JPH0671794B2 - Thermal head drive circuit for video printer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video printer, and more particularly to a thermal head drive circuit of a video printer suitable for expressing an image with accurate gradation.

[Conventional technology]

As shown in Japanese Patent Laid-Open No. 58-196784, the conventional apparatus is a thermal head driving method in which the thermal head is caused to generate heat according to the contents of the data and gradation is expressed.

[Problems to be solved by the invention]

The prior art described above does not consider the thermal head drive circuit, and particularly does not consider the accuracy of the energizing pulse for performing accurate gradation expression.

It is an object of the present invention to provide a thermal head drive circuit for a video printer which can express correct gradation.

[Means for solving problems]

The above object is to provide a thermal head, an energization pulse generation circuit connected to the thermal head, a data conversion circuit connected to the energization pulse generation circuit for converting gradation data into energization pulse width data, and the data conversion circuit. In a video printer equipped with a gradation counter for generating connected gradation data, and a comparator for comparing the size of the gradation data with the gradation data connected to the gradation counter,
This can be achieved by using the energization pulse generation circuit as an energization pulse generation circuit that generates the first gradation of the energization pulse transferred to the thermal head by dividing it into a plurality of times.

[Operation] The gradation counter counts the number of gradations and sends gradation data to the comparator and the energization pulse generating circuit.

The comparator compares the input data with the gradation data and sends the comparison data to the thermal head.

On the other hand, the energization pulse generation circuit receives the gradation data, generates an energization pulse, and controls the thermal head.
The energizing pulse generation circuit generates energizing pulses at each gradation to be printed, and the energizing pulse necessary for the first color development of the first gradation (which means that the density is expressed regardless of the color). It occurs in multiple times.

As a result, the precision of the energizing pulse can be set with higher precision, so that it is possible to realize a thermal head drive circuit that enables accurate gradation expression.

〔Example〕

The technique on which the present invention is based will be described below with reference to FIG. In FIG. 1, 1 is a comparator, 2 is a gradation counter, 3 is an energizing pulse generating circuit, 4 is a shift register, 5 is a thermal head, 2
0 is a switch and 21 is a head assembly.

Next, the operation of the present technology will be described with reference to FIGS. 1 and 2. Image data for one line is input to the comparator 1 from the line memory. On the other hand, gradation data is input from the gradation counter. Here, the two data are compared, and the data determined to be 1 or 0 is transferred to the shift register 4. Next, the data input to the shift register 4 is transferred to the thermal head 5. Next, the gradation data from the gradation counter is sent to the energization pulse generation circuit 3, where an energization pulse for controlling ON / OFF of the thermal head 5 is generated. The energizing pulse controls the switch 20 provided between the shift register 4 and the thermal head 5, thereby controlling energization. The thermal head 5 heats up and prints according to the data contents in the shift register 4 and ON / OFF of the switch. As described above, the data of the first gradation is transferred and printed. Similarly, the data of the 2nd gradation, the 3rd gradation, ... m gradation is printed. Second
The figure is a timing chart showing the operation of FIG. In the present technology, as shown in FIG. 2, the data of the first gradation and the data of the second gradation are sequentially transferred, and printing is performed after each transfer. By this method, printing up to m gradations is performed.

The internal structure of the head assembly shown in FIG. 1 is shown in FIG.
In FIG. 16, 4 is a shift register, 20 is a switch, 21
Is a head assembly, 22 is a heating element array, 23 is a heating element, 24
Is an AND circuit, and 25 is a transistor.

Next, the operation of FIG. 16 will be described. Data is input to the shift register 4. Next, the data of the shift register 4 is sent in parallel to the AND gate 24, and at the same time the energizing pulse is AND gated.
Send to 24. In the AND gate, only when the data from the shift register 4 and the energizing pulse come, a current is caused to flow through the resistor to the base of the transistor 25, the transistor is turned on, and a current is caused to flow to the heating element 23. As a result, the heating element generates heat, and the printing operation is performed.

