JPH11170526A - Ink jet printer and recording head driver and driving method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet printer in which generation of satellite drop can be suppressed, and a recording head driver and a driving method for ink jet printer. SOLUTION: Two piezoelectric element 116a, 116b are provided for each ink chamber 114 corresponding to a nozzle 118. The element 116b on the nozzle side is displaced previously in the contracting direction of the ink chamber. Under that state, the supply side element 116a is displaced in the contracting direction of the ink chamber to start jetting of ink drop and then the other element 116b is displaced in the expanding direction of the ink chamber to generate a negative pressure in the ink chamber 114. Consequently, the tail of an ink drop is pulled back and made thin and thereby it is cut quickly. According to the arrangement, generation of a satellite drop can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer for ejecting ink droplets from a nozzle to perform recording on a recording sheet, and a drive apparatus and method for a recording head for the ink jet printer.

[0002]

2. Description of the Related Art In recent years, an ink jet printer which discharges ink droplets from a nozzle portion communicating with an ink chamber and performs recording on recording paper has become widespread. Conventionally, in this type of ink jet printer, one piezoelectric element is provided corresponding to one nozzle. The piezoelectric element is, for example, fixed to a vibration plate forming an outer wall of an ink chamber to which ink is supplied via an ink flow path, and bends in accordance with a voltage waveform of a drive signal to be applied. The discharge pressure is generated by changing the volume of the ink droplet, and the ink pressure can be discharged from the nozzle by the discharge pressure.

[0003] In this type of ink jet printer, since the discharge pressure is generated by changing the volume of the ink chamber as described above, the ink discharged from the nozzles becomes columnar (trails). (In the form), and a time difference and a speed difference occur between the leading portion and the trailing portion of the flying ink. For this reason, a small satellite-like unnecessary ink droplet (hereinafter, referred to as a small ink droplet) accompanies the preceding main ink droplet.
Called satellite drops. ) Occurs and lands on the recording paper, resulting in an undesirable printing result.
In this case, the generation of satellite droplets does not have a great effect on the image quality in a dark image in which printing is performed with relatively large ink droplets, but small ink droplets such as when expressing a light-density image or a halftone image. When recording is performed by using, it is expected that the image quality is significantly reduced due to the generation of satellite droplets. Therefore, the generation of satellite droplets when discharging small-sized ink droplets is a serious problem.

[0004] To cope with this problem, several measures have been proposed in the past. For example, Japanese Patent Application Laid-Open No. 7-760
No. 87 proposes a method in which one piezoelectric element is provided for one nozzle, and the changing speed of the discharge voltage applied to the piezoelectric element is switched between two stages to discharge ink droplets. According to this method, as shown in FIG. 9, the discharge voltage is initially increased with the first voltage change speed v1,
The discharge voltage is increased from the middle with a second voltage change speed v2 greater than v1. Note that FIG.
The vertical axis represents voltage, and the horizontal axis represents time. According to this method, the ink is continuously ejected in a manner to follow the leading portion of the previously ejected ink, so that the speed difference between the leading portion and the trailing portion of the ink column is reduced,
Satellite drops are less likely to occur.

[0005] For example, see Japanese Patent Application Laid-Open No. Sho 59-133067.
Japanese Patent Application Laid-Open Publication No. H11-15083 proposes a method in which one piezoelectric element is provided for one nozzle, and two independent voltage pulses are applied to the piezoelectric element to discharge ink droplets. In this method, as shown in FIG. 10, first, a first pulse P1 is applied to a piezoelectric element to cause a first pressure fluctuation to start ejection of an ink droplet from a nozzle. The second pulse P2 is applied to the piezoelectric element after the pulse P1 is completed and before the ink droplet is ejected from the nozzle, to cause a second pressure fluctuation. FIG.
At 0, the vertical axis represents voltage and the horizontal axis represents time. According to this method, the ink column ejected from the nozzle is broken at an early stage,
Satellite drops are less likely to occur.

[0006] For example, in Japanese Patent Application Laid-Open No. Sho 51-45531, two pressure generating means are provided for one nozzle, and ink is vibrated by superimposing vibrations from these two pressure generating means. There has been proposed an ink droplet ejection apparatus which ejects ink droplets by using the above method.

[0007]

However, in the method described in Japanese Patent Application Laid-Open No. 7-76087, the first voltage change speed v1 must be always smaller than the second voltage change speed v2. . For this reason, the flying speed of the ejected ink droplets is inevitably reduced as compared with the case where the voltage is changed at the high voltage change speed v2 over the entire ejection process. A decrease in the flight speed of the ink droplets is caused by the deterioration of the linearity of the flight route and the dispersion of the flight speed.
Since instability of ejection is caused, there is a possibility that a shift of a recording dot occurs and print quality is deteriorated.

In the method described in Japanese Patent Application Laid-Open No. Sho 59-133067, after terminating the first pulse P1, the second pulse P2 is placed at a certain time interval Ti.
Therefore, if the time interval Ti is large, the trailing of the ink column becomes long, making it difficult to prevent the generation of satellite droplets. On the other hand, if the time interval Ti is small, the piezoelectric element cannot follow the voltage change, and the desired operation cannot be obtained. In general, a piezoelectric element has a unique vibration characteristic and cannot operate at a frequency higher than its natural frequency. It is thought that this problem can be solved by manufacturing a piezoelectric element having a high natural frequency.However, increasing the natural frequency of the piezoelectric element has a limit, and involves the technical difficulties. It is not realistic because it leads to high costs. Also, in the above publication,
The second pulse P2 is higher than the voltage value V1 of the first pulse P1.
Although the voltage value V2 of the first pulse P1 is smaller than the voltage value V1 of the first pulse P1, the voltage value V2 of the second pulse P2 is smaller than the voltage value V1 of the first pulse P1. It is necessary to increase the value V2. However, increasing the voltage applied to the piezoelectric element is expected to shorten the life of the piezoelectric element and the vibration plate excited by the piezoelectric element, and is expected to increase the residual vibration and deteriorate the frequency characteristics. You.

