JPH09277526A - Piezoelectric element driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate correction of driving wave caused by environmental temp. by providing a first group of voltage wave generating circuits provided with a plurality of different time const. for shrinking a piezoelectric element and a second group of voltage wave generating circuits provided with a plurality of different time const. for extending the piezoelectric element. SOLUTION: An NPN type transistor 72 and a PNP type transistor 73 are connected with a time const. setting capacitor 71 to be electric current buffers for amplifying electric current during charging and discharging of the capacitor 71. When driving wave is formed, charging circuits 50a, 50b...50f and discharging circuits 60a, 60b...60f not only respectively independently perform charging operation and discharging operation but also perform the charging operation and discharging operation by combining a plurality of charging circuits and discharging circuits in accordance with the slope of a driving wave and the driving voltage. Operation of the charging circuit 50a charges the capacitor 71 by a definite electric current value from the electric source voltage Vh when a charging signal is inputted to a terminal 58a from a control means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a piezoelectric element used in a printer head using an on-demand type ink jet recording head for ejecting ink droplets from nozzles by displacing a pressure chamber by a rod-shaped piezoelectric element. About.

[0002]

2. Description of the Related Art An on-demand type ink jet recording head used in a recording apparatus is disclosed in US Pat.
As described in Japanese Patent No. 7,193, the piezoelectric element is formed in a rod shape, and a vibration plate constituting a pressure chamber is brought into contact with the piezoelectric element to expand and contract the pressure chamber by longitudinal vibration, thereby forming an ink. Ink jet recording heads that fly droplets are known.

In the ink jet recording head utilizing such vertical vibration, the piezoelectric element is charged with electric charge immediately before dot formation, the piezoelectric element is contracted, and then the electric charge of the piezoelectric element is discharged to expand the piezoelectric element. A driving method based on a so-called pulling-out method, in which the pressure chamber is contracted to generate ink droplets, is adopted.

By the way, there are individual differences in the characteristics of the recording head and variations in piezoelectric elements in the recording head, and a method for correcting this has already been proposed (Japanese Patent Laid-Open No. 7-1444).
09 publication).

According to this, in order to correct the individual difference of the recording head, the time constant adjusting resistance of the drive waveform is unitized,
A time constant adjustment resistance unit is selected for each recording head so that individual differences of the recording head can be corrected.

However, the drive waveform is complicated to improve the printing speed, the fine vibration drive is added to prevent the ink droplets from being ejected to prevent the nozzle clogging, and the ink dot diameter is changed to improve the printing quality. In a drive circuit that attempts to cope with the above problems, if the time constant adjusting resistors of the drive wave are unitized, the number of units in which the time constant adjusting resistors are combined is greatly increased, which makes it difficult to cope.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its purpose is to easily generate a complicated drive waveform and to improve the recording head itself. It is an object of the present invention to provide a piezoelectric element drive circuit capable of easily correcting a drive waveform due to individual difference and environmental temperature.

[0008]

In order to solve such a problem, a first group of voltage waveform generating circuits having a plurality of different time constants for contracting a piezoelectric element and a piezoelectric element for expanding the piezoelectric element are provided. A second group of voltage waveform generating circuits having different time constants, wherein the voltage generating circuit combines one or more circuits from the first group of voltage generating circuits for contraction of the piezoelectric element. A voltage waveform having an arbitrary time constant is generated, and one or more circuits from the voltage generating circuits of the second group are combined to generate a voltage waveform having an arbitrary time constant in order to extend the piezoelectric element.

[0009]

FIG. 2 shows an embodiment of an ink jet recording head driven by a piezoelectric element driving circuit according to the present invention with a sectional structure of one pressure generating chamber. Is a nozzle plate, nozzle opening 1
Reference numeral 12 denotes a flow path forming plate, which is a through hole that partitions the pressure generating chamber 13, a through hole that partitions two ink supply ports 14, 14 communicating with both sides of the pressure generating chamber 13, or It is provided with a groove, and a through-hole for dividing two common ink chambers 15, 15 communicating with the ink supply ports 14, 14.

