JPH07323598A - Drive device of thermal head - Google Patents

Abstract

PURPOSE:To freely set the correction quantity of applied voltage to enable accurate correction while performing the optimum correction of applied voltage at every printing medium or model. CONSTITUTION:The drive device of a thermal head 3 constituted by parallelly connecting a plurality of heating resistor elements has head drive ICs 2, 4 outputting the data D of the number of current supply elements among a plurality of the heating resistor elements of the thermal head 3 and an applied voltage correction circuit 5 setting the current supply time of the element of the thermal head 3 corresponding to the number-of-current supply element data D from the head drive ICs 2, 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a thermal head used in, for example, a video printer.

[0002]

2. Description of the Related Art The conventional thermal head used in, for example, a video printer is shown in FIG. 7 in principle.

In FIG. 7, the thermal head TPH
Is a plurality of head heating resistors (hereinafter simply referred to as element hr)
The elements hr are connected in parallel, and the parallel connection points at both ends are connected to the power supply BAT.
In addition, between the power supply BAT and the thermal head TPH,
There is a resistance component of the power harness or the like, that is, a common resistance CMR.

When an image or the like is printed on the printing paper by the thermal head TPH, the drive current to each element hr is controlled by a head control circuit (not shown). When the drive current flows through the thermal head TPH, the element hr generates heat. At this time, by arranging a color ink ribbon (not shown) coated with, for example, a sublimable paint between the head heating resistor, that is, each element hr and the printing paper facing the element hr, The sublimable coating material applied to the color ink ribbon is heated and vaporized and is thermally transferred onto the photographic paper, whereby a color image is formed on the photographic paper.

[0005]

By the way, in the thermal head TPH having the configuration of the principle diagram as shown in FIG.
The power supply voltage of the power supply BAT is V _O , the resistance value of one element hr is R _H , the number of elements (the number of head heating resistors) is N, the resistance value of the common resistor CMR is R _O , and the actual thermal head is used. Assuming that the voltage applied to TPH is v, the number of ON elements of each element hr of the thermal head TPH is n, and the combined resistance value of ON elements is r,
The combined resistance value r is expressed by the following equation.

R = R _H / n

At this time, the voltage v applied to the head heating resistor
Is given by the following formula.

V = r / (R _O + r) · V _O = R _H / (nR _O + R _H ) · V _O

More specifically, for example, the actual number of elements N of the head is 2000 to 3000,
When all the elements hr are energized, since the elements hr are connected in parallel, the combined resistance value r of them is 1/2000 or 1/3000,
Therefore, the energy which gives resistance values included in the harness to the device hr head (the resistance value of the common resistor CMR R _O) to be can not be ignored element hr decreases.

As described above, when many elements hr are turned on and the combined resistance value r due to these elements hr becomes small, the influence of the voltage drop due to the resistance component (common resistance CMR) of the power harness or the like can be ignored. Therefore, there arises a problem that, for example, the printing density at the time of printing on printing paper becomes low.

Conventionally, in order to eliminate the above-mentioned change in print density, a decrease in the voltage applied to the thermal head has been corrected. As a method of correcting this decrease in applied voltage, for example, there is a method of attaching a capacitor to the power supply line of the thermal head, a method of using a circuit that corrects the applied voltage with a predetermined correction amount, or the like.

However, in the method of attaching a capacitor to the power supply line of the thermal head, although the applied voltage changes gently and the print density also changes gently, the change in the print density still remains. It is not a fundamental solution to eliminate the change in print density.

Further, in the method using the correction circuit for correcting the applied voltage with the predetermined correction amount, the correction amount is limited by the circuit used. Therefore, it is difficult to optimize each print medium such as photographic paper and each model such as the model of a video printer. Further, the correction rate is only linear, and if the correction rate must be non-linear, optimal correction cannot be performed.

In view of the above, the present invention allows the amount of correction of the applied voltage to be set freely, enables more accurate correction, and provides the optimum applied voltage for each print medium and model. An object of the present invention is to provide a thermal head driving device capable of performing correction.

[0015]

DISCLOSURE OF THE INVENTION The present invention has been proposed in order to achieve the above-mentioned object, and in a thermal head driving device in which a plurality of heating resistance elements are connected in parallel, a plurality of thermal heads are used. A current-carrying element number output means for outputting information on the number of current-carrying elements among the heating resistance elements of
An energization time setting means for setting the energization time of the heating resistance element of the thermal head according to the energization element number information from the energization element number output means.

Further, in the thermal head drive device of the present invention, the energization time setting means changes the energization time which is set according to the energization element number information from the energization element number output means. It also has means. Here, the energization time setting means includes a random access memory for writing / reading the energization time information, and the energization time can be changed by rewriting the information held in the random access memory. Is said.

[0017]

According to the present invention, the energization time of the heating resistance element is set according to the number of energized elements of the thermal head, thereby correcting the energy fluctuation due to the change of the applied voltage according to the change of the number of energized elements. There is.

Further, according to the present invention, the energization time set by the energization time setting means can be freely changed by the energization time setting changing means according to the information on the number of energization elements from the energization element number output means. This change can be easily realized by changing the information held in the random access memory.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the driving device for the thermal head 3 according to the embodiment of the present invention is used, for example, in a video printer, and is composed of a plurality of heating resistors (elements) as in FIG. The increase / decrease in energy at the time of printing due to the change in applied voltage due to the increase / decrease in the number of energized elements in the thermal head 3 is corrected by changing the energization time to each element. That is, in the apparatus of this embodiment, in order to eliminate the change in the print density, when the print density is high (when the number of elements in the thermal head 3 that are on is small), the energization time to the thermal head 3 is set. When the print density is shortened and the print density becomes low (when the number of elements of the thermal head 3 that are on is large), the applied voltage correction circuit 5 performs control such that the energization time to the thermal head 3 is lengthened. I have to.

First, the overall structure of FIG. 1 will be described. In FIG. 1, the memory transfer block 1 has, for example, an image memory, and image data from this image memory is sent to the head drive ICs (integrated circuits) 2 and 4 via an image data bus. The head drive IC 2, 4
Drives the thermal head 3 based on the image data, and the thermal head 3 drives the head drive IC.
Based on the head drive data from 2 and 4, the paint of a color ink ribbon (not shown) to which a sublimable paint is applied is thermally transferred to a printing paper. As a result, a color image is formed on the printing paper.

Here, the CPU (central processing unit) 6 in FIG. 1 uses the head active pulse H as shown in FIG.
Output AP. The head active pulse HAP
Is a pulse that indicates the timing for thermally transferring the primary colors of yellow, magenta, and cyan by subtractive color mixing from the color ink ribbon to the printing paper. Each is "L (low level)" for the yellow printing period and the magenta printing. It corresponds to the period and the cyan printing period.

The CPU 6 also outputs a print pulse PP as shown in FIG. The print pulse P
Each P is a pulse of "H (high level)" indicating how many lines (1 to n lines) are present in the printing of one of the primary colors of yellow, magenta and cyan. It should be noted that the number of lines in which the print pulse PP is present during printing of one of the primary colors (when the head active pulse HAP is "L") depends on the model of the video printer and the content of the image data. However, for example, a maximum of about 1500 lines or a maximum of about 4700 lines can be taken as an example (depending on the image data, it may be somewhat smaller than the number of these lines).

A head active pulse HAP and a print pulse PP from the CPU 6 are sent to the memory transfer block 1. As a result, the image data corresponding to the primary colors yellow, magenta, and cyan of the head active pulse HAP is read from the image memory of the memory transfer block 1 according to the number of lines, and the head drive IC 2 is read. , 4 sent to. At this time, the memory transfer block 1 also outputs the head active pulse HAP and the print pulse PP, which are sent to the head drive IC 2.

The head drive IC 2 sends the head drive data to the thermal head 3 and also sends a latch pulse LP as shown in FIG. The latch pulse LP has a density level of one cycle of the print pulse PP, that is, the density level of the print for one line, such as 256.
It is a pulse used for expressing in stages (the density is expressed in 256 gradations). The thermal head 3 uses the latch pulse L
The print density of one line is changed based on P.

For example, as shown in FIG. 3, the number of elements of the thermal head is considered to be 5 (elements dv1 to dv5) for convenience, and the density data de for each element of these elements dv1 to dv5 is shown in FIG. The case where the above is set will be described. For example, the density data de of a certain color is a (a
(Corresponding to 1/256 gradations), each element dv is heated a times in order to obtain its density. That is, for example, as shown in FIG. 3, density data d indicating 256 gradations with respect to the element dv1.
When e256 is given, the element dv1 is heated 256 times, and when density data de1 showing one gradation is given to the elements dv2 and dv3, the element dv2 and dv3 are given.
3 is heated once, and when the density data de3 showing 3 gradations is given to the element dv4, the element dv4 is heated 3 times and density data d showing 5 gradations to the element dv5.
When e5 is given, the element dv5 is heated five times, so that gradation is created by the number of times the element dv is heated.
Therefore, when viewed macroscopically, the printing result in one line is divided into a colored portion indicated by a circle in FIG. 3 and an uncolored portion indicated by a cross in the figure. However, there is no intermediate color (gradation of density) in the part indicated by ◯ in the figure. Here, in the example of FIG. 3, the number of energized elements is different between 1 gradation and 5 gradations. 1
When all the current is on like gradation, the resistance value becomes 1/5 because the elements are connected in parallel, and the resistance value contained in the harness to the head element cannot be ignored, The energy provided is reduced. Therefore, in this embodiment, as described later, the energization time control signal STB
The "L" section is lengthened to lengthen the energization time to cover the reduced energy.

Incidentally, the head active pulse HAP "
The L ″ section is set to be wider than just n print pulses PP, and one cycle of the print pulse PP is also set wider than just 256 latch pulses LP.

Returning to FIG. 1, the above head drive IC 2
From the above, the head active pulse HAP, the print pulse PP, the latch pulse LP, and the energization element number data D described later are sent to the applied voltage correction circuit 5. The head drive IC 4 also sends energization element number data D to the applied voltage correction circuit 5. The energization element number data D from these head drive ICs 2 and 4 is sent to the applied voltage correction circuit 5 via the energization element number transfer data bus.

Further, the applied voltage correction circuit 5 of the apparatus of this embodiment.
Include a chip select signal CS, a write enable signal WE, and a read enable signal RE, which will be described later.
And the correction data (thermal head 3
(Correction data of energization time for applying voltage to), adder control signal AP, line select signal LS, ON / OFF control signal OFS, and address data A via the address bus are supplied from the CPU 6.

The applied voltage correction circuit 5 of the apparatus of this embodiment is constructed as shown in FIG. 4, and when the number of energized elements of the thermal head 3 increases, the energized time for each element is lengthened, and conversely. When the number of energized elements decreases, the energization time for each element is shortened to correct the voltage drop during printing of the thermal head. Further, the applied voltage correction circuit 5 of the device of this embodiment is a RAM (random
An access memory) 33 is provided so that the CPU 6 can directly write the energization time correction data (correction data of energization time for applying voltage to the thermal head 3) C to the RAM 33.

In FIG. 4, terminals 19 to 22 are connected to
The energizing element number data D1 to D4 from the head drive ICs 2 and 4 are input via the energizing element number diversion data bus. The energizing element number data D1 to D4 are each represented by 7 bits (indicated by D [6: 0] in the figure).

