Control device of electric-charge control type inkjet printer, electric-charge control type inkjet printer, printing system, and method

Abstract

To provide a control device of an electric-charge control type inkjet printer, an electric-charge control type inkjet printer, a printing system, and a method capable of improving accuracy of a pump pressure suitable for printing.SOLUTION: A control device 200 of an electric-charge control type inkjet printer (inkjet printer 100) calculates a feature amount (amplitude growth rate μ) on the basis of an electric-charge phase waveform indicating correspondence between an electric-charge phase and a charge quantity of an ink particle 222 (characteristic measurement part 273). The control part 200 determines a pump pressure suitable for printing from correspondence between a pump pressure p of a pump (circulation pump 245) that supplies ink 241 from an ink tank 240 to a nozzle 211 and the feature amount (amplitude growth rate μ).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for a charge-controlled inkjet printer, a charge-controlled inkjet printer, and a printing system and method. [Background technology]

[0002] Among inkjet printers, charge-controlled inkjet printers are primarily used as industrial printers, printing serial numbers, expiration dates, and other information on products moving down a production line. In charge-controlled inkjet printers, liquid ink filled in an ink tank is pressurized by a pump and supplied to the nozzle of the print head. The nozzle continuously ejects the supplied ink as an ink column, and a periodic perturbation is imparted to the ink by applying an excitation voltage to a piezoelectric element or other device installed adjacent to the nozzle during ejection. The perturbed ink column is then cut off midway to form ink droplets that are generated continuously (periodically) and fly at high speed. The magnitude of the perturbation can be adjusted by the excitation voltage.

[0003] A charging electrode is placed at or near the location where the ink droplets are formed (the ink cutting location), and an electric field is generated in this charging electrode, charging each ink droplet as it flies at high speed. By applying an electric field corresponding to the print content to the charging electrode, each ink droplet is given the required amount of charge depending on the print content. A deflection electrode, consisting of two electrodes to which a constant voltage is applied, is placed downstream of the charging electrode. The charged ink droplets are deflected in flight according to the amount of charge given to them as they fly through the deflection electrode. The deflected ink droplets are then landed (adhered) on a moving print target by a conveying device, thereby printing with the ink droplets on the print target. Ink droplets that are not charged in the charging electrode travel straight through the deflection electrode, are captured by a gutter, and are collected in an ink container as recovered ink.

[0004] In such inkjet printers, if the position where the ink column ejected from the nozzle breaks off and becomes an ink droplet (the distance from the nozzle tip to the position where the ink droplet becomes an ink droplet), i.e., the "cutoff position," is not maintained at an appropriate position, the charging electrode cannot charge the ink droplets in flight with an appropriate charge, and high-quality printing cannot be achieved. Therefore, it is important to appropriately control this cutoff position so that it falls within a predetermined range. It is known that the cutoff position can be adjusted by the excitation voltage applied to a piezoelectric element or the like installed adjacent to the nozzle, and during printing, the excitation voltage that enables printing is adjusted to be applied to the nozzle (more specifically, the excitation voltage is applied to the piezoelectric element installed adjacent to the nozzle).

[0005] Incidentally, printing environments and print substrates vary widely, and multiple types of ink are available for inkjet printers. Furthermore, appropriate (printable) print settings (such as excitation voltage, excitation frequency, pump pressure, charging voltage, and deflection voltage) vary depending on various conditions, including the type of ink, nozzle, and temperature. As described above, achieving high-precision printing is difficult unless the pump pressure and excitation voltage conditions applied to the nozzles are appropriate for the type of ink and temperature. Therefore, printing requires that the excitation voltage conditions be appropriately set before printing. To address this issue, a technology aimed at appropriately setting the excitation voltage value is disclosed, for example, in JP-T-2011-502827 (Patent Document 1).

[0006] Patent Document 1 discloses a technology that takes into account the movement of the division point (division position) in the ink column, determines excitation voltage conditions that ensure that the characteristic showing the modulation voltage versus division position has a predetermined gradient or a gradient related to this predetermined gradient, and performs printing using an excitation voltage that ensures the determined excitation voltage conditions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2011-502827 Summary of the Invention [Problem to be solved by the invention]

[0008] By using the technology of the above-mentioned Patent Document 1, it is possible to determine the excitation voltage conditions that enable printing in accordance with the type of ink, temperature changes, etc., and apply this determined excitation voltage to the nozzle (built-in piezoelectric element).

[0009] However, even if a pump pressure value is appropriate under certain conditions, it may change in an environment where the temperature changes. Furthermore, even under the same temperature conditions, the appropriate pump pressure value may change when switching to a different type of ink. Patent Document 1 does not sufficiently consider that the appropriate pump pressure conditions may change depending on the temperature conditions or ink type, leaving the technical issue of a lack of robustness. If the pump pressure deviates from the appropriate conditions, the excitation voltage range that provides good print quality may not exist or may be extremely narrow, making it unsuitable for printing.

