JPH07242012A - Printer - Google Patents

Abstract

PURPOSE:To inexpensively obtain a printing result of high quality by measuring the resistance values of a plurality of heating elements and controlling the applying time widths of the voltage applied to the heating elements on the basis of the measured resistance values of the heating elements. CONSTITUTION:A resistance value measuring part 101 measures the resistance values of the respective heating elements of a thermal head 7 and a printing control part 105 sets voltage applying times of voltage applied to the heating elements on the basis of the resistance values of the heating elements measured by the resistance value measuring part 101. A printing density control part 103 sends out a control signal controlling strobe signal width to a strobe signal control part 102 on the basis of the resistance value at every heating element read by the resistance value measuring part 101 so as to uniformize the generation quantities of heat of the heating elements. A gradation printing control part 104 changes the generation quantities of heat by controlling signal width with respect to the strobe signal control part 102 on the basis of the resistance values of the heating elements to perform gradation printing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer using a thermal head.

[0002]

2. Description of the Related Art Today, a printer using a thermal head is used in a device such as a thermal printer or a facsimile. In such a printing apparatus, a plurality of heating elements are installed in a line, and by selectively heating these heating elements, printing is performed in the main scanning direction, and further such printing operation is performed in the sub scanning direction. By doing
The desired printing result is obtained.

[0003]

However, in the above-mentioned conventional printing apparatus, the heating elements constituting the thermal head have large variations in resistance value, which has been an obstacle to improvement of printing quality. For example, since the variation in the resistance value is large in the main scanning direction, variation in shading occurs in the main scanning direction, and there is a problem in that a high-quality printing result cannot be obtained.

Further, as a result of the existence of variations in resistance value,
It was not possible to perform gradation printing by controlling the print density. That is, since the resistance value of each heating element cannot be grasped, the correspondence relationship between the voltage application time and the amount of heat generation cannot be grasped, and therefore the printing apparatus using such a thermal head can perform gradation printing. There was a problem that I could not.

On the other hand, if the variation in the resistance value of the heating element is suppressed to a small value, for example, within ± 1%, the above problem can be solved, but in such a structure, the price of the thermal head becomes high. However, the advantage of the printing apparatus using the thermal head, which is low in price, is impaired. Therefore, such a method could not be adopted.

From such a point, there has been a demand for a printing apparatus which can obtain a high-quality printing result at a low cost.

[0007]

In order to solve the above-mentioned problems, the printing apparatus of the present invention measures the resistance value of each of a plurality of heating elements, and the print control unit determines the measured resistance of each heating element. The application time width of the voltage applied to each heating element is controlled based on the value.

[0008]

In the printing apparatus of the present invention, the resistance value measuring section is
All resistance values of the plurality of heating elements are measured. The print control unit changes the voltage application time for each heating element based on the resistance value measured by the resistance value measurement unit. As a result, even if the resistance value varies among the heating elements,
The voltage application time can be set according to the resistance value.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a printing apparatus of the present invention. In the figure, the printing device includes a control unit 1, a memory 2, a constant current power supply 3, a constant voltage power supply 4, and switching units 5, 6a, 6
b, a thermal head 7, and an A / D converter 8.

The control unit 1 is a central processing unit that controls each unit of the apparatus, and includes a resistance value measuring unit 101, a strobe signal control unit 102, a print density control unit 103, and a gradation print control unit 104. Signal control unit 102-
The gradation printing control unit 104 constitutes the printing control unit 105.

The resistance value measuring unit 101 includes a thermal head 7
It has a function of measuring the resistance value of each heating element. The print control unit 105 sets the voltage application time for each heating element based on the resistance value of each heating element measured by the resistance value measuring unit 101. Strobe signal control unit 102 constituting the print control unit 105
Outputs a strobe signal as an ON signal to each heating element of the thermal head 7.

The print density control unit 103 includes a resistance value measuring unit 1
Based on the resistance value of each heating element read in 01, the control signal is sent to the strobe signal control unit 102 so as to control the strobe signal width so that the heating value of the heating element becomes uniform. . Gradation printing control unit 104
Changes the amount of heat generation by controlling the signal width to the strobe signal control unit 102 based on the resistance value of each heating element read by the resistance value measurement unit 101,
It has a function for gradation printing.