Next, a signal processing system of the video printer including the thermal head drive circuit described with reference to FIG. 1 will be described with reference to FIG. Third
In the figure, 6 is an analog signal processing unit for converting an NTSC video signal into an RGB signal, 7 is an analog / digital converter (hereinafter abbreviated as A / D), 8 is an image memory, 9 is a digital / digital converter.
Analog converter (abbreviated as D / A below), 10 is RGB to N
An analog signal processing unit for creating a TSC video signal, 11 is a color selection circuit, and 12 is a line memory. The same reference numerals as those in FIG. 1 have the same functions.

Next, the operation of FIG. 3 will be described. The input image signal is converted into each color signal of RDB in the analog signal processing unit 6. Next, the A / D conversion circuit 7 converts the signals into RGB digital color signals. The digitized RGB color signals are simultaneously stored in the image memory 8. The three-color digital image data once stored in the image memory 3 is read out at the same speed as at the time of recording, passes through the D / A converter 9 and the analog signal processing unit 10, and regenerates the same video signal as when recorded, Send to monitor.

On the other hand, at the time of printing operation, one color of the RGB digital signals is selected by the color selection means 11 and stored in the line memory 12. Here, the data for one line is the data for one vertical line shown in FIG.

The image data for one line stored in the line memory is transferred to the comparator 1 in the next stage, and printing is performed by the operation described in FIG. 1 below.

When the printing of one line is completed, the data of the next line is taken into the line memory 12 and the printing of one line is performed again.

Here, the video printer is, for example, as shown in FIG.
A thermal head is arranged in the vertical direction of the TV screen, and the head sequentially advances from the left end of the TV screen to the right direction, and printing for one color is completed at the right end. In this manner, the video printer completes the printing of one sheet by printing the three colors.

Next, a technique which is another premise of the present invention will be described with reference to FIG. FIG. 5 is characterized in that a circuit for converting the data for determining the energizing pulse width sent to the energizing pulse generating circuit 3 by the gradation data from the gradation counter 2 in FIG. 1 is provided.

In FIG. 5, 13 is a data conversion circuit. In FIG. 5, those having the same reference numerals as those in FIG. 1 perform the same operation. The operation of FIG. 5 will be described below. The comparator 1 compares the input data with the gradation data from the gradation counter, and then transfers the data to the shift register. On the other hand, the grayscale data from the grayscale counter 2 is input to the data conversion circuit 13, where it is converted into data for determining the energization pulse width corresponding to each grayscale and sent to the energization pulse generation circuit 3. The energization pulse generation circuit 3 generates an energization pulse having a width suitable for each gradation based on the data for determining the energization pulse width, and transfers it to the switch 20 provided between the shift register 4 and the thermal head 5. After that, the same operation as that shown in FIG. 1 is performed and printing is performed. FIG. 6 is a timing chart showing the operation of FIG. As shown in FIG. 6, the data of the first gradation is transferred and the head is energized. Two
Data for the gradation is transferred and the head is energized. 3,4 ……
This operation is repeated m times to print data up to m gradations. Here, the print width of each gradation can be freely changed.

Fig. 7 shows the energizing time / when printing is possible with the configuration shown in Fig. 5.
It shows the relationship of the concentrations.

There is no proportional relationship between normal concentration and energization time. However, according to the present embodiment, since the energization time for expressing the color density of each gradation can be set, it is possible to express an accurate gradation.

Next, another technique on which the present invention is based will be described with reference to FIG. In FIG. 8, 14 is a read only memory (hereinafter abbreviated as ROM). The same reference numerals as those in FIG. 5 perform the same operation.

The difference between this technique and the technique described in FIG. 5 is that the data conversion circuit in FIG. 5 is a ROM.

Before explaining this operation, the operation in the energizing pulse generating means will be described with reference to FIG.

14 is a ROM, 26 and 30 are AND gates, 27 is a decoder, 28 is an energizing pulse width counter, 29 is an SR latch, 31 is an image data counter, and 32 is a decoder.

The image data is input to the image data counter 31, the output of the image data counter 31 is decoded by the decoder 31 to a certain number, and the decoded signal is sent to the AND gate 30.

At the same time, the gradation data is transferred to the ROM 14, and the load data is sent from the ROM 14 to the energization pulse width counter. The energization pulse width counter counts the reference clock of the energization pulse from the number of load data and outputs it to the decoder 27. The decoder 27 decodes a certain number, outputs the decoded signal, and outputs S
-Reset the R latch 29 and stop the energizing pulse.

