JPH0542351B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a thermal head that prints barcodes, etc., which is equipped with a circuit that easily detects destruction of a heating resistor, and a method for detecting the same. It is something.

[Conventional technology]

In recent years, thermal recording systems and thermal transfer recording systems have shown remarkable development as recording systems due to their simplicity, and various ideas have been made for the thermal heads that are their main parts.

FIG. 3 shows a plan view and a sectional view of the structure of the thermal head as a model. In the figure, 1 is an insulating substrate, 2 is a heating resistor formed on the insulating substrate 1, 3 is an individual lead drawn out from one end of each pair of heating resistors 2, and 4 is an individual lead 3 and the heating resistor 2. The common electrodes 5 are connected to the individual leads 3 and are drawn out oppositely through the common electrodes 5,
An integrated circuit (hereinafter referred to as an integrated circuit) equipped with a drive circuit composed of a switching element that turns on and off according to the information signal, a circuit that supplies a recording information signal, etc.
6 is a gold wire that electrically connects the conductor pattern on the insulating substrate 1 and the IC chip 5, 7 is a signal terminal of the IC chip, and 8 is a protective film (referred to as an IC chip) that covers the vicinity of the heating resistor 2. 9 is thermal paper on the heating resistor 2 (not shown in the plan view);
10 is a conveyor roller (not shown in the plan view) for the thermal paper 9, and 11 is a resin (not shown in the plan view) covering the IC chip 5 and the gold wire 6.

In addition, FIG. 4 is a circuit diagram showing a conventional thermal head, and in the figure, 12 to 15 are ICs, respectively.
In the signal terminal 7 of the chip 5, 12 is an input terminal to which a strobe signal S for controlling on/off the current flowing through the heating resistor 2 in a switch-like manner is input;
13 is an input terminal into which a latch signal L for latching print data D is input; 14 is a heating resistor 2;
15 is an input terminal to which print data D for driving and printing is input; and 15 is an input terminal to which a clock C for synchronizing with data D is input.

Next, the operation will be explained. One end of each heating resistor 2 is connected to the common electrode 4, and when a voltage VH is applied to the heating resistor 2 from the common electrode 4, the other end of the heating resistor 2 on the insulating substrate 1 When grounded, current flows through the heating resistor 2 and generates heat. This energization corresponds to one line of printing. The thermal paper 9 receives this heat, and continuous printing is performed on the thermal paper 9 by conveying the thermal paper 9 by the conveying roller 10 and generating heat from the heating resistor 2.

To selectively drive the grounding of these N heating resistors 2 based on one line of printed data,
A simple method is to control the driver transistor using the parallel output of the shift resist.

One line of print data is expressed as two values "1" and "0", and data D1, D2,...D(N-1), DN are output for one line from the signal input terminal 7 in synchronization with clock C. Enter the shift register.

When the latch signal L is applied to the signal input terminal 7, one line of serial print data L1, L2...(N-1), LN is held in the latch 5b.
Each of the print data L1, L2...L(N-1), LN is inputted together with a strobe signal S to a NAND circuit (including a switching element not shown) 5C.

Therefore, when the print data L1 to LN held in the latch 5b is "1", current flows through the heating resistor 2 connected to the output of the NAND circuit 5C only when the strobe signal S is "H". The heating resistor 2 generates heat.

The above timing chart is shown in FIG. Here, FIGS. 5a to 5e represent clock C, data D, latch L, strobe signal S, and applied voltage, respectively.
The waveform of _VH is shown.

Now, as shown in Figure 6, the life of the heating resistor 2 of the thermal head is determined by the number of applied pulses, and also by the abrasion resistance of the protective film, and generally the number of pulses is several tens of millions. ~ Hundreds of millions of pulses and a mileage of several tens of kilometers are guaranteed.

However, when printing labels that display the manufacturer, product name, etc. using binary black and white bars (barcode display), a large number of pulses may be applied to a specific heating resistor 2, or the bar code may be Thermal paper 9, which serves as a label for code display, is used in places with poor environments such as supermarkets and factories, and small particles such as sand are transported together with the thermal paper 9, damaging the protective film 8 and causing heat-generating resistors. This leads to the destruction of 2. If a bar code is printed in a state where this specific heating resistor 2 is destroyed, an incorrect bar code will be displayed and the reliability of the device will be questioned.

[Problem that the invention seeks to solve]

Since the conventional thermal head is constructed as described above, it is necessary to visually confirm whether or not the printing is correct after printing is completed, making barcode printing unreliable. In addition, since the pulse life point and mileage life point of the heating resistor are not known, it is necessary to replace the thermal head attached to the device early, resulting in problems such as increased operating costs.

This invention was made to solve the above-mentioned problems, and it is possible to detect the destruction of heating resistors, improve the reliability of devices that require reliability such as bar code printing, and improve the reliability of thermal heads. The purpose is to detect when it is time to replace it.

