JPH0310854A - video printer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a video printer that prints an image on photographic paper based on a supplied video signal, and is particularly suitable for improving the image quality of prints. The present invention relates to a video printer that controls the energization time of a thermal head.

[Conventional technology]

Conventional video printers, especially their No. 100 processing circuit (head control circuit), temporarily store the supplied video signal in a memory, as described in Japanese Patent Application Laid-open No. 58-138667, and A drive signal corresponding to the level of the video signal was generated in the thermal head drive circuit. The drive signal generated by the thermal head drive circuit is supplied to the thermal head, and as a result, the amount of heat generated by the thermal head is controlled.

Furthermore, as described in Japanese Patent Application Laid-Open No. 54-91540, the signal processing circuit of a conventional video printer synchronizes the drive signal for driving the thermal head with the AC voltage supplied to the video printer body, and this synchronization The image was printed on photographic paper using the generated drive signal.

In addition, the conventional thermal head is equipped with a signal processing circuit that changes the time for supplying a drive signal to the thermal head (hereinafter abbreviated as energization time) depending on the temperature around the thermal head (hereinafter abbreviated as ambient temperature). Video printers have also been proposed.

In a video printer using a thermal head, the amount of ink transferred from the ink paper to the photographic paper changes depending on the heat (temperature) that the thermal head applies to the ink paper. Therefore, in conventional video printers, the energization time is varied in order to set the temperature of the thermal head. In this way, since the amount of ink transferred from the ink paper to the photographic paper is controlled by the temperature, the amount of ink transferred changes as the ambient temperature changes. As a countermeasure for this, the energization time is generally varied by 8 depending on the ambient temperature. This allows the ink density (color depth) in the print to be selected appropriately.
This improves image quality.

[Problem to be solved by the invention]

However, the above-mentioned conventional technology does not take into account the fact that the waveform of the drive signal for driving the thermal head is set based on the state of heat generation (temperature distribution due to heat generation) of the thermal head. For this reason, the quality of images printed on photographic paper using a thermal head is still insufficient.

Note that even if the current application time was changed by 8 depending on the ambient temperature, the image quality deteriorated depending on the heat generation state of the thermal head.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a video printer that eliminates the drawbacks of the prior art described above and that controls the energization of the thermal head based on the state of heat generated by the thermal head to produce a printout with improved image quality.

[Means to solve the problem]

In order to achieve the above object, the video printer of the present invention includes an AD converting means for converting an externally supplied video signal into an analog-to-digital signal and outputting a digitized video signal, and a digital video printer supplied from the AD converting means. Based on memory means for temporarily storing the signal, the temporarily stored digitized video signal supplied from the memory means, and the print command signal supplied from the print control circuit,
a gradation control circuit that generates a pulse width modulation signal; a thermal head that generates an amount of heat proportional to the pulse width of the pulse width modulation signal supplied from the gradation control circuit and prints on photographic paper;
A sync separation circuit that separates the sync signal portion from the video signal and outputs the sync signal, and counts the sync signals supplied from the sync separation circuit to generate a write address and a write control signal for the memory means. a write circuit, a read circuit that generates a read address for the memory means and a read control signal from a print command signal, a print control circuit that generates a print command signal and a servo control signal, and a servo supplied from the print control circuit. A servo circuit that controls the motor that drives the platen roller using control signals to feed photographic paper at a constant speed, a write address and input control signal supplied from the write circuit, and a read circuit. In a video printer comprising a switching circuit that controls a printing means by switching between a supplied read address and a read control signal, the write control circuit determines the number of times the read circuit performs reading based on the print command signal of the print control circuit. The number of times of reading is set to an integral multiple of the number of times of writing.

Furthermore, in order to effectively achieve the above object, the present invention includes:
In the above means, there is a frequency divider circuit that divides the print command signal of the print control circuit into an integer and outputs a frequency divided signal, and a frequency divided signal output from the frequency divider circuit and a frequency divided signal output from the readout circuit. The memory means is provided with a gate circuit that is supplied with a read address and switches an output state based on a predetermined logic, and the memory means that is supplied with an output signal of the gate circuit.

