JPH1120165A - Apparatus and method for driving ink-jet recording head and printing apparatus using the apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen a range of a recording dot diameter more by selecting a first, a second driving pulses in one recording cycle when larger dots than dots formed by a first, a second ink drops are to be obtained, and driving a pressure generation element by a driving signal including the selected driving pulses. SOLUTION: A piezoelectric element circuit 50 controls a waveform of a driving signal in accordance with outputs of an address, a clock signals from a control circuit 40. The driving signal comprises a first, a second pulses discharging smaller or larger ink drops in a recording cycle corresponding to one recording pixel. The first pulses are selected singly, or the first, second pulses are selected continuously, whereby a small dot diameter, or a large dot diameter is obtained. When the first, second pulses are continuously selected, a small ink drop is discharged first and a large ink drop is discharged thereafter while a carriage 11 is moved in a main scan direction. A scan speed of the carriage and a discharge timing of both ink drops are adjusted in accordance with a distance between the carriage and a paper, so that both ink drops are brought to the paper with the same timing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving apparatus and method for an ink jet recording head for ejecting ink droplets of different sizes from the same nozzle, and a printing apparatus using the driving apparatus.

[0002]

2. Description of the Related Art An ink jet printer performs two or more multi-value processing on an image to be printed, and based on dot on / off signals obtained as a result of the multi-value processing, each nozzle of a recording head. Controls the formation of dots on the recording medium. Specifically, ink droplets are ejected from a plurality of nozzles on a recording head at predetermined timings, and each of these ink droplets forms dots on the surface of a recording medium such as recording paper to perform recording. I have.
The method of ejecting ink is basically to pressurize the ink for a very short time in the ink passage leading to the nozzle, so that the pressurized ink is ejected as ink droplets from the nozzle tip. is there. Depending on the difference in the generation mechanism of the pressure applied to the ink, there are known a method of generating pressure using an electrostrictive element and a method of applying pressure by generating bubbles due to heating. Regardless of which mechanism is adopted, the ink jet method that discharges ink from the nozzle tip determines whether or not to discharge ink droplets. It is extremely difficult to control it appropriately and freely, and it is not possible to record an intermediate gradation as it is.

Therefore, conventionally, methods such as area gray scale, dither method, and error diffusion method have been proposed in order to express intermediate gray scale. Taking the recording of the intermediate gradation by the area gradation as an example, the recording of the intermediate gradation is realized by expressing one pixel with a plurality of dots such as 4 × 4, 8 × 8, and the like. If one pixel is represented by a 4 × 4 dot matrix, shades can be represented by 16 gradations (17 gradations including all white). If the resolution of the pixel is increased, the gradation can be expressed more finely. However, if the gradation is increased without changing the recording dot diameter, the actual resolution will decrease. In addition, when the recording dot diameter on the recording paper is large, the granularity of the low density region becomes conspicuous. Therefore, it is necessary to reduce the weight of the ink droplet and the diameter of the dot to be recorded.

As a technique for ejecting an ink droplet having a small ink weight in order to reduce the dot diameter, for example, as described in JP-A-55-17589, etc.
There is known an apparatus which performs a so-called "pulling" in which the volume of a pressure generating chamber connected to an ink passage is once expanded and then contracted. By temporarily increasing the volume of the pressure generating chamber, the ink tip surface (meniscus) at the nozzle recedes, so that the ink droplet ejected from the nozzle at the time of pressurization becomes small, and the recording dot diameter can be reduced.

[0005] If the recording dot diameter is small, the granularity in a low density area is not conspicuous and the recording quality can be improved, but the recording speed is greatly reduced. For example, when using only small-diameter dots that are about half the normal recording dot diameter, a recording time four times as long as using a normal recording dot diameter is required. In order to prevent the printing speed from lowering, the driving frequency for ejecting ink droplets may be increased four times, or the number of nozzles may be increased four times, but neither is easy.

Therefore, a technique has been proposed in which ink droplets having different weights are ejected from the same nozzle to enable gradation recording (for example, US Pat. No. 5,285,215). In this technique, a plurality of the same pulse signals are generated within one recording cycle to generate a plurality of minute ink droplets. Trying to create drops.

[0007]

According to the technique described in the above publication, it is possible to control the ejection of minute ink droplets and the ejection of large ink droplets in which a plurality of ink droplets are combined. To ensure that multiple ink droplets of approximately the same size coalesce before landing on paper, there are many conditions, such as the distance from the nozzle tip to the recording paper and the relationship between the ink droplet ejection speed and the head moving speed. Must be satisfied. Similarly, there is a problem that the variable range of the recording dot diameter is narrow.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and uses an ink-jet recording head driving apparatus, a method thereof, and a recording head driving apparatus capable of further expanding the variable range of the recording dot diameter. And a printing device.

[0009]

Means for Solving the Problems and Their Functions and Effects To solve at least a part of such problems, the present invention employs the following constitution. That is, the driving apparatus for an ink jet recording head according to the present invention is a driving apparatus for an ink jet recording head that ejects ink droplets from the nozzle openings by activating pressure generating elements provided corresponding to each of the plurality of nozzle openings. A first drive pulse for discharging a first ink droplet from the plurality of nozzles, and a second driving pulse for discharging a second ink droplet larger than the first ink droplet from the plurality of nozzles. Drive signal generating means for generating a drive signal including two drive pulses, and drive pulse selecting means for selecting at least one of the drive pulses within one recording cycle corresponding to a recording pixel. An element driving unit for driving the pressure generating element by the driving signal including the selected driving pulse, and a first or second ink droplet. When a dot larger than the dot to be formed is to be formed, the first drive pulse and the second drive pulse are selected within the one recording cycle by the pulse selecting means, and both drive pulses are selected. A large dot forming means for forming a large dot on the recording medium by the corresponding ink droplet.

The invention of a method of driving a recording head corresponding to this recording head driving device is characterized in that a pressure generating element provided corresponding to each of a plurality of nozzle openings is actuated so that ink droplets are discharged from the nozzle openings. A method of driving an ink jet recording head for discharging, comprising: a first driving pulse for discharging a first ink droplet from the plurality of nozzles; and a second driving pulse larger than the first ink droplet from the plurality of nozzles. A drive signal including a second drive pulse for ejecting ink droplets is generated, and at least one of the drive pulses is selected within one print cycle corresponding to a print pixel, and the drive signal is selected. When forming a dot larger than the dot formed by the first or second ink droplet, the first drive pulse and the second Of selecting a driving pulse, by the driving signal including a driving pulse which is the selection, and summarized in that for driving the pressure generating element.

According to the driving apparatus and the driving method of the ink jet recording head, at least one of the driving pulses corresponding to the first and second ink droplets having different sizes within one recording cycle. Then, the pressure generating element is driven by a drive signal including the drive pulse. Therefore, the first drive pulse formed corresponding to the first drive pulse
, A dot formed by the second ink droplet formed in response to the second drive pulse, and first and second dots formed in response to both the first and second drive pulses. Can be formed with the ink droplets of
By using at least two of these dots,
It is possible to perform multi-valued processing, such as ternary or higher, in which dots are not formed, small dots are formed, and larger dots are formed.

Further, in the driving apparatus and the driving method of the ink jet recording head, the pressure generating chamber whose volume is reduced by deformation of the pressure generating element to increase the ink pressure is communicated with the ink passage to the nozzle. Set it up,
On the other hand, it is conceivable to determine and control the drive signal as follows. One is that a second drive pulse is formed as a pulse having at least a first signal for expanding the pressure generating chamber, a second signal for maintaining the expanded state, and a third signal for contracting the pressure generating chamber. In addition, the time difference between the timing of the ejection of the first ink droplet and the start timing of the first signal of the second drive pulse is determined by the first time.
Is set longer than the meniscus return time TR from the ink droplet ejection and shorter than TR + 3 · Tm / 8 (Tm is a meniscus natural oscillation cycle). By employing such a configuration, it is easy to make the second ink droplet a large ink droplet by utilizing the movement of the ink due to the meniscus return from the ejection of the first ink droplet.

In this case, the ease with which the ink is ejected is affected by various properties of the ink. For example, it is considered that the higher the viscosity of the ink, the more difficult it is to eject the ink, and the smaller the ink droplet even if the same drive signal is applied. Since the ease with which ink is ejected is affected by the viscosity of the ink or the temperature of the ink which has a strong correlation with the viscosity, if the timing of the first signal of the second drive pulse is always determined at the same timing, Depending on the viscosity, the size of the ink droplet may be undesired. Therefore, the viscosity of the ink or some parameter reflecting the viscosity (for example, the ink temperature) is detected, and the start timing of the first signal is determined based on the detected parameter. It is also preferable that the time difference from the start timing of the first signal is made variable.

Since the viscosity of ordinary ink decreases as the temperature increases, the time difference between the first ink droplet ejection timing and the start timing of the first signal of the second drive pulse is determined by the detected temperature. It is also preferable to change the length to a longer side as the temperature increases from a low temperature. In this case, the size of the second ink droplet can be kept substantially the same regardless of the ink temperature.

