JP2000246938A - Recording head driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent an erroneous operation of a driver IC due to a surge voltage by a method wherein the surge voltage generated on a power source line is markedly reduced even when multiple recording elements are simultaneously driven in a mode such as a solid printing mode. SOLUTION: This recording head driving device comprises multiple recording elements 2, a shift register 6 that serially transports image data by each one bit and multiple driving circuits 8 for driving the recording elements 2 in accordance with the image data from the shift register while a strobe signal is supplied thereto from an external section. The multiple driving circuits 8 are divided into a plurality of groups. A delay circuit 9 for delaying the input timing of a strobe signal is provided to the previous stage of the driving circuits 8 in the groups which are driven at least secondary or later so that drive timings for the recording elements 2 by the driving circuits 8 are shifted by 0.01-50.00 μsec by each of the groups and the driving periods for the groups are overlapped with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording head driving device incorporated as a printer mechanism such as a facsimile or a word processor.

[0002]

2. Description of the Related Art Conventionally, a thermal head, an LED array head, an ink jet head, and the like have been used as a recording head incorporated as a printer mechanism of a facsimile or the like.

In the case of a thermal head, for example, such a recording head is formed on a substrate made of alumina ceramics or the like.
A large number of heating elements linearly arranged at a predetermined dot density, a common electrode commonly connected to one end of all these heating elements, and a large number of individual electrodes individually connected to the other end of each heating element; And a driver IC that selectively causes the heating elements to individually generate Joule heat, and applies a predetermined power between the individual electrodes and the common electrode in accordance with the driving of the driver IC. Selectively and individually generate Joule heat based on the image data,
The generated heat is conducted to a recording medium such as thermal paper, and a predetermined print is formed on the recording medium to function as a recording head.

The driver IC is provided with a latch circuit for storing image data, a drive circuit for controlling energization to a heating element, and the like.
C outputs a predetermined output to a corresponding heating element based on image data in the latch circuit while a strobe signal is supplied from the outside (printer main body).

[0005]

By the way, in order to make one heating element generate heat in the above-mentioned thermal head, several tens of elements are required.
Although a current of about mA is sufficient, an extremely large current flows through the common electrode when all the heating elements are heated at the same time as in all black printing. For example, when performing all black printing using a thermal head having a width of 256 mm (for B4 size) and 8 dots / mm, even if all the heating elements are driven in four blocks, they flow to the common electrode when each block is driven. The current is 256 mm × 8 dots / mm × 50 mA ÷ 4 = 25.6
[A], and an extremely large current flows instantaneously (however, in the above formula, the current per heating element was calculated as 50 mA).

At this time, since the circuit on the substrate has an equivalent inductance, the inductance causes the power supply line connected from the common electrode to the power supply when the driver IC is switched on and off, as shown in FIG. A large surge voltage appears. Since this surge voltage is proportional to the magnitude of the changing current, it takes an extremely large value in all black printing. Therefore, the driver IC has a drawback that the surge voltage causes a malfunction of the driver IC, destroys an output transistor of the IC, and malfunctions a circuit such as a facsimile equipped with a thermal head.

On the other hand, there is known a thermal head in which a capacitor for absorbing surge is provided on a power supply line connecting a common electrode of a thermal head and a power supply in order to solve the above-mentioned drawbacks.

However, since a capacitor capable of withstanding a large surge voltage is extremely large, the size of a device in which the capacitor is incorporated is also increased, and a capacitor having good high-frequency characteristics is required because the surge voltage includes a high-frequency component. However, a capacitor having good high-frequency characteristics is very expensive, so that a device incorporating the capacitor has a disadvantage of being expensive.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and a recording head driving device according to the present invention comprises a large number of recording elements and a large number of serially connected shift register cells. A shift register that serially transfers image data bit by bit between adjacent shift register cells and stores the image data in predetermined shift register cells, and a strobe signal is provided corresponding to the shift register cells and provided. A plurality of drive circuits for driving print elements based on the image data of the shift register, wherein the plurality of drive circuits are divided into a plurality of groups, and The drive timing of the printing element by the drive circuit is shifted by 0.01 μsec to 50.00 μsec, and each group is shifted. A delay circuit for delaying the input timing of the strobe signal is provided at the preceding stage of the drive circuits of the groups that are driven at least for the second and subsequent groups so that the drive periods of the groups overlap each other.

The recording head driving apparatus according to the present invention comprises a large number of recording elements and a large number of serially connected shift register cells, and serially transfers image data between adjacent shift register cells one bit at a time. A shift register that stores the image data in a predetermined shift register cell, a number of latch circuits that receive and hold the image data of the number of shift register cells in parallel in synchronization with a latch signal, and are provided corresponding to the latch circuit. A plurality of drive circuits that drive recording elements based on image data of the latch circuit while the strobe signal is being supplied, wherein the plurality of drive circuits are grouped into a plurality of groups. And the drive timing of the printing elements by the drive circuits of each group is set to 0.01 μsec. A delay circuit for delaying the input timing of the strobe signal is provided at the preceding stage of the drive circuits of the groups to be driven at least the second and subsequent groups so that the drive periods of the groups are shifted by 0.00 μsec and the drive periods of the groups overlap each other. It is a feature.

Further, in the recording head driving device according to the present invention, the delay circuit comprises a buffer and / or an inverter.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a plan view showing an embodiment in which a recording head driving device of the present invention is applied to a thermal head, and FIG. 2 is an equivalent circuit diagram partially showing an electrical configuration of the thermal head of FIG. Is a heating element, 3 is a common electrode, 4 is an individual electrode, 5 is a driver IC, 6 is a shift register, 7 is a latch circuit, 8 is a drive circuit, and 9a, 9b and 9c are delay circuits.

The thermal head shown in FIG. 1 has a large number of heating elements 2 linearly arranged on an upper surface of a substrate 1 made of alumina ceramic or the like, and a common electrode commonly connected to one end of all the heating elements 2. 3, a number of individual electrodes 4 individually connected to the other end of each heating element 2,
A plurality of driver ICs 5 for controlling energization of the power supply 2 are mounted.

The heating elements 2 are arranged at a dot density of, for example, 8 dots / mm.
When a thermal head having a size is formed, 1,728 heating elements 2 are linearly arranged at a pitch of 127 μm.

The heating element 2 is made of a Ta-based resistance material or Ti
-Based resistance material, Nb-based resistance material, polysilicon (p-S
i) It is formed by applying and forming a system resistance material or the like in a predetermined pattern by a conventionally known thin film method, specifically, sputtering, photolithography, etching, or the like, which itself has a predetermined electric resistance value. , Driver IC5
When a predetermined electric power is applied in association with the drive, Joule heat is generated, and the temperature is required to form an image on a recording medium such as thermal paper.

The common electrodes 3 and the individual electrodes 4 connected to both ends of each heating element 2 are for supplying power from an external power supply to the heating element 2. For example, the common electrode 3 has a potential of 24V. (+) Of the external power source held in
On the other hand, the individual electrode 4 is connected to a driver I to be described later.
It is electrically connected to a negative (-) terminal of an external power supply held at a reference potential (eg, a potential of 0 V) via a switching transistor 8b of C5.

The common electrode 3 and a large number of individual electrodes 4 are made of aluminum, copper, or the like, and the electrodes 3 and 4 are also formed in a predetermined pattern by a well-known thin-film method or the like similarly to the heating element 2 described above. It is attached and formed.

Each of the plurality of driver ICs 5 is responsible for a predetermined number of the heating elements 2 and functions to individually and selectively generate Joule heat. A shift register 6 having a predetermined number of bits for serially transferring image data in synchronization with a clock signal; a plurality of latch circuits 7 receiving these image data from the shift register at the timing of a latch signal and holding and storing the image data A plurality of driving circuits 8 for controlling the energization of each heating element 2 based on an external strobe signal and image data in the latch circuit 7, and a plurality of driving timings for inputting the strobe signal to these driving circuits 8. Each circuit 8 has a plurality of delay circuits 9a, 9b, 9c, etc. for delaying little by little.

For example, when one driver IC 5 is responsible for 64 heating elements 2, an A4 size, 8 dots / m
In order to construct a thermal head of length m, 27 driver ICs are required, and a 64-bit shift register 6, 64 latch circuits 7, 64 drive circuits 8, 3 Delay circuits 9a, 9b, 9c
Are respectively provided. FIG. 1 is a simplified drawing in which the number of driver ICs 5 mounted on the substrate 1 is four.

The driving circuit 8 comprises an AND gate 8a and a switching transistor 8b.

The AND gate 8a is supplied with a strobe signal from the outside and image data in the corresponding latch circuit 7. The AND gate 8a supplies a switching transistor 8b based on the logical product of these two signals. It emits a predetermined output toward it. The strobe signal is a signal for determining the energizing time of the heating element 2 in each printing line, and is supplied to all the driving circuits 8 in a single pulse for each printing line. For example, when the whole is divided into four blocks and divided and driven, four pulses are supplied sequentially without overlapping each other.

On the other hand, the switching transistor 8b controls on / off of energization to the heating element 2 based on the output signal from the AND gate 8a described above, and the output signal from the AND gate 8a is supplied. During this time, a predetermined output is generated to the corresponding heating element 2 via the output terminal of the driver IC 5 and the individual electrode 4 to generate the heating element 2
Are individually selectively heated and driven based on image data.

The delay circuit 9 of the driver IC 5
a, 9b, 9c are 64 drive circuits 8 and 16 drive circuits 8
Are grouped into four groups, and one of these four groups is provided in front of the drive circuits of the second and subsequent groups from the strobe signal input side (hereinafter abbreviated as signal input side). Provided.

More specifically, on the strobe signal line 10 for supplying a strobe signal to the AND gate 8a, and before the 17th to 32nd drive circuits 8 from the signal input side, 3
One circuit is provided before the third to 48th drive circuits 8 and one before the 49th to 64th drive circuits 8.

The delay circuits 9a, 9b, and 9c set the drive timing of the heating element 2 for 0.01 μsec for each of the groups.
The strobe signal supplied to each group has a rising and falling timing of 0.01 μsec from the signal input side.
It will shift sequentially within the range of 5 sec to 50.00 μsec.

As the delay circuits 9a, 9b, 9c, inverters, buffers, or a combination of inverters and buffers are used. For example, when only an inverter is used, the output AC characteristic is 0.005 μsec to 25.0.
When an even number of 0 μsec are used in combination and only the buffer is used, the output AC characteristic becomes 0.01
Use the one of μsec to 50.00 μsec.

The strobe signal supplied to the drive circuit 8 is supplied to each driver IC 5 in parallel, and the pulse width thereof is 100 μm.
sec to 50,000 μsec. Thus, deviation of the driving timing of the heat generating element 2 pulse width of the strobe signal as described above w ₁ (0.01μsec~50.00
μsec), so that the delay circuits 9a, 9
The drive periods of the four groups divided by b and 9c overlap each other. This overlap time w _2, for example 50μsec~50000μs
ec.

As described above, a large number of driving circuits 8 in each driver IC 5 are divided into a plurality of groups, and the driving timing of the heating elements 2 by these driving circuits 8 is shifted by 0.01 μsec to 50.00 μsec for each group. And delay circuits 9a, 9b, 9c for delaying the input timing of the strobe signal before the driving circuit 8 of the group that is driven at least second from the signal input side so that the driving periods of the respective groups overlap each other. All heating elements 2
Even if an extremely large current flows through the common electrode 3 when the heat is generated simultaneously, the surge voltage that appears on the power supply line from the common electrode 3 to the external power supply when the driver IC 5 is switched on and off is extremely small. (See FIG. 3). This is because shifting the drive timing reduces the amount of current that changes at one time, which effectively prevents the driver IC 5 from malfunctioning due to a large surge voltage and malfunctioning of a facsimile or other circuit equipped with a thermal head. Is prevented.

In this case, the surge voltage appearing on the power supply line is extremely small as described above, and the influence of the surge voltage on the driver IC and the like can be suppressed to a negligible level. No capacitor or the like is required at all, and the thermal head driving device can be reduced in size, and the thermal head as a product can be manufactured at low cost.

It is to be noted that, as long as the aforementioned drive timing shift width w ₁ for each group is set to be smaller than the value obtained by dividing the pulse width of the strobe signal by the number of groups, the drive periods of the groups overlap each other. However, if the shift width w ₁ is shorter than 0.01 μsec, it is difficult to sufficiently suppress the surge voltage. Conversely, if the shift width w ₁ is larger than 50.00 μsec, printing is performed. There is a possibility that the speed will become slow and it will not be possible to respond to the recent demand for high-speed printing. Shift width w ₁ of the drive timing of each group is therefore 0.01μsec~50.00
It is specified within the range of μsec.

The overlap time w ₂ of the driving periods of the four groups is 90.0% to 99% of the pulse width of the strobe signal from the two viewpoints of increasing the printing speed and sufficiently reducing the surge voltage. It is preferably set within the range of 0.9%.

The plurality of driver ICs 5 are attached and mounted on the upper surface of the substrate 1 in a line substantially parallel to the arrangement of the heating elements 2 by employing conventionally known face-down bonding or the like. You.

Next, the action of reducing the surge voltage in the above-described thermal head will be described with reference to the timing chart of FIG.

The four strobe signals a, b,
The signals c and d are originally one signal at the time of input to the driver IC5, but are generated by three delay circuits 9a, 9b and 9c provided on the strobe signal line.

The strobe signal a has exactly the same waveform as the strobe signal input via the input terminal of the driver IC5, and the first to sixteenth drive circuits 8 from the signal input side.
Is input as is.

The strobe signal b is a signal generated by the delay circuit 9a, and is, for example, 1 μm smaller than the strobe signal a.
It rises with a delay of sec and falls with a delay of 1 μsec. The strobe signal b is input to the AND gate 8a and the delay circuit 9b of the 17th to 32nd drive circuits 8, respectively.

The strobe signal c is supplied to two delay circuits 9
a, 9b, and a strobe signal a
Rises with a delay of, for example, 2 μsec.
It falls with a delay of ec. The strobe signal c is 33
AND gate 8a and delay circuit 9c of the ~ 48th drive circuit 8
Respectively.

The strobe signal d is supplied to three delay circuits.
9a, 9b, 9c, and rises with a delay of, for example, 3 μsec from the strobe signal a.
It falls with a delay of sec. The strobe signal d is 4
It is input to the AND gate 8a of the 9th to 64th drive circuits 8.

Note that these strobe signals a, b, c,
d is a signal that is valid at a low level.

When the printing operation starts, first, the driver IC
The first line of image data is serially input to the 5th shift register 6 bit by bit in synchronization with the clock signal.

Next, the image data in the shift register 6 is transferred to the latch circuit at the timing of the latch signal supplied from outside.
7, the image data is held and stored in the latch circuit 7.

Next, a strobe signal is input from the outside,
While this strobe signal is valid, the latch circuit
A predetermined output is generated from the drive circuit 8 to the corresponding heat generating element 2 based on the image data in 7. As a result, the heating elements 2 individually generate Joule heat selectively based on the image data, and the generated heat is conducted to a recording medium such as thermal paper, and a printing dot of a predetermined pattern is formed on the recording medium. Printing of the first line is completed.
When each print line is divided and driven, as described above, a plurality of strobe signals that do not overlap each other are sequentially input.

At this time, as shown in the timing chart of FIG. 3, the strobe signal input to the driver IC 5 has the rising and falling timings of 0.01 μsec to 50.00 by the three delay circuits 9a, 9b and 9c.
The four strobe signals a, shifted by μsec (w ₁ )
b, c, and d, and these four strobe signals a to d are respectively supplied to the four driving circuit groups divided by the above-described grouping. Many heating elements 2 like black print
Even if they generate heat simultaneously,
The surge voltage appearing on the power supply line from the common electrode 3 to the external power supply at the time of switch-on and switch-off is extremely small, and the driver IC 5
Will be effectively prevented.

Thereafter, in a manner similar to the printing operation of the first line described above, the printing operation of the second line, the third line,... Is sequentially repeated to perform a series of printing operations. Is formed.

