JP2001158109A - Print head cleaner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a print head cleaner using a plurality of resonance points. SOLUTION: Efficiency of ultrasonic cleaning of a print head is improved through sweeping at a stimulus driving frequency. Cleaning frequency is swept with a constant driving amplitude. The driving amplitude and the upper and lower limit frequencies are stored in a print head memory. Under such an ultrasonic cleaning state as a print head is determined from a state table, a print station varies the frequency at a constant rate. The driving amplitude is kept constant during ultrasonic cleaning state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous ink jet printing, and more particularly to cleaning a print head of a continuous ink jet printing apparatus.

[0002]

BACKGROUND OF THE INVENTION Continuous ink jet printheads utilize a series of orifices spaced from a charge lead by a small gap. During operation of the printhead, fluid is expelled through the orifice. When deactivated, the ink wets the area around the leads and orifices. This fluid then dries, generating a non-volatile material in solid or gel form. Depending on the chemical properties of the ink, the ink polymerizes when it dries and becomes insoluble. At the next start-up, all this material in the orifices and gaps cannot be removed or dissolved, which hinders the shape or direction of the ejected jet. Heavy deposits and debris may also block the orifice. Deposits remaining on the charge leads may form a film that inhibits proper charging of the droplet during droplet formation and causes insufficient deflection of the droplet. Therefore, debris and dry in-deposits on the orifice plate can be caused by the formation of streaked curved jets (the jets constantly impinge on the media, whether charged or not) and shorts (shorts) in the charge plate. ).

[0003] Although current ink jet systems attempt to filter such debris, it is necessary to occasionally ultrasonically clean the printhead resonator and orifice plate to remove such deposits. is there. This can be achieved by applying a strong stimulus drive (known as "superstim") to the piezoelectric crystal, as described, for example, in U.S. Pat. No. 4,563,688.

The technique of US Pat. No. 4,600,928 improved the efficiency of the super-steam cleaning process by modulating the ink pressure in connection with high amplitude oscillations. As the ink pressure is modulated, ink flows outward and inward through the orifice. The inward flow of fluid through the orifice, in combination with the vibration, can assist in removing particles from the orifice.

In order to ultrasonically clean a fluid generator cavity, the surface of the fluid cavity must be vibrated with a large amplitude. In order to increase the amplitude of the vibration, it is effective to drive the droplet generator at or near the resonance point. Such an intent is proposed in U.S. Pat. No. 4,600,928, which shifts the frequency to a constant desired cleaning frequency and increases the amplitude of the drive signal. Alternatively, the frequency of the oscillator can be shifted across the resonance point in a cleaning mode until the feedback signal from the detector indicates a resonance state of the device coupled to the vibration of the transducer.

[0006] However, typical resonant vibration modes have one or more nodal regions that vibrate with little or no vibration at the surface of the fluid cavity. Regardless of the drive amplitude used, the cleaning efficiency in these areas is low. This problem can be overcome by using more than one resonant mode. U.S. Pat. Nos. 4,563,688 and 4,600,928.
The techniques of the above document have attempted to meet this requirement of driving multiple resonance points by driving a drop generator with a square wave. A square wave contains many harmonic signals at higher frequencies in addition to the fundamental frequency component. Therefore, the cleaning drive signal has at least some components at a higher frequency than the substantial sinusoidal drive signal.

[0007]

The above-mentioned U.S. Pat.
The techniques of U.S. Pat. Nos. 63,688 and 4,600,928 disclose vibration energy at higher harmonic element frequencies for most drop generator designs, including those illustrated therein. It could not be transmitted to the drop generator. For many droplet generator designs, this results in a droplet generator that does not have a resonance frequency corresponding to the harmonic frequency obtained from the square wave. For this reason, the use of a square wave drive function does not provide any advantages over the use of a sine wave.

It has been found desirable to provide a means for using more than one resonant mode to clean a printhead.

[0009]

SUMMARY OF THE INVENTION In order to improve the cleaning efficiency of a droplet generator, the present invention provides for supersteam cleaning at multiple frequencies. Improved versatility in the stimulus drive circuit enables the method of the present invention and allows for changing the super-stim frequency. By changing the drive frequency, more than one resonance point can be used to ensure that all surfaces inside the fluid cavity are vibrated with sufficient vibration amplitude for effective cleaning.

