JPH03208675A - Controlling system of thermal head - Google Patents

Abstract

PURPOSE:To record to various kinds of heat sensitive recording mediums always with good image quality by correcting the supplying power to a heat generating body of a thermal head corresponding to the kind of the heat sensitive recording medium. CONSTITUTION:When a signal C from a photodetecting element 19 is input to a central controlling part 7 before starting printing, the controlling part detects the kind of a using heat sensitive recording medium, and reads either one of the look-up tables 9 and 10 corresponding to the kind of the medium, so that the recording apparatus is set in a readable state. A counter 12 modulates the pulse width of a driving data transferred via a data bus 8 from the look-up table 9 or 10 in accordance with the instruction of the controlling part 7, and converts the data to an electric control signal PW. As a result, an output signal PE of a waveform approximately equal to that of the electric control signal PW is output from an OR gate 16 and further supplied to a driving transistor a1 through a demultiplexer 13. While the output signal PE is in the L level, a fixed current is fed to a first heat generating body R, thereby achieving printing of the recording data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head control method in a recording apparatus that uses a thermal head to print an image or print on a heat-sensitive recording medium.

[Conventional technology]

Conventionally, in such a recording apparatus, for example, each time the relative position of the thermal head with respect to the thermosensitive color recording paper is displaced in the main scanning direction and the sub-scanning direction at a predetermined timing,
Supplying recording data represented by pinary data of "marks" and "spaces" corresponding to each pixel to the thermal head, and controlling the amount of heat generated by the heating element of the thermal head in accordance with these recording data. The system is designed to record information using

[Problem to be solved by the invention]

By the way, in addition to such heat-sensitive color-forming recording paper, there are also known heat-sensitive recording media such as heat-sensitive transfer recording paper that performs heat-sensitive transfer recording by overlaying it on recording paper. Progress has been made in the development of technology for multicolor recording.

For example, a heat-sensitive transfer recording paper is placed on top of a heat-sensitive color recording paper, a thermal head is made to generate heat, and the heat-sensitive transfer recording paper performs thermal transfer recording onto the heat-sensitive color recording paper. Next, the thermal transfer recording paper is removed, the thermal head is made to generate heat again, the thermosensitive color recording paper develops color, and recording is performed. In this way, the area where the thermal transfer recording was performed using the thermal transfer recording paper and the area where the thermal color recording was performed overlapped each other, resulting in three different colors, and multicolor recording was performed. be exposed.

However, as is well known, in thermal recording devices, the quality of the images recorded on the recording medium depends on the accuracy of the temperature control of the thermal head. Even if good image quality can be obtained, a problem arises in that good image quality cannot be obtained for other types of recording media.

FIG. 6 shows the characteristics of print density with respect to applied temperature of thermosensitive color recording paper (shown by characteristic curve A) and the characteristics of print density with respect to applied temperature to heat-sensitive transfer recording paper (shown with characteristic curve B). As is clear from the figure, even when printing with thermal heads at the same temperature, there are differences in the print density.For example, printing on one recording medium at the same temperature as the other recording medium produces better results. image quality cannot be obtained.

The present invention has been made in view of such conventional problems, and provides a thermal head control method for a thermal recording device that can always record with good image quality on different types of thermal recording media. Do with the purpose of doing.

[Means to solve the problem]

First, the present invention is directed to a thermal recording method in which printing is performed on a thermal recording medium by supplying electric power corresponding to recording data to a heating element of a thermal head.

In order to achieve the above-mentioned object for such a thermal recording method, the present invention provides a recording medium discriminating means for discriminating the type of thermal recording medium, and a recording medium discriminating means for discriminating the type of thermal recording medium, and supplying a heating element to a heating element according to the recording data. Optimum data generation means is provided for correcting the electric power in accordance with the heat-sensitive characteristics of the recording medium determined by the recording medium determination means.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the same figure, ■ is a recording medium discrimination means, which includes an optical sensor that detects the light reflectance and light transmittance of the surface of the thermal recording medium that is input to the thermal head side, and a thermal recording medium that can be manually switched by the user. There is a changeover switch that specifies the type of

Reference numeral 2 denotes a recording data holding means for storing recording data corresponding to images and characters to be recorded, and is constituted by, for example, a semiconductor memory or the like for storing recording data corresponding to one frame's worth of pixel groups.

Reference numeral 3 denotes a temperature measuring means for measuring the temperature of the thermal head, and for example, a ξ star fixed to the thermal head is applied.

4 receives the discrimination signal S1 from the recording medium discrimination means 1, the record data D supplied from the record data holding means 2 in synchronization with a predetermined print timing, and the temperature signal S2 supplied from the temperature measurement means 3. This is an optimum data generating means that processes the print data D for correction in order to set the optimum print density for the determined print medium. That is, drive data S3 indicating the amount of power to be supplied to the heating element according to the recording data D and the temperature signal S2 is corrected according to the heat-sensitive characteristics of the recording medium determined by the recording medium determining means 1, and then outputted.

For example, the optimum data generation stage 4 stores in advance a plurality of drive data for a plurality of temperatures of the thermal head as a predetermined look-up table for each type of thermosensitive recording medium, and then stores a plurality of drive data for a plurality of temperatures of the thermal head as a predetermined look-up table for each type of thermal recording medium, and The drive data in the look-up table indicated by the discrimination signal S1 may be searched according to the recording data D and the temperature signal 3, or instead of providing a look-up table for each recording medium, It is also possible to apply a calculation means that generates drive data corresponding to the above through calculation processing.

Reference numeral 5 denotes a driving means, which supplies electric power proportional to the driving data S3 to the heating element of the thermal head 6.

For example, by pulse width modulation, a rectangular signal with a pulse width proportional to the drive data S3 is generated, and a constant value of current from a constant current source is supplied to the heating element only during the period when the rectangular signal is at a predetermined voltage level. Apply power control methods such as controlling the supplied power by

61 [Operation] According to the present invention having such a structure, the power supplied to the heating element of the thermal head is appropriately corrected according to the type of thermal recording medium, so that it is possible to use multiple types of thermal recording media. It is possible to realize a thermosensitive recording device that can perform

〔Example〕

The structure of a thermal recording apparatus according to an embodiment to which the thermal head control method of the present invention is applied will be described below with reference to FIG.

In the figure, 7 is a central control unit controlled by a microprocessor, etc., which controls look-up tables 9, 10, random access memory (RAM) 1, etc. via a data center 8.
1, counter l2, demultiplexer 13 and A/D
A converter 14 is connected.

Look amplifier table 9.10 is stored in read-only memory (
The optimum drive data for the temperature of the thermal head is stored for each type of thermal recording medium.

For example, lookup table 9 stores optimal drive data for thermal head temperature for thermosensitive color recording paper, and lookup table IO stores optimal drive data for thermal head temperature for thermal transfer recording paper. are doing.

FIG. 3 shows the contents of the drive data stored in these lookup tables 9.10. That is, as will be described later, in this embodiment, the power supplied to the heating element is controlled by pulse width modulating the drive data and supplying a constant value of current to the heating element for a period corresponding to the pulse width. Since the pulse width modulation method is adopted, FIG. 3 uses the optimum pulse width for the temperature change of the thermal head during recording as the drive data. The characteristic curve T, is the optimum data for the heat-sensitive color recording paper and is stored in the look-up table 9 in advance, and the characteristic curve T2 is the optimum data for the heat-sensitive transfer recording paper and is stored in the look-up table 10 in advance. be remembered.

Note that these lookup tables 9 and 10 are designed to read out the drive data stored at the address onto the data bus 8 when temperature data related to temperature is supplied as address data.

The random access memory 11 is provided to temporarily hold recording data transferred from a so-called microcomputer (not shown) or the like via an interface (not shown) connected to the data bus 8.

