JP2834072B2 - Thermal printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer, and more particularly to a thermal printer for performing printing on an IC built-in card or the like in which the printing result is likely to have shading because the surface of the printing medium has minute irregularities. For a suitable thermal printer.

[0002]

2. Description of the Related Art In a thermal printer, a technique is known in which a thermistor is provided on a thermal head as a heating and printing means to detect the temperature of the thermal head, and the power supplied to the thermal head is adjusted based on the detected temperature. is there.

For example, a thermal printer disclosed in Japanese Patent Application Laid-Open No. 147253/1993 receives an image signal and generates energy corresponding to the image in order to accurately control the density gradation of color printing. A thermal head having a plurality of heating resistance elements, one thermistor as temperature detecting means for detecting the head temperature of the thermal head, and calculating means for calculating the temperature of the thermal head from the detection result of the temperature detecting means And a counting means for counting the number of energized elements in the unit energization time of the thermal head, and the power supplied to the thermal head is corrected based on the calculation result of the calculation means and the counting result of the counting means.

The thermal printer disclosed in Japanese Patent Application Laid-Open No. 5-147253 has the best print quality even when there is a difference between the temperature of the thermal head itself and the temperature of the ink ribbon and recording paper around the head. The first thermistor as temperature detecting means for detecting the temperature of the thermal head itself and the second thermistor as temperature detecting means for detecting the temperature around the thermal head so that printing can be performed with A second thermistor; a head voltage determining means for determining a head voltage to be applied to the thermal head based on the temperatures detected by the first thermistor and the second thermistor; Printing is controlled by providing print control means for applying a head voltage to the thermal head.

[0005] The conventional thermal printer as described above,
A thermistor for detecting the temperature of the thermal head,
Rather than being provided for each of the heating elements of the thermal head, only one is provided for the entire thermal head. Therefore, since the IC is built in a specific position of the medium to be printed, the surface has minute irregularities, and the irregularities cause uneven pressing, resulting in a difference in thermal conductivity. When printing is performed on a medium such as a so-called IC built-in card in which shading tends to occur in a printing result,
Where the thermal head cannot be sufficiently adhered to the medium, the thermal conductivity is low and the heating element in that part cannot detect heat generation, so the printing result is uneven on the uneven surface and the flat surface without unevenness. Occurs.

[0006]

As described above, the conventional thermal printer having a thermistor for detecting the temperature of the thermal head is provided with only one thermistor for the entire thermal head. When printing on a printing medium having a smooth printing surface without irregularities, it is possible to perform printing on the printing medium with uniform density without shading in the printing result, A printing medium having irregularities has a drawback that unevenness causes uneven pressing, resulting in a difference in thermal conductivity, and as a result, shading occurs in a printing result.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal head with a plurality of thermistor-equipped temperature detecting circuits for detecting the temperatures of a plurality of heating elements in order to solve the above-mentioned drawbacks of the conventional thermal printer. Provided, when the unevenness of the surface of the print medium causes uneven pressing and a difference in thermal conductivity occurs, and a temperature difference occurs in each heating element, this is detected and the energization of each heating element is controlled. And to increase the thermal conductivity by changing the pressing force of the thermal head against the print medium to provide a thermal printer that can obtain good print quality without causing shading in the print result. is there.

[0008]

A thermal printer according to the present invention includes a thermal head having a plurality of heating elements and a plurality of thermistors attached to each of the plurality of heating elements, and the thermal head. A printing mechanism for performing printing by pressing the thermal head against a printing medium, and a plurality of heat sources for detecting a temperature of each of the plurality of thermistors and supplying a driving voltage to corresponding heating elements. a service over the thermal head drive control unit including an element driving circuit, the pressing force with respect to the printing medium of the thermal head when it is detected that the temperature of the portion of the heating element rises above a predetermined temperature by the heating element drive circuit A thermal head pressing force control unit for strengthening the thermal head. A drive circuit for supplying a flip-flop circuit for setting the operating state of the drive circuit, an amplifier for detecting and amplifying a voltage across said thermistor connected in series to the heating element, the output signal of the amplifier and the service over the thermal head drive control unit comprising the heating element driving circuit having a comparator for sending a signal to the thermal head pressing force control unit with by comparing the reference voltage to reset the flip-flop circuit The printing mechanism further includes a cam for moving the thermal head up and down and a step motor for driving the rotational movement of the cam, and the thermal head pressing force control unit controls the rotation angle of the cam. It is like that.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a front view showing a configuration of a first embodiment of the present invention, FIG. 2 is a front view showing an operation state of a printing mechanism of the embodiment of FIG. 1, and FIG. 3 is a view of the embodiment of FIG. FIG. 4 is a circuit diagram showing a thermal head drive circuit, FIG. 4 is a flowchart showing the overall operation of the embodiment of FIG. 1, and FIG. 5 is a flowchart showing a printing operation of the embodiment of FIG.

