JP2000177127A - Ink-jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always eject a constant amount of an ink from an ejection opening by providing a preliminary wave form to an electromechanical transducer element of a small voltage insufficient for ejecting the ink from the ejection opening prior to application of the initial ejection wave form after a pause in the case the duration of pausing the ink ejection is long. SOLUTION: In the case an electric signal by an ejection wave form is paused, a CPU 10 judges whether or not the pause time is same as or more than a predetermined value. In the case it is same as or more than the predetermined value, dummy data are generated, a preliminary wave form pattern is read out from a memory means 13, and an electric signal insufficient for ink ejection from an ejection opening is applied to an electromechanical transducer element 6 via a preliminary wave form generating circuit 12. Accordingly, the meniscus displacement rate at the ejection opening at the time of the ejection for the initial several times is controlled stably. Thereafter, the ejection wave form pattern is read out from the memory means 13 according to the printing information input so that the ink ejection is executed by driving the electromechanical transducer element according to a cyclic clock timing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-demand type ink jet recording apparatus which performs printing by discharging ink droplets from small discharge ports communicating with a pressure chamber. The present invention relates to an improvement for performing uniform printing. In particular, the present invention relates to an improvement for always discharging a fixed amount of ink from a discharge port even when a repetition time for discharging ink droplets changes at high speed and variously.

[0002]

2. Description of the Related Art In an ink jet recording apparatus, ink is introduced into a pressure chamber having a small discharge port provided on a wall surface, and an electric signal is applied from a drive circuit to an electromechanical transducer disposed in the pressure chamber. The pressure chamber is configured to be pressurized to eject ink droplets. The drive circuit pressurizes the print information coming from the information source when there is ejection data according to a certain clock timing, and does not perform pressurization when there is no ejection data. That is, printing is performed by ejecting ink droplets to desired positions on the printing paper surface which relatively moves in synchronization with the pressurization.

At this time, there are a case where the ink droplet is ejected at a continuous position of the clock timing according to the print information and a case where the ejection is stopped for a certain period of the clock timing, and the ink droplet is continuously ejected. In the case where the ink droplet is ejected after a pause for a while,
Even if the electromechanical transducer is driven by the same electrical signal,
It is known that the amount of ink ejected by one press changes. If the amount of ink discharged by one press is large, the dots printed by the discharge look dark, and if the amount of ink is small, the dots printed by the discharge look light, so that one press If the amount of ink ejected by the pressure changes carelessly, unevenness will occur in the printed characters and figures.

[0004] As a technique for improving the above, there is known a technique in which when the discharge is performed after the discharge is stopped, the pressure chamber is preliminarily deformed (Japanese Patent Publication No. 62-9432).
This is because before the first ejection after the suspension of ejection,
This is to apply a bias voltage which gradually increases with time to the electromechanical transducer provided in the pressure chamber.

[0005] As another conventional technique for improving this,
There is known a technique in which a waveform applied to an electromechanical transducer provided in a pressure chamber is devised so that the pressure in the pressure chamber is reduced once and then pressurized for discharge (Japanese Patent Publication No. Hei 5 (1993)).
-43508).

[0006] All of these have been improved by devising so that the state of the meniscus becomes uniform at the time of pressurizing for ejection from the result of microscopic observation of the meniscus of the ink formed at the ejection port. Things.

[0007]

As a result of repeated tests of such prior art, the inventors have found that they still have problems. The first problem is that any of the techniques disclosed in the above publications applies a bias voltage to the terminal of the electromechanical conversion element or instantaneously applies a negative pressure when supplying an electric signal for ejection. Therefore, there is a phenomenon that a negative voltage is applied. This has the disadvantage that extra energy is required to apply the electric signal for ejection, or the waveform (ejection waveform) of the electric signal for ejection cannot be made uniform. This complicates the configuration of the drive circuit and causes extra energy to be generated, making it impossible to reduce the size of the recording head for printing.