Further, the ink droplet discharge device described in the above-mentioned Japanese Patent Application Laid-Open No. 51-5931 is intended to discharge ink droplets efficiently with a small power supply input. In addition, while applying a high-frequency drive signal to each of the two pressure generating means, and changing the phase difference and the amplitude of these high-frequency drive signals, the vibrations from the two pressure generating means are overlapped well to vibrate the ink, In this way, ink droplets are ejected. That is, this ink droplet ejection device is not intended to prevent the generation of satellite droplets,
There is no configuration for that. There is no such suggestion.

As described above, conventionally, the flying speed of the ejected ink droplets, the life of the apparatus, and the frequency characteristics are not reduced, and the restriction is imposed by the natural vibration characteristics of the piezoelectric element. Therefore, it was difficult to sufficiently suppress the generation of satellite droplets.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to overcome the above-mentioned problems and to suppress the occurrence of satellite droplets during ink droplet ejection, and an ink jet printer. An object of the present invention is to provide a driving device and a method of a recording head for an inkjet printer.

[0012]

An ink jet printer according to the present invention is provided with a nozzle portion for discharging ink droplets, an ink chamber for supplying ink to the nozzle portion, and a displaceable nozzle provided for each nozzle portion. A discharge pressure generating means for generating a pressure for discharging ink droplets from the nozzles by changing the volume of the ink chamber, and a pressure change means provided for each nozzle to change the volume of the ink chamber by displacement. An auxiliary droplet preventing pressure generating means for generating pressure for suppressing the generation of incidental ink droplets at the time of ink droplet ejection from the nozzle portion; The ejection pressure generating means is displaced in the ink chamber contraction direction for ejecting ink droplets, and the displacement of the ejection pressure generating means in the ink chamber contraction direction is performed. Ink chamber in its contracted, and a discharge control means for performing control to displace the associated drop prevention pressure generating means in the ink chamber expands direction by. Here, “in a contracted state” mainly means a contracted state.

A drive device for a recording head for an ink jet printer according to the present invention is provided with a nozzle portion for discharging ink droplets, an ink chamber for supplying ink to the nozzle portion, and is provided for each nozzle portion, and is displaced. A discharge pressure generating means for generating a pressure for discharging ink droplets from the nozzles by changing the volume of the ink chamber, and a pressure change means provided for each nozzle to change the volume of the ink chamber by displacement. An apparatus for driving a recording head for an ink jet printer, comprising: a pressure generating means for preventing the generation of incidental ink droplets when an ink droplet is ejected from a nozzle unit; In addition, the accompanying small droplet preventing pressure generating means is displaced in the ink chamber contracting direction in advance, and the discharging pressure generating means is used for discharging the ink droplets. Control in which the accompanying small droplet preventing pressure generating means is displaced in the ink chamber expansion direction when the ink chamber is in a contracted state by the displacement operation of the ejection pressure generating means in the ink chamber contracting direction. And a discharge control means for performing the discharge control.

A method of driving a recording head for an ink jet printer according to the present invention is characterized in that a nozzle unit for discharging ink droplets, an ink chamber for supplying ink to the nozzle unit, and a nozzle unit are provided for each nozzle unit and are displaced. A discharge pressure generating means for generating a pressure for discharging ink droplets from the nozzles by changing the volume of the ink chamber, and a pressure change means provided for each nozzle to change the volume of the ink chamber by displacement. A method of driving a recording head for an ink jet printer, comprising: a pressure generating means for preventing the generation of incidental ink droplets when an ink droplet is ejected from a nozzle unit; Displacing the associated droplet prevention pressure generating means in the ink chamber contracting direction in advance, and setting the discharging pressure generating means for discharging the ink droplets to the ink chamber. A step of displacing in the contracting direction and a step of displacing the accompanying droplet preventing pressure generating means in the ink chamber expanding direction when the ink chamber is in a contracted state by the displacement operation of the ejection pressure generating means in the ink chamber contracting direction. And

In the ink jet printer or the apparatus or method for driving a recording head for an ink jet printer according to the present invention, the ejection of ink droplets is performed in a state where the accompanying small droplet preventing pressure generating means is displaced in the ink chamber contracting direction in advance. Therefore, when the ejection pressure generating means is displaced in the ink chamber contraction direction and the ink chamber is in a contracted state by the displacement operation of the ejection pressure generation means in the ink chamber contraction direction, accompanying small droplets are generated. An operation of displacing the prevention pressure generating means in the ink chamber expansion direction is performed. Thus, the trailing portion of the ink pushed out of the nozzle portion by the displacement of the ejection pressure generating means is pulled back by the displacement of the accompanying droplet preventing pressure generating means, and the ink droplet is cut off earlier before the ink droplet long trails. .

