Inkjet recording apparatus and inkjet recording method

Abstract

To provide an inkjet recording device that can automatically determine an exciting voltage of a piezoelectric element which is optimal for forming ink droplets.SOLUTION: Exciting voltages are applied to a piezoelectric element in multiple number of times of sweeping in a state where electricity is not distributed to a deflecting electrode, so that sweeping is performed from a high-voltage side toward a low-voltage side in a predetermined voltage range. Electrical charge is applied to ink droplets generated by the applied exciting voltages by applying charged voltages, in a plurality of arbitrary printing phases, to the ink droplets. A quantity of the electrical charge applied to the ink droplets is sensed with an electrical charge sensor and the printing phases are determined. When a relation between previous printing phases detected whenever sweeping is performed and current printing phases is inverted from an increase-side to a decrease-side and then decrease-determinations of the printing phases are made consecutively twice, a value of an exciting voltage corresponding to the printing phase on the sweeping occasion just before the first decrease-determination is made is set as a final value of an exciting voltage.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an inkjet recording apparatus, and more particularly to a continuous-jet charge-controlled inkjet recording apparatus and an inkjet recording method. [Background technology]

[0002] A typical continuous-jet charge-controlled inkjet recording device is provided with an ink container that stores ink in the main body, and the ink from the ink container is supplied to the print head by an ink supply pump. The ink supplied to the print head is continuously ejected from the ink nozzle and turned into ink droplets. Among the ink droplets, the ink droplets used for printing are charged and deflected, and then made to fly to the desired printing position on the printing target to form characters or symbols (hereinafter referred to as characters), while the ink droplets not used for printing are not charged and deflected, but are collected in a gutter and returned to the ink container by an ink recovery pump.

[0003] In a continuous-jet charge-controlled inkjet recording device, for example, as described in JP 2007-136839 A (Patent Document 1), a piezoelectric element provided in an ink nozzle is driven with a predetermined excitation voltage value to eject ink from the ink nozzle as ink droplets.

[0004] Incidentally, the excitation voltage value that drives the piezoelectric element of the ink nozzle affects the formation of ink droplets, and it is necessary to set an optimal excitation voltage value. In particular, since the ink characteristics vary depending on the environmental temperature, it is important to set an excitation voltage value that compensates for this.

[0005] To achieve this, for example, a method is known in which, when printing, the excitation voltage value of the piezoelectric element in the ink nozzle is adjusted, the ink droplets ejected from the ink nozzle are visually observed with a magnifying glass, and the excitation voltage value when the ink droplets have a shape suitable for printing is determined as the optimum excitation voltage value. Alternatively, a method is known in which characters are actually printed while adjusting the excitation voltage value of the piezoelectric element, and the median value of the excitation voltage range at which the operator can determine that good printing has been achieved is determined as the optimum excitation voltage value. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-136839 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the case of the above-mentioned method, the optimum excitation voltage value is determined by repeatedly performing test printing while changing the excitation voltage value supplied to the piezoelectric element while visually observing the ink droplets ejected from the ink nozzle with a magnifying glass, etc. Also, by changing the excitation voltage value according to the "temperature-excitation voltage characteristics" provided in the inkjet recording device, good print quality is obtained according to the environmental temperature.

[0008] However, to visually observe ink droplets with a magnifying glass and accurately judge the ink droplet shape suitable for printing, the skill of an expert is required, and there is a problem that individual differences occur because the judgment is made by visual inspection. Furthermore, when actually printing, there is a problem that the work is wasted, or that individual differences occur because the print result is judged by a human being by visual inspection.

