JPH04332650A - Liquid drop delivery device - Google Patents

Abstract

PURPOSE:To obtain a printing head for on-demand printer provided with a high-density nozzle alignment and a simple drive circuit relating to a liquid drop delivery device in which fluid to be delivered is delivered from nozzles as fine liquid drops. CONSTITUTION:Shape memory alloy wires 1 are provided in a cavity in a body 2. One end of the shape memory allay wire 1 is fixed through a conduction electrode B4. The shape memory alloy wire 1 can be electrothermally heated through a conduction electrode A3 and the conduction electrode B4. By inputting an image signal, the shape memory alloy wire 1 is electrothermally heated to be shrunk. Ink is charged into a cylinder chamber 11 from an ink injection port 7. Next, an electric current is interrupted, and the shape memory alloy wires 1 are expanded by being cooled naturally as well as forcibly by the ink to increase an ink pressure in the cylinder to deliver the ink. In this construction, a high-density multi-nozzle head is easily realized by arranging the shape memory alloy wires 1 of the order of 50mum in diameter, and ink can be delivered by a simple drive voltage of the order of several volts.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to droplet ejection in which a liquid to be ejected is intermittently ejected as minute droplets from a nozzle in response to an electrical signal, for example, on-demand for printing characters or figures on a recording medium. The present invention relates to a droplet ejecting device such as a type printer head.

0002

2. Description of the Related Art It is well known that piezo elements have been used as one of pressure generating means for ejecting ink in on-demand ink jet heads.

[0003] For example, a representative example is
A structure disclosed in Japanese Patent No. 12138 is known.

Hereinafter, a conventional inkjet head using a piezoelectric element will be explained with reference to FIG. In FIG. 4, a pressure chamber 22 has an ink discharge port 23 on one side and an ink supply port 21 on the other side. A part of the wall surface of the pressure chamber 22 is composed of a piezoelectric plate 24 and a metal plate 25 pasted together.

Now, in FIG. 4A, when an image signal 26 is applied between the piezoelectric plate 24 and the metal plate 25 with the pressure chamber 22 filled with ink, the piezoelectric plate 24 and the metal plate 25 move into the pressure chamber 22. It warps to the side, causing a sudden change in volume, and the pressure generated at that time causes ink to be ejected from the ink ejection port 23.

Next, in FIG. 4(b), by applying an image signal 26 in the opposite direction to that at the time of ejection, the piezoelectric plate 2
4 and the metal plate 25 in opposite directions to rapidly reduce the pressure inside the pressure chamber 22, ink is forcibly supplied into the pressure chamber 22 from the ink supply path 21. This figure 4
During the operation shown in (b), the ink discharge port 23 is
The resistance of the ink supply path 21 is made larger than that of the ink supply path 21.

Note that even if the operation shown in FIG. 4(b) is omitted, the piezoelectric plate 24 and the metal plate 25 return to their original positions due to their own elasticity after the operation shown in FIG. 4(a) is completed. Therefore, the same effect as that shown in FIG. 4(b) is performed, although there is a difference in degree.

[0008]

[Problems to be Solved by the Invention] However, in the above conventional configuration, the amount of displacement of the piezoelectric element is extremely small, so in order to eject ink stably, the tip of the piezoelectric plate must be at least 2 mm square or 2 mm in diameter. Although the structure is simple, it is difficult to manufacture a compact multi-nozzle head having a nozzle density of 4 nozzles/mm or more.

[0009] Furthermore, in order to drive the piezoelectric element, a signal voltage of at least several tens of volts or more is required, which imposes a large cost burden on the drive circuit.

The present invention solves the above-mentioned conventional problems, and provides a droplet ejecting device that has a simple structure, has a large number of nozzles arranged at high density, and can be driven at a low voltage.

[0011]

[Means for Solving the Problems] In order to achieve this object, the present invention uses a wire-shaped shape memory alloy as a displacement element for generating pressure for ink ejection, and a cylinder containing the shape memory alloy as a piston. The object is achieved by expanding and contracting the shape memory alloy piston by energizing and heating it in accordance with an image signal.

0012

[Operation] With the above configuration, the present invention contracts the shape memory alloy piston by heating it with electricity in response to an image signal, injects ink into the cylinder, and then cuts off the electricity, allowing natural heat dissipation and forced cooling by the injected ink. By expanding the shape memory alloy piston, a sudden pressure increase is caused in the ink in the cylinder, and an ink droplet can be ejected. In addition, by absorbing the heat generated in the shape memory alloy, the viscosity of the liquid to be discharged decreases, and by the high compression force of the liquid in the cylinder by the shape memory alloy piston, even highly viscous liquid to be discharged can be efficiently discharged as minute droplets. Therefore, a print head for high viscosity ink can be constructed.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing the structure of a printer head in a droplet ejecting device according to an embodiment of the present invention.

