JPH05261906A - Rotating ink jet head - Google Patents

Abstract

PURPOSE:To provide a new rotating ink jet head constituted for increasing further the printing speed. CONSTITUTION:A rotating ink jet head is provided with a cylindrical rotating head main body 12 with a plurality of ink jetting nozzles 12a disposed by the given pitch, and a vibration plate 12b provided for forming a ring ink pressure chamber communicated with the ink jetting nozzles is disposed inside the cylindrical rotating head main body. The rotating ink jet head is fixedly disposed on the inner side of the cylindrical rotating head main body and provided with an electric/mechanical conversion means being in slide contact with the vibration plate of the cylindrical rotating head main body, and small ink drops are jetted properly out of the ink jetting nozzles by vibrating locally and selectively the vibration plate by said electric conversion means based on the printing data during the rotation of the cylindrical rotating head main body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer, and more particularly to a rotary ink jet head mounted therein.

[0002]

2. Description of the Related Art A conventional ink jet head has a head body having a plurality of ink jet nozzles arranged at a predetermined pitch, and an ink flow path communicating with each ink jet nozzle is formed in the head body. It An ink pressure chamber is provided in the ink flow path, and ink is sequentially replenished from the ink supply source to the ink pressure chamber. Electromechanical conversion means, such as a piezoelectric element, is applied to a wall portion that defines each ink pressure chamber, and a drive pulse voltage is applied to the piezoelectric element to vibrate the wall portion to generate a pressure wave in the ink pressure chamber. Is generated, and at this time, the ink is ejected from the ink ejecting nozzle as ink droplets toward the recording medium (not shown). Such a head body is mounted on a carriage that is moved along the print scanning direction, and by selectively driving the piezoelectric element based on print data during the movement, ink droplets are appropriately ejected from the ink ejection nozzles. The ink is ejected toward a recording medium such as a recording paper, so that characters, symbols and the like are recorded on the recording medium by ink dots.

[0003]

By the way, in the ink jet head as described above, in order to increase the printing speed, it is necessary to increase the ejection frequency of the ink droplets from each ink ejection nozzle. In some cases, the injection frequency is kept below a few kilohertz. This is because if the ejection frequency of the ink droplets exceeds several kilohertz, the ink cannot be sufficiently supplied from the ink pressure chambers to the ink ejection nozzles, resulting in poor print quality. Therefore, it is an object of the present invention to provide a novel ink jet head configured to further increase the printing speed.

[0004]

A rotary ink jet head according to the present invention comprises a cylindrical rotary head body having a plurality of ink jet nozzles arranged at a predetermined pitch.
Inside the cylindrical rotary head body, there is provided a vibrating plate arranged to form an annular ink pressure chamber communicating with the ink jet nozzle. The rotary ink jet head according to the present invention further comprises electromechanical conversion means fixedly arranged inside the cylindrical rotary head body and in sliding contact with the vibration plate of the cylindrical rotary head body. The means locally and selectively vibrates the vibrating plate based on the print data during the rotation of the cylindrical rotary head main body to eject ink droplets appropriately from the ink ejecting nozzles.

[0005]

As is apparent from the above-described structure, in the rotary ink jet head according to the present invention, the ink in the ink pressure chamber receives a centrifugal force during the rotation of the cylindrical rotary head main body, which causes the ink pressure chamber. The ink supply to each ink ejecting nozzle is promoted.

[0006]

Embodiments of the rotary ink jet head according to the present invention will now be described with reference to the accompanying drawings.
Referring to FIG. 1, there is shown one embodiment of a rotary inkjet head according to the present invention, which comprises a carriage 10 which is moved along a platen (not shown) of the printer, i.e. along the print scan direction. A cylindrical rotary head body 12 rotatably and detachably mounted on the carriage 10.
2, only the carriage 10 is shown from which the head body 10 has been removed.

In the present embodiment, the carriage 10 itself is constructed as a drive motor, for example, a pulse motor, and the pulse motor comprises a motor housing 10a and an output shaft 10b protruding from the upper surface of the motor housing 10a. The motor housing 10a is slidably mounted on a guide bar (not shown) extending along the platen of the printer, and is moved along the guide bar during printing operation. The cylindrical rotary head main body 12 is detachably attached to the output shaft 10b, and is rotationally driven in the direction shown by the arrow in the drawing during printing operation (FIG. 1).

