JPH1158779A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the image quality by applying a driving waveform of such magnitude as causing no jetting of ink drop entirely to a plurality of energy generating elements for jetting an ink drop from a nozzle thereby suppressing fluctuation in the dot diameter while preventing the printing speed from lowering. SOLUTION: After finishing the line feed or reset operation of a carriage and before starting print operation, the non-jet drive waveform (pulse train) of a drive waveform in a head drive circuit is selected by a control signal and applied to each piezoelectric element of all nozzles. The non-jet drive waveform is a pulse train having a period of about 800 μs and a voltage of about 10 V. Since an energy generating means, i.e., the piezoelectric element 32, is displaced by an elongation δ, a faint vibration is applied in the arrow direction to an ink having increased viscosity in an nozzle 36 and the viscosity of ink is decreased.

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 for printing a high quality 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, etc., a plurality of nozzles for discharging ink droplets, an ink liquid chamber communicating with each nozzle, and ink in each ink liquid chamber are formed. An ink-jet head provided with an energy generating means such as an electromechanical conversion element such as a piezoelectric element or an electrothermal conversion element such as a heater for generating energy for discharging ink droplets from the nozzle by pressurization is mounted on a carriage. The paper is transported in the sub-scanning direction while moving the carriage in the main scanning direction, and the energy generation means of the head is driven in accordance with the print data, thereby discharging ink droplets from required nozzles and recording an image on the paper. There is a serial type ink jet recording apparatus.

In a serial type ink jet recording apparatus, a recording head for ejecting ink droplets of a plurality of colors and an ink cartridge for supplying ink of the recording head are mounted on a carriage, and the carriage is moved in the main scanning direction. 2. Description of the Related Art A color recording apparatus that records a color image on a sheet by ejecting ink droplets of a desired color from a recording head while scanning and feeding the sheet in the sub-scanning direction is generally used.

In an ink-jet recording apparatus, a recording head is configured to drive the ink-jet head at a high frequency in order to increase the recording speed, and the scanning speed of the carriage is also increased to be mounted on the carriage. The acceleration applied to the print head and ink cartridge increases, and the acceleration acts on the ink held in the print head and ink cartridge, causing pressure fluctuations. Is declining.

For this reason, as described in, for example, JP-A-6-99594, when a plurality of recording heads are provided, there is a mode in which one of the recording heads is used alone.
A means for selecting a mode in which a plurality of print heads are used in combination is provided. According to the result of the mode selection, when printing is performed only with a print head having a large allowable range of the head difference, the carriage is rapidly accelerated and decelerated for printing. When the print speed is increased and print heads with a small tolerance of the water head are mixed, the printing speed is reduced by slowing down the acceleration and deceleration of the carriage.
In some cases, defective ink droplet ejection due to pressure fluctuation is prevented.

[0006]

However, when a plurality of recording heads for ejecting ink droplets of a plurality of colors are used together as in the above-described conventional ink jet head, the printing speed is reduced by slowing the acceleration and deceleration of the carriage. Is controlled, the image quality can be maintained, but the printing speed decreases when a plurality of recording heads are used, such as in a color image.

[0007] Further, variation in dot diameter also occurs depending on a printed image. That is, the duty differs for each of a plurality of nozzles depending on a print image. For example, in the case of a character image, the nozzles at both ends have very low duty, so if printing is performed without performing the reliability maintenance recovery operation for a long time, the duty The ink in the nozzle having a low ink is dried because new ink does not enter for a long time, and the ink viscosity increases. Therefore, even if the same ink droplet ejection energy is applied, the ejection amount of ink droplets from nozzles with high ink viscosity decreases, and the dot diameter differs from the dot diameter of ink droplets from other nozzles, causing variations in dot diameter. I do. This can be dealt with by frequently repeating the reliability maintenance / recovery operation, but a reduction in printing speed cannot be avoided.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to improve the image quality by reducing the variation in dot diameter while suppressing the reduction in printing speed.

[0009]

According to another aspect of the present invention, there is provided an ink jet recording apparatus comprising: a plurality of nozzles for ejecting ink droplets; a plurality of ink liquid chambers communicating with the nozzles; In an ink jet recording apparatus in which an ink jet head having a plurality of energy generating elements for generating energy for discharging ink droplets from the nozzles by pressurizing ink in a liquid chamber is mounted on a carriage, all of the plurality of energy generating elements are And a means for giving a drive waveform that does not eject ink droplets.

