), and a gutter 25. The charging electrode 22 applies a charging voltage corresponding to the print content to the flying ink droplets, thereby charging the ink droplets. The deflection electrode deflects the charged ink droplets according to the amount of charge, causing ink droplets 111 to fly toward the print substrate 10. As a result, the ink droplets 111 reach and land on the print substrate 10. When these ink droplets land, printing is performed on the print substrate 10. Meanwhile, ink droplets 112 that are not charged by the charging electrode 22 (ink droplets not used for printing) travel straight without being deflected within the deflection electrode and are collected (captured) by the gutter 25. The ink droplets 112 collected by the gutter 25 are recovered in the ink tank 11 of the device main body 1.

[0020] 2, the control unit 3 performs head control, which includes charge control of the print head 2, and main body control, which controls the pumps and other components within the device main body 1. However, since the present invention is primarily concerned with charge control, the following explanation of the control unit will focus on head control, particularly charge control over ink droplets.

[0021] Next, to facilitate understanding of the embodiment of the present invention, a printing problem that has conventionally occurred will be described with reference to FIGS.

[0022] Figure 3 shows the relationship between typical deflection voltage and charging voltage control. In an inkjet recording device, a printing matrix consisting of N × M dots is scanned one column at a time in the vertical direction, while a printing target on a conveyor continues to be transported perpendicular to that direction, forming two-dimensional print content. During scanning of one vertical column, the ink droplets forming the lowest dot are charged with a lower limit of charging voltage 201, and the ink droplets forming the highest dot are charged with an upper limit of charging voltage 202. The charging voltage for ink droplets forming dots between the lowest and highest dots is determined by, for example, linear interpolation within a reference charging voltage range depending on the number of dots. The concept of character height is also used to express the size of printed characters. Character height is defined as the distance between the lowest and highest dots. When printing, once the size of the printing target and the print content are determined, the character height must be adjusted to take that size into account. Conventionally, the character height is changed by adjusting the deflection voltage 203 without changing the charging voltage lower limit 201 and the charging voltage upper limit 202 .

[0023] On the other hand, when using such control, taking into account the ink density, problems arise with the control to achieve a specified character height (character height controllability) and the control to eliminate deviations in the dot landing position (dot landing position controllability).

[0024] First, let us consider the controllability of character height. Character height can change due to changes in ink density caused by changes in the type of ink or changes in ink concentration over long periods of operation. The deflection amount D of the ink droplets is calculated from the deflection amount prediction formula: D = (VQ / 2tM)(b / Vd) 2 It can be expressed by the formula (1+(2L / b)). In this formula, V is the deflection voltage [V], Q is the charge amount [C], t is the gap between the deflection electrodes [m], M is the droplet mass [kg], b is the length of the deflection electrode [m], Vd is the initial velocity of the droplet [m / s], and L is the distance [m] from the end of the deflection electrode to the printing target.

[0025] Here, the ink density ρ [kg / m 3 ] is related to the droplet mass M. If we assume the droplet is a perfect sphere, the droplet mass M is M = (π / 6)ρd 3 d represents the droplet diameter [m].

[0026] Based on these relationships, as the ink density ρ increases, the droplet mass M increases and the deflection amount D decreases. Therefore, if the ink density used for printing is changed from a high-density ink to a low-density ink, the character height will be larger than the set value, even if the same character height is set. Furthermore, if the ink density changes during long-term operation of the inkjet recording device, the resulting change in ink density will cause the character height to change over time. For these reasons, implementing charge control is a challenge in order to improve character height controllability and achieve uniform character height despite density changes over time.

[0027] Next, we will discuss the controllability of dot landing positions. The problem of scatter occurrence changes due to changes in ink density caused by changes in ink type or ink concentration (viscosity) over long periods of operation. With the charge control shown in Figure 3, even if the ink density changes, the charging voltage and charge amount applied to the ink droplets do not change as long as the printed content and character height do not change. Here, the lower the ink density, the greater the influence of Coulomb force when droplets approach each other. This increases the deviation in flight trajectory due to repulsion, resulting in deviation in the dot landing position and reduced controllability. Given the above, the challenge is to perform charge control that minimizes the risk of scatter occurrence, even when the ink type changes or the ink density changes over time.

[0028] The first embodiment of the present invention aims to provide an inkjet recording apparatus that can solve the above-described problems, i.e., can print high-quality characters even when printing with inks of different densities, reducing the risk of the above-mentioned scatter occurring, and achieving the desired character height.

