JPH0970997A - Thermal recording device - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide an apparatus including a thermal line head that is inexpensive and has uniform printing characteristics by correcting the resistance value of each element with printing energy. And According to the present invention, a resistance value detecting means for detecting a resistance value for each element constituting a thermal line head, and a printing energy corresponding to the resistance value detected by the resistance value detecting means are supplied to each element. The printing energy supply means is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording device using a thermal line head, and more particularly to an improvement in the quality of printing characteristics.

[0002]

2. Description of the Related Art When gradation printing is performed in a thermal recording apparatus using a thermal line head, variations in the resistance value of each element constituting the head are directly reflected in the print density. Conventionally, the resistance value was adjusted for each element in order to make the print density of each element uniform.
The thermal line head was expensive. However, in spite of this, for example, in the gradation head, the variation of the relative resistance value of each element is about 3%, and in the case of the FAX, it is about 15%, which is directly shown as the printing characteristic.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and its purpose is to correct the difference in resistance value of each element with printing energy. Another object of the present invention is to provide a recording apparatus equipped with a thermal line head that is inexpensive and has uniform printing characteristics.

[0004]

SUMMARY OF THE INVENTION According to the present invention, there is provided resistance value detecting means for detecting a resistance value for each element constituting a thermal line head, and printing energy corresponding to the resistance value detected by the resistance value detecting means. A printing energy supply unit for supplying each element is provided.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. The figure shows an embodiment of a thermal recording apparatus according to the present invention. In the figure, 10 is a thermal line head, and 20 is a correction means provided by the present invention for correcting variations in the printing characteristics of the thermal line head 10. In the correction means 20, 21 is an A / D converter,
22 is a microprocessor, 23 is a memory, 24 is a pulse generation circuit, 25 is a changeover switch, 26 is a resistance element,
Reference numeral 27 indicates common. The changeover switch 25 is commonly used for each element constituting the thermal line head 10, and a contact point a thereof is supplied with a 24V power supply, and a contact point 25b thereof is supplied with a 5V power supply through a resistance element 26. The input end of the A / D converter 21 is connected to the connection point c between the resistance element 26 and the contact b of the switch 25,
The output terminal is connected to the microprocessor 22. The memory 23 is connected to the microprocessor 22 and also to the pulse generating circuit 24, and the output of the pulse generating circuit 24 is applied to each element of the thermal line head 10 as a control signal.

In the apparatus according to the present invention having such a structure, the shading of the print density due to the variation in the resistance value of each element constituting the thermal line head 10 is corrected as follows. That is, one of the elements constituting the thermal line head 10 is turned on under the control of the microprocessor 22, and the contact of the changeover switch 25 is connected to b. As a result, a current flows from the 5V voltage source to the element selected to be in the ON state via the resistance element 26, and a voltage corresponding to the current value is generated at the connection point c. The voltage generated at the point c is applied to the A / D converter 21 and converted into a digital signal.

Assuming that the resistance value of the resistance element 26 is R and the resistance value of the selected element of the thermal line head 10 is Rth, the resistance value Rth is expressed by equation (1). Rth = Vth.R / (5-Vth) (1) In the equation (1), Vth is a voltage generated at the connection point c, and this voltage is given to the A / D converter 21 and converted into a digital signal. The microprocessor 22 calculates Rth based on the value. The obtained resistance value is stored in the memory 23 under the control of the microprocessor 22.
The above is performed for all of the elements constituting the thermal line head 10, and the resistance value of each element is stored in a predetermined address of the memory 23.

The resistance value data of each element of the thermal line head 10 stored in the memory 23 is fetched from the memory under the control of the microprocessor 22 and given to the pulse generating circuit 24. Pulse generation circuit 24
Then, as the correction data for each element, for example, when the resistance value of the element is low, pulses having a narrow pulse interval or a narrow pulse width are generated. This pulse is supplied to the element of the thermal line head 10 as a control signal, whereby the operation of reducing the printing energy supplied to the element is performed. Such a printing energy control operation is performed for all elements based on the measured resistance value. In this way, even if the resistance value is different for each element, the printing energy corresponding to the resistance value is supplied to the element, whereby the printing density of all the elements is controlled to be constant.

The above correction may be performed only once, for example, when the power is turned on, or may be performed at a special timing during printing. Changeover switch 2 for printing
The contact of No. 5 is switched to the a side and a 24V power source is applied to each element of the thermal line head 10. At the time of printing, the control signal obtained by the pulse generating circuit 24 is given as correction data to each element, whereby the print density of each element is controlled to be constant.

Since the resistance value of each element is detected in the present invention, it is possible to detect the disconnection of the head, and it is also possible to detect the life of the head from the change in the resistance value. Further, since the high resistance state or the low resistance state of each element can be detected, there is an advantage that a warning or the like can be issued to notify the user in advance of head replacement or the like.

As described above, according to the present invention, the resistance value of each element of the thermal line head 10 is detected and the printing energy is controlled for each element. Even if there are variations, the print density can be made uniform, and a print head having excellent print characteristics can be obtained even when gradation printing is performed. Moreover, according to the present invention, since the method of adjusting the resistance value is not used, there is a feature that an inexpensive thermal recording device using a thermal line head can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a device of the present invention.

[Explanation of symbols]

 10 Thermal Line Head 20 Correction Circuit 21 A / D Converter 22 Microprocessor 23 Memory 24 Pulse Generation Circuit 25 Changeover Switch 26 Resistance Element

Claims (1)

[Claims] 1. A resistance value detecting means for detecting a resistance value for each element constituting a thermal line head, and a printing energy for supplying a printing energy corresponding to the resistance value detected by the resistance value detecting means to each element. A thermal recording device provided with a supply means.