JP2003094638A - Ink jet head driver, driving method for ink jet head, and ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a gradation representation by using an inexpensive driving signal source with a simple output waveform, and to realize high speed printing and cost reduction. SOLUTION: An individual electrode 34 of an ink jet head 18 is connected to a driving signal source via switching elements SW1, SW2, two or more of which having a desired current-carrying characteristics are parallel connected and selectively on/off controlled. Therefore, by selecting a plurality of switching elements SW1, SW2 which enable conduction states, a driving signal of a different wave form is generated by one kind of driving signal outputted from a single driving signal source and the ink jet head 18 can be driven, and the gradation representation is realized by using a driving signal source having a simple waveform, and high speed printing and cost down can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head drive circuit, an ink jet head drive method, and an ink jet printer in which ink droplets are ejected by supplying electric energy to an electrically capacitive actuator.

[0002]

2. Description of the Related Art On-demand type ink jet printers are characterized by a simple structure of an apparatus and easy colorization. The ink droplet ejection method of an on-demand type inkjet printer is a bubble jet (registered trademark) method that uses thermal energy due to film boiling, a piezo method that uses the distortion effect of a piezoelectric element, and power is applied between opposing electrodes. An electrostatic method using electrostatic attraction is typical. Among them, the piezo method and the electrostatic method control the ink energy on the nozzle surface by controlling the drive energy supplied to the actuator part, and it is possible to eject ink droplets of different volumes from the same nozzle, resulting in high image quality. Can be said to be excellent.

By the way, recent market demands for ink jet printers are to increase the printout speed and to improve the quality of output images. The main items for increasing the printout speed are increasing the number of nozzles and increasing the driving frequency of the inkjet head. The main items for achieving high image quality are to increase the density of print-recorded images and to increase the gradation by highly precise modulation of the volume of ejected ink droplets. In order to achieve high speed and high image quality at the same time, it is necessary to increase the number of nozzles of the inkjet head and improve the driving characteristics. The increase in the number of nozzles affects productivity and physical cost, and may be increased as much as possible depending on the balance between cost and performance. Increasing the frequency, that is, gradation at a high driving frequency, is an important factor that has a high technical aspect of head driving characteristics and can achieve the highest speed and high image quality most efficiently without increasing the cost.

By the way, in order to improve the image quality by modulating the volume of the ink droplet, it is necessary to accurately control the ink meniscus on the nozzle surface at the time of ejection, so the waveform applied to the head actuator is not a simple pulse waveform but a complicated waveform. It will be Further, since the drive waveform to the actuator is different for each ink droplet having a different volume, that is, for each gradation, it is natural that the drive waveforms for the number of gradations to be expressed are required. There are the following two techniques as a driving method that allows only one of a plurality of types of driving waveforms to be selectively applied to the actuator.

One is a time division method. First, a plurality of drive pulses having different waveforms are output within the dot recording cycle. These drive pulses are composed of two waveform elements whose pulse tops are divided in the pulse width direction.
A plurality of drive pulses composed of one waveform element are divided into a plurality of time slots, and drive pulses for each gradation or waveform elements of those drive pulses are assigned to each time slot. That is, if the signal of the drive signal source is connected to the actuator via the switching element and the drive pulse of the gradation to be expressed in the dot recording period is assigned to one time slot, When the switching elements are in the ON state and the others are in the OFF state, and the drive pulses of the gradation to be expressed are scattered as waveform elements in multiple time slots, the switching elements are turned on only during the required time slot period. , A driving method in which the others are turned off and input to the actuator (Japanese Patent Laid-Open No. 10-81014).
(See the official gazette).

The other is a method using a plurality of drive signal sources and a plurality of switching elements. That is, a drive signal of a required number of gradations is simultaneously generated by using a plurality of drive signal sources, and each output signal is connected to an actuator through a switching element that is independently provided. This is a method in which a switching element to which a tonal drive signal is input is turned on and the other switching elements are turned off (see Japanese Patent Application Laid-Open No. 10-217459).

[0007]

[Patent Document 1] Japanese Unexamined Patent Application Publication No.
In the driving method disclosed in Japanese Unexamined Patent Publication No. 0-81014, since a plurality of driving pulses or waveform elements are incorporated in one signal line in the recording cycle, the time for generating one dot is substantially lengthened and the printout speed is slow. It's just becoming. The method disclosed in Japanese Patent Publication No. 10-217459 does not have the problem as in Japanese Patent Publication No. 10-814014, but a plurality of drive signal sources, signal lines, and a large number of output switchings according to the number of gradations. There is a problem that the cost increase cannot be avoided because the element is required. Further, the above two techniques have a common problem that a complicated waveform must be output from the drive signal source.

