JPS6299164A - Thermal head driver - Google Patents

Abstract

PURPOSE:To contrive higher printing quality, by providing a temperature- controlling circuit for finely adjusting a control reference voltage set by a reference voltage setting circuit, and a head voltage controlling circuit which receives a voltage obtained by a head resistance discriminating circuit and maintains a head voltage at a voltage corresponding to the resistance of heating elements according to the control reference voltage finely adjusted by the temperature-controlling circuit. CONSTITUTION:The resistance of heating elements in a thermal head 3 is discriminated by a head resistance discriminating circuit 10, a combined resistance is formed according to the discriminated resistance, and an optimum head voltage Vh is obtained based on the combined resistance. A resistor R8 consisting of, for example, a cement resistor as an auxiliary heating element and inserted in a supply passage for an electric current flowing to the heating elements 4 is energized in synchronism with the energization of the heating elements, thereby causing the resistor R8 to generate heat. The temperature rise characteristics of the resistor R8 are set to be substantially coincident with those of the thermal head 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head driving device that changes a head applied voltage value in accordance with a heating element resistance value of a thermal head.

[Conventional technology]

When using thermal heads used in thermal printers, etc., if the voltage applied to the head exceeds a predetermined voltage value, the amount of heat accumulated in the heating element increases, affecting print quality, or in the worst case, causing damage. It is one of the causes of.

Therefore, it is necessary to specify and apply a head voltage according to the resistance of the heating element of each thermal head. Incidentally, since the resistance value of the heating element of the thermal head varies during manufacturing, each resistance value is classified into several ranks, and the head voltage is set for each rank. Therefore, the head voltage is adjusted each time according to the rank of the heating element resistance value.

[Problem that the invention seeks to solve]

However, the above head voltage adjustment method causes the following problems.

■ When adjusting the head voltage for each 1-marhead, 8
It is complicated and requires one device and tools.

■ Since the head voltage must be adjusted by operating the inside of the power supply circuit, only those with specific knowledge of electricity and power supply circuits can handle it.

(2) Furthermore, if thermal heads with the same resistance value rank are selected in order to eliminate head voltage adjustment, the price of the thermal heads will increase.

Furthermore, even if the head voltage is set to a value corresponding to the resistance value of the heating element.

If the heating element is energized for a long period of time, there is a concern that the temperature of the heating element may rise more than necessary due to the heat storage effect of the heating element itself.

The present EA/fi was developed based on these circumstances, and its purpose is to be able to apply an appropriate head voltage regardless of the resistance value of the heating element of the thermal head, and also to maintain the temperature. It is an object of the present invention to provide a thermal head driving device that can finely adjust the head voltage in response to changes, extend the life of the thermal head, and improve printing quality.

[Means for solving problems]

The present invention provides a connector in which a connection pattern corresponding to the resistance value of a heat generating element constituting a thermal head is formed, and a plurality of combined resistances connected to the connector formed in accordance with the connection pattern to increase the resistance value of the heat generating element. A head resistance identification circuit that creates a voltage corresponding to the thermal head, a reference voltage setting circuit that sets a reference voltage for adjusting the head voltage to be applied to the thermal head, and an auxiliary heating element inserted in the current supply path to the thermal head. A temperature adjustment circuit that finely adjusts the adjustment reference voltage set by the reference voltage setting circuit according to the temperature information output from the temperature detection element that detects the amount of heat generated, and a temperature adjustment circuit that receives the voltage obtained from the head resistance identification circuit. The head voltage adjustment circuit maintains the head voltage at a voltage value corresponding to the resistance value of the heating element in accordance with the finely adjusted vN adjustment reference sleep pressure.

[Effect]

The present invention is equipped with the above-mentioned means.C) The head resistance identification circuit identifies the resistance value of the heating element of the thermal head, forms a composite resistance corresponding to this, and forms a composite resistance corresponding to this composite resistance value. A head voltage is obtained, which becomes a constant head voltage corresponding to the adjustment reference voltage and the heating element resistance value.

Further, since the temperature adjustment circuit and the printing temperature are controlled to a substantially constant value by controlling the head voltage according to the thermal head temperature, deterioration of printing quality due to heat accumulation is prevented.

