JPH07132592A - Piezoelectric droplet ejector - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the characteristics of pressure fluctuations in the pressure chamber change due to changes in temperature, physical properties of ink, etc., it is possible to apply a drive voltage waveform matching the pressure fluctuations to the piezoelectric element. Provided is a liquid droplet ejection device. [Structure] A measurement drive pulse Pc is applied to a piezo element 106 prior to a printing operation to detect a pressure fluctuation in the pressure chamber 100 by the piezo element 106 and a detection circuit 32, and drive based on the characteristic of the pressure fluctuation. Waveform W
Calculate F. When printing, the drive voltage waveform Pa is applied to the piezo element 106 based on the calculated drive waveform WF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric droplet ejecting device, and more particularly to a technique for accurately determining a driving voltage waveform for ejecting droplets efficiently and stably.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric liquid droplet ejecting apparatus which ejects an ejected liquid in a pressure chamber from a nozzle by changing the volume of the pressure chamber using a piezoelectric element has been used in, for example, an inkjet printer. .

FIG. 9 shows an example of such a piezoelectric liquid droplet ejecting apparatus. A piezoelectric element 10 such as PZT is used as a piezoelectric element on a side wall 104 of a housing 102 forming a pressure chamber 100.
6 is provided, and the piezo element 106 has a drive circuit 10
A drive voltage is applied by means of 8.

When ejecting ink in this piezoelectric type droplet ejecting apparatus, a drive voltage is applied to the piezo element 106. The simplest drive voltage waveform applied at this time is, for example, a rectangular pulse 110. Piezo element 10
When pulse 110 is applied to 6, pulse 110
At the rising of the side wall 104, the side wall 104 is deformed together with the piezo element 106 as shown by a chain line. Due to this deformation, the volume of the pressure chamber 100 increases, and the pressure chamber 10 increases as the volume increases.
The pressure in 0 decreases and ink is sucked into the pressure chamber 100 from the ink supply passage 112.

When the voltage applied to the piezo element 106 becomes 0 V after a certain time corresponding to the pulse width of the pulse 110 has passed, the piezo element 106 returns to the shape before deformation indicated by the solid line. At this time, the volume of the pressure chamber 100 decreases, but the pressure in the pressure chamber 100 rises with this decrease,
The ink filled in the pressure chamber 100 becomes an ink droplet 120 and is ejected from the nozzle 114. It should be noted that the inkjet printer is provided with a large number of the above-mentioned piezoelectric type droplet ejection devices.

By the way, when the ink is ejected in the piezoelectric type droplet ejecting apparatus, a pressure wave is generated along with a change in the volume of the pressure chamber 100, and the pressure wave propagates vertically and horizontally in the pressure chamber 100 using ink as a medium. , Wall surface 104,
The ink is reflected by the ink supply passage 112 and the nozzle 114 with their respective reflectances, and attenuates while repeatedly reciprocating in the pressure chamber 100.

Even in the example of ink ejection by the rectangular pulse 110, the pressure wave generated when the ink is sucked still exists in the pressure chamber 100 when the ink is jetted. Therefore, in order to eject the ink stably and efficiently, the falling timing of the drive voltage pulse, that is, the pulse width is set to the pressure chamber 100.
It will have to be set taking into account the state of the pressure wave inside.

FIG. 10 is a timing chart showing in detail the pressure change in the pressure chamber 100 when a rectangular pulse 110 is applied to the piezo element 106. The solid line in the figure is a simplified illustration of the displacement state of the piezo element 106 and the pressure change in the vicinity of the nozzle 114 when only the rising of the drive voltage is applied, that is, when only the suction of ink is performed.

The pressure in the vicinity of the nozzle 114 becomes constant while the drive voltage rises, and the piezoelectric element 106 and the wall surface 1
Even after 04 is stabilized at the position indicated by the alternate long and short dash line in FIG. 9, it is fluctuated at a constant cycle determined by the propagation velocity of the pressure wave, the shape of the pressure chamber 100, and the like.

On the other hand, in order to eject the ink, it is necessary to return the drive voltage to 0 V and return the displacement of the piezo element 106 to the position before the deformation so as to increase the pressure in the pressure chamber 100. In this case, For example, the drive voltage is returned to 0 V at the timing when the pressure in the vicinity of the nozzle increases as shown by the broken line in FIG.
When the pressure in 00 is increased, the pressure by the piezo element 106 is added to the pressure in the vicinity of the nozzle, and a high injection pressure is obtained.

