JPH05338208A - Driving method for thermal head - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the picture quality of printing by reducing the dispersion of printing characteristics due to the wiring resistance of a common electrode. CONSTITUTION:In the heaters of infection elements 2a-2n, one electrodes are connected to a common electrode 5, and the other electrodes are connected to driver circuits 3a-3n. The driver circuits 3a-3n are driven successively in a time division manner by a switching logical circuit 4, and whether or not electricity is conducted is determined by ON/OFF signals from a signal source 8a. The voltage of a power supply 7 for driving is fluctuated periodically in conformity with the timing of the time-division driving, effective voltage by pulse voltage applied to the heaters can be corrected equally extending over all infection elements, and the quantities of infection drops can be equalized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head, for example, a method for driving a thermal head in a recording apparatus such as an ink jet recording apparatus or a facsimile apparatus.

[0002]

2. Description of the Related Art As a recording method suitable for high speed recording, there is an ink jet recording method. A thermal inkjet head used in an inkjet recording system is composed of a plurality of capillary-shaped nozzles for ejecting ink droplets, and a heating element for heating ink arranged in an ink flow path of each nozzle. It is configured. The thermal ink jet head includes, for example, JP-A-55-
As described in Japanese Patent No. 135673, there is a driving element mounting type multi-nozzle type in which an ejection element has a common electrode. The multi-nozzle type head is designed to increase the number of ejection elements in order to increase the speed. However, when the number of ejection elements increases, the length of the common electrode in the head increases, so that the arrangement of ejection elements is increased. In the element in the central part of, the wiring resistance of the common electrode part increases, and as a result, the effective applied voltage applied to the ejecting elements in the end part and the central part in the array varies and the ejection characteristics vary. There was a problem that the print quality deteriorates.

On the other hand, in the ink jet recording head, in order to satisfy the ejection characteristics, there are restrictions on the shape of the ejection element and the ink flow path, and the width of the common electrode portion cannot be unduly widened.

In order to solve these problems, JP-A-59-125858 and JP-A-61-169659 are used.
In the thermal inkjet heads described in Japanese Patent Laid-Open No. 61-31692, the effective width of the common electrode is increased by increasing the film thickness of the common electrode or extending the common electrode to the back surface of the substrate. By doing so, the wiring resistance of the common electrode portion is reduced.

However, when these thermal ink jet heads are considered in consideration of the actual head manufacturing process, increasing the film thickness of a part of the common electrode requires an additional process. In addition, it is very difficult to realize it in the actual head manufacturing process. Further, to extend the common electrode to the back surface of the substrate requires that a metal film be continuously formed on a three-dimensionally shaped portion such as a head cut surface, which is also very difficult to realize in the actual head manufacturing process. There is a problem that is difficult.

Further, Japanese Patent Application Laid-Open No. 64-9758 discloses that
In thermal transfer type recording devices such as copiers and facsimile machines, the basic energization data prepared for each ink type and gradation level is used to extend the energization time based on the voltage drop when the head power supply voltage drops. Therefore, regardless of the magnitude of the load at any gradation level,
A method for obtaining a constant print density is described. In this method, since the width of the drive pulse must be set for each heating element and each time printing is performed, there is a problem that the driving circuit becomes very complicated when the number of heating elements is large.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and while using a thermal head in which wiring resistance becomes a problem, without modifying the structure of a conventional common electrode, It is an object of the present invention to provide a method of driving a thermal head that can reduce variations in printing characteristics at the end portion and the central portion in an array of heating elements and prevent deterioration of print image quality.

[0008]

According to a first aspect of the present invention, there is provided a large number of heating elements each having one electrode connected to a common electrode, and each heating element or a plurality of heating elements. In a method of driving a thermal head in which each block including elements is driven in a time division manner, the time division drive is sequentially performed from one end of the array of the heating elements to the other end,
The invention is characterized in that the applied pulse of the heating element is periodically changed so as to correct the wiring resistance of the common electrode in accordance with the timing of time-division driving. Has a nozzle for ejecting ink and a heating element provided in the nozzle and having one electrode connected to a common electrode, and is time-divided for each heating element or for each block including a plurality of heating elements. In a driving method of a multi-nozzle type thermal ink jet head, a pulse applied to the heating element is periodically changed so as to correct a wiring resistance of a common electrode in accordance with a time-division driving timing. It is characterized by.

