Printing apparatus

Abstract

The piezoelectric voltage is maintained at an appropriate value while the image printing process is underway. [Solution] In a continuous inkjet printer 5, when an electric field is generated by the deflection electrode 15, when the piezoelectric voltage VA is changed from a first voltage value VA1, it is determined whether the maximum value at detection time t has moved to the high voltage side or the low voltage side of the piezoelectric voltage VA based on the change in the charge amount of ink droplet ID in accordance with the change in the timing of the application of the charging voltage, and the piezoelectric voltage VA is brought closer to the second voltage value which is the destination of the maximum value at detection time t.

Description

Technical Field

[0001] The present invention relates to a printing apparatus.

Background Art

[0002] In order to manage the manufacturing date, manufacturing lot, expiration date (shelf life, consumption deadline) of products, etc., in the manufacturing line and logistics line, such information is printed (marked) directly on the product or on the container in which it is packaged.

[0003] In recent years, an inkjet printer (hereinafter abbreviated as "IJP") has been used as a printing means because it is optimal for printing characters that change moment by moment, such as dates and lot numbers.

[0004] Particularly, in a continuous-type IJP in which the moving direction of ink droplets continuously ejected by an oscillator such as a piezo element is changed by a deflection electrode to form characters or the like, in order to improve the print quality, it is necessary to adjust the excitation voltage applied to the piezo element to an appropriate value in order to generate ink droplets with an appropriate droplet shape.

[0005] As a method of setting the excitation voltage value to an appropriate value, while sweeping the excitation voltage value in a state where the deflection electrode is not energized, one cycle of the excitation voltage applied to the piezoelectric element is divided into a plurality of phases, and the charging voltage application timing is synchronized with the divided phases, and based on the correspondence relationship between the excitation voltage application timing (printing phase) that can perform normal charging for each excitation voltage value and the amount of charge given to the ink droplets, a printing phase that can perform normal charging is specified for each excitation voltage value, and a method is known in which the excitation voltage value immediately after the increase / decrease direction of the printing phase value is reversed from the increasing side to the decreasing side is set as the appropriate value (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] However, the appropriate excitation voltage applied to the piezoelectric element changes due to changes in the surrounding environment during the image printing process, and may differ from the value when the deflection electrode is not energized. In the method described in Patent Document 1, a sweep across the entire range of settable excitation voltages is required to determine the appropriate value, and depending on the excitation voltage value, ink droplets may be generated at the position of the deflection electrode. In this case, in order to prevent the ink droplets from being charged by the energized deflection electrode and to correctly determine the appropriate value, the method described in Patent Document 1 does not energize the deflection electrode. For this reason, it is difficult to maintain the piezoelectric voltage at the appropriate value during the period when the image printing process is being performed, in which an electric field is generated by the deflection electrode, using the method described in Patent Document 1.

[0008] This invention has been made in view of the above circumstances, and aims to provide a printing apparatus capable of maintaining the piezoelectric voltage at an appropriate value while the image printing process is being carried out. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a printing apparatus for printing an image on an object by ejecting ink onto the object, comprising: an ink nozzle for ejecting the ink; a piezoelectric element for separating the ink into a plurality of continuous ink droplets by applying vibrations of a frequency corresponding to an applied piezoelectric voltage to the ink ejected from the ink nozzle; a charging electrode for charging the ink droplets by applying a charging voltage; and a deflection electrode for generating an electric field in a predetermined direction and deflecting the direction of movement of the ink droplets charged by the charging electrode. The printing apparatus comprises a detection electrode for detecting the amount of charge of the ink droplet, and a control unit for controlling the ink nozzle, the piezoelectric element, the charging electrode, and the deflection electrode. The control unit includes a piezoelectric voltage setting unit that sets the piezoelectric voltage to a first voltage value corresponding to the maximum value of the detection time based on the correlation between the detection time from the separation of the ink droplet to detection by the detection electrode and the piezoelectric voltage, a charging setting unit that sets the timing for applying the charging voltage to the charging electrode, and an adjustment unit that adjusts the piezoelectric voltage to a voltage other than the first voltage value based on the amount of charge detected by the detection electrode. When the electric field is generated by the deflection electrode, the adjustment unit, when the piezoelectric voltage is changed, determines whether the maximum value of the detection time has moved to the higher voltage side or the lower voltage side of the piezoelectric voltage based on the change in the amount of charge corresponding to the change in the application timing by the charging setting unit, and adjusts the piezoelectric voltage to approach a second voltage value which is the destination of the maximum value of the detection time. According to the present invention, in order to determine whether or not the piezoelectric voltage corresponding to the maximum value of the detection time has changed without sweeping the piezoelectric voltage, it is possible to avoid the generation of ink droplets at the position of the deflection electrode and their charging by the deflection electrode. As a result, even when an electric field is generated at the deflection electrode, the piezoelectric voltage can be set to approach the piezoelectric voltage corresponding to the maximum value of the detection time.