The resistance value measuring unit 101 to the gradation printing control unit 104 in the control unit 1 are dedicated processors or programs for realizing each function stored in the memory 2 are stored in the processor of the control unit 1. Is realized by executing.

The memory 2 is a semiconductor memory including a random access memory (RAM) and the like, and is a memory for storing a program executed by the control unit 1 and various data. The constant current power source 3 switches the constant current IDD to the switching unit 5
The thermal head 7 is supplied to the thermal head 7 via a known constant current circuit. Further, the constant voltage power source 4, like the constant current power source 2, supplies a constant voltage VDD to the thermal head 7 via the switching unit 5, and is composed of a known constant voltage circuit.

The switching unit 5 has a constant current I from the constant current power source 3.
This is a switching circuit for switching between DD and the constant voltage VDD from the constant voltage power source 4 and supplying it to the thermal head 8. The switching units 6a and 6b are selectors that switch between a uniform density printing operation and a gradation printing operation in a normal printing mode, which will be described later. The thermal head 7 has a plurality of heating elements arranged in a line, and details thereof will be described later. The A / D converter 8 is for A / D converting the voltage of each heating element in the thermal head 7 and transferring it to the control unit 1 in a resistance value read mode described later.

FIG. 2 shows details of the thermal head 7.
Further, FIG. 3 is a time chart for explaining the basic operation of the thermal head 7. In the figure, the thermal head 7 includes a serial shift register 71, a latch register 72, AND circuits 73-1 to 73-n, transistors 74-1 to 74-n, and heating elements 75-1 to 75-n.
It consists of

The serial shift register 71 is a register for storing a bit serial signal for one line, and S
-IN is serial-in data input to the serial shift register 71, and S-CLK is a clock signal for inputting the serial-in data S-IN to the serial shift register 71. The latch register 72 outputs the parallel output of the serial shift register 71 to the latch signal L.
This is a register that is latched by the touch, and the output of each bit is connected to the input of the AND circuit 73.

Further, the AND circuits 73-1 to 73-n are
These are circuits that respectively input the output of the latch register 72 and the strobe signals STB1 to STB10 and supply the output to the base of the transistor. Further, the heating elements 75-1 to 75-1
75-n has one end connected to the VDD terminal and the other end connected to the collectors of the transistors 74-1 to 74-n, respectively, and these heating elements 75-1 to 75-n and the transistors 74-1 to 74-1 are connected.
A constant voltage VDD is applied to 74-n. The heating elements 75-1 to 75-n are, for example, a thermal head 7 of a letter size with 8 dots / mm.
In the case of, it is provided such that the number is 1728.

Next, the basic operation of the thermal head 7 thus constructed will be described. First, the serial-in data S-IN for one line in the main scanning direction is transferred to the serial-shift register 71 by the serial-in clock S-C.
The signals are sequentially input in synchronization with LK. This is #n shown in FIG.
Suppose it is a line.

Serial-in data S-IN for one line
Is input to the serial shift register 71,
The latch signal Latch is turned on, and the parallel output of the serial shift register 71 is input to the latch register 72. The strobe signals STB1 to STB10 are
It consists of 10 signals from STB1 to STB10. For example, STB1 to STB1 are T1, STB4 and 5 are T2, and STB.
6 and 7 are output at T3 and STB8 to 10 are output at T4.

When the strobe signal STB is "1" and the output of the latch register 72 of the corresponding dot is "1", the heating elements 75-1 to 75-n have the transistors 7-1 to 75-n.
Since 4-1 to 74-n are turned on, an electric current flows and heat is generated, and black (or a corresponding color in the case of color printing or the like) is printed on the printing paper. That is, the printing operation of the #n line is performed. While the #n line is being printed, the serial shift register 71 stores the next # (n +
1) The line serial-in data S-IN is shifted in by the serial-in clock S-CLK.

Next, the operation of the printing apparatus of this embodiment will be described. The printing apparatus according to the present embodiment has two modes: a resistance value read mode in which the resistance values of the heating elements 75-1 to 75-n in the thermal head 7 are measured, and a normal printing mode.

[Resistance Value Read Mode] In the resistance value read mode, the resistance value measuring unit 101 has the switching devices 6a and 6b a.
Instruct to select the side 1 or b1. Where a1,
The signal on the b1 side is the same as the gradation printing operation during the normal printing operation. As a result, the S-IN on the a1 side and the S-IN on the b1 side
-CLK is supplied to the thermal head 7. Further, the resistance value measuring unit 101 switches the switch 5 to the constant current power source 3 side, and supplies the constant current IDD to the thermal head 7.

FIG. 4 is an explanatory view showing the contents of the latch register 72 in the thermal head 7 in the resistance value read mode and the gradation printing operation. The gradation printing operation will be described later, and the resistance value read mode will be described here.

Taking the thermal head 7 of 1728 dots as an example, only one dot is set to "1" (black), all other dots are set to "0" (white), and the dot of "1" is set. Set sequentially from # 1 to # 1728.

FIG. 5 is a time chart in the resistance value read mode. First, after shifting in all "0",
First, S-IN is set to "1" and a rising pulse of S-CLK is applied to set only # 1 dot to "1". At this time, all the other dots are "0", and in this state, the latch signal is turned on and the STB is turned on. After that, the output of the A / D converter 8 is read, and the resistance value is calculated based on this output value. This is the resistance value of the # 1 dot. And # 2 to # 1728 dots are S-IN
Each resistance value can be obtained by the same operation as described above while keeping “0”.

Here, for example, each heating element 75-1
~ 75-n resistance variation is ± 3 with respect to the nominal value
When it is 0%, the average variation is 0.76r · IDD.

FIG. 6 is a circuit diagram for explaining the resistance value read mode of the heating elements 75-1 to 75-n. The output of the latch register 72 is "1", the strobe signal STB
Is 1 and the transistor 74-i (i is 1 to n)
Is turned on, and a constant current IDD flows through the heating element 75-i. As a result, the heating element 75-i and the transistor 74
The voltage V across the series circuit with −i shows a voltage drop of the product “r · DD” of the resistance value r of the heating element 75-i and IDD, and this voltage value is 8 in the A / D converter 8, for example. Bit (256
In the case of gradation), the resistance value measuring unit 101 calculates the resistance value based on the digital value.

In the resistance read mode, the voltage is also applied to the other heating elements 75-1 to 75-n, but these heating elements 75-1 to 75-n are the transistors 74-1.
Since ~ 74-n is turned off, almost no current flows, and the influence of the other heating elements 75-1 to 75-n can be ignored. Then, the resistance value measuring unit 101 creates a resistance value table (not shown) of the heating elements 75-1 to 75-n in the memory 2, and measures the measured heating elements 75-1 to 75-n.
The value of 75-n is stored.

Further, as shown in FIG. 5, if it takes about 1 ms to read the resistance value of 1 dot of the thermal head 7, it takes about 1 ms to read the resistance value of all the thermal heads 7 (1728 dots). It is 1.7 sec. Therefore, this resistance value measurement process may be executed unconditionally first when the power of the printing device is turned on, or may be configured to shift to the resistance value read mode by an operation during the operation of the printing device. .

Next, the normal printing mode in the printing apparatus of this embodiment will be described. [Normal Printing Mode] In the normal printing mode, there are uniform density printing operation and gradation printing operation. First, the uniform density printing operation will be described.

During the uniform density printing operation, the print density controller 103 controls the thermal head 7. First, the print density control unit 103 switches the switching unit 5 to the constant voltage power source 4 side and supplies a constant voltage VDD to the thermal head 7. Also,
The switching units 6a and 6b are operated in a uniform density printing operation mode, that is,
The signals on the a2 and b2 sides are selected. Then, the print density control unit 103 supplies the strobe signal STB to each heating element 75-1 to 75-n based on the resistance value of each heating element 75-1 to 75-n measured by the resistance value measuring unit 101.
Control the time span of. For example, the heating elements 75-1 to 75
-N is 1728 dots, strobe signals STB1 to ST
In the case of B10, the average value of the resistance values of about 173 dots driven by one strobe signal is obtained, and the time width of each strobe signal STB1 to STB10 is determined according to the average value.

FIG. 7 shows a time chart in this case. That is, the time widths T1 to T10 of STB1 to STB10
Is determined based on the average resistance value of the heating elements 75-1 to 75-n driven by the respective STB1 to STB10 so that the heating values of these heating elements 75-1 to 75-n become uniform. Has been done. As a result, the print density of one main scanning line can be made uniform, and therefore the print quality can be improved.

Next, the gradation printing operation in the normal printing mode will be described. In the gradation printing operation, the gradation printing control unit 10
Reference numeral 4 controls the signal width of the strobe signal STB that turns on the heating elements 75-1 to 75-n, thereby performing gradation control of the heating elements 75-1 to 75-n.

FIG. 8 is an explanatory diagram of gradation printing in such a case. The figure shows changes in the time width of the strobe signal STB. First, STB is set to "0" to be all white, STB is set to all black for 2,56 ms, for example. The key is obtained. Alternatively, if the interval is 40 μs, there are 64 gradations. In this way, the step size can be freely set according to the desired gradation accuracy.

The gradation printing control unit 104 is provided with a table showing the relationship between the gradation and the time width of the strobe signal STB, and the resistance value measuring unit 101 measures the table data. Each heating element 75-1 to
Correction is performed based on the resistance value of 75-n. Further, the gradation printing control unit 104 gives an instruction to switch the switching units 6a and 6b to the gradation printing operation side (a1, b1), and the serial-in data S-IN during the gradation printing operation and the serial-in data S-IN. Serial in clock S corresponding to data S-IN
-CLK is applied to the thermal head 7.

FIG. 9 is a time chart during such gradation printing operation. The gradation print control unit 104 sets the serial-in data S-IN to the same data as in the resistance value read mode. That is, the serial-in data S-IN is not the data for one line, but the data in which only one dot is "1". In this way, the gradation printing control unit 104
Is the serial-in data S for the thermal head 7.
By "-IN", "1" is given in order from # 1 to # 1728, and on the other hand, gradation printing from white to black is performed for each dot according to the time width of the strobe signal STB. That is, the print pattern is not controlled by the serial-in data S-IN, but the print pattern is controlled by the time width of the strobe signal STB. In this case, it is assumed that the gradation information to be printed, that is, the print pattern and the gradation thereof are stored in the memory 2 or the like in advance by another means.

Now, let us say that the nominal value of the resistance value of each heating element 75-1 to 75-n is r, and the noted heating element 75-1 to 75-n.
The resistance value error [Delta] r, the average value of the strobe signal STB T (sec), when the heating value of the heating element 75-1 to 75-n to is Q, be considered as ^{Q = (VDD 2 / r)} · T it can.

FIG. 10 shows the relationship between the resistance value r, the time width T of the strobe signal, and the heat generation amount Q and their effects.
Here, the case is the case where the time width T of the strobe signal STB is set to the average value without considering the variation of the heating elements 75-1 to 75-n. In addition, in the following, from the resistance value r + Δr of each heating element 75-1 to 75-n, with respect to the time width T of the strobe signal STB, (Δr / r) · T
This is the printing operation in which the density variation in the normal printing mode in the present embodiment is reduced. Further, in the case of gradation printing, (Δr / r) · with respect to the time width T of the strobe signal STB.
(D / 256) · T is corrected. still,
Here, the value of d is 0 to 256, and gradation printing can be performed such that when the value is 1 step, 256 gradations and when it is 4 steps, 64 gradations are used. As described above, in the present embodiment, since gradation printing can be performed, it is also possible to perform halftone printing such as photography.

As described above, in the present embodiment, it is possible to reduce the print density variation in the main scanning direction and perform gradation printing, but this is not the case when the time width of the strobe signal STB is corrected. (In the case of FIG. 10 above)
As a comparative example, the effect of the present embodiment will be further described.

First, let us consider a case in which the time widths T1 to T4 of the strobe signals STB1 to STB10 are all the same in the basic configuration and operation of the printing apparatus shown in FIGS. In such a case, assuming that the resistance values of the heating elements 75-1 to 75-n have a variation of ± 30% of the nominal value r,
As described above, the heat generation amount Q of each of the heating elements 75-1 to 75-n is Q = (VDD ² / r) · T. Therefore, the variation ΔQ is ΔQ = {(1 / 0.7) -(1 / 1.3)} (VDD ² /
r) · T ≒ 0.76 (VDD 2 / r) , and the Therefore, the variation in print density of approximately ± 38% is generated in the print dot direction. FIG. 11 is an explanatory diagram showing this state.

