JPS61252755A - Thermal head driver - Google Patents

Abstract

PURPOSE:To attain recording with high quality by supplying repetitively a short pulse to each group for heating it without supplying a wide print pulse bringing unit heaters at once to a prescribed temperature to decrease the distortion in a recorded picture. CONSTITUTION:A print pulse supply section 42 is provided, which supplies a short pulse to strobe terminals 211-214 of a thermal head in a prescribed order. When the said short pulse is fed once to one of the strobe terminals. The current is applied to the unit heater connected to a driver NAND gate connected thereto by a time corresponding to the width of the short pulse. On the other hand, the unit heaters of the thermal head 40 are divided into groups 401-404, for example, and they are connected so that a short pulse is supplies separately from the print pulse supply section 42 respectively. The short pulse is supplied not continuously to the unit heaters of one specific group, supplied but alternately and exclusively in a prescribed order.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a thermal head drive circuit used in a device that performs thermal recording or display.

"Prior Art" Recording devices that perform thermal recording using thermal recording paper or transfer type recording media are widely used in facsimile machines, printers, and the like. Usually, such devices use a thermal head provided with a heating element that generates heat by electric pulses. Similar thermal heads are also used in certain types of devices that perform display using magnetized latent images.

An example of a thermal head used in this thermal recording apparatus is shown in FIGS. 8 and 9. These figures are perspective cutaway views of main parts of thermal heads with different configurations, respectively.

In the thermal head shown in FIG. 8, a glaze layer 2 is provided on the upper surface of a substrate 1 made of alumina, and a large number of heating resistors 3 arranged in a line in the shape of railroad ties are formed on this layer. A lead wire 4 is connected and the upper surface is covered with a protective film 5.

When an electric pulse is applied to the heating resistor 3 electrically connected to the lead wire 4, the heating resistor 3 generates heat while the electric pulse is applied.

When these heating resistors 3 selectively generate heat,
For example, a predetermined portion of the thermal paper moving at a constant speed in contact with the thermal head is heated and colored. In the case of an apparatus using a transfer-type recording medium, the ink of the transfer-type recording medium, such as an ink donor film, is heated, fluidized or sublimated, and transferred onto recording paper.

The thermal head shown in FIG. 9, like the one shown in FIG. 8, has a glaze layer 2 on the top surface of an aluminum board 1, and a strip-shaped heating resistor 3 continuous in a longitudinal direction on the top surface. is provided. The lead wires 4 are electrically connected to the heat generating resistor 3 by alternately crossing each other in a so-called zigzag pattern. Their upper surfaces are also covered with a protective film 5.

In the case of a conothermal head, two adjacent lead wires 4
When an electric pulse is applied to the heating resistor 3 sandwiched therebetween, the heating resistor 3 generates heat. The printing operation is similar to that shown in FIG.

The minimum unit heating element 31 sandwiched between each heating resistor 3 shown in FIG. 8 and the pair of lead wires 4 shown in FIG. 9 will hereinafter be referred to as a unit heating element.

FIG. 10 shows an example of a circuit that supplies electric pulses to the heating element.

This circuit is constructed by soldering necessary circuit elements to extensions of lead wires on the substrate of the thermal head, and is integrated with the substrate.

The thermal head shown in FIG. 10 has a heating element 12 as shown in FIG. 9, and odd-numbered lead wires 13 . ．． 135.13s・・・・・・
(extended upward in the figure), diode 16□,
162, 163... through the first common line 1
71 or the second common line 172 is connected.

The heating elements 12 in this figure are a total of 3583 unit heating elements 1.
21~1235$3 including both ends 3584 lead wires 13. ~1335114 are connected. Then, the first common line 17. is first connected to one end of the first unit heating element 121 via one diode 161, and then connected to the second and third unit heating elements 122.1.
A second common line 172 is connected to one end of 2 (that is, the boundary between the two) via one diode 16□. Thereafter, in the same manner, each unit heating element is made into a set of two, and each unit is alternately connected to the first common line 17. and a second common line 172.

