JPH0332850A - Ink jet head - Google Patents

Abstract

PURPOSE:To obtain an ink jet head provided with an ink amount detection means with high accuracy and high reliability using a small amount of ink by a method wherein a heating resistor is electrically conducted to be heated, and a contained ink amount is detected by the detection of the heat release efficiencies of the heating resistor when it exists in the air and in a liquid. CONSTITUTION:When an amount of liquid state ink remaining inside a head is detected to be not more than a predetermined value by an ink amount detector 27 inside the head, an ink refilling request signal is outputted. Namely, the liquid surface of ink 23 is required to be positioned lower than the axis of a nozzle opening 22 for keeping the inside of the head in a vacuum state. To keep an ink amount up to L2 or lower, an ink refilling signal is outputted when an ink liquid surface reaches L1 lower than L2, a predetermined amount of ink is refilled, and the ink liquid surface is raised. Therefore, whether or not an ink surface is present at a level L1 is detected by extending a heating resistor wire 29 at the position L1. In an ink refilling action, with the output of an ink refilling request signal from the head, the head opens a cover 26 and moves to an ink supply position, and a mass of ink is charged from an ink supply device.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an inkjet head used in an inkjet recording device such as a printer that flies ink droplets to form an ink image on a medium such as recording paper. This invention relates to an ink amount detection device.

[Conventional technology]

Conventional ink amount detection devices used in inkjet heads include a method that utilizes the fact that the vibration characteristics of a vibrator differ in air and liquid (Japanese Patent Application Laid-Open No. 6O-18350), and a method that uses static electricity between two flat plates depending on the presence or absence of ink. A method using the fact that the capacitances are different (Japanese Patent Application Laid-Open No. 60-187725) is known.

[Problem to be solved by the invention]

Of the above methods, the former requires a high-frequency signal processing circuit to detect changes in vibration characteristics, resulting in a complicated configuration, and the latter has the problem of low detection accuracy due to a small rate of change depending on the capacity and the presence or absence of ink. . On the other hand, as a simple method, it is also possible to provide a light emitting element and a light receiving element and detect a change in light transmittance depending on the presence or absence of ink existing between them. However, it has the problem that it is prone to malfunction due to adhesion of foreign matter and has low reliability.

An object of the present invention is to solve these problems and provide an inkjet head equipped with highly reliable ink amount detection means that can detect the amount of stored ink with high precision using a small amount of ink.

Yet another object is to provide an inkjet head having ink amount sensing means applicable to hot melt ink.

[Means to solve the problem]

The inkjet head of the present invention has a heating resistor provided so as to be below the ink liquid level when the amount of ink is above a predetermined amount, and the heating resistor is energized to generate heat, and the heating resistor is in the air. The present invention is characterized in that the amount of stored ink is detected by detecting the heat dissipation efficiency when the ink is in the liquid and when the ink is in the liquid.

[Effect]

In the above configuration of the present invention, the amount of ink is detected by causing the heating resistor to generate heat under predetermined conditions and detecting the equilibrium temperature difference between the liquid and the air.

〔Example〕

Next, the present invention will be explained based on examples. The principle of ink amount detection used in the inkjet head of the present invention will be explained using FIG. In the figure, a heating resistor 1 made of a thin metal wire is stretched across a terminal plate 6.7 provided on an insulating substrate 4 and connected to a constant voltage source 2 via a current detection means 3. A current determined by the circuit resistance and the applied voltage is passed through the heating resistor 1, causing the heat generating resistor 1 to generate heat, and the temperature rises to reach an equilibrium temperature determined by the heat radiation characteristics. This current value is determined by the current detection means 3.
Detected using In this case, when the heating resistor 1 is in the air, the amount of heat radiated is small (the thermal resistance is large), so the equilibrium temperature is high, and when the heating resistor 1 is in the liquid, the amount of heat radiated is large (the thermal resistance is small). Therefore, the equilibrium temperature is low. Heat generating resistor 1
For example, if the electrical resistance increases with temperature in metal, the current is small in air and large in liquid, and the current detection means 3 detects this change and determines whether the heating resistor is in the liquid or in the air. You can find out if there is.

Next, the present invention will be described based on an embodiment of an inkjet head equipped with an ink amount detection device based on the above principle.

FIG. 2 is a perspective view of a printer showing an embodiment of the present invention. In the figure, a recording paper 10, which is a recording medium, is wound around a platen 11 and pressed by a feed roller shaft 12.

The inkjet head 1 is mounted on a carriage 15 that is guided by guide shafts 13 and 14 and is movable in a direction parallel to the platen axis.
6 (hereinafter referred to as head) is installed.

The recording paper 10 is conveyed in a sub-scanning direction perpendicular to the scanning direction by rotation of the platen 11, and printing is performed on the recording paper. Inside the apparatus, an ink supply device 18 is provided on the side of the head scanning start position, and an ink container 17 for storing solid ink (not shown) is installed.

This head uses a method that melts ink that is solid at room temperature, and the head is maintained at a high temperature by a heater (not shown in this figure). The head has a plurality of nozzles that can independently control the ejection of ink droplets, and is scanned in the direction of the platen axis to selectively eject ink droplets to form an ink image on the recording paper 10.

