JPH11991A - Ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the quality of images through the reduction of dispersion in the diameter of dots, by providing pressure generation means for generating pressure variation generated as the movement of a carriage and pressure variation of reversed polarity. SOLUTION: A voltage bimorph type pump 50 being displacement generation means for generating the displacement of ink is communication connected to an ink supply pipe. In the voltage bimorph type pump 50, a deformable partition wall member 54 is provided with has a bimorph oscillator 52 secured by an elastic mold 53 in a case member 51. The interior part of the case member 51 is defined into two chambers S1, S2, one of which is communicated to an ink supply pipe 43 via a pipe member 55. The voltage waveform of the bimorph oscillator 54 is applied on the voltage bimorph type pump 50. The bimorph oscillator 54 deforms in proportion to voltage so as to vary the inner volume of the chamber S1, thus generating displacement to ink in the ink supply pipe being communicated to the chamber S1 via the pipe member 55.

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 nozzle holes for discharging ink droplets, an ink liquid chamber to which each nozzle communicates, Using a recording head, an ink jet head having an energy generating means such as an electromechanical transducer or an electrothermal transducer for generating energy for discharging ink droplets from the nozzle holes by pressurizing the ink, to generate energy for the head. By driving the means in accordance with the print data, an ink droplet is ejected from a required nozzle to record an image.

In such an ink jet recording apparatus, a recording head for discharging 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 caused to scan in the main scanning direction. In general, a serial scan type color recording apparatus which records a color image on a sheet by ejecting ink droplets of a required color from a recording head while feeding the sheet in the sub-scanning direction is generally used.

In the ink jet recording apparatus, the ink jet head constituting the recording head is driven at a high frequency in order to increase the recording speed, and the scanning speed of the carriage is also increased.

[0005]

As described above, if the scanning speed of the carriage is increased in response to the demand for a higher recording speed, it is necessary to increase the carriage speed in a short time. However, as the rise time of the carriage speed is shortened, the acceleration applied to the recording head and the ink cartridge mounted on the carriage increases, and the acceleration acts on the ink held in the recording head and the ink cartridge to cause pressure fluctuation. Occurs.

[0006] When the pressure in the recording head or the ink in the ink cartridge is changed due to the acceleration, the ink droplet ejection characteristics when ejecting minute ink droplets vary, and particularly, the dot diameter of the first dot is reduced. And the image quality deteriorates. In addition, the meniscus of the ink protrudes from the nozzle hole due to the pressure fluctuation, causing ink dripping on the nozzle surface, which easily causes the paper to become dirty.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has improved image quality by reducing variations in dot diameter due to pressure fluctuations caused by movement of a carriage, and ink dripping on nozzle surfaces due to pressure fluctuations. The purpose is to prevent.

[0008]

According to a first aspect of the present invention, there is provided an ink jet recording apparatus which pressurizes ink in a liquid chamber by means of energy generated by energy generating means to discharge ink droplets from nozzle holes. An ink jet recording apparatus having a recording head is provided with a pressure generating means for generating a pressure fluctuation having a polarity opposite to a pressure fluctuation generated with the movement of the carriage.

According to a second aspect of the present invention, in the inkjet recording apparatus of the first aspect, the pressure generating means generates a displacement in ink in an ink supply pipe for supplying ink to the recording head. Was provided.

According to a third aspect of the present invention, in the ink jet recording apparatus of the second aspect, when the flow of the ink in the ink supply pipe is x and the pressure generated by the movement of the carriage is p, d ² x / Dt ² =
−p, the displacement in the ink in the ink supply pipe is generated based on the displacement data (x) obtained by the differential equation.

According to a fourth aspect of the present invention, there is provided the ink jet recording apparatus according to the second or third aspect,
The displacement generating means is provided with a piezoelectric bimorph pump.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective 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, a carriage 5 is moved in a main scanning direction (indicated by an arrow A in FIG. 2) by a guide rod 3 and a guide plate 4 which are laid between left and right side plates 1 and 2 (see FIG. 2).
Direction), a recording head 6 composed of an inkjet head is mounted on the lower surface side of the carriage 5 with the ink droplet ejection direction facing downward, and 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 of 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 the recording head 6 (carriage 5) is moved and scanned 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.