According to a second aspect of the present invention, in the inkjet recording apparatus of the first aspect, immediately after the carriage starts a line feed or return operation and immediately before the start of printing.
The configuration is such that a drive waveform that does not eject the ink droplet is given.

According to a third aspect of the present invention, in the inkjet recording apparatus of the first aspect, the ink droplets are not ejected at a timing when a pressure fluctuation generated by an acceleration operation of the carriage to start printing substantially reaches a peak. The driving waveform is given.

According to a fourth aspect of the present invention, there is provided the ink jet recording apparatus according to the third aspect, wherein the driving waveform that does not discharge the ink droplet has a substantially peak pressure fluctuation generated by an acceleration operation of the carriage to start printing. The pressure is a waveform that generates a pressure having substantially the same peak value in the ink liquid chamber.

According to a fifth aspect of the present invention, there is provided the ink jet recording apparatus according to the third or fourth aspect, wherein
The drive waveform that does not eject the ink droplet has a configuration in which the rise time is short, the fall time is long, and the rise time and the fall time are long compared to the drive waveform that ejects the ink droplet. .

[0014]

Embodiments of the present invention will be described below 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, FIG. 2 is a schematic perspective view of a main part of FIG. 1, and FIG. 3 is a schematic cross-sectional view of a main part of FIG.

In this ink jet recording apparatus, the carriage 5 is moved in the 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 ink is applied to the recording head 6 on the upper surface side of the carriage 5. An ink tank (ink cartridge) 7 for supply is mounted.

The recording head 6 includes a yellow (Y) ink,
Four heads that eject magenta (M) ink, cyan (C) ink, and black (Bk) ink are arranged in the main scanning direction. In order to supply each color ink to these heads, the ink tank 7 also includes four ink tanks of each color.

The carriage 5 is driven by a driving pulley 9 rotated by a main scanning motor 8 comprising a stepping motor.
Belt 1 stretched between the motor and the driven pulley 10
1, the carriage 5, that is, the recording head 6, is moved in the main scanning direction by controlling the driving of the main scanning motor 8.

On the other hand, a platen roller (hereinafter, simply referred to as "platen") 15 for transporting the paper 14 in the sub-scanning direction (the direction indicated by the arrow B in FIG. 2), and the paper 14 is disposed by being pressed against the peripheral surface of the platen 15. The paper feed rollers 16, 17 and the pinch roller 18 defining the paper feed angle, the guide plate 19 facing the recording head 6, the paper discharge roller 20 downstream of the recording head 6 in the paper transport direction, and the paper discharge roller 20. And a spur roller 21 for pressing the sheet pressed against the sheet.

The rotation of the sub-scanning motor 23, which is a stepping motor, is transmitted to the platen 15 via the gears 24 to 26 and the platen gear 27, and the platen 15 is driven to rotate.
4 is fed between the recording head 6 and the guide plate 19 through the platen 15, the paper feed rollers 16, 17 and the paper pressing roller 18, and the platen 15 feeds the paper 14 by a predetermined amount, and the gear meshes with the platen gear 27. The paper 14 is sent out in the paper discharging direction (the direction indicated by the arrow B in FIG. 2) by the paper discharging roller 20 and the paper pressing spur roller 21 rotated via 29.

In the recording apparatus thus configured, the paper 14 is conveyed in the sub-scanning direction while moving and scanning the recording head 6 (carriage 5) in the main scanning direction, and ink droplets are ejected from the nozzles of the recording head 6. By injecting,
A required color image is recorded on the paper 14.

In this ink jet recording apparatus, a reliability maintenance / recovery mechanism (sub system) 30 for the recording head 6 is disposed on the right side of the main scanning area of the carriage 5 so that the host 5 is in a print standby state. When the print data is not transferred from the side for a predetermined 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, the ink jet head constituting the recording head 6 will be described with reference to FIG. In the inkjet head, a plurality of piezoelectric elements 32, which are laminated piezoelectric elements, are arranged and joined on an insulating substrate 31 made of ceramic, glass epoxy resin, or the like, to form a drive unit 33.

Then, on this drive unit 33, Ni
A diaphragm 34 manufactured by an electroforming method or the like, a liquid chamber partition member 35 made of a photosensitive resin film (DFR) or the like, and a nozzle 3
A liquid chamber unit 38 is formed by sequentially laminating and joining the nozzle forming members 37 manufactured by the Ni electroforming method or the like in which the nozzles 6 are formed.