FIG. 3 is a sectional view of a head showing an embodiment of the present invention. The container-shaped casing 20 is made of aluminum, and is installed so that the nozzle opening 22 faces the recording paper 10 wound around the platen 11. A vibrator 24, which is a pressure generating member, and electric wiring 25 are provided on the back side of the nozzle opening 22. The vibrator 24 is constructed by laminating a piezoelectric element and a nickel plate.

It has a cantilever structure in which one end is a fixed end and the other end is a free end. The free end of the vibrator 24 is placed opposite the nozzle opening 22.

Ink is stored in an ink reservoir 21. An ink amount detection device 27 is provided within the reservoir.

A heater 28 as a heat source is installed in the housing 20 on the back side of the pressure generating means.
installed on top. Thermal energy generated by the heater 28 is used to heat and melt the ink 23 and maintain its temperature.
0 Next, the operation will be explained. At the start of operation, the heater 28 is driven to heat the head. The head is heated from near the heater, and a small amount of ink existing near the pressure generating member is sequentially melted and liquefied. After a predetermined time period when the amount of molten ink required to start the printing operation is secured, the head starts the printing operation.

Next, the ink ejection operation will be explained. Multiple oscillators 2
When a selective electric signal is applied to a desired vibrator of 4, the vibrator deforms due to the piezoelectric effect and pressure is generated. This pressure causes ink droplets to be ejected.

When the ink amount detection device 27 inside the head detects that the amount of liquid ink remaining inside the head is less than a predetermined value, an ink replenishment request signal is output. That is, in this apparatus, the liquid level of the ink 23 must be located below the axis of the nozzle opening 22 in order to maintain a negative pressure inside the head. Therefore, in order to keep the ink amount below L2 in Figure 3, in this embodiment, when the ink level reaches Ll, which is lower than this, an ink replenishment signal is output, and a predetermined amount of ink is replenished, and the ink level rises to L2. . Therefore, the heating resistor wire 29 is placed at the position of Ll.
It is detected whether or not the ink surface is at the L1 level.

In the ink replenishment operation, when an ink replenishment request signal is output from the head, the head opens the lid 26, moves to the ink supply position, and receives ink lumps from the ink supply device 18.

In this example, the heating resistor has a diameter of 60 μm and a length of 1°5 mm.
tungsten wire was used. It has resistance temperature characteristics as shown in Fig. 4. The ink is a hot-melt ink whose main component is wax, and the head is maintained at 100°C to keep it in a liquid state. According to experiments, the heating resistor exhibited a thermal resistance of 56 C/W in ink and 300'C/W in air. For this reason, when an output of 0.5 W is applied, for example, when the ink liquid level has not reached the heating resistor, the ink level is balanced at 250'C, which is 150'C higher than the temperature inside the ink reservoir.

Therefore, the heating resistor shows approximately 1.5Ω from FIG.

On the other hand, when the amount of ink is such that the heating resistor is located below the liquid level, most of the input heat is supplied to the ink, and the heating resistor is maintained at the same temperature as the ink. Moreover, since the amount of heat generated is minute, the ink temperature does not rise.

Therefore, it exhibits a resistance of approximately 1Ω. In actual cases, by driving at about 0.5 .mu.m, a current change corresponding to the above-mentioned characteristics can be obtained, and this can be detected as a voltage change by a current detection resistor.

In this example, the posture can be adjusted by providing the reservoir near the center.
The influence of undulating liquid surface due to acceleration and deceleration can be minimized. Further, various methods such as constant current, constant voltage, constant power, pulse drive, etc. can be used as the disturbance method. The heating resistor preferably has an appropriate resistance value and a large temperature resistance coefficient, and various materials such as aluminum and aluminum can be used.

It can also be applied to inkjet heads that use liquid ink instead of hot melt ink. Furthermore, the ink ejection principle can be applied to various types of inkjet heads, such as a thermal inkjet type, in addition to the above-mentioned method.

[Effects of the Invention] As described above, according to the above structure of the present invention, the amount of ink stored in the head is detected with a simple structure by the heat dissipation effect of the ink in contact with the heating resistor, so the amount of ink is small. This has the effect that a signal with a large S/N ratio can be obtained using this ink. Further, it has the effect that a small-sized detection means can be realized and the head can be made smaller. Furthermore, since the structure is simple and there are no moving parts, it is highly reliable, and has the advantage that it is less likely to malfunction due to solidified ink or foreign matter and can be applied to heads using hot melt ink. It also has the effect that even color ink can be detected effectively.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram illustrating the operating principle of the ink amount detection means used in the inkjet head of the present invention. FIG. 2 is a perspective view of an inkjet printer showing an embodiment of the present invention. FIG. 3 is a sectional view of an inkjet head showing an embodiment of the present invention. FIG. 4 is a diagram showing the resistance temperature characteristics of a heating resistor used in an embodiment of the present invention. Heat-generating resistor current detection means twin to inkjet Ink amount detection device heat-generating resistor wire application

Claims (1)

[Claims] When the amount of ink exceeds a predetermined amount, a heating resistor is provided so as to be below the ink liquid level, and the heating resistor is energized to generate heat, and when the heating resistor is in the air and when it is in the liquid. An inkjet head characterized in that the inkjet head is configured to detect the amount of stored ink by detecting the heat dissipation efficiency of the case.