JPS63145058A - Method for detecting printing inferiority in thermal printer - Google Patents

Abstract

PURPOSE:To detect abnormal printing of blank paper or a blank ticket, by a method wherein the current flowing to a thermal head is detected at every printing line, and compared with the reference value corresponding to the min. number of printing dots per line to judge how many lines exceeding the reference value are there. CONSTITUTION:When a thermal head 8 performs the printing of a certain line, the number of heat generating elements r1-rn corresponding to the number of printing dots generate heat. The current proportional to the number of the heat generating elements is outputted from a DC constant voltage power source 5 and the voltage Va at a point P1 drops in proportion to the number of the heat generating elements. When the value of the voltage Va is looked at, the number of dots printed are cleared. When the min. number of printing dots per line are set to n1, reference voltage Vref is set to the intermediate value of the values of Va corresponding to the number n1 of dots and the number (n1-1) of dots. As a result, the output signal of a voltage comparator 9 becomes '1' when the number of printing dots per line are n1 or more and becomes '0' when said number is (n1-1) or less. The output signal of the voltage comparator 9 becomes '0' when no printing is performed at all or printing is abnormal.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for detecting printing defects in a thermal printer.

"Prior Art" Automatic ticket vending machines and the like often incorporate thermal printers, and print and issue tickets, etc. using the dot method. Here, FIG. 3 is a diagram showing a circuit configuration near the thermal head of a thermal printer used for the above purpose.

In this figure, ■ is a shift register, and print data SD for one dot line is serially transferred in synchronization with a clock signal ck. The first to
One input terminal of the Nant gates NA1 to NAn is connected to the Nth bit output terminal. This Nantes Gate NA
, ~NAn is the print strobe signal SB at the other input end.
is supplied, and a heating element r1 is connected to the output terminal.
~rn are connected at one end. Heat generating element r1~
Each other end of rn is connected to a positive printing power supply +V.

In the above configuration, as shown in FIGS. 4(a) and 4(b), the print data SD for N dots is supplied to the shift register 1 in synchronization with the clock ck, and the corresponding Nantes Gate NA + ~ NA
n. Next, when the strobe signal SB rises at time t, the Nant gates NA, ~NA,...
Among them, the one to which the "l" signal is supplied as the mark till data outputs the "0" signal. As a result, current flows only through the heating elements r1 to rn connected to the Nant gate N A l-N A n that output the 0" signal, generating heat, and as a result, the mark Ql + data becomes the "l" part. Thermal printing is performed only on the print line.This heat-generating printing operation is performed between time j+-it when the marking 11 strobe signal SB rises.After that, the same printing operation as above is performed sequentially for each printing line. I'm going to go.

"Problems to be Solved by the Invention" By the way, in the above-mentioned thermal printer, for example, the connector of the cable connecting the thermal head and the control circuit may be disconnected, or the circuit for transferring print data may be damaged. If there is an abnormality, the print data SD may not be supplied at all, or all "O" data may be supplied.

However, even in such a case, a series of printing controls such as paper transport and print data transfer control are performed regardless of the above abnormality, resulting in printing that is blank or close to it. There was a problem. That is, conventional printers have the disadvantage that they print out without detecting an abnormality.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for detecting printing defects in a thermal printer, which can detect abnormal printing such as blank paper or self-printing.

"Means for Solving the Problems" In order to solve the above problems, the present invention detects the current flowing through the thermal head for each mark 11' fill line, and the minimum number of printed dots per line. The reference value set according to the corresponding thermal head current and 117
It is characterized in that the quality of printing is detected by comparing the detection current with the detection current described in No. 7 and determining the number of lines in which the value of the detection current exceeds the reference value.

"Function" The thermal head current does not reach the reference value in the line with printing defects. Therefore, by determining the number of detected current values exceeding a reference value, it is possible to detect the quality of printing.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment to which the present invention is applied. Note that this embodiment is an embodiment in which the present invention is applied to a thermal printer for an automatic ticket vending machine.
Further, in FIG. 1, parts corresponding to those shown in FIG. 3 described above are given the same reference numerals, and their explanations will be omitted.

In FIG. 1, 5 is a DC constant voltage power source, which serves as a driving power source for a constant voltage power source 7 for printing. Reference numeral 6 denotes a resistor inserted in the positive power supply line between the DC constant voltage power supply 5 and the printing constant voltage power supply 7.

8 is a thermal head, which has the same configuration as the circuit shown in FIG. 3 described above. In other words, the thermal head 8 is located at the position corresponding to the print data SD.
The Jll elements r1 to rn are appropriately supplied with a +■ power supply from the printing constant voltage power supply 7.

