JPH0252759A - Driver for thermal head - Google Patents

Abstract

PURPOSE:To control pulse width without depending upon an external controller, and to control gradation pulse width accurately by simple circuit constitution by installing a strobe pulse-width control section controlling the pulse width of a strobe signal and obtaining the output of pulse with from a first composite counter while correcting and controlling pulse width by a second composite counter. CONSTITUTION:A controller 6A transfers a picture data in the direction of a first bit when a clock and the picture data are input to a shift register 4, and fixes the picture data by a latch 3. A strobe signal is output, and a heating resistor 2 is heat-generated. Printing to thermosensible paper, etc. is conducted by the heat generation while the temperature of thermal head itself is changed. The temperature change is input to a strobe pulse-width control section 9, and input to an AND gate 5 in a thermal head. Consequently, each heating resistor 2 generates heat for the time corresponding to pulse width, and a picture is printed out to thermosensible paper at gradations corresponding to the heat generation temperature. The gradations are controlled optimally in response to a temperature on a substrate 10 by the stroke pulse-width control section 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head driver used in image output devices such as facsimiles and printers.

[Conventional technology]

FIG. 5 is a block connection diagram showing part of a conventional thermal head driver announced at the 4th Non-Impact Printing Technology Symposium (held on July 23 and 24, 1987). ~21. is a flip-flop 2 constituting an 8-bit composite counter 22;
3 is an 8-bit image signal (26 gradation signals) input from the outside according to the mode signal and each flip-flop 2.
1□～21. and the inverted output of output terminal Q.

The flip-flops 211-21. The eight data selectors 24 input to each input terminal switch between the main clock from the clock controller and the output of the output terminal Q of the flip-flops 21□ to 21 in the previous stage according to the mode signal. Flip-flops 211-21.
This is a clock selector that inputs to the input terminal GK of.

Further, FIG. 6 is a block connection diagram showing the overall configuration of the thermal head driver. According to this, 64 sets of the composite counters 22 are provided.

On the output side of each compound counter 22 there is a zero detector 25. a clock controller 26 controlled by this zero detector 25;
A buffer 27 which receives the output of the zero detector 25 and the mode clock and obtains a driver output is connected as shown in the figure.

Next, the operation will be explained.

This thermal head driver operates as follows by switching the mode signal.

First, when operating in the shift mode, the composite counter 22 is connected to the flip-flops 21□~
21. It functions as an 8-bit parallel shift register and transfers gradation information as image information from the outside by
Transfer bits in parallel.

On the other hand, in the count mode, each flip-flop 211
Since the output of the output terminal Q of ~21° is input to each clock input terminal CK of the next stage, the composite counter 22 has a
The input gradation information loaded at this time operates as a down counter for each flip-flop 211 to 21.
．． held within.

In addition, in FIG. 6, in the count mode, if the input gradation information loaded from the outside is not zero, the zero detector 25 drives the buffer 27, and passes the clock controller 26 through which the clock signal is composited. The counter 22 is set to a state where it can be applied. Then, the composite counter 22 counts down by the number of input gradation information, and when its output becomes zero, the zero detector 25 stops applying the drive output to the buffer 27 and the clock signal from the clock controller 26. . Therefore, the drive output with a pulse width proportional to the input gradation information, which is image information, is
It is obtained for each pixel corresponding to each composite counter 22.

However, since the conventional thermal head driver is configured as described above, it has the ability to accurately control pulse width and is capable of recording images with as many as 256 gradations.
Deterioration of image quality due to variations in the resistance value of the heating resistor is unavoidable, and multi-gradation recording with sufficiently high precision cannot yet be achieved.

On the other hand, in response to this, a method has been proposed in which the image quality deterioration caused by variations in the resistance value of the resistor is solved by pulse width control using a strobe signal.

