JPH10193610A - Ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve good gradation printing and the stabilization of an emitting ink amt. or the enhancement of printing life by making it possible not only to perform gradation printing of several stages in a head nozzle number unit at every printing timing but also to change the drive pulse width of an arbitrary head nozzle at every one printing timing. SOLUTION: In an on-demand type ink jet head 107 equipped with a plurality of nozzles for emitting ink dropelst and a head drive means 106 for applying pressure to the ink in the nozzles corresponding to the nozzles, a pulse width variable means 105 for making head drive pulse width variable corresponding to printing data is provided. Further, a pulse generation means 109 for generating a plurality of pulse widths and a pulse width selecting means 108 for selecting the head drive pulse width are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an ink jet recording apparatus.

[0002]

2. Description of the Related Art An ink jet recording apparatus has many advantages, such as extremely low noise during recording, high-speed printing, and use of any recording paper. Among them, the so-called ink-on-demand method, which discharges ink only when printing is necessary, is currently the mainstream because it does not require collection of ink unnecessary for printing.

The ink-on-demand type ink-jet head (on-demand type ink-jet head) has a driving means of a piezoelectric element as disclosed in Japanese Patent Publication No. 2-51734, and Japanese Patent Publication No. 5
As disclosed in Japanese Patent Publication No. 9911, a method of discharging ink by pressure by heating ink to generate bubbles, as disclosed in Japanese Patent Publication No. 7-125196,
2. Description of the Related Art There is an ink jet recording apparatus in which a diaphragm in an ink nozzle is sucked by an electrostatic force and a pressure is applied to ink by a restoring force of the diaphragm by releasing static electricity to discharge the ink.

In order to print a high-quality image in an ink-jet printing apparatus, it is necessary to give print pixels gradation. For this purpose, the amount of ink ejected per pixel must be varied. As a method of changing the amount of ink ejected, for example, Japanese Patent Application Laid-Open No. 6-28615
As shown in JP-A-6-23981, a method of controlling the amount of ejected ink by varying the head drive voltage by a voltage varying means is disclosed in Japanese Patent Application Laid-Open No. 6-23981. There is a method in which the pulse width is varied according to the driving range of the ink jet system.
As shown in the 55110 bulletin, 1 pixel per pixel
There is a method in which the number of times of ejection of ink droplets is varied by applying a plurality of pulses from the above to perform gradation expression. There are other methods that use positional changes.

[0005]

However, in the above-mentioned prior art, it is difficult to perform high-speed gradation variable control with the method using positional change, and the method of varying the head drive voltage is generally used. Therefore, the amount of change in the ink ejection amount cannot be made large, and the linearity with respect to the change in voltage is not good. Further, since a relatively high voltage such as a head drive voltage is changed, there is a problem that a circuit becomes large.

As a method of controlling the ink discharge amount, a method of varying the head input pulse form is considered to be a relatively easy and effective method. However, in the prior art, for example, JP-A-6-23981
The variable pulse width method shown in the bulletin has a problem that it is difficult to change the pulse width instantaneously because of the method using a variable resistor. Therefore, there is a problem that the printing speed is limited.

On the other hand, if the vibration plate in the ink nozzle is sucked by electrostatic force and pressure is applied to the ink to discharge the ink, the amount of the discharged ink is different from other ink-on-demand methods. There has been a problem that arbitrarily variable control has not been established.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to enable excellent gradation printing by instantaneously changing the discharge ink amount. Further, it is possible to stabilize the discharge ink amount and improve the ink life.

[0009]

According to the present invention, there is provided an ink jet recording apparatus comprising: a plurality of nozzles for ejecting ink droplets; and a head driving means for applying pressure to ink in the nozzles corresponding to the nozzles. The demand type ink jet head has a pulse width varying means for varying a head driving pulse width according to print data of the head driving means. According to the present invention, the head drive pulse width can be varied by the pulse width varying means in units of the number of head nozzles for each print timing, and the amount of ejected ink can be changed instantaneously. Can be solved.

In this case, the apparatus further comprises a pulse generating means for generating a plurality of pulse widths, and a pulse width selecting means for selecting the head drive pulse width, and the head drive for an arbitrary head nozzle for each print timing. The pulse width can also be varied, and in this case, good gradation expression can be performed by one head scan.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of an inkjet head drive according to one embodiment of the present invention will be described. FIG.
FIG. 1 is a partially enlarged detailed view of a diaphragm 1 and an individual electrode 3 according to an embodiment of the present invention, schematically showing a state of electric charge, and shows an operation principle of the diaphragm 1. The diaphragm 1 is made of P-type silicon, and the diaphragm 1 side, that is, the common electrode 2 has a positive polarity and the individual electrode 3 has a negative polarity, and a pulse voltage is applied to the common electrode 2 and the individual electrode 3 by the drive circuit 101. . The holes in the P-type silicon are repelled to the insulating layer side 5 by the positive electric field of the common electrode 2. The negative charge generated by the movement of the holes receives the supply of the charge from the substrate electrode 2 and the whole diaphragm 1 is positively charged. On the other hand, the individual electrode 3 is negatively charged, and the positively charged diaphragm 1 bends toward the individual electrode 3 due to electrostatic force.