〔Example〕

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

FIG. 1 is a configuration diagram of a thermal head driving device. This device is for driving a thermal head 3 having a connector 1 connected to a cable 2 as shown in FIG. 4 is a plurality of heating elements arranged in series. The connector 1 is formed with a connection pattern corresponding to the resistance value of each heating element of the thermal head 3. For example, in FIGS.
) are four unique connection patterns.

Now, numeral 10 in FIG. 1 is a head resistance identification circuit, which has three connection terminals CI, C2, and C connected to the connector 1.
s, and Mj to the connecting terminals Cat and Cs! connected resistance hole 1
．． It is composed of R2.

Further, 11 is a head voltage detection circuit consisting of a series circuit of a resistor R3 and a resistor R4, and a resistor R1 in the head resistance identification circuit 10 is connected to a connection point between the resistors R3 and R4.
A voltage at the connection point between R2 and resistor R2 is applied.

Therefore, the resistances R, J, R2, R between the head voltage Vh(2) output terminal applied to each heating element 4 of the thermal head 3 and the connection point of the head voltage detection circuit 11 are
The value of the combined resistance formed by 3 changes as shown in the following table depending on the type 4-connection pattern of (a) to (d) of connector 1 (1111) shown in FIG. In the thermal head 3, a heating element 4 having a resistance value of 4 ranks (4 ranks) can be used.

Further, the paper pressure V at the connection point of the head voltage detection circuit 11 is input to the A input terminal of the comparator 12. This comparator 12 compares the voltage level of the B input terminal and the voltage level of the A input terminal, and calculates the voltage level of the B input terminal Vr.
When V is much higher than the voltage level V at the A input terminal, a conductive signal is sent from the C output terminal to the base of the npn transistor Q. Further, when the DC voltage Vin is input to the VC voltage input terminal, a constant voltage E0 is output from the VR[positive output terminal. Further, 13 is a reference voltage setting circuit, which is a reference voltage V for adjusting the head voltage vh to be applied to the thermal head 3.

This adjustment reference voltage V is sent to the B input terminal of the comparator 12.

Its configuration includes a variable resistor RT connected to the VR output terminal of the comparator 12, and a resistor R5 commonly connected to this resistor RT and the B input terminal of the comparator 12.

14 is a temperature adjustment circuit, and this temperature adjustment circuit 14 is
Adjustment reference voltage V set by the reference voltage setting circuit 13
r is adjusted according to the temperature of the thermal head 3Q to optimize the printing density, and the B input terminal of the comparator 12 is connected to a parallel circuit of a thermistor TH as a temperature detection element and a resistor R6. The resistor R7 is connected in series.

Further, the input terminal of the DC voltage Vin is connected to the transistor Q.
It is connected to an output terminal for outputting the head voltage Vh between the collector and emitter of the head and via a resistor R8 serving as an auxiliary heating element.

The resistor R8 as the auxiliary heat generating element is constructed of a cement resistor as shown in FIG. 4, generates heat when energized, and stores the heat for a certain period of time. Therefore, since there is little heat dissipation, when electricity is applied for a long time, the temperature increases due to the heat storage effect. Further, the thermistor TH is attached to the side surface of the resistor R8 with an adhesive as shown in the figure.
Detects temperature rise due to heat accumulation. Note that the temperature rise characteristic due to energization of the resistor 8 is approximated to the temperature rise characteristic due to the actual heating element 4 of the thermal head 3.

Next, the operation of the apparatus configured as described above will be explained. When the DC voltage Vin is supplied, the variable resistor RT is first adjusted to set the reference voltage vr to the head resistance identification circuit 1.
0 is set to a predetermined value for when each of the connection terminals C1 to C3 is in an open state. The adjustment reference voltage Vr at this time must be determined without considering the temperature adjustment circuit 14.

On the other hand, the voltage 3 applied to the input terminal of the comparator 12 is as follows. Therefore, the comparator 12 has a voltage Vs applied to the A input terminal and an adjustment reference voltage Vr applied to the B input terminal.
Transistor Q is made conductive (e) until these pressures are the same.

The head paper pressure Vh obtained as a result of this 04 times control is as follows.

v, : V, starts. In this way, when V becomes equal to Vr, the transistor Q is turned off and the head voltage Vh is held constant.