In the above-described configuration, when the first ink droplet is ejected, the meniscus vibrates at a unique frequency after the interface (meniscus) at the ink tip has once largely retreated and returned to the original position. Although a large movement of the ink is taken into consideration, when the movement of the ink is observed in detail, there is a vibration due to Helmholtz resonance which is considered to depend on the rigidity and shape of the ink passage and the pressure generating chamber. Therefore, it is also effective to generate a drive signal in consideration of the cycle of the vibration due to Helmholtz resonance. Also in this case, a pressure generating chamber whose volume is reduced by deformation of the pressure generating element to increase the liquid pressure of the ink is provided in communication with the ink path to the nozzle, and the pressure generating chamber for discharging the first ink droplet is provided. The time difference between the timing and the timing of the second ink droplet ejection is:
The time is determined in consideration of the cycle Tc of the oscillation of the ink in the pressure generating chamber due to Helmholtz resonance.

The size of the second ink droplet can be finely controlled by determining the timing of the second pulse for generating the second ink droplet in consideration of the natural vibration of the ink in the ink passage. . It is preferable that such control is performed in combination with the above-described control in consideration of the meniscus return time.

As a method of determining a time difference between the timing of the first ink droplet ejection in consideration of the natural frequency and the timing of the second ink droplet ejection, for example, the time difference is determined by the Helmholtz of the ink in the pressure generating chamber. It is conceivable to determine the period as an integral multiple of the period Tc of the vibration due to resonance.
In the case of the integral multiple, the weight of the second ink droplet can be increased by using the natural vibration.

If the ease of ink ejection increases or decreases due to a change in the properties of the ink, such as the temperature of the ink, the amount of ink ejected should always be increased in consideration of the cycle of oscillation due to Helmholtz resonance. As a result, an undesired amount of ink may be generated. Therefore, a parameter that reflects the ease of ink ejection, for example, the viscosity of the ink (or the temperature of the ink that reflects the ink) is detected, and the timing of the ejection of the first ink droplet is determined based on the parameter. The time difference from the timing of the second ink droplet ejection may be changed to (an integer + 倍) times the period Tc of the oscillation due to Helmholtz resonance as the ink is easily ejected by the detected parameter. Good. Also in this case, even if the properties of the ink change and the ink is easily ejected, the weight of the ink droplet is maintained at the same level.

Furthermore, the above-described ink jet recording head driving device can be considered as a printing device to which the driving method is applied. Such a printing apparatus includes an ink jet recording head that ejects ink droplets from the nozzle openings by operating pressure generating elements provided corresponding to each of the plurality of nozzle openings, and ink droplets ejected from the nozzles. Thus, a printing apparatus for recording an image on a recording medium, further, print data input means for inputting print data having a gradation value for each pixel constituting the image,
A first driving pulse for discharging a first ink droplet from the plurality of nozzles, and a second driving pulse for discharging a second ink droplet larger than the first ink droplet from the plurality of nozzles A drive signal generating means for generating a drive signal comprising: the first and second drive pulses based on a gradation value of the input print data within one print cycle corresponding to a print pixel. Is not selected and neither ink droplet is ejected, or only one of the first and second drive pulses is selected, or both the first and second drive pulses are selected. The gist of the present invention is to include a pulse selecting unit and an element driving unit that drives the pressure generating element by the driving signal including the selected driving pulse.

This printing apparatus is configured such that at least one of the driving pulses corresponding to the first and second ink droplets having different sizes within one recording cycle based on the gradation value of the input print data. A drive pulse is selected, and the pressure generating element is driven by a drive signal including the drive pulse. Therefore, a dot formed by the first ink droplet formed in response to the first drive pulse, a dot formed by the second ink droplet formed in response to the second drive pulse, and the first and second dots are formed.
Can be formed by the first and second ink droplets formed in response to both of the drive pulses, and by using at least two of these dots, a small dot that does not form a dot can be formed. It is possible to perform multi-leveling, such as ternary or higher, in which dots are formed or larger dots are formed. As a result, dots formed by small ink droplets,
Dots with large ink droplets can be easily and reliably formed, and the quality of the formed image can be significantly improved without lowering the printing speed.

In this printing apparatus as well, the first time is taken into consideration in consideration of the meniscus return time TR, the period Tm of the natural vibration thereof, or the natural frequency Tc of the ink in the ink passage.
It is also preferable to determine the relationship between the pulse signal and the second pulse signal.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples. A. Schematic Configuration of Printing Apparatus: First, the overall configuration of the printing apparatus will be described for convenience of explanation. FIG. 2 is a block diagram illustrating a configuration of a printing apparatus as one embodiment of the present invention. As shown, the scanner 12 and the color printer 22 are connected to the computer 90, and a predetermined program is loaded and executed on the computer 90, so that the computer 90 functions as a printing apparatus as a whole. As shown in the figure, the computer 90 includes the following units interconnected by a bus 80 centering on a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program. The ROM 82 previously stores programs and data necessary for the CPU 81 to execute various arithmetic processes.
Is a memory in which various programs and data necessary for executing various arithmetic processing are temporarily read and written. The input interface 84 includes the scanner 12 and the keyboard 14
, And the output interface 85
It is responsible for outputting data to the printer 22. CRTC86
Controls a signal output to the CRT 21 capable of color display, and a disk controller (DDC) 87 controls transmission and reception of data to and from the hard disk 16, the flexible drive 15, or a CD-ROM drive (not shown). The hard disk 16 stores various programs loaded and executed in the RAM 83 and various programs provided in the form of device drivers.

In addition, a serial input / output interface (SIO) 88 is connected to the bus 80. This SIO 88 is connected to the modem 18 and the modem 1
8 is connected to a public telephone line PNT. The computer 90 is connected to an external network via the SIO 88 and the modem 18. By connecting to a specific server SV, it is also possible to download a program required for image processing to the hard disk 16. In addition, it is also possible to load a necessary program from a flexible disk FD or a CD-ROM, and cause the computer 90 to execute the program.

FIG. 3 is a block diagram showing the software configuration of the printing apparatus. In the computer 90, an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and the application program 95 outputs intermediate image data MID to be transferred to the printer 22 via these drivers. An application program 95 for retouching an image reads an image from the scanner 12 and displays the image on the CRT display 21 via the video driver 91 while performing predetermined processing on the image. The data ORG supplied from the scanner 12 is read from a color original, and original color image data OR composed of three color components of red (R), green (G), and blue (B).
G.

This application program 95 is
When a print command is issued, the printer driver 96 of the computer 90 transmits the image information to the application program 9.
5 and converted into a signal that can be processed by the printer 22 (here, a multivalued signal for each color of cyan, magenta, yellow, and black). FIG.
In the example shown in FIG. 5, a resolution conversion module 97, a color correction module 98,
Color correction table LUT and halftone module 99
And a rasterizer 100.

The resolution conversion module 97 serves to convert the resolution of the color image data handled by the application program 95, that is, the number of pixels per unit length into a resolution that can be handled by the printer driver 96. The image data whose resolution has been converted in this way is still RGB.
The color correction module 98 refers to the color correction table LUT and uses the printer 22 for each pixel, cyan (C), magenta (M), yellow (Y), and black, with reference to the color correction table LUT. (K) is converted into data of each color. The data thus color-corrected is, for example, 2
It has a gradation value with a width such as 56 gradations. The halftone module executes halftone processing for expressing such gradation values in the printer 22 by forming dots in a dispersed manner. In the present embodiment, as will be described later, the printer 22 can express three values of no pixel, small dot formation, and large dot formation for each pixel.
Ternary conversion is performed. The image data processed in this way is rearranged by the rasterizer 100 in the order of data to be transferred to the printer 22, and the final image data FN
Output as L. In this embodiment, the printer 22 only plays a role of forming dots in accordance with the image data FNL, and does not perform image processing. Further, the printer driver 96 on the computer 90 side
Although adjustment of the internal piezo element drive signal described later is not performed, setting of a plurality of pulse signals included in the piezo element drive signal and the like are performed by using the bidirectional communication function with the printer 22 and the printer driver 96. It is also possible to do it on the side.

B. Schematic Configuration of Printer : Printer 22
As shown in FIG. 4, a mechanism for conveying the paper P by a paper feed motor 23, a mechanism for reciprocating a carriage 31 in the axial direction of a platen 26 by a carriage motor 24, and a print head 28 mounted on the carriage 31 And a control circuit 40 that controls the exchange of signals with the paper feed motor 23, the carriage motor 24, the print head 28, and the operation panel 32. And a piezo element driving circuit 50 for generating a driving signal for driving the piezo element in response to the signal.

A mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 includes a sliding shaft 34 laid parallel to the axis of the platen 26 and holding the carriage 31 slidably.
A pulley 38 for extending an endless drive belt 36 between the carriage motor 24 and a position detection sensor 39 for detecting the origin position of the carriage 31 are provided.

The carriage 31 has black ink (B
k) cartridge 71 and cyan (C1), light cyan (C2), magenta (M1), light magenta (M
2) A color ink cartridge 72 containing five colors of yellow (Y) ink can be mounted. For two colors, cyan and magenta, two types of inks are provided. A total of six ink ejection heads 61 to 66 are provided on the print head 28 below the carriage 31.
Are formed at the bottom of the carriage 31, and an introduction pipe 6 for guiding ink from the ink tank to the head for each color.
7 (see FIG. 5). When the cartridge 71 for black (Bk) ink and the cartridge 72 for color ink are mounted on the carriage 31 from above, the introduction pipe 67 is inserted into the connection hole provided in each cartridge, and the ejection heads 61 to 66 from each ink cartridge. Can be supplied to the printer.

