Inkjet heads and inkjet recording devices

Abstract

To provide an inkjet head that can accelerate printing by shortening ejection pulse, and to provide an image formation device.SOLUTION: An inkjet head includes an actuator and a driver. The actuator expands or contracts a pressure chamber into which ink is filled. The driver applies an ejection pulse constituted of an expansion pulse with a width of 0.75 to 1.25 times the pressure propagation time of the pressure chamber, an idle period and a contraction pulse to the actuator.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to an inkjet head and an inkjet recording apparatus.

Background Art

[0002] Some inkjet heads apply a discharge pulse to an actuator that expands and contracts a pressure chamber, and discharge ink droplets from the pressure chamber onto a medium such as paper. Such an inkjet head discharges ink droplets continuously to perform printing. In order to increase the printing speed, a technique for shortening the discharge pulse is desired.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to solve the above problems, there is provided an inkjet head and an image forming apparatus capable of shortening a discharge pulse and increasing the printing speed.

Means for Solving the Problems

[0005] According to an embodiment, an inkjet head includes an actuator and a driver. The actuator expands or contracts a pressure chamber filled with ink. The driver applies a discharge pulse composed of an expansion pulse having a width of 0.75 times or more and less than 0.88 times the pressure propagation time of the pressure chamber, a rest period, and a contraction pulse, to the actuator. The distance between the center of the expansion pulse and the center of the contraction pulse is twice the pressure propagation time.

Brief Description of the Drawings

[0006] [Figure 1]Figure 1 is a block diagram showing an example configuration of an inkjet recording apparatus according to an embodiment. [Figure 2] Figure 2 is a perspective view of an inkjet head according to this embodiment. [Figure 3] Figure 3 is an exploded perspective view of an inkjet head according to this embodiment. [Figure 4] Figure 4 is a cross-sectional view of the FF line in Figure 2. [Figure 5] Figure 5 is a block diagram showing an example of the configuration of the control system of an inkjet recording apparatus according to an embodiment. [Figure 6] Figure 6 shows an example of the operation of an inkjet head according to the present invention. [Figure 7] Figure 7 shows an example of the operation of an inkjet head according to the embodiment. [Figure 8] Figure 8 shows an example of the operation of an inkjet head according to the embodiment. [Figure 9] Figure 9 shows an example of a discharge pulse applied to an actuator according to the embodiment. [Figure 10] Figure 10 is a table showing an example of the configuration of the discharge pulse according to the embodiment. [Figure 11] Figure 11 is a graph showing the relationship between the width of the extended pulse and the recommended voltage according to the embodiment. [Figure 12] Figure 12 is a graph showing the dispensing speed of each drop according to the embodiment. [Figure 13] Figure 13 is a graph showing the variation in the discharge speed of each drop according to the embodiment. [Figure 14] Figure 14 is a graph showing the relationship between the width of the extended pulse and the velocity difference of ink droplets between drops according to the embodiment. [Figure 15] Figure 15 shows the flight state of ink droplets according to this embodiment. [Modes for carrying out the invention]

[0007] The inkjet recording apparatus according to this embodiment will be described below with reference to the drawings. The inkjet recording device according to this embodiment forms an image on a medium such as paper using an inkjet head. The inkjet recording device ejects ink droplets from a pressure chamber in the inkjet head onto the medium, printing an image on the medium. Examples of inkjet recording devices include office inkjet recording devices, barcode inkjet recording devices, POS inkjet recording devices, industrial inkjet recording devices, and 3D inkjet recording devices. The medium on which the inkjet recording device forms an image is not limited to a specific configuration. The inkjet head in the printer according to this embodiment is an example of a liquid ejection head, and the ink is an example of a liquid.

[0008] Figure 1 is a schematic diagram showing an example of the configuration of an inkjet recording apparatus 1 according to an embodiment.

[0009] The inkjet recording device 1 forms an image on an image-forming medium S or the like using a recording material such as ink. The inkjet recording device 1 includes, as an example, a plurality of liquid ejection units 2, a head support mechanism 3 that movably supports the liquid ejection units 2, and a medium support mechanism 4 (support unit) that movably supports the image-forming medium S. The image-forming medium S is, for example, a sheet made of paper, cloth, or resin.

