JPH0310855A - Thermal printer - Google Patents

Abstract

PURPOSE:To enable high precise temperature gradation control to be performed by a method wherein a means which controls an electrification duty ratio in a unit electrification cycle so that temperature of a thermal resistant element is varied by an optional characteristic in point of time, is established. CONSTITUTION:Thermal resistant elements R1 to R521 are selectively electrified to be heated in a unit electrification cycle DELTAT according to an information content of each corresponding bit. A radio of electrification time tE to unit electrification cycle DELTAT, i.e., an electrification duty ratio is not constant (fixed) through an electrification interval, and is varied each unit electrification cycle according to each level of density gradation under control of a CPU 40. Thereby, the thermal resistant element reaches minimum recording temperature TS in shortest time. Therefore, though electrification time is short (for instance, T2), required density (d2) corresponding thereto is obtained. Further, though electrification time continues, temperature is kept almost constant. Thereby, even when electrification time is short or long, required density corresponding each thereto is obtained. Besides, relation between a number of times of electrification and recording density becomes a linear proportional relation, and high precise density gradation control becomes capable of being performed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a density gradation system in which the density gradation of each pixel is controlled by energizing each heating resistor element for an energizing time that is an integral multiple of the unit energizing time. This invention relates to a gradation control type thermal printer.

[Prior Art] In general, the density gradation control method applies a constant voltage to each heating resistor element of a thermal head and controls the energization time, thereby giving gradation to the heat generated energy and gradating the density of the pixel. I try to give it some tone.

Figure 6 shows the energization time-1 used in the density gradation control method.
The temperature characteristic curve is shown below. When the heating resistor element is energized for the energizing time TI corresponding to the unit energizing time △T, the gradation level dl
1 degree of the gradation level d2 is obtained, and when the current is applied for a energization time T2 corresponding to twice the unit energization time ΔT, a gradation level d2 of 1 degree is obtained. In this example, unit energization time △
By energizing for a energizing time T64 corresponding to 64 times T, a maximum gradation level dG4 near the saturation density can be obtained.

[Problems to be Solved by the Invention] The one-degree gradation control method as described above has very high accuracy as long as the thermal energy given to the ink ribbon by the heat generated by the heating resistor per unit time is constant throughout the energization interval. A high level of control is possible. However, in reality, the heat generating resistor element or the thermal head has a heat capacity, so for example, if the heat generating resistor element is energized for the energization time 'IJ4,
The temperature of the heating resistor element changes with the characteristics shown in FIG.

That is, the minimum recording temperature (the lowest temperature required for recording) is reached after a time Ts has elapsed after the start of energization, and thereafter it continues to rise monotonically until the energization end time. As the temperature of the heating resistor element changes due to these characteristics, in reality,
Recording (thermal transfer) may not be performed when the current is applied for a short time (e.g. T2), or recording (thermal transfer) is not performed when the current is applied for a long time (e.g. T5).
0) When electricity was applied, the density sometimes became higher than the expected density d50.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a thermal printer that enables highly accurate gradation control by arbitrarily controlling the temporal characteristics of the temperature of a heating resistor element. With the goal.

[Means for Solving the Problems] In order to achieve the above object, the thermal printer of the present invention connects each of the plurality of heating resistive elements corresponding to the plurality of pixels on one printing line one to one. In the one-degree gradation control type, a predetermined density gradation is given to each pixel by energizing for a time that is an integral multiple of the unit energization cycle.
The structure includes means for controlling the energization duty ratio within a unit energization cycle so as to change the temperature of the heating resistor element temporally with arbitrary characteristics.

[Function] According to the present invention, the energization duty ratio within a unit energization cycle is not constant (fixed) throughout the energization interval;
Changes every unit energization cycle.

The energization duty ratio within each energization cycle may be set in advance as data based on experimental values, statistical values, etc. For example, the energization duty ratio may be set as data in advance based on experimental values, statistical values, etc. selected. With such characteristics, by changing the energization duty ratio for each unit energization cycle throughout the energization interval, it is possible to obtain characteristics of the temperature of the heating resistor element that has a good rise immediately after the start of energization and is maintained substantially constant throughout the energization interval. As a result, the desired 76 degrees can be obtained regardless of whether the energization time is short or long, and the relationship between the number of energization times and the recording density is linearly proportional, allowing highly accurate 1-degree gradation control. becomes possible.

[Example 1] FIG. 1 shows the main structure of a yla gradation control type thermal printer according to this example.

In FIG. 1, the thermal head 10 includes, for example, 51
A heating resistor 12 formed by arranging two heating resistive elements R1-R5]2 in a row, and a heating resistor 12 having the same number of heating resistive elements (51
2) By) A shift register 14 and a latch circuit 16 having a capacitance are provided. Furthermore, a thermistor 18 for temperature compensation is provided close to the heating resistor 12, and its output signal is converted into digital temperature detection data DT by an A/D converter 44 and then supplied to the CPU 40.

