Image forming apparatus, meniscus position adjustment method, and program

Abstract

To provide an image forming apparatus, a meniscus position adjusting method, and a program capable of improving ejection stability and suppressing reduction in productivity.SOLUTION: The image forming apparatus includes: an inkjet head that applies a drive waveform to a piezoelectric element to eject ink droplets; and a control unit that adjusts a meniscus position of a nozzle that ejects ink droplets. When a first drive waveform is a multi-waveform including multiple drive pulses, the control unit applies an adjustment waveform before a second drive waveform that is applied after the first drive waveform, for adjusting the meniscus position of the nozzle that ejects ink droplets by applying the first drive waveform.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus, a meniscus position adjusting method, and a program. [Background technology]

[0002] Conventionally, there is known an inkjet type image forming apparatus (hereinafter, appropriately referred to as "inkjet image forming apparatus") that ejects ink onto a recording medium such as paper to form an image on the recording medium. In an inkjet image forming apparatus, when a voltage is applied to an inkjet head having nozzles that eject ink droplets to eject ink droplets from the nozzles, meniscus vibration, which is a temporal interference caused by a previous ejection, occurs as reverberation. If the reverberation is large, the ejection of ink from the inkjet head may become unstable, or the ink droplet speed may fluctuate.

[0003] For this reason, recently, various techniques have been proposed to ensure stable ejection of ink. For example, Patent Document 1 discloses an image forming device that, when ejecting ink droplets from an ejection head using a drive signal including a plurality of drive pulses, sets the length between drive pulses to a length at which reverberation attenuates and settles. By setting the length between drive pulses in this manner, ejection stability of ink droplets ejected from the ejection head can be improved, and deterioration of the quality of the formed image can be suppressed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6534412 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the image forming apparatus described in Patent Document 1, the time between drive pulses is increased, so the drive signal is longer overall. When the drive signal is longer, the time to form dots on the recording medium is correspondingly longer. In other words, there is a problem in that the productivity of the image forming apparatus is reduced.

[0006] The present disclosure has been made in consideration of the problems in the above-mentioned conventional technology, and aims to provide an image forming apparatus, a meniscus position adjustment method, and a program that can improve ejection stability and suppress a decline in productivity. [Means for solving the problem]

[0007] The image forming apparatus according to the present disclosure includes: an inkjet head that applies a drive waveform to a piezoelectric element to eject ink droplets; A control unit that adjusts a meniscus position of a nozzle that ejects the ink droplets; Equipped with The control unit is When the first drive waveform is a multi-waveform including multiple drive pulses, an adjustment waveform for adjusting the meniscus position of the nozzle that ejects the ink droplets by applying the first drive waveform is applied before the second drive waveform that is applied after the first drive waveform.

[0008] Further, the meniscus position adjustment method according to the present disclosure includes the steps of: 1. A meniscus position adjustment method for an image forming apparatus including an inkjet head that applies a drive waveform to a piezoelectric element to eject ink droplets, and a control unit that adjusts a meniscus position of a nozzle that ejects the ink droplets, comprising: When the first drive waveform is a multi-waveform including multiple drive pulses, an adjustment waveform for adjusting the meniscus position of the nozzle that ejects the ink droplets by applying the first drive waveform is applied before the second drive waveform that is applied after the first drive waveform.

[0009] Furthermore, the program according to the present disclosure includes: The above meniscus position adjustment method is executed by a computer. Effect of the Invention

[0010] According to the present disclosure, it is possible to improve ejection stability and suppress a decrease in productivity. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of an inkjet printer according to this embodiment. [Diagram 2] FIG. 2 is a block diagram showing the main components of a control system of the inkjet printer. [Diagram 3] FIG. 3 is a functional block diagram illustrating an example of the configuration of the control unit in FIG. [Figure 4] FIG. 4 is a schematic diagram for explaining an example of a single waveform. [Diagram 5] FIG. 5 is a schematic diagram for explaining an example of a multi-waveform. [Figure 6] FIG. 6 is a schematic diagram for explaining an example of a meniscus adjustment waveform. [Figure 7] FIG. 7 is a schematic diagram showing a first example of successively applied drive waveforms. [Figure 8] FIG. 8 is a schematic diagram showing a second example of successively applied drive waveforms. [Figure 9] FIG. 9 is a schematic diagram showing a third example of successively applied drive waveforms. [Figure 10] FIG. 10 is a schematic diagram showing a fourth example of successively applied drive waveforms. [Figure 11] FIG. 11 is a schematic diagram showing an example of a driving waveform when a meniscus adjustment waveform is applied. [Figure 12] FIG. 12 is a schematic diagram showing another example of a driving waveform when a meniscus adjustment waveform is applied. [Figure 13] FIG. 13 is a schematic diagram showing an example of the relationship between the time interval and the voltage ratio of the meniscus adjustment waveform. [Figure 14] FIG. 14 is a flowchart showing an example of the flow of the meniscus position adjustment process performed by the inkjet printer according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the present disclosure. In addition, in each drawing, the same reference numerals are used to denote the same or equivalent parts, and this is common throughout the entire specification.

[0013] An embodiment of the present disclosure will be described with reference to the drawings. An image forming apparatus according to the present embodiment is, for example, an inkjet printer, which forms an image by ejecting ink droplets onto a recording medium such as paper. In the following, an inkjet printer, which is an example of an image forming apparatus, will be described as an example.