[0010] In the printing apparatus of the present invention, the piezoelectric voltage is preferably an AC voltage, and the application period of the charging voltage is preferably shorter than one cycle of the piezoelectric voltage. This prevents charging across two ink droplets and improves the accuracy of the maximum value change detection process. In particular, by not making the application period too short, a sufficient amount of charge for detection by the detection electrode can be ensured. [Effects of the Invention]

[0011] According to the present invention, it is possible to maintain the piezoelectric voltage at an appropriate value when an electric field is generated at the deflection electrode. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the configuration of a printing system according to one embodiment of the present invention. [Figure 2] This is a functional block diagram of a printing device used in a printing system. [Figure 3] This is a schematic diagram showing the configuration of the print head. [Figure 4] This figure shows an example of the correlation between detection time and piezoelectric voltage. [Figure 5] This figure shows an example of the relationship between the timing of applying the charging voltage and the amount of charge on an ink droplet. [Figure 6] This figure shows the relationship between changes in piezoelectric voltage characteristics and changes in charge information associated with changes in piezoelectric voltage. [Figure 7] This is a flowchart showing a piezoelectric voltage adjustment method according to one embodiment of the present invention. [Modes for carrying out the invention]

[0013] A printing apparatus according to one embodiment of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following embodiment.

[0014] FIG. 1 is a diagram showing the configuration of a printing system 1 according to an embodiment of the present invention. FIG. 2 is a functional block diagram of an inkjet printer (IJP) 5 used in the printing system 1. The IJP 5 is an example of a printing device. The printing system 1 prints an image on a side surface (printing surface) 31 of a workpiece 3 conveyed by a conveyor C using the IJP 5 installed adjacent to the conveyor C. The workpiece 3 is an example of an object.

[0015] As shown in FIGS. 1 and 2, the IJP 5 includes a controller unit 51, a print head 55, and a photoelectric sensor 57. The print head 55 discharges ink onto the workpiece 3 to print an image on the workpiece 3.

[0016] As an example, the photoelectric sensor 57 is installed near the conveyor C on the upstream side of the print head 55 as shown in FIG. 1, and generates a signal when the workpiece 3 crosses the photoelectric sensor 57. The output signal of the photoelectric sensor 57 is input to the controller unit 51 and used as a trigger signal when generating a timing signal, and the position where printing starts on the printing surface 31 is determined based on this signal.

[0017] The controller unit 51 controls the operation of the print head 55. Specifically, the controller unit 51 includes a control unit 52, an operation unit 53, a display 54, and a storage unit 56.

[0018] The operation unit 53 and the display 54 are configured by, for example, a touch panel type liquid crystal display or the like. The operation unit 53 receives input operations by the user. The display 54 is used for displaying printing contents and the like printed on the printing surface 31 of the workpiece 3. Note that the operation unit 53 and the display 54 are not limited to a touch panel type liquid crystal display, and may each be an independent operation switch and various displays.

[0019] The control unit 52 includes a processor such as a CPU (Central Processing Unit), reads out and executes a program stored in a storage unit 56 described later, and generates a drive signal and a timing signal for controlling the print head 55 in accordance with an operation input to the operation unit 53.

[0020] The print head 55 discharges ink onto the side surface of the workpiece 3 in accordance with the drive signal and the timing signal generated by the control unit 52 to perform image printing.

