JPH0796306B2 - Energization control method in multi-gradation thermal recording - Google Patents

Description

The present invention relates to an energization control method in multi-gradation thermal recording, and more particularly to a method of converting gradation data applied to a thermal head of a thermal recording apparatus and energization time control. The present invention relates to an energization control method that enables high-speed recording and downsizing of a control circuit.

[Prior Art] With the recent widespread use of video equipment, demand for color printers that record video images and still images in full color has increased, and development of multi-tone thermal recording printers centering on thermal transfer recording systems has been developed. ing.

In the multi-gradation printer of the thermal transfer recording system, the heat energy applied to the thermal sublimation or thermal melting type ink sheet is selectively applied to each heating resistor of the thermal head with a pulse width corresponding to the gradation data. Is used to control multi-gradation. Regarding this pulse width, a method using one continuous pulse is generally used, but paying attention to the fact that the energization pulse width is small with respect to the thermal time constant of each heating resistor part, A method using a total of a plurality of pulses has also been proposed to provide a margin (Japanese Patent Application No. 62-306728).

Further, the current thermal head unit has a configuration as shown in FIG. 8, and when recording one line with N dots, serial pixel data for N dots transferred from the host side is used. Is converted into gradation data by the data conversion circuit 51, which determines the energizing pulse width corresponding to each pixel data,
After transferring these gradation data to the N-bit shift register 52, each time one line is input to the shift register 52, one line data is held by the N-bit latch 53, and the enable terminal of each driver 54 is controlled. Then, a predetermined pulse determined by the gradation data is applied to each heating resistor 55 of the thermal head to perform thermal recording.

Therefore, in order to give a pulse width for expressing a predetermined gradation to each heating resistor 55, if n gradations, serial data is transferred n times and the gradation corresponding to the position of each heating resistor 55. The data is set to be "ON" data for the number of times corresponding to the required pulse width out of n times, and is set to "OFF" data for the rest.

[Problems to be Solved by the Invention] According to the thermal recording method as described above, in order to perform recording with more gradations, the number of times serial data is transferred must be increased correspondingly. To tune it, the serial transfer of data must be done so fast.

On the other hand, the transfer frequency of the shift register currently used in the thermal head is 4 to 5 MHz, and when high-speed transfer higher than that is required, the serial data is divided as shown in FIG. The current situation is to deal with this problem by performing parallel transfer to the divided shift registers 52.

However, when such a high-order parallel configuration is adopted, data control is naturally complicated and the circuit scale becomes enormous, which inevitably leads to an increase in size and cost of the printer.

Therefore, the present invention does not have a one-to-one correspondence between the expression of gradation steps and the transfer of serial data as in the conventional art, and the gradation of recording is increased with a very small number of times of transfer, and high gradation and high-speed recording are reduced. It was created for the purpose of providing an energization control method that can be realized on a circuit scale.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention divides the characteristic curve in the color density vs. energization time characteristic into a range in which each section can be linearly approximated in multi-gradation thermal recording. , The longest non-energization time between each pulse applied in time series to the heating resistor to express the gradation step in each section is the time constant composed of the relationship between the heating resistor and the recording paper. On the condition that it is set to be sufficiently short, a pulse train consisting of one of a plurality of weighted pulses or a combination thereof is made to correspond to the gradation data input in each gradation step. It is expressed by being selectively applied, and is obtained by the final pulse in the low gradation side section between the final pulse in the low gradation side section and the first pulse expressing the next high gradation side section. The gradation step is the high gradation side section The energization control method in the multi-gradation thermal recording is adopted, which is characterized by applying an adjustment pulse for supplying the thermal energy required to raise to the reference gradation step.

Here, how to set the weight of the weighted pulse is arbitrary, but as an example, a binary weighted pulse having a pulse width of 1, 2, 4, 8, ... Can be used.

Further, in the case of an ink sheet or the like in the case of the thermal transfer recording method, it is necessary to supply a considerable amount of energized heat energy before the start of color development, but this heat energy is separately pulse width based on the temperature data of the thermal head. It can be supplied by applying a set initial pulse.

