JPS62193835A - Ink jet printer - Google Patents

Abstract

PURPOSE:To obtain a small-size, low-cost, highly reliable and thermally controllable by detecting the temperature of a ceramic member using a temperature- sensitive element and thereby controlling a heating element. CONSTITUTION:A compressed ink is supplied to an ink liquid chamber 5 in a head body 1 consisting of ceramic material, and an ink pressure is applied by the distortion of an electrostrictive oscillator 4 on an oscillation signal applied to the electrostrictive oscillator 4. This injects ink through a nozzle outlet. The large diameter section 1B of the head body 1 has a heating element printed in thick film on the ceramic surface, and the A section represents a printed pattern in conductive paste indicating an installation pattern of heater terminal and thermistor. In the meantime, the B section represents a heater pattern region, and the C section has a chip thermistor soldered which detects the temperature of a heated ceramic body. The thermistor is installed in such a way that a temperature difference of ink at a heater and a nozzle outlet may equal the temperature difference at the heater and the thermistor. Under this arrangement, it is possible to make ink temperature constant by controlling thermistor-detected temperature at constant level.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an inkjet printing device, and more particularly, to temperature control of ink ejected from a nozzle in an inkjet printing device.

A conventional inkjet printing device guides ink from an ink supply section to a thin nozzle, and continuously sprays the ink in the form of particles from an opening at the tip of the nozzle to draw letters, figures, etc. on a recording medium. However, in order to perform recording, it is necessary that the frequency of occurrence of ink droplets ejected from a nozzle is stable and that the size of the ink droplets is uniform. However, the properties of the ink increase as the ambient temperature decreases. As the viscosity of the ink increases in this way, the frequency of ink droplet generation decreases, and the ink droplets become more suspicious. If the frequency of occurrence or the diameter of ink particles ejected from the nozzle becomes uneven due to the ambient temperature, the characters printed on the recording medium will become unstable and unclear, leading to a lack of reliability in quality. Become. Conventionally, a heat conductive member is attached to cover the back of the recording head and the ink tube near the head, and a nichrome wire is wrapped around the outer periphery of the heat conductive member and covered with a heat-resistant insulating material. It has been proposed to keep the ink warm by arranging a temperature sensing element in a space provided at a certain position (Japanese Patent Publication No. 54-24658), but it is difficult to completely contact the heat conductive member with the wound nichrome wire. Since this process is not carried out during the process, the thermal efficiency is not sufficient, and there are also problems with durability such as breakage of the nichrome wire.

In addition, some inkjet recording devices have a heater installed in the head liquid chamber to keep the ink warm (Japanese Patent Application Laid-Open No. 49-1989-1).
101473), when the ambient temperature is low and a large heating power is required because the heater is in direct contact with the ink, bubbles may be generated, which limits the control temperature range. There were drawbacks.

-15 The present invention was made in view of the above-mentioned circumstances,
In particular, the present invention aims to provide an inkjet head that is small, inexpensive, has good thermal efficiency, has excellent durability, and can control the temperature of ejected ink with high precision.

Supervisor Kazuhiro In order to achieve the above object, the present invention provides an inkjet printing apparatus that performs recording by ejecting ink from an ink supply section from a nozzle, and a head body that forms an ink liquid chamber or an ink flow path. Comprised of a ceramic member, a heating element is provided on or inside the ceramic member, and a temperature sensing element is provided in close contact with the surface, and the temperature of the ceramic member is detected by the temperature sensing element to control the heating element. It is characterized by Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a sectional view for explaining one embodiment of an inkjet head according to the present invention, in which l is a head body made of a ceramic material, 2 is a nozzle plate, 3 is a pattern portion, and 4 is a piezo vibration Reference numeral 5 denotes an ink liquid chamber or an ink flow path, and as is well known, pressurized ink is supplied to the ink liquid chamber 5 of the head body 1, and the vibrator 4 is distorted by a vibration signal applied to the electrostrictive vibrator 4. The ink pressure in the ink chamber increases, and ink droplets are ejected from the nozzle holes of the nozzle plate 2. A pattern portion 3 consisting of a heater pattern and a sensor pattern is thickly printed on the surface of the head body 1.

