JPH07237311A - Thermal head - Google Patents

Abstract

PURPOSE:To obtain a thermal head capable of performing correction of a density for every drive circuit. CONSTITUTION:Density correction data for every drive circuit 10 is added to printing data S1 and inputted to shift registers SR0A, SR0B. The density correction data inputted in the shift registers SR0A, SR0B is stored in latch circuits L0A, L0B on a latch signal LAT. The density correction data is inputted to a selection circuit 11, in which one signal is selected out of printing time control signal inversion CNT1-CNT4. The selected printing time control signal is outputted to gate elements G1-G64.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head for performing thermal recording on a recording medium such as thermal paper.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing an electrical configuration of an example of a conventional thermal head. This thermal head is composed of a large number of heating resistors R1 to R1728 and a plurality of drive circuits 2, etc.
4 blocks B1 connected to one drive circuit 2
The printing operation is performed by being classified into B4.

FIG. 6 is a circuit diagram showing an example of the drive circuit 2 shown in FIG. This drive circuit receives the print data SI consisting of serial data from the external clock signal CLK.
Shift register SR1 for converting into parallel data for each predetermined number of bits and outputting by converting the data in synchronization with
~ SR64 and external latch signal LAT
A plurality of latch circuits L1 to L64 that store the outputs of the shift registers SR1 to SR64, and a plurality of gate elements G that open and close the outputs of the latch circuits L1 to L64 by the strobe signal STB and the print control signal BEO from the outside.
1 to G64 and a plurality of switching elements T1 to T64 for controlling the current flowing through the heating resistor by the outputs of the gate elements G1 to G64.

One end of a large number of heat generating resistors formed in the thermal head is connected to the drain elements of the switching elements T1 to T64, and the heat generating resistors R1 to R6.
The other end of 4 is commonly connected to the output side of the external current,
The ground side of the external power supply is connected to the terminal GND2 to which the sources of the switching elements T1 to T64 are commonly connected.

This operation will be described with reference to the timing chart shown in FIG. The print data DATA for 1728 pixels formed as one scanning line is input to the shift registers SR1 to SR64 of each drive circuit 2 in synchronization with the clock signal CLK and transferred, and the print data for 64 pixels in each drive circuit 2 is transferred. The signals DATA are each converted into parallel data.

Next, the latch signal LAT is inverted, and the outputs of the shift registers SR1 to SR64 of the drive circuit 2 are stored in the respective latch circuits L1 to L64.

Next, when the print control signal BEO is inverted to the low level and the strobe signal inversion STB1 is inverted to the low level, each gate of the seven drive circuits 2 corresponding to the block B1 composed of the heating resistors R1 to R448. Element G1
When G64 is opened, each switching element T1 is opened based on the print signal DATA stored in each latch circuit L1 to L64.
~ T64 is selectively turned on. Then, an electric current selectively flows through the heating resistors R1 to R448 to generate heat, heat the thermal paper or the ink ribbon, and perform the printing operation of about 1/4 of one scanning line corresponding to the block B1.

Similarly, when the strobe signal inversion STB2 is inverted to the low level, the heating resistors R499 to R83 are similarly generated.
A current selectively flows to 2 to generate heat, and a printing operation is performed on about 1/4 of one scanning line corresponding to the block B2.
When the strobe signal inversion STB3 is further inverted to a low level, a current selectively flows through the heating resistors R833 to R1280 to generate heat, and a printing operation is performed on about a quarter of one scanning line corresponding to the block B3. When the strobe signal inversion STB4 is further inverted to a low level, a current flows selectively through the heating resistors R1281 to R1728 to generate heat, and the printing operation is performed on about 1/4 of one scanning line corresponding to the block B4. In this way, a series of images are stored by repeating the above-described operation while printing one scanning line and carrying the thermal paper or the ink ribbon stepwise.

The thermal head disclosed in Japanese Patent Laid-Open No. 3-227259 performs divided printing for each block. Since this thermal head can change the pulse width of the strobe signal in block units, it is possible to control the energization time of the heating resistor in block units.
Therefore, it is possible to correct the print density unevenness of the heating resistor for each block unit.

[0010]

However, when printing is performed by driving the thermal head as described above,
Due to variations in the characteristics of the drive switching element of the heating resistor in each drive circuit, variations in wiring resistance, etc.
There is a problem that the print density becomes non-uniform for each drive circuit as shown in FIG. In FIG. 8, it is shown that the densities differ depending on the number of diagonal lines. Therefore, it is not possible to obtain a thermal head with high print quality.

An object of the present invention is to provide a thermal head capable of density correction for each drive circuit.