[0014] [Configuration of the inkjet printer 100] Fig. 1 is a schematic diagram showing an example of the configuration of an inkjet printer 100 according to this embodiment. Fig. 2 is a block diagram showing the main parts of a control system of the inkjet printer 100. As shown in Figs. 1 and 2, the inkjet printer 100 includes a transport section 10, a supply section 20, a discharge section 30, an ink supply section 40, an image forming section 50, an operation display section 70, an input / output interface (I / F) 80, and a control section 90.

[0015] The transport section 10 has a plurality of members related to transport, such as a transport belt 11, a driving roller 12, and a driven roller 13. The transport section 10 transports the recording medium M by the transport operation of the plurality of members, such as the transport belt 11. Specifically, in the transport section 10, the transport belt 11 is stretched across the driving roller 12 and the driven roller 13, and is driven by driving the driving roller 12 to rotate. As a result, the recording medium M supplied from the supply section 20 is transported to the image forming section 50 while being placed on the transport surface 11a of the transport belt 11, and after an image is formed (printed) in the image forming section 50, it is transported to the discharge section 30.

[0016] The recording medium M may be any of various media capable of fixing ink ejected from an inkjet head 55 (described later). The recording medium M may be, for example, a sheet-like medium such as paper, cloth (woven fabric), or resin. Note that the recording medium M is not limited to a sheet-like medium, and may be a roll-like medium such as paper, cloth, or resin.

[0017] Further, while the conveying unit 10 is illustrated here as an example in which the conveying belt 11 conveys the recording medium M, the conveying unit 10 is not limited to the conveying belt 11 and may be configured to convey the recording medium M by a drum or roller.

[0018] The supply section 20 has a supply stacking section 21 and a supply conveying section 22. The supply stacking section 21 stacks and stores a plurality of recording media M. The supply conveying section 22 conveys and supplies the recording media M from the supply stacking section 21 to the conveying section 10. The supply stacking section 21 is configured to be able to rise and fall, and when the topmost recording medium M is conveyed to the conveying section 10 by the supply conveying section 22, the supply stacking section 21 rises so that the recording medium M that has become the topmost after the conveying can be conveyed to the supply conveying section 22.

[0019] The discharge section 30 has a discharge stacking section 31 and a discharge conveying section 32. The discharge stacking section 31 stacks and stores a plurality of recording media M. The discharge conveying section 32 conveys the recording media M discharged from the conveying section 10 to the discharge stacking section 31. The discharge stacking section 31 is configured to be capable of rising and lowering, and when the recording media M is conveyed from the discharge conveying section 32 to the discharge stacking section 31, the discharge stacking section 31 descends.

[0020] The supply conveying section 22 and the discharge conveying section 32 each have, for example, a plurality of rollers, and convey the recording medium M by rotating the rollers. The supply conveying section 22 and the discharge conveying section 32 are not limited to rollers, and may be configured with a belt, or may be configured with a combination of rollers and belts.

[0021] When a roll-shaped medium is used as the recording medium M, an unwinding roller on which the roll-shaped medium is stored in a wound state is used instead of the supply stacking unit 21. Also, a take-up roller that takes up the roll-shaped medium is used instead of the discharge stacking unit 31. The roll-shaped medium is transported to the transport unit 10 by rotating the unwinding roller, and is taken up by the take-up roller by rotating the take-up roller.

[0022] A post-processing device may be provided between the conveying section 10 and the discharging section 30 to perform post-processing on the recording medium M on which an image is formed by the image forming section 50. One example of the post-processing device is a fixing device that fixes ink to the recording medium M. When, for example, an ultraviolet-curable ink is used as the ink, a fixing device is used that irradiates the recording medium M with ultraviolet rays to fix the ink to the recording medium M. When, for example, an aqueous ink or a solvent ink is used as the ink, a fixing device is used that fixes the ink to the recording medium M by a method such as drying. Furthermore, a device other than a fixing device, such as a cutting device that cuts the recording medium M to a desired length, may be used as the post-processing device.

[0023] The ink supply unit 40 is connected to the image forming unit 50 via a flow path 42, which is an ink supply path, and is a device that supplies ink to a first sub-tank 52a of the image forming unit 50, which will be described later. The ink supply unit 40 has a main tank 41 and components (not shown) related to ink supply (e.g., a pump and a valve, etc.). The main tank 41 stores ink to be supplied to the first sub-tank 52a at room temperature. The ink supply unit 40 supplies ink from the main tank 41 to the first sub-tank 52a via the flow path 42 using a pump (not shown) or the like.

[0024] The image forming unit 50 has a carriage 51, a first sub-tank 52a, a second sub-tank 52b, flow paths 53a, 53b, and 53c, a head driving unit 54, and an inkjet head (hereinafter, simply referred to as a "head") 55, and the like.

[0025] 1, for the sake of simplicity, the ink supply units 40 and image forming units 50 for one color are shown, but the ink supply units 40 and image forming units 50 are arranged according to the number of colors to be used. For example, when four colors, yellow (Y), magenta (M), cyan (C) and black (K), are used, ink supply units 40 and image forming units 50 for four colors are arranged, and the image forming units 50 are arranged so as to be lined up at a predetermined interval along the transport direction T.

[0026] Although not shown, the second sub-tank 52b and the inkjet head 55 are connected in a tree-like configuration to the downstream side of the first sub-tank 52a. However, in FIG. 1, only one of each is shown for the sake of simplicity.

[0027] The carriage 51 is a housing that holds inside the first sub-tank 52a, the second sub-tank 52b, the flow paths 53a, 53b and 53c, the head drive unit 54, the head 55, and devices and members necessary for image formation.

[0028] The first sub-tank 52a is connected to the downstream side of the main tank 41. The first sub-tank 52a stores ink supplied from the main tank 41 in the carriage 51. The ink in the sub-tank 52 is supplied to the second sub-tank 52b via a flow path 53a, which is an ink supply path, by using a pump (not shown) or the like in the carriage 51.

[0029] Although not shown, the second sub-tank 52b is connected in plurality to the downstream side of the first sub-tank 52a. The second sub-tank 52b stores the ink supplied from the first sub-tank 52a in the carriage 51. The ink in the second sub-tank 52b is supplied to a manifold 56 of the head 55, which will be described later, through a flow path 53b, which is an ink supply path, by using a pump (not shown) or the like in the carriage 51. The ink supplied to the manifold 56 is returned to the second sub-tank 52b through a flow path 53c. In other words, the flow paths 53b and 53c form a circulation flow path that circulates the ink between the second sub-tank 52b and the manifold 56.

[0030] Based on the control of a control unit 90 (described later), the head driving unit 54 outputs a driving voltage corresponding to the image data of the image to be formed to a piezoelectric element 58 of a head 55 (described later). The driving voltage from the head driving unit 54 drives the piezoelectric element 58, causing it to eject an amount of ink corresponding to the image data from a nozzle 59 of the head 55 (described later).

[0031] A plurality of heads 55 are connected to the downstream side of each of the plurality of second sub-tanks 52b. In other words, although not shown, a plurality of second sub-tanks 52b and heads 55 are connected in a tree shape to the downstream side of the first sub-tank 52a.

[0032] The head 55 has a manifold 56, pressure chambers 57, piezoelectric elements 58, and nozzles 59. The head 55 has a plurality of nozzles 59, and the pressure chambers 57 and piezoelectric elements 58 are provided in accordance with the number of nozzles 59.

[0033] The manifold 56 communicates with a plurality of pressure chambers 57, and ink supplied to the manifold 56 is supplied to the pressure chambers 57. The pressure chambers 57 are spaces in which the ink to be ejected is stored, and have piezoelectric elements 58 provided on their walls. One end of the nozzle 59 communicates with the pressure chambers 57, and the other end is an open end.

[0034] A driving voltage is applied to the piezoelectric element 58 from the head driving unit 54. When the driving voltage from the head driving unit 54 is applied to the piezoelectric element 58, the piezoelectric element 58 deforms in response to the applied driving voltage, and the pressure chamber 57 deforms. Then, due to the deformation of the pressure chamber 57, the pressure on the ink in the pressure chamber 57 that is supplied to the nozzle 59 changes.

[0035] Therefore, when a drive voltage from the head drive unit 54 is applied to the piezoelectric element 58, the piezoelectric element 58 and the pressure chamber 57 are deformed, causing a pressure change in the ink inside the pressure chamber 57. As a result, the ink inside the pressure chamber 57 is ejected from the nozzle 59. In this manner, droplets of ink are ejected from the nozzle 59, forming an image on the recording medium M being transported.

[0036] In the carriage 51, the heads 55 may be configured to be a single-pass (one-pass) type that forms an image in one scan, or a scan (multi-pass) type that forms an image in multiple scans. In the case of the single-pass type, the carriage 51 has heads 55 arranged in the width direction of the recording medium M (direction perpendicular to the transport direction T of the recording medium M) in the number equal to the image formation width.

[0037] Although not shown, the inkjet printer 100 also includes a maintenance unit that performs maintenance such as cleaning of the head 55 .

[0038] The operation display unit 70 is, for example, a flat panel display such as a liquid crystal display or an organic EL (Electro Luminescence) display with a touch panel. The operation display unit 70 displays an operation menu for the user, information related to image data, and various states of the inkjet printer 100. The operation display unit 70 also includes a plurality of keys and accepts various input operations from the user.

[0039] The input / output I / F 80 mediates the transmission and reception of data between the external device 200 and the control unit 90. The input / output I / F 80 is configured, for example, by any one of various serial interfaces, various parallel interfaces, or a combination of these.

[0040] The external device 200 is, for example, a personal computer or a facsimile machine, and supplies print jobs, image data, and the like to the control unit 90 via the input / output I / F 80 .

[0041] The control unit 90 includes a CPU (Central Processing Unit) 91, a RAM (Random Access Memory) 92, a ROM (Read Only Memory) 93, and a storage unit 94.

[0042] The CPU 91 reads out various control programs and setting data stored in the ROM 93, stores them in the RAM 92, and executes the programs to perform various arithmetic processing. For example, the control unit 90 generates a drive signal for an image to be formed based on image data received from the input / output I / F 80, and outputs the drive signal to the head 55.

[0043] The RAM 92 provides a working memory space for the CPU 91 and stores temporary data. The RAM 92 may include a non-volatile memory.