[0029] Next, a charge control method in the first embodiment of the present invention will be described with reference to FIGS. First, referring to FIG. 4, the charging voltage control in the first embodiment will be described. The vertical axis of FIG. 4 represents the charging voltage, and the horizontal axis represents the ink density. As shown in FIG. 4, as the ink density changes, the voltage range between the upper and lower limits of the charging voltage changes. This voltage range of the charging voltage is referred to as the "reference charging voltage range." Based on the relationship shown in FIG. 4, for example, when printing using ink with a high ink density, the reference charging voltage range is widened (increased) and the reference charging voltage range is set to a high charging voltage range. On the other hand, when printing using ink with a low ink density, the reference charging voltage range is narrowed (decreased) and the reference charging voltage range is set to a low charging voltage range. By setting the reference charging voltage range as described above, it is possible to print with a predetermined character height maintained even when printing using inks with different densities when applying the same deflection voltage. Furthermore, changing the character height based on this reference charging voltage range can be achieved by changing the deflection voltage or by slightly changing the reference charging voltage range. Furthermore, by setting the reference charging voltage range for printing low-density ink to a low charging voltage range, the amount of charge held by ink droplets is reduced. This reduces the Coulomb force acting on droplets even when multiple droplets approach each other during flight, making it possible to minimize the occurrence of scattering and the resulting deterioration in controllability of landing positions.

[0030] This reference charge range can be determined for each type of ink using the deflection prediction formula described above, experiments, simulations, or other methods. The ink density for each ink can be determined in advance (for example, determined before shipping from the factory and stored in the inkjet recording device). Figure 5 shows an example of a correspondence table (ink-ink density table) between inks determined in advance in this way. Figure 5 shows a correspondence table that corresponds the ink density of each ink, determined in advance through experiments, etc., to each type of ink.

[0031] In an inkjet recording apparatus, to control the charging voltage using the relationship shown in Figure 4, information on the initial ink density for each ink is required when starting printing. For this reason, it is convenient to have a correspondence table like that shown in Figure 5 when initially setting the reference charging voltage range when starting printing. For example, by storing a correspondence table like that shown in Figure 5 in memory and inputting the type of ink from the operation display unit when starting printing, the ink density corresponding to that ink can be determined. The reference charging voltage range is set from the ink density corresponding to the ink used for that printing.

[0032] Next, a specific first embodiment of the present invention for solving the above-mentioned technical problems will be described with reference to FIGS. 6 to 8. FIG.

[0033] First, the overall configuration of the first embodiment will be described with reference to Fig. 6. In the description of Fig. 6, the description of the contents and operations of the devices already described in Fig. 1 and Fig. 2 will be omitted or only briefly explained. The inkjet recording device of the first embodiment shown in Fig. 6 has a device main body 1, a print head 2, a control unit 3, and an operation display unit 4.

[0034] In addition to the ink tank 11, ink supply pump 12, and ink recovery pump 13 already described, the device main body 1 is equipped with a mass meter 16 for measuring the mass of ink in the ink tank 11 and a liquid level sensor 15 for detecting the ink level in the ink tank 11. The mass of the ink can be calculated by subtracting the weight of the ink tank from the total weight. The shape of the ink tank 11 is known, and the volume of the ink in the ink tank 11 can be detected from the value detected by the liquid level sensor 15. Therefore, the ink density of the ink currently being used and held in the ink tank 11 can be calculated by dividing the ink mass by the calculated ink volume. In this embodiment, this ink density is measured by the control unit 3. That is, the detection values ​​of the liquid level sensor 15 and the mass meter 16 are input into the control unit 3, and are calculated and measured within the control unit 3.

[0035] As already explained, the control unit 3 controls (charge control) the device main body 1 and the print head 2. The control unit 3 in this embodiment 1 can be realized by a normal computer. In the case of Figure 6, the control unit 3 is made up of an arithmetic processing unit 31, a memory unit 32, an input / output unit 33, a communication control unit 34, and a bus 35 (bus communication path) for implementing communication between these devices.

[0036] The storage unit 32 stores programs to be used for control, as well as data, information, and calculation results to be used in control.

[0037] The calculation processing unit 31 is provided to perform calculation processing (control) of the entire device, and performs various calculations for control using programs, data, and information stored in the memory unit 32, and controls the device main body 1 and print head 2.