[Operation] The basic principle of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 shows a characteristic curve of color density vs. energization time characteristic in thermal recording. In the present invention, the characteristic curve is divided into ranges in which linear approximation is possible. That is, the energization time axis is T
(1) to T (n), and the characteristic curve is linearly approximated in each section.

As a result, n linear gradation expression sections can be created. By securing the linear sections in this way,
It becomes possible to represent the gradation step of the section by the weighted pulse.

Here, each section is represented by 2 ^m gradations, and an energization control method capable of expressing (2 ^m × n) gradations in total will be described.

As a means for expressing 2 ^m gradations in each section, as shown in FIG. 2, m weighted pulses P are used for gradation expression in each section.
_{1 (k) to} P _{m (k)} [where (k) is a subscript indicating each section] and the adjustment pulse RP _K are used. Here, the weighted pulse P _{1 (k)} ~ P
The pulse width of _{m (k)} varies depending on each section [value of (k)], and is proportional to the slope of the approximated straight line within each section, that is, the thermal energy required to raise the gradation by a unit step within the section. Then, the pulse width is selected.

By the way, the number of gradations that can be expressed using _m weighted pulses P _{1 (k) to} P _{m (k)} is one of the pulses or a combination thereof, and is [2 ^m −1 ] It becomes gradation.

Therefore, for example, if the gradation data is [2 ^m × i] gradation and [2 ^m
× (i + 1)] If a certain gradation (G) between the gradations is to be recorded, the adjustment pulse and all weighted pulses in each section of T (1) to T (i) After applying the adjustment pulse RP _i , the weighted pulse P _{1 (i)} for supplying the heat energy required to increase the color density from the [2 ^m × i] gradation to the G gradation A pulse consisting of one of P _{m (i)} or a combination thereof will be applied.

Here, the adjustment pulse RP _k plays the following role.

Focusing on the continuous part of the section T (i) and the section T (i + 1) of the characteristic curve, the maximum color density on the section T (i) side can be expressed only up to [2 ^m × i−1] gradation. On the other hand, on the side of the section T (i + 1), the expression above from the [2 ^m × i + 1] gradation is performed, so that it is impossible to express the [2 ^m × i] gradation corresponding to the continuous portion. Therefore, for this continuous portion, in the low gradation side section T (i), the thermal energy required to maintain the rate of change in color density (gradient of the characteristic curve) in the low gradation side section T (i), By applying the adjustment pulse PR _i having the thermal energy required to raise the gradation step obtained by the final pulse to the reference gradation step in the high gradation side section T (i + 1), It ensures the continuity of gradation expression.

That is, when the gradation step in each section is represented by a weighted pulse, no matter what weighting method is adopted, the section T
Even if the highest gradation step in (i) can be expressed by a combination of weighted pulses, the reference gradation step in the next section T (i + 1) cannot be given.
I am trying to compensate for this by PR _i . Further, in the present invention, each section is linearly approximated, but as is clear from the characteristic curve, the slope of the approximated straight line corresponding to each section changes for each section. The pulse width of PR _i of the adjustment pulse differs depending on the position of the section T (i) on the characteristic curve.

As for the method of weighting the weighted pulse, it is desirable to configure so that the frequency due to the combination of the code efficiency and the code becomes high in order to execute the high speed recording, but the weighting by the binary weighting and other codes is performed. Can be selected, and the application order of the weighting pulses in each of the sections T (1) to T (i) is not limited to the weight order and can be set arbitrarily.

As a result, according to the prior art, since it is assumed that the characteristic curve is non-linear, one gradation data must always be transferred to the thermal head in correspondence with the expression of the unit gradation. In order to express the highest gradation, data transfer of [2 ^m × n] times is required, but according to the present invention, the gradation expression of each section is performed in the highest gradation expression. [M + 1] times (the number of weighted pulses + the number of adjustment pulses) for n intervals, that is, [n (m + 1)]
It is sufficient to transfer the data once, and an extremely small number of times of data transfer will suffice.

By the way, as described above, it is good to perform gradation expression by the weighted pulses P _{1 (k) to} P _{m (k)} and the adjustment pulse RP _k , but in the thermal recording, the heating resistor, the ink sheet, and the recording paper. The relationship with the thermal time constant of the heat transfer circuit composed of, etc. is always a problem.