Further, in the invention according to claim 3,
The thermal head driving method according to claim 1 or 2, wherein the block composed of a plurality of heating elements is configured by adjacent heating elements.

[0010]

According to the present invention, each heating element or each block composed of a plurality of heating elements is sequentially time-divisionally driven from one end of the array to the other end, and the applied pulse of the heating element is The wiring resistance can be corrected with a simple configuration by periodically changing the wiring resistance of the common electrode so as to correct the wiring resistance at the timing of time-division driving. Further, by configuring each block with adjacent heating elements, the wiring resistances of the heating elements in one block can be made substantially equal, and the correction accuracy can be improved. The wiring resistance is corrected by changing the applied pulse with a preset value. For example, by setting the voltage, pulse width, etc. of the applied pulse for each heating element or each block, It is possible to improve the print image quality by reducing the variation in the printing state between the end portion and the central portion in the arrangement.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of a main part of an ink jet head for explaining an embodiment of a method of driving a thermal head according to the present invention. This inkjet head is
This is a multi-nozzle type thermal ink jet recording head with a drive element mounted type that has a common electrode with a high wiring resistance that is easy to fabricate. It is composed of a heater substrate and a channel substrate, but a channel substrate that is not necessary for explanation is shown. Absent. In the figure, 1 is an inkjet head, 2a, 2b, ...
.., 2m, ..., 2n are injection elements, 3a, 3b, ...
.., 3m, ..., 3n are driver circuits, 4 are switching logic circuits, 5 is a common electrode, 6a, 6b, 6c, 6
Reference numeral d is a print control signal input terminal, and 7 is a power source for driving the ejection element. 8a to 8d are various print signal sources, for example, 8
a is an ON / OFF signal of each ejection element, 8b is a pulse width of a current applied to the heater of the ejection element, 8c is a basic clock signal for driving each ejection element, and 8d is a low-voltage drive power supply of the switching logic circuit. Injection elements 2a, 2b, ...
.., 2n heaters have one electrode connected to the common electrode 5 and the other electrode via drive electrodes 3a, 3b ,.
m, ..., 3n. Drive circuits 3a, 3
, 3m, ..., 3n are sequentially selected by the switching logic circuit 4 and are turned on / off by the signal source 8a.
Whether or not to energize is determined by the OFF signal, and the pulse width of energization is determined by the signal source 8b. Therefore, the ejection elements 2a to 2n are sequentially time-division driven from one end 2a of the array to the other end 2n. Ink droplets are jetted by the driven jetting element to perform printing.

As for the wiring resistance of the jetting element, since the power supply from the driving power source 7 to the common electrode 5 is performed from both ends thereof, the wiring resistance of the jetting elements 2a to 2n is shown in FIG. As shown, it changes continuously in time and periodically. The arrows 2a to 2n indicate the wiring resistance in each ejection element, and the ejection elements 2a and 2n at both ends are the smallest and the ejection element 2m in the center is the largest.

Due to such a difference in wiring resistance, the current value flowing in the heater differs for each ejecting element, the ejecting drop amount differs, and the print quality deteriorates.

Therefore, in response to the temporal change of the wiring resistance, the voltage of the driving power source 7 supplied from the outside to the recording head is corrected as shown in FIG. 2B. Like, according to the timing of time-division drive,
Change cyclically. Thus, when printing the ejection element 2m having a high wiring resistance, the voltage of the driving power source 7 is increased so that the effective voltage due to the pulse voltage applied to the ejection element 2m becomes equal to that of the ejection elements 2a and 2n. Can be corrected. The effective applied voltage of the drive pulse is applied to the ejection element 2a.
By making it equal to, the ejection characteristics of the ink of the ejection element 2m can be corrected to be equivalent to that of the ejection element 2a.

In addition to the method of periodically changing the peak voltage of the drive pulse by changing the power supply voltage, the change of the wiring resistance can be corrected by periodically changing the print signal. For example, as shown in FIG. 2C, the pulse width of the signal source 8b may be changed periodically so as to correct the change in wiring resistance.
Thereby, when printing the ejection element 2m having a high wiring resistance, the energy applied to the ejection element is increased,
The ejection characteristics of the ink of the ejection element 2m are determined by
Can be corrected equivalently. Both the pulse width and the pulse voltage may be periodically changed to correct the change in wiring resistance.