During the printing time of each printing line, the data comparison circuit 28
512-bit serial gradation data [CK Plj-
CK P512J] multiple times at regular intervals, e.g. 64
The signal is continuously applied to the shift register 14 times (K: 1 to 64). Here, the n-th bit CKPnj specifies that the n-th heating resistance element Rn has a unit energization cycle △.
Contains information on whether or not electricity should be applied during T. In other words “
If it is 1", it instructs energization, and if it is &IQ", it instructs de-energization.

Thus, when each gray scale data is loaded into the shift register 14 in synchronization with the clock signal CK from the clock circuit 34, each bit CK PIJ- is then loaded at the timing of the latch signal LA from the launch signal generation circuit 36. C.K.
P512J is sent as an electric pulse to the heat generating resistor 12 via the latch circuit 16, and the heat generating resistive elements R1 to R512 are selectively energized and generate heat during a unit energization cycle ΔT according to the information content of the corresponding bit.

This unit energization cycle ΔT consists of an energization time tE in which current actually flows through the heating resistor element and a time tC in which current does not flow.
Defined by T. In this embodiment, the ratio of the energization time tE to the unit energization cycle ΔT, that is, the energization duty ratio, is not constant (fixed) throughout the energization interval, but is changed over the unit energization cycle according to each level of the density gradation under the control of the CPU 40. It changes every time.

FIG. 2 shows a unit energization cycle according to this embodiment.

As shown, the unit energization cycle ΔTn.

For every ΔT n+1, energizing time t E+n + t E,
The length of n+1 and thus the energization duty ratio change.

FIG. 3 illustrates a line printing cycle according to this embodiment. TE, N, TE, N+1 are energization intervals,
It consists of 64 (times) unit energization cycles ΔTl to ΔT64. TC,N and TC,Ni1 are cooling intervals.

In order to perform such variable control of the energization duty ratio for each unit energization cycle, the CPU 40 refers to data preset in a predetermined table in the memory 42. Then, based on the data, the time corresponding to each energization duty ratio is internally measured by software, or by setting the data in a timer/counter built into the strobe signal generation circuit 38, the circuit 38 generates a A strobe signal ST as shown in FIGS. 2 and 3 is generated.

FIG. 4 shows an example of setting energization duty ratio data for each unit cycle ΔTl to ΔTG4. In this figure, the energization duty ratio is the initial period of the energization interval (ΔT
l ~ ΔT 10), it gradually becomes smaller (becomes), and in the middle (ΔTl
l ~ △T55), it is constant (10%), and the telophase (ΔTAG
~ΔT64), it gradually becomes thicker.

With these characteristics, the energization duty ratio changes every unit energization cycle throughout the energization interval, so that the fifth
The temperature characteristics of the heating resistor element as shown in the figure are obtained. The first point in which this characteristic differs from the conventional characteristic (FIG. 7) is that the time TS required to reach the minimum recording temperature is extremely short. In particular, in this example, since the energization duty ratio of the first energization cycle is 100%, the minimum recording temperature TS is reached in the shortest time. As a result, even if the energization time is short (for example, T2), the corresponding expected 1 degree (d
2) is obtained. The second difference is that the temperature remains approximately constant even if the current is applied for a long time. As a result, the relationship between the number of times of energization and the thermal energy given to the ink ribbon, as well as the recording density, becomes a linear proportional relationship.
Highly accurate one-degree gradation control can be performed for any given energization time (number of times). The characteristic curve of the heat generating resistor element t'' degree according to this embodiment is just an example, and any characteristic curve can be obtained by appropriately selecting the energization duty ratio data.

Therefore, during the energization interval TE of one printing line,
By repeating the energization operation of the unit energization cycle according to the gradation data 64 times (=l-84),
Each pixel on one printing line is given one of 64 equally spaced density gradations. That is, the number of times the corresponding heat generating resistor Rn is energized is determined depending on how many times the information content of "1" is continued for each gradation pixel CKPnj, and thereby the one gradation level of the corresponding pixel is determined. For example, if the gradation bit CKPIJ continues to be "1" until the 10th gradation data, in this case,
CI PIJ-CIOPlj are each “1” and CII
P N #CB4P lj becomes "0", and the heating resistor R1 is energized for the energization time corresponding to the cumulative time of tE, 1 to tE, IO of each unit energization cycle ΔTl to ΔT10, and takes the corresponding action. The gradation level of the pixel is dlO. According to this embodiment, the relationship between the number of times of energization and 19 degrees is linearly proportional, and equally spaced 1 degree gradation levels can be obtained, so this level dlO
has a density that is, for example, twice the level d5 and 1/2 times the level d20.

