JPS6024969A - Driving method of thermal head - Google Patents

Abstract

PURPOSE:To obtain a recording with uniform density regardless of data contents by a method wherein a conducting timing of each block to a thermal element is controled so as not to exceed the preset value by calculating numbers of black data in every block inputted to a shift register. CONSTITUTION:For example, in case of thermal elements which constitute one line are 8 groups, a block counter 2 counts up the number of thermal elements by every one block, and a count output B varies as 0-7. A count output C of black data divided by 1/m varies, for example, as 0-2. After an input of recording data DI by one line is finished, because a strobe changing over circuit 4 energizes a count B block included in every count of count output C, so strobe signals SB1-8 are successively produced at time intervals of 1-3. Accordingly, the number of thermal elements which are simultaneously energized is controled nearly as a constant (m) value.

Description

[Detailed Description of the Invention] Technical Field The present invention is suitable for driving a thermal head that has a large number of heating elements constituting a line, such as a direct drive thermal head, and is divided into a plurality of blocks and driven. The present invention relates to a method of driving a thermal head, and more particularly, to a method of driving a thermal head capable of recording a dot pattern of uniform density regardless of the content of recording data.

Conventional technology When performing thermal recording using a thermal head.

Even if the recording voltage is kept constant, the number of energized heating elements changes depending on the content of the recording data, so the effective voltage fluctuates and the recording density becomes non-uniform.

In other words, if the number of heating elements that are energized at the same time is different,
The overall current value changes, causing a difference in voltage drop due to electrodes, lead wires, internal resistance of the power supply, etc.

The voltage actually applied to each heating element will be different.

This phenomenon is more noticeable in the case of direct drive type thermal heads, which have a significantly larger number of heating elements that are energized at the same time than diode matrix type thermal heads.
Recorded image quality deteriorates.

The conventional method for solving such inconveniences is the first method.
One known method is to control the drive current of a heating element depending on the number of black dots recorded simultaneously.

This method is effective when the number of heating elements that are energized at the same time is relatively small, but when the number of heating elements increases, such as in a direct drive type thermal head, the range in which the black data changes also increases. Since it has to be driven at a current value of 1, and is also affected by ambient temperature, it is not always possible to record a uniform density.

Furthermore, as the conventional method a, a constant bit drive method using a thyristor type direct drive head is also known.

Although this driving method has the advantage of not being subject to matrix fullness, it is necessary to control the number of heating elements that are energized at the same time to a constant value, which complicates the control.

The driving method of this invention takes advantage of the advantages of a direct drive thermal head equipped with a shift register that divides thousands of heating elements into multiple blocks and conducts high-speed recording by energizing each block. Simple control enables recording of uniform density.

In the order of explanation, a direct drive type thermal head suitable for carrying out the driving method of the present invention will be described.

FIG. 1 is a schematic block diagram showing a configuration example of a drive circuit for a direct drive type thermal head. In the drawing, U/~lJn each indicate a thermal head consisting of 32 heating elements and a circuit for driving them, and DIA and DIR indicate serial input data and CK
A and CKn are shift clocks, LDA and LDB are load signals, iB/~SBg are strobe signals, ■an is written f
j, power supply, vDD and Vl! 8 and GND indicate power supplies of respective voltages.

The following FIG. 2 is a block diagram showing the detailed internal structure of the thermal head U/ in FIG.
// is a shift register with a 3.2-bit configuration, and U and 2/ are latch circuits with a similar 32-bit configuration.

U31 and Uda/ represent inverters, R/ to R3 represent heating elements, and other symbols are the same as in FIG. 1.

As shown in FIG. 2, the thermal head U/ has three or two heating elements R/~R, ? arranged in a straight line. A switching element such as a transistor is connected to each of these heating elements R/ to R3, and an AND gate circuit is connected to each of these switching elements.

The shift register U// has 32 shift registers corresponding to the number of heating elements.
It has a bit configuration, and the recorded data is input serially.
The signal is output in parallel to the latch circuits U and 2/, which also have a 32-bit configuration, and is loaded.

