JPH056129Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a motor drive circuit for a thermal printer, and more particularly, to a motor drive circuit for a thermal printer that prints one line by moving a thermal head in the line direction using a motor.

Conventional technology Conventionally, there has been a thermal recording type in which a thermal head is brought into contact with thermal paper to change the temperature of the paper, or a thermal head is brought into contact with transfer paper coated with heat-melting ink to record the dissolved ink on the transfer paper. There are thermal printers that use heat-sensitive transfer recording to transfer images onto paper.

Among the above-mentioned thermal printers, there is one that prints one line in a line sequential manner by moving a serial dot type thermal head in the line direction. In this thermal printer, a constant voltage is applied to the motor for moving the thermal head,
The thermal head is moved at a constant speed, or the printing mode is determined based on the size of the font such as a gothic font or the font size of a subscript, etc., and the motor applied voltage is varied for each printing mode to adjust the thermal head according to the printing mode. There are things that move at speed.

Problems to be Solved by the Invention For example, the power consumption of a thermal head when printing a black square (■) is greater than the power consumption when printing a character (-). When the power consumption per unit time exceeds a predetermined value, the thermal head overheats and breaks down, and the power supply circuit of the thermal head also breaks down due to excessive current. Therefore, the moving speed of the thermal head needs to be slow enough to prevent the thermal head from overheating even when printing black squares (■), etc., which consume a lot of power, continuously, and the speed determined in this way is Since the thermal head is constantly moved during printing, there is a problem in that the printing speed is slow. This also applies to the case where the moving speed of the thermal head is varied for each print mode, since there are characters with different power consumption in each print mode.

Furthermore, when a battery is used as a power source, when the output voltage of the battery decreases, the amount of heat generated by the thermal head decreases, resulting in a pale print and a significant deterioration in print quality. For this reason, there is a problem in that the battery cannot be used once the output voltage drops slightly, and the usable time, that is, the life of the battery is short.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a motor drive circuit for a thermal printer that solves the above problems by using a subtraction circuit and an amplification circuit.

Means for Solving the Problems In the present invention, a subtraction circuit subtracts a constant voltage from the voltage applied to the thermal head to obtain a differential voltage.
The amplifier circuit amplifies this differential voltage and applies it to the motor.

Function In this invention, the subtraction circuit subtracts a constant voltage from the thermal recording voltage applied to the thermal head to obtain a differential voltage, and the amplifier circuit amplifies this differential voltage and applies it to the motor for moving the thermal head. do. That is, when the thermal recording load increases and the voltage applied to the thermal head decreases, the voltage applied to the motor decreases accordingly, and the moving speed of the thermal head is controlled to decrease.

Embodiment The figure shows a circuit diagram of an embodiment of the circuit of the present invention. In the figure, 1 is a DC power source such as a battery, the negative electrode of which is grounded, and the positive electrode connected to an input terminal 2a of a thermal head power supply circuit 2. The output of this DC power supply 1 is, for example, 6V. The thermal head power supply circuit 2 is a constant voltage circuit that boosts the voltage supplied from the DC power supply 1 to produce an output voltage of, for example, 13V. It is of the decreasing current limiting type.

The output terminal 2b of the thermal head power supply circuit 2 is connected to one end of each of heat generating resistors R ₁ to _Ro of the thermal head. The thermal head has a serial dot configuration, with heating resistors R ₁ to R _o
The number of the thermal heads is, for example, 7 or 9, and they are arranged in a line in a direction perpendicular to the direction of movement of the thermal head.
The other ends of the heating resistors R ₁ to _{R o} are each transistor Q ₁
~ Q _o is connected separately to the collector. The emitters of each of the transistors Q ₁ to Q _o are connected, and the base of each of the transistors Q ₁ to _{Q o} is connected to the terminal 3 ₁
~3 Connected to _o . Control pulses are supplied to the terminals 3 ₁ to 3 _o from a print control circuit (not shown). This control pulse is a pulse with a constant pulse width that remains at H level for a certain period _of time only for the heating resistor that performs printing every time the thermal head moves a predetermined _distance . Only the supplied transistor becomes conductive, and current flows through the heat generating resistor connected to its collector to perform printing.