[0009] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an ink jet recording apparatus and an ink jet recording method capable of automatically determining an excitation voltage value of a piezoelectric element suitable for forming ink droplets. [Means for solving the problem]

[0010] The present invention relates to A continuous jet type charge-controlled ink jet recording apparatus comprising: an excitation voltage circuit which applies an excitation voltage to a piezoelectric element provided in an ink nozzle which ejects ink droplets; a charging electrode which charges the ejected ink droplets; a deflection electrode which deflects the flight direction of the ink droplets charged by the charging electrode; a charge amount sensor which measures the amount of charge of the ink droplets charged by the charging electrode; and a control unit which controls the excitation voltage circuit, the charging electrode, the deflection electrode, and the charge amount sensor; The control unit an excitation voltage sweep setting unit that applies an excitation voltage value to the piezoelectric element over a plurality of sweeps so as to sweep the excitation voltage value from a high voltage side to a low voltage side within a predetermined voltage range while no current is applied to the deflection electrode; a print phase measurement unit that applies a charge voltage to ink droplets generated by the applied excitation voltage value at any of a plurality of print phases to give them a charge, and detects the amount of charge given to the ink droplets with a charge amount sensor to determine an appropriate print phase; The device is provided with an excitation voltage determination unit that, when the relationship of the current printing phase to the previous printing phase detected for each sweep is inverted from the increasing side to the decreasing side and two consecutive decrease determinations of the printing phase are established, sets the excitation voltage value corresponding to the printing phase of the sweep immediately before the first decrease determination as the final excitation voltage value. It is characterized by:

[0011] The present invention relates to An ink jet recording method for a continuous jet type charge-controlled ink jet recording apparatus including an excitation voltage circuit that applies an excitation voltage to a piezoelectric element provided in an ink nozzle that ejects ink droplets, a charging electrode that charges the ejected ink droplets, a deflection electrode that deflects the flight direction of the ink droplets charged by the charging electrode, a charge amount sensor that measures the amount of charge of the ink droplets charged by the charging electrode, and a control unit that controls the excitation voltage circuit, the charging electrode, the deflection electrode, and the charge amount sensor, The control unit applying an excitation voltage value to the piezoelectric element over a plurality of sweeps so as to sweep the excitation voltage value from a high voltage side to a low voltage side within a predetermined voltage range while no current is applied to the deflection electrodes; A charge is applied to the ink droplets generated by the applied excitation voltage value at any of a plurality of printing phases to give them a charge, and the amount of charge given to the ink droplets is detected by a charge amount sensor to determine an appropriate printing phase, When the relationship between the current printing phase and the previous printing phase detected for each sweep is inverted from the increasing side to the decreasing side and two consecutive decreases in the printing phase are determined, the excitation voltage value corresponding to the printing phase of the sweep immediately before the first decrease is set as the final excitation voltage value. It is characterized by: Effect of the Invention

[0012] According to the present invention, since the excitation voltage value of the piezoelectric element suitable for forming ink droplets can be automatically determined, it is possible to easily determine the optimum excitation voltage value without requiring skill. [Brief description of the drawings]

[0013] [Figure 1] 1A to 1C are schematic diagrams illustrating a printing method using an inkjet recording device. [Diagram 2] FIG. 1 is a diagram illustrating a configuration of an inkjet recording apparatus. [Diagram 3] FIG. 2 is a block diagram showing a control unit that controls components of the inkjet recording apparatus. [Figure 4] 5A and 5B are explanatory diagrams illustrating the influence of environmental temperature on the excitation voltage of a piezoelectric element in an ink nozzle and the length of an ink column. [Diagram 5] 2 is a block diagram showing a main part of a control unit of the inkjet recording apparatus according to the embodiment of the present invention. FIG. [Figure 6] 5 is an explanatory diagram illustrating the relationship between the printing phase and the excitation voltage applied to the piezoelectric element of the ink nozzle. FIG. [Figure 7] FIG. 11 is an explanatory diagram for determining a final excitation voltage value. [Figure 8]6 is a process flowchart for explaining the process of the block diagram shown in FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications and application examples within the technical concept of the present invention are also included in the scope of the present invention. First, the structure and operation of a typical continuous-jet charge-control type ink jet recording apparatus will be briefly described.

[0015] The external configuration of an inkjet recording device is shown in Figure 1. In this figure, the main body A of the inkjet recording device is equipped with a display B for display purposes. Ink is supplied to a print head D via a cable C, and the determined print content is sent to the print head D via the cable C, and ink droplets are continuously ejected based on this, thereby printing on a print target F transported on a transport line E such as a belt conveyor.

