JPS63283964A - Thermal head - Google Patents

Abstract

PURPOSE:To control energy to be applied from a driving circuit by using a resistance value of a temperature correction resistance and to enable printing of a constant density to be realized even though the same driving circuit is used for a thermal head of a different grade, by a method wherein the resistance for correction of temperature is solidly integrated into a thermal head body. CONSTITUTION:A head board 1 composed of a plularity of resistance thermal elements 11 and an insulating material having a connector 12 for connecting said resistance thermal elements 11 to outside is attached to a metallic attaching basic stand 2 by adhesion or the like. A thermistor 3 is located almost at a center of a back of the resistance thermal element 11. A resistance 13 for correction of a temperature coefficient of the thermistor 3 can equalize a temperature of the resistance heating element 11 and an apparent thermistor resistance value even for thermal heads of different heating characteristics by inserting the resistance 13 of which a resistant value is appropriately determined into the thermistor 3 for the thermal head body to be connected to an output lead wire (being not given in the figure) and the connector 12 for outside connection of the thermistor 3 by a conductor pattern provided on a print board 4 for connection. Therefore, a same driving circuit can be used without changing control characteristics of printing energy. Recording of a stable printing density can be simply obtained by using this same driving circuit.

Description

[Detailed Description of the Invention] [Summary] The present invention provides temperature compensation to the thermal head body so that the relationship between the temperature of the resistive heating element of the thermal head and the output resistance value of the thermistor is constant regardless of the type of thermal head. This is a built-in resistor.

[Industrial application field]

The present invention relates to a thermal printer that prints characters and figures by passing a current through a resistive heating element, and more particularly to an improvement of a thermal head incorporating a thermistor for controlling thermal characteristics.

For thermal printers and the like, it is desirable to be able to print over a wide environmental temperature range and at a density that is stable over time.

Therefore, the average temperature of the resistance heating element of the thermal head is detected, and the energy of the printing pulse is adjusted according to the detected temperature.
A method of maintaining a constant print density has been adopted. Normally, this control is performed by controlling the drive circuit using resistance changes in the thermistor mounted on the thermal head, but it would be extremely economical if a common drive circuit could be used regardless of the type of thermal head. It's advantageous.

The present invention provides a thermal head capable of doing the above.

[Conventional technology]

FIG. 4 is a sectional view of a conventional thermal head.

In the figure, reference numeral 1 denotes a head board having a plurality of resistance heating elements 11 (disposed in parallel in the direction perpendicular to the plane of the paper), which is made of metal along with a connecting printed board 4 having a connector 12 for connecting the resistance heating elements to the outside. It is attached to the mounting base 2 by adhesive or other method. The recording paper 5 on the paper feed roller 6 develops color due to heat generated by the resistance heating element 11 of the thermal head, and recording is performed. When the thermal head is in a continuous printing state, the heat generated by the resistance heating element 11 is gradually accumulated, and the average temperature rises, so that the print density shifts to the higher density side.

In order to prevent this and keep the print density constant, a thermistor 3 is attached to the mounting base 2 of the thermal head, and the applied energy (applied pulse width or current value) from the drive circuit is controlled according to the substrate temperature. .

At this time, it is desirable to detect the temperature of the resistance heating element 11, but due to the structure of the thermal head, it is impossible to place a thermistor on the printing surface, so it is usually built into the back side of the thermal head as shown in the figure, and its output is It was directly pulled out to the outside via the connector 12.

[Problem that the invention seeks to solve]

In order to keep the print density constant, it is necessary to reduce the applied energy when the temperature of the resistance heating element is high, and to increase it when the temperature is low. The relationship between this temperature and applied energy is approximately constant regardless of the type of thermal head, and the drive circuit is configured to control the pulse width of the applied pulse by the resistance value of the thermistor.

By the way, thermal heads have different heat capacities and heat dissipation characteristics depending on their type. Therefore, when the thermistors are installed apart as described above, the relationship between the temperature of the resistive heating element and the temperature at the detection point by the thermistor is not constant. Therefore, the relationship between the temperature of the resistive heating element and the resistance value of the thermistor is not constant. However, the same drive circuit cannot be used.

In other words, if a circuit adjusted for a certain type of thermal head is used as a drive circuit for another type of thermal head, such as one with a structure that has a large heat dissipation, the temperature difference between the heat generating part and the detecting part will be larger than that of the former. Because of the large temperature, the apparent temperature is detected to be low (that is, the resistance value of the thermistor is larger than the normal value), and the energy of the applied pulse from the drive circuit is therefore higher than the normal value, resulting in a darker print density. .

Conventionally, methods to solve this problem include selecting a thermistor according to the thermal characteristics of the thermal head, or adjusting the constants of circuit elements on the drive circuit side. However, the former has the problem that it is difficult and costly to change the characteristics of the thermistor each time, and the latter has the problem that a drive circuit must be prepared for each type of thermal head, making it difficult to standardize. .

[Means for solving problems]

FIG. 2 is a diagram showing a temperature coefficient correction circuit for a thermistor.

In order to solve the above problems, the present invention corrects the difference in thermal characteristics of the thermal head so that the relationship between the temperature of the resistive heating element and the resistance value of the thermistor is constant regardless of the type of thermal head. In addition, a thermistor temperature coefficient correcting circuit consisting of several resistance elements shown in FIG. 2 is appropriately selected and mounted on the thermal head.

