JP3228129B2 - Ink jet recording device - Google Patents

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 which forms ink dots having different sizes on a recording medium by causing ink droplets to fly from an ink jet head supported by the carriage while moving the carriage.

[0002]

2. Description of the Related Art As an ink jet recording apparatus, there is known an apparatus which deforms a piezoelectric member by applying a printing signal to the piezoelectric member, thereby pressurizing and flying ink to form dots on a recording medium. In this ink jet recording apparatus, the size of the flying ink droplet and the diameter of the dot formed by the ink droplet adhering to the recording medium are changed by switching the voltage and application time of the print signal for each dot, for example. Can be.

However, if the size of the ink droplet is changed by changing the voltage or application time of the print signal, the flying speed of the ink also changes, which causes a shift in the landing position of the ink droplet on the recording medium. More specifically, in the inkjet recording apparatus, printing is continuously performed while the inkjet head and the carriage supporting the inkjet head are moved in a direction perpendicular to the transport direction of the recording medium. Therefore,
When the flying speed of the ink is switched while the carriage is moving at a constant speed, the landing position of the ink droplet shifts from the target position according to the change in the flying speed. The displacement of the landing position of the ink droplet appears on an image if the displacement is large, and causes a deterioration in image quality. In particular, when the image to be printed is a line image, even a slight displacement of the ink dots can be remarkably recognized, and the image quality is significantly reduced.

In order to prevent the image quality from being deteriorated due to the displacement of the landing position of the ink droplet, Japanese Patent Publication No. 64-1035
No. 0 proposes a method of correcting the shift of the landing position by delaying the output timing of the print signal.
Japanese Patent Publication No. 1-56673 discloses a method of changing a dot density by changing a moving speed of a carriage.

[0005]

However, in the former method, when the dot misalignment is not uniform or when a large number of nozzles are provided in the ink jet head, the output timing of the print signal is often delayed. And the load on the driver circuit is increased.
On the other hand, in the latter method, it is necessary to change the speed of the carriage every time the size of the dot is switched, so that there are many problems in applying the method to an actual device.

Therefore, the present invention determines the moving speed of the carriage from printing conditions, specifically, the maximum flying speed and the minimum flying speed of the ink droplet, the dot diameter, and the like, and moves the carriage at the determined speed. Accordingly, it is an object of the present invention to provide an ink jet recording apparatus capable of obtaining a desired image quality while suppressing a displacement of an ink droplet landing position within a predetermined range.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for moving a carriage and ejecting ink droplets from an ink jet head supported by the carriage to form dots of different sizes on a recording medium. In the ink jet recording apparatus for forming the above, the moving speed of the carriage was set so as to satisfy the following expression (1). _{(L / V max) · (} V max / V min -1) · Vc ≦ D min / 2 ...... (1) L: distance between the inkjet head and the recording medium V _min: flying speed of the minimum ink drop V _max: flying speed V _c of the maximum ink drop: moving speed D _min of the carriage: the minimum dot diameter

[0008]

According to the ink jet recording apparatus set as described above, the displacement of the landing position of the ink droplet is less than half the diameter of the smallest dot printed by this recording apparatus.
On the other hand, in an ink jet recording apparatus, usually, a certain dot and a dot to be formed next are about 10 to 50% of their diameter.
The above is designed to overlap. Therefore, even if a certain dot and a dot to be formed next are connected or separated from each other, the gap between them is extremely small. Therefore, even in the case of a line image, no large irregularities are recognized in the contour,
A clear line image can be printed.

[0009]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a printing unit 10 in an ink jet recording apparatus. The printing unit 10 includes a base 12, on which a pair of opposed side walls 14 are provided at predetermined intervals.
A backup roll 16, a guide rod 18, and a ball screw 20 are stretched between the side walls 14 in parallel. The backup roll 16 and the ball screw 20 are rotatable, and the ball screw 20 is
2 is drivingly connected. In addition, a carriage 24 that engages with the guide rod 18 and the ball screw 20 is provided.
The carriage 24 has a screw hole (not shown), and the combination of the screw hole and the ball screw 20 allows the carriage 24 to rotate the guide rod 1 based on the rotation of the ball screw 20.
It can be reciprocated along arrow 8 and ball screw 20 in the direction of arrow 26. The carriage 24 also includes an ink-jet head 28 described later, and discharges ink droplets from the ink-jet head 28 onto a recording medium, for example, a sheet conveyed in the circumferential direction along the outer peripheral surface of the backup roll 16 to form a recording medium. An image is created on top.