[0016] Fig. 2 shows a schematic configuration of an inkjet recording device. In Fig. 2, an inkjet recording device 100 is provided with a main ink container 1, which is filled with ink 2a, and which is connected to a supply valve 3, a supply pump 4, a main filter 5, a pressure adjusting valve 6, a jet valve 7, and an ink nozzle 8 via an ink supply pipe 9. A piezoelectric element (not shown) is provided in the ink nozzle 8, which applies vibrations to the ink in the ink nozzle 8.

[0017] A charging electrode 23 and a deflection electrode 24 are arranged in the traveling direction of the ink droplets 10 ejected from the ink nozzle 8, and the ink droplets 10 used for printing are charged with a voltage corresponding to a character signal by the charging electrode 23. The charged ink droplets 10 fly in an electric field created by the deflection electrode 24, and are deflected according to the amount of charge until they reach the printing target 26, where they form characters, symbols, etc.

[0018] A gutter 11 for collecting the ink droplets 10 not used for printing is disposed in the traveling direction of the ink droplets 10 discharged from the ink nozzle 8. The gutter 11 is connected to a charge amount sensor 25 for measuring the amount of charge of the charged ink droplets 10, a recovery pump 12, and the main tank container 1 via an ink recovery pipe 13.

[0019] When the ink droplets 10 are collected by the gutter 11, the air surrounding the ink droplets 10 is also taken in together with the ink droplets 10 and transported to the main ink container 1. The air transported to the main ink container 1 is discharged to the outside of the inkjet recording device 100 through an exhaust port (not shown) provided in the inkjet recording device 100 via an external exhaust pipe 22 connected to the main ink container 1.

[0020] The inkjet recording device 100 is also provided with a sub-ink container 14, which is filled with ink 2b. The sub-ink container 14 is connected to the refill valve 3 and the supply pump 4 via an ink supply pipe 16.

[0021] Furthermore, the inkjet recording apparatus 100 is provided with an intensifying liquid container 17, and the intensifying liquid container 17 is replenished with an intensifying liquid 18. The intensifying liquid container 17 is connected to an intensifying pump 19 and an intensifying valve 20 via an intensifying liquid supply pipe 21.

[0022] As shown in FIG. 3, the inkjet recording apparatus 100 includes an MPU 32 (microprocessing unit) that functions as a control unit for controlling each component inside the inkjet recording apparatus 100 via a bus 200.

[0023] The MPU 32 (microprocessing unit) is connected to a RAM 30 (random access memory) for temporarily storing data within the inkjet recording apparatus 100, a ROM 29 (read only memory) for pre-storing programs and the like, a video RAM 31 for storing video data for charging the ink droplets 10, a charging signal generating circuit 27 for converting the video data into a charging signal, a charge sensor 25, a charge amplifier circuit 28 for amplifying the signal from the charge sensor 25, and an excitation voltage application circuit 33 for exciting and driving the ink nozzles 8, and is configured to control these circuits and the like.

[0024] In addition, the supply valve 3, the nozzle 8, the supply pump 4, the recovery pump 12, the intensifying liquid pump 19, the supply valve 3, the pressure regulating valve 6, the jet valve 7, the make-up valve 15, the intensifying valve 20, the charging electrode 23, the deflection electrode 24, and the operation display unit 300 are connected to the MPU 32 (microprocessing unit) via a bus 200, and the MPU 32 (microprocessing unit) is configured to control the operation of these components.

[0025] Next, the operation when printing will be described. When printing, the supply pump 4, the recovery pump 12, and the intensifying liquid pump 19 each operate in response to a signal input from the operation display unit 300, the supply valve 3 and the jet valve 7 are opened, and the pressure is adjusted to an arbitrary pressure by the pressure adjusting valve 6.

[0026] An excitation voltage is then applied from the excitation voltage application circuit 33 to the piezoelectric element of the ink nozzle 8, causing ink to be ejected from the ink nozzle 8. A charging voltage is then applied from the charging signal generation circuit 27 to the charging electrode 23 of the ink droplet 10 ejected from the ink nozzle 8, and the ink droplet 10 is charged by the charging electrode 23.

[0027] The flying direction of the charged ink droplets 10 is deflected by an electric field generated by a deflection electrode 24, and the droplets land on a print target 26 for printing. Ink droplets 10 not used for printing fly in the direction of a gutter 11. The ink droplets 10 captured in the gutter 11 are sucked by a recovery pump 12 and are recovered in the main ink container 1 via a recovery pipe 13.