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of a main part of an ink jet printer according to an embodiment of the present invention.
In the present embodiment, an ink jet printer having a multi-nozzle head having a plurality of nozzles will be described. However, the present invention is also applicable to an ink jet printer having a single nozzle head having a single nozzle. The driving apparatus and method for a recording head for an ink jet printer according to the embodiment of the present invention are embodied by the ink jet printer according to the present embodiment, and will be also described below.

The ink jet printer 1 has a recording head 11 for discharging ink droplets onto a recording sheet 2 for recording, an ink cartridge 12 for supplying ink to the recording head 11, a position of the recording head 11, and recording. A head position / paper feed controller 13 for controlling the paper feed of the paper 2; a head controller 14 for controlling the ink droplet ejection operation of the recording head 11 by a drive signal 21; and performing predetermined image processing on input image data. An image processing unit 15 that supplies the print data 22 to the head controller 14, and a system controller 16 that controls the head position / paper feed controller 13, the head controller 14, and the image processing unit 15 by control signals 23, 24, and 25, respectively. Have. Here, the head controller 14 corresponds to “ejection control means” in the present invention.

FIG. 2 shows a perspective sectional structure of the recording head 11 in FIG. 1, and FIG. 3 shows a sectional structure of the recording head 11 in FIG. As shown in these drawings, the recording head 11 includes a thin nozzle plate plate 111, a flow path plate 112 stacked on the nozzle plate 111, and a vibration plate 113 stacked on the flow path plate 112. It is configured. These plates are bonded to each other by, for example, an adhesive (not shown).

Concave portions are selectively formed on the upper surface side of the flow path plate 112, and these concave portions and the vibrating plate 1 are formed.
13 form a plurality of ink chambers 114 and a common channel 115 communicating with these ink chambers. The communicating portion between the common flow channel 115 and each of the ink chambers 114 is a squeezed path, and has a structure in which the width of the flow channel increases in the direction toward each of the ink chambers 114 from here. A pair of piezoelectric elements 1 made of, for example,
16a and 116b are fixed at a fixed distance from each other. Electrodes (not shown) are laminated on the upper and lower surfaces of the piezoelectric elements 116a and 116b, respectively. A drive signal from the head controller 14 (FIG. 1) is applied to these electrodes to apply the piezoelectric elements 116a and 116b, By flexing the vibration plate 113, the ink chamber 114
Can be increased (expanded) or decreased (contracted). Here, the ink chamber 114 corresponds to the “ink chamber” in the present invention.

In this embodiment, the piezoelectric element 116
a and 116b are displacement amounts (hereinafter, referred to as the displacement amounts) for the same applied voltage.
It is called displacement capacity. ) Are configured to be equal. Therefore, in the present embodiment, the piezoelectric elements 116a,
The material, thickness, and area of 116b are equal. Thus, the same change in volume can be given to the ink chamber 114 for the same applied voltage. However, by changing the area and thickness of the two piezoelectric elements 116a and 116b,
You may comprise so that the displacement capability of both may differ. Here, the piezoelectric element 116a corresponds to the "discharge pressure generating means" of the present invention, and the piezoelectric element 116b corresponds to the "assisting droplet preventing pressure generating means" of the present invention.

The common channel 115 in each ink chamber 114
The portion on the opposite side to the side that communicates with the channel has a structure in which the width of the flow channel gradually narrows.
12 is provided with a channel hole 117 drilled in the thickness direction. The passage hole 117 communicates with a minute nozzle 118 formed in the lowermost nozzle plate 111, and an ink droplet is ejected from the nozzle 118. In the present embodiment, the recording head 1
1, a plurality of nozzles 118 are formed at regular intervals in a row along the paper feed direction (arrow X in FIG. 2) of the recording paper 2 (FIG. 1). However, another arrangement (for example, a staggered two-row arrangement) may be used. Here, the nozzle 118 corresponds to the “nozzle part” in the present invention.

The common flow path 115 communicates with the ink cartridge 12 shown in FIG. 1 (not shown in FIGS. 2 and 3). Then, the ink is always supplied from the ink cartridge 12 to the respective ink chambers 114 via the common flow channel 115 at a constant speed. The supply of the ink can be performed by using, for example, a capillary phenomenon. Alternatively, the ink may be supplied by providing a predetermined pressurizing mechanism in the ink cartridge 12 and pressurizing the ink.

The recording head 11 having the above-described configuration is configured such that ink droplets are reciprocated in a direction Y (FIG. 2) perpendicular to the paper feeding direction X of the recording paper 2 by a carriage driving motor (not shown) and a carriage mechanism associated therewith. Is ejected to record an image on the recording paper 2.

The head controller 14 shown in FIG.
For example, although not shown, a microprocessor, a ROM (Read Only Memory) storing a program to be executed by the microprocessor, and a work memory used for a predetermined operation and temporary data storage by the microprocessor. RAM (Random Access Me)
mory), a driving waveform storage unit including a non-volatile memory,
Digital / analog (D / A) for converting digital data read from the drive waveform storage into analog
It comprises a converter and an amplifier for amplifying the output of the D / A converter. Here, the driving waveform storage unit
The piezoelectric elements 116a and 116 of each nozzle of the recording head 11
The waveform data indicating the respective voltage waveforms of the drive signals 21a and 21b for driving b respectively is stored in the form of a set.
These waveform data are created by, for example, setting various parameters (time parameter and voltage parameter) shown in FIG. 4 to various values. However, a certain relationship described later is maintained between the drive signal 21a and the drive signal 21b of each set. These waveform data are read out by the microprocessor, respectively, and D /
After being converted into an analog signal by an A converter, the signal is amplified by an amplifier, and the same number of drive signals 21a and 21b as the number n of nozzles
Is output as a set. The head controller 14
Is not limited to the above-described configuration, and may be configured differently.

