JPS6280051A - Ink jet printer - Google Patents

Abstract

PURPOSE:To improve the temperature control of highly efficient head discharged ink and miniaturization/reliability by changing the power supply voltage used of a heater depending on occasion, i.e. an initial stage of power supply connection and normal use time. CONSTITUTION:When a power supply voltage is turned ON under a condition that a sensor temperature is lower than a control temperature Ts, the output of an operational amplifier OP2 is at 'H' level because of the output of an operational amplifier OP1 lower than a reference level Vref1. Accordingly, the collector of transistor Tr1 is at 'L' level and transistor Tr2 is in 'ON' condition with a heater RH applied with VccH voltage. Then a sensor resistance Rs increases by a soaring ink temperature under the heating of a heater. This results in the operational amplifier OP1 output>Vref1. If the output of the operational amplifier OP2 reaches 'L' level, a positive feedback occurs to the reference value input Vref1 through a resistor R4, causing a drop in the reference level Vref1. Consequently an electric current running through transistor Tr3 is controlled according to the difference between the output of the operational amplifier OP1 and a reference voltage Vref2 and a voltage is supplied from Vcch so as to obtain a stable ink temperature.

Description

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

The conventional inkjet printing device guides ink from an ink supply unit to a narrow nozzle, and continuously sprays the ink in the form of particles from an opening at the tip of this nozzle to draw a letter 9 shape on a recording medium. 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 are affected by changes in ambient temperature, and in particular, the viscosity of the ink increases as the ambient temperature decreases.

As the viscosity of the ink increases in this manner, the frequency of ink droplet generation decreases, and the diameter of the ink droplets increases. 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 over time, the thermal efficiency is not sufficient, and there are also problems with durability such as deterioration of nichrome wire over time. In addition, some inkjet printing devices keep the ink warm by installing a heater inside the head liquid chamber (
However, since the heater is in direct contact with the ink, various problems occur with the ink, and especially when the ambient temperature is low and a large heating power is required, bubbles may be generated. This has the disadvantage that the rise time, control temperature range, etc. are limited.

Purpose The present invention was made in view of the above-mentioned circumstances.
Particularly, in a single or multi-nozzle inkjet printing device, the purpose of this invention is to efficiently control the temperature of the ink ejected from the head, thereby reducing the size and improving reliability.

Structure In order to achieve the above object, the present invention includes a head body made of a ceramic material, a heating heater provided on the surface of the head body, and a changing means for changing the power supply voltage used for the heating heater. The power supply voltage used by the heating heater is changed between the initial stage when the power is turned on and during regular use. An explanation will be given below based on one embodiment of the present invention.

FIG. 1 is an electric circuit diagram for explaining one embodiment of the present invention. In the figure, Rs is a temperature sensor (
For example, thermistor), OP, ~OP3 are operational amplifiers, R
H is a heater, HC is a hysteresis comparison circuit, and when the temperature sensor Rs exhibits positive resistance change characteristics, the sensor and voltage characteristics become as shown in Figure 2 (however, this is a state in which feedback of heater heating has never occurred). When). When thermal feedback is applied to this by a control circuit as shown in FIG. 1, a current flows to the heater at a temperature below Ts, and the temperature of the sensor section is controlled to be constant at Ts.

In FIG. 1, a high input impedance operational amplifier ○P is a voltage follower in which a voltage is divided according to changes in a resistor R1 and a sensor resistor Rs.

It is output from The output of the operational amplifier OP is input to a comparison circuit HC including an operational amplifier oP2 having hysteresis and an operational amplifier circuit OP3. The basic level V ref of the operational amplifier ○P and the reference voltage ref2 of the operational amplifier OP are the sensor output voltages Vref = V ref, -V ref corresponding to the control temperature (for example, Ts = 30°C)
Set to 2. Therefore, when the power supply voltage is turned on with the sensor temperature lower than Ts, the output of the operational amplifier OP2 is at H level because the output of the operational amplifier ○P1 is less than Vref, and therefore the collector of the transistor Tr At L level, the transistor Tr2 is turned on, and a voltage of VccH is applied to the heater RH. At this time, the output of the operational amplifier oP2 applies an H level voltage to the base of the transistor Tr via the diode D1.
VccH is applied to the heater RH regardless of the output level of the operational amplifier ○P3. Then, the ink temperature rises due to the heating of the heater, and the sensor resistance Rs
becomes large and the operational amplifier is OP.