FIG. 3 is a schematic configuration diagram of a main part of an ink jet head for explaining another embodiment of the thermal head driving method of the present invention. This embodiment is a method in which a plurality of ejection elements are divided into blocks and a plurality of ejection elements in one block are simultaneously driven.

When a plurality of ejection elements are divided into blocks and driven, as described in JP-A-55-135673 and JP-A-61-106884,
There is a driving method in which ejection elements that are driven at the same time are not adjacent to each other. In the case of such a driving method, since the wiring resistance of the common electrode in a plurality of ejection elements that eject at the same time differs depending on each ejection element, there is a problem that the correction accuracy decreases.

Therefore, in the present invention, in the case of a driving method in which a plurality of jetting elements are divided into blocks and the plurality of jetting elements are jetted at the same time, jetting elements jetting simultaneously are arranged adjacent to each other and this block is arranged at one end of the array. By further performing time-divisional driving to the other end in sequence, the wiring resistances of the ejection elements that eject simultaneously are made substantially equal to improve the correction accuracy. As a result, even in a multi-nozzle type inkjet recording head that is easy to manufacture and has a high wiring resistance, the dispersion of the ejection elements in the end portion and the central portion in the ejection element array is reduced, and the print image quality can be improved.

The ink jet head shown in FIG. 3 is also composed of a heater substrate and a channel substrate as in FIG. 1, but a channel substrate unnecessary for explanation is not shown. In the figure, parts corresponding to those in FIG. 8a to 8e are various print signal sources, for example,
8a is an ON / OFF signal of each ejection element, 8b is a pulse width of a current applied to a heater of the ejection element, 8c is a basic clock signal for driving each ejection element, 8d is a low-voltage drive power source for a switching logic circuit, and 8e driver circuit. And is a ground common to switching logic circuits.

Injection elements 2a, 2b, ..., 2m, ...
The heaters of 2n are connected to the common electrode 5 at one electrode, and the other electrodes are connected to the drive circuits 3a, 3b, ..., 3m ,.
It is connected to the. Drive circuits 3a, 3b, ..., 3
m, ..., 3n are selected by the switching logic circuit 4, but the injection elements are divided into blocks for every adjacent predetermined number, and the injection elements in one block are simultaneously injected, and the injection element array is arranged. Time division driving is sequentially performed for each block from one end 2a side to the other end 2n side. ON / OFF from the signal source 8a to each ejection element
Whether or not to energize is determined by a signal, and the pulse width of energization is determined by the signal source 8b.

A specific example will be described. The head manufacturing method and material are described in JP-A-60-206663, JP-A-61-230954, and JP-A-1-166696.
As described in Japanese Unexamined Patent Publication No. 5 (1999), a silicon substrate is used, and a channel groove and an ink reservoir are formed in the channel substrate by anisotropic etching. The inkjet head 1 had a shape of 5 × 25 mm in the plane direction and a thickness of 0.625 mm, the number of ejection elements 2a to 2n was 256 bits, and the ejection elements 2a to 2n were arranged at a pitch of 85 μm and a length of about 22 mm. The common electrode 5 is formed of aluminum having a thickness of 1.2 μm by a sputtering method. The ejection element portion of the common electrode 5 has a width of 50 μm.
m × about 22 mm. The voltage of the driving power source 7 is 4
The resistance value of the ejection element section and the driver circuit section was 200Ω in total.

As a driving method of each ejection element, adjacent 4 bits are ejected at the same time, and time division driving is performed by sequentially dividing into 64 blocks from one end 2a of the ejection element array to the other end 2n. From one end 2a of the ejection element array to the other end 2n
4A shows the wiring resistance of the common electrode in FIG. Here, the ejection element 2m is the ejection element at the center of the array of the ejection elements 2a to 2n. The wiring resistance of the common electrode 5 was about 0Ω, which was the lowest in the ejection elements 2a and 2n at both ends, and was about 5Ω which was the maximum in the ejection element 2m in the central portion, and the difference was about 5Ω. Since the total resistance value of the ejection element portion and the driver circuit portion is 200Ω, the increase of the wiring resistance of 5Ω is seen from the total resistance value of the head including the ejection element portion, the driver circuit portion and the wiring resistance. , An increase of 2.5%. The decrease in the effective applied voltage to the ejection element portion due to the increase of 2.5% is 1 from the voltage 40V of the driving power source 7.
The voltage dropped to V, and as shown in FIG. 5, the injection drop amount decreased by about 3 pl.