[Effect]

That is, Fig. 2 (a), (b), (c), (
As shown in d), by connecting a resistor Rs in series or a resistor Rp in parallel to the thermistor 3, the temperature coefficient of the thermistor can be changed arbitrarily. Generally, by inserting this resistor, the temperature characteristics of the thermistor as seen from the output side are flattened (that is, the sensitivity is lower than when directly extracting the resistance change of the thermistor), but as the temperature rises, the thermistor's resistance value decreases. Since it is an extremely highly sensitive temperature sensing element that rapidly decreases, it is sufficient for practical use.

By appropriately selecting the above resistor and mounting it on the thermal head, the relationship between the temperature of the resistive heating element and the apparent output resistance value of the thermistor when viewed from the outside of the thermal head can be adjusted to the thermal characteristics of the thermal head. It can be made irrelevant. Therefore, if the energy applied from the drive circuit is controlled using this resistance value, printing with constant density can be achieved even if the same drive circuit is used for different types of thermal heads.

〔Example〕

The present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view of a thermal head according to the present invention,
FIG. 3 is a diagram showing the relationship between resistance value and print density.

In FIG. 1, reference numeral 1 denotes a head board made of an insulator and having a plurality of resistance heating elements 11 (aligned in a direction perpendicular to the paper) and a connector 12 for connecting the resistance heating elements to the outside. It is attached to the base 2 by adhesive or the like. 3 is a thermistor attached to the mounting base 2, and is located approximately at the center of the back surface of the resistance heating element 11 (in the direction perpendicular to the plane of the paper).

Reference numeral 13 indicates a series resistance or parallel resistance for correcting the temperature coefficient of the thermistor, and the output lead wire (not shown) of the thermistor 3 and the connector 12 for external connection are connected by a conductor pattern arranged on the printed circuit board 4 for connection. The temperature characteristic correction circuit shown in FIG. 2 is configured.

FIG. 3 shows data obtained by performing a printing test using a thermal head configured as described above and a drive circuit prepared for a thermal head having different thermal characteristics. The horizontal axis of the figure shows the number of consecutive prints, and the vertical axis shows the rate of change in print density 0-D value.
The dotted line represents an example of the allowable limit value of print density change. When the temperature of the resistance heating element increases due to continuous printing from a normal temperature state with no heat storage in the thermal head (ie, the number of sheets printed is 0), the resistance value of the thermistor decreases, and the printing energy decreases according to a predetermined relationship. In the figure (a), only the thermistor that is easily available as a standard product is used without a correction resistor, Rp = ■,
Rs=O), the resistance change is too large, so the printing energy decreases rapidly, and the printing density changes to the negative side (that is, becomes thinner than the allowable limit). Also, in (b) of the figure, Rp = 10 KΩ, Rs =
10 KΩ, (c) Rp = 30 KΩ, Rs=
When a series resistor Rs and a parallel resistor Rp are inserted into the same thermistor, such as 157Ω, the change in the apparent resistance value of the thermistor becomes too flat, and the decrease in printing energy cannot keep up with the rise in temperature, resulting in more printing than the allowable limit. Indicates a state of increased concentration.

(d) of the same figure shows data when Rp=oo and Rs=235Ω.In the case of a thermal head having the thermal characteristics of this embodiment, by inserting a 235Ω resistor in series, for example, as shown by the dotted line in the figure, The allowable concentration change can be kept within the range of ±2%.

As described above, by inserting a resistor with an appropriately determined resistance value in series or parallel with the thermistor into the thermal head body, thermal heads with different thermal characteristics can be used.
Since the temperature of the resistive heating element and the apparent thermistor resistance value can be made the same, the same drive circuit can be used without changing the printing energy control characteristics.

In the above embodiment, a case was described in which a correction circuit was constructed by a conductive pattern formed on a printed board for connection and an individual resistor mounted on the printed board, but in addition to this, the correction circuit is The correction resistor may be directly mounted on the substrate, or may be formed integrally with a thin film on the head substrate. Further, by using a semi-fixed resistor or the like instead of a fixed resistor, it is also possible to correct variations in thermal characteristics of individual thermal heads within the same product type.

〔Effect of the invention〕

According to the present invention, it is possible to easily obtain a stable record of print density by using the same drive circuit for different types of thermal heads, which is effective in standardizing the drive circuits of thermal printers, etc., and is economical. The effect is significant.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the thermal head according to the present invention, FIG. 2 is a diagram showing the temperature coefficient correction circuit of the thermistor, FIG. 3 is a diagram showing the relationship between resistance value and print density, and FIG. 4 is a diagram showing the relationship between resistance value and print density. , a cross-sectional view of a conventional thermal head. In the figure, 1 - head substrate, 11 - resistance heating element, 12
- Connector, 13 - Resistor, 2 - Mounting base, 3 - Thermistor, 4 - Printed board, 5 - Recording paper, 6 - Paper feed low step. The present invention f; I-type thermal head W1 set 16 feet
i21 Length - Mista's Eagle (Seed 44th) Upper E1 Drinking Crime% 2 Sword

Claims (1)

[Claims] A head substrate (1) on which a plurality of resistance heating elements (11) are formed.
), a mounting base (2) for mounting the head board (1) and a printed board (4) for drawing out external terminals from the head board (1); a thermistor (3) for detecting the temperature of the head substrate (1); and a resistor (13) connected in series or parallel with the thermistor (3) for temperature coefficient correction of the thermistor (3).
A thermal head comprising: