JPS62234954A - Thermal head driving system - Google Patents

Abstract

PURPOSE:To prevent heat accumulation of a thermal head and resultantly enable density-stable recording to be performed by dividing recording data of each single line into plural data per single dot, giving each of the data to a shift register while updating in accordance with a latch signal and adjusting the drive pulse width of the thermal head in accordance with the variation of a latch cycle. CONSTITUTION:Recording data of each single line is converted to a parallel data by a series/parallel conversion part 7, and this parallel data is divided into an initial data and an updated data at a data processing part 8 so that it may become plural data per single dot. After this, each divided data is converted to a serial data at a parallel/series conversion part 9, then is supplied to a thermal head drive circuit. At that time, a detection signal of a substrate temperature on a thermal head obtained by a temperature sensor 51 is read by a latch cycle selection part 10. As a result, a latch signal having a latch cycle T which enables the drive energy of each heating element on the thermal head to become constant is supplied to the thermal head drive circuit 11. Thus the effect of a heat accumulation of the thermal head can be eliminated by controlling the latch cycle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a thermal head in a thermal printer using a thermal type or a thermal transfer type.

In general, in thermal printers that use a heat-sensitive type or a thermal transfer type, a thermal head that has one line of dot-based heating elements distributed in the main scanning direction generates heat according to the recorded data for each line. While being driven, each line is sequentially recorded on the recording paper that is fed in the sub-scanning direction.

FIG. 2 shows an example of the configuration of a thermal head drive circuit. Here, the thermal head 1 in which heating elements H1 to H2O48 for one line are arranged is divided into eight blocks 81 to B.
The block 81 to B8 are time-divisionally driven for each line of recording data DATA.

That is, one line of binary recording data DATA sent serially is taken into the shift register 2 with a capacity of 2048 bits, and the register contents are held in the latch circuit 3 according to the latch signal LATCH. Then, each of the first to eighth strobe signals 5TBI~
5TB8 are sequentially activated to drive each block 81 to B8 in the thermal head 1 in a time-division manner via the driver 4.

The thermal head 1 has the problem of thermal effects in that as each heating element is repeatedly driven, the substrate gradually accumulates heat, thereby increasing the recording density and crushing the recording dots. Therefore, in order to always record with stable density without being affected by heat accumulation in the thermal head, it is necessary to detect the temperature of the substrate of the thermal head with a sensor and respond to the detected temperature as shown in Figure 3. It is necessary to adjust the energy applied to each heating element.

Conventionally, as a means of adjusting the energy applied to the heating element in a thermal head, the pulse width of the strobe signal STB is controlled to make the energization time of the heating element variable while keeping the applied voltage constant. If such a method is used, each strobe signal S will be
All pulse widths of TB1 to TB8 must be made variable, and the circuit configuration for this purpose has become complicated.

- The present invention has been made in consideration of the above points, and provides a thermal head drive method that allows easy adjustment of the drive pulse width of the thermal head, that is, the energization time of each heating element. It is.

In order to achieve this objective, the present invention provides each line of recording data to a shift register, holds the contents of the register in parallel in a latch circuit, and then thermally transfers the data via a driver according to the latch contents. When driving each heating element in the head, each line of recording data is
The data is divided into multiple pieces of data per dot, and each divided data is updated according to the latch signal and fed to the shift register, and the latch period at that time is varied to adjust the driving pulse width of the thermal head. I have to.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

For convenience of explanation, one block when time-divisionally driving the thermal head consists of two dots Di and D2.
For example, "1"' (black) for dot D1.
, when recording u Ou (white) on the dot D2, it is sufficient to divide the recording data into two, and the divided recording data is as shown in the table below.

The control timing according to the thermal head drive method according to the present invention will be explained below with reference to FIG. 4.

First, initial data 1 and 0 are transferred to bit positions in block 1 in the shift register corresponding to Di and D2, respectively. After that, the first latch signal LATCH-■ is output at a predetermined timing, and S1="
l”, S2="Opt". Here, each signal of SL and S2 corresponds to the dot D in one block of the thermal head.
This is a drive signal for each heating element for i and D2, and when it is 1'', it is driven to generate heat, and when it is 0'', it is not driven. The states of the SL and S2 signals change to the second latch signal LATCH- after T time.
It is held until ■ is issued. Also, the first latch signal L
After ATCH-■ is output, the second latch signal LATC
) (Before -■ is issued, the shift register has updated its contents, and the updated data 0, 0 according to the table above
The contents are as follows. Then latch signal LATC for tube 2
H-■ is issued, and S1=“O” and S2=“O”.