The energizing element number data D1 to D4 are added by the adder 31 to calculate the total energizing element number. The output of the adder 31 is sent to the RAM 33 as address data represented by 8 bits. The adder 31 is supplied with an adder control signal AP, which is a control signal for the addition operation from the CPU 6, via the terminal 23.

As will be described later, correction data for controlling the energization time of the thermal head 3 corresponding to the number of energization elements is written in the RAM 33 in advance, and the correction data for the energization time is stored in accordance with the address data. Read out. Address data A represented by 8 bits (indicated by [7: 0] in the drawing) is directly supplied to the RAM 33 from the CPU 6 via the terminal 18.
Further, the RAM 33 is supplied with a chip select signal CS indicated by 3 bits (indicated by [2: 0] in the figure) output from the CPU 6 through a terminal 14, and thereafter, similarly, a read enable signal RE. The write enable signal WE is supplied through the terminal 15 and the writing / reading is controlled based on these signals. The energization time correction data previously written in the RAM 33 is supplied from the CPU 6 via the terminal 17 as the correction data C represented by 8 bits (indicated by [7: 0] in the figure) as described later. .

The energization time correction data read from the RAM 33 is sent to the counter 35 via the data selector 34. The counter 35 operates according to the head active pulse HAP supplied from the head drive IC 2 via the terminal 11, the print pulse PP supplied via the terminal 12, and the latch pulse LP supplied via the terminal 13. , The energization time control signal STB of the thermal head 3 is generated from the correction data. More specifically, the counter 35 is composed of a down counter, and RA via the data selector 34.
The value of the correction data supplied from M33 is used as an initial value for down counting, and the energization time control signal STB which becomes "L" is output during the down counting operation. Therefore, the thermal head 3 is active "L", and is turned on in response to the "L" energization time control signal STB. After that, when the down count value of the counter 35 becomes "0", the energization time control signal STB becomes "0".
H ", and the energization of the thermal head 3 is terminated.

The counter 35 operates in response to the head active pulse HAP, the print pulse PP, and the latch pulse LP because these pulses correspond to the thermal head 3 during printing. Therefore, FIG. 3 described above also shows the relationship between the energization time control signal STB and the latch pulse LP at the same time.

The counter 35 uses the data supplied from the RAM 33 via the data selector 34 as an initial value for down counting. For example, the CPU 6
It is also possible to use the address data A supplied from the terminal 18 through the terminal 18 as the initial value, or to use the preset fixed value data from the fixed value data generating circuit 32 as the initial value to perform the above down counting. Therefore, in addition to the data from the RAM 33, the address data A supplied from the CPU 6 via the terminal 18 and the fixed value data from the fixed value data generation circuit 32 are also supplied to the data selector 34. CPU6
Line select signal L supplied from the terminal 24 via the terminal 24
It is configured to selectively output based on the ON / OFF control signal OFS supplied via S and the terminal 25.

As described above, in the thermal head drive device of this embodiment, the thermal head 3 is stored in the RAM 33.
The energization time correction data corresponding to the number of energization elements is written, and the energization time correction data is read according to the number of energization elements of the thermal head 3 supplied from the head drive ICs 2 and 4, and the read energization time is read. Energization time control signal ST of the thermal head 3 according to the correction data of
B, that is, for example, a signal that lengthens the current-carrying time (longs the “L” section) when the number of current-carrying elements is large, conversely shortens the current-carrying time when the number of current-carrying elements is small (the “L” section is short)
The signal to output is output.

By the way, the optimum data of the energization time correction data previously written in the RAM 33 is determined as the value of the energization time corresponding to the number of energization elements by conducting an experiment. The correction data obtained in advance by this experiment is
8-bit correction data C supplied from the CPU 6 via the terminal 17 is sent to the RAM 33, and the terminal 18
It is written in the RAM 33 in accordance with the address data A represented by 8 bits supplied from the CPU 6 via.

The correction data of the energization time will be described below.