Reference numeral 16 denotes a vibrating plate, which is a thin plate that is elastically deformed by coming into contact with the tip of the piezoelectric element 17, and is fixed in a liquid-tight manner integrally with the nozzle plate 10 with the flow path forming plate 12 interposed therebetween. Is formed. Reference numeral 19 denotes a base, which includes a housing chamber 20 for housing the piezoelectric element 17 in a vibrating manner, and an opening 21 for supporting the flow path unit 18.
Is fixed at the fixed substrate 22 by selecting its tip from the opening 21, and the island portion 16a of the vibration plate 16 is brought into contact with the piezoelectric element 17 so that the flow path unit 18 is opened.
It is fixed to the recording head. With such a configuration, when the piezoelectric element 17 contracts and the pressure generating chamber 13 expands, the ink in the common ink chambers 15, 15 flows into the pressure generating chamber 13 via the ink supply ports 14, 14.
When the piezoelectric element 17 expands and the pressure generating chamber 13 contracts after a lapse of a predetermined time, the ink in the pressure generating chamber 13 is compressed and ink droplets are ejected from the nozzle openings 11 to form dots on the recording paper.

When the piezoelectric element 17 is contracted by a minute amount by applying a minute vibration pulse to the piezoelectric element 17 so as not to eject ink droplets, the pressure generating chamber 13 is also slightly expanded, so that the meniscus near the nozzle opening 11 is generated. Pressure generation chamber 13
When the piezoelectric element 17 is returned to the original state, the pressure generating chamber 13 contracts and the meniscus is slightly pushed back to the nozzle opening 11 side.

FIG. 4 shows an embodiment of the drive circuit of the present invention. In the figure, reference numerals 58a, 58b, ..., 58f are charge control signals of the charge circuits 50a, 50b ,. Yes, the control means 30 shown in FIG.
Is supplied at the same timing as the printing. Similarly, reference numerals 68a, 68b, ..., 68f in the drawing are discharge control signals of the discharge circuits 60a, 60b, ..., 60f, respectively, which are supplied from the control means 30.

Charging circuits 50a, 50b, ..., 50f
Are constant current charging circuits having the same configuration, and only the circuit 50a is shown as a representative thereof.

Discharge circuits 60a, 60b, ..., 60f
In the same manner, the constant current discharge circuits having the same configuration are similarly shown, and only the circuit 60a is shown as a representative thereof.

Regarding the charging circuit 50a, the base of an NPN transistor 51a is connected to one terminal of the reference numeral 58a through a current limiting resistor 55a, and the collector of the transistor 51a is connected to a P terminal through a current limiting resistor 56a.
The base of the NP transistor 52a and the collector of the PNP transistor 53a are connected. The base of the transistor 53a and one terminal of a time constant setting resistor 54a are connected to the emitter of the transistor 52a. The charging circuit 50b is connected to the collector of the transistor 52a.
Not shown transistor 52 of 50c, ..., 50f
The collectors of b, 52c, ..., 52f and one terminal of the time constant setting capacitor 71 are connected. The emitter of the transistor 53a has a power source Vh and a time constant setting resistor 54.
One terminal of a is connected to form a constant current charging circuit.

On the other hand, the discharge circuit 60a has a reference numeral 68a.
The base of the NPN transistor 62a and the collector of the NPN transistor 63a are connected to one of the terminals through a current limiting resistor 65a. Transistor 62
Discharge circuits 60b, 60c, ..., 6 are provided in the collector of a.
0f transistors 62b, 62c, not shown, ...
.., 62f, and one terminal of the time constant setting capacitor 71. The emitter of the transistor 62a is connected to the base of the transistor 63a and one terminal of the time constant setting resistor 64a. The emitter of the transistor 63a is grounded together with one terminal of the time constant setting resistor 64a, and constitutes a constant current discharge circuit.

An NPN-type transistor 72 and a PNP-type transistor 73 are connected to the time constant setting capacitor 71, which serves as a current buffer for amplifying the current when the capacitor 71 is charged and discharged.

Charging circuits 50a, 50b, ..., 50f
The discharge circuits 60a, 60b, ..., 60f not only perform the charging operation and the discharging operation individually in generating the driving waveform, but also configure a plurality of charging circuits and discharging circuits according to the inclination of the driving waveform and the driving voltage. The charging operation and the discharging operation are performed in combination.

The operation of the charging circuit 50a is such that when the charging signal is inputted to the 58a terminal from the control means 30, the power source voltage Vh is reached.
, The capacitor 71 is charged with a constant current value Ica expressed by the equation (1).

Ica = VBE53a / R54a (Equation 1) The charging circuits 50b, 50c ,.
The charging circuit has the same configuration as that of 0a, and includes the reference numerals 58b and 58.
When a charging signal is input from the control means 30 to the terminals c, ..., 58f, the power source voltage Vh changes to Icb and Ic, respectively.
The capacitor 71 is charged with a constant current of c, ..., Icf.