The second problem is to speed up printing. It has been found that when high-speed printing is to be realized by the above-described conventional technique, unevenness occurs in the printing result. Further, the study was repeated, and the phenomenon shown in FIG. 11 was found. That is, as shown in FIG. 11A, when only one short electric signal pulse for ejecting an appropriate amount of ink is applied to the electromechanical transducer, the position of the meniscus formed at the ejection port becomes as shown in FIG. 11B. As shown, repeated damping oscillations were observed for some time thereafter. This is considered to be vibration caused by the ink being introduced from the ink tank to replenish the ink lost from the pressure chamber due to the ejection. And
When high-speed printing is performed, the next ejection timing arrives before this vibration is attenuated, and a phenomenon roughly as shown in FIG.

That is, when the cycle T of the electric signal having the ejection waveform as shown in FIG. 12A becomes a short time equivalent to the oscillation cycle shown in FIG. The meniscus position is shown in FIG.
The state is as shown in FIG. As a result, the amount of ink droplet by one ejection changes, and the dot by one ink ejection printed on the paper surface has a difference in size as shown in FIG. turn into.

When the state shown in FIG. 12 is further analyzed, the meniscus position of the discharge port is once depressed due to the discharge of the ink droplet, and this time is recovered from ink replenishment to reach a flat state Tr (referred to as ink refill time).
However, it turned out that it becomes uneven by the number of repetition cycles. That is, the ink refill time T for each successive cycle
When plotting r ₁ , Tr ₂ , Tr ₃ ,... according to the number of ejections, it can be seen that they vibrate as shown in FIG. If it is considered that a large amount of ink is replenished in the pressure chamber if the infill time is short, and a sufficient amount of ink is not replenished in the pressure chamber if the infill time is long, this coincides with unevenness in the printing state.

FIG. 14 shows the displacement velocity of the meniscus position for further analysis. FIG.
4A and 4B are the same as FIGS. 12A and 12B. When the meniscus position shown in FIG. 14B is time-differentiated and its displacement speed is obtained, FIG. Become like From this analysis result, it is important to always equalize the meniscus position throughout the repetition of ink ejection, but it has been found that equalizing the displacement speed of the meniscus is extremely important for uniform printing.

The present invention has been made in view of such a background, and is capable of always discharging a fixed amount of ink from a discharge port even when the repetition time for discharging ink droplets varies variously. It is intended to provide a device. An object of the present invention is to increase the speed of an ink jet recording apparatus. According to the present invention, at the time of the rising of the ejection waveform for ejecting the ink droplet, the remaining voltage such as the bias voltage is not applied to the electromechanical transducer of the pressure chamber, and the rational setting can be made independently. An object of the present invention is to provide an ink jet recording apparatus capable of efficiently changing the pressure of a pressure chamber with a proper discharge waveform. SUMMARY OF THE INVENTION It is an object of the present invention to provide an ink jet recording apparatus in which energy applied to an electromechanical transducer in a pressure chamber can be efficiently used for ejecting ink droplets. SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus which supplies a small amount of energy for discharging ink droplets.

[0013]

SUMMARY OF THE INVENTION According to the present invention, when the timing for suspending the ejection of ink is prolonged, the ink is not ejected from the ejection port prior to the application of the first ejection waveform after the suspension. It is characterized in that a pre-waveform of the voltage is applied to the electromechanical transducer, and the displacement speed of the meniscus of the discharge port during the first few discharges is controlled to a stable state. The present invention is different from the above-described prior art in that the control is performed by focusing on not only the state of the meniscus but also the displacement speed of the meniscus. The present invention also differs from the above-described prior art in that a bias voltage or a signal for pressure reduction is not substantially applied to the electromechanical transducer at the time when the first ejection waveform rises after the ejection is stopped.

That is, the present invention provides a pressure chamber, an ink tank for supplying ink to the pressure chamber via an introduction path,
In an ink jet recording apparatus comprising: an ink discharge port communicating with the pressure chamber; an electromechanical transducer for applying a pressure change to the pressure chamber; and a drive circuit for applying an electric signal to the electromechanical transducer. When the pause time of an electric signal based on a discharge waveform that gives a change in pressure at which an appropriate amount of ink droplet is discharged from the discharge port becomes longer, ink droplets may be discharged from the discharge port prior to the electric signal based on the discharge waveform. Means for providing an electrical signal with a pre-waveform that provides no small pressure changes.
The pre-waveform is characterized in that the electric signal level becomes almost zero at the time of the subsequent rise of the ejection waveform.

