JPH04133743A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To prevent a rapid temperature increase of a recording head to make an ink delivery remain stable by providing a drive condition changing means for changing a recording head drive condition in accordance with the ink delivery number per dot of the recording head. CONSTITUTION:An ink delivery during a time TA and a delivery quiescence during a time TB are repeated. The output number of a coincidence signal of a second comparison circuit 18 corresponding to the repeat number is counted by a third counter 16. Namely, the coincidence signal of the second comparison circuit 18 is counted as a heat count signal HC. When the count value reaches a comparison reference value in a register 22, a third comparison circuit 19 outputs a coincidence signal to reset a flip flop 12 to stop the output of a heat enable signal HE, thereby completing a heating of an electrothermal conversion body 11. The ink delivery number per dot can be changed in accordance with the set value in the register 22. In this case, according as a delivery cycle is shortened by increasing the ink delivery number, the pulse width of the heat pulse HP is reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an inkjet recording apparatus.

[Prior Art] An inkjet recording device discharges ink from ink discharge ports formed in a recording head based on an input image signal, and deposits droplets of the ink on a recording medium to form dots. This is a device that records an image using a group of dots, and is becoming widely used in printers, facsimile machines, copying machines, and the like.

There are two types of inkjet recording devices: a serial print type in which the print head is mounted on a carriage that moves along the recording medium and scans in the width direction of the recording medium, and the other is a serial print type in which the print head is mounted on a carriage that moves along the recording medium and scans in the width direction of the recording medium. There is a line print type that uses arrayed multi-heads to record while moving the recording medium. Also yellow, magenta.

Full-color printing is also possible by arranging a plurality of print heads so that inks of different colors such as cyan and black can be ejected, or by providing one print head with ejection ports corresponding to each color. In addition, in the method of ejecting ink, a heating element (electrical-thermal energy converter) is provided near the ink ejection port, and by applying an electric signal to this heating element, the ink is locally heated and bubbles are generated. There are a method using an electric-to-thermal energy converter in which ink is generated and the pressure change caused by this bubbling causes ink to be ejected from an ejection port, and a method using an electro-mechanical converter such as a piezoelectric element.

Conventionally, image recording using the inkjet method involves digitally turning on and off the ejection of ink from a recording head according to an input image signal to form dots of a fixed size on a recording medium. This is done by controlling the number of recorded dots per unit area.

However, in the above recording method, when the dither method is used as a binarization method for expressing halftones, there are problems such as restrictions on the number of gradations and a decrease in resolution, and there are also problems with the error caused by other binarization methods. Even when the diffusion method is used, there is a problem in that graininess tends to be noticeable in bright areas of the image.

These problems can be greatly improved if the size of the print dots can be controlled according to the gradation of the image by varying the amount of ink ejected from the print head.

However, depending on the method of ink ejection in an inkjet recording device, it is difficult to control the amount of ink ejected. Although it is easy to implement and can achieve high density and high definition recording, it has been difficult to effectively vary the amount of ink ejection.

Therefore, for example, in the case of a serial print type thermal foaming inkjet recording device, the ink ejection cycle is shortened compared to the moving speed of the carriage, and multiple ink droplets are deposited near the same location on the recording medium. , it is conceivable to change the size of the recording dots. Using this method not only improves the image quality when recording halftone images, but also improves the recording medium's coated paper for inkjet, which has an ink-receiving layer and has large ink smudges, and the ink-receiving layer that is used as a recording medium. When recording on paper with small bleeding, by varying the ink ejection cycle according to the ink-receptive characteristics of the recording medium, an image can be formed with the optimal recording dot size, making it possible to create a rich image that is not affected by the recording medium. Good images can be obtained.

[Problems to be Solved by the Invention] However, for example, in the case of an inkjet recording device using an electric-thermal energy converter, if the recording head is driven at high frequency to shorten the ink ejection cycle, the temperature of the recording head will rise. There was a risk that stable ink ejection would not be possible because the bubbles that were generated were difficult to disappear.

Such a problem also exists in inkjet recording apparatuses using other ejection methods in which the temperature tends to rise by shortening the ejection cycle, and there is a possibility that stable ink ejection may not be possible.