Further, in this printer, a reliability maintenance / recovery mechanism (subsystem) 30 for the recording head 6 is arranged on the right side of the main scanning area of the carriage 5 so that when the printer is in a printing standby state, it can be read from the host. When print data is not transferred 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, an 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.

On the 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 jet head formed by joining the drive unit 33 and the liquid chamber unit 38 is housed in a head case 44, and the head case 44 is used to drive the piezoelectric element 32 according to 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 caused by 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.

Then, 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 driving pulse (driving 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.

In this ink jet recording apparatus,
As shown in FIG. 3, an ink supply pipe 43 for supplying ink from the ink cartridge 7 to the recording head 6 is provided.
Further, a piezoelectric bimorph pump 50, which is a displacement generating means for generating a displacement of ink, is communicatively connected. As shown in FIG. 6, the piezoelectric bimorph pump 50 includes a bimorph vibrator 52 in an elastic mold 5 in a case member 51.
A deformable partition member 54 fixed at 3 is provided to define the interior of the case member 51 into two chambers S1 and S2, and one chamber S1 is connected to the ink supply pipe 43 via a pipe member 55.
Is communicated to.

The piezoelectric bimorph pump 50
In the above, by applying a voltage waveform to the bimorph oscillator 54, the bimorph oscillator 54 is deformed in proportion to the voltage as shown by a broken line in the figure, thereby changing the inner volume of the chamber S1. Displacement can be generated in the ink in the ink supply pipe 43 communicating with S1 via the pipe member 55.

Next, an outline of a control unit in the ink jet recording apparatus will be described with reference to FIG. The control unit includes a microcomputer (hereinafter, referred to as a “CPU”) 60 that controls the entire recording apparatus, and a ROM 6 that stores necessary fixed information such as displacement data according to the present invention.
1, a RAM 62 used as an image memory, a working memory, etc., and a parallel input / output (PIO) port 63
An input buffer 64, an output buffer 65, parallel input / output (PIO) ports 66 and 67, a common driver 69 for applying a drive waveform to a common electrode of each piezoelectric element of the head 6, and each of the heads 6. A driver 70 for providing a selection signal for selecting a piezoelectric element according to the printing data, a motor driver 71 for driving and controlling the main scanning motor 8 and the sub-scanning motor 23, and a driving control for a displacement generating means (bimorph pump) 50 Driver 72 and the like.

Here, print data from the host side, instruction signals from an operation panel (not shown), and the like are input to the PIO 63. Also, the input buffer 64
The print data received from the host via the IO 63 is temporarily stored, subjected to predetermined processing, and then transferred to the output buffer 65. The print data stored in the output buffer 65 is read out at a required timing and sent to the PIO 66 as print data. The print data is supplied from the PIO 66 to the driver 69, and is supplied from the driver 69 as a selection signal to the recording head 6.
To send to.

A drive control signal is output to the motor driver 71 via the PIO 67, the carriage 5 is moved and scanned in the main scanning direction, and the platen 15 is rotated to convey the sheet 14 by a predetermined amount. Further, a signal for driving the bimorph vibrator 54 of the displacement generating means 50 is output to the driver 72 via the PIO 66 at the time of acceleration / deceleration such as at the start of movement of the carriage 5 so that the ink supply pipe 4
A displacement is given to the ink in 3.

Next, the operation of the thus configured ink jet recording apparatus will be described with reference to FIGS. First, the shortest distance print mode (a mode in which the carriage is moved from the stop position of the carriage to the print dot position closer to the print line in the bidirectional print mode to perform printing).
When the carriage 5 is moved at a high speed to the target print start position to perform printing, the carriage 5 is temporarily stopped, accelerated and changed to a constant speed movement for printing, the carriage speed is changed as shown in FIG. It changes as shown in FIG.

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 measurement of the internal pressure of the cartridge 7 was performed by installing a pressure sensor in the ink cartridge 7.