Furthermore, the print control circuit of the present invention includes a position detection circuit for detecting that the photographic paper is set at a predetermined position by the paper feeding mechanism, and sequentially reads out the digitized video signal from the memory means. The above object can be effectively achieved by including an energization time control circuit that energizes the thermal head for a period of time corresponding to the level of the digitized video signal.

[Effect]

In the present invention, in a signal processing circuit (gradation control circuit) that generates a signal for driving a thermal head from a video signal, 1
The ink adhering to the photographic paper is averaged by energizing the thermal head multiple times for each line of paper feeding to average the temperature distribution due to the heat generated by the thermal head. In other words, when changing the energization time to compensate for the influence of ambient temperature, the temperature of the thermal head can be averaged by inserting a small amount of rest time during the energization period without changing the length of the energization time. A smooth surface print can be obtained.

The paper to be printed (photographic paper) is conveyed to a predetermined position by the paper feeding mechanism, and the position detection circuit detects that the photographic paper is set at the predetermined position (the thermal head has reached the printing start position ζ of the photographic paper). When detected, the print control circuit outputs a print command signal to the energization time control circuit to start printing. At this time, the energization time control circuit sequentially reads the image data (digitized video signal) from the memory and controls the thermal head I for a time corresponding to the level of the image data.
Turn on the power. Therefore, the heating element of the thermal head generates heat.

At this time, in proportion to the progress of paper feeding, the print control circuit outputs a print command signal a plurality of times to print one line divided into a plurality of times to obtain a smooth print.

Further, the energization time control circuit stores energization time data for each gradation in a memory, reads out this memory data at the time of printing, and generates an energization control signal. At this time, the thermal head is driven by controlling the energization pause time and energization time set for each gradation depending on the temperature of the thermal head. However, the sum of the energization time and the energization stop time must be controlled to be constant.
Therefore, by keeping the current supply time for printing one line constant and preventing the print width from changing, prints without image quality deterioration can be obtained.

〔Example〕

Embodiments of the video printer of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of a video printer of the present invention, and is a block diagram showing the configuration of its signal processing circuit.

In FIG. 1, 1 is a decoder circuit that decodes a video signal, and 2 is a decoder circuit that decodes a video signal.
an AD converter that performs analog-to-digital conversion (hereinafter abbreviated as AD conversion) of a part (video signal) related to an image;
5 is a memory that stores AD-converted image data; 4 is a switching circuit (hereinafter abbreviated as selector) that switches between a write control signal and a read control signal for the memory 3;
5 is a write control circuit that generates an address signal and a write control signal for the memory 3; 6 is a read control circuit that generates an address signal and a read control signal for the memory 3; 7 is a synchronization separation circuit that separates a synchronization signal from a video signal; 8 is a sampling clock generation circuit that is supplied with the output signal of the synchronous separation circuit 7 and generates a signal for sampling the video signal of the video signal; 9 is supplied with the output signal of the synchronous separation circuit 7 and a detection signal from the mechanism. a print control circuit for generating print timing control signals;
is a servo circuit that controls the speed of paper feed.

11 is ink paper, 12 is a platen roller that wraps and conveys the paper, and 13 is a paper position detection circuit that detects the position of the paper. Further, 14 is a line head type thermal head that can print one line at the same time.

The thermal head 14 includes a shift register 15 that converts serially input data into parallel data, a latch circuit 16 that latches the parallel-converted data, and a gate that controls whether the output signal of the latch circuit 16 is energized or not. It is composed of a gate circuit 17 that performs this, and a heating element 18 that is controlled by an output signal of the gate circuit 17. Input signals to the thermal head 14 are a clock and serial data supplied to the shift register 15, a latch clock supplied to the latch circuit 16, and a strobe signal supplied to the gate circuit 17. Note that the thermal head 14 is connected to a temperature detection circuit 20 that detects the ambient temperature at the start of printing and the rise in head temperature during printing. Reference numeral 19 denotes a gradation control circuit that converts the image data written in the memory 173f into energization data for the thermal head 14. This gradation control circuit 19 is controlled by the output signal l of the print control circuit 9. 50 is a strobe signal, 51 is a latch signal, 52 is a serial data signal, 53 is a read control signal, 54 is a print signal, and 55 is a temperature detection signal.

The operation of this printed circuit will be explained below with reference to the drawings.

