Inkjet printer

Abstract

To suppress deviations in the impact position of ink droplets when a distance between a nozzle surface of an ink head and a recording medium varies.SOLUTION: A printer 10 comprises a height detection sensor 50 that measures a printing distance H which is a distance between a recording medium 5 placed on a table 35 and a nozzle surface 68 on which a nozzle 65 is formed, and a control device 80 that controls an ink head 60. The control device 80 comprises: a driving signal generation circuit 82 that generates reference driving signals SP having at least a first driving pulse P1 and a second driving pulse P2, for each driving cycle; a driving signal correction circuit 84 that corrects the reference driving signals SP by increasing a driving voltage of the second driving pulse P2, for each printing distance H measured by the heigh detection sensor 50; and a driving signal supply circuit 86 that supplies some or the whole of the corrected reference driving signals corresponding to the printing distance H to a piezoelectric element 66 of the ink head 60, for each printing distance H.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to inkjet printers. [Background technology]

[0002] For example, as described in Patent Document 1, there is known an inkjet printer that includes an ink head having a pressure chamber in which ink is stored, a partition plate that partitions part of the pressure chamber, an actuator connected to the partition plate, and a nozzle that communicates with the pressure chamber, and a control device that drives the actuator by supplying a drive signal to the actuator.

[0003] In the inkjet printer, when the control device supplies a drive pulse signal (hereinafter referred to as a drive pulse) to the actuator, the actuator deforms, and the partition plate deforms accordingly. This increases or decreases the volume of the pressure chamber, and the pressure of the ink in the pressure chamber changes. This change in pressure causes ink to be ejected from the nozzle. The ejected ink flies as ink droplets and lands on a recording medium such as recording paper. As a result, one dot is formed on the recording paper. Then, an image or the like is formed by forming many such dots on the recording paper. In the inkjet printer, the size of the dot is adjusted by a so-called multi-dot method, which generates a drive signal having multiple drive pulses within a drive cycle for forming one dot. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-131677 A [Patent Document 2] JP 2010-142978 A Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, a wide variety of recording media are used in the inkjet printer, and the thickness of each recording medium varies. For this reason, the printing distance, which is the distance between the recording medium and the nozzle face on which the nozzles are formed, may vary depending on the recording medium. If the printing distance is long, the landing position of the ink droplets ejected from the nozzles may shift, and the quality of the formed image may deteriorate.

[0006] Therefore, it is conceivable to change the timing of ink ejection and correct the landing position of ink droplets by shifting the generation timing of the drive pulse in accordance with the change in printing distance, as described in Patent Document 2. However, if shifting the generation timing of each drive pulse in accordance with the printing distance as in Patent Document 2 is applied to an inkjet printer that adjusts the size of dots by a multi-dot method as in Patent Document 1, the ink vibration period will change, causing the ejection of ink droplets to become unstable, which may result in a decrease in image quality.

[0007] The present invention has been made in consideration of these points, and its object is to provide an inkjet printer that can suppress deviations in the landing position of ink droplets without causing unstable ink droplet ejection when the distance between the nozzle face of the ink head and the recording medium changes. [Means for solving the problem]

[0008] The inventors of the present application have noted that the possible landing distance varies greatly depending on the size of the ink droplets ejected from the nozzle (i.e. the size of the dots formed on the recording medium), that the smaller the ink droplet size, the greater the deviation in the landing position, and that the larger the ink droplet size, the smaller the deviation in the landing position, and that by changing the driving voltage, the ink vibration period does not change and ink droplets can be ejected stably, and have discovered that by increasing the driving voltage for ejecting ink droplets in accordance with the printing distance, it is possible to suppress deviation in the landing position without unstable ejection of ink droplets.

[0009] The inkjet printer according to the present invention includes a mounting table on which a recording medium is placed, an ink head having a nozzle for ejecting ink droplets toward the recording medium placed on the mounting table and a nozzle surface on which the nozzle is formed, a sensor for measuring a printing distance which is the distance between the recording medium placed on the mounting table and the nozzle surface, and a control device for controlling the ink head. The ink head includes a case having a pressure chamber inside which ink is stored, a partition plate provided in the case and partitioning a part of the pressure chamber, an actuator connected to the partition plate and deformed when an electric signal is supplied thereto, and the nozzle formed in the case and communicating with the pressure chamber. The control device includes a drive signal generating circuit that generates a reference drive signal having at least a first drive pulse for ejecting a first ink droplet by expanding and contracting the pressure chamber for each drive cycle, and a second drive pulse for ejecting a second ink droplet smaller than the first ink droplet by expanding and contracting the pressure chamber, a drive signal correction circuit that corrects the reference drive signal by increasing the drive voltage of the second drive pulse for each printing distance measured by the sensor, and a drive signal supply circuit that supplies to the actuator a part or all of the corrected reference drive signal corresponding to the printing distance for each printing distance.

[0010] According to the inkjet printer of the present invention, the printing distance, which is the distance between the recording medium placed on the placement table and the nozzle surface, can be measured by a sensor. Then, the drive signal correction circuit of the control device corrects the reference drive signal by increasing the drive voltage of the second drive pulse for ejecting the second ink droplet for each printing distance measured by the sensor. Here, the first ink droplet, which is larger than the second ink droplet, is used as the reference ink droplet because the deviation of the landing position is relatively small. Then, the drive signal supply circuit supplies a part or all of the corrected reference drive signal corresponding to the printing distance to the actuator for each printing distance. This makes it possible to suppress the deviation of the landing position of the second ink droplet even when the printing distance changes. In this way, the deviation of the landing position is suppressed by increasing the drive voltage, so that the ink can be ejected stably without changing the vibration period of the ink droplet. Effect of the Invention

