JPH0111465Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wire printhead having a temperature sensing element.

As is well known, wire print heads generate heat during printing operations. In particular, when printing kanji or graphics, the printing density increases and the temperature becomes high. To this end, a temperature detection element has traditionally been attached to the wire print head, and when this temperature detection element detects a temperature higher than a predetermined temperature, the printing speed is reduced or temporarily stopped to prevent burnout and shorten the life of the print head. That's what I was doing.

For example, in the conventional wire printing head shown in FIG. The armature 2 is released by canceling the magnetic attraction force of the magnet 1, and the dot wire 5 fixed to the tip of the armature 2 is driven.The temperature sensing element 6 is composed of two coils as shown in FIG. 5, and is further filled with a resin 7 having good thermal conductivity. In the following description, the core 4a and the coil 4b will be collectively referred to as an electromagnet.

In the conventional method, the temperature of the coil 4b that is in close contact with the temperature sensing element 6 can be detected accurately and quickly, but the temperature of the coil 4b that is located far from the temperature sensing element 6 is detected as a lower temperature than the actual temperature. Moreover, even if the resin 7 is filled, heat transfer is slow, so there is a drawback that detection is delayed.

In order to eliminate the above-mentioned drawbacks, the present invention has a resistor whose resistance changes depending on the temperature is shaped to match the arrangement of the electromagnets and is brought into contact with all the electromagnets, and electrodes are formed at both ends of this resistor so that each electromagnet The wire print head is equipped with a temperature sensing element in which all the resistors in contact with the wire are connected in parallel, and will be explained in detail below with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 2A is a side sectional view, and FIG. 2B is a layout diagram with the upper half removed. In FIG. 2, 8 is an annular thermistor that uniformly contacts all the coils 4b, and as shown in FIG. a sintered body 8a mixed and sintered; electrode plates 8b fixed to both upper and lower surfaces of this sintered body 8a;
It consists of a lead wire 8c welded to this electrode plate 8b.

In the embodiment with the above configuration, the dot wire 5 is driven in the same manner as in the conventional case, but the resistance value of the annular thermistor 8 mainly detects the temperature of the coil 4b where the temperature rise is the largest.

This point will be explained in more detail using FIG. 4. In other words, the annular thermistor 8 is equivalent to a large number of micro thermistors connected in parallel as shown in FIG.
Rs can be expressed by equation (1).

Rs=1/1/r(1)+1/r(2)+...1/r(n)
...(1) In equation (1), for example, if r(2) becomes an extremely low value due to the temperature rise of the electromagnetic coil 4b, the resistance value
Rs is approximately r(2). That is, the resistance value of the annular thermistor 8 as a whole is most influenced by the one having the highest temperature among the plurality of coils 4b.

Further, the annular thermistor 8 is connected to the coil 4 which is a heat source.
b, the thermal resistance between the heat source and the annular thermistor 8 is extremely small.
The temperature of the coil 4b can be detected accurately and early.

Fig. 5 is a characteristic diagram comparing a conventional example using a 24-pin wire printing head to show the effect of this embodiment. It is compared in terms of time,
According to this embodiment, the conventional best condition, that is, the case where a coil to which the temperature sensing element is in close contact is driven, and
The same temperature is detected at almost the same time, and it is no exaggeration to say that the temperature of the coil with the largest temperature rise is detected. In addition, Figure 5 (b) shows the time until the alarm occurs on the vertical axis, and the number of drive wires on the horizontal axis, and the total number of dots per second when the number of wires is driven, for comparison. In this case, when a coil far from the temperature sensing element is driven, the coil burnout region D is reached before an alarm occurs, but in this embodiment, the result is the same no matter which coil is driven, and under the best conditions in the conventional example. The alarm is issued as accurately and early as the previous one.

Furthermore, when the resistance value of the annular thermistor 8 in the embodiment described above drops to a predetermined value, various known circuits can be used as a circuit that issues an alarm signal indicating that the coil 4b has become high temperature.

For example, the detection circuit shown in Figure 6 has a resistor _R1 and a resistor
The voltage divided by R ₂ is used as the reference voltage, and the voltage divided by the resistance Rs of the annular thermistor 8 and the other resistance R _L is used as the detection voltage. When this detection voltage becomes larger than the reference voltage, the voltage comparator CMP Outputs a logic "1" signal, that is, an alarm signal. This alarm signal is used to stop the printing operation.

Note that the present invention is not limited to the above-mentioned embodiments; for example, the shape of the temperature sensing element can be made into various shapes depending on the arrangement of the coils. For example, in a dot line printer in which a large number of electromagnets are arranged in the printing line direction and a wire is driven by the electromagnets, a rectangular flat temperature sensing element 9 shown in FIG. The surface may be in contact with all electromagnets. Note that the flat temperature sensing element 9 uses a thermoelectric material 9 whose resistance value changes depending on the temperature.
It is preferable to form an electrode plate 9b on the end face in the lateral direction of a, and to weld the lead wire 9c to this electrode plate 9b.

Furthermore, the temperature sensing element only needs to be in contact with all the electromagnets, and therefore may be in contact with the core.

As explained in detail above, according to the present invention, a resistor whose resistance changes depending on temperature is shaped to match the arrangement of the electromagnets, is brought into contact with all the electromagnets, and electrodes are formed at both ends of this resistor. The wire printing head is equipped with a temperature detection element in which all the resistors in contact with each electromagnet are connected in parallel, making it possible to accurately and quickly detect the temperature of the electromagnet that has reached the highest temperature among all the electromagnets. There is an effect that can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view and layout diagram showing a conventional print head, FIG. 2 is a side sectional view and layout diagram showing an embodiment of the present invention, FIG. 3 is a perspective view showing the structure of an annular thermistor, and FIG. The figure shows an equivalent circuit of an annular thermistor, FIG. 5 shows a characteristic diagram showing the effects of this embodiment, FIG. 6 shows a detection circuit suitable for this embodiment, and FIG. 7 shows another implementation of the present invention. FIG. 2 is a perspective view showing the structure of a temperature sensing element used in an example. 1... Permanent magnet, 2... Armature, 3...
Leaf spring, 4a...core, 4b...coil, 5...
Dot wire, 7... Resin, 8... Annular thermistor, 9... Flat temperature sensing element.

Claims (1)

[Claims for Utility Model Registration] (1) In a wire printing head that performs printing by driving wires using a plurality of electromagnets, a resistor whose resistance changes depending on temperature is shaped to match the arrangement of the electromagnets. A wire printing head characterized in that it is provided with a temperature detection element which is brought into contact with all the electromagnets, electrodes are formed at both ends of the resistor, and all the resistors at the parts that come into contact with the electromagnets are connected in parallel. (2) The wire printing head according to claim 1, wherein the temperature sensing element has an annular shape. (3) The wire printing head according to claim 1, wherein the temperature sensing element has a flat shape.