[0010] As shown in FIG. 1, a plurality of liquid ejection units 2 are supported by a head support mechanism 3 in a state of being arranged in parallel in a predetermined direction. The head support mechanism 3 is attached to an endless belt 3b hung on a roller 3a. The inkjet recording apparatus 1 can move the head support mechanism 3 in a main scanning direction A orthogonal to the conveyance direction of the image forming medium S by rotating the roller 3a. The liquid ejection unit 2 integrally includes an inkjet head 10 and a circulation device 20. The liquid ejection unit 2 performs a ejection operation of ejecting, for example, ink I as a liquid from the inkjet head 10. As an example, the inkjet recording apparatus 1 forms a desired image on the oppositely arranged image forming medium S by performing an ink ejection operation while reciprocating the head support mechanism 3 in the main scanning direction A, which is a scanning method. Alternatively, the inkjet recording apparatus 1 may be a single pass method in which an ink ejection operation is performed without moving the head support mechanism 3. In this case, the roller 3a and the endless belt 3b may not be provided. Also in this case, the head support mechanism 3 is fixed to, for example, the housing of the inkjet recording apparatus 1.

[0011] The plurality of liquid ejection units 2 eject, for example, four colors of ink corresponding to CMYK (cyan, magenta, yellow, and key (black)), that is, cyan ink, magenta ink, yellow ink, and black ink, respectively.

[0012] Hereinafter, the inkjet head 10 will be described based on FIGS. 2 to 4. As the inkjet head 10, a circulation type side shooter type inkjet head of a shared mode shared wall method is illustrated in each figure. Note that the inkjet head 10 may be other types of inkjet heads.

[0013] FIG. 2 is a perspective view showing an example of the configuration of the inkjet head 10. FIG. 3 is an exploded perspective view showing an example of the configuration of the inkjet head 10. FIG. 4 is a cross-sectional view taken along the line F-F of FIG. 2.

[0014] The inkjet head 10 is mounted on the inkjet recording apparatus 1 and is connected to an ink tank via a component such as a tube. Such an inkjet head 10 includes a head body 11, a unit section 12, and a pair of circuit boards 13. The inkjet head 10 is an example of a waveform generation device.

[0015] The head body 11 is a device for discharging ink. The head body 11 is attached to the unit section 12. The unit section 12 includes a manifold that forms a part of the path between the head body 11 and the ink tank and a member for attachment inside the inkjet recording apparatus 1. The pair of circuit boards 13 are respectively attached to the head body 11.

[0016] As shown in FIGS. 3 and 4, the head body 11 includes a base plate 15, a nozzle plate 16, a frame member 17, and a pair of drive elements 18. Inside the head body 11, as shown in FIG. 4, an ink chamber 19 to which ink is supplied is formed.

[0017] As shown in FIG. 3, the base plate 15 is formed in a rectangular plate shape from ceramics such as alumina, for example. The base plate 15 has a flat mounting surface 21. A plurality of supply holes 22 and a plurality of discharge holes 23 are open on the mounting surface 21 of the base plate 15.

[0018] The supply holes 22 are provided side by side in the longitudinal direction of the base plate 15 at the central portion of the base plate 15. The supply holes 22 communicate with an ink supply portion 12a of the manifold of the unit section 12. The supply holes 22 are connected to an ink tank in the circulation device 20 via the ink supply portion 12a. The ink in the ink tank is supplied to the ink chamber 19 through the ink supply portion and the supply holes 22.

[0019] The discharge holes 23 are arranged in two rows, flanking the supply holes 22. The discharge holes 23 communicate with the ink discharge section 12b of the manifold in the unit section 12. The discharge holes 23 are connected to the ink tank in the circulation device 20 via the ink discharge section 12b. The ink in the ink chamber 19 is recovered into the ink tank through the ink discharge section 12b and the discharge holes 23. In this way, the ink circulates between the ink tank and the ink chamber 19.

[0020] The nozzle plate 16 is formed from, for example, a rectangular film made of polyimide with a liquid-repellent surface. The nozzle plate 16 faces the mounting surface 21 of the base plate 15. Multiple nozzles 25 are provided on the nozzle plate 16. The multiple nozzles 25 are arranged in two rows along the longitudinal direction of the nozzle plate 16.

[0021] The frame member 17 is formed in a rectangular frame shape, for example, from a nickel alloy. The frame member 17 is interposed between the mounting surface 21 of the base plate 15 and the nozzle plate 16. The frame member 17 is bonded to the mounting surface 21 and the nozzle plate 16, respectively. That is, the nozzle plate 16 is attached to the base plate 15 via the frame member 17. As shown in Figure 4, the ink chamber 19 is formed surrounded by the base plate 15, the nozzle plate 16, and the frame member 17.

