JPH0615245B2 - Halftone recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention corrects a change in recording density due to heat accumulation of a halftone recording apparatus in thermal recording or thermal transfer recording, particularly a thermal head, and adjusts the density of each gradation level. The present invention relates to a halftone recording device that can be faithfully reproduced.

[Prior Art] Thermal recording devices and thermal transfer recording devices are widely used as recording means for printers, copiers, facsimiles, etc. because of their relatively simple configurations. Among them, as a method for recording a halftone, there is, for example, thermal transfer recording using a sublimation type ink sheet. In this recording method, the dye ink is sublimated according to the heating amount of the thermal head and thermal transfer recording is performed on the image receiving paper. The heating amount is applied to the heating resistor, and the heating amount is applied to the heating resistor. It is controlled by the number of pulses applied or the pulse width.

This recording method can obtain good halftone recording with a simple control method, but since the temperature of the heating resistor of the thermal head is the main factor that determines the recording density at each gradation level, changes in environmental temperature, heat storage, etc. However, there is a problem that the temperature fluctuation caused by the influence on the recording density greatly affects the faithful recording. Therefore, many correction methods for recording density changes have been devised.

FIGS. 7 and 8 show a conventional halftone recording method disclosed in, for example, Japanese Patent Laid-Open No. 60-9271.
FIG. 7 is a diagram showing the waveform of a pulse signal for energizing the thermal head (hereinafter, this signal is referred to as strobe signal), and FIG. 8 is a diagram showing the relationship between temperature and strobe signal. In Figure 7, (t _w) is a strobe signal having a pulse width, (t _p) is the repetition period thereof, (N) is the number of pulses. In FIG. 7, three pulses are used to obtain the density of a predetermined gradation level. The number of pulses is set in advance corresponding to the density of each gradation level. However, even if the number of pulses is fixed to obtain an arbitrary gradation level, the recording density changes due to the influence of temperature, and therefore the recording density of the same gradation level changes. Therefore, with respect to variations in temperature and the like, the temperature detection element such as the thermistor is referred to for each line and the pulse width ( _tw ) of the strobe signal is controlled as shown in FIG. It was corrected to obtain the recording density of.

[Problems to be Solved by the Invention] In the conventional halftone recording apparatus as described above, the time constant of the thermistor or the like is about several seconds, and the heat generation temperature of the thermal head changes with the time constant of several tens μs to several ms. Since it is impossible to control accurately, it is not possible to obtain a sufficient effect even if correction is performed by temperature detection by a thermistor, etc. Especially when there are many pixels with high gradation levels in one screen, the heat storage effect is There is a big problem that the gradation level changes by a dozen gradation levels at the start and end of printing, and the recording density at each gradation level cannot be faithfully reproduced.

The present invention has been made to solve such a problem, and by using a simple circuit, it is possible to prevent the occurrence of fluctuations in the recording density at the same gradation level due to the environmental temperature and the heat storage phenomenon, and to make the recording density uniform. It is an object of the present invention to obtain a halftone recording device that can obtain various recording densities.

[Means for Solving Problems] A halftone recording apparatus according to the present invention comprises a reference level generating means for generating a reference gradation level, a gradation level input signal and an output signal from the reference level generating means. Judgment means for judging whether or not the gradation level input signal is higher than or equal to the reference gradation level, and counting the number of output dots from the judgment means, and outputting thermal energy information accumulated in the thermal head. And a pulse generator for generating a pulse number or pulse width corresponding to a gradation level input signal according to the heat storage information from the counting means or the heat storage information and the temperature information from the thermal head. is there.

[Operation] In the present invention, with respect to the change in heat storage, which makes it difficult to faithfully reproduce halftones, the gradation level signals of the reference value or more from the start of printing to immediately before the line to be printed are counted, By reducing the applied energy for each line with reference to the heat storage correction value based on the counting result, it is possible to prevent the occurrence of density fluctuation of the same gradation level and obtain uniform recording density.

