JPH0373473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for determining the quality of a heating element provided in a thermal printing device.

In general, printing is performed by pressing heating elements arranged to form predetermined characters, symbols, codes, etc. on printing paper coated with a heat-sensitive and color-producing chemical, and then applying electricity to the heating elements to generate heat to print. There is a device. In such printing devices, the heating element is pressed against the printing paper, so the heating element may be worn out by the printing paper, or
The heating element may be damaged as a result of the heating element generating heat by itself and melting, or being scraped off by dust or the like adhering to the printing paper. One way to check whether a heating element is damaged or not is to apply voltage to each heating element in turn for a short period of time and determine whether the heating element is good or bad based on the amount of current at that time. If the voltage applied when printing is used as the voltage applied when checking, there is a problem that the heating element will generate heat even for a short time and the printing paper will develop color.Also, since the voltage for printing is applied, Another problem was that the heating element experienced the same level of fatigue as when printing.

The purpose of this invention is to provide a device for determining the quality of a heating element that solves both of the above problems, and for this purpose, a voltage lower than the printing voltage is used as the voltage applied to the heating element when determining the quality of the heating element. be.

Hereinafter, this invention will be described in detail based on two embodiments in which the invention is implemented in a barcode label printer. Note that a barcode printer prints a barcode in which each number is represented by a combination of black bars or seven white bars.

A first embodiment is shown in FIGS. 1 to 3. 1st
In the figure, 2-1, 2-2, . . . 2-n are resistance heating elements, which are not shown in the figure, but are arranged in a horizontal row. One end of each of these transistors is grounded via a collector-emitter conductive path of the transistors 4-1, 4-2, . . . , 4-n. The bases of these transistors 4-1 to 4-n are connected to corresponding stages of the n-stage shift register 6, respectively. Note that 8, 8...10, 10... are bias resistors.

The other ends of the resistance heating elements 2-1 to 2-n are connected to the printing power supply line 14 via the emitter-collector conductive path of the transistor 12. Further, the other ends of the resistance heating elements 2-1 to 2-n are connected to the diode 1.
6 and a resistor 18 in series, it is also connected to a power supply line 20 for discrimination. The voltage of the power supply line 14 for printing is normally 10 to 30V, and the voltage of the power supply line 20 for discrimination is 5V, and this 5V voltage is also supplied as a power supply voltage to a central processing unit, which will be described later. In addition, 22,
24 is a bias resistor for the transistor 12. A print signal 27 is supplied from a central processing unit 26 to the base of the transistor 12 via a bias resistor 24 . The central processing unit 26 is also supplied with a signal from a voltage detection section 30 that detects the voltage at the connection point 28 between the resistor 18 and the diode 16 .

The central processing unit 26 controls the transistor 12 and the shift register 6 based on the print data, and
It is programmed to print on printing paper by causing a predetermined resistance heating element to generate heat, and further controls the shift register 6 to control each resistance heating element 2-1 to 2-1 based on the output of the voltage detection section 30. It is also programmed to determine whether 2-n is good or bad.

The printing program will be explained with reference to FIG. 2. Based on the input printing data, the central processing unit 26 selects a stage of the shift register 6 corresponding to the resistance heating element to be heated, for example, the resistance heating element 2.
-2, the print data signal 34 is supplied to set the second stage to H level.
Next, the output enable signal 36 supplied to the shift register 6 is set to H level. As a result, an H level signal is supplied to the base of transistor 4-2. Next, the print signal 27 supplied to the transistor 12 is set to L level. As a result, the transistor 12 is made conductive, and the power supply line for printing 14 is connected to the heating element 2-2 and the transistor 4-2.
A current flows through the heating element 2-2, and the heating element 2-2 generates heat, thereby starting to color the printing paper. After sufficient time has elapsed for the color to develop (this time is measured by a timer), the print signal 27 is set to H level, the transistor 12 is rendered non-conductive, and the resistive heating element 2-
2. Stop supplying current to transistor 4-2. Thereafter, it is determined whether all printing has been completed, and if not, printing is repeated in the same manner as described above, and if it has been completed, printing is stopped.