FIG. 2 shows the structure of the ink jet head 28.
3 is shown. The inkjet head 28 has a substrate 30 and a top plate 32. A plurality of grooves 34 and 35 are formed in the substrate 30 and the top plate 32 in parallel at predetermined intervals, respectively, and the substrate 30 and the top plate 32 are opposed to each other so that the groove 34 and the top plate 32 face each other. The top plate 32 is arranged.
At the bottom of each groove 34, a bar-shaped piezoelectric member 36 having a rectangular cross section is arranged. As shown in FIG. 3, the piezoelectric member 36 has a common electrode 38 and an individual electrode 4 on an upper surface and a lower surface, respectively.
0, which are connected to a recording head ejection drive unit described later. The piezoelectric member 36 is also polarized by applying a high voltage between the common electrode 38 and the individual electrode 40 at a high temperature, and applying a pulse signal between the common electrode 38 and the individual electrode 40 from the print command circuit. By doing so, it can be transformed into the dotted line state shown in FIG.

A partition 42 made of a thin film of metal or resin is fixed between the substrate 30 and the top plate 32. The partition 42 is in contact with the upper surface of each piezoelectric member 36. A space surrounded by the partition wall 42 and the groove 35 provided on the top plate 32 side is an ink cavity 44 for storing ink. An ink supply chamber 48 for supplying ink 46 to each of the ink cavities 44 is formed at a rear portion (left side in FIG. 2) of the top plate 32, and ink is supplied to a wall 50 separating the ink supply chamber 48 and the ink cavity 44. A mouth 52 is provided. In addition, a front wall 54 is provided at the front of the opposite side of the inkjet head (the right side in FIG. 2), and a plurality of ink discharge nozzles 56 are provided on the front wall 54 corresponding to each ink cavity 44. .

In the ink jet head 28 having the above configuration, when a print signal is applied to the common electrode 38 and the individual electrode 40 from a recording head ejection drive unit, which will be described later, the piezoelectric member 36 becomes an ink as shown by a dotted line in FIG. It expands and deforms toward the cavity 44, and pressurizes the ink 46 in the ink cavity 44. As a result, the ink droplet 58 flies through the nozzle 56. The flying ink droplet 58 is
The dots 62 adhere to the paper 60 conveyed along the backup roll 16 and form dots 62.

In the ink-jet head 28, the voltage of the pulse signal applied between the common electrode 38 and the individual electrode 40 is switched, for example, for each dot to change the size of the ink droplet to be ejected, thereby improving the gradation of the image. Can be operated. However, as described in the section of the problem to be solved by the invention, when the size of the ink droplet changes, the flying speed of the ink changes, which causes deterioration in image quality. Therefore, in the present invention, the inkjet head 28
The moving speed of the carriage 24 is set in advance based on the flying speed of the ink droplet 58 ejected in step S2, the size of the dot 62 created by the flying ink droplet, and the like. The image quality is not impaired.

FIG. 4 is a block diagram of a control circuit for controlling the printing section of the ink jet recording apparatus shown in FIG.
As shown in FIG. 4, the control circuit includes a central processing unit (CPU) 100 which is a main control unit, and a data receiving unit 10 which receives image data from a host computer (not shown) or the like.
3. Random access storage means (RAM) 101 for storing image data and data such as the number of ejections sent from the data receiving unit 103, and storing information relating to the control procedure of each unit of the printing unit such as the moving speed of the carriage 24 and the paper feed amount A print head ejection drive unit 105 for causing the head 28 to eject ink by outputting a print signal based on image data stored in the read only storage means (ROM) 102 and the RAM 101, It comprises a carriage driving unit 106 for moving in synchronization with the timing, a paper feed control unit 107 for rotating the backup roll 16 to convey a recording medium, and other input / output 104.