Next, 9 is a voltage comparator, which compares the voltage value Vλ obtained at the connection point P between the resistor 6 and the constant voltage power supply 7 for illumination with the output voltage Vref of the reference power supply 15, and determines that Vref>Va When this happens, a “1” signal is output. 10 is an AND gate that takes the logical product of the strobe signal SB and the output signal of the voltage comparator 9, and the result of the logical product is used as the count pulse c.
Binary counter 12 via or gate 11 as p
Supplied to the clock input terminal of the The binary counter 12 is a 4-bit counter that counts up every time the signal supplied to the clock input terminal falls, and outputs a detection signal sp from the third bit (23rd bit). This detection signal sp is supplied to an OR gate 11, where it is logically summed with the count pulse cp.

Next, the operation of this embodiment with the above configuration will be explained.

Now, when the thermal head 8 prints on a certain line, the number of heat generating cords r1 to rn corresponding to the number of dots printed on this line generate heat.

Therefore, the DC constant voltage power supply 5 outputs a current proportional to the number of heating elements. Since all of this current flows through the resistor 6, the voltage Va at point P+ drops in proportion to the number of heating elements.

Therefore, by looking at the value of the voltage Va, it can be seen how many dots are being printed on one line during printing. here,
If the minimum number of 11 dots to be marked per line on the ticket to be issued is 01, then the base '! The $ voltage Vref is set to an intermediate value between Va corresponding to the number of dots n and the value of Va corresponding to the number of dots (n, -1). As a result, the output signal of the voltage comparator 9 shows that the number of printed dots per line is n.
When it is 1 or more, it is "l", and when it is (n+1) or less, it is "0". That is, when no printing is performed at all, or when abnormal printing (printing less than the number of dots to be printed) is performed, the output signal of the voltage comparator 9 becomes "0".

In this embodiment, it is determined that normal printing is performed when the output signal of the voltage comparator 9 is "1" for eight lines or more. This normal printing determination process will be explained below with reference to FIG. 2.

When the strobe signal SB shown in FIG. “Since the signal is output, the AND gate 10 outputs the count pulse cp. The binary counter 12 then counts up at the falling edge of the count pulse CP. Then, at the time shown in Fig. 2, the count value of the binary counter 12 becomes "8" (see (c) in the same figure), and as a result, the detection signal sp becomes the l" signal, and printing is normal. The detection signal Sp is then supplied to the clock input terminal of the binary counter 12 via the OR gate 11, thereby inhibiting further counting.
Thereafter, the detection signal sp maintains the "]" level. In this case, the detection signal Sp is reset, for example, when printing of the ticket is completed.

In this way, in the above embodiment, if eight or more lines exceeding the minimum number of print dots per line are detected, it is determined that printing has been performed normally and the detection signal s is output.
p is made into an "I" signal.

This is because if about 8 lines are printed normally, it can be considered that the 11 tickets to be printed are almost normally printed. Note that the method for determining normality/abnormality is not limited to this, and for example, it may be determined that the line is abnormal when a line with less than the minimum number of printed dots is detected a predetermined number of times (one or more times).

Alternatively, the signal SP may be used to generate an alarm when an abnormality occurs, and furthermore, the detection signal Sp may be used as a start signal to automatically collect/reprint the abnormally printed volumes.

"Effects of the Invention" As explained above, according to the present invention, the current flowing through the thermal head is detected for each mark Gi line, and the current flowing through the thermal head is detected according to the thermal head current corresponding to the minimum number of marks 1ii+l dots per line. The thermal It is possible to reliably detect printing defects (blank page printing, etc.) due to disconnection of the connector of the head, defects in the head itself, defects in transfer of print data, and the like. Furthermore, even if printing is performed in a format that is different from the standard format, it should be possible to determine pass/fail with a certain degree of certainty. Furthermore, the third point is that the circuit for making the determination can be configured extremely easily.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the ÷1 configuration of a thermal printer which is an embodiment of the present invention; Fig. 2 is a waveform diagram showing waveforms of various parts of the circuit in the same embodiment; Fig. 3 is a general diagram. A block diagram showing +II+¥ configuration of a thermal head.
FIG. 4 is a waveform diagram of various signals that drive the thermal head mt+. 6... Resistor, 7... Constant voltage power supply for printing,
8...Thermal head, 9...Voltage comparator, IO...Ant gate, II...OR gate, 12...Binary counter, 15...
...Kitei power supply, Sp...detection signal.

Claims (1)

[Claims] The current flowing through the thermal head is detected for each printing line, and the detected current is compared with a reference value set according to the thermal head current corresponding to the minimum number of printed dots per line, and the value of the detected current is determined. A method for detecting printing defects in a thermal printer, characterized in that the quality of printing is detected based on the number of lines in which the value exceeds the reference value.