[0021] The storage unit 56 is composed of a non-volatile memory such as a ROM and a flash memory, and a volatile memory such as a RAM. The non-volatile memory stores an OS and programs for realizing the functions of each block of the controller unit 51. On the other hand, the volatile memory functions as a working memory when generating the drive signal and the timing signal.

[0022] FIG. 3 is a schematic diagram showing the configuration of the print head 55. The print head 55 has a gun 12, a charging electrode 13, a detection electrode 14, a deflection electrode 15, and a gutter 16. The gun 12, the charging electrode 13, the detection electrode 14, the deflection electrode 15, and the gutter 16 are accommodated in, for example, a cylindrical case 11 and are controlled by the control unit 52 (FIG. 2).

[0023] The gun 12 discharges the ink supplied from the ink tank 2 provided in the IJP5 toward the slit 111 provided on the outer wall of the case 11 through the pipe 17a. Specifically, between the gun 12 and the slit 111, the charging electrode 13, the detection electrode 14, and the deflection electrode 15 are arranged in this order. The gun 12 includes a piezo element 122 and an ink nozzle 123. The ink supplied to the gun 12 is discharged from the ink nozzle 123 as an ink column IP extending from the gun 12 toward the slit 111 side.

[0024] The piezoelectric element 122 is an element that vibrates at a frequency f, which is also the frequency of the piezoelectric voltage VA, when a predetermined piezoelectric voltage VA is applied. In IJP5, the piezoelectric element 122 adds vibration at frequency f to the ink column IP. Typically, the piezoelectric voltage VA applied to the piezoelectric element 122 is an AC voltage. The voltage value and frequency f of the piezoelectric voltage VA are set by the control unit 52 (Figure 2). As a result, ink droplets ID are separated from the ink column IP at each period T corresponding to frequency f. In other words, the piezoelectric element 122 separates the ink column IP into a plurality of consecutive ink droplets ID. The ink droplets ID separated from the ink column IP move through the internal space 110 of the case 11 toward the slit 111 side.

[0025] The charging electrode 13 charges the ink droplet ID. Specifically, when a positive charging voltage is applied to the charging electrode 13 by the control unit 52, an electric field is formed between the ink column IP and the charging electrode 13 based on the potential difference between the ink column IP, which has a reference potential via the grounded gun 12, and the charging electrode 13. The duration and timing of the application of the charging voltage applied to the charging electrode 13 are set by the control unit 52 (Figure 2). For example, in the IJP5, when the image printing process is performed, the control unit 52 controls the application of the charging voltage once per cycle T of the piezoelectric voltage VA. As a result, when the ink droplet ID separates while the charging voltage is applied to the charging electrode 13, a negative charge is induced in the ink droplet ID during separation due to the electric field between the ink column IP and the charging electrode 13, and the ink droplet ID becomes charged. When the application of the charging voltage ends, the ink column IP is discharged.

[0026] The charge level of the ink droplet ID moving through the internal space 110 of case 11 is detected by the detection electrode 14 as it passes through it, and an electrical signal indicating the charge level of the ink droplet ID is output to the control unit 52. The control unit 52 acquires the charge level of the ink droplet ID based on the electrical signal from the detection electrode 14. The control unit 52 also calculates the detection time t from when the ink droplet ID is separated until it is detected by the detection electrode 14, based on the timing of applying the charging voltage to the charging electrode 13 and the timing of acquiring the electrical signal from the detection electrode 14. In other words, the detection time t can be considered as the separation position of the ink droplet ID, and the longer the detection time t, the closer the ink droplet ID is to the ink nozzle 123.

[0027] The deflection electrode 15, under the control of the control unit 52, generates an electric field of a strength corresponding to the printed image in a direction intersecting the movement direction of the ink droplet ID, thereby deflecting the movement direction of the charged ink droplet ID.

[0028] Gutter 16 collects ink droplets ID that are not charged, or ink droplets ID that are charged but not used for printing. The ink collected by gutter 16 is transferred to ink tank 2 through pipe 17b and reused.

