JPH10138475A - Ink jet recorder and head drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform gradation recording through a simple constitution. SOLUTION: The ink jet recorder comprises a waveform generation circuit 101 for generating a driving waveform group consisting of three different driving waveforms P1, P2, P3 to the common electrode Com of an ink jet head H, and a channel selection circuit 104 for selecting one or more driving waveform from the driving waveform group and applying the selected driving waveform to a piezoelectric element PZT in the ink jet head H.

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 a head driving circuit, and more particularly to an ink jet recording apparatus capable of recording a gradation image and a head driving circuit capable of driving an ink jet head for recording the gradation image.

[0002]

2. Description of the Related Art An ink jet recording apparatus has almost no vibration and noise during recording, and is particularly easy to colorize.
In addition to a printer that outputs data from a digital processing device such as a computer, it is also used for facsimile machines, copiers, and the like. This inkjet recording device
In accordance with a recording signal, an inkjet head having a plurality of nozzles for ejecting ink droplets and an actuator element such as an electromechanical transducer or a heating resistor provided corresponding to each nozzle is used as a recording head. High-speed, high-density, high-quality printing is performed by discharging ink droplets from a nozzle onto a recording medium (on which ink droplets adhere).

In such an ink jet recording apparatus, conventionally, a gradation image is recorded as follows.
For example, as described in JP-A-57-160654, an electromechanical transducer is driven by selectively using an appropriate pulse from a pulse train composed of a plurality of voltage pulses, and a particle velocity and a particle diameter are output from a nozzle. In some cases, a plurality of different ink particles are ejected, combined with one ink particle during flight, and landed on a recording medium to form a dot.

[0004]

However, in a recording apparatus which drives an electromechanical transducer by appropriately selecting a voltage pulse from a pulse train as in the above-mentioned conventional ink jet recording apparatus, high integration and high density are required. In planning for
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. Also,
The carriage speed is increased by increasing the recording speed,
If the repetition period of dot formation becomes short, it becomes difficult to combine ink droplets continuously ejected in time during flight.

[0005] The present invention has been made in view of the above points, and has as its object to enable gradation recording with a simple configuration.

[0006]

According to a first aspect of the present invention, there is provided a head driving circuit including a plurality of nozzles for ejecting ink droplets and a plurality of electromechanical transducers corresponding to each nozzle. One electrode of each electromechanical conversion element is shared and used as a common electrode, and the other electrode is separated into n electrodes in a head drive circuit that drives an ink jet head that is individualized and used as an individual electrode for each electromechanical conversion element. Waveform generating means for generating a drive waveform group composed of drive waveforms and outputting the generated drive waveform group to the common electrode; and selecting means for selecting one or more drive waveforms from the drive waveform group and applying the selected drive waveform to the electromechanical transducer. The configuration was provided.

According to a second aspect of the present invention, in the head driving circuit according to the first aspect, the selecting means has a shift register having the same number of bits or more as the number m of nozzles of the ink jet head. The nozzle selection data of (m × n) bits is transferred to the shift register at each repetition period, and the nozzle to be driven at each timing of the n drive waveforms is selected.

According to a third aspect of the present invention, in the head drive circuit of the first or second aspect, the waveform generating means can adjust a voltage value of a generated drive waveform and / or a rise time of the drive waveform. The configuration was adopted.

According to a fourth aspect of the present invention, there is provided the head drive circuit according to any one of the first to third aspects, wherein each of the n drive waveforms constituting the drive waveform group output from the waveform generating means is delayed. In time td (k), the distance between the nozzle and the recording paper surface is d, and the moving speed of the head in the main scanning direction is V.
When the ejection speed of the ink droplet ejected by the c-th and k-th drive waveforms is Vj (k), the following formula (1) is satisfied.

[0010]

(Equation 3)

A head drive circuit according to a fifth aspect of the present invention is the head drive circuit according to any one of the first to third aspects, wherein each of the n drive waveforms constituting the drive waveform group output from the waveform generation means is delayed. In time td (k), the distance between the nozzle and the recording paper surface is d, and the moving speed of the head in the main scanning direction is V.
When the ejection speed of the ink droplet ejected by the c-th and k-th drive waveforms is Vj (k), the following formula (2) is satisfied.

[0012]

(Equation 4)

According to a sixth aspect of the present invention, there is provided an ink jet recording apparatus having a plurality of nozzles for ejecting ink droplets, and a plurality of electromechanical transducers corresponding to each nozzle, and one electrode of each electromechanical transducer is shared. 5. An ink jet head, which is a common electrode, and the other electrode is an individual electrode which is individualized for each electromechanical transducer, and the head drive circuit according to any one of claims 1 to 4, wherein the n drive waveforms are used. Select at least one drive waveform from a group of drive waveforms
A plurality of ink droplets are ejected to form a plurality of dots in the main scanning direction, and the sub-scanning is performed h times to form one pixel with a maximum of (n × h) dots.

According to a seventh aspect of the present invention, there is provided an ink jet recording apparatus having a plurality of nozzles for ejecting ink droplets and a plurality of electromechanical transducers corresponding to each nozzle, and one electrode of each electromechanical transducer is shared. 6. An ink jet head which is a common electrode, and the other electrode is an individual electrode which is individualized for each electromechanical transducer, and the head drive circuit according to any one of claims 1 to 3, and n drive waveforms. Have different ink droplet ejection volumes and have substantially the same landing positions, so that one and a plurality of ink droplets are overlapped to form dots having different diameters.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic plan view of an ink jet recording apparatus provided with a head drive circuit to which the present invention is applied, and FIG. 2 is a schematic side view of the recording apparatus.

