JPH0721350U - Thermal head - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a thermal head capable of easily and accurately measuring the resistance value of each heating resistor. A switching element 30 capable of electrically controlling opening and closing is connected in series with a noise absorbing capacitor 29 between a GNDH line and a VH line of a driving power supply circuit.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a thermal head for arranging a plurality of heating resistors in a line and performing thermal recording.

[0002]

[Prior art]

 FIG. 4 is a sectional view showing a schematic configuration of the conventional thermal head 1, and FIG. 5 is a bottom view of the thermal head 1 shown in FIG. As shown in FIG. 4, the thermal head 1 is composed of a plurality of heating resistors 3 arranged in a line on a heat-resistant and electrically insulating head substrate 2 and is composed of a semiconductor integrated circuit for driving the driving resistors. The circuit 4 is formed. The head substrate 2 is mounted and mounted on the heat dissipation plate 5. On the heat dissipation plate 5, a wiring board 6 for supplying control signals and power to the drive circuit 4 is mounted and mounted on the reinforcing plate 7. As shown in FIG. 5, on the back surface of the wiring board 6, a connector 8 for connecting the wiring board 6 to the head substrate 2 and a common electrode (not shown) and a ground are arranged in series, and for example, about 22 μF. And the noise absorbing capacitor 9 is attached. The lead portion 9a of the noise absorbing capacitor 9 is mounted by penetrating the lead insertion holes 9b provided in the wiring board 6 and the reinforcing plate 7. The surface of the wiring board 6 is covered and protected by a cover 11 mounted on the wiring board 6 by the mounting screws 10.

FIG. 6 is an enlarged plan view showing a mounting portion of the noise absorbing capacitor 9 of the wiring board 6. A drive power supply circuit 12 is formed on the surface of the wiring board 6 covered with the cover 11. The VH line 13 and the GNDH line 14 of the driving power supply circuit 12 are provided with lead insertion holes 9b of the noise absorbing capacitor 9, respectively. A land 15 is formed around the lead insertion hole 9b, and the lead portions 9a of the noise absorbing capacitor 9 inserted into the lead insertion hole 9b are soldered and connected to the land 15 respectively.

If the noise absorbing capacitor 9 is not provided, in a circuit in which the resistor R and the power source E are connected in series and opened and closed by the switch S, the current flows to the resistor R from the moment the circuit is closed by the switch S. The current does not reach the equilibrium value determined by E / R, but reaches the equilibrium value by repeatedly overshooting and undershooting in a short time. This occurs because the power supply E cannot keep up with the switching speed. When the current temporarily overshoots, an excessive current flows through the resistor R, which may damage the resistor R. Therefore, the capacitor C is connected in parallel with the resistor R. The impedance of the capacitor C is represented by 1 / 2πfC, where f is the frequency of the current. Since the impedance of the capacitor C decreases as the frequency of the AC component increases, almost all the current flows through the capacitor C and hardly flows through the resistor R when 1 / 2πfC << R. As a result, almost all of the transient current flows through the capacitor C, and only the direct current component flows through the resistor R.

The same applies to the thermal head 1, and in order to prevent damage to the heating resistor 3 due to transient current overshoot, a noise absorbing capacitor 9 is connected in parallel with the heating resistor 3 for noise absorption. It The heating resistor 3 of the thermal head 1 is normally driven in about 2 msec when performing a printing operation. In order to effectively bypass the overshoot and undershoot of the transient current at this time, the capacitance of the noise absorbing capacitor 9 is determined with a time constant of about 0.1 msec.

Separately from this, if the resistance value of the heating resistor 3 of the thermal head 1 varies, even if a current of the same magnitude is applied for the same period of time, the heat generated by the heat-generating antibody 3 will increase due to the difference in resistance value. The amount changes, which causes printing defects such as uneven printing. At the time of manufacturing the thermal head 1, trimming for making the resistance values of the heating resistors 3 uniform and correction of the applied energy for variations in the resistance value of the heating resistors 3 are performed. Further, the resistance value of the heating resistor 3 of the thermal head 1 changes with time according to the total amount of energy applied. Therefore, if the number of times of heat generation of the heating resistor 3 and the amount of electric energy applied to the heating resistor 3 are different for each heating resistor 3, the resistance value of the heating resistor 3 varies with time. Therefore, in a color printer or the like that continues to apply high energy to the heating resistor 3, in order to maintain the same density characteristics as in the initial state, the heating resistor 3 is corrected in order to correct the change with time of the resistance value of the heating resistor 3. It is necessary to make adjustments such as measuring the resistance value of 3 and inputting the correction data.

When the resistance value of each heating resistor 3 is measured using a resistance value measuring device, a voltage of about 24 V is usually applied as a rated voltage, and the current flowing through the heating resistor 3 is measured. At this time, if a pulse of, for example, 2 msec, which is about the same as during printing, is applied to each heating resistor 3, the time required to measure the resistance value becomes long, and the resistance values of all the heating resistors 3 are measured. Takes several minutes. The heating resistor 3 is in contact with the thermal paper during the printing operation, and no problem occurs. However, when measuring the resistance value, the surface of the heating resistor 3 is in contact with air and the heating resistor 3 is empty. The temperature rises more than necessary due to the burning condition. As a result, the heating resistor 3 may be damaged or modified. In order to prevent this, it is possible to reduce the applied voltage. However, if the voltage of the resistance value measurement pulse is lowered, the current flowing through the resistance value measurement circuit will decrease and the measurement error will become very large. Therefore, the applied voltage is set to 20 to 24 V so that the resistance value of about 2000 to 3000 Ω can be measured with an error of several Ω, and the voltage application time is set to 0.05 to reduce the influence on the heating resistor 3. The resistance value is measured at about 0.1 msec.

[0008]

[Problems to be solved by the device]

 However, if a resistance value measuring pulse is applied to each of the heating resistors 3 with the noise absorbing capacitor 9 attached so that the voltage application time is 0.05 to 0.1 msec, the current at this time becomes Like the transient current from the power supply, the current flows to the noise absorbing capacitor 9 and hardly flows to the heating resistor 3. This occurs because the time constant between the resistance value measuring pulse and the resistance value measuring circuit including the noise absorbing capacitor 9 approximates. In addition, since the impedance of the noise absorbing capacitor 9 at this time is small, the measured value is a value as if the heating resistor 3 had a low resistance of several Ω to several tens of Ω.

Therefore, when the resistance value of the heating resistor 3 is measured by such a resistance measuring device, the noise absorbing capacitor 9 must be removed from the thermal head 1. On the other hand, as shown in FIG. 4, in the noise absorbing capacitor 9, the lead 9a is inserted into the wiring base plate 6 and the reinforcing plate 7, and the lead 9a is a land formed on the wiring substrate 6. Soldered to 15. For this reason, in order to remove the noise absorbing capacitor 9 from the thermal head 1, it is necessary to remove the thermal head 1 from the apparatus equipped with the thermal head 1 and disconnect the soldered portion each time the resistance value is measured. Further, after the trimming is completed, the noise absorbing capacitor 9 must be re-soldered to the thermal head 1 and the thermal head 1 must be attached to the device. As described above, it is laborious and time-consuming and inconvenient to remove the thermal head 1 from the device equipped with the thermal head 1 each time the resistance value is measured and reattach it.

An object of the present invention is to solve the above problems and to provide a thermal head capable of easily and accurately measuring the resistance value of a heating resistor.

[0011]

[Means for Solving the Problems]

 According to the present invention, a plurality of heating resistors are formed, one end of each heating resistor is connected to one end of a power source through a common electrode, and the other end of each heating resistor is provided for each heating resistor. In a thermal head that is connected to a ground via electrodes, a capacitor that connects between the common electrode and the ground, and a capacitor that is connected in series between the capacitor and the common electrode or between the capacitor and the ground. And a switching element for shutting off the capacitor.

[0012]

According to the present invention, in the thermal head, the capacitor is connected between the common electrode and the ground, and further, between the capacitor and the common electrode, or between the capacitor and the ground, A switching element is interposed in series. Therefore, the capacitor can be cut off by the switching element. This allows the capacitor to be connected to bypass the transient current from the power supply during the printing operation of the thermal head, and when measuring the resistance value of the heating resistor, the switching element shuts off the capacitor to accurately generate heat. The resistance value of the resistor can be measured.

[0013]

【Example】

 FIG. 1 is a circuit diagram showing the overall configuration of a thermal head 21 which is an embodiment of the present invention. As shown in FIG. 1, the thermal head 21 is configured to include a plurality of heating resistors 23 corresponding to pixels of one scanning line and a plurality of drive circuits 24 including semiconductor integrated circuits. For example, 64 heating resistors 23 are connected to one drive circuit 24. The drive circuit 24 converts the print signal D ATA input as serial data into parallel data every predetermined number of bits in synchronization with the clock signal CLOCK from the outside. Further, the drive circuit 24 temporarily holds the parallel data for each bit in synchronization with the latch signal LATCH, and selectively outputs the parallel data to each heating resistor 23 based on the strobe signals STROBE1-8. As a result, the heating resistor 23 selectively generates heat and prints one scanning line on the thermal paper or the thermal transfer film pressed by the thermal head 21. A series of images is printed by repeating the above-mentioned operation while carrying the thermal paper and the thermal transfer film stepwise.

Further, a noise absorbing capacitor 29 having a capacity of 22 μF, for example, is connected in series between the VH line and the GNDH line connected to the common electrode of a driving power supply circuit (not shown) having a power supply voltage of 35 V. , And a switching element 30 such as an electrically openable and closable relay. As long as the noise absorbing capacitor 29 and the switching element 30 are in series, either one may be connected to the common electrode side.

FIG. 2 is a bottom view of the thermal head 21. The thermal head 21 of the present embodiment is similar to the thermal head 1 shown in FIGS. 4 to 6 and has the same configuration except the switching element 30. Similar to the thermal head 1 shown in FIG. 4, the thermal head 21 is a ceramic in which a heat generating resistor 23 and a drive circuit 24 which form pixels for one scanning line are formed on a heat sink 25 made of alumina or the like. A head substrate made of a heat-resistant, electrically insulating material such as is attached. Further, a wiring board connected to the head board is provided on the reinforcing plate 27 attached on the heat dissipation plate 25. In the noise absorbing capacitor 29 shown in FIG. 2, the leads 29a are attached by penetrating the lead insertion holes provided in the reinforcing plate 27 and the wiring board. A drive power supply circuit (not shown) is formed on the wiring board, and one lead 29a of the noise absorbing capacitor 29 is soldered and connected to a land formed on the VH line of the drive power supply circuit. To be done. The other lead 29a of the noise absorbing capacitor 29 is connected to one connection terminal of a switching element 30 such as a relay mounted in proximity to the noise absorbing capacitor 29 from the bottom surface side of the reinforcing plate 27. The other connection terminal of the switching element 30 is connected to the GND line of the driving power supply circuit. Further, on the bottom surface side of the reinforcing plate 27, a connector 28 for connecting the wiring substrate and the head substrate and supplying power and control signals to the heating resistor 23 and the drive circuit 24 is attached.

