JP2715917B2 - Printing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus for use in a facsimile machine, for example, and more particularly to a printing apparatus for printing using a thermal head.

[0002]

2. Description of the Related Art Generally, in a facsimile apparatus, image data is transmitted in a coded state, and the coded data has a different information amount for each line. Therefore, when transmitting image data, the transmission time of each line changes, and the time required for the encoding and decoding processing of each line also changes. Therefore, when such image data is received and printed on recording paper, 1
The time between the printing of a line and the start of printing of the next line changes according to the change of the transmission / processing time for each line.

However, in a printing apparatus using a thermal head, if the time between printing one line and starting printing the next line becomes long, the heat generation of the thermal head is not controlled during that time. The temperature of the head decreases. Therefore, when printing on the next line, even if the heat generation of the thermal head is controlled, the temperature of the thermal head is not sufficiently increased, and the print density is reduced.

For this reason, in a printing apparatus using such a thermal head, if the time between printing one line and starting printing the next line becomes long, the thermal head is required. Conventionally, the thermal head is preheated so that the temperature does not decrease.

That is, in this conventional apparatus, as shown by a solid line in FIG.
Table data in which a print pulse width to be applied to the head is set is provided. The thermal head is provided with a temperature sensor for detecting the temperature of the head. When printing each line by the thermal head, the optimum print pulse width to be applied to the thermal head is set by referring to the table data based on the temperature detected by the temperature sensor, and the print head sets the optimum print pulse width. A printing pulse having the specified time width is applied. After the printing of the line, a pulse signal for preheating is applied to the thermal head. The time width of the preheating pulse is a percentage (eg, 50%) of the time width of the previously applied printing pulse. Such a setting was made. In other words, as shown by a broken line in FIG. 5, in the related art, after printing is performed with a predetermined print pulse width based on table data, the thermal head always applies a fixed time width to the print pulse width. Was applied.

[0006]

However, if the preheating pulse width is always set to a constant ratio with respect to the printing pulse width as in the above-described conventional case, the following problem occurs. That is, if the transmission / processing time for each line does not exceed a predetermined time width (for example, 10 ms) set in advance, the recording paper is sent one line at a time in the predetermined time width. Therefore, as shown by the solid line in FIG. 5, even when the temperature of the thermal head is low and the print pulse width needs to be increased, the maximum value of the print pulse width is actually limited to the time width. And cannot be set any larger. Therefore, when the temperature of the thermal head is low as shown by the broken line in FIG. 5, the maximum value of the preheating pulse width determined by the print pulse width is also limited, and the thermal head is sufficiently preheated. There was a problem that it was not possible.

On the other hand, even if the temperature of the thermal head is high and the print pulse width needs to be reduced, the preheat pulse width is set to be larger than necessary, and the thermal head is set to an appropriate preheat temperature. There was also a problem that would exceed. As a result, there arises a problem that unevenness occurs in the print density and a high-quality print image cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to always preheat a thermal head with an appropriate preheating pulse width without causing unevenness in print density. An object of the present invention is to provide a printing apparatus capable of obtaining a high-quality printed image.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, after printing is performed by a thermal head with a predetermined printing pulse width based on image data, the printing is performed until the next printing starts. In the meantime, in a printing apparatus provided with control means for preheating the thermal head with a predetermined preheating pulse width, the control means corresponds to a temperature of the thermal head and sets a table in which a printing pulse width to be applied to the thermal head is set. Ru comprising data and a preheating pulse width table data set each
The value of the print pulse width depends on the temperature of the thermal head.
In the range higher than the specified temperature, the lower the temperature of the head, the larger
The head is set at a predetermined temperature.
The temperature is limited to a certain value in the range below
The width value is the ratio of the printing pulse width to the thermal head.
The higher the head temperature, the higher the head temperature
The gist is that it is set to be small
Things.

[0010]

According to the second aspect of the present invention, there is provided the first aspect.
In the printing apparatus, the control means repeats the preheating control at a predetermined cycle until the next printing starts.

[0012]

Therefore, according to the first aspect of the present invention, table data in which a print pulse width to be applied to the thermal head and table data in which a preheat pulse width is set are provided corresponding to the temperature of the thermal head. Therefore, the preheating pulse width can be set to an appropriate value regardless of the printing pulse width.

[0013]

According to the second aspect of the present invention, even if the time from the start of printing to the start of the next printing becomes very long, the preheating temperature of the thermal head can be adjusted appropriately until the start of the next printing. Temperature can be maintained.