[Means to solve the problem]

The thermal head according to the present invention includes a plurality of heat generating resistors provided on an insulating substrate, and a driving element which is connected to each of these heat generating resistors and is turned on and off according to recorded information. A circuit, a potential detecting means for detecting a potential at a connection point between the heating resistor and the switching element, and a comparing means for comparing the output of the potential detecting means with a predetermined value and outputting the result. .

[Effect]

In the thermal head according to the present invention, the potential at the connection point between the heating resistor and the switching element is set by applying a voltage from the common electrode to either when the switching element is on or off when all the heating resistors are normal. Using the fact that the connection point potentials between the broken heating resistor and the switching element are different, the comparing means compares the difference, and outputs a signal to detect a failure of the heating resistor.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 2 is a heating resistor, 4 is a common electrode, 5 is an IC chip, and 12 is an input terminal to which a strobe signal S for controlling on/off the current flowing through the heating resistor 2 is input. , 13
is the latch signal L for latching the print data D.
14 is an input terminal to which print data D for driving the heating resistor 2 to print is input; 15 is an input terminal to which a clock C for synchronizing with data D is input; 16 is a resistor (hereinafter referred to as a detection resistor) connected to the connection point between the heating resistor 2 and the IC chip 5 and serving as a potential detection means;
Reference numeral 17 indicates a signal that is the result of the OR circuit 17, for example, an OR circuit which serves as a comparison means and which is inputted from the connection point of the heating resistor 2 and the detection resistor 16, respectively.
This is the output terminal where EO is output.

The driving of the heating resistor of the thermal head is the same as in the conventional example, and the detection of destruction of the heating resistor of the present invention,
and its signal output operation will be explained.

Now, in Fig. 1, a NAND circuit 5C is used as a switching element between the heating resistor 2 and the IC chip 5.
The potential at the connection point with the common electrode 4 is determined by setting the resistance value of the heating resistor 2 to R, the resistance value of the detection resistor 16 to r, and
If the applied voltage from V _H is the logical sum circuit 17
Otherwise, if the strobe signal S is “L”,
The potential at the connection point is VH×r/R+r. If the heating resistance value increases, the potential at the connection point will fall below the potential at the normal connection point.

Note that the detection resistor 16 has a resistance several times higher than that of the heating resistor 2 so that printing will not occur even when the NAND circuit 5C is off.

OR circuit 17 which inputs each connection point potential
If all heating resistors 2 are normal, the output signal will be output when the strobe signal S is “L”.
EO is output as "H" and is output from the output terminal 18. Conversely, if even one heating resistor is broken and open, the strobe signal S becomes "L".
At this time, the output signal EO is output as "L" and is output from the output terminal 18.

The timing chart at this time is shown in Figure 2.
In this FIG. 2, the strobe signal S is “L”
If the output signal EO is “H” when , it is normal.
If it is "L", it can be detected as the lifespan of the heating resistor.
That is, abnormality detection of the heating resistor is checked only during the timing period when the strobe signal S is "L", that is, during non-printing.

By the way, at the timing when the strobe signal S is "H", the EC output can be either "H" or "L", but if even one heating resistor is open,
EO output becomes “L”.

The resistance value of the heating resistor, which is the lifespan point, is determined by whether or not it can withstand printing, so the connection point potential at that time is set by the resistance value r of the detection resistor 16, the resistance value in the logical sum circuit 17, etc. Then, the input determination level of the OR circuit 17 is determined.

In addition, in the above embodiment, a resistor is used to detect the connection point potential and the comparison is performed using an OR circuit, but other potential detection methods and comparison circuits may be used.
The same effects as in the above embodiment are achieved.

〔Effect of the invention〕

As described above, according to the present invention, since the circuit is configured to detect the potential at the connection point between the heating resistor and the switching element and output a signal resulting from the comparison, it is possible to detect the destruction of the heating resistor. In addition, it has the effect of increasing the reliability of devices that require reliability, such as bar code printing, and detecting when it is time to replace the thermal head.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the thermal head of the present invention, Fig. 2 is a timing chart of Fig. 1, Fig. 3 is a model diagram showing the structure of the thermal head, and Fig. 4 is a conventional thermal head. FIG. 5 is a timing chart of a conventional thermal head, and FIG. 6 is a diagram showing the number of pulses applied and changes in resistance of the heating resistor of the thermal head. In the figure, 1 is an insulating substrate, 2 is a heating resistor,
5 is an IC chip, 16 is a detection resistor, 17 is an OR circuit, and 18 is an EO signal output terminal. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 Consists of a plurality of heat generating resistors provided on an insulating substrate and connected to a power source at one end, and a switching element connected to the other end of each of these heat generating resistors and turned on and off according to recorded information. a potential detecting means having one end connected to a fixed potential point with respect to the power supply and the other end connected to each of the heat generating resistors, and a potential at a connection point between the heat generating resistor and the potential detecting means and a predetermined potential. 1. A thermal head comprising a comparison means for comparing and outputting a value, and detecting a failure of the heating resistor based on the output of the comparison means.