In this ink jet recording apparatus, a carriage 4 is slidably mounted on a front guide 2 and a guide shaft 3 provided between left and right main scanning frames 1 and 1, and a yellow (Y) ), Magenta (M), cyan (C) and black (K), a recording head 5 composed of a plurality of ink jet heads for ejecting ink droplets, and an ink cartridge 6 of each color ink on the upper surface. Is detachably provided.

A main scanning motor 8 is attached to a substantially L-shaped stay 7 provided between the left and right main scanning frames 1 and 1, and a motor pulley 9 and a stay 7 mounted on a rotating shaft of the main scanning motor 8 are attached to the main scanning motor 8. A belt 11 is stretched between the attached side pulley 10 and the carriage 4 as shown in FIG.
Is fixed to the belt 11 by a belt clamp 12, and the main scanning motor 8 is rotated to drive the carriage 4 in FIG.
(The main scanning direction). The side pulley 10 is attached so as to be able to move slightly in the main scanning direction, and tension is applied to the belt 11 by a tension spring 13.

On the other hand, a platen 16 is rotatably mounted between the left and right sub-scanning frames 15 and 15, and as shown in FIG.
7 and 18, and a paper pan 19 for guiding the paper along the peripheral surface of the platen 16. Then, the sheet feed tray 21 set at the lower front side of the recording apparatus
The paper 24, which is a recording medium loaded on the ascending tray 23 urged by the ascending spring 22, is fed out one by one by a paper feed roller 25 and a corner claw 26 of the paper feed tray 21, and is fed along a paper feed guide 27. The guide is guided to the peripheral surface of the platen 16.

A paper guide 28 serving as a paper guide is disposed near the paper exit of the platen 16 so as to face the carriage 4, and the paper 24 sent from the platen 16 is pressed near the entrance of the paper guide 28. A paper press 29 is disposed, and a paper discharge roller 31 and a spur roller 3 for discharging the paper 24 to a paper discharge tray 30 near the exit.
2 are arranged.

Further, a sub-scanning motor 34 is mounted on a sub-frame 33 mounted on the main scanning frame 1 as shown in FIG. 1, and a motor gear 35 is mounted on a rotating shaft 34a of the sub-scanning motor 34 as shown in FIG. This motor gear 35
The idler gear 36 meshes with the idler gear 3
6 is engaged with a platen gear 38 attached to the end of the platen 16 to transmit the rotation of the sub-scanning motor 34 to the platen 16 and also to various rollers and rollers, so that the sub-scanning motor 34 , The platen 16 and various rollers and rollers rotate to convey the paper 24 on the paper guide 28 in the direction indicated by the arrow B (the sub-scanning direction).

With such a configuration, the recording head 5
While moving (carriage 4) in the main scanning direction and scanning,
The paper 24 is conveyed in the sub-scanning direction, and a desired color image is recorded on the paper 24 by ejecting ink droplets of a desired color from nozzles of each inkjet head of the recording head 5.

Next, an example of the ink jet head constituting the recording head 5 will be described with reference to FIGS. FIG. 3 is an exploded perspective view of the inkjet head,
FIG. 4 is an enlarged sectional view of a main part of the head in a direction orthogonal to a channel direction (a nozzle arrangement direction), and FIG. 5 is an enlarged sectional view of a main part of the head in a channel direction.

In this ink jet head, a plurality of piezoelectric elements 42, which are laminated piezoelectric elements, are joined and arranged in two rows on an insulating substrate 41 made of ceramic, glass epoxy resin or the like. A frame 43 surrounding the periphery of the frame 42 is joined. Here, the piezoelectric element 4
Reference numeral 2 denotes alternately arranged drive units 44 serving as actuator elements and non-drive units 45 which simply fix and support the liquid chamber member. The upper surfaces of the multilayer piezoelectric element 42 and the frame 43 are positioned or ground on substantially the same plane.

A vibration plate 47 is joined to the upper surface of each of the piezoelectric elements 42 and the frame 43. The vibration plate 47 is formed of a diaphragm 48 serving as a displacement portion, a beam 49 connected to the non-driving portion 45, and a base 50 connected to the frame 43. The diaphragm 48 has an island shape which faces and connects to the driving portion 44. It is formed from a convex portion 51 and a thin film portion 52. The bonding between the substrate 41, the piezoelectric element 42, and the vibration plate 47 is performed by an adhesive 46.

A two-layer liquid chamber partition member 53 made of a photosensitive resin film or the like is bonded and provided on the vibration plate 47,
A nozzle plate 55, which is a nozzle forming member in which a plurality of nozzles 54 are formed in two rows, is bonded to the liquid chamber partition member 53. The liquid chamber partition member 53 forms an upper partition 57 and a lower partition 58, respectively, and is located together with the vibration plate 47 and the nozzle plate 55 on the pressurized liquid chamber 59 facing the drive unit 44, on both sides of the pressurized liquid chamber 59, and the like. Common liquid chamber 60, pressurized liquid chamber 5
An ink supply path 61 which also serves as a fluid resistance portion communicating the common liquid chamber 60 with the common liquid chamber 60 is formed.

Here, as shown in FIGS. 4 and 5, the piezoelectric element 42 has a PZT (= P
b (Zr · Ti) O ₃ ) 63 and internal electrodes 64 made of silver / palladium (AgPd) having a thickness of several μm / 1 layer are alternately laminated. The piezoelectric element has a thickness of 10 to 50 μm
The drive voltage can be reduced by using a multi-layer structure of / 1 layer. For example, an electric field strength of 1000 V / mm of the piezoelectric element can be obtained with a pulse voltage of 10 to 50 V. The material used for the piezoelectric element is not limited to the above,
BaTiO ₃ , PbT generally used as a piezoelectric element material
It is also possible to use a ferroelectric material such as TiO ₃ , (NaK) NbO ₃ , and other electromechanical transducers.

Each of the internal electrodes 64 of the piezoelectric element 42 has left and right end electrodes (external electrodes) 6 made of AgPd every other layer.
5,66. On the other hand, on the substrate 41, a pattern of a common electrode 67 for applying a driving waveform to the driving unit 44 is formed between the columns of the piezoelectric elements 42, and the driving unit 44 A pattern of an individual electrode 68 for providing a selection signal is provided. Then, the external electrode 65 of the driving unit 44 is connected to the conductive adhesive 7 such as a silver paste.
0 is connected to the common electrode 67, and the external electrode 66 is also connected to the individual electrode 68 via the conductive adhesive 70.

The pattern portions connected to the respective driving portions 44 of the common electrode 67 are electrically connected to each other by applying a conductive adhesive 70 into a hole 71 formed in the center of the frame 43. I have to. The common electrode 67 and the individual electrode 68 are respectively connected to the FPC cable 7.
2, 73 are connected. In addition, ink supply holes 75, 76, 77 for supplying ink supplied from the outside to the common liquid chamber 60 are provided in the substrate 41, the frame 43, and the vibration plate 47.
Are formed respectively.

In this ink-jet head, a required drive waveform is applied to a common electrode 67 which is connected in common with one electrode to each drive section 44, and the other electrode of each drive section 44 is individually connected to each drive section. By applying a selection signal to the individual electrodes 68 that are formed and connected, the ink is generated in the predetermined driving section 44 in the stacking direction, and the ink in the corresponding pressurized liquid chamber 59 is pressurized. Nozzle 5 communicating with
4 ejects ink droplets. Although the driving unit 44 (piezoelectric element) is driven by the driving waveform, the expression of driving the nozzle may be used for convenience.

Next, a head drive circuit according to the present invention for controlling the driving of the piezoelectric element (drive unit) of the ink jet head in the ink jet recording apparatus will be described with reference to FIG. In the following description, the inkjet head is H, the piezoelectric element serving as a driving unit is PZT, the common electrode 67 is Com, and the individual electrode 68 is S.
Each code of EL is used.

FIG. 6 is a block diagram showing an example of the head drive control unit according to the present invention. Inkjet head H
Are a plurality of (m) nozzles for ejecting ink droplets (the number of nozzles is m = 64) as described above, and 64 piezoelectric elements PZT, which are electromechanical conversion elements corresponding to each nozzle.
One of the electrodes of each piezoelectric element PZT is shared and used as a common electrode Com, and the other electrode is individualized for each piezoelectric element PZT and used as an individual electrode (selection electrode) SEL.

On the other hand, a head drive control section for controlling the drive of the ink jet head H is provided with a head drive circuit 1
00 and a control signal generator 102 for providing a control signal and the like to the head drive circuit 100.
Numeral 02 can be composed of, for example, a microcomputer or the like that controls the whole of the ink jet recording apparatus.

The head drive circuit 100 receives a drive timing signal (pulse) STB from the control signal generator 101 and receives n drive waveforms (here, three voltage waveforms).
Generating circuit 103 for generating and outputting a driving waveform group composed of
And a low-voltage output circuit 104 that outputs the output of the waveform generation circuit 103 to the common electrode Com of the inkjet head H, and a print data signal DI from the control signal generation unit 101. A channel (c) for providing selection signals Do1 to Do64 to the plurality of piezoelectric elements PZT of the inkjet head H
h) a selection circuit 105.

The waveform generating circuit 10 of the constant voltage driving circuit 102
3 can be composed of, for example, a ROM, a D / A converter or another pulse generation circuit and a waveform deformation circuit such as a calculus circuit, a clip circuit, or a clamp circuit. This waveform generation circuit 10
3 includes a drive timing signal ST for determining a timing for generating and outputting a drive waveform from the control signal generator 101.
In addition to B, Vp control signals SVp1 to SVp3 for adjusting and selecting the drive voltage (voltage value) Vp of the drive waveform, and tr control signals Str1 to Str3 for adjusting and selecting the rising time constant tr of the drive waveform are also input. However, these Vp control signals SVp1 to SVp3 and tr control signal St
r1 to Str3 will be described later.

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 104, the output of the driving 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 driving channels.

Further, as shown in FIG. 7, the channel selection circuit 105 includes a 64-bit shift register 106 having the same number of bits or more as the number m of nozzles for taking in the serial input SI with the clock CLK, and a register value of the shift register 106. Is latched with a latch signal / LAT (the sign “/” means inversion), a latch circuit 107 of one bit receives an output of the latch circuit 107 as one input, and outputs a drive timing signal / STB to a knot circuit NG. Gate circuit G corresponding to each piezoelectric element PZT which is input to the other via the
Circuit array 108 composed of transistors Q, a transistor array 109 composed of transistors Q corresponding to each piezoelectric element PZT and turned on / off by the output of each gate circuit G, and a diode array 110 composed of diodes D connected to each transistor Q And

Then, the print data signal DI input as the serial input SI is taken into the shift register 106 in response to the clock signal CLK, and the latch circuit 107 uses the latch signal / LAT to output the shift register 10 at that time.
6 is latched, the required gate circuit G is opened by the drive timing signal / STB from the control signal generator 101, and the transistor Q is turned on to output the selection signal Don (n = 1 to 64). Then, a driving waveform from the low impedance output circuit 104 is applied to one or a plurality of required piezoelectric elements PZT to drive.

Next, the operation of the head drive control unit configured as described above will be described with reference to FIGS. First, from the waveform generation circuit 103 of the head drive circuit 100, as shown in FIG. 8A, three drive waveforms P1, P2, and P3 having different drive voltages Vp (the voltage value of each waveform is Vp
1, Vp2, and Vp3, and a relationship of Vp1 <Vp2 <Vp3 is set. ) Is output at a repetition cycle Tc, and the drive waveforms P1, P2, and P3 are applied to the common electrode Com of each piezoelectric element PZT. At this time, the moving speed (carriage speed) Vc of the carriage 4 is Vc = Gp * Tc (G
p: pixel pitch).

On the other hand, the control signal generator 101 outputs a drive timing signal STB as shown in FIG.
3 as the generation timing signals of the driving waveforms P1, P2, and P3, and the selection signal Dom of the channel selection circuit 105.
(M = 1 to 64).

In the channel selection circuit 105, the nozzle (piezoelectric element PZT) driven in accordance with the driving of the driving waveforms P1, P2 and P3 by the clock signal CLK and the serial input SI as shown in FIG. Is serially transferred to the 64-bit shift register 106, and the drive waveforms P1, P2, and P3 are applied to the common electrode Com by the latch signal / LAT as shown in FIG. Just before being applied, the nozzle selection data is latched in the latch circuit 107,
Selection signals Do1 to D in accordance with the drive timing signal STB
Outputs o64.

Thus, the drive timing signal STB
Is "H", the transistor Q is turned on to charge the corresponding (selected) piezoelectric element PZT according to the drive waveforms P1, P2, P3, and when the drive timing signal STB is "L", the transistor Q is turned on. Q is turned off and discharged by diode D.

This is expanded by temporally expanding the nozzle selection data (serial input SI) and the clock signal CLK in FIG.
A description will be given with reference to FIG. 9 in which the driving waveform of the piezoelectric element for the nozzle selection data is enlarged. Control signal generator 101
Transfer the print data signal DI (nozzle selection data) for selecting the piezoelectric element PZT (nozzle) to be driven from the shift register 1 with the clock CLK as shown in FIG.
The 64-bit nozzle data is fetched from the serial input SI 06 and the selection signal Dom is output to the corresponding piezoelectric element PZT as described above. For example, if the channels ch64 and ch62 of the nozzle selection data transferred during the period are at “H” level as shown in FIG. ch
The piezoelectric element PZT corresponding to 64 and ch62 has the drive waveform P
1 is driven.

If the channels ch64 and ch63 of the 64-bit nozzle selection data transferred during the period are at the "H" level, as shown in FIG. ), Channels ch64 and c
The piezoelectric element PZT corresponding to h63 is driven by the drive waveform P2.

Therefore, by repeatedly transferring the nozzle selection data of 64 bits in a period, the piezoelectric element PZT of each channel chm (m = 1 to 64) is driven by one or more of the driving waveforms P1, P2, P3. It can be selectively driven by a waveform.

In this case, in the ink-jet head, generally, the higher the drive voltage Vp of the drive waveform P, the larger the amount Mj of ink droplets ejected from the nozzles. The ink droplet ejection amount Mj2 due to P2 and the ink droplet ejection amount Mj3 due to the driving waveform P3 are in a relationship of Mj1 <Mj2 <Mj3, and the size of the dot on the paper is the smallest for the ink droplet ejected with the driving waveform P1. The dot due to the ink droplet ejected with the drive waveform P3 is the largest, and the dot due to the ink droplet ejected with the drive waveform P2 has an intermediate size.

For example, when the channel ch64 is driven by the drive waveforms P1 and P2 as shown in FIG. 9E, the ink droplet discharge amount Mj1 discharged by the drive waveform P1 and the ink droplet discharge by the drive waveform P2 are discharged. The quantity Mj2 is Vp1 <V
p2, Mj1 <Mj2, and when this is viewed from the dots formed on the recording paper, (L
As shown in the (+1) -th row, the dots Pd2 formed by ejection with the drive waveform P2 are larger than the dots Pd1 formed by ejection with the drive waveform P1. Similarly, as shown in the (L + 2) -th row, the dots Pd3 formed by ejection with the drive waveform P3 are larger than the dots Pd2 formed by ejection with the drive waveform P2.

Therefore, these drive waveforms P1, P2, P
By selecting 3 and driving the piezoelectric element, a gradation image can be easily formed.

As described above, a plurality of nozzles for ejecting ink droplets, and a plurality of electromechanical transducers corresponding to each nozzle are provided, and one electrode of each electromechanical transducer is shared and used as a common electrode. The electrodes are individually individualized for each electromechanical transducer, and as individual electrodes, a drive waveform group including n different drive waveforms is generated and output to the common electrode, and one or more drive waveforms of these drive waveform groups are generated. Is selected and applied to the electromechanical conversion element, it is possible to easily eject different amounts of ink droplets, and it is possible to obtain a gradation image at low cost.

In this case, a shift register having the same number of bits or more as the number m of nozzles of the ink jet head is provided, and (m × n) bits of nozzle selection data (nozzle data) are input to the shift register at each repetition period of the driving waveform group. Then n
By selecting a nozzle to be driven at each timing of the individual drive waveforms, the drive timing can be easily controlled without adding a special circuit.

Next, an embodiment in which a gradation image is formed using this head drive control section will be described with reference to FIG. 10 and subsequent figures. FIG. 10 is an explanatory diagram for explaining an example in which one pixel is formed by a 3 × 3 dot matrix of three dots in the main scanning direction and three dots in the sub-scanning direction. Thus, one pixel is 3
In the case of forming with a dot matrix of × 3, if the nozzle pitch (nozzle interval) Np in the sub-scanning direction is larger than the pixel pitch Gp (Np> Gp), the dot pitch after forming the dot in the L-th row in FIG. The dots in the (L + 1) -th row may be formed by performing sub-scanning by Dp, and the dots in the (L + 2) -th row may be formed by further performing sub-scanning by the dot pitch Dp.

