JP2002137429A - Apparatus for measuring value of resistance of heating element of thermal head, and apparatus for judging breakage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which when value of resistance of a heating element is measured and connection of a condenser is released, change in electric voltage can be sped up but the electric voltage is easily influenced by noises and changes in electric voltage of an electric source to generate an error in the result of the measurement. SOLUTION: A capacitor C is forcibly charged for a first specified time and after the charge is finished, the capacitor C is forcibly discharged for a second specified time and after the discharge is finished, the heating element r is energized and the value of electric voltage or electric current of the heating element r when the third specified time passes from the beginning of the energization is detected and the value of resistance of the heating element r is measured from the detected value of the electric voltage or the electric current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a resistance value measuring device for measuring the resistance value of a heating element of a thermal head, and a damage judging device for judging whether or not the heating element is damaged.

[0002]

2. Description of the Related Art Generally, a thermal head used in a thermal printer is provided with a plurality of heating elements for heating an ink film or a heat-sensitive recording material, and these heating elements are connected in parallel to a power supply. The thermal head is connected with a capacitor in parallel with the heating element in order to eliminate the influence of noise on the voltage applied to the heating element and changes in the power supply voltage.

[0003] The resistance value of the above-mentioned heating elements varies from one heating element to another and changes with time. Therefore, if the heating element is used as it is for heating an ink film or the like, density unevenness occurs in printing or image recording. Conventionally, in order to prevent the density unevenness, the heating elements are sequentially energized one by one to detect a voltage value or a current value of the heating element during energization, and to determine a resistance value of the heating element from the detected voltage value or current value. Is measured, and the output is corrected based on the measured resistance value.

As a resistance value measuring device for measuring the resistance value of a heating element of such a thermal head, for example, one described in Japanese Patent Application Laid-Open No. 2-248262 is known. In this conventional resistance value measuring device, a switch means is connected in series to a capacitor connected in parallel with a heating element, and when measuring the resistance value of the heating element, the switch means is opened to connect the capacitor. Is configured to be released.

[0005]

SUMMARY OF THE INVENTION In the above prior art,
Since the connection of the capacitor is disconnected when measuring the resistance of the heating element, the voltage and current values of the heating element are quickly stabilized in a steady state without being affected by the charging and discharging of the capacitor, and the measurement time is reduced. Although shortening can be achieved, there has been a problem that the voltage between terminals is easily affected by noise and a change in power supply voltage, and an error easily occurs in the measurement result.

Accordingly, the present invention has been made in view of the above-described problems, and is not susceptible to the effects of noise and variations in power supply voltage. It is possible to measure the resistance of a heating element accurately and quickly. A first object is to provide a value measuring device. It is another object of the present invention to provide a method for determining the damage of a heating element of a thermal head, which is less susceptible to noise and a change in power supply voltage, and is capable of accurately and quickly determining whether or not the heating element is damaged. Make it an issue.

[0007]

According to a first aspect of the present invention, a plurality of heating elements connected in parallel to a power supply, and a plurality of heating elements connected to the power supply are provided. A measuring device for measuring the resistance value of each heating element of a thermal head comprising a heating element and a capacitor connected in parallel. Detecting the resistance value of the heating element from the detected voltage value or current value, and forcing the capacitor to a first predetermined value after energizing the heating element in a prioritized order. Charging means for charging for a time, and discharging means for forcibly discharging a capacitor for a second predetermined time after charging by the charging means. ,
A voltage value or a current value of the heating element at a time when a third predetermined time has elapsed from the start of the energization is detected, and a resistance value of the heating element is measured from the detected voltage value or current value.

In order to solve the second problem,
According to the second feature of the present invention, each heat generation of the thermal head including a plurality of heating elements connected in parallel to the power supply and a capacitor connected in parallel to the heating elements with respect to the power supply. A determining device for determining whether or not the heating elements are damaged; energizing the heating elements one by one in order, detecting a voltage value or a current value of the heating element being energized, and detecting the heating value based on the detected voltage value or current value; In the method for determining the presence or absence of damage to the element, charging means for forcibly charging the capacitor for a first predetermined time after energizing the heating element having the earlier energization order, and forcing the capacitor after charging by the charging means Discharging means for discharging a second predetermined time, and after the discharge by the discharging means, power is supplied to the heating element having a higher power supply order, and the heating element is turned off when a third predetermined time has elapsed from the start of the power supply. Voltage or voltage Detecting the value, and so as to determine the presence or absence of breakage of the heat generating element from the voltage value or current value the detected.

According to the first feature, since the heating element is energized in a state where the capacitor is connected, the voltage or current value of the heating element is hardly affected by noise or a change in the power supply voltage, and the heating element can be accurately measured. Can be measured. On the other hand, since the heating element is energized with the capacitor connected, the voltage value or the current value of the heating element changes asymptotically from the value at the start of energization, and it takes time to stabilize.
However, according to the present invention, the capacitor is forcibly charged for the first predetermined time before energizing the heating element, and the capacitor is forcibly discharged for the second predetermined time after the charging. The voltage value or the current value of the heating element can be made substantially constant. Therefore, by setting the first and second predetermined times so that the constant value becomes a predetermined value, for example, a voltage value or a current value corresponding to the average resistance value of the heating element, the voltage value of the heating element is set. Alternatively, the time until the current value stabilizes in the steady state can be shortened. Therefore, the third predetermined time can be set short, and the measurement time can be shortened.