The AND gate circuit is controlled by the recorded data of this latch circuit Ul/, selectively drives the switching element, and energizes the heating elements R/ to R3.

In this way, the direct drive type thermal head is provided with the shift register U// and the latch circuit U//, so that the serial input of data to the shift register U// and the latch circuits U and 2/ are possible. The operation of energizing the heating element based on the latched data can be performed in parallel.

The direct drive type thermal head shown in Fig. 1 uses n thermal heads U/ shown in Fig. 2.
,? , 2Xn (dots) /line can be recorded. In Fig. 1, the thermal heads U/~Un are arranged in a zigzag pattern in order to clearly show the circuit configuration, but the respective heating elements are arranged in a straight line and arranged to record the minutes.

FIG. 3 is a time chart for explaining a method of driving the thermal head shown in FIG. 1. FIG. The code assigned to each No. 16 waveform corresponds to code position f'1' in FIG.

(O) @ Figure 3 shows one drawing in a simplified manner, but D
7 each for IA and D I B, and CKA and CKB.
The number of pulses is actually 32 pulses from 1)' to (
1q has been completed. In the case of DIA and DIR, black recording data is given as 17' and white data is given as 10', so when 32 pieces of black data are consecutive, 3.
If there are two pulses and there is white data between them, the pulse at that position will be 1L level and will not actually be a pulse.

Now, the 7947 minutes of recorded data that is serially input is alternately distributed to channels A and B every 3 bits, and as shown in DIA and DIB in FIG. 3, the input data DIA and DIB to the circuit shown in FIG. These input data DIA and DIR are
Thermal heads U, 2. are operated in synchronization with shift clocks CKA and CKB, respectively. and U/ shift register (U
/2 and U//) in the final state.

794 in the shift register of thermal head 1Jn-U/
It is stored as 7 minutes of data. For example, if the / line has a 72g bit configuration, the input data DIA and DIR
are each g611 bits, and these are stored in the shift register of each thermal head every 3 bits.

In this way, when the transfer of 7947 minutes of data is completed, the data stored in the shift register (U//~U/n) is transferred to the load signals σDA and τDB given at the timing of LDA and LDH in FIG. is transferred in parallel to the latch circuits (U, 2/ to U, 2n).

In this case, the thermal head U/~Un is divided into t blocks in advance, and as shown in FIG.
Strobe signal 8 shown only partially as /, SB-
It is dividedly driven at g timings of B/~SBg,
Each heating element It/-1'L (J2xn) is energized in a time-sharing manner according to the data latched in the latch circuit.

In addition, after the stored data is transferred in parallel to the latch circuit, the shift register transfers the data regardless of the energization of one heating element, that is, regardless of the on/off state of the strobe signals SB/~SBg. input becomes possible, and serial input of the next 7947 minutes of data begins.

In this way, with the direct drive type thermal head, the data of the next line can be serially input to the shift register while the heating element is being energized according to the recording data latched in the latch circuit, so high-speed recording is possible. It becomes possible.

As already explained, in the case of such a direct drive type thermal head, the recording power supply V in FIG.
Even if the HD voltage is kept constant, the effective voltage will drop in blocks with a large number of black dots.

There was an inconvenience that the concentration also became light.

Purpose Therefore, in the method for driving a thermal head of the present invention, the heating element is divided into a plurality of blocks in this way, and the thermal head is energized to the heating element of each block at the energization timing such as the strobe signal SB/~SBg. It is an object of the present invention to improve a head driving method so that recording with uniform density can be obtained regardless of the contents of recording data.

composition Therefore, in the driving method of the present invention.

Counting means for counting the number of black data among the recording data serially input to the shift register for each block, and storage means for storing the counted value.

block selection means for selecting one or more blocks so that the number of black data in the blocks simultaneously driven by the values stored in the storage means does not exceed a preset value; The timing of energizing the heating elements of each block is controlled by the output of the selection means.