The pressure plate 40 corresponding to each piezoelectric element 32 and the common ink chamber 41 located on both sides of the pressure chamber 40 are formed by the vibrating plate 34, the liquid chamber partition member 35, and the nozzle forming member 37 of the liquid chamber unit 38. An ink supply path 42 for supplying ink from each common ink chamber 41 to the pressure chamber 40 is formed. An ink supply pipe 43 is connected to supply ink to the common ink chamber 41. The ink supply pipe 43 is connected to the ink cartridge 7 as shown in FIG. The ink cartridge 7 has a structure in which ink is absorbed in a porous body 7a such as a urethane foam body as shown in FIG.

The ink-jet head formed by joining the drive unit 33 and the liquid chamber unit 38 is housed in a head case 44, in which the piezoelectric element 32 is driven in accordance with an image signal. The drive circuit 45 is also accommodated. The driving circuit 45 applies a common voltage to the common electrodes of the plurality of piezoelectric elements 32, 32,.
7 is applied to each of the selection electrodes of the plurality of piezoelectric elements 32, 32,... In accordance with the image signal to selectively drive the plurality of piezoelectric elements 32, 32,. .

The operation of the ink-jet head will be described with reference to FIG. 5. As shown in FIG. 5A, in the steady state of the pressure chamber 40, the meniscus 49 due to the surface tension of the ink It is formed on the ink ejection side, and the surface tension of the ink and the ink internal pressure are balanced. In this state, by applying a drive waveform (pulse voltage of 10 to 50 V) to the selection electrode of the piezoelectric element 32 in accordance with the image signal, the piezoelectric element 32 is displaced in the arrow δ direction (stacking direction) shown in FIG. As a result, the internal volume of the pressure chamber 40 decreases through the vibration plate 34, the pressure in the pressure chamber 40 increases, and ink droplets are ejected from the nozzle 36, as shown in FIG.

With the end of the ink droplet ejection, the ink pressure in the pressure chamber 40 decreases, and the inertia of the ink flow and the discharge process of the drive pulse (drive waveform) cause the pressure chamber 40 to discharge.
And a transition to the ink filling process occurs. At this time, the ink supplied from the ink cartridge 7 via the ink supply pipe 43 flows into the common ink chamber 41,
The pressure chamber 4 from the common ink chamber 41 via the ink supply path 42
Filled into zero. Then, the vibration of the ink meniscus surface at the outlet of the nozzle 36 is attenuated, and after returning to a steady state to some extent, the operation shifts to the next ink droplet ejection operation.

Next, a head drive control device for controlling the driving of the piezoelectric element (drive unit) of the recording head in the ink jet recording apparatus will be described with reference to FIGS. The inkjet head H has a plurality of (m) nozzles (the number of nozzles is assumed to be m = 64) for ejecting the above-described ink droplets, and 64 piezoelectric elements (PZT), which are electromechanical conversion elements corresponding to each nozzle. 32, and one electrode of each of the piezoelectric elements 32 is commonized to be a common electrode Com,
The other electrode is individualized for each piezoelectric element 32 to form an individual electrode (selection electrode) SEL.

On the other hand, the head drive control device for controlling the drive of the ink jet head H comprises a head drive circuit 60 and a main control section 61 for supplying a control signal and the like to the head drive circuit 60. The main control unit 61 is constituted by a microcomputer or the like that controls the entire operation of the inkjet recording apparatus, and outputs a drive timing signal STB that determines a timing for generating and outputting a drive waveform, and a drive voltage (voltage value) Vp of the drive waveform. Vp control signal S for selection
Vp1 and SVp2, tr control signals Str1 and Str2 for selecting the rising time constant tr of the driving waveform, tf control signals Stf1 and Stf2 for selecting the falling time constant tf of the driving waveform, the print data signal DI, etc. It is given to the drive circuit 60.

The head drive circuit 60 receives a drive timing signal (pulse) STB from the main control section 61 and generates and outputs a drive waveform P to be applied to the ink jet head H. The waveform generation circuit 63 And a low-voltage output circuit 64 for outputting the output of the inkjet head H to the common electrode Com, and a plurality of piezoelectric elements of the inkjet head H based on a print data signal DI from the main control unit 61. Channel (c) for providing selection signals Do1 to Do64 to
h) a selection circuit 65;

Waveform generation circuit 63 of constant voltage drive circuit 62
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, or a clamp circuit. The waveform generation circuit 63 receives the drive timing signal S from the main control unit 61 described above.
TB, Vp control signals SVp1, SVp2, tr control signals Str1, Str2, tf control signals Stf1, Stf2
Is entered.