[0015]

An embodiment in which the present invention is embodied in a facsimile machine will be described below with reference to the drawings. FIG. 1 shows a circuit configuration of the facsimile apparatus of this embodiment. CPU
The (central processing unit) 1 is connected to a ROM (read only memory) 2 storing a program for controlling the operation of the entire apparatus, and a RAM (random access memory) 3 for temporarily storing various information. ing. In this embodiment, the control means is constituted by the CPU 1, the ROM 2, and the RAM 3. In the ROM 2, two table data Td1 and Td2 shown in FIGS. 3 and 4, respectively, are stored in advance. The contents of these table data Td1 and Td2 will be described later in detail. An NCU (network control unit) 4 controls connection with a telephone line. The modem 5 modulates and demodulates transmission and reception data.

The reading section 6 reads an image on a document. The encoding / decoding circuit 7 encodes the read image data and decodes the received image data. Head drive circuit 8
Generates a print pulse based on one line of image data (line data) sent from the CPU 1 and a predetermined print pulse width signal described later. The head drive circuit 8 includes a line memory (not shown), and the input line data is temporarily stored in the line memory. Then, when receiving the print request signal from the CPU 1, the head drive circuit 8 applies a print pulse to the thermal head 9.
Then, based on the print pulse, a large number of heating elements (not shown) provided on the thermal head 9 are selectively heated to print one line on the recording paper. In the present embodiment, as a printing apparatus provided with the thermal head 9, a thermal transfer type printing apparatus that thermally transfers ink on an ink ribbon onto recording paper may be applied, or thermal recording on thermal recording paper may be performed. A heat-sensitive recording type printing device may be applied. The head drive circuit 8 sends a print display signal to the CPU 1 while the heat-sensitive head 9 is under heat control.

The interrupt timer 13 is started at the same time as the CPU 1 outputs the print request signal, and generates an interrupt signal a predetermined time (10 ms in this embodiment) from the start. Then, based on the input of the interrupt signal, the CPU 1 outputs a predetermined preheating pulse width signal to be described later to the head drive circuit 8 and outputs a print request signal again. Then, the head drive circuit 8 creates a preheating pulse based on the line data held in the line memory and the preheating pulse width signal, and applies the preheating pulse to the thermal head 9. Thus, the heating resistor of the thermal head 9 is selectively heated based on the preheating pulse.
In addition, due to this heat generation, overwriting printing is performed on the printing location on the recording paper. Also, the head drive circuit 8 sends a print display signal to the CPU 1 while the thermal head 9 is under the preheating control.

The temperature sensor 10 comprises a thermistor or the like,
The thermal head 9 is mounted on a substrate (not shown) that supports a heating resistor. The temperature sensor 10 detects the temperature of the substrate of the thermal head 9 each time before the start of printing for one line by the thermal head 9 and outputs a temperature detection signal to the CPU 1. Then, the CPU 1 recognizes the temperature of the substrate of the thermal head 9 (hereinafter simply referred to as the temperature of the thermal head 9) based on the input temperature detection signal.

The motor drive circuit 11 generates a drive signal based on a motor drive command sent from the CPU 1,
The drive signal is output to the paper feed motor 12. Then
The paper feed motor 12 is rotated by the drive signal, and the recording paper is fed one line at a time. Note that the image data has different transmission time and time required for the decoding process for each line. Here, the CPU 1 performs transmission / transmission for each line.
If the processing time does not exceed a predetermined time width (10 ms in this embodiment), a motor drive command is output every 10 ms, and the recording paper is sent every 10 ms.

As shown in FIG. 3, the table data T
In d1, the time width (print pulse width) of a print pulse to be applied to the thermal head 9 is set in accordance with the temperature of the thermal head 9. As shown in the drawing, the value of the print pulse width increases as the temperature of the thermal head 9 decreases.
Is set to be smaller as the temperature is higher. However, when the temperature of the thermal head 9 is in a range below a predetermined temperature,
The value of the print pulse width is limited to a constant value of less than 10 ms so that the time width during the paper feeding does not become longer than 10 ms.

As shown in FIG. 4, the table data T
In d2, the time width (preheating pulse width) of the preheating pulse to be applied to the thermal head 9 is set in accordance with the temperature of the thermal head 9. As shown in the figure, the value of the preheating pulse width increases as the temperature of the thermal head 9 decreases.
Is set to be smaller as the temperature is higher. In addition, as is apparent from FIG. 5, the ratio of the preheating pulse width to the value of the printing pulse width set in the table data Td1 in FIG. 3 increases as the temperature of the thermal head 9 decreases. The temperature is set to be smaller as the temperature of the head 9 is higher.