[0012]

SUMMARY OF THE INVENTION According to the present invention, a plurality of heating resistors that form a printing pixel, a plurality of switching elements that control the current flowing through each heating resistor, and a plurality of gate elements that drive each switching element. And a plurality of drive circuits each having a shift register for inputting print data composed of serial data in synchronization with a clock signal and converting the parallel data to output to each gate element. A storage unit for storing print density correction data interposed in the data, and a print time control signal is selected from a plurality of print time control signals having different pulse widths based on the print density correction data stored in the storage unit. And a selection means for outputting the result to the gate element.

[0013]

According to the present invention, the storage means stores the print density correction data for each drive circuit interposed in the print data. The selection means selects a printing period control signal from a plurality of printing time control signals having different pulse widths based on the printing density correction data stored in the storage means, and outputs it to the gate element. Therefore, the printing time can be controlled for each drive circuit. As a result, it is possible to obtain a thermal head capable of performing density correction for each drive circuit.

[0014]

1 is a circuit diagram showing the electrical construction of a thermal head according to an embodiment of the present invention. This thermal head is composed of a large number of heating resistors R1 to R1728 and a plurality of drive circuits 10 and the like. In FIG.
Four heating resistors are connected to one drive circuit 10, and further divided into four blocks B1 to B4 to perform a printing operation.

Strobe signal inversions STB1 to STB4 for controlling the energization time for each block are input to the drive circuits 10 of the blocks B1 to B4, respectively. Print data SI, print control signal BEO, latch signal inversion LAT,
Clock signal CLK, printing time control signal CNT1 to CNT for controlling energization time for each drive circuit
4 is input to each drive circuit 10.

FIG. 2 is a circuit diagram showing an example of the drive circuit 10. The drive circuit 10 transfers print data SI composed of serial data in synchronization with an external clock signal CLK to convert parallel data at predetermined bits and outputs the shift registers SR1 to SR6.
4, a plurality of latch circuits L1 to L64 that store the outputs of the shift registers SR1 to SR64 in response to a latch signal LAT from the outside, and a strobe signal ST from the outside.
B, a plurality of gate elements G1 to G64 for opening and closing the outputs of the latch circuits L1 to L64 by the print control signal BEO and the output of the selection circuit 11, and the gate elements G1 to G64.
It is composed of a plurality of switching elements T1 to T64, etc., which control the current flowing through the heating resistor by the output of.

Further, shift registers SR0A and SR0B are connected in series to the shift registers SR1 to SR64, and latch circuits L0A and L0 are connected to the latch circuits L1 to L64.
0B is connected in parallel. External latch signal LAT
The latch circuits L0A and L0B store the outputs of the shift registers SR0A and SR0B. Latch circuit L0
The outputs of A and L0B and the printing time control signals CNT1 to CNT4 are input to the selection circuit 11, and the printing time control signals selected by the selection circuit 11 are gate elements G1 to G64.
Is output to.

The density correction data for each drive circuit 10 is added to the print data SI and is added to the shift registers SR0A, SR.
Input to 0B. Shift registers SR0A, SR0B
The density correction data input to the latch signal is the latch signal LAT described above.
Are stored by the latch circuits L0A and L0B. This density correction data is input to the selection circuit 11,
One signal is selected from among the print time control signal inversion CNT1 to inversion CNT4.

A circuit diagram of the selection circuit 11 is shown in FIG. The print time control signal CNT is inverted by the combination of the levels of the density correction data stored in the latch circuits L0A and L0B.
1 to inverted CNT4 are selected. When the density correction data stored in the latch circuit L0A is low level, the latch circuit L0
When the density correction data stored in B is at the low level, the printing time control signal inversion CNT1 is selected and the gate element G1 is passed through the AND gate element 21 and the OR gate element 25.
Is output to G64. When the density correction data stored in the latch circuit L0A is high level and the density correction data stored in the latch circuit L0B is low level, the printing time control signal inversion CNT2 is selected and the AND gate element 2 is selected.
2, through the OR gate element 25, the gate elements G1 to G
To 64. When the density correction data stored in the latch circuit L0A is low level and the density correction data stored in the latch circuit L0B is high level, the printing time control signal inversion CNT3 is selected and the AND gate elements 23, O
It is output to the gate elements G1 to G64 via the R gate element 25. When the density correction data stored in the latch circuit L0A is high level and the density correction data stored in the latch circuit L0B is high level, the printing time control signal inversion C
NT4 is selected and output to the gate elements G1 to G64 via the AND gate element 24 and the OR gate element 25.

The operation of the circuit shown in FIG. 2 will be described with reference to the timing chart shown in FIG.
The print data DATA for 1728 pixels formed as one scanning line is input to the shift registers SR1 to SR64 of each drive circuit 10 in synchronization with the clock signal CLK, and at the same time, 2 bits added to the print data of each drive circuit. Of the density correction data of the shift register SR0 of each drive circuit 10.
A, SR0B are input and transferred. Each drive circuit 10
In, the print data for 64 pixels and the 2-bit density correction data are converted into parallel data. Next, the latch circuit LAT is inverted, and the outputs of the shift registers SR1 to SR64, SR0A and SR0B of the drive circuit 9 are stored in the respective latch circuits L1 to L64, L0A and L0B. Next, the print control signal BEO is inverted to the low level,
The strobe signal inversion STB1 is inverted to low level.
At the same time, the printing time control signal CNT1 to CNT4 inverted
Is selected on the basis of the density correction data stored in the latch circuits L0A and L0B as described above, is output to the gate elements G1 to G64, and the gate elements G1 to G64 are opened. Printing time control signal inversion CNT1 to inversion CNT4
As shown in FIG. 4, the pulse width of the active state (low level) is different while the strobe signal STB1 is in the active state (low level). Therefore, the density correction data is set to a predetermined value for each drive circuit in advance, and a printing time control signal having a predetermined pulse width is selected and output to the gate elements G1 to G64, thereby generating a heating resistor for each drive circuit. The printing time can be controlled. That is, the print density of each drive circuit 10 can be controlled to a desired value.

In this way, the heating resistors R1 to R44 are provided.
Seven drive circuits 10 corresponding to the block B1 composed of eight
The respective gate elements G1 to G64 are opened and the respective latch circuits L1
.. to L64, the switching elements T1 to T64 are selectively turned on based on the print signal DATA stored in the. Then, a current selectively flows through the heating resistors R1 to R448 to generate heat, heat the thermal paper or the ink ribbon, and perform the printing operation of about 1/4 portion of one scanning line corresponding to the block B1.

Similarly, strobe signal inversion STB2
When is turned to low level, the heating resistors R499 to R
A current selectively flows through 832 to generate heat, and a printing operation is performed on about a quarter of one scanning line corresponding to the block B2.
When the strobe signal inversion STB3 is further inverted to a low level, a current selectively flows through the heating resistors R833 to R1280 to generate heat, and a printing operation is performed on about a quarter of one scanning line corresponding to the block B3. When the strobe signal STB4 is further inverted to the low level, the heating resistor R1
Current is selectively flowed to 281 to R1728 to generate heat, and the printing operation is performed on a portion of about 1/4 of one scanning line corresponding to the block B4. In this way, a series of images are stored by repeating the above-described operation while printing one scanning line and carrying the thermal paper or the ink ribbon stepwise.

As described above, by adding 2-bit density correction data to the print data for each drive circuit and transferring it to each drive circuit, the density correction for each drive circuit can be easily performed. In the present embodiment, 2-bit density correction data is added to select a predetermined signal from four types of printing time control signals, but the present invention is not limited to 2-bit density correction data. For example, 4-bit density correction data may be added to select a predetermined signal from 16 types of printing time control signals.

[0024]

As described above, according to the present invention, the printing time control is performed based on the printing density correction data for each drive circuit stored in the storage means from among the plurality of printing time control signals having different pulse widths. The signal is selected and output to the gate element. Therefore, the printing time can be controlled for each drive circuit. This allows density correction for each drive circuit,
It is possible to obtain a thermal head with high print quality.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an electrical configuration of a thermal head that is an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an electrical configuration of a drive circuit 10 shown in FIG.

FIG. 3 is a circuit diagram showing an electrical configuration of a selection circuit 11 shown in FIG.

FIG. 4 is a time chart when the drive circuit 10 is operated.

FIG. 5 is a circuit diagram showing an electrical configuration of a conventional thermal head.

6 is a circuit diagram showing an electrical configuration of a drive circuit 2 shown in FIG.

FIG. 7 is a time chart when the drive circuit 2 is operated.

FIG. 8 is a diagram showing a print density for each drive circuit 2 of the thermal head.

[Explanation of symbols]

10 drive circuit 11 selection circuit 21-24 AND gate element 25 OR gate element SR0A, SR0B SR1-SR64 shift register L0A, L0B, L1-L64 latch circuit G1-G64 gate element T1-T64 switching element

Claims (1)

[Claims] 1. A plurality of heating resistors forming a printing pixel, a plurality of switching elements for controlling a current flowing through each heating resistor, a plurality of gate elements for driving each switching element, and printing data composed of serial data. In a thermal head that has a plurality of drive circuits that have a shift register that inputs in synchronization with a clock signal, converts the data into parallel data, and outputs the data to each gate element, each drive circuit has a print density that is present in the print data. A storage unit for storing correction data and a selection for selecting a printing time control signal from a plurality of printing time control signals having different pulse widths based on the printing density correction data stored in the storage unit and outputting it to a gate element. And a thermal head.