JPS60254874A - Thermal head driving device - Google Patents

Abstract

PURPOSE:To stabilize the heating temperature of a unit heating body for a long period by identifying the image information pattern of the periphery of a dot in every process and setting applied energy according to the identified result. CONSTITUTION:When image data 41 is supplied, only 10 dots of up to five lines of image data which affects the print of an aimed dot are extracted and inputted to a pattern discrimination ROM45. The pattern decision ROM45 decides on image information pattern of the periphery of the aimed dot and read peripheral pattern information 48 is applied to a comparator 52, RAM53, and applied energy arithmetic ROM54 respectively. The comparator 52 compares the peripheral pattern information with one-line delay information 55, and the applied energy arithmetic ROM54 calculates the applied energy of a corresponding group by using the peripheral pattern information 48 as address information and supplies the feeding time of applied pulses to a selector 67, controlling the applied energy.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a thermal head driving device used in a recording device or display device using a thermal head.

"Prior Art" A thermal head consisting of one or more unit heating elements (heating elements) arranged one-dimensionally or two-dimensionally can selectively cause these unit heating elements to generate heat according to image information. can. The heat pulses thus generated are used to record an image in a thermal recording device or a thermal transfer recording device, and are used to form a magnetized latent image in some types of display devices.

By the way, since recording devices and display devices using thermal heads use thermal energy to record or display (hereinafter simply referred to as recording), thermal fluctuations in the thermal head do not affect image quality. Of course. Therefore, a thermal head driving device that can correct heat accumulation in a thermal head, etc. has been proposed.

FIG. 7 schematically shows a conventional heat storage correction device. A buffer memory 11 of this device is supplied with an image signal 12 obtained by plane-scanning a document (not shown). The buffer memory 11 is a memory that sequentially stores image signals for three lines, for example, and stores pixels (hereinafter referred to as reference dots) located around a pixel (hereinafter referred to as a dot of interest) whose applied energy is currently being calculated. The signal state 13 is output to the first arithmetic unit 14. As shown in FIG. 8, if the dot 15 of interest is the MWth pixel on the Nth line, then the M-1 and M+1th dots on the same line and the M-1 pixel on the N-1th line one line before. ~M4-1st dot,
Furthermore, the Mth dot in the N to 2 lines one line before is used as a reference dot, for example. First computing unit 1
In step 4, these six reference dots are weighted according to the contribution rate of heat storage, and the weights of the dots to be printed are added. In this way, the heat storage contribution rate of the surrounding dots to the dot of interest is calculated. For example, the weighting is as shown in FIG.

The heat storage calculation result 16 is supplied to a second calculation unit 17 . The second calculator 17 calculates the energization time of the applied pulse used to print the dot of interest, depending on the amount of heat storage. At this time, other data 18 such as the energization time of the applied pulse used in the previous line may be supplied to the second arithmetic unit 17 to correct the applied pulse width. The applied pulse width 19 determined by the second calculator 17 is applied to the recording section (or display section) 2.
1 and the applied pulse width when recording the image signal 22 supplied from the buffer memory 11 is set. That is, in the recording section 21, the applied pulse width is set for each unit heating element, for example, in steps of 0.1 m5ec. When heat storage is progressing, the applied pulse width is set to be short depending on the degree of heat storage.

FIG. 9 shows how the temperature of a unit heating element is controlled by this conventional heat storage correction device.

In the figure, symbols t1 to t4 are the time widths of the applied pulses for each process calculated by the second calculation unit 17 described above. As heat accumulation progresses over time, the time width of the applied pulse decreases from tl to t2 and from t2 to t3. In this example, these time widths are in increments of Q, 1 m5 ec, which are only approximate values of the theoretically calculated ideal value of the applied pulse width. Therefore, heat storage control is not necessarily performed in a direction that reduces heat storage. In the example shown in FIG. 9, while the calculation result of the heat storage state is changing sequentially, the time width of the applied pulse is changed to t accordingly.

