JPH04255366A - Thermal head type recording apparatus - Google Patents

Abstract

PURPOSE:To provide the recording apparatus driving the respective heating elements of a thermal head on the basis of black-and-white image data expressed by a plurality of dots of one line only for a strobe pulse period. CONSTITUTION:Higher driving voltage is applied to a thermal head from a voltage altering part 2 as the count value of a counter part 3 counting the number of the black images in black-and-white image data at every one line becomes more. The effective voltage applied to the heating elements becomes constant regardless of the number of the heating elements to which a current is supplied at once and uniform recording density is obtained regardless of the number of said heating elements.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a thermal printer that prints black and white image data by moving a thermal head and thermal paper relative to each other, or by moving a head block composed of a thermal head and a thermal transfer ribbon relative to plain paper. This invention relates to a head type printing device.

0002

2. Description of the Related Art A conventional thermal head printing device is constructed as shown in FIG. Although this figure shows an example of an 8-dot thermal head with heating elements e1 to e8, an actual thermal head has a large number of heating elements, such as 256 dots or 384 dots. A black and white image per line is input as a serial signal to the pattern input IN, and the shift pulse S shifts the inside of the shift register SR from left to right in FIG. The black and white pattern is temporarily held at the position. It is transferred to latch memory M by latch signal LO and held until the next latch instruction is given to latch memory M. Then, at an appropriate timing until the next latch instruction, the strobe pulse P
When given, at that timing, electricity is applied from the power supply +E to the heat generating element located at the black pattern position among the heat generating elements e1 to e8, via the gates G1 to G8 and the amplifiers A1 to A8, according to the contents of the latch memory M. The area in contact with the driven heating element changes color to black due to the thermal properties of the thermal paper, recording a black image.

In those using a thermal transfer ribbon, a black image is recorded by thermally transferring ink from the thermal transfer ribbon onto plain paper using heat from a heating element. FIG. 5 shows the relationship between pattern input IN, strobe pulse P, and latch signal LO. Here, as shown in FIG. 5(a), the Nth line and the (N+
In the example of the 1)th line, L1 represents the serial signal period for one line, and W1 represents the pulse width of the strobe pulse P that defines the energization period to the heating element.

0004

As described above, when the number of black images per line is large, the number of elements that are energized and heated at one time increases, and the load on the power supply +E increases. If the regulation of the power supply +E is poor, the voltage will drop as the load increases. Additionally, as the load current increases, the voltage drop due to the electrical resistance of the wiring to the heat generating element increases, causing the effective voltage actually applied to the heat generating element to drop, resulting in a problem with the recording of a black image becoming fainter. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal head printing device that can prevent black images from being recorded too faintly.

[0006]

[Means for Solving the Problems] The thermal head type printing device of the present invention has each heating element of the thermal head.
It is configured to be driven only during a strobe pulse period based on black-and-white image data represented by a plurality of dots per line, and includes a counter unit that counts the number of black images in the black-and-white image data for each line, and a count value of the counter unit. The present invention is characterized in that it is provided with a voltage changing unit that drives the heating element with a higher driving voltage as the heating element is larger.

[0007]

[Function] According to this configuration, the larger the number of black images per line, the higher the voltage for driving the heating element. In other words, the driving voltage is increased to compensate for the increase in the number of heat generating elements that are energized at once, so that the effective voltage applied to the heat generating elements does not decrease and the input energy does not decrease.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. It should be noted that the same reference numerals are given to the parts having the same functions as those shown in FIGS. 4 and 5 showing the conventional example.

The thermal head type printing device of the present invention is constructed as shown in FIG. The drive voltage VT applied to the thermal head 1, which is composed of a large number of heat generating elements, a shift register SR necessary to drive the heat generating elements, a latch memory M, a gate, and an amplifier, is generated from the voltage changing section 2. There is.

[0010] A power supply +E is connected to the input side of the voltage changing unit 2, and if its output voltage is V0, the driving voltage VT generated at the output side of the voltage changing unit 2 is as shown in FIG. , the count value CNT of a counter section 3 that counts the number of black images in the black and white image data for each line of the pattern input IN is controlled to increase as the number of black images increases.

Specifically, as shown in FIG. 3(a),
The number of black images in the Nth line, where the number of black images is small, is counted by the counter unit 3, and the counted value CNT for one line is temporarily stored in the latch 4 by the latch signal LO shown in FIG. 3(c). The voltage changing section 2 is held by the latch 4.
The level V1 shown in (d) of FIG.
is applied from the voltage changing section 2 to the heat generating element of the thermal head 1. The heating element at the position corresponding to the black image of the thermal head 1 is driven by the drive voltage VT at level V1 over a period of pulse width W1 shown in FIG. 3(c). The contents of the counter section 3 are cleared for counting the next line.

In the case of the (N+1)th line in which the number of black images is greater than the Nth line, the count CNT temporarily held in the latch 4 by the latch signal LO is large and is lower than the level V1. The drive voltage VT at the high level V2
is generated from the voltage changing unit 2, and even if the number of heating elements that are energized at once is large and the voltage drop due to the electrical resistance of the wiring to the heating elements increases by ΔV, here V2
= V1 + ΔV, so the effective voltage actually applied to the heat generating element must be driven with the same effective voltage value as the Nth line even on the (N+1)th line, which has many black images. is created, the Nth line and the (N+1)th line
Uniform recording density can be obtained with the line.

In the above embodiment, the case of black and white binary recording was explained as an example, but printing is performed by moving a head block composed of a thermal head and a thermal transfer ribbon relative to plain paper. In this type, it is possible to record in colors other than black by selecting the color of the thermal transfer ribbon, and the description of "number of black images" in the claims limits the color of recording to black. It's not a thing.

[0014]

As described above, according to the present invention, there is provided a counter section that counts the number of black images in monochrome image data for each line, and a heating element is driven with a higher drive voltage as the count value of the counter section is larger. As a result, the effective voltage value applied to the heat generating elements can be compensated to a constant value regardless of the number of heat generating elements that are energized at once. This eliminates the drop in recording density that occurs when the voltage drop due to electrical resistance increases and the effective voltage actually applied to the heat generating elements decreases, making it possible to achieve uniform energization regardless of the number of heat generating elements that are energized at once. Recording density can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a thermal head type printing device of the present invention.

FIG. 2 is a characteristic diagram of a voltage changing section of the device.

FIG. 3 is a waveform diagram showing the relationship between one line image data input to the device and the output voltage of a voltage changing section.

FIG. 4 is a configuration diagram of a conventional thermal head printing device.

FIG. 5 is a waveform diagram showing the relationship between conventional one-line image data and strobe pulses.

[Explanation of symbols]

e1 to e8 Heat generating element IN pattern input S
Shift pulse SR Shift register LO Latch signal M Latch memory +E
Power supply P Strobe pulse 1
Thermal head 2
Voltage change unit 3 Counter unit 4 Latch V1 Output voltage value V2 of voltage change unit 2 for lines with few black images Output voltage value of voltage change unit 2 for lines with many black images

Claims (1)

[Claims] 1. Each heating element of the thermal head is configured to be driven for a strobe pulse period based on black-and-white image data represented by a plurality of dots per line, and the number of black images in the black-and-white image data for each line is determined. A thermal head type printing device that is provided with a counter section that counts the number of digits, and a voltage change section that drives the heat generating element with a higher drive voltage as the count value of the counter section becomes larger.