[0038] The input / output unit 33 inputs the detection values ​​from each detection device, stores them in the memory unit 32 at the instruction of the calculation processing unit 31, and outputs the control data and control signals stored in the memory unit 32 to the equipment within the device main body 1 and the print head 2 at the control instruction of the calculation processing unit 31.

[0039] The communication control unit 34 receives information, data, etc. transmitted from an external device (not shown) via the communication path 40, stores it in the memory unit 32 at the instruction of the calculation processing unit 31, and transmits the information, data, etc. stored in the memory unit 32 to the external device in accordance with the instruction of the calculation processing unit 31.

[0040] The bus 35 is a communication path for transmitting and receiving information between the devices in the control unit 3. The operation display unit 4 is connected to this bus 35, and can store data from the operator in the memory unit 32 in the control unit 3.

[0041] When printing, the inkjet recording apparatus shown in FIG. 6 receives data indicating the ink type from some input device. In this example, the ink type can be input by operating the operation / display unit 4 or from an external device via the communication control unit 34. Alternatively, a barcode or the like may be printed on an ink bottle and read by a barcode reader (not shown). By inputting the ink type in this manner, the control unit 3 can select an ink density corresponding to the ink (ink type). Specifically, when the ink type is input, this information is temporarily stored in the memory unit 32, and the calculation processing unit 31 selects an ink density by referring to the ink type and a correspondence table, such as that shown in FIG. 5, which is stored in advance in the memory unit 32. The ink density obtained by this selection is stored in the memory unit 32 as the initial ink density of the ink to be used for printing. Next, the control unit 3 (specifically, the calculation processing unit 31) sets a reference charging voltage range for the start of printing based on the selected ink density using the relationship shown in FIG. 4. This reference charging voltage range is also stored in the memory unit 32. Furthermore, when the print content to be printed on the print substrate 10 is input, for example, from the operation and display unit 4, it is stored in the memory unit 32. The calculation processing unit 31 determines the charging voltage for charging the ink droplets for each print dot based on the print content and the reference charging voltage range, and supplies the charging voltage (control signal) to the charging electrode 22 via the input / output unit 33. The charging electrode 22 applies the determined charging voltage to the ink droplets, thereby printing. The charging voltage for charging each ink droplet in flight can be determined based on the position of the ink droplet in the N×M printing matrix that is determined and stored for each character. This charging voltage is applied to the ink droplets by the charging electrode 22. As a result, the ink droplets are deflected in the deflection electrode according to the amount of charge, and are printed on the print substrate 10. Printing on the printing object 10 begins when a sensor (not shown) detects the printing object 10 during movement and the printing object 10 reaches the printing start position.

[0042] Next, the operation of the control unit 3 when printing starts will be described with reference to Figure 7. First, in step S01 of Figure 7, when ink liquid is replenished into the ink tank 11, the type of ink is input to the inkjet recording device as shown in step S02. The input method is to display a GUI installed in the inkjet recording device on the operation display unit and input the information by operating it. Alternatively, in the case of an ink cartridge injection method, a tag can be attached to the ink cartridge itself and the ink type can be automatically read by a sensor.

[0043] In step S03, the ink type is input and the ink density is selected from the correspondence table (ink type and ink density correspondence table) shown in Fig. 5. Note that the ink density may also be measured by inputting the detected values ​​of the mass meter 16 and the liquid level sensor 15. In step S04, the reference charging voltage range is determined (set) from the selected ink density.

[0044] Next, in step S05, a charging voltage waveform to be output during printing is generated based on the determined reference charging voltage range and the content to be printed. After that, in step S06, the deflection voltage is adjusted to determine the character height. Then, in step S07, printing begins. Operations at the start of printing are performed in this manner. This makes it possible to print with the same character height and with a reduced risk of reduced control of dot landing position due to scattering, even if the ink density changes.

[0045] Even if an appropriate reference charging voltage range is determined based on the ink density at the start of printing and printing is initiated, it is possible that the ink properties will change over time. In this case, it may be difficult to perform stable printing using charging voltage control based on the initially set reference charging voltage range. For this reason, in Example 1 shown in FIG. 6, a control is performed to correct the reference charging voltage range in accordance with the ink density that changes over time. That is, the control unit 3 inputs detection values ​​from the liquid level sensor 15 and the mass meter 16 at predetermined intervals, calculates the ink density of the ink at that time, and performs control to correct the initial reference charging voltage range based on the measured ink density.

