JPH0514620B2 - - Google Patents

Description

[Detailed description of the invention]

``Industrial Application Field'' The present invention relates to a drive circuit for a thermal head used in a thermal recording or display device (hereinafter simply referred to as display). "Prior Art" Recording devices that perform thermal display using thermal recording paper or transfer type thermal recording media are widely used in facsimile machines, printers, and the like. Usually, such a recording apparatus uses a thermal head, in which unit heating elements (heating elements) are arranged in a row, as a recording head. The same applies to certain types of display devices that display images using magnetized latent images. Since thermal heads generate thermal energy to create images for display, there is a problem of image quality deterioration caused by this energy. In display devices that create a display image by driving a thermal head for each line, the following five causes have been cited as causes of image quality deterioration. Heat storage in thermal head. Thermal history data. Thermal head board temperature. Difference in resistance value of unit heating element. Voltage drop due to black ratio. Among these, heat storage in the thermal head refers to the fact that the heat storage state of each unit heating element differs depending on the display pattern. The heat storage state is also influenced by other unit heating elements arranged around the unit heating element. Thermal history data mainly refers to the state of display information one line before. In a thermal recording device that performs recording by changing the width and voltage value of a voltage pulse (recording pulse) applied to a thermal head, this thermal history data affects the recording of the next line. The substrate temperature of a thermal head refers to the temperature of a substrate on which a large number of unit heating elements are formed. Differences in resistance values of unit heating elements refer to variations in resistance values due to manufacturing reasons, and include variations in unit heating elements within one thermal head and variations in the average resistance value of unit heating elements between thermal heads. There is. There is a wide range of resistance values. For example, the former has a resistance value of about ±25%, and the latter has a resistance value in the range of 200 to 300Ω.
Voltage drop due to black ratio means that the degree to which the power supply voltage drops when a unit heating element is energized varies depending on the ratio of so-called printed dots (black dots) in each line. As the power supply voltage decreases, the density of the displayed dots also decreases. Conventionally, attempts have been made to correct thermal energy by combining some or all of the above factors. For example, the inventors have proposed a thermal recording device and a thermal head drive circuit that correct these problems (Japanese Patent Application No. 179350/1984, etc.). FIG. 10 shows an example of this proposed thermal recording device. In this thermal recording device, the thermal energy is corrected by combining the voltage drop due to the black ratio with the heat storage of the thermal head and the thermal history data. Therefore, in this device, peripheral image data 12 regarding the line (raster) currently being recorded and the line recorded in the past is supplied to the heat storage state calculator 11, and the heat storage state of the unit heating element currently being recorded is calculated. I'm starting to let them do it. The calculation output 13 is supplied to a pulse width calculation unit 14 and is calculated together with the pulse width information T _i-1 16 of the previous line outputted from the pulse width memory 15. The pulse width determining circuit 17 outputs a calculation output 18
Tentatively determine the pulse width based on Then, the AND gate group 19 is controlled, and the image information print data 26 is stored in the five data buffers 21-25. On the other hand, the image information print data 26 is supplied to a first counter circuit 27 and counted. Counting result 28
Based on this, the basic pulse width determining circuit 29 determines the basic pulse width of the recording pulse for each unit heating element, and outputs the basic pulse width signal 31. On the other hand, in the second counter circuit 32,
The print data 34 is counted while selecting the output of each data buffer 21 to 25 using the data buffer select signal 33. This counting result 35 is then supplied to an auxiliary pulse width determining circuit 36 to determine an auxiliary (additional) pulse width for each unit heating element. The auxiliary pulse width signal 37 outputted by this
The basic pulse width signal 31 mentioned above is the print data 3.
