JPH1191143A - Ink-jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably jet out ink drops and form high-quality images by generating a plurality of driving waveforms to drive energy generation elements, and selecting one of the generated driving waveforms in accordance with image information. SOLUTION: Nozzle data and a timing signal are output as a driving control signal from a main control part 101 to a driving waveform selection circuit 105 of a head-driving part 102. Moreover, the main control part 101 outputs a driving timing signal with a predetermined timing to waveform generation circuits 103A, 103B of the head-driving part 102. The waveform generation circuits 103A, 103B output driving waveforms SAi, SBi. The driving waveform SAi or SBi is output to selection electrodes Do1-Do32 (each piezoelectric element PZT) through an analog switch turned on among analog switches of the driving waveform selection circuit 105, so that a driving voltage is impressed to each piezoelectric element PZT. A discharge amount of ink is changed through control of the driving voltage, whereby a size of dots is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus capable of recording a gradation image.

[0002]

2. Description of the Related Art In an ink jet recording apparatus used as an image forming apparatus such as a printer, a facsimile, a copying apparatus, or the like, variations in dots can be corrected by controlling a driving waveform to vary an ink droplet ejection amount or a dot diameter. As a device capable of recording a gradation image, for example, as described in JP-A-57-160654, an electromechanical conversion is performed by selectively using an appropriate pulse from a pulse train composed of a plurality of voltage pulses. Drive the element,
There is a type in which a plurality of ink particles having different particle velocities and particle diameters are ejected from a nozzle, are combined into one ink particle during flight, and land on a recording medium to form a dot.

Further, as described in Japanese Patent Application Laid-Open No. 6-8428, a pulse signal output means for outputting a plurality of signals having different pulse widths synchronized with a driving signal, Signal selection means for selecting a signal, and switching on / off of the piezoelectric element driving means in an unsaturated region of the drive signal, thereby varying the voltage applied to the piezoelectric element, and changing the ink discharged from each nozzle. A driving method for making the droplet amount constant is known.

[0004]

However, as described above, in the former recording apparatus in which the voltage pulse is appropriately selected from the pulse train to drive the electromechanical conversion element, the higher the integration and the higher the density, the higher the recording density. When the number of nozzles of the inkjet head increases, a circuit for selecting a pulse of a driving circuit corresponding to each electromechanical transducer is required, and the circuit scale of the entire driving circuit increases, and the number of signal lines also increases. The cost is high. Further, when the recording speed is increased and the carriage speed is increased, and the repetition period of dot formation is shortened, it becomes difficult to combine ink droplets continuously ejected in time during flight.

[0005] Further, a plurality of signals having different pulse widths synchronized with the driving signal are output, and a driving means (transistor) for selecting one signal from the plurality of signals and charging each piezoelectric element is switched from on to off. In the latter recording apparatus in which the applied voltage is varied, the applied voltage varies when the turn-off time of the transistor varies, so that the applied voltage cannot be controlled with high accuracy. Also, when controlling the drive voltage, increasing the voltage can increase the amount of ink droplets, but also increases the ink droplet ejection speed,
The ink droplet landing position on the paper surface is shifted, and the dot accuracy is reduced, or unnecessary satellites are generated, and the image quality is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an ink jet recording apparatus capable of forming a high quality image by stably ejecting ink droplets.

[0007]

In order to solve the above-mentioned problems, an ink jet recording apparatus according to claim 1 includes a plurality of nozzles for discharging ink droplets, a plurality of pressurized liquid chambers communicating with the nozzles, and A plurality of energy generating elements for generating energy for discharging ink droplets from the nozzles by pressurizing the ink in the pressurized liquid chamber, and having an inkjet head in which one electrode of each energy generating element is shared In the inkjet recording apparatus, a driving waveform generating means for generating a plurality of driving waveforms for driving the energy generating element, and one of the plurality of driving waveforms generated by the driving waveform generating means is used as image information. And a driving waveform selecting means for selecting the driving waveform in accordance with the driving waveform.

According to a second aspect of the present invention, in the inkjet recording apparatus of the first aspect, the image information is converted into serial nozzle data for selecting a drive nozzle for each drive waveform, and the nozzle data is converted into the drive waveform. The configuration was provided to the selection means.

According to a third aspect of the present invention, in the ink jet recording apparatus of the second aspect, the nozzle data is constituted by serial data of the same number or less as the number of the driving waveforms.

According to a fourth aspect of the present invention, in the inkjet recording apparatus of the first aspect, the plurality of drive waveforms are different from each other in at least one of a drive voltage, a time constant, and a pulse width. did.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic view of a mechanism of an ink jet recording apparatus according to the present invention, and FIG. 2 is a schematic perspective view of a main part of FIG.

In this ink jet recording apparatus, a carriage 5 is moved in a main scanning direction (indicated by an arrow A in FIG. 2) by a guide rod 3 and a guide plate 4 which are laid between left and right side plates 1 and 2 (see FIG. 2).
Direction), a recording head 6 composed of an inkjet head is mounted on the lower surface side of the carriage 5 with the ink droplet ejection direction facing downward, and the recording head 6 is mounted on the upper surface side of the carriage 5 for each color. An ink tank (ink cartridge) 7 for supplying ink is mounted.

The recording head 6 ejects a yellow (Y) ink, a magenta (M) ink, a cyan (C) ink, and a black (Bk) ink. The head is arranged in the main scanning direction. The carriage 5 is connected to a timing belt 18 stretched between a driving pulley 16 and a driven pulley 17 which are rotated by a main scanning motor 15 composed of a stepping motor, and controls the driving of the main scanning motor 15 to control the carriage 5. That is, the recording head 6 is moved in the main scanning direction.

On the other hand, a platen roller (hereinafter, simply referred to as "platen") 21 for transporting the paper 20 in the sub-scanning direction (the direction of arrow B in FIG. 2), and the paper 20 is disposed by being pressed against the peripheral surface of the platen 21. The paper feed rollers 22 and 23 and the pinch roller 24 for defining the paper feed angle, the guide plate 25 facing the recording head 6, the paper discharge roller 26 downstream of the recording head 6 in the paper transport direction, and the paper discharge roller 26 And a paper pressing spur roller 27 which is pressed and abutted.

The rotation of the sub-scanning motor 28, which is a stepping motor, is transmitted to the platen 21 via the gears 29 to 31 and the platen gear 32, and the platen 21 is driven to rotate.
0 is sent between the recording head 6 and the guide plate 25 via the platen 21, the paper feed rollers 22 and 23, and the paper pressing roller 24, and the paper 20 is moved to the platen gear 32 while the paper 20 is moved in the sub-scanning direction by the platen 21. Meshing gear 34
The paper 20 is ejected by the paper ejection roller 26 and the paper holding spur roller 27 which are rotated through the sheet (the direction indicated by the arrow B in FIG. 2).
To send out.

In the printing apparatus thus configured, the paper 20 is conveyed in the sub-scanning direction while moving and scanning the printing head 6 (carriage 5) in the main scanning direction. The required color image (including the black image) is recorded on the paper 20 by ejecting the ink droplets of the color (1).

In this recording apparatus, a reliability maintenance / recovery mechanism (subsystem) 35 for the recording head 6 is provided on the right side of the main scanning area of the carriage 5, and when the printer is in a printing standby state, the host side operates. When the print data is not transferred for a predetermined period of time, or at a predetermined time interval, a reliability maintenance / recovery operation such as removal of stains on the nozzle surface and nozzles of the recording head 6 is performed.

Next, an example of the ink-jet head constituting the recording head will be described with reference to FIGS. 3 is an exploded perspective view of the ink jet head, FIG. 4 is an enlarged cross-sectional view of a main part of the head in a direction orthogonal to a channel direction (nozzle arrangement direction), and FIG. It is.

This ink jet head includes a drive unit 41, a liquid chamber unit 42, and a head cover 43. The drive unit 41 includes a ceramic substrate,
For example, a plurality of laminated piezoelectric elements 45, which are energy generating elements, are arranged and joined in two rows on an insulating substrate 44 made of, for example, barium titanate, alumina, or forsterite. Frame member (support) 46 made of resin, ceramic, or the like surrounding the periphery of 45
Are bonded by an adhesive 47.

The plurality of piezoelectric elements 45 are provided between piezoelectric elements (which are referred to as “drive units”) 48 to which drive pulses for applying ink to droplets and flying are provided, and drive units 48, 48. A piezoelectric element (hereinafter, referred to as a “non-driving unit”) that serves as a liquid chamber support member that simply fixes the liquid chamber unit 42 to the substrate 44 without being provided with a driving pulse.
9 are alternately configured.

Here, as the piezoelectric element 45, a laminated piezoelectric element having ten or more layers is used. This laminated piezoelectric element has a thickness of 10 to 50 μm / 1, for example, as shown in FIG.
Layer of lead zirconate titanate (PZT) 50 and thickness of several μ
Although the internal electrodes 51 made of silver / palladium (AgPd) of m / 1 layer are alternately laminated, the material used for the piezoelectric element is not limited to the above, and other electromechanical conversion elements may be used. Can also.

The internal electrodes 51 of each piezoelectric element 45 are left and right end electrodes 52 and 53 made of AgPd every other layer (the opposing surfaces of the two piezoelectric element rows are end electrodes 52, and the non-opposing surfaces are end electrodes. 53). On the other hand, as shown in FIG.
Each pattern of the common electrode 54 and the selection electrode 55 is provided by Au plating, AgPt paste printing, AgPd paste printing, or the like.

The opposite end electrodes 52 of each row of the piezoelectric elements 45 are connected to the common electrode 54 via a conductive adhesive 56.
On the other hand, the non-opposing end face electrodes 53 of the piezoelectric elements 45 in each row are connected to the selection electrodes 55 via the conductive adhesive 56 in the same manner. Thereby, the driving unit 48
By applying a drive voltage (drive energy) to
An electric field is generated in the stacking direction, and a displacement in the stacking direction (displacement in the direction d33) is generated in the driving unit 48. In addition,
The common electrode 54 is connected to the frame member 4 as shown in FIG.
By filling the conductive adhesive 56 in the hole 46a provided in the 6, the pattern connected to each piezoelectric element is conducted.