The decode signal is stopped by the AND gate 26, input to the AND gate 30, and the next load signal is sent to S-.
The R latch 29 is set to generate an energizing pulse.

This series of operations is repeated the same number of times as the number of gradations.

By returning the output of the AND gate 30 to the line memory as an end signal for one line, a handshake with the line memory is performed and the overall printing time is shortened.

In the operation shown in FIG. 8, the gradation data "1" representing the gradation is first input to the ROM 14 as an address.

Data for determining the energization pulse width of the first gradation is stored in the first address in ROM14, and the data for determining the energization pulse width is output in response to the address "1", and the energization pulse generation circuit 13
To load.

In the ROM 14, the second gradation data is stored in the second address, and the third gradation data is stored in the third address. The energizing pulse generation circuit generates an energizing pulse having a pulse width from this load value. Hereinafter, as described above, the energizing pulses of the second and third gradations are sequentially generated, and the printing operation is performed as in the technique shown in FIG.

Here, the technology is characterized by using a ROM as a data conversion circuit. The adoption of the ROM has the effect that the pulse width can be easily changed even if the ambient temperature changes, paper, ink paper, etc. are changed. can get.

Next, FIG. 9 shows a technique which is another premise of the present invention. First
FIG. 10 is a timing chart showing the operation of FIG.

In FIG. 9, 16 is a latch. The same reference numerals as those in FIG. 5 have the same operation.

In the present technology shown in FIG. 9, a latch is provided after the shift register 4.
By providing 16, the data input to the shift register 4 can be sent to the latch 16 and the next data can be input to the shift register at the same time when the thermal head 5 is operating.

Next, the operation of FIG. 9 will be described. The input data is input to the comparator 1, compared with the grayscale data from the grayscale counter 2, and input to the shift register 4. After that, the contents of the shift register are transferred to the latch 16. First the gradation counter 2
The value of 1 is input to the comparator 1, the data above this value is set to 1, and the data below this value is set to 0 and input to the shift register 4. Next, the grayscale data from the grayscale counter 2 is transferred to the data conversion circuit 13, outputs data for determining the energization pulse width, and transfers it to the energization pulse generation circuit 3. In the energization pulse generation circuit 3, an energization pulse for controlling the switch between the latch 16 and the thermal head 5 is generated, and the thermal head is generated only while the switch 20 is closed.

In this way, the next data is sent during the printing.

Next, an embodiment of the present invention will be described with reference to FIG. 11, FIG. 12 and FIG.

This embodiment is characterized in that, when the data conversion circuit 13 in FIG. 9 is a ROM, the first gradation data to be stored in the ROM is divided into two. The structure of this embodiment is the same as that shown in FIG.

FIG. 10 is a timing chart showing this operation. First
As shown in FIG. 10, the data of the second gradation is sent when printing the first gradation, and the data of the third gradation is transferred when printing the second gradation.

In the present embodiment, since the next data is transferred during the printing operation, the energizing pulse can be output without interruption as shown in FIG. Therefore, the thermal head does not turn off and cool during the time spent for data transfer between the gradations. With this, it is possible to obtain an effect that the density for each gradation can be accurately expressed. Further, since the printing operation and the transfer of the next data are performed at the same time, there is an effect that the entire printing time is shortened.

The method will be described below. As shown in FIG. 7, the energization time and the color density have no proportional characteristic. Particularly, the low gradation portion is shown in FIG. In Figure 11, the concentration axis 0, 1, 2,
3, the gradation is represented, and the energization time axes t ₁ , t ₂ , and t ₃ are the energization time required to develop the density of one gradation and the energization time necessary to generate the density of two gradations, respectively. It represents the energization time required to develop the three gradations of color. Generally, in a thermal printer, it takes a considerable amount of time for energization to develop a color. Delta] t ₁ the energization time required to print the density of 1 gradation, 1 when the energization time required for printing a concentration of 2 gradations from density gradation and Δt ₂ Δt ₁ »Δt ₂ (Δt The relationship of ₁ / Δt ₂ > 10) is established.