The pre-waveform may be given only once before the ejection waveform, but it is desirable to give it repeatedly a plurality of times. That is, by repeatedly giving the pre-waveform according to the clock timing, the vibration of the pressure chamber becomes a steady state equivalent to the case where the ejection is repeated,
The displacement speed of the meniscus in the first several ejection timings can be equalized.

In order to provide the pre-waveform, the driving circuit comprises a memory means for storing the ejection waveform and the pattern of the pre-waveform, and a memory for storing the ejection waveform when the printing information includes ejection data in accordance with a periodic clock timing. Means for reading the pattern of the ejection waveform from the memory means and for reading the pattern of the pre-waveform from the memory means when there is no ejection data; and converting the pattern read from the memory means to an electric signal to the electromechanical transducer. It is desirable to provide a configuration including a supply unit.

[0017] This reading means, when the state where there is no ejection data continues over a plurality of clock timings, the pattern of the pre-waveform at the last one or several clock timings of the continuous clock timings. , And the pre-waveform is not necessarily repeatedly read at the clock timing in which the pause state continues. Thus, it is possible to prevent unnecessary energy from being supplied to the pressure chamber due to the pre-waveform.

The pre-waveform pattern is preferably set so that its rising point is slightly delayed from the clock timing with respect to the rising point of the ejection waveform pattern. This is advantageous in that the starting point of the pre-waveform is slightly shifted backward since the energy of the pre-waveform is small, so that the meniscus displacement speed is constant at the starting point of the next ejection waveform.

With such a configuration, a constant amount of ink can always be ejected from the ejection port even when performing high-speed printing or when the repetition time for ejecting ink droplets varies in various ways. Further, since the bias voltage or the remaining voltage can be prevented from being applied to the electromechanical transducer of the pressure chamber at the rising point of the waveform for performing the pressurization for ejection, the pressure of the ink chamber can be efficiently reduced with small energy. Can be changed.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

[0021]

Next, an embodiment of the present invention will be described with reference to the drawings. 1 is an overall hardware configuration diagram of the apparatus of the embodiment of the present invention, FIG. 2 is a conceptual diagram showing the structure of a recording head of the apparatus of the embodiment of the present invention, and FIG. 3 is a configuration diagram of an electric circuit of the apparatus of the embodiment of the present invention.

The apparatus according to the embodiment of the present invention is provided with a recording head 1, an ink tank 2 in which ink is stored, and an electronic circuit 3 for supplying an electric signal to the recording head 1 to drive it.

The recording head 1 is provided with a pressure chamber 5 which is surrounded by a wall partially formed with a small ink discharge port 4 and is filled with ink, and is provided inside the wall of the pressure chamber 5 to fluctuate the internal pressure. And an electromechanical conversion element 6 to be used. The pressure chamber 5 is communicated with the ink tank 2 via an introduction path 7, and the electromechanical transducer 6 is connected to the electronic circuit 3 by a movable signal line 8.

The recording head 1 includes a rail 2 provided along an axis of a platen 22 around which a recording paper 21 is wound.
3 is driven by a recording head driving motor 24 via a wire 25 to control the position. For example, the recording head 1 ejects ink from the ink ejection ports 4 while moving from left to right along the recording paper 21. For example, 48 ink ejection ports 4 are arranged, and a pressure chamber 5 for pressurizing ink and a pressure chamber 5
Is provided. When printing on the line is completed, the platen 22 is rotated by a platen driving motor (not shown), and the recording head 1 is moved to the left side of the next line by the recording head driving motor 24.

The electronic circuit 3 has a CP as shown in FIG.
U10, a discharge waveform generating circuit 11 for generating an electric signal with a discharge waveform for giving a pressure change to discharge an appropriate amount of ink droplet from the ink discharge port 4 under the control of the CPU 10, and an electric signal for the electromechanical transducer 6. When the pause time of the signal exceeds a predetermined value, an electric signal is generated according to a pre-waveform that gives a small pressure change that does not cause ink droplets to be ejected from the ink ejection port 4 prior to the electric signal according to the ejection waveform under the control of the CPU 10. A pre-waveform generation circuit 12 for storing the ejection waveform and the pre-waveform, and a memory means 13 for storing a drive voltage pattern with respect to the passage of time.
The output signals of the ejection waveform generation circuit 11 and the pre-waveform generation circuit 12 which are individually connected to the electromechanical
Switch circuit 14 for switching under control of PU 10
And are provided. This switch circuit 14 is composed of a large number of semiconductor switch elements.