[0022] The driving element 18 is formed of two plate-shaped piezoelectric materials, for example, made of lead zirconate titanate (PZT). The two piezoelectric materials are bonded together so that their polarization directions are opposite to each other in the thickness direction.

[0023] As shown in Figure 3, the pair of drive elements 18 are bonded to the mounting surface 21 of the base plate 15. As shown in Figure 4, the pair of drive elements 18 are arranged parallel to each other in the ink chamber 19, corresponding to the two rows of nozzles 25. The drive elements 18 are formed in a trapezoidal cross-section. The tops of the drive elements 18 are bonded to the nozzle plate 16.

[0024] The drive element 18 is provided with a plurality of grooves 27. Each groove 27 extends in a direction intersecting the longitudinal direction of the drive element 18 and is aligned along the longitudinal direction of the drive element 18. The plurality of grooves 27 face the plurality of nozzles 25 of the nozzle plate 16. As shown in Figure 4, the drive element 18 of this embodiment has a plurality of pressure chambers 50 for filling with ink arranged in the grooves 27.

[0025] Each of the multiple grooves 27 is provided with an electrode 28. The electrode 28 is formed, for example, by photoresist etching of a nickel thin film. The electrode 28 covers the inner surface of the groove 27.

[0026] As shown in Figure 3, multiple wiring patterns 35 are provided extending from the mounting surface 21 of the base plate 15 to the drive element 18. These wiring patterns 35 are formed, for example, by photoresist etching of a nickel thin film.

[0027] The wiring pattern 35 extends from one side edge 21a and the other side edge 21b of the mounting surface 21, respectively. Note that the side edges 21a and 21b include not only the edges of the mounting surface 21 but also the surrounding area. Therefore, the wiring pattern 35 may be provided inside the edges of the mounting surface 21.

[0028] The following description will represent the wiring pattern 35 extending from one side end 21a. The basic configuration of the wiring pattern 35 at the other side end 21b is the same as that of the wiring pattern 35 at the side end 21a.

[0029] As shown in Figures 3 and 4, the wiring pattern 35 has a first portion 35a and a second portion 35b. The first portion 35a of the wiring pattern 35 is the portion that extends linearly from the side edge 21a of the mounting surface 21 toward the drive element 18. The first portion 35a extends parallel to each other. The second portion 35b of the wiring pattern 35 is the portion that straddles the end of the first portion 35a and the electrode 28. The second portion 35b is electrically connected to the electrode 28.

[0030] In a single driving element 18, some of the multiple electrodes 28 constitute a first electrode group 31. The other multiple electrodes 28 constitute a second electrode group 32.

[0031] The first electrode group 31 and the second electrode group 32 are separated by the longitudinal center of the driving element 18. The second electrode group 32 is adjacent to the first electrode group 31. The first and second electrode groups 31 and 32 each contain, for example, 159 electrodes 28.

[0032] As shown in Figure 2, each of the pair of circuit boards 13 has a board body 44 and a pair of film carrier packages (FCPs) 45. Note that FCPs are also called tape carrier packages (TCPs).

[0033] The main board 44 is a rigid printed circuit board formed in a rectangular shape. Various electronic components and connectors are mounted on the main board 44. In addition, a pair of FCPs 45 are attached to the main board 44.

[0034] Each pair of FCPs 45 has a flexible resin film 46 on which multiple wires are formed, and a head drive circuit 47 connected to the multiple wires. The film 46 is tape automated bonding (TAB). The head drive circuit 47 is an integrated circuit (IC) for applying voltage to the electrodes 28. The head drive circuit 47 is fixed to the film 46 by resin.

[0035] One end of the FCP 45 is thermocompressed to the first portion 35a of the wiring pattern 35 by an anisotropic conductive film (ACF) 48. This electrically connects the multiple wires of the FCP 45 to the wiring pattern 35.

[0036] When the FCP45 is connected to the wiring pattern 35, the head drive circuit 47 is electrically connected to the electrode 28 via the wiring of the FCP45. The head drive circuit 47 applies a voltage to the electrode 28 via the wiring of the film 46.

[0037] When the head drive circuit 47 applies a voltage to the electrode 28, the drive element 18 undergoes shear-mode deformation, thereby increasing or decreasing the volume of the pressure chamber 50 in which the electrode 28 is located. This changes the pressure of the ink in the pressure chamber 50, causing the ink to be ejected from the nozzle 25. In this way, the drive element 18 separating the pressure chamber 50 acts as an actuator for applying pressure vibrations inside the pressure chamber 50.