FIG. 2 is an enlarged view of the surface of the head body 1 shown in FIG.
Section 18 is the large diameter section of the head body 1 (corresponds to section 18 in Fig. 1), and about 50 to 1000 heating elements are thickly printed on the ceramic surface, and section A is a printed pattern of conductive paste such as silver baladium,
The heater terminal and thermistor installation pattern is shown below.
Part B indicates the heater pattern area, and part 0 indicates the mounting position of the thermistor. A chip thermistor having the shape shown in Fig. 3 is soldered to this position to detect the temperature of the heated ceramic body. . The thermistor is installed at such a position that the temperature difference between the heater and the nozzle outlet ink is equal to the temperature difference between the thermistor and the heater.

Ink temperature can be kept constant by controlling the temperature detected by the thermistor to be constant. Note that it is also easy to configure the pattern shown in FIG. 2 by using a metallization method in which a tungsten material is used as a heating element, and after printing, it is internally pressed into a ceramic material and fired.

FIG. 4 is a diagram showing the temperature-resistance characteristics of the thermistor. Although the sensor has a negative temperature coefficient, by using a metal oxide thermistor, the temperature coefficient is as high as 10'Ppm or more. Highly accurate temperature control becomes possible.

FIG. 5 is a diagram showing an example of an electric circuit used in an inkjet printing apparatus according to the present invention. In FIG.
1 to ○P3 are operational amplifiers, RH is a heater, and HC is a hysteresis comparator circuit. When the temperature sensor Rs shows positive resistance change characteristics, the sensor and voltage characteristics are as shown in Figure 5. (when there is no heating feedback). When thermal feedback is applied to this using a control circuit as shown in Figure 4.

At a temperature below Ts, a current flows through the heater, and the temperature of the sensor section is controlled to be constant at Ts.

In FIG. 4, a voltage divided according to changes in resistor R7 and sensor resistor Rs is output from a voltage follower high input impedance operational amplifier OP1. The output of operational amplifier oP1 is operational amplifier O with hysteresis.
The signal is input to a comparison circuit HC including P2 and an operational amplifier circuit OP3. The reference level Vref of the operational amplifier OP2 and the reference voltage Vref of the operational amplifier oP are determined by the control temperature (
For example, the sensor output voltage Vref corresponding to Ts=30°C
= V rafl - V ref2. Therefore, when the power supply voltage is turned on with the sensor temperature lower than Ts, the output of the operational amplifier OP1 is <Vref, so the output of the operational amplifier OP is at H level, and therefore the collector of the transistor Tr is L level, transistor T
r2 is turned on, and a voltage of VccH is applied to heater RH. At this time, the output of the operational amplifier OP2 is applied to the base of the transistor Tr via the diode D, and the heater RH is connected to the operational amplifier OP2.
This means that VccH is applied regardless of the output level of P. Then, the ink temperature rises due to the heating of the heater, and the sensor resistance Rs increases, so that the output of the operational amplifier ○P1 becomes > Vraf, and when the output of the operational amplifier OP becomes L level, the reference value input Vraf is input through the resistor R4. Since positive feedback is applied to ref, Vref,
The standard level of will decrease. Therefore, operational amplifier OP
Even if the output level of operational amplifier ○P2 decreases somewhat, the output of operational amplifier ○P2 will not become H level, and V ccH will not be applied to the heater.
The current flowing through the transistor Tr is controlled according to the amplified output level of the difference between the output of the operational amplifier P, that is, the output of the operational amplifier ○P, and the reference voltage V ref2, and the voltage is set such that the ink temperature is stable without ripples. is supplied from V cch.

Through the above control operations, even when the ambient temperature is as low as 5°C, the ink temperature inside the head, which has a heat capacity, can be controlled to a constant temperature of 30°C or higher in a short time of 15 to 30 seconds or less after the power is turned on. It becomes possible to stabilize particle formation. In the normal operating state after startup, the heater applied voltage is reduced to a low voltage Vc.
By switching to channel, the loss caused by the transistor Trff can be reduced to 1 W or less, and heat generation can be suppressed.