[0010] SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for a charge-controlled ink jet printer, a charge-controlled ink jet printer, a printing system, and a method that can improve the accuracy of the pump pressure suitable for printing. [Means for solving the problem]

[0011] In order to achieve the above object, one example of the present invention is a control device for a charge-controlled inkjet printer, which calculates a feature value based on a charge phase waveform that indicates the correspondence between the charge phase and the charge amount of ink particles, and determines a pump pressure suitable for printing from the correspondence between the pump pressure of a pump that supplies ink from an ink tank to a nozzle and the feature value. [Effects of the Invention]

[0012] According to the present invention, it is possible to improve the accuracy of the pump pressure suitable for printing. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing the appearance of an inkjet printer according to a first embodiment of the present invention. [Figure 2] 1 is a diagram illustrating an internal configuration of an inkjet printer according to a first embodiment. [Figure 3] 10 is a diagram showing an example of the relationship characteristic (charge phase waveform) between the charge phase and the charge amount of ink particles. FIG. [Figure 4] This is an LV diagram (a diagram showing the relationship between the cutting position L of the ink column and the excitation voltage V) created from an image captured by a camera. [Figure 5] FIG. 5 is a diagram clearly showing the linear region of the LV diagram of FIG. 4. [Figure 6] This is an LV diagram created using the optimal phase. [Figure 7] This is a comparison diagram between an LV diagram created from a camera image and an LV diagram created using the optimal phase. [Figure 8] FIG. 7 is a diagram clearly showing the linear region of the LV diagram of FIG. 6. [Figure 9] This is a diagram in which the pressure at which the amplitude growth rate is maximized is estimated as the optimal pressure based on the relationship between the amplitude growth rate and pressure. [Figure 10] This is a diagram showing the relationship between amplitude growth rate and pressure, where the pressure at which the amplitude growth rate is maximum is estimated as the optimal pressure (actual measurement). [Figure 11] FIG. 10 is a diagram showing the contents of the display screen when pump pressure adjustment is being performed (in the case of a circulation pump capable of automatic pressure adjustment). [Figure 12] FIG. 10 is a diagram showing the contents of the display screen when pump pressure adjustment is being performed (in the case of a circulation pump with manual pressure adjustment). [Figure 13] FIG. 10 is a diagram showing the contents of the display screen when pump pressure adjustment is completed (in the case of a circulation pump capable of automatic pressure adjustment). [Figure 14] FIG. 10 is a diagram showing the contents of the display screen when pump pressure adjustment is completed (in the case of a circulation pump with manual pressure adjustment). [Figure 15] 10A and 10B are examples of print patterns when the print evaluation results in a determination of "printable" and "unprintable." [Figure 16] As a result of the print evaluation, the width of the excitation voltage that allows printing under each pressure condition is plotted, and the optimum pressure range is clearly shown. [Figure 17] FIG. 10 is a configuration diagram of a printing system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below with reference to specific embodiments. The purpose of these embodiments is to provide, for example, a highly robust inkjet printer that estimates and adjusts the pump pressure optimal for printing.

[0015] It should be noted that the present invention should not be construed as being limited to the embodiments described below, and it will be readily understood by those skilled in the art that the configuration can be modified within the scope of the technical idea or intent of the present invention. Furthermore, in the configurations of the embodiments described below, the same reference numerals are used for the same devices and parts having similar operations or functions, and redundant explanations may be omitted. Furthermore, the position, size, shape, range, etc. of each component shown in the drawings are simplified to facilitate understanding of the present invention, and do not represent the actual position, size, shape, range, etc. of each component.

[0016] [Example 1] In the first embodiment, a method for extracting a pressure-dependent feature that serves as an index for determining whether print quality is good or bad will be described. In this embodiment, the amplitude growth rate μ is extracted as the feature.

[0017] An inkjet printer according to a first embodiment of the present invention will be described in detail with reference to Figs. 1 to 16. Fig. 1 is a diagram showing the appearance of the inkjet printer according to the first embodiment, and Fig. 2 is a block diagram showing the internal configuration of the inkjet printer according to the first embodiment. Figs. 3 to 16 are diagrams used to explain the first embodiment.

[0018] (Overall structure of inkjet printer) First, the overall configuration of an inkjet printer will be outlined with reference to Figure 1. In Figure 1, the inkjet printer 100 comprises a main body 1 and a print head 2. The main body 1 and print head 2 are connected by a cable 4. The main body 1 contains an ink tank that stores ink for printing, a circulation pump that draws ink from the ink container and supplies it to the print head 2, a pressure reducing valve that adjusts the ink pressure to a predetermined level, and piping that connects these components. The ink output from the main body 1, adjusted to a predetermined pressure, is supplied to the nozzles in the print head 2 via the cable 4. The print head 2 receives a supply of ink, generates ink particles internally, imparts a necessary electrical charge to the ink particles, and deflects them to print (dot printing) on ​​the printing target. The front of the main body 1 is also provided with a display unit 5 and a reading unit 7. The display unit 5 displays information such as operations that the user should perform. The display unit 5 has a touch panel input function on the top surface of the screen, allowing the user to input information (data). The reader 7 is provided to read information recorded on an information recording medium attached to an ink cartridge or the like. The information recording medium may be, for example, an IC tag, a barcode, or a two-dimensional code (e.g., QR Code (registered trademark)). Since the user may simultaneously bring the IC tag of the ink cartridge close to the reader 7 when performing input operations via the display unit 5, the reader 7 is provided near the display unit 5. Furthermore, the main body 1 is provided with a control device 200 (not shown in FIG. 1 ) that performs control using information input from the display unit 5 and the reader 7. The control device 200 controls the pumps and valves within the main body 1, as well as the nozzles and charging electrodes within the print head. Control signals (drive signals) from the control device 200 are sent to the print head 2 via lines within the cable 4.

[0019] (Internal structure of an inkjet printer) Next, a specific configuration of the inkjet printer in Example 1 will be described with reference to Figure 2. In Figure 2, the inkjet printer 100 includes a main body 1, a print head 2, and a control device 200. A print object detector 3 is also installed outside the inkjet printer 100. This print object detector 3 detects a print target 261 (product, etc.) moving on a conveying device 260, and outputs the detection signal to the control device 200. The control device 200 can optimally adjust the timing of the start of printing by using this detection signal.