The input video signal is guided to a decoder circuit 1 and a sync separation circuit 7. A portion of the video signal indicating an image (video signal) is decoded by a decoder circuit 1, and then an ADf converter 2
The analog signal is converted into digital data. A
The D-converted data is temporarily stored in the memory 3. On the other hand, the synchronization signal added to the video signal is sent to the synchronization separation circuit 71.
Therefore, only the synchronous signal portion is separated. Thereafter, one is supplied to the printer control circuit 9 and the other to the sampling generation circuit 8.

A sampling generation circuit 8 generates a conversion clock for the AD converter 2. Based on this clock, the write control circuit 5 also generates an address for the memory 3 and controls the memory 5 by switching the selector 4 to the write control circuit 5 side. During printing, a control signal is output from the print control circuit 9 to the mechanism, and the platen roller 12 and ink paper 11 are first set and the photographic paper is wound around the platen roller 12.

Next, a rotation start signal is sent to the servo circuit 10 to rotate the platen roller 12. The paper position detection circuit 13 detects that the photographic paper wrapped around the platen row 212 is at a predetermined position (the thermal head 14 has come to the print head position of the photographic paper), and the gradation control circuit 19 and readout control circuit are activated. 6, a print start signal is sent to the memory 5, the video data stored in the memory 5 is sequentially read out, and a gradation control circuit 19 generates a drive signal for the thermal head 14.

Here, the configuration of the gradation control circuit 19 is shown in FIG.

In FIG. 2, 70 is a comparison circuit that compares the image data read from the memory 5 with the count value of the gradation counter 71, 71 is a counter that counts up for each gradation, and 72 is the gradation counter 71. The comparator circuit 70 outputs a latch signal after the operation is completed based on the count value of the count value and the clock of the comparator circuit 70, and at the same time, the count value of the temperature detection circuit 20 and the gradation counter 71 is also set to 7 to control the amount of heat generated by the thermal head 14. FIG. 6 is a diagram for explaining the operation of the gradation control circuit 19 shown in FIG. 2, which is a strobe generation circuit that generates a strobe signal.

The gradation control circuit 19 controls the energization time of each heating element 18 of the thermal head 14 according to the level of the input video signal. However, since the number of heating elements 1B is generally close to 500, it is first determined whether or not to energize the first gradation, and it is sent to the shift register 15 in the thermal head 14, latched, and then energized. Thereafter, it is similarly determined whether or not to energize the second gradation, and energization on/off data is sent to the shift register 15 to energize it.

In this way, by energizing, for example, 64 times, heat is generated corresponding to the energizing time, thereby controlling the amount of ink that adheres to the photographic paper. The operation of the gradation control circuit 19 that performs such conversion is as follows. Gradation counter 71
is reset in units of 1 line/unit and counted up for each gradation, and this count value is sent to the comparator 70. Strobe generation circuit 72. It is applied to the readout circuit 6. The readout circuit 6 reads image data from the memory 3 based on the count value, and the comparison circuit 70 compares the data read from the memory 5 with the count value to generate serial data to be sent to the thermal head 14. The strobe generating circuit 72 generates a strobe signal 50 and a latch signal 51 based on the count value of the gradation counter to control the thermal head 14.

Each time the servo circuit 10 feeds one line of paper, data for one line is read out from the memory 3 and the thermal head 148 is controlled. However, considering the heat generation state of the thermal head 14, the temperature of the heat generating element 18 increases even at the center of one line, resulting in ink adhering to this area. Therefore, if the servo circuit 10 divides the time for feeding one line of paper into four, for example, and energizes the thermal head 14 for each divided time, the temperature distribution of the heating element of the thermal head 14 will be averaged within one line and specified. Figure 4 shows such an energizing waveform, and one line l
This is the one that was energized twice. To obtain such an energizing waveform, the print control circuit 9 issues a print command twice for one line, and the gradation control circuit 19 receives the read address of the readout circuit 6 twice from the print command before starting the next line. All you have to do is make a komaru to read the data.