On the other hand, the liquid chamber unit 42 is composed of a diaphragm 57 having a multilayer structure composed of a laminate of metal thin films and a photosensitive resin layer composed of a dry film resist (DFR).
A liquid chamber partition member 58 having a layered structure and a nozzle plate 59 made of metal, resin or the like are sequentially laminated and formed by heat fusion. By each of these members, one piezoelectric element 45
(Drive unit 48), a diaphragm 60 corresponding to the one piezoelectric element 45, a pressurized liquid chamber 61 pressurized through each diaphragm 60, and both sides of the pressurized liquid chamber 61. Common liquid chambers 62, 62 for introducing ink to be supplied to the pressurized liquid chamber 61, and the pressurized liquid chamber 61 and the common liquid chambers 62, 62.
Ink supply paths 63 and 6 which also serve as fluid resistance portions
3 and a nozzle 64 communicating with the pressurized liquid chamber 61.
One channel is formed, and a plurality of the channels are provided in two rows.

The diaphragm 57 is made of a nickel plating film having a two-layer structure, and is formed integrally with the diaphragm portion 60 corresponding to the driving portion 48 and at the center portion of the diaphragm portion 60 for joining with the driving portion 48. Island-shaped convex portion 65, beam 66 to be joined to non-drive portion 49 and frame member 4
6 and a peripheral thick portion 67 to be joined.

The liquid chamber partition member 58 is formed by first applying a dry film resist on the vibration plate 57 side, exposing it using a required mask, and developing it to form a first liquid chamber pattern.
The photosensitive resin layer 68 and the second photosensitive resin layer 69 having a predetermined liquid chamber pattern formed by applying a dry film resist in advance on the nozzle plate 59 side, exposing with a required mask, and developing to form a predetermined liquid chamber pattern are heated. It is joined by crimping.

The nozzle plate 59 has a large number of nozzles 64, which are fine discharge ports for ejecting ink droplets. The internal shape (inner shape) of this nozzle 64 is
It is formed in a substantially cylindrical shape, a substantially frustum shape, a horn shape, or the like.
The diameter of the nozzle 64 is about 25 to 35 μm in diameter on the ink droplet outlet side. The ink ejection surface (nozzle surface side) of the nozzle plate 59 is a water-repellent surface 70 that has been subjected to a water-repellent surface treatment as shown in FIG. For example, PTFE-Ni eutectoid plating, electrodeposition coating of fluororesin, vapor-deposited coating of evaporable fluororesin (for example, pitch fluoride), baking after solvent application of silicon-based resin or fluororesin, etc. A water-repellent treatment film selected according to the physical properties of the ink is provided to stabilize the ink droplet shape and flying characteristics and to obtain high-quality image quality. The periphery of the nozzle plate 59 is a non-water-repellent surface 71 on which no water-repellent film is formed.

After the drive unit 41 and the liquid chamber unit 42 are separately processed and assembled, the vibration plate 57 of the liquid chamber unit 42 and the piezoelectric element 45 and the frame member 46 of the drive unit 41 are bonded with an adhesive. It is joined at 72.

Then, the substrate 44 is supported and held on a spacer member (head holder) 73 serving as a head support member, and the head driving I
A PCB board having C or the like is connected to each electrode 54, 55 connected to each piezoelectric element 45 (drive unit 48) of the drive unit 41 via FPC cables 74, 74.

The nozzle cover (head cover) 43
Is formed in a box shape to cover the periphery of the nozzle plate 59 and the side surface of the head. An opening is formed corresponding to the water-repellent surface 70 of the nozzle plate 59, and is left at the periphery of the nozzle plate 59. It is bonded to the non-water-repellent surface 71 with an adhesive. Further, in order to supply ink from an ink cartridge (not shown) to the liquid chamber, the ink supply holes 75 are provided in the spacer member 73, the substrate 44, the frame member 46, and the vibration plate 57, respectively.
To 78 are provided.

In this ink jet head, by applying a drive waveform (pulse voltage of 10 to 50 V) to the drive section 48 in accordance with the recording signal, a displacement in the laminating direction occurs in the drive section 48, and the vibration plate 57 Diaphragm part 6
The pressure of the pressurized liquid chamber 61 is increased through the pressure 0, and the pressure is increased, and ink droplets are ejected from the nozzle 64. At this time, the ink supply paths 63 and 6 communicating from the pressurized liquid chamber 61 to the common liquid chamber 62 are provided.
Although ink flow also occurs in three directions, the ink supply path 6
By reducing the cross-sectional area of 3, 63, it functions as a fluid resistance part to reduce the flow of ink to the common liquid chambers 62, 62, thereby preventing a drop in ink ejection efficiency.