As can be seen from FIG.
The residual vibration 81 of the pressure wave is generated in the head due to the acceleration when the head is moved. The residual vibration 81 causes a change in the internal pressure of the recording head 6 (substantially equal to the internal pressure of the ink cartridge 7).

FIG. 9 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 81 shown in FIG. 8C, the pressure in the head becomes a positive pressure, so that the meniscus surface 49 is at a position protruding from the discharge surface of the nozzle 36 as shown in FIG. 9A. Similarly, in the portion of the residual vibration 81, the pressure in the head becomes negative, so that the meniscus surface 49 is at a position retracted from the discharge surface of the nozzle 36 as shown in FIG.

Further, since the pressure in the head becomes a positive pressure at the portion of the residual vibration 81, 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 Furthermore, since the pressure in the head becomes negative at the portion of the residual vibration 81, 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. 10 shows a print sample obtained by this measurement, and FIG. 11 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.

As can be inferred from the above, the meniscus surface 49 at the start of printing is at the position shown in FIG. 9A. At this time, when a driving pulse is applied to the energy generating means of the head, the meniscus in a steady state is 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 the present invention, the pressure fluctuation generated by the acceleration / deceleration operation of the carriage is opposite in polarity, and the pressure vibration having substantially the same amplitude is generated, and the two pressure fluctuations are canceled out, so that the acceleration / deceleration of the carriage is performed. Pressure fluctuation due to deceleration is made as close to "0" as possible.

That is, as described with reference to FIG. 8C, when the carriage 5 is moved at a high speed and then the acceleration / deceleration operation is performed, a pressure fluctuation occurs as shown in FIG. Is referred to as “actually measured pressure fluctuation P1”) and acts on the head, and a residual vibration 81 is generated after acceleration / deceleration. Therefore, as shown in FIG.
When a pressure fluctuation P2 having substantially the same amplitude with the opposite polarity is generated and added to the actually measured pressure fluctuation P1, the pressure fluctuations P1 and P2 cancel each other as shown in FIG. The pressure fluctuation P3 acting on the head becomes substantially "0".

As a result, it is possible to prevent the first dot from being enlarged (increased ink droplet mass) due to the pressure fluctuation caused by the movement of the carriage 5, and it is possible to reduce the variation of the dot diameter as a whole, and Since the quality is improved and the pressure fluctuation itself is suppressed, the protrusion of the meniscus from the nozzle surface (ejection surface) can be suppressed, and ink dripping can be prevented.

Here, the generation of the pressure fluctuation P2 by the displacement generating means (bimorph pump) 50 will be described with reference to FIG. 12A shows a pressure fluctuation P4 obtained by linearly approximating the polarity of the pressure fluctuation P1 in FIG. 12A by reversing the polarity, and FIG. 12B shows a differential equation obtained by solving FIG. 12A on the right side. FIG. 4C shows the displacement (x) obtained, FIG. 4C shows the pressure fluctuation P2 generated by applying the displacement (x) to the ink supply pipe 43, and FIG. 4D shows the pressure fluctuation measured by the ink cartridge 7. P3 is shown.

That is, since the ink supply system can be regarded as a substantially one-dimensional system, by controlling the ink displacement (flow of ink in the ink supply pipe) x, the polarity of the pressure fluctuation P1 due to the movement of the carriage is opposite to that of the pressure fluctuation P1. Generates a pressure fluctuation P2 having substantially the same amplitude. Displacement is generated in the ink in the ink supply system, and pressure is generated by acceleration generated at that time.

At this time, the displacement (x) of the ink is represented by d ² x / d where p is the pressure of the actually measured pressure fluctuation P1 and t is the time.
It can be obtained by solving a differential equation represented by dt ² = −p. The initial condition is that at t = 0, the ink in the ink supply system is stationary, so that dx / dt = 0
And x = 0.