Of these sets of drive signals, each drive signal 21a is applied to the corresponding nozzle piezoelectric element 116a, and each drive signal 21b is applied to the corresponding nozzle piezoelectric element 11a.
6b. In FIG. 1, n
The set of drive signals 21 a and 21 b is drawn together as a drive signal 21.

FIG. 4 shows an example of the waveform of one cycle (T) of each of the drive signals 21a and 21b. FIG. 3A shows the drive signal 21a, and FIG. 3B shows the drive signal 21b. Here, the vertical axis represents voltage and the horizontal axis represents time, and time proceeds from left to right in the figure. Among these, the drive signal 21a is an ejection drive signal for generating a pressure for ejecting ink droplets, and can take a pull-in voltage Vp and an ejection voltage Va in addition to the reference voltage 0V. The drive signal 21b is an auxiliary drive signal for generating a pressure that suppresses the generation of satellite droplets when ejecting ink droplets, and can take a reference voltage 0V and a pull-in voltage Vp.
The set of drive signals 21a and 21b is
4 is switched appropriately for each discharge cycle and supplied to the corresponding nozzle.

Here, referring to FIG. 5, drive signal 21a
Will be described. FIG. 5 shows the waveform of the drive signal and the piezoelectric element 116a to which the drive signal is applied.
And the change of the position of the tip of the ink in the nozzle 118 (hereinafter referred to as meniscus position). (A) of this figure represents almost one cycle of a waveform obtained by generalizing the drive signal 21a, and (b) of the figure shows a case where a drive signal having a waveform as shown in (a) is applied to the piezoelectric element 116a. FIG. 4C shows a change in the state of the ink chamber 114, and FIG. 4C shows a change in the meniscus position in the nozzle 118 at that time.

In FIG. 5A, first, a process of changing the drive voltage from the reference voltage 0V to the pull-in voltage Vp (from A to B) is a first preceding process, and a process of holding the pull-in voltage Vp for a predetermined time ( B to C) is the second previous step.
Further, a process (from C to D) of changing the drive voltage from the pull-in voltage Vp1 to the reference voltage 0V is defined as a first process, and a time required for the first process is defined as t1. Also, a process (from D to E) of holding the reference voltage 0V and waiting is defined as a second process, and a time required for the process is defined as t2. Further, the process (from E to F) of changing the reference voltage from 0 V to the ejection voltage Va is performed in the third step.
This is a process, and the time required for this is t3.

In the present embodiment, the time point E, which is the start point of the third stroke, is the timing at which the discharge starts, and prior to this timing, the first preceding stroke, the second preceding stroke, and the first stroke. , And the second step are performed.

First, at time A and before,
Since the voltage applied to the piezoelectric element 116a is 0 V, FIG.
As in the state P _A of FIG. 3B, the vibration plate 113 has no deflection, and the volume of the ink chamber 114 is the maximum.
At time A, the meniscus position in the nozzle 118, as shown in state M _A in FIG. 5 (c), assumed to be located set back from the nozzle edge by a predetermined distance.

Next, when the first pre-process of gradually increasing the drive voltage from the voltage 0 V at the time A to the pull-in voltage Vp at the time B is performed, the vibration plate 113 bends inward and the ink chamber 114 contracts. (State P _{B in} FIG. 5B). Since the contraction speed of the ink chamber 114 at this time is slow, the decrease in the volume of the ink chamber
Advancing the meniscus position in 18 also causes a backflow of ink to the common channel 115 shown in FIG. At this time, the ratio between the amount of ink advance and the reverse flow rate is determined mainly by the ratio between the flow path resistance in the nozzle 118 and the flow path resistance in a narrow path connecting the ink chamber 114 and the common flow path 115. By optimizing this, FIG.
As shown in the state M _B of (c), without meniscus position at the time B is protruded from the nozzle opening end it may be set to come to approximately the same position as the nozzle edge.

Next, from the time point B to the time point C, a second pre-process for maintaining the volume of the ink chamber 114 constant by holding the drive voltage at the pull-in voltage Vp is performed. However, during this time, since the ink supply from the ink cartridge 12 is continuously performed, the meniscus position in the nozzle 118 is displaced toward the nozzle opening end. At the time C, for example, the state M in FIG. _As shown by _C , the nozzle advances to a position slightly protruding from the nozzle opening end.

Next, when the first step of reducing the drive voltage from the pull-in voltage Vp at the time point C to the reference voltage 0V at the time point B is performed, the voltage applied to the piezoelectric element 116 becomes 0, and the deflection of the vibration plate 113 is reduced. Disappears, and the ink chamber 114 expands (the state P _{D in} FIG. 5B). Therefore, the nozzle 1
Meniscus in 18 is retracted in the direction of the ink chamber 114, the time point D, and retracted as shown in state M _D, for example, FIG. 5 (c) (i.e., away from the nozzle edge). It should be noted that the amount of meniscus pull-in in the first step changes by changing the level of the pull-in voltage Vp, which is the potential difference between the point C and the point D, so that the size of the ink droplet can be controlled. . This is because the size of the ink droplet depends on the meniscus position at the start of ejection, and the deeper the meniscus position, the smaller the ink droplet size.