An object of the present invention is to speed up printing.

It is an object of the present invention to generate a drive signal having a different waveform from one type of drive signal output from a single drive signal source so that an ink jet head can be driven.

An object of the present invention is to realize gradation expression by using one drive signal source whose output waveform is simple and inexpensive.

[0011]

According to another aspect of the present invention, there is provided an ink jet head driving device in which ink droplets are ejected from nozzles by supplying electric energy to electrodes arranged to face each other. The electrode is connected to a reference potential portion to which a reference potential is applied, and the other electrode is connected to one end of two or more switching elements that are connected in parallel and have a desired energization characteristic and are selectively on / off controlled, The other ends of the plurality of switching elements connected in parallel are connected to a drive signal source.

Therefore, by selecting a plurality of switching elements to be made conductive, a drive signal having a different waveform is generated from one type of drive signal output from a single drive signal source to drive the ink jet head. Is possible. As a result, gradation expression can be realized by using one drive signal source that has a simple output waveform and is inexpensive.

According to a second aspect of the invention, in the ink jet head driving device according to the first aspect, the plurality of switching elements have different energization characteristics.

Therefore, by selecting the combination of the switching elements that are turned on, it becomes possible to generate more drive signals having different waveforms from one type of drive signal output from the drive signal source. Thereby, the number of gradations can be increased.

According to a third aspect of the present invention, in the ink jet head driving apparatus according to the first or second aspect, the energization characteristic of at least one of the plurality of switching elements is independently switched to an ON state. The drive signal output from the drive signal source is limited to such an extent that ink is not ejected from the nozzle.

Therefore, it is possible to stabilize the ink meniscus in the nozzle by controlling the ON state of the switching element having the energization characteristic that cannot reach the state where ink is ejected from the nozzle, and this meniscus is in a stable state. By controlling the other switching elements in the ON state, the ink droplets can be stably ejected.

According to a fourth aspect of the present invention, in the ink jet head drive device according to the first, second or third aspect, the switching element is a MOS analog switch.

Therefore, it is possible to stabilize the operation of the switching element, and it is possible to perform more accurate gradation expression.

The invention according to claim 5 is the invention as defined in claims 1, 2, and 3.
Or in the inkjet head driving device described in 4,
The switching elements are integrated in one semiconductor.

Therefore, it is possible to improve the uniformity of the performance of the switching elements provided for each channel corresponding to the number of nozzles and improve the printing quality.

According to a sixth aspect of the present invention, there is provided a method of driving an ink jet head in which ink droplets are ejected from nozzles by supplying electric energy to electrodes arranged to face each other. Is connected to a reference potential portion, the other electrode is connected to one end of two or more parallel-connected switching elements having desired energization characteristics, and the other ends of the plurality of parallel-connected switching elements are connected. When connected to a drive signal source and ejecting ink droplets from the nozzle, the conduction state of the switching element is changed when the output level from the drive signal source is a steady value.

Therefore, by selecting a plurality of switching elements to be turned on, driving signals of different waveforms are generated from one type of driving signal output from a single driving signal source to drive the ink jet head. Is possible. As a result, gradation expression can be realized by using one drive signal source that has a simple output waveform and is inexpensive.
Further, since it is possible to process the waveform applied to the inkjet head while avoiding the influence of the delay time when the state of the switching element changes, it is possible to reliably apply the desired waveform to the head.

According to a seventh aspect of the present invention, in the method of driving an ink jet head according to the sixth aspect, the drive signal source supplies a pulse voltage having the same rise and fall times.

Therefore, it is possible to easily generate a complicated drive signal waveform required for applying to the ink jet head by using a simple pulse signal and a plurality of switching elements without using an AD converter or the like. Become.

An ink jet printer according to an eighth aspect comprises a printing mechanism having an ink jet head, and the ink jet head driving device according to the first, second, third, fourth or fifth aspect.

Therefore, by selecting a plurality of switching elements to be turned on, a drive signal having a different waveform is generated from one type of drive signal output from a single drive signal source to drive the ink jet head. Is possible. As a result, it is possible to provide an inkjet printer that can realize gradation expression by using one drive signal source that has a simple output waveform and is inexpensive.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention.
Or, it demonstrates based on FIG. 1 is a perspective view showing a schematic structure of an inkjet printer, FIG. 2 is a vertical sectional side view showing the schematic structure of an inkjet printer, FIG. 3 is a vertical sectional side view showing a part of an inkjet head, and FIG. 4 is an electrical system of the inkjet printer. FIG. 5 is a block diagram showing the structure, FIG. 5 is a circuit diagram of an inkjet head and a head driver, FIG. 6 is an explanatory view showing a drive signal waveform for driving an actuator of the inkjet head, and FIG. 7 is a rise time and gradation level of the drive signal waveform. And FIG. 8 is a time chart of each signal, and FIG. 9 is an explanatory diagram showing changes in drive signal waveforms.