[0020] (Main body configuration) In FIG. 2, the main body 1 is the portion of the inkjet printer 100 excluding the print head 2. That is, in this embodiment, the main body 1 includes an ink supply unit, an ink recovery unit, and a control device 200. Note that the control device 200 may be provided outside the main body 1. The ink supply unit is a device for supplying ink to the print head 2 (more directly, to the nozzles 211). The "ink supply unit" in this embodiment is composed of an ink tank 240 that stores ink 241, a circulation pump 245, a pressure reducing valve 246, a filter 250, an auxiliary ink tank 251, an intensifying liquid tank 252, and a pipe 232a. The "ink recovery unit" recovers ink (ink particles) captured by the gutter 215 into the ink tank 240, and in this embodiment is composed of a recovery pump 233 and a pipe 232b.

[0021] The ink tank 240 is connected to the nozzles 211 via a pipe 232a. Meanwhile, the gutter 215 is connected to the ink tank 240 via a pipe 232b. The pipes 232a and 232b form an ink flow path. A circulation pump 245 and a pressure reducing valve 246 are installed midway along the pipe 232a. A filter 250 is installed between the circulation pump 245 and the pressure reducing valve 246. Note that the location of the filter 250 is not limited to the above-mentioned position. Since the filter's main purpose is to prevent clogging of the pipe 232a and the nozzles 211, it can be installed at any position on the pipe 232a as long as this purpose can be achieved. Ink 241 in the ink tank 240 is sucked up by the circulation pump 245 and supplied to the nozzles 211 with the pressure adjusted by the pressure reducing valve 246.

[0022] Furthermore, in this embodiment, an auxiliary ink tank 251 and an intensifying liquid tank 252 are connected to the ink tank 240, allowing the respective liquids to be replenished. Here, the auxiliary ink tank 251 replenishes ink when the ink in the ink tank is consumed. The intensifying liquid tank 252 supplies intensifying liquid to the ink tank 240 and is used to appropriately adjust the viscosity of the ink 241. The intensifying liquid is a liquid that replenishes highly volatile components (solvents) contained in the ink.

[0023] (Print head configuration) Next, the configuration of the print head 2 shown in Figure 2 will be described in detail. The print head 2 is equipped with a nozzle 211 that receives a supply of ink pressure-fed through a pipe 232a and ejects an ink pillar 221. This nozzle 211 is provided with a piezoelectric element 212 (vibrator) that imparts vibrations to the ejected ink pillar. By applying an excitation voltage from the control device 200 to the piezoelectric element 212, vibrations are imparted to the ink pillar 221, causing the ink pillar to break midway and generating ink droplets 222. By vibrating the ink pillar 221, ink droplets are generated continuously and fly at high speed.

[0024] The print head 2 also includes a charging electrode 213 that forms an electric field for charging the ink droplets 222 generated by the nozzles 211, a deflection electrode 214 that changes the trajectory of the charged ink droplets 222 depending on the amount of charge on the droplets, and a gutter 215 that collects ink droplets that did not contribute to printing. The charging electrode 213 imparts a charge corresponding to the shape of the character to be printed to the flying ink droplets, thereby charging the ink droplets. The charged ink droplets fly within the deflection electrode 214. A constant voltage is applied to the deflection electrode 214, and the flight direction of each charged ink droplet is deflected depending on the amount of charge imparted to it as it flies within the deflection electrode.

[0025] The ink droplets 222 deflected by the deflection electrode 214 fly toward the print target 261 being transported by the transport device 260 and land (adhere) on the print target 261, thereby printing on the print target 261. The movement of the transport device 260 is monitored by a rotary encoder 262. The rotary encoder 262 generates a pulse signal according to the movement speed of the transport device 260. The movement speed detected by the rotary encoder 262 is input to the control device 200 of the inkjet printer 100 and is used by the control device 200 to adjust the printing timing.

[0026] In this way, while the inkjet printer 100 is in operation, it is operated so that ink droplets 222 are continuously ejected even when the print target 261 has arrived at the print position and printing is not being performed. For this reason, the charge control type inkjet printer 100 is also called a continuous type inkjet printer or a continuous inkjet printer.

[0027] (Control device configuration) Next, we will explain the control device 200 that controls the print head 2 and main body 1. The control device 200 controls the excitation voltage (excitation voltage value and excitation frequency) applied to the nozzle 211 (more specifically, the piezoelectric element 212), the charging voltage applied to the charging electrode, the deflection voltage applied to the deflection electrode, the pressure of ink supplied to the nozzle, etc., in accordance with set software parameters. Note that, below, detailed explanations regarding the control of the ink supply unit and ink recovery unit of the main body 1 will be omitted, as they are not directly related to the explanation of the present invention.

[0028] First, the control device 200 in this embodiment includes an MPU 201 (microprocessing unit) that executes calculations to control the main body 1 and print head 2, a ROM 202 (read-only memory) that stores control programs and data necessary for the operation of the MPU 201, and a RAM 203 (random access memory) that temporarily stores data required during program execution. ROM 202 stores ink information about the ink 241 and software parameter values ​​optimal for control. The ink information includes, for example, the ink model name or information about the solvent of the ink 241. Software used to control the printing of the ink 241 and the operation of the inkjet printer sets various parameter values ​​for print control.

[0029] The control device 200 also includes an input panel 204 for inputting print content, setting values, etc., and a display control unit 205. The input panel 204 corresponds to the touch panel of the display unit 5. The display control unit 205 controls the content to be displayed on the display unit 5, such as the input data and print content.