FIG. 8 is an explanatory diagram showing the arrangement of the ink jet nozzles Nz in the ink discharge heads 61 to 66. The arrangement of these nozzles is composed of six sets of nozzle arrays that eject ink for each color, and 48 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k. The positions of the nozzle arrays in the sub-scanning direction coincide with each other. The 48 nozzles Nz included in each nozzle array need not be arranged in a staggered manner, but may be arranged on a straight line. However, the arrangement in a staggered manner as shown in FIG. 8 has the advantage that the nozzle pitch k can be easily set small in manufacturing.

The ejection of ink from the nozzles Nz is controlled by the control circuit 40 and the piezo element driving circuit 50. FIG. 10 shows the internal configuration of the control circuit 40. As shown in the figure, an interface (hereinafter, referred to as “I / F”) 4 that receives print data including multi-value gradation information from the computer 90 is provided inside the control circuit 40.
3, a RAM 44 for storing various data, a ROM 45 for storing various data processing routines and the like,
A control unit 46 composed of a PU or the like, an oscillation circuit 47, and a drive signal generation circuit 48 as "drive signal generation means" for generating a drive signal for each piezo element of the print head 28 described later.
And the print data and the drive signal developed into the dot pattern data are transmitted to the paper feed motor 23 and the carriage motor 2.
4 and I / O for transmitting to the piezo element drive circuit 50
F49.

From the computer 90, in this embodiment,
Since the print data subjected to the ternarization processing by the printer driver 96 is sent, the control circuit 40 stores the print data in the reception buffer 44A, and then temporarily stores the output buffer in accordance with the arrangement of the nozzle array of the print head. 44
It is sufficient to develop the data in C and output it via the I / F 49. On the other hand, when the data transmitted from the computer 90 is print data including multi-valued gradation information (for example, when the data is PostScript format data),
The printer 22 may perform ternarization processing or the like in the control circuit 40. In this case, the print data is I
The data is stored in the reception buffer 44A inside the recording device via the / F43. After the command analysis is performed on the recording data stored in the reception buffer 44A, the intermediate buffer 4
4B. In the intermediate buffer 44B, the control unit 4
6, the recording data in the intermediate format converted into the intermediate code is held, and the printing position of each character, the type of decoration,
The process of adding the size, font address, and the like is performed by the control unit 46. Next, the control unit 46 analyzes the print data in the intermediate buffer 44B, performs ternarization in accordance with the gradation information, and develops and stores the dot pattern data in the output buffer 44C.

In any case, the ternary dot pattern is developed and stored in the output buffer 44C. The print head is provided for each color 4 as described later.
Since eight nozzles are provided, dot pattern data corresponding to one scan of the head is output to the output buffer 4.
After preparing the dot pattern data for I / O 4C,
Output via F49. The print data developed as dot pattern data is composed of, for example, 2 bits as gradation data for each nozzle, as described later.
“00” has no dots, “10” has small dots,
“11” corresponds to large dot formation. The data structure and the state of dot formation will be described later.

C. Ink ejection mechanism: A mechanism for ejecting ink and forming dots will be described. FIG. 5 is an explanatory diagram showing a schematic configuration inside the ink discharge head 28, and FIG. 6 is a schematic diagram showing a state in which ink is discharged by expansion and contraction of the piezo element PE. When the ink cartridges 71 and 72 are mounted on the carriage 31, the ink in the ink cartridge is sucked out through the introduction pipe 67 by utilizing the capillary phenomenon as shown in FIG. Each color head 61 of the head 28
To 66. When the ink cartridge is first mounted, the operation of sucking the ink into the heads 61 to 66 of the respective colors by a dedicated pump is performed. In this embodiment, a pump for suction and a cap for covering the print head 28 at the time of suction are provided. The illustration and description of such a configuration are omitted.

As will be described later, the heads 61 to 66 for each color are provided with 48 nozzles Nz for each color (see FIG. 8).
Piezo element PE which is one of the electrostrictive elements and has excellent response
Is arranged. As shown in the upper part of FIG. 6, the piezo element PE has an ink passage 6 that guides ink to the nozzle Nz.
It is installed at a position in contact with 8. The piezo element PE is
As is well known, the crystal structure is distorted by the application of a voltage, and the element performs electro-mechanical energy conversion at a very high speed.
In the present embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE contracts by the voltage application time as shown in the lower part of FIG. One side wall 68 is deformed. As a result, the volume of the ink passage 68 shrinks in accordance with the shrinkage of the piezo element PE, and the ink corresponding to this shrinkage is reduced to particles Ip.
As a result, the liquid is discharged at a high speed from the tip of the nozzle Nz. Printing is performed by the ink particles Ip penetrating into the paper P mounted on the platen 26.

The principle of ink droplet ejection using a piezo element has been described with reference to a schematic diagram. Details of an actual ink ejection mechanism using a piezo element PE are shown in FIG. FIG. 7 is a sectional view showing an example of a mechanical sectional structure of the recording heads 61 to 66. As shown in the drawing, this head is mainly composed of an actuator unit 121 and a flow path unit 122. The actuator unit 121 includes a piezo element PE and a first lid member 13.
0, a second lid member 136, a spacer 135 and the like. The first lid member 130 is formed of a thin plate of zirconia having a thickness of about 6 μm, has a common electrode 131 formed on one surface thereof as one pole, and has a piezo on its surface so as to face a pressure generating chamber 132 described later. The element PE is fixed, and a drive electrode 134 made of a relatively flexible metal layer such as Au is formed on the surface of the element PE.

Here, the piezoelectric element PE and the first lid member 130 form a flexural vibration type actuator. The piezoelectric element PE contracts when charge is added and deforms in a direction to reduce the volume of the pressure generating chamber 132, and expands when the added charge is discharged and expands based on the volume of the pressure generating chamber 132. Deform to.

The spacer 135 provided below the first lid member 130 has a through hole formed in a ceramic plate made of zirconia (ZrO 2) having a thickness suitable for forming the pressure generating chamber 132, for example, 100 μm. The pressure generating chamber 132 is formed by sealing both surfaces with a second lid member 136 and a first lid member 130 described later.

The second lid member 136 fixed to the other end of the spacer 135 is made of a ceramic material such as zirconia similarly to the spacer 135. In the second lid member 136, two communication holes 138 and 139 forming an ink flow path with the pressure generating chamber 132 are formed. The communication hole 138 connects an ink supply port 137 to be described later and the pressure generating chamber 132, and the communication hole 13
Reference numeral 9 denotes a connection between the nozzle opening Nz and the other end of the pressure generating chamber 132.

Each of these members 130, 135, 136
The actuator unit 121 is formed by forming a clay-like ceramic material into a predetermined shape, laminating and firing the same, without using an adhesive.

Next, the flow channel unit 122 will be described. The flow path unit 122 includes the ink supply port forming substrate 14.
0, an ink chamber forming substrate 143, a nozzle plate 145, and the like. Ink supply port forming substrate 140
Is also used as a fixed substrate of the actuator unit 121, and has an ink supply port 137 at one end of the pressure generating chamber 132, and a nozzle opening N at one end of the pressure generating chamber 132.
z are provided respectively. Ink supply port 137
Are the ink chamber 141 and the pressure generating chamber 132 common to each nozzle.
And the cross-sectional area thereof is the communication hole 138.
It is designed to be sufficiently smaller than the others and function as an orifice.

The ink chamber forming substrate 143 is a member that forms the ink chamber 141 together with the ink supply port forming substrate 140 with the other surface sealed by the nozzle plate 145, and a nozzle communication hole connected to the nozzle opening 123. 144
Is provided. The ink chamber 141 is connected to an ink channel (not shown) connected to the ink cartridges 71 and 72 so that ink flows from an ink tank (not shown).

The ink supply port forming substrate 140, the ink chamber forming substrate 143, and the nozzle plate 145 are each provided with an adhesive layer 146, 1 such as a heat welding film or an adhesive.
47, and as a whole, the flow path unit 1
22.

The channel unit 122 and the above-mentioned actuator unit 121 are fixed by an adhesive layer 148 such as a heat-sealing film or an adhesive, and constitute the recording heads 61 to 66.

According to the above configuration, when a voltage is applied between the driving electrodes 131 and 134 of the piezo element PE to apply an electric charge, the piezo element PE contracts and the volume of the pressure generating chamber 132 is reduced. Discharges the piezo element PE
Expands, and the volume of the pressure generating chamber 132 increases. When the pressure generating chamber 132 expands, the pressure in the pressure generating chamber 132 decreases and the common ink chamber 141 moves to the pressure generating chamber 132.
The ink flows into the inside. When an electric charge is applied to the piezo element PE, the volume of the pressure generation chamber 132 is reduced, and the pressure generation chamber 1
The pressure in the pressure generating chamber 132 rises in a short time, and the ink in the pressure generating chamber 132 is discharged to the outside via the nozzle opening Nz. At this time, the ink droplet IP is ejected to the outside.

In the ink jet recording print head 28 thus configured, the ink present in the flow path leading to the nozzle Nz causes a vibration phenomenon as a fluid with a change in the pressure of the pressure generating chamber 132. . This vibration has at least two types of natural vibrations. One is a relatively long-period vibration in which a meniscus, which is an ink interface, swings back after an ink droplet is ejected. This is called natural vibration (period Tm). The other is the pressure generating chamber 13
2 is a vibration called Helmholm resonance that occurs in the fluid due to the presence of 2, and is a vibration having a relatively short period (period Tc) as compared with the natural vibration. The Helmholm resonance frequency f of the pressure generating chamber 132 indicates the fluid compliance due to the compressibility of the ink in the pressure generating chamber 132 as Ci, and the first lid member 130 or the piezo element PE forming the pressure generating chamber 132. If the rigidity compliance of the material itself is Cv, the inertance of the nozzle opening 123 is Mn, and the inertance of the ink supply port 137 is Ms, it is expressed by the following equation (1).

F = 1 / (2π) × {(Mn + Ms) / (Mn × Ms) / (Ci + Cv)} (1)

The meniscus compliance is defined as C
Assuming that n, if the viscous resistance of the ink flow path is ignored, the natural oscillation period Tm of the meniscus is expressed by the following equation (2).

Tm = 2π × {(Mn + Ms) Cn} (2)

When the volume of the pressure generating chamber 132 is V, the density of the ink is ρ, and the sound velocity in the ink is c, the fluid compliance Ci is expressed by the following equation (3).

Ci = V / ρc ² (3)

Note that the rigidity compliance Cv of the pressure generating chamber 132 matches the static deformation rate of the pressure generating chamber 132 when a unit pressure is applied to the pressure generating chamber 132. Can be obtained.

The period Tc of the natural vibration excited in the meniscus by the contraction and expansion of the piezo element PE is the same as the period obtained by the reciprocal of the Helmholm resonance frequency f. As an example of the calculation according to the embodiment, the fluid compliance Ci is 1 × 10 ⁻²⁰ m ⁵ N ⁻¹ and the rigidity compliance Cv
Is 1.5 × 10 ⁻²⁰ m ⁵ N ⁻¹ , and the inertance Mn is 2 × 1
0 ⁸ kgm ^-4, Herumuhorumu resonance frequency f when the inertance Ms of 1 × 10 ⁸ kgm ^-4 is 125 kHz, the period Tc becomes 8 .mu.s.

D. Outline of formation of large and small dots: 48 nozzles Nz of each color provided in the printer 22 of the present embodiment
The inner diameters are formed equally. Two types of dots having different diameters can be formed using the nozzle Nz. This principle will be described. FIG. 9 shows the driving waveform of the nozzle Nz when ink is ejected and the ink I ejected.
FIG. 4 is an explanatory diagram schematically showing a relationship with p. The drive waveform indicated by a broken line in FIG. 9 is a waveform when a normal dot is ejected. In the section d2, once a negative voltage is applied to the piezo element PE, the piezo element PE is deformed in a direction to increase the volume of the pressure generating chamber 132.
As shown in the state A, the meniscus Me is the nozzle Nz
Will be indented inside. On the other hand, when a negative voltage is rapidly applied as shown in a section d2 using the driving waveform shown by the solid line in FIG.

The shape of the meniscus differs depending on the pulse waveform of the negative voltage applied to the piezo element PE for the following reason. The piezo element deforms according to the pulse shape of the applied voltage, and increases or decreases the volume of the pressure generating chamber 132. When the volume of the pressure generating chamber 132 increases, if the change is extremely slow, the pressure generating chamber 13
With the increase in the volume of the ink chamber 141, the ink is supplied to the common ink chamber 141.
And the meniscus changes little. On the other hand, when the expansion and contraction of the piezo element PE are performed in a short time and the volume of the pressure generating chamber 132 changes rapidly, the ink chamber 1
The supply of ink from 41 is limited by the ink supply port 137 and cannot be made in time, and the meniscus is affected by a change in the volume of the pressure generating chamber 132. When the change in the voltage applied to the piezo element PE is gradual (see the broken line in FIG. 9), the meniscus retreat is small, and
In the case where the applied voltage changes rapidly (see the solid line in FIG. 9), the meniscus retreat is increased by the balance of the ink supply.

Next, when the voltage applied to the piezo element PE is made positive from the state where the meniscus has receded (section d3),
The ink is ejected based on the principle described above with reference to FIG. At this time, large ink droplets are ejected as shown in states B and C from the state where the meniscus is not much depressed inward (state A). As shown in the state c, a small ink droplet is ejected.

As described above, the dot diameter can be changed according to the change rate when the drive voltage is made negative (section d1, d2). However, in a printer having a plurality of nozzles Nz, it is extremely difficult to perform control for making the waveform of the drive signal different for each dot. Therefore, in the present embodiment, large and small dots are formed by preparing a drive signal including two pulse signals having different waveforms and preparing print data according to this signal. This technique will be described next.

E. Piezo element drive circuit and drive signal: In this embodiment, a drive waveform for forming a small dot having a small dot diameter and a drive waveform for forming a large dot having a large dot diameter are based on such a relationship between the drive waveform and the dot diameter. Two types of drive waveforms for forming dots are prepared (see FIG. 11).
The manner in which large and small ink droplets are formed due to the difference in the drive signal will be described later together with details of the generation of the drive signal.

First, a configuration for generating a drive signal having the waveform shown in FIG. 11 will be described. The drive signal shown in FIG. 11 is generated by the piezo element drive circuit 50. FIG.
FIG. 2 is a block diagram showing an internal configuration of the piezo element driving circuit 50. As shown, a memory 51 for receiving and storing signals from the control circuit 40, a latch 52 for reading and temporarily storing the contents of the memory 51, An adder 53 for adding the output to an output of another latch 54 described later, a D / A converter 56 for converting the output of the latch 54 into analog data, and a voltage amplitude for driving the piezo element PE using the converted analog signal. Amplifying unit 5 that amplifies up to
And a current amplifying unit 58 for supplying a current corresponding to the amplified voltage signal. Here, the memory 51 stores predetermined parameters for determining the waveform of the drive signal. As described later, the waveform of the drive signal is determined by predetermined parameters received from the control circuit 40 in advance. The piezo element driving circuit 50
As shown in FIG. 12, the control circuit 40 receives clock signals 1, 2, 3, data signals, address signals 0 to 3, and a reset signal.

FIG. 13 shows the piezo element driving circuit 5 described above.
FIG. 7 is an explanatory diagram showing how a waveform of a drive signal is determined by a configuration of 0. First, prior to generation of the drive signal, the control circuit 40 sends several data signals indicating the slew rate of the drive signal and the address signal of the data signal to
The signal is output to the memory 51 of the piezo element driving circuit 50 in synchronization with the clock signal 1. Although the data signal has only one bit, as shown in FIG. 14, data is exchanged by serial transfer using the clock signal 1 as a synchronization signal. That is, when transferring a predetermined slew rate from the control circuit 40, first, a data signal of a plurality of bits is output in synchronization with the clock signal 1, and then the address for storing this data is synchronized with the clock signal 2. Output as address signals 0 to 3. Memory 51
Reads the address signal at the timing when the clock signal 2 is output, and writes the received data to the address. Since the address signal is a 4-bit signal of 0 to 3, a maximum of 16 types of slew rates can be stored in the memory 51. Note that the most significant bit of the data is used as a code.

After the setting of the slew rate for each of the addresses A, B,... Is completed, when the address B is output to the address signals 0 to 3, the first clock signal 2 causes
The slew rate corresponding to the address B is held by the first latch 52. In this state, when the clock signal 3 is output next, the value obtained by adding the output of the first latch 52 to the output of the second latch 54 is held in the second latch 54. That is, as shown in FIG. 13, once the slew rate corresponding to the address signal is selected, each time the clock signal 3 is received thereafter, the output of the second latch 54 increases or decreases according to the slew rate. The slew rate stored at the address B is a value corresponding to increasing the voltage by the voltage ΔV1 per unit time ΔT. The increase or decrease is determined by the sign of the data stored at each address.

In the example shown in FIG.
The slew rate stores a value of 0, that is, a value when the voltage is maintained. Therefore, when the address A is made valid by the clock signal 2, the waveform of the drive signal is kept in a state of no increase or decrease, that is, a flat state. Also, the address C stores a slew rate corresponding to a decrease in voltage per unit time ΔT by ΔV2. Therefore, after the address C becomes valid by the clock signal 2, the voltage decreases by this voltage ΔV2.

By simply outputting the address signal and the clock signal 2 from the control circuit 40 by the method described above, the waveform of the drive signal can be freely controlled. Each pulse constituting the drive signal in the embodiment will be described with reference to FIG. First, the driving signal is roughly composed of a first pulse and a second pulse in a recording cycle corresponding to one recording pixel. In the first pulse, the voltage value starts from the intermediate potential Vm (T11) and reaches the maximum potential VP.
The maximum potential VP is maintained for a predetermined time (T13). Next, the first pulse falls at a constant gradient to the first lowest potential VLS (T1
4), the minimum potential VLS is maintained for a predetermined time (T1
5). Thereafter, the voltage value of the first pulse rises again at a constant gradient to the maximum potential VP (T16), and maintains the maximum potential VP for a predetermined time (T17). Thereafter, the first pulse falls at a constant gradient to the intermediate potential Vm (T18).

Here, the charging pulse T12 is applied to the piezo element P
When applied to E, the piezo element PE becomes
Of the pressure generating chamber 132 to generate a positive pressure. As a result, the meniscus rises from the nozzle opening 123. When the potential difference of the charging pulse T12 is large and the voltage gradient is steep, the charging pulse T12
In this embodiment, the potential difference of the charging pulse T12 is set within a range in which the ink droplet is not discharged by the charging pulse T12.
Further, in this embodiment, the charging time of the charging pulse T12 is set to a period equal to or longer than Tc (substantially the same period as Tc in this embodiment) so that the meniscus does not excite the oscillation of the Helmholtz cycle Tc. .

During the application of the hold pulse T13, the meniscus raised by the charging pulse T12 is vibrated at a period Tm due to the surface tension of the ink.
It turns into a move back inside. When the discharge pulse T14 is applied, the piezo element PE bends in a direction to expand the pressure generating chamber 132, and a negative pressure is generated in the pressure generating chamber 132. The movement of the meniscus into the inside of the nozzle opening 123 due to the negative pressure is superimposed on the above-described vibration of the period Tm, and the meniscus is largely drawn into the inside of the nozzle opening 123. As described above, by applying the discharge pulse T14 at the timing when the meniscus moves toward the inside of the nozzle opening 123, the meniscus can be largely drawn into the nozzle opening 123 even with a relatively small potential difference of the discharge pulse T14. In the present embodiment, the meniscus pull-in as described above is guaranteed by setting the duration of the hold pulse T13 to about 1/2 of Tm.

When the charging pulse T16 is applied from the state where the meniscus is drawn, a positive pressure is generated in the pressure generating chamber 132, and the meniscus rises from the nozzle opening 123.
At this time, since the meniscus is largely drawn into the inside of the nozzle opening 123, even if a pressure in the positive pressure direction is applied, the ejected ink droplets are small ink droplets. The discharge pulse T18 is a discharge pulse for suppressing the natural vibration of the meniscus excited by the discharge pulse T14 and the charge pulse T16. Discharge pulse T for inward
18 is applied. As a result, the retreat of the meniscus after the ejection of the minute ink droplet is completed is suppressed to a relatively small value.

Next, the second pulse will be described. Second
The pulse starts from the intermediate potential Vm following the first pulse (T19). The voltage drops to a second minimum potential VLL with a constant gradient (T21), and the minimum potential VLL is maintained for a predetermined time (T22). The minimum potential V of the second pulse
LL is lower than the lowest potential VLS of the first pulse. Then, the voltage value of the second pulse rises at a constant gradient to the maximum potential VP (T23), and maintains the maximum potential VP for a predetermined time (T24). Thereafter, the second pulse falls at a constant gradient to the intermediate potential Vm (T25).

When the discharge pulse T 21 is applied, a negative pressure is generated in the pressure generating chamber 132 as described above, and the meniscus is drawn into the nozzle opening 123. However, by setting the potential difference of the discharge pulse T21 to be smaller than the potential difference of the discharge pulse T14 of the first pulse, the slew rate is set so that the meniscus is not greatly drawn into the nozzle opening 123 as compared with the first pulse. You have set.

When the charging pulse T23 is applied, a positive pressure is generated in the pressure generating chamber 132 and the meniscus is
It rises from 3. At this time, since the pressure change in the positive pressure direction occurs in a state where the meniscus is not so much drawn into the nozzle opening 123, the ejected ink droplet becomes an ink droplet larger than the first pulse. Note that the last discharge pulse T25 of the second pulse is a discharge pulse for suppressing the natural vibration of the meniscus excited by the discharge pulse T21 and the charge pulse T23, and the meniscus is discharged from the nozzle opening 123 by the natural vibration of the cycle Tc. It is applied at the timing heading in the direction.

When the first pulse and the second pulse are successively selected, two ink droplets are eventually displaced from the nozzle Nz, but the two ink droplets are substantially the same on the paper. Land at a position. This is shown in FIG.
5 As shown in the figure, the largest ink dot IPs corresponding to the first pulse and the larger ink droplet IPm corresponding to the second pulse land at almost the same position on the sheet, thereby forming the largest dot. You. When two types of dots are formed by using the drive signals shown in FIG. 11, the amount of change of the piezo element PE is larger in the second pulse, so that the ink droplet IP is ejected vigorously.
The flight speed of the large ink droplet IPm is determined by the small ink droplet I
It is larger than Ps. As described above, since there is a difference in the flying speed of the ink droplet, when the carriage 31 is moved in the main scanning direction, a small ink droplet is ejected first, and then a large ink droplet is ejected. The speed and the ejection timing of both ink droplets are determined by the carriage 31
If the adjustment is made in accordance with the distance between the sheet P and the sheet P, both ink droplets can reach the sheet P at substantially the same timing. In this embodiment, a large dot having the largest dot diameter is thus formed from the two types of drive pulses shown in FIG.

F. Meniscus vibration and tie of second pulse
Mining: As described above, in the present embodiment, the ejection of the ink droplet corresponding to the first pulse and the ejection of the ink droplet corresponding to the second pulse can be performed singly or continuously. In consideration of the vibration of the meniscus, the sum of the ink weights when ink droplets are continuously formed by the pulse and the second pulse is significantly larger than the sum when each ink droplet is formed alone, 1st, 2nd
The pulse formation timing is adjusted. This will be described below. FIG. 16 shows pulse selection and 1
FIG. 4 is an explanatory diagram illustrating a relationship with an ink droplet weight per recording cycle. As shown in the figure, when the first pulse and the second pulse are continuously selected, the ink weight is smaller than the sum of the ink droplet weights when the first pulse and the second pulse are individually selected. It turns out that it increased by 5 ng in total.
This increase in ink weight is obtained by forming the second ink droplet at a predetermined timing in consideration of the movement of the meniscus after ejecting a small ink droplet.
As a result, the ink weight of the small dot (5 ng in the embodiment)
Weight of large dot with respect to (20 ng in the example)
, And the variable range of the recording dot diameter can be substantially widened. Specifically, in the present embodiment, the first timing, which is “the timing of the first ink droplet ejection”, is used.
The time between the end point of the charge pulse T16 of the pulse and the start point of the charge pulse T21 of the second pulse, which is the “start timing of the first signal for expanding the pressure generating chamber”, is referred to as “(1 Of the meniscus return time) + (よ う of the meniscus natural vibration period Tm).

FIGS. 17 and 18 are explanatory views showing the movement of the meniscus in the first embodiment. The vertical axis indicates the meniscus displacement amount, and the horizontal axis indicates time. Reference numeral 707 in the figure indicates the opening surface of the nozzle opening 123, and the nozzle opening surface 707
Below corresponds to the inside of the nozzle opening 123. A curve 708 in the figure indicates the displacement of the meniscus. Therefore, the slope (differential value) of the tangent of the curve 708 in the figure
Indicates the velocity of the meniscus. When an ink droplet is ejected, a curve 7 corresponding to the timing is obtained.
08 is between the horizontal axis and above the horizontal axis, the area of one closed region (hatched portion in the drawing) is substantially proportional to the weight of the ink droplet.

FIG. 17 shows the meniscus displacement when the first pulse is applied alone. Meniscus oscillation peak 7
04, an ink droplet is ejected. That is, at this point, the ink droplets are separated from the meniscus and ejected as minute ink droplets. Thereafter, the meniscus is moved to the nozzle opening surface 7.
07 is drawn in. The meniscus once drawn in starts to return toward the nozzle opening surface 707 due to the surface tension of the meniscus, and reaches the nozzle opening surface 707 at time 701. Here, the elapsed time from the timing of the first ink droplet ejection to the time 701 is “the meniscus return time from the first ink droplet ejection” TR. Further, the meniscus exceeds the nozzle opening surface 707 and starts to return soon. That is, the meniscus causes damped oscillation. Assuming that the time when the meniscus reaches the nozzle opening surface 707 again is 709, the elapsed time from the time 701 to the time 709 is about の of the natural oscillation period Tm of the meniscus. Time 703 is the point at which the meniscus displacement after the first ink droplet ejection becomes maximum, and from time 701 to time 7
The elapsed time of 03 is about 1 of the natural oscillation period Tm of the meniscus.
/ 4. The time 702 is a substantially intermediate time between the time 701 at which the speed of the meniscus going to the outside of the nozzle opening 123 becomes maximum and the time 703, and the elapsed time from the time 701 to the time 702 is about 1/1 / the natural oscillation period Tm of the meniscus. Equal to 8. The time 710 is almost halfway between the time 703 and the time 709, and the elapsed time from the time 701 to the time 710 is equal to about ／ of the meniscus natural oscillation period Tm.