Further, the CPU 10 reads out a pattern of the ejection waveform from the memory means 13 when there is ejection data at every periodic clock timing, and generates dummy data when there is no ejection data, and reserves the dummy data from the memory means 13. Means for reading the waveform pattern, and the electromechanical transducer 6 using the pattern read by the means for reading as an electric signal.
And a means for reading out dummy data at the last clock timing of the continuous clock timing when a state where there is no ejection data continues at a plurality of clock timings.

The pre-waveform generated by the pre-waveform generation circuit 12 is
A waveform having a sufficiently zero value at the time of the subsequent rising of the ejection waveform is used, and the pattern of the pre-waveform is set so that the rising point is slightly delayed from the rising point of the pattern of the ejection waveform applied last.

Next, the ink discharging operation of the apparatus according to the embodiment of the present invention will be described.

First, the ink ejection operation using the first drive pattern will be described. This first drive pattern is
This is a driving pattern when a discharge state is performed after a pause for a long time. FIG. 4 is a flowchart showing a flow of an ink ejection operation by the first drive pattern of the apparatus according to the embodiment of the present invention.

When the electric signal based on the ejection waveform is stopped, the CPU 10 determines whether or not the stop time exceeds a predetermined value. If the pressure exceeds the predetermined value, the pressure chamber 5 is not pressurized for a long time, and the state of the meniscus in the ink discharge port 4 is concave or flat as shown in FIG. 5A or 5B. , Dummy data is generated to read out a pre-waveform pattern from the memory means 13, and the pre-waveform pattern is supplied to the electromechanical transducer 6 as an electric signal by the pre-waveform generation circuit 12.

Next, the ejection waveform pattern is read out from the memory means 13 in accordance with the input of the print information, and the ejection waveform pattern is converted into an electric signal by the ejection waveform generation circuit 11 as an electric signal in accordance with the periodic clock timing. To discharge ink. FIG.
(A) shows an example of the pattern of the pre-waveform and the ejection waveform. The supply of the electric signal to the electromechanical transducer 6 based on the pre-waveform and the discharge waveform is performed by switching the switch circuit 14 under the control of the CPU 10.

As described above, once the ink discharge is stopped, and the meniscus state at the ink discharge port 4 is concave or flat as shown in FIGS. By supplying as a signal, the meniscus change speed is always the same.
The pressure chamber 5 can be pressurized in the vicinity of the convex shape shown in (c) and FIG. 6 (b), and the initial pressurization based on the pre-waveform makes the meniscus state and the meniscus change speed during the subsequent continuous discharge substantially constant. Can be

After the ink is ejected, the ink is pressure-fed from the ink tank 2 to fill the pressure chamber 5, and the next ejection is performed in the vicinity of the convex meniscus as shown in FIG. 6B. , Discharge and filling of ink are repeatedly performed. As a result, the amount of ink filled in the pressure chamber 5 becomes almost constant at all times, and the printing state becomes almost uniform as shown in FIG.

In the present embodiment, the trapezoidal wave as shown in FIG.
Any waveform may be used as long as it can keep the rate of change of the meniscus and the position of the meniscus constant, for example, by using a sine wave or a waveform having the opposite polarity to the discharge waveform. The effect can be obtained.

In the embodiment of the present invention, as an example in which the meniscus state and the rate of change of the meniscus become substantially constant, the ejection in the state in which the meniscus shape is convex is shown. However, the meniscus shape does not need to be convex, Even when flat
It suffices that the meniscus shape and the meniscus change speed during ejection become constant.

Next, an ink ejection operation by the second driving pattern of the apparatus according to the embodiment of the present invention will be described. This second drive pattern is a pattern that is all performed when there is a clock timing without ejection. FIG. 7 (a)
FIG. 7 is a diagram showing a printing state of the apparatus according to the embodiment of the present invention using a second drive pattern, and FIG.