FIG. 1 shows a non-contact method for an IC card (card) in which an integrated circuit (IC) including a memory capable of writing and reading (reading) data is embedded. This is a line printer type thermal printer that performs printing by thermal transfer on the surface while writing and reading data.

In FIG. 1, an IC card (card) 25 is loaded and stored in a card storage box 1, and the lowest card is sent out one by one by a card feeding mechanism (not shown). The antenna unit 2 wirelessly writes and reads data to and from the IC of the card 25 sent out of the card storage box 1 by a wireless method. Printing mechanism 3
Prints by thermally transferring the ink of the ink ribbon 5 to the card 25 conveyed to the platen 6 by the thermal head 4. The thermal head 4 is provided with a plurality of heating elements. The card 25 sent from the card storage box 1 is conveyed to the printing mechanism 3 through the antenna unit 2 by the feed roller 7a, and the card 25 printed by the printing mechanism 3 is printed.
Is discharged by the feed roller 7b. The thermal head drive control unit 8 supplies a drive voltage for printing to each heating element of the thermal head 4 (details will be described later). The thermal head pressing force control unit 9 controls the force by which the printing mechanism unit 3 presses the card 25 against the platen 6.
The printer controller 10 controls operations of the thermal head drive control unit 8 and the thermal head pressing force control unit 9.

Next, the configuration and operation of the printing mechanism 3 will be described in detail with reference to FIG.

FIG. 2A is a view showing a state when printing is not performed. The thermal head 4 mounted on the mount section 11 is waiting above the platen 6. The mount 11 is held by an arm 14 via a spring 12, and a cam follower 16 provided on the upper surface of the arm 14 is in contact with a cam 24 by a cam spring 13. The cam 24 is a step motor 15
The stepping motor 15 is driven by the thermal head pressing force controller 9.

When the printing operation is started, as shown in FIG. 2B, the cam 24
Arrow A by step motor 15 driven by
Rotate in the direction. As a result, the arm 14 descends because the cam follower 16 is pushed down, and the spring 12
The mount 11 connected to the arm 14 via the arm also descends, and the thermal head 4 attached to the mount 11 comes into contact with the card 25. In this state, the spring 12 is still in its natural length, and the thermal head 4 is in contact with the card 25 but no pressing force is applied.

When the cam 24 continues to rotate in the direction of arrow A, the cam follower 16 is pushed down and the arm 14 is lowered as shown in FIG.
Is in contact with the card 25, the mount section 11 cannot descend. Therefore, the spring 12 is extended (extension distance x = 0 to 3.5 mm), and the thermal head 4 is extended.
Applies a pressing force to the card 25. Since the extension distance of the spring 12 at this time depends on the rotation angle of the step motor 15 by the thermal head pressing force control unit 9, the pressing force on the card 25 by the thermal head 4 can be controlled.

Next, the configuration and operation of the thermal head drive controller 8 will be described in detail with reference to FIG.

The thermal head drive controller 8 controls each of the plurality of heating elements of the thermal head 4 as shown in FIG.
The heating element drive circuit shown in FIG. In FIG.
When the flip-flop circuit 17 is set, the drive circuit 18 supplies a drive voltage to the heating element 19 according to a signal from the print cycle signal generation circuit 26. As a result, the heating element 19 generates heat. The thermistor 20 connected in series with the heating element 19 also changes its resistance value according to the heating of the heating element 19. Thermistor 20
Is amplified by an amplifier 21 and input to a comparator 22, where it is compared with a reference voltage. This reference voltage is a value that is set based on data obtained in advance through experiments from the relationship between the temperature of the heating element 19 and the voltage across the thermistor 20 amplified by the amplifier 21. It is stored as a database in a memory built in the unit 8. In this manner, the driving voltage is supplied to the heating element 19 until the heating element 19 reaches the target temperature. When the comparator 22 detects that the voltage across the thermistor 20 has exceeded the reference voltage, the switching circuit 23 operates to activate the flip-flop circuit 17.
Is reset, and the thermal head pressing force controller 9 is reset.
To send a signal. Thereby, the drive circuit 1
8 stops, and the heat generation of the heat generating element 19 also stops. In this way, the thermal head 4 can control the supply of the driving voltage for each heating element so that the temperature of each heating element reaches the target temperature.