[0046] By this control, it is possible to realize appropriate charge control corresponding to the ink density that changes from moment to moment.

[0047] Next, a control flow for dealing with changes in ink density over time during printing will be described with reference to FIG. 8. In step S11 of FIG. 8, the ink density in the ink tank 11 is measured using the detection values ​​of the mass meter 16 and the liquid level sensor 15. This measurement is performed periodically. Note that the measurement does not have to be periodic, but it is necessary to measure it frequently enough so that the ink density does not change significantly. When measuring ink density periodically, it is desirable to determine the periodic interval taking into account the environment during printing. For example, when printing in a high-temperature environment, it is expected that the amount of solvent volatilizing from the ink liquid will be large. In this case, shortening the time period for measuring ink density makes it possible to capture small changes in ink density.

[0048] Next, in step S12, it is determined whether the change in the measured ink density exceeds a threshold value. If this determination (judgment) shows that the measured ink density is within the threshold value (NO), then in step S13, operation continues as is, that is, without modifying the charging voltage control based on the set reference charging voltage range. If in step S12 the measured ink density is equal to or greater than the threshold value (YES), then the process proceeds to step S14.

[0049] In step S14, the reference charging voltage range is reset (corrected) based on the measured ink density. In the following step S15, the charging voltage waveform is corrected based on the reset (corrected) reference charging voltage range and the print content. Then, in step S16, printing is resumed using charging voltage control based on this corrected charging voltage waveform.

[0050] This type of control makes it possible to always print with a uniform character height even when the ink density changes over time.

[0051] [Example 2] Next, a second embodiment of the present invention will be described with reference to Figures 9 and 10. Figure 9 is a diagram showing the configuration of an inkjet recording apparatus in the second embodiment. The first embodiment and the second embodiment have basically the same configuration, except for the difference in the method of measuring ink density. Therefore, a description of matters similar to those described above will be omitted, and the second embodiment will be described focusing on the differences from the first embodiment.

[0052] 9, a viscometer 17 that detects ink viscosity is provided inside the device main body 1. Then, relationship information showing the relationship between viscosity and ink density is stored in the memory unit 32 of the control unit 3, for example, as a relationship table. This relationship table is obtained in advance through experiments or the like and stored in the memory unit 32. Therefore, once the control unit 3 detects the ink viscosity, it can uniquely measure the ink density by applying (applying) the detected value to the relationship table.

[0053] In this embodiment, the viscometer 17 is disposed midway along the path that supplies ink from the ink tank 11 to the ink nozzles 21, but it may be disposed elsewhere. Also, in this embodiment, the viscometer directly detects the viscosity itself, but it may also be configured to indirectly detect the viscosity by utilizing, for example, the phenomenon in which the speed of ink ejected from the ink nozzles changes depending on the viscosity.

[0054] In this second embodiment, as in the first embodiment, a correspondence table such as that shown in FIG. 4 is stored in the memory unit 32, and by inputting the type of ink, the control unit 3 selects the ink density of the ink to be used for printing from the correspondence table. Based on the ink density obtained by this selection, the relationship shown in FIG. 4 is used to set a reference charging voltage range at the start of printing. The calculation processing unit 31 determines a charging voltage based on the print content and the reference charging voltage range, applies the charging voltage (control signal) to the charging electrode 22, and starts printing by applying the determined charging voltage to the ink droplets at the charging electrode 22. These operations are the same as those in the first embodiment. Furthermore, the operation of the control unit 3 at the start of printing is the same as that shown in FIG. 7 described in the first embodiment. Therefore, a description of the operation at the start of printing in the second embodiment will be omitted.

[0055] Next, the control flow for dealing with changes in ink density over time in this embodiment 2 will be described with reference to Fig. 10. The operation in Fig. 10 is basically almost the same as the operation in Fig. 8 in embodiment 1, and only the differences from embodiment 1 will be described.

[0056] In FIG. 10, in step S21, the detection value of the viscometer 17 is input. When detecting ink viscosity periodically, the periodic interval is desirably determined taking into consideration the environment during printing. For example, when printing in a high-temperature environment, it is predicted that the amount of solvent volatilizing from the ink liquid will be greater. In this case, shortening the time period for measuring ink viscosity makes it possible to capture small changes in ink density. Next, in step S22, the ink density is measured using this detection value and a pre-stored relationship table showing the relationship between viscosity and ink density. In step S12, it is determined whether the change in measured ink density is equal to or greater than a threshold value.