This is used as the pulse width of the No. 4 recording pulse. Although the proposed thermal recording apparatus has been outlined above, the portion for calculating the heat storage state of the thermal head will be explained in more detail. FIG. 11 shows the arrangement of image data for calculating the heat storage state of the thermal head. The data column i placed at the bottom in this figure is
It represents the data on the line that is about to be recorded. Also, by this, the column i one above
-1 represents data one line temporally past this. Similarly, the topmost data row i-4 represents data from the past four lines. Now, in the data string i, attention is paid to arbitrary data D0 marked with an x in the figure. This data (hereinafter referred to as data of interest D0) corresponds to one unit heating element for which printing processing, ie, calculation of applied energy, is about to be performed. In this case, a total of 10 pieces of data d ₁ to _{d 10} located around this area are a reference data group for calculating the heat storage state. Among these reference data groups, reference data adjacent to the unit heating element to which the focused data D0 belongs has a relatively large thermal effect when printing the focused data D0.
d ₁ and d ₂ . Also, what has the greatest thermal influence is the reference data _d4 regarding the same unit heating element in the data row i-1 one line before (past). As described above, each reference data that has an effect on heat storage when printing the data of interest D0 has a different degree of importance depending on the arrangement relationship with the data of interest D0. Therefore, each of the reference data d ₁ to _{d 10} is weighted in advance, and only the data in the print state are added, and the heat storage state is calculated from the sum. For example, the weighting is as follows.

[Table] According to the numerical value of the heat storage data added in this way, the thermal energy for printing the data of interest D0 is set. That is, the time width and voltage of the applied pulse applied to the corresponding unit heating element of the thermal head are adjusted, and thermal energy is applied. By the way, in this proposed device, as shown in FIG. 10, the heat storage state is calculated using five lines of data. In addition to calculating the heat storage state, if the current printing is performed while taking into consideration the state of future print lines or display lines, data for even more lines will be required as reference data. As an example, a patent application filed in 1983-
In the specification of No. 088438, data strings i-4 to i+2 for six lines are used as shown in FIG.
The data string used to calculate the heat storage state here is:
It is 4 lines i-3 to i, which is smaller than that of the device shown above. ``Problems to be solved by the invention'' In this way, in conventional thermal head drive circuits, it is necessary to calculate the heat storage state from several lines.
We have used data of about 10 lines. However, in recent years, as the production speed of display images has become even faster, the heat generation state of unit heat generating elements of lines in the past has come to have an effect on the production of current display images. Therefore, this has become an even more pressing problem when trying to express delicate density to reproduce halftones. For example, suppose that after a series of black print areas, a white print area exists with a length of several millimeters. When performing high-resolution display, this corresponds to several tens of lines, but when performing high-speed printing, the printing operation takes one-tenth of a second or less. Therefore, past data from only about 10 lines cannot adequately grasp the current state of heat storage. However, if we try to use data from more lines to calculate the heat storage state, a large capacity memory will be required, which will increase the cost of the equipment.
Furthermore, it has the disadvantage of increasing its size, making it difficult to realize. In addition, when attempting to secure enough data for calculation of the heat storage state, there is also a problem in that data for consideration of future printing conditions as described above becomes insufficient. In view of the above circumstances, it is an object of the present invention to provide a thermal head drive circuit that can calculate the heat storage state by sufficiently considering past lines and obtain a high-quality display image. ``Means for Solving the Problems'' In the present invention, as shown in principle in FIG. a heat storage level calculator 43 that calculates the calculated heat storage level; a heat storage level data return means 45 that returns the calculated heat storage level to the heat storage level calculator 43 as data 44 for calculating a future heat storage level; Thermal head 42 depending
An applied energy calculator 46 determines the applied energy for driving the thermal head, and a thermal head drive control means 47 controls the heat generation of each heating element using the applied energy determined by the applied energy calculator 46. Provided in the drive circuit. Here, as the heat storage level data feedback means 45, for example, heat storage level storage means (memory) that writes and reads the calculation results of the heat storage level calculator 43 is used. According to the present invention, since the heat storage level is calculated by feeding back the heat storage level data, the heat storage calculation can be performed with sufficient consideration given to the past state. "Example" The present invention will be described in detail with reference to Examples below. FIG. 2 schematically shows the thermal head drive circuit of this embodiment. An image signal 51 obtained by plane scanning by a reading device (not shown) is supplied to this device as serial data, and is input to a peripheral recording data memory 52 in synchronization with a video clock (not shown). ing. FIG. 3 shows a specific configuration of the peripheral record data memory 52. As shown in FIG. The image signal 51 is a binary bit serial signal string, and after being sequentially latched bit by bit in the latch circuit 53, it is stored in the i+1 line memory 54 _i+ in the line memory group 54.