First, the ink jet head will be described with reference to FIGS. The casing 2 of the inkjet printer 1 includes a paper feed port 4 in which a paper feed cassette 3 for stacking and holding the paper S is mounted, an openable / closable manual feed tray 5 for feeding a manual paper, and a printed paper S. A discharge tray 6 for discharging is provided. On the upper side of the casing 2, there is provided an upper cover 8 which can be opened upward with the support shaft 7 as a rotation center to open the inside thereof.
Although not shown, the casing 2 is provided with a power switch and various operation keys. In the casing 2, a paper feed path 10 from the paper feed cassette 3 or the manual feed tray 5 to the paper discharge tray 6 via the print mechanism 9 and a paper feed mechanism 11.
And are provided. The paper feed mechanism 11 is composed of a paper feed roller 12 and a friction pad 13, and separates the sheets S stacked and held in the paper feed cassette 3 by the paper feed roller 12 and the friction pad 13 one by one. And has a function of feeding paper to the paper transport path 10. At the end of the paper feed path 10 on the manual feed tray 5 side, the papers that are stacked and held in the manual feed tray 5 are conveyed one by one.
A paper feed roller 14 for feeding the paper is provided. In the paper conveyance path 10, the paper S in the paper feed cassette 3 is printed by the printing mechanism 9
A conveyance roller 15 and a plurality of pairs of conveyance rollers 16 that are turned toward each other are provided. These transport rollers 15, 1
6 is rotatably driven by the feed motor 26 (see FIG. 4) and conveys the paper S in the paper conveyance path 10.

The printing mechanism 9 is a carriage 17 which is capable of reciprocating in the main scanning direction (the direction perpendicular to the paper surface in FIG. 2), and the ink jet head 1 mounted on this carriage 17.
8. An ink cartridge 19 for holding ink to be supplied to the inkjet head 18 and the like. The carriage 17 is slidably supported in the main scanning direction by a main guide rod 20 provided in the casing 2 and extending in the main scanning direction, and a sub guide rod 21 parallel to the main guide rod 20. As shown in FIG. 1, a timing belt 24, which is wound around a drive pulley 22 and a driven pulley 23 and rotates along the axial direction of the main guide rod 20, is provided in the casing 2. The drive pulley 22 is rotationally driven by the main scanning motor 25. On a part of the timing belt 24,
A carriage 17 is attached. As a result, the carriage 17 can be moved in the main scanning direction by driving the main scanning motor 25 and rotating the timing belt 24. Printing is performed on the paper S by driving the inkjet head 18 in this process.

The ink jet head 18 has yellow (Y), cyan (C), magenta (M), and
A plurality of black (Bk) ink droplets are provided to eject the ink droplets. Inkjet head 18 for each color
Ink cartridge 1 for supplying ink of each color to
Reference numeral 9 is replaceably mounted on the carriage 17.

Further, at the end of the secondary guide rod 21,
A reliability maintaining device A is provided for restoring the reliability of the inkjet head 18 when the carriage 17 is on standby at the home position. Since this reliability maintaining device A is a known technique, illustration and detailed description of each part will be omitted. However, a capping mechanism that covers the nozzles of the inkjet head 18 with a cap, and ink from the nozzles of the capped inkjet head 18 It is composed of a suction mechanism for sucking and a cleaning mechanism for cleaning the nozzle and the periphery of the nozzle. The capping mechanism serves to cover the nozzle with a cap while the carriage 17 is at the home position so as to maintain a wet state around the nozzle. The suction mechanism is driven in a state where the nozzle is capped by the capping mechanism and generates a negative pressure in the cap, thereby sucking ink and bubbles in a pressure chamber described later from the nozzle. The suction mechanism has a waste ink reservoir that collects the sucked ink. The waste ink reservoir is provided with an ink absorber (not shown) formed of a porous body in a waste ink case (not shown).

The cleaning mechanism wipes the nozzle and the periphery of the nozzle with, for example, a wiper (not shown),
Prevents clogging of the nozzle by removing ink and dust adhering to the area around the nozzle.

Next, the ink jet head 18 will be described. The inkjet head 18 includes yellow (Y), cyan (C), magenta (M), and black (B).
Although it is provided for each color of k), one inkjet head having nozzles for ejecting ink droplets of each color may be used. Further, in the case of a printer intended for monaural printing, one ink jet that ejects ink droplets of one color may be used. Furthermore, the present invention provides a piezoelectric type that presses ink through a vibration plate that forms a wall surface of a liquid chamber with an electromechanical conversion element such as a piezoelectric element, or a vibration plate that forms a wall surface of an ink flow path and an electrode facing the vibration plate. Although it can be applied to an electrostatic type or the like in which the diaphragm is displaced by the electrostatic force between them to press the ink, the piezo type inkjet head 18 is used in the present embodiment.