Further, according to the second feature, it is possible to determine whether or not the heating element is damaged based on the detected voltage value or current value. That is, since the resistance value of the damaged heating element is infinite, the voltage value of the heating element becomes equal to the power supply voltage after a predetermined time has elapsed, and the current of the heating element becomes 0 A. Therefore, by setting the first and second predetermined times so that the voltage value of the capacitor at the end of discharging by the discharging means becomes a predetermined value, it is possible to quickly determine whether the heating element is damaged. . For example, the first and second predetermined times are set so that the voltage value of the capacitor at the end of the discharge becomes larger than the range of the voltage value of the normal heating element in the steady state after the heating element is energized. If set, if the heating element is damaged,
The energization of the heating element increases the voltage value of the heating element and decreases the current value of the heating element. Therefore, even if the third predetermined time is set to be short, it is possible to accurately determine whether or not the heating element is damaged, thereby shortening the determination time.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes a thermal head for heating an ink film or a thermosensitive recording material.
This is for performing printing, image recording, and the like. The thermal head 1 is connected to the power supply unit 2 and has a plurality of heating elements r (r1, r2,..., Rn) arranged in a line.
And a capacitor C connected to the power supply unit 2 in parallel with these heating elements. Each heating element r is connected in series with a transistor T (T1, T2,..., Tn) for controlling the energization of the heating element. The thermal head 1 includes a shift register 3, a latch array 4, and an AND gate array 5.
The shift register 3, the latch array 4, and the AND gate array 5 are connected to a control unit 6 outside the thermal head 1, respectively.

When performing printing or the like, a serial signal corresponding to the image data to be printed is sent from the control unit 6 to the shift register 3, and the shift register 3 converts the serial signal into a parallel signal. The parallel signal is supplied to the control unit 6
Latched by the latch array 4 in synchronization with the latch signal from When a strobe signal is input from the control unit 6, the AND gate array 5 outputs a signal to each transistor T in accordance with the parallel signal. Upon receiving the signal, the transistor T is turned on, and the heating element r connected in series to the transistor T is energized by the DC power supply of the power supply unit 2 to heat the ink film or the like to perform printing or the like.

A reference resistor R is provided between the thermal head 1 and the power supply unit 2. The control unit 6 is connected to a charging circuit 7 serving as charging means and a discharging circuit 8 serving as discharging means. The charging circuit 7 and the discharging circuit 8
Is connected to the high-potential side. Control unit 6 to charging circuit 7
When the charging signal is output to the charging circuit 7, the charging circuit 7 forcibly charges the capacitor C while the charging signal is being input to the charging circuit 7. When a discharge signal is output from the control unit 5 to the discharge circuit 8, the discharge signal is output to the discharge circuit 8.
, The discharging circuit 8 forcibly discharges the capacitor C.

One end of an A / D input line L is connected between the thermal head 1 and the reference resistor R, and the other end of the A / D input line L is connected to the control unit 6. With the A / D input line L, a voltage value V between terminals of the thermal head 1, that is, a voltage value V of the heating element r is detected by an A / D input of the control unit 6.

When measuring the resistance value of the heating element r, the transistor T1 is turned on and the transistor T1 is turned on.
A serial signal set to turn off the other transistors T is sent from the control unit 6 to the shift register 3, and the shift register 3 converts the serial signal into a parallel signal. The parallel signal is latched by the latch array 4 in synchronization with the latch signal from the control unit 6. In parallel with these series of processes, as shown in FIG.
A charging signal having a pulse width t1 is output to the charging circuit 7, and the capacitor C is forcibly charged for a first predetermined time t1. After the charging, the control unit 6 sends a pulse width t2 to the discharging circuit 8 to the discharging circuit 8. The discharge signal is output, and the capacitor C is forcibly discharged for the second predetermined time t2. After the discharge, a strobe signal is input from the control unit 6 to the AND gate array 5, the AND gate array 5 receives a parallel signal from the latch array 4, and outputs a signal only to the transistor T1 in response to the parallel signal. Upon receiving the signal, the transistor T1 is turned on, and the heating element r1 connected in series to the transistor T1 is energized by the DC power supply of the power supply unit 2. When a third predetermined time t3 has elapsed from the start of the energization, the voltage value V of the heating element r is detected by the A / D input of the control unit 6 via the A / D input line L. Then, using the voltage value V, the resistance value of the heating element r1 is calculated by the equation r = VRR / (E−
V). After charging and discharging of the capacitor C in the same procedure, the heating elements r2 to r
n is sequentially energized one by one, and the voltage value V is detected for each of the heating elements r2 to rn, and the resistance value is measured.