When there is such a clock timing that there is no ejection, data that does not eject ink droplets is added to the head of a series of image data as dummy data to be drive data for the recording head 1.

FIG. 8 is a flow chart showing the flow of the ink ejection operation by the second driving pattern of the apparatus according to the embodiment of the present invention.

The CPU 10 determines whether or not to eject ink droplets based on the ejection data. If an ink droplet is to be ejected, the CPU 10 reads a pattern of the ejection waveform from the memory means 13 and uses the pattern of the ejection waveform as an ejection waveform generating circuit. 11 to the electromechanical transducer 6 through the switch circuit 14 as an electric signal.

When ink droplets are not ejected, a pre-waveform pattern is sequentially read from the memory means 13 in accordance with the dummy data, and the pre-waveform pattern is used as an electric signal from the pre-waveform generating circuit 12 via the switch circuit 14 via the switch circuit 14. Applied to the mechanical conversion element 6.

By performing such processing, the pre-waveform is always applied even when the apparatus is in the stationary state where ejection is not performed, and when the ejection is performed from the stationary state as shown in FIG. 7B. As described above, the electric signal based on the pre-waveform is always applied immediately before that, and as shown in FIG. 6B, the meniscus in the ink ejection port 4 is in a convex state, and the ejection is performed at a constant changing speed. Therefore, even if there is a subsequent ejection from the stationary state, constant printing is performed in the same pattern.

Further, when the ejection timing is not continuous, printing is performed by the third driving pattern in which the application of the pre-waveform is temporarily interrupted until the next ejection timing.

FIG. 9A is a diagram showing a printing state according to the third drive pattern of the apparatus according to the embodiment of the present invention, and FIG. 9B is a diagram showing its waveform.

As described above, when the ejection timing is not continuous, data that does not eject ink droplets is added to the head of a series of image data as dummy data to generate drive data for the recording head 1. When the next ejection timing occurs, Generate a pre-waveform and print.

FIG. 10 is a flowchart showing the flow of the ink ejection operation by the third drive pattern of the apparatus according to the embodiment of the present invention. The CPU 10 determines whether or not to eject ink droplets based on the ejection data. If an ink droplet is to be ejected, the CPU 10 reads a pattern of the ejection waveform from the memory unit 13 and outputs the pattern of the ejection waveform from the ejection waveform generation circuit 11 to the electrical circuit. The electromechanical conversion element 6 via the switch circuit 14 as a signal
Is applied.

If the ink droplet is not to be ejected, it is determined whether or not to perform the next ejection. When the next ejection is to be performed, the pattern of the pre-waveform is read from the memory means 13 and the pattern of the pre-waveform is converted to the pre-waveform. The electric signal is applied from the generating circuit 12 to the electromechanical transducer 6 via the switch circuit 14 as an electric signal. Next, when the ejection is not performed, the application of the electric signal based on the pre-waveform is stopped until the ejection data is generated.

Thus, even when the stationary state where ejection is not performed is continuous, the recording head 1 is driven with dummy data added. When ejection is performed, an electric signal based on a pre-waveform is always applied. Various printing can be performed.

[0048]

As described above, according to the present invention, even when the repetition time for ejecting ink droplets from the recording head changes variously or when high-speed printing is performed, a fixed amount of ink is always discharged from the ejection port. Ink can be ejected.
In addition, at the time of rising of the waveform for performing pressurization for discharge, the bias voltage or the remaining voltage is not applied to the electromechanical transducer in the pressure chamber, and the pressure in the pressure chamber is changed with an independent discharge waveform. Therefore, ink droplets can be efficiently ejected with small energy.

[Brief description of the drawings]

FIG. 1 is an overall hardware configuration diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a configuration of a recording head of the apparatus according to the embodiment of the present invention.

FIG. 3 is an electric circuit configuration diagram of the device according to the embodiment of the present invention.

FIG. 4 is a flowchart showing a flow of an ink ejection operation according to a first drive pattern of the apparatus according to the embodiment of the present invention.

FIGS. 5A to 5C are diagrams illustrating a meniscus state at an ink ejection port of the apparatus according to the embodiment of the present invention.

