JP2907600B2 - Thermal printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer provided with a thermal head including a plurality of heating resistors.

[0002]

2. Description of the Related Art Generally, a thermal printer is provided with an overcurrent protection circuit in order to prevent an operation failure due to an excessive load applied to a power supply due to an overcurrent. For example, an overcurrent protection circuit for preventing an overcurrent from flowing is necessary, for example, when print data is output that energizes all the heating resistors of a thermal head provided in a thermal printer. .

[0003]

However, there is a high demand for downsizing and cost reduction of recent devices, and if an overcurrent protection circuit is not required, a circuit board can be downsized and the entire device can be downsized. . Further, the cost can be reduced by the cost of the electronic components of the overcurrent protection circuit.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal printer which can prevent an overcurrent without providing an overcurrent protection circuit and can reduce the size and cost of the apparatus.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a thermal printer which includes a thermal head comprising a plurality of heating resistors and prints predetermined printing information on paper based on image data drawn in a print buffer. And a printing dot number counting means for counting the number of printing dots per one line of printing, and according to an increase in the number of printing dots counted by the printing dot number counting means, the energizing time is lengthened and the printing speed is slowed down. and print control means for controlling low for optimal printing the voltage applied to the heating resistor of the thermal head as well as providing printing for each line
Printing is performed by controlling the speed and applied voltage .

[0006]

[Action] In the present invention having such a configuration, it counts the number of print dots of each line by the print dot number counting means
However, if the number of print dots on a certain line increases,
Control the printing speed by increasing the
Controlling the voltage applied to the antibody low so that optimal printing can be performed
I do. In this way, the printing speed and applied voltage are
Control and prevent overcurrent.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to a label printer using a thermal head, and FIG. 1 shows a block diagram of the circuit configuration. Reference numeral 1 denotes a CPU (central processing unit) constituting the control unit main body. A ROM (Read Only Memory) 2 in which program data for processing performed by the CPU 1 is stored, and a RAM in which areas of various memories used when the CPU 1 performs processing are formed.
(Random access memory) 3 is a system bus 4
Is connected to the CPU 1 via the. The RAM
Reference numeral 3 denotes a PM (pulse motor) timer 3a for setting a cycle of one-step driving of the pulse motor 5 during printing, and an ENB (enable) timer 3b for setting an energizing time for supplying a current to each heating resistor of the thermal head 6. Is provided.

A motor drive circuit 7 and a head drive circuit 8 for controlling the pulse motor 5 and the thermal head 6, respectively, are connected to the CPU 1 via the system bus 4.
Is connected to A communication I / F (interface) 9 connected to the host computer via a line, and a print buffer in which print information is drawn into image data based on data transmitted from the host computer via the communication I / F 9 Is also connected to the CPU 1 via the system bus 4. When a label issuing command is received from the host computer via the communication I / F 9 in FIG.
2 shows a flowchart of a print control process performed by the printer. First, the received print information is drawn as label image data in the drawing buffer 10 in accordance with the label issuing command.

Next, the number of print dots in one line of data to be printed is counted from the label image data drawn in the drawing buffer 10 (print dot number counting means), and the ratio of the number of print dots to the total number of dots in the line is calculated. The printing rate is calculated, and it is confirmed whether the calculated printing rate is equal to or less than a preset upper limit printing rate, for example, 60%.

If the calculated printing rate is larger than the upper limit printing rate, P is set so that the cycle for one step of the pulse motor 5 becomes the cycle for speed 1 shown in FIG.
The time "T1p" is set in the M timer 3a, and the time "T1e" is set in the ENB timer 3b as half of the time during which the heating resistor of the thermal head 6 can be energized. Then, an applied voltage is set for the energization time “T1e” set by the ENB timer 3b so that the heating resistor of the thermal head 6 can perform optimal printing.

If the calculated printing rate is equal to or less than the upper limit printing rate, the time "T2p" is set in the PM timer 3a so that the cycle for speed 2 shown in FIG. The time “T2” is supplied to the ENB timer 3b as a half of the time during which the heating resistor of the thermal head 6 can be energized.
e "is set. Then, an applied voltage is set for the energization time “T2e” set by the ENB timer 3b so that the heating resistor of the thermal head 6 can perform optimal printing. (Print control means)

FIG. 3 shows a signal "PM" for step-controlling the pulse motor 5, a signal "ENB1" for giving a timing to energize a half of the heating resistor of the thermal head 6, and a heat generation for the other half. FIG. 9 is a diagram showing a timing of a signal “ENB2” for giving a timing for energizing a resistor.