[0011] According to the present invention, it is possible to provide an inkjet printer that can suppress deviations in the landing position of ink droplets without causing the ejection of ink droplets to become unstable when the distance between the nozzle surface of the ink head and the recording medium changes. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view of a printer according to an embodiment. [Diagram 2] FIG. 2 is a front view of the printer according to one embodiment with the front cover open. [Diagram 3] FIG. 3 is a plan view of the printer according to the embodiment with the front cover and case removed. [Figure 4] FIG. 4 is a cross-sectional view of a portion of an ink head according to an embodiment. [Diagram 5] FIG. 5 is a block diagram showing the configuration of a printer according to an embodiment. [Figure 6] FIG. 6 is a waveform diagram of a reference driving signal according to an embodiment. [Figure 7] FIG. 7 is a front view showing the printing distance between a recording medium and a nozzle face according to one embodiment. [Figure 8] FIG. 8 is a diagram showing a test pattern printed on a test paper. [Figure 9] FIG. 9 is a diagram showing an example of a waveform of the corrected reference driving signal. [Figure 10] FIG. 10 is a waveform diagram of an example of a corrected reference drive signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of an inkjet printer (hereinafter referred to as printer) according to the present invention will be described with reference to the drawings. Note that the embodiment described here is, of course, not intended to limit the present invention in any particular way. Furthermore, the same reference numerals are used for members and parts that perform the same functions, and duplicated descriptions will be omitted or simplified as appropriate.

[0014] FIG. 1 is a perspective view of a printer 10 according to this embodiment. The printer 10 prints on a recording medium 5 (see FIG. 2). In the following description, when the printer 10 is viewed from the front, the side away from the printer 10 is the front, and the side approaching the printer 10 is the rear. The terms left, right, top, and bottom refer to the left, right, top, and bottom of the printer 10 when viewed from the front. The symbols F, Rr, L, R, U, and D in the drawings refer to the front, back, left, right, top, and bottom, respectively. The symbol Y in the drawings indicates the main scanning direction. Here, the main scanning direction Y is the left-right direction. The symbol X indicates the sub-scanning direction. Here, the sub-scanning direction X is the front-rear direction, and is perpendicular to the main scanning direction Y in a plan view. The symbol Z indicates the up-down direction. The up-down direction Z is perpendicular to the main scanning direction Y in a front view. However, the above directions are merely defined for the convenience of explanation, and do not limit the installation mode of the printer 10 or the present invention in any way.

[0015] The recording medium 5 used in this embodiment may be, for example, a flat sheet such as recording paper or transfer paper, or may be a three-dimensional object such as various cases such as mobile phone cases, small electronic devices, small parts such as key holders, photo frames, and pens, daily necessities, and accessories. The material forming the recording medium 5 may be paper such as plain paper and inkjet printing paper, as well as resins such as polyvinyl chloride, acrylic resin, polycarbonate, polystyrene, and acrylonitrile-butadiene-styrene (ABS) copolymer, metals such as aluminum and stainless steel, carbon, pottery, ceramic, glass, rubber, leather, wood, and the like. In the printer 10 of this embodiment, a three-dimensional object having an uneven shape is preferably used as the recording medium 5.

[0016] As shown in FIG. 1, the printer 10 includes a box-shaped housing 12. The housing 12 has an internal space 12S. The housing 12 includes a base member 13, a case 15, a front cover 23, and an operation panel 25. As shown in FIG. 2, the base member 13 includes a bottom wall 13A, a left side wall 13L, a right side wall 13R, and a support wall 13T. The bottom wall 13A extends in the main scanning direction Y and the sub-scanning direction X. The left side wall 13L extends in the up-down direction Z and the sub-scanning direction X. The right side wall 13R extends in the up-down direction Z and the sub-scanning direction X. The right side wall 13R is disposed to the right of the left side wall 13L. The left side wall 13L and the right side wall 13R are provided on the bottom wall 13A. The support wall 13T extends in the main scanning direction Y. The support wall 13T is supported by the left side wall 13L and the right side wall 13R. The case 15 is attached to the base member 13. An opening 28 is formed in the front of the case 15. The front cover 23 is provided so as to be able to open and close the opening 28 of the case 15. Here, the front cover 23 is supported by the case 15 so as to be rotatable about its rear end. By rotating the front cover 23 upward, the internal space 12S of the housing 12 communicates with the external space. The internal space 12S is a space in which printing is performed on the recording medium 5 by an ink head 60 (see FIG. 2) described later and a printing distance H (see FIG. 7) is measured by a height detection sensor 50 (see FIG. 2) described later. In this way, the internal space 12S is formed surrounded by the case 15 and the front cover 23, so that dust and dirt from the external space are unlikely to enter the internal space 12S during printing or measurement, and light irradiated from ultraviolet irradiation devices 41, 42 (see FIG. 2) described later is unlikely to leak into the external space.

[0017] 1, a window 23A is provided in the front and upper part of the front cover 23. The window 23A is formed of, for example, a transparent acrylic plate. The window 23A is treated so that light from the external space (for example, ultraviolet light) does not reach the internal space 12S. The user can view the inside of the housing 12 through the window 23A.

[0018] The operation panel 25 is provided on the case 15. The operation panel 25 is provided on the right side of the top surface of the case 15. The operation panel 25 is a panel through which the user performs operations related to printing an image, setting (changing) the irradiation intensity of light irradiated from the ultraviolet irradiation devices 41, 42 (see FIG. 2), printing a test pattern (to be described later), measuring the printing distance, and inputting a correction value. The operation panel 25 is provided with a display screen 25A that displays information related to printing, such as the type of printing (e.g., whether or not there is a glossy finish), resolution, printing status, and other printing-related information, and input buttons 25B for setting information related to printing and the recording medium 5.

