JPS61167576A - Thermal printer - Google Patents

Abstract

PURPOSE:To enable highly effective transmission of electric power from a power supply to a printing head and subsequently miniaturize the power supply for the title printer by inserting a pi type filter consisting of a serial coil and parallel condensers between a printing head and a power supply. CONSTITUTION:A pi type filter consisting of a single piece of serial coil and two pieces of parallel condenser C1, C2 is inserted between the printing head 3 of a thermal printer and a power supply 4. As a result, an electric charge is accumulated in the condenser C1, C2 during a non-printing period T3, and at the same time, the accumulated electric charge is released to the printing head 3 during a printing period T2, thus averaging a current supplied to the printing head. Concurrently, a peak current is controlled by the coil L and a charge to the condenser C2 is selected during the period T3. In this way, the power supply capacity can be reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in power supplies in thermal printers.

A description will be given below using a thermal transfer printer as an example.

The print head of a thermal transfer printer is made up of multiple resistors, which are energized to generate heat.

Printing is done by thermally transferring ink from an ink ribbon onto recording paper.

The resistors are arranged in vertical dots that constitute the characters, and the resistors necessary for the printed characters are selected and energized for each printing period corresponding to the movement (spacing) of the print head.

The energization time in the printing cycle is less than 1/2, and in order to improve the responsiveness of heat generation, the unselected resistors are also energized to some extent for preheating. As a result, a large current flows intermittently during printing, requiring a power source with a large capacity compared to the actual power required, which poses a problem that hinders miniaturization of printers.

Thermal printers have a simple structure and are small and lightweight, so they are expected to be portable, but there is also a demand for printers that solve the above problems and have a smaller power supply.

[Conventional technology]

The conventional technology will be explained below.

FIG. 2 (al is a block diagram showing the head driving part.

FIG. 2(b) is a time chart of the current consumed in the head portion.

In Figure 2 (al), 1 is a control unit that performs drive control such as paper feeding and spacing, receives printed character information, converts it into a character dot pattern, and drives the head drive unit 2, and 2 is a plurality of resistors. A head driving section is composed of switch notching elements Q1 to Qn that turn on and off the current supply to R1 to Rn and a section that selectively drives them; 3 is a print head section; 4 is a power source that supplies voltage to each section.

Resistors R1 to Rn are prepared for the number of dots in the vertical direction that make up a character (usually about 24), and the resistors selected according to the printed character pattern are energized at the same time, but as mentioned above, the resistors R1 to Rn are energized at the same time. The resistor is also preheated and energized. As a result, as shown in FIG. 2(b), a large current I flows intermittently during the printing cycle.

In FIG. 2 (bl), Tl is one dot space time, that is, a printing period, T2 is a printing energization period, and a peak current I flows.

Although the preheating energization time is shorter than the printing energization time, it is within the printing energization period T2, and therefore the current waveform is approximately an intermittent waveform as shown in FIG. 2 (bl).

The above-mentioned peak current I usually ranges from 1 to 2 A, and the power source 4 is required to have a capacity that can sufficiently flow that current.

[Problem that the invention seeks to solve]

As explained above, a power source capable of sufficiently passing one intermittent current requires several times the power actually required, which poses a problem that hinders miniaturization.

[Means for solving problems]

The above-mentioned conventional problems can be solved by the thermal printer of the present invention, in which a π-type filter consisting of one series coil and two parallel capacitors is inserted between the print head and the power supply that supplies current. It can be solved.

[Effect]

According to the present invention, a π-type filter consisting of a coil and a capacitor C is inserted in the line supplying the head driving voltage, and the constant of the element is adjusted to the driving conditions of the head, such as the printing cycle, peak current, etc. Since the selection is made accordingly, power can be efficiently transmitted from the power supply to the print head, and the power supply can be made smaller.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 (at is a block diagram of a print head driving portion of a printer embodying the present invention, and FIG. 1 (bl is a time chart showing the print head current).

In FIG. 1(a), the coil and capacitor CI.

π inserted into the power supply line supplied to the head by C2
Configure type filters.

The above filter has a print head current I2 shown in Fig. 1 (bl).
It smoothes the capacitor C1,
Charge is accumulated in C2, and the charge is released to the print head section 3 during the printing period T2. Therefore, during the period T2, the power supply 4 maintains the voltage v2 or supplies a current 1111 to compensate for the charge shortage, and during the period T3, the capacitors C1 and C2 are charged i! A current 112 flows, resulting in an averaging of the printhead supply current I2.

That is, the charge required for the print head section 3 in the print cycle T1 is 12*T2, and the maximum charge accumulated in the capacitor C2 is C2*V2.

Assuming that the current of voltage #4 is not supplied during the printing period T2,
Due to the above accumulated charge, the load (R1 to R) has a time constant C2*
A decreasing current flows through R, and a current is supplied from the power source 4 to supplement this current.

A value is selected for the coil L that can suppress the peak current and charge the capacitor C2 during the period T3.

Approximate values of the constants of the coil and capacitors C1 and C2 can also be determined using the formulas shown below.

Inductance of coil L, capacitors C1 and C2
If the capacitances of are respectively C1 and C2, and the characteristic impedance of the π-type filter is ZO2, and the transfer ratio is n, then the impedance Z01 on the power supply side and the impedance Z02 on the print head side are zo2=t/n*zo=p Here, A = 1 + Z a / Z cB = Za C = (Za + Zb + Zc) / ZbZcD = 1 + Za
/Zb Za=j ωL zb=1/jωC1 zc=1/jωC2 ω=2π f where f is expressed as the energization period.

Here, in order to extract a large capacity current from a small capacity power supply, ZOl>ZO2, that is, n Z O> 1 / n Z O, so n>1.

・=J〒 Here, if ωLC>1, it becomes clear that C2>CI should be set. In this case, 11=1/n*
I2* (transfer constant) In reality, it is often selected depending on the size of the element, economical efficiency, etc., but experimentally, the printing cycle is 2 mS, and the peak current is 1.5 A.
Under the conditions, L=300. czH, C1=470μF, C
It has been confirmed that if a value of about 1=470 μF is adopted, the power capacity can be reduced by about 30% compared to the conventional method.

As described above, by inserting a filter made of LC into the power supply to the print head portion, peak current can be suppressed, and the power supply can be expected to be made smaller.

〔Effect of the invention〕

As explained above, according to the present invention, the power capacity can be reduced by a simple method of inserting an LC filter into the power line that supplies the printer for printing.

Even smaller printers can be supplied.

[Brief explanation of drawings]

Figure 1 (al is a block diagram of the head drive section of a thermal transfer printer representing an embodiment. Figure 1 (b) is a time chart of the print head current of the embodiment. Figure 2 (a) is a block diagram of the head drive section of a conventional head drive section. Block diagram. Fig. 2 (bl is a time chart of print head current. In the figure. 1 is a control section, 2 is a head drive section, 3 is a print head section, 4 is a power supply. Q1 to Qn are switching elements. R1-Rn are resistors, L is a coil. C1 and C2 are capacitors. T1 is a printing period, T2 is a printing period, T3 is a non-printing period, Il is a power supply current, and T2 is a load current. So Tokikawa

Claims (1)

[Claims] A thermal printer that prints on recording paper by intermittently energizing the print head, which has one series coil and two parallel capacitors between the print head and a power source that supplies current to the print head. A thermal printer characterized in that it is formed by inserting a π-type filter.