[0010] According to one aspect of the invention, the efficiency of ultrasonic cleaning of the printhead sweeps the stimulation frequency.
It is improved by that. The cleaning frequency is swept with a constant drive amplitude. The drive amplitude, the lower frequency limit and the upper frequency limit are stored in the memory of the print head. When the print head is in the ultrasonic cleaning state as determined by the state table, the print station is powered by Analog Devices, Inc.
logue Devices Corp.) Direct Digital Synthesizer (DDS) AD
9850 using a constant rate (currently 3KHz /
Change the frequency in seconds). The drive amplitude is kept constant during the ultrasonic cleaning state.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, as shown in FIG. 1, a cleaning device is used to cross-flash a droplet generator 10 at a high flow rate. To enhance the removal of particles from the drop generator, the drop generator is driven by its stimulus-driven transducer 12 fixed to a resonator body 18.
Is driven ultrasonically. When ultrasonically driven at high amplitude, the particles can be vibrated and released from the surface of the droplet generator and orifice plate 14 with a vibration amplitude several times that used for normal stimulation of droplet breakage. .

While ideal drop generators have a uniform amplitude throughout the length of the drop generator, most real drop generators, especially those with long jet trains, have an amplitude along the length. There is a certain change. This has been found to be the result of a number of resonance points at a resonance frequency close to the desired operating frequency. It has been found that in such a droplet generator, when the drive frequency is shifted across the operating resonance point, the relative drive amplitude for these closely spaced resonance points changes. As a result, shifting the drive frequency across the resonance point can shift the higher vibration region along the length of the droplet generator. Therefore, it is desirable to continuously sweep the drive frequency across the resonance point to obtain consistent cleaning along the length of the drop generator. Therefore, a continuous sweep of the drive frequency across the resonance frequency has been found to be more effective than operating at any constant frequency.

[0013] US patent application Ser.
In some drop generator designs, such as the drop generator described in U.S. Pat. No. 1,059, the fluid in the drop generator is sufficient to make it difficult to determine the resonance frequency from drive or feedback signals. Causes attenuation. Again, in this case,
Continuous sweeping of the frequency range known to include the resonance point is equally advantageous.

To provide effective cleaning of the droplet generator,
The present invention improves the ultrasonic cleaning of the printhead by sweeping the stimulation frequency. Cross-flushing is accomplished by flushing the cleaning fluid from one mount 16 to the opposite mount 16. The cleaning frequency is swept continuously at a constant drive amplitude.

In a preferred embodiment, the printing station changes frequency at a fixed rate (currently 3 KHz / sec) when the printhead is in an ultrasonic cleaning state determined by a state table. In a preferred embodiment, the frequency sweep is
Provided by Devices Direct Digital Synthesizer (DDS) AD9850.

Due to manufacturing variations, the drive amplitude and frequency range to be used for ultrasonic cleaning varies from drop generator to drop generator. To address this problem, the preferred embodiment of the present invention provides a means for storing the desired drive amplitude, lower frequency limit and upper frequency limit in memory in the printhead. During production,
These values are determined and written to the printhead memory. Other uses of the printhead memory and means for incorporating data stored in the printhead memory are described in commonly assigned US patent application Ser. No. 08 / 810,653.
It is described in the specification.

Even with a well-designed drop generator that has a completely uniform oscillation amplitude over the length of the jet train, the oscillation amplitude will not be uniform throughout the fluid cavity of the drop generator. FIG. 2 shows the above-mentioned US patent application Ser. No. 09/2.
1 is a cross-sectional view of a droplet generator as described in the specification of US Pat. No. 11,059. The droplet generator 27 has a fluid cavity 23,
Through this cavity, ink is supplied to an orifice formed in the orifice plate 25. The piezoelectric actuator 21 attached to the droplet generator is an electronic circuit (not shown)
To vibrate the droplet generator. When driven at the operating frequency, proper drop formation is provided and the drop generator assembly oscillates as shown by deformed shape 27 '.
The deformed shape corresponds to the peak amplitude of the oscillation, and every part of the droplet generator oscillates before and after the undeformed shape. Here, 21 ', 23' and 25 'indicate the vibration amplitudes of the piezoelectric actuator, the fluid cavity and the orifice plate, respectively. As shown, most of the fluid cavities have a large vibration amplitude, while the sections at the top of the fluid cavities 31 and the lower portion of the fluid cavities 32 experience small vibrations. Ultrasonic vibration is not significantly effective in cleaning these parts of the droplet generator, as there is little or no vibration amplitude in these areas.

