JPH07248250A - Weight measuring apparatus for liquid droplet - Google Patents

Abstract

PURPOSE:To provide a smaller and inexpensive weight measuring apparatus for liquid droplet which enables the measuring of the weight of a viscous liquid droplet stably in a very short time. CONSTITUTION:A heater 20 is attached to a piezo-electric vibrator 31 with a diaphragm 25 and a piezo-electric element 30 stuck together. The piezo-electric vibrator 31 is controlled to a temperature at which a viscous ink to be adhered thereto will not peel or evaporate to blow a viscous ink jet thereto. When the viscous ink is adhered to, an electromechanical coupling constant of the piezo-electric vibrator 31 changes and the impedance of the piezo-electric element 30 varies in proportion to the weight of the ink adhered to. The adhesion weight of the ink is determined from a variation of the impedance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the weight of microdroplets of about 1 .mu.g, and more particularly to a device for measuring the weight of microdroplets of hot melt ink jet.

[0002]

2. Description of the Related Art FIG. 8 shows a method for measuring the weight of a minute amount of ink droplets ejected from a print head of a conventional hot melt ink jet printer. Since the liquid droplet 15 ejected from the inkjet head is extremely light at about 0.8 μg, the electronic balance 200 is normally used in the unit of tens of thousands of drops.
Then, the total weight of the ink was discharged to the ink receiver 210, and the total weight was divided by the total number of discharges to obtain the weight per drop.
For example, when an electronic balance manufactured by Shimadzu is used, the minimum reading is 0.1 mg. Therefore, in order to obtain the weight of one drop, 50000 times of discharge were obtained to obtain a measured value of about 4 mg, and the average drop weight was calculated. I was measuring.

[0003]

However, since the above-mentioned printer head requires 125 μsec for each ejection, it takes about 6 seconds to eject 50000 shots. Furthermore, the hot melt ink jet is about 125 when ejected.
Since the temperature is 0 ° C., when 50,000 shots are discharged, an imbalance occurs in the temperature distribution in the weighing chamber 205 of the balance, causing convection, and an unstable measurement value is displayed immediately after the end of discharge. In order to obtain a stable measurement value, there is a disadvantage that it takes another ten and several seconds to wait for the weighing chamber to reach a thermal equilibrium state again.

The present invention has been made in order to solve the above-mentioned problems, and several hundred to 1,000 drops of hot melt ink are ejected and brought into close contact with a thermally controlled vibration plate. (EN) A small droplet weight measuring device capable of instantaneously measuring a stable value by measuring an impedance change of a piezoelectric element at this time and obtaining a minute weight from the amount of change.

[0005]

In order to achieve such an object, a micro-droplet weight measuring device of the present invention is a micro-droplet weight measuring device using a piezoelectric vibrating body composed of a vibration plate and a piezoelectric vibrator. An oscillator for applying an alternating electric charge to the piezoelectric vibrator, and a heating means for applying heat to the diaphragm,
Temperature control means for controlling the temperature of the vibration plate heated by the heating means, measuring circuit means for measuring the impedance change of the piezoelectric vibrating body due to adhesion of fine droplets, and the impedance And a calculating means for calculating an appropriate amount of the adhered micro liquid based on the change of

[0006]

In the microdrop weight measuring device of the present invention having the above construction, the vibrating plate to which the hot melt ink adheres is heated by the heating means, and the ink can be kept sticky by the temperature control means. Kept at temperature. When ink adheres to the vibrating plate, the mechanical vibration of the piezoelectric vibrating body is loaded and the impedance changes. The impedance change is detected by the oscillator and the measuring circuit means and converted into a minute weight by the calculating means.

[0007]

An embodiment of the present invention will be described below with reference to the drawings.

The hot melt ink jet is characterized by using a viscous ink containing paraffin as a main component. The ink is heated to about 125 ° C. in a head to be in a molten state, and a minute amount of about 0.8 μg is applied by pressure of a piezoelectric element. A liquid droplet is ejected. In order to measure the average weight of the special droplets, the present embodiment has a configuration as shown in FIG.