[0019] Next, the internal configuration of the printer 10 will be described. As shown in Fig. 2, the printer 10 includes a guide rail 18, a carriage 20, an ink head 60, ultraviolet irradiation devices 41 and 42, a height detection sensor 50, and a control device 80. The guide rail 18 is disposed in a case 15. As shown in Fig. 3, the guide rail 18 is fixed to a support wall 13T of the base member 13, and extends in the main scanning direction Y. The height detection sensor 50 is an example of a sensor.

[0020] As shown in FIG. 2, the carriage 20 is equipped with an ink head 60, ultraviolet irradiation devices 41 and 42, and a height detection sensor 50. The carriage 20 is slidably mounted on a guide rail 18. The printer 10 is equipped with a carriage movement mechanism 21. The carriage 20 reciprocates along the guide rail 18 in the main scanning direction Y by the carriage movement mechanism 21. The carriage movement mechanism 21 is controlled by a control device 80. The carriage movement mechanism 21 is equipped with a left pulley 21L, a right pulley 21R, an endless belt 21A wound around the left pulley 21L and the right pulley 21R, and a carriage motor 21B connected to the left pulley 21L. The belt 21A extends in the main scanning direction Y. The belt 21A is fixed to the upper part of the rear surface of the carriage 20. Here, the carriage motor 21B is driven to rotate the left pulley 21L, causing the belt 21A to run between the left pulley 21L and the right pulley 21R. This causes the carriage 20 to move in the main scanning direction Y. As the carriage 20 moves in the main scanning direction Y, the ink head 60, the ultraviolet ray irradiation devices 41 and 42, and the height detection sensor 50 mounted on the carriage 20 also move in the main scanning direction Y.

[0021] As shown in FIG. 2, a plurality of ink heads 60 are mounted on the carriage 20. As shown in FIG. 4, the ink head 60 has nozzles 65 that eject photocurable ink (i.e., ink having photocurability, for example, ultraviolet curable ink) onto the recording medium 5 placed on the table 35 (see FIG. 2) described later, and a nozzle surface 68 on which the nozzles 65 are formed. The ink head 60 ejects ink droplets from the nozzles toward the recording medium 5 to form ink dots on the recording medium 5. By arranging a large number of these dots, an image or the like is formed on the recording medium 5. Each of the ink heads 60 is connected to an ink cartridge 34 (see FIG. 2) housed in the case 15 by a flexible ink tube (not shown). Each of the ink cartridges 34 stores photocurable ink. Here, three ink heads 60 are mounted on the carriage 20. However, the number of ink heads 60 is not limited to three.

[0022] As shown in FIG. 4, the ink head 60 includes a hollow case 61 having an opening 61a, and a partition plate 62 attached to the case 61 so as to cover the opening 61a. A pressure chamber 63 in which ink is stored is formed in the case 61. The partition plate 62 partitions a part of the pressure chamber 63. The partition plate 62 is elastically deformable inward and outward of the pressure chamber 63. The partition plate 62 is configured to be deformable so as to increase and decrease the volume of the pressure chamber 63. The partition plate 62 is typically a resin film.

[0023] As shown in Fig. 4, an ink inlet 64 through which ink flows in is formed in the side wall of the case 61. The position of the ink inlet 64 is not limited as long as it is in communication with the pressure chamber 63. Ink is supplied to the pressure chamber 63 from the ink cartridge 34 through the ink inlet 64, and a predetermined amount of ink is temporarily stored therein. A nozzle surface 68 is formed in the lower part of the case 61. The nozzle 65 is in communication with the pressure chamber 63. The liquid level (free surface) of the ink inside the nozzle 65 forms a meniscus 65a.

[0024] As shown in FIG. 4, the ink head 60 includes a piezoelectric element 66. The piezoelectric element 66 is an example of an actuator. The piezoelectric element 66 is connected to the partition plate 62. More specifically, the piezoelectric element 66 is connected to the partition plate 62 on the side opposite to the pressure chamber 63 side. A part of the piezoelectric element 66 is fixed to a fixing member 69 provided on the case 61. The piezoelectric element 66 is connected to the control device 80 via a flexible cable 67. An electric signal is supplied to the piezoelectric element 66 via the flexible cable 67. In this embodiment, the piezoelectric element 66 is a laminate in which a piezoelectric material and a conductive layer are alternately laminated. When the piezoelectric element 66 receives an electric signal from the control device 80, it expands or contracts, and functions to elastically deform the partition plate 62 to the outside or inside of the pressure chamber 63. Here, a piezoelectric element (PZT) in a longitudinal vibration mode is adopted. The PZT in the longitudinal vibration mode is freely expandable in the lamination direction, and for example, it contracts when discharged and expands when charged. However, the type of the piezoelectric element 66 is not particularly limited.

[0025] In the ink head 60, for example, the potential of the piezoelectric element 66 is raised from a reference potential (intermediate potential), so that the piezoelectric element 66 extends (expands) in the stacking direction. As a result, the partition plate 62 is elastically deformed toward the inside of the pressure chamber 63, and the pressure chamber 63 is contracted. The contraction of the pressure chamber 63 means that the volume of the pressure chamber 63 is reduced by the deformation of the partition plate 62. As a result, the ink in the pressure chamber 63 is pressurized, and is ejected from the nozzle 65 as an ink droplet. Thereafter, the potential of the piezoelectric element 66 is lowered from the reference potential (intermediate potential), so that the piezoelectric element 66 contracts. Following this, the partition plate 62 is elastically deformed toward the outside of the pressure chamber 63, and the pressure chamber 63 expands. The expansion of the pressure chamber 63 means that the volume of the pressure chamber 63 is increased by the deformation of the partition plate 62. As a result, the pressure inside the pressure chamber 63 is reduced, and ink flows into the pressure chamber 63 from the ink inlet 64. At the reference potential, the piezoelectric element 66 is not driven, no ink is ejected from the nozzle 65, and no ink flows into the pressure chamber 63.

[0026] The ultraviolet irradiation devices 41 and 42 irradiate light (typically ultraviolet light). The ultraviolet irradiation devices 41 and 42 irradiate light (here, ultraviolet light) toward the photocurable ink (here, ultraviolet curable ink) ejected onto the recording medium 5 to cure the photocurable ink. The irradiation intensity is controlled by the control device 80. The photocurable ink is cured by being irradiated with light from the ultraviolet irradiation devices 41 and 42, and an image is formed on the recording medium 5. As shown in FIG. 2, the ultraviolet irradiation devices 41 and 42 are disposed above a table 35, which will be described later. The ultraviolet irradiation device 41 is disposed to the left of the ink head 60. The ultraviolet irradiation device 42 is disposed to the right of the ink head 60.

[0027] As shown in FIG. 2, the printer 10 is a so-called flatbed type printer. The printer 10 includes a table 35 disposed below the carriage 20, a first table moving mechanism 37, and a second table moving mechanism 38. The table 35, the first table moving mechanism 37, and the second table moving mechanism 38 are provided in the internal space 12S. The table 35 is an example of a mounting table. The recording medium 5 is placed on the table 35. The table 35 is configured to be movable in the vertical direction Z by the first table moving mechanism 37. The table 35 is configured to be movable in the sub-scanning direction X by the second table moving mechanism 38. The table 35 is disposed below the ink head 60. The table 35 is disposed to the right of the left side wall 13L and to the left of the right side wall 13R.

[0028] As shown in FIG. 2, the first table moving mechanism 37 includes a height adjustment member 37a and a first motor 39A (see FIG. 5). The height adjustment member 37a is provided on the lower surface of the table 35. The height adjustment member 37a is connected to the first motor 39A. The first motor 39A is electrically connected to the control device 80 and is controlled by the control device 80. When the first motor 39A is driven, the height of the height adjustment member 37a changes, and the height of the table 35 is adjusted. That is, the first table moving mechanism 37 moves the table 35 in the up-down direction Z.

[0029] As shown in FIG. 3, the second table moving mechanism 38 includes slide rails 38a and 38b, a conveying member 38c, and a second motor 39B (see FIG. 5). The slide rails 38a and 38b extend in the sub-scanning direction X. The conveying member 38c is provided so as to be slidable relative to the slide rails 38a and 38b. Above the conveying member 38c, the table 35 is supported via a height adjustment member 37a (see FIG. 2). The second motor 39B is electrically connected to the control device 80 and is controlled by the control device 80. When the second motor 39B is driven, the conveying member 38c moves along the slide rails 38a and 38b. This causes the table 35 to move in the sub-scanning direction X. That is, the second table moving mechanism 38 moves the recording medium 5 placed on the table 35 in the sub-scanning direction X.

[0030] The height detection sensor 50 measures the height of the recording medium 5 placed on the table 35. That is, the height detection sensor 50 measures a printing distance H (see FIG. 7), which is the distance in the up-down direction Z between the recording medium 5 placed on the table 35 and the nozzle surface 68 of the ink head 60. The height detection sensor 50 is, for example, a non-contact type sensor. The height detection sensor 50 is, for example, a reflective type laser displacement sensor. In this embodiment, the height detection sensor 50 is disposed to the left of the ultraviolet irradiation device 41, but the position of the height detection sensor 50 is not particularly limited.

[0031] As shown in FIG. 5, the control device 80 is communicatively connected to the operation panel 25, the carriage motor 21B of the carriage movement mechanism 21, the first motor 39A of the first table movement mechanism 37, the second motor 39B of the second table movement mechanism 38, the ink head 60, the ultraviolet ray irradiation devices 41 and 42, and the height detection sensor 50. The control device 80 controls the operations of these devices. The control device 80 is typically a computer. The control device 80 includes, for example, an interface (I / F) for receiving print data and the like from an external device such as a host computer, a central processing unit (CPU) for executing instructions of a control program, a ROM for storing a program executed by the CPU, a RAM used as a working area for expanding the program, and a storage device such as a memory for storing the above-mentioned program and various data.

[0032] As shown in FIG. 5, the control device 80 includes a drive signal generating circuit 82, a drive signal correcting circuit 84, a drive signal supplying circuit 86, a print distance measuring circuit 87, a height adjusting circuit 88, and a pattern printing circuit 90. The signal supplied to the piezoelectric element 66 by the drive signal supplying circuit 86 is called a supply signal. The supply signal is a signal consisting of a part or all of the reference drive signal generated by the drive signal generating circuit 82, or a part or all of the reference drive signal corrected by the drive signal correcting circuit 84. The hardware configurations of the drive signal generating circuit 82, the drive signal correcting circuit 84, the drive signal supplying circuit 86, the print distance measuring circuit 87, the height adjusting circuit 88, and the pattern printing circuit 90 are not limited in any way and may be the same as those of the conventional ones.

[0033] The drive signal generating circuit 82 generates a reference drive signal for driving the ink head 60. The reference drive signal has a plurality of drive pulses. The drive pulse is typically a waveform including a waveform element that increases the voltage to contract the pressure chamber 63, a waveform element that maintains the voltage to maintain the state of the pressure chamber 63, and a waveform element that decreases the voltage to expand the pressure chamber 63. As shown in FIG. 6, the reference drive signal SP of this embodiment includes a first drive pulse P1, a second drive pulse P2, and a third drive pulse P3 in one drive cycle.