Next, the operation performed by the CPU 1 when receiving one page of image data will be described with reference to FIG.
A description will be given according to the flowcharts shown in FIGS. As shown in FIG. 2A, when receiving the image data, the CPU 1 firstly starts decoding the line data by the encoding / decoding circuit 7 and sends the decoded data to the head driving circuit 8 in step S1. Transfer to the line memory. Then, the CPU 1 determines in step S2
Waits for the end of the decoding of the line data in.
It is determined whether or not is currently under heat control. This determination is made based on the presence or absence of a print display signal from the head drive circuit 8.

When a print display signal is input, the CPU 1 waits for the thermal head 9 to end the heat generation control. If there is no input of the print display signal, the CPU 1 shifts to step S4 and executes the interrupt timer 1
If 3 has been activated, stop it. Next, CP
U1 drives the paper feed motor 12 by the motor drive circuit 11 in step S5 to feed the recording paper by one line. Subsequently, in step S6, the CPU 1 recognizes the temperature of the thermal head 9 based on the detection signal from the temperature sensor 10. Then, in step S7, based on the temperature of the thermal head 9 previously recognized, the CPU 1 refers to the table data Td1 shown in FIG.
The print pulse width to be applied is set, and the print pulse width signal is sent to the head drive circuit 8.

Then, the CPU 1 sends a print request signal to the head drive circuit 8 in step S8. As a result, heat generation of the thermal head 9 is controlled by the previously set print pulse width, and printing is performed on recording paper by the thermal head 9. The CPU 1 outputs the print request signal simultaneously with the output of the print request signal.
Starts the interrupt timer 13 in step S9. Then, the interrupt timer 13 is set to 1
After 0 ms, an interrupt signal is generated and output to the CPU 1.

The CPU 1 executes an interrupt routine shown in FIG. 2B based on the input of the interrupt signal. The description of this interrupt routine will be made with reference to the timing chart shown in FIG. FIG. 2 (b)
As shown in, the CPU 1 determines in step S11
A preheating pulse width to be applied to the thermal head 9 is set with reference to the table data Td2 shown in FIG. 4 based on the previously recognized temperature of the thermal head 9, and the preheating pulse width signal is sent to the head drive circuit 8. . Then, the CPU 1 sends a print request signal to the head drive circuit 8 in step S12. As a result, the thermal head 9 is preheat-controlled with the preheat pulse width set previously, and the overwriting printing is performed at the printing location on the recording paper. Simultaneously with the output of the print request signal, the CPU 1 restarts the interrupt timer 13 in step S13. Then, the interrupt timer 13 again generates an interrupt signal 10 ms after its activation, so that the above-described interrupt routine is executed again, and the preheating control for the thermal head 9 is repeated at intervals of 10 ms as shown in FIG.

Returning to FIG. 2A, in step S10, the CPU 1 determines whether or not the reception of one page has been completed. If the reception has been completed, the processing is temporarily terminated. , And returns to step S1 to start decoding the next line data.

During the execution of the interrupt routine,
When decoding of the next line data is completed in step S2, it is determined in step S3 whether the thermal head 9 is under preheating control. If the preheating control is not being performed, the process proceeds to step S4 and the interrupt timer 13 is immediately stopped. If the preheating control is being performed, the process proceeds to step S4 after the preheating control is completed and the interrupt timer 13 is stopped. You. As a result, the interrupt routine is terminated, and the operation shifts to the printing operation of the next line data.

As described above, in this embodiment, the preheating control of the thermal head 9 is performed even when the time from printing one line to starting printing the next line becomes long. As a result, the temperature of the thermal head 9 does not drop before the start of the next printing. For this reason, when the thermal head 9 is controlled to generate heat during the printing of the next line, the temperature of the thermal head 9 can be increased to a sufficient temperature, and the print density does not decrease.

In this embodiment, table data Td1 in which a print pulse width to be applied to the thermal head 9 is set and table data Td2 in which a preheat pulse width is set, corresponding to the temperature of the thermal head 9, respectively. Provided. For this reason, unlike the above conventional technique, the preheating pulse width applied to the thermal head 9 can be set to an appropriate value regardless of the printing pulse width. As shown in FIG. 5, the ratio of the preheating pulse width to the printing pulse width in this embodiment increases as the temperature of the thermal head 9 decreases.
The higher the temperature, the smaller. In other words, since the preheating pulse width can be set regardless of the printing pulse width,
In the present embodiment, the value of the preheating pulse width is compared with the value of the conventional preheating pulse width indicated by a dotted line in the figure, and is larger when the temperature of the thermal head 9 is low and higher when the temperature of the head 9 is high. Can be made smaller.

As a result, in the present embodiment, even when the temperature of the thermal head 9 is low, the preheating pulse width can be set to a sufficiently large value without being limited by the printing pulse width, and Can be preheated. or,
Even when the temperature of the thermal head 9 is high, the preheating pulse width is not set unnecessarily large, and the head 9 does not exceed an appropriate preheating temperature. Therefore, a high-quality printed image can be obtained without causing unevenness in print density in an actual printing operation.

Further, by storing data of the preheating pulse width corresponding to the temperature of the thermal head 9 in the form of table data Td2, the preheating to be applied to the thermal head 9 can be performed without performing complicated arithmetic processing. The pulse width can be set easily and quickly.

In the present embodiment, the preheating control for the thermal head 9 is repeated at a predetermined cycle until the next printing is started. For this reason, even if the time between printing and the start of the next printing becomes very long, it is necessary to ensure that the preheating temperature of the thermal head 9 is maintained at an appropriate temperature until the start of the next printing. Can be.

The present invention is not limited to the above embodiment, but can be embodied in the following manner, for example. (1) Limit the number of repetitions of the preheating control to a predetermined number. In this case, it is possible to prevent the printing density from becoming too high due to the overwriting printing accompanying the preheating control.

(2) The temperature of the thermal head 9 is detected by the temperature sensor 10 every time the preheating pulse width is set. By doing so, the temperature of the thermal head 9 before the preheating control can be detected more accurately, and the preheating pulse width can be set to a more appropriate value.

(3) The present invention is embodied in a printing apparatus other than a facsimile apparatus, for example, a printer. The technical ideas other than the claims that can be grasped from the above embodiment will be described below together with their effects.

(1) In Claims 1 to 3, a temperature sensor for detecting the temperature of the thermal head is provided, and the control means applies the temperature to the thermal head by referring to each table data based on the temperature detected by the temperature sensor. A printing device that sets the printing pulse width and preheating pulse width to be applied.

In this way, the appropriate print pulse width and preheat pulse width can be set easily and quickly based on the temperature of the thermal head detected by the temperature sensor.

[0038]

According to the present invention as described in detail above,
It has the following excellent effects. According to the first aspect of the invention, the preheating pulse width can be set to an appropriate value regardless of the printing pulse width. For this reason, the thermal head can always be preheated with an appropriate preheating pulse width, and a high-quality printed image can be obtained without causing unevenness in print density.

[0039]

According to the second aspect of the present invention, even if the time from the start of printing to the start of the next printing becomes very long, the preheating temperature of the thermal head can be adjusted appropriately until the start of the next printing. Temperature can be reliably maintained.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an embodiment in which the present invention is embodied in a facsimile apparatus.

FIG. 2 is a flowchart showing an operation performed by the CPU when receiving one page of image data;
Particularly, (b) is a flowchart showing an interrupt routine executed based on the input of an interrupt signal.

FIG. 3 is an explanatory diagram showing table data in which a print pulse width to be applied to a thermal head is set according to the temperature of the thermal head;

FIG. 4 is an explanatory diagram showing table data in which a preheating pulse width to be applied to a thermal head is set in accordance with the temperature of the thermal head.

FIG. 5 is an explanatory diagram showing a comparison between a value of a printing pulse width corresponding to a temperature of a thermal head, a value of a preheating pulse width in the present embodiment, and a value of a preheating pulse width in the related art.

FIG. 6 is a timing chart showing an operation at the time of reception.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CPU which comprises a control means, 2 ... ROM which comprises a control means, 3 ... RAM which comprises a control means, 8 ... Head drive circuit, 9 ... Thermal head, 10 ... Temperature sensor, 13 ...
Interrupt timer, Td1, Td2 ... table data.

Claims (2)

(57) [Claims] 1. A control means for preheating control of a thermal head with a predetermined preheating pulse width after printing is performed by a thermal head with a predetermined printing pulse width based on image data and before the next printing is started. in the printing apparatus, said control means, in response to the temperature of the thermal head, respectively <br/> a table data set table data and preheat pulse width set the printing pulse width to be applied to the head The value of the printing pulse width is determined by the heat-sensitive head.
If the head temperature is higher than the specified temperature,
The lower the temperature, the higher the setting, and the temperature of the head.
The temperature is limited to a certain value in the range below the predetermined temperature.
The value of the preheating pulse width is different from the value of the printing pulse width.
The higher the temperature of the thermal head, the greater
It is set so that the higher the head temperature, the smaller
That printer. 2. The printing apparatus according to claim 1, wherein the control unit repeats the preheating control at a predetermined cycle until the next printing starts.