First, the energization time control signal STB shown in FIG.
5, the data is set in the thermal head 3 when the latch pulse LP is "L", and the energization time control signal S
TB includes a period T _A which is a waiting time from the fall of the latch pulse LP to the energization, a period T _B which is a constant energizing time, and a period T _C which is an energizing time corresponding to the number of energizing elements. The period T _A is determined by the specifications of the thermal head used, and each period T _{A to} T _B is set by the number of system clocks.

For example, the period T _A shown in FIG.
Is the period of 24 system clocks, and the period T
_{When B} is the period of 488 system clocks,
The period T _C, which is the energization time, is set as shown in Table 1. It should be noted that in Table 1, the upper eight outputs of the adder 31
Bits (upper 8 bits of the total number of energization elements) are used to set an energization time (the above-mentioned period T _C ) indicated by the number of system clocks. Further, the relationship between the number of conducting elements and the number of system clocks in the case of Table 1 is as shown in FIG.

[0042]

[Table 1]

When the correction data of the energization time as shown in Table 1 is written in the RAM 33, the adder output is used as the address data or the CPU 6 as described above.
The correction data value is written based on the address data directly supplied from the. The values of the periods T _A and T _B are stored in the RAM 3 according to the designated address.
Written in 3.

As described above, in the thermal head driving apparatus of the embodiment of the present invention, the applied voltage correction circuit 5 lengthens the energizing time when the number of energizing elements increases during printing of the video printer, and conversely. If the number of energizing elements decreases, make correction so that the energizing time is shortened.
Further, a RAM 33 is provided inside the applied voltage correction circuit 5 so that the correction amount can be freely set (rewritten) by the CPU 6. As a result, it is possible to optimize the correction for each print medium and for each model, and it is possible to optimize the correction ratio with respect to the number of energizing elements linearly or non-linearly, and to optimize almighty.

[0045]

According to the present invention, by setting the energization time of the heating resistance element in accordance with the number of energized elements of the thermal head, the energy fluctuation due to the change of the applied voltage in accordance with the change of the number of energized elements is more accurate. Therefore, when applied to, for example, a video printer, excellent printing can be performed.

Further, in the present invention, the energization time setting means can freely change the energization time to be set in accordance with the energization element number information from the energization element number output means, and this change is performed by random access.・ Since it can be easily realized by changing the information held in the memory, it is possible to correct the applied voltage optimally for each print medium and model. Therefore, if it is applied to a video printer, for example, good printing is possible. Becomes

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing an overall configuration of a device according to an embodiment of the present invention.

FIG. 2 is a waveform chart of each part in color printing.

FIG. 3 is a diagram for explaining an example of density data and gradation corresponding to each element.

FIG. 4 is a block circuit diagram showing a schematic configuration of an applied voltage correction circuit.

FIG. 5 is a waveform diagram showing a relationship between a latch pulse and a conduction time control signal.

FIG. 6 is a diagram showing a relationship between the number of conducting elements and the number of system clocks.

FIG. 7 is a circuit diagram showing a principle configuration of a thermal head.

[Explanation of symbols]

 1 Memory Transfer Block 2, 4 Head Drive IC 3 Thermal Head 5 Applied Voltage Correction Circuit 6 CPU 31 Adder 32 Fixed Value Data Generation Circuit 33 RAM 34 Data Selector 35 Counter

Claims (3)

[Claims] 1. A thermal head drive device comprising a plurality of heating resistance elements connected in parallel, wherein a current-carrying element number output means for outputting information on the number of current-carrying elements among the plurality of heating resistance elements of the thermal head, An energization time setting means for setting the energization time of the heat generating resistance element of the thermal head according to the energization element number information from the energization element number output means. 2. An energization time setting changing means for changing the energization time to be set by the energization time setting means in accordance with the energization element number information from the energization element number output means. 1. The thermal head drive device according to 1. 3. The thermal head drive device according to claim 2, wherein the energization time setting means has a random access memory for writing / reading energization time information.