Specifically, conventionally, a pulse generator (FG, not shown), which is attached to the output shaft of the motor that drives the platen roller 12 and generates pulses in proportion to the rotation angle, is used to print every N pieces. The circuit 9 outputs a print command once, but in this embodiment, it outputs a print command every y2 times. However, the readout control circuit 6 ignores the print command received via the gradation control circuit 19 one out of two times according to the output signal of the print control circuit 9, thereby reading out the same data for two print lines. This is how it was done.

Next, FIG. 5 is a diagram showing a second embodiment of the video printer of the present invention. In the energization method shown in FIG. 1, the amount of data sent to the thermal head 14 is, for example, N times per line.
If the data is energized, it will increase N times. Therefore, in this embodiment, electricity is applied to odd-numbered gradations first and even-numbered gradations the second time to obtain a smooth print.

In FIG. 5, the same reference numerals as in FIG. 1 indicate components having the same functions. 50 is a frequency divider that divides the print command; 3
1 is a gate circuit that gates the divided output.

52 is a signal indicating the first gradation from the print control circuit 9, and this signal is controlled by the gate circuit 518.

The operation will be explained below using the drawings. The print command output from the print control circuit 9 is input to the gradation control circuit 19 as before. The lower bits of the address output from the read control circuit 6 are replaced by the outputs of the frequency divider circuit 50 and gate circuit 51.

As a result, as shown in FIG. 6, only the even-numbered gradations are sent to the thermal head 14 at first, and at the n1st order, only the odd-numbered gradations are sent to the thermal head 14 and energized.

In this case, the energization time is generally set to be long for the first gradation in order to cause the heating element 18 to generate heat above a certain temperature. Note that if the current is applied as it is, the first energization time for even-numbered gradations will be short, and the amount of heat generated by the thermal head 14 will decrease in the latter half.
It is thought that the amount of ink may not be sufficient only in the latter half of printing.Therefore, the v11th gradation was added to both the odd and even gradation openings. In this embodiment, the print control circuit 9 outputs a control signal specifying only the first gradation, and the gate circuit 31 fixes the read address.

According to this embodiment, the temperature of the heating element for one day can be averaged, and smooth prints can be obtained.

The next figure, $7, is a diagram showing a third embodiment of the video printer of the present invention. In this embodiment, a dual port memory is used as the memory so that data can be sent to the thermal head 14 at higher speed.

In FIG. 7, the same reference numerals as in FIG. 1 indicate components having the same functions. 110 is a gate circuit that takes the exclusive OR of the edge deviation of the shift register 15 in the thermal head 14 and the serial output of the dual hoard memory 120; 120 is a dual hoard memory for temporarily recording image data;
1 is a gate circuit that gates data sent to the thermal head 14 for a certain period of time; 122 is a switch circuit (hereinafter abbreviated as 1, SW) that fixes the serial input/output terminal of the dial port memory 120 to 10"data; 12 !l,
124 is a switching circuit (hereinafter referred to as a selector) that switches the address of the dial port memory 120;
125 is a SAM shift clock generation circuit that generates a clock for reading the serial port of the dial port memory 120;

a read/write timing control circuit (hereinafter abbreviated as R/W timing control circuit) that controls writing and reading of the 126 dual port memory 120;
A write address counter 127 generates an address for data to be written into the memory 120.

128 is an input data latch circuit that latches data from the AD converter 2 (not shown); 129 is an image data input terminal; and 130 is a write clock input terminal.

151 is a write reset terminal, 132 is a memory 120
133 is a control signal for exchanging data between a serial access memory (hereinafter abbreviated as SAM) and a random access memory (hereinafter abbreviated as RAM) in the memory 120, and a shift register 133 in the SAM in the memory 120 and the thermal head 14. 15 shift clocks.

134 is W that controls writing and reading of the memory 120;
E scratch signals 155 to 135'' are control signals for controlling data in the thermal head 14 and memory 120.

In this embodiment, when reading one line of image data input to the gradation control circuit from the memory 120, it is necessary to read out rotated image data (number of gradations x image data), and this is performed multiple times for one line. Once again, the printing speed may be limited by the operating speed of the memory. Therefore, memory 120
The inner number energization pattern is stored in advance, and when read out, this energization pattern is sent directly to the thermal head 14, thereby increasing the speed.