As shown in FIG. 3, the ink jet head 18 includes a drive unit 27, a frame 28 and a diaphragm 29.
It is a laminated structure of the photosensitive film resin 30 and the nozzle plate 31.

The drive unit 27 has a substrate 32 made of an insulating material such as ceramic or glass epoxy resin, and a large number of piezoelectric elements 33. Piezoelectric element 3
3 is a plurality of individual electrodes 3 as electrodes in this example.
4 and a plurality of common electrodes 35 are alternately stacked in a layered form. A large number of piezoelectric elements 33 are arranged in the direction perpendicular to the paper surface of FIG. 3 with a number corresponding to the number of nozzles. When the nozzles are arranged in a plurality of rows, the piezoelectric elements 33 may be arranged in a plurality of rows in the horizontal direction in FIG. In this example, the piezoelectric elements 33 are arranged in a plurality of rows. The individual electrode 34 of the piezoelectric element 33 is connected to the individual electrode pattern 36, and the common electrode 35 is the conductive film 36a.
Via a common electrode pattern (not shown). The individual electrode pattern 36 and the common electrode pattern are formed by printing a pattern of Ni, Al or the like on the device mounting surface of the substrate 32.

The drive unit 27 forms a conductive film of Ni, Al or the like on the entire surface of the device mounting surface of the substrate 32 by printing, and insulates the substrate 32 from a long piezoelectric member that is the basis of many piezoelectric elements 33. In this state, the piezoelectric members are joined together, and the piezoelectric member is divided by a large number of grooves to form the piezoelectric elements 33 arranged in the direction perpendicular to the paper surface of FIG. At this time, the Ni / Al film on the substrate 32 is cut by a groove cut using a dicer or a wire saw or the like to divide the piezoelectric member, whereby a large number of individual electrode patterns 36 formed by the Ni / Al conductive film. And the common electrode pattern are formed in a non-conductive state. For this reason, the individual electrode patterns 36 are arranged in parallel in the direction perpendicular to the paper surface of FIG. 3, but are connected to a flexible cable (not shown) so that every other voltage is applied. That is, in the piezoelectric element 33 according to the present embodiment, the piezoelectric element 33 driven by voltage application and the non-driven piezoelectric element 33 to which no voltage is applied are arranged alternately in the direction perpendicular to the paper surface of FIG. Is configured. Non-driving piezoelectric element 33
Function as a pillar member that supports the diaphragm 29.

The piezoelectric element 33 has a layer thickness of 20 to 50 μm.
m PZT (= Pb (Zr.Ti) O3),
The individual electrode 34 and the common electrode 35 are formed of silver palladium (AgPd) having a thickness of several μm. As described above, by using the laminated piezoelectric element 33 having the thickness of one layer of 20 to 50 μm, the voltage of the drive signal can be lowered. For example, with a pulse voltage of 20 to 50 V, the piezoelectric element 33
The electric field strength of 1000 V / mm can be obtained.

The diaphragm 29 has a diaphragm portion 29a which is a displacement portion joined to a piezoelectric element 33 which constitutes a driving portion to which a voltage is applied, and a piezoelectric element 33 which constitutes a columnar member of a non-driving portion to which a voltage is not applied. Beams to be bonded to (not shown)
Also, it has a base 29b joined to the frame 28 and a thin film portion 29c formed around each diaphragm portion 29a, and is formed of a thin film of metal or resin. The diaphragm portion 29a is projected in an island shape by the thin film portion 29c.

The photosensitive film resin 30 is formed of a photoresist film, and the nozzle plate 31 has a large number of nozzles 37 and is formed of metal or resin. The vibration plate 29, the photosensitive film resin 30, and the nozzle plate 31 are sequentially laminated and heat-sealed to form a liquid chamber unit 39 having a large number of pressurized liquid chambers 38 communicating with the nozzles 37. . The photosensitive film resin 30 functions as a partition member of each pressurized liquid chamber 38. A space other than the pressurizing liquid chamber 38 inside the photosensitive film resin 30 is a common ink chamber 40. The common ink chamber 40 and the pressurizing liquid chamber 38 have an ink supply path having a relatively large fluid resistance (not shown). Communication).