Here, RO is used as a means for converting energization pulse width from gradation data.
Considering M, since Δt ₁ is very long, it is necessary to make a very rough step-like setting to set the pulse width after Δt ₂ .

FIG. 12 shows the relationship between the color density and the energization time in this example.

In this embodiment divides the Delta] t ₁ to Δt ₀ '+ Δt _1'.

Next, a concrete method of this embodiment is shown in FIG. Figure 13 shows RO
Representing the data in M, the upper diagram of FIG. 13 corresponds to FIG. 11 explained above, and the lower diagram of FIG. 13 is the data in ROM corresponding to FIG. Here, in the figure below, Dt ₁
It is divided into t ₀ ′ and Dt ₁ ′ and input to ROM, and then Dt _{2 and} subsequent ones are sequentially input.

Therefore Delta] t ₂ after the pulse width has the effect that about two times more accurate than the pulse width setting method of Figure 11 is obtained.

Next, a reference example of the present invention is shown in FIG.

In the figure, 4-1 and 4-2 are obtained by dividing the shift register 4 shown in FIG. 11 into two, 16-1 and 16-2 are obtained by dividing the latch 16 shown in FIG. 11, and 5-1 and 5 Reference numeral -2 is the thermal head of FIG. 11 divided into two blocks.

Next, the operation of this reference example will be described. First, input data is input to the comparator. The comparator compares it with the gradation data from the gradation counter 2 and transfers it to the second dividing means 17 in the next stage. The two-division means 17 divides the data into those to be transferred to the thermal head of the upper block and those to be transferred to the thermal head of the lower block, and transfer them to the shift registers 4-1 and 4-2, respectively. The data transferred to the shift registers 4-1 and 4-2 are transferred to the latches 16-1 and 16-2, respectively, and the switch 20 is opened / closed by controlling the energizing pulse from the energizing pulse generating circuit 3 and the data is transferred to the thermal head. Transfer to 5-1 and 5-2 and print.

In this reference example, by dividing each of the shift register, the latch, and the thermal head into two, there is an effect that the transfer speed to be sent to the shift register is 1/2 as compared with the input speed of the input data.

〔The invention's effect〕

According to the present invention, the time control of the head necessary for gradation expression can be performed with higher accuracy, so that an image with accurate gradation can be printed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the technology on which the present invention is based,
FIG. 2 is a timing chart showing the operation of FIG.
FIG. 4 is a block diagram showing the entire video printer, FIG. 4 is a schematic diagram showing a printing operation, FIG. 5 is a block diagram showing another premised technique, and FIG. 6 is an operation shown in FIG. FIG. 7 is a timing chart, FIG. 7 is a graph showing color density characteristics, FIGS. 8 and 9 are block diagrams showing other premised techniques, and FIG. 10 is a timing chart showing the operation of FIG. 11 and 12 are graphs showing color density characteristics for explaining the embodiment of the present invention, FIG. 13 is a schematic diagram of arrangement of ROM data of the embodiment of the present invention, and FIG. 14 is a reference of the present invention. FIG. 15 is a block diagram showing an example, FIG. 15 is a block diagram in an energization pulse generation circuit, and FIG. 16 is a circuit diagram showing a head assembly. 1 ... comparator, 2 ... gradation counter, 3 ... energizing pulse generating means, 4 ... shift register, 5 ... thermal head, 13 ... data conversion circuit, 14 ... ROM, 16 ... latch, 20 ... switch.

Claims (2)

[Claims] 1. A thermal head, an energization pulse generation circuit connected to the thermal head, a data conversion circuit for converting gradation data connected to the energization pulse generation circuit into energization pulse width data, and the data conversion. A video printer equipped with a gradation counter connected to a circuit for generating gradation data and a comparator for comparing the size of the gradation data with the image data connected to the gradation counter and the thermal head. A thermal head drive circuit for a video printer, wherein the energization pulse width data of the first gradation of the conversion circuit is divided into a plurality of pieces. 2. The thermal head drive circuit for a video printer according to claim 1, wherein the first gradation energization pulse divided into the plurality (N) is
First energizing pulse, or M (M <N) from the beginning
A thermal head drive circuit for a video printer, wherein the energizing pulses up to the third are set to a pulse width near the time required to start color development.