The operation will be explained below using the drawings. The image data is connected to the horizontal address number of the memory 120 through the input data latch 128. The vertical address is generated by the write counter 127. Data 11" is written to the address generated in this way. As a result, after one line of writing is completed, the memory 120 has exactly 11" written only at the ax conversion point. ing. After writing one line of data in this way, the R/W timing circuit 126 writes the data to the memory 1.
The energization pattern written in the RAM in 20 is read every other gradation in the vertical direction using a data transfer signal 132 and transferred to the SAM. The data for one gradation thus transferred is read out from the memory 120 using the clock 133 generated by the SAM clock generation circuit 125, and is read out from the memory 120 by the clock 133 generated by the SAM clock generation circuit 125. It is logically summed with the shift register output and inputted to the thermal head 14 again.

Here, the shift register 15 in the thermal head 14 is reset to "1" by the R/W timing control circuit 126 at the start of energization.
Data is written in advance to the EX-OR circuit 110 and the shift register 15 from '1' to '10' only at the energization change point.
change the value of. In this way, the thermal head 14 is driven by repeating the process for every gradation. Such a circuit configuration eliminates the need for the gradation control circuit 19, and since the SAM in the dual port memory can be read out at high speed, signals can be sent to the shift register in the thermal head 14 quickly. After the reading is completed, the serial input/output terminal is set to 10'' by the SW circuit 122 to make all the SAM data in the memory 10''. By transferring this data back to the RAM, the memory 120 is cleared and preparations are made for capturing the next line of image data.

In this way, in a circuit that can read data at high speed, the sequential address circuit 105 that reads the SAM at the time of reading can generate the same address twice, for example, so that the thermal head 14 can be driven with the same data twice in one line. can. FIG. 8 shows this situation. 8th
In the figure, the serial R/W control signal is set to 10" and one line of data is written to the memory 120. After writing is completed, the serial R/W control signal is set to 11", and the data transfer signal 132 is used to The 11th order is read out from the key and transferred to the thermal head 14. In synchronization with this, a strobe signal 50 is generated to cause the thermal head 14 to generate heat. Since the sequential address control circuit 105 generates the same address the second time, the same data is sent to the thermal head 14 to generate heat. After two confirmations, the next transfer cycle begins.
The serial R/W control signal becomes '0'. The data of the next line is written.

As explained above, according to the present example, by writing the energization pattern in the memory in advance, data can be read out faster than ever before. This allows the same data to be applied multiple times to one line, making it possible to obtain smoother prints.By the way, as mentioned above, in a thermal transfer printer, the ink increases in proportion to the amount of heat generated by the thermal head 14. The amount of ink transferred from paper 11 to photographic paper is controlled. Therefore, even if the thermal head 148 is made to generate heat for the same amount of time, the amount of ink transferred to the photographic paper differs depending on the ambient temperature. In order to correct this problem, general printers attach a temperature detection circuit 20 to the thermal head 14, and control the amount of ink transferred to the photographic paper by changing the energization time depending on the temperature of the thermal head 14. However, if the energization time is simply lengthened or shortened, the temperature distribution of the thermal head 14 becomes uneven and smooth printing cannot be obtained. Therefore, temperature correction is performed by changing the on-time and off-time for each gradation depending on the temperature, and without changing the energizing time for one line as a whole. An embodiment of the video printer of the present invention will be described next.

Now, FIG. 9 is a diagram showing a fourth embodiment of the video printer of the present invention.

@9 In Figure 9, the same reference numerals as in Figure 1 indicate components having the same functions. 70 is a comparison circuit that compares the magnitude of image data with the gradation counter 75; 71 is a strobe generation circuit;
Addressed by a gradation counter 75 indicating the number of currently energized gradations, a latch clock generation circuit 76 that generates a latch signal for each gradation of the gradation counter 75, and a gradation counter 75, on-time and off-time data are It is composed of a recorded memory (for example, a read-only memory) 73, 74 and a timing generation circuit 72 that generates a signal for energization based on the data from this memory 75, 74.

Further, FIG. 10 is a diagram showing a strobe waveform of the thermal head 14 according to this embodiment.

The operation will be explained below using the drawings.

