JPS62256667A - Corrective circuit for thermal head driving circuit - Google Patents

Abstract

PURPOSE:To enable a simpler thermal head driving circuit and precise correction, by correcting driving pulses outputted from a shift register, based on correction data stored in a correction data memory. CONSTITUTION:An AND circuit 12 is supplied with correction data from a comparator 10 and with basic driving data from a latch circuit, and outputs an H signal only when both of the data are H signals. Head elements TH-1-TH-240 are connected respectively to output terminals of the AND circuits 12. The AND circuits 12 output driving pulses obtained by combining the basic driving data with correction driving data, to the head elements TH-1-TH-240. Each of the driving pulses has an increment or decrement accord ing to a correction quantity, and nonuniformity of color density due to the deviations in resistance can be obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a correction circuit for accurate color reproduction in a thermal head drive circuit of a gradation color printer or the like.

[Summary of the Invention] The present invention provides a thermal head drive circuit in which the drive pulses of each of a plurality of head elements are shifted to a shift register (FF5), and the head elements are driven based on the drive pulses of the shift register. The thermal head drive circuit is simplified by providing a correction data memory that corresponds to variations in the resistance values of each of the head elements and correcting the drive pulses output from the shift register based on the correction data in the correction data memory. It is possible to make precise corrections.

[Prior Art] For example, in a gradation color printer having a thermal head, in order to obtain color density depending on the drive time of the thermal head, a pulse width modulation signal (PWM signal) according to gradation information is used.
A drive control circuit is known that drives a thermal head in response to an image (Japanese Unexamined Patent Publication No. 115280/1983).

A conventional thermal head drive circuit that drives a thermal head using such a PWM signal, as shown in FIG.
The drive data corresponding to -240 is sent to the shift register 6. This shift register 6 has all the head elements TI.
-1-TH-240 drive data is sent, a strobe signal is sent from the counter 16 to the latch circuit 7, the latch circuit 7 latches the drive pulse of the shift register 6, and based on the drive data, each head element TI (-1-
T) I-240 is driven.

Various correction circuits are used in such thermal head drive circuits to ensure accurate color reproduction. For example, this is correction for compensating for the resistance value deviation of the head elements TH-1-TH-240, substrate temperature correction, or heat generating pixel number correction.

Conventionally, for example, a correction circuit was provided in the head control section 15 to correct the data itself before being sent to the shift register 6.

[Problems to be Solved by the Invention] However, in the above-mentioned means, since a drive pulse is created by superimposing correction data on basic drive data and this drive pulse is sent to the shift register 6, the head control section 15 configuration becomes complicated. Therefore, the thermal head drive circuit becomes complicated, and a high shift clock frequency is required during signal processing, which limits correction and prevents accurate correction.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a correction circuit for a thermal head driving circuit that can simplify the thermal head driving circuit and perform precise correction.

[Means for Solving the Problems] Therefore, the configuration of the present invention for achieving the above object includes a plurality of head elements and a shift register that stores drive pulses for each of the head elements. , in a thermal head drive circuit in which the head element is driven based on the drive pulse stored in the shift register, a correction data memory is provided in which correction data corresponding to the resistance value deviation of each of the head elements is stored; The present invention is characterized in that the drive pulse output from the shift register is corrected based on the correction data in the correction data memory.

[Operations] Therefore, since correction data is added to the basic drive data while it is being output from the shift register to the head element, the drive circuit does not become complicated and high precision can be achieved without using very high shift clock pulses. Can be corrected. Furthermore, by providing the correction data memory integrally with the head, head conversion becomes extremely simple.

[Example] Embodiments of the present invention will be described below based on the drawings.

It is described as a 240-dot horizontal print screen capable of producing 16 gradations.

The pulse generator l outputs a shift clock pulse from an output terminal a, and outputs a correction clock pulse from an output terminal a.

The address counter 2 is supplied with shift clock pulses from the pulse generator 1, outputs an address signal for reading out the gray scale data stored in the line memory 3, and sends a carry signal to the gray scale counter 4 every 240 counts. Output to.

The line memory 3 stores gradation data for one vertical line (1 dot = 4 bits), and gradation data from the 1st dot to the 240th dot is stored in accordance with the address signal from the address counter 2. Image data (4 bits) is sequentially output to the comparator 5 in parallel.

In order to compare the image data from the 1st dot to the 240th dot, the gradation counter 4 sequentially converts the 4-bit reference gradation for each gradation from the 1st to the 16th gradation to a comparator 5. compares the gradation data from the line memory 3 with the reference gradation from the gradation counter 4, and outputs an H signal when the gradation data is greater than or equal to the reference gradation; When it is small, the L signal is output to the shift register 6 as basic drive data.

The soft register 6 includes head elements TH-1 to TH-24.
It has a storage capacity capable of storing each drive data of 0, and stores the drive data sent from the comparator 5 at a predetermined location using the not clock pulse of the pulse generator 1.

In this embodiment, 240 head elements T11-1-TH-240 are arranged in parallel, corresponding to 256 vertical dots.

The latch circuit 7 latches the storage state of the soft register 6 when the strobe signal is input manually, and this state is output to the correction circuit 8 described below. Furthermore, when the next strobe signal is input, the next storage state is latched. The strobe signal is sent to the shift register 6 through 240 H signals and L signals.
A signal is generated from the address counter 2 every time a signal is input.

As shown in detail in FIG. 2, the correction circuit 8 includes a correction data memory 9 for each head element TH-1-TI-240.
The correction data memory 9 is composed of a RAM and stores correction data based on the resistance value deviation of each head element Tl1-1-TH-240, and has a storage capacity of 3 bits to perform correction in 8 ranks. The ranks are divided. This correction data is input by measuring the resistance value of each head element T11-1 to T11-240 before shipment from the factory or at the time of replacing the thermal head. The correction data in the correction data memory 9 is output to each comparator 10, respectively.

The counter 11 operates according to the correction clock of the pulse generator 1 and outputs 8 ranks of correction comparison data to all the comparators 10. The minimum correction time width can be varied by changing the frequency of this correction clock, and temperature correction and head element number correction can be performed by varying this frequency. This counter 11 is reset by the carry signal (ie, strobe signal) of the address counter 2.

The comparator 10 compares the correction data from the correction data memory 9 with the correction comparison data from the counter 11, and outputs an H signal to the AND circuit 12 when the correction comparison data is large.

The AND circuit 12 inputs the correction data from the comparator 10 and the basic drive data from the latch circuit 7, and outputs an H signal only when both data are H signals. Each head element TH-1 is connected to the output terminal of
-TH-240 is connected.

The operation of the above configuration will be explained below.

Line memory 3 is read by address counter 2.
The gradation data of each dot is sequentially sent to the comparator 5 from the 1st dot to the 240th dot.

The comparator 5 compares this gradation data with the reference gradation (1 gradation) from the gradation counter 4, and outputs basic drive data to the shift register 6 (for example, ■).

1.0.0. ...l, 0). When the drive data for all of the 240 vertical dot areas is stored in a predetermined position of the shift register 6, a strobe signal is input to the latch circuit 7.
The above memory state is manually input to the AND circuit 12 of the correction circuit 8. First, in response to the strobe signal, the comparator 5 moves to the comparison of the two gradation ports, the next drive data is inputted to the soft register 6, and the recorded state is inputted to the AND circuit 12 by the strobe signal in the same manner as above. Man-powered. Therefore, when the image data stored in the line memory 3 is of gradation level 4, the PWM signal shown in FIG. 3(a) is output to the AND circuit 12.

On the other hand, the comparator 10 compares the correction data in the correction data memory 9 with the correction comparison data in the counter 11 and outputs corrected drive data to the AND circuit 12 . Therefore, for example, if the correction data is of two ranks, a pulse signal as shown in FIG. 3(b) is output to the AND circuit 12.

The AND circuit 12 sends a drive pulse that is a combination of the basic drive data and the corrected drive data to the head element Ttl-1.
〜Ding H-240, and in the above example, in Figure 3 (c
) is applied to the head elements TH-1 to T1.
Output to 1-240. The drive pulse includes correction increments, eliminating unevenness in color density due to resistance value deviation.

In this embodiment, since the driving pulses are increments at predetermined intervals, the peak temperature due to heat generation is lowered and the lifespan of the head elements TH-1-TH and -240 is extended.

The correction data is for head element TI-1-TH-'240.
Since they are unique, it is very effective to form the shift register 6, latch circuit 7, and correction circuit 8 on the head substrate 13 as shown in FIG. Further, depending on the case, an AD conversion circuit etc. for measuring the resistance values of the head elements TH-1 to TH-240 may also be placed on the head substrate 13.

[Effects of the Invention] As described above, according to the present invention, since the drive pulse is corrected in the section where the drive pulse is output from the shift register to the head element, the drive circuit does not become complicated, and the high frequency This has the advantage that precise correction can be made without using shift clock pulses or the like.

Further, according to the present invention, since the correction circuit is built into the thermal head, there are advantages such as miniaturization of the printer and ease of design and manufacture.

[Brief explanation of drawings]

1 to 3 show embodiments of the present invention, FIG. 1 is a block diagram of a thermal head drive circuit, FIG. 2 is a block diagram of its correction circuit, and FIG. 3 is a block diagram of each part of the thermal head drive circuit. FIG. 4 is an output waveform diagram, and FIG. 4 is a block diagram of a conventional thermal head drive circuit. TH-1-TI-240... Head element, 6... Shift register, 9... Correction data memory.

Claims (1)

[Scope of Claims] The head element has a plurality of head elements and a shift register that stores drive pulses for each of the head elements, and the head element is driven based on the drive pulses stored in the shift register. In the thermal head drive circuit, a correction data memory is provided in which correction data corresponding to the resistance value of each of the head elements is stored, and the drive pulse output from the shift register is corrected based on the correction data of the correction data memory. A correction circuit for a thermal head drive circuit characterized by the following.