Icb = VBE53b / R54b (Equation 2) Icc = VBE53c / R54c (Equation 3) Icd = VBE53d / R54d (Equation 4) Ice = VBE53e / R54e (Equation 5) ) Icf = VBE53f / R54f (Equation 6) In this embodiment, the charging time constant setting resistors 54a, 54b,
The value of the charging time constant setting resistor 54a is set to RxΩ so that each value of 54f is about half of the maximum charging current required by the driving circuit when the charging circuit 50a is driven. Next, the value of the charging time constant setting resistor 54b is set to 2RxΩ so that the charging current of the charging circuit 50b becomes half that of the charging circuit 50a. Hereinafter, up to the charging circuit 50f, the charging current is set to be half, which is expressed as follows.

R54a = Rx Ω R54b = 2Rx Ω R54c = 4Rx Ω R54d = 8Rx Ω R54e = 16Rx Ω R54f = 32Rx Ω That is, a 63-step current value that sets the current value Icf charged in the charging circuit 50f to the minimum value is set. it can.

The operation of the discharging circuit 60a is such that when the charging signal is inputted from the control means 30 to the terminal 58a, the capacitor 7
The electric charge charged to 1 is extracted with a constant current value Ida shown in Expression 7.

Ida = VBE63a / R64a (Equation 7) The discharge circuits 60b, 60c, ..., 60f are also discharge circuits 6
0a is a discharge circuit having the same structure as that of the reference numeral 68b, 68.
When a discharge signal is input from the control means 30 to the terminals c, ..., 68f, the electric charges charged in the capacitor 71 are extracted by currents of constant values Idb, Idc ,.

Idb = VBE63b / R64b (Equation 8) Idc = VBE63c / R64c (Equation 9) Idd = VBE63d / R64d (Equation 10) Ide = VBE63e / R64e (Equation 11) ) Idf = VBE63f / R64f (Equation 12) In the present embodiment, the discharge time constant setting resistors 64a, 64b,
The value of the discharge time constant setting resistor 64a is set to RyΩ so that each value of 64f is about half of the maximum discharge current required by the drive circuit when the discharge circuit 60a is driven. Next, the value of the discharge time constant setting resistor 64b is set to 2RyΩ so that the discharge current of the discharge circuit 60b becomes half that of the discharge circuit 60a. The discharge circuit 60f is set so that the discharge current is halved, and is expressed as follows.

R64a = Ry Ω R64b = 2Ry Ω R64c = 4Ry Ω R64d = 8Ry Ω R64e = 16Ry Ω R64f = 32Ry Ω That is, a 63-step current value that sets the minimum current value Idf discharged in the discharge circuit 50f is set. it can.

FIG. 5 shows an embodiment of drive waveforms output by the drive circuit of the present invention. When a print timing signal is applied, charge 1 operation-discharge 1 operation-charge 2 operation-discharge 2 operation. Perform charge 3 operation.

In the charging 1 operation, the charging time is Tc1 and the charging voltage is Vra. If the electrostatic capacity of the charge / discharge time constant setting capacitor 71 is C71, the charging current is Ic1 = Vra × C71 / Tc1 (equation 13).

The current value of the charging 1 operation in this embodiment corresponds to 15 times the charging current value Icf of the charging circuit 50f, and the required charging circuits are 50c, 50d, 50e,
It is sufficient to drive four circuits of 50f.

The charging / discharging current in the charging 2 operation, the charging 3 operation, the discharging 1 operation, and the discharging 2 operation is similarly obtained, and Ic2 = Vrb × C71 / Tc2 (Equation 14) Ic3 = Vrc × C71 / Tc3 (Equation 15) Id1 = Vfa × C71 / Td1 (Equation 16) Id2 = Vfb × C71 / Td2 (Equation 17) FIG. 6 shows a combination of the charging / discharging voltage, the charging / discharging time, the charging / discharging current, and the required charging / discharging circuit in the standard driving waveform in this embodiment. The charge voltage in the charge 1 operation and the discharge voltage in the discharge 1 operation are 20% of the discharge voltage in the discharge 2 operation, and the sum of the charge voltage in the charge 2 operation and the charge voltage in the charge 3 operation is discharge 2 It is equal to the discharge voltage of operation, and the respective percentages are 76% and 24%.

FIG. 7 is a diagram showing a drive waveform adjusting method for variations in the characteristics of the head of an ink jet printer equipped with the piezoelectric element drive circuit of the present invention.

The waveform indicated by Vn0 in the figure is a standard drive waveform, and the ratio of each charge / discharge voltage is determined based on the discharge voltage of the discharge 2 operation as described above. In the waveform adjustment of, the charging / discharging time of each charging / discharging operation was kept at a constant value,
Adjust with the drive voltage. When the driving voltage is increased, other charging / discharging voltages are increased in accordance with the increase of the discharge voltage Vfb in the discharge 2 operation as indicated by Vp1 and Vp2 in the figure, and when the driving voltage is decreased, Vm1, V in the figure
Other charging / discharging voltages are lowered in accordance with the decrease amount of the discharging voltage in the discharging 2 operation as indicated by m2.

