JPH04329152A - Thermal head control circuit - Google Patents

Abstract

PURPOSE:To provide a control circuit for simultaneously realizing high speed recording and high accuracy gradation recording in a thermal head repeating a recording cycle consisting of a heating time and a cooling time. CONSTITUTION:A heating raising control circuit 16 determines the heating raising time in the recording cycle of this time on the basis of the current supply time data corresponding to the recording cycle of this time from an image processing circuit 12 and the data showing the heating energy generated in the recording cycle of the previous time from a history data operation circuit 14 to output a current supply time control signal corresponding to the determined heating raising time. A heating holding control circuit 18 determines the heating holding time in the recording cycle of this time on the basis of the current supply time data corresponding to the recording cycle of this time from the image processing circuit 12 and the temp. compensation data JH from a temp. correction circuit 20 to output the current supply control signal corresponding to the heating holding time. A head driving circuit 22 supplies a current for raising heating according to the current supply control signal from the heating raising control circuit 16 at every recording cycle and supplies a current for holding heating according to the current supply control signal from the heating holding control circuit 18.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for controlling a thermal head of a printer, and more particularly to a control circuit for a thermal head that repeats a recording cycle consisting of a heating time and a cooling time.

0002

2. Description of the Related Art A thermal line printer uses a thermal head in which a large number of heating resistive elements are arranged in a line in a line direction (main scanning direction) perpendicular to a paper feeding direction (sub scanning direction). During recording, this thermal head is pressed against the paper through the ink film, and each heating resistor element is energized and generates heat for a predetermined time according to the image signal, and the ink (sublimable dye) on the ink film is heated by the heating energy. The light is sublimated discretely and transferred to the paper in the form of dots, and pixels are recorded on one recording line. Such a recording operation is performed at a predetermined pitch in the sub-scanning direction for a predetermined number (for example, 600 lines).
One image is recorded by repeating this process for the recording lines.

As described above, each heating resistor element of the thermal head repeats the recording operation at a constant period. This constant period, that is, the recording period, as shown in FIGS. 4 and 5,
It consists of heating time and cooling time. The length of the heating time changes depending on the image signal, and becomes longer as the density of the pixel to be recorded becomes higher. The cooling time is the remaining time from the end of the heating time to the end of the relevant recording cycle, and it becomes shorter as the heating time gets longer, but remains constant (minimum) even at the maximum heating time.
cooling time is ensured. Generally, the heating time consists of a heating start-up period and a heating holding period. During the heating start-up period, in order to quickly raise the ink heating temperature to the ink sublimation temperature or higher, the driving voltage of the heating resistor element is changed as shown in FIG. Control is performed to increase the duty of the energization cycle, or to increase the duty of the energization cycle (for example, to 100%) as shown in FIG.

0004

Conventionally, the heating start-up time has been set to be a constant time for each recording cycle, whether the method shown in FIG. 4 or the method shown in FIG. 5 is used. That is, as soon as each recording cycle is started, heating is started for a certain period of time.

However, when the heating time in the previous recording cycle is quite long, for example when the heating time is close to the maximum heating time,
The heating resistor element may not be sufficiently cooled from the end of the heating time to the start of the current recording cycle (that is, during the cooling time).

However, conventionally, even in such a case, the heating start-up is normally performed for a (fixed) time, so the effect of the heating start-up is too effective, and as a result, the heating energy generated in the current recording cycle is There was a problem in that the recording density became excessive. In order to solve this problem, it is conceivable to lengthen the cooling time, but then the recording cycle must also be lengthened, resulting in another (new) problem that the recording speed decreases.

Furthermore, when the ambient temperature is high and the cooling effect on the thermal head is not sufficient, the rate of fall of the temperature of each heat generating resistor element or the entire thermal head after the heating time ends is reduced, and as a result, each recording cycle is There was a problem in that the heating energy generated was excessive, resulting in poor recording density.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a thermal head control circuit that can perform high-speed recording and obtain highly accurate recording density.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the first thermal head control circuit of the present invention controls each heating resistor element of the thermal head for a predetermined period of time in accordance with image data at each predetermined recording cycle. In a thermal head control circuit that heats the ink by energizing and generating heat, and records pixels with multi-tone density on paper according to the heating energy, each heat generation occurs at the start of heating in each recording cycle. The heating start-up control means is provided for controlling the heating energy to be generated by the resistive element in accordance with the heating energy generated by each heating resistive element in the immediately preceding recording cycle or in a plurality of consecutive recording cycles.

The second thermal head control circuit of the present invention also controls the heating energy to be generated by each heating resistor element at the time of heating start-up in each recording cycle in the immediately preceding one or in a plurality of consecutive recording cycles. The heating resistor is configured to include heating start-up control means that controls according to the heating energy generated by the heating resistor element and the plurality of adjacent heating resistor elements.

The third thermal head control circuit of the present invention also includes a head cooling characteristic detection means for detecting the cooling characteristic of the thermal head, and a head cooling characteristic detection means for detecting the cooling characteristic of the thermal head, and a head cooling characteristic detection means for detecting the cooling characteristic of the thermal head, and a head cooling characteristic detection means for detecting the cooling characteristic of the thermal head. The heating energy control device is configured to include a heating energy control device that performs control based on an output signal of the head cooling characteristic detection device.

Further, in a fourth thermal head control circuit of the present invention, in the third thermal head control circuit, the head cooling characteristic detection means is replaced with a first temperature detection means for detecting the temperature of the thermal head; The apparatus is configured to include a second temperature detection means for detecting the temperature around the thermal head, and a means for determining the cooling characteristic of the thermal head based on the output signals of the first and second temperature detection means. .

[0013]

[Operation] In the first thermal head control circuit, the heating start-up of each recording cycle is performed based on the heating energy generated by each heat generating resistor element in one or several consecutive recording cycles immediately before each recording cycle. Variably controlled. However,
For example, if a considerable amount of heating energy was generated in the previous recording cycle, the heating start-up for the current recording cycle will be performed in a shorter time than in normal times, and therefore will require less heating energy than in normal times. As a result, a heating holding temperature close to normal can be obtained.

[0014] In the second thermal head control circuit, historical data of heating energy is determined not only for each heating resistor element, but also for a plurality of adjacent heating resistive elements, and the average and comprehensive history data is determined. Based on the data, the heating start-up of each heating resistor element in the current recording cycle is controlled. Therefore, although the arithmetic control becomes complicated, more accurate heating start-up control is performed and more accurate recording density can be obtained.

In the third thermal head control circuit, when the cooling effect of the thermal head decreases, the head cooling characteristic detection means detects the situation, generates required temperature correction data, and applies the temperature correction data to the temperature correction data. Based on this, the heating energy control means variably controls the heating energy to be generated by each heating resistor element during each recording cycle.

In the fourth thermal head control circuit, the cooling effect state of the thermal head control circuit is determined from the difference between the output signals of the first and second temperature detection means, that is, from the difference between the temperature of the thermal head and the ambient temperature. is detected and determined, and the heating energy to be generated in the recording cycle is controlled based on the detection result.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a block diagram showing the circuit configuration of the main parts of a thermal printer to which a thermal head control circuit according to this embodiment is applied, and FIGS. 2 and 3 are temperature characteristic diagrams for explaining the action of heating control according to this embodiment. be.

In FIG. 1, a thermal head control circuit 10 according to this embodiment includes an image processing circuit 12, a history data calculation circuit 14, a heating start-up control circuit 16, a heating holding control circuit 18, a temperature correction circuit 20, and a head drive circuit. A circuit 22 is included. The thermal head 30 also includes a thermistor (not shown) that detects the temperature of the thermal head 30.
This thermistor is also functionally included in the thermal head control circuit 10.

The image processing circuit 12 subjects the image signal VS inputted from a computer, television receiver, etc. to inverse γ correction, color masking, etc. in one line period, and then calculates a current application time representing the current application time corresponding to the recording density. Convert to data. The energization time data for one line obtained from the image processing circuit 12 is given to the heating start-up control circuit 16, the heating holding control circuit 18, and also to the history data calculation circuit 14.

The temperature correction circuit 20 includes a thermal head 30.
The output signal C1 from the thermistor attached to
and the output signal C2 from a thermistor (not shown) placed at a suitable location to detect the ambient temperature or environment temperature of the thermal head 30, and refer to the built-in look-up table. , both signals C1,
Output temperature compensation data JH corresponding to C2. The relationship between this temperature compensation data JH and both signals C1 and C2 is C
The larger the difference between C1 and C2 (the more effective the cooling effect is on the thermistor 30), the smaller the value of JH (compensation value);
The relationship is selected such that the value of JH (compensation value) becomes larger as the cooling effect with respect to 0 becomes smaller. Temperature compensation data JH obtained from the temperature compensation circuit 20 is given to the heating holding control circuit 18. In this embodiment, the head cooling characteristic detection means is composed of a thermistor that detects the temperature of the thermal head 30, a thermistor that detects the ambient temperature, and the temperature correction circuit 20.

