JP3484798B2 - Ink jet recording device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus for printing images and characters by expanding and contracting a piezoelectric vibrator based on print data corresponding to images and characters and ejecting ink droplets from nozzle openings.

[0002]

2. Description of the Related Art An ink jet recording apparatus is an ink droplet that has landed on a recording medium in order to perform recording by expanding and contracting a pressure generating chamber by a piezoelectric vibrator and ejecting ink droplets from a nozzle opening onto the recording medium. The print quality is greatly affected by the degree of bleeding. For this reason, it is necessary to use a specific paper because it is a condition for maintaining the print quality to the standard to use the recording paper that matches the quality of the ink, that is, the penetrating force. Coated paper coated with a chemical that adjusts the penetrating power of ink is recommended as the paper satisfying such conditions, but it is not only costly as compared with copying paper used in offices, but also various types of paper. You need to stock the paper. Various proposals have heretofore been made in order to solve the problem that the print quality of the ink jet recording apparatus largely depends on the quality of the recording paper.

For example, JP-A-5-16359 and JP-A-5-3
As seen in Japanese Patent No. 18766 and Japanese Patent Laid-Open No. 5-338165,
By positively utilizing the vibration of the meniscus in the vicinity of the nozzle opening that occurs after ink droplet ejection, by adjusting the timing of the next ink droplet ejection, the amount of ink of one droplet is adjusted, and the amount of ink suitable for the recording paper is adjusted. It has been proposed to eject ink drops. According to this method, two parameters, the ink amount and the flight speed of the ink droplet, change simultaneously.
And, because the dripping position of the ink droplets is varied, there is a problem that print quality varies depending on the recording paper.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to print the size of dots and ink droplets regardless of the quality of the recording medium. It is an object of the present invention to provide an ink jet recording apparatus capable of maintaining a constant flying speed.

[0005]

In order to solve such a problem, in the present invention, a piezoelectric vibrator expands and contracts a pressure generating chamber to eject an ink droplet from a nozzle opening.
The recording head to be used and the amount of ink droplets to be ejected
Before changing the expansion speed of the pressure generating chamber
First driving means for applying a signal to the serial piezoelectric vibrator, and before
The slower the expansion speed of the first drive means is,
The piezoelectric vibrator for increasing the contraction speed of the pressure generating chamber
A recording head drive means comprising a second driving means for applying a signal to displace the was to comprise a.

[0006]

The amount of expansion of the pressure generating chamber is determined based on the data specifying the recording paper input from the outside to control the amount of drawing of the meniscus, and at a predetermined speed during movement of the meniscus regardless of the amount of expansion. The pressure generating chamber is contracted, and ink droplets of an amount corresponding to the paper quality are ejected at a constant speed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 shows an embodiment of an ink jet recording apparatus to which the present invention is applied, in which reference numeral 1 is a carriage, which is supported by a guide member 2.
The timing belt 4 driven by the pulse motor 3 reciprocates in parallel with the platen 5.

The carriage 1 is equipped with a recording head 6 for ejecting ink droplets from nozzle openings in accordance with a print signal, and an ink cartridge 7 for supplying ink to the recording head 6.

The recording head 6 has a flexible cable 8
It is connected to a drive device which will be described later via the ink jet device, and ejects ink droplets onto the recording paper 9 in response to a signal from the drive device. Reference numeral 10 in the drawing denotes a paper feeding motor, and 11 denotes a cleaning unit for cleaning the recording head 6.

FIG. 2 shows an embodiment of the recording head 6 described above. In the figure, reference numeral 20 is a spacer, which is composed of a pressure generating chamber 21, a common ink chamber 22, and an ink supply port 23 connecting these. A nozzle plate 25 having a nozzle opening 24 on one side and a vibrating plate 26 on the other side.
It is sealed by.

The diaphragm 26 has an elastically deformable diaphragm portion 26a in a region facing the pressure generating chamber 21, and an island portion 26 that abuts on a tip of a piezoelectric vibrator 27 described later.
b is formed, and the pressure generating chamber is contracted and expanded by the expansion and contraction of the piezoelectric vibrator 27.

Reference numeral 27 denotes the above-mentioned piezoelectric vibrator, which contracts in the longitudinal direction when a drive signal is applied and is charged in this embodiment, and contracts in the longitudinal direction when the charge accumulated by the charging is discharged. The upper end is fixed to a base (not shown) so that the lower end contacts the island portion 26b. Reference numeral 28 in the figure denotes an ink supply pipe that supplies the ink in the ink cartridge 7 to the common ink chamber 22.