On the contrary, when the pressure in the vicinity of the nozzle becomes negative as shown by the alternate long and short dash line, the driving voltage is returned to 0 V to return the piezo element 106 to the shape before the deformation so as to increase the pressure in the pressure chamber 100. Also, the pressure generated by the piezo element 106 is canceled by the pressure in the vicinity of the nozzle, and a sufficient ejection pressure cannot be obtained, and the ink droplet 120 is not ejected, or even if ejected, a predetermined flight speed or ejection amount cannot be obtained. Therefore, high print quality cannot be obtained.

As is apparent from the above description, when determining the drive waveform, the characteristics of the pressure wave in the pressure chamber must be grasped and the drive waveform that matches the characteristics must be designed. For the simplest rectangular pulse as described above,
The vibration cycle of pressure shown in FIG. 10 is most important, but when a drive pulse having a more complicated waveform shape is used, in addition to that, for example, it is necessary to consider, for example, the phase of pressure vibration and the damping rate. come.

The cycle of the pressure wave depends on the shape of the pressure chamber 10, specifically, the dimension from the ink supply passage 24 to the nozzle 22, the propagation velocity of the pressure wave in the pressure chamber 10, and the like. The rate depends on the shape of the nozzle and the like. Conventionally, these pressure wave characteristics are obtained in advance by experiments or calculations.

[0014]

However, the characteristics of the pressure wave, such as the period, phase, and attenuation rate, change depending on the physical properties of the ink and the environment in which it is used. For example, the propagation speed of the pressure wave changes depending on the temperature, and the attenuation rate of the pressure wave changes depending on the physical properties of the ink and the inclusion of bubbles. Therefore, the characteristics of the pressure wave change due to the above change. Therefore, the predetermined drive pulse does not always match the pressure wave in the pressure chamber 100.

The present invention has been made in order to solve the above-mentioned problems, and its purpose is not to be influenced by the physical properties of the ink or changes in the usage environment, etc., but the characteristics of the pressure wave in the pressure chamber are always maintained. It is an object of the present invention to provide a piezoelectric liquid droplet ejecting apparatus capable of applying a suitable drive waveform to a piezo element.

[0016]

In order to achieve the above object, a piezoelectric liquid droplet ejecting apparatus according to the present invention comprises a measuring voltage waveform applying means for applying a specific voltage waveform pulse to a piezoelectric element, and a measuring voltage waveform applying means. A pressure fluctuation detecting means for detecting a pressure wave in the pressure chamber containing the injection liquid caused by the voltage waveform applying means, and a characteristic characteristic of the pressure chamber and its characteristic characteristic based on the pressure wave detected by the pressure fluctuation detecting means. Drive waveform calculation means for calculating a matched drive voltage waveform for droplet ejection, and waveform storage means for storing the drive voltage waveform,
A droplet ejecting unit that ejects the ejecting liquid by using the drive voltage waveform.

[0017]

In the piezoelectric liquid droplet ejecting apparatus of the present invention having the above-mentioned structure, the pressure detecting means detects the actual pressure wave in the pressure chamber, and calculates the drive voltage waveform that matches the characteristic of the pressure wave. Since the jetting liquid is jetted by being applied to the piezoelectric element, the timing of the movement of the piezoelectric element and the timing of the pressure fluctuation are deviated even if the period of the pressure wave or the attenuation rate changes due to the usage environment such as temperature or the physical properties of the jetting liquid. Therefore, it is possible to always eject a droplet having a predetermined flight speed and a predetermined droplet amount.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In the following embodiments, the same parts as those in the conventional example of FIG. 9 are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 1 is a diagram showing one droplet ejecting device of an ink jet printer, which is a drive circuit 30 and a detection circuit 3.
2, an arithmetic circuit 34 and a memory circuit 35. The output side of the drive circuit 30 is connected to the piezo element 106, and the piezo element 106 and the input side of the detection circuit 32 are connected. The output side of the detection circuit 32 is connected to the input side of the arithmetic circuit 34, and the output side of the arithmetic circuit 34 is connected to the input side of the storage circuit 35. The output side of the storage circuit 35 is connected to the input side of the drive circuit 30.

The drive circuit 30, for example, comprises a pulse generator 36, an amplifier 38, and an analog switch 40 as shown in FIG. 2, and the pulse generator 36 and the analog switch 40 are connected via the amplifier 38. ing. Further, the pulse generation of the analog switch 40 is controlled by the pulse generator 36.