The counter 12 pulse-width modulates the drive data transferred from the look-up table 9 or 0 via the data bus 8 according to instructions from the central control unit 8, and converts it into a power control signal pw. That is, when drive data is input in synchronization with the preset signal PR, the power control signal PW is inverted from "H" to "L'" level at the same time as the manual operation, and the drive data is input in synchronization with a clock signal of a predetermined frequency. count down. Then, when the count value due to the down count reaches zero, the power control signal PW is inverted from "L" to "H" level.Therefore, the power control signal PW remains "'L゜゜level" for a period proportional to the input drive data. A power control signal PW is applied.

15 is a monostable multi-by break, and counter 12
The power control signal PW changes from “H” to “L” as described above.
If the power control signal pw does not invert from "H" to "L" level again within a predetermined period (i.e., it is not reset), the output signal E is reset to the "L" level. case), the output signal E is inverted to the "H" level.

Reference numeral 16 denotes an OR gate that performs a logical sum operation of the power control signal PW of the counter 12 and the output signal E of the monostable multi-bi break 15, and the output signal PE of the OR gate 16 is input to the demultiplexer 13.

The demultiplexer 13 selects an output terminal according to channel switching data transferred via the data bus 8 according to instructions from the central control unit 7, and transfers the output signal PE to the selected output terminal.

10 Further, each output terminal of the demultiplexer 13 has a driving transistor a1 connected as a source follower between the power supply terminal VDD and each heating element R, to R7 of the thermal head.
~a7 is connected, and a constant current is supplied to the heating element specified by the channel switching data for a period specified by the output signal PE.

Reference numeral 17 denotes a thermistor fixed to one end of the thermal head to measure the temperature of the thermal head, and the measurement signal St is converted into digital data Dt by the A/D converter 14 and transferred to the central control unit 8 via the data bus 9. be done.

18 is a light emitting element such as a light emitting diode that irradiates light onto the front side of the recording medium 20.

Reference numeral 19 denotes a light receiving element such as a photodiode, which receives light emitted from the light emitting element 18 and reflected from the surface of the thermosensitive recording medium 20 . Then, a signal C corresponding to the reflected light is supplied to a predetermined manual port of the central control unit 7. Then, the central control unit 7 determines the type of thermal recording medium used for printing by comparing the voltage level of the signal C with each darkness value set in advance for each type of thermal recording medium.

Note that in this embodiment, the space information of each pixel is
Printing is performed based on recorded data that represents I+ and mark information in the form of a pinary data of "l°". For example, heat-sensitive coloring recording paper is rotated in a predetermined direction in the main scanning direction and the sub-scanning direction with respect to the thermal head. Each time you move relatively, print data for one pixel at a time.
By repeating printing pixel by pixel, the entire image is finally printed.

Next, the operation of the embodiment having such a structure will be explained based on FIGS. 4 and 5. In these figures, printing for one pixel is performed during the period τ, and in this example,
It is set to τ-1.8mS.

First, the central control unit 7 selects the light receiving element l9 before starting printing.
The type of heat-sensitive recording medium used is determined by inputting signal C from . Then, only one of the lookup table 9 and IO corresponding to the type of thermal recording medium is set to a readable state (enabled). For convenience of explanation, the explanation will be made assuming that lookup table 9 is enabled and lookup table 10 is disabled.

Next, the central control unit 7 controls the heating element R at the position to be printed first. After channel switching data corresponding to is transferred to the demultiplexer 13 to perform channel switching, recording data to be printed first is read from the first address of the random access memory 11. When the recorded data is a binary data of "0" which means a space, the drive data of "O II" is transferred to the counter 12, and when the recorded data is a binary data of "1" which means a mark,
By supplying the temperature data Dt from the A/D converter 14 to the lookup table 9 as address data, drive data corresponding to the temperature data Dt is transferred from the lookup table 9 to the counter 12. Then, the preset signal RP is inverted to the “L” level (at time t
Drive data is set in the counter 12 in synchronization with step o).

13 Furthermore, in synchronization with the inversion of the preset signal RP to the "L" level, the power control signal PW of the counter 12 and the output signal E of the monostable multi-bi break 15 are inverted to the "L" level, and furthermore, The output signal PE of the OR gate 16 is also "'
I warn you that it is L level.