As the nozzle plate 31, for example, a Ni (nickel) metal plate manufactured by the electron forming method (electroforming) is used, but Si or another metal material can also be used. Nozzle plate 3
The quality of No. 1 determines the droplet shape and the flight characteristics of the ink and has a great influence on the image quality. Since the surface homogenization processing is indispensable for obtaining higher quality image quality, the ink ejection is performed. A water repellent layer is formed on the side surface. The drive unit 27 and the liquid chamber unit 39 are assembled separately and then bonded by an adhesive.

Next, the structure of the electrical system of the ink jet printer will be described with reference to FIG. The command or image data transmitted from the external host is the I / F circuit 4
1 is received. Information from the printer side can be transmitted from the I / F circuit 41 to the outside. I / F
The data from the circuit 41 is the CPU 42 and the controller 43.
It is possible to send and receive. The CPU 42 executes the program written in the ROM 44 and executes the processing of the transmitted command and the arithmetic processing of the image data. This CP
During the operation of U42, work data is rewritably written in the RAM 45. The controller 43 controls the operation sequence of the entire printer. Main scanning motor 2 described above
5. The operation of the feed motor 26 is also controlled by the controller 43. Further, the controller 43 also prompts the head drive signal generation circuit 46 as a drive signal generation unit to generate a drive signal for each recording cycle, and further, the inkjet head 18 provided for each color at the same timing (only as a head in FIG. 4). Enter (Y), (M), (C),
The print data for each (color distinction by (K)) is transmitted to the head driver 47. These head drivers 47 are mounted on the carriage 17 (see FIG. 1) together with the inkjet head 18. The use environment information on the printer side such as the temperature is fed back to the controller 43 by the detection signal of the sensor 48 provided for each item of the information. In FIG. 4, the CPU 42 and the controller circuit 4
3, head drive signal generation circuit 46, head driver 47
Thus, a drive device D for driving the inkjet head 18 is formed.

Next, since the individual electrode 34 and the common electrode 35, which are arranged to face each other for each channel, form a capacitive capacitor C as shown in FIG. 5, the ink jet head 18 in this embodiment has the above-mentioned structure. This is a configuration having an electrically capacitive actuator 49 formed by the capacitor C and the piezoelectric element 33. The common electrode 35 for each channel is connected to the ground GND as a reference potential portion to which a low-impedance reference potential is applied, and the individual electrode 34 is connected to the head driver 47. As shown in FIG. 5, the head driver 47 shown in FIG. 4 shifts the print data sent from the controller to each channel, a latch circuit 51 for latching the print data, a decoder 52, and a latch. A level shifter 53 for boosting the output of the circuit 51, and an analog switch circuit 54
It is composed of and.

There are four drive signals applied to the individual electrodes 34 of the ink jet head 18 in the present embodiment: a state in which ink droplets of three sizes are selectively ejected and a state in which ink droplets are not ejected. In order to obtain the above state, the latch circuit 51 is composed of two-bit latches L1 and L2 for each channel. The analog switch circuit 54 has a configuration in which two switching elements SW1 and SW2 are connected in parallel for each channel, and the switching elements SW1 and S connected in parallel for each channel.
W2 is connected between the individual electrode 34 of the inkjet head 18 and the level shifter 53. The switching elements SW1 and SW2 are composed of so-called CMOS analog switches composed of PMOS and NMOS, respectively, and are integrally integrated on a semiconductor substrate as an IC together with a shift register 50, a latch circuit 51, a decoder 52, and a level shifter 53.

Inkjet head 1 in this embodiment
Reference numeral 8 indicates a period T, which makes it possible to eject ink droplets by applying a pulse-shaped drive signal having a different rise time and fall time. The ink is ejected from the nozzle 37 at the rise of the pulse of the drive signal. The inkjet head 18 performs so-called push-out to stabilize the ink surface at the nozzles 37 by performing the following waveform. FIG. 6 shows the waveform of the drive signal applied to the inkjet head 18. By rapidly applying a voltage to the inkjet head 18 up to VP at the rising time Tr, an ink droplet is ejected from the nozzle 37.
After the voltage reaches VP, the voltage is set to VP for a certain time (Tp).
By suppressing the decrease of the displacement due to the response time delay of the piezoelectric element 33 and gradually lowering the voltage over the time of Tf and returning to the common potential of the ground GND, the liquid level at the nozzle 37 is stabilized. To convert.

Here, Tr is a voltage from 0.1 VP to 0.
Time to rise to 9 VP and Tf are defined as time to fall voltage from 0.9 VP to 0.1 VP.
FIG. 7 shows the ejection volume of ink droplets when the rise time Tr in FIG. 6 is used as a parameter. Here, the ink jet head 18 shown in the present embodiment has ink discharge volumes Mja and Mj that have three gradation levels 1, 2, and 3.
b and Mjc can be discharged from the same nozzle 37, and the characteristics shown in FIG. 6 are used. As specific values, for example, VP = 25V, Tp = 20 μsec, Tra =
2.0 μsec, Trb = 1 μsec, Trc = 0.66 μse
c, Tf = 15 μsec, Mja = 14 pl, Mjb
= 18 pl and Mjc = 25 pl. The capacitance value of the capacitor C for each channel is about 2.5 nF.