[0044] The ROM 93 stores various control programs and setting data executed by the CPU 91. Note that, instead of the ROM 93, a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used.

[0045] The storage unit 94 stores print jobs and image data related to the print jobs input from the external device 200 via the input / output I / F 80. As the storage unit 94, for example, a non-volatile semiconductor memory (so-called flash memory) or an HDD (Hard Disk Drive) is used, and a DRAM (Dynamic Random Access Memory) or the like may also be used in combination.

[0046] The control unit 90 is connected to the transport unit 10, supply unit 20, discharge unit 30, ink supply unit 40, image forming unit 50, operation display unit 70, input / output I / F 80, etc. The control unit 90 controls the overall operation of the inkjet printer 100. The transport unit 10, supply unit 20, discharge unit 30, ink supply unit 40, image forming unit 50, operation display unit 70, input / output I / F 80, etc. are controlled by the control unit 90 to execute predetermined processes.

[0047] In this embodiment, the control unit 90 performs a meniscus position adjustment process to adjust the meniscus position when ink droplets are ejected from the head 55. The meniscus position adjustment process will be described in detail later.

[0048] Fig. 3 is a functional block diagram showing an example of the configuration of the control unit 90 in Fig. 2. As shown in Fig. 3, the control unit 90 has an image data acquisition unit 95, a drive waveform generation unit 96, a determination unit 97, a drive waveform setting unit 98, and a storage unit 94. Note that Fig. 3 shows only functions related to the meniscus position adjustment process according to this embodiment.

[0049] The image data acquisition unit 95 acquires image data for the formed image. In this embodiment, the image data acquisition unit 95 acquires the image data from the external device 200 via the input / output I / F 80 connected to the control unit 90.

[0050] The drive waveform generating unit 96 generates a drive waveform for forming an image based on the image data acquired by the image data acquiring unit 95. The drive waveform is a waveform of a drive voltage applied to the piezoelectric element 58 in order to drive the piezoelectric element 58.

[0051] The determination unit 97 determines whether or not a meniscus adjustment waveform is necessary based on the drive waveform generated by the drive waveform generation unit 96. Specifically, the determination unit 97 determines that a meniscus adjustment waveform is necessary when a preceding drive waveform in successive drive waveforms is a multi-waveform.

[0052] The meniscus adjustment waveform is a drive waveform for adjusting the meniscus position that has shifted from the appropriate position due to application of a drive voltage having a drive waveform that precedes the meniscus adjustment waveform in time to an appropriate position. In other words, the meniscus adjustment waveform is a drive waveform for adjusting the meniscus position in the nozzle 59 that ejects the ink droplet.

[0053] The drive waveform setting unit 98 sets a drive waveform so as to add a meniscus adjustment waveform when the determination unit 97 determines that a meniscus adjustment waveform is necessary. The drive waveform setting unit 98 supplies the set drive waveform to the head driving unit 54 of the image forming unit 50.

[0054] The storage unit 94 stores various data used by the control unit 90. For example, the storage unit 94 stores image data acquired by the image data acquisition unit 95.

[0055] [Operation of the inkjet printer 100] The operation of the inkjet printer 100, which is an image forming apparatus according to this embodiment and has the above configuration, will be described.

[0056] In the inkjet printer 100, when an image is formed on a recording medium M, the recording medium M is supplied from the supply unit 20 to the conveying unit 10. The image forming unit 50 ejects ink onto the recording medium M conveyed by the conveying unit 10, and forms an image on the recording medium M.

[0057] At this time, the ink stored in the main tank 41 of the ink supply unit 40 is supplied to the image forming unit 50 via the flow path 42. The ink supplied to the image forming unit 50 is supplied to the head 55 via the first sub-tank 52a, the flow path 53a, the second sub-tank 52b, and the flow paths 53b and 53c. The ink supplied to the head 55 is supplied to the pressure chamber 57 via the manifold 56 and stored therein.

[0058] When a drive voltage is applied to the piezoelectric element 58 forming the wall surface of the pressure chamber 57, the piezoelectric element 58 deforms, thereby deforming the pressure chamber 57. As a result, the ink stored in the pressure chamber 57 is ejected as droplets from the nozzle 59, and an image is formed on the recording medium M.

[0059] Then, the recording medium M on which the image has been formed by the image forming section 50 is conveyed to the discharge section 30 by the conveying section 10.

[0060] [Meniscus position adjustment] Next, adjustment of the deviation of the meniscus position that occurs when ink droplets are ejected from the inkjet head 55 will be described.

[0061] In the inkjet printer 100, when ink droplets are ejected from the nozzles 59 of the head 55, a drive voltage having a waveform that differs depending on the size of one dot is applied to the piezoelectric element 58. For example, when the size of one dot is relatively small, a drive voltage having a drive waveform that is a single waveform composed of a single drive pulse is applied to the piezoelectric element 58. Also, when the size of one dot is relatively large, a drive voltage having a drive waveform that is a multi-waveform composed of a plurality of drive pulses is applied to the piezoelectric element 58.

[0062] Here, when ink droplets are ejected from the nozzle 59, reverberation occurs due to the vibration of the meniscus caused by the ejection of the ink droplets, and the meniscus position may be significantly shifted from the appropriate position.