Then, the counter 12 counts down the drive data in synchronization with a clock signal of a predetermined frequency, and when the count value becomes zero, 1. The power control signal PW of the counter 12 is
is inverted to "H" level.

Also, since the single pulse width of the monostable multi-bi break 15 is set to approximately 3.5 mS, the period τ (τ = 1.8
During the period (mS), the output signal E remains at the "L" level. As a result, an output signal PE having a waveform substantially equal to that of the power control signal PW is output from the OR gate 16, and is further supplied to the driving transistor a through the demultiplexer 13. During the period when the output signal PE is at the "L" level, a constant current is supplied to the first heating element R, and printing corresponding to the recording data is performed.

Printing for the next pixel will be performed in the same way (14-), and the next heating element R2 will be selected and the counter 12 will be printed.
Printing is performed by operating in synchronization with the preset signal PR, and by repeating the same process every cycle τ, it is possible to print all the recorded data. Then, as shown by the dotted line in FIG. 4, the period during which the output signal PE is at the "L" level is automatically adjusted depending on the magnitude of the drive data manually input to the counter 12.
Feedback control is achieved in response to temperature fluctuations in the thermal head.

Note that when normal printing processing is performed in synchronization with the cycle τ, the monostable multi-bi break l5 is reset in synchronization with the generation of the preset signal PR every cycle τ, so the output signal E continues to be at the "L" level, and the output signal PE and the power control signal PW become almost equal. However, due to a malfunction of the counter 12, etc., the power control signal PW
If an abnormality occurs in the monostable multi-by-break 1
5 acts as a means to suppress such abnormalities. That is, as shown in FIG. 5, at a certain time t3, the power control signal PW becomes "
Although it should be reversed from 'H' level to 'L' level,
If no reversal occurs, monostable multi-by-break 1
Simultaneously with the passage of the single pulse width period (approximately 3.5 mS) of 5, the output signal E inverts to the "H" level.As a result, the output signal PE of ○R game 16 is forced to become "H". ” level, power supply to the heating element is stopped to prevent incorrect printing.

In this way, in this embodiment, the type of heat-sensitive recording medium is determined from the surface reflectance of the heat-sensitive recording medium, and the amount of heat generated by the thermal head is controlled according to the heat-sensitive characteristics specific to each heat-sensitive recording medium. Clear recording can be performed on different types of thermal recording media.

Further, in this embodiment, the type of thermosensitive recording medium is determined by the photodetecting means, but a changeover switch may be provided for the user to specify the type.

〔Effect of the invention〕

As explained above, according to the present invention, the power supplied to the heating element of the thermal head is appropriately corrected according to the type of thermal recording medium, so it is versatile enough to use multiple types of thermal recording media. It is possible to provide a thermosensitive recording device rich in properties.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the structure of an embodiment showing the structure of an embodiment according to the present invention, FIG. 2 is an explanatory diagram of the structure of an embodiment of the present invention, and FIG. FIG. 4 and FIG. 5 are tying charts for explaining the operation of the embodiment, and FIG. 6 is for explaining the problems of the conventional method. FIG. Symbols in the figure: 1; Recording medium discrimination means 2; Recorded data holding means 7 3; Temperature measurement means 4; Optimal data generation means; 5; Drive means 6/thermal head 7; Central control section 8; Data path 9; 10; Lookup table 11; Random access memory 12; Counter 13; Demultiplexer 14; A/D converter 15; Monostable multi-bi break 16; OR gate 17/thermistor 18; Light emitting element 19; Light receiving element 20; Thermosensitive recording medium a1~a,,; Drive transistor R1~Rni heating element 18

Claims (1)

[Scope of Claims] In a thermal recording method in which printing is performed on a thermal recording medium by supplying electric power corresponding to recording data to a heating element of a thermal head, a recording medium determining means for determining the type of the thermal recording medium; A thermal head control system comprising: optimum data generating means for correcting the power supplied to the heating element according to the recording data according to the heat-sensitive characteristics of the recording medium determined by the recording medium determining means.