JPH0768827A - Preheating method of thermal head - Google Patents

Abstract

PURPOSE:To preheat a thermal head during waiting when a printing operation is performed. CONSTITUTION:When a signal wherein black and white data are continued and a pulse width of the black data is set up to such an extent as to a recording paper does not color by the heating of heating and resistance elements R1...Rn each is taken as preheating data and a signal expressing only white data is taken as radiation data, during waiting other than printing operation, a strobe signal is supplied to the heating and resistance elements R1...Rn. At the same time, based on a detected result of a temperature sensor 13, when a temperature of the thermal head 11 is not exceeding a lower limit temperature for which preheating is necessary, preheating data is supplied continuously to a shift register 12, the heating and resistance elements R1...Rn each are preheated and driven, when the temperature of the thermal head 11 attains to the upper limit temperature wherein preheating is not necessary, the radiation data expressing only the white data is supplied continuously to the shift register 12 and the heating and resistance elements R1...Rn each are made into a radiation state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preheating method for a thermal head, and more particularly, to prevent the printing cycle from being prolonged at a low temperature, the thermal head is set in a predetermined standby state during a printing operation. It relates to a method of preheating to a temperature.

[0002]

2. Description of the Related Art Recently, a printer using a thermal head is widely used in a facsimile machine or the like.
Generally, a printing apparatus using a thermal head is configured to apply a voltage based on line data to each heating resistance element of the thermal head, and the heating effect causes the recording paper (thermal paper) to develop color.

Therefore, a conventional thermal head is provided with a shift register to which line data is input and a latch circuit for latching the line data supplied to this shift register, and the line data transferred from the shift register to the latch circuit. In accordance with this, the heating resistance element is driven. Then, while the printing operation is being performed according to the line data latched by the latch circuit, the next line data is supplied to the emptied shift register to shorten the replacement time of the line data to the shift register. I am trying. That is, the printing speed is increased as a whole.

Further, since the thermal head is one for coloring the recording paper by the heat generating action of each heat generating resistance element,
The temperature of the heating resistor element may cause uneven printing density. That is, since the thermal head basically lowers the sensitivity when the temperature is low, the print density may be low when the temperature is low, and in some cases, the color may not be developed unless the energy supply amount is increased. This causes uneven printing density.

Therefore, the following two methods are conceivable as a method for increasing the amount of energy supplied to the heating resistance element. One is a method of increasing the applied voltage to the heating resistor element to increase the current supply amount (that is, a method of increasing the power consumption), and the other is to leave the applied voltage as it is and to generate the heating resistor. This is a method of increasing the supply time of current to the element.

The former method of increasing the voltage has a narrow allowable range in view of the rated voltage of the thermal head and is not a general method. Therefore, conventionally, the latter method of increasing the current supply time to the heating resistance element has generally been used to realize stable print density independent of temperature.

According to this latter method, if the ambient temperature is high, the amount of energy supplied to the heating resistance element can be small, so that the current supply time (that is, the pulse width of the data showing black among the line data) is reduced. It can be short. Further, if the ambient temperature is low, it is necessary to supply a large amount of energy to the heating resistance element, and therefore the current supply time (that is, the pulse width of the data showing black among the line data) becomes long.

In particular, when a printing device using a thermal head is applied to a facsimile device, its communication speed is predetermined according to the communication speed set with the facsimile device on the other side, regardless of the printing ability of the printing device. Will be sequentially processed in accordance with the communication procedure. Therefore, in the case of processing communication data in real time without a buffer, the printing speed cannot catch up with the communication speed, and a situation occurs in which all the communication contents cannot be printed.

Such a situation occurs when the ambient temperature at the start of communication is low (for example, 0 degrees, 5 degrees, 10 degrees, etc.) and does not occur when the ambient temperature is high (for example, 20 degrees or more). That is, in other words, even if the ambient temperature is low, such a situation does not occur if the temperature of the head (the temperature of the portion in contact with the recording paper) is high.