FIG. 3 shows an embodiment of the above-described recording head drive device, in which reference numeral 30 is a recording control circuit, and a timing signal (see FIG. 6) is applied to a first input terminal 31.
(I)), a recording signal is input to the second input terminal 32, a latch signal is input from the first output terminal 33, a recording signal is input from the second output terminal 34, and a recording signal is input from the third output terminal 35. It is configured to output the shift clock signal.

The recording signal output from the second output terminal 34 is sequentially shifted by the shift clock signal from the third output terminal 35 in the flip-flop circuits 36, 36, 36 ... And is temporarily stored and held in the flip-flop circuits 37, 37, 37 by the latch signal from the first output terminal 33 when the transfer is completed.

Reference numeral 40 denotes a drive signal generation circuit, which is a charge pulse, a discharge pulse, and a drive voltage VH generated by a pulse width adjustment circuit 42 described later in accordance with the timing signal input to the first input terminal 31. A trapezoidal drive signal is generated on the basis of the above, and its output terminal 41 has piezoelectric vibrators 27, 27, 27 constituting the recording head 6.
One of the electrodes is connected.

The other electrodes of the piezoelectric vibrators 27, 27, 27 ... Are connected to the ground via a switching transistor 47. The control electrodes of the switching transistor 47 are connected to the flip-flop circuits 37, 37, 3 described above.
7 are connected to the output terminals of the flip-flop circuit 37.
The piezoelectric vibrator 27 for ejecting ink droplets is selectively made conductive by a signal from the.

FIG. 4 shows an embodiment of the pulse width adjusting circuit 42 described above. In the figure, reference numeral 50 is a counter, which divides the clock signal from the clock oscillator 48 by the frequency divider 4.
9, the count operation is started in synchronization with the H level signal output from the Q terminal of the flip-flop circuit 54, which will be described later, and the output terminal is one of the comparison means 51 described later. Is connected to the input terminal of. A latch circuit 52 for receiving a signal from a host 53 that outputs recording paper and density setting data is connected to the other input terminal of the comparison means 51.

Reference numeral 54 is the above-mentioned flip-flop circuit,
Upon receiving the timing signal input from the first input terminal 31 described above, the terminal Q changes to the H level, and is reset by the coincidence signal from the comparison means 51 to switch to the L level, so that the paper quality or the printing commanded by the host 53 is obtained. A charging pulse (FIG. 6 (II)) having a pulse width corresponding to the concentration is output.

Reference numerals 55 and 56 denote first and second one-shot multivibrators, respectively. The first one-shot multivibrator 55 receives a charging pulse output from the flip-flop circuit 54 in synchronization with a timing signal to charge the same. After the end of the pulse, a pulse signal for setting an appropriate time Δt, that is, the time for turning on the transistor 67 after the transistor 62 is turned off is output, and this pulse signal is also output to the second one-shot multivibrator 56.
Then, the discharge pulse (FIG. 6 (III)) in which the time Td required for the discharge is set is output. As a result, the discharge pulse is output from the terminal 44 at the optimum timing.

57 is a digital-analog converter,
The digital data instructing the drive voltage VH from the host 53 is converted into an analog signal and output to the voltage amplifier 58. The voltage amplifier 58 outputs a voltage VP higher than the voltage VH.
Is used as an operating voltage, and an appropriate driving voltage VH is output to the terminal 45 in accordance with the recording paper selection data and the density data from the host 53.

FIG. 5 shows an embodiment of the drive signal generating circuit 40 described above, in which the terminal 43 receives the charging pulse of the terminal 43 of the pulse adjusting circuit 42, and the terminal 4
4, a discharge pulse from the terminal 44 of the pulse width adjusting circuit 42 is input, and a driving voltage VH from the terminal of the pulse width generating circuit 42 is input to the terminal 45.

In the figure, reference numeral 61 is an NPN type transistor, 6
Reference numeral 2 is a PNP type transistor, which constitutes a flow type constant current source. The switching transistor 63 is turned on and off by the charging pulse input to the terminal 43 to operate.

Reference numeral 64 denotes a current adjusting circuit, which is composed of a data selector 65 operated by data from the host 53 and a plurality of resistors R1, R2, R3, ...
A data selector 65 based on the data from the host 50
Select resistors R1, R2, R3, ... by flow current i1
Is adjusted.

In the figure, reference numeral 66 is a PNP type transistor, 6
Reference numeral 7 is an NPN transistor, which constitutes a sink type constant current source having a voltage V2 as an input voltage, and is operated by a switching transistor 68 which is turned on / off by a discharge pulse input from the terminal 44 of the pulse width generating circuit 42 described above.