The history data calculation circuit 14 calculates the heating energy generated in the corresponding recording line for each heating resistor element based on the energization time data for one line received from the image processing circuit 12, and uses the calculated data for the next generation. is applied to the heating start-up control circuit 16 when recording the line.

Before the start of the recording cycle of each line, the heating start-up control circuit 16 receives energization time data for that (current) recording cycle from the image processing circuit 12, and also receives data for the previous recording cycle from the history data calculation circuit 14. receives data representing the heating energy generated by the head drive circuit 22, determines the heating start-up time in the current recording cycle based on the data, and sends an energization time control signal corresponding to the determined heating start-up time to the head drive circuit 22. give to

Before the start of the recording cycle of each line, the heating and holding control circuit 18 receives energization time data for that (current) recording cycle from the image processing circuit 12, and also receives temperature compensation data JH from the temperature correction circuit 20. , based on these data, determines the heating retention time in the current recording cycle, and provides the head drive circuit 22 with an energization control signal corresponding to the determined heating retention time.

The head drive circuit 22 performs the following in each recording cycle:
Each heating resistor element of the thermal head 30 is energized and generates heat for heating start-up at a timing corresponding to the energization control signal from the heating start-up control circuit 16, and then specified by the energization control signal from the heating hold control circuit 18. Electrification and heat generation to maintain heating are performed only for the time required.

The CPU 32 is connected to the image processing circuit 12, the head drive circuit 22, and the mechanism control circuit 3 via the CPU bus 34.
6 etc., give necessary control signals and timing signals.

FIG. 2 shows the operation of this embodiment by the heating start-up control circuit 16. In this figure, the curve Li-1
is the heating time TAi in the previous recording cycle Ti-1
This is a heating temperature characteristic curve when the time is not very long. At this time, since the temperature of the heating resistor element has fallen to a sufficiently low value STO at the start of the current recording period Ti, heating is started for a steady time period tn in the current recording period Ti.

On the other hand, the curve Li-1' is a heating temperature characteristic curve when the heating time TAi' in the previous recording cycle Ti-1 is close to the maximum heating time. In this case, since the temperature of the heating resistor element is still maintained at a relatively high value ST1 at the start of the current recording cycle Ti, if heating was started for a steady time tn as in the past, it would be The heating temperature characteristic curve of the recording period Ti is the curve LM
This results in excessive heating energy being generated. However, in this embodiment, under the control of the heating start-up control circuit 16, the start of the recording period Ti is delayed (reduced) by the time Δt corresponding to the heat generation energy of the previous recording period Ti-1, and the time tn' Since the heating start-up is performed, the heat generation energy at the heating start-up is less than normal, and as a result, the heating temperature characteristic curve in the current recording cycle Ti becomes a curve Li' that almost overlaps the curve Li, indicating normal heating. A holding temperature is obtained. Therefore, there is no need to lengthen the cooling time in the recording period Ti, and high-speed recording can be performed.

FIG. 3 shows the operation of this embodiment by the heating and holding control circuit 18. In this figure, a curve Pi is a heating characteristic curve when electricity is applied for the original heating holding time THi. However, when the cooling function of the thermal head 30 decreases due to, for example, an increase in ambient temperature, the rate of fall of the temperature of the heating resistor element after the heating retention time THi decreases, as shown by the dotted line p', and the recording The temperature remains relatively high even at the end of the period Ti. In this case, the heating energy generated in this recording period Ti will be larger than the expected value, and there is also a possibility that the heating control for the next recording period Ti+1 will be adversely affected. but,
In this embodiment, the heating holding control circuit 18 is the temperature correction circuit 2.
By shortening and correcting the heating holding time THi in the recording period Ti to THi' according to the temperature compensation data JH from 0, the heating temperature characteristic becomes like the curve Pi',
As a result, the deterioration in head cooling function as described above is compensated for.

In the above-described embodiment, the history data calculation circuit 14 calculates the heating energy generated in the immediately preceding recording cycle for each heating resistor element to control the heating start-up in the current recording cycle. I made it. However, the heating energy generated not only in the immediately preceding recording cycle but also in the immediately preceding multiple recording cycles is calculated, and based on the historical heating energy, cooling characteristics are added as necessary.
It is also possible to configure the heating start-up in the current recording cycle to be controlled. Alternatively, it is also possible to configure the heating start-up in the current recording cycle to be controlled by taking into account historical data of heating energy generated not only by each heating resistor element but also by multiple adjacent heating resistive elements. It is.