The low impedance output circuit 64
Buffer amplifier, SEPP (Single Ended Push)
Pull) and the like. By using the low impedance output circuit 64, the output of the driving waveform becomes a low impedance output to the piezoelectric element 32, and the waveform is not distorted due to the variation of the piezoelectric element and the difference in the number of driving channels.

Here, an example of the waveform generating circuit 63 and the low impedance output circuit 64 in the constant voltage driving circuit 62 will be described with reference to FIG. This constant voltage drive circuit 62
An input terminal IN to which a drive timing pulse (drive timing signal) STB is supplied 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 collector of the transistor Tr1 is connected to a power supply. The voltage Vpp is applied, and 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 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 64 composed of the transistor Tr6 and the transistor Tr
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 62, a drive timing pulse STB is input to an input terminal IN,
When "H" level is input to buffer B, buffer B
Outputs a voltage level lower than the power supply voltage Vpp, turning on the transistor Tr1.
And the transistor Tr2 is turned off, so that charging of the capacitor Ck is started with a charging time constant determined by the charging resistor Ra and the capacitor Ck by the power supply voltage Vpp.

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 drive voltage Vp of the drive waveform can be variably controlled by changing the voltage Vout applied to the waveform generation circuit 63 of the constant voltage drive circuit 62.

The circuit configuration of the Vp control unit that generates and outputs the voltage Vout that defines the drive voltage Vp will be described with reference to FIG. The voltage Vout generator includes a three-terminal regulator 71 and a resistance selection circuit 72. By supplying a constant voltage source to the voltage input terminal Vin, the three-terminal regulator 71 provides a resistance R1a connected between the adjustment terminal adj and the voltage output terminal Vout and a resistance R1a of the resistance selection circuit 72 connected between the adjustment terminal adj and the ground. A voltage corresponding to the value R2 is output from the voltage output terminal Vout. For example, LM317T (trade name) manufactured by National Semiconductor
Etc. can be used. Therefore, the output voltage Vout from the three-terminal regulator 71 is, for example, Vout
= 1.25 × (1 + R2 / R1).

The resistor selection circuit 72 includes a resistor Rs and a resistor R
A parallel circuit of p and resistors R21 and R22 selected by the switching transistors Q1 to Q3 is connected in series, for example, SN7406 manufactured by Texas Instruments.
(Product name) or the like. The resistance selection circuit 72 includes Vp from the main control unit 61 described above.
Control signals SVp1 and SVp2 are applied to transistors Q1 and Q2.
Each is entered in the base.

Therefore, the power supply voltage Vpp is supplied to the three-terminal regulator 71, and the 2-bit Vp control signals SVp1 and SVp2 are supplied from the main control unit 61 to the resistance selection circuit 7.
2, the output voltage Vout of the three-terminal regulator 71 can be changed at a maximum of eight different levels.
By inputting as the voltage Vout of 2, the drive voltage Vp of the drive waveform can be set to a predetermined value.

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 between both ends of the capacitor is output as the voltage Vout. Thus, it is also possible to change the variable resistance.

Next, the channel selection circuit 65 will be described with reference to FIG. This channel selection circuit 65
Is a 64-bit shift register 81 that is at least the same number of bits as the number m of nozzles (here, m = 64) for taking in the serial input SI with the clock CLK, and the register value of the shift register 81 is latched by a latch signal / LAT. (Note that the sign “/” means inversion.) A 64-bit latch circuit 82 that latches the data at one end, the output of the latch circuit 82 as one input, and the drive timing signal / STB is input to the knot circuit NG
A gate circuit group 83 including a gate circuit G corresponding to each of the piezoelectric elements PZT to be the other input through
2, a transistor array 84 composed of transistors Q that are turned on / off by the output of each gate circuit G, and a diode array 85 composed of diodes D connected to each transistor Q.

Then, the print data signal DI input as the serial input SI in response to the clock signal CLK is taken into the shift register 81, and the latch circuit 82 latches the current take-in signal of the shift register 81 by the latch signal / LAT. When the required gate circuit G is opened by the drive timing signal / STB from the main control unit 61 to turn on the transistor Q, the selection signal Don (n = 1 to
64) to drive the piezoelectric element 32 by applying the drive waveform from the low impedance output circuit 64 to the piezoelectric element 32.

Next, the operation of the thus configured ink jet recording apparatus will be described with reference to FIGS. As described above, as a result of the duty being different for each of a plurality of nozzles depending on the print image, when printing is performed without performing the long-term reliability maintenance / recovery operation, the ink in the nozzles with low duty contains new ink for a long time. Since the ink does not come dry, the ink viscosity increases, and as a result, the dot diameter varies.