Next, the phenomenon of an increase in the amount of ink droplets when the second pulse is applied following the first pulse will be described with reference to FIG. In the present embodiment, as shown in FIG.
At the point of time 702, “the first time to expand the pressure generation chamber”
The drive signal is set so that the application of the discharge pulse T21 which is the "signal start timing" starts. At this time 702, the state of the meniscus is such that the meniscus displacement speed and the meniscus displacement are both outward of the nozzle opening 123, and thus the discharge pulse T21 of the second pulse
Thus, the effect of drawing the meniscus into the nozzle opening 123 is canceled out, and the amount of pull-in of the meniscus displacement 708 is reduced. As a result, the peak 705 of the meniscus vibration increases due to the application of the charging pulse T23,
The size of the ink droplet separated from the meniscus increases. In FIG. 18, reference numeral 706 in the figure denotes the end point of the charging pulse T16, which is "the timing of the first ink droplet ejection", and the discharge pulse T21, which is "the start timing of the first signal for expanding the pressure generating chamber". The time difference from the starting point is shown.

FIG. 19 shows the relationship between the phase of the "start timing of the first signal of the second pulse" and the total weight of ink droplets ejected by the first and second pulses. The vertical axis indicates the total value of the ink droplet weights ejected by the first pulse and the second pulse, and the horizontal axis indicates the time. Ink drop weight curve G
I indicates the start timing of the first signal of the second pulse at time 7
The total value of the ink amount is measured while varying from 01 to 710. The total sum of the ink droplet weights reaches a maximum value of 20 ng when the start timing of the first signal of the second pulse is around time 702, and as the start timing of the first signal of the second pulse increases, the first pulse and the second pulse increase. Ink droplet weight when each pulse is ejected independently (5 + 10
=) Approaching 15 ng. Conversely, the first pulse of the second pulse
Even when the start timing of the signal is shortened, the sum of the ink droplet weights is reduced. This is because the meniscus has nozzle opening 1
23, the meniscus is further discharged by the discharge pulse T21 of the second drive pulse.
It is thought that it is to try to draw in the inside of No.3. From FIG. 18, the time difference between the timing of the first ink droplet ejection and the start timing of the first voltage drop waveform of the second drive pulse is longer than the meniscus return time TR from the first ink droplet ejection, (The meniscus return time TR from the first ink droplet ejection) + (3/3 of the meniscus natural oscillation period Tm)
8) It is understood that it is desirable to make the length shorter. That is,
If the start timing of the first signal of the second pulse is the time from time 701 to time 710, the weight of the ink droplet can be increased as compared with the case where ink droplets are ejected by two pulses.

G. Modified Example of Driving Circuit 50: In the first embodiment described above, the driving signal added to the piezo element PE is generated using the D / A converter 56 based on a command from the control circuit 40 side. A driving circuit for generating a signal can be realized by a circuit 50A illustrated in FIG. An example of the configuration of such a driving circuit 50A is shown in FIG.
It will be described based on. The driving circuit 50A includes the head 2
8 corresponding to the shift registers 253A to 253A.
3N, latch elements 254A to 254N, level shifter 2
55A to 255N, switch elements 256A to 256N,
It is composed of piezo elements 257A to 257N. The print data is composed of 2-bit data for each nozzle as shown in (10) and (11). Then, the bit data of each digit for all nozzles is input to the shift registers 253A to 253N within one recording cycle.

That is, after the data of bit 2, which is the upper bit for all nozzles, is serially transferred to the shift registers 253A to 253N, the data of bit 2 for all nozzles is latched by the latch elements 254A to 254N. By this latch, next, the data of bit 1 which is the lower bit for all nozzles is transferred to the shift registers 253A to 253A-2.
It is serially transferred to 53N.

When the bit data applied to each of the switch elements 256A to 256N configured as, for example, analog switches is “1”, the drive signal (COM) is directly applied to the piezo elements 257A to 257N, and the respective piezo elements 257A 257N are displaced in accordance with the signal waveform of the drive signal. Conversely, if the bit data applied to each of the switch elements 256A to 256N is "0",
The drive signals to 57A to 257N are cut off, and each of the piezo elements 257A to 257N holds the charge immediately before.

In this circuit 50A, too, the drive signal (COM)
Has the waveform shown in FIG. 1 as in the first embodiment.
The first pulse and the second pulse form a small ink droplet and a large ink droplet.

The first pulse is for discharging a small ink droplet of, for example, about 5 ng. When recording a small dot, the first pulse is selected independently, and a small dot diameter is obtained. In the example shown in FIG. 1, the second pulse is always selected following the first pulse, and the second pulse alone is not selected. In the case of printing a large dot, the first and second pulses are successively selected so that a large ink droplet of, for example, about (5 + 15 =) 20 ng is ejected and a large dot diameter is obtained in the first embodiment. As described in the example.

Regarding the gradation expression, when no dots are formed, no dots are formed (gradation value 1), when only small dots are formed (gradation value 2), when large dots are formed (gradation value 3).
If recording dots are formed on recording paper in the three patterns
It is possible to perform dot gradation of gradation. Note that each gradation value can be represented by 2-bit data such as (00), (01), and (10).

In the case of the gradation value 2 of a small dot that discharges only a small ink droplet, the first
When "1" is applied in synchronization with the generation of the pulse and "0" is applied in the generation of the second pulse, only the first pulse can be supplied to the piezo element 257. That is, the 2-bit data (01) indicating the gradation 2 is converted into the 2-bit data (1
By translating (decoding) to (0), only the first pulse can be applied to the piezo element 257, and the gradation value 2 of the small dot can be realized.

Similarly, when the decoded 2-bit data (11) is given to the switch element 256, the first pulse and the second pulse are applied to the piezo element 257, whereby two small and large ink droplets are printed on the recording paper. Continue to land, and each ink droplet mixes to form a substantially large dot,
A gradation value of 3 can be realized. Similarly, in the case of a non-dot gradation value of 1 where no ink droplet is ejected, 2-bit data (0
0) to the switch element 256, the piezo element 25
No pulse is applied to 7, so that a dot-free tone value of 1 can be realized.

The print data of each 2 bits is transferred to the switch element 2
The specific configuration given to 56 etc. will be supplemented. First,
The output buffer 44C stores 2-bit print data (D1, D2) decoded by the control circuit 46. Here, D1 is a selection signal of the first pulse, and D2 is a selection signal of the first pulse. The 2-bit print data is supplied to the switch elements 256 corresponding to the respective nozzles of the recording head 28 within one recording cycle. Specifically, the number of nozzles of the recording head 28 is n, and the print data of the first nozzle at a certain position in the sub-scanning direction is (D11,
D21) Change the print data of the second nozzle to (D12, D12
22), the data (D11, D12, D13,... D1n) of the first pulse selection signal D1 for all nozzles is serially input to the shift register 253 in synchronization with the clock signal. . Similarly, the data of the second pulse selection signal D2 (D
21, D22, D23,. . . D2n) is transferred to the shift register 253 within one recording cycle. This situation,
This is shown at the bottom of FIG.

As shown in FIG. 11, before the timing at which a target drive pulse is generated, print data for selecting the drive pulse is transferred to the shift register 253. Then, in synchronization with the generation of the target pulse,
The print data set in the shift register 253 is transferred to the latch element 254 and stored. Latch element 254
Is boosted by the level shifter 255 and then added as a drive signal to the piezo element 257 via the switch element 256.

H. Second Embodiment: Next, a second embodiment of the present invention will be described. The overall configuration of the printing apparatus according to the second embodiment is the same as that of the first embodiment. The second embodiment is the first
The difference from the embodiment is that the time difference between the timing of the first pulse of ink droplet ejection and the start timing of the first signal of the second pulse is made variable according to the environmental temperature of the print head 28 for inkjet recording. It is.

FIG. 21 shows a printer 2 according to the second embodiment.
FIG. 2 is a block diagram showing an internal configuration of the second embodiment. The printer 22 of this embodiment includes a timing storage unit 192, a timing control unit 191, a temperature sensor 194, and an AD converter 19 in addition to the control circuit 40 and the piezo element driving circuit 50.
3 is provided. The temperature sensor 194 is a sensor that detects the temperature around the print head 28. This temperature sensor 19
Reference numeral 4 indicates that the environmental temperature is detected as a parameter reflecting the ease of ink ejection. The temperature data measured by the temperature sensor 194 is supplied to the AD converter 193
Is taken into the timing control means 191 via the. The timing control means 191 is based on the temperature data input from the temperature sensor 194,
2 is read in advance, and the “start timing of the first signal of the second pulse” condition is read out and output to the drive signal setting circuit 47 of the control circuit 40. Drive signal setting circuit 47
Takes this condition, determines the start timing condition of the first signal of the second pulse, and adjusts the timing of the signal that outputs the information to the piezo element drive circuit 50 via the I / F 49. Therefore, it is possible to adjust the timing of the drive signal of the second pulse according to the environmental temperature. It is also possible to provide a configuration in which only the temperature sensor 194 is provided and the control circuit 40 determines all timings and the like.