It changes from to t3. After this, when the calculation result of the heat storage state becomes constant, the corresponding time width t1 is continuously set during this time. However, if this time width t is slightly longer than the ideal value for heat storage correction, heat storage will progress over time. .

In the figure, the fact that the lowest temperatures T2 and Tb1TC increase in sequence every time the application of the pulse with the time width t4 is started indicates the fact that heat storage is progressing.

As heat storage progresses, a situation may occur in which the temperature of the unit heating element during printing exceeds the permissible temperature TMAX. If the thermal head is driven at a temperature that exceeds the allowable temperature TMAX, printing will be performed even in background areas where printing is not normally performed, due to slight temperature fluctuations, resulting in so-called "collapse" of the image. I end up. Furthermore, in a recording apparatus using a thermal transfer recording method, not only the ink in the printed area but also the surrounding ink is transferred onto the recording paper in a trailing manner, resulting in so-called "tailing".

Above we have explained the heat accumulation phenomenon of the unit heating element that occurs when the applied pulse set by the calculation for heat accumulation correction differs from the ideal value, but there are other thermal factors that affect recording or display. There are various types, and similar problems will occur if proper energy control is not performed for these. Particularly in today's world, where recording or displaying has become faster and has higher image quality, and more emphasis has been placed on reproduction of halftones, there is a strong demand for higher accuracy in thermal head temperature control.

"Problems to be Solved by the Invention" In view of the above circumstances, the present invention aims to provide a thermal head driving device that can stabilize the heat generation temperature of a unit heating element constituting a thermal head over a long period of time. That purpose.

"Means for Solving the Problems" In the present invention, as shown in principle in FIG. From these image information, manually extract a predetermined range of image information centered on the image information corresponding to the unit heating element for which energization control is currently being attempted, and convert this image information into multiple image information patterns set in advance. Image information pattern determining means 32 for determining which of the image information patterns it belongs to.
and applied energy calculation means 35 for calculating the energy 34 to be applied to the unit heating element in one or more ways according to the determined image information pattern 33, When the applied energy calculation means 35 calculates a plurality of energies to be applied to a unit heating element in a state where an information pattern is determined, applied energy control is performed to select these and control energization of the unit heating element in each process. means 36 is provided in the thermal head driving device.

In other words, this thermal head driving device determines the optimum energy to be applied to the unit heating element for which energization control is currently being performed by using an image information pattern consisting of a predetermined range of image information extracted with the image information corresponding to this unit heating element as the core. Calculate by determining. The extracted image information may include various information such as future print information in addition to heat storage information. When the applied energy calculation means calculates the ideal energy that can be controlled by the applied energy control means, only one type of applied energy is applied to one image information pattern. In other cases, two or more applied energies will be calculated. When two types of applied energy are calculated with the ideal applied energy as the approximate midpoint, these two types of applied energy, large and small, are alternately applied to the unit heating element of each process while the same image information pattern is being determined. will be done.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 2 shows the main parts of a recording apparatus using the thermal head driving device of this embodiment. Image data 41 obtained by raster scanning a document is supplied to this device from a facsimile transmitter (not shown) or the like. The image data 41 is a digital signal that is binarized according to the density of the original. The thermal head drive device has four line memos 'J42-1~
42-4 and five shift registers 43-0 to 43-4. The image data 41 is manually input to the 0th shift register 43-0 and the first line memories 42-1 in synchronization with a video clock (not shown). First line memory 4
The image data 41 manually entered in 2-1 is delayed by exactly l lines (raster) and is transferred to the first shift register 43-1.
And second line memo! It is input to J42-2. 1st~
Fourth line memo! Since J42-1 to 42-4 are connected in series, the image data 44-1 to 44-4 each delayed by l lines (one process) correspond to the first to fourth shift registers 43-. 1 to 43-4 will be done manually.