In FIG. 1(a), 1 is a wire-shaped shape memory alloy, 2 is a body made of an insulating material containing the shape memory alloy,
Reference numerals 3 and 4 are current-carrying electrodes for heating the shape-memory alloy 1 through current-carrying, and the end of the shape-memory alloy 1 and the body 2 are fixed via the current-carrying electrode 4. 1 (
A cylinder chamber 11 as shown in b) is formed. Reference numeral 5 denotes an ink supply port through which high electrical resistance oil-based ink 9 is supplied to the ink chamber 6. 7
8 is an ink injection port into the cylinder chamber 11, and 8 is an ink discharge port to the recording medium.

Next, the principle of ink ejection operation will be explained using FIG. 1. In FIG. 1(a), the image signal 10 is not sent to this inkjet head. In this state, the shape memory alloy 1 is expanded in a non-energized state, and blocks the ink injection port 7 to prevent the ink 9 from being injected into the cylinder chamber 11. Next, the state in which the image signal 10 is sent to this inkjet head is shown in FIG. 1(b). The sent image signal 10 causes the current-carrying electrode A3 and the current-carrying electrode B to
4, the shape memory alloy 1 is heated with electricity, and the shape memory alloy 1 contracts in the length direction with the energized electrode B4 as a fixed point,
A space for the cylinder chamber 11 is created. At this time, the ink 9 is injected into the cylinder chamber 11 through the ink injection port 7. When the injection of ink into the cylinder is completed, the power supply to the shape memory alloy is ended as shown in FIG. 1(c). The shape memory alloy 1 expands due to natural heat dissipation in a non-energized state and forced cooling by the injected ink 9. The ink 9 that has cooled the shape memory alloy 1 increases in temperature and reduces its own viscosity.
The pressure inside the cylinder increases due to the piston movement due to the strong shape restoring force of the shape memory alloy 1, and the ink is eventually ejected from the ink ejection port 8.

FIG. 2 is a front view of a printer head in which a plurality of micro droplet discharge nozzles are arranged side by side using shape memory alloy wire with a wire diameter of 50 μm, and has a high nozzle density of 10 nozzles/mm. . Further, ink can be ejected with a drive power of about several volts per nozzle.

FIG. 3 shows a full multi-function printer using this droplet ejecting device, in which the shape memory alloy piston is heated and
It has a structure in which the decrease in printing speed due to the time required for the heat dissipation process is compensated for by the number of high-density nozzles. In this configuration, the ink ejection port 8 and the recording paper 14 are in a fairly close positional relationship, but since the ink ejection distance increases by applying an electric field between the shape memory alloy piston and the roller 13, the ink ejection port 8 and recording paper 1
A configuration in which there is a distance between 4 and 4 is also possible.

[0019]

As described above, the present invention utilizes a droplet ejecting device comprising a wire-shaped shape memory alloy piston and a cylinder containing the shape memory alloy piston as a means for ejecting ink droplets from an on-demand printer head. By doing so, it is possible to increase the density of the nozzles compared to inkjet heads using piezo elements, and the drive circuit can be simplified because the drive voltage can be reduced to about a few volts, and it is also possible to eject highly viscous ink. This makes it possible to realize an excellent printer head that can perform

[Brief explanation of drawings]

FIG. 1: (a) A cross-sectional view of a printer head in a static state in a droplet ejection device according to an embodiment of the present invention; (b) A cross-sectional view of a printer head in a state where the same device has started operation; Printer head cross section

[Fig. 2] Front sectional view of the printer head in the droplet ejection device of the same embodiment.

[Fig. 3] Conceptual diagram of a full multi-type printer with a droplet ejection device according to an embodiment of the present invention.

[Figure 4] Cross-sectional view of a conventional inkjet head

[Explanation of symbols]

1 Shape memory alloy 2 Body 3 Current-carrying electrode A 4 Current-carrying electrode B 5 Ink supply port 6 Ink chamber 7 Ink inlet 8 Ink discharge port 9 Ink 10 Image signal 11 Cylinder chamber 12 Full multi-printer head 13 Roller 14 Recording paper 21 Ink supply port 22 Pressure chamber 23 Ink discharge port 24 Piezoelectric plate 25 Metal plate 26 Image signal

Claims (1)

[Claims] 1. A cylinder composed of a wire-shaped shape memory alloy piston, a body containing the shape memory alloy piston, a micro droplet discharge port provided at the end of the body, and a cylinder configured by electrically heating the shape memory alloy piston. The wire is contracted in the longitudinal direction and the liquid to be discharged is injected into the cylinder, and then the shape memory alloy piston is expanded by natural heat dissipation in a non-energized state and forced cooling by the injected liquid to be discharged, and the cylinder is A droplet ejecting device comprising a pressure generating means for increasing the pressure of a liquid to be ejected inside the device and ejecting a droplet from a micro droplet ejection port.