FIG. 2 is a cross-sectional side view showing an ink jet head at the time of electrostatic charge according to one embodiment of the present invention, and FIG. 3 is a cross-sectional side view showing the ink jet head at the time of electrostatic discharge according to one embodiment of the present invention. FIG. 4 shows a circuit configuration of a drive circuit 101 according to an embodiment of the present invention. In the standby state, the driving circuit 10
The input to 1 is OFF. Therefore, the transistor of the drive circuit 101 is in the OFF state, and the potential of the head individual electrode 3 is the same as the potential of the common electrode 2, so that no electrostatic force acts between the individual electrode 3 and the diaphragm 1. The head is driven by inputting a pulse as a print command to the drive circuit 101. When the rising of this pulse enters the drive circuit 101, the transistor of the drive circuit 101 is turned on, the potential of the head individual electrode 3 shifts from the head voltage to the ground level, and a potential difference occurs between the individual electrode 3 and the common electrode 2, As a result, static electricity is charged between the individual electrode 3 and the diaphragm 1. When the static electricity is charged, the diaphragm 1 is bent toward the individual electrode 3 by the electrostatic force as described above (FIG. 2). When the pulse falls, the transistor of the drive circuit 101 is turned off, the potential of the individual electrode 3 returns to the head potential from the ground level again, the static electricity between the individual electrode 3 and the diaphragm 1 is discharged, and the diaphragm 1 It is restored by the rigidity of. As a result, the pressure in the ejection chamber 16 rises rapidly, and the ink droplets 103 are ejected from the nozzle holes 14 to the recording paper 104.
(FIG. 3). Next, the diaphragm 1 bends downward again, so that the ink 102 is supplied from the ink cavity 18 into the ejection chamber 16 through the orifice 17.

FIG. 5 is a graph showing the relationship between the drive pulse width and the print dot size in one embodiment of the present invention.
The print dot size varies depending on the head voltage, head drive frequency, temperature, paper quality of the recording paper, etc., but the conditions of the present embodiment are as follows: the head voltage is 38 V, the print frequency is 3 kHz, the temperature is room temperature, and the recording paper is a postcard equivalent paper. And The inkjet head of the present embodiment in the present invention has an application time of 32 hours.
It is designed so that a stable ink ejection amount can be obtained at the designed center value of μS. As can be seen from FIG. 5, the width of the print dot hardly changes even when the head drive pulse width changes, but the height of the print dot increases with an increase in the application time of the head drive pulse. It reaches its maximum and hardly changes thereafter. In the present embodiment, the gradation expression is performed in a range of the print dot size, that is, a head drive pulse width of 10 to 30 μs.

FIG. 6 shows a dot shape according to an embodiment of the present invention. The figure shows that the head drive pulse width is (1) 1
5 μs, (2) 20 μs, (3) 25 μs, (4) 30
The print dot shape when μs is used. As shown in the figure, in the present embodiment, it can be seen that the area of the print dot gradually increases in the downward direction as the head drive pulse width increases. In the present invention, gradation expression is performed by the variable control of the dot area.

FIG. 7 is a block diagram of a head control circuit showing one embodiment of the present invention. Printing is performed by developing and storing print data in a buffer of one row in the CPU 105 and outputting a head drive pulse for 12 nozzles for each drive frequency based on this data. When the print timing comes, the CPU 105 having a built-in timer outputs a head drive pulse from the I / O port. The head drive pulse is input to the head drive circuit 106. The head drive circuit 106 incorporates twelve drive circuits 101 of FIG. 4 and a potential inversion circuit (not shown) for inverting the head potential at regular intervals in order to operate the diaphragm 1 satisfactorily. And a safety circuit (not shown) for preventing abnormal energization. The head drive circuit 106
The head 107 is operated by an input pulse from the PU 105. The head 107 is a head having 12 nozzles, has a common electrode 2 and 12 individual electrodes 3, and has an FPC
Is connected to the head drive circuit 106.

FIG. 8 shows a CPU according to an embodiment of the present invention.
5 is a head drive control flowchart showing the head drive pulse width variable control performed in 105. First, a 2-bit gradation flag corresponding to the print data is prepared, and this value is set to 0.
In each case of 0, 01, 10, and 11, the energization width is 15
μs, 20 μs, 25 μs, and 30 μs. Note that the number of gradation divisions is not limited to four,
It is also possible to divide it further finely. In that case, the number of bits of the gradation flag increases according to the number of divisions. When the print timing comes, the process enters this flowchart. First, in S1, the time of the timer according to the gradation flag is set. Next, in S2, the head drive signal is turned ON and the timer is started. Next, in S3, it waits until the time set in S1 comes, and in S4, the head drive signal is turned off.
Set to F and stop the timer. With this series of operations, a head drive signal having a set pulse width is input to the drive circuit 106 side. By this control, the pulse width can be varied for each head nozzle for each print timing.

