JPH0584902A - Method for driving ink jet type printing head - Google Patents

Abstract

PURPOSE:To obtain good printing quality by decreasing cross talk by a method wherein a piezoelectric element corresponding to a nozzle opening is divided into a plurality of blocks, and drive of each block is time-shared. CONSTITUTION:A condenser 13 is charged or discharged by driving alternately current mirror circuits respectively composed of PNP type transistors 9, 10 and NPN type transistors 7, 8 by control signals 14, 15. A scan voltage signal is emitted by repeating this procedure, and a current is amplified with the NPN type transistor 11 and the PNP type transistor 12 to be inputted to a switch 20A-. When only a block selective signal 60 is made to be of an enabling state in synchronization with the scan voltage signal, a gate circuit 40A-performs on off operation of the switch 20A-according to a printing signal 50A-to be inputted to each. A piezoelectric element to be connected to the turned on switch is expanded anal contracted according to the waveform of the scan voltage signal. Hereafter, all piezoelectric elements are driven by repeating the same operation in the order of block selective signals 61, 62.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a print head used in an ink jet printer.

[0002]

2. Description of the Related Art A conventional ink jet print head is
As shown in Japanese Patent Publication No. 60-8953, a plurality of nozzle openings are formed on the wall surface of a container constituting an ink tank, and the expansion and contraction directions are aligned so as to face each nozzle opening. A piezoelectric element is arranged and configured. In this print head, a drive signal is applied to a piezoelectric element to expand and contract the piezoelectric element, and the dynamic pressure of ink generated at this time causes ink droplets to be ejected from nozzle openings to form dots on printing paper.

In a print head of this type,
It is desirable that droplet formation efficiency and flight force are large. However, since the unit length of the piezoelectric element and the expansion / contraction rate per unit voltage are extremely small, it is necessary to apply a high voltage in order to obtain the flying force required for printing, which complicates the drive circuit and electrical insulation measures. There is a problem of turning into.

In order to solve such a problem, as disclosed in Japanese Patent Laid-Open No. 63-295269, a piezoelectric for an ink jet print head in which electrodes and piezoelectric materials are alternately laminated in a sandwich shape. Elements have been proposed. According to this piezoelectric element, the distance between the electrodes can be made as small as possible, so that the voltage of the drive signal can be lowered.

[0005]

However, such a piezoelectric element can reduce the voltage of the drive signal, but has a large capacitance, and as a result, a large peak current is required when the piezoelectric element expands and contracts. In particular, in a print head that drives a plurality of piezoelectric elements, a peak current that is a multiple of the number of the piezoelectric elements is required. The large peak current when the piezoelectric element expands and contracts causes a significant voltage drop due to wiring resistance or the like, so that a so-called crosstalk occurs in which a drive signal varies depending on the number of selected piezoelectric elements. Crosstalk affects the flight characteristics of ink droplets and deteriorates print quality. As measures against this crosstalk, a large-capacity capacitor is added to the power supply unit, wiring resistance is reduced, and the like, but there has been a problem of high cost.

[0006]

In order to solve the above problems, according to the present invention, a piezoelectric element corresponding to a nozzle opening is divided into a plurality of blocks, and each block is driven in a time division manner. did.

[0007]

FIG. 1 shows an example of a drive circuit for an ink jet type print head using the drive method of the present invention. In FIG. 1, 1 to 5 are resistors, 6 to 8 are NPN type transistors, 9 and 10 are PNP type transistors, 11 is an NPN type transistor, 12 is a PNP type transistor, 13 is a capacitor, and 14 and 15 are control signals. , 20A, 20B, 2
0C, ..., 21A, 21B, ... 22A, 22
B, ... are analog switches, 30A, 30B, 30
C, ..., 31A, 31B, ... 32A, 32B,
... is a piezoelectric element, 40A, 40B, 40C, ...
41A, 41B, ... 42A, 42B, ... Are gate circuits, 50A, 50B, 50C ,.
1B, ... 52A, 52B, ... are print signals, 6
0, 61, 62, ... Are block selection signals.