That is, a drive waveform group consisting of n drive waveforms is generated and output, and at least one or more drive waveforms are selected from the drive waveform group consisting of the n drive waveforms to eject a plurality of ink droplets. In this way, a plurality of dots are formed in the main scanning direction, and the sub-scanning is performed h times to form one pixel with a maximum of (n × h) dots. ) Can form a gradation image.

It is to be noted that, for example, three or more nozzles in the sub-scanning direction have a nozzle pitch smaller than the pixel pitch (Np <Gp)
When the ink jet heads arranged as shown in FIG. 10 are used, the L-th row, (L + 1) -th row, (L +
2) The dots in the row can be formed by one main scan.

Here, the dot pitch Dp and the pixel pitch G
Considering the relationship with p, it is desirable that the dot pitch Dp be uniform within one pixel. In order to equalize the dot pitch Dp, the delay times td1 and td2 between the respective drive waveforms P1, P2 and P3 are predetermined. It should be set to the time.

That is, referring to FIG. 11, drive waveform P
1, the ejection speed of the ink droplet ejected by P2 is Vj
1, Vj2 (Vj1 <Vj2), the delay time of the drive waveforms P1 and P2 is td1, the distance between the nozzle surface of the head and the recording paper is d, and the moving speed of the carriage (carriage speed) is Vc. The distance X1 between the impact position of the ink droplet ejected by the waveform P1 on the paper surface and the position at the time of ejection (t = 0), the impact position of the ink droplet ejected by the drive waveform P2 on the paper surface and the ejection time ( The distance X2 from the position of t = td1) is expressed by the following equations (3) and (4).

[0055]

(Equation 5)

[0056]

(Equation 6)

Therefore, the dot pitch Dp, which is the distance (interval) between the landing positions of the ink droplets ejected by the driving waveforms P1 and P2, is obtained by the following equation (5).

[0058]

(Equation 7)

As described above, it is desirable that the dot pitch Dp of adjacent dots is equal to the pixel pitch Gp. For example, when one pixel is formed by a 3 × 3 dot matrix, the dot pitch Dp is It is desirable to set Dp and the pixel pitch Gp in the relationship of the following equation (6).

[0060]

(Equation 8)

Therefore, the above-mentioned equations (5) and (6)
From the equation, the delay time td1 of the drive waveforms P1 and P2 is
What is necessary is just to set the relationship of the following equation (7). Similarly, the delay time td2 of the drive waveforms P2 and P3 may be set to the relationship of the following equation (8).

[0062]

(Equation 9)

[0063]

(Equation 10)

That is, one or more drive waveforms are selected from a group of n different drive waveforms, and a plurality of ink droplets are ejected by driving the electromechanical conversion element, thereby forming a plurality of dots in the main scanning direction. Are formed, and h dots are formed by, for example, performing h sub-scans, and 1 × n × h dots are formed.
When a pixel is formed, the delay times td (1) to td (n-1) of each of the n drive waveforms are set so that the relationship of the following equation (1) is established, and the dot is formed. The pitch Dp can be made substantially equal to the pixel pitch Gp.

[0065]

[Equation 11]

Next, a case where a plurality of ink droplets land at substantially the same position to form dots having different diameters as one pixel will be described with reference to FIG. The piezoelectric element PZ is generated by the three different drive waveforms P1, P2, and P3 as described above.
When the ink droplet is ejected by driving T, as shown in FIG.
Is the dot Pd2 with the ink droplet ejected with the drive waveform P2.
Is the dot Pd3 with the ink droplet ejected with the drive waveform P3.
(Pd1 <Pd2 <Pd3) are respectively formed, so that a plurality of ink droplets land at almost the same position, for example, three ink droplets are ejected with drive waveforms P1, P2, and P3, respectively.
When the ink droplets land on substantially the same position, dots (Pd1 + Pd2 + Pd3) as shown in FIG.

Here, in order to cause a plurality of ink droplets to land at substantially the same position, for example, to land ink droplets by the drive waveforms P1, P2, and P3 at substantially the same position, Dp in the above-described equation (5) is used. = 0, so
Each delay time td between drive waveforms P1, P2 and P3
1 and td2 may be set as in the following equations (9) and (10).

[0068]

(Equation 12)

[0069]

(Equation 13)

For example, Vj1 = 4 m / s, Vj2 = 5 m /
s, Vj3 = 6 m / s, the distance between the nozzle and the paper surface d =
In the case of 1 mm, td1 = 50 μs, td2 = 3
3.3 μs.

As described above, a plurality of nozzles for ejecting ink droplets, and a plurality of electromechanical transducers corresponding to each nozzle are provided, and one electrode of each electromechanical transducer is shared and used as a common electrode. Are individually generated for each of the electromechanical transducers to generate and output a drive waveform group including n different drive waveforms as individual electrodes, and the n drive waveforms cause the corresponding ink droplet ejection volumes to differ, respectively. By forming dots having different diameters by superimposing one or a plurality of ink droplets with the landing positions substantially coincident with each other, it is possible to obtain a high gradation and high resolution image without lowering the pixel density.

In this case, the delay time td (k) of the n drive waveforms constituting the drive waveform group is represented by d, the distance between the nozzle and the recording paper surface is represented by d, and the moving speed of the head in the main scanning direction is represented by Vc. When the ejection speed of the ink droplet ejected by the k-th drive waveform is Vj (k), the following (2)
By adopting a configuration that satisfies the formula, the landing positions on the paper surface can be easily made to substantially match regardless of the difference in the ink droplet ejection speed Vj due to the difference in the ink ejection amount.