[0028] When the piezoelectric element of the ink nozzle 8 is vibrated by application of the excitation voltage, the ink is turned into droplets by the pressure pulsation of the ink inside the ink nozzle 8 and the surface tension of the ejected ink. The shape of the ink droplets 10 is affected by the magnitude of the excitation voltage value, which affects the print quality. Furthermore, there is an appropriate excitation voltage range for this excitation voltage value that ensures print quality.

[0029] Figure 4 shows the change in excitation voltage / ink column length characteristics for each environmental temperature, with excitation voltage (labeled as excitation oscillation voltage in the figure) on the horizontal axis and ink column length on the vertical axis as parameters. As the ink column length increases, there is a tendency for print quality to deteriorate, with dashed line A indicating poor print quality due to a charging system error, and print quality becoming unstable between dashed lines A and B. Therefore, it can be seen that print quality is guaranteed when the ink column length is shorter than dashed line B.

[0030] In this way, the excitation voltage value is set so that the ink column length is in the range shorter than dashed line B, but when the environmental temperature changes, the excitation voltage / ink column length characteristics fluctuate, and the excitation voltage range fluctuates accordingly. As can be seen in Figure 4, the higher the environmental temperature, the longer the ink column length becomes, the narrower the excitation voltage range becomes, and the lower the excitation voltage value becomes.

[0031] Therefore, it is difficult for an operator to set an appropriate excitation voltage value, and in order to accurately determine the ink droplet shape suitable for printing, an expert's skill is required, such as visually observing the ink droplets with a magnifying glass, and there is a problem that individual differences occur because the judgment is made visually. For this reason, there is a demand for an inkjet recording device that can automatically determine an excitation voltage value of a piezoelectric element suitable for forming ink droplets.

[0032] From the results of various experiments and simulations, the inventors have found that the excitation voltage value at which appropriate ink droplets can be obtained should be set to a value lower than the excitation voltage value at which the ink column length is shortest and close to the excitation voltage value at which the ink column length is shortest, and have also found a specific method for achieving this, which makes it possible to automatically set appropriate excitation voltage values ​​without visually judging the print result or relying on the skills of an expert.

[0033] Hereinafter, a specific embodiment of the present invention will be described with reference to the drawings. Fig. 5 shows an automatic excitation voltage setting function unit that automatically sets the excitation voltage value according to this embodiment. This automatic excitation voltage setting function unit is configured by a control program executed by an MPU32 (microprocessing unit).

[0034] In FIG. 5, the excitation voltage sweep setting unit 40 has the function of applying an excitation voltage value over multiple sweeps to the piezoelectric element of the ink nozzle 8 while no current is applied to the deflection electrode 24, so as to sweep from the high voltage side to the low voltage side within a predetermined voltage range.

[0035] In addition, the print phase measurement unit 41 has a function of applying a charging voltage from the charging electrode 23 at any of a plurality of phases to the ink droplets generated by the applied excitation voltage value, thereby charging the ink droplets, and detecting the amount of charge applied to the ink droplets with the charge amount sensor 25 to determine the appropriate print phase.

[0036] Furthermore, the excitation voltage determination unit 42 has a function of determining, as the final excitation voltage value, the excitation voltage value corresponding to the printing phase of the sweep immediately preceding the first decrease judgment when the relationship of the current printing phase to the previous printing phase detected by the printing phase measurement unit 41 for each sweep is reversed from the increasing side to the decreasing side and two consecutive decrease judgments of the printing phase are established.

[0037] Next, the specific functions of the excitation voltage sweep setting unit 40, the printing phase measurement unit 41, and the excitation voltage determination unit 42 will be described with reference to Fig. 6. Here, the horizontal axis of Fig. 6 indicates the excitation voltage setting value and the number of sweeps thereof. Also, the vertical axis indicates the printing phase at each excitation voltage setting value. Note that the printing phase shown in Fig. 6 corresponds to a phase obtained by dividing one period of the excitation frequency of the piezoelectric element into 16 equal parts, as will be described later.