As can be seen from FIG. 10, even if the temperature changes, the energization start point of each gradation does not change, but the ratio of on time to off time (duty ratio) changes. This is gradation counter 7
Read only memory (ROW) 75.74 is selected, which determines the on time and off time based on the count value of 5. At this time, the sum of the on time and off time of each gradation is set to be constant #C even if the temperature is changed. The timing generation circuit 72 first reads the on-time data from the ROM 73, sets the strobe signal to 10'', and maintains the time indicated by the data at 10''. Next, off time data 8ROM74
Read out the strobe signal yy,, % 1//
As explained above, in this example, even if the temperature changes,
Since the current is applied so that the energization time of the thermal head 14 on the line remains the same, smooth printing can be achieved.

〔Effect of the invention〕

According to the present invention, the temperature distribution caused by the heat generated by the thermal head can be averaged, and the ink transferred from the ink paper to the photographic paper is not concentrated at one point.As a result, smoother prints with improved image quality can be achieved. A video printer can be provided to create the video.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the signal processing circuit of the video printer of the present invention, FIG. 2 is a diagram showing an example of the configuration of the gradation control circuit of the signal processing circuit shown in FIG. 1, and FIG. is an explanatory diagram for explaining the energization status of the thermal head shown in FIG. 1, FIG. 4 is a waveform diagram showing the waveform of the thermal head passing through the thermal head obtained by the present invention, and FIG. It is a figure showing an example of. FIG. 6 shows the embodiment ζ shown in FIG.
FIG. 2 is a waveform diagram showing the shape of a thermal head that is obtained in this manner. FIG. 7 is a diagram showing a third practical example of the video printer of the present invention, FIG. 8 is a waveform diagram showing a thermal head energization waveform obtained by the embodiment shown in FIG. 7, and FIG. 9 is a diagram showing the video printer of the present invention. Figure 10 shows the fourth embodiment of the 9th embodiment.
FIG. 2 is a waveform diagram showing a waveform of energization to a thermal head obtained by the illustrated example. 3...Memory 9...Print control circuit 1
4... Thermal head 19... Gradation control circuit 70
... Comparator 71 ... Gradation counter A Patent attorney Masaru Ogawa Reinversion 2, 42 ηJ diagram (α) (b) To month 5 Mourning color A middle 12 Rabbit 4 diagram Zoro diagram 〒 5 father

Claims (1)

[Scope of Claims] 1. AD conversion means for converting an input video signal into an analog-to-digital format and outputting a digitized video signal; and memory means for temporarily storing the digitized video signal supplied from the AD conversion means. , a gradation control circuit that generates a pulse width modulation signal based on the temporarily stored digitized video signal supplied from the memory means and a print command signal supplied from the print control circuit; and the gradation control circuit. a thermal head that prints on photographic paper by generating heat proportional to the pulse width of a pulse width modulation signal supplied from the video signal; and a synchronization separation circuit that separates the synchronization signal from the video signal and outputs the synchronization signal. and a write circuit that counts the synchronization signals supplied from the synchronization separation circuit to generate a write address and a write control signal for the memory means, and a read address and read control signal for the memory means from the print command signal. a readout circuit that generates the print command signal and the servo control signal; a print control circuit that generates the print command signal and the servo control signal; and a motor that drives the platen roller is controlled by the servo control signal supplied from the print control circuit. A servo circuit for feeding photographic paper at a constant speed; a write address and a write control signal supplied from the write circuit; and a read address and read control signal supplied from the read circuit. and a switching circuit for controlling the print control circuit, the readout number setting means for setting the number of times the readout circuit is read in response to a print command signal from the print control circuit to an integral multiple of the number of times the write control circuit performs writing. A video printer characterized by comprising: 2. A frequency dividing circuit that divides the print command signal of the print control circuit into an integer and outputs a frequency divided signal, and a frequency divided signal outputted from the frequency dividing circuit and outputted from the readout circuit. 2. The video printer according to claim 1, further comprising: a gate circuit supplied with a read address; and the memory means supplied with an output signal of the gate circuit. 3. The print control circuit includes a position detection circuit for detecting that the photographic paper is set at a predetermined position by the paper feeding mechanism, and a position detection circuit for sequentially reading digitized video signals from the memory means and storing the digitized video signals. The video printer according to claim 1, further comprising: an energization time control circuit that energizes the thermal head for a time corresponding to a signal level.