FIG. 10 shows the result of measuring the change in dot diameter from the start of printing for each nozzle. As shown in the figure, the variation in the dot diameter of each nozzle at the start of printing (dot no. 1) is large, and the dot no. From 2 onward, it can be seen that the variation in the dot diameter for each nozzle becomes smaller. This is because, in the case of ink having an increased viscosity, the required ejection energy is increased. Therefore, when the same ejection energy is applied, the ejection amount of the ink droplet is reduced and the dot diameter is reduced.
Then, after the first ink droplet is ejected, ink having a high viscosity disappears from the nozzles, so that the variation in the dot diameter between the nozzles is reduced.

Therefore, in this ink jet recording apparatus, a drive waveform is applied to the piezoelectric elements PZT of all the nozzles so that ink droplets are not ejected before the start of printing after the carriage returns or the return operation is completed. .

That is, in the above-described head drive circuit 60, the voltage Vp1 of the drive waveform is set to a voltage for ejecting ink droplets (this drive waveform is referred to as an "ejection drive waveform"), and the voltage Vp2 is not ejected. (This drive waveform is referred to as a “non-ejection drive waveform”), and the voltage Vp1 of the drive waveform is applied by the Vp control signal SVp1.
Is selected, and the voltage Vp of the drive waveform is applied by the Vp control signal SVp2.
Select 2.

Therefore, before the carriage starts a line feed or return operation and before printing starts, the non-ejection drive waveform of the voltage Vp2 is selected by the Vp control signal SVp2, and this non-ejection drive waveform (pulse train) is applied to all nozzles. Applied to the piezoelectric element PZT. The non-ejection drive waveform has a voltage Vp2 with a period of about 800 μs, for example, as shown in FIG.
= A pulse train having a waveform of about 10V.

As a result, as shown in FIG. 12, the piezoelectric element 32, which is the energy generating means, is displaced by the amount of expansion δ ', and the ink whose viscosity is rising in the nozzle 36 undergoes micro-vibration in the direction indicated by the arrow. In addition, the viscosity of the ink whose viscosity has increased due to the fine vibration decreases. Thereby,
When printing is started, variations in dot diameter between nozzles are eliminated.

As described above, this ink jet recording apparatus is provided with a means for giving a drive waveform that does not eject ink droplets, that is, a non-ejection drive waveform, to all of the plurality of energy generating elements. Since the non-ejection drive waveform is applied immediately after the end and immediately before the start of printing, the first speed between the nozzles of each printing row can be reduced without causing a reduction in printing speed due to frequent repetition of the reliability maintenance recovery operation. The image quality can be improved by preventing variation in dot diameter.

Next, another embodiment of the present invention will be described with reference to FIGS. FIG. 13 is a circuit diagram showing a constant voltage driving circuit in this embodiment. This constant voltage driving circuit is different from the constant voltage driving circuit shown in FIG. 7 in that charging resistors Ra1 and Ra2 are connected in parallel as a charging resistor connected in series with a diode D1, and these charging resistors Ra1 and Ra2 are connected to a power supply. Switching transistors Tr11 and Tr12 are connected to the voltage Vpp, respectively.

Then, the transistors Tr11, Tr12
Are connected to buffers B1 and B2, respectively, and drive timing pulses STB are input to these buffers B1 and B2 via gate circuits G1 and G2. These gate circuits G1 and G2 are connected to the t
When the r control signals Str1 and Str2 are at "H", the drive timing pulse STB is opened and the buffer B1
Output to B2.

Therefore, the main control unit 61 sets the 2-bit t
By outputting the drive timing pulse STB in a state where one of the r control signals Str1 and Str2 is set to “H”, the buffers B1 and B2 selected by the tr control signals Str1 and Str2 are at a voltage lower than the power supply voltage Vpp. Output the level, and the transistors Tr11,
One of the transistors Tr12 is turned on, and the capacitor Ck is charged with a rising time constant tr determined by one of the selected resistors Ra1 and Ra2 and the capacitor Ck.

Therefore, two types of drive waveforms, the start time constants of which are tr1 and tr2, can be generated and output by the tr control signal.

The discharge resistors Rb1 and Rb2 are connected in parallel as discharge resistors connected in series with the diode D2, and these discharge resistors Rb1 and Rb2 are connected to the power supply voltage Vpp.
Between the switching transistors Tr2
1 and Tr22 are connected.

