JPS646956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a printing thermal head that reduces unevenness in printing density that occurs when the printing speed is slowed down or increased.

FIG. 3 shows a conventional printing thermal head.

A heating resistor 1 divided into blocks a, b, c, and d, a switching transistor 2 that controls the energization of the heating resistor 1, an AND circuit 3 that controls the operation of the switching transistor 2, and a serial record. Input the signal from terminal e and each
It has a shift register 4 that outputs a parallel signal to the AND circuit 3.

In the above configuration, for example, in order to prevent the power supply capacity from increasing, the number of black dots in one line is counted, and if the percentage is less than 25%, all dots (black) are driven at once, When the number of lines exceeds the limit, there is a system in which one line is divided into a predetermined number of lines and driven in a time-division manner. Figure 1 shows that when the proportion of black dots in one line is less than 25%, t ₂ = 2.2 m.
It shows that all dots are driven at a period of sec over a time period of t ₁ = 0.9 msec, and Fig. 1 shows that when the proportion of black dots in one line is 25% or more, one line is driven by a, b, c, Divide into 4 blocks of t ₄ each
This shows that the drive is time-divisionally driven over a period of t ₃ =1.1 msec with a cycle of =5.0 msec.

According to this thermal head for printing, since the drive mode is changed depending on the proportion of black dots, it is possible to prevent the power supply capacity from increasing even if the density of the thermal head is increased, and it is possible to speed up printing. In addition, in the case of time-division driving in which the cooling time of the heating resistor becomes longer depending on the off time, the driving time is increased, so that it is possible to prevent the concentration from decreasing.

However, with conventional printing thermal heads, the off time (t ₂ - _{t 1} ) during batch drive is much shorter than the off time (t ₄ - t ₃ ) during time-division drive, so black dots When switching from batch drive to time-division drive (Figure 2) due to an increase in the ratio of Printing unevenness may similarly occur when switching from drive to batch drive and increasing speed).

The present invention has been made in view of the above, and in order to prevent uneven print density from occurring when the print speed is slowed down or increased between batch drive and time-division drive, the drive immediately after switching is changed to the drive immediately before switching. The present invention provides a method for controlling a printing thermal head in which printing is performed in a driving time of .

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method and apparatus for a thermal head for printing according to the present invention will be explained in detail below.

One embodiment of the present invention during deceleration (the same can be considered during speed increase) is explained using the time charts of FIGS. 3 and 4, which are common to conventional thermal heads. When the ratio is less than 25%, when pulses with time period t 1 are simultaneously applied to terminals a, b, c, and d of AND circuit ₃ (period t ₂ ), the record converted from serial to parallel by shift register 4 A signal is applied to the base of transistor 2. The transistor 2 that receives the recording signal "1" is turned on, and the transistor 2 that receives the recording signal "0" remains off, and the heating resistor 1 connected to the transistor 2 that is turned on generates heat. next,
When the proportion of black dots reaches 25% or more, the time limit for batch driving is applied to terminals a, b, c, and d of AND circuit 3 in sequence.
Pulses of t ₁ are applied in time division (period t ₄ ). As a result, the heat generating resistors 1 of blocks a, b, c, and d generate heat in accordance with the recording signal. From the second cycle of time-division driving, the pulse of time t ₃ is sent to terminal a,
Blocks b, c, and d are time-divisionally input, and the heating resistor 1 is energized in the order of blocks a, b, c, and d according to the recording signal. Incidentally, apart from the embodiment, in the first cycle, only the drive time of blocks a and b may be set to _t1 , and the drive time of blocks c and d may be set to _t3 .

As explained above, according to the printing thermal head control method according to the present invention, when switching between batch drive and time-division drive, the drive immediately after the switch is performed during the drive time immediately before the switch, so that the printing speed due to the switch is It is possible to reduce unevenness in print density during deceleration or speed increase.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams showing drive modes of a conventional thermal head. FIG. 3 is an explanatory diagram showing one embodiment of the present invention. FIG. 4 is a time chart showing the operation in FIG. 3. Explanation of symbols, 1... Heat generating resistor, 2... Switching transistor, 3... AND circuit, 4...
shift register.

Claims (1)

[Scope of Claims] 1. A printing thermal head control method that sets the number of divisions of energization of a heating resistor group and the energization time of the heating resistors according to the proportion of black dots, comprising: switching the number of divisions; A method for controlling a printing thermal head, characterized in that the energizing time of the heating resistor immediately after is set equal to the energizing time immediately before switching the number of divisions.