The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above embodiment, the shift register cell
The latch circuit 5 is interposed between the drive circuit 8 and the drive circuit 8, and the image data once held by the latch circuit 5 is supplied to the drive circuit 8.However, the latch circuit is omitted from this configuration.
The image data in the shift register cell 6 may be directly supplied to the drive circuit 8.

In the above embodiment, one driver IC is used.
Are provided, but the number of delay circuits provided in one driver IC may be one, two, or four or more. The delay time of the strobe signal by the delay circuit Is 0.01 μsec to 50.00
As long as the time is set within the range of μsec, the same effect as in the above embodiment can be obtained.

Further, in the above embodiment, the embodiment in which the recording head driving device of the present invention is applied to a thermal head has been described as an example. However, the present invention can be applied to other recording heads such as an LED array head and an ink jet head. In such a case, the same effect as in the above embodiment can be obtained.

[0049]

According to the present invention, a large number of driving circuits for driving the recording elements are divided into a plurality of groups, and the driving timing of the recording elements by these driving circuits is set to 0.01 μsec to 50.00 μsec for each group. All black printing is provided by providing a delay circuit for delaying the input timing of the strobe signal at the preceding stage of the drive circuit of the group that is driven at least after the second so that the drive periods of the groups are shifted and the drive periods of each group overlap each other. Even when a large number of recording elements are driven simultaneously as described above, the surge voltage appearing on the power supply line is extremely small, and malfunctions of the driver IC and the like due to the surge voltage are effectively prevented.

Further, according to the present invention, as described above, the surge voltage appearing on the power supply line can be made extremely small and its influence can be suppressed to a negligible level. Is completely unnecessary,
It is possible to reduce the size and cost of the recording head drive device.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment in which a recording head driving device of the present invention is applied to a thermal head.

FIG. 2 is an equivalent circuit diagram partially showing an electrical configuration of the thermal head of FIG. 1;

FIG. 3 is a timing chart showing a waveform of a surge voltage generated when printing is performed using the thermal head of FIG. 1;

FIG. 4 is a timing chart showing a waveform of a surge voltage generated when printing is performed using a conventional thermal head.

[Explanation of symbols]

1 ... substrate, 2 ... heating element (printing element), 3 ...
・ Common electrode, 4 ・ ・ ・ Individual electrode, 5 ・ ・ ・ Driver I
C, 6: shift register, 7: latch circuit, 8
... Drive circuit, 8a ... And gate, 8b ... Switching transistor, 9a, 9b, 9c ... Delay circuit

Claims (3)

[Claims] The present invention comprises a number of recording elements and a number of shift register cells connected in series, and serially transfers image data bit by bit between adjacent shift register cells and stores the image data in predetermined shift register cells. And a plurality of drive circuits provided corresponding to the shift register cells and driving a print element based on image data of the shift register while a strobe signal is supplied. A drive device, wherein the plurality of drive circuits are divided into a plurality of groups, the drive timing of the printing elements by the drive circuits of each group is shifted by 0.01 μsec to 50.00 μsec, and the drive period of each group is Groups that drive at least the second and subsequent ones so that And a delay circuit for delaying the input timing of the strobe signal at a stage preceding the drive circuit of (1). 2. A printing apparatus comprising: a plurality of recording elements; and a number of serially connected shift register cells. Serially transferring image data bit by bit between adjacent shift register cells and storing the image data in predetermined shift register cells. A plurality of shift registers, a plurality of latch circuits for receiving and holding image data of the plurality of shift register cells in parallel in synchronization with a latch signal, and a plurality of latch circuits provided corresponding to the latch circuits, while the strobe signal is supplied. A plurality of drive circuits for driving print elements based on image data of the latch circuit, wherein the plurality of drive circuits are divided into a plurality of groups, and each group is driven. The drive timing of the printing element by the circuit is shifted by 0.01 μsec to 50.00 μsec, and A print head driving device, wherein a delay circuit for delaying the input timing of a strobe signal is provided at a stage preceding a driving circuit of at least a second driving group so that driving periods of the respective groups overlap each other. . 3. The recording head driving device according to claim 1, wherein said delay circuit comprises a buffer and / or an inverter.