Each shift register 43-0 to 43-4 has a three-stage configuration. Among these, the output of the second stage [stock] of the 0th shift register is the input terminal A of the pattern discrimination ROM 45.
1 to 3 of the first shift register 43-1.
The outputs of stages ■ to ■ are input terminal A of the pattern discrimination ROM 45.
3 to Δ1, respectively. Also, the output of the first stage (■) of the second shift register 43-2 is the pattern discrimination ROM4.
5, the output of the third stage (■) is supplied to the input terminal A4, and the output of the second stage is supplied to the thermal head control circuit 46 as image data D1 representing the dot of interest as the target of calculation of applied energy. Supplied. Furthermore, the third
The outputs of the first to third stages ■ to ■ of the shift register 43-3 are input to the input terminals Δ8 to A6 of the pattern discrimination ROM 45, and the output of the second stage ■ of the fourth shift register 43-4 is input to the pattern discrimination ROM 45. They are respectively supplied to terminal A9.

FIG. 3 shows the correspondence between each piece of image data that is manually entered into the pattern discrimination ROM 45 as address information and the dots on the recording surface. Among these, the dot marked with an X corresponds to the image data D+ for which the applied energy calculation is to be performed, and the dots indicated by the round numbers ■ to [phase] around it correspond to the shift register 43 shown in FIG. -O~
This corresponds to the image data of numbers 2 to 0 shown in each row of 43-4. In other words, pattern discrimination ROM4
5 contains the image data that affects the printing of the dot of interest.
Only 10 dots are extracted across the line and then manually processed.

The pattern discrimination ROM 45 discriminates the image information pattern around the dot of interest based on the image data for these 10 dots. The number of image information patterns that the pattern discrimination ROM 45 can discriminate is 1024 (210) if combinations of image data of all 10 dots are to be discriminated.
becomes. Therefore, strictly speaking, there are 1024 different energies to be applied to these dots of interest. However, some of the calculated applied energies may be considered to be the same. Therefore, in the thermal head driving device of this embodiment, there are 12 image information patterns to be determined.
It is divided into eight groups, and the pattern discrimination ROM 45 discriminates which of these groups it belongs to. The following Table 1 shows the relationship between the address of the pattern discrimination ROM and the number of the group to be discriminated.

(Hereinafter, blank spaces) Table 1 For example, it is assumed that image information as shown in FIG. 4 is extracted as corresponding to FIG. 3. Signal “l” for printed dots
", and if a non-printing dot is represented by a signal "0", then the address information (binary) input to the input terminals .DELTA.9 to AO of the pattern discrimination ROM 45 is as follows.

1101001000 This is 348 when expressed in hexadecimal notation, which is 8 from Table 1.
It can be seen that this is the image information pattern of group number 0.

The group number discriminated by the pattern discrimination ROM 45 is read out for each dot as peripheral pattern information 48.

This read peripheral pattern information 48 is supplied to an input terminal ASRΔM (random access memory) 53 of a comparator 52 and an applied energy calculation ROM 54, respectively. Among these, RAM 53 contains peripheral pattern information 4
8 is delayed by one line and is supplied to the input terminal B of the comparator 52 as one line delay information 55. The comparator 52 receives peripheral pattern information 48 and 1 line delay information.
Compare the information 55, and if the two are equal, the output terminal 01
A comparison result signal 56 of H (high) level is output.

Also, if the former is larger than the latter, the output terminal is 0.
2, and vice versa, H level comparison result signals 57 and 58 are output to the output terminal 03, respectively. In this way, the surrounding pattern information of the dot that is currently being printed is compared with the surrounding pattern information of one line before.
This is because applied energy control according to the present invention is performed at locations where the same peripheral pattern information is continuous.

That is, peripheral pattern information 48 and one line delay information 55
If they are equal, highly accurate applied energy control according to the present invention is executed. The operation of the device at this time is as follows.