Then, with the end of the ink droplet ejection, the ink pressure in the pressurized liquid chamber 61 is reduced, and a negative pressure is generated in the pressurized liquid chamber 61 due to the inertia of the ink flow and the discharge process of the drive pulse. To the ink filling process. At this time, the ink supplied from the ink tank flows into the common liquid chambers 62, 62, and from the common liquid chambers 62, 62 to the ink supply paths 63, 6.
After that, it is filled into the pressurized liquid chamber 61. Then, the vibration of the ink meniscus surface near the outlet of the nozzle 64 is attenuated,
When the ink is returned to the vicinity of the outlet of the nozzle 64 by the surface tension (refill) and reaches a stable state, the operation shifts to the next ink droplet ejection operation.

Next, an outline of a control section of the ink jet recording apparatus will be described with reference to FIG. The control unit includes a microcomputer (hereinafter, referred to as a “CPU”) 80 that controls the entire recording apparatus, a ROM 81 that stores necessary fixed information, a RAM 82 that is used as a working memory, and the like. An image memory 83 for storing processed data, and a parallel input / output (PIO)
A port 84, an input buffer 85, and a gate array (G
A) or a parallel input / output (PIO) port 86, a head drive circuit 87, a driver 88, and the like.

Here, in addition to image information from the host side, data such as paper type data indicating the type of paper, various instruction information from an operation panel (not shown),
A detection signal from a paper presence / absence sensor for detecting the start and end of the paper, a signal from various sensors such as a home position sensor for detecting a home position (reference position) of the carriage 5, and the like are input. Required information is transmitted to the host side and the operation panel side.

The head drive circuit 87 responds to image information in an energy generating element (piezoelectric element) corresponding to each nozzle of the recording head 6 based on various data and signals provided via the PIO port 86. A driving waveform selected from a plurality of driving waveforms is applied to the energy generating elements of the driving nozzles (nozzles that eject ink droplets).

Further, the driver 88 includes the PIO port 8
By controlling the driving of the main scanning motor 15 and the sub-scanning motor 28 in accordance with the driving data given through the
The carriage 5 is moved and scanned in the main scanning direction, and the platen 21 is moved.
Is rotated to convey the sheet 20 by a predetermined amount.

Next, the details of the control section relating to the drive control of the recording head will be described with reference to FIG. It should be noted that FIG. 2 shows only a portion related to drive control of one head. Here, the ink-jet head H constituting the recording head 6 has the 32 piezoelectric elements PZT which are 32 energy generating elements corresponding to the plurality of (here, 32) nozzles 64 as described above. One electrode of the piezoelectric element PZT is shared, and the common electrode Com is used.
(The above-mentioned common electrode 54), and the other electrode is individualized for each piezoelectric element PZT to form a selection electrode SEL (the above-mentioned individual electrode 55). In addition, since the nozzles 64 are actually provided in two rows, the nozzles 64 have 64 nozzles 64.

On the other hand, the head drive control section for controlling the drive of the head includes the CPU 80, ROM 81,
A main control unit 101 including a RAM 82 and peripheral circuits, and a head drive unit 10 for driving an inkjet head H
2 is provided. Since the head driving unit 102 is provided for each head of each color, the head driving circuit 8 described above is used.
7 is provided with four head driving units 102.

The main control unit 101 inputs image information given from a host such as a personal computer or the like, and sends a drive timing signal MM defining a timing for generating a drive waveform to the head drive unit 102; Each time, serial data (nozzle data) DiA and DiB for designating a nozzle for ejecting an ink droplet and a timing signal (shift clock SCLK, latch signal / LAT) are output as a drive control signal.

The head drive unit 102 receives a drive timing signal MM from the main control unit 101 and receives two types of drive waveforms (drive waveform SAi and drive waveform SAi) for driving the energy generating element (piezoelectric element PZT) of the drive nozzle. Drive waveform SB
i) each of the waveform generating circuits 103A and 103B,
Low impedance output circuits 104A and 104B that output the 3B outputs (drive waveforms SAi and SBi), and two drive waveforms S based on a drive control signal from the main control unit 101.
A drive waveform selection circuit 105 that selects one of Ai and SBi and outputs it to the selection electrodes Do1 to Do32 of the inkjet head H.

Each of the waveform generation circuits 103A and 103B can be composed of, for example, a ROM, a D / A converter or another pulse generation circuit, and a waveform transformation circuit such as a calculus circuit, a clip circuit, and a clamp circuit. This waveform generation circuit 103A, 1
03B is a drive timing signal MM for determining a timing for generating and outputting a drive waveform from the main control unit 101, and a Vp control signal SVp (and / or) for selecting a drive voltage (voltage value) Vp of the drive waveform. A tr control signal S for selecting a rising time constant tr of a driving waveform described later.
tr) and the like are also input.

The low impedance output circuit 104
Is a buffer amplifier, SEPP (Single Ended Pu)
sh Pull) and the like. By using the low impedance output circuit 64, the output of the drive voltage waveform becomes a low impedance output to the piezoelectric element, and the waveform is not distorted due to the variation of the piezoelectric element and the difference in the number of drive channels.