By performing such processing, the result is 81
The signal will have the same pulse width as the latch period T.

In that case, the S2 signal is of course off. What must be noted here is that when initial data 1.0 is transferred to block 1 of the shift register,
It is necessary to transfer the update data 0°0 in block 1 to block 2 next to it, and to transfer the initial data in block 2 to block 3 next to it. FIG. 5 shows the state of data transfer for each block in the shift register at this time. If such recording data is transferred, the data transfer can be carried out efficiently, and the loss of transfer time can be significantly reduced. At that time, while printing block 1, the corresponding strobe signal 5TB-1
only is active.

Therefore, according to the present invention, by making the period T of the latch signal LATCH variable, it becomes possible to easily adjust the energization time of the heating element in the thermal head. However, the period T of the latch signal LATCH requires at least the time required to update the data of all bits in the block. For example, the second
As shown in the figure, when a thermal head with a 2048-dot configuration is divided into eight blocks and time-division driving is performed, the shift clock CLK of the shift register is set to ZMFI.
z, Tm1n=0.128m5.

FIG. 1 shows a configuration example when the thermal head driving method according to the present invention is specifically implemented. Here, the substrate temperature in the thermal head 1 is detected by a temperature sensor 5, and the thermal head is driven according to the detected temperature. Temperature compensation is performed by controlling the energization time of the heating element during driving.

That is, each line of recording data that is sent serially is converted into parallel data in the serial-to-parallel converter 7 in the DATAti-CPU 6, and then initialized in the data processor 8 so that each dot has a plurality of pieces of data. The data is divided into data and update data, each divided data is converted into serial data in a parallel-to-serial converter 9, and then sequentially applied to the shift register of the thermal head drive circuit 11. At this time, the detection signal of the substrate temperature of the thermal head 1 by the temperature sensor 5 is read by the latch cycle selection unit 10 in the CPU 6, so that the drive energy of each heat generating element in the thermal head 1 becomes constant according to the substrate temperature at that time. A latch signal LATC having a predetermined period T is generated by selecting a latch period T.
H is applied to the latch circuit of the thermal head drive circuit 11. For example, when the latch period selection unit 10 is used, the latch period T is 0.8 ms when the substrate temperature of the thermal head 1 is normal.

T=0.4 ms... Latch signals with multiple periods T that correspond to high temperatures are prepared in advance, and a latch signal with an optimal period T is determined according to the output of the temperature sensor 5. The signal LATCH is selected.

As mentioned above, in the thermal head driving method according to the present invention, the driving pulse width of the thermal head can be easily adjusted by simply dividing the recording data and changing the period of the latch signal. This makes it possible to control the pulse width of each block using multiple strobe signals when time-divisionally driving the thermal head, regardless of the number of times the thermal head is time-divisionally driven. This has the excellent advantage that temperature compensation for eliminating the influence of heat accumulation in the thermal head can be easily performed simply by controlling the latch period.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a configuration example for concretely implementing the thermal head drive method according to the present invention, FIG. 2 is an electric circuit diagram showing a general configuration example of a thermal head drive circuit, and FIG. A diagram showing the characteristics of applied energy with respect to substrate temperature in a thermal head, FIG. 4 is a time chart showing each timing of latch signal 2-divided data and drive pulse signal when the present invention is applied, and FIG. FIG. 3 is a diagram showing a data transfer state for each block.

Claims (1)

[Claims] When giving each line of recording data to a shift register, holding the register contents in parallel in a latch circuit, and driving each heating element in the thermal head via a driver according to the latch contents. , each line of recording data is divided into multiple pieces of data per dot, each divided data is updated in accordance with a latch signal and fed to a shift register, and the latch cycle at that time is made variable. A thermal head drive method that adjusts the thermal head drive pulse width.