JP2530171Y2 - Thermal head disconnection check device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a thermal head disconnection check device.

[Prior Art] Conventionally, as a thermal head disconnection check device, one shown in FIG. 6 is known. This connects the respective heating elements 2-1 to 2-n of the thermal head 1 to the selection circuit 3. The selection circuit 3 is provided for each of the heating elements 2
It comprises NPN-type transistors 4-1 to 4-n connected in series to -1 to 2-n, respectively, and a data control unit 5 for selectively turning on and off these transistors.

The other ends of the heating elements 2-1 to 2-n are commonly connected and connected to a power supply via a resistor R1 and an NPN transistor Q1, and to the same power supply via an NPN transistor Q2. I have.

The transistor Q1 is turned on by receiving a signal from the check power supply control circuit 6 when a disconnection is checked, and the transistor Q2 is turned on by receiving a signal from the print power supply control circuit 7 during a print operation.

On the other hand, an operational amplifier 8 is provided, and the resistor R1 and each of the heating elements 2-1 are connected to one input terminal of the operational amplifier 8.
-N is connected to a common connection terminal, and another input terminal is connected to a voltage dividing point of a voltage dividing circuit of resistors R2 and R3 connected to a DC power supply V, and a disconnection check reference. Voltage V _S
Is applied.

In this conventional apparatus, when performing a disconnection check, the transistor Q1 is turned on by the power supply control circuit 6, and a voltage having a lower voltage level than that in the printing operation is applied to the thermal head 1 via the resistor R1. Each of the transistors 4-1 to 4-n is sequentially and selectively controlled to be turned on by the control unit 5 so that each of the heating elements 2-1 to 2-n is controlled.
A current is alternatively supplied to n. In this case the voltage generated in the thermal head 1 is disconnected checked are compared with the reference voltage V _S is performed by applying the operational amplifier 8. That is, if the heating element is disconnected, the voltage generated in the thermal head 1 at that time becomes higher than the reference voltage V _S , and a signal corresponding to the voltage is output from the operational amplifier 8.

However, when all the transistors 4-1 to 4-n are turned off, a leak current flows through each of the heat generating elements 2-1 to 2-n. Therefore, a voltage generated in the resistor R1 due to the leak current is always supplied to the operational amplifier 8. Will be applied.
Accordingly, when the transistors 4-1 to 4-n are actually turned on selectively, the voltage applied to the operational amplifier 8 is a voltage obtained by superimposing the voltage generated by the leak current on the voltage generated by the current flowing through the heating element. There was a problem that an accurate disconnection check could not be performed.

Therefore, the applicant has solved this problem.
A method for checking the disconnection shown in FIG. 7 was proposed and filed. (Japanese Patent Application No. 62-23982) In this method, when the transistor Q1 is turned on, a current flowing through the thermal head 1 is detected as a voltage generated between both ends of the current detecting resistor R4, and the voltage is amplified by the amplifier circuit 9. After that, the digital value is converted into a digital value by the A / D conversion circuit 10 and the digital value is taken into the main control unit 11.

The main control unit 11 has a CPU 12, ROM 13, RAM 14, I / O ports 15, 16
The CPU 12 includes signals S ₁ , S ₂ , S ₃ for driving the data control unit 5 and the power supply control circuits 6, 7 via the I / O port 15.
And the digital signal from the A / D conversion circuit 10 is taken in.

In this circuit, normal determination data X is stored in RAM 14 in advance.
Set. The I / if O port 16 to the disconnection checking start signal H is input, I / O from the port 15 the signal S _1, the data control unit 5 with by sending the S ₂ to turn on the transistors Q1 all transistors 4- 1 to 4-n are kept in an off state, and a leak current flows through the resistor R4. And this voltage generated across the resistor R4 by the leakage current amplified by the amplifying circuit 9, stored in the RAM14 as the incorporation leak current value D _L is converted into a digital signal by the A / D converter circuit 10.

Next, the data control unit 5 controls each of the transistors 4-1 to 4-1.
4-n are sequentially turned on one by one to turn on each heating element 2.
The current is sequentially applied to -1 to 2-n, and the voltage generated at the resistor R4 at that time is detected, and the A / D conversion circuit 10 converts the voltage to digital and captures it. If the current value at this time is D _E , the CPU 12
It is determined whether _E -D _L <X, so that it is determined as a disconnection if D _E -D _L <X.