The gradation data [CK
PH-CK B512j (K=1 to 64) is produced as follows.

First, the digital video signal DV is input to the frame memory 20 as pixel data. Frame memo IJ 20
Each row corresponds to a horizontal scan line of the television image, and pixel data is written in an order corresponding to the rask scan. Next, starting from the first column of the frame memory 20, one line of pixel data a Ij, a 2L . . . is generated for each column (j).
......A 512j is read out and supplied to the color processing circuit 22, where it is subjected to image processing such as inverse gamma correction, and then converted into 8-bit one-time data b.
Converted to IJ, b 2J, b 512j. Each of these concentration data bN is (0)(
It has a value (gradation level) corresponding to 1 degree of the corresponding pixel within the range of (minimum density) to (84>(maximum density)).

Density data for one printing line outputted from the color process circuit 22 blj, b2j, . . .
b 512j is 8-bit energization time data Blj, B2j, . . .
... are respectively converted to B512j. During this conversion, the energization time data undergoes temperature correction in accordance with the temperature correction value δb from the CPU 40.

The energization time data BIJ, B4C open/open B512 for one printing line generated by the density-to-energization time conversion circuit 24 is once taken into the line buffer 26 and then applied to one input terminal of the data comparison circuit 28.

The other input terminal of the data comparison circuit 28 is supplied with an 8-bit comparison reference value DN, which is incremented by 1 at a constant cycle, from the gradation counter 32 during the energization interval TE. The data comparison circuit 28 compares this comparison reference value DN with each density data, and sets the bit to "1" when the latter is equal to or larger than the former, and sets the bit to "O" when the latter is equal to or larger than the former. Generate bits as tone bits.

For example, the energization time data B lj, B 2j,...
・The values of B512j are <10>, <2>, etc., respectively.
・Assume (1). In this case, in the first comparison,
The comparison reference value DN is (1), and the first gradation data output at this time [CI Plj, CI P2j, . . .
・CIP512jl becomes [1, 1, ... 1 piece.

In the second comparison, the comparison reference value DN is (2), and the second tone data [C2Plj, C2
P2J.

...C2B512j becomes [1, 1, . . . O. In the third comparison, the comparison reference value DN is (
3), the third gradation data [C3Plj, C3P2
J.

...C3P512j] becomes ci, o, ...0.

In this way, during the energization interval TE, each time the density gradation comparison reference value DN increments by one step, it is compared once with each of the data Blj, B2L...B512J. The gradation data corresponding to each comparison result [:CI Plj, CI P2J,...C
IP512j, mouth C2PH, C2P2J,
...C2B512j.

. . . are sequentially and serially sent to the register 14 of the thermal head 10 at a constant period.

[Effects of the Invention] By having the above-described configuration, the present invention provides the following effects.

By changing the energization duty ratio for each unit energization time cycle throughout the energization interval, it is possible to temporally control the temperature of the heating resistor element to desired characteristics,
For example, it is possible to improve the rise characteristics so that the desired recording density can be obtained even with a short energization time, or to make the relationship between the number of energizations and the recording density into a linear proportional relationship to perform highly accurate density gradation control. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main circuit configuration of a thermal printer with intensity gradation control according to an embodiment of the present invention. FIG. 2 is a diagram showing the timing of a unit energization cycle according to the embodiment. is a diagram showing the timing of the line printing cycle according to the embodiment, and FIG. 4 is a diagram showing the timing of the line printing cycle according to the embodiment.
Figure 5 is a diagram showing an example of setting the energization duty ratio data for TG4. Figure 5 is a diagram illustrating the characteristics (temporal changes) of the temperature of the heating resistor element according to the embodiment. Figure 6 is the energization rate used in the density gradation control method. A diagram showing a time-moisture characteristic curve and FIG. 7 are diagrams showing characteristics (temporal changes) of the heating resistor element temperature according to the prior art. 10...Thermal head, RI R2,~R512...Heating resistance element, 36...
... Latch signal generation circuit, 38 ... Strobe signal generation circuit, 40 ... C
P.U. 42...Memory, 44...Thermistor. Figure 2 Figure 3

Claims (1)

[Claims] By energizing each of a plurality of heat generating resistive elements that correspond one-to-one to a plurality of pixels on one printing line for a time that is an integral multiple of a unit energization cycle, each pixel is given a predetermined density level. In a thermal printer of a density gradation control type that applies a gradation, it is provided with means for controlling the energization duty ratio within a unit energization cycle so as to change the temperature of the heating resistor element temporally with arbitrary characteristics. A thermal printer with special features.