FIG. 7 is a functional block diagram showing an example of a drive control circuit used when carrying out the thermal head drive method of the present invention. In the drawing, / is an outer counter, % is a block counter, %3 is a black dot counter, Hiroshi is a strobe switching circuit, CK is a tarok signal for shifting, DI is input recording data, and SB/~SBg are strobes. Signal B shows the count output of the block kalantaco.

Figure 1 shows a control circuit for controlling the number of heating elements that are energized at the same time so that it does not exceed a certain number m.
Strobe signals SB/-SBg are generated corresponding to the g blocks t-%7N, respectively.

The block counter tacho is a counter that counts the shift clock CK of the recording data DI input to a shift register (not shown). occurs.

Therefore, this count output B indicates the block number.

Also, //In counter/ is input recording data D
This counter counts the black data of I, and provides an output to the black dot counter 3 every time a preset m pieces of black data are counted.

Therefore, the black dot counter 3 counts a multiple of the number m of black dots, and its count output C represents the count value of //m of the actual number of black dots.

FIG. 3 is a time chart for explaining the control operation by the control circuit of FIG. 7. The symbols assigned to each signal waveform correspond to the symbol positions in Figure 1, and A indicates a capture signal for capturing count outputs B and C within the strobe switching circuit.

For example, if the heating elements constituting the / line are divided into g groups, the block kalantco will be counted up every time data input corresponding to seven blocks is completed, and the count output B will be 10'~' Changes to 7″.

In addition, the count output of black data divided by //m is
In the case of FIG. 3, it changes from '0'' to '''λ'.

The strobe switching circuit takes in count outputs B and C in response to the take-in signal A, and stores each block and the previous black data value in the storage means.

In the case of Figure 3, Count output B　θ/,! 3 geta 67 Count output CθOθ//l/yu is stored in the storage means in the strobe switching circuit l.

The strobe switching circuit has 7942 minutes of recorded data DI.
When the input of is completed, first, the count output C passes through the block of 1θ', that is, 01 to w, 2# at the same time.
1, a strobe signal SB/~8133 is generated four times in a time interval/.

Next, count output C is /' block, that is '3
' to 16' at the same time.

A slobe signal is generated over a time period.

Finally, count output C is 1″ block, i.e. 1
In order to energize the block 7', use the strobe buoy 11.
The signal S B g is generated over a time interval 3.

By driving in this manner, the number of heating elements that are energized at the same time can be controlled to be approximately constant m, and recording with uniform density can be obtained.

Effects Therefore, the thermal head of the present invention has an effect of +17
According to this method, regardless of the content of the recorded data, it is possible to simultaneously energize the M emitters not exceeding a certain number m, and the recording density can be kept constant.

Furthermore, in the case of Fig. S, the energizing operation of the / line ends at the rising edge of strobe buoy No. 1 SRg.

Speed-up is also achieved for images with a low black percentage.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an example of the configuration of a drive circuit for a direct drive type thermal head, FIG. FIG. 3 is a time chart for explaining the method of driving the thermal head shown in FIG. Block diagram.
i1 It is timed to explain uJ's work. In the drawings, / indicates a 4-bow square counter 1.2 indicates a block counter, 3 indicates a black dot counter, and % indicates a strobe switching circuit. Patent applicant Rico Co., Ltd. −

Claims (1)

[Claims] A heating element divided into a plurality of blocks. A shift register into which recorded data is serially input,
Driving a line-type thermal head that is equipped with a latch circuit to which the record data of this shift register is transferred in parallel, and a means for controlling energization of the heat generating elements in units of blocks according to the record data latched in this latch circuit. In the circuit, a counting means for counting the number of black data among the recording data serially input to the shift register for each block, and a storage means for storing the counted value;
block selection means for selecting seven or more blocks so that the number of black data in the blocks simultaneously driven by the values stored in the storage means does not exceed a preset value; A driving method characterized in that the timing of energizing the heating elements of each block is controlled by the output of the selection means.