The drive circuit 30 drives the measurement drive voltage waveform Pc according to the measurement signal SC used for measuring the characteristics of the pressure wave and the print signal SP used for normal printing.
Alternatively, the drive voltage waveform Pp for printing is applied to the piezo element 106. When detecting a pressure wave, the analog switch 40 is cut off according to the switch signal SS, and the piezo element 106 is electrically disconnected from the drive circuit 30.

The detection circuit 32 uses the measurement drive waveform Pc.
Is for detecting the electric signal Vs generated in the piezo element 106 in accordance with the pressure fluctuation in the pressure chamber 100 after the application of the electric field Vs is completed. For example, the electric signal Vs is configured by including the operational amplifier 42 as shown in FIG. Is output to the arithmetic circuit 34 as the detection signal SV. The voltage signal Vs and the detection signal SV correspond to the average pressure in the pressure chamber 100 shown at the bottom of FIG. 6, which is a timing chart during pressure wave measurement.

The arithmetic circuit 34 calculates characteristics such as the period and the attenuation rate of the pressure wave in the pressure chamber 100 based on the detection signal SV. For example, each functional unit shown in FIG. 4 includes a microcomputer and the like. It is configured with. In FIG. 4, the shaping section 44 is a section for removing noise included in the detection signal SV by a filter or the like, and the peak detection section 46 is a peak P of pressure fluctuation from the detection signal SV.
1, which is a part for detecting P2, and the peak level detecting part 4
Reference numeral 8 is a detection portion for detecting the voltage value of the detection signal SV at each peak as peak levels Q1 and Q2, and the cycle calculation portion 50
Is a portion for calculating the period T of pressure fluctuation from the time between the detected peaks, and the damping rate calculation unit calculates the damping rate Q1 / Q2 of pressure fluctuation from the temporal change of the detected peak level. It is the part to do. Then, the drive waveform calculation unit 54 is a unit that calculates the drive waveform using the parameters required for determining the drive waveform, such as the calculated pressure fluctuation period and the damping rate. The calculated drive waveform is stored in the storage circuit 35 as WF.

The memory circuit 35 is a RAM as shown in FIG.
The above-mentioned drive waveform WF is stored by using a memory element such as, and the drive waveform WF is always sent to the drive circuit during the printing operation.
Is the part that allows us to provide.

When calibrating the drive waveform WF, the calibration signal SC is input to the drive circuit 30, and a drive waveform for measuring the pressure wave (hereinafter referred to as a measurement drive waveform) is applied to the piezo element 106. As time goes by, the voltage is 0V
When it is suddenly started from, the average pressure in the pressure chamber 100 suddenly decreases, and then the drive voltage is kept at a constant value.
The pressure also fluctuates and decays. When the driving voltage is returned to 0V after the pressure fluctuation is sufficiently attenuated, the pressure fluctuation occurs again in the pressure chamber 100. At this point, the analog switch 40 of FIG. 2 is turned off, and at the same time, the detection circuit 32 and the arithmetic circuit 34
Is operated to obtain the drive waveform WF.

As described above, in the droplet ejecting apparatus of this embodiment, the actual pressure fluctuation in the pressure chamber 100 is measured by the piezo element 1.
6 and the detection circuit 32, and the drive voltage waveform for actual printing is calculated based on the detected pressure wave, the cycle of pressure fluctuations in the pressure chamber 10 depending on the use environment such as temperature and the physical properties of ink. Even if the attenuation rate changes, the drive pulse can be applied at a timing that always matches the pressure fluctuation, and the stable ink droplet 20 is ejected.

In particular, in this embodiment, all the liquid droplet ejecting apparatuses constituting the ink jet printer independently detect the pressure fluctuation and calculate the driving waveform.
Regardless of individual differences of such droplet ejecting devices, all devices can print with a drive waveform suitable for each device.

Next, another embodiment of the present invention will be described.

The embodiment shown in FIG. 7 is different from the above-mentioned embodiment in that the pressure detecting piezoelectric element 6 is provided separately from the driving piezoelectric element 106.
0 is provided, and the detection piezo element 60 and the detection circuit 3
2 inputs are connected. In this embodiment, since the drive circuit 30 and the detection circuit 32 are electrically insulated, the pressure fluctuation can be detected more accurately, and the analog switch 40 is not always necessary.