At locations where the peripheral pattern information is continuous, the comparison result signal 56 becomes H (high)-level, the AND gate 59 opens, and the clock signal 61 synchronized with the image signal 41 is supplied to the clock input terminal CK of the binary counter 62. be done. In this state, the gate output signal 6, which is also at H level, is output from the NOR gate 63 which manually outputs the other two comparison result signals 57 and 58.
4 has been output, and the binary counter 62 has been released from its reset state. Therefore, while the image information patterns of the same group are being discriminated from the binary counter 62, the signals P1'' and O'' are repeatedly output as the count output signal 65.The gate output signal 64 and the count output signal 65 is supplied to a selector 67 as a parallel 2-bit applied energy selection signal 66.

Now, the applied energy calculation ROM 54 calculates the applied energy of the corresponding group using the peripheral pattern information 48 as address information. Then, the energization time (applied pulse width) of the applied pulse to realize this applied energy is set as the first energy information 68-1 and the second energy information 68-2 at the data input terminal 1 of the selector 67. , I2.

FIG. 5 shows the number of each group, the corresponding ideal applied energy, and the ideal value of the energization time of the unit heating element. The applied energy or energization time was determined for each group through experiments.

Incidentally, the ideal value of the energization time shown in FIG. 5 is not necessarily written as is in the applied energy calculation ROM 54 for each group. This is because in the thermal head drive device of this embodiment, the current application time is controlled by the thermal head control circuit 46, but the current application time that can be controlled by this circuit is in units of 0.1 m5ec, and 0.1m5ec.
This is because finer control than this is impossible.

For example, in the group No. 80 shown earlier as an example, the applied energy of 0.18 mJ is the ideal value as shown in Fig. 5, and the energization time of the unit heating element is 0.45 mJ under the predetermined applied voltage.
m5ec is an ideal value.

This value cannot be directly set by the thermal head control circuit 46. Therefore, in this case, two energizing times Q, 4m5ec and 3m5ec, sandwiching this ideal value are used.
．． 5m5ec is the first and second energy information 68-1.
68-2 are selected one by one, and the applied energy calculation R
It is written in OM54.

On the other hand, for example, in the group No. 128, the ideal value of the energization time is 9.9 m5ec, which is a time width that can be directly controlled by the thermal head control circuit 46. Therefore, in this case, the first and second energy information 68
-1.68-2 can both have the same energization time of 0.9 m5ec. The following Table 2 shows the contents of the applied energy calculation ROM 54.

Table 2 By the way, in places where the same image information pattern information is continuous, the applied energy selection signal 66 is the signal "11'"
and “10” are repeated. Therefore, at this time, the selector 67 selects the two data input terminals 1. , I2, the first and second energy information 68-1.68
-2 is alternately selected in synchronization with the signal change of the applied energy selection signal 66, and is supplied to the thermal head control circuit 46 from the output terminal ○ as applied energy information 71. The thermal head control circuit 46 performs a logical product of the applied energy information 71 and the data of interest D, and controls the energization of the unit heating element of the thermal head 72 using the applied pulse width. As in the example shown in Fig. 4, in a state where group No. 80 is continuously determined for the same unit heating element, this unit heating element is repeatedly subjected to energization control of 0.4 m5ec and 0.5m5ec. and the average is 0.4
An ideal applied energy of 5 mJ would be given. On the other hand, when group No. 128 is determined, the first and second energy information both contain 0.9 m5ec, so the ideal Q, 9. The unit heating element is repeatedly energized with an applied pulse width of m5ec.

On the other hand, to explain the case where the peripheral pattern information 48 and the 1-line delay information 55 are not equal, in this case the comparison result signal 56 becomes L (low) level and the AND gate 5
9 closes. At this time, the gate output signal 64 also becomes L level, and the binary counter 62 is maintained in a reset state. Therefore, the applied energy selection signal 66 is always fixed at the "OO" state. At this time, the selector 67 selects only the first energy information 68-1 as the applied energy information 71. Of course, in this case, the number of the group to be determined changes for each process, and the energization time of the unit heating element also changes from moment to moment. Therefore, heat storage and heat radiation are statistically canceled out, and a phenomenon in which the temperature of the unit heating element inappropriately increases or decreases does not occur.