[0038] The circulation device 20 shown in Figure 1 is integrally connected to the upper part of the inkjet head 10 by connecting parts made of metal or other materials. The circulation device 20 has a predetermined circulation path configured to allow liquid to circulate through the ink tank and the inkjet head 10. The circulation device 20 has a pump for circulating the liquid. The liquid is supplied from the circulation device 20 to the inkjet head 10 through the ink supply unit by the action of the pump, passes through a predetermined flow path, and is sent from inside the inkjet head 10 to the circulation device 20 through the ink discharge unit.

[0039] Furthermore, the circulation device 20 supplies liquid to the circulation path from a cartridge, which serves as a replenishment tank and is located outside the circulation path.

[0040] The main circuit configuration of the inkjet recording device 1 will now be described. Figure 5 is a block diagram showing an example of the main circuit configuration of the inkjet recording device 1 according to this embodiment.

[0041] The inkjet recording device 1 includes a processor 101, a ROM 102, a RAM 103, a communication interface 104, a display unit 105, an operation unit 106, a head interface 107, a bus 108, and an inkjet head 10.

[0042] The processor 101 corresponds to the central part of the computer that performs the processing and control necessary for the operation of the inkjet recording device 1. Based on programs such as system software, application software, or firmware stored in the ROM 102, the processor 101 controls each part to realize various functions of the inkjet recording device 1. The processor 101 is, for example, a CPU (central processing unit), MPU (micro processing unit), SoC (system on a chip), DSP (digital signal processor), or GPU (graphics processing unit). Alternatively, the processor 101 is a combination of these.

[0043] ROM 102 is a non-volatile memory that corresponds to the main memory portion of a computer centered around processor 101, and is used exclusively for reading data. ROM 102 stores the program described above. Furthermore, ROM 102 stores data or various setting values ​​used by processor 101 in performing various processes.

[0044] RAM103 is the main memory portion of a computer centered around processor 101, and is used for reading and writing data. RAM103 is used as a so-called work area, where data temporarily used by processor 101 during various processes is stored.

[0045] The communication interface 104 is an interface for the inkjet recording device 1 to communicate with a host computer or the like via a network or communication cable.

[0046] The display unit 105 displays a screen for notifying the operator of the inkjet recording device 1 of various information. The display unit 105 is, for example, a liquid crystal display or an organic EL (electro-luminescence) display.

[0047] The operation unit 106 receives input from the operator of the inkjet recording device 1. The operation unit 106 can be, for example, a keyboard, keypad, touchpad, or mouse. Alternatively, the operation unit 106 can be a touchpad superimposed on the display panel of the display unit 105. In other words, the display panel of the touch panel can be used as the display unit 105, and the touchpad of the touch panel can be used as the operation unit 106.

[0048] The head interface 107 is provided for the processor 101 to communicate with the inkjet head 10. Under the control of the processor 101, the head interface 107 transmits gradation data and other information to the inkjet head 10.

[0049] Bus 108 includes a control bus, an address bus, and a data bus, and transmits signals exchanged between various parts of the inkjet recording device 1.

[0050] The inkjet head 10 is equipped with a head driver 100.

[0051] The head driver 100 is a drive circuit for operating the inkjet head 10. The head driver 100 consists of a head drive circuit 47, etc. The head driver 100 is, for example, a line driver. The head driver 100 stores waveform data WD.

[0052] The head driver 100 repeatedly generates a single drive signal based on waveform data WD. The head driver 100 then controls the number of times a droplet is ejected to each pixel on the image forming medium S, based on grayscale data. With each application of a single ejection pulse, one ink droplet (main droplet) is ejected from the nozzle 25. Therefore, the inkjet recording device 1 expresses shades of gray, for example, by determining how many ink droplets are ejected to each pixel. In other words, the more sets of ink are ejected for a single pixel, the darker the corresponding color becomes in that pixel.

[0053] The head driver 100 is an example of a waveform generation device. The head driver 100 also operates as a generation unit by generating drive signals.

[0054] For example, the head driver 100 is transferred to the administrator of the head driver 100 with the waveform data WD stored in it. Alternatively, the head driver 100 may be transferred to the administrator without the waveform data WD being stored in it. Furthermore, the head driver 100 may be transferred to the administrator with other waveform data stored in it. The waveform data WD may then be transferred separately to the administrator and written to the head driver 100 under the operation of the administrator or service technician. This transfer of the waveform data WD can be achieved, for example, by recording it on a removable storage medium such as a magnetic disk, magneto-optical disk, optical disk, or semiconductor memory, or by downloading it via a network.