The cathode of a Zener diode _D1 is connected to the output terminal 2b of the thermal head power supply circuit 2.
Its anode is grounded via a resistor Ra.
A subtraction circuit is configured by a Zener diode _D1 and a resistor Ra. Further, the emitter of a transistor Qa is connected to the positive electrode of the DC power supply 1, and the collector of the transistor Qa is connected to a DC motor 4 that drives the movement of the thermal head.
It is grounded via series-connected resistors Rb and Rc. The base of transistor Qa is a transistor
The base of the transistor Qb is connected to the anode of the Zener diode _D1 , and the emitter is connected to the connection point of the resistors Rb and Rc, respectively. Above transistors Qa, Qb, resistors Rb, Rc
The amplifier circuit is configured by:

Zener Diode _D1 Zener Diode
V _D1 is, for example, 11V, and the resistance values of the resistors Rb and Rc are, for example, 2:1. Therefore, the voltage at the output terminal 2b is set to V ₁ and the transistor Qb
If the base-emitter voltage V _BE of is 0.6v, then
The emitter voltage Vb of the transistor Qb and the collector voltage Va of the transistor Qa are expressed by the following equation.

Vb=V ₁ −V _D1 −V _BE ……(1) Va=3・(V ₁ −V _D1 −V _BE ) ……(2) In other words, when the voltage V ₁ of output terminal 2b is 13V, (2)
According to the formula, the voltage Va applied to the motor 4 is 4.2v.

For example, when printing a character (-), current flows only through a single heating resistor, so output terminal 2b
The voltage V ₁ is approximately 13v, and the voltage applied to the motor 4 is
The rotation speed corresponds to 4.2v.

In addition, when printing black squares (■), current flows through all of the heating resistors R ₁ to R _o , and the voltage at the output terminal 2b of the current-limiting type thermal head power supply circuit 2 drops by, for example, 0.2V. It becomes 12.8v. As a result, the voltage applied to the motor 4 becomes 3.6V, and the rotational speed of the motor 4 becomes slow. Therefore, the time it takes to print a black square (■) with a large current flowing through the thermal head is longer than the time it takes to print a small character (-) with a small current flowing through the thermal head, and the thermal head radiates heat during that time. This prevents overheating and destruction of the thermal head. By the way, the moving speed of the thermal head when printing black squares (■) is approximately the same as the moving speed (constant speed) of the thermal head of a conventional printer. In other words, the thermal head prints faster as the amount of heat generated by the characters it prints becomes smaller.
The total printing time is reduced compared to the conventional method.

Also, if the output voltage of DC power supply 1 decreases,
The output voltage V ₁ of the thermal head power supply circuit 2 decreases, and the voltage Va applied to the motor 4 decreases, so the rotational speed of the motor 4 slows down, and the printing density remains the same as before the output voltage of the DC power supply 1 decreased. Ru. In this case, although the printing speed becomes slower, there is no deterioration in printing quality, and the usable time, that is, the lifespan of the DC power source (battery) 1 becomes longer.

Here, the subtraction circuit, the amplifier circuit, and the motor 4 constitute a feedback loop for the thermal head power supply circuit 2. Since the motor 4 includes an integrator circuit, the stability of the loop is good, and there is no worry of oscillation occurring. do not have.

Note that a subtraction circuit may be constructed using an operational amplifier or the like instead of the diode D ₁ and the resistor Ra, or an amplifier circuit may be constructed using an operational amplifier or the like instead of the transistors Q ₁ and Q ₂ and the resistors Ra and Rb. Of course, the present invention is not limited to the above embodiments.

Effects of the invention As mentioned above, the motor drive circuit of the thermal printer according to the invention consists of an arithmetic circuit and an amplifier circuit, so the current flowing through the thermal head reduces the movement speed of the thermal head when printing small characters, etc. The overall printing time is significantly shortened compared to the conventional method, and when a battery is used as a DC power source, there is no deterioration in print quality even if the battery output voltage decreases, and the usable time of the battery is reduced. It has features such as long life.

[Brief explanation of the drawing]

The figure is a circuit diagram of one embodiment of the circuit of the present invention. 1...DC power supply, 2...Power supply circuit for thermal head, 4...Motor, _D1 ...Zener diode, _Q1 ~ _Qo , Qa, Qb...Transistor, _R1 ~
R _o , Ra, Rb, Rc...resistance.

Claims (1)

[Scope of utility model registration request] A subtraction circuit that obtains a differential voltage by subtracting a constant voltage from the voltage applied to the thermal head for thermal recording, and an amplifier circuit that amplifies the differential voltage and applies it to a motor that moves the thermal head in the line direction. A motor drive circuit for a thermal printer configured to vary the moving speed of a thermal head in accordance with changes in voltage applied to the thermal head.