Focusing on this point, a technique for eliminating the unevenness of the printing density by preheating the heating resistance element has been disclosed in, for example, Japanese Patent Publication No. 60-22630 and Japanese Patent Publication No. 63.
No. 26712, Japanese Patent Publication No. 3-72470, Japanese Patent Publication No. 4-39433.

[0011]

However, the preheating techniques proposed by the above publications are all in the printing operation and perform appropriate preheating in the standby state before the printing operation. Has not been proposed yet. Further, in the conventional thermal head, the latch circuit is provided between the heating resistor element and the shift register as described above in order to increase the printing speed in consideration of the communication speed of the facsimile device. Since the circuit requires as many memory elements for one line as the shift register, there is a problem that the manufacturing cost becomes high.

The present invention was devised in view of the above problems, and in order to prevent the printing cycle from being prolonged at low temperatures,
It is an object of the present invention to provide a preheating method for preheating a thermal head to a predetermined temperature during a standby state in which no printing operation is performed.

[0013]

In order to solve the above problems, a method of preheating a thermal head according to the present invention is a heating resistor element for one line in which a strobe signal for controlling an applied voltage is applied to one of the terminals. A shift register that outputs line data for printing to each of the other terminals of the heating resistance elements to drive each heating resistance element, and a temperature sensor that detects the temperature of the entire head including the heating resistance elements. In the thermal head equipped with
A signal in which a pulse showing black data and a pulse showing white data are consecutive, and the pulse width of black data is set to a length such that the recording paper does not develop color due to the heat generated by each heating resistor element. When the signal indicating only the white data is used as the heat dissipation data, the strobe signal is continuously supplied to each heating resistor element in the ON state during standby except the printing operation, and the detection result of the temperature sensor Based on the above, when the temperature of the head is equal to or lower than the lower limit temperature that requires preheating, the preheating data is continuously supplied to the shift register to preheat drive each heating resistance element, and the upper limit of the temperature of the head that does not require preheating. When the temperature is reached, the heat dissipation data is continuously supplied to the shift register to bring each heat generating resistance element into a heat dissipation state, so that the temperature of the head is kept below the lower limit temperature. And controls between the upper limit temperature.

[0014]

The strobe signal for controlling the applied voltage is continuously supplied to each heating resistance element in the ON state during standby other than the printing operation. Then, based on the detection result of the temperature sensor at this time, when the temperature of the head is equal to or lower than the lower limit temperature (for example, 20 degrees) that requires preheating, the preheating data is continuously supplied to the shift register and each heating resistance element is supplied. Preheat drive, the head temperature does not require preheat.
When the temperature reaches 5 degrees), heat radiation data indicating only white data is continuously supplied to the shift register to bring each heat generating resistance element into a heat radiation state (non-operating state).

That is, when the head temperature is 20 ° C. or less, by supplying preheat data in which black and white data are continuous to the shift register, a pulse indicating black data included in the preheat data is supplied in accordance with the clock signal. The corresponding heating resistance elements generate heat only for a predetermined time, and preheating is performed. As a result, each heating resistance element is gradually heated, and the temperature of the head (specifically, the temperature of the portion in contact with the recording paper) exceeds 20 degrees.

On the other hand, the head temperature is 20
When the temperature exceeds the temperature and reaches the upper limit temperature of 25 degrees, the heat radiation data indicating only the white data is continuously supplied to the shift register from that point. In other words, even if the strobe signal is in the ON state, each heating resistor element maintains the non-operating state, becomes the heat radiation state, and the head temperature gradually decreases. As a result of heat dissipation, the temperature of the head is 2
When the temperature becomes 0 degrees or less, preheating data in which black and white data are continuous is given to the shift register again, and each heating resistor element performs preheating operation. That is, the head temperature is the lower limit temperature of 20 degrees and the upper limit temperature of 2 regardless of the ambient temperature (at low temperature in this case) during standby other than the printing operation.
It will be controlled between 5 degrees.