That is, the charging / discharging current for all charging / discharging operations is adjusted. However, in the drive circuit of this embodiment, an arbitrary charge / discharge current can be realized by changing the combination of charge / discharge circuits.

FIG. 1 shows a structure around a printing mechanism of an ink jet printer equipped with the above-mentioned piezoelectric element drive circuit. Reference numeral 1 is a carriage, which is connected to a pulse motor 3 via a timing belt 2. The guide member 4 guides the recording paper 5 to reciprocate in the paper width direction.

An ink jet recording head 6, which will be described later, is attached to the surface of the carriage 1 facing the recording paper 5, that is, the lower surface in this embodiment. The ink jet type recording head 6 receives ink replenishment from an ink cartridge 7 mounted on the upper part of the carriage 1 and ejects ink droplets on a recording paper 5 in accordance with the movement of the carriage 1 to form dots to perform recording. Images and characters are printed on the paper 5.

Reference numeral 8 denotes a capping device, which is provided in the non-printing area and seals the nozzle opening of the recording head 6 during the pause of printing, while ink drops from the recording head 6 due to the flushing operation performed during the printing operation. To receive.

A cleaning means 9 is provided in the vicinity of the capping device 8 and is configured to wipe the surface of the nozzle plate of the recording head 6 with a blade or the like to wipe off ink residue and paper dust on the surface of the nozzle plate. .

Reference numeral 36 denotes a linear encoder which is read by a sensor mounted on the carriage and generates a pulse at a specific moving distance by the operation of the carriage,
This is a reference for the print timing signal.

A pulse motor 37 conveys the recording paper 5 in accordance with the operation of the carriage 1 via a reduction gear (not shown).

FIG. 3 shows an embodiment of a control device for controlling the above-mentioned ink jet printer, which is designated by reference numeral 30.
The control means controls the driving circuit 31, the carriage driving circuit 33, and the paper transport driving circuit 35, which will be described later, in response to a print command signal and print data from the host to execute a printing operation. Cleaning, flushing and the like are executed.

The print timing generation circuit 34 is configured to detect the movement of the carriage by the linear encoder 11 mounted on the carriage and generate a print signal to the control means 30.

In the present embodiment, both the charging circuit and the discharging circuit are composed of 6 kinds of circuits having different current values, but the number of kinds is not limited to 6 kinds, and more or less than this is possible. good.

[0043]

As described above, in the present invention,
An arbitrary drive waveform can be easily obtained by changing the combination of input signals of the drive circuit. Further, since it is easy to deal with recording heads having different structures, the drive circuit can be configured as a general-purpose integrated circuit,
It is possible to reduce the number of parts and cost.

[Brief description of drawings]

FIG. 1 is a diagram showing one embodiment of an ink jet recording apparatus to which a piezoelectric element drive circuit of the present invention is applied.

FIG. 2 is a diagram showing one embodiment of an ink jet recording head.

FIG. 3 is a diagram illustrating control blocks of the inkjet recording apparatus.

FIG. 4 is a diagram showing one embodiment of a piezoelectric element drive circuit of the present invention.

FIG. 5 is a diagram showing an input signal and an output waveform of the piezoelectric element driving circuit.

FIG. 6 is a diagram showing values of output waveforms of the drive circuit of the same.

FIG. 7 is a diagram showing a method of adjusting the output waveform of the drive circuit of the same.

[Explanation of symbols]

 Reference Signs List 6 inkjet recording head 8 capping device 9 cleaning device 11 nozzle opening 13 pressure generating chamber 17 piezoelectric element

Claims (2)

[Claims] 1. A piezoelectric element drive circuit for generating a voltage waveform for contracting and expanding a piezoelectric element, comprising: a first group of voltage waveform generating circuits having a plurality of different time constants for contracting the piezoelectric element; A piezoelectric element drive circuit, comprising a second group of voltage waveform generation circuits having a plurality of different time constants for extending the element. 2. The voltage generating circuit generates a voltage waveform having an arbitrary time constant by combining one or more circuits out of the voltage generating circuits of the first group for contraction of the piezoelectric element to expand the piezoelectric element. 2. The piezoelectric element drive circuit according to claim 1, wherein one or more circuits from the second group of voltage generation circuits are combined to generate a voltage waveform having an arbitrary time constant.