In this embodiment, the switching element SW
1 and SW2 have different energization characteristics when energized. Specifically, the resistance of the switching element SW1 is set to 90Ω, and the resistance of the switching element SW2 is set to 180Ω. These resistance values are the PMO of the switching elements SW1 and SW2.
It can be set by selecting the gate length W of S and NMOS.

Here, the output of the strobe signal STB, the outputs of the latches L1 and L2, and the switching elements SW1 and SW
Table 1 shows the relationship between the volume of ejected ink droplets and the combination of two on / off states.

[0048]

[Table 1]

Next, the printing operation of the ink jet printer 1 based on the above configuration will be described. When a print request command is sent from the external host, the CPU 42 analyzes the subsequently sent command such as the print mode and sets the inkjet printer 1 in the printable state. When the image data is transmitted, the CPU 42 performs appropriate image processing, converts the image data into predetermined recording data, and stores the data in the RAM 45. At the same time, the feed motor 26 conveys the paper S to the inkjet head 18. When data for one reciprocating scan of the carriage 17 is stored in the RAM 45, the controller 43
Drives the main scanning motor 25 and shifts to the printing operation. During the printing operation, the controller 43 prompts the head drive signal generation circuit 46 to generate a signal for each recording cycle, and further transmits the recording data for each inkjet head 18 to each head driver 47 at the same timing. The head drive signal generation circuit 46 has a steep rise time (0.1 μm).
sec or less), and a signal with a gentle fall time (15 μsec) is output.

The voltage application state of each channel according to the signal of the head driver 47 and the outputs of the latches L1 and L2 at the time of recording is shown in FIGS. After the serial data Data1i and Data2i (i = 1 to n) are input to the elements S1 and S2 of the shift register 50 of the head driver 47, the data is latched by the two latches L1 and L2 for each channel by the Latch signal. After the data latch, the STB signal becomes active, and the signals output from the latches L1 and L2 pass through the decoder 52 and the level shifter 5
The voltage is boosted by 3 to a level at which the switching elements SW1 and SW2 can be operated, thereby controlling the opening / closing operation of the switching elements SW1 and SW2. As shown in Table 1, when the outputs of the latches L1 and L2 are 0, the switching elements SW1 and SW2 are both turned off, and no voltage is applied to the inkjet head 18 and the ejection operation does not occur. When the latch L1 output = 1 and the latch L2 output = 0, only the switching element SW1 is turned on and Tra = 2 μ
A voltage is applied to the inkjet head 18 at the rise of sec, and the discharge volume Mja (14 pl) from the nozzle 37.
Ink droplets are ejected. When the latch L1 output = 0 and the latch L2 output = 1, only the switching element SW2 is turned on, the voltage is applied to the inkjet head 18 at the rise of Trb = 1 μsec, and the ink droplet of the ejection volume Mjb (18pl) is ejected from the nozzle 37. Is ejected. Latch L
When 1 output = 1 and latch L2 output = 1, both switching elements SW1 and SW2 are turned on, and Trc = 0.66.
A voltage is applied to the inkjet head 18 at the rise of μsec, and the discharge volume Mjc (25 p
The ink droplet of l) is ejected. The waveform of the drive signal with Tr as a parameter is as shown in FIG. When ink droplets are ejected by the above-described operation, the channel to which each ejection state is assigned holds the voltage of VP for a certain period of time, the drive signal follows the slow falling waveform, the ink meniscus on the nozzle surface becomes stable, and one recording is performed. The operation ends. The above operation is performed for one scan, and the printing operation is completed by repeating the same operation.

Next, a second embodiment of the present invention will be described with reference to FIG.
Or, it demonstrates based on FIG. The same parts as those in the above-mentioned embodiment are designated by the same reference numerals and the description thereof will be omitted. FIG. 10 is a circuit diagram of an inkjet head and a head driver, FIG.
Is a time chart of each signal, and FIG. 12 is an explanatory diagram showing changes in drive signal waveforms.

As shown in FIG. 10, in the present embodiment,
Three switching elements SW1, SW2, SW3 having different resistances when energized are connected in parallel and connected to the individual electrode 34 for each channel. Specifically, the resistance of the switching element SW1 is 93Ω, and the switching element S is
The resistance of W2 is 186Ω and the resistance of the switching element SW3 is 2.7 kΩ. Each switching element SW1, SW
2, the total sum of the transistor sizes occupied by the SW3 in the IC is almost the same as that in the first embodiment.