To explain this, FIG. 7 is a circuit diagram showing a conventional thermal head driver shown, for example, in the thermal head N series manufactured by Mitsubishi Electric Corporation. 2 is a plurality of heating resistors provided on the substrate 10 corresponding to each pixel;
4 is a shift register that transfers image data every clock, 3 is a latch that temporarily holds the image data transferred from this shift register 4, and 5 is the output of latch 3.

6 is a controller that outputs the above-mentioned image data, clock, latch signal and strobe signal; 12 is a plurality of strobe signal input terminals, and 13 is a latch signal input terminal.

14 is an image data input terminal, and 15 is a clock input terminal, which are provided on the substrate 10 and connected to the controller 6, which is an external circuit.

Next, the operation will be explained. First, the controller 6 outputs the clock and image data shown in FIG. 8 to the substrate 10 of the thermal head. Image data input from the controller 6 is transferred within the shift register 4 in synchronization with a clock. thus.

After outputting a predetermined number of clocks and image data, the controller 6 stops outputting these clocks and image data, and then outputs a latch signal. The switch 3 receives this latch signal, fixes the image data in the shift register 4, and then inputs the image data to the AND gate 5 together with a strobe signal that controls the time for energizing the first heating resistor 2. The heating resistor 2 is energized during the above period, and the heating resistor 2 generates heat. At this time, the temperature of the substrate 10 on which the heat generating resistor 2 is installed changes, and the resistance value of the heat sensitive resistance element 1 changes. This change is output to the external controller 6 as the temperature of the thermal head. Upon receiving this output, the controller 6 controls the pulse width of the strobe signal.

[Problem to be solved by the invention]

Since the conventional thermal head driver is configured as described above, the controller 6 provided outside the substrate 10 is used to control the pulse width of the strobe signal according to the resistance value of the heat-sensitive resistance element 1. Therefore, the internal circuit of the controller 6 becomes complicated, the entire system becomes expensive, and the applications of the controller 6 are limited.

The invention according to the first claim has been made to solve the above-mentioned problems, and it is possible to monitor the resistance value of the heat-sensitive resistance element and control the pulse width of the strobe signal without using an external controller. The objective is to obtain a thermal head driver that can.

Further, the invention according to the second claim allows accurate gradation pulse width control with a simple circuit configuration.

The present invention aims to provide a thermal head driver that can realize highly accurate multi-gradation recording by correcting variations in the resistance value of heating resistors.

[Means to solve the problem]

The thermal head driver according to the first aspect of the invention includes a strobe pulse width control section that controls the pulse width of the strobe signal according to the output of the heat-sensitive resistance element on the substrate.
This is provided on the above substrate.

Further, the thermal head driver according to the invention of the second claim obtains an output with a pulse width corresponding to the number of input gradation information from the first composite counter, and also corrects variations in the resistance value of one heating resistor. , the pulse width is corrected and controlled by the second composite counter based on the resistance value data in the memory.

[Effect]

The strobe pulse width control section in the invention of the first claim operates to control the pulse width of the strobe signal in the substrate on which the one heating resistor is located according to a change in the resistance value of the heat-sensitive resistance element. .

Further, the second composite counter for correcting variations in resistance values in the invention of the second claim reads in advance data larger than the maximum number of gradations, and adjusts the number of data according to the resistance value data in the memory. By reading blankly,
Adjust the applied pulse width.

[Embodiments of the invention]

An embodiment of the invention according to the first claim will be described below with reference to the drawings. In FIG. 1, 1 is one or more heat-sensitive resistance elements attached to the substrate 10 of the thermal head, 2 is a heating resistor, 3 is a latch that holds image data, 4 is a shift register that transfers image data, 9 is a strobe pulse width control unit that controls the pulse width of the strobe signal according to the resistance value of the heat-sensitive resistance element 1; 6A is a clock;
This is an external controller for outputting image data, latch signals, strobe signals, etc.

Note that the heat-sensitive resistance element 1 and the strobe pulse width control section 9 constitute pulse width control means.