[0073]

[Equation 14]

Next, details of the constant voltage driving circuit 102 will be described with reference to FIG. FIG. 13 is a circuit diagram showing an example of the waveform generating circuit and the low impedance output circuit in the constant voltage driving circuit 102. This constant voltage drive circuit includes a drive timing pulse (drive timing signal) ST
B 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. Are 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 is applied to the connection point a via the diode Dk.

The connection point a is connected to the transistors Tr3 to Tr3.
The base of the transistor Tr3, which is the input side of the low impedance output circuit 104 composed of Tr6, and the transistor T
The common electrode Com of the inkjet head H is connected between the emitter of the transistor Tr5 and the collector of the transistor Tr6 on the output side.

In this constant voltage drive circuit, when drive timing pulse STB is input to input terminal IN and "H" level is input to buffer B, buffer B outputs a voltage level lower than power supply voltage Vpp. As a result, the transistor Tr1 is turned on, the inverter I becomes "L", and the transistor Tr2 is turned off. Therefore, the charging of the capacitor Ck is started with the charging time constant determined by the charging resistor Ra and the capacitor Ck by the power supply voltage Vpp. You.

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 +
Vd) and the drive voltage V
It becomes the maximum value of p (Vp = Vout + Vd).

When the drive timing pulse STB 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.
As a result, the transistor Tr1 is turned off, while the output of the inverter I is inverted with respect to the output of the buffer B. Therefore, the transistor Tr1 is turned off and the transistor Tr2 is turned on at the same time. The discharging of the capacitor Ck charged to the voltage Vp with the determined discharging time constant starts.

Therefore, the voltage V of the constant voltage driving circuit
By changing out, the drive voltage Vp of the drive waveform P can be controlled. Therefore, a circuit configuration for generating and outputting the voltage level Vout for changing the drive voltage Vp will be described with reference to FIGS. 6 and 14 described above.

This circuit comprises a three-terminal regulator 111 and a resistance selection circuit 112. Three-terminal regulator 11
1, a resistor R1a connected between the adjustment terminal adj and the voltage output terminal Vout and a resistance value R2 of the resistor selection circuit 112 connected between the adjustment terminal adj and the ground by supplying a constant voltage source to the voltage input terminal VIN. Is output from the voltage output terminal Vout. For example, LM317T (trade name) manufactured by National Semiconductor can be used. Therefore, the output voltage Vout from the three-terminal regulator 111 is, for example, Vo
ut = 1.25 × (1 + R2 / R1).

The resistor selection circuit 112 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 112 includes the control signal generator 10 described above.
The Vp control signals SVp1 to SVp3 from 1 are input to the bases of the transistors Q1 to Q3, respectively.

Therefore, the power supply voltage Vpp is supplied to the three-terminal regulator 111 and the control signal generator 102
To the resistor selection circuit 112, the output voltage Vout of the three-terminal regulator 111 can be changed at up to eight different levels, and the output voltage Vout is changed to the above-described constant voltage. By inputting as the voltage Vout of the drive circuit, the drive voltage Vp of the drive waveform P can be changed.

That is, as shown in FIG. 15A, the control signal
The drive timing signal STB is set to "H" three times within the repetition period Tc for a predetermined time to the input terminal IN of the waveform generation circuit 103 shown in FIG. At the same time, while the drive timing signal STB is first set to “H” within the repetition period Tc from the control signal generation unit 101, FIG.
By setting the Vp control signal SVp1 to "H" as shown in FIG.
As shown in FIG. 7, a voltage Vout that defines the drive voltage Vp as the voltage Vp1 is output.

Similarly, while the drive timing signal STB is set to "H" for the second time within the repetition period Tc from the control signal generator 101, the Vp control signal SVp2 is set to "H" as shown in FIG. , The voltage Vout that regulates the drive voltage Vp to the voltage Vp2 is output from the three-terminal regulator 111, as shown in FIG.
While the drive timing signal STB is set to “H” for the third time, the Vp control signal SVp3 is set to “H” as shown in FIG.
The drive voltage Vp is changed to the voltage Vp as shown in FIG.
3 is output.

Accordingly, a drive waveform group consisting of drive waveform P1 of drive voltage Vp1, drive waveform P2 of drive voltage Vp2, and drive waveform P3 of drive voltage Vp3 is output from waveform generation circuit 103 at a repetition period Tc, and a low impedance output is provided. This is applied to the piezoelectric element PZT via the circuit 104.

The different voltage Vout is generated by, for example, connecting a resistor R1 and a parallel circuit of a variable resistor R2 and a capacitor C in series as shown in FIG. 16 and outputting the voltage across the capacitor C as a voltage Vout. It is also possible to change the variable resistor R2 by using a voltage dividing circuit configured to perform this operation.

In the above embodiment, different driving voltages Vp are used as a driving waveform group including n different driving waveforms.
Drive waveforms P1, P2, P3 having 1, Vp2, Vp3
Is applied to the piezoelectric element PZT of each channel. In general, in an ink jet head, the shorter the rising time constant tr of the driving waveform, the larger the ink droplet ejection amount Mj and the larger the ink droplet ejection speed Vj. Will also be faster.
Therefore, n (here, three) different start-up time constants tr1, tr2, tr3 (tr1> tr
2> tr3) drive waveforms P1 ′, P2 ′, P3 ′
The same operation and effect as described above can be obtained by using.