Output > Vref, and the output of operational amplifier ○P2 becomes L.
When the level is reached, the reference value human power ■ref is applied via the resistor R4.
Since positive feedback is applied to , the basic level of Vref, decreases. Therefore, even if the output level of the operational amplifier oP decreases somewhat, the output of the operational amplifier oP will never reach the TI level, and VccH will not be applied to the heater. Therefore, from now on, the output of operational amplifier ○P3, that is, the output of operational amplifier OP, and the reference voltage V ref
Transistor T depending on the amplified output level
The current flowing through r3 is controlled and a voltage is supplied from V cch that provides a stable ink temperature with no ripple.

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 within a short time of 15 to 30 seconds after the power is turned on. It becomes possible to stabilize the particle formation. In normal operating conditions after startup, the heater applied voltage is reduced to a low voltage V.
By switching to cch, the loss caused by the transistor Tr3 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, and the change in discharge amount becomes a problem in obtaining stable particle formation without satellites. For example, when the ink temperature changes by 5 to 40 degrees Celsius, the ink viscosity changes significantly to 5 to 5 cp.

To obtain stable particle formation without satellites, temperature control within a narrow range is required.

FIG. 3 is a configuration diagram for explaining an example of an inkjet head to which the present invention is applied. In the figure, 1 is a spatula body, 2 is a nozzle plate, and 3 is a heater resistor (RH).
, 4 is a temperature sensor (Rs), 5 is a piezo vibrator, 6 is a head holder, 7 is an ink supply tube, and as is well known, the ink in the head body 1 is supplied to the nozzle plate 2.
The head body 1
The ink temperature within is controlled as described with respect to FIG. The example shown in FIG. 3 is an example in which a ceramic material is used for the head body 1 that constitutes the liquid chamber that supplies ink to the nozzle section, and the ceramic material in contact with the liquid chamber is directly heated by the heater 3. As a result, efficiency and control response are greatly improved. Furthermore, since the ceramic material has good corrosion resistance and chemical resistance, there is no problem of contact with ink, and temperature control is possible. In addition, alumina content 9
By using 0% or more ceramic material, sUs
Thermal conductivity is equal to or higher than that of other metals, and the above effects can be further improved. According to the present invention, since the heating element and the heating element are in close contact with each other, the thermal conductivity is good.
By using a planar heater pattern, it is possible to design a high watt density per unit area. Also, as a heating resistor.

A resistor paste whose main ingredients are nickel, platinum, etc. is used, and this resistor paste is thick-film printed on a ceramic material.

FIG. 4 is a sectional view showing another embodiment of the present invention.

In this embodiment, the head body and heater are made of insulating resin material 8.
This improves thermal efficiency.

FIG. 5 is a perspective view of a multi-nozzle head using a head according to the present invention, and FIG. 6 is a cross-sectional view. and are given the same reference numerals as in FIG.

Effects As is clear from the above description, according to the present invention, ink temperature control with little loss is possible using a small, low-cost control circuit.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram for explaining one embodiment of the present invention, FIG. 2 is a characteristic diagram of a temperature sensor, and FIGS. 3 and 4 are diagrams of an inkjet head to which the present invention is applied. 5 is a perspective view showing an example of a multi-nozzle head, and FIG. 6 is a sectional view showing an example. Rs... Temperature sensor resistance, CP, ~QP3... Operational amplifier, RH... Heater resistance, 1... Head body, 2... Nozzle plate, 3... Heater resistance (RH
), 4... Temperature sensor (Rs), 5... Piezo vibrator, 6... Head holder, 7... Ink supply tube, 8... Insulating resin material.

Claims (3)

[Claims] (1) A head body made of ceramic material,
It has a heating heater provided on the surface of the head body, and a changing means for changing the power supply voltage used by the heating heater, and the power supply voltage used by the heating heater is changed between the initial stage when the power is turned on and the power supply voltage used during regular use. An inkjet printing device characterized by changing voltage. (2) It has an ink temperature detection means and a comparison circuit having hysteresis, and the output signal of the temperature detection means is input to the comparison circuit, and the output signal of the comparison circuit is used for regular use at the initial stage of power-on. The inkjet printing apparatus according to claim 1, wherein a voltage higher than that applied to the heating heater is applied to the heating heater. (3) Reference voltage Vref_1 of the comparator circuit that determines the applied voltage at the initial rise when the power is turned on, and reference voltage Vref_ of the comparator circuit that determines the applied voltage during normal use after the power has started up.
2, the reference voltage is set to Vref_1≒Vref_
2. The inkjet printing apparatus according to claim 1, wherein the inkjet printing apparatus is set to the following relationship.