Next, during the time t2 from the time point D to the time point E, the driving voltage is fixed to the reference voltage 0V and the vibration plate 1
The ink chamber 1 is maintained by maintaining the deflection of the ink chamber 13c.
Performing a second step of maintaining the 14 volume constant (state P _D to P _E in FIG. 5 (c)). However, during this time, since the ink supply from the ink cartridge 12 is continuously performed, the meniscus position in the nozzle 118 is displaced toward the nozzle opening end, and at the time E, for example, the state M in FIG. _Move forward to the position shown in _E. The amount of advance of the meniscus position is changed by changing the required time t2 of the second stroke, and the meniscus position at the start of the third stroke can be adjusted. Can be controlled.

Next, a third step of rapidly increasing the drive voltage from the voltage 0 V at the point E to the discharge voltage Va at the point F is performed. Here, the time point E is the ejection start timing as described above. At this time, at the time point F, the vibration plate 113 is largely bent inward as shown in a state P _F of FIG. 5B, and the ink chamber 114 is rapidly contracted.
As shown in state M _F in FIG. 5 (c), the meniscus in the nozzle 118 is pressed once towards the nozzle edge,
From here, ink droplets are ejected. The ejected ink drops fly in the air and land on the recording paper 2 (FIG. 2).

Thereafter, when a predetermined time has elapsed while the drive voltage is maintained at the discharge voltage Va, the reference voltage is reduced to 0 V again. In this way the time H, as shown in state P _H in FIG. 5 (b), the vibration plate 113 returns to the state with no deflection. This state is maintained until the start point I of the first previous step in the next ejection operation. At the time point H immediately after the drive voltage is again reduced to 0 V, the volume of the ejected ink droplet and the increase in the volume of the ink chamber 114 are added as shown in the state _MH of FIG. The meniscus position is retracted by an amount corresponding to the volume of the ink that has been discharged. However, due to ink filling (refilling) performed thereafter, the meniscus position at the start point I of the first previous process in the next ejection operation is changed to the state shown in FIG. As shown in the state M _I of FIG. 10C, the state M _A becomes the same as the state M _A at the initial time point A.

Thus, one ejection operation is completed. Hereinafter, by repeating such a cycle operation in parallel for each nozzle 118, the recording paper 2
Image recording on (FIG. 2) is performed continuously.

In the present embodiment, it is assumed that the required time t2 of the second stroke is equal to or less than the required time for the meniscus drawn in the first stroke to reach the nozzle opening end.
It is assumed that the ejection voltage Va in the third step falls within a range sufficient for ejecting ink droplets. FIG. 4 (a)
The time required for the steps other than the above steps CD, DE, and EF will be described as follows. AB = τ
1, BC = τ2, FG = t4, GH = t5.

Next, returning to FIG. 4 again, the drive signal 21b
Will be described. In this embodiment, the drive signal 21b has the same reference voltage 0 as the drive signal 21a during the stroke AB.
The voltage changes from V to the pull-in voltage Vp. Then, the pull-in voltage Vp is held until a predetermined time point C 'after the time point F at which the drive signal 21a has finished rising to the discharge voltage Va, from which the reference voltage is rapidly dropped to 0V. In this figure, starting from the ejection start timing te of the drive signal 21a (ie, the rising start time E from the reference voltage 0V to the ejection voltage Va), the fall of the drive signal 21b from the pull-in voltage Vp to the reference voltage 0V is started. Assuming that the time until the time point C 'is td, the time required for the step BC' for holding the pull-in voltage Vp is t1 + t2 + td. here,
td> t3. In FIG. 4B, the drive signal 2
The time required for the process C'D 'in which 1b changes from the pull-in voltage Vp to the reference voltage 0V is represented as t6. Here, an appropriate setting of the delay time td is one feature of the present invention, which will be described later.

Next, the overall operation of the ink jet printer 1 shown in FIG. 1 will be briefly described.

In FIG. 1, when print data is input to the ink jet printer 1 from an information processing device such as a personal computer (not shown), the image processing section 15 performs predetermined image processing (for example, compression) on the input data. Data decompression, etc.) and print data 2
2 is sent to the head controller 14.

The head controller 14 controls the recording head 1
When the print data 22 for n dots corresponding to the number of nozzles of 1 is acquired, the size of the ink droplet for forming a dot is determined for each of the n nozzles based on the print data 22. From the result, each set of drive signals 21a and 21b to be supplied to each nozzle is selected.
For example, when expressing high density, a driving waveform (t2, Va is large and Vp
A set of drive waveforms (waveforms with small t2 and Va and large Vp) that can reduce the ink droplet size when a low density or high resolution expression is selected by selecting a set of waveforms Select Also, when expressing a subtle intermediate gradation, the ink droplet size should be slightly different between adjacent dots.For example, if the ink ejection characteristics vary between nozzles, Is selected as a set of drive waveforms that can correct the above.

After selecting a set of drive signals for n dots (that is, drive signals supplied to the n nozzles 118), the head controller 14 selects each of the nozzles in the recording head 11 at the switching timing of the ejection cycle. 1
The selected drive signal 21 is applied to the 18 piezoelectric elements 116a.
a and the piezoelectric element 11 of each nozzle 118
6b is supplied with the selected drive signal 21b. The piezoelectric element 116a in each nozzle performs each process as described with reference to FIG. 5 according to the supplied voltage waveform of the drive signal 21a, and ejects ink droplets. At this time, the piezoelectric element 116b of each nozzle is displaced as described later according to the voltage waveform of the supplied drive signal 21b, and performs an operation for assisting the ejection operation by the piezoelectric element 116a.