In order to perform gradation printing for every dot of all 12 nozzles under the control of one embodiment of the present invention, one line of data is divided into a maximum of four print data for each gradation and four carriages are performed. There is a method of performing 4-pass printing by scanning. However, this method has a drawback that the scanning must be performed at the maximum for the number of gradation divisions, and the printing speed is reduced accordingly.

FIG. 9 is a block diagram of a head control circuit according to another embodiment of the present invention which compensates for this disadvantage. CPU105
Has a built-in pulse generating means 109, and the pulse generating means 109 can simultaneously output pulse waveforms corresponding to four types of set times from the I / O port. CP
U105 is based on the presence or absence of print data and the gradation flag.
Outputs 3-bit data per nozzle to the / O port. One bit is used as a signal indicating the presence or absence of printing, and the other two bits are used as a gradation signal. When the data output for all nozzles is completed, the CPU 105 triggers the timer. The timer starts operating by a trigger, and pulses of four types of timer setting time widths are output from the I / O port. These signals are input from the CPU 105 to the selector 108. FIG. 10 is a diagram showing the logic of one nozzle inside the selector 108. This circuit has seven input ports and one output port. Input side C0, C
1, C2, and C3 are sent from the CPU 105 to 15,
Pulse signals having four pulse widths of 20, 25, and 30 μs are input. A and B are input with a gradation signal, and G is input with a signal indicating whether or not printing is performed. When the signal G is 1, the output Y becomes 0 and the head is not driven. When the signal G is 0, a pulse corresponding to the gradation signals A and B is selected from the output Y from C0, C1, C2, and C3. The selector 108 shown in FIG.
The drive pulse width of all the nozzles can be selected.
The drive pulse for each nozzle selected by the selector 108 is input to the drive circuit 106. The head drive circuit 106 operates the head 107 by an input pulse from the selector 108.

In this embodiment of the present invention, the control of the ejection ink amount is performed for the purpose of performing gradation printing, but the present control may be performed for other purposes. For example, there is a case where the discharge ink amount is always kept constant and stable printing is intended. The ejected ink amount changes depending on the surrounding environment such as a head voltage, a head driving frequency, and a temperature. This change can be recognized using a detector, and the head drive pulse width can be varied by the apparatus of the present invention in accordance with the information to maintain a stable amount of ejected ink.

In other cases, the purpose is to improve the life of the ink, for example, by controlling the amount of ejected ink. The required printing density varies depending on the printing situation on the user side. For example, if it is used for a post card or the like, dark printing is required. However, if it is used for a memo, it may be dark enough to recognize characters. When the print density is changed in accordance with the use condition as described above, as a result, the used ink can be saved and the ink life can be improved. The switching of the printing mode can be performed by the apparatus of the present invention.

[0021]

As described above, according to the present invention, it is possible to perform gradation printing in several stages in units of head nozzles at each printing timing. Further, the drive pulse width of an arbitrary head nozzle can be changed for each print timing. Therefore, good gradation printing, stabilization of the amount of ejected ink, and improvement of the printing life can be achieved.

[Brief description of the drawings]

FIG. 1 is a partial detailed schematic view of a diaphragm and electrodes according to an embodiment of the present invention.

FIG. 2 is a cross-sectional side view showing the inkjet head when charging with static electricity according to the embodiment of the present invention.

FIG. 3 is a cross-sectional side view showing the inkjet head at the time of discharging static electricity in one embodiment of the present invention.

FIG. 4 is a drive circuit configuration showing one embodiment of the present invention.

FIG. 5 is a graph showing a relationship between a drive pulse width and a print dot size in one embodiment of the present invention.

FIG. 6 is a diagram showing a dot shape according to an embodiment of the present invention.

FIG. 7 is a block diagram of a head drive control circuit showing one embodiment of the present invention.

FIG. 8 is a flowchart illustrating head drive control according to an embodiment of the present invention.

FIG. 9 is a block diagram of a head drive control circuit showing another embodiment of the present invention.

FIG. 10 is a selector circuit logic diagram showing another embodiment of the present invention.

[Explanation of symbols]

 105 CPU 106 drive circuit 107 head 108 selector 109 pulse generating means

Claims (2)

[Claims] 1. An on-demand type ink jet head comprising a plurality of nozzles for ejecting ink droplets and a head driving means for applying pressure to the ink in the nozzles corresponding to the nozzles, wherein printing by the head driving means is performed. Pulse width varying means for varying the head drive pulse width in accordance with the data;
An ink jet recording apparatus wherein the head drive pulse width is varied in units of the number of head nozzles for each print timing. 2. An ink jet recording apparatus according to claim 1, further comprising: a pulse generating means for generating a plurality of pulse widths; and a pulse width selecting means for selecting said head drive pulse width. An ink jet recording apparatus, wherein the head drive pulse width for the head nozzle is varied.