[0030] The control device 200 is provided with a bus line 206. The MPU 201, ROM 202, RAM 203, input panel 204, and display control unit 205 are connected via the bus line 206, allowing signals to be transmitted and received between the devices. Other devices within the control device 200, which will be described below, are also connected to the bus line 206, allowing signals to be transmitted and received between the devices. The bus line 206 also has the function of transmitting data signals, address signals, and control signals from the MPU 201.

[0031] The control device 200 can also be connected to a storage device 209 (storage unit) that stores programs, print data, and the like. The control device 200 stores information (data) stored in the storage device 209 in an internal RAM 203. A typical example of the storage device 209 is a USB memory. The control device 200 controls the excitation voltage (excitation voltage value and excitation frequency), pump pressure, charging voltage, deflection voltage, and the like in accordance with set software parameters.

[0032] The control device 200 also includes a charging voltage generating circuit 207 and an excitation voltage generating circuit 208. The charging voltage generating circuit 207 applies a voltage to the charging electrode 213 such that the amount of charge imparted to the ink droplets 222 corresponds to the character signal. The excitation voltage generating circuit 208 generates a high-frequency excitation voltage to be imparted to the piezoelectric element 212 provided in the nozzle 211. As for this excitation voltage, an excitation voltage that guarantees the excitation voltage conditions that enable printing, calculated by an excitation voltage calculation unit 274, as will be described later, is selected.

[0033] By applying an excitation voltage to the piezoelectric element 212, the ink column 221 immediately after being ejected from the nozzle 211 is vibrated, thereby generating ink droplets continuously. The charging voltage generating circuit 207 and the excitation voltage generating circuit 208 are also connected to the bus line 206.

[0034] Furthermore, the control device 200 in this embodiment is equipped with an optimum phase detection circuit 210, a characteristic measurement unit 273 (diagram measurement unit) that measures characteristics that indicate the relationship between the cutting position of the ink pillar 221 and the excitation voltage, and an excitation voltage calculation unit 274 that calculates optimum excitation voltage conditions for each nozzle. The characteristic measurement unit 273 and the excitation voltage calculation unit 274 calculate excitation voltage conditions that enable printing for the implemented nozzles 211. A specific method for calculating these printable excitation voltage conditions will be described later. The optimum phase detection circuit 210, characteristic measurement unit 273, and excitation voltage calculation unit 274 may be realized by hardware such as an integrated circuit, or may be realized by software as a function of the MPU 201.

[0035] The optimal phase detection circuit 210 divides one period of vibration generated by the piezoelectric element 212 into, for example, 16 phases and automatically determines the timing (phase) at which the electric field application is most suitable for charging the ink particles. Specifically, a weak electric field that does not affect printing is first applied to the ejected ink particles by the charging electrode 213 at each phase using the charging electrode 213. After the ink particles with a weak charge on the ink under each phase condition are sucked into the gutter 215, the weak charge on the ink particles is measured by the charge amount measuring unit 234 installed in the ink recovery pipe 232b, and a charge phase waveform diagram such as that shown in Figure 3 is created. The phase with the measured charge amount that is most suitable for printing (for example, the phase with the maximum charge amount) is detected (determined) as the optimal phase.

[0036] Next, we will explain the details of the characteristic measurement unit 273 in the control device 200. The characteristic measurement unit 273 is provided to measure the characteristic that indicates the relationship between the cutting position L of the ink pillar ejected from the nozzle and the excitation voltage V. In this specification, the characteristic that indicates the relationship between the value that indicates the cutting position L of the ink pillar and the value that indicates the excitation voltage V is referred to as the "LV characteristic."

[0037] The LV characteristic is a characteristic that represents the correspondence relationship between the cut position and the excitation voltage, and is easy to understand when represented as a diagram that plots the correspondence relationship on a graph. The LV characteristic represented as a diagram is called an "LV diagram." In the following description, the characteristics measurement unit 273 is described as measuring the LV diagram. Note that in the following description, an embodiment will be described using the LV diagram, but the measurement method using the LV diagram is just one example. The present invention can be implemented as long as the LV characteristic can be obtained.

[0038] Next, a specific method for measuring the LV diagram will be described. The characteristics measurement unit 273 measures the LV diagram that shows the relationship between the cutting position of the ink pillar 221 ejected from the nozzle 211 and the excitation voltage, and there are two possible methods for this measurement.

[0039] The first method is to obtain the ink cutting position directly from the image captured by the camera while changing the excitation voltage. The second method is to use the optimal phase obtained by the optimal phase detection circuit 210. Either method may be used to measure the LV diagram using the characteristic measurement unit 273. Note that the embodiment in FIG. 2 describes a case in which the LV diagram is measured using an image captured by the camera. Therefore, in FIG. 2, a camera 271 is provided near the charging electrode 213 to detect the cutting position where the ink column is cut into ink particles, and the image captured by this camera 271 is input to the characteristic measurement unit 273, which processes this image to measure the LV diagram. When using the second method, the LV diagram can be measured by inputting the optimal phase detected by the optimal phase detection circuit 210 to the characteristic measurement unit 273, as indicated by the dashed arrow in FIG. 2.

[0040] (How to measure LV diagrams using a camera) First, the first method (a method for measuring an LV diagram using images captured by a camera) will be described in detail. In FIG. 2, the intersecting position of the ink pillar 221 ejected from the nozzle 211 is measured by capturing an image of the ink pillar 221 illuminated by a strobe light 272 installed near the charging electrode 213 with a camera 271. To enable capturing a still image of the ink pillar 221 ejected from the nozzle 211, the excitation frequency of the strobe light 272 is set to the same value as the excitation frequency of the excitation voltage applied to the piezoelectric element 212. By capturing images with the camera 271 while changing the excitation voltage, a group of still images of the ink pillar 221 under each excitation voltage condition is obtained. This group of still images is sent to a characteristics measurement unit 273. The characteristics measurement unit 273 extracts from the group of still images the intersecting position of the ink pillar 221 corresponding to each excitation voltage, with the ejection port of the nozzle 211 as the reference point. In this way, the characteristic measuring unit 273 can obtain (measure) the LV diagram by processing the still images taken by the camera 271.