A NPN type transistor 70 and a PNP type transistor 71 are connected in a Darlington connection to a capacitor 69 which is charged and discharged by these constant current sources, and an emitter flow type power amplifier circuit is connected to the capacitor 69.
The charging current and discharging current of 9 are amplified and a drive signal is output to the terminal 41.

Transistor 6 which constitutes these constant current sources
The base-emitter saturation voltages of 1, 62, 66 and 67 are VBE61, VBE62, VBE66 and VBE67, respectively, and the voltage generated at the emitter resistor R62 of the transistor 62 is V6.
2. If the voltage generated in the emitter resistance R67 of the transistor 67 is V67, then V62 = V1−VBE61 + VBE62 V67 = V2 + VBE66−VBE67. In general, the base-emitter saturation voltage of the transistor exhibits a substantially constant value with respect to the polarity and the temperature change, so that V1 = V3 and V4 = V2.

Therefore, the flow current i1 from the flow type constant current source is i1 = V1 / (emitter resistance R62 of the transistor 62), and the sink current i2 of the sink type constant current source is i2 = V2 / (transistor It becomes the emitter resistance R67 of 67.

Next, the operation of the apparatus thus constructed will be described with reference to the timing chart shown in FIG. Host 5
3 is a type of recording paper, for example, plain paper, coated paper, OH
Data of the width of the charging pulse and the value of the driving voltage VH are stored in advance for each type of P sheet, glossy film, and the like, regardless of the paper quality, so that the reference density is obtained. When a certain recording paper is selected from the host, the data of the charging pulse corresponding to this recording paper is output to the comparing means 51 via the latch circuit 52, and the data of the corresponding driving voltage VH is output to the analog-digital converter 57. To be done.

When one recording sheet, for example, plain sheet is selected and printing is started in this way, the timing signal (FIG. 6 (I)) is input to the first input terminal 31 and the recording signal is input to the second input terminal 31. Input to the terminal 32.

The recording signal is sequentially shifted by the flip-flop circuits 36, 36, 36 ... In response to the clock signal, and the flip-flop circuit 37 of the corresponding nozzle opening 37,
The switching transistors 47, 47, 47, ... Latched to 37, 37, ... And connected to the piezoelectric vibrators 27, 27 ,.

On the other hand, the pulse width adjusting circuit 42 is used by the host 5
The data of the charging pulse width Tc1 and the driving voltage VH suitable for the plain paper which is the recording paper to be printed now are received from 3. As a result, a charging pulse (FIG. 6 (II)) having a width Tc1 suitable for this recording sheet is output to the terminal 43.

The drive signal generating circuit 40 turns on the transistor 63 by the charging pulse input to the terminal 43,
The capacitor 69 is charged with the constant current of the flow current i1 set by the host for a time corresponding to the width of the charging pulse.

This charging current is applied to the transistors 70 and 71.
Is amplified by and flows into the piezoelectric vibrator 27, which is charged with a constant voltage gradient α1. As a result, the piezoelectric vibrator 27 belonging to the nozzle opening from which ink droplets should be ejected for recording an image contracts and expands the pressure generating chamber 21, and the ink in the common ink chamber 22 passes through the supply port 23 and the pressure generating chamber. It flows into 21.

In parallel with this, the meniscus (FIG. 7 (A)) formed in the vicinity of the nozzle opening begins to be drawn into the pressure generating chamber 21 side, and after being drawn to the maximum, is inverted to the nozzle opening side. It will vibrate after that.

At the stage where the charging has proceeded to the drive voltage VH1 set for this recording sheet, the charging is stopped and the piezoelectric vibration is performed with a constant gradient β1 after a predetermined time Δt considering the switching time of the transistor. The charge of the child 27 is discharged, the piezoelectric vibrator 27 is expanded at a constant speed to contract the pressure generating chamber 21, and the ink droplet A (FIG. 7) is ejected.

For the predetermined time Δt, the first one-shot multivibrator 5 which operates by turning off the charging pulse is used.
5, the discharge pulse is cascaded to the first one-shot multivibrator 55 by setting the time interval (about 5 μS in this embodiment) so that the flow type constant current source and the sink type constant current do not operate simultaneously. The signal is output from the second one-shot multivibrator 56 to the terminal 44.

The vibration cycle of the meniscus caused by the expansion of the pressure generating chamber 21 is determined by the flow path system, but the maximum amount of pulling in the meniscus is the higher the expansion speed of the pressure generating chamber 21, that is, the rising of the drive signal. The larger the gradient α, the larger. According to the present invention, by positively utilizing this property, the drawing amount of the meniscus is controlled to arbitrarily adjust the meniscus position at the time of ejecting the ink droplet to adjust the liquid amount of the ink droplet.