Then, the transistors Tr21, Tr22
Are connected to inverters I1 and I2, respectively.
Gate circuits G3, G4 are connected to these inverters I1, I2.
, A drive timing pulse STB is input. When the tf control signals Stf1 and Stf2 from the main control unit 61 are “L”, these gate circuits G3 and G4 respectively output the drive timing pulse STB as it is to the inverters I1 and ST4.
I2, and when the tf control signals Stf1 and Stf2 are "H", the output sides of the inverters I1 and I2 are set to "L" regardless of the drive timing pulse STB to open the transistors Tr21 and Tr22.

Therefore, the main control unit 61 sets the 2-bit t
By outputting the drive timing pulse STB in a state where one of the f control signals Stf1 and Stf2 is set to “L”, the corresponding transistor Tr2 is connected via the inverters I1 and I2 selected by the tf control signals Stf1 and Stf2.
1 and Tr22 are turned on, and the capacitor Ck is discharged with a fall time constant tf determined by one of the selected resistors Rb1 and Rb2 and the capacitor Ck.

Accordingly, two types of drive waveforms having fall time constants tf1 and tf2 can be generated and output by the tf control signal.

The operation of this embodiment is shown in FIG.
The description will be made with reference to the following. First, the carriage 5 is used to perform printing in the shortest distance printing mode (mode in which the carriage is moved from the stop position of the carriage to the printing dot position closer to the printing line in the bidirectional printing mode and printing is performed). When the carriage is temporarily stopped, accelerated, and then changed to a constant speed movement for printing, the carriage speed changes as shown in FIG. 14A.

When the acceleration generated by the movement of the carriage 5 and the change in the internal pressure of the ink cartridge 7 caused by the movement of the carriage 5 are measured, the results are as shown in FIGS. The internal pressure of the cartridge 7 was measured by installing a pressure sensor in the ink cartridge 7.

As can be seen from FIG.
Vibration caused by pressure wave
1 occurs. This residual vibration causes a change in the internal pressure of the recording head 6 (substantially equal to the internal pressure of the ink cartridge 7).

FIG. 15 shows the relationship between the residual vibration and the meniscus surface 49 of the ink jet head (recording head 6). In the portion of the residual vibration 51 shown in FIG. 14C, the pressure in the head becomes a positive pressure.
As shown in (a), the meniscus surface 49 is located at a position protruding from the discharge surface of the nozzle 36. Similarly, residual vibration 5
Since the pressure in the head becomes a negative pressure in the portion of 1, the meniscus surface 49 is at a position retracted from the discharge surface of the nozzle 36 as shown in FIG.

Further, in the portion of the residual vibration 51, the pressure in the head becomes a positive pressure, so that it protrudes from the discharge surface of the nozzle 36 of the meniscus surface 49 as shown in FIG. The projecting amount is smaller than that of Further, in the portion of the residual vibration 51, the pressure in the head becomes a negative pressure, so that the head is retracted from the discharge surface of the nozzle 36 of the meniscus surface 49 as shown in FIG. 4D, but the residual vibration is attenuated. , The amount of retraction is smaller than that of. Then, the state gradually shifts to a steady state as shown in FIG.

In addition, the paper (medium)
Imprinting accuracy (adjacent dot pitch accuracy) and dot diameter were measured. FIG. 16 shows a print sample obtained by this measurement, and FIG. 17 shows the measurement results of the adjacent dot pitch accuracy and the dot diameter. As can be seen from these figures, the adjacent dot pitch accuracy (adjacent dot position accuracy) is not significantly affected by the pressure fluctuation due to the movement of the carriage.
The dot diameter of the dots is greatly affected.

From the above, it can be inferred from the above that the meniscus surface 49 at the start of printing is at the position shown in FIG. 15A. At this time, when the driving pulse is applied to the energy generating means of the head, the meniscus in the steady state is obtained. It is considered that the volume of the ink droplet is increased since the ink droplet protrudes from the position (the position of FIG. 3E), and as a result, the diameter of the dot formed on the medium is also increased. After the ink droplet of the first dot is ejected, a pressure fluctuation due to the ejection occurs, and the pressure fluctuation is several times larger than the residual vibration caused by the movement of the carriage. Fluctuations in volume are also reduced.

Therefore, in this ink jet recording apparatus, a driving waveform (non-ejection driving waveform) that does not eject ink droplets at the timing when the pressure fluctuation generated by the acceleration operation of the start of printing of the carriage becomes substantially a peak is generated. This is given to a piezoelectric element which is an element.