[0038] The excitation voltage sweep setting unit 40 sets the number of sweeps and the excitation voltage set value of the excitation voltage to be applied to the piezoelectric element provided in the ink nozzle 8. In this embodiment, the excitation voltage sweep setting unit 40 sets the number of sweeps and the excitation voltage set value ...

[0039] The difference (ΔV) between the excitation voltage setting values ​​of adjacent sweeps is arbitrary, but the difference (ΔV) is set to about 2 [V] to 4 [V]. Therefore, the excitation voltage setting value "Vn" increases by the difference (ΔV) from the low voltage side to the high voltage side.

[0040] The print phase measurement unit 41 measures the print phase in each sweep. As is well known, the print phase can be obtained by the charge sensor 25. In this embodiment, in order to detect the separation timing (print phase) of the ink droplets, during non-printing, as shown on the vertical axis of Fig. 6, the phase is divided into 16 equal parts (M = 0 to 15) for the period of the excitation frequency, and a phase search voltage (pulse voltage) is generated with a changed charging timing for charging the ink droplets in synchronization with the divided phases, thereby charging the ink droplets.

[0041] The charge amount of the ink droplets charged for each phase is detected by the charge amount sensor 25, and the detected charge amount is compared with a predetermined threshold value to determine the phase at which normal charging can be performed as the printing phase. Note that, normally, multiple phases at which normal charging can be performed occur consecutively, and a representative phase of these may be selected, and generally the central printing phase of multiple consecutive printing phases is selected.

[0042] For example, in Figure 6, the excitation voltage setting value (Vn) is "V 15 In the case of "Ph", the printing phase is indicated by "○". 11 ~Ph 15 " is the phase in which charging can be performed normally. 11 ~Ph 15 ", the printing phase "Ph 12 " is determined as the selected representative printing phase.

[0043] Similarly, if the excitation voltage setting (Vn) is "V 11 In the case of "Ph7~Ph 11 " is the phase in which charging can be performed normally. 11 Among them, the printing phase "Ph9" indicated by "★" is determined as the selected representative printing phase. The same applies to the printing phases of each excitation voltage setting value (Vn) below.

[0044] Therefore, the characteristics of the excitation voltage setting value and the representative printing phase are those indicated by "★", and this relationship shows the same tendency even if the environmental temperature changes. Note that this characteristic is within 16 equal phases.

[0045] Finally, as shown by the horizontal axis of FIG. 6, the printing availability “○, ×” is set as the excitation voltage setting value (Vn), and the excitation voltage setting values ​​“V3 to V 15 " is the excitation voltage range in which printing is possible. Next, it is necessary to determine an optimal excitation voltage setting value (Vop) from within this excitation voltage range, and this is determined by the excitation voltage determination unit 42 described below.

[0046] As described above, the inventors have found from the results of various experiments and simulations that the excitation voltage value at which appropriate ink droplets can be obtained should be set to a value that is lower than the excitation voltage value at which the ink column length is shortest, and close to the excitation voltage value at which the ink column length is shortest.

[0047] It was then discovered that the excitation voltage value closest to the excitation voltage value at which the ink column length is shortest is desirably the excitation voltage value immediately after the direction of increase or decrease in the printing phase value of adjacent sweeps has reversed from the increasing side to the decreasing side.

[0048] Therefore, in Fig. 6, the excitation voltage setting value "V5" which is on the lower voltage side of the excitation voltage value at which the increase / decrease direction of the print phase value reverses from the increase side to the decrease side and is close to the excitation voltage value at which the increase / decrease direction of the print phase value reverses is determined as the optimum excitation voltage value. The method for determining the excitation voltage setting value "V5" will be described below.

[0049] The print phase measurement unit 41 detects an appropriate representative print phase for each sweep, and the measurement result is input to the excitation voltage determination unit 42. Here, when detecting the representative print phase for each sweep, the sweep is performed from the high voltage side to the low voltage side. In other words, the excitation voltage setting value "V 19 ", "V 18 ", "V 17 " ....The representative printing phase is detected in the order of "V2", "V1", and "V0".

