JPH05215589A - Device for detecting amount of remaining ink - Google Patents

Abstract

PURPOSE:To obtain a device for detecting amount of remaining ink which accurately operates even in the case when a highly viscous ink is used and can detect the level of a liquid surface quantitatively. CONSTITUTION:The title device consists of a tungsten wire 20 which is mounted so that the amount which is buried into an ink 24 changes according to the amount of remaining ink 24 and whose resistance changes according to the temperature and a current supply part 2 which allows current to flow so that the resistance of the tungsten wire 20 becomes constant. By detecting a current value which is supplied to the tungsten wire 20, the amount of remaining ink is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting the remaining amount of ink in an ink tank in an ink jet printer or the like.

[0002]

2. Description of the Related Art An image forming apparatus such as an inkjet printer has an ink tank for storing liquid ink inside the apparatus. In such an apparatus, it is desirable to have a configuration that monitors the amount of ink in the ink tank and informs the user of that when the remaining amount is low.

Conventionally, the following two configurations are known as an ink remaining amount detecting apparatus for realizing such a configuration.

One is to use the conductivity of ink,
In this type of structure, two electrodes are arranged in the ink tank, and the electric resistance value between the electrodes is changed by the presence or absence of ink between the electrodes or the change of the ink liquid level. The electrical resistance value is detected to detect the remaining amount of ink.

A structure using an optical sensor is also known. In this configuration, the light emitting element and the light receiving element are arranged on both sides of the ink tank, and it is determined whether or not the light emitted from the light emitting element is blocked by the ink to detect the remaining amount of the ink.

[0006]

However, since the former structure utilizes the conductivity of the ink, it cannot be used in the case of wax-based solid ink having no conductivity. There is a point.

The latter cannot block the light when the ink is a light color. In addition, even when using a dark ink, especially when using a highly viscous ink, the ink adheres to the side surface of the tank even if the liquid level drops,
It blocks the light. Further, in this latter configuration, there is a problem in that it is not possible to quantitatively detect the remaining amount of ink, although it is possible to know whether the ink surface is above the light emitting element or the light receiving element.

The present invention has been made in order to solve the above-mentioned problems, has a good responsiveness, and operates accurately even when used for an ink having a high viscosity, and the remaining amount of the ink can be quantitatively determined. It is an object of the present invention to provide an ink remaining amount detecting device capable of detecting the remaining amount.

[0009]

In order to achieve this object, an ink remaining amount detecting device of the present invention is installed in an ink tank such that the amount of immersion in ink changes according to the amount of remaining ink. A heat generating portion that generates heat by passing an electric current and whose resistance value changes according to the temperature,
It is characterized by comprising a current supply unit for supplying a current to the heat generating unit so that the resistance value of the heat generating unit becomes constant, and means for detecting the current value of the current supplied to the current supply unit. is there.

[0010]

In the ink remaining amount detecting device of the present invention having the above structure, the heat generating portion generates heat by the current supplied from the current supplying portion, and at the same time, the generated heat is released to the surrounding ink and air. The current value supplied from the current supply unit is always adjusted so that the resistance value of the heat generating unit is constant, and the resistance value corresponds to the temperature of the heat generating unit, resulting in a constant temperature of the heat generating unit. The flowing current is adjusted so as to be maintained at the value of. Therefore, the amount of heat generated is always kept to be the same as the amount of heat released.

On the other hand, the amount of immersion of the heat generating portion into the ink changes according to the remaining amount of the ink, and the heat transfer rates of the ink and the air also differ, whereby the average heat flux when releasing heat from the heat generating portion. Also changes according to the remaining amount of ink. As a result, the current value required to keep the temperature of the heat generating part at a constant value also changes according to the remaining amount of ink. Therefore, the remaining amount of ink is detected by measuring the current value.