Written to ₁ . Memory for i+1 line 54 _i+1
is a memory that stores future image signals for one line. The image signal of one bit pushed out from the i+1 line memory 54 _i+1 in synchronization with a video clock (not shown) is latched by a latch circuit 55, and then sent to the i line memory 54 in the line memory group.
It is input to the shift register 56 _i+1 for _i and i+1 lines. The i-line memory 54 _i is a memory that stores the image signal of the line to be currently recorded, and the image signal pushed out from this memory one bit at a time is latched by the latch circuit 55 and stored in the line memory group. It is input to the i-1 line memory 54 _i-1 and the i-line shift register 56 _i . Thereafter, in the same manner, each bit of image signal pushed out from the memory 54 _i-3 for the i-3 line in the line memory group is latched by the latch circuit 55 and input to the shift register 56 _i-3 for the i-3 line. Ru. On the other hand, the image signal latched by the latch circuit 53 is also input to the i+2 line shift register 56 _i+2 . Therefore, each shift register 56 _i+2 ~
56 _i-3 receives 6 lines of image signals from i+2 to i-3 lines in synchronization with the video clock.
It will be input bit by bit. Each of the shift registers 56 _i+2 to 56 _i-3 is a five-stage shift register, and reference data D15 is output from the third stage flip-flop circuit of the i+2 line shift register 56 _i+2 . Reference data D14 to D12 are output from the second to fourth stage flip-flop circuits of the i+1 line shift register 56 _i+1 , respectively. i
Line shift register 56 _i 1, 2, 4, 5
The flip-flop circuits in each stage output reference data D9, D2, D1, and D8, respectively.
Reference data D4 to D8 are output from the i-1 line shift register 56 _i-1 . Furthermore, reference data D6 and D7 are output from the third stage flip-flop circuits of the i-2 line shift register 56 _i-2 and the i-3 line shift register 56 _i-3 , respectively. These reference data D1 to D15 and the i-line shift register 56 _i
The arrangement of the target data D0 outputted from the third stage flip-flop circuit on the recording surface is as shown in FIG. Future reference data D12 to D15 are supplied to the applied energy calculator 57. The past and present reference data D1 to D11 are also supplied to the heat storage level calculator 58. The heat storage level calculator 58 is a circuit portion that calculates the heat storage level HS _i for the unit heating element when printing the data of interest D0. Calculation of heat storage state The heat storage level calculator 58 is equipped with a ROM (read only memory), and first calculates the heat storage state X _i using 11-bit reference data D1 to D11 as address information. Figure 4 shows this calculation.
It shows the contents of the ROM, and the horizontal axis shows the value added after weighting each reference data. Weighting is performed as shown in FIG. 5, which corresponds to FIG. 12, and the maximum value of the added value is "455". The heat storage state X _i is calculated by the heat storage level calculator 58 together with the past heat storage level data HS _i-1 of one line supplied from the heat storage level calculator 58 to obtain the heat storage level data HS _i of the current line. This heat storage level data HS _i is delayed by one line in the heat storage level memory 59 and output as heat storage level data HS _i-1 , and is also supplied to the applied energy calculator 57 and used for calculating applied energy. By the way, FIG. 6 is for explaining how the heat storage level calculation unit 58 calculates the heat storage level data HS _i . Now, suppose reference data D1 to D
If the added value of 11 is "305", the heat storage state X _i is at the stage of "3" from FIG. 4. At this time 1
If the past line heat storage level data HS _i-1 is also at the "3" level, the current line's heat storage level data HS _i is kept at the "3" level. On the other hand, if the heat storage level data HS _i-1 is at a stage of "4" in which the heat storage state is significant, the current line heat storage level data HS _i levels up to "4". On the contrary, past heat storage level data for one line
If HS _i-1 is in the “1” stage with low heat storage state,
The heat storage level data HS _i of the current line drops to “2” and becomes “1” when there is almost no heat storage.
