JPH0134155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a head driving method for an inkjet recording apparatus.

A conventional drive circuit of this type will be explained with reference to FIGS. 1 and 2. FIG. 1 shows a conventional circuit configuration, and FIG. 2 shows one circuit of a piezoelectric element head driver. In FIG. 1, the voltage generated by the head voltage source 1 is supplied to the head driver group 2, and the recording signal input group 3
The head driver group 2 selectively switches the piezoelectric element group 4 according to the signal input to the head driver group 2. The signal input to the recording signal input 3 is not input continuously, so the head voltage source 1 does not require constant output and constantly maintaining a specified voltage is a waste of power. This is uneconomical as it consumes a lot of energy. Further, in FIG. 2, when the piezoelectric element 4-n is switched in accordance with the recording signal input 3-n, the accumulated charge is transferred to the discharging resistor 5-n.
When the switching element 6-n is on, a current unrelated to the current flowing into the piezoelectric element 4-n flows through the discharging resistor 5-n, thereby wasting power. Because of the consumption, the output current capacity becomes large as a voltage source for a head, making it uneconomical and bulky. Further, this head voltage source 1 requires an output voltage of several tens to several hundreds of volts, and since a pulsed current flows when charging the piezoelectric element group 4, a large-capacity output capacitor is required.
Therefore, holding the output even when it is not needed may be dangerous in some cases.

Also, as shown in Japanese Patent Application Laid-Open No. 55-148169,
A piezoelectric element is connected in series to the switching element, an inductive element is connected in parallel to the piezoelectric element,
There was one in which ink was ejected by applying a back electromotive force generated in an inductive element to a piezoelectric element. However, in this case, since positive and negative alternating voltages are applied to the piezoelectric element, the piezoelectric element tends to deteriorate, which has the disadvantage of adversely affecting the life of the head.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the need for a high-voltage power supply to drive an inkjet head, to enable driving with a small and low power consumption drive power supply and drive circuit, and to apply a voltage to a piezoelectric element of a single polarity. That's all,
The object of the present invention is to provide a method for driving an ink jet head in which deterioration of the piezoelectric element is extremely unlikely to occur.

The present invention will be explained below based on Examples.

FIG. 3 shows an embodiment of the present invention. Input terminal 8
A recording signal having an appropriate pulse width as shown in FIG. 4A is input from the switching element 6-n.
, the switching element 6-n alternately turns on and off in accordance with the signal. When the switching element 6-n is on, a current supplied from the power supply terminal 7 flows through the inductive element 9 and the diode 10. Thereafter, at the moment when the switching element 6-n is turned off at the time point shown in FIG.
join. If the diode 10 is not present, LC oscillation occurs, but since the diode 10 prevents current from flowing into the inductive element 9, the voltage waveform across the piezoelectric element 11 is always unipolar as shown in FIG. 4B. Therefore, the piezoelectric element does not deteriorate. When this voltage is applied, the piezoelectric element deforms and ejects ink droplets. In the experiment, an inductor with an inductance of about 30mH was used as the inductive element 9, and 5V was applied to the power supply terminal 7.
Apply a voltage of approx.
After turning it on for 500μsec and turning it off,
A voltage of about 100V was obtained across the piezoelectric element 11.

FIG. 5 shows another embodiment of the present invention, in which a method for changing the voltage applied to the piezoelectric element 11 is added. This configuration is the same as the circuit shown in FIG. 3 except for the variable pulse width circuit 12. However, due to the action of the variable pulse width circuit 12, the switching element 6
-The time that n is turned on can be changed. As a result, the magnitude of the back electromotive force generated at the moment the switching element 6-n is turned off differs. That is, as shown in FIG. 6, the signal C applied to the switching element 6-n and the piezoelectric element 11
Voltage waveform D across both ends of (as in Figure 4, diode 1
If the current flowing through the inductive element 9 does not saturate and is used within the range where the magnetic saturation does not occur, the relationship between switching elements 6-n and 0 (always unipolar) is reversed when the switching element 6-n is on for a short time. Since the electromotive force is small, the voltage across the piezoelectric element 11 is low, and the longer it remains on, the higher the voltage becomes. If the voltage applied to the piezoelectric element 11 changes,
The size of the deformation of the piezoelectric element 11 changes, and as a result, the size of the ink droplet pushed out and the speed at which it pops out changes, so the recorded density can be changed, or conversely, unevenness in density due to temperature can be prevented. One possible application is correction.

7 and 8 show other embodiments in which a method for adjusting the voltage applied to the piezoelectric element 11 is added. In FIG. 7, the variable resistor 13 is connected to the inductive element 9.
By connecting in series with the diode 10,
The magnitude of the current flowing through the inductive element 9 is changed. As a result, the magnitude of the back electromotive force generated in the inductive element 9 changes, and the voltage applied to the piezoelectric element 11 changes.

In FIG. 8, a variable inductor 14 is used instead of the inductive element 9, and by changing the inductance, the magnitude of the back electromotive force is changed and the voltage applied to the piezoelectric element 11 is changed.

As described above, the present invention is completely different from the above-mentioned conventional method in that a high voltage is generated only when necessary, so it is possible to drive a piezoelectric element with a low supply voltage. Furthermore, as a result, a dedicated high-voltage power source is no longer required, so miniaturization, lower power consumption, and lower cost can be realized, which is advantageous in terms of safety. Furthermore, according to the driving method of the present invention,
A diode inserted between the inductive element and the piezoelectric element applies a unipolar drive voltage to the piezoelectric element, which prevents deterioration of the piezoelectric element, which can be a problem when driving the piezoelectric element to eject ink. It has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional configuration, and FIG. 2 is a circuit diagram showing a conventional piezoelectric element drive circuit. Fig. 3 is a circuit diagram showing one embodiment of the present invention, Fig. 4 is a signal waveform thereof, Fig. 5 is a circuit diagram showing another embodiment of the invention, Fig. 6 is a signal waveform thereof, and Fig. 7 is a circuit diagram showing an embodiment of the present invention. , 8th
The figures are circuit diagrams showing other embodiments of the present invention. 1... Head voltage source, 2... Head driver group,
3...recording signal input group, 4...piezoelectric element group, 5-n...
Discharge resistor, 6-n... Switching element, 7... Power supply terminal, 8... Recording signal input terminal, 9... Inductive element, 10... Diode, 11... Piezoelectric element, 12... Pulse variable circuit, 13... Variable resistor, 1
4...Variable inductor.

Claims (1)

[Claims] 1. Ink-on-demand in which a piezoelectric element is used as an electromechanical transducer, and a back electromotive force generated in an inductive element is applied to the piezoelectric element to pressurize an ink chamber and eject ink from pores for recording. In this method of driving an ink jet head, the piezoelectric element, the diode, and the inductive element are connected in series between power supplies, a switching element is connected in parallel to the piezoelectric element, and the switching element is turned on to turn on the inductive element. After passing a current through the element, the switching element is turned off and a unipolar back electromotive force generated in the inductive element is applied to the piezoelectric element via the diode, thereby pressurizing the ink chamber and ejecting ink. A method of driving an inkjet head characterized by performing the following steps.