[0050] The reason for this is that the optimal excitation voltage exists on the lower voltage side of the excitation voltage value at which the increase / decrease direction of the printing phase value that results in the shortest ink column length is reversed. Therefore, when sweeping the excitation voltage, it is more advantageous to detect the printing phase from the high voltage side toward the low voltage side, where the reversal of the increase / decrease direction of the printing phase value can be determined earlier.

[0051] If the voltage is swept from the low voltage side to the high voltage side, the optimum excitation voltage setting value on the low voltage side must be found after the print phase value has passed the reversal of the increase / decrease direction, which creates the problem of complicated rules for the control program. However, even if the voltage is swept from the low voltage side to the high voltage side, it is possible to find the optimum excitation voltage value.

[0052] Then, the excitation voltage determination unit 42 judges the change direction (increase / decrease direction) of the measured printing phase and detects the reversal of the increase / decrease of the printing phase value. In FIG. 7 (a different example from FIG. 6), for example, the printing phase "Ph 9」 and the printing phase in the adjacent sweep (N=9) 12」 The difference (ΔPh=Ph9-Ph 12 ) it can be determined that the value of the printing phase is increasing, which indicates that the printing phase is approaching an area where the direction of increase and decrease is reversed.

[0053] Conversely, for example, the printing phase in the previous sweep (N=4) is “Ph 1」 and the printing phase in the adjacent sweep (N=3) 14」 The difference (ΔPh=Ph1-Ph 14 ) it can be determined that the value of the printing phase is decreasing, which indicates that the printing phase is moving away from the region where the increase / decrease direction is reversed.

[0054] Then, after the direction of increase / decrease of the print phase value is reversed, the print phase "Ph14" in the current sweep (N=3) is judged to have decreased twice in succession, so the print phase "Ph 1」 For this, the excitation voltage setting value "V5" in the immediately previous sweep (N=5) is finally determined as the optimum excitation voltage setting value "Vop".

[0055] Furthermore, depending on conditions such as the type of ink and the viscosity of the ink, the excitation voltage value has a tolerance range, and the tolerance range can be automatically set not only to the excitation voltage value just before the first excitation voltage value determined to have decreased, but also to an excitation voltage value between two values ​​before and two values ​​after the first excitation voltage value.

[0056] Next, a process flow when the operation of the automatic excitation voltage setting function unit shown in Fig. 5 is executed by the MPU 32 (microprocessing unit) will be briefly explained with reference to Fig. 8. This process flow explains the concept of the operation of the automatic excitation voltage setting function unit.

[0057] In the following description, the voltage of the deflection electrode 24 is set to 0 [V] so that the ink droplets are not deflected. This is to prevent the charged ink droplets 10 from not being collected in the gutter 11 during the period from when the ink droplets 10 are charged to when they enter the gutter 11.

[0058] <Step S10> In step S10, the first sweep (N=19) is performed from the high voltage side, and the excitation voltage setting value "V 19 This excitation voltage setting value "V 19 " is applied to the piezoelectric element of the ink nozzle 8, vibrating the piezoelectric element. The excitation voltage setting value "V 19 Once " is set, the process proceeds to step S11.

[0059] <Step S11> In step S11, ink droplets are charged at multiple printing phases obtained by dividing the excitation frequency by 16, and the charge of the charged ink droplets is compared with a threshold value to determine whether a printing phase has been detected. This determination is as described above. If a printing phase is detected, the process proceeds to step S12. On the other hand, if a printing phase is not detected, it is determined that good printing cannot be performed, and the process proceeds to step S13 to execute the next sweep.

[0060] <Step S12> In step S12, a representative printing phase value, which is the median value, is determined from the multiple detected printing phases and is stored in the RAM area. When the printing phase detection process is completed in the first sweep, the process proceeds to step S13.

[0061] <Step S13> In step S13, the excitation voltage setting value "V 18 This excitation voltage setting value "V 18 " is also applied to the piezoelectric element of the ink nozzle 8, causing the piezoelectric element to vibrate. 18 " is set, the process proceeds to step S14.

[0062] <Step S14> In step S14, ink droplets are also charged at multiple printing phases obtained by dividing the excitation frequency by 16, and the charge of the charged ink droplets is compared with a threshold value to determine whether a printing phase has been detected. This determination is also as described above. If a printing phase is detected, the process proceeds to step S15. On the other hand, if a printing phase is not detected, it is determined that good printing cannot be performed, and the process proceeds to step S13 to execute the next sweep. In step S13, the number of sweeps is increased, and similar processing is executed thereafter.