[0034] FIG. 6 is a waveform diagram of a reference drive signal SP according to an embodiment. The horizontal axis t represents time, and the vertical axis V represents potential. tx represents one drive cycle. The drive signal generating circuit 82 is configured to repeatedly generate a reference drive signal SP as shown in FIG. 6 for each drive cycle tx. The reference drive signal SP has a first drive pulse P1, a second drive pulse P2, and a third drive pulse P3 within one drive cycle tx. The first drive pulse P1 is located (generated) behind the second drive pulse P2. The third drive pulse P3 is located (generated) ahead of the second drive pulse P2. In this embodiment, as described later, the reference drive signal SP generates the first drive pulse P1 to eject a first ink droplet from the nozzle 65. This allows one large dot to be formed on the recording medium 5. In addition, the reference drive signal SP generates the second drive pulse P2 to eject a second ink droplet from the nozzle 65. This allows one medium dot to be formed on the recording medium 5. The second ink droplet is smaller than the first ink droplet. Furthermore, the reference driving signal SP generates a third driving pulse P3 to eject a third ink droplet from the nozzle 65. This makes it possible to form one small dot on the recording medium 5. The third ink droplet is smaller than the second ink droplet.

[0035] 6, the first driving pulse P1 includes a front first rising waveform T11 rising from a reference potential V0 to a first maximum potential V1A, a first maximum potential maintaining waveform T12 maintaining the first maximum potential V1A, a first falling waveform T13 falling from the first maximum potential V1A to a first minimum potential V1B, a first minimum potential maintaining waveform T14 maintaining the first minimum potential V1B, and a rear first rising waveform T15 rising from the first minimum potential V1B to the reference potential V0. The first driving pulse P1 causes a first ink droplet to be ejected from the nozzle 65 at a predetermined ejection speed.

[0036] As shown in FIG. 6, the second driving pulse P2 includes a front-side second rising waveform T21 that rises from the reference potential V0 to the second maximum potential V2A, a second maximum potential maintaining waveform T22 that maintains the second maximum potential V2A, a second falling waveform T23 that falls from the second maximum potential V2A to the second minimum potential V2B, a second minimum potential maintaining waveform T24 that maintains the second minimum potential V2B, and a rear-side second rising waveform T25 that rises from the second minimum potential V2B to the reference potential V0. The second driving pulse P2 causes the second ink droplet to be ejected from the nozzle 65 at a predetermined ejection speed. The second maximum potential V2A is smaller than the first maximum potential V1A. The second minimum potential V2B is the same as the first minimum potential V1B. The driving voltage applied to the piezoelectric element 66 to eject the second droplet from the nozzle 65 is smaller than the driving voltage applied to the piezoelectric element 66 to eject the first droplet from the nozzle 65.

[0037] As shown in FIG. 6, the third driving pulse P3 includes a front third rising waveform T31 rising from the reference potential V0 to the third maximum potential V3A, a third maximum potential maintaining waveform T32 maintaining the third maximum potential V3A, a third falling waveform T33 falling from the third maximum potential V3A to the third minimum potential V3B, a third minimum potential maintaining waveform T34 maintaining the third minimum potential V3B, and a rear third rising waveform T35 rising from the third minimum potential V3B to the reference potential V0. The third driving pulse P3 causes the third ink droplet to be ejected from the nozzle 65 at a predetermined ejection speed. The third maximum potential V3A is smaller than the second maximum potential V2A. The third minimum potential V3B is larger than the second minimum potential V2B. The driving voltage applied to the piezoelectric element 66 to eject the third droplet from the nozzle 65 is smaller than the driving voltage applied to the piezoelectric element 66 to eject the second droplet from the nozzle 65.

[0038] The drive signal correction circuit 84 corrects the reference drive signal SP by increasing the drive voltage of at least one of the second drive pulse P2 and the third drive pulse P3 for each print distance H measured by the height detection sensor 50. The drive signal correction circuit 84 corrects the reference drive signal SP using a correction value of a test pattern TP (see FIG. 8) described later. As described later, when the number of print distances H measured by the height detection sensor 50 is four or more, the drive signal correction circuit 84 corrects the reference drive signal SP with the minimum print distance, which is the shortest distance among the print distances H, the maximum print distance, which is the longest distance, and an intermediate print distance, which is intermediate between the minimum print distance and the maximum print distance. When the print distance H is other than the minimum print distance, the intermediate print distance, and the maximum print distance, the drive signal correction circuit 84 corrects the reference drive signal SP by linearly interpolating the reference drive signals corrected with the minimum print distance, the intermediate print distance, and the maximum print distance, respectively.

[0039] The drive signal supply circuit 86 supplies, for each printing distance H, a part or all of either the reference drive signal SP and a corrected reference drive signal corresponding to the printing distance H to each piezoelectric element 66 of the ink head 60. By appropriately selecting the drive pulses to be supplied to the piezoelectric elements 66, it is possible to change the amount (volume) of ink ejected from the nozzles 65 of the ink head 60 during one drive cycle. This makes it possible to change the size of the ink dots formed on the recording medium 5. The printer 10 according to this embodiment is capable of forming three types of dots of different sizes.

[0040] The print distance measurement circuit 87 measures the print distance H (see FIG. 7) between the recording medium 5 placed on the table 35 and the nozzle surface 68 of the ink head 60 by the height detection sensor 50. The print distance measurement circuit 87 controls the carriage motor 21B and the second motor 39B to measure the print distance H. The print distance H is measured, for example, by moving the carriage 20 in the main scanning direction Y and moving the table 35 in the sub-scanning direction X with the recording medium 5 placed on the table 35 before starting printing of the test pattern TP (see FIG. 8). This allows the height detection sensor 50 to pass over the recording medium 5 and measure the print distance H. For the recording medium 5 shown in FIG. 7, the height detection sensor 50 measures four print distances H, namely, the first print distance HA, the second print distance HB, the third print distance HC, and the fourth print distance HD.