As described above, by determining the disconnection after removing the influence of the leak current, an accurate disconnection can be determined.

[Problem to be Solved by the Invention] In the circuit shown in FIG. 7, when each of the transistors 4-1 to 4-n of the selection circuit 3 performs an on / off operation sequentially and selectively, the voltage is applied to the thermal head 1. It has been found that the voltage generated across the resistor R4 fluctuates in the first half of the switching operation as shown in FIG. 3 (b). Therefore, in this circuit, if the current value is read at a relatively early timing of the switching operation of the transistor, the current value is read when the voltage fluctuates, and as a result, the current when the applied voltage is reduced is reduced. A problem occurs in which a disconnection check is performed based on the value. As a result, D _E
There was a problem that −D _L <X was erroneously determined.

Therefore, the present invention can keep the voltage applied to the thermal head constant even when the heating elements are selectively energized sequentially by the selection circuit, so that the thermal disconnection can be checked more accurately. It is an object of the present invention to provide a head disconnection check device.

As shown by the dotted line in FIG. 7, a relatively large-capacitance capacitor is provided in a series circuit of each of the heating elements 2-1 to 2-n of the thermal head 1 and each of the transistors 4-1 to 4-n of the selection circuit 3. It is conceivable to further stabilize the voltage applied to the thermal head 1 by connecting 17 in parallel. However, in this case, the transistors 4-1 to 4-n
If the switching on and off operations are fast, it is difficult to rapidly discharge the charge of the capacitor 17 following it,
If the capacitor 17 is not sufficiently discharged, the voltage applied to the thermal head 1 will not decrease, and a problem will occur in which a normal current for checking for a disconnection does not flow through the resistor R4. Therefore, the switching on and off operations of the transistors 4-1 to 4-n must be delayed, which causes a problem that it takes time to check for disconnection.

Therefore, another idea is to stabilize the applied voltage by arranging a capacitor in the thermal head. In this method, the capacitor can be discharged in a short time, and therefore, the speed of the disconnection check can be increased. It is an object of the present invention to provide a head disconnection check device.

Yet another idea is to provide a thermal head disconnection check device that can reliably stabilize the voltage applied to the thermal head, and thus can more reliably perform a disconnection check, and can speed up the disconnection check. Is what you do.

[Means for Solving the Problems] The present invention provides a selection circuit for selecting a plurality of heating elements constituting a thermal head for energization, a power supply for disconnection check to the thermal head, and the thermal head. A power control circuit for checking that detects the actual applied voltage and automatically adjusts the power so that the applied voltage is constant, and a current that detects the amount of current flowing from this power control circuit to the power supply path to the thermal head The amount detection circuit and the amount of current detected by the current amount detection circuit when the selection operation of each heating element by the selection circuit is stopped, and the detection by the current amount detection circuit when each heating element is selectively selected by the selection circuit A determination means for determining a difference from the current amount and performing a disconnection determination when the difference is equal to or less than a preset allowable value is provided.

Another idea is to use a relatively large capacitor connected between the power supply path from the power control circuit to the thermal head and ground to stabilize the power supply from the power control circuit to the thermal head. And a head voltage clearing circuit for forcibly discharging the capacitor before the selection circuit starts selecting operation of each heating element.

Yet another idea is to supply power to the thermal head for disconnection checking, detect the actual applied voltage to the thermal head, and automatically adjust the power so that the applied voltage is constant. A control circuit, a relatively large capacitor connected between the power supply path from the power supply control circuit to the thermal head and the ground to stabilize the power supply from the power supply control circuit to the thermal head; A head voltage clear circuit is provided for forcibly discharging the capacitor before starting the alternative selection operation of each heating element by the circuit.

[Operation] In the present invention having such a configuration, the power supply control circuit for checking detects the applied voltage actually applied to the thermal head and automatically adjusts the power supply so that the applied voltage becomes constant. The voltage applied to the head is controlled to be always constant.

In another invention, since the electric charge of the capacitor is forcibly discharged by the head voltage clear circuit before the selection operation of each heating element by the selection circuit, the selection operation of each heating element is performed even at high speed. A normal current can always flow through the generated heating element.