[0041] An example of an LV diagram of ink pillar 221 ejected from nozzle 211, created by characteristics measurement unit 273, is shown in Figure 4. The horizontal axis of the diagram in Figure 4 is the excitation voltage, and the vertical axis indicates the ink cut position when each excitation voltage is applied. As can be seen from the LV diagram shown in Figure 4, as the excitation voltage is increased, a minimum point first appears at the cut position of ink pillar 221, and as the excitation voltage is further increased, a maximum point is observed. Note that a maximum point may not be observed depending on the excitation voltage range and other conditions used for measurement.

[0042] (Method for extracting amplitude growth rate μ from LV diagram) If the initial minute constriction amount that occurs in the ink column immediately after ejection from the nozzle is h0, the constriction amount h after time t is expressed by the following equation (1):

[0043]

number

[0044] where μ is the amplitude growth rate with the dimension of the reciprocal of time. When the constriction h grows to the nozzle radius a, the ink is cut off from the ink column. This point is called t=t b Then, rearranging the equation, we get the following equation (2).

[0045]

number

[0046] The length of the ink pillar is called the ink pillar length L, and is expressed by the following equation (3) using the ink flight velocity v.

[0047]

number

[0048] The initial constriction amount h0 depends on the amplitude of the perturbation applied to the ink column, and this amplitude is controlled by the excitation voltage V. Assuming that there is a proportional relationship between h0 and the excitation voltage V, this is expressed by the following equation (4) using proportionality constants A and A'.

[0049]

number

[0050] From the LV diagram in Figure 4, a linear relationship of equation (4) holds between L and lnV up to the minimum point. As shown in Figure 5, the value of v / μ can be obtained from the slope of this linear region. The ink flight speed v can be obtained from the inter-ink particle distance λ and excitation frequency f using equation (5) below, so μ can be calculated.

[0051]

number

[0052] (Measurement method for LV diagram measured from charge phase waveform) Next, we will explain a second method for measuring the LV diagram by using the optimal phase. Here, we consider a case where one cycle of the vibration generated by the piezoelectric element 212 is divided into 16 phases and the optimal phase is detected. If the optimal phase is shifted by Δn phases between two excitation voltage conditions, the time difference Δt between the timing of cutting off the ink pillar 221 is expressed by the following equation using the cycle T of the vibration generated by the piezoelectric element 212.

[0053]

number

[0054] The interval between the excitation voltage conditions must be small enough so that the difference Δn in the optimal phase is within one period (within 16 phases). The difference ΔL in the ink cutoff point between two excitation voltage conditions is expressed by the following equation using the flow velocity v of the ink column 221:

[0055]

number

[0056] Since v and T are constant between the two excitation voltage conditions, equation (2) shows that there is a proportional relationship between the difference ΔL in the ink cutoff point and the phase difference Δn in the optimal phase. By integrating ΔL, the ink column length L at the excitation voltage V can be calculated.

[0057]

number

[0058] In equation (8), L0 is the ink column length at excitation voltage V0. Therefore, by plotting the integrated value of the phase difference Δn between excitation voltage conditions against the excitation voltage, the cutting position L can be determined, and a diagram showing the same trend as Figure 4 can be drawn. To confirm this, the optimal phase for each excitation voltage condition was detected by optimal phase detection circuit 210 while ejecting ink column 221 from nozzle 211 under the same conditions as the first method, and the detected optimal phase was sent to characteristic measurement unit 273. Figure 6 shows the LV diagram generated by characteristic measurement unit 273, in which the minimum point of the excitation voltage is set as the reference point on the vertical axis, and the integrated value of the phase difference of the optimal phase between each excitation voltage is plotted against the excitation voltage. In Figure 6, as the excitation voltage was increased, local minimums and maximums were observed, as in Figure 4.

[0059] To compare the two measurement methods, the LV diagram obtained by the first method and the LV diagram obtained by the second method are superimposed on each other in Figure 7. As can be seen from Figure 7, the overall trend and the positions of the minimum and maximum points are nearly identical between the two measurement methods.

[0060] (Method for measuring the amplitude growth rate μ from the LV diagram) From equations (4) and (8), the following relational expression (9) holds between the excitation voltage V and Δn using the constant A″.

[0061]

number

[0062] Equation (9) is rearranged using the constant A'' to derive equation (10).

[0063]

number

[0064] As shown by the bold line in Figure 8, in the excitation voltage region from V0 to the minimum point, there is a range where the linear relationship of equation (10) holds between the vertical axis value (integrated value of phase difference at the optimal phase) and the horizontal axis value (lnV), and the value of -16 / (μT) can be obtained from the slope of this range. In equation (10), the period T can be calculated from the reciprocal of the excitation frequency f, so the amplitude growth rate μ can be calculated from the slope of the linear region of LV.

[0065] The above description of the embodiment has shown a method for obtaining the amplitude growth rate μ from an LV diagram obtained from an image captured by a camera or an electrostatic charge phase waveform. μ can be obtained using either method, but considering the load and efficiency of the calculation processing in the characteristics measurement unit 273, obtaining the LV diagram from the electrostatic charge phase waveform is more suitable.