A schematic equivalent circuit of this heat transfer circuit is as shown in FIG. 3, and the thermal conductivity Rh of the heating resistor, the same heat capacity Ch, the thermal conductivity Ri of the ink sheet, the same heat capacity Ci, and the heat of the recording paper. Consists of conductivity Rp and same heat capacity Cp. Therefore, if the non-energization time between each pulse in the pulse train for gradation expression becomes long, heat diffusion and cooling occur, and the thermal energy in the recording portion simply does not correspond to the sum of the pulse widths.

Therefore, the condition is that the longest non-energization time between the pulses applied in the present invention is set sufficiently shorter than the thermal time constant in the above circuit. This longest non-energization time is at various positions depending on the setting mode of the weighted pulses P1 _{(k) to} Pm _(k) and the application order, but a combination of weighted pulses is selected in a certain gradation expression. The longest non-energization time is P _{a (k)} and P _{b (k)}
When it is located between the two, it becomes as shown in FIG. 4, and in this case, it is required that tmax is sufficiently shorter than the thermal time constant.

Further, in general, in a coloring medium such as an ink sheet,
As shown in FIG. 1, a considerable amount of heat energy is required from 0 gradation to the start of color development, and this also changes depending on the temperature environment.

Regarding this problem, in the present invention, a method of expanding the concept of the adjusting pulse and applying the initial pulse having the thermal energy while referring to the temperature of the thermal head during the time to until color development starts is also adopted. Therefore, it is possible to start color development immediately when a weighted pulse for gradation expression in the section T (1) is applied and improve the linear approximation in the section T (1). Becomes

[Embodiment] An embodiment in which the present invention is applied to a thermal transfer recording apparatus will be described below with reference to FIGS. 5 and 6.

In this embodiment, when the color density-current-carrying time characteristic of the ink sheet used in the apparatus is as shown by the characteristic curve of FIG. 1, the characteristic curve is divided into 16 sections (n =
16), and the gradation control in each section T (1) to T (16) is 16 steps (m = 4), and the energization control method of the thermal air recording device capable of expressing 256 gradations is explained. To do.

In this case, the adjustment pulse and the four binary weighted pulses are used to express the gradation step in each section. That is,
As shown in FIG. 5, by using the weighted pulses P _w1 , P _w2 , P _w3 , and P _w4 having the pulse widths of the ratios of 1, 2, 4, and 8, the total pulse width is 1 15 different pulse trains can be configured for each, and by adding the adjustment pulse RP to this
Express 16 steps. Further, the adjustment pulse RP is applied after the pulse train of the weighted pulse applied in the low gradation side section, and the thermal energy required to maintain the color density change rate in the low gradation side section. That is, it has a pulse width corresponding to the thermal energy required to raise the gradation step obtained by the final pulse in the low gradation side section to the reference gradation step in the next high gradation side section.

The pulse widths of the weighted pulses P _w1 , P _w2 , P _w3 , P _w4 and the adjustment pulse RP differ depending on the sections T (1) to T (16). This is because each section T in which the characteristic curve is linearly approximated
This is because the slopes of the straight lines in (1) to T (16) are different, and the thermal energy for giving the gradation step is different in each section, and weighting is applied to each section T (1) to T (16). The pulse width of the pulses P _{1 (k) to} P _{m (k)} is set in consideration of the differential thermal characteristics of the section.