Therefore, in this embodiment, as shown in FIG. 4B, when the ejection element 2m having a high wiring resistance is printed, the driving power source 7 is driven when the block to which the ejection element 2m belongs is driven.
The voltage was increased from 40 V to 41 V for driving. As a result, the effective applied voltage of the ejection element 2m becomes
It is 40V, which is the same as the ejection element 2a, and as shown in FIG.
The effective applied voltage of the ejection element 2m can be made equal to that of the ejection element 2a, and the ejection drop amount of the ejection element 2m can be corrected to be equal to that of the ejection element 2a. The voltage of the driving power source for the intermediate block is an intermediate value between 40 V and 41 V as shown in FIG. 4 (B), and is set to a value that corrects the wiring resistance of the common electrode 5. Therefore, when printing, The set value of the driving power supply voltage is selected and changed in synchronization with the timing of time-divisional drive for each block.

Instead of changing the voltage of the driving power source 7, the pulse width of the current applied to the ejection element, which is supplied from the print signal source 8b, may be changed. As shown in FIG. 7, since the injection drop amount changes according to the pulse width, it is also possible to correct the wiring resistance by changing the pulse width. For example, as a normal pulse width,
When 3 μsec is adopted, as shown in FIG. 4C, when the ejection element 2m having a high wiring resistance is printed, the pulse width is periodically increased from 3 μsec to 4 μsec for driving. As shown in FIG. 7, by increasing the pulse width of the ejection element 2m from 3 μsec to 4 μsec, the ejection drop amount of the ejection element 2m can be increased by about 3 pl, and the ejection drop amount can be increased.
It was able to be corrected in the same way as.

In the embodiments, the thermal ink jet head has been mainly described, but the present invention is not limited to this, and a recording device including a recording device of a facsimile machine and a thermal head including a large number of heating elements. Obviously, it can be applied to a device.

[0026]

As is apparent from the above description, according to the present invention, it is possible to correct the influence of the wiring resistance in the heating element connected to the common electrode, and the end portion and the intermediate portion in the heating element array can be corrected. There is an effect that it is possible to reduce the variation in the printing characteristics and improve the printing image quality.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a main part of an inkjet head for explaining an embodiment of a thermal head driving method of the present invention.

FIG. 2 is a diagram for explaining the operation of the driving method of FIG.

FIG. 3 is a schematic configuration diagram of a main part of an inkjet head for explaining another embodiment of the thermal head driving method of the present invention.

FIG. 4 is a diagram for explaining the operation of the driving method of FIG.

FIG. 5 is a diagram showing a relationship between a drive voltage and an injection drop amount.

FIG. 6 is a diagram showing a relationship between a corrected drive voltage and an injection drop amount.

FIG. 7 is a diagram showing a relationship between a drive pulse width and an injection drop amount.

[Explanation of symbols]

1 Inkjet head, 2a to 2n jetting element, 3
a to 3n driver circuit, 4 switching logic circuit,
5 common electrode, 6a to 6e print control signal input terminal, 7
Ejection element driving power supply, 8a ON / OFF of ejection element
Signal, 8b Pulse width of heater applied current, 8c Basic clock signal.

Claims (3)

[Claims] 1. A method of driving a thermal head, comprising: a plurality of heating elements, one electrode of which is connected to a common electrode, and time-divisionally driven for each heating element or for each block of a plurality of heating elements. The heating elements are sequentially driven from one end of the array to the other end in a time-divisional manner, and the applied pulse of the heating elements is periodically adjusted so as to correct the wiring resistance of the common electrode in accordance with the time-divisional driving timing. A method of driving a thermal head, characterized in that the thermal head is changed. 2. A nozzle for ejecting ink and a heating element provided in the nozzle and having one electrode connected to a common electrode, each heating element or each block including a plurality of heating elements. In a method for driving a multi-nozzle type thermal inkjet head that is time-divisionally driven, the application pulse of the heating element is periodically changed to correct the wiring resistance of the common electrode in accordance with the timing of time-divisional driving. A method of driving a thermal head, characterized in that 3. The method of driving a thermal head according to claim 1, wherein the block composed of a plurality of heating elements is composed of adjacent heating elements.