Next, referring to FIGS. 4, 6 and 7,
The characteristic operation of the ink jet printer according to the present embodiment will be described.

As described in the section of the prior art, satellite droplets, which are incidental small ink droplets generated when ink droplets are ejected, are often used in a method of ejecting ink droplets by generating ejection pressure by a piezoelectric element. The tail part is separated from the head part due to the time difference and speed difference between the head part and the tail part of the ink flying in a columnar shape, and this tail part becomes a small ink droplet. It is thought that it became.

In this embodiment, in order to prevent the generation of such satellite droplets, as shown in FIG. 4, the auxiliary (satellite droplet prevention) drive signal 21b is held in advance at the pull-in voltage Vp. The ink chamber 114 is kept in a contracted state. In this state, the above-described first to third steps (FIG. 5) are performed by the ejection drive signal 21a, and the piezoelectric element 116a is contracted by the ejection drive signal 21a. In the state in which the piezoelectric element 116b is displaced in the ink chamber expansion direction, the auxiliary drive signal 21b falls and the piezoelectric element 116b is displaced in the ink chamber expansion direction. This point will be further described with reference to FIG.

FIG. 6 shows the relationship between the change in the voltage waveform of the drive signals 21a and 21b and the displacement of the piezoelectric elements 116a and 116b. Specifically, (a) of this figure shows a main part waveform of the drive signal 21a, and (b) shows the piezoelectric element 116a.
(C) shows the waveform of the main part of the drive signal 21b, and (d) shows the displacement of the piezoelectric element 116b. here,
The horizontal axis indicates time, the vertical axis in (a) and (c) indicates voltage, and the vertical axis in (b) and (d) indicates displacement.

As shown in FIGS. 6C and 6D, by holding the drive signal 21b at the pull-in voltage Vp in advance, the piezoelectric element 116b on the nozzle side is kept displaced in the ink chamber contraction direction. ing. In this state, FIG.
As shown in (b), the piezoelectric element 116a on the supply side is
From time E, displacement in the ink chamber contraction direction starts with the voltage increase of the drive signal 21a. Then, the piezoelectric element 116a
Is the time F when the voltage reaches the ejection voltage Va due to the inertial force.
At the time point P when an overrun occurs. On the other hand, as shown in FIGS.
b is a predetermined time point C 'after the time point F when the drive signal 21a reaches the ejection voltage Va (that is, the ejection start timing tc
At the time (elapse of the time td from the time point E), the fall from the pull-in voltage Vp to the reference voltage 0V starts, and the reference voltage becomes 0V at the time point D '. As a result, the piezoelectric element 116b is rapidly displaced in the ink chamber expansion direction.

As shown in FIGS. 6A and 6B, the piezoelectric element 116a, to which the application of the ejection voltage Va of the drive signal 21a has been started at the time point E, is displaced in the ink chamber contraction direction. A pressure is generated in 114 and the pressure pushes ink out of nozzle 118. At this point, the ink ejected from the nozzle 118 is still trailing, forming an ink column. On the other hand, a time point C ′ at which time td has elapsed from the start of the displacement of the piezoelectric element 116a.
The piezoelectric element 116b whose applied voltage has fallen from the pull-in voltage Vp to the reference voltage 0V at, generates a negative pressure in the ink chamber 114 by rapidly displacing in the ink chamber expansion direction. Then, the trailing portion of the ink column already being pushed out of the nozzle 118 is pulled back by the negative pressure. For this reason, a discontinuity occurs in the flow of the ink, and the space between the head and the tail of the ink column is cut off. This suppresses a long tail of the ink column and suppresses the generation of satellite droplets.

It should be noted that the piezoelectric element 116a is provided with a discharge voltage Va.
Is maintained while the driving signal 21a
Changes from the discharge voltage Va at the time point G to the reference voltage 0V at the time point H, the displacement of the piezoelectric element 116a returns to 0, and further, the natural vibration gradually attenuates. Also, the piezoelectric element 1
16b, after time D 'when the voltage reaches the reference voltage 0V,
A natural vibration that attenuates gradually around the intended displacement position.

FIG. 7 shows the discharge start timing te (time E).
This shows the ejection state of ink droplets when the delay time td from the time t to the falling timing C 'of the drive signal 21b is variously changed. (A) of this figure shows the change at the time of cutting the tail of the ink droplet when the delay time td is set to 10, 9, 8, and 7 μsec, respectively, and (b) shows only the piezoelectric element 116a by the drive signal 21a. And the delay time td is set to 10, 9,
This represents the state of the ink droplet 32 μsec after the ejection start timing te when set to 8.7 μsec. Note that the piezoelectric elements 116a, 1
16b is 25 μm, the thickness of the vibrating plate 113 is 25 μm, and the driving signals 21a and 21 shown in FIG.
Each time parameter and voltage parameter of 1b are set as follows. The unit of the time parameter is μsec, and the unit of the voltage parameter is volt.