First, the vibrating plate 25 is made of, for example, a conductive elastic body such as a circular or rectangular plate having a thickness of 100 μm and made of stainless steel, aluminum, copper or the like. The vibrator 30 is configured to be vibrated. Further, a heater made of, for example, a stainless steel foil or a carbon film, that is, a heating means 20 is attached to the vibrating plate 25, which is ejected from the inkjet head 10 and adheres to the vibrating plate surface or the heater surface. Heat is applied to the formed ink droplets 16.

A temperature sensor 45 for controlling the temperature of the vibrating plate 25, such as a thermocouple or a thermistor, is attached to the vibrating plate 25, and the temperature control circuit means 85, the bus 105 and the computer are provided. The temperature is controlled by the calculation means 115. The piezoelectric element 30 is electrically connected to the resistor 35 and the oscillator 40 by the vibrating plate 25 having conductivity and an electrode (not shown), and both ends of the resistor 35 are connected to the piezoelectric element 30.
Is connected to the measuring circuit means 80 for measuring the impedance.

The measuring circuit means 80 is connected via a bus 105 to a calculating means 115 composed of a computer,
As described in detail later, the impedance change of the piezoelectric element is measured. Also, calculation means 115
As is well known, is a central processing unit CPU 100 and a storage means ROM 9 for storing programs and constants.
0, a RAM 95 for storing various data, and an I / O 110 for controlling external input / output.

Next, the function of each element will be described step by step. The ink 15 ejected from the hot melt inkjet head 10 becomes viscous ink while being cooled by air and reaches the vibrating plate 25 and adheres thereto. In general, droplets adhere to a vibrating object, and if they remain liquid, they are evaporated by the energy of the vibrating body and dissipated as vapor, as is clearly seen in an ultrasonic humidifier. On the contrary, when solidified after being attached to the vibrating body, the solidified body is peeled off from the attached surface by the energy of the vibrating body as clearly seen in the part feeder, and moves or moves on the surface. Dissipate from above. In either case, it is not suitable for accurate measurement.

Therefore, a heating means 20, for example, a heater made of a stainless steel foil of about 50Ω is attached to the surface of the diaphragm 25, which is one of the constituent elements of this embodiment, with an insulating layer (not shown) interposed therebetween. When the relay circuit 65 is ON, current is supplied from the power source 50 to heat the adhered viscous ink. Further, as described above, on the surface of the diaphragm 25,
For example, a temperature sensor 45 such as a thermocouple or a thermistor is attached, and the temperature of the vibrating body 31 warmed by the heater is detected by the temperature sensor 45.

In the case of a thermocouple, it is converted into a voltage corresponding to temperature, and in the case of a thermistor, it is converted into a partial voltage due to a change in its resistance value. The sensed voltage is converted into a digital amount by the A / D conversion circuit 60, and further, the comparator 75.
Is compared with the temperature constant set by the calculation means 115 consisting of a micro computer. When the temperature is smaller than the temperature constant, the comparator 75 issues an ON command to the relay circuit 65, and when it is larger than the temperature constant, an OFF command is issued. In this way, the vibrating plate 25 is controlled so as to reach the temperature set by the calculating means 115, and as a result, the viscosity of the viscous ink is maintained so that it does not evaporate or peel.

In the case of the ink containing paraffin as the main component of this embodiment, the temperature is 80 ° C. which is the melting point.
To 120 ° C increased by 40 ° C to 40 ° C, and the viscosity is suitably between about 70 cps and about 40 cps. A piezoelectric element 30 having a thickness of, for example, about 200 μm is attached to the back surface of the vibrating plate 25, and the vibrating plate 25 and the resistor 35, which are electrically conductive with the electrodes (not shown) as described above.
After that, the oscillator 40 is set to a resonance state in advance. When the viscous ink adheres to the piezoelectric vibrating body 31 in the resonance state, the impedance of the piezoelectric vibrating body changes according to the amount of attachment and changes to the anti-resonance state.

FIG. 3 shows an electrically equivalent circuit of the piezoelectric element for explaining the resonance state and the anti-resonance state. Piezoelectric vibrator 31
Is represented as being connected in parallel with R ₁ , C ₁ and L ₁ corresponding to the electrical capacitance C ₀ and the mechanical piezoelectric constant as shown in FIG. The current flowing through each is represented by the following equation.