[0030]

[Effects of the Invention] By having the above-described configuration, the present invention achieves the following effects. According to the thermal head control circuit of claim 1, the heating energy that should be generated by each heating resistor element at the time of heating start-up in each recording cycle is generated by each heating resistor element in the immediately preceding recording cycle or in a plurality of consecutive recording cycles. Since the heating energy is controlled according to the generated heating energy, even if there is a large variation in the heating energy, highly accurate heating control can be performed at all times in each recording period, and good recording density can be obtained. Furthermore, since there is no need to make the cooling time particularly long, the recording speed can also be increased.

According to the thermal head control circuit of the second aspect, the heating energy to be generated by each heating resistor element at the time of heating start-up in each recording cycle is changed to each heating resistor in the immediately preceding recording cycle or in a plurality of consecutive recording cycles. Since the heating energy is controlled according to the heating energy generated by the element and the plurality of heat generating resistive elements adjacent to the element, even more precise heating control can be performed, and even more accurate recording density can be obtained.

According to the third aspect of the thermal head control circuit, the cooling characteristic of the thermal head is detected, and based on the detection result, the heating energy to be generated by each heating resistor element during each recording period is controlled. Therefore, even if the cooling function of the thermal head decreases, the decrease can be compensated for and highly accurate recording density can be obtained.

According to the thermal head control circuit of the fourth aspect, since the cooling characteristics of the thermal head are determined from the temperature of the thermal head and the ambient temperature, the cooling characteristics of the thermal head can be monitored with a simple configuration. Appropriate heating control can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of the main parts of a thermal printer to which a thermal head control circuit according to an embodiment of the present invention is applied.

FIG. 2 is a diagram for explaining the action of heating start-up control in the embodiment.

FIG. 3 is a diagram for explaining the effect of heat retention control in the embodiment.

FIG. 4 is a diagram for explaining an example of a typical heating control method.

FIG. 5 is a diagram for explaining another example of a typical heating control method.

[Explanation of symbols]

10 Thermal head control circuit 12 Image processing circuit 14 Historical data calculation circuit 16 Heating start-up control circuit 18 Heating and holding control circuit 20 Temperature correction circuit 22 Head drive circuit 30 Thermal head

Claims (4)

[Claims] [Claim 1] Each heating resistor element of the thermal head is energized and generated for a predetermined time according to image data at each predetermined recording cycle to heat the ink, and pixels with multi-gradation density according to the heating energy are generated. In a thermal head control circuit configured to record on paper, the heating energy to be generated by each heating resistor element at the time of heating start-up in each recording cycle is changed to each heating resistor in the immediately preceding one or several consecutive recording cycles. 1. A thermal head control circuit comprising heating start-up control means for controlling according to heating energy generated by an element. 2. At each predetermined recording cycle, each heating resistor element of the thermal head is energized and generated for a predetermined time according to image data to heat the ink, and pixels with multi-gradation density according to the heating energy are generated. In a thermal head control circuit configured to record on paper, the heating energy to be generated by each heating resistor element at the time of heating start-up in each recording cycle is changed to each heating resistor in the immediately preceding one or several consecutive recording cycles. 1. A thermal head control circuit comprising: heating start-up control means for controlling heating energy generated by an element and a plurality of heat generating resistive elements adjacent thereto. 3. Each heating resistor element of the thermal head is energized and generated for a predetermined period of time in accordance with image data at each predetermined recording cycle to heat the ink, thereby forming pixels with multi-gradation density according to the heating energy. The thermal head control circuit is configured to record on paper a head cooling characteristic detecting means for detecting the cooling characteristic of the thermal head, and a head cooling characteristic detecting means for detecting the cooling characteristic of the thermal head, and a head cooling characteristic detecting means for detecting the cooling characteristic of the thermal head, and a head cooling characteristic detecting means for detecting the cooling characteristic of the thermal head, and 1. A thermal head control circuit comprising heating energy control means for controlling based on an output signal of the cooling characteristic detection means. 4. The head cooling characteristic detection means includes a first temperature detection means for detecting the temperature of the thermal head, a second temperature detection means for detecting the temperature around the thermal head, and a first temperature detection means for detecting the temperature around the thermal head. 4. The thermal head control circuit according to claim 3, further comprising means for determining cooling characteristics of said thermal head based on an output signal of said second temperature detecting means.