[0057] As a result of this determination, the operation procedure of steps S13 to S16 is executed, which are the same operations as steps S12 to S16 shown in Fig. 8. Therefore, the description thereof will be omitted.

[0058] In this way, the ink density, which changes over time, is measured and the reference charging voltage range is corrected in accordance with the ink density, so that appropriate charging voltage control can be performed, and printing can always be performed with a uniform character height even when the ink density changes over time.

[0059] [Example 3] Next, a third embodiment of the present invention will be described with reference to Figures 11 and 12. Figure 11 is a diagram showing the configuration of an inkjet recording apparatus in the third embodiment. This third embodiment has a configuration basically similar to that of the first and second embodiments already described, but differs in the control content after printing starts. Therefore, the same description as in the first and second embodiments will be omitted here, and the third embodiment will be described focusing on the differences from the first and second embodiments.

[0060] 11, the device main body 1 is not provided with sensors for measuring ink density, but is provided with a camera 70 that photographs the printing state of the printing substrate 10 and outputs the image signal. The control unit 3 is also provided with an image processing unit 36 ​​that inputs the image signal from the camera 70 and extracts the printing state, i.e., the print height and deviation of the print dot position from the planned location, through image processing. Other points are the same as in Examples 1 and 2.

[0061] In this third embodiment, as in the first embodiment, a correspondence table such as that shown in FIG. 4 is stored in the memory unit 32, and by inputting the type of ink, the control unit 3 selects the ink density of the ink to be used for printing from the correspondence table. Based on the ink density obtained by this selection, a reference charging voltage range at the start of printing is set. The calculation processing unit 31 determines the charging voltage based on the print content and the reference charging voltage range, applies the charging voltage (control signal) to the charging electrode 22, and starts printing by applying the determined charging voltage to the ink droplets at the charging electrode 22. These operations are the same as those in the first embodiment. Furthermore, the operation of the control unit 3 at the start of printing is the same as that shown in FIG. 7 described in the first embodiment. Therefore, a description of the operation at the start of printing in the second embodiment will be omitted.

[0062] Next, a control flow for dealing with changes in ink density over time in this third embodiment will be described with reference to FIG.

[0063] 12, in step S31, an image signal is input from camera 70, and the print state (character height) of the print result is evaluated based on the image signal. This image processing is performed by image processing unit 36, and the print state is stored in memory unit 32. Processing unit 31 then executes control operations using this print state. That is, in step S32 in FIG. 12, it is determined whether the deviation in character height (the difference between the initially planned character height and the character height obtained by image processing) is equal to or greater than a threshold value.

[0064] If the result of this determination is that it is within the threshold (NO), proceed to step S33 and continue printing. If the result of the determination is that it is above the threshold (YES), proceed to the next step S34. In step S34, the reference charging voltage range is corrected according to the character height. In step S35, the charging voltage waveform is corrected based on this corrected reference charging voltage range and the contents of the instruction. Then, in step S36, the printing operation is resumed.

[0065] After printing is resumed, in step S37, the print result on the print target 10 after printing is resumed is photographed by the camera 70. The image signal is processed by the image processing unit 36 ​​in the control unit 3, and the character height of the print result is evaluated. This operation is the operation of step S37.

[0066] Next, the process proceeds to step S38, where it is determined whether the deviation in character height is equal to or greater than a threshold. If the deviation in character height is within the threshold (YES) in step S38, the process returns to step S34. That is, the operations of steps S34 to S38 are repeated until the deviation in character height becomes equal to or less than the threshold. If the deviation in character height is equal to or less than the threshold (NO) in step S38, printing continues as is.