[0055] When a drive signal is applied, the piezoelectric drive element 18 undergoes shear-mode deformation. This deformation changes the volume of the pressure chamber 50.

[0056] The pressure chamber 50 is considered to be in its normal state when the potential of the drive signal is zero. When the potential of the drive signal is positive, the pressure chamber 50 contracts, and its volume decreases compared to the normal state. Conversely, when the potential of the drive signal is negative, the pressure chamber 50 expands, and its volume increases compared to the normal state. The pressure of the ink inside the pressure chamber 50 changes in accordance with these changes in the volume of the pressure chamber 50. The inkjet head 10 ejects ink when an ejection pulse having a specific waveform is applied.

[0057] Next, we will describe an example of the state of the pressure chamber 50. The pressure chamber 50 changes to a standby state, a PULL state, or a PUSH state.

[0058] First, let's explain the standby state. Figure 6 is a diagram illustrating the standby state.

[0059] Here, we will explain using pressure chamber 50b, one of the pressure chambers 50, as an example. Pressure chamber 50b is formed between pressure chamber 50a and pressure chamber 50c. Pressure chamber 50b is also formed by drive elements 18a and 18b. Electrodes 28a to 28c are formed in pressure chambers 50a to 50c.

[0060] In standby mode, pressure chamber 50b is the default state. As shown in Figure 6, the head driver 100 sets the potential between the electrode 28b formed in pressure chamber 50b and the electrodes 28a and 28c formed in the adjacent pressure chambers 50a and 50c to a voltage of +V. In this state, neither the drive element 18a sandwiched between pressure chambers 50a and 50b nor the drive element 18b sandwiched between pressure chambers 50b and 50c experiences any distortion. Furthermore, the head driver 100 may have electrodes 28a to 28c set to GND potential.

[0061] Next, we will explain the PULL state. Figure 7 is a diagram illustrating the PULL state.

[0062] The PULL state is a state in which the pressure chamber 50b is expanded. As shown in Figure 7, the head driver 100 sets the electrode 28b of the pressure chamber 50b to potential GND and applies a voltage +V to the electrodes 28a and 28c of the pressure chambers 50a and 50c. In this state, an electric field of voltage V acts on each of the drive elements 18a and 18b in a direction perpendicular to the polarization direction of the drive element 18. Due to this action, each of the drive elements 18a and 18b deforms outward to expand the volume of the pressure chamber 50b.

[0063] Next, we will explain the PUSH state. Figure 8 is a diagram illustrating the PUSH state.

[0064] The PUSH state is when the pressure chamber 50b is contracted. As shown in Figure 8, the head driver 100 applies a voltage +V to the electrode 28b of the pressure chamber 50b, and sets the electrodes 28a and 28c of the pressure chambers 50a and 50c to GND potential. In this state, an electric field with voltage V acts on each of the drive elements 18a and 18b in the opposite direction to the drive voltage in the PULL state. Due to this action, each of the drive elements 18a and 18b deforms inward to contract the volume of the pressure chamber 50b.

[0065] When the volume of the pressure chamber 50b expands or contracts, pressure oscillations occur within the pressure chamber 50b. These pressure oscillations increase the pressure within the pressure chamber 50b, causing ink droplets to be ejected from the nozzle 25 that communicates with the pressure chamber 50b.

[0066] Thus, the drive elements 18a and 18b separating the pressure chambers 50a, 50b, and 50c act as actuators for applying pressure vibrations inside the pressure chamber 50b, with the drive elements 18a and 18b forming its walls. In other words, the pressure chamber 50 is expanded or contracted by the operation of the drive element 18.

[0067] Furthermore, each pressure chamber 50 shares a drive element 18 (partition) with the adjacent pressure chamber 50. For this reason, the head driver 100 cannot drive each pressure chamber 50 individually. The head driver 100 drives each pressure chamber 50 by dividing it into (n+1) groups, with n (where n is an integer of 2 or more) groups apart. In this embodiment, we illustrate the case where the head driver 100 drives each pressure chamber 50 by dividing it into three groups, with two groups apart, a so-called three-part drive. Note that the three-part drive is merely an example, and it may also be a four-part drive or a five-part drive, etc.

[0068] Next, we will explain the discharge pulse that the head driver 100 applies to the drive element 18. The head driver 100 applies an ejection pulse to the drive element 18 to eject a predetermined amount of ink droplets from the nozzle 25.

[0069] Figure 9 shows the waveform of the discharge pulse applied by the head driver 100 to the drive element 18. In Figure 9, the horizontal axis represents elapsed time, and the vertical axis represents the drive voltage. A drive voltage higher than a reference voltage (for example, 0V) causes the volume of the pressure chamber 50 to contract. Conversely, a drive voltage lower than the reference voltage causes the volume of the pressure chamber 50 to expand.

