JPH03190748A - Ink jet head - Google Patents

Abstract

PURPOSE:To enhance the detection accuracy of an ink amount by reducing the effect of a temp. sensor due to the up-and-down movement of the liquid level of ink by providing a radiation part member to the temp. sensor. CONSTITUTION:A thermistor 36 is directly provided to the lower end of a radiator 32 in such a state that the detection part thereof protrudes from a radiator 32 by about 0.5mm and connected to a constant current source 30 through a voltage detection means 31. At this time, since the thermistor 36 is provided in an ink reservoir 14, the quantity of heat supplied to the thermistor 36 and the quantity of heat radiated from the radiator 32 reaches certain equlibrium temp. and the detection temp. due to the thermistor 36 is determined. At this time, a voltage value is detected using the voltage detection means 31.

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 forms an ink image on a medium such as recording paper by ejecting ink droplets. The present invention relates to an improvement in a means for detecting the amount of ink within a head.

[Prior Art] Conventionally, as an ink amount detection device for hot melt ink used in an inkjet head having an ink tank on a carriage, as disclosed in Japanese Utility Model Application Publication No. 62-90137, etc., A device that detects the amount of ink by attaching a thermistor to the ink and detecting the temperature is widely known.

[Problems to be Solved by the Invention] In the above-mentioned conventional apparatus, when the carriage vibrates for printing and the ink tank on the carriage vibrates, the part where the thermistor is attached is damaged by the ink in the ink tank. The temperature rises due to the vertical movement of the liquid level due to vibrations.

For this reason, there was a problem in that the detected temperature fluctuated and the accuracy of ink amount detection deteriorated. Furthermore, since the detection time becomes longer, throughput is affected and the effective printing speed becomes slower.

SUMMARY OF THE INVENTION An object of the present invention is to solve this problem and provide an inkjet head that improves ink amount detection accuracy, shortens detection time, and improves throughput.

[Means for Solving the Problems] The inkjet head of the present invention uses hot melt ink that is solid at room temperature and liquid at high temperature, and uses a temperature sensor as a means for detecting the amount of ink stored in an ink tank on a carriage. The inkjet head is characterized in that the temperature sensor is provided with a heat radiating member.

[Example] Next, the present invention will be explained based on examples.

FIG. 1 is a perspective view showing a head section of a printer that is an embodiment of the present invention. In the figure, recording paper 20 is guided by paper guide shafts 21 and 22, and is conveyed while maintaining a distance from an inkjet head 23 (hereinafter abbreviated as head).

The head 23 has a plurality of nozzles 24 arranged in two rows on a surface facing the recording paper 20, is guided by head guide shafts 25 and 26, and is configured to scan the recording paper by a drive member (not shown).

FIG. 2 is a sectional view of the head. In the same figure, l is a container-shaped head frame 1, and an upper casing 4 is attached to this.
, and a lid 9 are provided. The interior of the head frame 1 is partitioned into two chambers by a partition wall 13 having a communication passage 13a at the bottom, and the - chamber serves as an ink reservoir tank 14. Ink 16 is stored in this reservoir tank 14.

A heater 2.3 is provided at the bottom of the head frame 1. A holder 5 that accommodates a member forming a plurality of slits for ink supply is inserted into a part of the upper casing 4, but the details are not shown. A plate-shaped filter 12 having a large number of microscopic holes is attached to the lower part of the holder 5 . A part of the holder 5 is provided with a temperature detection sensor 7 and an auxiliary heater 8 for heating ink near the ink ejection section. A nozzle forming substrate 17 is arranged on the upper part of the holder 5, and a piezoelectric transducer increases pressure behind the nozzle provided on the nozzle forming substrate 17 to selectively eject ink. The principle of ink ejection and the configuration of the piezoelectric transducer are detailed in Japanese Patent Laid-Open No. 63-297052, and since they are not directly related to the gist of the present invention, a detailed explanation will be omitted. The ink 16 in the head is solid at room temperature, and is melted by the heater 2.3 at the start of operation. In this example, a solid ink whose main component is wax is used, so in order to prevent the ink from deteriorating in a high-temperature environment, it is liquefied by heating to 80° C., which is slightly higher than the melting point, and maintained at a constant temperature. On the other hand, in the vicinity of the nozzle, it is necessary to maintain the ink at a predetermined temperature of 100°C to 200°C to reach the desired viscosity due to the relationship with the ejection characteristics. energize intermittently,
The holder 5 is controlled to a predetermined temperature. liquid ink 1
6 reaches the lower part of the holder 5 from the ink reservoir tank 14 through the communication path 13a at the lower part of the partition wall 13. Then, the slit-shaped member 6 is raised by capillary force, filled between the piezoelectric transducer arranged near the nozzle forming substrate 17 and the nozzle forming substrate, and heated to the discharge temperature. Ink droplets are selectively ejected from the nozzle by applying a voltage to a desired one of the plurality of piezoelectric transducers.

An ink amount detection device 18 attached to the lid 9 is provided inside the ink reservoir tank 14 . When the ink amount detection device 18 detects that the amount of liquid ink remaining inside the head is less than a predetermined value, it outputs an ink replenishment request signal.

