JPH06218930A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To prevent a position which a jetted ink drop impacts from being shifted from a regular position owing to an air current or the like generated by transfer of a medium to be recorded in an ink jet recorder which jets ink by concentration of waves being transmitted in the ink. CONSTITUTION:An electric field is generated with a high voltage generation circuit 8 between a recording head 11 and a medium to be recorded 20 on a platen 21, and an ink liquid drop jetted from the recording head 11 is accelerated.

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 using a so-called acoustic ink jet recording head of the type in which ink droplets are ejected from the ink surface by the concentration of waves propagating in ink.

[0002]

2. Description of the Related Art A conventionally known recording apparatus using an ink jet recording head has many advantages such as low noise, low running cost, easy miniaturization, and easy colorization. It is used as an information output device in etc.

The ink jet recording head used here has a discharge port (orifice) having a diameter of 20 μm to 300 μm, and most of the decrease in reliability of the recording head is due to this orifice. For example, clogging of the orifice may occur, ink thickening or sticking in the orifice and its vicinity, deformation of the orifice shape, etc. In such a case, ejection failure such as reduction of ink ejection amount or ejection failure may occur. Further, since it is necessary to process the orifice with high precision, the recording head becomes relatively expensive.

In contrast to the recording head having such a structure, a so-called nozzleless recording head which does not use an orifice has been proposed. One of them is to eject ink droplets from the ink surface by concentration of waves propagating in ink. It is an acoustic inkjet recording head. The basic principle of this ink ejection is, for example, the IBM Technical Disclosure Bulletin (IBM Technical Di).
sclossure Bulletin, Vol. 16,
No. 4, 1973, Sep. , 1168-).

[0005]

By the way, since such a so-called acoustic ink jet recording head has a structure in which a pressure wave propagating in ink is concentrated at a specific point in the recording head, conventionally, one recording head is not used. Only one dot can be ejected and simultaneously recorded on the recording medium. For this reason, at the time of recording, it is necessary to move the recording medium and the recording head relative to each other at a higher speed than in other types of inkjet recording apparatuses.

However, in order to perform high-speed recording, for example, when the recording medium is fixed to a platen (drum) capable of high-speed rotation and ink droplets ejected from the recording head are landed to perform recording, the relative movement is performed. The airflow generated by the rotation of the drum sometimes deflects the flight direction of the ejected ink droplets having a minute volume, which may cause the landing position to deviate from the normal position. As a result, there is a problem that the recording quality is degraded.

The present invention has been made in order to solve the above-mentioned conventional problems, and is always highly accurate without being affected by the air flow generated when the recording head and the recording medium move relative to each other. An object of the present invention is to provide an ink jet recording apparatus using an acoustic ink jet recording head, which enables droplets to land and thereby perform high quality recording.

Another object of the present invention is to provide an ink jet recording apparatus capable of gradation recording.

[0009]

Therefore, according to the present invention,
In an ink jet recording apparatus that uses a recording head that ejects ink by concentrating a pressure wave at a predetermined position on the ink surface, and performing recording by ejecting ink from the recording head to the recording medium, A means for forming an electric field between the recording medium and the ink ejected from the recording head is accelerated toward the recording medium by the electric field.

Further, the means forms the electric field by a potential difference between the recording head and the recording medium generated by a voltage generating circuit, and the voltage generating circuit, when ink is ejected, It is characterized in that a potential difference different from other times is generated.

Further, it is characterized in that the value of the potential difference and / or the generation time of the potential difference different from the above-mentioned other cases are variable.

[0012]

According to the above construction, the ink ejected from the recording head is accelerated toward the recording medium, so that the ejection direction may be disturbed by the air flow generated by the high speed movement of the recording medium. Instead, it can land in a regular position.

Further, the ejection amount can be controlled by changing the potential difference for forming the electric field that provides the acceleration force when the ink is ejected.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic perspective view showing the main structure of an ink jet recording apparatus according to an embodiment of the present invention. 2 is a schematic sectional view of the configuration shown in FIG.

As shown in these figures, the recording medium 20 is wound around a platen (drum) 21, and the pressing member 19 is held.
It is fixed to the platen 21 by. Platen 21
The surface of the platen 21 is conductive.
Is electrically connected to the center of rotation of the device, thereby forming a conductive position with the case (not shown) of the device. Platen 21
Is rotatably supported by a support mechanism (not shown), and is rotated at high speed in the direction of arrow E by a drive mechanism (not shown). The recording head 11 that ejects ink droplets according to the above-described principle can be reciprocated in the direction of arrow D and the opposite direction by the linear motor 18.
The rotation of the platen 21 and the linear movement of the linear motor 18 enable the recording head 11 to scan all the positions of the recording medium 20, and thus the recording medium 20.
Characters such as ABC, images, etc. can be recorded on the top.

The high-voltage generating circuit 8 has the same timing as the ink droplets are ejected from the recording head 1.
An electric field is applied between the ink surface in 1 and the recording medium 20. The magnitude of this electric field is 800 v / mm in this example.
Is. The ejected ink droplets are
The recording medium 20 receives a force toward the recording medium 20. As a result, the recording medium 20 flies while being accelerated and lands on the recording medium 20. As described above, by forming an electric field having a direction toward the recording medium 20 from the recording head 11, even if an airflow is generated by the rotation of the platen 21, the recording head 1 is caused by the airflow.
The ink droplets ejected from No. 1 are prevented from being deflected. To produce such an effect, the magnitude of the electric field may be between about 200 and 2000 v / mm.