[0063] <Step S15> In step S15, a representative printing phase value, which is the median value, is determined from the multiple detected printing phases and stored in the RAM area. When the printing phase detection process is completed in the second sweep, the process proceeds to step S16.

[0064] <Step S16> In step S16, it is determined from the previous print phase value stored in the RAM area and the current print phase value also stored in the RAM area whether (1) the print phase value is increasing or decreasing, and further whether (2) it has decreased twice consecutively after increasing (decrease determination). This determination is as described above.

[0065] Then, (1) if it is determined that the print phase value is increasing or decreasing, the process proceeds to step S18, and (2) if it is determined that the print phase value is decreasing twice consecutively after increasing, the process proceeds to step S17.

[0066] <Step S17> In step S17, since the print phase value is determined to have decreased twice consecutively after the direction of increase / decrease is reversed, the excitation voltage setting value in the previous sweep for the print phase in the first sweep determined to have decreased is finally determined as the optimum excitation voltage setting value "Vop", and then the process goes to END.

[0067] As described above, depending on conditions such as the type of ink and the viscosity of the ink, the excitation voltage value has a tolerance range, and the tolerance range can be automatically set not only to the excitation voltage value just before the first excitation voltage value determined to have decreased, but also to an excitation voltage value between two values ​​before and two values ​​after the first excitation voltage value.

[0068] Here, once the optimum excitation voltage setting value "Vop" is determined, no further sweeping is performed, so unnecessary sweeping time can be omitted and quick operation can be achieved.

[0069] <Step S18> In step S18, it is determined whether (1) the sweep has been completed up to N=0 and the direction of increase or decrease of the print phase value has not reversed and is still increasing or decreasing, or (2) the sweep has not yet reached N=0.

[0070] (2) If it is determined that the number of sweeps has not yet reached N=0, the process proceeds to step S13, where the next sweep is executed for the current sweep. On the other hand, (1) if the number of sweeps has reached N=0 and it is determined that the increase / decrease direction of the print phase value has not reversed and is still increasing or decreasing, the process proceeds to step S19.

[0071] <Step S19> In step S19, the sweep is completed up to N=0, and the increase / decrease direction of the print phase value is not reversed, and it is still determined to be increasing or decreasing, so this is deemed to be an abnormality, an alarm is issued, and then the process exits to END. When the alarm is issued, an inspection is performed by an operator.

[0072] As described above, the present invention is characterized in that, with no current being applied to the deflection electrode, an excitation voltage value is applied to the piezoelectric element over a plurality of sweeps so as to sweep from the high voltage side to the low voltage side within a predetermined voltage range, a charging voltage is applied to the ink droplets generated by the applied excitation voltage value at any of a plurality of printing phases to give them a charge, the amount of charge given to the ink droplets is detected by a charge sensor to obtain the printing phase, and when the relationship of the current printing phase to the previous printing phase detected for each sweep is reversed from the increase side to the decrease side and two consecutive decrease determinations of the printing phase are established, the excitation voltage value corresponding to the printing phase of the sweep immediately preceding the first decrease determination is set as the final excitation voltage value.

[0073] According to this, since the excitation voltage value of the piezoelectric element suitable for forming ink droplets can be automatically determined, it is possible to easily determine the optimum excitation voltage value without requiring skill.

[0074] The present invention is not limited to the above-mentioned embodiments, but includes various modified examples. The above-mentioned embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace other configurations with respect to the configuration of each embodiment. [Explanation of symbols]

[0075] 1...main ink container, 2...ink, 3...supply valve, 4...supply pump, 5...main filter, 6...pressure regulating valve, 7...jet valve, 8...nozzle, 9...supply pipe, 10...ink droplet, 11...gutter, 12...recovery pump, 13...recovery pipe, 14...sub-ink container, 15...supply valve, 16...supply pipe, 17...intensifying liquid container, 18...intensifying liquid, 19...intensifying liquid pump, 20...intensifying valve, 21...intensifying supply pipe, 22...exhaust tube, 23...charging electrode, 24...deflection electrode, 25...charge sensor, 26...printed object, 27...charging signal generating circuit, 28...charge amplifier circuit, 29...ROM, 30...RAM, 31...video RAM, 32...MPU, 33...excitation voltage application circuit, 100...inkjet recording device, 200...bus.