FIG. 6 shows the actual temperature control of the thermal head driving device that performs the operations as described above, in association with FIG. 9. In places where predetermined gradations are continuous, the energy applied to the same unit heating element is set at different time widths (current application time) tn and t5 for each process, and the average value of these is approximately Ideal temperature control will be achieved.

In the embodiment described above, a binary counter is used to alternately set two types of applied pulse widths, but in general, an N-ary counter (N is an integer of 2 or more) is used to repeatedly set N types of applied pulse widths. You may also do so. Of course, when N is set to 3 or more with this N-ary counter, only two types of applied pulses are prepared, and one applied pulse appears more often than the other applied pulse, and the applied energy can be controlled. It is also possible to do so. For example, when the ideal applied energy is 0.425 mJ, use a quaternary counter to apply 0.4 mJ three times and Q.
Ideal temperature control can be performed by setting the applied energy of 5 mJ once.

In addition, in the example, the voltage of the applied pulse applied to the unit heating element of the thermal head was kept constant and the applied energy was controlled by the energization time. The applied energy may also be controlled.

"Effects of the Invention" As described above, according to the present invention, the image information pattern around the dot to be printed is identified for each process, and the applied energy is set accordingly, so that the printing quality is not affected. It is possible to immediately determine the ideal applied energy, the voltage and time width of the applied pulse to be set, etc. without having to perform calculations individually for each of the various thermal factors.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the principle of the present invention, Fig. 2 is a block diagram showing the main parts of a recording device equipped with a thermal head drive device according to an embodiment of the invention, and Fig. 3 is a block diagram showing the identification of image information patterns. 4 is a dot arrangement diagram showing the arrangement of each dot on the recording surface used for identifying the image information pattern. FIG. An explanatory diagram showing the relationship between each group as a result of discrimination and the ideal values of applied energy and energization time, FIG. 6 is a characteristic diagram showing the state of temperature control of the unit heating element according to this embodiment, and FIG. Block diagram showing a configuration example of a conventional thermal head driving device, No. 8
The figure is an explanatory diagram showing the weight of each dot used in calculating the heat storage contribution rate, and FIG. 9 is a characteristic diagram showing the state of temperature control of a unit heating element in a conventional thermal head driving device. 31... Image information, 32... Image information pattern discrimination means, 35...
... Applied energy calculation means, 36 ... Applied energy control means, 45 ... Hatern discrimination ROM
. 46...Thermal head control circuit, 54...
...Applied energy calculation ROM. 62...Binary counter, 67...Selector. Applicant Fuji Xerox Co., Ltd. Agent Patent Attorney Umeo Yamauchi Figure 1 Figure 3 Figure 4 Figure 7

Claims (1)

[Claims] 1. One or more unit heating elements are one-dimensional or two-dimensional.
In an apparatus that includes a thermal head arranged dimensionally and performs recording or display by driving and controlling the thermal head for each process, a plurality of consecutive images containing image information of the process currently being recorded or displayed are used. The image information for the process is input, and from this image information, a predetermined range of image information is extracted with the image information corresponding to the unit heating element for which current energization control is to be performed as the core, and this image information is set in advance. image information pattern determining means for determining which of a plurality of image information patterns it belongs to; and an applied energy calculation unit that calculates one or more ways of energy to be applied to the unit heating element according to the determined image information pattern. When the applied energy calculating means is calculating the energy to be applied to the unit heating element in multiple ways in a state where the same image information pattern is determined for each process for the same unit heating element, select these. 1. A thermal head driving device comprising applied energy control means for controlling energization of unit heating elements in each process. 2. When the applied energy calculation means calculates two types of applied energy, the applied energy control means alternately allocates these values to control the energization of the unit heating element in each process. The thermal head drive device according to item 1.