JPH0312529Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Technical field of the invention The present invention relates to a printing device equipped with an abnormality detector that detects abnormalities in a plurality of heating elements constituting a thermal head that performs printing and failures in power supply circuits, etc.

(b) Prior art and problems In a media conveyance printing device, a thermal head prints using the heat generated by energizing a heating resistor built into the thermal head. The resistance value changes when it receives electric power or is scratched by foreign matter mixed into the printing paper, and as the resistance value increases, the heat generation effect decreases and the print density becomes thinner, and as the resistance value decreases, it leads to burnout and deterioration. Further, due to a failure of the power supply circuit or the like that supplies current to the heating resistor, excess dots or missing dots may occur in printing.

As mentioned above, printing quality deteriorates due to an abnormality in the heating resistor or a failure in the power supply circuit, but conventionally, abnormal heating resistors and malfunctioning parts are detected visually, and all work is done after printing. It has the disadvantage of causing a decline in quality.

(c) Purpose of the invention In view of the above-mentioned drawbacks of the conventional technology, the present invention automatically detects abnormalities and failures in the heating resistor and the power supply circuit that supplies current to the heating resistor during printing without visual inspection. An object of the present invention is to provide a printing device equipped with an abnormality detector capable of detecting abnormalities.

(d) Structure of the invention According to the invention, the object is to provide a printing head having a plurality of heating elements, a power supply circuit that supplies a driving current to the heating elements, and a printing control that controls supply and disconnection of the current. a resistance element that is provided in series with a current supply line that supplies a drive current from the power supply circuit to the print head and generates a voltage corresponding to the current value of the drive current; a reference voltage generation circuit that generates upper and lower limit reference voltages corresponding to the number of dots; and a comparator section that compares the upper and lower limit reference voltages output from the reference voltage generation circuit with the voltage generated in the resistive element. , and an abnormality detector that notifies an abnormal state of the drive current based on the output of the comparator section. This can be achieved by

(e) Example of implementation of the idea Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is a block diagram of the abnormality detector according to the present invention, Fig. 2 is a diagram for explaining the operation of the heating resistor, and Fig. 3 is a voltage diagram for explaining the operation of the comparator according to the present invention. is a thermal head, 1-1 to 1-n are heating resistors, 2-1 to 2-
n is a switch circuit, 3 is a printing control circuit, 4 is a power supply circuit, 5 is a resistance element (resistance), 6 is an amplifier, 7 is a reference voltage generation circuit, 8 is a comparator section, 8a is an upper limit comparator, 8b is a lower limit Comparator, 9
is the abnormality display generation circuit, V ₁ is the upper limit tolerance, V ₂ is the lower limit tolerance, V ₃ is the detection voltage (Example-1), V ₄ is the detection voltage (Example-2), and t is the heating resistor energization time. .

The abnormality detector provided in the printing device has a switch circuit in which one end is connected in parallel and the other end is connected in response to a printing (dot printing) command from the printing control unit 3 to the heating elements 1-1 to 1-n. 2-1 to 2-n, and a resistance element (resistance) for detecting the current value flowing to the heating elements 1-1 to 1-n connected in parallel. The heating resistors 1-1 to 1 connected in parallel through
-n is connected in series with the power supply circuit, and the current flowing through the heating resistors 1-1 to 1-n amplifies the detected voltage generated across the resistor 5, and increases the detected voltage to the upper limit comparator 8a, and The amplifier 6 supplies the lower limit comparator 8b, and the upper limit allowable voltage V ₁ and lower limit allowable voltage V ₂ corresponding to the number of dots sent from the printing control circuit 3, that is, one heating element specified in advance. The reference voltage generating circuit 7, which generates a voltage obtained by multiplying the upper limit allowable voltage and the lower limit allowable voltage by the number of dots, compares the above-mentioned upper limit allowable voltage with the detected voltage from the amplifier 6, and determines the upper limit allowable voltage V. an upper limit comparator 8a that detects a voltage of ₁ or more, and a lower limit comparator 8b that similarly compares the lower limit allowable voltage _V2 with the detected voltage from the amplifier 6 and detects a voltage that is less than the lower limit allowable voltage _V2 . and an abnormality display generation circuit 9 that generates an abnormality signal based on the output voltages of the upper limit comparator 8a and the lower limit comparator 8b.