Here, the output of the strobe signal STB, the outputs of the latches L1 and L2, and the switching elements SW1 and SW
Table 2 shows the relationship between the ejected ink droplet volumes depending on the combination of 2 and SW3.

[0054]

[Table 2]

The operation of the head driver 47 during recording in this embodiment will be described. Serial data Data1i and Data2 are stored in the elements S1 and S2 of the shift register 50.
After i is input, data is latched in the two latches L1 and L2 for each channel by the Latch signal. After data latch, STB signal becomes active and latch L
The signals output from L1 and L2 pass through the decoder 52 and the level shifter 53 controls the switching elements SW1 and S1.
It is boosted to a level at which W2 and SW3 are operable and controls the on / off operation of the switching elements SW1, SW2, and SW3. The head drive signal generation circuit 46 outputs a pulse signal having a steep rise time and a fall time of 0.1 μsec or less after the data latch. Latch L1,
When L2 output = 0, switching elements SW1 and SW
No discharge operation occurs because all of 2 and SW3 are off.
When the latch L1 output = 1 and the latch L2 output = 0, the switching elements SW1 and SW3 are turned on and Tra = 2.
A voltage is applied to the inkjet head 18 at the rise of μsec, and the ink droplets of the ejection volume Mja are ejected from the nozzle 37. Latch L1 output = 0, Latch L2 output =
In the case of 1, the switching SW2 and SW3 are turned on and a voltage is applied to the inkjet head 18 at the rise of Trb = 1 μsec, and the ink droplet of the ejection volume Mjb is ejected from the nozzle 37. Latch L1 output = 1, Latch L
When 2 outputs = 1, switching elements SW1, SW
2, SW3 are all turned on and Trc = 0.66 μsec
A voltage is applied to the inkjet head 18 at the rising edge of and the ink droplets of the ejection volume Mjc are ejected from the nozzle 37. The waveform of the drive signal with Tr as a parameter is shown in FIG.
As shown in.

In the present embodiment shown in FIG. 10, when the latch L1 output = 1 and the latch L2 output = 0, the switching elements SW1 and SW3 are turned on (see Table 2) and the drive signal rise time Tra = 2 μsec
(See FIG. 12) The STB is deactivated after the charging time when the voltage of the channel for ejecting the ink of the ejection volume Mja at the latest is Vp becomes Vp, so that only the switching element SW3 of the ejection channel is turned on. . Here, after STB changes, the switching element SW
Until the time 3 changes, the level of the drive signal is constant and does not change. The drive signal sharply falls after a predetermined time has elapsed, but the current value is limited by the resistance of the switching element SW3 when the switching element SW3 is energized, so that the drive signal applied to the channel after the discharge uniformly and gently follows the falling waveform. The ink meniscus on the nozzle surface becomes stable, and one recording operation is completed. The printing operation is completed by performing the above operation for one scan and repeating the following operation.

[0057]

According to the ink jet head drive device of the first aspect of the present invention, the electrodes of the ink jet head are connected in parallel to each other through two or more switching elements which are connected in parallel and which are selectively turned on and off. Since it is connected to the drive signal source, by selecting a plurality of switching elements to be in the conductive state, a drive signal of a different waveform is generated from one type of drive signal output from a single drive signal source, and the inkjet It is possible to drive the head, thereby realizing gradation expression by using one drive signal source having a simple output waveform, and it is possible to speed up printing and reduce cost.

According to the second aspect of the present invention, in the ink jet head drive device according to the first aspect, since the plurality of switching elements have different energization characteristics, the combination of the switching elements to be brought into the conductive state is selected. Further, it is possible to generate more drive signals having different waveforms from one type of drive signal output from the drive signal source, thereby increasing the number of gradations.

According to a third aspect of the present invention, in the ink jet head driving device according to the first or second aspect, at least one of the plurality of switching elements has a current-carrying characteristic,
When it is independently switched to the ON state, the drive signal output from the drive signal source is limited to such an extent that the nozzle does not eject ink, so ink is ejected from the nozzle. It is possible to stabilize the ink meniscus at the nozzle by controlling the ON state of the switching element that has a current-carrying characteristic that cannot reach the state, and to control other switching elements to the ON state when this meniscus is stable. The ink droplets can be stably ejected with.

According to the invention of claim 4,
In the inkjet head driving device described in 2 or 3, since the switching element is a MOS analog switch, the operation of the switching element can be stabilized, and more accurate gradation expression can be performed.

According to the invention of claim 5, claim 1,
In the inkjet head driving device described in 2, 3, or 4, since the switching elements are integrally integrated in one semiconductor, the uniformity of the performance of the switching elements provided for each channel corresponding to the number of nozzles is improved, and the printing quality is improved. Can be improved.