That is, in the above-described head driving circuit, the ejection driving waveform is the voltage Vp1, the rising time constant tr
1, set to fall time constant tf1, non-ejection drive waveform is voltage Vp2, rise time constant tr2, fall time constant t
Set to f2. Here, Vp1> Vp2, tr1 <t
As r2, tf1 <tf2, and tr2 <tf2, the non-ejection drive waveform is a waveform having a short rise time, a long fall time, and a long rise time and fall time compared to the ejection drive waveform. I have.
Specifically, for example, it is set as shown in Table 1, and the non-ejection drive waveform is as shown in FIG.

[0070]

[Table 1]

Here, when a non-ejection drive waveform as shown in FIG. 18 is given to the piezoelectric element 32, the non-ejection drive waveform rises from time t1, and the pressure chamber 40 is opened by the nozzle 36 and the ink supply path. However, since the rise of the non-ejection drive waveform is relatively steep, a positive pressure wave is generated in the pressure chamber 40 as shown in FIG. Then, from time t2, the non-ejection drive waveform starts to fall, but since this rise is relatively gentle, the negative pressure wave generated in the pressure chamber 40 is small as shown in FIG.

Therefore, when pressure fluctuation I occurs due to the acceleration operation of the start of printing of the carriage as shown by the solid line in FIG. 20, the pressure fluctuation I shown by the dashed line in FIG. Opposite pressure waves of the same magnitude
By giving a non-ejection drive waveform that generates II,
Since the pressure fluctuation I and the pressure wave II cancel each other, the amplitude of the residual vibration 51 (see FIG. 14C) becomes an extremely small level.

As described above, by giving the non-ejection drive waveform at the timing when the pressure fluctuation generated by the acceleration operation at the start of the printing of the carriage becomes substantially peak, the pressure fluctuation can be canceled, and the same nozzle can be used. Variations in dot diameter can be reduced, image quality can be improved, and ink dripping on the nozzle surface can be prevented.

In this case, the non-ejection drive waveform is such that a pressure having substantially the same peak value as the pressure fluctuation generated by the acceleration operation at the start of printing of the carriage is generated in the ink liquid chamber. The variation can be canceled, the variation of the dot diameter in the same nozzle can be reduced, the image quality can be improved, and the dripping of the ink on the nozzle surface can be prevented.

As the non-ejection drive waveform, the rise time is short, the fall time is long, and
By using a waveform whose rise time and fall time are longer than the drive waveform for ejecting ink droplets, pressure is generated in the ink liquid chamber only to cancel the pressure fluctuation caused by the acceleration operation of the carriage to start printing. be able to.

The driving waveform is not limited to a rectangular pulse as in the above embodiment, but may be a triangular waveform or other waveforms.
It is also possible to use a shape such as an in (sine) waveform, and any waveform may be used as long as it can stably eject ink droplets. Also,
An electrothermal transducer may be used as an energy generating element instead of an electromechanical transducer such as a piezoelectric element.

[0077]

As described above, according to the ink jet recording apparatus of the first aspect, there is provided a structure including a means for providing a drive waveform that does not eject ink droplets to all of the plurality of energy generating elements. Therefore, it is possible to reduce variation in dot diameter and improve image quality.

According to the ink jet recording apparatus of claim 2, in the ink jet recording apparatus of claim 1,
Immediately before the start of printing after the carriage line feed or return operation is completed, it is desired to provide a drive waveform that does not eject ink droplets, so that the viscosity of the ink whose viscosity has increased can be reduced, and the dot diameter can be reduced. Variation is reduced, and image quality can be improved.

According to the ink jet recording apparatus of claim 3, in the ink jet recording apparatus of claim 1,
Since a drive waveform that does not eject ink droplets at the timing when the pressure fluctuation generated by the acceleration operation at the start of printing of the carriage substantially reaches a peak is given, it is possible to cancel the pressure fluctuation due to the acceleration operation, Variations in dot diameter for the same nozzle can be reduced, image quality can be improved, and ink dripping on the nozzle surface can be prevented.

According to the ink jet recording apparatus of claim 4, in the ink jet recording apparatus of claim 3,
The drive waveform that does not eject ink droplets is a waveform that generates a pressure in the ink liquid chamber having substantially the same peak value as the pressure fluctuation generated by the acceleration operation at the start of printing of the carriage. Pressure fluctuation can be canceled, fluctuation of dot diameter in the same nozzle can be reduced, image quality can be improved, and ink dripping on the nozzle surface can be prevented.