[0029] [Setting the piezo voltage] Typically, it is desirable for the separation position of the ink droplet ID to be closer to the ink nozzle 123, i.e., for a longer detection time t. Generally, there is a correlation between the detection time t and the piezoelectric voltage VA. Figure 4 shows an example of the correlation between the detection time t and the piezoelectric voltage VA. As shown in Figure 4, among the correlations between the detection time t and the piezoelectric voltage VA, there is one in which the detection time t1 is maximized at a certain first voltage value VA1. Therefore, by setting the first voltage value VA1 in which the detection time t1 is maximized as the piezoelectric voltage VA, the separation position of the ink droplet ID can be brought closer to the ink nozzle 123.

[0030] Therefore, in this embodiment, the control unit 52 includes a piezo voltage setting unit 521 that identifies a first voltage value VA1 at which the detection time t1 reaches its maximum value before the image printing process is performed, and sets the first voltage value VA1 as the piezo voltage VA when the image printing process is performed. Specifically, the control unit 52 functions as the piezo voltage setting unit 521 by reading and executing a program stored in the storage unit 56.

[0031] For example, when the power to the IJP5 is turned on, the piezo voltage setting unit 521 calculates the correlation between the detection time t and the piezo voltage VA. Specifically, when the piezo voltage setting unit 521 sets the piezo voltage VA to its minimum value, the control unit 52 controls the charging electrode 13 and the detection electrode 14 to obtain the detection time t corresponding to the minimum value of the piezo voltage VA. Next, the piezo voltage setting unit 521 and the control unit 52 repeat the above process while increasing the piezo voltage VA until the piezo voltage VA reaches its maximum value. Based on the correspondence between the acquired multiple piezo voltages VA and the detection time t, the piezo voltage setting unit 521 calculates the correlation between the detection time t and the piezo voltage VA. The piezo voltage setting unit 521 stores the calculated correlation between the detection time t and the piezo voltage VA as the piezo voltage characteristic S1 in the storage unit 56.

[0032] Furthermore, the piezo voltage setting unit 521 identifies a first voltage value VA1 corresponding to the detection time t1, which is the maximum value of the detection time t, based on the calculated piezo voltage characteristic S1, and sets the first voltage value VA1 as the piezo voltage VA when the image printing process is performed.

[0033] [Adjusting the piezo voltage] Generally, the piezoelectric voltage characteristic S1 changes due to changes in the surrounding environment while the image printing process is underway. In other words, the maximum value of detection time t in the piezoelectric voltage characteristic S1 shifts from the first voltage value VA1 to the higher or lower voltage side of the piezoelectric voltage VA. Hereinafter, the maximum value of detection time t in the piezoelectric voltage characteristic will be simply referred to as the maximum value, and the change in the piezoelectric voltage characteristic will be referred to as the change in the maximum value.

[0034] In this embodiment, the control unit 52 determines whether the piezoelectric voltage characteristic S1 has changed while the image printing process is being performed. For example, the control unit 52 determines whether the maximum value has changed between the printing of one image and the printing of the next image during the period when the electric field is being generated by the deflection electrode 15.

[0035] In this embodiment, the correspondence between the timing of the charging voltage application and the charge amount of ink droplet ID is used to determine whether or not the maximum value has changed. As shown in Patent Document 1, by dividing one period of the excitation voltage applied to the piezoelectric element into multiple phases and synchronizing the timing of the charging voltage application with the divided phases, the correspondence between the timing (phase) of the charging voltage application and the charge amount of ink droplet ID can be obtained. Furthermore, as shown in Patent Document 1, it is known that the rise or fall of the piezo voltage VA corresponding to the detection time t corresponds to an increase (advancement) or decrease (delay) in the phase, respectively. Therefore, in this embodiment, it is possible to determine whether or not the maximum value has changed based on the correspondence between the timing of the charging voltage application and the charge amount of ink droplet ID.

[0036] In detail, the control unit 52 changes the application period and timing of the charging voltage to the charging electrode 13 to a different application period and timing than those used in the image printing process. Thus, the control unit 52 includes a charging setting unit 522 that sets the application period and timing of the charging voltage. Specifically, the control unit 52 functions as the charging setting unit 522 by reading and executing a program stored in the storage unit 56.

[0037] Figure 5 shows an example of the correspondence between the timing of the application of the charging voltage and the amount of charge on ink droplet ID. Figure 5(a) shows the time variation of the piezoelectric voltage VA. Figure 5(b) shows the application period and timing of the charging voltage in the process of determining the change in the maximum value. Figure 5(c) shows the amount of charge on ink droplet ID obtained when the charging voltage is applied at the application timing shown in Figure 5(b).