As a result, when the facsimile apparatus equipped with this thermal head starts the receiving operation, the thermal head is already in the printable state even if the ambient temperature is low. Real-time printing is possible. This makes it possible to eliminate the latch circuit described as the prior art, so that the manufacturing cost can be reduced accordingly.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an electrical configuration when a thermal head to which the preheating method of the present invention is applied is installed in a facsimile apparatus.

In FIG. 1, a modem 2 connected to a telephone line 1 is connected to a buffer circuit 3 for matching transfer units and transfer rates. The output of this buffer circuit 3 is the operation of the entire device. It is connected to the CPU 4 that performs control. The CPU 4 has an R storing an operation program.
The OM 5 and the RAM 6 for temporarily storing the received data are bidirectionally connected. Further, the CPU 4 has a preheat data creation circuit 1 for creating preheat data and heat radiation data.
The output of 0 and the output of the temperature sensor 13 which will be described later are introduced. The output of the temperature sensor 13 is
It is A / D converted and taken into the CPU 4.

The output of the CPU 4 is a print pulse generating circuit 7 for outputting a strobe signal and a print data buffer 8 for outputting print data (line data) for one line.
And a data transfer clock generation circuit 9 for outputting a clock signal for data transfer.

On the other hand, the thermal head 11 has one line (for example, 1024) heating resistor elements R1, R2 ... Rn to which the strobe signal from the print pulse generating circuit 7 is applied to one terminal, respectively. A shift register 12 that outputs line data for printing to each of the other terminals of the heating resistance elements R1, R2, ... Rn.
And a temperature sensor 13 including, for example, a thermistor for detecting the temperature of the entire head including the heating resistance elements R1, R2, ... Rn.
The line data output from the print data buffer 8 and the clock signal from the data transfer clock generation circuit 9 are given. That is, the shift register 11 sequentially transfers the given line data according to the speed of the clock signal.

Here, the preheat data created by the preheat data creating circuit 10 is a continuous signal of a pulse indicating black data and a pulse indicating white data, and the pulse width of the black data is Heating resistor elements R1, R2 ...
The signal is set to a length such that the recording paper does not develop color due to the heat generated by Rn. Specifically, for example, the heating resistor element R
When R1, R2, ..., Rn are driven in four divisions, the pulse width of each strobe signal that provides a sufficient density when the ambient temperature is about 20 degrees is about 1.5 ms.
The pulse width showing the black data of the preheating data is 1/5 of that.
It is set to about 1/10 and about 200 to 300 μs.
In addition to this, the preheat data creation circuit 10 creates heat radiation data indicating only white data.

Such preheat data is used for the shift register 1
2, the shift register 12 sequentially transfers the preheat data according to the speed of the clock signal. The preheating is performed as a result of turning on the corresponding heating resistance element as a result of being turned on only during the time when the black data stays in each storage location (composed of binary elements) of the shift register 12. The on-time at this time is a short time such that the recording paper does not develop color as described above.

Next, the operation of the facsimile apparatus having the above-described structure will be described separately for (1) normal facsimile receiving operation and (2) preheating operation during standby other than printing operation. Note that FIG. 2 is a timing chart during the preheating operation, and FIG. 3 is an operation flowchart during the preheating operation, which will be appropriately referred to in the description of the preheating operation.

(1) Normal Facsimile Receiving Operation The image data sent from the facsimile apparatus on the other side through the telephone line 1 is usually MH (Modifid Huffman).
It is transmitted in a band-compressed state by an encoding method or an MR (Modifid Read) encoding method. The transmitted image data is converted into a digital signal by the modem 2, temporarily stored in the buffer circuit 3, then taken in by the CPU 4 and stored in the RAM 6.