FIG. 8 shows an example of the temperature rise characteristics of a recording head in a recording apparatus that utilizes thermal energy. Curve a is for driving at 4 kHz, and curve 2 is for driving at 8 kHz. The temperature of the recording head was determined by measuring the temperature near the Si substrate on which a heating resistor, which is an electric-thermal energy converter, was formed.

As is clear from the figure, when driven at a high frequency, heat tends to accumulate because the cooling time of the heating resistor and the ink in the ejection ports is short, and the temperature rises rapidly. If the cooling is not done in time (if this happens, the foamed bubbles will not disappear, and the remaining bubbles will block the inside of the ejection port and ink will not be supplied to the ejection port surface, which will adversely affect ink ejection.

An object of the present invention is to eliminate the problem of heat accumulation in foam type or other types of inkjet recording devices as described above, and to prevent rapid temperature rise of the recording head even if the ink ejection cycle is shortened. An object of the present invention is to provide an inkjet recording device capable of stably ejecting ink.

[Means for Solving the Problems] In order to achieve the above object, the inkjet recording apparatus of the present invention prints an input image while varying the number of ink ejections of the recording head per dot formed on a recording medium. An inkjet recording apparatus that records an image according to a signal, characterized by comprising a driving condition variable means for changing the driving conditions of the recording head according to the number of times ink is ejected per one dot of the recording head. .

[Function 1] The inkjet recording apparatus of the present invention, when recording an image while varying the number of ink ejections per one dot, controls the driving of the print head according to the number of times the ink is ejected per one dot. Conditions, such as the time per ink ejection, the ink ejection interval time, or the drive voltage of the recording head, are changed.

This prevents a rapid temperature rise due to heat accumulation in the recording head, and always performs stable ink ejection.

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described based on FIGS. 1 to 8.

1 to 3 are diagrams for explaining a first embodiment of the present invention. This embodiment is an example of application to a thermal foaming type recording device which is a serial print type and uses an electric-to-thermal energy converter as described above. First, the configuration of the main parts of the thermal foaming type recording device will be explained with reference to FIG.

In FIG. 3, IA is a print head that ejects cyan ink, IB is a print head that ejects magenta ink, IC is a print head that ejects cyan ink, and ID is a print head that ejects black ink. These print heads LA, IB, IG, and ID are installed on the carriage 2. Each of these recording heads LA, IB, Ic, and ID has a plurality of ink ejection openings each having a liquid path for guiding color ink, and each of these liquid paths has an ejection energy generating element. An electrothermal converter (not shown) is provided.

The carriage 2 is moved left and right along a guide shaft 3, and the recording medium 6 is conveyed by conveyance rollers 4 installed above and below. The recording medium 6 includes a recording head LA,
The ink ejection ports IB, Ic, and ID are maintained parallel to and opposite to the formation surfaces of the ink ejection ports. The respective color inks are deposited as ink droplets on the recording medium 6 in the order of yellow, magenta, cyan, and black, forming a multicolor image. Reference numeral 5 denotes an encoder, which detects the moving position of the carriage 2 corresponding to the ink ejection position.

When recording on the recording medium 6, while moving the carriage 2 at a constant speed, a large number of electro-thermal converters in each recording head LA, IB, IC, and ID are selectively driven according to the input image signal. to generate heat. The generated electrothermal converter heats and foams the ink in the liquid path equipped with it, and the pressure change caused by the foaming causes the ink to be ejected from the ejection port, and the ink droplets are transferred to the recording medium. 6.

In this example, the electro-thermal converter is driven at high frequency to shorten the ink ejection period (and each recording head LA, IB,
One recording dot for each of Ic and ID.
It is possible to record by ejecting ink twice.

In the following, one of the recording heads LA, IB, l(: and 10) will be looked at, and a control circuit for that one recording head will be explained.

In FIG. 1, reference numeral 11 is one of a plurality of electro-thermal converters provided in the recording head, and a control circuit similar to that shown in the figure is also connected to the other electro-thermal converters. This electricity-
The heat converter 11 is energized twice and generates heat every time the corresponding heat trigger signal HT is input.