[0038] As shown in Figures 5(a) and 5(b), the charging setting unit 522 controls the application of a charging voltage that has an application period of half a period (T / 2) of the piezoelectric voltage VA, while changing it by ΔT each time period T is applied. For example, ΔT is regularly 1 / 16 of the period T, but it may be larger or smaller than 1 / 16, or it may be irregular. The magnitude of the charging voltage applied at this time is smaller than that used during the image printing process, and is sufficient to charge the ink droplet ID so that it can be recovered in the gutter 16 even if it is deflected by the deflection electrode 15. The charging setting unit 522 may also change the application timing at intervals of multiple periods, rather than every period T. By making the application period shorter than one period of the piezoelectric voltage VA, it is possible to prevent the two ink droplets ID from being charged and to improve the accuracy of the maximum value change determination process. In particular, by not making the application period too short, a sufficient amount of charge can be secured for detection by the detection electrode 14.

[0039] Figure 5(c) shows time on the horizontal axis and the amount of charge on the vertical axis. As shown in Figure 5(c), the charge setting unit 522 acquires the amount of charge of the ink droplet ID obtained for each application timing via the detection electrode 14, associates the application timing with the amount of charge, generates charge information J1, and stores it in the storage unit 56. The charge information J1 shows the characteristic that the amount of charge gradually increases from application timing TM1 to application timing TM4, reaches its maximum value at application timing TM4, gradually decreases from application timing TM4 to application timing TM13, reaches its minimum value at application timing TM13, and gradually increases from application timing TM13 to application timing TM16. If the application timing changes every multiple cycles, the charge setting unit 522 calculates and uses the sum, representative value, or average value of the amounts of charge at the same application timing as the amount of charge to associate with the application timing.

[0040] The following explanation uses the case where the piezoelectric voltage characteristic S1 changes to the piezoelectric voltage characteristic S2 as an example. Figure 6 shows the correspondence between the change in piezoelectric voltage characteristic and the change in charge information associated with the change in piezoelectric voltage. Figure 6(a) shows that the piezoelectric voltage characteristic S1 (Figure 4) changed to the piezoelectric voltage characteristic S2 during the printing process. Piezoelectric voltage characteristic S2 shows a characteristic where the voltage value VA2 corresponding to the maximum value of the detection time t is on the higher voltage side than the first voltage value VA1. Figure 6(b) shows the correspondence between the change in piezoelectric voltage VA and the change in charge information.

[0041] After generating the charge setting unit 522, it generates charge information J2 similar to the charge information J1 by changing the piezoelectric voltage VA set in the piezoelectric element 122 from the first voltage value VA1. For example, the charge setting unit 522 generates charge information J2 when the piezoelectric voltage VA is increased or decreased by ΔVA from the first voltage value VA1. The case in which the piezoelectric voltage VA is increased by ΔVA from the first voltage value VA1 will be described below.

[0042] The charge information J2 (Figure 6) obtained under the state of the piezoelectric voltage characteristic S2 shows that the amount of charge gradually increases from application timing TM1 to application timing TM3, reaches its maximum value at application timing TM3, gradually decreases from application timing TM3 to application timing TM14, reaches its minimum value at application timing TM13, and gradually increases from application timing TM14 to application timing TM16.

[0043] As described above, the charge information J1 and charge information J2 can be considered as "waves" that show the change in the charge state of the ink droplet ID over time, and the difference between charge information J1 and charge information J2 can be considered as a change in the "phase" of the "wave". Specifically, when comparing charge information J1 and charge information J2, charge information J2 can be considered to have an increased (advanced) "phase" compared to charge information J1.

[0044] When the charge information J2 is generated, the control unit 52 compares the charge information J2 with the charge information J1 in the storage unit 56 and determines whether or not the position of the maximum value has changed.