Then, the band-compressed image data is decoded according to the operation program stored in the ROM 5, and converted into print data suitable for printing by the thermal head 11. That is, when one line is composed of 1728 heating resistance elements R1, R2 ... Rn, and one set is divided into four blocks of 432, the 1728 heating resistance elements R1, R2. ... Rn
Is converted into 1728 line data of black (energized) or white (non-energized).

This line data is written in a storage area for a print buffer (not shown) in the CPU 4. Thereafter, the written line data is transferred to the print data buffer 8 by serial communication, and is sent from the print data buffer 8 to the shift register 12 by serial communication. The shift register 12 sequentially transfers the input line data according to the speed of the clock signal from the data transfer clock generation circuit 9.

On the other hand, when the print pulse generation circuit 7 is divided into four blocks, four strobe signals corresponding to the respective blocks are sequentially output to the respective blocks. As a result, when the strobe signal is in the ON state, the heating resistor element to which the signal indicating the black data (energization signal) is applied from the shift register 12 generates heat, and the printing operation for one line is performed.

By repeating such a printing operation for one line for all the line data of the transmitted data signal, the image data is printed on the recording paper.

(2) Preheating operation during standby other than printing operation First, the following conditions are set as a precondition for preheating operation.
That is, since the thermal paper, which is a recording paper, usually develops color at about 70 degrees, in this embodiment, the upper limit temperature of preheating is set to 25 degrees when controlling the preheating operation. Also,
Since the problem of the relationship between the communication speed and the printing speed of the facsimile is at a low temperature of 10 degrees or less, the lower limit temperature of preheating is set to 20 degrees in this embodiment.

Under these conditions, the preheating operation is started. That is, when the facsimile apparatus is installed at a predetermined place and the power is turned on at time t1 (step S1), the CPU 4 confirms that it is in the standby state other than the printing operation (step S2), and then generates the print pulse. The strobe signal from the circuit 7 is always turned on [Fig.
(B)], and continue supplying to each heating resistance element R1, R2 ... Rn (step S3).

Thereafter, the CPU 4 causes the thermal head 11 to
Is determined by the temperature data from the temperature sensor 13. When the temperature of the thermal head 11 is lower than or equal to the lower limit temperature that requires preheating, the black and white continuous preheating data created by the preheating data creating circuit 10 is read and transferred to the print data buffer 8, Preheat data from the print data buffer 8 to the shift register 12 [Fig.
(Indicated by reference numeral 21 in (c)] is continuously supplied to preheat and drive the heating resistance elements R1, R2, ..., Rn (steps S4, S5).

As a result, the temperature of the thermal head 11 gradually rises from the time t1 when the power is turned on (see FIG. 2A). This temperature increase is determined by the temperature data supplied from the temperature sensor 13 to the CPU 4
Is constantly monitored by.

When the temperature of the thermal head 11 reaches the upper limit temperature that does not require preheating at the time t2, the CPU 4 causes the preheating data creating circuit 10 to generate heat radiation data [FIG. (indicated by reference numeral 22 in c)) is continuously read out and continuously supplied to the shift register 12 to generate the respective heating resistance elements R1, R2 ...
・ Rn is set to the heat radiation state (non-operating state) (step S
6, S7, S8).

As a result, the temperature of the thermal head 11 that has reached the upper limit temperature will gradually decrease from the time t2 due to the heat radiation effect. This temperature decrease is constantly monitored by the CPU 4 by the temperature data given from the temperature sensor 13. And the thermal head 11
When the temperature of No. 1 decreases to the lower limit temperature that requires preheating again at time t3, the CPU 4 causes the black and white continuous preheating data 21 created by the preheating data creating circuit 10 to continue.
Is read out again and transferred to the print data buffer 8, and the preheat data is continuously supplied from the print data buffer 8 to the shift register 12 to generate the heating resistance elements R1, R2 ...
Rn is preheated (steps S4 and S5).