Here, an example of the waveform generation circuit 103A and the low impedance output circuit 104A will be described with reference to FIGS. Note that the waveform generation circuit 103B and the low impedance output circuit 104B have the same configuration.
First, as shown in FIG. 8, the waveform generation circuit 103A receives a drive timing signal MM, generates a drive waveform, and supplies the generated drive waveform to the low impedance output circuit 104A according to the Vp control signal SVp. And a Vp control unit 107 that generates and outputs a voltage Vout that determines the voltage Vp of the drive waveform of the drive waveform generation unit 106.

As shown in FIG. 9, the drive waveform generator 106 and the low impedance output circuit 104A (both of which constitute a constant voltage drive circuit) have a drive timing signal MM.
Is connected to the base of the transistor Tr1 via the buffer B, to the base of the transistor Tr2 via the inverter I, and the power supply voltage Vpp is applied to the collector of the transistor Tr1,
The emitter of the transistor Tr2 is grounded.

A series circuit of a charging resistor Ra and a diode D1 is connected to the emitter of the transistor Tr1, and a series circuit of a discharging resistor Rb and a diode D2 is connected to the collector of the transistor Tr2.
Is connected to the anode side of the diode D2, a capacitor Ck is connected between this connection point a and the ground, and a time constant circuit at the time of charging with the charging resistor Ra and the capacitor Ck is formed by the discharging resistor Rb and the capacitor Ck. Constitutes a time constant circuit at the time of discharge. Further, the voltage Vout from the Vp control unit 107 is applied to the connection point a via the diode Dk.

The connection point a is connected to the transistors Tr3 to Tr3.
A drive waveform that is connected between the base of the transistor Tr4 and the base of the transistor Tr4 on the input side of the low impedance output circuit 104A composed of Tr6, and is obtained between the emitter of the transistor Tr5 on the output side and the collector of the transistor Tr6. SAi is output to the drive waveform selection circuit 105.

In this circuit, the drive timing signal MM is input to the input terminal IN, and “H” is input to the buffer B.
When the level is input, the buffer B outputs a voltage level lower than the power supply voltage Vpp to turn on the transistor Tr1 and the inverter I to "L" to turn off the transistor Tr2. Accordingly, charging of the capacitor Ck is started with a charging time constant determined by the charging resistor Ra and the capacitor Ck.

At this time, the diode Dk is connected to the connection point a.
Since the voltage Vout is applied via the (drop voltage Vd), the charging voltage of the capacitor Ck does not rise to the power supply voltage Vpp, and the voltage (Vout + V
d), and this voltage is applied to the drive waveform SA.
Maximum value of drive voltage VpA of i (VpA = Vout + Vd)
Becomes

When the drive timing signal MM is not inputted to the input terminal IN and the "L" level is inputted to the buffer B, the output of the buffer B becomes the power supply voltage Vpp and the transistor Tr1 is turned off. On the other hand, since the output of the inverter I is inverted with respect to the output of the buffer B, the transistor Tr1 is turned off and the transistor Tr2 is turned on at the same time, and the transistor Tr1 is charged to the voltage Vp with the discharge time constant determined by the discharge resistor Rb and the capacitor Ck. The discharge of the capacitor Ck is started.

Therefore, by changing the voltage Vout applied to the drive waveform generator 106, the drive voltage VpA of the drive waveform SAi can be variably controlled.
Similarly, the drive voltage VpB of the drive waveform SBi output from the waveform generation circuit 103B and the low impedance output circuit 104B can be variably controlled.

The voltage Vout which defines the drive voltage VpA
As shown in FIG. 10, the Vp control unit 107 for generating and outputting a signal includes a three-terminal regulator 108 and a resistance selection circuit 109. By supplying a constant voltage source to the voltage input terminal Vin, the three-terminal regulator 108 adjusts the adjustment terminal adj.
A voltage corresponding to the resistance R1a connected between the output terminal Vout and the resistance value R2 of the resistance selection circuit 109 connected between the adjustment terminal adj and the ground is output from the voltage output terminal Vout, for example, manufactured by National Semiconductor. LM
317T (product name) or the like can be used. Therefore, output voltage V from three-terminal regulator 108
out is, for example, Vout = 1.25 × (1 + R2 / R1)
Will be determined by

The resistor selection circuit 109 is formed by connecting in series a resistor Rs, a resistor Rp and a parallel circuit of resistors R21 to R23 selected by switching transistors Q1 to Q3, for example, a Texas Instruments SN740.
6 (product name) or the like. The resistance selection circuit 109 receives the Vp control signals SVp1 to SVp3 from the main control unit 101 described above in the transistor Q1.
To Q3.

Therefore, while supplying the power supply voltage Vpp to the three-terminal regulator 108, the main control units 101 to 3
By applying the bit Vp control signals SVp1 to SVp3 to the resistor selection circuit 109, the three-terminal regulator 1
The output voltage Vout of the driving waveform SAi can be changed to a predetermined value by inputting the output voltage Vout as the voltage Vout of the driving waveform generator 106 described above. Can be set to

The different voltage Vout is generated, for example, by using a voltage dividing circuit in which a resistor and a parallel circuit of a variable resistor and a capacitor are connected in series, and the voltage across the capacitor is output as the voltage Vout. Thus, the variable resistance can be changed, and the D / A
The voltage Vout can also be changed by using a converter.