The use of multiple resonant frequencies to clean the drop generator can eliminate this problem. FIG. 3 shows a resonance shape for another resonance point that can be used to clean the droplet generator 27. This resonance point has a large vibration amplitude at the top 31 'of the cavity 31, where the normal operating resonance point in FIG. 2 has a small amplitude. This resonance point also has no vibration at the previous resonance point and has a vibration difference of 3
Vibration is provided to the region 32 with 2 '. However, this resonance point is in the region 3 (on the side of the fluid cavity) of low vibration amplitude.
Seven. Thus, while this resonance point is more effective for cleaning the top of the fluid cavity than the previous resonance point,
Less effective for cleaning the sides of the fluid cavity. By using these two resonance points, vibrations useful for cleaning can be generated throughout the fluid cavity.
Additional resonance points can be used to further enhance the cleaning effect of these resonance points. In general, any droplet generator design has two or more complementary resonances that can be used to provide vibratory cleaning to the entire interior surface of the fluid cavity. Although the resonance shapes for these two resonances are symmetric across the fluid cavity, asymmetric resonances can be used for cleaning as well. For such asymmetric resonances, it may be necessary to drive only some of the piezoelectric elements or some of them out of phase with each other.

To provide effective cleaning of the droplet generator,
The present invention provides a means for utilizing such a complementary resonance point. In a preferred embodiment, this is achieved by stepping (jumping) the frequency at each resonance point. A frequency sweep between resonance points can be used, but is slow and has poor cleaning efficiency.

In a preferred embodiment of the present invention,
Means are provided for continuously sweeping the drive frequency across the effective resonance point. After a period of time, the drive frequency can jump to the frequency of the complementary resonance point. Next, the drive frequency is continuously swept across the resonance point. In a particularly preferred embodiment, the frequency sweep range and amplitude are stored in a printhead memory.

INDUSTRIAL APPLICABILITY AND ADVANTAGES The present invention is useful for cleaning printheads in ink jet printing devices. The device according to the invention for cleaning the print head by sweeping the stimulation frequency has the particular advantage of improving the efficiency of the cleaning operation.

Although the invention has been described in detail with reference to certain preferred embodiments, it should be understood that modifications and variations are possible within the spirit of the invention.

[Brief description of the drawings]

FIG. 1 is an exploded view of a droplet generator showing cross flushing.

FIG. 2 is a diagram showing resonance shapes at different resonance points being swept.

FIG. 3 is a diagram showing resonance shapes at different resonance points being swept.

[Explanation of symbols]

 10, 27 Droplet generator 18 Resonator 21 Piezoelectric actuator 23, 31, 32 Fluid cavity 25 Orifice plate

Claims (10)

[Claims] 1. An apparatus for cleaning a printhead of a continuous ink jet printing apparatus having a droplet generator having a plurality of resonators, an associated orifice plate, and a piezoelectric element stimulating the orifice plate. Means for applying a stimulus drive frequency to the piezoelectric element; means for flushing fluid through the droplet generator; and among a plurality of resonance points of the droplet generator for ultrasonic cleaning of the droplet generator. The stimulus drive frequency is changed to use two or more of the above, so that the low amplitude region of the droplet generator caused by driving one resonance point is made the same by driving at least one other complementary resonance point. Changing means for cleaning an area by high-amplitude vibration; 2. The cleaning device according to claim 1, wherein said changing means includes means for continuously sweeping the stimulus driving frequency across one frequency range. 3. The cleaning apparatus according to claim 1, wherein said changing means includes means for increasing a stimulus driving frequency from one frequency to another frequency. 4. The means for changing comprises: means for sweeping the stimulus drive frequency across one frequency range; and means for increasing the stimulus drive frequency to sweep at least one other frequency range. The cleaning device according to claim 1, wherein: 5. The cleaning apparatus according to claim 1, further comprising a print head memory for storing a frequency sweep range and an amplitude. 6. An apparatus for cleaning a printhead of a continuous ink jet printing apparatus having a fluid cavity and an associated orifice plate and a droplet generator having piezoelectric elements stimulating the orifice plate, wherein the droplets are Means for identifying a corresponding resonance point in the generator;
Means for applying a stimulus drive frequency to the piezoelectric element; and changing means for changing the stimulus drive frequency to a resonance frequency of the complementary resonance point to provide vibration cleaning to the entire inner surface of the fluid cavity. A cleaning device characterized by the above-mentioned. 7. The cleaning apparatus according to claim 6, wherein said changing means includes means for continuously sweeping the stimulus driving frequency across one frequency range. 8. The cleaning apparatus according to claim 6, wherein said changing means includes means for increasing a stimulus driving frequency from one frequency to another frequency. 9. Apparatus for providing an optimum cleaning state for a print head of a continuous ink jet printer, means for applying a stimulus drive frequency to a piezoelectric element; a stimulus drive frequency for optimal ultrasonic cleaning of a constant print head. Means for determining an optimum drive amplitude and frequency range for the printhead; and means for sweeping an optimum cleaning frequency at a constant optimum drive amplitude to improve cleaning of the printhead. 10. The print head memory according to claim 9, further comprising a print head memory for storing an optimal drive amplitude, an optimal cleaning frequency upper limit, and an optimal cleaning frequency lower limit from the determined optimal frequency range. The described device.