The cylindrical rotary head body 12 is made of a suitable metal material such as stainless steel, and a plurality of ink jet nozzles 12a are formed on its peripheral surface. The ink ejection nozzles 12a are arranged in a plurality of columns in the vertical direction, and each column includes, for example, four ink ejection nozzles 12a.
In reality, a larger number of ink ejection nozzles are formed. For example, when performing print recording with a 24 × 24 dot matrix, 24 ink ejection nozzles are formed in each column. That is, the arrangement pitch of the ink ejection nozzles 12a in each column corresponds to the pitch of the ink dots on the recording paper. Further, for convenience of illustration, each ink ejection nozzle 12a is exaggeratedly illustrated in a large size, but in reality, the diameter thereof is on the order of several microns. For this reason, in FIG. 1, the arrangement pitch of the ink ejecting nozzles 12a is shown to be substantially equal to the interval pitch along the circumferential direction of the column. The pitch is much larger than the arrangement pitch of the ink ejection nozzles 12a included in the column.

As shown in FIG. 3, a sleeve-shaped vibrating plate 12b is provided inside the cylindrical rotary head body 12, and the vibrating plate 12b forms an annular ink pressure chamber 12c communicating with the ink ejecting nozzle 12a. It When the cylindrical rotary head main body 12 is mounted on the output shaft 10b, the vibrating plate 12b is slidably engaged with the four support plates 10c protruding from the upper surface of the motor housing 10a, whereby the cylindrical rotary head is rotated. The rotational drive of the head body 12 is stabilized. The four support plates 10c are arranged around the output shaft 10b at an angle of 90 ° to each other,
The electromechanical converting means 14 is supported by one of the supporting plates 10c, that is, the supporting plate 10c arranged on the front side of the printing side. In this embodiment, the electromechanical converting means 14 is equal to the number of the ink ejecting nozzles 12a included in each column.
The piezoelectric elements 14a are arranged at the same pitch as the arrangement pitch of the ink jet nozzles 12a. Therefore, during the rotational driving of the cylindrical rotary head body 12, each of the ink jet nozzles 12a included in each column passes over the corresponding piezoelectric element 14a. When a drive pulse voltage is applied to the electrode plate of the piezoelectric element 14a, the vibrating plate 12b is locally vibrated, which causes a pressure wave in the ink in the ink pressure chamber 12c,
Ink droplets are ejected from the corresponding ink ejection nozzle 12a.

As is clear from the above description, according to the present invention, since the cylindrical rotary head body 12 is driven to rotate during the printing operation, the ink ejecting nozzle 12a in the ink pressure chamber 12c constantly applies centrifugal force. Therefore, the supply of ink from the ink pressure chamber 12c to the ink ejecting nozzle 12a is promoted, and the printing speed can be increased. This will be described in detail. The ink supply force F that supplies ink from the ink pressure chamber 12c to the ink ejection nozzle 12a can be expressed by the following formula. _{F = f r + f n (} 1) Here, f _r centrifugal force acting on the ink, f _n is the force due to the surface tension of the ink in the ink ejection nozzles 12a. The centrifugal force _fr is determined by the rotation speed _Vh (m / s) of the cylindrical rotary head body 12. That is, f _r ∝ V _h ² (2) Ink supply time t of ink to the ink jet nozzle 12a
_r and the ink supply force F can be expressed by the following relational expression (note that the inertial force of ink is ignored). That is, _tr ∝ 1 / F (3) The following equation is obtained from the above equations (1), (2) and (3). ^{_{t r α1 / (V h 2}} + f n) (4) As apparent from the above equation, as the V _h is the larger the f _r increases, it can be seen that t _r is reduced. Next, the relationship between the rotation speed V _h (m / s) of the cylindrical rotary head body 12 and the print scanning speed V _c of the carriage 10 will be described. The arrangement pitch of the vertical rows of the ink ejection nozzles 12a is Y
(μm), the dot pitch of the ink dots to be recorded is D
(μm), in order to record the ink droplets ejected from the ink ejecting nozzles 12a of each column at the dot pitch D, each column of the ink ejecting nozzles 12a should have a piezoelectric element 14a every D / V _c seconds. Of the cylindrical rotary head body 12 for this purpose, the rotational speed V _h (m / s) of the cylindrical rotary head body 12 must satisfy the following conditions. _{That, V h = V c · Y} / D (5) by transforming the equation (4), when rewriting the print scanning speed V _c of the carriage 10, the following equation. V _c = V _h · D / Y (5) As is clear from the above equation, it is understood that the more V _h increases, the larger V _c must be. This is the print scanning speed of the carriage 10. It means that V _c can be increased.