As can be seen from the above operating principle,
To know the remaining amount of ink, it suffices to measure the value of the current flowing through the heat generating portion, so that it takes almost no time. Also, use it for highly viscous materials such as wax-based solid ink, and even if the ink adheres to the heat generating part when the ink level drops, the heat transfer in that part is basically performed in the air. Has little effect on accuracy. By further lengthening the heat generating portion, the height of the liquid surface can be quantitatively measured.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a concrete configuration of the ink remaining amount detecting apparatus of this embodiment.

A liquid insulating ink (hereinafter simply referred to as ink) 24 is contained in the ink tank 10.
The ink 24 is supplied to a print head (not shown) via a supply passage 28 provided below the ink tank 10. The mechanism for transporting the ink 24 from the ink tank 10 to the print head and the control of the print head are not related to the gist of the present invention, and therefore a detailed description thereof will be omitted.

A holder 14 provided on the upper lid 12 of the ink tank 10 has two long and short conductive columns 16 and 18 which are stretched so as to extend in the vertical direction. A thin tungsten wire 20 is vertically mounted between the lower ends of the conductive columns 16 and 18 and electrically connected to the conductive columns 16 and 18. The upper ends of the columns 16 and 18 are electrically connected to the current supply unit 22 to form an electrically closed circuit.

As is well known, tungsten has the property that it generates heat when an electric current is passed through it, and its electrical resistance becomes high at high temperatures, like a general good conductor.

The tungsten wire 20 is designed so that even if the liquid surface height of the ink 24 in the ink tank 10 changes, part of the tungsten wire 20 is immersed in the ink 24 and the rest is exposed to the air. The amount of immersion changes according to the consumption of. Further, the heat generated from the tungsten wire 20 is radiated to the ink 24 or the air 26 around it.

FIG. 2 is a diagram showing a circuit of the current supply unit 22 of this embodiment. The voltage at the output terminals c and d of the bridge circuit 32, which is composed of a resistor R _P including the sensor unit 30 including the tungsten wire 20 and resistors R _A , R _B , and R _C having a constant resistance value, a total of four resistors. Is R1, R2, R3, R
4 and the amplifier A are applied to the inverting input terminal and the non-inverting input terminal of the differential amplifier circuit 34. The output terminal e of the operation amplification circuit 34 is connected to the power supply via the resistors R5 and R6. Further, power is supplied to the input end a of the bridge circuit 32 from the connection point f of the resistors R5 and R6. The terminal b of the bridge circuit 32 is connected to the ground via the resistor R7. The non-ground side terminal of the resistor R7 is hereinafter referred to as a terminal g. By measuring the voltage between the terminal g and the ground, the value of the current flowing through the resistor R7, that is, the current flowing through the bridge circuit 32 can be known.

The voltage at this terminal g is the A / D converter 35.
Input to the input terminal of. A one-chip type central processing unit (CPU) 36 is connected to the output terminal of the A / D converter 35. The CPU 36 operates according to a program written in the built-in read-only memory, and displays the remaining amount of ink according to the output of the A / D converter 35. At this time, the ink remaining amount and the current flowing through the resistor R7 (proportional to the voltage of the terminal g) are not linear as shown in FIG.
The CPU 36 linearly corrects and displays by a look-up table or calculation, for example. When the voltage at the terminal g falls below a predetermined value, a message prompting ink supply is displayed.

The operation of the present apparatus having the above structure will be described below. First, when the power is turned on, a predetermined amount of current flows to raise the temperature of the tungsten wire 20 slightly above the temperature of the ink and the outside air. As the temperature rises, the resistance value of the resistor R _P including the tungsten wire 20 rises. When the resistance value R _P reaches a predetermined value corresponding to the values of the resistors R _P , R _A , R _B , R _C , and R1 to R4, the temperature of the tungsten wire 20 is increased by the action of the circuit. Ink tank 10
At some value higher than the temperature of the ink 24 and air in it, the current becomes stable. That is, the tungsten wire 20
The same amount of power as the amount of heat radiated is supplied.