[0063] In general, when ink droplets are ejected by applying a driving voltage having a multi-waveform, the reverberation that occurs has a significant effect on the subsequent ejection of ink droplets. In particular, when the multi-waveform is a waveform for 4 dpd drive or more, the effect of the reverberation is large. Therefore, in such a case, it is necessary to adjust the meniscus position in the nozzle 59 that ejects the ink droplets.

[0064] Therefore, in this embodiment, when the ejection of ink droplets based on a predetermined drive waveform at a certain timing is affected by reverberation caused by a drive waveform preceding the predetermined drive waveform, a meniscus position adjustment process is performed. The meniscus position adjustment process applies a drive voltage having a meniscus adjustment waveform for adjusting the meniscus position before applying a drive voltage having a predetermined drive waveform to the piezoelectric element 58, thereby adjusting the meniscus position to an optimal position.

[0065] In the following, to avoid complicating the explanation, "applying a drive voltage having a drive waveform (multi-waveform or single waveform)" to piezoelectric element 58 will be described as "applying a drive waveform (multi-waveform or single waveform)."

[0066] (Drive waveform) The following describes the drive waveform applied to the piezoelectric element 58. As described above, in this embodiment, a single waveform or a multi-waveform is applied to the piezoelectric element 58 depending on the state of the image to be formed on the recording medium M. Also, in this embodiment, a meniscus adjustment waveform is applied to the piezoelectric element 58 to adjust the meniscus position, which has shifted from the appropriate position due to the application of the multi-waveform, to the appropriate position.

[0067] (single waveform 500) 4 is a schematic diagram for explaining an example of the single waveform 500. The single waveform 500 is a drive waveform for 1 dpd (drop per dot) drive applied to the piezoelectric element 58 when ejecting one drop of ink droplet per pixel in an image formed on the recording medium M.

[0068] 4, a single waveform 500 is made up of one drive pulse. The drive pulse constitutes the voltage applied to the piezoelectric element 58.

[0069] (Multi Waveform 600) 5 is a schematic diagram for explaining an example of the multi-waveform 600. The multi-waveform 600 is a drive waveform of 2 dpd or more that is applied to the piezoelectric element 58 when ejecting two or more ink droplets per pixel in an image formed on the recording medium M. In this example, the multi-waveform 600 is a drive waveform for 8 dpd drive that ejects eight ink droplets per pixel.

[0070] 5, the multi-waveform 600 is made up of a number of drive pulses that are applied in succession. Each drive pulse constitutes a voltage applied to the piezoelectric element 58.

[0071] In this example, a multi-waveform 600 having eight drive pulses is applied to the piezoelectric element 58, causing eight ink droplets to be ejected from the nozzle 59. At this time, the ink droplets ejected by applying each drive pulse to the piezoelectric element 58 combine in the air or land at the same pixel position on the recording medium M to form a single dot. In this way, by applying a multi-waveform having 8 dpd drive to the piezoelectric element 58, ink droplets with a larger ejection volume land on the recording medium M compared to ink droplets ejected by applying a single waveform 500 to the piezoelectric element 58.

[0072] (Meniscus adjustment waveform 700) 6 is a schematic diagram for explaining an example of a meniscus adjustment waveform 700. The meniscus adjustment waveform 700 is a 1 dpd drive waveform (single waveform) that is applied to the piezoelectric element 58 in order to adjust the meniscus position that has shifted from the appropriate position due to the application of the multi-waveform 600 to the appropriate position.

[0073] 6, the meniscus adjustment waveform 700 is composed of one drive pulse, similar to the single waveform 500. The drive pulse constitutes the voltage applied to the piezoelectric element 58.

[0074] Here, the ink droplets ejected by applying the meniscus adjustment waveform 700 to the piezoelectric element 58 are slower in speed than the ink droplets ejected by applying the next drive waveform. Therefore, the ink droplets ejected by applying the meniscus adjustment waveform 700 merge in mid-air with the ink droplets ejected by applying the next drive waveform, or land at the same pixel position on the recording medium M.

[0075] (Classification of continuous driving waveforms) Incidentally, when forming an image on the recording medium M, drive waveforms are normally applied successively to the piezoelectric element 58 in accordance with the image to be formed. In this case, combinations of a drive waveform applied first and a drive waveform applied thereafter are classified into the first to fourth examples shown below. In the following description, in the case of drive waveforms applied successively, the drive waveform applied first is referred to as the "first drive waveform" and the drive waveform applied thereafter is referred to as the "second drive waveform."

[0076] (1) First example: Multiwaveform 600 + Multiwaveform 600 7 is a schematic diagram showing a first example of driving waveforms that are applied consecutively. The first example is an example in which both the first driving waveform and the second driving waveform are multi-waveforms 600. In this first example, the multi-waveform 600 is a driving waveform for 4 dpd driving. This also applies to the second to fourth examples described below.

[0077] In this case, reverberation that occurs when ink droplets are ejected by the first drive waveform, which is the multi-waveform 600, affects the ejection of ink droplets by the second drive waveform, which is the multi-waveform 600. Therefore, in the first example, the meniscus adjustment waveform 700 is applied at a timing before the second drive waveform.