Referring to FIG. 5, a part of the cylindrical rotary head main body 12, that is, a part of the region where the ink jet nozzle 12a is formed is shown in a developed manner on a plane, in which three ink jet nozzles 12a are formed. The columns are designated by the reference signs a, b and c for convenience. As mentioned above, the column a,
The interval pitch Y between b and c is much larger than the arrangement pitch D of the ink ejection nozzles 12a included in each column. Therefore, the ink ejection nozzles 12a included in the column a
The ink dots recorded on the recording paper with the ink droplets ejected from are arranged with the ink dots ejected from the ink ejection nozzles 12a included in the column b adjacent to the ink dots recorded on the recording paper. Must be recorded at pitch D. That is, as shown in FIG. 6, 4 ×
In order to record ink droplets with a dot matrix of 4, an ink dot row a'obtained from column a and a column b
The distance between the ink dot row b ′ and the ink dot row b ′ must be the arrangement pitch D.

In order to obtain the above ink dot recording, the rotational speed of the cylindrical rotary head main body 12 and the drive pulse voltage to the piezoelectric element 14a are determined based on the speed of the cylindrical rotary head main body 12 in the print scanning direction. The application of and must be controlled. That is, as shown in FIG.
When the cylindrical rotary head main body 12 is moved along the print scanning direction indicated by the arrow 16, if the ink droplets S are ejected from the ink ejection nozzles 12a in the column a toward the recording paper P, As shown in FIG. 7B, the cylindrical rotary head main body 12 is rotated by an angle θ while the cylindrical rotary head main body 12 advances in the print scanning direction by a distance corresponding to the arrangement pitch D, and the column b The piezoelectric element 14a
It is necessary to move the piezoelectric element 14a to the installation location and apply a drive voltage pulse to the piezoelectric element 14a, thereby ejecting the ink droplets from the ink ejecting nozzles 12a in the column b. In FIG. 7, reference numeral 18 indicates the direction of rotation of the cylindrical rotary head body 12.

Referring to FIG. 8, there is shown an example of a control block diagram for performing the control described above. In the block diagram, reference numeral 20 indicates a scanning sensor that detects the scanning position of the carriage 10 when it moves in the printing scanning direction. The scanning sensor 20 is a predetermined drive belt that drives the carriage 10 in the printing scanning direction. It may be of a type that optically detects slits formed at intervals, or of a type that converts the amount of movement of the drive belt into the amount of rotation of a gear and reads the amount of rotation with an encoder or the like. It may be. Reference numeral 22 is the scanning sensor 20.
The control circuit 22 outputs various control signals based on the detection signal detected by the control circuit 22. The control circuit 22 outputs the control signal every time the scanning sensor 20 outputs the detection signal.
A print command signal for controlling the drive of a and a trigger signal for controlling the rotational drive of the cylindrical rotary head body 12 are output.

Further, in FIG. 8, reference numeral 26 indicates a latch circuit for fetching print data, and the latch circuit 26 includes ink ejection nozzles 12a included in each of the columns a, b, c (FIG. 7). 4 latch circuit elements corresponding to the number of The print data is so-called binary image data, and each latch element holds a high level signal, that is, "1" when an ink dot is generated,
When the ink dots are not generated, each latch element holds a low level signal, that is, "0". Reference code 2
Reference numeral 6 denotes an AND circuit, and the AND circuit 26 includes a number of AND circuit elements corresponding to four latch elements. Each AND circuit element has two input terminals, and one of the input terminals receives print data from the corresponding latch circuit element. A print command signal from the control circuit 22 is input in parallel to the other input terminal side of the four AND circuit elements, and this print command signal is a high level signal, that is, "1".
It is said that. Therefore, of the four AND circuit elements, only the one to which the high level signal, ie, “1”, is input as the print data outputs the high level signal, ie, “1”. Reference numeral 28 indicates a drive circuit for driving the four piezoelectric elements 14 a, and the drive circuit 24 includes four drive circuits.
One drive circuit element is included. When a high-level signal, that is, "1" is input to each drive circuit element from the corresponding AND circuit element, a drive pulse voltage is output from the drive circuit element and applied to the corresponding piezoelectric element 14a, whereby the corresponding ink Ink droplets are ejected from the ejection nozzle.

Further, in FIG. 8, reference numeral 30 indicates a motor drive circuit for driving the pulse motor (carriage) 10. The motor drive circuit 30 is a pulse motor each time a trigger signal from the control circuit 22 is input. Then, a predetermined number of drive pulses are output to drive the cylindrical rotary head body 12 to rotate.