In still another invention, the power control circuit for checking detects the applied voltage actually applied to the thermal head, automatically adjusts the power so that the applied voltage is constant, and uses a capacitor to supply power to the thermal head. By stabilizing the supply and forcibly discharging the capacitor, a normal current can always flow through the selected heating element even if the operation of selecting each heating element is performed at high speed.

An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the thermal head 1 is composed of n heating elements 2-1, 2-2, 2-3,... 2-n.
Further, the selection circuit 3 includes the heating elements 2-1 to 2-n.
NPN transistors 4-1 and 4 connected in series to
−2,4-3,... 4-n and each of the transistors 4-1 to 4-
and a data controller 5 for selectively turning on and off n. The data control unit 5 includes a main control unit 11 described later.
The transistors 4-1 to 4-n is a signals S ₁ at disconnection check is sequentially supplied alternatively from ON to OFF control,
At the time of printing, each of the transistors 4-1 to 4-1 is printed according to data.
4-n is selectively turned on and off.

Power is supplied to the thermal head 1 via a thyristor SCR, and power for disconnection check is supplied from a check power supply control circuit 21 via a resistor R4 and a diode D. The power supply voltage for the disconnection check supplied from the check power supply control circuit 21 is set lower than the power supply voltage supplied via the thyristor SCR. The power supply control circuit 21 also detects an anode voltage of the diode D. The power control circuit 21 is adapted to be operated controlled during disconnection check by the signal S ₂ from the main control unit 11 to be described later.

The conduction of the thyristor SCR is controlled by a printing power supply control circuit 22. The print power control circuit 22 is adapted to be operated controlled during normal printing operation by a signal S ₃ from the main control unit 11 to be described later.

The power supply control circuit 21 for checking is as shown in FIG.
A constant voltage regulator with a voltage detection terminal composed of IC elements ｛μA723 (Fairchild)｝ 211, consisting of a series voltage circuit consisting of two NPN transistors 212 and 213 and resistors 214 and 215, and a power supply terminal V of the constant voltage regulator 211 _CC
And V _C are connected to the terminals V ₁ to be connected to the power supply.
The transistor 213 is connected to terminal V ₂ which is connected to the emitter to one end of the resistor R ₄ together with connecting the collector to the terminal V _1, and connecting its base to the output terminal V _out of the constant voltage regulator 211 doing. The transistor 212 has its collector connected to the input terminal _Cmp of the constant voltage regulator 211 via a resistor 216, its emitter grounded, and its base connected via a resistor 217 to a signal S from the main controller 11. ₂ is connected to the input terminal _VS2 . The voltage divider circuit is connected to the connection point of the resistors 214 and 215 to the voltage detection terminal V- of the constant voltage regulator 211, is connected one end (resistance 215 side) to the terminal V ₃ which is connected to the anode of the diode D, Other end (resistance 214
Side) is grounded.

The voltage generated between both ends of the resistor R4 is amplified by an amplifier circuit 9 and converted into a digital signal by an A / D converter circuit 10 to be converted to a main control unit 1
Supplying one.

The main control unit 11 includes a CPU 12 constituting a control unit main body,
A ROM 13 in which program data for the PU 12 to control each unit is stored, a memory in which setting data is stored, a memory in which processing data is temporarily stored, and a RAM 14 in which a register used for calculation is provided, and the A / D conversion circuit It is configured by an I / O port 15 for inputting a digital signal from 10 and outputting the signals S ₁ , S ₂ , S ₃ respectively, an I / O port 16 for inputting a disconnection check start signal from the outside, and the like. I have. The CPU 12, the ROM 13, the RAM 14, and the I / O ports 15, 16 are electrically connected by a bus line.

Normal determination data X is set in the RAM 14 in advance.

The CPU 12 starts a disconnection check control operation when a disconnection check start signal H is input from the outside. This first the data controller 5 to output the signals S ₁ causes the all the transistors 4-1 to 4-n in the OFF state by outputting a signal S ₂ to the checking power supply control circuit 21 leakage current value Let D _{L be} detected.

Subsequently, the transistors 4-1 to 4-
Then, control is performed such that n is sequentially turned on to detect the current value _DE flowing through each of the heating elements 2-1 to 2-n. Each of the heating elements 2-1 to 2-1
Each for detecting a current value D _E flowing through the 2-n perform the check whether D _E -D _L <X, to determine the disconnection if D _E -D _L <X, also D _E -D _L If ≧ X, normality is determined.