[0017]

[Equation 1]

[0018]

[Equation 2]

The resonance state is (L ₁ ω-in the denominator term of Equation 1).
C ₁ ^-1 ω ^-1 ) is 0, and the maximum current constant I _max = E ₀ / R ₁ C
OS (ωt−φ) + C ₀ E ₀ ωCOS (ωt) is flowing. On the other hand, the vibration plate 25 in which the temperature of the ink is controlled
When it is attached and accumulated in, the mass of the diaphragm 25 increases and its mechanical vibration is suppressed, and the electromechanical coupling constant of the piezoelectric element changes. Above all, the change in mass affects the L component, and as a result, the combined impedance changes, and the resonance state is lost. If the accumulation continues, (L ₁ ω-C
_{The term of 1} ⁻¹ ω ⁻¹ ) becomes much larger than that of R ₁ , that is, I _{1 to} 0, and the current value flowing through the whole is approximately I _{min to} C _0.
It converges to E ₀ ωCOS (ωt). Since this current flows through the resistor 35, these changes are detected as voltage changes by the measuring circuit means 80 including the smoothing circuit 55 and the A / D conversion circuit 70 as the voltage value V = (I ₀ + I ₁ ) * R. .

FIG. 4 shows that these phenomena are experimentally obtained.
It is FIG. The horizontal axis shows the number of ejections, and the vertical axis shows the voltage value V. In ROM, the address corresponds to the number of discharges,
The voltage value is stored as data. At the time of calibration, these data are measured automatically every 10 droplets by using a standard machine which is measured and guaranteed by a conventional method in advance, and the voltage values are stored in order in the ROM 95. For the actual measurement, refer to the table of FIG.
It is calculated according to the flow of.

In step S1, first, the parameters used in this program are initialized.

I is an index representing a jet number, and j is an index representing an address of a memory for storing data. In step S2, the temperature constant for setting the temperature of the diaphragm 25 is output from the calculation means 115 to the temperature control means 85. Temperature control means 85
When the temperature set value is set as described above, the automatically operates until the diaphragm warms to that temperature. In S3, the calculation means 115 reads the current temperature from the temperature control means 85 and waits until the set temperature is reached. When the set temperature is reached, the process proceeds to S4 and the initial voltage V ₀ is read from the measuring circuit means 80.

In S5, the calculation means 115 issues a command to the ink jet head 10 to eject 1000 jets of the i-th jet. Ink jet is about 0.125 per discharge
Since it takes m seconds, a total of 0.125 seconds or more is required when 100 shots are discharged. Further, after the end of discharge, it takes several tens of milliseconds until the diaphragm stabilizes, so a total of 0.2 seconds is waited in S6. Then, in S7, as in S4, the measuring circuit means 8
The measured voltage V _i is read from 0.

At S8, the amount of change ΔV from the initial voltage V ₀
Find (i). This change amount has a correlation with the amount of ink adhered to the vibration plate 25 or the heating means 20 as shown in FIGS. 4 and 5, so that in S9, Vj ≧ ΔV from the data table of FIG.
The address of (i) is searched, and conversely, the attached amount w _js is obtained. The back calculation of the adhered amount is calculated as shown in S10. The table in FIG. 5 records the voltage change every 10 shots during the calibration, so the corresponding weight is j *, where wρ is the weight per shot. Calculated as 10 * wρ.
For example, when i = 1, the reverse calculation address index j
Is 105 (when there is no error from the standard machine, the back calculation address is 100). The table reference weight is w.
_{Since js} = j * 10 * Wρ and the standard Wρ is 0.8 μg, w _js is 0.84 mg. To further determine the weight per droplet and obtains an average of 1000 shots min at S11 w _h = 0.84μg next, the value w _h measured de in S12 - stored in Taeria, such as a CRT in S13 It is displayed on the display.

This series of work is performed for all jet numbers.
Until (for example, i = 1 to 100), the process is returned to the point B shown in the middle of the program and repeated. S1
In S4 and S15, it is determined whether or not the above-described series of operations have been performed on all the jets, and if the measurement of the total jets is completed, the process proceeds to the next S16. As a result S1
The average weight data stored in 2 is accumulated as shown in FIG. In S16 and S17, in order to prepare for the next measurement, the temperature of the vibration plate is set to 150 ° C., and all the accumulated ink is liquefied and then poured. Therefore, in S18, the program is ended by waiting for about 3 minutes.