Next, the drive waveform selection circuit 105 will be described with reference to FIG. This drive waveform selection circuit 105
Is the serial clock SCLK and the serial data Di.
Two sets of 32-bit shift register circuits 111A and 111B for inputting A or DiB;
1A and 111B are latched by a latch signal / LAT.
(Note that the symbol “/” means inversion.) A 64-bit latch circuit 112 for latching with “64”, a 64-bit level shifter circuit 113, and an analog switch group 114 whose on / off is controlled by the level shifter circuit 113 Consists of By cascading two 32-bit shift register circuits, two data lines (DiA, DiB) corresponding to the driving waveform can be unified into 64-bit data.

The analog switch group 114 includes a pair of analog switches ASA1, ASA1 to ASA32, and ASB32 connected to the selection electrodes Do1 to Do32 of each PZT. The analog switches ASA1 to ASA32 receive the drive waveform SAi, and the analog switches ASB1 to ASB3
2, the drive waveform SBi is input.

The shift clocks SCLK are supplied to the shift register circuits 111A and 111B, respectively.
, The latch circuit 112 latches the serial data DiA, DiB into the shift register circuits 111A, 111B in response to the latch signal / LAT, and latches the serial data DiA, DiB into the level shifter circuit 113.
To enter.

The level shifter circuit 113 turns on one of the two analog switches ASAm and ASBm (m = 1 to 32) connected to each PZT and turns off the other in accordance with the contents of the data. Or turn off both. Thereby, the driving waveform SAi or the driving waveform SB
i is selected and applied to the piezoelectric element PZT.

Next, the operation of the ink jet recording apparatus configured as described above will be described with reference to FIGS. Referring to FIG. 12, main controller 101 drives serial data (nozzle data) DiA and DiB and a timing signal (shift clock SCLK, latch signal / LAT) to drive waveform selection circuit 105 of head driver 102. Output as a control signal.

As a result, as shown in FIG.
FIG. 4B shows a 2-bit shift clock SCLK.
32-bit nozzle data (serial data) D shown in
iA is taken into the shift register circuit 111A, and the 32-bit nozzle data (serial data) DiB shown in FIG. 4C is taken into the shift register circuit 111B, and the latch signal / LAT shown in FIG. The signal is input to the circuit 113.

The main control section 101 outputs the drive timing signal MM shown in FIG. 7E to the waveform generation circuits 103A and 103B of the head drive section 102 at a predetermined timing, and thereby, as shown in FIG. As shown, the drive waveform SAi of the drive voltage Vp = VpA is output from the waveform generation circuit 103A with the rising time constant tr, and the rising time constant tr (tr = tr2) as shown in FIG.
Then, the drive waveform SBi of the drive voltage Vp = VpB is output from the waveform generation circuit 103B.

Therefore, through the analog switches in the ON state of the analog switches ASAm and ASBm of the driving waveform selection circuit 105,
As shown in (i) and (j) (the others are not shown), the drive waveform SAi or SBi is output to the selection electrodes Do1 to Do32 (each piezoelectric element PZT). Therefore, the voltages 0, VpB, VpA (0 <Vp
B <VpA) is applied.

In this case, the ink ejection amount (ink droplet ejection amount) M ejected from each nozzle of the inkjet head H
Since j increases as the drive voltage Vp increases,
By controlling the drive voltage Vp, it is possible to change the size of a dot formed by landing an ink droplet on the paper as shown in FIG.

As described above, a plurality of drive waveforms are generated, one of the plurality of drive waveforms is selected in accordance with image information, and given to the energy generating element, thereby achieving a simple circuit configuration. It becomes possible to record a gradation image by modulating the size of the dot.

In this case, the image information is converted into nozzle data (nozzle selection data), which is serial data for each drive waveform, and the drive waveform is selected according to the nozzle data. Even when the circuit is formed into an IC and mounted on an inkjet head, the circuit can be realized with a simple circuit configuration without the need for an image information processing unit.
Even if the number of nozzles of the head increases, the number of signal lines does not increase.

Further, by cascading two sets of shift registers as shown in FIG. 19, two data lines corresponding to the drive waveform can be unified into 64-bit data, and a plurality of drive waveforms can be obtained. , The number of signal lines for serial data can be reduced, and the cost of the signal transmission unit can be reduced.

Next, another embodiment of the head drive control section will be described with reference to FIGS. In this embodiment, the drive waveform generator shown in FIG. 14 is used as the drive waveform generator of the waveform generator of the above embodiment. The drive waveform generation unit includes a tr control circuit 75 that changes the rise time constant tr by changing the charging resistance Ra connected in series with the diode D1.

The tr control circuit 75 includes a diode D1
And a parallel circuit of charging resistors Ra1, Ra2, and Ra3 is connected in series, and switching transistors Tr11, Tr12, and Tr13 are connected between the charging resistors Ra1, Ra2, and Ra3 and the power supply voltage Vpp, respectively. .