Heat trigger signal HT is R-S flip-flop 12
is also input as a set signal, and the output of the flip-flop 12 is ANDed as a heat enable signal HE.
It is input to one input terminal of the circuit 13. This heat enable signal HE puts the electro-thermal converter 11 into a heat mode in which it can generate heat.

In addition, heat trigger signal 1 (T is one input terminal of the OR circuit 23 and the clear signal input terminal C of the third counter 16
It is input to L. The output terminal of the OR circuit 23 is connected to the clear signal input terminal CL of the first counter 14. The first counter 14 and the second counter 15, which will be described later, each count clock pulses CP from the time when the count value is cleared. This clock pulse cp is
This is a pulse signal with a constant period that serves as a reference for determining the energization time of the electrothermal converter 11 and the energization interval time. On the other hand, the third counter 16 is connected to a second comparison circuit 1 which will be described later.
Count 8 match signals.

1st. Second and third counters 14.15 and 16
The count value (in this example, it is output as 4 bits) is the corresponding 1st . Second and third comparison circuit 1
7.11! 11; and 19, and is input to register 20.
．． 21 and 22. register 2
0.21 and 22 are each connected to a data bus so that comparison reference values can be set.

The first comparator circuit sets the heat pulse HP to H level only from when the count value of the first counter 14 is cleared until the comparison reference value in the register 20 is reached.

The heat pulse HP is input to the other input terminal of the AND circuit 13 and drives the drive transistor Tr of the electric-thermal converter 11 in the heat mode. Also, 1st.
The second and third comparison circuits 17, 18 and 19 each output a match signal when two corresponding values to be compared match. The match signal from the first comparator circuit 17 is input as a clear signal for the count value of the second counter 15. Further, the coincidence signal of the second comparison circuit 18 is
The signal is input as a clear signal for the count value of the counter 16, and is also input to the other input terminal of the OR circuit 23. Further, the coincidence signal of the third comparison circuit 19 is inputted as a reset signal of the flip-flop 12.

Next, the operation will be explained with reference to FIG.

By inputting the heat trigger signal HT, a heat enable signal HE is output from the flip-flop 12, and the electric-thermal converter 1 enters a heat mode in which it can generate heat. Furthermore, by the heat trigger signal HT, the first $5
Then, the count values of the third counters 14 and 16 are cleared, the first counter 14 starts counting the clock pulse CP, and the first comparison circuit 17 outputs the heat pulse HP. The transistor Tr is driven by the heat pulse HP, and the electric-thermal converter 11 is energized to generate heat and eject ink.

Pulse width TA of heat pulse HP (ink ejection time)
corresponds to the time until the count value of the first counter 14 reaches the comparison reference value in the register 20, and when the first comparison circuit 17 outputs a match signal, the heat pulse I
P becomes L level, and the electricity supply to the electro-thermal converter 11 is stopped.

Then, the match signal from the first comparison circuit 17 clears the count value of the second counter 15, and the counter 15 starts counting clock pulses CP. The count value of this second counter 15 is stored in the register 21.
The time it takes to reach the comparison reference value within corresponds to the time TB of the ink ejection interval. Then, when the second comparison circuit 18 outputs a coincidence signal, the first counter 14
When the count value of is cleared, the transistor Tr is driven by the heat pulse HP and 2
Ink is ejected for the second time.

In this way, ink ejection 8 for the TA time and ejection pause for 78 hours are repeated, and the third counter 16 counts the number of times the second comparison circuit 18 outputs a coincidence signal corresponding to the number of repetitions. Ru. That is, the coincidence signal of the second comparison circuit 18 is counted as a heat count signal HC (see FIG. 2).

When the count value reaches the comparison reference value in the register 22, the third comparison circuit 19 outputs a match signal to reset the flip-flop 12, and the heat enable signal H
The output of E is stopped to complete the heating operation of the electric-thermal converter 11. In this example, the comparison reference value of the register 22 is set to "2" so that the same dot is formed by repeating ink ejection twice.