Next, a program for determining the quality of a resistance heating element will be explained with reference to FIG. First, the central processing unit 26 calculates the total number n of resistance heating elements 2-1 to 2-n.
is set in an appropriate register X. Next, the first stage of the shift register 6 is set to H by the data signal 34.
level. Then, the output enable signal 36 is set to H level. This results in transistor 4-
The H level is supplied to the base of 1, and the power supply line 20 for discrimination is supplied to the transistor 4-1 and the resistance heating element 2-1.
Current flows from Here, since the transistor 12 is in a non-conductive state, no current flows from the printing power supply line 14 to the resistance heating element 2-1 and the transistor 4-1. At this time, the voltage _V28 at the connection point 28 is measured by the voltage detection unit 30, and compared with a predetermined upper and lower limit value, and if the lower limit value< _V28 <the upper limit value, it is determined to be normal. That is, _V28 is expressed as _V28 =( _V20 - _V16 - _V4-1 )×r/r+R+( _V16 + _V4-1 ). However, V ₂₀ : Voltage of the discrimination power supply line 20 V ₁₆ : Voltage between the anode and cathode of the diode 16 V _4-1 : Voltage between the collector and emitter of the transistor 4-1 r: Resistance of the resistance heating element 2-1 Value R: resistance value of the resistor 18. Now, if the resistance heating element 2-1 is disconnected, r becomes infinite and _V28 becomes _V28 = _V20 . Further, if the resistance heating element 2-1 is short-circuited, r becomes 0 and V ₂₈ becomes V ₂₈ =V ₁₆ +V _4-1 . Therefore, the upper limit is somewhat lower than V ₂₀ and V ₁₆
By comparing V ₂₈ with a lower limit value that is somewhat higher than +V _4-1 , it can be determined that the condition is normal if the lower limit value < V ₂₈ < the upper limit value. However, in reality, in addition to disconnections and short circuits, normal heat generation may not occur due to friction of the resistance heating element, partial short circuits, etc., and this also needs to be determined as an abnormality. On the other hand, since the resistance values of each resistance heating element vary, it is necessary to avoid erroneously determining that those within this variation range are abnormal. Therefore, the upper limit value V _H and lower limit value V _L are as follows: V _H = (V ₂₀ − V ₁₆ − V _4-1 )×r+Δr/r+Δr+R+(
V ₁₆ +V _4-1 ) V _L = (V ₂₀ −V ₁₆ −V _4-1 )×r−Δr/r−Δr+R+(
V ₁₆ + V _4-1 ), and if V _L < V ₂₈ < V _H , it is determined to be normal.

However, +Δr: Allowable upper limit deviation of the resistance value of the resistance heating element 2-1 -Δr: Allowable lower limit deviation of the resistance value of the resistance heating element 2-1.

After this determination, the value of register X is subtracted by one, and it is determined whether the value of register X is 0 or not. If it is not 0, the shift register 6 is shifted by one stage, the output enable signal 36 is set to H level, and this process is repeated thereafter. When the value of the register X is 0, that is, when all the resistance heating elements 2-1 to 2-n have been determined, the program ends.

As shown in Fig. 4, the second embodiment performs printing and quality determination without using a central processing unit, and the same parts as the first embodiment are given the same reference numerals and explained. Omitted. An H level signal is supplied to the data signal supply terminal 38 of the shift register 6, and a shift signal is supplied to the shift signal supply terminal 39, thereby setting a predetermined stage, for example, the second stage 6-2, to the H level. Then, an H-level enable signal is supplied to the enable terminal 40, and an H-level signal is supplied to the base of the transistor 4-2 via the AND gate 42-2. In this state, when an H level signal is supplied to the S terminal of the R-S flip-flop 44, the Q output becomes H level, and the transistor 46
An H level signal is supplied to the base of. As a result, the transistors 46 and 12 become conductive, and current flows from the printing power supply line 14 to the resistive heating element 2-2 and the transistor 4-2, and the resistive heating element 2-2 generates heat. After sufficient time has elapsed for the printing paper to develop color, an H level signal is automatically supplied to the R terminal of the R-S flip-flop 44 using a timer or the like, and the Q output is set to L level to supply current. The printer stops and printing of one barcode is completed. below,
A predetermined barcode is printed in the same manner.

When determining the quality of the resistance heating element, a signal of H level is supplied to the data signal supply terminal 38, a shift signal is supplied to the shift signal supply terminal 39, and the first stage 6-1 of the shift register 6 is set to H level. do. Then, an H-level enable signal is supplied to the enable terminal 40, and an H-level signal is supplied to the base of the transistor 4-1 via the AND gate 42-1. As a result, current flows from the discrimination power supply line 20 to the resistance heating element 2-1 and the transistor 4-1 via the resistor 18 and diode 16.

At this time, the voltage V ₂₈ at the connection point 28 is measured by the comparator 48
is compared with the upper limit voltage by the comparator 50.
Compare with the lower limit voltage by The upper limit voltage is given by a reference power supply 52, and the lower limit voltage is given by a reference power supply 54. The comparator 48 generates an H level signal when _V28 is higher than the reference upper limit voltage,
Comparator 50 generates an H level signal when V ₂₈ is lower than the lower limit voltage. Therefore, both comparators 48,5
The OR circuit 56 to which a signal of 0 is supplied indicates the failure indicator 5 when the lower limit voltage < V ₂₈ < the upper limit voltage.
8 is supplied with an H level signal to operate it.
Thereafter, the stages at the H level are sequentially changed by the shift signal, and the quality is determined in the same way.

In these quality determination devices, when determining the quality of each resistance heating element, current is passed through each heating resistor from the determination power line 20 whose voltage is lower than the printing power line 14, so the amount of heat generated is small. The printing paper does not develop color, and each resistance heating element does not suffer from fatigue. For example, if you try to determine the quality of each resistance heating element without coloring the printing paper by using the voltage of the printing power supply line 14 as it is, the time for applying the voltage of the printing power supply line 14 to each resistance heating element may be In addition to the device for controlling the time that the shift register 6 is at H level for color development, the shift register for quality determination must be at H level. A device for controlling time is required, and the circuit configuration becomes complicated. However, in the present invention, there is no need for a device for controlling the time period during which the shift register is at the H level for such quality determination. Moreover, the voltage supplied to the heating element is considerably higher than the voltage used to operate the comparison means, etc., so printing devices generally use two power sources, one with a high voltage and the other with a low voltage.
It has a lot of variety. Therefore, as the voltage for discrimination, the voltage supplied as a power supply voltage to the comparing means etc. can be used, and there is no need to provide a separate power supply for discrimination. In this way, there is no need for a separate device to control the time during which the shift register is at the H level, and there is no need to provide a special power source for discrimination, so the circuit configuration is simplified. Moreover, in the present invention, the upper limit reference voltage is determined by subtracting the voltage drop of each semiconductor switching element from the voltage of the low voltage power supply, and the sum of the resistance value of the common resistor and the allowable upper limit value of each heating element. The value obtained by dividing the allowable upper limit value of is selected as the value obtained by adding the voltage drop of each semiconductor switching element to the multiplied value. In addition, the lower limit reference voltage is the value obtained by subtracting the voltage drop of each semiconductor switching element from the voltage of the low voltage power supply, and the allowable lower limit value of each heating element is determined by the sum of the resistance value of the common resistor and the allowable lower limit value of each heating element. The value obtained by dividing is selected as the value obtained by adding the voltage drop of each semiconductor switching element to the multiplied value. Therefore, abnormal heat generation due to friction of the heating element, partial short circuit, etc. other than wire breakage and short circuit can also be determined as a defect.

Note that when printing, current also flows from the discrimination power supply line 20 to each resistance heating element, but there is no problem because it does not particularly affect printing. In the second embodiment, the comparators 48 and 50 are used, but instead of these, an A/D converter may be used to determine the quality of the product from the converted value.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of a thermal printing device implementing a quality determining device according to the present invention;
Fig. 2 is a flowchart showing the printing process of the first embodiment, Fig. 3 is a flowchart showing the discrimination process of the first embodiment, and Fig. 4 is a block diagram of the second embodiment. be. 2-1 to 2-n... heating element, 4-1 to 4-n
...first semiconductor switching element, 6...shift register, 12...second semiconductor switching element,
14... Power supply for printing, 18... Resistor, 20... Power supply for discrimination, 26, 44... Second energizing signal supply means, 3
0, 48, 50... Comparison means.

Claims (1)

[Claims] 1 Arrange a plurality of heating elements in a predetermined shape, which are pressed against the printing paper whose heat-sensitive portion develops color, and connect a plurality of semiconductor switching elements, which are conductive only during the period when the energizing signal is supplied, in series with each of the heating elements. and connect these series circuits in parallel with each other,
In a thermal printing device comprising means for connecting this parallel circuit to a printing power source and supplying the energizing signal to each of the semiconductor switching elements, there is a connection between the parallel circuit and the printing power source during printing. The parallel circuit is connected to a low voltage power source having a voltage lower than the printing power source via a common resistor, and the energizing signal supply means is connected to each of the semiconductor switching elements. Comparing means is provided for comparing the voltage at the connection point between the common resistor and the parallel circuit with an upper limit reference voltage and a lower limit reference voltage respectively in a state where the energizing signal is supplied one by one, and the upper limit reference voltage is , the allowable upper limit value of each heating element is calculated by subtracting the voltage drop of each semiconductor switching element from the voltage of the low voltage power supply, plus the resistance value of the common resistor and the allowable upper limit value of each heating element. Select the value obtained by adding the voltage drop of each semiconductor switching element to the value obtained by multiplying by the value obtained by dividing , and the lower limit reference voltage is
Subtract the voltage drop of each of the semiconductor switching elements from the voltage of the low-voltage power supply, and divide the allowable lower limit value of each of the above heating elements by the sum of the resistance value of the common resistor and the allowable lower limit value of each of the above heating elements. A heating element quality determining device for a thermal printing device, wherein a value obtained by multiplying the above value by the voltage drop of each of the semiconductor switching elements is selected as a value obtained by adding the voltage drop of each of the semiconductor switching elements.