[0041] The height adjustment circuit 88 adjusts the position of the table 35 in the vertical direction Z for each printing distance H measured by the height detection sensor 50. That is, the height adjustment circuit 88 adjusts the position of the table 35 in the vertical direction Z so that the distance in the vertical direction Z between the nozzle surface 68 and the test paper 6 (see FIG. 8) placed on the table 35 is the printing distance H for each printing distance H measured by the height detection sensor 50. The height adjustment circuit 88 controls the first motor 39A to adjust the height of the table 35. Note that the height adjustment circuit 88 is configured to adjust the position of the table 35 in the vertical direction Z for each printing distance H when printing a test pattern TP (see FIG. 8) described later on the test paper 6, and does not adjust the position of the table 35 in the vertical direction Z for each printing distance H when printing an image or the like on the recording medium 5. That is, when printing an image or the like on the recording medium 5, the corrected reference drive signal is used to suppress deviation of the landing position of the ink droplets, and the height of the table 35 is not changed during printing. As described later, in order to print a test pattern TP for each printing distance H measured by the height detection sensor 50, after the test pattern TP is printed for one printing distance H, the position of the table 35 in the vertical direction Z is adjusted so as to print another printing distance H. When the measured printing distances H are four or more, the height adjustment circuit 88 adjusts the position of the table 35 in the vertical direction Z when printing the test pattern TP so as to print the minimum printing distance (e.g., printing distance HA) which is the shortest printing distance among the printing distances H, the maximum printing distance (e.g., printing distance HD) which is the longest printing distance (e.g., printing distance HM) which is intermediate (preferably the center) between the minimum printing distance and the maximum printing distance. That is, in the example shown in FIG. 7, it is not necessary to print the test pattern TP at the printing distances HB and HC.

[0042] The pattern printing circuit 90 controls the ink head 60 to print a test pattern TP (see FIG. 8) for which a correction value for correcting the drive voltage is set on the test paper 6 (see FIG. 8) placed on the table 35 adjusted by the height adjustment circuit 88. The test pattern TP is printed using a reference drive signal SP. The pattern printing circuit 90 controls the ink head 60, the carriage motor 21B, and the second motor 39B. The test paper 6 is a flat sheet such as a recording paper without unevenness. The test pattern TP shown in FIG. 8 is printed at a printing distance HD. Here, the inventor of the present application has conducted various studies and found that the deviation of the landing positions of the second and third droplets can be suppressed by appropriately increasing the driving voltage of the second driving pulse P2 for ejecting the second droplet and the driving voltage of the third driving pulse P3 for ejecting the third droplet for each printing distance H.

[0043] As shown in FIG. 8, the test pattern TP includes a plurality of graduation groups C1 to C5. Each of the graduation groups C1 to C5 has a first graduation line L1, a second graduation line L2, and a third graduation line L3. The first graduation line L1 is formed by a second droplet discharged from the nozzle 65 when the carriage 20 moves from right to left in the main scanning direction Y. The second graduation line L2 is formed by a first droplet discharged from the nozzle 65 when the carriage 20 moves from right to left in the main scanning direction Y. The third graduation line L3 is formed by a third droplet discharged from the nozzle 65 when the carriage 20 moves from right to left in the main scanning direction Y. In FIG. 8, "M" is displayed to clarify that the first graduation line L1 is formed by the second droplet, "L" is displayed to clarify that the second graduation line L2 is formed by the first droplet, and "S" is displayed to clarify that the third graduation line L3 is formed by the third droplet, but "M", "L", and "S" are not actually printed. The first droplets forming the second graduation line L2 are suitable as a reference because the deviation of the landing position is relatively small. For this reason, it is preferable to form the second graduation line L2 behind the first graduation line L1 and in front of the third graduation line L3. The front end of the second graduation line L2 is located in front of the rear end of the first graduation line L1. The rear end of the second graduation line L2 is located behind the front end of the third graduation line L3. That is, the second graduation line L2 is printed so that it can partially overlap the first graduation line L1 and the third graduation line L3. For example, when the table 35 on which the test paper 6 is placed is moved from the rear to the front, the first graduation line L1, the second graduation line L2, and the third graduation line L3 are formed in this order.

[0044] As shown in FIG. 8, the increase in the drive voltage at the first scale line L1, the second scale line L2, and the third scale line L3 is different for each of the scale groups C1 to C5. In this embodiment, when the drive voltage of the reference drive signal SP is used as a reference, the drive voltage differs by 0.2 V between adjacent scale groups C1 to C5. For example, the scale group C1 is 0.2 V higher than the drive voltage of the reference drive signal SP, and the scale group C5 is 1.0 V higher than the drive voltage of the reference drive signal SP. Note that the interval between the drive voltages is not limited to 0.2 V. Different numbers are printed in front of the first scale line L1 of each of the scale groups C1 to C5. These numbers are printed as part of the scale groups C1 to C5. These numbers are correction values ​​that indicate the increase in the drive voltage. However, this is a setting in the printer 10, and does not represent the actual increase in the drive voltage. The number "1" in this number corresponds to, for example, increasing the drive voltage by "0.2 V". In other words, the drive voltage increases by 0.2 V every time the number increases by 1. For example, when the number is 5, the drive voltage increases by 1.0 V.

[0045] In the example shown in FIG. 8, in the scale group C4, the third scale line L3 and the second scale line L2 are at the same position in the main scanning direction Y. As a result, for the drive pulse P3 that ejects the third droplet, as shown in FIG. 9, the potential is increased by 0.8 V from the third maximum potential V3A, thereby increasing the drive voltage of the drive pulse P3. Also, in the scale group C3, the first scale line L1 and the second scale line L2 are at the same position in the main scanning direction Y. As a result, for the drive pulse P2 that ejects the second droplet, as shown in FIG. 9, the potential is increased by 0.6 V from the second maximum potential V2A, thereby increasing the drive voltage of the drive pulse P2. As described above, the drive signal correction circuit 84 corrects the reference drive signal SP by increasing the drive voltage of the drive pulse P2 by 0.6 V and the drive voltage of the drive pulse P3 by 0.8 V for the printing distance HD. In this way, the drive signal correction circuit 84 corrects the reference drive signal SP using the correction value of the test pattern TP printed on the test paper 6. The correction value is input, for example, by the user operating the operation panel 25 (see FIG. 1). FIG. 9 shows an example of the corrected reference drive signal RSP1. Note that in FIG. 9, the waveform of the reference drive signal SP is shown by a dashed line for reference. When printing an image or the like on the recording medium 5, the drive signal supply circuit 86 supplies the corrected reference drive signal RSP1 to each piezoelectric element 66 of the ink head 60 for the portion of the recording medium 5 that is within the printing distance HD.

