JPH11207964A - Method for driving piezoelectric element in continuous ink-jet printer, and continuous ink-jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for controlling a break point of various piezoelectric elements to a required position with a low drive voltage in a continuous ink-jet printer. SOLUTION: A frequency variable device 4 outputs a control signal Fa for controlling a frequency of a voltage to be generated at a drive voltage generation device 2 to the drive voltage generation device 2 on the basis of the control of a CPU 1, and a control signal Fb for controlling a frequency of a charging voltage at a charging voltage generation circuit 3 to the charging voltage generation circuit 3 on the basis of the control of the CPU 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous ink jet printer constructed so that ink is pulsated by a piezo element.

[0002]

2. Description of the Related Art Conventionally, in a continuous ink jet printer configured to pulsate ink by a piezo element, a piezo element is used to control a distance from a tip of a nozzle to a position where an ink droplet is formed. Control of a voltage applied to an element has been performed.

For example, in the conventional continuous ink jet printer shown in FIG. 3, the ink immediately after being ejected from the nozzle 100 is a continuous ink flow which is not separated into particles. However, pressure fluctuation, that is, pulsation is given by the piezo element 101 to which the driving voltage of a predetermined frequency generated by the driving voltage generating device is applied. When the pulsation leaves the nozzle 100 to some extent (this is called a break point), the particles are separated and ink droplets are formed. The charging electrode 10 to which the charging voltage generated by the charging voltage generating circuit according to the dot pattern to be printed is applied to the separated ink droplets.
When passing between the two, the electric field charges the ink droplets in accordance with the font pattern.

When the charged ink droplet passes between the deflection electrodes to which a constant deflection voltage is applied, the flight path of the ink droplet is deflected according to the level of the charged electric charge of the ink droplet, and the printing path is printed. A desired print dot is formed at a predetermined position on the surface of the object. In the case of an uncharged ink droplet, the flight path is straight and does not hit the print target, but is hit by the gutter tube to be collected and reused.

In order to properly charge an ink droplet,
It is necessary to determine a drive voltage to be applied to the piezo element so that the break point is at a predetermined position. For this purpose, a charge detection electrode 103 and a charge detection circuit are provided after the charge electrode 102 so that a charge detection signal is obtained when a charged ink droplet passes therethrough.
It is possible to measure the time from the application of the pulse voltage to the detection of the charge detection signal (hereinafter referred to as detection time) at 102 and calculate the breakpoint based on the detection time and the flying speed of the ink. it can. When the drive voltage is increased, the break point approaches the nozzle side, and when the drive voltage is decreased, the break point is separated. Therefore, the drive voltage is controlled so that the break point is at an optimum position.

As specific examples, the flying speed of the ink droplet is 22 m / s, the distance from the nozzle to the charging electrode is 3.5 mm, the length of the charging electrode is 5.0 mm, and the distance from the charging electrode to the charging detection electrode is 0.5 mm. As shown in FIG. 4, when the frequency is 64 kHz, the timing at which the charging pulse voltage is applied is set to t0. When the charging detection signal is obtained after a predetermined detection time, and when the driving voltage is 20 V, the detection is performed. Time is 2
The drive voltage had to be increased to 60 V in order to make the detection time 350 μs.

[0007] As shown in FIG.
At the time of 00 μs, the break point is closer to the charge detection electrode as shown in FIG. 4B, and the drive voltage is changed from 20 V to 60 V at the same frequency as shown in FIG. If it is raised, the detection time becomes long as 350 μs,
The break point approaches the nozzle side as shown in (c ′) of FIG. In this way, the break point is moved by changing the drive voltage.

For this purpose, a drive voltage generating circuit for variably controlling the drive voltage is provided.

[0009]

However, due to variations in the mounting accuracy of the piezo element and the mechanical manufacturing accuracy, it is necessary to obtain a drive voltage control range that can obtain a desired break point for various piezo elements. Requires a drive voltage generation circuit that can control up to a sufficiently high voltage, which increases the cost to ensure the withstand voltage characteristics and insulation characteristics of the circuit, and safety measures to prevent electric shocks to operators. Is necessary.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a continuous ink jet printer capable of controlling the breakpoints of various piezo elements at desired positions with a low driving voltage.

[0011]

According to the present invention, there is provided a method of driving a piezo element in a continuous ink-jet printer, comprising the steps of changing a drive voltage when a frequency of the drive voltage is changed under a condition that a break point is a predetermined position. And driving the piezo element at a frequency at which the driving voltage is the lowest.

In the continuous ink jet printer according to the present invention, means for providing a frequency control means for controlling the frequency of the drive voltage output from the drive voltage generation circuit is provided.

When the inventor changes the frequency of the drive voltage,
Based on the phenomenon that the drive voltage at which a certain breakpoint can be obtained can be changed, the change in the drive voltage when the frequency of the drive voltage is changed under the condition that the same breakpoint is obtained is investigated. It has been found that by driving a piezo element at a certain frequency, the piezo element can be driven at the lowest drive voltage.

For example, as shown in FIGS. 4 (c) and 4 (d), when the frequency is 64 kHz and the driving voltage is 60 V, the same is true when the frequency is 61 kHz and the driving voltage is 20 V. You get breakpoints.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A continuous ink jet printer according to the present invention will be described below in detail with reference to the drawings showing an embodiment.