In the embodiment shown in FIG. 8, a piezoelectric material such as PZT is grooved to form a large number of pressure chambers 100, and electrodes are formed on both surfaces of a plurality of partition walls 62 separating the pressure chambers 100. Are formed so that the partition walls 62 function as piezoelectric elements as they are.
In this case, since the pressure fluctuation can be detected from the partition walls 62 on both sides of one pressure chamber 100, the drive waveform can be calculated with higher accuracy.

In each of the above-mentioned embodiments, all of the liquid droplet ejecting apparatuses constituting the ink jet printer are configured to include the detecting circuit 32, the arithmetic circuit 34 and the memory circuit 35, respectively. Alternatively, it is also possible to configure only some of the droplet ejecting devices as in the above-described embodiment and apply the drive waveforms obtained by those droplet ejecting devices to other droplet ejecting devices.

In addition, one or a plurality of dummy droplet ejecting devices dedicated to measurement, which are not used for printing, are provided, and the drive waveforms obtained by these dummy ejecting devices are applied to another droplet ejecting device for printing. Is also possible.

The series of operations from the detection of the pressure fluctuation to the calculation of the drive waveform described in each of the above-described embodiments may be carried out at a fixed time interval or a fixed number of prints, or the printer power supply. May be performed at the time of inputting or when any switch is operated. Further, the voltage waveform for measurement applied to the piezoelectric element does not necessarily have to reach a voltage value at which the ink droplet 120 can be ejected. That is, the cycle T of the pressure fluctuation is constant regardless of the magnitude of the driving voltage, while the peak value of the fluctuation corresponds to the driving voltage, so that the attenuation rate of the pressure wave can be calculated.

Although not illustrated one by one, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[0035]

As is apparent from the above description,
The droplet ejecting apparatus of the present invention, even if the cycle of the pressure wave or the attenuation rate changes due to the use environment such as temperature or the physical properties of the ejected liquid,
A droplet having a predetermined flight velocity and a predetermined droplet amount can be ejected at all times without shifting the timing of the movement of the piezoelectric element and the pressure fluctuation, and efficient and stable printing can be performed.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a basic configuration of an embodiment of a piezoelectric droplet ejecting device of the invention.

FIG. 2 is a diagram showing a specific example of a drive circuit used in the piezoelectric liquid droplet ejecting apparatus of the invention.

FIG. 3 is a diagram showing a specific example of a detection circuit used in the piezoelectric liquid droplet ejecting apparatus of the invention.

FIG. 4 is a block diagram illustrating a function of an arithmetic circuit used in the piezoelectric liquid droplet ejecting apparatus of the invention.

FIG. 5 is a block diagram illustrating a function of a memory circuit used in the piezoelectric liquid droplet ejecting apparatus of the invention.

FIG. 6 is a timing chart regarding the drive voltage, the displacement of the piezo element, and the pressure fluctuation in the pressure chamber of the piezoelectric liquid droplet ejection apparatus shown in FIG.

FIG. 7 is a diagram illustrating the basic configuration of another embodiment of the piezoelectric type droplet ejection device of the present invention.

FIG. 8 is a diagram illustrating the basic configuration of yet another embodiment of the piezoelectric liquid droplet ejection apparatus of the present invention.

FIG. 9 is a diagram showing an example of a conventional droplet ejection device.

10 is a timing chart regarding the drive voltage, the displacement of the piezo element, and the pressure fluctuation near the nozzle in the conventional example of FIG.

[Explanation of symbols]

 10 Pressure Chamber 16 Piezo Element 22 Nozzle 30 Drive Circuit 32 Detection Circuit 34 Arithmetic Circuit 35 Memory Circuit 60 Pressure Variation Detection Piezo Element 62 Partition Wall (Piezoelectric Element) WF Drive Voltage Waveform

Claims (1)

[Claims] 1. A piezoelectric liquid droplet ejecting apparatus for ejecting an ejecting liquid in a pressure chamber from a nozzle by changing the volume of the pressure chamber using the piezoelectric element, wherein a specific voltage waveform pulse is applied to the piezoelectric element. Measuring voltage waveform applying means, pressure fluctuation detecting means for detecting a pressure wave in the pressure chamber containing the injection liquid caused by the measuring voltage waveform applying means, and the pressure fluctuation detecting means Drive waveform calculation means for calculating a characteristic characteristic of the pressure chamber and a drive voltage waveform for droplet ejection based on the characteristic characteristic, a waveform storage means for storing the drive voltage waveform, and the drive voltage waveform And a liquid droplet ejecting means for ejecting the ejection liquid.