[0070] As shown in Figure 9, the head driver 100 may apply an auxiliary pulse before applying the ejection pulse to the drive element 18. The auxiliary pulse is applied prior to the ejection pulse to promote pressure oscillation within the pressure chamber 50. Here, the auxiliary pulse causes the pressure chamber 50 to contract from a standby state and then transition back to the standby state. The auxiliary pulse is a pulse that does not eject ink.

[0071] For example, the head driver 100 applies an auxiliary pulse when ejecting only one ink droplet in multi-drop drive mode.

[0072] As shown in Figure 9, the ejection pulse consists of an expansion pulse, a pause period, and a contraction pulse. The ejection pulse is the pulse that ejects an ink droplet and fits within one drop period (DC).

[0073] First, the head driver 100 applies an extended pulse to the drive element 18. The width of the extended pulse is D. The extended pulse is a pulse that applies a predetermined drive voltage for a predetermined time (D).

[0074] The extended pulse expands the volume of the pressure chamber 50 formed by the drive element 18. In other words, the head driver transitions the pressure chamber 50 from a standby state to a PULL state. When the pressure chamber 50 enters the PULL state, the pressure in the pressure chamber 50 decreases. When the pressure in the pressure chamber 50 decreases, ink is supplied to the pressure chamber 50 from the common ink chamber.

[0075] The head driver 100 applies an extended pulse and then pauses. The width of the pause is R. That is, the head driver 100 transitions the pressure chamber 50 from PULL to standby.

[0076] When the rest period has elapsed, the head driver 100 applies a contraction pulse to the drive element 18. The width of the contraction pulse is P. The contraction pulse is a pulse that applies a predetermined drive voltage for a predetermined time (P). The contraction pulse causes the volume of the pressure chamber 50 formed by the drive element 18 to contract.

[0077] In other words, the head driver 100 transitions the pressure chamber 50 from the standby state to the PUSH state. After a predetermined time (P) has elapsed, the head driver 100 transitions the pressure chamber 50 from the PUSH state to the standby state.

[0078] As described above, the head driver 100 ejects ink from the pressure chamber 50 by applying ejection pulses to the drive element 18.

[0079] Here, the contraction pulse width P is 0.9 μs.

[0080] Furthermore, the difference between the center of the expansion pulse and the center of the contraction pulse is 2 UL. UL is the pressure propagation time, which is the time it takes for the pressure wave to propagate from the rear end to the front end of the pressure chamber 50. That is, R, which is the width of the pause period, is calculated by the following formula.

[0081] R = 2UL - D / 2 - P / 2 (1) Next, we will explain D, which is the width of the extended pulse. Here, the head driver 100 ejects ink droplets by setting several D values.

[0082] Figure 10 shows the discharge pulses that the head driver 100 applies to the drive element 18. As shown in Figure 10, the head driver 100 applies five discharge pulses to the drive element 18, each with a different D value.

[0083] Figure 10 shows the correspondence between "UL", "D", "R", "P", "DC", "drop", "F", "CT", and "CD".

[0084] As mentioned earlier, "UL" represents the pressure propagation time. Here, "UL" is 1.64 μs.

[0085] "D" indicates the width of the extended pulse. Here, "D" is one of the following: 2.04 μs (UL + 0.4 μs, 1.25 times UL), 1.84 μs (UL + 0.2 μs), 1.64 μs (UL), 1.44 μs (UL - 0.2 μs), and 1.24 μs (UL - 0.4 μs, 0.75 times UL).

[0086] "R" indicates the length of the pause period. "R" is calculated by formula (1).

[0087] "P" indicates the width of the contraction pulse. As mentioned above, "P" is 0.9 μs.

[0088] "DC" represents the drop cycle. "DC" decreases as "D" becomes smaller.

[0089] "drop" is the maximum number of ink droplets in a multi-drop drive. Here, "drop" is 7.

[0090] "F" represents the driving frequency. In this case, "F" is 8.71 kHz.

[0091] "CT" is the cycle time, which indicates the time it takes for the three divided channels to sequentially perform multidrop driving. In this case, "CT" is 114.811 μs.

[0092] "CD" is the cycle delay, which indicates the time between output pulses. "CD" increases as "DC" decreases.