[0078] (2) Second example: 600 multi-waveforms + 500 single-waveforms 8 is a schematic diagram showing a second example of driving waveforms applied in succession. The second example is an example in which the first driving waveform is a multi-waveform 600 and the second driving waveform is a single waveform 500. In this case, similar to the first example, reverberation occurring when ink droplets are ejected by the first driving waveform, which is the multi-waveform 600, affects the ejection of ink droplets by the second driving waveform, which is the single waveform 500. Therefore, in the second example, the meniscus adjustment waveform 700 is applied at a timing before the subsequent single waveform.

[0079] (3) Third example: 500 single waveforms + 600 multi-waveforms 9 is a schematic diagram showing a third example of driving waveforms applied in succession. The third example is an example in which the first driving waveform is a single waveform 500 and the second driving waveform is a multi-waveform 600. In this case, reverberation that occurs when ink droplets are ejected by the first driving waveform, which is the single waveform 500, has almost no effect on the ejection of ink droplets by the second driving waveform, which is the multi-waveform 600. Therefore, in the third example, the meniscus adjustment waveform 700 is not applied at a timing before the subsequent multi-waveform 600.

[0080] (4) Fourth example: Single waveform 500 + single waveform 500 10 is a schematic diagram showing a fourth example of driving waveforms applied in succession. The fourth example is an example in which both the first driving waveform and the second driving waveform are single waveforms 500. In this case, similar to the third example, the reverberation that occurs when ink droplets are ejected by the first driving waveform, which is the single waveform 500, has almost no effect on the ejection of ink droplets by the second driving waveform, which is the single waveform 500. Therefore, in the fourth example, the meniscus adjustment waveform 700 is not applied at a timing before the subsequent single waveform 500.

[0081] In this way, when the first drive waveform applied before the second drive waveform is the multi-waveform 600, the reverberation caused by the first drive waveform has a large effect on the ejection of ink droplets by the second drive waveform, regardless of whether the second drive waveform is the multi-waveform 600 or the single waveform 500. Therefore, in this embodiment, when the first drive waveform applied prior to the second drive waveform is a multi-waveform, the meniscus adjustment waveform 700 is applied before the second drive waveform.

[0082] (Example of application of meniscus adjustment waveform) Fig. 11 is a schematic diagram showing an example of a driving waveform when applying a meniscus adjustment waveform. The example shown in Fig. 11 corresponds to the above-mentioned first example, and shows a case where a second driving waveform 802, which is a multi-waveform 600 of 8 dpd drive, is applied after a first driving waveform 801, which is a multi-waveform 600 of 8 dpd drive. In the example shown in Fig. 11, the meniscus adjustment waveform 700 is applied, for example, at a timing between the first driving waveform 801 and the second driving waveform 802, which are applied consecutively.

[0083] At this time, the meniscus adjustment waveform 700 is applied so that the time between the two multi-waveforms does not change. In other words, the meniscus adjustment waveform 700 is applied so that the application timing of the second driving waveform 802 is not delayed compared to when the meniscus adjustment waveform 700 is not applied. This makes it possible to prevent the time required for image formation from being lengthened by applying the meniscus adjustment waveform 700, and thus to prevent a decrease in productivity of the inkjet printer 100.

[0084] 11, the meniscus adjustment waveform 700 is applied between two multi-waveforms 600 (the first driving waveform 801 and the second driving waveform 802), but the application timing of the meniscus adjustment waveform 700 is not limited to this example. For example, the meniscus adjustment waveform 700 may be applied between a plurality of driving pulses that make up the multi-waveform 600, which is the first driving waveform 801.

[0085] Fig. 12 is a schematic diagram showing another example of the drive waveform when applying the meniscus adjustment waveform. The example shown in Fig. 12 shows a case where the second drive waveform 802, which is the multi-waveform 600 of 8 dpd drive, is applied after the first drive waveform 801, which is the multi-waveform 600 of 8 dpd drive, as in the example of Fig. 11. In the case of the example shown in Fig. 12, the meniscus adjustment waveform 700 is applied, for example, at the timing between the fourth drive pulse 814 and the fifth drive pulse 815 in the first drive waveform 801 having the first drive pulse 811 to the eighth drive pulse 818.

[0086] In this example, the overall time of the first driving waveform 801 becomes longer, but similar to the example of Fig. 11, the meniscus adjustment waveform 700 is applied so that the application timing of the second driving waveform 802 is not delayed compared to when the meniscus adjustment waveform 700 is not applied. This makes it possible to suppress a decrease in productivity of the inkjet printer 100.

[0087] In this example, the meniscus adjustment waveform 700 is applied between the fourth drive pulse 814 and the fifth drive pulse 815. However, this is not limiting, and it is preferable that the meniscus adjustment waveform 700 is applied, for example, at a timing when the meniscus position starts to deviate from the appropriate position in the multi-waveform 600.

[0088] More specifically, the meniscus position begins to shift at the timing after the fourth drive pulse 814 in the multi-waveform 600. For this reason, it is preferable to apply the meniscus adjustment waveform 700 at the timing after the fourth drive pulse 814 (in this example, after the fourth drive pulse 814 to the eighth drive pulse 818).

[0089] (Meniscus adjustment waveform application timing and applied voltage) When applying the meniscus adjustment waveform 700 to the piezoelectric element 58, depending on the application timing and voltage of the meniscus adjustment waveform 700, the effect of adjusting the meniscus to an appropriate position may not be fully obtained. For example, if the time between the application of the meniscus adjustment waveform 700 and the application of the second drive waveform 802 is short, it is considered that reverberation caused by the application of the meniscus adjustment waveform 700 affects the ejection of ink droplets by the second drive waveform 802. Also, for example, if the voltage of the meniscus adjustment waveform 700 is low, it is considered that reverberation caused by the application of the multi-waveform 600, which is the first drive waveform 801, cannot be sufficiently suppressed.