[0066] (Estimation of optimal pressure conditions and pressure adjustment method) This section describes how the MPU201 (processor) estimates the optimal pressure from the amplitude growth rate μ. The amplitude growth rate μ depends on the pump pressure, but the larger μ, the more efficient the ink droplets are formed from the ink column, and the higher the print quality. As shown in Figure 9, by plotting the amplitude growth rate μ against pressure, the pressure conditions at which μ is maximized can be estimated as the optimal pressure conditions for printing.

[0067] Figure 10 shows the experimental results of extracting the amplitude growth rate μ from an LV diagram obtained from the charge phase waveform under various pump pressure conditions for the circulation pump 245, ranging from 0.145 to 0.275 MPa. The experimental results of extracting the amplitude growth rate μ from each LV diagram obtained from an LV diagram obtained from a camera-captured image also yielded results similar to those shown in Figure 10. While the inkjet printer 100 extracts μ for each pressure condition, if the circulation pump 245 is capable of automatic pump pressure adjustment, it may display a message indicating that the pump pressure is being automatically adjusted, as shown in Figure 11. If manual pump pressure adjustment is required, a screen may be displayed instructing the operator to set the next pressure condition, as shown in Figure 12. Figure 10 shows that μ was maximized at 0.20 MPa, which suggests that 0.20 MPa is the optimal pressure condition for printing.

[0068] Next, the estimated optimal pressure is set as the pump pressure value of the circulation pump 245. If the circulation pump 245 is capable of automatically adjusting the pump pressure, a message indicating that the pressure has been adjusted to 0.20 MPa may be displayed as shown in Figure 13. If the pump pressure needs to be adjusted manually, a screen may be displayed as shown in Figure 14, instructing the operator to set the pressure to 0.20 MPa.

[0069] The estimation of the optimum pressure conditions and the pressure adjustment of the circulation pump may be performed periodically or at any timing.

[0070] (Confirmation of optimal pressure conditions) The consistency between the optimal pressure conditions estimated by the above method and the optimal pressure conditions for actual printing was confirmed. The pressure with the widest printable excitation voltage range was defined as the optimal pressure condition for printing. An example of the procedure for specifically determining the printable excitation voltage range is described below. A printing evaluation was performed under specified pressure and excitation frequency conditions using an inkjet printer 100 filled with ink 241, and the printable excitation voltage range was experimentally determined. The print evaluation used the print pattern shown in Figure 15. In Figure 15, (a) shows a normal printing state, and (b) shows an abnormal printing state. A visual judgment was made that "printing is possible" when ink particles landed in the designated positions on the print substrate (printed object) and characters were drawn, and "printing is not possible" when ink particles did not land in the designated positions on the print substrate and characters were not drawn.

[0071] Figure 16 shows a graph plotting the range of excitation voltages that can be printed under each pump pressure condition. The widest range of excitation voltages that can be printed was found to be between 0.20 and 0.23 MPa. The optimal pressure estimated from the amplitude growth rate μ was 0.20 MPa, so the estimated value matched the actual measured value of the optimal pressure for printing. Note that it is also possible to use a pressure condition that is increased or decreased by a constant from the pressure condition that maximizes μ as the estimated value.

[0072] The main features of the first embodiment can be summarized as follows.

[0073] The control device 200 of the charge-controlled inkjet printer (inkjet printer 100, FIG. 2) calculates (characteristics measurement unit 273, FIG. 2) a feature quantity (amplitude growth rate μ) based on a charge phase waveform (FIG. 3) that indicates the correspondence relationship between the charge phase and the charge amount of ink particles 222. The control device 200 determines a pump pressure suitable for printing from the correspondence relationship (FIG. 9) between the pump pressure p of the pump (circulation pump 245, FIG. 2) that supplies ink 241 from the ink tank 240 to the nozzles 211 and the feature quantity (amplitude growth rate μ).

[0074] Because the feature value (amplitude growth rate μ) is calculated from the charge phase waveform (electrical signal), there is less error in the feature value compared to methods that calculate feature values ​​from camera images. This makes it possible to improve the accuracy of the pump pressure suitable for printing. In addition, because the feature value is calculated from the charge phase waveform (electrical signal), the calculation load is low. There is no need to add sensors to the charge-controlled inkjet printer, such as a camera to measure the cutting position or a speed sensor to measure the speed of ink ejected from the nozzle, which reduces manufacturing costs. The accuracy of the pump pressure suitable for printing can be improved from the feature value even when the temperature or ink type changes.

[0075] The feature quantity is, for example, the amplitude growth rate μ of the constriction amount h of the ink column 221 formed by the ink 241 ejected from the nozzle 211. The inventors of the present application have found that, among the feature quantities that can be extracted from the charge phase waveform, the amplitude growth rate μ is highly correlated with the pump pressure suitable for printing.

[0076] The control device 200 determines a pump pressure suitable for printing based on the maximum value of the amplitude growth rate μ in the correspondence relationship between the pump pressure p and the characteristic quantity, the amplitude growth rate μ (FIG. 9). This makes it possible to easily determine (estimate) a pump pressure suitable for printing from the maximum value of the amplitude growth rate μ. The control device 200 may determine the pump pressure p corresponding to the maximum value of the amplitude growth rate μ as the pump pressure suitable for printing, or may determine a value obtained by adding or subtracting a predetermined value to or from the pump pressure p corresponding to the maximum value of the amplitude growth rate μ as the pump pressure suitable for printing.

[0077] The control device 200 determines the pump pressure suitable for printing periodically or at any timing (FIG. 9). By periodically determining the pump pressure, the pump pressure suitable for printing can be updated automatically or manually at regular intervals. The pump pressure suitable for printing may also be determined at any timing, for example, based on a predetermined event such as power-on, a pulse signal from the rotary encoder 262, etc.