Τ1 = 30, τ2 = 10, t1 = 9, t2
= 2, t3 = 5, t4 = 50, t5 = 50, t6 = 1,
td = 9, Vp = 35, Va = 35, Vb = 35

As shown in FIG. 7A, the delay time td
Are set to 10, 9, 8, and 7 μsec, respectively, the cutting timings of the ink droplets are the ejection start timings t.
e, 23, 21.8, 22.8, 36 μse respectively
This is the time when c has elapsed. In addition, as shown in FIG.
Looking at the state after elapse of c, the delay time td is 10,
In any of the cases set at 9.8 μsec, the tail of the ink droplet is cut off earlier than when the ejection is performed only by the piezoelectric element 116a. In particular, when the delay time td is 9
When set to μsec, unlike the case where the delay time td is set to another value, no satellite drops are generated. However, when the delay time td is set to 7 μsec or less, the discharge pressure of the piezoelectric element
The speed of the ink droplet to be ejected is reduced by being offset by the negative pressure due to b. In particular, when the delay time td is set to 5 μsec, the ink droplet is not ejected.

From the above, it can be seen that by applying the drive signal 21b to the piezoelectric element 116b, the timing of cutting off the tail of the ink droplet can be advanced, and the generation of satellite droplets can be suppressed. In particular, when the delay time td is set to 9 μsec, the tail of the ink droplet is cut off earliest, and it can be seen that the generation of satellite droplets can be suppressed most effectively. In the present embodiment, the delay time of 9 μsec is substantially equal to the time required from when the piezoelectric element 116a starts to be displaced to when it reaches the maximum displacement position P (FIG. 6B). That is, when the displacement of the piezoelectric element 116a becomes maximum due to the ejection voltage Va of the drive signal 21a, the drive signal 21b falls and the piezoelectric element 116
By starting the displacement of b in the ink chamber expansion direction, the generation of satellite droplets can be suppressed most effectively.

As described above, according to the present embodiment, two piezoelectric elements 116a and 116b are provided for each ink chamber 114 corresponding to each nozzle, and the piezoelectric element 116b on the nozzle side is previously moved in the ink chamber contracting direction. Displaced,
In this state, after the piezoelectric element 116a on the ink supply side is displaced in the ink chamber contraction direction to start ejection of ink droplets,
Since the negative pressure is generated in the ink chamber 114 by displacing the other piezoelectric element 116b in the ink chamber expansion direction, the tail of the ink drop can be thinned and cut off early, and as a result, the satellite drop Can be suppressed. In particular, by starting the displacement of the piezoelectric element 116b in the ink chamber expansion direction when the piezoelectric element 116a is displaced the most in the ink chamber contraction direction, the generation of satellite droplets can be suppressed most effectively. .

Although the present invention has been described with reference to the embodiment, the present invention is not limited to this embodiment, and can be variously modified.

For example, in the example shown in FIG.
Although the displacement of the piezoelectric element 116b is started at the time when the displacement of the piezoelectric element 116b is greatest, the present invention is not limited to this, and the displacement of the piezoelectric element 116b is started at another timing after the flat start of the piezoelectric element 116a. A considerable effect can be obtained by starting.

Further, the set values of each time parameter and voltage parameter in FIG. 4 are not limited to the values exemplified above, but can be changed as appropriate. For example, in the present embodiment, the pull-in voltage in both of the drive signals 21a and 21b is the same Vp, but they may be different.

In the above-described embodiment, the piezoelectric element 116a on the ink supply side is used as the discharge pressure generating means, and the piezoelectric element 116b on the nozzle side is used as the satellite drop preventing pressure generating means. On the contrary, the piezoelectric element 1 on the nozzle side serves as a discharge pressure generating means.
16b, and the piezoelectric element 116a on the ink supply side may be used as the satellite drop preventing pressure generating means.

In the above embodiment, the case where two piezoelectric elements are provided for one nozzle has been described. However, three or more piezoelectric elements are provided for one nozzle.
These piezoelectric elements are divided into those for ejection and those for satellite drop suppression, and a drive signal 21a for ejection is applied to the piezoelectric element for ejection, and a drive signal 21b for satellite drop suppression is applied to the piezoelectric element for satellite drop suppression. You may do so.
In this case, the displacement capabilities of three or more piezoelectric elements may be equal to each other or may be different. By doing so, satellite droplet suppression control can be performed more finely.

In the above embodiment, one ink chamber 114 is provided for one nozzle 118,
Two piezoelectric elements 1 corresponding to this one ink chamber 114
16a and 116b are provided, for example, as shown in FIG.
As shown in FIG. 2, two ink chambers 114a and 114b are provided for one nozzle 118, and the piezoelectric elements 116a and 1b are respectively associated with the ink chambers 114a and 114b.
16b may be provided. FIG. 8 shows a state in which a part of the recording head 11 is viewed from directly above. The same elements as those shown in FIG. Is omitted.
According to the configuration shown in this figure, one ink chamber 114a
Of the piezoelectric element 116a in the other ink chamber 11
4b has little effect on the state of the piezoelectric element 116b.
a, 116b can be reduced, and higher-precision printing quality can be obtained.