FIG. 22 is a diagram illustrating the movement of the meniscus when the environmental temperature changes to 15 ° C., 25 ° C., and 40 ° C. in the printer using a certain ink. Indicates time. Reference numeral 901 in the figure
Is the displacement of the meniscus at 15 ° C.
Numerals 2 and 903 indicate the displacement of the meniscus at 25 ° C. and 40 ° C., respectively.

The ink of this example is a type of ink whose viscosity changes with temperature.
It has the property of decreasing viscosity. The meniscus displacement 901 at 15 ° C. is larger than the meniscus displacement 902 at 25 ° C., because the flow path resistance increases due to the temperature dependence of the ink viscosity, so that the meniscus vibration is greatly attenuated, and The amplitude of the meniscus due to Helmholtz resonance and the amplitude of the meniscus due to natural vibration are both small. Further, the vibration period Tm of the natural vibration becomes longer due to an increase in the flow path resistance. Conversely, the displacement 901 of the meniscus at 40 ° C. decreases the flow path resistance, so that the attenuation of the meniscus vibration decreases, and the amplitude of the meniscus due to Helmholtz resonance and the amplitude of the meniscus due to the natural vibration both increase. Further, the period T of the natural vibration
m becomes shorter as the flow path resistance decreases.

Thus, the ink used for the printer is
In the case of an ink of a type whose viscosity changes greatly with temperature, the meniscus vibration state changes greatly due to the temperature dependence of the viscosity. If the time difference from the timing is constant irrespective of the environment, the weight of the ink droplet may greatly differ depending on the temperature. This is because the meniscus position and the meniscus velocity at the start timing of the first signal of the second pulse change.

Therefore, when such an ink is used, as shown in FIG. 22, the start timing of the first signal of the second pulse is changed to 25 at 15 ° C. at time 904.
At 90 ° C at 90 ° C and 90 at 40 ° C.
6, and so on, depending on the environmental temperature. As a result, the environmental dependence of the meniscus position and the meniscus velocity can be offset to some extent, and a change in the ink droplet weight of the second pulse due to the environmental temperature can be suppressed with a simple configuration. It should be noted that if there are other parameters related to the ease of ink ejection, the parameters may be similarly detected and reflected on the start timing of the first signal of the second pulse. Various parameters can be considered as such parameters, for example, the density of the ink, the atmospheric pressure, and the secular change of the characteristics of the piezo element. It is desirable to detect these parameters directly, but if it is difficult to detect them directly,
It may be estimated or set by the user. For example, it is possible to estimate the ink density from the weight of the entire ink cartridge immediately after the replacement, or to estimate the secular change in characteristics based on the elapsed time from the start of use.
Further, a sensor for the information such as the atmospheric pressure may be provided in the printer. For example, the computer 90 may receive data from a predetermined measurement period via a telephone line and transfer the data to the printer 22. .

I. Third Embodiment: Next, a third embodiment of the present invention will be described. The printing apparatus, the printer, and the head driving device of the third embodiment conform to the configuration of the second embodiment. The third embodiment is different from the second embodiment in that
The point is that the time difference between the timing of the ink droplet ejection of the pulse and the start timing of the first signal of the second pulse can be changed to a longer side as the temperature becomes higher.

FIG. 23 shows a case where the environmental temperature is 15 ° C., 25 ° C.,
It is a figure which shows the movement of the meniscus when it changes to 0 degreeC, a vertical axis | shaft shows the displacement of a meniscus, and a horizontal axis | shaft shows time.

As shown in FIG. 23, in this embodiment, the start timing of the first signal of the second pulse is set to 15 ° C.
At time 914 and at 25 ° C. at time 915
In addition, at 40 ° C., at time 916, it is variable to a longer side as the temperature becomes higher. In this embodiment, as in the second embodiment, the environmental dependence of the meniscus position and meniscus velocity can be offset to some extent, and the change in the ink drop weight of the second pulse due to the environmental temperature can be suppressed with a simple configuration. . Further, in the present embodiment, by varying the length to a longer side as the temperature becomes higher, the influence of the meniscus Tc vibration immediately after the ejection of the first ink droplet is less likely to occur at the start timing of the second pulse. It has the advantage of realizing a stable flying state with less noise.

J. Fourth Embodiment: Next, a fourth embodiment of the present invention will be described. The fourth embodiment has the same hardware configuration as the first embodiment, but is characterized in that the ejection timing of the second ink droplet is determined in consideration of the period Tc of the form-Holtz resonance. As illustrated in FIGS. 22 and 23, when the movement of the meniscus after the ejection of the small ink droplet by the first pulse is observed in detail, in addition to the large movement of the meniscus according to the period Tm of the natural oscillation of the meniscus, Oscillation of the period Tc due to the Holmhertz resonance whose period is considerably shorter than the period Tm is observed. Therefore, by determining the ejection timing of the second ink droplet in consideration of the period Tc due to the form Hertz resonance, the weight of the ink droplet ejected in accordance with the second pulse can be varied.

For example, FIG. 24 shows the movement of the meniscus in a case where a certain ink is used. FIG. 24 shows that the vibration of the period Tc due to Helmholtz resonance is superimposed on the period Tm due to the natural vibration of the meniscus. I understand.
In FIG. 2, reference numeral 921 denotes the first vibration peak due to Helmholtz resonance after the end of the ejection of the ink droplet by the first pulse, reference numeral 922 denotes the second peak, and reference numeral 923.
Indicates a third peak, and reference numeral 924 indicates a fourth peak. Therefore, the ejection timing of the ink droplet by the second pulse is set to an integral multiple of this cycle Tc (1
2 times, 3 times. ..), the weight of the ink droplet ejected in response to the second pulse can be increased. Also, if the ejection timing of the ink droplet by the second pulse is set to (integer +＋ １) times this cycle Tc,
The weight of the ink droplet ejected in response to the second pulse can be reduced.

As a result, it is possible to finely control the weight of the ink droplet by considering the period Tc of the Helmholtz resonance of the meniscus. Using this feature,
For example, as the viscosity of the ink decreases and the ink droplets are easily ejected, the ejection timing of the second ink droplet is extended (or contracted) from an integral multiple of the period Tc to (integer + ／) times, It is also possible to control such that the weight of ink droplets is kept constant irrespective of the change in viscosity, by canceling out the portion that is more likely to be ejected due to the change in viscosity. Of course, it is also preferable to determine the timing of the first signal of the second pulse and the timing of discharging the second ink droplet in consideration of both the period Tm due to the natural vibration of the meniscus and the period Tc due to the Helmholtz resonance. In this case, it is possible to obtain the widest variable range of the ink weight from the state where both are optimally selected and the ink weight is maximized, to the state where both are worst conditions and the ink weight is minimized. .

Although several embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and may be implemented in various modes without departing from the scope of the present invention. It is possible. For example, in the above embodiment, the piezo element employs PZT of a flexural oscillator type, but may employ PZT of a longitudinal vibration lateral effect. However, in this case, charging and discharging are switched with respect to the flexural oscillator type PZT. Further, the pressure generating element is not limited to a piezo element, and another element such as a magnetostrictive element may be used.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a driving signal of a piezo element according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a printing apparatus according to the present invention.

FIG. 3 is a block diagram illustrating a configuration of a printer driver.

FIG. 4 is an explanatory diagram mainly showing a drive system of an internal configuration of the printer 22.

FIG. 5 is an explanatory diagram illustrating a schematic configuration around an introduction pipe 67 of the printing head.

FIG. 6 is an explanatory view showing the principle of ejecting ink droplets by expansion and contraction of a piezo element.

FIG. 7 is a cross-sectional view illustrating a mechanical structure of an ink ejection mechanism provided in a head.

FIG. 8 is an explanatory view illustrating the arrangement of nozzles in a print head according to the embodiment.

FIG. 9 is a schematic view illustrating the relationship between a drive signal applied to a piezo element and ejection of ink droplets.

FIG. 10 is a block diagram illustrating an electrical configuration inside the printer 22 used in the first embodiment of the present invention.

FIG. 11 is an explanatory diagram illustrating each waveform of a drive signal.

FIG. 12 is a block diagram illustrating an internal configuration of a piezo element driving circuit 50;

FIG. 13 is an explanatory diagram showing a process of generating a drive pulse.

FIG. 14 is a timing chart showing the timing of each signal when a slew rate is set in the memory 51 using a data signal.

FIG. 15 is a schematic diagram illustrating a state where ejected two large and small ink droplets land on a paper P.

FIG. 16 is an explanatory diagram showing a relationship between pulse selection and ink droplet weight per recording cycle.

FIG. 17 is a graph showing an example of meniscus displacement when ink is ejected by a single pulse.

FIG. 18 is a graph showing an example of meniscus displacement when ink is ejected by two consecutive pulses.

FIG. 19 is a graph showing the relationship between the start timing of a first signal of a second pulse and the weight of ink droplets ejected by two pulses.

FIG. 20 is a block diagram illustrating a schematic configuration of a piezo drive circuit according to a modification of the first embodiment.

FIG. 21 is a block diagram illustrating an internal configuration of a printer according to a second embodiment of the present invention.

FIG. 22 is a graph showing the displacement of the meniscus in the second embodiment.

FIG. 23 is a graph showing the displacement of the meniscus in the third embodiment of the present invention.