[0045] Specifically, the control unit 52 compares the charge information J2 with the charge information J1 in the storage unit 56 and determines that the "phase" of the charge information J2 has advanced compared to the charge information J1 because the application timing indicating the maximum charge amount has been advanced from application timing TM4 to application timing TM3. As described above, an increase (advancement) or decrease (delay) in the "phase" of the charge state corresponds to an increase or decrease in the piezoelectric voltage VA corresponding to the detection time t. Therefore, the control unit 52 determines that the voltage value VA1 + ΔVA is located on the maximum value side of the first voltage value VA1 because the "phase" of the charge state has advanced in response to the increase in the piezoelectric voltage VA. In other words, the control unit 52 determines that the maximum value at detection time t has moved to the high voltage side of the piezoelectric voltage VA.

[0046] When the control unit 52 determines that the maximum value at detection time t has shifted, it adjusts the piezoelectric voltage VA set on the piezoelectric element 122 to a value other than the first voltage value VA1. Thus, the control unit 52 includes an adjustment unit 523 that adjusts the piezoelectric voltage VA set on the piezoelectric element 122. Specifically, the control unit 52 functions as the adjustment unit 523 by reading and executing a program stored in the memory unit 56. For example, when the adjustment unit 523 determines that the voltage value VA1 + ΔVA is located on the maximum value side of the first voltage value VA1, it changes the piezoelectric voltage VA set on the piezoelectric element 122 to the voltage value VA1 + ΔVA to bring it closer to the voltage value VA2, which is the destination of the shifted maximum value.

[0047] The charging setting unit 522 may also generate charging information J3 (Figure 6) when the piezoelectric voltage VA is decreased by ΔVA from the first voltage value VA1. In this case, the charging information J3 shows the characteristic that the amount of charge gradually increases from the application timing TM1 to the application timing TM5, reaches its maximum value at the application timing TM5, gradually decreases from the application timing TM5 to the application timing T16, and reaches its minimum value at the application timing TM13. In other words, the "phase" of the charging information J3 is reduced (delayed) compared to the charging information J1.

[0048] The control unit 52 determines that the voltage value VA1-ΔVA is located on the opposite side of the maximum value from the first voltage value VA1 because the "phase" of the charged state has lagged in response to the decrease in the piezoelectric voltage VA. Therefore, the control unit 52 determines that the maximum value at detection time t has moved to the higher voltage side of the piezoelectric voltage VA. At this time, the adjustment unit 523 changes the piezoelectric voltage VA set in the piezoelectric element 122 to a voltage value higher than the first voltage value VA1 (for example, voltage value VA1+ΔVA) to bring it closer to the voltage value VA2, which is the destination of the maximum value.

[0049] Conversely, if the piezoelectric voltage characteristic S3 (Figure 6) changes to one in which the voltage value VA3 corresponding to the maximum value at detection time t is on the lower voltage side than the first voltage value VA1, then charge information J3 can be obtained when the piezoelectric voltage VA is increased by ΔVA from the first voltage value VA1. In this case, the control unit 52 determines that the voltage value VA1 + ΔVA is located on the opposite side from the maximum value side of the first voltage value VA1 because the "phase" of the charge state has been delayed in response to the increase in piezoelectric voltage VA. At this time, the adjustment unit 523 may change the piezoelectric voltage VA set in the piezoelectric element 122 to a voltage value lower than the first voltage value VA1 (for example, voltage value VA1 - ΔVA) to bring it closer to the voltage value VA3, which is the destination of the maximum value.

[0050] Furthermore, if the piezoelectric voltage characteristic S3 has changed, when the piezoelectric voltage VA is decreased by ΔVA from the first voltage value VA1, charge information J2 is obtained. In this case, the control unit 52 determines that the voltage value VA1-ΔVA is located on the maximum value side of the first voltage value VA1 because the "phase" of the charge state has advanced in accordance with the decrease in the piezoelectric voltage VA. At this time, the adjustment unit 523 changes the piezoelectric voltage VA set in the piezoelectric element 122 to the voltage value VA1-ΔVA to bring it closer to the voltage value VA3, which is the destination of the maximum value.

[0051] When the piezoelectric voltage VA is adjusted, the control unit 52 updates the charge information J1 in the memory unit 56 to charge information J2 or charge information J3.

