JPS62207657A - Apparatus for protecting thermal head - Google Patents

Abstract

PURPOSE:To prevent the abnormal generation of heat from a thermal head, by mounting a gate circuit blocking the supply of a current to the thermal head when output is emitted from one of a timer and an abnormal temp. setting circuit. CONSTITUTION:A timer 12, to which the max. printing time of a thermal head 6 is set, begins to count a time on the basis of a start signal S and emits output (H-level) when reaches the set time. The timer is resent when a resetting signal R is inputted prior to reaching the set time. The resetting signal R is taken from the output of a voltage applying time control circuit 10. The abnormal temp. of the thermal head 6 is set to an abnormal temp. setting circuit 13 and, when the detection temp. of a temp. detection element reaches the set temp. said circuit 3 emits output (H-level). When at least one of the timer 12 and the abnormal temp. setting circuit 13 emits output, the output of a NOR gate 15 is converted to a L-level and the gate of a gate circuit 14 is closed. By this method, the supply of a current to the thermal head 6 is blocked.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a protection device for protecting a thermal head used in a thermal transfer printer or the like from both printing time and heat generation temperature.

Previously used as a protection device for Mengfushiki Ibarei thermal head was
As seen in Publication No. 0150+U, a timer is provided to set the maximum printing time of the thermal head, and the thermal head drive pulse is controlled by the output signal of the timer to prevent damage to the head due to long-time printing. There is a means.

However, since this method only protects the thermal head in terms of printing time, it has the following problems. Namely, ■ Voltage of the thermal head. Noise may get on the voltage application line, and in that case, even if the printing time is short, the superimposed noise will actually lengthen the voltage application time.
The conventional means described above cannot prevent the head from generating heat due to abnormal characters.

■The maximum printing time must be set for the timer, but in practice it is difficult to set an appropriate time. In other words,
When you drive the thermal head for the first time, it takes relatively little time for the head to reach abnormal temperature because it is cold, but if you are printing repeatedly, the next drive pulse is applied before the head has cooled down. It reaches high temperatures in a relatively short time. For this reason, if the maximum printing time is set based on the first time the head is driven, it will not be possible to prevent abnormally high temperatures when repeatedly printing. If the head is driven for the first time, the timer will operate and limit the drive pulse even though the head has not reached an abnormally high temperature.

On the other hand, instead of protecting the thermal head by printing time as described above, it is possible to adopt a method of detecting the head temperature with a thermistor or the like and stopping the drive when the head reaches an abnormally high temperature. Since the detection accuracy of abnormally high temperature depends on the reliability of the thermistor, the abnormally high temperature setting level must be set slightly lower than the predetermined temperature level, which causes the problem of narrowing the temperature control range. be.

An object of the present invention is to provide a thermistor head protection device that solves the above-mentioned problems.

-How to solve the problem The purpose of the above is to provide a timer that outputs an output when the printing time of the thermal head reaches a predetermined time, and an abnormal temperature setting circuit that outputs an output when the heat generation temperature of the thermal head reaches a set temperature. This is achieved by including a gate circuit that cuts off power to the thermal head when an output is generated from at least one of the timer and the abnormal temperature setting circuit.

The reason why this configuration can solve the problems caused by the conventional means will be explained in the following example.

FIG. 3 shows a schematic configuration of a color printer as an example of a thermal transfer printer to which the protection device of the present invention is applied. The transfer paper 1 is wound around a platen roller 2 in the transfer section A, and is configured to be freely fed in the forward direction and reverse direction indicated by a in the figure by a paper feed drive section consisting of a pulse motor (not shown). The ink film 3 is a so-called field-sequential ink film in which three colors of ink, for example, yellow, magenta, and cyan, are sequentially applied in the longitudinal direction.
and the take-up roller 5, and is in close contact with the transfer paper 1 at a part of the outer periphery of the platen roller 2. The take-up roller 5 is driven by an ink film feed motor (not shown) and takes up the ink feed in the direction shown in the figure. The transfer section A is provided with a thermal head 6 that transfers the hot-melt ink of the ink film onto the transfer paper 1 by heating. A roller 7 for separating the ink film and the transfer paper is provided a predetermined distance ahead of the transfer section A in the ink film feeding direction, and further ahead are sensors 8 for detecting the leading position of the ink film and for detecting each color.

