JP2000272146A - Ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved mechanism for unclogging the nozzles in the print head of an ink jet printer without requiring a significant amount of extra cost and providing a better ink supply performance of print head. SOLUTION: The ink jet printer comprises a piezoelectric print head arranged to eject ink upon application of a voltage pulse to a piezoelectric element 12. A print signal generator 44 generates a first magnitude print voltage pulse being applied to the piezoelectric element 12 in order to eject a print ink drop from the print head, and a second magnitude unclogging voltage pulse larger than the first magnitude for unclogging the print head. A controller 16 applies the print voltage pulse or the unclogging voltage pulse selectively to the print head.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to an ink jet printing apparatus, and more particularly to an ink jet printer having a print head driven by a piezoelectric effect and a means for unclogging the print head.

[0002]

2. Description of the Related Art In a drop-on-demand type ink jet printer, if a time interval between ink ejection from nozzles is longer than an evaporation time of an ink liquid carrier, ink starts to solidify. This will clog the nozzles and prevent ejection of the proper amount of ink from these nozzles. In addition, small solid particles, such as dust particles, can clog the nozzle. In this case, the printhead may be moved to a cleaning station to clean or evacuate the orifice plate to clear the nozzle clog. The printhead may be removed and cleaned manually.

[0003] In the prior art, various techniques have been proposed for removing ink clogging in nozzles and reducing nozzle clogging. "Methods and Apparatus for Avoiding Drying of Ink-Jet in Ink-Jet Printers" published September 10, 1985 to Biggs et al.
aratus for avoiding the drying of ink in the ink j
U.S. Pat. No. 4,540,997 entitled "ets of ink jet printers" describes an ink jet printer that prevents nozzle clogging by ensuring that drops are ejected from the nozzles within a specified time period. It has been disclosed. The Siliconics Model 30790-02 inkjet printer uses a microprocessor during normal printing to monitor the number of drops ejected by each ink channel. If a channel is not used for a period of 100 seconds, the microprocessor commands the channel to fire an ink drop. On December 9, 1975, Casio (K
The ink jet printer described in U.S. Pat. No. 3,925,789, entitled "Ink jet recording apparatus", issued to Asio, uses a timer during normal printing. The elapsed time between ink ejection from each ink nozzle is counted. If the elapsed time between firings from any of the nozzles exceeds a preselected time, the control unit is triggered, which in turn drives the pump, which pumps ink from its unused nozzles. Inject In addition, this patent discloses that ink is ejected from each nozzle for several seconds after the printer is turned on. March 1, 1986
“Ink jet recording appa” issued to Kawamura on the 8th
ratus) ", U.S. Patent No. 4,577,203.
Discloses an ink jet recording apparatus capable of separating an ink channel from an ink reservoir.
During this time, the nozzle is turned on using the suction mechanism. "Maintenance station of ink jet printer and cap a contained therein, issued to Maeno on April 8, 1997.
U.S. Pat. No. 5,619,232, entitled "nd pump included therein", discloses a maintenance station for an ink jet printer that uses the same suction method to conduct a plugged nozzle. 19
On February 21, 1989, Koto et al.
Ink jet printer of the ink-on-de
US Patent No. 4,806,9 entitled "mand type)"
In the ink jet printer described in No. 55,
A cap covers the nozzle and a pump ejects ink through the nozzle to avoid clogging the nozzle with ink.

[0004] An alternative method used in some ink jet printers is to clean the nozzles after printing a selected number of pages. In these methods, the nozzle is transported to a cleaning station, where the nozzle is cleaned or wiped by different means.

[0005]

SUMMARY OF THE INVENTION The method described above provides a method of preventing clogging of a nozzle or a method of removing a clog from a nozzle. Each of the above methods has some disadvantages.
When cleaning the nozzle to remove ink, the orifice plate may be damaged. The use of suction caps and vacuum or pressure pumps can add to the complexity of the printer device, which can increase the cost of the printer device. The method of ejecting drops at regular time intervals to prevent clogging requires a timing circuit,
In addition, ink is wasted. Therefore, the clogging of the nozzle can be eliminated (dec) without adding a large cost.
improved declutter (log) and can provide better feed performance of the printhead
There is a need for an (ogging) mechanism.