FIG. 6 is a block circuit diagram for executing energization control in the present embodiment, 11 is a gradation control unit for executing sequence control for multi-gradation recording, 12 is externally written by some means. 1 line of binary image data to be inserted [upper bit data is interval data (4 bits),
Lower-order bit data is a raster memory that stores gradation data (4 bits) in each section], 13 is a raster memory
A memory read control unit that accesses 12 to read image data to the gradation conversion circuit side and outputs a transfer clock to the thermal head at a predetermined timing, and 14 is a gradation control unit 11
A pulse count unit that increments the count value each time there is a START signal and counts the number of pulse applications (0 to 5) in each section T (1) to T (16), and 15 is a pulse count unit 14 Is incremented by +1 by the carry of the section and the section counting section for counting the number of sections (0 to 15), 16 is the pulse counting section 14 and the section counting section 15
When the count number of is 0, the first section T (1)
An initial state detection unit that notifies the gradation control unit 11 that
Reference numeral 17 compares the count number (B) of the section counting unit 15 with the higher-order bit data (A) read by the raster memory 12, and when A> B, sets “1” to the OR circuit 19 described later, and A = When B, "1" is output to the data selector 18 described later, and when A <B, a comparator that outputs an enable signal to the data selector 18, and 18 is a comparator 17 corresponding to the count data of the pulse counting unit 14. "1" (0 terminal) when A = B, and either of the lower bid data (one of 1 to m terminals) of the raster memory 12 is selected, and "0" is output by the enable signal of the comparator 17. A data selector which is in a state, 19 is an OR circuit, 20 is a thermal head, 21 is a pulse width data format as shown in FIG. 7, and is RO addressed by the data of the section counting section 15 and the pulse counting section 14.
M and 22 are pulse width control units that output a strobe signal to the thermal head 20 to control the energization time based on the pulse width data read from the ROM 21, 23 is a temperature sensor that detects the temperature of the thermal head 20, and 23a is A. / D converter, 24 is section T
This is a ROM that stores the initial pulse data in (1) in association with the temperature data.

The energization control operation by this circuit will be described below.

When one line of image data is accumulated in the raster memory 12, the gradation control unit 11 outputs a START signal to the memory reading unit 13, and the END signal of the memory reading unit 13 due to the completion of the reading and By checking the END signal of the pulse width control unit 22 due to the completion of gradation recording in the previous section, the
It outputs a T signal and a latch signal to the thermal head 20.

As a result, the data in the shift register of the thermal head 20 is held in the latch and the shift register becomes empty. Further, the pulse counting section 14 and the section counting section 15 are also incremented according to the conditions at that time to show the section and the pulse regarding the data to be transferred next.

At this time, if the END signal is not output from the section counting unit 15, the gradation control unit 11 outputs a START signal to the memory reading unit 13 to perform the next data transfer.

On the other hand, if the section counting unit 15 outputs the END signal, the pulse width control unit 22 waits until the END signal is output, and when the END signal is output, all gradation recording ends. Become.

By the way, the memory reading unit 13 reads grayscale data for one line by addressing the raster memory 12 based on the START signal, and outputs the upper bit data to the comparator 17 and the lower bit data to the data. selector
Transfer to 18 (terminal 1 to m).

Here, first, it is assumed that the data up to the [16i−1] th gradation has already been recorded by the thermal head 20.
i] A case will be described as an example where data transfer after the gray scale and its conversion are performed. In this case, if the gradation data is larger than the [16i] th gradation, the upper bit data (A) transferred by the raster memory 12 and the count number (B) of the section counting unit 15 are always A before that. In the relation of> B, the comparator 17 outputs “1” to the thermal head 20 via the OR circuit 19, and the pulse width control unit 22 determines the upper / lower order by the section counting unit 15 and the pulse counting unit 14. Recording is completed by the pulse width data up to the [16i-1] th gradation read from the ROM 2 based on the addressing.

On the other hand, at this point, the pulse counting unit 14 counts “5” and then becomes “0”, and outputs a carry signal to the section counting unit 15 to increment the count number of the section counting unit 15 by +1. It becomes "i".
The section count unit 15 outputs an END signal to the gradation control unit 11 when counting "16" by incrementing the count number, but after confirming that the gradation control unit 11 has not output this END signal. , START the pulse counting unit 14
Output a signal.

By the way, the upper data in the gradation data from the [16i] th gradation to the [16 (i + 1) -1] th gradation accumulated in the raster memory 12 is set as "i", and by reading this data, , The comparison result in the comparator 17 is A =
It becomes B.