Next, the operation of the thermal printer configured as described above will be described with reference to FIGS.

As shown in FIG. 4, the overall operation of the embodiment shown in FIG.
Is sent out by the card feeding mechanism unit and conveyed to the position of the antenna unit 2 by the feed roller 7a (step 31), the antenna unit 2
The data of the IC of the card 25 is written in a wireless manner in a non-contact manner and the verify read of the written data is performed (step 32). When this operation is completed, the card 25 is conveyed to the printing mechanism 3, where the printing is performed by the printing mechanism 3 (step 33), and discharged by the feed roller 7b.

The printing mechanism 3 operates as shown in FIG. That is, when the cam 24 is rotated by being driven by the step motor 15, the thermal head 4 stands by above the platen 6 (the state of FIG. 2A).
Descends and comes into contact with the card 25 (the state of FIG. 2B). When the cam 24 is continuously rotated from this state,
When the spring 12 is extended (the state shown in FIG. 2C), the thermal head 4 applies a normal pressing force (200 g) to the card 25.
/ Cm) (step 41). In this state, the thermal head drive control unit 8
The printing voltage is applied to the heating elements (step 4).
2). When printing is performed on a flat printing medium having no unevenness on the surface, each heating element of the thermal head 4 comes into close contact with the printing medium and melts the ink on the thermal transfer ink ribbon 5 to transfer the ink to the printing medium. temperature x ₀ of generating thermal energy, i.e. the heating elements of the heating elements required to melt the ink at this time, have been found in advance with time t ₁ to reach it. Thus the progress of the printing operation while detecting the temperature of the heating elements by heating element drive circuit of FIG. 3 the temperature x ₀ as the reference temperature (Step 4
3). That is, when the temperature of the heating elements has reached a temperature x ₀ all elapsed time t _1, the next dot line conveying the card 25 stops applying the printing voltage by one-dot lines perform printing, but when there is a heating element does not reach the temperature x ₀ even after time t _1, to continue the application of the printing voltage to the heating element.

Before time t ₁ elapses, that is, time t ₀
(T ₀ <t ₁₎ until the have heating elements has reached a temperature x ₀ (step 44), the heating element is high temperature x ₁ than the temperature x ₀ at the time of the lapse of time t ₁ (x ₀ <x _{When 1} ) is reached (step 48), the surface of the print medium at this time has irregularities.
It is determined that the thermal energy of the heating element is not sufficiently transmitted to the ink ribbon 5 and is accumulated in the heating element because the adhesion between the heating element and the printing medium is insufficient. The pressing force of the thermal head 4 is increased by driving the step motor 15 to increase the rotation angle of the cam 24 (step 4).
9). Thereafter, the temperature of the heater element measured (step 50), (step 51) when being lowered to the vicinity of the temperature x _0, sufficient to improve adhesion between the thermal head 4 and the printing medium again It is determined that the ink has been transferred at the density, and the process proceeds to step 46. When not lowered to the vicinity of the temperature x ₀ in step 51 to repeat the above operation returns to step 49.

In step 44, time t ₀ (t ₀ <
If no heating element has reached the temperature x ₀ by t ₁ ),
The temperature of the heating element is measured at regular intervals (step 4).
5), the temperature of all of the heating element shifts to step 46 when it reaches the temperature x _0. In step 46, it is determined whether or not the dot line feed for all the print ranges has been completed. If not completed, the line feed for one dot line is performed (step 47), and the process returns to step 41 and ends. If so, the printing operation ends.