In this embodiment having such a configuration, when the disconnection check start signal H is input to the main control unit 11, the CPU 12 starts the disconnection check. And all transistors 4-1 to 4-n in the OFF state by the data control unit 5 first, the capture leakage current value D _L the voltage generated between both ends of the time the resistor R4 as a digital signal from the A / D converter 10 To detect.
And stores the leakage current value D _L in RAM 14.

Next, the data controller 5 is controlled to control each transistor 4-1.
To 4-n are sequentially turned on, and the voltage generated between both ends of the resistor R4 by the on operation is converted to an A / D conversion circuit 10
To detect a taken current value _DE as a digital signal. Then, a calculation of D _E -D _L is performed to detect whether D _E -D _L <X. If D _E −D _L ≧ X, it is determined that the heating element that is energized at that time is normal, and D _E −D _L <
If it is X, it is determined that the heating element that is energized at that time is disconnected.

In this way, the disconnection of each of the heating elements 2-1 to 2-n can be checked by removing the influence of the leak current, so that an accurate disconnection check can be performed.

However since the voltage source voltage supplied from the terminal V ₂ of checking the power control circuit 21 is applied to the thermal head 1 when varying changes, and turned on the transistors 4-1 to 4-n at the time of change When the disconnection check is performed, even if the heating element is normal, the voltage generated in the resistor R4 changes, so that an accurate disconnection check cannot be performed.

However, in this embodiment, when the power supply voltage from the power supply control circuit 21 changes, the voltage on the anode side of the diode D also changes, so that the voltage input to the voltage detection terminal V− of the constant voltage regulator 211 of the power supply control circuit 21 also changes. Will be. Thus, when the voltage input to the voltage detection terminal V- changes, the constant voltage regulator 211 changes the level of the signal output from the output terminal _Vout so that the voltage becomes a predetermined value. so that the voltage output to the V ₂ is kept constant.

In this way, the voltage applied to the thermal head 1 is kept constant, and the voltage generated between both ends of the resistor R4 changes from the beginning when the transistors 4-1 to 4-n are turned on as shown in FIG. It will keep a constant value. Therefore, regardless of the timing of detecting the voltage generated in the resistor R4, the correct current value _DE can always be read,
A more accurate disconnection check can be performed.

When a normal printing operation is performed, the operation of the power supply control circuit 21 for checking is stopped, and the power supply control circuit 22 for printing is operated to turn on the thyristor SCR. , The transistors 4-1 to 4-n are selectively turned on.

In the above-described embodiment, a case where a constant voltage regulator including an IC element is used for the check power supply control circuit has been described. However, it is needless to say that the present invention is not necessarily limited to this.

Next, another embodiment of the present invention will be described with reference to the drawings.
The same parts as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 4, a relatively large-capacitance capacitor C is connected to a series circuit of the heating elements 2-1 to 2-n of the thermal head 1 and the transistors 4-1 to 4-n of the selection circuit 3. Are connected in parallel to stabilize the power supply to the thermal head 1.

The head voltage clear circuit 23 is connected to the capacitor C. As shown in FIG. 5, the head voltage clear circuit 23 comprises one NPN transistor 231. The collector of the transistor 231 is connected to the terminal CLR connected to the positive terminal of the capacitor C via a resistor 232. its emitter grounded, and is connected to the terminal V _S4 of signal S ₄ from the I / O port 15 is an input of the main control unit 11 the base via a resistor 233 as well as.

The main control unit 11 is to output at the timing immediately before the transistors 4-1 to 4-n are turned on by the data control unit 5 a signal S ₄ from the I / O port 15.

In this embodiment having such a configuration, the capacitor C
, The power supply voltage applied to the thermal head 1 is further stabilized.

Then, the data control unit 5 controls each of the transistors 4-1 to 4-
Since just before the n is an ON operation by a signal S ₄ from the main control unit 11 transistors 231 of the head voltage clear circuit 23 is turned on charges of the capacitor C will be discharged instantaneously through the transistor 231 Therefore, when each of the transistors 4-1 to 4-n is turned on, the capacitor C is in a sufficiently discharged state, and each of the heating elements 2
A current normally flows through -1 to 2-n.