Hereinafter, setting of the carriage moving speed will be described. Now, the ink jet head moving at a predetermined speed has different flight speeds from the same nozzle.
Assuming that two ink droplets are ejected at the same time, the displacement of the positions where both ink droplets land on the recording medium is given by the following equation (2). δ = L (1 / V1-1 / V2) · Vc (2) where δ is the displacement of the landing position, L is the distance from the inkjet head to the recording medium, and V1 and V2 are the flight of each ink droplet. The speed (V1 <V2) and Vc are the moving speeds of the carriage.

If V1 = kV2 (k <1),
The expression (2) can be rewritten as the following expression (3). δ = (L / V2) · (1 / k−1) · Vc (3) From this equation (3), it can be seen that the displacement of the landing positions of both ink droplets is proportional to the moving speed of the carriage. by the way,
From the design conditions of the ink channel and the piezoelectric member to be placed in it, the size and the flying speed of the ink droplet are uniquely determined by the voltage applied between the individual electrode and the common electrode. It is impossible to change only the flying speed of the ink droplet.

On the other hand, an ink jet recording apparatus is usually
A certain dot and a dot to be formed next are designed to overlap by about 10 to 50% or more of their diameter. Therefore, if the carriage speed is set so that the landing position shift is equal to or less than half the diameter of the smallest dot created by the inkjet head, the dots formed on the recording medium may or may not be connected. Even without them, the gap between them is extremely small.

Therefore, if the moving speed of the carriage is set in the relation of the formula (4) so that the landing position of the ink droplet is equal to or less than half of the diameter of the minimum dot formed by the ink jet recording apparatus, the displacement of the dot becomes conspicuous. Instead, even if it is a line image, the outline is drawn clearly. (L / V _max ) · (1 / k−1) · Vc ≦ D _min / 2 (4) where V _max is the maximum ink flying speed and k is V _min / V _max
(V _min : minimum flying speed of ink) and D _min is the diameter of the minimum dot.

Since the influence of dirt near the ink discharge nozzle on the ink droplet is greater as the flying speed of the ink droplet is lower, the minimum flying speed V _{min of the} ink is 1.5 m / _min.
It is preferably set to seconds or more. On the other hand, in consideration of the scattering when the ink droplet lands on the recording medium, the maximum ink flying speed is preferably 15 m / sec or less. The smaller the distance L between the inkjet head and the recording medium, the better the landing accuracy. However, in consideration of the type of the recording medium and maintenance, it is desirable that the distance be 0.5 mm or more and 1.5 mm or less.

In consideration of the above, the moving speed of the carriage will be specifically obtained. The distance L between the ink jet head and the recording medium is 0.5 μm, and the maximum ink flying speed V
_max to 15 × 10 ³ mm / sec, minimum ink flight speed V _min
Is 1.5 × 10 ³ mm / sec, and the minimum dot diameter D _min is 2
Assuming that 5 μm, k = 0.1. Therefore, by substituting these values into the equation (4), the carriage moving speed Vc
Is calculated to be 41.7 mm / sec or less.

When the distance L between the ink jet and the recording medium is changed to 1.5 μm under the above conditions, the carriage moving speed is similarly calculated to be 13.9 mm / sec or less from the equation (4).

Next, the minimum dot diameter D _{min is set} to 100 μm.
m, the maximum ink flying speed V _max is 15 × 10 ³ mm / sec,
The interval L between the inkjet head and the recording medium is set to 0.5 μ
m, the maximum ink flying speed V _max is 15 × 10 ³ mm / sec,
When the minimum ink flying speed V _min is 1.5 × 10 ³ mm / sec, the carriage moving speed is similarly calculated to be 166.7 mm / sec or less from Expression (4).

When the distance L between the ink jet and the recording medium is changed to 1.5 μm under the above conditions, the carriage moving speed is similarly calculated to be 55.5 mm / sec or less from the equation (4).

The value of k (= V _min / V _max ) is 0 <k <1, as is clear from the gist of the invention, and is substantially 0.1 ≦ k ≦ 0.9.