In the above embodiment, the resistance value of the heating element r is calculated by detecting the voltage value V of the heating element r, but the current value flowing through the heating element r is detected instead of the voltage value V. Then, the resistance value of the heating element r may be calculated.

In the above embodiment, the resistance value measuring device for measuring the resistance value of the heating element r has been described.
It is also possible to configure a damage determination device that determines whether the heating element r is damaged based on the detected voltage value or current value.
Hereinafter, the determination of the damage of the heating element will be described with reference to FIG.

In the damage determination of the heating element, the first predetermined time t1 'for forcibly charging and the second predetermined time t2' for forcibly discharging are determined by the voltage value of the capacitor at the end of the discharge. From the third predetermined time t3 ′ (for example, 5 m
msec) is set to a value (for example, about 3.6 V) larger than the range of the voltage value of the normal heating element (here, 2.0 V to 3.4 V) at the time of elapse of msec.

Under these settings, in the case of a normal heating element, the graph of the voltage value V falls to the right like the heating elements r1 and r2 in FIG. 3, and when the third predetermined time t3 'has elapsed. Is smaller than the voltage value at the start of energization. On the other hand, in the case of the damaged heating element, the resistance value of the heating element is much higher than the resistance value of the normal heating element, so that the graph of the voltage value V rises to the right as shown by r4 in FIG. When the third predetermined time t3 'has elapsed, the voltage value V of the heating element becomes larger than the voltage value at the start of energization. Therefore, the third predetermined time t3 from the start of energization
'The voltage value V of the heating element at the time of elapse is detected, and if the detected voltage value V is higher than the voltage value at the start of the measurement, it is determined that the heating element is damaged. Actually, when the threshold value rises to 3.8 V or more, it is determined that the heating element is damaged.

It is needless to say that the numerical values of the voltage value and the time of the present invention are not limited to the numerical values described in the present embodiment. In particular, the first predetermined time t1 'and the second predetermined time t2' at the time of the damage determination need only be longer than the range in which the voltage value of the capacitor is detected by the normal heating element as a result of charging and discharging. Preferably, it is short. When the current value of the heating element is detected, if the current value is lower than the current value at the start of the measurement, it is determined that the heating element is damaged.

[0021]

As is clear from the above description, according to the present invention, since the heating element is energized with the capacitor connected, the voltage value or the current value of the heating element is affected by noise or a change in the power supply voltage. It is difficult to accurately measure the resistance value of the heating element. Similarly, it is possible to accurately determine whether the heating element is damaged.

Further, by charging / discharging the capacitor, the voltage value or the current value at the start of energization of the heating element can be made substantially constant. Therefore, by setting the charging time and the discharging time so that the constant value becomes an appropriate value, the resistance value of the heating element can be quickly measured. Similarly, it is possible to quickly determine whether the heating element is damaged.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing signals of the resistance value measuring device of the present invention.

FIG. 3 is a diagram showing signals of the damage determination device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal head 7 Charge circuit 8 Discharge circuit r Heating element C Capacitor

Claims (3)

[Claims] 1. A resistance value of each heating element of a thermal head including a plurality of heating elements connected in parallel to a power supply and a capacitor connected in parallel with the heating element to the power supply. A heating device that sequentially energizes these heating elements one by one, detects a voltage value or a current value of the heating element during energization, and measures a resistance value of the heating element from the detected voltage value or current value. A charging means for forcibly charging the capacitor for a first predetermined time after energizing the heating element in the order of energization, and forcibly discharging the capacitor for a second predetermined time after charging by the charging means. A discharge means for performing a power supply to the heating element, which is energized after the discharge by the discharge means, and detects a voltage value or a current value of the heating element when a third predetermined time has elapsed from the start of the current supply. The detected An apparatus for measuring a resistance value of a heating element of a thermal head, wherein the resistance value of the heating element is measured from a voltage value or a current value. 2. A thermal head comprising: a plurality of heating elements connected in parallel to a power supply; and a capacitor connected in parallel with the heating elements to the power supply. A determination device for determining whether the heating elements are energized one by one sequentially, detecting a voltage value or a current value of the heating elements during energization, and determining whether the heating elements are damaged based on the detected voltage value or current value. In the judgment,
Charging means for forcibly charging the capacitor for a first predetermined time after energizing the heating element whose energization order is earlier, and discharging means for forcibly discharging the capacitor for a second predetermined time after charging by the charging means. After the discharge by the discharge means, energizes the heating element whose energization order is later, and detects a voltage value or a current value of the heating element at a lapse of a third predetermined time from the start of the energization. A device for determining damage to a heating element of a thermal head, wherein the presence or absence of damage to the heating element is determined from the voltage value or the current value. 3. The method according to claim 1, wherein the voltage value of the capacitor at the end of the discharging by the discharging means is larger than a range of a voltage value of a normal heating element in a steady state after energizing the heating element. 3. The apparatus according to claim 2, wherein the second predetermined time is set.