Next, when the recording paper is changed to a paper of high ink permeability, when this recording paper is designated by the host 53, the data of the charging pulse corresponding to the new recording paper is stored in the latch circuit 52. Through comparison means 5
1, and resistors R1 and R2 that set the flow current i1 to
Data for selecting one of R3, ... Is output to the data selector 65, and corresponding data of the drive voltage VH2 is output to the digital-analog converter 57.

When printing is started, the piezoelectric vibrator 27 is charged and the pressure generating chamber 21 expands as described above. The rising gradient α2 of the drive signal at this time is determined by the data selector 65 to be the flow current i1. Since the resistance to be increased is selected, it is larger than the rising slope α1 for plain paper described above, and thus the amount of pulling in of the meniscus (FIG. 7B) is large. For this reason, as shown in FIG. 7B, the meniscus position at the time of ink droplet ejection is such that the ink droplets are ejected in a state in which the meniscus position is largely retracted toward the pressure generating chamber 21 side as compared with the case of plain paper, and the liquid amount Ink droplet B with a small amount is ejected.

By the way, when ink droplets are ejected while the meniscus is returning to the nozzle opening side, the moving speed of the meniscus is superposed on the contracting speed of the pressure generating chamber 21, and the viscosity is 1.5 to 3.0 mPa · S. In the case of ink of a relatively small size, the ink ejection speed may greatly change and the print position may shift. However, in the present embodiment, the ejection speed is maintained constant by adjusting the contraction speed of the pressure generating chamber 21. ing.

That is, when the rising gradient α of the drive signal is increased in order to reduce the liquid volume of the ink droplet, the meniscus is largely drawn to the pressure generating chamber 21 side, while the nozzle is ejected at a constant cycle regardless of the drawn amount. Since it returns to the opening side, the moving speed of the meniscus becomes higher than that in the case of printing on the plain paper described above. Therefore, the operating voltage VH of the drive signal generating circuit 40 is set to VH2 which is lower than VH1 at the normal time to reduce the voltage V2 that sets the value of the sink current i2, and to set the falling slope of the drive signal to β2 (β1> By changing to β2), the contraction speed of the pressure generating chamber 21 is slowed down, and thus the flight speed of the ink droplet is maintained constant.

By the way, when the operating voltage of the drive signal generating circuit 40 is lowered, the maximum voltage of the drive signal is lowered,
The expansion amount of the pressure generating chamber 21 also becomes small, and these two phenomena are combined to make it possible to further reduce the ink droplet amount, thereby expanding the adjustment range of the ink droplet liquid amount.

In this way, by changing the degree of contraction of the piezoelectric vibrator by the drive voltage VH in accordance with the type of recording paper, the amount of ink filled in the pressure generating chamber 21 can be made to form dots of the same size. By adjusting to an appropriate amount, the ink ejection speed can be maintained constant during discharge regardless of the type of recording paper.

Although the case where the types of recording papers are different has been described above, even when it is desired to change the recording density for the same recording paper, the piezoelectric vibrator 27 corresponding to each density is provided to the host 53 as described above. Data that specifies the extension degree of
That is, by storing the data in which the pulse width of the charging pulse, the resistance value selected by the data selector 65, and the drive voltage VH are stored in advance, only the ink droplet amount can be changed without changing the flight speed of the ink droplet. The recording density can be changed.

In the above description, the case of selecting from two types of recording paper has been described, but by preparing data corresponding to the type of recording paper, it is possible to support many types of recording paper. For example, there are many kinds of plain paper such as recycled paper, high-quality paper, copy paper, etc. Therefore, by preparing data corresponding to these, high quality paper can be obtained regardless of the kind of recording paper. Printing is possible.

By the way, after the nozzle droplet is ejected from the nozzle opening, the meniscus repeats the residual vibration of moving in and out of the nozzle, and it takes time to settle, so that the ink droplet ejection repetition rate is limited. However, an embodiment for improving this will be described below.

FIG. 8 shows a second embodiment of the pulse width adjusting circuit 42. In this embodiment, the output terminal of the second one-shot multivibrator 56 is further provided with third and fourth one-shots. Multivibrator 75, 76
Connect the 4th one-shot multivibrator 76
The output from is output to the terminal 43 via the OR gate 77. The pulse width is set to the third one-shot multi-vibrator 75 at a certain time t1 after the discharge pulse (FIG. 9 (III)) is output, that is, at the time when the meniscus after ink ejection returns to the nozzle opening. In addition, the fourth one-shot multivibrator 76 is set with a pulse width Tc ′ which is a charging voltage for causing the piezoelectric vibrator 27 to undergo a displacement for expanding the pressure generating chamber 21 sufficient to pull back the meniscus. There is.