Then, the transistors Tr11, Tr1
2 and Tr13 have buffers B1 and B
2 and B3, and these buffers B1, B2 and B3
, A drive timing signal MM is inputted through gate circuits G1, G2, G3. These gate circuits G1, G2,
G3 is a tr control signal St from the main control unit 101, respectively.
When r1 to Str3 are "H", the circuit is opened and outputs the drive timing signal MM to the buffers B1, B2 and B3.

Therefore, the main control unit 101 sets the drive timing signal MM to “H” and sets any of the 3-bit tr control signals Str1, Str2, and Str3 to “H”, thereby setting the tr control signal Str1 , St
Buffers B1, B2, B3 selected by r2, Str3
Outputs a voltage level lower than the power supply voltage Vpp, and the corresponding transistors Tr11, Tr12, Tr
13 is turned on, and the selected resistor Ra
The capacitor Ck is charged with a start-up time constant tr determined by any one of 1 to Ra3 and the capacitor Ck.

As described above, the capacitor Ck can be charged with a maximum of eight types of start-up time constants tr by the tr control signal.
It is possible to select and generate and output three types of drive waveforms of 1, tr2 and tr3.

In this case, the drive voltage Vp of the drive waveform
May be fixed, but here, it is varied using a Vp control circuit as shown in FIG.
A drive waveform having different rise time constant tr and drive voltage Vp is generated and output.

The operation of this embodiment will be described with reference to FIG. 15 and subsequent figures. As shown in FIG. 15A, the ink discharge amount Mj increases as the drive voltage Vp increases (however, the rising time constant). (It is assumed that tr = tr2 is constant.)
Therefore, the voltage value Vp of the drive waveform is set high to form a large dot diameter, and the voltage value Vp is set low to form a small dot diameter.

On the other hand, as shown in FIG.
When p is increased, the ink ejection speed (ink droplet ejection speed) V
j becomes faster, but in the region of Vj> Vjh, satellites are generated and bubbles are easily mixed in from the nozzles, so that an unstable ejection state is obtained. When the drive voltage Vp is reduced, the ink ejection speed Vj is reduced. However, in the region of Vj <VjL, the ink ejection direction becomes unstable, and the ink droplet landing position is shifted from that when the ink ejection speed Vj is fast. .

Therefore, when printing (every dot) is performed on the paper in the state of particles in the unstable region, the result is as shown in FIG. That is, when the driving voltage Vp is high, the dot diameter is large, but the image quality is degraded due to the satellite adhering to the paper surface. When the driving voltage Vp is low, the dot diameter is small, but the dot landing position is shifted and the dot position is shifted. Accuracy decreases.

Therefore, in this embodiment, the rise time constant tr is changed in accordance with the drive voltage Vp, and the drive voltage Vp
Are set so that the ink ejection speed Vj falls within the stable region even when the value of is changed. That is, the start time constant tr is defined as tr =
Drive voltage Vp = Vp1 and Vp when fixed at tr2
When Vp3 = Vp3, the particleization state is in the unstable region. However, if the start-up time constant tr is set long as shown in FIG. 3D, the ink discharge speed Vj becomes slow, and the start-up time constant tr Is set shorter, the ink ejection speed Vj increases. Therefore, the ink ejection speed Vj can be set in a stable region by selecting the start-up time constant tr at each drive voltage Vp.

For example, as shown in FIG.
= Vp1, the start-up time constant tr = tr1, similarly, when Vp = Vp2, tr = tr2, Vp = V
When p3, tr = tr3 is set (Vp1 <Vp
2 <Vp3, tr1 <tr2 <tr3). FIG. 17 shows an example of these drive waveforms.

Therefore, the drive voltage Vp is used as the drive waveform SAi and the drive waveform SBi output from the head drive unit.
By generating and outputting drive waveforms having different rise time constants tr and selecting the drive waveforms by the drive waveform selection circuit in the same manner as in the above embodiment, the ink droplets can be ejected in a stable particle state and the dot diameter can be determined. In this case, a dot is formed, and a gradation image can be obtained. Also, when correcting variations in the ink ejection amount Mj and the ink ejection speed Vj, the drive voltage Vp
By selecting a combination of the start-up time constant tr and an image, a high-quality image can be obtained.

In addition to the drive voltage Vp and the start time constant tr as shown in FIG. 18, depending on the head structure and the energy generating element (electromechanical element or electrothermal element) used, Time constant tf and pulse width P
By controlling w, dots having different dot diameters can be formed by controlling the ink ejection amount Mj and the ejection speed Vj.

For example, a head structure in which ink droplets are ejected when the drive waveform falls (the polarization direction of the piezoelectric element is positive) as in the case of using the displacement of the piezoelectric element in the direction d31 as the energy generating means of the ink jet head. In this case, the fall time constant tf may be controlled instead of the rise time constant tr.

The configuration and drive waveform of the head drive section are as follows:
The drive waveform is not limited to the one in the above-described embodiment, as long as ink droplets can be stably ejected, and the drive waveform may be any shape such as a triangular waveform and a Sin (sine) waveform. Further, a plurality of different drive waveforms can be three or more in addition to the two types described in the above embodiment.