Now, a circuit example of a constant voltage driving circuit capable of varying the rising time constant tr of the driving waveform will be described with reference to FIG. This constant voltage driving circuit is the same as that shown in FIG.
In the constant voltage driving circuit shown in FIG. 1, the charging resistors Ra1, Ra2, R3 are connected in series with the diode D1.
a3 are connected in parallel, and these charging resistors Ra1, Ra
2, Ra3 and the power supply voltage Vpp, switching transistors Tr11, Tr12, Tr13 are connected 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 pulse STB is input via gate circuits G1, G2, and G3. These gate circuits G1, G
2 and G3 are opened when the tr control signals Str1, Str2 and Str3 from the control signal generator 101 are "H", respectively, and output the drive timing pulse STB to the buffers B1, B2 and B3.

Therefore, the control signal generator 101 sets the drive timing pulse STB to “H” and sets any one of the 3-bit tr control signals Str1, Str2, and Str3 to “H”, whereby the tr control signal Str
Buffers B1, B selected in 1, Str2, Str3
2 and B3 output a voltage level lower than the power supply voltage Vpp, and the corresponding transistors Tr11 and Tr1 are output.
2, Tr13 is turned on, and the capacitor Ck is charged with the start-up time constant tr determined by any of the selected resistors Ra1 to Ra3 and the capacitor Ck.

Therefore, a maximum of 8
Since the capacitor Ck can be charged with the different start-up time constants tr, for example, as shown in FIG. 18, the start-up time constants tr are three types of driving waveforms P1 ′, P2 ′, tr1, tr2, and tr3, respectively. P3 ′ can be generated and output with a repetition period Tc.

In this case, the drive voltage Vp of the drive waveform
Can be fixed or can be varied using the circuit shown in FIG. 14 or FIG. 16 described above. If the voltage Vout is made variable, the rising time constant as shown in FIG. A plurality of drive waveforms having different tr and drive voltage Vp, for example, drive waveform P1 ″ of drive voltage Vp1 with time constant tr1, drive waveform P2 ″ of drive voltage Vp2 with time constant tr2, and drive voltage Vp3 with time constant tr3 The waveform P3 ″ can be generated and output.

The configuration and the drive waveform of the head drive circuit are not limited to those in the above-described embodiment, as long as ink droplets can be stably ejected.
Any shape such as a (sine) waveform may be used.

[0095]

As described above, according to the head driving circuit of the first aspect, a waveform generating means for generating a driving waveform group consisting of n different driving waveforms and outputting the group to the common electrode of the ink jet head; Selection means for selecting one or more drive waveforms from the drive waveform group and applying the selected drive waveforms to the electromechanical transducer of the inkjet head, so that different amounts of ink droplets can be ejected with a simple configuration, A gradation image can be obtained at low cost.

According to the head drive circuit of the second aspect, in the head drive circuit of the first aspect, the selection means has a shift register having the same number of bits or more as the number m of nozzles of the ink jet head, and repeats the drive waveform group. (M
× n) The nozzle selection data of bits is transferred to the shift register, and the nozzles to be driven at the respective timings of the n driving waveforms are selected, so that the driving waveform is applied without adding a special circuit. A mechanical conversion element can be selected, and the cost can be further reduced.

According to the head drive circuit of the third aspect, in the head drive circuit of the first or second aspect, the waveform generating means can adjust the voltage value of the generated drive waveform and / or the rise time of the drive waveform. With such a configuration, the dot diameter and / or the dot formation position can be varied and controlled with high precision.

According to the head drive circuit of the fourth aspect, in the head drive circuit of any one of the first to third aspects,
N constituting a driving waveform group output from the waveform generating means
The delay time td (k) of each drive waveform is d, the distance between the nozzle and the recording paper surface, Vc is the moving speed of the head in the main scanning direction, and Vj is the ejection speed of the ink droplet ejected by the kth drive waveform. When (k) is set, the configuration satisfying the expression (1) is satisfied. Therefore, even if the ink droplet ejection speed is different due to the different ink droplet ejection amount, the ink droplet landing position by each drive waveform is within the pixel pitch. Thus, the image quality when one pixel is formed by a dot matrix can be improved.

According to the head drive circuit of claim 5, in the head drive circuit of any one of claims 1 to 3,
N constituting a driving waveform group output from the waveform generating means
The delay time td (k) of each drive waveform is d, the distance between the nozzle and the recording paper surface, Vc is the moving speed of the head in the main scanning direction, and Vj is the ejection speed of the ink droplet ejected by the kth drive waveform. When (k) is adopted, the configuration satisfying the above formula (2) is satisfied, so that even if the ink droplet ejection speed is different due to the different ink droplet ejection amount, the ink droplet landing position by each drive waveform is substantially the same position. It is possible to form a gradation image by superimposing a plurality of ink droplets to form dots having different diameters, and to obtain a high gradation and high resolution image without lowering the pixel density.

According to the ink jet recording apparatus of the present invention, a plurality of nozzles for ejecting ink droplets and a plurality of electromechanical transducers corresponding to each nozzle are provided, and one electrode of each electromechanical transducer is common. 5. An ink jet head comprising: a common electrode; and the other electrode is an individual electrode which is individualized for each electromechanical transducer, and the head drive circuit according to claim 1; And at least one drive waveform is selected from the drive waveform group consisting of: forming a plurality of dots in the main scanning direction by ejecting a plurality of ink droplets; Since it was configured to be formed with the maximum (n × h) dots,
A gradation image can be formed with a nozzle arrangement density wider than the pixel pitch.

According to the ink jet recording apparatus of the present invention, a plurality of nozzles for ejecting ink droplets and a plurality of electromechanical transducers corresponding to each nozzle are provided, and one electrode of each electromechanical transducer is common. And an ink jet head which is individualized for each electromechanical transducer and is used as an individual electrode, and the head drive circuit according to any one of claims 1 to 3, and n. The drive waveforms differed in the corresponding ink droplet ejection volumes, and the landing positions were almost matched to form dots with different diameters by superimposing one or more ink droplets. A high-gradation, high-resolution image can be formed without lowering.