[0093] Next, we will explain D and the volume of the ink droplets that are ejected. Figure 11 is a graph showing the relationship between D and the volume of the ejected ink droplet. In Figure 11, the horizontal axis shows the difference between UL and D (the value obtained by subtracting UL from D, the amplitude). The vertical axis shows the voltage of the extended pulse (recommended voltage) adjusted so that the volume of the ink droplet is a predetermined value.

[0094] Here, the recommended voltage is the voltage of the extended pulse that results in a volume of 28 pL for seven ink droplets.

[0095] The vertical axis also shows the ratio to the recommended voltage (reference recommended voltage) when the amplitude is "0.2 μs" or "0.4 μs".

[0096] As shown in Figure 11, the smaller the amplitude (i.e., the smaller D), the higher the recommended voltage. When the amplitude is "-0.4μs" (i.e., D is UL-0.4μs), the recommended voltage increases by about 6 percent from the standard recommended voltage.

[0097] Next, I will explain the ink droplet ejection speed. Figure 12 is a graph showing the ink droplet ejection speed. In the example shown in Figure 12, the ejection speed is when the head driver 100 ejects seven ink droplets sequentially in each segment (double drive). In Figure 12, the horizontal axis represents the amplitude. The vertical axis represents the ejection speed of each drop. Here, the vertical axis represents the average ejection speed of each drop in multiple double drives.

[0098] Graph 201 shows the dispensing rate for the first drop. Graph 202 shows the dispensing rate for the second drop. Graph 203 shows the dispensing rate for the third drop. Graph 204 shows the dispensing rate for the fourth drop. Graph 205 shows the dispensing rate for the fifth drop. Graph 206 shows the dispensing rate for the sixth drop. Graph 207 shows the dispensing rate for the seventh drop.

[0099] As shown in Figure 12, the discharge rate increases as the amplitude changes from "0.4 μs" to "-0.2 μs". In other words, the discharge rate decreases as the amplitude changes from "-0.2 μs" to "0.4 μs". Also, when the amplitude is "-0.4 μs", the discharge rate is lower than when the amplitude is "-0.2 μs". However, the discharge rate does not decrease drastically and does not cause any problems in use.

[0100] Next, we will explain the variation in the discharge rate of each drop. Figure 13 is a graph showing the variation (σ) in the discharge speed of each drop. In the example shown in Figure 13, as mentioned above, it shows the variation in discharge speed when the head driver 100 performs multiple double-drive cycles. In Figure 13, the horizontal axis represents the amplitude of the variation, and the vertical axis represents the variation in discharge speed of each drop.

[0101] Graph 301 shows the variation in dispensing rate for the first drop. Graph 302 shows the variation in dispensing rate for the second drop. Graph 303 shows the variation in dispensing rate for the third drop. Graph 304 shows the variation in dispensing rate for the fourth drop. Graph 305 shows the variation in dispensing rate for the fifth drop. Graph 306 shows the variation in dispensing rate for the sixth drop. Graph 307 shows the variation in dispensing rate for the seventh drop.

[0102] As shown in Figure 13, the variation in the discharge rate of the first drop is minimized when the amplitude is "-0.4 μs". Furthermore, the variation in the discharge rate of the second to sixth drops is minimized when the amplitude is "0 μs" or "0.2 μs".

[0103] Next, we will explain the difference in dispensing speed between drops. Figure 14 is a graph showing the difference in dispensing velocity between drops. In Figure 14, the horizontal axis represents the amplitude of the difference, and the vertical axis represents the maximum value (velocity difference) within the difference in dispensing velocity between drops.

[0104] Graph 401 shows the speed difference between drops at each amplitude. As Graph 401 shows, the speed difference increases as the amplitude decreases.

[0105] Next, I will explain the flight characteristics of ink droplets. Figure 15 is a photograph illustrating the flight state of ink droplets. The example shown in Figure 15 illustrates how the head driver 100 ejects ink droplets from seven channels. Here, the seven channels are referred to as channels No. 1 through 7. Channels No. 1, 4, and 7 constitute the first division. Channels No. 2 and 5 constitute the second division. Channels No. 3 and 6 constitute the third division.

[0106] In Figure 15, an inkjet head 10 is installed at the left edge of each photograph. Channels No. 1 to 7 are formed from top to bottom. Ink droplets are ejected from the left edge to the right edge of each photograph.

[0107] Figure 15 shows the ink droplet flight state for D=UL-0.4μs, D=UL-0.2μs, D=UL, D=UL+0.2μs, and D=UL+0.4μs. In other words, Figure 15 shows the ink droplet flight state when D is set from 0.75UL to 1.25UL.