According to this embodiment, as shown in FIG. 9, when the discharge pulse is output and the predetermined time t1 has elapsed,
Since the auxiliary pulse Tc ′ is output to the terminal 43, the piezoelectric vibrator 27 contracts to expand the pressure generating chamber 21 to an extent sufficient to stop the meniscus. As a result, the vibration of the meniscus can be forcibly suppressed, the time until the next ink droplet can be ejected can be shortened, and the printing speed can be improved.

FIG. 10 shows the third embodiment of the present invention with the drive timing. In this embodiment, the first discharge pulse (III in the drawing) is provided at a constant time interval t2.
And a second discharge pulse (IV) to generate a discharge of a gradient β that discharges a main ink droplet and a discharge of a gradient γ that discharges satellites incidentally generated after the main ink droplet. , The gradient γ in the second discharge is increased to make the flight speed of the satellite larger than that of the main ink droplet.

According to this embodiment, in addition to the above-mentioned effects, the satellite can be made as close to the main ink droplet as possible to form a dot close to a perfect circle.

In such an operation, for example, the output from the second one-shot multivibrator 56 in FIG.
The second discharge pulse (FIG. 10IV) is delayed by delaying the output of the second discharge pulse to the terminal 44 via the OR gate, and connecting the one-shot multivibrator that generates a pulse corresponding to the second discharge pulse. Then, it can be easily realized by making the rising slope of the drive signal steep in synchronization with the pulse.

To change the gradient in this manner, a circuit having the same configuration as the current adjusting circuit 64 shown in FIG.
It can be realized by inserting it instead of the emitter resistance and switching the emitter resistance so as to temporarily increase the sink current, or temporarily increasing the drive voltage VH.

As described above, since the size of the dot formed on the recording paper by the ink droplet and the flight speed of the ink droplet are constant regardless of the quality of the recording paper, the gap length between adjacent dots is constant. When applied to color printing in which ink bleeding between dots is prevented, color dullness is eliminated, and a high-quality color image can be obtained regardless of the type of recording paper.

In the above embodiment, the ink jet recording head using the piezoelectric vibrator which contracts by charging and expands by discharging from the charged state has been described as an example. Also, it is apparent that the same effect can be obtained by applying the present invention to a recording head using a piezoelectric vibrator that contracts when discharged from a charged state.

[0055]

As described above, according to the present invention,
Regardless of the quality of recording paper, while maintaining the flying speed of ink droplets that form dots of the same size as constant as possible, the adjustment range of the ink amount is expanded to achieve high printing regardless of the quality of recording paper. Can be printed with quality.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an ink jet recording apparatus of the present invention.

FIG. 2 is a diagram showing a main part of an ink jet recording head used in the above apparatus.

FIG. 3 is a block diagram showing an embodiment of a drive circuit used in the same apparatus.

FIG. 4 is a block diagram showing an embodiment of a pulse width adjusting circuit.

FIG. 5 is a circuit diagram showing an embodiment of a drive signal generation circuit.

FIG. 6 is a timing chart showing the operation of the above apparatus.

FIG. 7 is an explanatory diagram showing a relationship between movement of a meniscus, ink droplet size, and speed in a printing process by the same apparatus.

FIG. 8 is a block diagram showing a second embodiment of the pulse width adjusting circuit in the same device.

FIG. 9 is a timing chart showing the operation of the pulse width adjustment circuit of the second embodiment.

FIG. 10 is a timing chart showing the operation of the pulse width adjusting circuit of the third embodiment.

[Explanation of symbols]

1 carriage 5 Platen 6 Inkjet recording head 7 ink cartridges

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/045 B41J 2/055 B41J 2/205

Claims (2)

(57) [Claims] 1. A recording head which expands and contracts a pressure generating chamber by a piezoelectric vibrator to eject an ink droplet from a nozzle opening, and an expansion speed of the pressure generating chamber corresponding to an ink amount of the ink droplet to be ejected. The first driving unit that applies a signal to the piezoelectric vibrator to change the piezoelectric vibrator, and the slower the expansion speed by the first driving unit, the faster the contraction speed of the pressure generation chamber becomes. An ink jet recording apparatus, comprising: a recording head driving unit that includes a second driving unit that applies a signal for displacing the recording head. 2. The ink jet recording apparatus according to claim 1, wherein the signals of the first drive unit and the second drive unit are changed by a paper selection operation.