JPS5815168Y2 - Ink head drive circuit of inkjet printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink head drive circuit for an inkjet printer.

FIG. 1 is a cross-sectional view showing an ink head of an inkjet printer called a pulse pressure type inkjet printer. 1 is a bimorph in which a piezoelectric element 2 and a metal plate 3 are bonded together, and this bimorph 1 is to which a pulse signal is applied. It has the characteristic of being curved.

4 is an annular spacer with one end attached to one surface of the bimorph 1; 5 is a front plate that covers the other end of the spacer 4; a space surrounded by the front plate 5, the annular spacer 4, and the bimorph 1; That is, the ink chamber 6 is filled with ink from the outside.

Incidentally, an ejection lower for ejecting ink is provided approximately at the center of the front plate 5.

When a pulse signal is applied to an ink head with such a structure,
The bimorph 1 is curved in a direction that reduces the volume of the ink chamber 6, and ink droplets are ejected from the ejection lower part of the front plate 5.

The size of the ink droplet ejected in this manner is proportional to the curvature of the bimorph 1.

That is, by controlling the pulse signal applied to the bimorph 1, ink droplets of any size can be easily obtained.

The present invention relates to a drive circuit suitable for controlling the size of ink droplets ejected from the above-mentioned ink head according to pixel signals having halftones to obtain prints having halftones. This will be explained in detail with reference to.

FIG. 2 is an electrical circuit diagram of the present invention, in which numeral 10 is the ink head detailed in FIG.
Trl is a main transistor inserted in series between the high reference power source 11 and the ink head 10, and Tr2 is a drive transistor that controls drive in response to a drive signal applied to the ink head 10 as a base. A main circuit is composed of the transistor Tr2, the ink head 10, and the main transistor Tr1.

The feature of the present invention is a control circuit that controls the main transistor Tr1 to eject ink droplets of a size according to a pixel signal.

This control circuit includes a control transistor Tr3 whose collector is connected to the base of the main transistor Tr1, a Zener diode D as a reference voltage element provided between the emitter of the control transistor Tr3 and the ground,
an inverting amplifier 13 inserted between the base of the control transistor Tr3 and a pixel signal source 12 having a halftone;
an amplification variable resistor Ra connected between the input and output of the inverting amplifier 13 and setting the amplification factor of the inverting amplifier 13; and a first variable resistor between the inverting amplifier 13 and the base of the control transistor Tr3. R1, and a second variable resistor R2 between the base of the control transistor Tr3 and ground;
The output of the main transistor Tr1 is controlled by the control transistor T.
A feedback resistor Rf provides negative feedback to the base of r3.

The present invention uses three variable resistors Ra, R of such a control circuit.
1 and R2 to drive the ink head 10 with an applied voltage suitable for the ink head 10.

A pixel signal Vi output from the pixel signal source 12 is input to a non-inverting input terminal of an inverting amplifier 13 via an input resistor Ri.

On the other hand, a comparison voltage Vr is applied to the inverting input terminal of the inverting amplifier 13.

The output V of the inverting amplifier 13 at this time.

is the resistance value of the input resistor Ri, and the amplification factor variable resistor R is
If the resistance value of a is Ra, then Vs=-Ra/R1・Vi
+'(1+Ra/R1)Vr -------(1).

In equation (1), Ra/R1 is the amplification factor of the inverting amplifier 13, and if Ra/Ri-α is substituted, equation (1) can be rewritten as %.

If these two equations are represented graphically, it will look like Figure 3.

When the amplification factor α of this inverting amplifier 13 is increased, (2)
The slope and intercept change as if the equation is not clear.

Rotate clockwise around the center.

On the other hand, if the amplification factor a is decreased, ■. rotates counterclockwise.

Note that this amplification factor α is determined by the resistance value Ra of the amplification factor variable resistor Ra.
A desired value can be obtained by varying .

Next, the applied voltage vh applied to the ink head 10 is the first voltage vh.
・If the resistance values of the second variable resistors R1, R2 and the feedback resistor Rf are R1, R2, Rf, then the above vh is: Vh: (1+payment)vg-1(vo-vz)--
(3) Approximately obtained by R2R1.

However, Vz is determined by the Zener voltage of the Zener diode D at the base potential of the control transistor Tr3.

In formula (3), 1+Rf/R2=β, Rf/R□=γ
(3) Formula % Formula % (4)

Figure 4 shows ■ in equation (4) above. This is a graph showing the relationship between vh and vh. When β is constant, that is, R2 is fixed, when γ (R1) is varied, only the slope of vh changes as shown from a to b.

On the other hand, when γ=constant (that is, the slope) is constant and β (R2) is varied, the intercept moves from b to C in parallel to the vh axis direction.

FIG. 5 is a graph showing the relationship between the pixel signal Vi and the voltage vh applied to the ink head 10.
and a′.

b' and C' correspond.

Ink head 1 while referring to the graphs in FIGS. 3 to 5 above.
A method of adjusting the applied voltage vh suitable for 0 will be described below.

As mentioned earlier, the ink head 10 ejects ink droplets with different diameters depending on the magnitude of the applied voltage vh applied to the ink head 10, but the operating voltage varies depending on the individual ink heads 10. Therefore, even if the maximum pixel signal Vim that causes ink droplets with the largest diameter to be ejected arrives, only small ink droplets are ejected, or because the rate of change of the voltage applied to the ink head is different with respect to the intermediate tone pixel signal Vi. Printing with shifted gradations may not be possible.

In that case, it can be adjusted independently using the second and first variable resistors R2 and R1.

That is, first, when the amplification factor α of the inverting amplifier 13 is the maximum pixel signal Vim at the amplification factor variable resistor Ra, the output ■ is generated.

is set so that it becomes approximately the Zener voltage Vz.

(Figure 3A). Next, the resistance value R1 of the first variable resistor R1 is varied so that the diameter of the ink droplet changes according to the rate of change of the pixel signal Vi (FIG. 5 a', 1)').

Then, the second variable resistor R2 is varied so as to eject an ink droplet with the largest diameter for the largest pixel signal Vim, and the first variable resistor R1 is first adjusted to obtain a slope β.
(Fig. 5 b', C')
.

Finally, a curve of the applied voltage vh applied to the ink head 10 with respect to the pixel signal Vi is set.

The output Vs of the high reference power source is applied to the ink head 10 via the main transistor Tr1 controlled according to the pixel signal Vi, and ink droplets are ejected from the ink head 10 in synchronization with the driving of the drive transistor Tr2. Injected.

As is not clear from the above description, the present invention uses a first variable resistor to connect a main transistor that is connected in series to a high reference power source and supplies an applied voltage to an ink head that ejects ink droplets to generate a pixel signal. The rate of change of the voltage applied to the ink head relative to the maximum pixel signal is controlled by the second variable resistor, so that the optimum voltage applied to the ink head can be adjusted. It can be driven by

Further, the adjustment can be performed separately using independent first and second variable resistors.

Therefore, by simply adjusting two independent variable resistors, it is possible to obtain ink droplets with a diameter that corresponds to the pixel signal, and it is possible to obtain elegant printing.

This effect is particularly remarkable when printing pixel signals having intermediate tones.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing an example of an ink head driven by the ink head drive circuit of the present invention, Figure 2 is an electric circuit diagram of the drive circuit of the present invention, and Figure 3 shows the relationship between pixel signals and the output of the inverting amplifier. FIG. 4 is a diagram showing the relationship between the output of the inverting amplifier and the voltage applied to the ink head, and FIG. 5 is a diagram showing the relationship between the pixel signal and the voltage applied to the ink head.
10 is an ink head, 12 is a pixel signal source, 13 is an inverting amplifier, Trl is a main transistor, Tr2 is a drive transistor, Tr3 is a control transistor, Ra is an amplification variable resistor, R1, 'R2 are first . The second variable resistors, D each represent a Zener diode.

Claims (1)

[Scope of utility model registration request] In the ink head drive circuit of an inkjet printer, which prints characters, symbols, etc. by ejecting ink droplets when a pulse signal is applied, there is a main transistor connected in series to a high standard power source, and a main transistor that receives the output of the main transistor. The main transistor includes an ink head that ejects ink droplets, and a drive transistor that drives the ink head. a reference voltage element provided between the ground, an inverting amplifier inserted between the base of the control transistor and the pixel signal source, and a first variable resistor between the inverting amplifier and the base of the control transistor. a second variable resistor between the base of the control transistor and ground, and a feedback resistor for negative feedback of the output of the main transistor to the base of the control transistor. , the first variable resistor adjusts the rate of change of the voltage applied to the ink head with respect to the pixel signal, and the second variable resistor determines the maximum voltage applied to the ink head with respect to the maximum pixel signal. An ink head drive circuit for an inkjet printer, characterized in that the ink head is driven by an applied voltage according to the applied voltage.