The number of ink ejections per dot can be arbitrarily changed according to the setting value in the register 22, and in that case,
When increasing the number of ink ejections to shorten the ejection cycle, the pulse width of the heat pulse [(P) is shortened accordingly.This shortens the heat generation time of the electro-thermal converter 11, that is, the ink ejection time TA. to reduce heat accumulation,
Prevents rapid temperature rise. The ink ejection time TA and the ejection interval time TB can be arbitrarily changed according to the set values of the registers 20 and 21, for example, as shown in TA' and TB' in FIG. Discharge interval time TB is 1
When changing the number of ink ejections per dot, the cooling time of the electro-thermal converter 11 is set optimally,
Heat accumulation can be kept to a minimum.

Note that it is also possible to use the first and second comparison circuits 17 and 18 in common, or to use the first and second counters 14 and 15 in common.

FIG. 4 and FIG. 5 are diagrams for explaining a second embodiment of the present invention.

In the case of this embodiment, the length of time for ejecting ink multiple times per dot can be changed individually, and the length of time for ejecting ink multiple times per dot can be changed individually.
A register 24 is provided in each of the comparator circuits 17 and 18.
and 25 new features. These registers 2
4 right and 25 are connected to the data bus similarly to registers 20 and 21, and are connected to the first and second comparison circuits 1 and 25.
7 and 18 comparison reference values can be set. The first comparison circuit I7 uses 2 as its comparison reference value.
The set values in the two registers 20 and 24 are selectively used, and the ink ejection time is changed according to the comparison reference value used. Similarly, the second comparison circuit 18 selectively uses the set values in the two registers 21 and 25 as its comparison reference value, and changes the ink ejection interval time according to the comparison reference value used. do.

The other configurations are the same as those of the first embodiment described above.

According to such a configuration, as shown in FIG. 5, for example, the first and second ink ejection times TA-1 and TA
-2, or the times TB-1 and TB-2 between the first and second ink ejection intervals. In that case, the second ink ejection time TA-2 is made shorter than the first ink ejection time TA-1.
Because the ink is heated by the heat generated by the ink, the viscosity of the ink decreases, and the second time the ink is ejected, the ink can be foamed and ejected more easily than the first time.
By shortening the second ejection time TA-2, it is possible to suppress the temperature rise due to wasteful generation of heat.

Furthermore, when increasing the number of ink ejections per dot, the ink ejection time is shortened accordingly.

Furthermore, by adding registers 24 and 25, it is possible to individually change the length of time for multiple ejections of ink per dot.

FIG. 6 and FIG. 7 are diagrams for explaining a third embodiment of the present invention.

In the case of this embodiment, the voltage applied to the electro-thermal converter 11, that is, the drive voltage vh of the recording head that generates the heat pulse HP, can be varied in accordance with the number of ink ejections per dot. Therefore, as shown in FIG.
are connected.

The voltage dividing circuit 30 has voltage dividing resistors R+, R*, Ra, and R
4 connection status can be changed. On the other hand, in the constant voltage power supply circuit, in order to always match the feedback voltage Vfd and the reference voltage Vref of the reference voltage generation circuit 33, the difference between them is amplified by the error amplifier 34 to generate a phase pulse in the phase pulse generator 35. The generation timing is adjusted, thereby controlling the output power of the control rectifier circuit 36. As a result, the drive voltage vh of the recording head that is smoothed by the filter circuit 37 and generates the heat pulse HP is divided into four stages depending on the combination of the switch states of the transistors 31 and 32 based on the heat power down signal HPDI and HFO2. It's going to change.

Heat power down signals HPDI and HFO2 are 1
Control is performed according to the number of times ink is ejected per dot. For example, when ink is ejected twice as shown in Fig. 7, the heat power down signal H is used for the first time.
Both PDI and HFO2 are set to "High" to set the drive voltage vh and hence the heat pulse HP to be high voltages, and in the second time, they are both set to "Low" to set the drive voltage vh and therefore the heat pulse HP to be a low voltage.

In this manner, by varying the voltage value of the heat pulse I (P), the amount of heat generated by the electrothermal converter 11 can be controlled and heat accumulation can be prevented.

Note that the number of control stages for the voltage value of the heat pulse HP is arbitrary, and the control may be performed steplessly.

Furthermore, the heat pulse HP control methods in each of the embodiments described above may be combined as appropriate.

(Others) The present invention brings about excellent effects particularly in a bubble jet type recording head and recording apparatus proposed by Canon Co., Ltd. among inkjet recording types. This is because such a system can achieve higher recording density and higher definition.

Regarding typical configurations and principles, it is preferable to use the basic principles disclosed in U.S. Pat. No. 4,723,129 and U.S. Pat. No. 4,740,796. , continuous type, but especially in the case of on-demand type, electrothermal converters are placed corresponding to the sheet holding the liquid (ink) or the liquid path. To,
Generating thermal energy in the electrothermal transducer and producing film boiling on the thermally active surface of the recording head by applying at least one drive signal that corresponds to recorded information and provides a rapid temperature rise above nucleate boiling. As a result, bubbles in the liquid (ink) can be formed in a one-to-one correspondence with this drive signal, which is effective. The growth and contraction of this bubble causes the liquid (ink) to be ejected through the ejection opening to form a small droplet (at least one droplet).If this drive signal is in the form of a pulse, the growth and contraction of the bubble will occur immediately and appropriately. Because you will be exposed to
Particularly responsive liquid (ink) ejection can be achieved,
More preferable pulse-shaped drive signals include those described in U.S. Pat. Nos. 4,463,359 and 4,345,262.
Those described in the specification are suitable. Furthermore, if the conditions described in US Pat. No. 4,313,124 concerning the invention regarding the temperature increase rate of the heat acting surface are adopted, even more excellent recording can be performed.

The configuration of the recording head includes, in addition to the combination configuration of ejection ports, liquid paths, and electrothermal converters (straight liquid flow path or right-angled liquid flow path) as disclosed in the above-mentioned specifications, a heat acting section. The present invention also includes configurations using US Pat. No. 4,558,333 and US Pat. No. 4,459,600, which disclose configurations in which the wafer is placed in a bending region. In addition, Japanese Patent Application Laid-Open No. 1989-5 discloses a configuration in which a common slit is used as a discharge part of a plurality of electrothermal converters.
No. 9-123670 and Japanese Patent Application Laid-Open No. 59/1989 which discloses a configuration in which a discharge portion is made to correspond to an opening that absorbs pressure waves of thermal energy.
The effects of the present invention are also effective even if the structure is based on the publication No.-138461. That is, regardless of the form of the recording head, according to the present invention, recording can be performed reliably and efficiently.

Furthermore, the present invention can be effectively applied to a full-line type recording head having a length corresponding to the maximum width of a recording medium that can be recorded by a recording apparatus.

Such a recording head may have either a configuration in which the length is satisfied by a combination of a plurality of recording heads, or a configuration in which a single recording head is formed integrally.

In addition, even with the serial type shown above, the recording head is fixed to the device body, or by being attached to the device body, electrical connection to the device body and ink supply from the device body are possible. The present invention is also effective when using a replaceable chip type recording head or a cartridge type recording head in which an ink tank is integrally provided in the recording head itself.

Further, it is preferable to add recovery means for the recording head, preliminary auxiliary means, etc., which are provided as a configuration of the recording apparatus, to the present invention, because the effects of the present invention can be further stabilized. Specifically, these include capping means for the recording head, cleaning means, pressure or suction means, preheating means using an electrothermal transducer or another heating element, or a combination thereof; It is also effective to perform a preliminary ejection mode in which ejection is performed separately from printing in order to perform stable printing.

In addition, regarding the type and number of recording heads installed, for example, in addition to one type that corresponds to single-color ink, there is also a plurality of recording heads that correspond to multiple inks with different recording colors and densities. It may be something that can be done. That is, for example, the recording mode of the recording apparatus is not limited to a recording mode for only a mainstream color such as black, but may also be a recording mode in which the recording head is configured integrally or in a combination of multiple colors, The present invention is also extremely effective for devices equipped with at least one full color by color mixture.