In FIG. 1, reference numeral 1 denotes a CPU for systematically controlling the whole system, 2 denotes a driving voltage generator whose generated voltage is controlled by the CPU 1, and 3 denotes a charging voltage controlled by the CPU 1 in accordance with a dot pattern to be printed. Charging voltage generating circuit. Reference numeral 4 denotes a frequency variable device which outputs a control signal Fa for controlling the frequency of the voltage generated in the drive voltage generator 2 to the drive voltage generator 2 based on the control of the CPU 1, and Control signal Fb for controlling the frequency of the charging voltage at
It outputs to the charging voltage generation circuit 3 based on the control of PU1.

Reference numeral 5 denotes an ink droplet generating device, which oscillates a piezo element by a driving voltage applied from a driving voltage generating circuit 2 to give a pulsation to an ink flow blown out from the nozzle tip, so that the ink flow is separated from the nozzle to some extent. However, the ink flow is in a state where ink droplets separated and independent from each other fly in a row. Reference numeral 6 denotes a charging electrode, which selectively charges flying ink droplets by a charging voltage corresponding to a dot pattern provided from the charging voltage generation circuit 3. Reference numeral 7 denotes a charge detection electrode that detects a change in an electric field when a charged ink droplet passes.
Reference numeral 8 denotes a charge detection circuit, which detects a timing at which a charged ink droplet passes based on a change in an electric field detected by the charge detection electrode 7.

Reference numeral 9 denotes a deflection electrode, to which a deflection voltage from a deflection circuit 10 is applied. The ink droplets charged according to the dot pattern are deflected according to the charging voltage to form desired print dots on the surface to be printed.

In the above configuration, at the time of test operation,
The operation of determining the optimum driving voltage frequency for the piezo element mounted on the nozzle of the ink droplet generating device 5 is performed as follows. First, under the condition that the break point is set to a desired position near the charged electrode, a change in the drive voltage when the frequency of the drive voltage is changed is investigated, and the frequency at the lowest voltage at which the break point is obtained is obtained.

At this time, for example, a graph showing the relationship between the drive voltage and the frequency as shown in FIG. 2 is obtained.
That is, from the graph of FIG.
When driving at about 4 V at a frequency of 61 kHz, the same breakpoint is obtained, and it can be said that the most efficient driving frequency is 61 kHz.

Therefore, when driving at a general frequency of 64 kHz, 60 V is required, but when driving at a frequency of 61 kHz, a position at a predetermined distance at 20 V can be set as a break point. That is, a driving voltage of 60 V is unnecessary, and a driving voltage of 20 V
It just needs to be able to control it. Therefore, the control signal Fa is set to be output from the frequency variable device 4 to the drive voltage generator 2 so that the frequency of the drive voltage generated in the drive voltage generator 2 becomes 61 kHz.

After setting as described above and starting operation,
The drive voltage in the drive voltage generator 2 is controlled based on a signal from the charge detection circuit 8 so that a predetermined position of the charging electrode 6 becomes a break point.

With the above-described operation, the conventional drive voltage of 60 V is not required, and the breakpoint can be controlled to a desired position with a lower drive voltage. It is possible to simplify and prevent the occurrence of accidents such as electric shock.

When the variation of the piezo element is small, an optimum frequency of the driving voltage is obtained by performing a test in advance.
By setting the frequency in the drive voltage generator, the frequency variable device can be omitted. In any case, the frequency at which the lowest drive voltage optimal for the piezo element to be used is obtained is investigated in advance, and a drive voltage of that frequency may be generated.

[0025]

According to the present invention, since the frequency of the driving voltage output from the driving voltage generating circuit is controlled, a driving voltage generating circuit capable of generating a high voltage as in the prior art is not required. It is possible to provide a continuous ink-jet printer which can reduce the cost and has a low risk of electric shock and high safety.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of a continuous ink jet printer according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a driving voltage and a frequency of a piezo element.

FIG. 3 is a configuration diagram of a conventional continuous ink jet printer.

FIG. 4 is a timing chart illustrating timings of a charging pulse voltage and a charging detection signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU 2 Drive voltage generator 3 Charging voltage generation circuit 4 Frequency variable device 5 Ink drop generator 6 Charging electrode 7 Charging detecting electrode 8 Charging detecting circuit 9 Deflection electrode

Claims (2)

[Claims] 1. A method for driving a piezo element in a continuous ink jet printer, comprising: a piezo element to which a driving voltage whose voltage fluctuates at a predetermined frequency is applied; and a driving voltage generating circuit for generating the driving voltage. A continuous ink-jet printer characterized by investigating a change in the drive voltage when the frequency of the drive voltage is changed under the condition that the point is set to a predetermined position, and driving the piezo element at the frequency at which the drive voltage is the lowest. Driving method of the piezo element. 2. A continuous ink jet printer comprising a piezo element to which a driving voltage whose voltage fluctuates at a predetermined frequency is applied, and a driving voltage generating circuit for generating the driving voltage, wherein an output from the driving voltage generating circuit is provided. A continuous ink jet printer comprising frequency control means for controlling a frequency of a drive voltage to be applied.