[0006]

SUMMARY OF THE INVENTION An ink jet printer according to the present invention has a piezoelectric printhead configured to eject ink in response to application of a voltage pulse to a piezoelectric element. The signal generator includes a first magnitude print voltage pulse for the piezoelectric element for ejecting a print drop of ink from the printhead, and a second magnitude greater than the first magnitude for clearing the printhead jam. And a clog clearing voltage pulse having a magnitude of The controller selectively applies a printing voltage pulse or a deblocking voltage pulse to the printhead.

[0007]

DETAILED DESCRIPTION OF THE INVENTION A piezoelectric printhead used for drop-on-demand printing uses a piezoelectric element located in the printhead to create a pressure wave or volumetric displacement to create an ink drop in the printhead. Discharge through orifice inside. The piezoelectric element is driven by a voltage pulse waveform having a magnitude V. Voltage V is fairly small, for example in the range of 10 to 100 volts. According to the present invention, the limit voltage Vstress is greater than the printing voltage but
(Above which the piezoelectric element is damaged or stressed) or smaller than the voltage Vingest (above which air may be sucked into the print head at the fill position of the print cycle). When a voltage (V + ΔV volts) is applied to the piezoelectric element, it generates a large pressure wave, which can clear the clogging of nozzles in the printhead.

FIG. 1 shows the general structure of an array of piezoelectric elements and drivers found in a piezoelectric printhead.
This structure is well known in the prior art and includes an array of switching transistors 10 connected to an array of capacitors 12 corresponding to piezoelectric elements.

The digital image data is input to digital logic module 14 one row at a time. The digital logic module 14 has a plurality of shift registers and a plurality of latches. The digital logic module clocks a column of digital print data into a set of shift registers. The controller module 16 sets the timing and synchronizes the functions of the printer. The print signal generator 18 provides a voltage V from a power supply 20 to the switching transistor array 10, which applies a voltage that drives a piezoelectric element 12, shown as an array of capacitors. The print signal generator 18 supplies an optimally shaped signal to the piezoelectric element for printing.

The above-described device can generate a driving waveform as shown in FIG. The print cycle 21 includes a filling period 22, a printing period 23,
And a rest period 24. In the filling period 22, a negative voltage is applied to the piezoelectric element 12, whereby the nozzle is filled with ink. During the printing period 23, a positive voltage is applied to the piezoelectric element 12, which causes the nozzles to eject ink. In the idle period 24, the voltage applied to the piezoelectric element returns to zero before the nozzles are refilled with ink for the next print cycle. The waveform shown in FIG. 2 is only one example of the waveform used for driving the piezoelectric inkjet head. The print cycle pulse can be designed to have different shapes to achieve different functions. It can also have various voltage (V) magnitudes. Piezoelectric actuators are typically equipped with two electrodes that receive electrical signals and
This is converted into mechanical energy by the actuator. In the example described, one electrode is grounded and the other electrode receives the electrical signal shown in FIG.
The positive and negative voltage polarities are selected such that a negative voltage causes mechanical expansion of the chamber holding the ink, and a positive voltage causes mechanical compression of the chamber holding the ink. If the voltage is constant, the chamber size is kept constant. Thus, only the transition of the voltage waveform is active at the time of ink filling or ejection. First (downward) transition 25 in the waveform of FIG.
Causes the chamber to be filled with additional ink. This size is called Vfill. Second (upward) transition 26 of the waveform
Fires a drop. This size is referred to as Vfire or simply V. A third (downward) transition 27 returns the chamber to its original size. This transition may be chosen to help cancel residual meniscus motion at the nozzle exit, and is referred to as Vcancel. The rest period Trest may be set after these portions of the waveform, and the print cycle described above may be executed again after this rest period.

A method for operating a printhead according to the present invention is described below. Referring to FIG. 3, an unclogging pulse 2
8, but the second (upward) transition 26 in this signal is V + ΔV instead of V. Where V
+ ΔV is the unclogging v
oldage) Vunclog. Referring to FIG. 4, the clog clearing pulse control unit 30 can receive an input signal from any of a number of input sources. Input sources in this case include a manual jam clear button 32, an off-time counter 34 that monitors the time elapsed since the last drive of the printhead, and a jam due to missing print dots in the printed test pattern 37. An optical sensor 36 that detects the nozzle that has been turned off is included. The test pattern is stored in the image memory 38 of the printer. An example of the test pattern 37 is shown in FIG. 5, where at the location indicated by reference numeral 39, it is shown that some nozzles are clogged.