Although one embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, in the above embodiment, the piezoelectric vibrating body 31 is used.
Although the circular or rectangular vibration plate 25 is used as the piezoelectric vibrator 30, the piezoelectric vibrator 30 may be attached to the tuning fork type vibrator 26 as shown in FIG. In the above-described embodiment, the diaphragm is made of a conductive elastic body, but a conductive metal may be coated on the insulating elastic body by vapor deposition or the like to form an electrode. Further, in the above-described embodiment, the resistor R is used as the resistor in order to measure the impedance change of the piezoelectric element. However, as in the modification of FIG.
6 or a coil (not shown) may be used.
Further, in the above-described embodiment, the oscillator 40 constantly vibrates the piezoelectric vibrator 30 to detect the impedance change due to the ink adhesion. However, when the ink is ejected, the oscillator 40 is stopped to ensure that the ink adheres, and After attachment, the oscillator may be turned on again and the impedance change may be read.

Further, in the above-mentioned embodiment, the measuring circuit means 80
A so-called smoothing circuit 55 was used to convert the AC voltage into the DC voltage in the inside, but the peak value of the AC voltage is A / D converted using the peak-hold circuit 56 as shown in FIG. Alternatively, the peak and valley values (peaks and valleys) may be A / D converted. Other modifications are not listed, but those skilled in the art can make various modifications without departing from the spirit of the above description.

[0029]

As is clear from the above description, in the present invention, a temperature controlled piezoelectric vibrating body is used to measure the weight of minute droplets of hot melt ink, and its impedance change is measured. Circuit means and micro computer
Since the weight is converted by means of a computer, a stable value can be measured with a speed of 0.2 seconds per jet, which is unprecedented in spite of heat droplets, so that the inspection time of the inkjet head can be greatly shortened. is there.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a fine droplet weight measuring apparatus of the present invention.

FIG. 2 is a block diagram showing a modified example of the fine droplet weight measuring apparatus of the present invention.

FIG. 3 is a circuit diagram showing an electrically equivalent circuit of the piezoelectric vibrating body of the apparatus for measuring the weight of microdroplets of the present invention.

FIG. 4 is a correlation diagram between the measured voltage and the number of ink ejections in the microdroplet weight measuring apparatus of the present invention.

FIG. 5 is a diagram in which the number of discharges in FIG. 4 is replaced with an address,
FIG.

FIG. 6 is a flow chart of measurement in the microdrop weight measuring device of the present invention.

FIG. 7 is a flow chart of measurement in the microdroplet weight measuring apparatus of the present invention.

FIG. 8 is a flow chart of measurement in the microdrop weight measuring device of the present invention.

FIG. 9 is a diagram showing a memory structure of measurement results in the microdroplet weight measuring apparatus of the present invention.

FIG. 10 is a schematic view of minute weight measurement of a conventional hot melt inkjet.

[Explanation of symbols]

 15 Micro Droplet 20 Heating Means 25 Vibration Plate 30 Piezoelectric Vibrator 31 Piezoelectric Vibrating Body 40 Oscillator 80 Measuring Circuit Means 85 Temperature Control Means 115 Conversion Means

Claims (2)

[Claims] 1. A micro-droplet weight measuring device using a piezoelectric vibrating body composed of a vibrating plate and a piezoelectric vibrator, wherein an oscillator for applying an alternating electric charge to the piezoelectric vibrating device, and heat for applying the vibrating plate. Heating means, a temperature control means for controlling the temperature of the diaphragm heated by the heating means, and a measuring circuit means for measuring the impedance change of the piezoelectric vibrating body due to the adhesion of microdroplets. And a calculation means for calculating an appropriate amount of the adhering micro liquid based on the change in the impedance described above. 2. The micro controller according to claim 1, wherein the temperature control means controls the temperature of the vibration plate within a range of a melting point of the droplet and a temperature increased by 40 ° C. from the melting point. Drop weight measuring device.