Further, FIG. 2 shows an embodiment of the strobe pulse width control section 9 that controls the strobe signal pulse width, where 7 is a resistor that controls the pulse width together with the resistance value of the heat-sensitive resistance element 1, and 8 is a heat-sensitive resistor. This is a one-shot circuit that generates a pulse width according to the resistance value of the element 1.

Next, the operation will be explained.

The thermal head is driven by the controller 6A in a conventional manner, and generates heat in one of the heating resistors 2 according to input image data. This heat generation causes printing to be performed on thermal paper or the like. Namely, first.

The controller 6A inputs the lock and image data to the shift register 4 as shown in FIG. This shift register 4 synchronizes with the clock and transfers one image data sequentially from the last bit in the direction of one bit.Next, when the clock and image data have been transferred for a predetermined number of bits, the controller 6A outputs a latch signal. is output, and the image data in the shift register 4 is fixed by the latch 3. moreover,
A strobe signal is output, and the heating resistor 2 is caused to generate heat for a time corresponding to the strobe signal. and.

This heat generation causes printing to be performed on thermal paper or the like, but at the same time, this heat generation changes the temperature of the thermal head itself. This temperature change is captured as a change in the resistance value of each heat-sensitive resistance element 1 attached to the substrate 10 of the thermal head, and is input to the strobe pulse width control section 9. This strobe pulse width control section 9 is triggered by an external trigger signal (strobe signal), and inputs the strobe signal to the AND gate 5 within the thermal head. For this reason.

Each heating resistor 2 generates heat for a time corresponding to the pulse width of the strobe signal, and prints out an image on thermal paper at a gradation corresponding to the temperature of the generated heat. And this gradation is
Strobe pulse width control section 9 possessed by the thermal head itself
Therefore, the temperature on the substrate 10 can be optimally controlled.

In this embodiment, the strobe pulse width control section 9 is constructed from external parts, but when the AND gate 5 and the like constitute the driver integrated circuit of the thermal head, Alternatively, the same effect as in the above embodiment can be obtained.

Further, an embodiment of the invention according to the second claim will be described with reference to FIG. In Figure 4, 281-28m
, 291-29m are flip-flops constituting the second composite counter 30, 311-31o are flip-flops constituting the first composite counter 32 having the same functions as conventional ones, 331-33 are switches, 341-343
is a zero detector, 35 is a clock selector, and 36 is a data selector.

37 is a clock controller, and 38 is a read-only memory (a memory for storing m-bit resistance value data).
(hereinafter referred to as ROM).

1st. Second composite counter 32, 30 and memory 38
constitutes a pulse width control means.

Next, the operation will be explained. Here, the maximum number of gradations recorded is 2' (n bits), and the maximum correction rank of the resistance value of the heating resistor is ±2'' (m bits).

First, in FIG. 4, n-bit Ni1l information is transferred to the flip-flops 31□ to 31. before loading into.

Flip-flop 281-28m1, 29. 21 clocks are counted from 29 to 29 degrees, and the operation differs depending on whether the resistance value R of the heating resistor is larger than or smaller than the average resistance value R, so this will be explained separately below.

i) In the case of R>R First, the flip-flops 28□ to 281 constituting the second composite counter 30 count down by the number of resistance ranks of the corresponding heating resistor. During this down count, the output of the zero detector 341 is "L", and the output of the zero detector 34. Since both are "L", the pulse width increases. At this time, switch 33. is on, and switch 33□ is off. In this way, the down count ends, and the zero detector 3
41 becomes "H", the switch 331 is turned off, the switch 332 is turned on, and the flip-flops 281 to 2a are turned off.
The operation of llI ends. At this time, the zero detector 34□ is “
H'', switch 33. is off, switch 334 is on, flip-flops 291-291 are not operated, and the first composite counter 3 is turned off until zero detector 343 becomes 'H'.
Flip-flops 311 to 31o forming part 2 count down by the actual n-bit gradation data. As a result, an output with a large pulse width is applied as the resistance value of the heating element in question is large.