Claims

1. A continuous jet charge-controlled ink jet recording apparatus comprising: an excitation voltage circuit which applies an excitation voltage to a piezoelectric element provided in an ink nozzle which ejects ink droplets; a charging electrode which charges the ejected ink droplets; a deflection electrode which deflects the flight direction of the ink droplets charged by the charging electrode; a charge amount sensor which measures the amount of charge of the ink droplets charged by the charging electrode; and a control unit which controls the excitation voltage circuit, the charging electrode, the deflection electrode, and the charge amount sensor, The control unit is an excitation voltage sweep setting unit that applies an excitation voltage value to the piezoelectric element over a plurality of sweeps so as to sweep the excitation voltage value from a high voltage side to a low voltage side within a predetermined voltage range while no current is applied to the deflection electrode; a print phase measurement unit that applies a charge voltage to ink droplets generated by the applied excitation voltage value at any of a plurality of print phases to give them a charge, and detects the amount of charge given to the ink droplets with the charge amount sensor to determine an appropriate print phase; The excitation voltage determination unit is provided with an excitation voltage value that, when the relationship of the current printing phase to the previous printing phase detected for each sweep is inverted from the increasing side to the decreasing side and two consecutive decreasing determinations of the printing phase are established, sets the excitation voltage value corresponding to the printing phase of the sweep two before and two after the first decreasing determination as the final excitation voltage value.

1. An ink jet recording apparatus comprising:

2. 2. The inkjet recording apparatus according to claim 1, The excitation voltage determination unit sets the excitation voltage value corresponding to the printing phase of the sweep immediately before the first decrease determination as the final excitation voltage value.

1. An ink jet recording apparatus comprising:

3. 3. The ink jet recording apparatus according to claim 2, The control unit does not execute sweeping by the excitation voltage sweep setting unit when the final excitation voltage value is determined by the excitation voltage determination unit.

1. An ink jet recording apparatus comprising:

4. 3. The ink jet recording apparatus according to claim 2, The control unit issues an alarm when the excitation voltage determination unit determines that the relationship of the current printing phase with respect to the previous printing phase is inverted from the increasing side to the decreasing side in every sweep and two consecutive decreases in the printing phase are not established.

1. An ink jet recording apparatus comprising:

5. An ink jet recording method for a continuous jet type charge-controlled ink jet recording apparatus including an excitation voltage circuit that applies an excitation voltage to a piezoelectric element provided in an ink nozzle that ejects ink droplets, a charging electrode that charges the ejected ink droplets, a deflection electrode that deflects the flight direction of the ink droplets charged by the charging electrode, a charge amount sensor that measures the amount of charge of the ink droplets charged by the charging electrode, and a control unit that controls the excitation voltage circuit, the charging electrode, the deflection electrode, and the charge amount sensor, The control unit is applying an excitation voltage value to the piezoelectric element over a plurality of sweeps so as to sweep the excitation voltage value from a high voltage side to a low voltage side within a predetermined voltage range while no current is applied to the deflection electrodes; A charge is applied to the ink droplets generated by the applied excitation voltage value at any of a plurality of printing phases to give them a charge, and the amount of charge given to the ink droplets is detected by a charge amount sensor to determine an appropriate printing phase, When the relationship of the current printing phase to the previous printing phase detected for each sweep is inverted from the increasing side to the decreasing side and two consecutive decrease judgments of the printing phase are established, the excitation voltage value corresponding to the printing phase of the sweep two before and two after the first decrease judgment is set as the final excitation voltage value.

23. An ink-jet recording method in an ink-jet recording apparatus comprising:

6. 6. The inkjet recording method for the inkjet recording apparatus according to claim 5, The excitation voltage value corresponding to the printing phase of the sweep immediately before the first decrease judgment is set as the final excitation voltage value.

23. An ink-jet recording method in an ink-jet recording apparatus comprising:

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