[Embodiment] FIG. 1 is a block diagram showing a halftone recording apparatus according to an embodiment of the present invention. In the figure, (1) is a gradation level signal input terminal to which a 6-bit gradation level signal is input, (2) is a judging means, and its input side is a gradation level signal input terminal (1) And the reference level generator described below
It is connected to (3), and it is determined whether it is equal to or higher than the reference gradation level signal. Further, the reference level generator (3) outputs a reference gradation level to the judging means (2). Reference numeral (4) is a counting means, the input side of which is connected to the output side of the determination means (2) to count the number of dots which is equal to or higher than the reference gradation level signal and output 4-bit heat storage information. (5) is a pulse generator, the input side of which is connected to the input terminal (1) and the counting means (4) and is applied to the input terminal (1) according to the heat storage information from the counting means (4). The number of pulses corresponding to the control level signal is generated. A thermal head (6) is connected to the pulse generator (5) and is composed of, for example, 1024 heating resistors.

FIG. 2 is a characteristic diagram showing the relationship between the recording density and the cumulative number of print dots. In the figure, (A) shows the case where the entire surface is printed at the gradation level 20, and (B) shows the case where the entire surface is printed at the gradation level 64.

In the halftone recording apparatus configured as described above, the principle of the halftone recording system of the present invention will be described before the operation is explained.
It will be described with reference to the drawings.

FIG. 2 shows the relationship between the recording density and the cumulative number of print dots, but when printing is performed entirely at the gradation level 64 as shown in FIG. 2 (B), the heat storage amount increases as the number of print dots increases,
As a result, the recording density is greatly increased. On the other hand, the second
As shown in FIG. 3A, when the entire surface is printed at the gradation level 20, the recording density hardly changes even if the number of print dots increases. FIG. 2 (A) shows that since the heat generating resistor is caused to generate heat at a low gradation level, the heat storage amount is small, and in such a case heat storage need not be considered. The present invention focuses on such a phenomenon, and counts the gradation level signals of the reference value or more from the print start time to immediately before the print line, and corrects the heat storage amount of the thermal head according to the print progress from the print start. It is a thing. Specifically, as shown in FIG. 3, the total number of gradation level signals above the reference value is 16
The heat storage correction coefficient is determined for each group. For example, when the cumulative print dot number is 20480 dots, the heat storage correction coefficient is 0.96 for the group 3 and the number of energizing pulses corresponding to the input gradation level is limited to 0.96 times. Avoid heat storage.

Next, the operation of the present invention will be described with reference to FIG.

The gradation level signals representing the gradation levels 1 to 64 are sequentially judged through the gradation level signal input terminal (1) by the judging means (2).
Entered in. The judging means (2) is for judging whether or not the gradation level signal is equal to or higher than the reference value, and if it is equal to or higher than the reference value output from the reference level generator (3), "1" is given, If it is less than "0", information "0" is input to the counting means. This counting means counts the output of the judging means (2) and outputs 4-bit heat storage information corresponding to the counting result to the pulse generator (5). The pulse generator (5) outputs the number of pulses corresponding to the gradation level signal input according to the heat storage information, and controls the thermal head (6). Here, the pulse generator (5) is provided with a table showing the relationship between the gradation level signal, the heat storage information and the number of pulses as shown in FIG. For example, in FIG.
When the gradation level is 8 and the cumulative number of printed dots is 5120 dots or less, the thermal head is controlled by the reference value (40 pulses) without heat storage assuming that heat accumulation does not occur. Further, when the gradation level 8 is obtained when the cumulative number of printed dots is 10000, the value obtained by multiplying the reference value (40 pulses) by the heat storage correction coefficient (0.98) (3
The thermal head is controlled by 9 pulses.

The above reference value and heat storage correction coefficient
Although it depends on the thermal response characteristics of (6), it can be easily obtained by a simple recording experiment or from the thermal calculation results.

In the above embodiment, the grouping of the cumulative print dot number is set to 16, but it is set in consideration of the characteristics of the thermal head.

Further, in the above-described embodiment, the change in the heat storage is dealt with by correcting the pulse number, but even if the pulse width is corrected instead of the pulse number, the same effect as in the above-described embodiment is obtained.

Further, FIG. 5 shows another embodiment of the present invention. 5 is the same as FIG. 1 except that a temperature detecting means (7) provided near a heating resistor (not shown) of the thermal head (6) is newly provided. The temperature detecting means (7) is composed of a thermistor or the like, performs A / D conversion on the detected analog quantity, and outputs temperature information to the pulse generator (5).

Next, as the operation, first, immediately before the start of printing, the temperature detection means
The temperature information of (7) is input to the pulse generator (5). Here, the temperature information is constant within one screen. Thereafter, the heat storage information which is the output of the counting means (4) is input to the pulse generator (5) as in the operation of FIG. The pulse generator (5) outputs the number of pulses corresponding to each gradation level signal input according to the temperature information and the heat storage information, and controls the thermal head (6). Here, in the pulse generator (5), as shown in FIG. 6, since the number of pulses is determined by the matrix table of temperature information, heat storage information, and gradation level signal, more accurate control can be performed.

[Effects of the Invention] As described above, the present invention compares the reference level generating means for generating the reference gradation level with the gradation level input signal and the output signal from the reference level generating means to obtain the gradation level. From the counting means, there is provided a judging means for judging whether or not the input signal is at or above the reference gradation level, a counting means for counting the number of output dots from the judging means, and outputting the stored heat information to the thermal head. And a pulse generator for generating the number of pulses or the pulse width corresponding to the gradation level input signal according to the heat storage information or the heat storage information and the temperature information from the thermal head, and it is difficult to faithfully reproduce halftone recording. Since the factors such as the ambient temperature and the heat storage that were set are corrected to obtain the pulse number or pulse width corresponding to the gradation level signal, the same gradation level is obtained. There is an effect that the occurrence of the fluctuation of the recording density of the bell is prevented and the uniform recording density can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a halftone recording apparatus according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing a relationship between recording density and cumulative print dot number, and FIG. 3 is a cumulative print dot number for each group. FIG. 4 shows a table of correction coefficients, FIG. 4 shows a table of heat storage correction and gradation level signals, FIG. 5 shows another embodiment of the present invention, and FIG. 6 shows cumulative print dots by group. FIGS. 7 and 8 are diagrams showing a table of numbers and gradation levels, and FIGS. 7 and 8 are diagrams showing a conventional halftone recording method. In the figure, (1) ... gradation level signal input terminal, (2) ...
... determination means, (3) ... reference level generator, (4) ... counting means, (5) ... pulse generator, (6) ... thermal head, (7) ... temperature detection means. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A thermal recording apparatus having a plurality of heat generating resistors and comprising a thermal head for recording a dot pattern by selectively energizing these heat generating resistors according to recording data. In the reference level generating means for generating the reference gradation level, and comparing the gradation level input signal with the output signal from the reference level generating means, the gradation level input signal is equal to or higher than the reference gradation level. Determination means for determining whether or not, counting means for counting the number of output dots from the determination means, and outputting heat storage information stored in the thermal head, and a gradation level input signal according to the heat storage information from the counting means And a pulse generator for generating a pulse number or pulse width corresponding to the pulse number from the pulse generator so that the density of the same gradation becomes constant. Halftone recording apparatus being characterized in that so as to energize the thermal head by. 2. A thermal recording apparatus having a plurality of heat generating resistors and comprising a thermal head for recording a dot pattern by selectively energizing these heat generating resistors according to recording data. In the reference level generating means for generating the reference gradation level, and comparing the gradation level input signal with the output signal from the reference level generating means, the gradation level input signal is equal to or higher than the reference gradation level. A determination means for determining whether or not, the counting means for counting the number of output dots from the determination means, and outputting the heat storage information stored in the thermal head, the heat storage information from the counting means and the thermal head With a pulse generator that generates the number of pulses or pulse width corresponding to the gradation level input signal according to the temperature information, the density of the same gradation is constant Halftone recording apparatus by a pulse from the pulse generator such that it is characterized in that so as to energize the thermal head. 3. The halftone recording apparatus according to claim 1, wherein the temperature information is obtained by temperature detecting means provided in the vicinity of the thermal head.