Therefore, "1" by A = B of the comparator 17 and the lower data from the raster memory 12 are input in parallel to the data selector 18, and the data selector 18 counts by the START signal. Corresponding to 14 count data, "1" (0 terminal) → (1 to 4 terminals)
Gradation data of is sequentially selected. That is, the pulse counting unit 14 counts binary numbers from [000] to [100], and in [000], "1", in [001], the data of the terminal 1 (LSB of image data), ... , [100], the data of the terminal 4 (4th bit from the lower order of the image data) is sequentially output, and the thermal head 20 is output via the OR circuit 19.
Output to.

The thermal head 20 transfers this data to the memory read control unit.
The data is transferred to the shift register in synchronism with the clock of 13, and the data is held in the latch by the latch signal output by the gradation control unit 11 at a predetermined timing.

On the other hand, the count data of the section counting unit 15 and the pulse counting unit 14 are used as the read address of the ROM 21, the former data is given to the ROM 21 as an upper read address, and the latter data is given to the ROM 21 as a lower read address.

By the way, the ROM 21 stores, as a table, pulse width data for gradation expression in each section T (1) to T (16) of the characteristic curve as shown in FIG. That is, WO for setting the pulse width corresponding to the adjustment pulse RP in FIG.
_i and weighted pulses W _{i1 to} W _i4 (where W _i1 : W _i2 : W _i3 : W _i4 = 1: 2: 4: 8) that sets the pulse widths corresponding to P _{w1 to} P _w4 are 16 steps Stored separately.

The upper read address given to the ROM 21 specifies the gradation step, and the lower read address sequentially specifies the pulse width of the adjustment pulse PR and the weighted pulses P _{w1 to} P _w4 for expressing the gradation step. It is used as a trailer and the pulse width control unit is based on this read data.
22 outputs a STROBE signal to the thermal head 20 and enables gradation expression of 16 steps by selectively applying the adjustment pulse PR and 15 kinds of pulse train formats shown in FIG.

In the pulse train format shown in FIG. 5, the longest non-energization time is at the 8th step [16i +
8] It is a format for expressing the gradation, but this longest non-energization time tmax is sufficiently shorter than the thermal time constant of the heat transfer circuit of the thermal head 20, which is composed of the heating resistor, recording paper, ink sheet, etc. It is set in advance.

By the way, at the start of recording one line, as shown in the ink sheet characteristic curve, a very long energization time to is required by the start of color development as compared with other sections. In addition, this energization time to varies greatly depending on the temperature environment.

Therefore, it is impossible to control the energization time to by the adjustment pulse RP in the control sequence.

Therefore, regarding this energization time, when the count data of the section count unit 15 and the pulse count unit 14 is “0”, the initial state detection unit 16 detects that the recording is started in the section T (1). Based on this detection signal, the gradation control unit 11 reads the initial pulse width data of the ROM 24 specified by the temperature data of the temperature sensor 23, and the pulse width control unit 22 applies the initial pulse. There is.

This is why the data corresponding to WO ₁ in FIG. 7 is blank, and the recording control after the initial pulse is applied is naturally executed by the above sequence.

[Advantages of the Invention] Since the present invention has the above-described configuration, the following advantages are exhibited.

Invention of Claim (1): In the prior art, since the characteristic curve of the color density-current-carrying time characteristic in thermal recording is non-linear, one gradation data must be transferred to the thermal head for each gradation step. However, in the present invention, the characteristic curve is divided and each section is linearly approximated to be regarded as a linear section, and the gradation step of each section is determined from one of a plurality of weighted pulses or a combination thereof. It is possible to express the loss of gray scale steps between each section that is inevitably generated by applying the weighting pulse and the adjustment pulse set with the adaptive pulse width. Since the compensation is performed, it is possible to perform multi-gradation recording with high quality without trouble, while extremely reducing the number of times of data transfer.

As a result, more data can be transferred within the same time, and the recording speed can be dramatically improved. From the viewpoint of the control system, the parallelism of the serial data transfer circuits can be reduced, and the circuit scale can be reduced, thereby making it possible to reduce the size of the printer.