Then, in each section which is linearly approximated, the displacement (x) of the ink is determined by solving this differential equation. Therefore, the displacement (x) satisfying the above expression is calculated by the displacement generating means 50 in the ink supply pipe 43. By giving the ink to the ink, a pressure fluctuation (pressure waveform) P2 having substantially the same amplitude as the actually measured pressure fluctuation P1 and having the opposite polarity is generated, and as shown in FIG.
Becomes extremely small.

In the above embodiment, an example was described in which the present invention was applied to an ink jet recording apparatus having an ink jet head used for a piezoelectric element as the energy generating means. However, an electromechanical conversion element other than the piezoelectric element was used as the ink jet head. Alternatively, the present invention can be similarly applied to an ink jet recording apparatus provided with an apparatus using an electrothermal conversion element as an energy generating means instead of an electromechanical conversion element.

[0046]

As described above, according to the ink jet recording apparatus of the first aspect, since the pressure generating means for generating the pressure fluctuation of the polarity opposite to the pressure fluctuation generated by the movement of the carriage is provided, Pressure fluctuation in the head due to the movement of the ink can be suppressed, the variation in the dot diameter can be reduced and the image quality can be improved, and the pressure fluctuation itself due to the movement of the carriage can be reduced to prevent the ink dripping.

According to the ink jet recording apparatus of claim 2, in the ink jet recording apparatus of claim 1,
Since the pressure generating means includes the displacement generating means for generating a displacement in the ink in the ink supply pipe for supplying the ink to the recording head, the pressure fluctuation due to the movement of the carriage can be easily suppressed.

According to the ink jet recording apparatus of claim 3, in the ink jet recording apparatus of claim 2,
When the flow of ink in the ink supply pipe is x and the pressure generated by the movement of the carriage is p, d ² x / dt ²
= −p, the displacement in the ink in the ink supply pipe is generated based on the displacement data (x) obtained by the differential equation, so that the pressure fluctuation due to the movement of the carriage can be easily suppressed. Can generate substantially the same pressure fluctuation.

According to the ink jet recording apparatus of the fourth aspect, in the ink jet recording apparatus of the second or third aspect, the displacement generating means is provided with the piezoelectric bimorph type pump. Substantially the same pressure fluctuation can be easily generated with the opposite polarity that can be suppressed. .

[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 sectional view of a displacement generating unit of the recording apparatus.

FIG. 7 is a schematic block diagram of a control unit of the recording apparatus.

FIG. 8 is a diagram illustrating a relationship among carriage speed, acceleration, and pressure fluctuation.

FIG. 9 is an enlarged sectional view of a main part for explaining a relationship between a pressure fluctuation and a meniscus position.

FIG. 10 is an explanatory diagram illustrating an example of a printing pattern in the vicinity of first to tenth dots in a print line.

FIG. 11 is an explanatory diagram illustrating measurement results of adjacent dot pitch and dot diameter of each dot in FIG. 10;

FIG. 12 is an explanatory diagram for explaining suppression of pressure fluctuation according to the present invention;

FIG. 13 is an explanatory diagram for explaining drive control of a displacement generating unit;

[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, 43: ink supply pipe, 5
0: Displacement generating means.

Claims (4)

[Claims] 1. An ink jet recording apparatus having a recording head which pressurizes ink in a liquid chamber by means of energy generated by energy generating means and discharges ink droplets from nozzle holes, a pressure fluctuation generated as the carriage moves. An ink jet recording apparatus comprising a pressure generating means for generating a pressure change having a polarity opposite to that of the ink jet recording apparatus. 2. The ink jet recording apparatus according to claim 1, wherein said pressure generating means includes a displacement generating means for generating a displacement in ink in an ink supply pipe for supplying ink to said recording head. Characteristic inkjet recording device. 3. The ink jet recording apparatus according to claim 2, wherein when the flow of the ink in the ink supply pipe is x and the pressure generated by the movement of the carriage is p, d ² x / dt ² = −p. An ink jet recording apparatus for causing a displacement of ink in the ink supply pipe based on displacement data (x) obtained by a differential equation of (1). 4. An ink jet recording apparatus according to claim 2, wherein said displacement generating means includes a piezoelectric bimorph type pump.