[0063]

As described above, according to the ink jet printer according to the first aspect, the recording head driving device for the ink jet printer according to the second aspect, or the driving method for the recording head for the ink jet printer according to the third aspect, A discharge pressure generating means and an accompanying droplet preventing pressure generating means are provided for each nozzle portion, and in a state where the accompanying droplet preventing pressure generating means is displaced in the ink chamber contracting direction in advance, the discharge of the ink droplet is performed. For this reason, the ejection pressure generating means performs an operation of displacing in the ink chamber contraction direction, and when the ink chamber is in a contracted state by the displacement operation of the ejection pressure generation means in the ink chamber contraction direction, accompanying small droplets are prevented. Pressure generating means is displaced in the ink chamber expansion direction, so that the trailing of the ink pushed out from the nozzle portion by the displacement of the discharge pressure generating means. Min, drawn back by the displacement of the associated drop prevention pressure generating means, are cut off early before tailing long ink droplets. For this reason, it is possible to suppress the occurrence of incidental ink droplets, and it is possible to prevent the quality of the recorded image from deteriorating. In particular, it is possible to effectively prevent deterioration in image quality even in an image that is easily affected by unnecessary ink droplets, such as a light image or a halftone image that needs to be expressed using small ink droplets. . In addition, since the two ejection pressure generation means and the associated small drop prevention pressure generation means provided for one nozzle portion are independently controlled, the flying speed of the ejected ink droplets is reduced. In addition, there is an effect that the pressure generating means is not restricted by the natural vibration characteristics of the pressure generating means without shortening the apparatus life or deteriorating the frequency characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an inkjet printer according to an embodiment of the present invention.

FIG. 2 is a perspective sectional view illustrating a configuration example of a recording head.

FIG. 3 is a cross-sectional view illustrating a structural example of a recording head.

FIG. 4 is a diagram illustrating an example of a waveform of a drive signal output from a head controller in FIG.

FIG. 5 is a diagram for explaining the relationship between the ejection drive signal waveform shown in FIG. 4 and the state of the ink chamber and the change in the meniscus position in the nozzle.

6 is a diagram illustrating an example of a relationship between a drive signal waveform illustrated in FIG. 4 and a displacement amount of a piezoelectric element.

FIG. 7 is a diagram illustrating an example of an ink droplet ejection state according to the drive signal waveform illustrated in FIG.

FIG. 8 is a plan view illustrating a modification of the recording head used in the ink jet printer according to the present embodiment.

FIG. 9 is an explanatory diagram for explaining a driving method of a conventional inkjet printer.

FIG. 10 is an explanatory diagram for explaining a driving method of another conventional inkjet printer.

[Description of Signs] 1 ... Inkjet printer, 11 ... Recording head, 14
... head controller, 21a, 21b ... drive signal, 2
2: Print data, 113: Vibration plate, 114: Ink chamber, 115: Common flow path, 116a, 116b: Piezoelectric element, 118: Nozzle, Vp: Pull-in voltage, Va: Discharge voltage, Vb: Auxiliary voltage, td: Delay Time, te ... Discharge start timing

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Tokunaga 6-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (3)

[Claims] A nozzle for discharging ink droplets; an ink chamber for supplying ink to the nozzle; and a nozzle provided for each of the nozzles, wherein the volume of the ink chamber is changed by displacement. A discharge pressure generating means for generating a pressure for discharging ink droplets from the nozzle portion; and a discharge pressure generating means provided for each of the nozzle portions, wherein the displacement of the ink chamber changes the volume of the ink chamber so that the ink from the nozzle portion is changed. An auxiliary droplet preventing pressure generating means for generating pressure for suppressing the generation of incidental ink droplets at the time of droplet ejection; and displacing the auxiliary droplet preventing pressure generating means in the ink chamber contracting direction in advance. In addition, the ejection pressure generating means is displaced in the ink chamber contraction direction for ejection of ink droplets,
Discharge control means for controlling the displacement of the accompanying small droplet preventing pressure generation means in the ink chamber expansion direction when the ink chamber is in a contracted state by the displacement operation of the discharge pressure generation means in the ink chamber contraction direction. An ink jet printer comprising: 2. A nozzle unit for discharging ink droplets,
An ink chamber for supplying ink to the nozzle section, and an ejection chamber that is provided for each of the nozzle sections and generates pressure for ejecting ink droplets from the nozzle section by changing the volume of the ink chamber by being displaced. Pressure generating means, provided for each of the nozzles, for changing the volume of the ink chamber by displacing and suppressing the generation of incidental ink droplets when ink droplets are ejected from the nozzles. And a driving unit for driving a recording head for an ink jet printer, comprising: a pressure generating means for preventing the accompanying small droplets, the pressure generating means for preventing the accompanying small droplets being displaced in the ink chamber contracting direction in advance. Along with displacing the ejection pressure generating means in the ink chamber contraction direction for ejection of ink droplets,
Discharge control means for controlling the displacement of the accompanying small droplet preventing pressure generation means in the ink chamber expansion direction when the ink chamber is in the contracted state by the displacement operation of the discharge pressure generation means in the ink chamber contraction direction. A recording head driving device for an ink jet printer, comprising: 3. A nozzle unit for discharging ink droplets,
An ink chamber for supplying ink to the nozzle section, and an ejection chamber that is provided for each of the nozzle sections and generates pressure for ejecting ink droplets from the nozzle section by changing the volume of the ink chamber by being displaced. Pressure generating means, provided for each of the nozzles, for changing the volume of the ink chamber by displacing and suppressing the generation of incidental ink droplets when ink droplets are ejected from the nozzles. A method for driving a recording head for an ink jet printer, comprising: a pressure generating means for preventing small droplets, the pressure generating means for generating small pressure, wherein the pressure generating means for preventing small droplets is displaced in the ink chamber contracting direction in advance. A step of displacing the ejection pressure generating means in the ink chamber contraction direction for ejecting ink droplets; and a step of displacing the ejection pressure generating means in the ink chamber contraction direction. When the ink chamber by the displacement operation is in a contracted state, a driving method for an ink jet printer recording head which comprises a step of displacing the associated drop prevention pressure generating means in the ink chamber expands direction.