When the NPN transistor 6 is turned on by the control signal 14, the PNP transistor 9 is turned on. At this time, the PNP transistor 9 and the PNP
The type transistor 10 constitutes a current mirror circuit, and charges the capacitor 13 with a constant current determined by the resistor 4. When the charge of the capacitor 13 is continued, the potential of the capacitor 13 becomes close to the potential of the emitter of the PNP transistor 10 and the resistor 4, and the charge is terminated. NP by control signal 14 after a certain time
The N-type transistor 6 is turned off, and the control signal 1
5, the NPN transistor 8 is turned on. N
The PN type transistor 7 and the NPN type transistor 8 form a current mirror circuit as described above, and discharge the capacitor 13 with a constant current determined by the resistor 5. A trapezoidal scanning voltage waveform is generated by repeatedly charging and discharging the capacitor 13 with a constant current. This trapezoidal scanning voltage waveform is current-amplified by the NPN type transistor 11 and the PNP type transistor 12 which form a complementary push-pull circuit. With the above operation, FIG.
A trapezoidal scanning voltage waveform (hereinafter referred to as a scanning voltage signal) as shown in FIG. 2 is output from the emitters of the NPN transistor 11 and the PNP transistor 12 and the analog switch 20.
A, 20B, 20C, ..., 21A, 21B ,.
22A, 22B, ... Here, the block selection signal 60 is enabled, and the other block selection signals 61, 62, ... Are disabled. Gate circuit 4 opened by block selection signal 60
0A, 40B, 40C, ... are analog switches 20A, 20B, 20C, ... Connected according to print signals 50A, 50B, 50C ,.
・ Turn on and off. At this time, the block selection signal 6
0 is enabled at the timing shown in FIG. 2 in synchronization with the scanning voltage signal. The piezoelectric element connected to the analog switch in the ON state is charged and discharged according to the waveform of the scanning voltage signal to expand and contract. This expansion / contraction operation of the piezoelectric element presses ink between the piezoelectric element and the nozzle opening to cause ink droplets to fly from the nozzle opening. Here, if the period in which the selection of all the piezoelectric elements is completed is the driving cycle, then the block selection signal 61,
By repeating the same operation in the order of 62, ...
One driving cycle is completed. With the above operation, the drive signals applied to the selected piezoelectric elements of each block become the drive signals 30, 31, 32 in FIG.

The relationship between the number of divisions N (N is a natural number of 2 or more), one cycle period T of the scanning voltage signal (from the start of rising of the voltage waveform to the end of falling), and the driving cycle is: driving cycle ≧ N × T (Driving period, unit of T is [s]).

Further, when the nozzle openings of the print head are arranged in a line in the sub-scanning direction, a time shift occurs due to division drive for each block of each piezoelectric element, and as a result, the print head is scanned in the main scanning direction. The lines in the sub-scanning direction become jagged. Therefore, good print quality can be obtained by arranging the nozzle openings corresponding to the divided piezoelectric elements in the main scanning direction as shown in FIG.
In FIG. 3, 101 is a nozzle opening and 102 is a nozzle plate. If the shift amount of this nozzle opening 101 (shift from the block to be selected first) is W (m) (m is the block selection order), and the resolution in the main scanning direction is D (D unit is dots / inch) The amount W (m) is obtained by W (m) = 1 / D × T ÷ driving cycle × (m−1).

As described above, by dividing the piezoelectric element into N blocks and performing time-division driving, the maximum peak current value required for driving all the piezoelectric elements can be reduced to 1 / N. Further, in this embodiment, the analog switches 20A, 20
B, 20C, ..., 21A, 21B, ... 22A,
22B, ... have been described with the simple symbols shown in FIG.
A concrete example is the CMOS transmission gate shown in FIG. In FIG. 4, 201 is a control signal for determining on / off, 202 is an inverter, 203, 204
Is an input / output terminal. However, this transmission
The on-state resistance of the analog switch by the gate causes a time delay with respect to the scanning voltage signal due to the capacitance of the piezoelectric element, and is therefore preferably 300Ω or less.

In the present embodiment, the scanning voltage signal has been described with the trapezoidal waveform shown in FIG. 2. However, the same effect can be obtained even if the circuit for generating the constant current waveform shown in FIG. 1 is constituted by the constant voltage circuit. It's obvious.

In the present embodiment, the driving circuit using the scanning voltage signal as the common electrode has been described, but it is obvious that the same effect can be obtained by the method of generating the scanning voltage signal for each piezoelectric element.

[0014]

By dividing the piezoelectric element corresponding to the nozzle opening into a plurality of blocks and selecting each block by time division, it is possible to realize an inexpensive circuit with less crosstalk and good print quality. It was

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a circuit using a method for driving an inkjet print head of the present invention.

FIG. 2 is a diagram showing a time chart of a circuit using the method for driving the inkjet print head of the present invention.

FIG. 3 is a diagram showing an arrangement of nozzle openings when the method for driving an inkjet print head of the present invention is used.

FIG. 4 is a diagram showing a specific example of an analog switch.

[Explanation of symbols]

20A, 20B, 20C, ..., 21A, 21B,
21C, ..., 22A, 22B, 22C ,.
Analog switches 30A, 30B, 30C, ..., 31A, 31B,
31C, ..., 32A, 32B, 32C, ...
Piezoelectric elements 40A, 40B, 40C, ..., 41A, 41B,
41C, ..., 42A, 42B, 42C ,.
Gate circuit 60, 61, 62, ...
Block selection signal

Claims (1)

[Claims] 1. A method of driving an ink jet print head, wherein a plurality of piezoelectric elements are arranged corresponding to a plurality of nozzle openings, and ink is ejected from the nozzle openings to the outside by a drive signal to the piezoelectric elements. Then, the piezoelectric element is divided into a plurality of blocks, and each block is driven in a time-division manner.