On the other hand, even-numbered lead wires 132, 13. ．． 13゜・・・・・・(
(extended downward in the figure) have one driver NAND (NAND) gate 181, 182...
is connected. This time, first, the first unit heating element 12. and the second unit heating element 122 are made into one set, and one driver gate 181 is connected to the other end of these.
is connected. Below, the third and fourth unit heating elements 12. ．． 12. , the fifth and the sixth, etc., and so on, a total of 1792 driver nant gates 18, .about.18.7.degree.2 are connected to each other.

These driver nant gates 18 are divided into four groups of 448 each in the longitudinal direction of the thermal head. For each group, one input terminal of the driver Nant gate 18 is connected to one point.
Main strobe signal supply circuit 21. ~21. It is connected to the. In addition, a latch circuit 22 is connected to the other input terminal of all the driver Nandt gates 18, which can latch the same number of image signals as the driver Nandt gates and output the image signals in parallel to the driver Nandt gates. There is. That is, this latch circuit 22 has a total of 1792 human power lines 221 and output lines 222.

Moreover, the parallel input terminal 221 of this latch circuit 22
is divided into 14 groups in its longitudinal direction, each with 128
Shift register 24 with two parallel output terminals 23
．． ~24I4 is connected.

These shift registers 24 have a total of 14 data lines 26. This is a circuit that accumulates image signals inputted serially through each input terminal from 2614 to 2614 while sequentially shifting the timing to the clock frequency of the clock pulse 29, and outputs the image signal from the parallel output terminal 23.

In the above circuit, first, a total of 17
The 92 image signals are divided into 14 and 128 signals are sent to each shift register 24. When accumulated in ~24I, respectively,
The latch signal 2"8 is input to the latch circuit 22 and this 17
Ninety-two image signals are latched into the latch circuit 22. Each side signal has a binary value of 0'' or m1ll, and is set to ``1'' when printing is to be performed, and ``0'' when printing is not to be performed.

Here, for example, the first dry Nando game) 1
Strobe signal supply circuit 21 is connected to one input terminal of 8+.
．． A strobe signal (its content “l”) is supplied from
If the image signal supplied from the latch circuit 22 to the other input terminal is "1", then the driver Nant gate 18. The output terminal becomes "0", that is, low level. At this time, the first common line 17. If the power supply voltage is applied to the first diode 16. through the first unit heating element 12. A power supply current is supplied to the unit heating element 121, and the unit heating element 121 generates heat.

On the other hand, when the image signal is "0", it's a Draino Nando game)
The output terminal of I L is always at the noise level, and no current flows through the unit heating element 121 connected thereto. Also, driver nant gate 18. If no strobe signal is supplied to the common line 17, or if no power supply voltage is applied to the unit heating element 12. No current flows through. FIG. 11 shows the accumulation of image signals during these operations (a), the latch signal 11(b) and the strobe signal supply circuits 211 to 21. Signals (C) to (
d) and common wire 17. ．． Signal (g) supplied to 17□
, (h) are shown.

As described above, due to its structure, the thermal head shown in FIG. 9 must operate unit heating elements divided into two groups, odd-numbered and even-numbered (see g and h of FIG. 11).

In addition to this, if there are a large number of unit heating elements, when they generate heat at once, the total supplied power will be, for example, I KVA
However, providing a power source sufficient to supply the power may lead to an increase in the size of the device. For this reason, in the above example, the unit heat generating elements are divided into four groups, and current is supplied to the groups in sequence (FIG. 11C to F).

However, with this method, when printing at high speed,
There was a problem in that the linearity of the inline parallel to the longitudinal direction of the thermal head was disturbed. This is because there is a lag in the time it takes for the unit heating element in the group that generated heat first and the unit heating element in the group that generated heat subsequently to reach the temperature that would cause the thermal paper to develop color, for example, and is slightly exaggerated. If drawn, a line 32 sloping to the right as shown in FIG. 12 will be recorded.

In order to prevent this phenomenon, an invention has been introduced that shifts the recording start time for each group (
(Japanese Unexamined Patent Publication No. 58-24465).

``Problems to be Solved by the Invention'' However, this method has the drawback that the thermal head drive device becomes complicated and a significant increase in cost is unavoidable. Furthermore, even with this method, there is a problem in that it is difficult to faithfully record straight lines parallel to the longitudinal direction of the thermal head when high-speed printing is performed.

Further, a similar problem occurs when driving a thermal head having the structure shown in FIG. In the case of this type of thermal head, as shown in FIG.
are each one diode 16 and driver band gate 1
8 and connected to one power supply line 17 in parallel.

Therefore, if there is sufficient power supply, it is possible to generate heat from all the unit heating elements at the same time, but from the point of view of downsizing the power supply described above, the units are divided into several groups and operated. Therefore, there is still a drawback that the linearity of the recorded image parallel to the longitudinal direction of the thermal head is disturbed.

The present invention has been made with attention to the above points, and an object of the present invention is to provide a thermal head driving device that can record lines parallel to the longitudinal direction of the thermal head with high quality even in high-speed printing. That is.

"Means for Solving the Problems" The thermal head driving device of the present invention includes a thermal head in which a number of unit heating elements each of which generates heat independently when supplied with electric current are arranged in a row in the longitudinal direction; A print control section supplies an image signal to the thermal head for selecting a unit heating element, and turns on and off the current supplied to the unit heating element selected by this image signal until the unit heats up to a predetermined temperature. The unit heating element is divided into two or more groups, and the printing pulse supply section supplies short pulses repeatedly and intermittently for off-control. It is characterized by supplying the following information alternately and exclusively once in a predetermined order.

Here, the widths of the short pulses alternately supplied to each group may be equal to each other.

Further, the width of the short pulses repeatedly supplied to one unit heating element may be always constant.

It is preferable that the width of the short pulse be minimized before and after the unit heating element reaches the temperature necessary for its recording operation.

It is also more preferable to provide a certain pause time between the short pulses supplied to one group and the pulses supplied to the next group.

"Function" The reason why each unit heating element to generate heat is divided into two or more groups is to reduce the burden on the power supply, as explained earlier. Instead of supplying a wide printing pulse that causes the unit heating element to heat up to a predetermined temperature all at once, short pulses are repeatedly and intermittently supplied to generate heat.

The short pulses are then supplied alternately and exclusively to each group in a predetermined order.

Therefore, the temperature of the unit heating elements in each group increases little by little on average due to this short pulse. Then, when a certain amount of short pulses are supplied, all the unit heating elements reach a predetermined temperature, that is, a temperature necessary for recording operation, one after another. The time error is less than the time required for one cycle in which short pulses are supplied to all groups in sequence.

Therefore, if the width of the short pulse is made sufficiently short, the difference in arrival time between the unit heating element that reaches the predetermined temperature first and the unit heating element that reaches the predetermined temperature last can be made sufficiently short. It is possible.

If these short pulses are supplied with equal width to each group and are always constant, the operation of the printing pulse supply section can be simplified. However, it is sufficient that the short pulse has a sufficiently short width at least before and after the unit heating element reaches the temperature necessary for its recording operation.

Embodiment FIG. 1 is a block diagram showing an embodiment of the thermal head driving device of the present invention, and FIG. 2 is a timing chart explaining its operation.

The thermal head drive device shown in FIG.
0, a print control section 41 that supplies image signals to this, and a print pulse supply section 42 that supplies short pulses for printing to the thermal head 40.

For this thermal head 40, for example, the conventional circuit configuration shown in FIG. 10 is used as is. The print control unit 41 transfers a certain amount of the image signal to the data line 26 of the thermal head 40, supplies a clock pulse 29 to control the timing of the transfer, and outputs a latch signal 28 that causes the latch circuit to latch the image signal. do. This can also be done using a circuit similar to a known one, and there is no change in its operation.

Here, this thermal head driving device includes a strobe terminal 21 of the thermal head. A printing pulse supply section 42 is provided for supplying short pulses in a fixed order to 214.