FIG. 3 is a schematic sectional view of the recording head shown in FIGS.

The recording head 11 contains ink 10. The detection of the amount of stored ink, that is, the position detection of the ink surface 16 is performed by the ink surface sensor 13. When the contained ink amount is smaller than a predetermined amount, ink is supplied by an ink supply mechanism (not shown). The ink level sensor 13 is a reflection type photo sensor and detects whether or not the ink has reached a predetermined level.

The ink droplets 15 are ejected as follows. By applying a high AC frequency voltage for about 100 μsec to the piezoelectric element 9 by means not shown, the piezoelectric element 9 vibrates, and this vibration propagates to the solid substrate 7. Vibration of the solid substrate 7 is a thin film 6 having conductivity.
And propagate through the ink 10 to generate a pressure wave. The film 6 plays a role of acoustic impedance matching so that the pressure wave generated based on the vibration of the piezoelectric element efficiently propagates in the ink. Further, as described above with reference to FIGS. 1 and 2, it also serves as an electrode for generating an electric field between the ink liquid surface 16 and the recording medium 20. The pressure wave transmitted in the ink is concentrated at almost one point on the ink surface 16, and the ink droplet 15 is ejected upward in the figure.

The ejected ink droplets 15 are accelerated by an electric field formed between the conductive film 6 and the surface of the conductive platen 21 and fly toward the recording medium to reach a predetermined position. Land with high accuracy.

The charging of the ink droplets occurs at the timing when the ink droplets separate from the ink surface.

In the above-described embodiments, the piezoelectric element is used as the source of the pressure wave propagating in the ink. However, any element can be used as long as it can generate the pressure wave, and the piezoelectric element is not limited thereto. It is not something that will be done.

(Embodiment 2) In Embodiment 1, the high voltage generating circuit 8 for forming the electric field between the recording head and the recording medium outputs a constant high voltage.
It is not limited to this. Hereinafter, another example of this voltage application will be described.

FIG. 4 is a diagram showing the timing (a) of applying the drive voltage to the piezoelectric element 9 and the timing (b) of the voltage output by the high voltage generating circuit 8 during ink ejection.

In FIG. 4, T2 is the time for accelerating the ejected ink droplets. Further, T1 is the width of the voltage applied at the timing when the ink droplets are ejected, and here, a voltage higher than that at the time T2 is output. In this case, larger ink droplets can be ejected as compared with the case of T1 = T2. Also. Larger ink droplets can be ejected by increasing V1 and / or increasing T1.

As described above, the volume of the ink droplet to be ejected can be changed by controlling the magnitude of the voltage applied near the timing when the ink droplet is ejected and / or the application time thereof. Is. As a result, gradation recording can be performed by changing the size of ink dots attached to the recording medium.
Further, it is possible to correct the volume of the ejected ink droplets even when the volume of the ejected ink droplets is set to a constant value regardless of the temperature of the ink, the change of the ink component, and the like.

Although FIG. 4 shows an example in which T1 is output at the same time when the drive voltage is applied to the piezoelectric element 9,
T1 may be a timing slightly ahead of this.
In addition, a constant voltage V2 is always applied, and T1 is applied almost at the same time as the driving voltage is applied to the piezoelectric element 9.
May be output. In controlling the ink volume, V1 may be smaller than V2.

[0029]

As described above, according to the present invention, the ink ejected from the recording head is accelerated toward the recording medium, so that the ejection direction of the ink is increased by the air flow generated by the high speed movement of the recording medium. Can be landed in the proper position without being disturbed.

Further, the ejection amount can be controlled by changing the potential difference for forming the electric field that provides the acceleration force when ejecting the ink.

As a result, ink droplets can always be landed with high accuracy and high-quality recording can be performed, regardless of the airflow generated when the recording head and the recording medium move relative to each other at high speed. .

Further, since the volume of the ejected ink droplets can be changed, gradation recording can be performed.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing the main configuration of an inkjet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the configuration shown in FIG.

FIG. 3 is a schematic cross-sectional view showing details of the recording head shown in FIGS. 1 and 2.

FIG. 4 is a waveform diagram showing output timing of a high voltage generating circuit according to another embodiment of the present invention.

[Explanation of symbols]

 6 Film 7 Solid Substrate 8 High Voltage Generation Circuit 9 Piezoelectric Element 10 Ink 11 Recording Head 13 Ink Liquid Level Sensor 14 Ink Liquid Level Sensor 2 15 Ink Droplet 16 Ink Liquid Level 20 Recording Medium 21 Platen

Claims (3)

[Claims] 1. An inkjet recording apparatus for recording by using a recording head for ejecting ink by concentrating a pressure wave at a predetermined position on an ink liquid surface, and ejecting the ink from the recording head onto a recording medium. Ink jet recording, characterized by comprising means for forming an electric field between a recording head and the recording medium, and for accelerating ink ejected from the recording head toward the recording medium by the electric field. apparatus. 2. The means for forming the electric field by a potential difference between the recording head and the recording medium generated by a voltage generating circuit, wherein the voltage generating circuit, when ink is ejected, The inkjet recording apparatus according to claim 1, wherein a potential difference different from that at other times is generated. 3. The ink jet recording apparatus according to claim 2, wherein the value of the potential difference different from the other time and / or the generation time of the potential difference are variable.