JPS6097872A - Thermal head - Google Patents

Abstract

PURPOSE:To enable to reduce size and cost, by a construction wherein temperature-detecting elements are provided at a plurality of parts of a thermal head, and are connected in series with each other. CONSTITUTION:A thermal head 1 comprises a heat-radiating substrate 2, a ceramic substrate 3 provided on the substrate 2, and a heating resistor 4 provided on the substrate 3 in a rectilinear form in a main scanning direction. A multiplicity of electrodes orthogonally intersecting with the heating resistor 4 are provided on the ceramic substrate 3 so that the heating resistor 4 can be made to generate heat with a dot as a unit by selectively passing an electric current to the electrodes. Thermistors 5 are fitted to the back side of the heat-radiating substrate 2 at regular intervals. For example, thermistors 5a-5c are provided at quadrisecting points of the rectilinear form heating resistor 4 drawn in a dotted line.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application) The present invention relates to a thermal head equipped with a plurality of thermistors for temperature detection.

(Prior Art) Thermistors are widely used as temperature detection sensors. The basic method is to know the temperature of the object to be measured by bringing a thermistor into contact with the object to be measured and detecting the change in resistance of the thermistor due to temperature.

A conventional thermal head is equipped with one thermistor for temperature measurement.However, when this thermal head is actually driven, the temperature has a certain distribution, and the measured temperature is not close to the thermistor. Therefore, the measured temperature will not be the average value of the temperature of the heat dissipation board of the thermal head.

Taking these points into account, other conventional thermal heads set multiple measurement points on the thermal head, measure the temperature with a thermistor at each point, and calculate the average of the measured values at each measurement point. There are also some that take . However, in this thermal head, one measurement circuit is provided for each thermistor, so as the number of measurement points increases, the number of measurement circuits also increases. Therefore, a thermal head equipped with a plurality of thermistors has the disadvantage that the number of peripheral circuits for temperature measurement increases.

(Objective) An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to improve the average value of the temperature of the heat dissipating board of a thermal head by using a plurality of thermistors while making the measurement peripheral circuit comparable to that of one thermistor. The purpose is to enable measurement using a thermistor.

(Summary) The present invention is characterized in that in a thermal head in which a plurality of heating resistors are arranged in one or two dimensions, temperature detection elements are provided at a plurality of locations on the thermal head, and the plurality of temperature detection elements are connected in series. At the connected point.

(Example) Below, an example in which the present invention is applied to a transfer type thermal recording system will be described. In transfer type thermal recording methods, image quality deteriorates due to the thermal history of the thermal head. In order to provide stable, high-quality images, the amount of energy supplied to the heating resistor of the thermal head must be corrected to take into account the effects of thermal history, and the temperature of the resistor must be adjusted to a predetermined height. . The thermal history can be roughly divided into two types: heat storage in the resistor and heat storage in the heat dissipation board of the thermal head.

This embodiment is directed to the latter type of heat storage.

FIG. 1 is a sectional view of a thermal head according to an embodiment of the present invention, and FIG. 2 is a plan view of the thermal head as viewed from the back side. Note that FIG. 1 is a cross-sectional view of FIG. 2 taken along line A-A.

As is well known, the thermal head 1 includes a heat dissipation substrate 2, a ceramic substrate 3 disposed on the heat dissipation substrate 2, and a heat generating resistor 4 disposed linearly in the main scanning direction and on the ceramic substrate 3. Furthermore, a large number of electrodes (not shown) are disposed on the ceramic substrate 3 and perpendicularly intersect with the heating resistor 4, and by selectively energizing the electrodes, , the heating resistor is made to be able to generate heat in dot units.

Furthermore, a thermistor 5 is disposed on the back surface of the heat dissipation board 2 of the thermal head 1. This thermistor 5 Ll:
, are mounted at equal intervals as clearly shown in FIG. In FIG. 2, thermistors 5a to 5C are provided at points that equally divide the linear heating resistor 4 drawn by dotted lines into four parts.