[0090] Therefore, when applying the meniscus adjustment waveform 700 after the multi-waveform 600, it is necessary to appropriately set the application timing and application voltage of the meniscus adjustment waveform 700. Figure 13 is a schematic diagram showing an example of the relationship between the time interval and the voltage ratio of the meniscus adjustment waveform 700.

[0091] The time interval indicates the time interval from when the meniscus adjustment waveform 700 is applied to when the second drive waveform 802 is applied. In this example, the time interval is set to 3AL to 7AL. "AL" is 1 / 2 the acoustic resonance period of the pressure wave in the channel filled with ink. AL is obtained, for example, by measuring the speed of ink droplets ejected from the nozzle 59 when a square wave pulse is applied to the piezoelectric element 58, and by changing the pulse width while keeping the voltage of the square wave constant, as the pulse width at which the ejection speed of the ink droplets becomes maximum.

[0092] The time interval 3AL is a time during which the reverberation caused by the application of the meniscus adjustment waveform 700 does not decay completely. Therefore, when the time interval is set to 3AL, the reverberation caused by the meniscus adjustment waveform 700 affects the ejection of ink droplets caused by the application of the second drive waveform 802.

[0093] On the other hand, the time interval from 4AL to 7AL is a time during which the reverberation caused by the application of the meniscus adjustment waveform 700 decays to a certain extent or sufficiently. Therefore, when the time interval is set to 4AL to 7AL, the reverberation caused by the meniscus adjustment waveform 700 has little or no effect on the ejection of ink droplets caused by the subsequent application of the drive waveform.

[0094] The voltage ratio indicates the ratio of the voltage of the meniscus adjustment waveform 700 to the maximum voltage of the multi-waveform 600 (first driving waveform 801) applied before the meniscus adjustment waveform 700. In this example, the voltage ratios are set to 30%, 50%, and 70%. Note that the maximum voltage of the multi-waveform 600 is set so that the speed of the ink droplets ejected from the nozzle 59 is about 6 m / s, for example.

[0095] The voltage of the meniscus adjustment waveform 700 with a voltage ratio of 30% and 50% is a voltage at which ink droplets are not ejected even when the meniscus adjustment waveform 700 is applied to the piezoelectric element 58. Therefore, when the voltage ratio is set to 30% and 50%, even if the meniscus adjustment waveform 700 is applied, the meniscus generated by the application of the previous multi-waveform 600 (first driving waveform 801) cannot be positioned appropriately.

[0096] On the other hand, the voltage of the meniscus adjustment waveform 700 with a voltage ratio of 70% is the voltage at which ink droplets are ejected when the meniscus adjustment waveform 700 is applied to the piezoelectric element 58. Therefore, when the voltage ratio is set to 70%, the meniscus generated by the application of the previous multi-waveform 600 (first drive waveform 801) is placed in an appropriate position by applying the meniscus adjustment waveform 700. Note that the ejection speed of the ink droplets ejected at this time is slower than the ejection speed of the ink droplets ejected by the normal drive waveform.

[0097] Therefore, in this embodiment, the meniscus adjustment waveform 700 is applied so that the voltage ratio is 70% or more and the time interval is 4AL to 7AL. If the voltage ratio is 100% or more, the ejection speed of the ink droplets ejected by the application of the meniscus adjustment waveform 700 becomes faster than normal, and the ink droplets may not be absorbed by the ink droplets ejected by the second driving waveform 802. Therefore, it is preferable to set the voltage ratio to less than 100%.

[0098] (Meniscus position adjustment process) FIG. 14 is a flowchart showing an example of the flow of the meniscus position adjustment process performed by the inkjet printer 100 according to the present embodiment.

[0099] First, in step S1, the image data acquisition unit 95 of the control unit 90 acquires image data of an image to be formed from the external device 200 via the input / output I / F 80. In step S2, the drive waveform generation unit 96 generates a drive waveform for forming an image based on the image data.

[0100] In step S3, the determination unit 97 determines whether or not a meniscus adjustment waveform is required based on the generated drive waveform. At this time, the determination unit 97 focuses on a portion where a predetermined drive waveform continues from among the data of the generated drive waveform.

[0101] The determination unit 97 determines whether or not the first drive waveform 801 in the focused consecutive drive waveforms is a multi-waveform 600. The "multi-waveform" here refers to a waveform of 4 dpd or more drive waveforms in which the effect of reverberation on the second drive waveform 802 is particularly large.

[0102] If the first driving waveform 801 is the multi-waveform 600 (step S3: YES), the judgment unit 97 judges that it is necessary to apply the meniscus adjustment waveform 700. Then, the process proceeds to step S4. On the other hand, if the first driving waveform 801 is not the multi-waveform 600 (step S3: NO), the judgment unit 97 judges that it is not necessary to apply the meniscus adjustment waveform 700. Then, the process proceeds to step S5.

[0103] In step S4, the drive waveform setting section 98 sets the meniscus adjustment waveform 700 before the second drive waveform 802. In step S5, the drive waveform setting section 98 outputs the set drive waveform to the head drive section .