When the PM timer 3a and the ENB timer 3b are set, respectively, and the voltage applied to the heating resistor of the thermal head 6 is set, the pulse motor 6 is driven by one step according to the cycle set by the PM timer 3a. The platen (not shown), which is disposed to face the printer via the label paper, is driven to perform one-line printing.

Then, it is checked whether or not the next line to be printed is in the drawing buffer 10. If there is a line to be printed, the number of dots printed on the line to be printed is counted again. The process returns to the process of calculating the printing rate. Here, if the line to be printed next is not in the drawing buffer 10, this print control process is terminated.

In this embodiment having such a configuration, a label issuing command is transmitted from the host computer, and the image data is drawn in the drawing buffer 10 by the label issuing command.

Then, the number of print dots in one line of data to be printed is counted from the image data, and the ratio of the number of print dots to the total number of dots in the line is calculated as a print ratio. It is checked whether the printing rate is equal to or lower than the upper limit printing rate, for example, 60%. If the calculated printing rate is larger than the upper limit printing rate, the printing speed is set to speed 1, and if the calculated printing rate is equal to or less than the upper limit printing rate, the printing speed is set to speed 2. That is, as shown in FIGS. 3A and 3B, the speed 1 and the speed 2 are controlled by controlling the speed of the pulse motor in one step by the PM timer 3a. This is executed by controlling the energization time to the resistor by the ENB timer 3b. The ENB timer 3b
The voltage applied to the heating resistor is controlled based on the energization time set by (1). Then, one-line printing is performed.

The printing rate is calculated for each line to be printed from the image data drawn in the drawing buffer 10 as described above. If the calculated printing rate is larger than the upper limit printing rate, that is, the number of print dots is large. When the calculated printing rate is equal to or lower than the upper limit printing rate, that is, when the number of printing dots is small, the faster speed 2 is set. Then, the voltage to be applied is controlled based on the power supply time to the heating resistor of the thermal head 6 set by the printing speed. In other words, the best sign
To do character, the voltage applied to the heating resistor of the thermal head 6 when the speed 1, should Ru be lower than the voltage applied to the heating resistor at the time of speed 2. Then, printing is performed while controlling the printing speed for each line, and a label is issued.

As described above, according to the present embodiment, the printing 1
The printing speed is controlled in two stages according to the number of printing dots on the line. If the number of printing dots is large, the printing speed is reduced to lower the voltage applied to the heating resistor, and if the number of printing dots is small, printing is performed. The speed is increased to return the voltage applied to the heating resistor to a normal voltage. By doing so, it is possible to prevent an overcurrent that may occur when many heating resistors are turned on at once in the thermal head. Therefore, there is no need to provide a special overcurrent protection circuit on the circuit, the circuit board can be made smaller, and the cost of the electronic components required for the overcurrent protection circuit can be reduced. Can be achieved.

In this embodiment, the printing speed is controlled by calculating the printing rate from the number of printing dots. However, the printing speed may be directly controlled by the numerical value of the number of printing dots. Although the control is performed in stages, the control may be performed in several stages, or the print speed may be linearly controlled with respect to the number of print dots.

[0020]

As described in detail above, according to the present invention,
It is possible to provide a thermal printer that can prevent overcurrent without providing an overcurrent protection circuit and can reduce the size and cost of the apparatus.

[Brief description of the drawings]

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

FIG. 2 is a view showing a flow of a print control process of the embodiment.

FIG. 3 is a diagram showing timings of a step control signal of the pulse motor 5 of the embodiment and two timing signals for energizing a heating resistor.

[Explanation of symbols]

1 ... CPU, 3a ... PM timer, 3b ... ENB timer,
5 pulse motor, 6 thermal head, 8 head drive circuit, 10 drawing buffer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/35-2/37

Claims (1)

(57) [Claims] 1. A thermal printer, comprising: a thermal head comprising a plurality of heating resistors, for printing predetermined paper information on paper based on image data drawn on a print buffer. Printing dot number counting means for counting the number of printing dots, and in accordance with the increase in the number of printing dots counted by the printing dot number counting means, the energizing time is lengthened to control the printing speed to be slow, and the heat generation of the thermal head is performed. Print control means is provided to control the voltage applied to the resistor so low that optimum printing can be performed. The print speed and applied voltage are controlled for each line.
A thermal printer that performs printing under control .