FIG. 3 is a circuit diagram of this embodiment in which the average temperature of the heat dissipation board 2 of the thermal head is detected by thermistors 58 to 5C provided on the heat dissipation board 2 of the thermal head. The total resistance R of the three thermistors 5a, 5b, and 5c is a fixed resistance "
is connected in series to a constant voltage power supply V. Here, the total resistance R is a function of the average temperature T of the heat dissipation board 2. now,
When the voltage across R(T) is V, ■ is calculated by the following formula.

5- ■ = □ ・V Y+R As is clear from this equation, the average substrate temperature T of the heat dissipation substrate 2 of the thermal head is a function of the voltage V.

FIG. 4 is a block diagram when the thermal head shown in FIG. 3 having a temperature detection function is applied to a transfer type thermal recording device. The symbol V in the figure corresponds to ■ in FIG.

The average substrate temperature T of the heat dissipation substrate 2 of the thermal head 1 is detected as a voltage signal V, and converted into a digital signal by the AD converter 6. The digital signal of voltage signal V is stored in ROM7.
Specify an address with .

ROM7 has a thermistor resistance R1, that is, a voltage signal.
Since the relationship between R and average substrate temperature T is written, the R
Temperature information about the average substrate temperature T is output from OM7.

This temperature information is input to the correction circuit 8 together with the image output signal 9. The image output signal 9 is a digitized version of the size of the dot to be printed.

The correction circuit 8 is formed of, for example, a ROM.

This correction circuit 8 uses the temperature information outputted from the ROM 7 and the size of the dot to be printed in the image output signal 9 as an address, and uses the drive pulse width to print the dot as stored data. Therefore, the correction circuit 8 outputs to the drive circuit 10 data regarding the width of the drive pulse to be printed, which corresponds to the temperature information and the size of the dot to be printed. The drive circuit 10 causes current to flow through a large number of parallel electrodes of the thermal head 1 with a drive pulse width corresponding to the data, thereby causing the heating resistor 4 to generate heat. As a result, an image corrected for the influence of thermal history is transferred onto the recording paper.

If the image signal 9 is sent to the correction circuit 8 in parallel, a plurality of ROMs constituting the correction circuit 8 may be provided and the correction circuits 8 may be operated in parallel. Although the above embodiments have been described using a transfer type thermal recording method as an example, the present invention is not limited thereto, and can be applied to any recording method that utilizes heat, such as a direct thermal recording method.

Further, as shown in the above embodiment, the number of thermistors is 3.
It doesn't matter if there are two or more. In addition to the locations explained in the examples, the thermistor can also be mounted on the front side of the heat dissipation board, on the ceramic board, embedded in the heat dissipation board, or between the ceramic board and the heat dissipation board. be. Furthermore, the selection of temperature measurement points is not limited to that shown in the embodiments, and can be freely selected.

(Effects) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) One or more temperature sensing elements, such as thermistors, are placed at each of several approximately equally divided locations on the thermal head, and the temperature detected by the multiple temperature sensing elements is used to detect the thermal Since the temperature of the head is determined, the average substrate temperature of the thermal head can be determined.

(2) Since the temperature sensing elements are connected in series, only one measuring circuit is required for a plurality of temperature sensing elements. Therefore, it becomes possible to reduce the size and reduce the cost.

[Brief explanation of drawings]

Fig. 1 is a sectional view of an embodiment of the present invention, Fig. 2 is a plan view of the thermal head shown in Fig. 1 when viewed from the back side, Fig. 3 is a circuit diagram of this embodiment, and Fig. 4 is a bookmark. FIG. 2 is a block diagram when the invention is applied to a transfer type thermal recording device. 1... Thermal head, 2nd heat dissipation board, 3... Ceramic substrate, 4... Heat generating resistor, 5... Patent attorney representing thermistor Michito Hiraki and 1 other person 9- 1st Figure 2 figure

Claims (1)

[Claims] (1) A thermal head in which a plurality of heating resistors are arranged in one or two dimensions, characterized in that temperature detection elements are provided at a plurality of locations on the thermal head, and the plurality of temperature detection elements are connected in series. thermal head. (a) The thermal head according to item 1 of the patent, characterized in that one or more temperature sensing elements are disposed at each of a plurality of locations obtained by dividing the thermal head into approximately equal parts.