JPH0820124A - Thermal printer - Google Patents

Abstract

PURPOSE:To eliminate uneven printing of characters by a method in which a memory which registers the number of heat generation elements and the current time corresponding to each other is provided, the number of the elements to which the current is turned on is calculated before printing, and the current time corresponding to the number of the elements is selected from the memory to control the current time. CONSTITUTION:When printing data for a printing sheet are inputted, in CPU 1, the number of dots to be printed is calculated by analyzing the printing data, the electricity turning on to a thermal head 4 is controlled by the application time corresponding to the calculated number of dots through a drive head 5. For example, when the calculated number of dots is 16, an energy correction coefficient 1.60 corresponding to the standard application time of voltage to the thermal head 4 is read out from a table in RAM 3 to multiply the value. In this way, the electricity is turned on for the time which is 1.6 times the current for only one heat generation element so that the uniform density of characters can be kept.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer for printing on recording paper by energizing each heating element provided in a thermal head.

[0002]

2. Description of the Related Art This type of thermal head is used for printing 1
If one character consists of 16 dots,
As shown in (1), it is composed of one common resistor and 16 heating resistors (heating elements). That is, R1 to R16 are heating resistors corresponding to the respective dots, and RC is each heating resistor R1 to R16.
This is a common resistor through which this current commonly flows when a current is passed through R16.

By the way, a 5V power source is supplied to the thermal head, and when each heating resistor is individually selected, a current is supplied from the 5V power source to each selected resistor to energize it. Printing on the recording paper is performed due to heat generated by energization.

[0004]

As shown in FIG. 4, it is assumed that the common resistor RC has a resistance value of 0.45Ω and the heating resistors R1 to R16 have the same resistance value of 25Ω. When, for example, only the heating resistor R1 is selected and energized from among the heating resistors, the applied voltages at both ends of the common resistor RC and the heating resistor R1 are as shown in FIG. 4 (a). To 0.09V and 4.91V, respectively.

On the other hand, when all the heating resistors and R1 to R16 are selected and energized, since the heating resistors are connected in parallel, the combined resistance value of one heating resistor is smaller than that when energized. As a result, the applied voltage across the common resistor RC and across the heating resistors R1 to R16 connected in parallel is 1.12 V, respectively, as shown in FIG. 4 (b).
And 3.88V. As described above, in the conventional thermal head, the value of the energization current per heating resistor becomes smaller as the number of heating resistors selected and energized at one time among all the heating resistors R1 to R16 increases. , The print density becomes light. Therefore, when printing is performed on the recording paper with such a thermal head, the printing density differs for each character, and there is a problem that uneven printing occurs.

Therefore, it is an object of the present invention to prevent printing unevenness and perform uniform printing when printing is performed by energizing each heating resistor of the thermal head.

[0007]

In order to solve such a problem, the present invention relates to a memory for registering the number of heating elements to be energized and the energizing time in association with each other, and a plurality of heating elements prior to printing. Of these, a calculating means for calculating the number of heating elements to be energized, a selecting means for selecting an energizing time corresponding to the calculated number of heating elements from the memory, and a selecting means for each heating element of the thermal head An energization control unit that energizes for the selected energization time is provided.

[0008]

The number of heating elements to be energized is calculated before printing, and the energization time corresponding to the calculated number of heating elements is selected from the memory, and each heat is generated for the selected energization time. The element is energized. As a result, when printing with a thermal head, uneven printing between characters can be prevented, and uniform printing can be performed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a thermal printer according to the present invention. In the figure, 1 is a CPU, and the CPU 1 executes a program in the ROM 2 to control the entire thermal head. Reference numeral 3 denotes a RAM, and the RAM 3 temporarily stores data necessary for the processing control of the CPU 1, and also stores table data as shown in Table 1 described later. Further, 4 is a thermal head, and when the thermal head 4 is composed of 16 dots for one character, as shown in FIG.
It consists of C and 16 heating resistors R1 to R16. 5
Is a head driver, which is connected to each heating resistor R1 to R16 of the thermal head 4 and each heating resistor R1 to R16.
The 16 are individually energized.

That is, when data is given from the CPU 1, the head driver 5 energizes the heating resistors corresponding to the data among the heating resistors R1 to R16. As a result, one character is printed on the recording paper (not shown). By the way, in the thermal head 4, all the heating resistors R1 ...
If the number of energized heating resistors of R16 is different, the print density is different for each character, and as a result, print unevenness may occur. Therefore, in this embodiment, when the heating resistors of the thermal head 4 are energized for printing, uneven printing is prevented and uniform printing is controlled. Here, in order to perform control for preventing printing unevenness, first, a table as shown in Table 1 is provided in the RAM 3.

[0011]

[Table 1]

According to this table, the relationship between the number of printed dots (that is, the number of energized heating resistors) and the voltage applied to the energized heating resistors in the thermal head 4 is, for example, one printed dot. The applied voltage decreases as the number of printed dots increases, such as 4.91 V in the case and 3.88 V in the case of 16 printed dots. Therefore, the voltage application time to the thermal head 4 is kept constant, and
The applied energy when printing 1 dot at ° C is "1".
Then, the energy in the case of 16-dot printing is about “0.625”, the amount of heat generation (heating energy) due to energization for each heating resistor is small, and the print density is thin.

Therefore, by setting the energy correction coefficient as shown in Table 1 according to the number of print dots, the voltage application time (energization time) to the thermal head 4 is made variable according to the number of print dots, and each energization is performed. Keep the amount of heat generated by the heating resistor constant. That is, if the energy correction coefficient when the number of printed dots is 1 is "1", the energy correction coefficient when the number of printed dots is 16 is approximately "1.6".
Becomes Therefore, if this correction coefficient "1.6" is multiplied by the application time (reference application time) when the number of print dots is 1 dot and this is taken as the voltage application time for 16 print dots, each heating resistor is Is equal to that of one print dot, and the heat generation amount of each heating resistor is constant regardless of the number of print dots. As a result, the print density becomes constant regardless of the number of print dots, and print unevenness can be prevented.

Next, FIG. 2 is a flow chart showing the operation of the CPU 1. The operation of the main part of the present invention will be described in more detail based on this flowchart. First, when the print data to be printed on the recording paper is input, step S in FIG.
The determination at T1 is “Y”, and in this case, the CPU 1 executes the printing process at step ST2. In this printing process, as shown in FIG. 2 (b), before printing, the print data is first analyzed in step ST11 to calculate the number of dots to be printed, and the application time according to the calculated number of dots is used. The energization control process for the thermal head 4 is executed after step ST12.

That is, the calculated number of dots is 16 dots, and the judgment of "n = 16" in step ST12 is "Y".
Then, in step ST13, the corresponding energy correction coefficient “1.60” is read from the table in the RAM 3 with respect to the reference application time of the voltage to the thermal head 4 and multiplied by this value. Then, the process proceeds to step ST18, where the print data is output to the head driver 5 and at the same time, the print process for maintaining the output of this print data for the application time calculated in step ST13 is performed.

As a result, each heating resistor corresponding to the print data of the thermal head 4 (in this case, all the heating resistors) has a current-carrying time when only one heating resistor is energized. Since electricity is supplied for 1.6 times, the same amount of heat is generated from each of the heat generating resistors as when only one heat generating resistor is applied, and therefore the print density is the same. The letters are kept in a homogeneous density. If the calculated number of dots is 15 and the determination of “n = 15” in step ST14 is “Y”, the energy correction coefficient “1.56 in the table at the reference application time described above is calculated in step ST15. ", Step ST18
Move to and perform the same print processing

The number of dots n calculated in step ST11 will be referred to as "n = 14", "n = 13", ...
・ Sequentially, in each step (not shown), if “Y” is determined in these steps, the reference application time is multiplied by the energy correction coefficient in the table according to the determined number of dots, and the application time is set. Establish. Here, step ST
If the number of dots calculated in 11 is 2 and the determination of “n = 2” in step ST16 is “Y”, the energy correction coefficient “1.04 in the table at the above-mentioned reference application time is calculated in step ST16. , ”And the process proceeds to step ST18. If the determination of “n = 2” in step ST16 is “N”, the calculated number of dots is 1 dot. In this case, the reference application time is not multiplied by the energy correction coefficient, In ST18, print data is output to the head driver 5 for the reference application time.

As described above, the number of dots forming the print data of the thermal head 4 is calculated, the energy correction coefficient corresponding to the calculated dot number is selected from the table, and the energy correction coefficient is applied to the reference application time. The application time obtained by multiplying by is calculated, and a voltage is applied to each heating resistor corresponding to the print data to energize for the application time. As a result, the same amount of heat is generated from each of the heating resistors that are energized, so that the print density is the same and each character is kept at a uniform density.

[0019]

As described above, according to the present invention, the number of heating elements to be energized and the energization time are associated and registered in the memory, and the number of heating elements to be energized is calculated before printing. , The energization time corresponding to the calculated number of heating elements is selected from the memory, and each heating element is energized for the selected energization time, so when printing with the thermal head Printing unevenness is prevented, and uniform printing can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a thermal printer of the present invention.

FIG. 2 is a flowchart showing an operation of the apparatus in the embodiment.

FIG. 3 is a diagram showing a configuration of a thermal head in the apparatus of the embodiment.

FIG. 4 is a diagram showing how a voltage is applied to each heating resistor of the thermal head.

[Explanation of symbols]

1 ... CPU, 2 ... ROM, 3 ... RAM, 4 ... Thermal head, 5 ... Head driver, RC ... Common resistor, R1 ...
R16: Heating resistor (heating element).

Claims (1)

[Claims] 1. A thermal printer comprising a thermal head composed of a plurality of heating elements, wherein each heating element of the thermal head is energized to generate heat to print on a recording paper. A memory for registering the number of elements and the energization time in association with each other, a calculation unit for calculating the number of heating elements to be energized among the plurality of heating elements prior to the printing, and the calculated number of heating elements Selection means for selecting an energization time from the memory, and energization control means for energizing each heating element of the thermal head for the energization time selected by the selection means. Thermal printer.