JPS6139560Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet printer having an improved ink supply system for supplying ink.

There are currently two types of inkjet printers: (a) ink-on-demand type, which ejects ink droplets as needed, and (b) deflection type, which constantly ejects ink droplets and deflects and extracts only the necessary ink droplets. It can be broadly classified. In particular, the ink-on-demand type is seen as promising because it has a simple configuration and the size of the ink droplets can be easily varied.

Figure 1 shows this ink-on-demand type ink head, in which 1 is a bimorph that bends in its thickness direction when an electrical signal is applied, 2 is an annular spacer having one end fixed to one surface of the bimorph 1, 3 is a front plate that covers the other end of the spacer 2 and forms an ink chamber 4 together with the bimorph 1, 5 is a nozzle with a diameter of several tens of μm drilled approximately in the center of the front plate 3, and 6 is an inlet hole that leads ink to the ink chamber 4.

When a pulsed electric signal is applied to the bimorph 1 of the ink head having such a structure, the bimorph 1
curves in a direction that reduces the volume of the ink chamber 4. Therefore, the pressure of the ink in the ink chamber 4 increases, and finally a minute ink droplet is ejected from the nozzle 5. When the pulsed electric signal disappears, the bimorph 1 returns to its original state and leads ink into the ink chamber 4 through the inflow hole 6.

In this way, the ink-on-demand type has four ink chambers.
Ink droplets are ejected using pressure changes within the ink chamber 4, but air bubbles often enter (generate) into the ink chamber 4, absorb pressure changes caused by the curvature of the bimorph 1, and eject ink from the nozzle 5. There is a risk that droplet ejection may be blocked. The cause of the intrusion (occurrence) of the bubbles into the ink chamber 4 is considered as follows.

() Separation of air dissolved in the ink () Infiltration from the ink tank () Air remaining in the ink supply system at the beginning () Inhalation of air from the nozzle 5 () Cavitation in the ink chamber 4 The invention is due to the causes () to () above,
This is to detect in advance the intrusion of air bubbles into the ink chamber 4 () to (), and will be described in detail below with reference to FIGS. 2 and subsequent figures.

FIG. 2 is a schematic diagram showing the inkjet printer of the present invention, in which 10 is the ink-on-demand type ink head detailed in FIG. 1, 11 is an ink tank filled with ink, and 12 is the ink tank 1.
1 is an ink supply system that communicates with the ink head 10; 13 is a recording paper that is placed opposite the ink head 10 and on which ink droplets 14 ejected from the nozzle 5 adhere; and 15 is a platen that transfers the recording paper 13. The feature of this invention is the above-mentioned ink supply system 1.
A detection means 16 for detecting the presence or absence of air bubbles is provided immediately before the second ink head 10. This detection means 16 includes a pair of electrodes 17, 17 which are in contact with the flowing ink at a certain distance apart, and both electrodes 1
7 and 17, the details of which are shown in FIG. Then, the distance between the electrodes 17, 17 is set according to the conductivity of the ink so that the resistance value is suitable for detecting a change in resistance value due to the intrusion of air bubbles between the electrodes 17, 17. As is clear from FIG. 3, the pair of electrodes 17, 17 are made of a cylindrical metal, cylindrical conductive rubber, etc. that is incorrosive to the ink, and one is connected to the ink tank 11 using the electrodes 17, 17 as a joint. , the other forming an ink supply system 12 communicating with the ink head 10.
2', 12' and an insulating tube 19 forming a constant distance between the electrodes 17, 17. The inner diameter of the insulating tube 19 is as large as the fluid resistance of the ink supply system 12 allows for the supply tube 12',
It is preferable that the diameter is thinner than that of 12', and in the above example, a diameter of 0.5 mm was used.

Therefore, if a bubble 20 is generated in the ink supply system 12, the bubble 20 is ejected from the ink head 1 in synchronization with the ejection operation of the ink droplets 14 of the ink head 10.
It moves in the 0 direction due to capillary action. This bubble 2
0 passes through the electrode 17 on the ink tank 11 side and enters the insulating tube 19 as shown in FIG.
The resistance value of the pair of electrodes 17, 17, which had previously indicated the specific resistance value of the ink, increases rapidly. This change in resistance value is electrically monitored by the detection circuit 18 to detect the generation of bubbles 20. By associating alarm means such as a buzzer circuit or a light emitting point reduction circuit with this detection circuit 18, it is possible to notify an operator etc. of the occurrence of the bubble 20, or to stop the operation of the device at the same time as the bubble 20 is detected. is possible,
It is possible to quickly take some measures against the generation of bubbles 20.

FIG. 4 is a sectional view showing another embodiment of the present invention.
Ink supply system 12 formed by insulating tube 19
A pair of needle electrodes 17', 17' are installed inside the needle electrode 17', and a change in resistance value between the needle electrodes 17', 17' is detected by a detection circuit 18. According to such a configuration, it is only necessary to insert the needle electrode 17'17' into the insulating tube 19, and the distance can be adjusted as desired due to the simple structure, and the specific resistance value can be adjusted depending on the composition of the ink. It is possible to easily deal with fluctuations in

Furthermore, another embodiment of the invention is shown in FIG. According to this embodiment, the insulation tube 1
A pair of opposing electrodes 17'', 17'' are placed on the inner wall of the air bubble 9 to detect air bubbles 20.

As is clear from the above description, the present invention includes an ink supply system that supplies ink to an ink head.
The generation of bubbles can be detected by providing a pair of electrodes separated by a certain insulating distance and monitoring changes in the resistance value of ink flowing between the electrodes. Therefore, it is possible to know in advance whether air bubbles have entered the ink head, and it is possible to prevent the air bubbles from blocking the ejection of ink droplets.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of an ink-on-demand type ink head of an inkjet printer, FIG. 2 is a model diagram showing the inkjet printer of the present invention, FIG. 3 is a cross-sectional view showing the main parts of the present invention, and FIG. The figure is a cross-sectional view showing the main parts of another embodiment of the present invention, and FIG. supply system, 16 is a detection means, 1
7, 17', 17'' are electrodes, 19 is an insulating tube,
20 indicates bubbles, respectively.

Claims (1)

[Claims for Utility Model Registration] 1. In an inkjet printer that prints characters, symbols, etc. by ejecting minute ink droplets, an ink tank filled with ink and an ink head that ejects the ink droplets are provided. A pair of electrodes that are in contact with the flowing ink are provided at a certain distance in the supply tube forming the communicating ink supply system, and the intrusion of air bubbles is detected by monitoring the change in resistance value between the electrodes. Inkjet printer. 2. The above-mentioned pair of electrodes are made of a cylindrical conductive material, and an insulating tube is inserted between the electrodes to provide a certain distance between the two electrodes. Inkjet printer. 3. The above-mentioned pair of electrodes are made of needle-shaped conductive material, and by inserting the electrodes into any part of an insulating tube, a certain distance can be obtained depending on the conductivity of the ink. An inkjet printer according to scope 1. 4. The inkjet printer according to claim 1, wherein the pair of electrodes are disposed opposite to each other on the inner wall of the ink supply system.