For example, the operation is as shown in FIG. 2, when printing a character in a thermal head 1 in which 5 heating resistors 1-1 to 1-n are installed in a matrix and 7 heating resistors 1-1 to 1-n are installed in a matrix. Printing is performed by controlling the printing control circuit 3 to connect the relay circuit corresponding to the letter A so that current flows through the nine heating resistors corresponding to the letter A (see FIG. 2).

At this time, nine heating resistors are operating, and the printing control circuit 3 outputs the fact that the number of dots is 9 to the reference voltage generation circuit 7 as an enable signal, and at the same time outputs the number of dots in the matrix of nine heating resistors. Record your location.

Next, the current flowing through the nine heating resistors (seven of 1-1 to 1-n) causes a voltage drop by the resistor 5, which is detected as a voltage across the resistor 5, and the detected voltage increases. The signal is amplified by the width converter 6 and input in parallel to each of the upper limit converter 8a and the lower limit converter 8b.

On the other hand, in response to the enable signal outputted from the printing control circuit 3 and representing the number of printed dots, the reference voltage generation circuit 7 simultaneously generates an upper limit allowable voltage V ₁ and a lower limit allowable voltage V ₂ corresponding to the number of dots. However, the upper limit allowable voltage V ₁ is supplied to the other end of the upper limit comparator 8a, and the lower limit allowable voltage V ₂ is supplied to the other end of the lower limit comparator 8b.

Next, the operation of the comparator 8 is such that the upper limit comparator 8a compares the upper limit allowable value V ₁ with the detected voltage from the amplifier 6 described above, and detects a detected voltage that is greater than the upper limit allowable value V ₁ , for example, as shown in FIG. −1) V ₃ −V ₁ =
Detect _V5 . Similarly, the lower limit comparator 8b detects the lower limit permissible value V ₂ and the detection voltage from the amplifier 6, for example, V ₂ −V ₄ =V ₆ in FIG. 3 (Example 2).
V ₅ and V ₆ are upper tolerance value V ₁ and lower tolerance value V ₂
This is an abnormal voltage that exceeds the voltage and is input to the abnormality display generation circuit. The electric circuit of the comparator section described above uses a commonly used comparator circuit, and the abnormality indication generation circuit amplifies the abnormal voltage when it is input, and operates an abnormality indicator lamp etc. by the output voltage to detect abnormality. This is a circuit that works to display information.

As described above, the printing dots corresponding to the printing symbol are treated as one unit, and abnormalities in the heating resistor within that unit and failures in the electric circuit connected to the heating resistor are automatically detected and displayed during printing. to be carried out.

(f) Effects of the invention According to the invention, it is possible to automatically detect abnormalities or failures in the heating resistor, the power supply circuit that supplies current to the heating resistor, etc., without visual inspection. It has a great effect in preventing dot mistakes and uneven print density.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the abnormality detector according to the present invention, FIG. 2 is a diagram for explaining the operation of the heating resistor, and FIG. 3 is a voltage diagram for explaining the operation of the comparator according to the present invention. In the figure, 1 is a thermal head, 1-1 to 1-n are heating elements, and 2-
1 to 2-n are switch circuits, 3 is a print control circuit,
4 is a power supply circuit, 5 is a resistance element (resistance), 6 is an amplifier, 7 is a reference voltage generation circuit, 8 is a comparator section 8a which is an upper limit comparator, 8b is a lower limit comparator, and 9 is an abnormality display generation circuit.

Claims (1)

[Claims for Utility Model Registration] A printing device comprising a printing head including a plurality of heating elements, a power supply circuit that supplies a driving current to the heating elements, and a printing control circuit that controls supply and disconnection of the current. A resistor element is provided in series with a current supply line that supplies a drive current from the power supply circuit to the print head and generates a voltage corresponding to the current value of the drive current, and an upper limit and an upper limit voltage corresponding to the number of printing dots are provided. a reference voltage generation circuit that generates a lower limit reference voltage; a comparator section that compares the upper and lower limit reference voltages outputted from the reference voltage generation circuit with the voltage generated in the resistive element; A printing device characterized by comprising: an abnormality detector that notifies an abnormal state of a drive current.