By repeating the above operation, the thermal head 11 is controlled between the lower limit temperature of 20 degrees of preheating and the upper limit temperature of 25 degrees irrespective of the ambient temperature during standby other than the printing operation. Will be. As a result, when the facsimile machine equipped with the thermal head 11 starts the receiving operation, even if the ambient temperature is low,
Since the thermal head 11 is already in the printable state, it is possible to print in real time according to the communication speed. This allows the latch circuit described in the related art to be deleted without deteriorating the communication quality, and thus the manufacturing cost can be reduced accordingly.

Further, according to the preheating method of the present invention, the strobe signal is always on during the preheating operation, and it is sufficient to transfer the preheating data and the heat radiation data to the shift register 12, so that the preheating operation is performed. The control for this is also simple.

In the above embodiment, the thermal head 1
When the temperature of 1 reaches the upper limit temperature that does not require preheating, the shift register 12 is configured to continuously supply preheating data indicating only white data, but separately from this, the clock signal is stopped. By doing so, each of the heating resistance elements R1, R2 ... Rn can be brought into a heat radiation state (non-operating state). Further, in the above embodiment, the lower limit temperature of preheating is set to 20 degrees and the upper limit temperature is set to 25 degrees, but the temperature is not limited to these temperatures.

[0039]

According to the preheating method of the thermal head according to the present invention, the strobe signal is continuously supplied to each heating resistance element in the ON state during the standby other than the printing operation, and the head temperature is detected based on the detection result of the temperature sensor. When the temperature is below the lower limit temperature that requires preheating, preheat data is continuously supplied to the shift register to preheat each heating resistance element, and when the head temperature reaches the upper limit temperature that does not require preheating, the shift register turns white. In this case, the ambient temperature is low because the temperature of the head is controlled between the lower limit temperature and the upper limit temperature by continuously supplying the heat dissipation data showing only the data of 1. However, since the thermal head is already in the printable state, it is possible to print in real time according to the communication speed of the facsimile. As a result, the latch circuit described in the related art can be deleted without deteriorating the communication quality, and the manufacturing cost can be reduced accordingly. Further, according to the preheating method of the present invention, the strobe signal is always in the ON state during the preheating operation, and since it is sufficient to simply transfer the preheating data and the heat radiation data to the shift register, the strobe signal can be turned on / off. Except for this, the preheating operation can be performed under the same control as the normal printing operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration when a thermal head to which a preheating method of the present invention is applied is installed in a facsimile apparatus.

FIG. 2 is a timing chart during a preheating operation.

FIG. 3 is an operation flowchart during a preheating operation.

[Explanation of symbols]

 10 Preheating data creation circuit 11 Thermal head 12 Shift register 13 Temperature sensor

Claims (1)

[Claims] 1. A heating resistor element for one line to which a strobe signal for controlling an applied voltage is applied to one terminal, and line data for printing is output to each of the other terminals of these heating resistor elements. In a thermal head including a shift register that drives each heating resistance element and a temperature sensor that detects the temperature of the entire head including the heating resistance element, a pulse indicating black data and a pulse indicating white data Preheating data is a signal that is a continuous signal, and the pulse width of black data is set to a length that does not cause the recording paper to develop color due to the heat generated by each heating resistance element, and the signal showing only white data is the heat dissipation data. In this case, the strobe signal is continuously supplied to each of the heating resistance elements in the ON state during the standby other than the printing operation, and the detection result of the temperature sensor is detected. Based on the above, when the temperature of the head is equal to or lower than the lower limit temperature that requires preheating, the preheating data is continuously supplied to the shift register to preheat drive each heating resistance element, and the upper limit of the temperature of the head that does not require preheating. The temperature of the head is controlled between the lower limit temperature and the upper limit temperature by continuously supplying the heat radiation data to the shift register when each temperature is reached to bring each heat generating resistance element into the heat radiation state. How to preheat the thermal head.