When the ink amount detection device 18 outputs an ink replenishment request signal, the head opens the lid 9 and moves to the ink supply position. Then, at this position, the ink mass is introduced into the ink reservoir 14 from the ink supply device.

Details of the ink amount detection device 18 will be explained with reference to FIG. As shown in the figure, the ink amount detection device 18
The thermistor 36 is a temperature sensor, and the heat radiation member is a heat radiation member! ! 32, a constant current source 0, and a voltage detection means 31. The thermistor 36 is directly attached to the lower end of the heat radiator 32 with its detection portion protruding from the heat radiator by approximately 0.5 mm, and is connected to the constant current source 30 via the voltage detection means 31. The thermistor 36 used here has a diameter of 1°3
This is a high heat resistant thermistor with a length of 5mm and a length of 3.5mm. The reason why the thermistor 36 is extended from the lower end of the 0.5 mm radiator 32 is to increase the detection speed and detection efficiency. The thermistor 36 is connected to the ink reservoir tank 1
4, the amount of heat supplied to the thermistor 36 and
A certain equilibrium temperature is reached depending on the amount of heat radiated from the radiator 32, and the temperature detected by the thermistor 36 is determined. The voltage value at this time is detected using the voltage detection means 31.

When the thermistor 36 is in the air (that is, when it is not in contact with liquid ink), the heat capacity of air is small, so the amount of heat supplied from the air in the ink tank is small, and the equilibrium temperature is low. When the thermistor 36 is in liquid ink, the heat capacity of the liquid ink is greater than that of air;
The amount of heat supplied by the liquid ink in the ink tank is greater than the amount of heat supplied by air, and the equilibrium temperature is higher than if it were in air. For example, if the thermistor 36 is an element whose electrical resistance decreases exponentially with temperature, the resistance of the thermistor 36 is large in air, so the detection voltage is small, and in liquid, the resistance of the thermistor is small, so the detection voltage is large and the detection voltage is large. This change is detected by the voltage detection means 31, and it can be determined whether the thermistor 36 is in the air or in the liquid. Therefore, the amount of ink in the ink tank can be detected.

FIG. 4 shows an embodiment of the heat shielding member. As shown in FIG. 1, during printing, the ink tank 14 is reciprocating with the carriage. For this reason, the high temperature ink comes into contact with the lid 9 due to the vibration of the surface of the ink 16 in the ink tank 14, reducing the efficiency of the radiator 32 and reducing the temperature difference between the air and the liquid. It may take time to detect the presence or absence of 45. Therefore, in FIG. 4, a heat shielding plate 42 is provided between the ink tank 14 and the lid 9. By providing the heat shield plate 42, the vibrated high-temperature ink 16 does not come into direct contact with the lid 9. Therefore, the efficiency of the heat radiator 32 does not decrease, and the detection speed of the thermistor 36 can be increased. The heat shield plate 42 is made of a material such as plastic, which has a lower thermal conductivity than metal.

FIG. 5 shows an embodiment of the ink level vibration prevention mechanism. In order to prevent the liquid level of the ink 16 from vibrating, two plate members 54 are installed inside the ink tank 14, and a thermistor 3 is installed here.
It is attached so as to surround 6. By attaching the plate member 54, the vibration of the high temperature ink 16 is reduced. Therefore, the efficiency of the heat radiator 32 does not decrease, and the detection speed of the thermistor 36 can be increased.

Note that both the embodiments shown in FIGS. 4 and 5 may be performed simultaneously.

[Effects of the Invention] As described above, in the present invention, since the temperature sensor is provided with a heat dissipation member, it is possible to reduce the influence of vertical movement of the ink liquid level on the temperature sensor, thereby making it possible to detect the amount of ink. Accuracy can be improved. Furthermore, the detection time can be shortened and the throughput can be improved. In addition, if a heat shielding member is provided between the heat dissipation member and the ink liquid surface, or if a mechanism is provided to prevent ink liquid level vibration, the negative layer detection error will be small and the detection speed will be large. This has the effect of improving the effective printing speed because the throughput is less reduced due to ink amount detection.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a head section of an inkjet recording apparatus. FIG. 2 is a sectional view of the inkjet head. FIG. 3 is a diagram showing the configuration of an ink amount detection device used in an inkjet head. FIG. 4 is a diagram showing an embodiment of the ink heat shielding member of the inkjet head of the present invention. FIG. 5 is a diagram showing an embodiment of the ink liquid level vibration prevention mechanism of the inkjet head of the present invention. 3 16 4 8 6 2 1 2 4 To the inkjet Twin cup lid Ink tank Ink amount detection device Thermistor Radiator Voltage detection means Heat shield plate Plate member or more

Claims (1)

[Claims] 1) In an inkjet head that uses hot melt ink that is solid at room temperature and liquid at high temperature and uses a temperature sensor as a means to detect the amount of ink stored in an ink tank on a carriage, heat is radiated to the temperature sensor. An inkjet head characterized by being provided with a member. 2) The inkjet head according to claim 1, further comprising a heat shielding member provided between the heat radiation member and the ink liquid surface. 3) The inkjet head according to claim 1 or 2, further comprising a plate-shaped member surrounding at least a portion of the temperature sensor within the ink tank.