Clog removal pulse controller unit 3
0 includes a logic block 40 and a look-up table (LUT) 42 based on the results of previous experiments. Based on the results of previous experiments, the look-up table (LUT) 42 may select the clogging pulse intensity index n and clogging pulse shape index m based on elapsed time, optical error results, or operator input. it can. The output of the clog clearing pulse controller unit 30 is supplied to the print signal generator 44 via the switch 46. One of the output components is an intensity index n, which signals a switch 46 to supply any one of several available voltages from a variable power supply 48 to a print signal generator 44. In this embodiment, the print signal generator 44 is usefully used to generate a jam clearance signal. With this feature, the cost of manufacturing and maintaining the printing system of the present invention can be reduced.

In the alternative embodiment shown in FIG. 6, the shape index (m) and the intensity index (n), which are the outputs of the clogging pulse controller unit 30, are provided to a clogging signal generator 50. . The de-clog signal generator 50 can generate any one of several pulse shapes specifically tailored to the de-clog function.

As shown in FIG. 3, the shape of the de-clogging pulse is shown in FIG. 7, except that the magnitude V of the injection transition is chosen to be larger by an amount specified by the intensity index n. As described above, the shape of the clog removal pulse may be chosen to be different, as specified by the shape index m. In the example shown, the slope of the cancel transition 27 (Vcancel) has been chosen to be smaller to minimize the possibility of air being drawn into the nozzle.

Importantly, the de-jamming pulse is preferably applied to the printhead when the printhead is at a capping or cleaning station or an ink receiving station, rather than during a page printing operation. It is. this is,
This is because the generated jam removal drops are much larger than normal print drops and can be noticeable when deposited on a page. Thus, whether the deinking signal is generated by operator involvement, or generated by an optical sensor or by a timer, the printhead is preferably applied with a de-clogging pulse. Prior to being moved to a particular deblocking station.

In any of the embodiments, it is important that the magnitude (V + ΔV) of the clogging removal pulse is smaller than one of the two limit voltages, that is, V + ΔV <Vstress V + ΔV <Vingest. .

It has been found that the added voltage (.DELTA.V) in the range of 10-20 volts, even well below the limit voltage, is useful for clearing clogged nozzles. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a driving circuit of a conventional piezoelectric inkjet print head.

FIG. 2 is a waveform diagram showing a conventional inkjet drive signal generated by the drive circuit shown in FIG. 1;

FIG. 3 is a waveform chart showing a jet clog removal driving signal according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing a driving circuit of the piezoelectric inkjet print head according to the embodiment of the present invention.

FIG. 5 is a diagram showing a test pattern used in a predetermined mode according to the embodiment of the present invention.

FIG. 6 is a schematic diagram showing a drive circuit according to another embodiment of the present invention.

FIG. 7 is a waveform diagram illustrating an alternative pulse shape according to an embodiment of the present invention.

[Explanation of symbols]

10 switching transistors, 12 piezoelectric elements shown as capacitors, 14 digital logic modules, 16 controller modules, 18 print signal generators, 20 power supplies, 21 print cycles, 22
Filling period, 23 printing period, 24 pause period, 2
5 First transition, 26 Second transition, 27 Third transition, 28 Clog clear pulse, 30 Clog clear pulse control unit, 32 Manual clear button, 3
4 Off-time counter, 36 optical sensor, 37 printed test pattern, 38 image memory, 39 clogged nozzle position, 40 logic block, 42 look-up table (LUT), 44 print signal generator, 46 switch, 48, Variable power supply, 50 clog removal signal generator.

Claims (1)

[Claims] 1. A piezoelectric printhead configured to eject ink in response to a voltage pulse applied to a piezoelectric element, and a first magnitude relative to the piezoelectric element for ejecting a print drop of ink from the printhead. A signal generator for generating a print voltage pulse having a second magnitude greater than the first magnitude for eliminating the clogging of the print head; and A controller for selectively applying a clogging voltage pulse to the printhead;
An inkjet printer comprising: