JPS6073865A - Noise suppresion apparatus of thermal head - Google Patents

Abstract

PURPOSE:To effectively suppress noise generated in a direct drive type thermal head, by inserting a series circuit consisting of a resistor and a condenser between a power source line for supplying a drive current to a heat generating element from an external power source and earth. CONSTITUTION:A remote terminal circuit 7 is one connected between a terminal point farthest from an external power source 6 and comprises a series circuit of a resistor R and a condenser C. A near terminal circuit 8 is one connected to the external power source 6, a power source supply line 11 and an earthed line 12 and is formed of an RC series circuit and inductance elements L respectively inserted into the power source supply lines 11, 12 in series. Therefore, generated high frequency noise advances toward both terminals of the power source wiring and the earthed line in a thermal head 1 therethrough but noise advancing to the remote terminal side is consumed as heat energy by the resistor R in the remote terminal circuit 7 without being reflected from the terminal point. On the other hand, noise advancing to the side of the external power source 6 is inhibited in advance by the inductance elements L in the near terminal circuit 8 and also consumed as heat energy by the resistor R.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to a noise suppression device for a thermal head in which a plurality of heat generating elements and their respective drive circuit systems are mounted on the same substrate.

[Technical Background of the Invention and Problems Therewith] A thermal head is a recording device in a thermal recording type or thermal transfer type printer that has been frequently used in facsimiles and various data terminal devices in recent years. A direct drive type is known as one type of thermal head.

This combines a driving element that individually drives a heating element consisting of a plurality of resistors as a recording element, and a signal distribution circuit that distributes image signals to be recorded from the outside to these driving elements on a single substrate together with the heating element. It is placed above.

However, in this Tiref 1-drive type multi-head, all heating elements are driven at the same time, so the inductive nose generated by the switching of large currents by the driving elements affects the signal distribution circuit made up of logic circuits. There is a risk of giving.

This type of recording method is becoming more dense and faster, and the induced noise itself also tends to increase accordingly, which poses a big problem in terms of the stability of the recording operation.

In addition, CMO3'-, which is more advantageous than bipolar type in terms of consumption type, transfer speed, and chip area, etc.
When an IC is used in a signal distribution circuit, the input impedance is high, so the influence is significant and there is a high risk of malfunction.

[Object of the Invention] An object of the present invention is to provide a noise suppressing means that effectively suppresses the noise generated by the switching operation of the driving element in a direct drive type linear head.

[Summary of the Invention] The present invention is characterized in that a series circuit of a resistor and a capacitor is inserted between a power supply line for supplying drive current from an external power supply to the heating element and the ground to suppress noise. There is. Here, the resistor is used to absorb noise, and the capacitor is used to suppress power consumption by the resistor and prevent it from burning out.

Moreover, the power supply line mentioned here includes, of course, the power supply line on the substrate of the thermal head and the power supply line between this power supply line and the main power supply.

[Effects of the Invention] According to the present invention, inductive noise generated by switching of a large current by a driving element is absorbed and suppressed by a series circuit of a resistor and a capacitor through a power supply line. Therefore, even in the case where this noise is large and the signal supply circuit is composed of C to IO3-ICs etc. that are weak against noise, a stable recording operation can be obtained without causing post-operation.

[Embodiments of the invention] FIG. 1 shows an embodiment of the present invention.

In the figure, reference numeral 1 denotes a direct drive type linear head, which includes a plurality of heating elements 2 arranged in -rows,
Drive elements 3 individually connected to these heating elements 2, and a shift register that transfers image signals serially supplied from an external circuit 5 together with various control signals and distributes them to each drive element 3 in parallel. A signal distribution circuit 4 including a latch circuit and a circuit 1 is disposed on a single substrate such as a ceramic substrate.

The driving element 3 is selectively turned on in accordance with the image signal supplied from the signal distribution circuit 4, and supplies current from the external power supply 6 to the corresponding heating element 2. By this energization, the heating element 2 generates heat in response to the image WA signal, which causes the thermal paper moving in opposition to the heat-sensitive paper to develop color, or melts the ink on the ink ribbon to create a visible image in the form of thermal transfer. Make a record.

Here, assuming that the thermal spatula 1 has a width of 216 mm with a resolution of 16 lines/'mm, and that the photothermal elements 2 are driven by shifting the phase by half, the resistance value of the heating element 2 is 4.
000. When the applied voltage is 15V, a large current of about 65A at maximum flows. If the noise generated by such large current switching is left untreated, it will cause large power ringing and cross-crossing to the signal line due to stray capacitance and stray interface, and the signal distribution circuit 4 consisting of logic circuits will
This may cause malfunction.

Therefore, in this embodiment, such a problem is solved by providing a far end circuit 7J'3 and a near end circuit 8 as shown in the figure as noise suppressing means. It is connected between the end point of the power supply wiring on the board farthest from the external power supply 6 and the ground, and has a resistance (R).
It consists of a series circuit of a capacitor (C) and a capacitor (C). This far end circuit 7 can also be provided on the substrate of the square head 1.

On the other hand, the near-end circuit 8 connects the external IR source 6 and the thermal head 1.
Power supply line 11.12 connecting with the power supply wiring on the board of
(However, 12 is the ground line), and the RC series circuit similar to the far end circuit 7 and the power supply line 11.
It consists of an inductance element inserted in series with each.

Here, the resistor R in the far-end circuit 7 is a matching resistor that suppresses the reflection of the switching noise at the end point of the power supply wiring, and the capacitor C prevents power consumption or burnout in this resistor R due to direct current. be. In other words, the high-frequency noise generated by the switching of the large current by the drive element 3 travels along the power supply wiring and ground wire within the thermal head 1 toward both ends of the line, but the noise that travels toward the far end is reflected at the end point - (reflection). far end circuit 7 without being
It is consumed as thermal energy by the resistance R inside. Assuming that the line impedance of the power supply wiring is ZO, the value (R) of the resistance R is preferably R=Zo, and is generally around 100. Further, if each frequency of ringing that occurs when there is no noise suppression means is ωd, the field (C) of capacitor C for DC cutter 1 is R>>1, /ω(1
・It is desirable to satisfy C.

On the other hand, noise traveling toward the external power supply 6 side, that is, toward the near end, is prevented from advancing by one inductance element in the near end circuit 8, and is consumed by the resistor R as thermal energy. However, the value (L) of the inductance element is ω(1
/L≧1, and furthermore, to prevent new noise due to back electromotive force, 1 /L −C< (R2/
4 L2. ) is required.

As described above, according to the present invention, by using a simple configuration including RIC and even L, it is possible to stabilize the recording operation by suppressing the noise caused by the switching of the large current applied to the direct drive type thermal head. can be achieved.

FIGS. 2(a) to 2(d) show other embodiments of the present invention, and in particular, show coupled examples in which the near-end circuit 8 is modified in various ways. These configurations can also provide the same effects as those of the above embodiments.

This invention can be modified in various ways without departing from the gist; for example, in the embodiment, a circuit for noise suppression is provided at both the far end and the near end, but it may also be provided only at either one. However, they may also be provided at locations other than the end points.

Also, the far end circuit 7. The near-end circuit 8 may be provided within the thermal head substrate or may be provided externally.

As for the inductance element, it may be replaced with something that functions similarly, for example, a ferrite heather, or it may not be provided as long as the stray inductance of the power supply line satisfies the conditions. Further, the inductance element on the ground side may not be provided at all.

Furthermore, it goes without saying that similar results can be obtained even if the positional relationship between R and C is switched.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2(a) to
(D> is a diagram showing another embodiment. 1... Thermal head, 2... Heat generating element, 3...
Drive element, 4... Signal distribution circuit, 5... External circuit,
6... External circuit, 7... Far end circuit for noise suppression, 8
...Noise 4111 Near @ circuit for M. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] (1) A plurality of heating elements arranged in a line, driving elements that individually drive these heating elements, and image signals inputted from the outside to these driving elements are distributed. A device for suppressing noise generated by the driving elements in a thermal head, in which a signal distribution circuit for operating these driving elements is disposed on the same substrate, and a device for supplying driving current from an external power source to the heating element. A thermal noise suppression device characterized by inserting a series circuit of a resistor and a capacitor between a power supply line and ground. (2) The noise of the thermal head according to claim 1, wherein the series circuit of the resistor and the capacitor is connected to the farthest end point of the power supply wiring on the board from the external power supply. Suppressor. (3) The series circuit of the resistor and the capacitor is connected to a power supply line between the power supply and the power supply wiring on the board, as set forth in claim 1. (4) The series circuit of the resistor and the capacitor is connected to a power supply line between the external power supply and the power supply wiring on the board, and 2. The thermal head noise suppression device according to claim 1, wherein an inductance element inserted in series with said power supply line forms a low-pass filter.