FIG. 24 is a graph showing displacement of a meniscus in the fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Scanner 14 ... Keyboard 15 ... Flexible drive 16 ... Hard disk 18 ... Modem 21 ... CRT display 22 ... Printer 23 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 28 ... Ink ejection head 31 ... Carriage 32 ... Operation panel 34 ... Sliding shaft 36 ... Drive belt 38 ... Pulley 39 ... Position detection sensor 40 ... Control circuit 43 ... I / F 44 ... RAM 44A ... Reception buffer 44B ... Intermediate buffer 44C ... Output buffer 45 ... ROM 46 ... Control unit 47 ... Oscillation circuit 48 drive signal generation circuit 48A drive signal setting circuit 49 I / F 50 piezo element drive circuit 51 memory 52 first latch 53 shift register 53 adder 54 second latch 55 level shifter 56 ... D / A converter 57 ... Part 5 A to 57N Piezoelectric element 58 Voltage amplifying unit 59 Current amplifying unit 61 to 66 Ink ejection head 67 Introduction tube 68 Ink passage 71, 72 Ink cartridge 80 Bus 81 CPU 82 ROM 83 RAM 84 input interface 85 output interface 86 CRTC 88 SIO 90 computer 91 video driver 95 application program 96 printer driver 97 resolution conversion module 98 color correction module 99 halftone module 100 rasterizer 121 actuator Unit 122: Flow path unit 123: Nozzle opening 130: First lid member 132: Pressure generating chamber 134: Drive electrode 135: Spacer 136: Second lid member 137: Ink supply ports 138, 139 Communication hole 140 ... Ink supply port forming substrate 141 ... Ink chamber 143 ... Ink chamber forming substrate 144 ... Nozzle communication hole 145 ... Nozzle plate 146, 147, 148 ... Adhesive layer 191 ... Timing control means 192 ... Timing storage means 193 ... AD conversion Unit 194 Temperature sensors 253A to 253N Shift registers 254A to 254N Latch elements 255A to 255N Level shifters 256A to 256N Switch elements 257A to 257N Piezo elements

Claims (14)

[Claims] 1. A driving device for an ink jet recording head for ejecting ink droplets from said nozzle openings by activating pressure generating elements provided corresponding to each of said plurality of nozzle openings, wherein: From a plurality of nozzles, and a second drive pulse for discharging a second ink droplet larger than the first ink droplet from the plurality of nozzles. Drive signal generation means for generating a drive signal, and drive pulse selection means for selecting at least one of the drive pulses within one recording cycle corresponding to a previous recording pixel; and the selected drive pulse. Element driving means for driving the pressure generating element by the driving signal including: a dot larger than a dot formed by the first or second ink droplet In the case where the recording medium is to be formed, the first drive pulse and the second drive pulse are selected within the one recording cycle by the pulse selection means, and the recording medium is formed by ink droplets corresponding to both drive pulses. A driving device for an ink jet recording head comprising: a large dot forming means for forming a large dot thereon. 2. The ink jet recording head driving device according to claim 1, wherein a pressure generating chamber whose volume is reduced by deformation of the pressure generating element to increase the liquid pressure of the ink is provided in an ink passage to the nozzle. The drive signal generating means is configured to transmit the second drive pulse to a first signal for expanding the pressure generating chamber, a second signal for maintaining the expanded state, and to contract the pressure generating chamber. A pulse having at least a third signal, and a time difference between the timing of the first ink droplet ejection and the start timing of the first signal of the second drive pulse.
Meniscus return time TR from the first ink droplet ejection
A driving device for an ink jet recording head, which is set to a time longer than TR + 3 · Tm / 8 (Tm is a meniscus natural oscillation period). 3. The driving apparatus for an ink jet recording head according to claim 2, wherein: a detecting unit for detecting a parameter reflecting a property of the ink related to a degree of ejection of the ink; and the detecting unit detects the parameter. A drive device for an ink jet recording head, comprising: timing change means for changing a start timing of the first signal based on a parameter and a time difference between a timing of discharging the first ink droplet and a start timing of the first signal. 4. A sensor for detecting the temperature of the ink as the parameter, wherein the detecting means detects the time difference between the timing of discharging the first ink droplet and the start timing of the first signal. 4. The driving device for an ink jet recording head according to claim 3, wherein the temperature changes from a low temperature to a high temperature to a longer side. 5. The ink jet recording head driving device according to claim 1, wherein a pressure generating chamber, whose volume is reduced by deformation of the pressure generating element to increase the ink pressure, is connected to the ink passage to the nozzle. And the drive signal generating means determines the time difference between the timing of the first ink droplet ejection and the timing of the second ink droplet ejection by the vibration of Helmholtz resonance of the ink in the pressure generating chamber. A driving device for an ink jet recording head, which is a means for determining a time considering a period Tc. 6. The driving apparatus for an ink jet recording head according to claim 2, wherein the drive signal generating means determines a time difference between the timing of discharging the first ink droplet and the timing of discharging the second ink droplet. A drive unit for an ink jet recording head, wherein the time is determined in consideration of a cycle Tc of oscillation of the ink in the pressure generating chamber due to Helmholtz resonance. 7. The driving apparatus for an ink jet recording head according to claim 5, wherein the drive signal generating means determines a time difference between the timing of discharging the first ink droplet and the timing of discharging the second ink droplet. A driving device for an ink jet recording head, wherein the driving frequency is determined as an integral multiple of a period Tc of the vibration caused by Helmholtz resonance. 8. The driving apparatus for an ink jet recording head according to claim 5, wherein: a detecting unit that detects a parameter that affects a degree of ejection of the ink; and The time difference between the timing of the first ink droplet ejection and the timing of the second ink droplet ejection is set to be (an integer + 1 /
2) A driving device for an ink jet recording head, comprising: means for changing the size to twice. 9. A method of driving an ink jet recording head for ejecting ink droplets from said nozzle openings by activating pressure generating elements provided corresponding to each of said plurality of nozzle openings, comprising: From a plurality of nozzles, and a second drive pulse for discharging a second ink droplet larger than the first ink droplet from the plurality of nozzles. And selecting at least one of the driving pulses within one recording cycle corresponding to a recording pixel, and selecting a dot larger than the dot formed by the first or second ink droplet. When the first drive pulse and the second drive pulse are selected within the one recording cycle, the drive including the selected drive pulse is selected. The signal, the driving method of ink jet recording head which drives the pressure generating element. 10. The method of driving an ink jet recording head according to claim 9, wherein, when the drive pulse is generated, the second drive pulse is generated by reducing the volume of the ink by deforming the pressure generating element. Forming a pulse having at least a first signal for expanding the pressure generating chamber for increasing the hydraulic pressure, a second signal for maintaining the expanded state, and a third signal for contracting the pressure generating chamber; Is longer than the meniscus return time TR from the first ink droplet discharge, and is TR + 3 · Tm / 8 (Tm). Is a method of driving the inkjet recording head in which the time is shorter than the meniscus natural oscillation period. 11. The method of driving an ink jet recording head according to claim 9, wherein, when generating the drive pulse, a time difference between the timing of discharging the first ink droplet and the timing of discharging the second ink droplet. The method of driving an ink jet recording head, wherein the time is determined in consideration of a period Tc of the oscillation of the ink in the pressure generating chamber due to Helmholtz resonance. 12. An ink jet recording head for ejecting ink droplets from said nozzle openings by operating pressure generating elements provided corresponding to each of said plurality of nozzle openings, wherein said ink droplets are ejected from said nozzles. A printing apparatus for printing an image on a printing medium, further comprising: printing data input means for inputting printing data having a gradation value for each pixel constituting the image; and a first ink from the plurality of nozzles. Generating a drive signal including a first drive pulse for discharging a droplet and a second drive pulse for discharging a second ink droplet larger than the first ink droplet from the plurality of nozzles; A drive signal generating means for causing the first and second drive pulses to be selected based on a gradation value of the input print data within one recording cycle corresponding to a recording pixel. Drive pulse selecting means for deciding whether to eject ink droplets without selection, to select only one of the first or second drive pulses, or to select both the first and second drive pulses And a device driving means for driving the pressure generating device by the drive signal including the selected drive pulse. 13. A printing apparatus according to claim 12, wherein a pressure generating chamber, whose volume is reduced by deformation of said pressure generating element to increase the ink pressure, is communicated with an ink passage to said nozzle. The drive signal generating means includes: a first signal for expanding the pressure generating chamber, a second signal for maintaining the expanded state, and a third signal for contracting the pressure generating chamber. And a time difference between the timing of the first ink droplet ejection and the start timing of the first signal of the second drive pulse.
Meniscus return time TR from the first ink droplet ejection
A printing apparatus which is means for determining a time longer than TR + 3 · Tm / 8 (Tm is a meniscus natural oscillation cycle). 14. The printing apparatus according to claim 12, wherein a pressure generating chamber whose volume is reduced by deformation of said pressure generating element and which increases the ink pressure is communicated with an ink passage to said nozzle. The driving signal generating means may be configured to determine a time difference between the timing of the first ink droplet ejection and the timing of the second ink droplet ejection in consideration of a period Tc of vibration of the ink in the pressure generating chamber due to Helmholtz resonance. A printing device as a means for determining the time taken