On the other hand, in the present embodiment, since the resistance values of the heating elements 75-1 to 75-n are measured and the correction is performed according to the resistance values, such a variation in the print density is prevented. It does not occur.

In the above embodiment, in order to reduce the density variation, each ST of the strobe signals STB1 to STB10.
Although 10 types of time width control were performed for each B, the present invention is not limited to this, and can be appropriately selected depending on the accuracy of density variation control and the demand of printing speed. Further, even when the density variation is reduced, the print pattern is not controlled by the serial-in data S-IN, but is controlled by the time width of each strobe signal STB, as in the gradation printing. May be. That is, in this case, it can be considered that the operation is performed when there is only one kind of gradation.

Further, in the above embodiment, the thermal head 7
The case where the heat generating elements 75-1 to 75-n are installed in the main scanning direction has been described.
A plurality of printers are installed in the sub-scanning direction and the thermal head moves in the main scanning direction. The printing apparatus of the present embodiment can be applied not only to thermal printers and facsimiles, but also to copy boards and the like that print characters and figures drawn on the board on printing paper.

[0045]

As described above, according to the printing apparatus of the present invention, the resistance value of the heating element for one line in the thermal head is measured, and the voltage application time to each heating element is measured based on this resistance value. Since it is controlled, it is possible to obtain high print quality at a low price.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a printing apparatus of the present invention.

FIG. 2 is an internal configuration diagram of a thermal head in the printing apparatus of the present invention.

FIG. 3 is a time chart for explaining the basic operation of the thermal head in the printing apparatus of the present invention.

FIG. 4 is an explanatory diagram showing the contents of a latch register in the thermal head in the resistance value read mode in the printing apparatus of the present invention.

FIG. 5 is a time chart in the resistance value read mode in the printing apparatus of the present invention.

FIG. 6 is a circuit diagram for explaining resistance value reading in the printing apparatus of the present invention.

FIG. 7 is a time chart at the time of correcting the density variation in the normal printing mode in the printing apparatus of the present invention.

FIG. 8 is an explanatory diagram of gradation printing in a normal printing mode in the printing apparatus of the present invention.

FIG. 9 is a time chart during gradation printing in the normal printing mode in the printing apparatus of the present invention.

FIG. 10 is an explanatory diagram showing a relationship between a resistance value, a time width of a strobe signal, and a heat generation amount in the printing apparatus of the present invention.

FIG. 11 is an explanatory diagram of occurrence of variations in print density in a comparative example of the printer of the present invention.

[Explanation of symbols]

 7 Thermal Head 71 Serial Shift Register 72 Latch Register 75-1 to 75-n Heating Element 101 Resistance Value Measuring Section 102 Strobe Signal Control Section 103 Print Density Control Section 104 Gradation Print Control Section

Claims (4)

[Claims] 1. A printer, wherein a plurality of heating elements are installed in a line, a voltage is applied to these heating elements, and heat generation is selectively controlled to perform printing for one line. A resistance value measuring unit that measures a value, and a print control unit that controls the voltage application time to each heating element based on the resistance value of each heating element measured by the resistance value measuring unit And printing device. 2. A printing apparatus for printing one line by installing a plurality of heating elements in a line, applying a voltage to these heating elements, and selectively controlling heat generation, wherein the resistance of each heating element is A resistance value measuring unit that measures a value, and a print that changes the voltage application time so that the heat generation amount of each heating element becomes uniform based on the resistance value of each heating element measured by the resistance value measuring unit. A printing apparatus comprising a density control unit. 3. A printer, wherein a plurality of heating elements are arranged in a line, a voltage is applied to these heating elements, and heat generation is selectively controlled to perform printing for one line. A resistance value measuring unit for measuring a value and a reference value of a voltage application time width corresponding to a gradation level are set in advance, and the reference value is set based on the resistance value of each heating element measured by the resistance value measuring unit. And a gradation printing control unit that performs gradation printing by applying a voltage to each of the heating elements with the corrected voltage application time width. 4. The printing device according to claim 3, wherein the gradation printing control unit sequentially applies a voltage to each heating element,
Further, the printing device is characterized in that a printing pattern for one line is determined by changing a voltage application time width to a heating element to which the voltage is applied.