According to a sixth aspect of the present invention, there is provided a method for driving an ink jet head, in which the electrodes of the ink jet head are driven through two or more switching elements which are connected in parallel and which are selectively on / off controlled. When connecting to the signal source and ejecting ink droplets from the nozzle, the conduction state of the switching element is changed when the output level from the drive signal source is a steady value, so select multiple switching elements to be in the conduction state. By
It is possible to drive the inkjet head by generating drive signals of different waveforms from one type of drive signal output from a single drive signal source, and this allows one drive signal source with a simple output waveform to be inexpensive. It is possible to realize gradation expression by using it, and further, it is possible to process the applied waveform to the head while avoiding the influence of the delay time at the time of state transition of the switching element, so that the desired waveform can be reliably applied to the inkjet head. You can

According to the seventh aspect of the present invention, in the method of driving an ink jet head according to the sixth aspect, since the drive signal source supplies a pulse voltage having the same rise and fall times, it is applied to the ink jet head. Therefore, a complicated drive signal waveform required for that purpose can be easily generated only by a simple pulse signal and a plurality of switching elements without using an AD converter or the like.

An ink jet printer according to an eighth aspect comprises a printing mechanism having an ink jet head and the ink jet head driving device according to the first, second, third, fourth or fifth aspect, and therefore a plurality of ink jet printers are brought into a conductive state. It is possible to drive the inkjet head by generating drive signals having different waveforms from one type of drive signal output from a single drive signal source by selecting the switching element of. Accordingly, it is possible to provide an inkjet printer that can realize gradation expression by using one drive signal source that has a simple output waveform and is inexpensive.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic structure of an inkjet printer.

FIG. 2 is a vertical cross-sectional side view showing a schematic structure of an inkjet printer.

FIG. 3 is a vertical sectional side view showing a part of an inkjet head.

FIG. 4 is a block diagram showing a structure of an electrical system of the inkjet printer.

FIG. 5 is a circuit diagram of an inkjet head and a head driver.

FIG. 6 is an explanatory diagram showing drive signal waveforms for driving an actuator of an inkjet head.

FIG. 7 is an explanatory diagram showing a relationship between a rising time of a drive signal waveform and a gradation level.

FIG. 8 is a time chart of each signal.

FIG. 9 is an explanatory diagram showing changes in drive signal waveforms.

FIG. 10 is a circuit diagram of an inkjet head and a head driver according to a second embodiment of the present invention.

FIG. 11 is a time chart of each signal.

FIG. 12 is an explanatory diagram showing changes in drive signal waveforms.

[Explanation of symbols]

18 inkjet head 34,35 electrodes 37 nozzles 46 Drive signal source SW1 to SW3 switching elements GND reference potential part D drive

Claims (8)

[Claims] 1. A drive device for an ink jet head, which discharges ink droplets from a nozzle by supplying electric energy to electrodes arranged to face each other, wherein one of the electrodes is connected to a reference potential part to which a reference potential is applied. The other electrode is connected to one end of two or more switching elements which are connected in parallel and have desired energization characteristics and are selectively on / off controlled, and the other ends of the plurality of switching elements connected in parallel are drive signal sources. A drive device for an inkjet head, characterized in that it is connected to. 2. The drive device for an inkjet head according to claim 1, wherein the plurality of switching elements have different energization characteristics. 3. The drive signal source outputs at least one of the energization characteristics of the plurality of switching elements to an extent that does not result in ink being ejected from the nozzles when the energization characteristic is independently switched to an on state. The drive device for an inkjet head according to claim 1 or 2, wherein the drive signal is set to be limited. 4. The ink jet head driving device according to claim 1, wherein the switching element is a MOS analog switch. 5. The switching element is integrally integrated in one semiconductor.
The inkjet head driving device according to item 3 or 4. 6. A method of driving an ink jet head in which ink droplets are ejected from nozzles by supplying electric energy to electrodes arranged to face each other, wherein one of the electrodes is connected to a reference potential part to which a reference potential is applied, The other electrode is connected to one end of two or more switching elements connected in parallel having desired energization characteristics, the other ends of the plurality of switching elements connected in parallel are connected to a drive signal source, and A method for driving an inkjet head, wherein when the ink droplets are ejected, the conduction state of the switching element is changed when the output level from the drive signal source is a steady value that does not change. 7. The method of driving an inkjet head according to claim 6, wherein the drive signal source supplies a pulse voltage having the same rise and fall times. 8. An ink jet printer comprising a printing mechanism having an ink jet head, and the ink jet head drive device according to claim 1, 2, 3, 4 or 5.