FIG. 3 is a circuit diagram showing an electrical configuration of the switching element 30. The switching element 30 is a relay that connects the pair of terminals 31a and 31b by applying the principle of an electromagnet. As shown in FIG. 3, one terminal 31a of the switching element 30 is connected to the VH line of the driving power supply circuit, and the other terminal 31b is connected to the + pole side of the noise absorbing capacitor 29. The negative pole side of the noise absorbing capacitor 29 is connected to the GNDH line. In this embodiment, the switching element 30 is connected between the driving power supply circuit and the noise absorbing capacitor 29, but if it is in series, it is connected between the noise absorbing capacitor 29 and the GNDH line. May be. When a current flows through the coil 32, a magnetic field is generated in the axial direction of the winding of the coil 32. Due to this magnetic field, the connecting piece 33 is displaced in a direction in which it comes close to the terminals 31a and 31b and in a direction in which it separates from it. The connection piece 33 is made of a conductive magnetic material, and the connection piece 33 is displaced and pressed by the terminals 31a and 31b to electrically connect the terminals 31a and 31b. It Further, when the connecting piece 33 is separated from the terminals 31a and 31b, the connection between the terminals 31a and 31b is cut off. In this way, by the direction of the current flowing in the coil 32 or the conduction and interruption of the current flowing in the coil 32, the VH line between the terminals 31a and 31b, that is, the VH line of the driving power supply circuit and the noise absorbing capacitor 29 are connected. The electrical connection between can be controlled. This allows noise absorption even when the resistance value of the heating resistor 23 is measured for the purpose of trimming in the manufacturing process of the thermal head 21, failure analysis of the thermal head 21 and investigation of the change over time of the heating resistor 23. The resistance value can be accurately measured without removing the capacitor for use 29 from the thermal head 21.

Further, by registering a program for measuring the resistance value of the heating resistor 23 in the apparatus main body equipped with the thermal head 21, the noise absorbing capacitor 29 is automatically shut off, and the heating resistor is automatically turned off. The resistance value of 23 can be measured. Furthermore, the program registered in the device can automatically correct the drive signal based on the measured resistance value.

As described above, according to this embodiment, in the thermal head 21, the electrically openable and closable switching element 30 is connected in series between the driving power supply circuit and the noise absorbing capacitor 29. . Therefore, even when the resistance value of each heating resistor 23 is measured, the noise absorbing capacitor 29 is cut off by electrically opening and closing the switching element 30 to open between the terminals 31a and 31b. can do. Therefore, it is not necessary to remove the noise absorbing capacitor 29 from the thermal head 21, and the resistance value can be easily and accurately measured.

In this embodiment, a relay is used as the switching element 30. However, the present invention can be preferably implemented by using a switching element 30 such as a transistor instead of the relay.

[0020]

[Effect of device]

 According to the present invention, the thermal head is provided with a capacitor connecting between the common electrode and the ground, and the capacitor is cut off between the capacitor and the common electrode or between the capacitor and the ground. The switching elements for switching are connected in series. By electrically opening and closing the switch of the switching element, it is possible to cut off the capacitor without removing the capacitor as in the conventional case. As a result, during the printing operation of the thermal head, the transient current from the power supply can be bypassed by the capacitor, and when measuring the resistance value of the heating resistor, the capacitor is cut off by the switching element, and the heating resistance is accurately measured. The resistance value of the antibody can be measured.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an overall configuration of a thermal head 21 which is an embodiment of the present invention.

2 is a bottom view of the thermal head 21. FIG.

FIG. 3 is a circuit diagram showing an electrical configuration of a switching element 30.

FIG. 4 is a cross-sectional view showing a schematic configuration of a conventional thermal head 1.

5 is a bottom view of the thermal head 1 shown in FIG.

6 is an enlarged plan view showing a mounting portion of a noise absorbing capacitor 9 of the wiring board 6. FIG.

[Explanation of symbols]

 21 Thermal Head 23 Heating Resistor 24 Drive Circuit 29 Noise Absorption Capacitor 30 Switching Element

Claims (1)

[Scope of utility model registration request] 1. A plurality of heating resistors are formed, one end of each heating resistor is connected to one end of a power source through a common electrode,
In a thermal head in which the other end of each heating resistor is connected to the ground via an individual electrode provided for each heating resistor, a capacitor connecting between the common electrode and the ground, the capacitor and the common electrode And a switching element for shutting off the capacitor, which is connected in series between the capacitor and the ground.