In the printing operation, the thermal head 6 is driven to generate heat through a driver circuit and a selector circuit (not shown) so that a predetermined image can be formed on the transfer paper, and the ink film feed motor and paper feed drive section are also driven to transfer a certain color. When the process is completed, the ink film is advanced so that a different color comes to the transfer area, and the transfer paper is returned to its original position.

The thermal head 6 is equipped with a protection device shown in FIG. 1, which protects the head from both head temperature and printing time and prevents burnout of the ink film.
11 is a temperature detecting element built into the thermal head 6, such as a thermistor; 12 is a timer; 13 is an abnormal temperature setting circuit; and 14 is a gate circuit.

When printing is to be performed using the thermal head 6, a start signal S is issued from a CPU (not shown), and this start signal S is applied to the voltage application time control circuit 10 and timer 12 to start each circuit 10.12.

The voltage application time control circuit 10 is a circuit that sets the time for applying voltage to the thermal head 6, and adds information from the temperature detection element 11 to set the pulse width to be appropriate for printing.

The timer 12 has a maximum printing time set by the thermal head 6, starts counting the time from the start signal S, and outputs an output ("H'" level) when the set time is reached. If the reset signal OR is input before the set time is reached, it will be reset. This reset signal R is taken from the output of the voltage application time control circuit 10.

The set time of the timer 12 is set to be long in consideration of the case where the head temperature is low before being driven, such as when the head is energized after a long rest period. However, if the set time is made longer, as described above, if the head is repeatedly driven and the head temperature is high, there is a risk that the head will reach an abnormally high temperature before the timer operates. However, in the present invention, such a fear is solved by setting the abnormal temperature in the abnormal temperature setting circuit 13 and operating the abnormal temperature setting circuit even if the timer 12 does not operate.

The abnormal temperature setting circuit 13 is set to an abnormal temperature of the thermistor head, and outputs an output ("H" level) when the temperature detected by the temperature detection element 11 reaches the set temperature. The temperature set in this circuit 13 can literally be set to an abnormal temperature without considering the reliability of the thermistor. The reason is that if the thermistor's detection accuracy is poor and the thermal head attempts to reach an abnormal temperature before the abnormal temperature setting circuit 13 is activated, in many cases the printing time will be longer than the specified time and the timer 12 will be set. This is because, as a result of this, the thermal head can be prevented from reaching an abnormal temperature. In addition, since the present invention protects the thermal head in terms of both printing time and head temperature, even if the thermistor is unreliable, the thermal head can be fully protected without lowering the temperature setting level. .

When at least one of the timer I2 or the abnormal temperature setting circuit 13 outputs an output, the output of the NOR gate 15 becomes "L".
level, and the gate of the gate circuit 14 closes. As a result, power to the thermal head 6 is cut off.

Next, Figure 2 shows an improved version of the protection device shown in Figure 1, with timer 1.
By connecting 2 and the temperature detection element 11 with the signal line 16, the head temperature is also input to the timer 12, and the timer 12
The set time can be increased or decreased depending on the head temperature. When changing the set time in this manner, the set time may be shortened as the head temperature becomes higher, and lengthened as the head temperature becomes lower.

Since the present invention is configured as described above, abnormal heat generation of the head that cannot be prevented by regulating only the printing time, such as when noise is added to the voltage application line of the thermal head, can be prevented by controlling the abnormal temperature/setting circuit. can be effectively prevented by the presence of
On the other hand, from the viewpoint of the reliability of the thermistor, the timer has the effect of preventing abnormal heat generation in the head, which cannot be prevented by regulating the head temperature alone, from the viewpoint of printing time.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a thermal heat shield protection device as an embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the present invention, and Fig. 3 is a block diagram showing a protection device for a thermal herad as an embodiment of the present invention. 1 is a schematic configuration diagram showing a thermal transfer color printer. Step 2...Timer Step 3...Abnormal temperature setting circuit 14...Gate circuit. Patent applicant Minolta Camera Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] (1) A timer that outputs an output when the printing time of the thermal head reaches a predetermined time; an abnormal temperature setting circuit that outputs an output when the heat generation temperature of the thermal head reaches a set temperature; and at least one of the timer and the abnormal temperature setting circuit. A thermal head protection device comprising a gate circuit that cuts off power to the thermal head when an output is generated from the thermal head.