Additionally, in one or more embodiments of the invention described above,
Although ink is described as a liquid, it is an ink that solidifies at room temperature or below, but softens or liquefies at room temperature, or in an inkjet method, the ink itself is
Generally, the temperature is adjusted within the range of 0°C or more and 70°C or less so that the viscosity of the ink is within the stable ejection range, so even if the ink is in a liquid state when the recording signal is applied. In addition, the temperature increase caused by thermal energy can be actively prevented by using it as energy to change the state of the ink from a solid state to a liquid state, or the ink can be left to solidify to prevent evaporation. Some methods use ink, but in any case, the ink is liquefied by applying thermal energy according to the recording signal, and the liquid ink is ejected, or the ink already begins to solidify by the time it reaches the recording medium. Note that the present invention is also applicable when using ink that is liquefied only by thermal energy. The ink used in this case is
Publication No. 4-56847 or JP-A-60-71260
As described in the above publication, the porous sheet may be held in a liquid or solid state in the recesses or through-holes of the porous sheet, facing the electrothermal converter. In the present invention, the most effective method for each of the above-mentioned inks is to implement the above-mentioned film boiling method.

In addition, in addition to being used as an image output terminal for information processing equipment such as a computer, the inkjet recording apparatus of the present invention may also take the form of a copying machine combined with a league, etc., or a facsimile machine having a transmission/reception function. It may also be something.

[Effects of the Invention] As explained above, the inkjet recording apparatus of the present invention records an image while varying the number of ink ejections per dot from the recording head. Depending on the driving conditions of the recording head, for example, the ejection time per ink ejection,
Since the configuration changes the ink ejection interval time or the drive voltage of the print head, it is possible to prevent a sudden temperature rise due to heat accumulation in the print head and always perform stable ink ejection.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram of a control circuit for an electrothermal converter of a recording head in a first embodiment of the present invention; FIG. 2 is a time chart for explaining the operation of the control circuit shown in FIG. 1; FIG. 3 is a perspective view showing the configuration of essential parts of an inkjet recording apparatus according to the first embodiment of the present invention, and FIG. 4 is a control for the electro-thermal converter of the recording head according to the second embodiment of the present invention. FIG. 5 is a time chart for explaining the operation of the control circuit shown in FIG. 4; FIG. 6 is a control diagram for the electro-thermal converter of the recording head in the third embodiment of the present invention. FIG. 7 is a time chart for explaining the operation of the control circuit shown in FIG. 6, and FIG. 8 is a curve diagram of temperature rise characteristics of a recording head in a conventional example. LA, 1B, IG... Recording head, 2... Carriage, 3... Guide shaft, 4... Conveyance roller, 5... Encoder, 6... Recording medium, 11... Electricity. Heat converter, 12... Flip-flop, 13... AND circuit, 14... First counter, 15... Second counter, 16... Third counter, 17... Third counter. 1 comparison circuit, 18... second comparison circuit, IG... third comparison circuit, 20.21, 22.24.25... register, 23.
...OR circuit, 30...Voltage divider circuit, 31.32...Transistor, 33...Reference voltage generation circuit, 34...Error amplifier, 35...Phase pulse generator, 3G... Control rectifier circuit, 37... Filter circuit.

Claims (1)

[Scope of Claims] 1) In an inkjet recording apparatus that records an image according to an input image signal while varying the number of ink ejections of the recording head per dot formed on a recording medium, one of the recording heads An inkjet recording apparatus characterized by comprising a drive condition variable means for changing the drive conditions of the recording head according to the number of ink ejections per dot. 2) The driving condition variable means adjusts the number of times of ink ejection per dot of the recording head.
The inkjet recording apparatus according to claim 1, characterized in that the ejection time per time is variable. 3) The inkjet recording according to claim 1, wherein the drive condition variable means varies the ink ejection interval time according to the number of ink ejections per dot of the recording head. Device. 4) The inkjet recording apparatus according to claim 1, wherein the driving condition variable means varies the driving voltage of the recording head in accordance with the number of times of ejection per dot of the recording head. 5) The recording head is characterized in that the ink is foamed by the heat generated by an electric-thermal energy converter provided near the ink ejection opening, and the ink is ejected by a pressure change caused by the foaming. 5. The inkjet recording device according to 1, 2, 3 or 4.