From this state, the ink 24 is printed by the printing operation.
When the remaining amount decreases and the liquid level becomes low, the heat of the ink 24
If the transmissibility is greater than that of air, for example, the tongue
The heat flux near the stainless steel wire 20 becomes small,
The temperature of the tungsten wire 20 rises and its resistance
Chi R_PWill increase. On the other hand, R_PAs the bridge times
The potential at the point c with respect to the output d of the path 32 rises, which is the difference.
When the voltage at the point e is lowered by being amplified by the dynamic amplification circuit 34,
As a result, the voltage at point a drops. After all, it flows to the bridge circuit
The current decreases and the temperature of the tungsten wire 20 is the original temperature.
Down to R _P'S resistance also returns. Because of this
Although it is in a stable state, the voltage of output terminal g is
Is detected, it is detected that the ink level is low.
Be done.

By measuring the voltage applied to the terminal g in this manner, the remaining ink amount can be detected. This voltage is digitized by the A / D converter 35 and read by the CPU 36. Then, the CPU 36 displays the remaining amount of the ink 24 (which is linearly corrected by the calculation of the CPU or the reference of the look-up table) corresponding to the numerical value on the display 37. Also this A
If the output value of the / D converter 35 is less than or equal to the predetermined value, a display for instructing the replenishment of the ink 24 is displayed. At this time, processing such as sounding a buzzer may be performed.

Since the relationship between the remaining amount of the ink 24 and the current value shown in FIG. 3 changes depending on the heat transfer coefficient of the ink 24 and is not universal, the value of the lookup table for the above correction is used. Alternatively, the calculation formula needs to be changed according to the characteristics of the ink.

In addition, in the configuration of FIG.
By applying insulating coating to the wires 6 and 18 and the tungsten wire 20 and completely insulating the ink 24 from the ink 24, it can be applied to the case where a conductive ink is used.

Further, in this embodiment, the tungsten wire 2
Although 0 is stretched vertically, it may be stretched in an oblique direction, or may be spirally arranged along the wall surface of the ink tank. By doing so, since a long tungsten wire can be used, the amount of change in the resistance value R _P due to the decrease in the liquid level can be made larger than in the above embodiment, and detection can be performed with higher accuracy. Becomes

If this device is constructed such that, for example, the ink tank is a thin tube and the ink is pressed from one side to the end side having the supply port of the other, the tungsten wire is inevitably stretched. Is the direction in which the thin tube extends.

In this embodiment, a relatively inexpensive tungsten wire is used as the heat generating portion, but any material may be used as long as it generates heat by passing an electric current and its resistance value changes according to temperature. Absent. Further, in this embodiment, the property that the resistance value of the good conductor (tungsten) increases as the temperature rises is used, but the property that the resistance value decreases as the temperature rises like a semiconductor may be used. In this case, the terminal c in the above embodiment may be connected to the non-inverting input terminal and the terminal d may be connected to the inverting input terminal.

In addition, the present invention can be variously modified without departing from the spirit of the present invention.

[0030]

As is apparent from the above description, when the ink remaining amount detecting device provided by the present invention is used, the measurement takes almost no time. In addition, it is used for solid ink such as solid ink, and even if the ink adheres to the heat generating portion, the measurement accuracy is hardly affected. Furthermore, the remaining amount of ink can be quantitatively measured.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an example.

FIG. 2 is a circuit diagram of a current supply unit according to an embodiment.

FIG. 3 is a diagram showing a relationship between an ink remaining amount and a current value.

[Explanation of symbols]

 10 Ink Tank 12 Upper Lid 14 Holder 16 Conductive Strut 18 Conductive Strut 20 Heat Generation Section 22 Current Supply Section 24 Ink 26 Air 28 Ink Supply Passage 30 Sensor Section 32 Bridge Circuit 34 Operation Amplification Circuit

Claims (1)

[Claims] 1. An ink tank is mounted so that the amount of immersion in the ink changes according to the remaining amount of the ink, heat is generated by passing an electric current, and the resistance value changes according to the temperature. A heat generating part, a current supplying part for supplying a current to the heat generating part so that the resistance value of the heat generating part is constant, and a detection means for detecting the current value of the current supplied to the current supplying part. An ink remaining amount detecting device characterized in that.