Here, when the connector 1 is connected, each of the connection terminals C1 to C3 of the head resistance identification circuit 10 becomes open and connected. This connection state is as shown in Figure %@3.
Either or both of Cx and C3 are connected, and the combined resistance value for each connection state is as shown in the above figure. Each of these combined resistance values is round depending on the resistance value (by rank) of the heating element of each thermal head 3, and thus a head voltage Vh is applied to the thermal head 3 according to the resistance value of the heating element. be done.

In addition, the temperature adjustment circuit 14 also provides a reference voltage Vr for adjustment.
has been adjusted. The combined resistance of the temperature adjustment circuit 14 is 0.

becomes. Since this combined resistance R01 is connected in parallel to the resistor R5, the combined resistance Ro2 is as follows. Therefore, by substituting this equation (5) for the resistor R5 in equation (1), the adjusted reference voltage vr
is required.

In this embodiment, the head resistance identification circuit 10
The resistance value of the heating element of the thermal head 3 is identified, a combined resistance is formed according to this, and the optimum head voltage vh is obtained from this combined resistance value.
Once the setting is performed by the variable resistor RT, even if the thermal head 3 with any heating element resistance value is connected, a combined resistance corresponding to the heating element resistance value will be formed, and the optimum resistance value will be set according to the heating element resistance value. Head voltage is automatically obtained. Therefore, each time the thermal head 3 is replaced, the head voltage V
There is no need to adjust h, making handling easier.

Further, the print density of the thermal head 3 is optimized by the temperature adjustment circuit 14. That is, by energizing a resistor R8 formed of, for example, a cement resistor as an auxiliary heating element inserted in the supply path of the current flowing to the heating element 4 of the thermal head 3, in synchronization with the energization of the heating element 4. This resistor R8 generates heat. The temperature rise characteristic of this resistor R8 is made to substantially match the temperature rise characteristic of the thermal head 3. therefore.

The head voltage Vh applied to the thermal head 3 is automatically adjusted according to the temperature without directly measuring the temperature of the thermal head 3. For example, when the temperature of the thermal bed 3 increases, the head voltage Vh decreases, and when the temperature decreases, the head voltage Vh increases. As a result, the temperature of the thermal head 3 remains almost constant, and an optimal constant print density can always be obtained.

Furthermore, since the temperature of the thermal head 3 does not rise abnormally, it is also possible to extend the life of the thermal head 3.

〔Effect of the invention〕

As explained above, according to the present invention, an appropriate head voltage can be applied regardless of the resistance value of the heating element of the thermal head, and the head voltage can be finely adjusted in response to temperature changes. It is possible to extend the service life of the printer and improve the printing quality.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a thermal head driving device according to the present invention, FIG. 2 is an external view of a thermal head applied to the device of the present invention, and FIG. 3 is a diagram of a connector connected to the thermal head. FIG. 4 is an external view of the resistor 8 showing the connection pattern. DESCRIPTION OF SYMBOLS 1... Connector, 2... Cable, 3... Thermal head, 4... Heating element, 10 Head resistance identification circuit, 1 No... Head voltage detection circuit, 12... Comparator, 13 ...Reference voltage setting circuit, 14...Temperature adjustment circuit, TH...Thermistor (temperature detection element) 1R
8...Resistance (auxiliary heating element), Vh...Head voltage, Vr...Reference voltage for adjustment. Applicant's agent Patent attorney Takehiko Suzue Figure 1 (C) (d) Figure 3 Figure 4

Claims (1)

[Claims] A connector formed with a connection pattern corresponding to the resistance value of the heating element constituting the thermal head, and a connector connected to this connector to form a plurality of composite resistances according to the connection pattern to correspond to the resistance value of the heating element. a head resistance identification circuit that creates a voltage that is applied to the thermal head; a reference voltage setting circuit that sets a reference voltage for adjusting the head voltage to be applied to the thermal head; and an auxiliary heating element that is inserted in a current supply path to the thermal head. a temperature adjustment circuit that finely adjusts the adjustment reference voltage set by the reference voltage setting circuit according to temperature information output from a temperature detection element that detects the amount of heat generated; A thermal head drive device comprising: a head voltage adjustment circuit that maintains the head voltage at a voltage value corresponding to a resistance value of a heating element according to the adjustment reference voltage that has been finely adjusted by a temperature adjustment circuit.