In an inkjet printing device, the temperature of the ink ejected from the inkjet head changes by 30μ.
The resistance of the fluid flowing out from a minute nozzle of about m size changes, which poses a problem in obtaining stable particle formation without variations in discharge amount or satellites. For example, when the ink temperature changes from 5 to 40'C, the ink viscosity changes greatly, from 5 to 1.5 cp, so it is necessary to control the temperature within a narrow range in order to obtain stable particle formation without satellites.

Effects As is clear from the above explanation, the present invention provides a compact, low-cost device that is stable even under fluctuations in ambient temperature.

It is now possible to provide an inkjet head that can perform highly reliable temperature control, and it is possible to guarantee reliability of printing quality.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining one embodiment of an inkjet head according to the present invention, FIG. 2 is a developed view of the pattern portion of FIG. 1, and FIG. 3 is a diagram showing an example of a thermistor.
FIG. 4 is a diagram showing an example of an electric circuit used in carrying out the present invention, and FIG. 5 is a diagram showing the temperature-resistance characteristics of a thermistor. 1...Head body, 2...Nozzle plate, 3.
...Pattern section, 4...Piezo vibrator, 5...Ink liquid chamber. Figure 1 Figure 3 Figure foil 2 Figure 4 Cause 5 Ward procedural amendment (voluntary) 1. Indication of the case 1985 Patent Application No. 36188 2. Name of the invention Inkjet printing device 3. Case of the person making the amendment Relationship with Patent applicant Ri Ota Nakamagome Address 1-3-6 Nakamagome, Ota-ku, Tokyo Name (674) Ricoh Co., Ltd. Representative Hama 1)
Hiro 4, Agent address: 1-2-7 Furocho, Naka-ku, Yokohama 231
6. Target of correction 7. Contents of correction (1), [Ink particle occurrence frequency] stated in the 1st and 2nd lines of page 3 of the specification is changed to ``Ink particle occurrence frequency is not generated by satellites etc. of ink particles.'' Corrected to ``. (2), page 3, line 4, “The characteristics of the ink are”
is corrected to "What are the viscosity characteristics of the ink?" (3), "The frequency of occurrence becomes lower and . . . increases" written in the 6th and 7th lines of page 3 is corrected to "the occurrence state becomes unstable." (4) The "sensor pattern" described in page 5, line 16, 11 is corrected to "conductor pattern." (5) "The sensor and voltage characteristics will be as shown in FIG. 5" written on page 7, line 9 of the same page will be corrected to "The voltage characteristics of the sensor will be as shown in FIG. 6." (6) ``Figure 4'' written on page 7, lines 11 and 15 is corrected to ``Figure 5''. (7), “4th
The figure is a diagram showing temperature-resistance characteristics used in implementing the present invention. "Figure 4 shows the temperature of the thermistor -
FIG. 5 is a diagram showing an example of an electric circuit used in carrying out the present invention, and FIG. 6 is a diagram showing the temperature-output voltage characteristic of the thermistor. ”. (8), as shown in the attached sheet, Figure 4 is changed to Figure 5, and Figure 5 is changed to Figure 6.
The figure has been corrected and a new figure 4 has been added. Figure 4 'JL seat (C0)

Claims (4)

[Claims] (1) In an inkjet printing device that performs recording by ejecting ink from an ink supply unit from a nozzle, a head body that forms an ink chamber or an ink flow path is constructed of a ceramic member, and the surface or interior of the ceramic member is A heating element is provided on the surface, and a temperature sensing element is provided in close contact with the surface.
An inkjet printing apparatus characterized in that the temperature of the ceramic member is detected by the temperature sensing element to control the heating element. (2) Claim (1) characterized in that the heating element is arranged in the circumferential direction of the ceramic member on the side closer to the nozzle, and the temperature sensing element is provided on the side farther from the nozzle. The inkjet printing device described in 2. (3) The heating element and Claim No.
The inkjet printing device according to item 1). (4) A chip thermistor is used as the temperature-sensitive element, and a signal of a change in resistance value is extracted by a conductive pattern directly printed on the surface of a ceramic member constituting the head body. The inkjet printing device according to item (1).