Therefore, even if the capacitor C is used to stabilize the voltage applied to the thermal head 1, there is no need to provide a time period for waiting for the discharge of the capacitor C, and the disconnection check can be performed at a high speed as in the case where the capacitor C is not used. Can do it.

In this embodiment, it is needless to say that a more accurate disconnection check can be performed as in the above embodiment.

The configuration of the head voltage clear circuit is, of course, not limited to that of the above embodiment.

[Effects of the Invention] As described in detail above, according to the present invention, the voltage applied to the thermal head is always kept constant even when the heating circuit is selectively and sequentially energized by the selection circuit. Accordingly, it is possible to provide a thermal head disconnection check device capable of performing a more accurate disconnection check.

According to another invention, a capacitor can be discharged in a short time in a thermal head in which a capacitor is juxtaposed to stabilize an applied voltage, and therefore, the speed of disconnection check can be increased. It is possible to provide a possible thermal head disconnection check device.

According to yet another aspect of the present invention, there is provided a thermal head disconnection check device capable of reliably stabilizing a voltage applied to a thermal head, thereby performing a more reliable disconnection check, and speeding up the disconnection check. You can do it.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a configuration of a check power supply control circuit of the embodiment, and FIG. 3 (a) is for checking a disconnection in the embodiment. FIG. 3 (b) is a detection waveform diagram for checking a disconnection in the prior application circuit, FIG. 4 is a circuit diagram showing another embodiment of the present invention, and FIG. FIG. 6 is a circuit diagram showing a conventional example, and FIG. 7 is a circuit diagram showing a prior art example. 1 thermal head, 2-1 to 2-n heating elements, 3 selection circuit, 11 main control unit, 12 CPU, 1
3… ROM, 14… RAM, 21… Check power control circuit, 211… Constant voltage regulator, R4… Current detection resistor.

Claims (3)

(57) [Scope of request for utility model registration] A selection circuit for selecting a plurality of heating elements constituting a thermal head for energization, a power supply for checking a disconnection to the thermal head, and detecting an actual voltage applied to the thermal head. A power control circuit for automatically adjusting a power supply so that the applied voltage is constant; a current amount detection circuit for detecting an amount of current flowing from the power supply control circuit to a power supply path to the thermal head; The amount of current detected by the current amount detection circuit when the selection operation of each heating element by the selection circuit is stopped, and the amount of current detected by the current amount detection circuit when each of the heating elements is selectively selected by the selection circuit And determining means for determining a disconnection when the difference is equal to or less than a preset allowable value. Disconnection checking device of Maruheddo. A selection circuit for selecting a plurality of heating elements constituting the thermal head for energization, a power supply control circuit for supplying power to the thermal head for disconnection check, and a power supply control circuit. A relatively large-capacitance capacitor connected between a power supply path from the power supply control circuit to the thermal head and ground to stabilize power supply to the thermal head, and a current flowing through the power supply path A current amount detection circuit for detecting the amount, and the selection of each heating element by the current amount detection circuit and the selection circuit when the selection operation of each heating element by the selection circuit is stopped. At the time when the difference between the current amount detected by the current amount detection circuit is obtained, and when the difference is equal to or less than a predetermined allowable value, disconnection determination is performed. And a head voltage clearing circuit for forcibly discharging the capacitor before the start of the selection operation of each of the heating elements by the selection circuit. . 3. A selection circuit for selecting a plurality of heating elements constituting a thermal head for energization, supplying power for disconnection check to the thermal head and detecting an actual voltage applied to the thermal head. A power control circuit for automatically adjusting the power so that the applied voltage becomes constant; and a power control circuit from the power control circuit to the thermal head for stabilizing power supply from the power control circuit to the thermal head. A relatively large capacitor connected between the power supply path and the ground, a current amount detection circuit for detecting an amount of current flowing through the power supply path, and stopping the selection operation of each heating element by the selection circuit. When the amount of current detected by the current amount detection circuit and the selection circuit selectively operate each of the heating elements. Determining a difference between the detected current amount by the current amount detection circuit, and performing a disconnection determination when the difference is equal to or less than a predetermined allowable value; and selecting operation of the selection circuit for selecting each of the heating elements by the selection circuit. A head voltage clearing circuit for forcibly discharging the capacitor before the start, and a disconnection check device for the thermal head.