[Brief description of the drawings]

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

FIG. 2 is a schematic side view of a mechanism section of the recording apparatus.

FIG. 3 is an exploded perspective view of an ink jet head constituting a recording head of the recording apparatus.

FIG. 4 is an explanatory sectional view of the inkjet head.

FIG. 5 is an explanatory cross-sectional view of the inkjet head in a direction orthogonal to FIG. 4;

FIG. 6 is a block diagram of a head drive control unit according to the present invention.

FIG. 7 is a block diagram of a channel selection circuit of the head drive circuit.

FIG. 8 is a timing chart for explaining the head drive control unit;

FIG. 9 is an enlarged timing chart of a main part showing an enlarged main part of FIG. 8;

FIG. 10 is an explanatory diagram for explaining an example of gradation image recording by the head drive control unit;

FIG. 11 is an explanatory diagram for explaining an ink droplet landing position in the first example;

FIG. 12 is an explanatory diagram for explaining another example of gradation image recording by the head drive control unit;

FIG. 13 is a main part circuit diagram showing an example of a constant voltage drive circuit of the head drive control unit.

FIG. 14 is a block diagram illustrating an example of a voltage Vout generation unit of the identification voltage drive circuit.

FIG. 15 is a timing chart for explaining the operation of the voltage Vout generation unit;

FIG. 16 is a block diagram showing another example of the voltage Vout generation unit of the identification voltage drive circuit.

FIG. 17 is a circuit diagram showing another example of the constant voltage drive circuit of the head drive control circuit.

18 is an explanatory diagram for explaining the operation of the circuit in FIG. 17;

FIG. 19 is an explanatory diagram for explaining still another example of the constant voltage driving circuit of the head drive control circuit;

[Explanation of symbols]

4 ... carriage, 5 ... recording head, 16 ... platen, 3
4 ... Sub-scanning motor, 42 ... Piezoelectric element, 44 ... Drive section, 5
4 ... Nozzle, 59 ... Pressurized liquid chamber, 100 ... Head drive circuit, 101 ... Control signal generator, 102 ... Constant voltage drive circuit, 103 ... Waveform generation circuit, 104 ... Low impedance output circuit, 105 ... Channel selection circuit, 106: shift register, 107: latch circuit, 108: gate circuit group, 109: transistor array, 110: diode array, 111: three-terminal regulator, 112: resistor selection circuit, H: inkjet head.

Claims (7)

[Claims] A plurality of nozzles for ejecting ink droplets; and a plurality of electromechanical transducers corresponding to the respective nozzles. One electrode of each of the electromechanical transducers is commonly used as a common electrode, and the other electrode is used as a common electrode. In a head drive circuit that drives an ink jet head that is individualized for each electromechanical conversion element and is an individual electrode, a waveform generation unit that generates a drive waveform group including n different drive waveforms and outputs the generated drive waveform group to the common electrode; And a selecting means for selecting one or more drive waveforms from the group of drive waveforms and applying the selected drive waveform to the electromechanical transducer. 2. The head drive circuit according to claim 1, wherein said selection means has a shift register having the same number of bits or more as the number m of nozzles of said ink jet head, and (m) for each repetition period of said drive waveform group. × n) bits of nozzle selection data are transferred to the shift register,
A drive circuit for a head, wherein a nozzle to be driven at each timing of each of the drive waveforms is selected. 3. The head drive circuit according to claim 1, wherein said waveform generating means is capable of adjusting a voltage value of a generated drive waveform and / or a rise time of the drive waveform. Drive circuit. 4. The head drive circuit according to claim 1, wherein each of the delay times td (k) of the n drive waveforms constituting the drive waveform group output from the waveform generating means is When the distance between the nozzle and the recording paper surface is d, the moving speed of the head in the main scanning direction is Vc, and the ejection speed of the ink droplet ejected by the k-th drive waveform is Vj (k), the following (1) A head drive circuit characterized by satisfying the following expression. (Equation 1) 5. The head drive circuit according to claim 1, wherein each of the delay times td (k) of the n drive waveforms constituting the drive waveform group output from the waveform generating means is When the distance between the nozzle and the recording paper surface is d, the moving speed of the head in the main scanning direction is Vc, and the ejection speed of ink droplets ejected by the k-th drive waveform is Vj (k), the following (2) A head drive circuit characterized by satisfying the following expression. (Equation 2) 6. A plurality of nozzles for ejecting ink droplets, and a plurality of electromechanical transducers corresponding to the respective nozzles, one electrode of each electromechanical transducer is shared and used as a common electrode, and the other electrode is used as a common electrode. A head drive circuit according to any one of claims 1 to 4, comprising: an ink jet head that is individualized for each electromechanical transducer, and a head drive circuit according to claim 1; At least one or more drive waveforms are selected, a plurality of ink droplets are ejected to form a plurality of dots in the main scanning direction, and sub-scanning is performed h times to maximize one pixel (n × h). An ink jet recording apparatus formed by dots. 7. A plurality of nozzles for ejecting ink droplets, and a plurality of electromechanical transducers corresponding to the respective nozzles, wherein one electrode of each electromechanical transducer is shared and used as a common electrode, and the other electrode is used as a common electrode. A head drive circuit according to any one of claims 1 to 3, and an ink jet head that is individualized for each electromechanical conversion element to be an individual electrode;
An ink-jet printing method wherein n drive waveforms have different ink droplet ejection volumes and have substantially the same landing positions to form dots having different diameters by superimposing one or more ink droplets. Recording device.