[0078] The control device 200 determines a charging phase suitable for printing from the charging phase waveform (FIG. 3). The control device 200 calculates a value representing the cutting position L of the ink pillar 221 (the phase difference integral value of the optimal phase) from the charging phase suitable for printing (characteristics measurement unit 273). The control device 200 calculates the amplitude growth rate μ, which is a feature quantity, from the correspondence relationship (FIG. 8) between the value representing the excitation voltage V (lnV) applied to the piezoelectric element 212 that excites the ink pillar 221 and generates ink droplets 222, and the value representing the cutting position L of the ink pillar 221 (the phase difference integral value of the optimal phase).

[0079] By calculating a value representing the cutting position L of the ink pillar 221 from the charge phase suitable for printing (the phase difference integral value of the optimal phase), the error in the value representing the cutting position L is smaller than in the method of calculating the cutting position L from a camera image. By calculating the amplitude growth rate μ from a value representing the cutting position L with high accuracy, the accuracy of the amplitude growth rate μ can be improved.

[0080] The value representing the cutting position L of the ink pillar 221 is, for example, the integral value of the phase difference of the optimal phase (FIG. 8). This makes it possible to easily calculate the value representing the cutting position L of the ink pillar 221 from the phase difference of the optimal phase.

[0081] The control device 200 calculates the amplitude growth rate μ, which is a feature, from the slope (solid line in FIG. 8) of the linear region where the correspondence relationship between the value (lnV) representing the excitation voltage and the value (integral value of the phase difference of the optimal phase) representing the cutting position L of the ink pillar 221 is linear. This makes it possible to easily calculate the amplitude growth rate μ.

[0082] The value representing the excitation voltage is the logarithm (natural logarithm) of the excitation voltage V. This makes the correspondence between the value representing the excitation voltage (lnV) and the value representing the cutting position L of the ink pillar 221 (the phase difference integral value of the optimal phase) linear.

[0083] The charge phase is the timing obtained by equally dividing one period (period T) of vibration generated by the piezoelectric element 212, which excites the ink column 221 formed by the ink 241 ejected from the nozzle 211 to generate ink droplets 222 (FIG. 3). This makes it possible to easily determine the charge phase from the vibration period T or the excitation frequency f.

[0084] The pump pressure p of the pump (circulation pump 245, FIG. 2) is automatically or manually adjusted based on the determined pump pressure suitable for printing, thereby achieving good printing.

[0085] A charge-controlled inkjet printer (inkjet printer 100, FIG. 2) equipped with control device 200 includes an ink tank 240 that stores ink 241, a nozzle 211 that ejects the ink 241, a pump (circulation pump 245) that supplies ink 241 from the ink tank 240 to the nozzle 211, a piezoelectric element 212 that excites an ink column 221 formed by the ink 241 ejected from the nozzle 211 to generate ink droplets 222, a charging electrode 213 that charges the ink droplets 222, and a deflection electrode 214 that changes the trajectory of the ink droplets 222 in accordance with the amount of charge on the ink droplets 222. By including control device 200 in the charge-controlled inkjet printer, the pump is driven at a pump pressure suitable for printing, resulting in good printing.

[0086] [Example 2] Next, a printing system 400 according to a second embodiment will be described with reference to Fig. 17. Fig. 17 is a configuration diagram of the printing system 400.

[0087] The printing system 400 is made up of an inkjet printer 100A and a control device 200A. The inkjet printer 100A and the control device 200A are connected via a communication network 300. The communication network 300 may be wired or wireless.

[0088] The inkjet printer 100A of the second embodiment corresponds to the inkjet printer 100 of the first embodiment minus the characteristic functions of the control device 200 (for example, the optimum phase detection circuit 210, the characteristic measurement unit 273, and the excitation voltage calculation unit 274).

[0089] The control device 200A of the second embodiment is a PC (Personal Computer), a mobile terminal, a server, etc., and is composed of, for example, a processor such as a CPU (Central Processing Unit), a memory, a storage device such as an HDD (Hard Disk Drive), an input device such as a keyboard, a mouse, a touch panel, etc., a display device such as a display, and a communication device such as a network I / F, etc.

[0090] The processor executes a program stored in the storage device to realize functions similar to those of the optimum phase detection circuit 210, the characteristics measurement unit 273, and the excitation voltage calculation unit 274 of the first embodiment, for example.

[0091] The main features of the second embodiment can be summarized as follows.

[0092] Printing system 400 is composed of control device 200A and a charge-controlled inkjet printer (inkjet printer 100A). By providing the control device external to the charge-controlled inkjet printer, the charge-controlled inkjet printer can be made smaller and controlled remotely.

[0093] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0094] Furthermore, the above-described configurations, functions, etc. may be realized in part or in whole by hardware, for example, by designing them as integrated circuits. Furthermore, the above-described configurations, functions, etc. may be realized in software by a processor interpreting and executing a program that realizes each function. Information such as the programs, tables, and files that realize each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0095] The embodiment of the present invention may be configured as follows.

[0096] (C1) An inkjet printer having a main body having an ink tank that stores ink, a print head that applies an excitation voltage to a piezoelectric element that excites the ink supplied from the ink tank to a nozzle by a pump to charge the generated ink particles, and changes the trajectory of the ink particles according to the amount of charge on the ink particles to print on a substrate, and a control unit (control device) that controls the print head, wherein the control unit measures a charge phase waveform that shows the relationship between the charge phase and the amount of charge on the ink particles, measures pressure characteristics that show the relationship between a feature calculated from the charge phase waveform and the pressure of the pump, calculates an optimal pressure setting value based on the pressure characteristics, and drives the pump using the calculated pressure setting value.