The value has dropped to . Similar calculations are performed for other addition values using heat storage level data HS _i-1 . Heat storage level calculator 58 and heat storage level memory 59
constitutes a loop circuit, and heat storage level data
HS _i-1 is fed back to the heat storage level calculator 58. Therefore, the heat storage level calculator 58 performs calculations that fully take into account past heat storage conditions. Calculation of applied energy Now, as shown in FIG. 7, the applied energy calculation unit includes a first calculation unit 61 that calculates the applied energy of the thermal head from the heat storage state, and a second calculation unit that corrects this calculation result using future reference data, etc. It is equipped with a computing unit 62. In the thermal head drive circuit of this embodiment, the applied energy is controlled by changing the time width of the recording pulse applied to each unit heating element constituting the thermal head. Therefore, the output of the first arithmetic unit 61 is the time width information T _iA of the recording pulse, and the second arithmetic unit 62 corrects this and outputs the final time width information T _iB . The first arithmetic unit 61 is composed of a ROM, and includes heat storage level data HS _i-1 and reference data D1.
~D11 is input as address information, and time width information T _iA is output. The reference data D1 to D11 are data for calculating the heat storage state X _i described above. FIG. 8 shows the contents of this ROM in terms of the relationship between the heat storage level data HS _i-1 and the heat storage state X _i . For example, as shown above, reference data D1 to D1
Assuming that the added value of 1 is "305", the heat storage state X _i is at the stage of "3". At this time, if the heat storage level data HS _i-1 is "3" or "4", the heat storage state is progressing, so the recording pulse time width information T _iA is 0.6 msec. On the other hand, for example, if the heat storage level data HS _i-1 is "0", the time width information T _iA has a value increased to 0.9 msec. Other heat storage status and heat storage level data HS _i-1
In this way, the time span information T _iA is calculated with sufficient consideration even to the past heat storage state. Note that this time width information T _iA represents the time width under the assumption that the unit heating element is energized, similar to the time width information T _iB from the second arithmetic unit 62, and the so-called black dots are printed. Recording pulses are not applied to unit heating elements that are not applied regardless of the time width information T _iA . Whether or not to apply a recording pulse is determined by the thermal head controller 64 (FIG. 2), which receives the data of interest D0. On the other hand, the second arithmetic unit 62 predicts the future printing state using a total of 4 bits of reference data D12 to D15, and outputs future determination information F _i . The time span information T _iA is corrected based on this future discrimination information F _i , and the time span information T _iB is obtained.
Here, the future discrimination information F _i refers to the future judgment of the printing state, such as whether the record several lines ahead is solid black or black and white edges appear, and the energy applied to the unit heating element is determined. This is an attempt to make adjustments. Depending on the device, the time span information T _iA may be further modified with other information. Such information includes information on the substrate temperature of the thermal head, information on the resistance value of each unit heating element, and the like. Time width information output from the second arithmetic unit 62
T _iB is the thermal head controller 64 shown in FIG.
is supplied to In the thermal head controller 64,
As described above, the application of recording pulses is controlled so that recording is performed for each unit heating element with the respective time width information T _iB only in the portion where the data of interest D0 represents the printing state. At this time,
It is also possible to further modify the time width information and adjust the applied energy according to the ratio of simultaneous energization of unit heating elements, that is, the black ratio. FIG. 9 shows a modification of this thermal head drive circuit. The peripheral record data memory 71 of this device receives the image signal 51, and receives data of interest D0 and reference data D1 to D1 shown in FIG.