For example, the number of 1-line recording dots (the number of heating resistors) of the thermal head is 1024, and the transfer frequency of the shift register is
When executing 4MHz, 256 gradation expression in 5msec,
According to the conventional technology, 1024 pieces of data are stored in 255 times in 5 msec.
Since it is necessary to transfer twice, it is 19.608 μsec (= 5 msec / 255) to express the maximum gradation for one line, and the number of data that can be transferred at 4 MHz in this time is 78 (=
4MHz × 19.608μsec). Therefore, 1 in 1024 data
To transfer within 9.608 μsec, it is necessary to configure 13.12 (= 1024 ÷ 78), that is, 14 parallelized transfer circuits. On the other hand, in the present invention, the number of 1-line recording dots of the thermal head, the transfer frequency of the shift register, and the number of gradation representations are set to the same conditions as described above, and the section is n = 16 and the number of weighted pulses in each section is m. == 4, the number of adjustment pulses is also adjusted to express 256 gradations, 80 times [= n × (m +
1)] will be sufficient. So in this case,
The time allowed for expressing the unit gradation for one line is 62.5 μsec, and the number of data that can be transferred within this time is 250 (= 4 MHz × 62.5 μsec).
For a dot thermal head, 4.096 (= 1024/2
50), that is, it is sufficient to make 5 transfer circuits in parallel.

On the contrary, if the same number of transfers as in the conventional method is used, it is possible to express higher gradations, and if the number of gradations increases,
Since the characteristic curve can be divided into sections with smaller energization times and a better linear approximation can be made, more faithful multi-tone thermal recording becomes possible.

Invention of Claim (2): By making the weighted pulse a binary weighted pulse, the structure of the data for the gradation expression in the section is facilitated, and simple energization control is enabled.

Invention of claim (3): The problem that the time until the start of color development in the color density-current-carrying time characteristic is very long compared to other sections and that it fluctuates depending on the temperature environment is caused by a specially set initial pulse. It is canceled by applying the voltage, and proper control at the start of recording is realized.

[Brief description of drawings]

FIG. 1 is a graph showing the characteristics of color density vs. energization time in thermal recording, where the abscissa represents the energization time and the ordinate represents the color density, and FIG. 2 shows the characteristic curve in the graph in the range in which linear approximation is possible. FIG. 3 is a diagram showing a pulse train to be applied in each section, FIG. 3 is a schematic equivalent circuit of the heat transfer circuit in the thermal recording unit, and FIG. 4 is a pulse train to be applied in the section T (k) and its longest non- FIG. 5 is a diagram showing energization time, FIG. 5 is a diagram showing kinds of pulse trains when gradation representation in a section is performed by binary weighted pulses, and FIG. 6 is a system block circuit diagram for executing energization control in the embodiment. , Fig. 7 shows ROM21
FIG. 8 is a diagram showing the storage state of the thermal head, FIG. 8 is a diagram showing the circuit configuration of the thermal head unit, and FIG. 9 is a diagram showing the circuit configuration when the serial transfer units are parallelized. T (1) to T (n) ... Section P _{1 (k) to} P _{m (k)} (where (k) is a subscript indicating each section)
Weighted pulse RP _k …… Adjustment pulse tmax …… Longest non-energization time

Claims (3)

[Claims] 1. In a multi-gradation thermal memory, a characteristic curve in color density-current-carrying time characteristics is divided into sections in which each section can be linearly approximated, and a heating resistor is used to express a gradation step in each section. On the other hand, if the longest non-energization time between each pulse applied in time series is set sufficiently short with respect to the time constant composed of the relationship between the heating resistor and the recording paper, The gradation step is expressed by selectively applying a pulse train consisting of one of a plurality of weighted pulses or a combination thereof in correspondence with the input gradation data, and at the same time, in the low gradation side section, In order to raise the gradation step obtained by the final pulse in the low gradation side section to the reference gradation step in the high gradation side section between the final pulse and the first pulse expressing the next high gradation side section Heat energy required Energization control method in multi-gradation thermal printing which is characterized by applying an adjustment pulses fed to. 2. The energization control method in multi-gradation thermal recording according to claim 1, wherein the weighted pulse is a binary weighted pulse. 3. The heat energy up to the start of color development of the characteristic curve of the color density / current distribution characteristic is supplied by applying an initial pulse having a pulse width set based on the temperature data of the thermal head. The method for controlling energization in multi-gradation thermal recording according to claim 1 or 2.