When this short pulse is supplied once to one of the strobe terminals, as explained in FIG. Current is supplied. As explained above, this single short pulse does not raise the temperature of the unit heating element to a recordable temperature. In the present invention, the width of the short pulse is set in advance to such a sufficiently short width.

On the other hand, the thermal head 400 unit heating elements are arranged in, for example, four groups 40. ~40
．． It is divided into two parts, and wires are connected so that short pulses are separately supplied from the printing pulse supply section 42 to each part.

In the present invention, these short pulses are not continuously supplied to the unit heating elements of one specific group, but are supplied alternately and exclusively in a fixed order. A specific example will be explained using FIG. 2.

In FIG. 2(a), the image signal 51 is transmitted to the thermal head 40 (
The timing at which data is stored in the shift register in FIG. 1) is illustrated, and the latch signal 28 for latching it into the latch circuit is shown in FIG. 1(b).

The image signal 51 latched in the latch circuit in this manner selectively opens and closes the driver gate connected to each unit heating element. The first group 40 of unit heating elements shown in FIG. Six short pulses 52 are intermittently supplied at the timing shown in FIG. 2(C). Third group 40. In this first group 40. A short pulse 52 with the same width as the short pulse supplied to the pulse is supplied after being delayed by a time corresponding to the width of this short pulse (see e in the same figure). The short pulse 52 is supplied with a delay of one minute (d) in the fourth group 40. Also, the short response 52 is supplied with a similar delay (f in the same figure).

That is, short noculus are supplied alternately and exclusively in the order of the first group 408, the third group 405, the second group 402, and the fourth group 404. In order to supply such short pulses, for example, the main part of the printing pulse supply section 42 shown in FIG. 1 is configured as shown in FIG. 3.

In FIG. 3, the short pulse generator 421 generates a short pulse 4
230 width and outputs it continuously at regular intervals. The output of this pulse generator is connected to a selector 422 of the one-manufacturer four-output type. The output of this selector 422 is outputted from each of the four unit heating element groups 40 shown in FIG. ~404. Selector 42. Select terminal 42. for,
Input short pulse 42. Which output terminal 422. ~42
A selection signal indicating whether to output is input to 24. For example, when this selection signal changes to 00'', 01'', 1O'', and 111, the short pulse 423 is sent to the output terminal 422 in that order.
1-422. will be output in turn.

FIG. 4 is an explanatory diagram showing the temperature rise characteristics of a unit heating element to which short pulses 52 are intermittently supplied in this manner.

In this figure, when a short pulse 52 as shown in (a) is supplied to one unit heating element, the temperature gradually increases while heating and cooling are alternately repeated as shown by the solid line 56. , exceeds the temperature T required for recording operation. After the temperature T is exceeded, recording is performed until the temperature drops below this temperature. Let this time be t.

For example, as shown in (b) of the same figure, a unit heating element to which the supply of short pulses is started later than in (a) has similar temperature rise characteristics, and reaches the temperature required for recording with a slight delay. exceed. This delay is equal to the delay in the supply start time of the short pulse, and here corresponds to the width W of the short pulse 52. The time t during which this unit heating element is maintained at a temperature higher than that required for the recording operation is the same as the previous one.

As a result, as shown in FIG. 5, the dot 62 recorded by the unit heating element supplied with the short pulse in FIG. 4(b) is the unit heating element supplied with the short pulse in FIG. The recording paper is shifted downward by the length of movement of the recording paper in the time corresponding to the width of this short pulse, with respect to the dot 61 caused by the body.

However, this deviation can be made sufficiently small by making the short pulse sufficiently short. Moreover, in reality, for example, when thermal paper is used as recording paper, the boundary between dots can be seen on a microscopic scale, for example, as the temperature of the unit heating element increases, the recording paper first becomes gray and the density gradually increases. However, Figure 5 is not necessarily clear. Therefore, the temperature T necessary for the recording operation shown in FIG. 4 is not a single point but has a certain range. Therefore,
If the width of the short pulse is sufficiently smaller than this width, the difference in level of the recorded dots will be unrecognizable.