[0097] (C2) In the inkjet printer described in (C1), the control unit obtains an amplitude growth rate as the characteristic amount of the pressure characteristic.

[0098] (C3). In the inkjet printer described in (C2), the control unit calculates the pressure corresponding to the maximum value of the amplitude growth rate included in the pressure characteristics as the pressure setting value.

[0099] (C4) In the inkjet printer described in (C1), the control unit calculates the pressure setting value periodically or at an arbitrary timing.

[0100] (C5). In the inkjet printer described in (C2), the amplitude growth rate is calculated from an LV diagram representing the relationship between the ink cutting position calculated from the charging phase waveform and the excitation voltage.

[0101] According to (C1)-(C5), it is possible to provide a highly robust inkjet printer that achieves high print quality. [Explanation of symbols]

[0102] 1...Main unit 2...Print head 4...Cable 5...Display section 7...Reading unit 100, 100A... Inkjet printer 200, 200A...control device 201...MPU 202...ROM 203...RAM 204...Input panel 205...Display control unit 206...Bus line 207...Charged voltage generating circuit 208...Excitation voltage generating circuit 209...Storage device 210...Optimal phase detection circuit 211...Nozzle 213...Charged electrode 214...Deflection electrode 215…Gutter 221...Ink pillar 222...ink particles 232a, 232b...Piping 233...Recovery pump 234...Charge amount measuring unit 240...ink tank 241...Ink 245...Circulation pump 246...Reducing valve 250...filter 251...Auxiliary ink tank 252...Intensifying fluid tank 260...Transportation device 261…Printed material 262...Rotary encoder 271...Camera 272...Strobe lighting 273...Characteristics measurement section 274...Excitation voltage calculation unit 300...Communication Network 400...Printing system

Claims

1. A control device for a charge-controlled inkjet printer, comprising: Calculating a feature amount based on a charge phase waveform that indicates a correspondence relationship between the charge phase and the charge amount of the ink particle; A pump pressure suitable for printing is determined based on the correspondence between the pump pressure of the pump that supplies ink from the ink tank to the nozzles and the characteristic amount.

1. A control device for a charge-controlled inkjet printer.

2. 2. A control device for a charge-controlled ink jet printer according to claim 1, The feature amount is an amplitude growth rate of the constriction amount of the ink column formed by the ink ejected from the nozzle.

1. A control device for a charge-controlled inkjet printer.

3. 3. The control device for the charge-controlled ink jet printer according to claim 2, A pump pressure suitable for printing is determined based on the maximum value of the amplitude growth rate in the correspondence relationship between the pump pressure and the amplitude growth rate, which is the characteristic amount.

1. A control device for a charge-controlled inkjet printer.

4. 2. A control device for a charge-controlled ink jet printer according to claim 1, Determine the pump pressure suitable for printing periodically or at any time 1. A control device for a charge-controlled inkjet printer.

5. 3. The control device for the charge-controlled ink jet printer according to claim 2, determining a charging phase suitable for printing from the charging phase waveform; calculating a value representing a cutting position of the ink pillar from the charging phase suitable for printing; The amplitude growth rate, which is the characteristic quantity, is calculated from the correspondence relationship between a value representing an excitation voltage applied to a piezoelectric element that excites the ink pillar and generates ink droplets, and a value representing a cutting position of the ink pillar.

1. A control device for a charge-controlled inkjet printer.

6. 6. The control device for the charge-controlled ink jet printer according to claim 5, The value representing the cutting position of the ink pillar is the integrated value of the phase difference of the charging phase suitable for printing.

1. A control device for a charge-controlled inkjet printer.

7. 7. A control device for a charge-controlled ink jet printer according to claim 6, The amplitude growth rate, which is the characteristic quantity, is calculated from the slope of a linear region in which the correspondence relationship between the value representing the excitation voltage and the value representing the cutting position of the ink pillar is linear.

1. A control device for a charge-controlled inkjet printer.

8. 8. The control device for the charge-controlled ink jet printer according to claim 7, The value representing the excitation voltage is the logarithm of the excitation voltage 1. A control device for a charge-controlled inkjet printer.

9. 2. A control device for a charge-controlled ink jet printer according to claim 1, The charging phase is a timing obtained by equally dividing one period of vibration generated by a piezoelectric element that excites an ink column formed by the ink ejected from the nozzle to generate ink droplets.

1. A control device for a charge-controlled inkjet printer.

10. 2. A control device for a charge-controlled ink jet printer according to claim 1, The pump pressure of the pump is automatically or manually adjusted based on the determined pump pressure suitable for printing.

1. A control device for a charge-controlled inkjet printer.

11. A charge-controlled inkjet printer equipped with the control device according to claim 1, the ink tank in which the ink is stored; the nozzles that eject the ink; the pump that supplies the ink from the ink tank to the nozzles; a piezoelectric element that excites an ink column formed by the ink ejected from the nozzle to generate ink droplets; a charging electrode for charging the ink particles; a deflection electrode that changes the trajectory of the ink particle in accordance with the charge amount of the ink particle; A charge-controlled inkjet printer comprising:

12. A printing system comprising the control device according to claim 1 and a charge-controlled inkjet printer.

13. calculating a feature quantity based on a charge phase waveform that indicates a correspondence relationship between the charge phase and the charge amount of the ink particle; determining a pump pressure suitable for printing based on a correspondence relationship between the pump pressure of a pump that supplies ink from an ink tank to the nozzles and the characteristic amount; A method for causing a control device to execute the above.

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