1t) In the case of R<R, first, set the zero detector 341 to “L” and turn off the switch 33.
1 on, switch 33. is turned off, and the flip-flops 281 to 281 are turned off until the zero detector 34□ becomes "H".
28 Count down by 2-1 at So 6 Next, turn on switch 33 □, turn on switch 333, switch 33
4 is turned off until the zero detector 34□ becomes “H”.
The flip-flops 291 to 292 count down by the number of ranks of the resistance value of the heating resistor read from the ROM 38. During this operation, the zero detector 34□ is 'L', so no pulse is applied. On the other hand, after the zero detector 34 becomes 'HTj', the flip-props 31□ to 31
．． counts down and increases the applied pulse width, but when the clock controller 37 counts 2°+2', the counting ends. As a result, compared to actual n-bit gradation data, a pulse width shorter by the smaller resistance value rank is applied.

ni) In the case of R=H, first set both the zero detectors 341 and 34□ to "HI+", turn on the switches 33□ and 33., and count down the n-bit gradation data as it is with the flip-flops 31 to 31n. As a result, as before,
A gradation pulse width without resistance value correction is applied.

〔Effect of the invention〕

As described above, according to the invention according to the first claim, the strobe pulse width control in the thermal head controls the strobe signal for controlling the energization to the heating resistor according to the resistance value of the heat-sensitive resistance element. Since the output is output from the section, it is possible to easily and inexpensively create a thermal head that can independently control the temperature of the heating resistor.

Further, according to the invention according to the second claim, the Samar head driver that performs gradation recording includes a memory that holds resistance value data for correcting variations in resistance values for heat generation, and a memory that stores resistance value data for correcting variations in resistance values for heating. Accordingly, it is configured to include a built-in composite counter that can control the applied pulse width, making it possible to perform thermal recording with high gradation control accuracy, which has the effect of printing out high-quality images. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a thermal head driver according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a strobe pulse width control section in FIG. 1, and FIG. 3 is a circuit diagram showing each part of the circuit shown in FIG. 1. A time chart showing signals, FIG. 4 is a block connection diagram showing a thermal head driver according to another invention of the present invention, FIG. 5 is a circuit diagram showing a conventional thermal head driver, and FIG. 6 is a circuit shown in FIG. Block connection diagram showing the entire thermal to rad driver system including
FIG. 7 is a block connection diagram showing another conventional thermal head driver, and FIG. 8 is a time chart showing signals of various parts of the circuit of the thermal head driver shown in FIG. 1 is a heat-sensitive resistance element, 2 is a heating resistor, 9 is a strobe pulse width control section, 1 and 9 are pulse width control means, and 30 is a second
32 is a first composite counter, 38 is a memory, and 30, 32.38 is a pulse width control means. In addition, in FIG. 1, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In order to print on thermal paper by energizing heat generation, multiple heating resistors are provided on the board and the pulse width due to the energization is controlled in response to variations in the resistance values of these heating resistors. In the thermal head driver, the pulse width control means includes a heat-sensitive resistance element that detects the temperature of the heat-generating resistor, and a heat-sensitive resistance element that detects the temperature of the heat-sensitive resistance element, and a thermal head driver that is provided on the substrate and controls the output of the heat-sensitive resistance element. and a strobe pulse width control section that controls a pulse width of a strobe signal that sets the energization time in accordance with the above. (2) In order to print on thermal paper by energizing heat generation, a plurality of heat generating resistors are provided on the board, and the pulse width due to the above energization is controlled in response to variations in the resistance values of these heat generating resistors. In the thermal head driver, the pulse width control means includes a first composite counter that outputs a pulse width according to input gradation information, and a thermal head driver that controls variations in the resistance value of the heating resistor. A memory that stores resistance value data for correcting variations according to the
and a second composite counter that controls the pulse width based on the resistance value data in the memory.