[0046] FIG. 10 shows the reference drive signal RSP2 corrected based on a test pattern (not shown) printed at the printing distance HA. In the example shown in FIG. 10, for the drive pulse P3 for ejecting the third droplet, the potential is increased by 0.2 V from the third maximum potential V3A to increase the drive voltage of the drive pulse P3, and for the drive pulse P2 for ejecting the second droplet, the potential is increased by 0.4 V from the second maximum potential V2A to increase the drive voltage of the drive pulse P2. As described above, the drive signal correction circuit 84 corrects the reference drive signal SP by increasing the drive voltage of the drive pulse P2 by 0.4 V and the drive voltage of the drive pulse P3 by 0.2 V for the printing distance HA. Note that in FIG. 10, the waveform of the reference drive signal SP is shown by a dashed line for reference. When printing an image or the like on the recording medium 5, the drive signal supply circuit 86 supplies the corrected reference drive signal RSP2 to each piezoelectric element 66 of the ink head 60 for the portion of the recording medium 5 at the printing distance HA.

[0047] 7, for the printing distances HB and HC, the driving signal correction circuit 84 corrects the reference driving signal SP by linearly interpolating a corrected reference driving signal RSP1 corresponding to the printing distance HD, a corrected reference driving signal RSP2 corresponding to the printing distance HA, and a corrected reference driving signal (not shown) corresponding to the intermediate printing distance HM. When printing an image or the like on the recording medium 5, the driving signal supply circuit 86 supplies a reference driving signal (not shown) corrected by linear interpolation to each piezoelectric element 66 of the ink head 60 for the portions of the recording medium 5 that are at the printing distances HB and HC. Note that the reference driving signal corrected by linear interpolation differs for each printing distance H. In the example shown in Figure 7, when printing an image or the like on the recording medium 5, the drive signal supply circuit 86 supplies a corrected reference drive signal RSP2 to the portion corresponding to printing distance HA, supplies a reference drive signal corrected by linear interpolation to the portion corresponding to printing distance HB, supplies a reference drive signal corrected by linear interpolation (different from the signal used for printing distance HB) to the portion corresponding to printing distance HC, and supplies a corrected reference drive signal RSP1 to the portion corresponding to printing distance HD.

[0048] As described above, according to the printer 10 of this embodiment, the printing distance H, which is the distance between the recording medium 5 placed on the table 35 and the nozzle surface 68, can be measured by the height detection sensor 50. Then, the drive signal correction circuit 84 of the control device 80 corrects the reference drive signal SP by increasing the drive voltage of the second drive pulse P2 for ejecting the second ink droplet for each printing distance H measured by the height detection sensor 50. Here, the first ink droplet, which is larger than the second ink droplet, is used as the reference ink droplet because the deviation of the landing position is relatively small. Then, the drive signal supply circuit 86 supplies a part or all of the corrected reference drive signal SP corresponding to the printing distance H to the piezoelectric element 66 for each printing distance H. This makes it possible to suppress the deviation of the landing position of the second ink droplet even when the printing distance H changes. In this way, the deviation of the landing position is suppressed by increasing the drive voltage, so that the ink vibration period does not change and the ink droplets can be stably ejected.

[0049] In the printer 10 of this embodiment, the drive signal generation circuit 82 includes a third drive pulse P3 for ejecting a third ink droplet smaller than the second ink droplet by expanding and contracting the pressure chamber 63, and the drive signal correction circuit 84 corrects the reference drive signal SP by increasing the drive voltage of the third drive pulse P3 for each printing distance H measured by the height detection sensor 50. According to the above aspect, it is possible to suppress deviation of the landing position of the third ink droplet even when the printing distance H changes.

[0050] In the printer 10 of this embodiment, the third drive pulse P3 is located ahead of the second drive pulse P2, and the first drive pulse P1 is located behind the second drive pulse P2. Since the longer the printing distance, the slower the landing of small ink droplets becomes and the greater the deviation in landing position becomes, it is necessary to increase the drive voltage. For this reason, by positioning the third drive pulse P3 for ejecting the smallest third ink droplets at the very front, the ejection start time can be made earlier and the landing can be made earlier, so the increase in the drive voltage can be relatively suppressed.

[0051] In the printer 10 of this embodiment, the table 35 is configured to be movable in the vertical direction Z, and the control device 80 includes a height adjustment circuit 88 that adjusts the position of the table 35 in the vertical direction Z for each printing distance H measured by the height detection sensor 50, and a pattern printing circuit 90 that controls the ink head 60 to print a test pattern TP, for which a correction value for correcting the drive voltage is set, on the test paper 6 placed on the adjusted table 35, and the drive signal correction circuit 84 corrects the reference drive signal SP using the correction value. According to the above aspect, the reference drive signal SP can be corrected with greater accuracy.