Extract 1. The reference data D1 to D11 are supplied to a weight sum calculation unit 72, and the sum of weights is determined by the weighting shown in FIG. Weight sum data 7
3 is supplied to an applied energy calculator 74 and a heat storage level calculator 75. The heat storage level data HS _i is output from the heat storage level calculator 75, is supplied to the applied energy calculator 74, and is also input to the heat storage level memory 59, where it is delayed by one line and becomes the heat storage level data HS _i-1 . Created. The applied energy calculator 74 performs the calculation shown in FIG. 8 to create recording pulse time width information T _iA . According to this modification, it is not necessary for the applied energy calculator 74 and the heat storage level calculator 75 to create the weight sum data 73 redundantly. "Effects of the Invention" As explained above, according to the present invention, it is possible to grasp the state of heat storage with sufficient accuracy, so it is possible to further speed up the creation of display images without deteriorating the image quality. Further, even in a halftone image with a high black ratio, a trailing phenomenon due to ink heating does not occur, and disadvantages such as an increase in the line width of a thin line portion and an increase in the density of a halftone image can be solved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the present invention, and FIGS. 2 to 8 are for explaining one embodiment of the present invention. Of these, FIG. 2 shows an outline of the thermal head drive circuit. 3 is a block diagram showing the specific configuration of the peripheral recording data memory, FIG. 4 is an explanatory diagram showing the contents of the ROM for heat storage state, and FIG. 5 is a weighting of reference data for heat storage calculation. Figure 6 is an explanatory diagram showing the heat storage level data.
An explanatory diagram showing the principle of calculating HS _i , FIG. 7 is a block diagram of the applied energy calculator, and FIG. 8 is an explanatory diagram showing the principle of calculating the recording pulse time width information T _iA from heat storage level data HS _i . FIG. 9 is a block diagram showing the main parts of a modified example of this thermal head drive circuit, FIG. 10 is a block diagram showing a conventional thermal head drive circuit, and FIG. 11 is a block diagram showing the main part of a modified example of this thermal head drive circuit. FIG. 12 is an explanatory layout diagram showing the layout of image data. FIG. 12 is an explanatory layout diagram showing the layout of reference data used in the embodiments of the present invention. 41, 51... Image signal, 43... Heat storage level calculator, 45... Heat storage level data feedback means, 4
6, 57, 74...applied energy calculator, 47...
...Thermal head drive control means, 52... Peripheral recording data memory, 58, 75... Heat storage level calculator, 59... Heat storage level memory, 64... Thermal head controller, 72... Weight sum calculator.

Claims (1)

[Scope of Claims] 1 Image signals for driving the thermal head line by line are sequentially input pixel by pixel, and data of interest as an image signal corresponding to the pixel that is processed for display and its focus for display. a peripheral recording data memory that temporarily stores reference data as image signals corresponding to a plurality of pixels located in a predetermined range around the data; and the data of interest stored in the peripheral recording data memory. a weight sum calculator that calculates the degree of influence of applied energy on the display of the pixel corresponding to the pixel as weight sum data of each of the reference data; and a heating element for displaying the pixel corresponding to the data of interest of the thermal head. a heat storage level calculator that calculates the current heat storage level of the heating element using the weight summation data; and a heat storage level calculator that stores the heat storage level of the heating element calculated in the past by this heat storage level calculator for the current calculation. a heat storage level data return means for feeding back the heat storage level data to the heat storage level calculator; an applied energy calculator that determines the applied energy required by the corresponding heating element when the heating element becomes a target; and a device that determines whether or not the heating element generates heat using the applied energy determined by the applied energy calculator. A thermal head drive circuit comprising a thermal head drive control means for controlling according to the data of interest.