[0108] As shown in Figure 15, in each photograph, ink droplets are ejected simultaneously from the first division (channels No. 1, 4, and 7). In addition, ink droplets are ejected simultaneously from the second division (channels No. 2 and 5) at a different timing than when the first division ejects ink droplets. Furthermore, ink droplets are ejected simultaneously from the third division (channels No. 3 and 6) at a different timing than when the first and second divisions eject ink droplets.

[0109] As shown in Figure 15, there is no difference in the ink droplet flight state in any of the D locations. Therefore, there is no problem with the ink droplet flight state in any of the D locations.

[0110] Furthermore, the expansion pulse may have a shape in which the voltage increases or decreases in steps. Similarly, the contraction pulse may have a shape in which the voltage increases or decreases in steps. Furthermore, the contraction pulse width P does not necessarily have to be 0.9 μs. The value of P is not limited to a specific value.

[0111] The inkjet head configured as described above ejects ink droplets by applying ejection pulses, including extended pulses with a width of 0.75 UL to 1.25 UL, to the drive element. The ink droplets ejected by these extended pulses can be printed properly without any problems in their flight state. As a result, the inkjet head can print at high speed by reducing the width of the extended pulses.

[0112] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. The invention described in the original claims of this application is listed below. [1] An actuator that expands or contracts the pressure chamber into which the ink is filled, A driver that applies a discharge pulse to the actuator, comprising an expansion pulse having a width of 0.75 to 1.25 times the pressure propagation time in the pressure chamber, a pause period, and a contraction pulse. An inkjet head equipped with this feature. [2] The distance between the center of the expansion pulse and the center of the contraction pulse is twice the pressure propagation time. [1] The inkjet head described above. [3] The pressure chamber is divided into multiple groups, The driver applies the discharge pulse to the actuator for each group. The inkjet head described in [1] or [2]. [4] The width of the contraction pulse is 0.9 μs. An inkjet head as described in any one of items [1] through [3]. [5] An inkjet recording device that ejects ink droplets onto a medium, A support part that supports the medium, An inkjet head as described in any one of items [1] through [4], An inkjet recording device equipped with the following features. [Explanation of Symbols]

[0113] 1... Inkjet recording device, 2... Liquid ejection unit, 3... Head support mechanism, 3a... Roller, 3b... Endless belt, 4... Media support mechanism, 10... Inkjet head, 11... Head body, 12... Unit part, 12a... Ink supply unit, 12b... Ink discharge unit, 13... Circuit board, 15... Base plate, 16... Nozzle plate, 17... Frame member, 18... Drive element, 18a... Drive element, 18b... Drive element, 19... Ink chamber, 20... Circulation device, 21... Mounting surface, 21a... Side end, 21b... Side end, 22... Supply hole, 23... Discharge hole, 25... Nozzle, 27... Groove, 28... Electrode, 28a... Electrode, 28b... Electrode, 28c... Electrode, 31... First electrode group, 32... Second electrode group, 35... Wiring pattern, 35a... First part, 35b... Second Part, 44...Main board body, 45...Film carrier package (FCP), 46...Film, 47...Head drive circuit, 48...Anisotropic conductive film (ACF), 50...Pressure chamber, 50a...Pressure chamber, 50b...Pressure chamber, 50c...Pressure chamber, 100...Head driver, 101...Processor, 102...ROM, 103...RAM, 104...Communication interface, 105...Display unit, 106...Operation unit, 107...Head interface, 108...Bus, 201...Graph, 202...Graph, 203...Graph, 204...Graph, 205...Graph, 206...Graph, 207...Graph, 301...Graph, 302...Graph, 303...Graph, 304...Graph, 305...Graph, 306...Graph, 307...Graph, 401...Graph.

Claims

1. An actuator that expands or contracts the pressure chamber into which the ink is filled, A driver that applies a discharge pulse to the actuator, comprising an expansion pulse having a width of 0.75 times or more and less than 0.88 times the pressure propagation time in the pressure chamber, a pause period, and a contraction pulse. Equipped with, The distance between the center of the expansion pulse and the center of the contraction pulse is twice the pressure propagation time. Inkjet head.

2. The pressure chamber is divided into multiple groups, The driver applies the discharge pulse to the actuator for each group. The inkjet head according to claim 1.

3. The width of the contraction pulse is 0.9 μs. The inkjet head according to claim 1 or 2.

4. An inkjet recording device that ejects ink droplets onto a medium, A support part that supports the medium, An inkjet head according to any one of claims 1 to 3, An inkjet recording device equipped with the following features.

Images