According to the ink jet recording apparatus of the fifth aspect, in the ink jet recording apparatus of the third or fourth aspect, the drive waveform that does not eject ink droplets has a short rise time, a long fall time, and Since the rise time and the fall time are longer than the drive waveform for ejecting ink droplets, pressure can be generated in the ink liquid chamber only to cancel the pressure fluctuation due to the acceleration operation of the carriage.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic sectional view of a main part of FIG. 1;

FIG. 4 is an exploded perspective view of the inkjet head.

FIG. 5 is an enlarged sectional view of a main part used for describing the operation of the inkjet head.

FIG. 6 is a block diagram of a head drive control device of the recording apparatus.

FIG. 7 is a circuit diagram showing an example of the constant voltage drive circuit of FIG.

FIG. 8 is a block diagram illustrating an example of a Vp control unit included in the waveform generation circuit.

FIG. 9 is a block diagram illustrating an example of a channel selection circuit of the head drive control device of FIG. 6;

FIG. 10 is an explanatory diagram for explaining a change in dot diameter;

FIG. 11 is an explanatory diagram illustrating an example of a non-ejection drive waveform in the printing apparatus.

FIG. 12 is an explanatory diagram for describing a micro vibration of the ink liquid chamber when the non-ejection drive waveform is given.

FIG. 13 is a circuit diagram showing a constant voltage driving circuit in another embodiment of the ink jet recording apparatus according to the present invention.

FIG. 14 is a diagram illustrating the relationship among carriage speed, acceleration, and pressure fluctuation.

FIG. 15 is an enlarged sectional view of a main part for explaining a relationship between a pressure fluctuation and a meniscus position.

FIG. 16 is an explanatory diagram illustrating an example of a printing pattern in the vicinity of first to tenth dots of a print line.

FIG. 17 is an explanatory diagram illustrating the measurement results of the adjacent dot pitch and dot diameter of each dot in FIG. 16;

FIG. 18 is an explanatory diagram for explaining a non-ejection drive waveform in the embodiment.

FIG. 19 is an explanatory diagram for explaining a change in pressure of the ink liquid chamber when the non-ejection drive waveform is given.

FIG. 20 is an explanatory diagram illustrating a relationship between residual vibration and a change in pressure of an ink liquid chamber when the same non-ejection drive waveform is given.

[Explanation of symbols]

5 carriage, 6 print head, 8 main scanning motor,
15: Platen, 23: Sub-scanning motor, 31: Substrate, 3
2 ... piezoelectric element, 33 ... drive unit, 34 ... vibrating plate, 3
5: liquid chamber partition member, 36: nozzle, 37: nozzle forming member, 38: liquid chamber unit, 60: head drive circuit, 61
.., A main control unit, 62, a constant voltage drive circuit, 63, a waveform generation circuit, 64, a low impedance output circuit, 65, a channel selection circuit, and H, an inkjet head.

Continued on the front page (72) Inventor Yoshihisa Ota 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (5)

[Claims] 1. A plurality of nozzles for discharging ink droplets, a plurality of ink liquid chambers communicating with the respective nozzles, and energy for generating ink for discharging ink droplets from the nozzles by pressurizing ink in each ink liquid chamber. An ink jet recording apparatus in which an ink jet head having a plurality of energy generating elements is mounted on a carriage, comprising means for giving a drive waveform that does not eject ink droplets to all of the plurality of energy generating elements. Inkjet recording apparatus. 2. An ink jet recording apparatus according to claim 1, wherein a drive waveform is provided to such an extent that said ink droplets are not ejected immediately before the start of printing after completion of a line feed or return operation of said carriage. Recording device. 3. The ink jet recording apparatus according to claim 1, wherein the drive waveform is such that the ink drop is not ejected at a timing when a pressure fluctuation generated by an acceleration operation of the carriage to start printing substantially reaches a peak. An inkjet recording apparatus characterized by the above-mentioned. 4. The ink jet recording apparatus according to claim 3, wherein the drive waveform such that the ink droplets are not ejected is substantially the same as the peak value of the pressure fluctuation generated by the acceleration operation of the carriage to start printing. An ink jet recording apparatus having a waveform for generating a pressure having a pressure in the ink liquid chamber. 5. The ink jet recording apparatus according to claim 3, wherein the drive waveform that does not discharge the ink droplet has a short rise time, a long fall time, and a drive that discharges the ink droplet. An ink jet recording apparatus characterized in that the rise time and the fall time are longer than the waveform.