In this way, when the thermal head 4 and the print medium are not in close contact with each other due to the unevenness of the surface of the print medium and the temperature rise of some of the heating elements becomes insufficient, Continue applying the printing voltage to the elements and wait until the temperature of all the heating elements reaches the specified temperature.If the temperature rise of some of the heating elements rises above the specified temperature, the thermal head By increasing the pressing force on the print medium and improving the adhesion between the thermal head and the print medium, increasing the thermal conductivity and lowering the temperature of the heating element, the print result does not have shading. Good printing quality can be obtained.

The embodiment shown in FIG. 1 is an example in which the present invention is applied to a line printer type thermal printer, but it is easy to apply the present invention to a serial printer type thermal printer. In this case, since the width of the thermal head is approximately 1/4 of the width of the thermal head of the line printer type thermal printer having substantially the same width as the width of the print medium, the thermal head pressing force control unit controls the thermal head against the print medium. When the pressing force is increased, the effect of increasing the degree of adhesion is further enhanced. Therefore, it is easy to ensure the uniformity of the print density, and it is possible to obtain excellent print quality.

[0026]

As described above, in the thermal printer of the present invention, thermistors are attached to all the heating elements of a thermal head having a plurality of heating elements, and the thermistors are connected to detect the temperature of each heating element. The thermal head is operated by a thermal head drive control unit having a heating element drive circuit, and the pressing force on the card by the thermal head of the printing mechanism can be controlled by the thermal head pressing force control unit. When the temperature rise of the heating elements is insufficient, it is possible to continue applying the printing voltage to the heating elements and wait until the temperatures of all the heating elements reach the specified temperature. When the temperature of the heating element rises above a predetermined temperature, the pressing force of the thermal head against the print medium is increased to increase the thermal head. By improving the adhesion between the printing element and the printing medium, the temperature of the heating element can be reduced, so that printing can be performed without causing shading in the printing result even on a printing medium having an uneven surface. This makes it possible to obtain a thermal printer capable of obtaining good print quality.

[Brief description of the drawings]

FIG. 1 is a front view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a front view showing an operation state of a printing mechanism of the embodiment of FIG. 1;

FIG. 3 is a circuit diagram showing a thermal head drive circuit of the embodiment of FIG.

FIG. 4 is a flowchart showing an overall operation of the embodiment of FIG. 1;

FIG. 5 is a flowchart showing a printing operation of the embodiment of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Card storage box 2 Antenna unit 3 Printing mechanism unit 4 Thermal head 5 Ink ribbon 6 Platen 7a, 7b, feed roller 8 Thermal head drive control unit 9 Thermal head pressing force control unit 10 Printer controller 11 Mount unit 12 Spring 13 Cam spring 14 Arm 15 Step motor 16 Cam follower 17 Flip-flop circuit 18 Drive circuit 19 Heating element 20 Thermistor 21 Amplifier 22 Comparator 23 Switching circuit 24 Cam 25 IC card (card) 26 Print cycle signal generation circuit 31-33.41-51 Step

Claims (3)

(57) [Claims] 1. A thermal head having a plurality of heating elements and a plurality of thermistors attached to each of the plurality of heating elements, and mounting the thermal head and pressing the thermal head against a print medium. a printing mechanism for printing by support over having a plurality of heat generating element drive circuit for supplying respective drive voltage to the heating element indicative of the sensed temperature of said plurality of thermistor <br/> A thermal head pressing force control unit for increasing the pressing force of the thermal head against the printing medium when detecting that the temperature of some of the heating elements has risen to a predetermined temperature or higher by the heating element driving circuit; And a thermal printer. 2. A drive circuit for supplying a drive voltage to the heating element of the thermal head, a flip-flop circuit for setting an operation state of the drive circuit,
An amplifier for detecting and amplifying a voltage between both ends of the thermistor connected in series with the heating element, comparing the output signal of the amplifier with a reference voltage, and
According to claim 1, characterized by comprising the service over the thermal head drive control unit comprising the heating element driving circuit having a comparator for sending a signal to the thermal head pressing force control unit resets the circuit Thermal printer. 3. A printing mechanism comprising: a cam for elevating and lowering the thermal head; and a step motor for driving a rotational movement of the cam, wherein a rotation angle of the cam is controlled by the thermal head pressing force control unit. The thermal printer according to claim 1 or 2, wherein