Using the ink-jet head shown in FIGS. 2 and 3, the voltage of the pulse signal applied between the common electrode and the individual electrodes was changed to determine the change in dot diameter and the flying speed of the ink droplet. The applied pulse signals are three types of rectangular pulses having a pulse duration (pulse width) of 30 μs and voltages of 10, 20, and 30 V. The nozzle diameter is 35 μm, and the size of the surface where the piezoelectric member contacts the ink cavity is width 200.
μm, the length was 10 mm, and the distance between the ink jet head and the recording medium was 0.8 mm. results of the experiment,
As shown in FIGS. 4 and 5, the dot diameter and the ink droplet flying speed tended to increase as the applied voltage was increased. When the pulse voltage is 10, 20, and 30 V, the maximum deformation amount of the piezoelectric member is 0.3 μm, 0.2 μm, and 0.2 μm, respectively.
It was 1 μm. The pressure generated in the ink when the piezoelectric member was deformed was 2.0 kgf / mm ² .

As shown in FIGS. 4 and 5, in the present ink jet head, if the voltage of the print signal is changed within the range of 10 to 30 V, the minimum flying speed of the ink droplet is 1.2 m / sec. The maximum flight speed is 5.4 m / sec.
Therefore, in the ink jet recording apparatus using this ink jet head, the moving speed of the carriage is a value obtained by substituting the above flying speed and the like into the equation (4), that is, 3
8.57 mm / sec or less. Thereby, a line image can be reproduced well. By the way, when the moving speed of the carriage was set to 45 mm / sec with this ink jet head and a character image was created, disorder was confirmed in the image. Also,
When the moving speed of the carriage was set to 60 mm / sec, natural images such as landscapes and photographic images of portraits were also disturbed. On the other hand, when the moving speed of the carriage was set to 35 mm / sec, a very good image without disturbance was obtained.

In the above-described ink jet head,
Although the ink and the piezoelectric member are separated by a partition, the partition is not always required. However, the provision of the partition prevents the piezoelectric member from directly contacting the ink, thereby preventing the ink from penetrating the piezoelectric member and reducing the performance. The piezoelectric member is not limited to a single-layer type in which electrodes are provided only on the surface opposite to the ink cavity and the surface on the opposite side, but is a multilayer type in which thin piezoelectric members are laminated and electrodes are interposed between them. Can also be used. Further, the present invention can be applied not only to the ink jet head having the grooves provided with the piezoelectric members disposed therein as described above, but also to the ink jet heads having only a space between the adjacent piezoelectric members.

[Brief description of the drawings]

FIG. 1 is a perspective view of a printing unit of an ink jet recording apparatus according to the present invention.

FIG. 2 is a longitudinal sectional view of the inkjet head.

FIG. 3 is a sectional view taken along line III-III in FIG. 2;

FIG. 4 is a block diagram of a control circuit that controls a printing unit of the inkjet recording apparatus.

FIG. 5 is a diagram illustrating a change in dot diameter when a voltage of a pulse signal applied to a piezoelectric member of an inkjet head is changed.

FIG. 6 is a diagram illustrating a change in an ink droplet flying speed when a voltage of a pulse signal applied to a piezoelectric member of an inkjet head is changed.

[Explanation of symbols]

10 printing section, 22 motor, 24 carriage, 28
... Inkjet head, 100 ... Central processing unit, 10
DESCRIPTION OF SYMBOLS 1 ... Random access storage means, 102 ... Read-only storage means, 103 ... Data receiving part, 105 ... Recording head discharge drive part, 106 ... Carriage drive part, 107 ... Paper feed control part.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/01

Claims (1)

(57) [Claims] In an ink jet recording apparatus which forms dots of different sizes on a recording medium by ejecting ink droplets from an ink jet head supported on the carriage while moving the carriage, the moving speed of the carriage is as follows: 1) An ink jet recording apparatus set to satisfy the equation. _{(L / V max) · (} V max / V min -1) · Vc ≦ D min / 2 ...... (1) L: distance between the inkjet head and the recording medium V _min: Ink minimum flying speed V _max: Ink Maximum Flying speed _Vc : carriage moving speed _Dmin : minimum dot diameter