6A is a diagram showing a pre-waveform and an ejection waveform in the apparatus according to the embodiment of the present invention, FIG. 6B is a diagram showing a change in a meniscus position at an ink ejection port, and FIG. 6C is a diagram showing a printing state.

FIG. 7A is a diagram illustrating a printing state according to a second drive pattern of the apparatus according to the embodiment of the present invention, and FIG. 7B is a diagram illustrating a waveform thereof.

FIG. 8 is a flowchart showing a flow of an ink ejection operation according to a second drive pattern of the apparatus according to the embodiment of the present invention.

9A is a diagram illustrating a printing state according to a third drive pattern of the apparatus according to the embodiment of the present invention, and FIG. 9B is a diagram illustrating a waveform thereof.

FIG. 10 is a flowchart showing a flow of an ink ejection operation by a third driving pattern of the apparatus according to the embodiment of the present invention.

FIG. 11A is a diagram showing an electric signal based on a discharge waveform,
FIG. 6B is a diagram illustrating a change in a meniscus position after ink ejection by an electric signal.

12A is a diagram illustrating a state in which an electric signal based on a discharge waveform is continuously applied, FIG. 12B is a diagram illustrating a state of a meniscus after ink discharge using the electric signal, and FIG. 12C is a print state thereof FIG.

FIG. 13 is a diagram illustrating a refill time of ink into a pressure chamber for each ejection count.

14A is a diagram showing a state where an electric signal based on a discharge waveform is continuously applied, FIG. 14B is a diagram showing a state of a meniscus after ink discharge by the electric signal, and FIG. The figure which shows the change of the speed which performs.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 recording head 2 ink tank 3 electronic circuit 4 ink discharge port 5 pressure chamber 6 electromechanical transducer 7 introduction path 8 movable signal line 10 CPU 11 discharge waveform generation circuit 12 pre-waveform generation circuit 13 memory means 14 switch circuit 21 recording paper 22 Platen 23 Rail 24 Recording head drive motor 25 Wire

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 EA01 EA06 EB08 EB38 EC08 EC63 FA04 FA10 2C057 AF06 AF25 AF41 AF54 AG12 AG44 AL33 AN01 AR08 BA03 BA14

Claims (6)

[Claims] A pressure chamber, an ink tank that supplies ink to the pressure chamber via an introduction path, an ink discharge port that communicates with the pressure chamber, and an electromechanical transducer that changes the pressure in the pressure chamber. A drive circuit for supplying an electric signal to the electromechanical transducer, wherein the drive circuit is configured to perform a pause of the electric signal based on a discharge waveform that gives a change in pressure at which an appropriate amount of ink droplet is discharged from the discharge port. An ink jet recording apparatus comprising: means for giving an electric signal with a pre-waveform that gives a small pressure change that does not lead to the ejection of an ink droplet from the ejection port prior to the electric signal with the ejection waveform when the length of the ink becomes long. . 2. The ink jet recording apparatus according to claim 1, wherein the pre-waveform is a waveform whose electric signal level becomes almost zero at the rising point of the subsequent ejection waveform. 3. The ink jet recording apparatus according to claim 1, wherein said drive circuit includes means for repeatedly applying an electric signal based on said pre-waveform a plurality of times prior to an electric signal based on said ejection waveform. 4. A driving circuit comprising: a memory for storing the pattern of the ejection waveform and the pre-waveform; and a memory for storing the ejection waveform when the printing information includes ejection data in accordance with a periodic clock timing. Means for reading a pattern and reading a pre-waveform pattern from the memory means when there is no ejection data, and means for converting the pattern read from the memory means into an electric signal and supplying the electric signal to the electromechanical transducer. An ink jet recording apparatus according to claim 2 or 3. 5. The read means reads the pattern of the pre-waveform at the last portion of the clock timing having no continuous discharge data when the state without the discharge data continues over a plurality of clock timings. 5. The ink jet recording apparatus according to claim 4, further comprising a discharging unit. 6. The ink jet recording apparatus according to claim 4, wherein the rising point of the pattern of the pre-waveform is set to be slightly delayed from the rising point of the pattern of the ejection waveform.