[0052] As described above, according to the IJP5 of this embodiment, it is possible to determine whether or not the piezoelectric voltage corresponding to the maximum value of the detection time has changed without sweeping the piezoelectric voltage VA, thereby avoiding the generation of ink droplet ID at the position of the deflection electrode 15 and its charging by the deflection electrode 15. As a result, even when an electric field is generated at the deflection electrode, the piezoelectric voltage can be set to approach the piezoelectric voltage corresponding to the maximum value of the detection time. Therefore, it is possible to maintain the piezoelectric voltage at an appropriate value while the printing process is in progress.

[0053] In this embodiment, the destination of the maximum value is determined based on either an increase or decrease in the piezoelectric voltage VA, but the destination of the maximum value may also be determined based on both an increase and a decrease in the piezoelectric voltage VA. Specifically, the charge setting unit 522 generates two pieces of charge information: one for when the piezoelectric voltage VA is increased by ΔVA from the first voltage value VA1, and another for when the piezoelectric voltage VA is decreased by ΔVA from the first voltage value VA1. Based on the two pieces of charge information generated, the control unit 52 determines whether the maximum value is on the higher voltage side or the lower voltage side of the first voltage value VA1.

[0054] In this case, when the first voltage value VA1 corresponds to the maximum value (piezo voltage characteristic S1), the "phase" of both charge information values ​​lags behind that of the charge information J1. Therefore, the control unit 52 determines that the maximum value is at the first voltage value VA1. The adjustment unit 523 maintains the piezoelectric voltage VA set in the piezoelectric element 122 at the first voltage value VA1. In this way, by determining the destination of the maximum value in accordance with both the rise and fall of the piezoelectric voltage VA, it is possible to suppress the piezoelectric voltage VA from moving away from the maximum value, making it easier to maintain the piezoelectric voltage VA at the maximum value.

[0055] Furthermore, in this embodiment, instead of acquiring the charge amount of the ink droplet ID, the charge setting unit 522 may identify and acquire a period in which the charge amount exceeds a predetermined value based on the electrical signal from the detection electrode 14, and use the correspondence between the application timing and the period in which the charge amount exceeds the predetermined value as charge information.

[0056] Figure 7 is a flowchart showing a piezoelectric voltage adjustment method according to one embodiment of the present invention.

[0057] The control unit 52 repeatedly calculates the detection time t for multiple stages of piezoelectric voltage VA via the charging electrode 13 and the detection electrode 14, identifies a first voltage value VA1 corresponding to the detection time t1 which is the maximum value of the detection time t, and sets the first voltage value VA1 as the piezoelectric voltage VA when the image printing process is performed on the piezoelectric element 122 (step S11).

[0058] The control unit 52 applies a voltage to the deflection electrode 15 to generate an electric field (step S12), and controls the application timing to periodically change so that a charging voltage is applied to the charging electrode 13, thereby generating charging information J1 that associates the application timing with the amount of charge, and storing it in the storage unit 56 (step S13).

[0059] The control unit 52 periodically or irregularly changes the piezoelectric voltage VA from a first voltage value VA1 to a voltage value VA1+ΔVA obtained by increasing the voltage by ΔVA, and controls the application timing to periodically change so that a charging voltage is applied to the charging electrode 13, thereby generating charging information (step S14).

[0060] The control unit 52 compares the charge information generated in step S15 with the charge information J1 and determines whether the "phase" of the generated charge information is ahead or behind the charge information J1 (step S15).

[0061] If the "phase" of the charge information generated in step S15 is ahead of the charge information J1 (YES in step S15), the control unit 52 determines that the voltage value VA1 + ΔVA is located on the maximum value side of the first voltage value VA1, and that the maximum value at detection time t has moved to the higher voltage side of the piezoelectric voltage VA. It then changes the piezoelectric voltage VA set in the piezoelectric element 122 to the voltage value VA1 + ΔVA to bring it closer to the voltage value VA2, which is the destination of the maximum value (step S16). The process proceeds to step S21.

[0062] On the other hand, if the "phase" of the generated charge information is delayed compared to the charge information J1 (NO in step S15), the control unit 52 changes the piezoelectric voltage VA to a voltage value VA1-ΔVA obtained by decreasing the first voltage value VA1 by ΔVA, and controls the application timing to periodically change so that a charging voltage is applied to the charging electrode 13, thereby generating charge information (step S17).