[0104] When performing the above-mentioned meniscus position adjustment process, it is preferable to use ink that has a low viscosity and is easily affected by reverberation (the meniscus position is easily shifted from the appropriate position). In particular, it is more preferable for the ink viscosity to be 9 cP (centipoise; 1 cP = 1 mPa s) or less, since this allows the meniscus position to be adjusted more appropriately.

[0105] This is also preferable when using ink having thixotropy, since it is possible to adjust the deviation of the meniscus position from the appropriate position caused by a decrease in viscosity due to shear stress in the nozzle or in the flow passage in its vicinity.

[0106] As described above, in the inkjet printer 100 which is the image forming apparatus according to this embodiment, when the first driving waveform 801 applied to the piezoelectric element 58 is the multi-waveform 600, the meniscus adjustment waveform 700 is applied before the second driving waveform 802 which is applied thereafter. By applying the meniscus adjustment waveform 700, the meniscus position which has been shifted from the appropriate position by the first driving waveform 801 is adjusted to the appropriate position. This improves the ejection stability in the inkjet printer 100 and suppresses a decrease in productivity. [Explanation of symbols]

[0107] 10. Conveyor 20 Supply section 30 Discharge section 40 Ink supply unit 50 Image forming section 70 Operation display section 80 Input / Output Interface 90 Control section 54 Head drive unit 55 Inkjet head 58 Piezoelectric element 59 Nozzle 91 CPU 92 RAM 93 ROM 94 Memory section 95 Image data acquisition section 96 Drive waveform generator 97 Judgment section 98 Drive waveform setting section 100 Inkjet Printer 200 External device 500 Single Waveforms 600 Multi-Waveforms 700 Meniscus adjustment waveform 801 First drive waveform 802 Second drive waveform 811 First drive pulse 814 4th drive pulse 815 5th drive pulse 818 8th drive pulse

Claims

1. an inkjet head that applies a drive waveform to a piezoelectric element to eject ink droplets; A control unit that adjusts a meniscus position of a nozzle that ejects the ink droplets; Equipped with The control unit is When the first drive waveform is a multi-waveform including a plurality of drive pulses, an adjustment waveform for adjusting the meniscus position of the nozzle that ejects the ink droplet by applying the first drive waveform is applied before a second drive waveform that is applied after the first drive waveform. Image forming device.

2. The control unit is Applying the adjustment waveform between the first drive waveform and the second drive waveform. The image forming apparatus according to claim 1 .

3. The control unit is The adjustment waveform is applied between the plurality of drive pulses included in the first drive waveform. The image forming apparatus according to claim 1 .

4. The control unit is The adjustment waveform is applied at a voltage that results in droplets smaller than the droplets of the ink ejected by applying the first drive waveform. The image forming apparatus according to claim 1 .

5. The control unit is The adjusted waveform is applied so that the voltage is equal to or greater than 70% and less than 100% of the maximum voltage of the first driving waveform. The image forming apparatus according to claim 4 .

6. The control unit is The adjustment waveform is applied so that a time interval from application of the adjustment waveform to application of the second drive waveform is equal to or longer than a time required for reverberation caused by application of the adjustment waveform to decay. The image forming apparatus according to claim 1 .

7. The control unit is The adjusted waveform is applied so that the time interval is 4AL or more.

7. The image forming apparatus according to claim 6.

8. The control unit is The adjusted waveform is applied so that the ink droplets ejected by the adjusted waveform merge in the air with the ink droplets ejected by the second driving waveform or land at the same position. The image forming apparatus according to claim 1 .

9. The tailored waveform is a single waveform that includes a single drive pulse. The image forming apparatus according to claim 1 .

10. The ink droplets have a viscosity of 9 cP or less when ejected from the nozzle. The image forming apparatus according to claim 1 .

11. The ink droplets have thixotropy. The image forming apparatus according to claim 1 .

12. The control unit is When the first driving waveform and the second driving waveform are the multi-waveform, the adjustment waveform is applied before the second driving waveform. The image forming apparatus according to claim 1 .

13. The control unit is When the first driving waveform is a single waveform including a single driving pulse and the second driving waveform is the multi-waveform, the adjustment waveform is not applied before the second driving waveform. The image forming apparatus according to claim 1 .

14. The control unit is When the first drive waveform and the second drive waveform are a single waveform including a single drive pulse, the adjustment waveform is not applied before the second drive waveform. The image forming apparatus according to claim 1 .

15. The control unit is When the first driving waveform is the multi-waveform and the second driving waveform is a single waveform including a single driving pulse, applying the adjustment waveform before the second driving waveform. The image forming apparatus according to claim 1 .

16. 1. A meniscus position adjustment method for an image forming apparatus including an inkjet head that applies a drive waveform to a piezoelectric element to eject ink droplets, and a control unit that adjusts a meniscus position of a nozzle that ejects the ink droplets, comprising: When the first drive waveform is a multi-waveform including a plurality of drive pulses, an adjustment waveform for adjusting the meniscus position of the nozzle that ejects the ink droplet by applying the first drive waveform is applied before a second drive waveform that is applied after the first drive waveform. Method for adjusting meniscus position.

17. A program for causing a computer to execute the meniscus position adjustment method according to claim 16.

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