[0067] By using this control, according to the third embodiment of the present invention, the reference charging electrode range can be set in accordance with the ink density, and even if the ink density changes during printing, the print result (print state) is recognized based on the image from the camera and an appropriate reference charging voltage range is reset (corrected), thereby realizing high-quality printing at a specified print height. [Explanation of symbols]

[0068] 1...device main body, 2...print head, 3...control unit, 4...operation display unit, 5...cable, 6...conveyor device, 10...printed material, 11...ink tank, 12...ink supply pump, 13...ink recovery pump, 15...liquid level sensor, 16...mass meter, 17...viscometer, 21...ink nozzle, 22...charging electrode, 23...deflection electrode positive electrode, 24...deflection electrode negative electrode, 25...gutter, 31...arithmetic processing unit, 32...memory unit, 33...input / output unit, 34...communication control unit, 35...bus, 36...image processing unit, 70...camera

Claims

1. An inkjet recording apparatus comprising: a print head including an ink nozzle that ejects supplied ink as ink droplets; a charging electrode that applies a charging voltage to the ink droplets to charge them; a deflection electrode that deflects the ink droplets; and a gutter that collects the ink droplets that have not been used for printing; and a control unit that controls the charging electrode to charge the ink droplets, the control unit determines a reference charging voltage range that defines a range of the charging voltage to be applied to the ink droplets based on the ink density of the ink used, and controls the charging electrode based on the reference charging voltage range; the control unit stores a correspondence table between the ink and the ink density, and when the type of ink is input, selects the ink density using the correspondence table, and determines the reference charging voltage range based on the selected ink density.

2. 2. The inkjet recording apparatus according to claim 1, an ink density measuring unit that measures the ink density, and the control unit corrects the reference charging voltage range determined at the start of printing based on the measured ink density.

3. 3. The ink jet recording apparatus according to claim 2, an ink jet recording apparatus, characterized in that the ink density measurement unit measures the ink density by utilizing a detection value of a liquid level sensor that detects the liquid level of an ink tank that stores ink to be supplied to the ink nozzles, and a detection value of a mass meter that measures the mass of the ink stored in the ink tank.

4. 3. The ink jet recording apparatus according to claim 2, The inkjet recording apparatus is characterized in that the ink density measuring unit measures the ink density by utilizing the viscosity of ink in an ink tank that stores ink to be supplied to the ink nozzles.

5. 2. The inkjet recording apparatus according to claim 1, further comprising a camera for photographing the printed result and outputting an image signal; The control unit processes the image signal to measure the printing state, determines the difference between the printing state and a reference printing state, and corrects the reference charging voltage range if the difference exceeds a threshold value.

6. 2. The inkjet recording apparatus according to claim 1, the control unit determines the reference charging voltage range and the deflection voltage using the ink density, controls the charging electrode based on the determined reference charging voltage range, and controls the deflection electrode based on the deflection voltage.

7. A control method for an inkjet recording apparatus having a print head including an ink nozzle that ejects supplied ink as ink droplets, a charging electrode that charges the ink droplets, a deflection electrode that deflects the ink droplets, and a gutter that collects the ink droplets that have not been used for printing, and a control unit that controls a charging voltage for charging the ink droplets, determining a reference charging voltage range that defines a range of the charging voltage based on the ink density of the ink used for printing, and controlling the charging electrode based on the reference charging voltage range; A control method for an inkjet recording device, comprising: storing a correspondence table between the ink and the ink density; selecting the ink density using the correspondence table when the type of ink is input; and determining the reference charging voltage range based on the selected ink density.

8. 8. The method for controlling an inkjet recording apparatus according to claim 7, A control method for an ink jet recording apparatus, comprising: measuring the ink density during printing; and correcting the reference charging voltage range determined at the start of printing based on the measured ink density.

9. 9. The method for controlling an inkjet recording apparatus according to claim 8, a control method for an inkjet recording apparatus, characterized in that the ink density is measured based on a liquid level of an ink tank that stores ink to be supplied to the ink nozzles and a mass of the ink stored in the ink tank;

10. 9. The method for controlling an inkjet recording apparatus according to claim 8, A method for controlling an inkjet recording apparatus, wherein the ink density is measured using the viscosity of ink that stores ink to be supplied to the ink nozzles.

11. 8. The method for controlling an inkjet recording apparatus according to claim 7, A control method for an inkjet recording device, comprising: measuring a print state by processing an image signal from a camera that photographs a print result; determining a difference between the print state and a reference print state; and correcting the reference charging voltage range if the difference exceeds a threshold value.

12. 8. The method for controlling an inkjet recording apparatus according to claim 7, A control method for an inkjet recording device, comprising determining the reference charging voltage range and deflection voltage using the ink density, controlling the charging electrode based on the determined reference charging voltage range, and controlling the deflection electrode based on the deflection voltage.

Images