Next, the operation of the control block diagram shown in FIG. 8 will be described with reference to the timing chart of FIG. At time T ₀ , the scanning sensor 20 detects the scanning position of the carriage 10, and as a result, the control circuit 22 outputs a print command signal and a trigger signal.
However, at this stage, since the print data is not input to the latch circuit 24, that is, the AND circuit 2
Since the print data for all the AND circuit elements 6 are low level signals, that is, "0", the drive circuit 28
No driving pulse voltage is output from the piezoelectric element 14a to the piezoelectric element 14a, and therefore, ink droplets are not ejected from the ink ejection nozzle 14a. On the other hand, a trigger signal is sequentially input to the motor drive circuit 30, and at this time, the motor drive circuit 30 outputs a predetermined number of drive pulses to the pulse motor (carriage) 10, and the cylindrical rotary head main body 12 has a predetermined rotation angle. It is driven to rotate. That is, each time the trigger signal is output, the column of the ink jet nozzles 12a is sequentially made to reach the installation location of the piezoelectric element 14a.

At time T ₁ , when the input of the print data to the latch circuit 24 is started, the drive pulse voltage is selectively output from the drive circuit element of the drive circuit 28 based on the print data, and in response thereto, the drive pulse voltage is output. The ejection of ink droplets is started from the ink ejection nozzles 14a in each row. After that,
When a detection signal is output from the detection sensor at times T ₂ , T ₃ and T _n , the above-described operation is repeated, whereby characters, symbols, etc. are recorded on the recording medium by ink dots having a dot pitch D. It will be.

[0018]

As is apparent from the above description, in the rotary ink jet head according to the present invention, the ink in the ink pressure chamber receives a centrifugal force, and the ink from the ink pressure chamber to each ink ejecting nozzle is ejected. Is promoted, the printing operation can be performed at a higher speed than that of the conventional inkjet head. Needless to say, if the rotational speed of the cylindrical rotary head main body is increased too much, ink will seep out from the ink ejection nozzles, and thus the rotational speed cannot be increased indefinitely.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an embodiment of a rotary inkjet head according to the present invention.

FIG. 2 is a perspective view similar to FIG. 1, showing the rotary inkjet head with the cylindrical rotary head body removed.

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

FIG. 4 is a partial cross-sectional view taken along the line IV-IV in FIG.

FIG. 5 is a development view showing a part of the cylindrical rotary head body of FIG. 1 in an expanded manner.

6 is a plan view showing an ink dot recorded on a recording paper with a small ink droplet ejected from the ink ejection nozzle of FIG.

FIG. 7 is a schematic explanatory diagram for explaining the operating principle of the rotary inkjet head according to the present invention.

FIG. 8 is a control block diagram of the rotary inkjet head according to the present invention.

9 is a timing chart for explaining the operation of the control block diagram of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Carriage (pulse motor) 10a ... Motor housing 10b ... Output shaft 12 ... Cylindrical rotary head main body 12a ... Ink jet nozzle 12b ... Vibration plate 12c ... Ink pressure chamber 14 ... Electromechanical conversion means 14a ... Piezoelectric element 20 ... Scan sensor 22 ... Control circuit 24 ... Latch circuit 26 ... AND circuit 28 ... Drive circuit 30 ... Motor drive circuit

Claims (3)

[Claims] 1. A cylindrical rotary head body (1) having a plurality of ink jet nozzles (12a) arranged at a predetermined pitch.
2), and an annular ink pressure chamber (12) communicating with the ink ejection nozzle is provided inside the cylindrical rotary head body.
a diaphragm (12b) arranged to form c), and further fixedly arranged inside the cylindrical rotary head body and in sliding contact with the diaphragm of the cylindrical rotary head body. A mechanical conversion unit (14) is provided, and the electric conversion unit locally and selectively vibrates the diaphragm based on print data during rotation of the cylindrical rotary head main body to cause ink to be ejected from the ink ejecting nozzles. A rotary ink jet head characterized by appropriately ejecting small droplets. 2. The rotary ink jet head according to claim 1, wherein the cylindrical rotary head body (12) is rotatably mounted on a carriage (10) which is moved in a print scanning direction, and the carriage is A drive motor (10) for rotationally driving a cylindrical rotary head body, and a support (10) for supporting the electromechanical conversion means (14).
and an inkjet head. 3. The rotary ink jet head according to claim 2, wherein ink droplets from the ink jet nozzles of the cylindrical rotary head body (12) are recorded on a recording medium at a predetermined dot pitch. The carriage (1
0) detecting means for detecting movement in the print scanning direction (2)
0) and control means (22, 24, 26, 2) for controlling the drive of the drive motor (10) and the electromechanical conversion means (14) based on the detection signal from the detection means.
8, 30) are provided.