[0052] In the printer 10 of this embodiment, when the number of printing distances H measured by the height detection sensor 50 is four or more, the drive signal correction circuit 84 corrects the reference drive signal SP for the minimum printing distance HA, which is the shortest distance among the printing distances H, the maximum printing distance HD, which is the longest distance, and the intermediate printing distance HM, which is intermediate between the minimum printing distance HA and the maximum printing distance HD, and when the printing distance H is other than the minimum printing distance HA, the intermediate printing distance HM, and the maximum printing distance HD, the reference drive signal SP is corrected by linearly interpolating the corrected reference drive signals corresponding to the minimum printing distance HA, the intermediate printing distance HM, and the maximum printing distance HD, respectively, and the height adjustment circuit 88 adjusts the position of the table 35 in the vertical direction Z so as to be the intermediate printing distance HM. According to the above aspect, even if there are multiple printing distances H because the recording medium 5 has a complex shape, the reference drive signal SP can be easily corrected by linearly interpolating the reference drive signals corrected for the minimum printing distance HA, the intermediate printing distance HM, and the maximum printing distance HD. In particular, the greater the number of printing distances H, the less it is necessary to print the test pattern TP for every printing distance H, which can reduce ink consumption and ease the adjustment burden on the user.

[0053] In the printer 10 of this embodiment, the intermediate printing distance HM is the center between the minimum printing distance HA and the maximum printing distance HD. According to the above aspect, the reference driving signal SP can be corrected with higher accuracy.

[0054] Although the preferred embodiments of the present invention have been described above, the above-described embodiments are merely examples, and the present invention can be embodied in various other forms.

[0055] In the above-described embodiment, when the number of printing distances H measured by the height detection sensor 50 is four or more, the drive signal correction circuit 84 corrects the reference drive signal SP by linear interpolation, but it is also possible to print test patterns TP for all printing distances H and correct the reference drive signal SP respectively.

[0056] In the above-described embodiment, during linear interpolation, the test pattern TP was printed at printing distance HM, which is the center between printing distance HD and printing distance HA, but the intermediate printing distance is not limited to the center between printing distance HD and printing distance HA, and may be any position between printing distance HD and printing distance HA.

[0057] In the above-described embodiment, the height detection sensor 50 is a non-contact type sensor, but it may be a contact type sensor.

[0058] In the above-described embodiment, the reference drive signal SP has three drive pulses, but is not limited to this. The reference drive signal SP may have two drive pulses, or may have four or more drive pulses. [Explanation of symbols]

[0059] 5 Recording media 6 Test Papers 10 Printer (inkjet printer) 35 Table (Placement stand) 37 First table movement mechanism 38 Second table movement mechanism 39A First Motor 39B Second motor 50 Height detection sensor (sensor) 60 Ink Head 62 Partition plate 63 Pressure Chamber 65 Nozzle 66 Piezoelectric element (actuator) 68 Nozzle surface 80 Control device 82 Drive signal generation circuit 84 Drive signal correction circuit 86 Drive signal supply circuit 87 Print distance measurement circuit 88 Height adjustment circuit 90 Pattern Printed Circuit SP Reference drive signal RSP1 Corrected reference drive signal (HD) RSP2 Corrected reference drive signal (HA) P1 First drive pulse P2 Second drive pulse P3 Third drive pulse

Claims

1. a mounting table on which a recording medium is placed; an ink head having a nozzle that ejects ink droplets toward the recording medium placed on the mounting table and a nozzle surface on which the nozzle is formed; a control device for controlling the ink head, The ink head is a case having a pressure chamber formed therein for storing ink; a partition plate provided in the case and partitioning a part of the pressure chamber; an actuator connected to the partition plate and deforming when an electric signal is supplied thereto; the nozzle formed in the case and communicating with the pressure chamber; The control device a drive signal generation circuit that generates, for each drive cycle, a reference drive signal having at least a first drive pulse for ejecting a first ink droplet by expanding and contracting the pressure chamber, and a second drive pulse for ejecting a second ink droplet that is smaller than the first ink droplet by expanding and contracting the pressure chamber; a drive signal correction circuit that corrects the reference drive signal by increasing a drive voltage of the second drive pulse for each printing distance, which is the distance between the recording medium placed on the placement table and the nozzle face; a drive signal supply circuit that supplies, for each of the printing distances, a part or all of the corrected reference drive signal corresponding to the printing distance to the actuator.

2. the drive signal generation circuit includes a third drive pulse for expanding and contracting the pressure chamber to eject a third ink droplet smaller than the second ink droplet; 2. The inkjet printer according to claim 1, wherein the drive signal correction circuit corrects the reference drive signal by increasing the drive voltage of the third drive pulse for each printing distance.

3. the third drive pulse is positioned before the second drive pulse, 3. The inkjet printer according to claim 2, wherein the first drive pulse is positioned after the second drive pulse.

4. The mounting table is configured to be movable in the vertical direction, The control device a height adjustment circuit for adjusting the vertical position of the mounting table for each of the printing distances; a pattern printing circuit that controls the ink head to print a test pattern, in which a correction value for correcting the driving voltage is set, on a test paper placed on the adjusted mounting table; 4. The inkjet printer according to claim 1, wherein the drive signal correction circuit corrects the reference drive signal using the correction value.

5. When the number of printing distances is four or more, the drive signal correction circuit corrects the reference drive signal for the minimum printing distance, which is the shortest of the printing distances, the maximum printing distance, which is the longest, and an intermediate printing distance that is intermediate between the minimum printing distance and the maximum printing distance, and when the printing distance is other than the minimum printing distance, the intermediate printing distance, and the maximum printing distance, corrects the reference drive signal by linearly interpolating the corrected reference drive signals that correspond to the minimum printing distance, the intermediate printing distance, and the maximum printing distance, respectively; 5. The inkjet printer according to claim 4, wherein the height adjustment circuit adjusts the vertical position of the mounting table so as to achieve the intermediate printing distance.

6. 6. The inkjet printer of claim 5, wherein the intermediate printing distance is midway between the minimum printing distance and the maximum printing distance.

Images