[0063] The control unit 52 compares the charge information generated in step S17 with the charge information J1 and determines whether the "phase" of the generated charge information is ahead or behind the charge information J1 (step S18).

[0064] If the "phase" of the charge information generated in step S17 is ahead of the charge information J1 (YES in step S18), the control unit 52 determines that the voltage value VA1-ΔVA is located on the maximum value side of the first voltage value VA1, and that the maximum value at detection time t has moved to the lower voltage side of the piezoelectric voltage VA. It then changes the piezoelectric voltage VA set in the piezoelectric element 122 to the voltage value VA1-ΔVA to bring it closer to the voltage value VA2, which is the destination of the maximum value (step S19). The process proceeds to step S21.

[0065] On the other hand, if the "phase" of the charge information generated in step S17 is delayed compared to the charge information J1 (NO in step S18), the control unit 52 determines that the maximum value is at the first voltage value VA1 and maintains the piezoelectric voltage VA set in the piezoelectric element 122 at the first voltage value VA1 (step S20). The process proceeds to step S21.

[0066] When the control unit 52 adjusts the piezoelectric voltage VA set on the piezoelectric element 122, it updates the charge information J1 with the charge information generated in step S15 or step S17 (step S21). Thereafter, steps S14 to S21 are repeated.

[0067] In the piezo voltage adjustment method, the order of steps S14 and S17 may be reversed. Also, either step S15 or step S18 may be performed, and step S20 may be omitted.

[0068] As described above, the printing apparatus of the present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention. Furthermore, the multiple components disclosed in the above embodiments can be modified as appropriate. For example, some components from all the components shown in one embodiment may be added to the components of another embodiment, or some components from all the components shown in one embodiment may be deleted from the embodiment.

[0069] Furthermore, the drawings schematically show each component in order to facilitate understanding of the invention, and the thickness, length, number, spacing, etc. of each component shown may differ from the actual dimensions due to the convenience of drawing creation. Also, the configuration of each component shown in the above embodiments is merely an example and is not particularly limiting, and it goes without saying that various modifications are possible without substantially departing from the effects of the present invention. [Explanation of symbols]

[0070] 13: Charged electrode 14: Detector electrode 15: Deflection electrode 52: Control Unit 122: Piezo element 521: Piezo voltage setting section 522: Charging setting unit 523: Adjustment section T :period VA: Piezoelectric voltage VA1: First voltage value t: Detection time t1: Maximum value of detection time

Claims

1. A printing apparatus that ejects ink onto an object and prints an image onto the object, The ink nozzle that ejects the aforementioned ink, A piezoelectric element that applies vibrations of a frequency corresponding to the applied piezoelectric voltage to the ink ejected from the ink nozzle, thereby separating the ink into a plurality of consecutive ink droplets, A charging electrode that charges the ink droplet by applying a charging voltage, A deflection electrode that generates an electric field in a predetermined direction and deflects the direction of movement of the ink droplet charged by the charging electrode, A detection electrode for detecting the amount of charge of the aforementioned ink droplet, A control unit that controls the ink nozzle, the piezoelectric element, the charging electrode, and the deflection electrode. Equipped with, The control unit, A piezoelectric voltage setting unit sets the piezoelectric voltage to a first voltage value corresponding to the maximum value of the detection time, based on the correlation between the detection time from when the charging voltage is applied to the charging electrode until the amount of charge of the ink droplet is detected by the detection electrode and the piezoelectric voltage. A charging setting unit that sets the timing for applying the charging voltage to the charging electrode, An adjustment unit that adjusts the piezoelectric voltage to a value other than the first voltage value based on the amount of charge detected by the sensing electrode. It has, In a state in which the electric field is generated by the deflection electrode, the adjustment unit, when the piezoelectric voltage is changed, determines whether the maximum value of the detection time has moved to the high voltage side or the low voltage side of the piezoelectric voltage based on the change in the amount of charge corresponding to the change in the application timing by the charge setting unit, and adjusts the piezoelectric voltage to approach the second voltage value which is the destination of the maximum value of the detection time.

2. The aforementioned piezoelectric voltage is an AC voltage. The printing apparatus according to claim 1, wherein the application period of the charging voltage is shorter than one cycle of the piezoelectric voltage.

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