Groups 401 to 40 of the four unit heating elements in FIG. 1 are arranged in the order shown in FIG. If a short pulse is supplied to the dots and the recorded dots are arranged horizontally one by one, the result will be as shown in FIG. That is, at the maximum, the deviation L' between the dots 63 is only about three times the width of the short pulse. Therefore, even if the recording paper moves at high speed, straight lines parallel to the longitudinal direction of the thermal head are recorded clearly and with good linearity.

Here, the correlation between the unit heating elements supplied to each group of unit heating elements shown in FIG. 1 will be explained in more detail using FIG. 7.

Figure 7 shows a series of short pulses supplied to one group when the unit heating element is divided into two groups (a
), and a series of short pulses applied to the other group is shown in (b).

Here, a fixed time d is left between the short pulses supplied to one group and the short pulses supplied to the other group. Logically, this interval may be zero, but in reality, the time required for the rise and fall of this short pulse has a certain width, and the short pulses before and after partially overlap, creating a high load on the power supply. This is the interval provided to prevent this from occurring. If the width of the short pulse is, for example, 100 microseconds, this interval may be several microseconds.

"Variation" The present invention is not limited to the above embodiments.

The short pulses may be supplied to virtually any part of a circuit for turning on and off the current supplied to a unit heating element to control its supplied power. In addition, the width of the short pulse supplied to one unit heating element is initially made long,
The width may be made sufficiently short from just before the temperature necessary for recording operation is reached. Further, the ring and number of short pulses supplied to each group may be appropriately varied as necessary. It goes without saying that the order in which the short pulses are supplied can be freely selected.

"Effects of the Invention" According to the thermal head driving device of the present invention described above, the difference in temperature rise rate of each unit heating element becomes extremely small over the entire length of the thermal head, so disturbances in recorded images are reduced and high Quality records can be made. This makes it possible to further improve the recording speed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the thermal head driving device of the present invention, FIG. 2 is a timing chart explaining its operation, and FIG. 3 is a block diagram showing a specific embodiment of the print pulse supply unit. , FIG. 4 is an explanatory diagram showing the temperature rise characteristics of the unit heating element, FIG. 5 is an explanatory diagram showing the recording dots thereof, and FIG. 6 is an explanatory diagram of the recording dots of the thermal head driving device of the embodiment of FIG. 1. , FIG. 7 is an explanatory diagram of the correlation of short pulses, FIGS. 8 and 9 are partially cutaway perspective views of a thermal head suitable for implementing the present invention, and FIG. 10 is a general view of the thermal head shown in FIG. 9. 11 is an operation timing chart thereof, FIG. 12 is an explanatory diagram of an image recorded by a conventional thermal head, and FIG. 13 is a general wiring diagram of the thermal head shown in FIG. 8. 40...Thermal head, 40, ~40. ...Group of unit heating elements, 4
1...Print control unit, 42...Print pulse supply unit, 52...Short pulse.

Claims (1)

[Scope of Claims] 1. A thermal head in which a number of unit heating elements each generating heat independently when supplied with electric current are arranged in a row in the longitudinal direction thereof, and an image signal for selecting a unit heating element to generate heat. The print control unit supplies this image signal to the thermal head, and repeats short pulses intermittently to control the on/off of the current supplied to the unit heating element selected by this image signal until the unit heats up to a predetermined temperature. The unit heating element is divided into two or more groups, and the printing pulse supply section alternately supplies the short pulse once to each group in a predetermined order. A thermal head drive device characterized in that it supplies exclusively to. 2. The thermal head driving device according to claim 1, wherein the widths of the short pulses alternately supplied to each group are equal to each other. 3. The thermal head driving device according to claim 1 or 2, wherein the width of the short pulse repeatedly supplied to one unit heating element is always constant. 4. The thermal head drive device according to claim 1 or 2, wherein the width of the short pulse is minimized before and after the unit heating element reaches the temperature necessary for its recording operation. . 5. Claims 1 to 4, characterized in that a certain pause time is provided between the short pulses supplied to one group and the short pulses supplied to the next group.
The thermal head drive device described in .