[0082]

As described above, according to the head driving apparatus of the first aspect, a plurality of drive waveforms for driving the energy generating element are generated, and one of the plurality of drive waveforms is imaged. As we select according to information,
With a simple circuit configuration, high-quality recording can be performed by stably ejecting ink droplets. This facilitates gradation recording by dot diameter modulation and dot diameter variation correction.

According to the head driving device of the second aspect, in the head driving device of the first aspect, the image information is converted into nozzle data which is serial data for selecting a driving nozzle for each driving waveform, and is converted into the nozzle data. Since the driving waveform is selected in accordance with this, even when the driving waveform selecting means is integrated into an IC and mounted on the head, the image information processing means is not required, and the driving waveform selecting means can be realized with a simple circuit configuration. Even if the number of nozzles of the head increases, the number of signal lines does not increase.

According to the head driving device of the third aspect, in the head driving device of the second aspect, the nozzle data is constituted by the same number or less of serial data as the number of driving waveforms. Can be reduced, and the cost of the signal transmission unit can be reduced.

According to a fourth aspect of the present invention, in the head driving apparatus of any one of the first to third aspects,
Since the plurality of drive waveforms have a configuration in which at least one of the drive voltage, the time constant, and the pulse width is different, more stable ink droplet ejection becomes possible, and dot position accuracy can be secured.

[Brief description of the drawings]

FIG. 1 is a schematic view of a mechanism of an ink jet recording apparatus according to the present invention.

FIG. 2 is a schematic perspective view of a main part of FIG.

FIG. 3 is an exploded perspective view of an inkjet head constituting the recording head of FIG. 1;

FIG. 4 is an enlarged sectional view of a main part of the head in a direction orthogonal to a channel direction.

FIG. 5 is an enlarged sectional view of a main part of the head in a channel direction.

FIG. 6 is a schematic block diagram of a control unit.

FIG. 7 is a block diagram of a part related to head drive control of the control unit.

FIG. 8 is a block diagram illustrating an example of the waveform generation circuit of FIG. 7;

FIG. 9 is a circuit diagram showing an example of a driving waveform generator and a low impedance output circuit of FIG. 8;

FIG. 10 is a block diagram illustrating an example of a Vp control unit in FIG. 8;

FIG. 11 is a block diagram showing an example of a drive waveform selection circuit of FIG. 7;

FIG. 12 is an explanatory diagram for explaining the operation of the head driving device;

FIG. 13 is an explanatory diagram illustrating a relationship between a driving voltage and a dot diameter.

FIG. 14 is another circuit diagram showing a driving waveform generator and a low impedance output circuit for explaining another embodiment of the present invention.

FIG. 15 is an explanatory diagram for explaining a relationship among a drive voltage Vp, an ink ejection amount Mj, an ink ejection speed Vj, a rise time constant tr, and dots.

FIG. 16 is an explanatory diagram for explaining a drive voltage Vp and a rise time constant tr of a drive waveform.

FIG. 17 is a waveform diagram showing an example of driving waveforms having different driving voltages Vp and rising time constants tr.

FIG. 18 is an explanatory diagram for explaining a plurality of different driving waveforms;

FIG. 19 is an explanatory diagram illustrating an example of a cascade connection.

[Explanation of symbols]

5 carriage, 6 print head, 15 main scanning motor, 21 platen, 28 sub-scan motor, 45, PZ
T: piezoelectric element, 54, Com: common electrode, 55, SEL
... Selection electrode, 61 ... Pressurized liquid chamber (ink liquid chamber), 64 ... Nozzle, 87 ... Head drive circuit, 101 ... Main control unit, 10
2. Head drive unit, 103A, 103B: Waveform generation circuit, 104A, 104B: Low impedance output circuit,
105: drive waveform selection circuit, 106: drive waveform generator,
107 ... Vp control circuit.

Claims (4)

[Claims] 1. A plurality of nozzles for discharging ink droplets, a plurality of pressurized liquid chambers communicating with each nozzle, and energy for pressurizing ink in each pressurized liquid chamber to discharge ink droplets from the nozzles. And a plurality of energy generating elements for generating the same, and an ink jet recording apparatus having an ink jet head in which one electrode of each of the energy generating elements is shared, a drive for generating a plurality of drive waveforms for driving the energy generating elements An ink jet recording apparatus comprising: a waveform generating unit; and a driving waveform selecting unit that selects one of a plurality of driving waveforms generated by the driving waveform generating unit in accordance with image information. 2. An ink jet recording apparatus according to claim 1, wherein said image information is converted into serial nozzle data for selecting a drive nozzle for each drive waveform, and said nozzle data is provided to said drive waveform selection means. Characteristic inkjet recording device. 3. The ink-jet recording apparatus according to claim 2, wherein said nozzle data is composed of serial data whose number is equal to or less than the number of said driving waveforms. 4. The ink jet recording apparatus according to claim 1, wherein the plurality of driving waveforms are:
An ink jet recording apparatus, wherein at least one of a driving voltage, a time constant, and a pulse width is different.