Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-11-28
2002-09-03
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000
Reexamination Certificate
active
06443547
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving device and an inkjet recording apparatus, more particularly to a driving device for an inkjet recording apparatus which uses an acoustic transducer in the image recording system with liquid ink to supply alternative current signal to a piezoelectric element in order to eject liquid ink, and to an inkjet recording apparatus using the driving device.
2. Description of the Related Art
Inkjet printers, which may record images by ejecting fine particles of ink fluid so-called ink drops onto a recording medium to form dots thereon, have been in practical use. Some inkjet printers are known which make use of the operation of acoustic transducer for the device for ejecting ink drops onto a recording medium.
As an example, there is known technology described in the Japanese Patent Application Laid Open No. 5-278218 corresponding to the U.S. Pat. No. 5,191,354. An inkjet printer using the acoustic transducer may periodical perturbation on the free surface of liquid ink at any appropriate exciting frequency. If the amplitude of the perturbation pressure is more than the level of critical rising oscillation then one or more surface standing waves may be generated on the free surface of the liquid ink to cause to eject the ink drops to the recording medium. In order to generate such perturbation, the transducer may be driven by connecting it to a driver.
Also in the Japanese Patent Application Laid Open No. 8-187853 corresponding to the U.S. Pat. No. 5,589,864, a method using a piezoelectric device driven by RF signal for the transducer is disclosed. This method uses PIN diodes or varactors connected in series to the piezoelectric element to alter the impedance in case of a varactor to switch on and off the RF signal applied to control the ink drops being ejected.
In order to control the RF signal, another method in relation to the RF controller and the RF driver has been proposed by the inventor of the present invention for generating AC signal to the piezoelectric element without using any AC signal power supply (Japanese Patent Application Laid Open No. 11-72211). In this method the inductance connected in parallel to the piezoelectric element constitutes a parallel resonant circuit. A switching means supplies to the piezoelectric element alternatively the electric charge from a charge storage means and the energy from the resonant circuit to eject ink drops, without the need to ever supply AC signals, thereby resulting in the save of power consumed.
To speed up printing, a plurality of ink ejecting mechanisms, i.e., ink-drop ejectors may be provided aligned in one row to allow printing simultaneously in a plurality of positions. Nevertheless, the resulting dots with ink drops ejected by the RF signal may be dispersed. There is a need of restraining such dispersion.
A method has been proposed (Japanese Patent Application Laid Open No. 63-166545) which carries out the pulse-width modulation, amplitude modulation, frequency modulation of the RF signal to alter the size of ink drops. With this method, in other words, the appropriate use of frequency modulation and amplitude modulation as well as pulse-width modulation allows also the dispersion of the size of ink drops to be constant when a plurality of ink pools are provided.
In general, an RF power amplifier of class-A or class-AB is used for the RF controller, i.e., transducer driving circuit. In order to achieve higher speed printing by providing a plurality of ink ejectors as a printing head, a plurality of driver circuits should also be provided, one for each respective ejector. In this condition in the plural drivers the output impedance of the RF power amplifiers is usually 50 &OHgr;, the impedance of connecting wires also is 50 &OHgr;. In such circuit, the “Q” of the resonant circuit will become about 1 by the output impedance if the load varies, since the load is much greater than the output impedance. The resonant circuit thereby will be in a forced drive condition (Q<1) or the like to prevent frequency shift from occurring when the load capacitance is varied by the printing patterns.
However, it is difficult to hold constant the energy to be transferred to each respective of the printing heads in case of the fluctuation of load, provided that the constant voltage characteristics are ensured in each of printing heads. As a result, it is supposed that the dispersion of energy transferred to each of printing heads may affect to the printing quality. Thus it has been required to prevent the dispersion of energy transferred to each printing head by using frequency modulation, amplitude modulation, and pulse-width modulation as described above.
The frequency modulation, amplitude modulation, and pulse-width modulation, as well as the combination thereof, makes the driver circuit complex and costly.
In addition, inkjet printers have the problem of low efficiency of ink-drop ejection. In other words, driving current is supplied to the piezoelectric elements for producing ink drops, however only a fraction thereof is used for producing ink drops.
When considering that large amplitude is required for the signal input to the switching means for supplying the energy to the piezoelectric element in the inkjet printers, the ejecting efficiency of ink drops is not sufficient if the power consumption for generating input signal is included.
In order to control the ink ejection by turning on and off the RF signal, a switching circuit may be used for switching on and off to control AC signal. On example of AC signal control is the method disclosed in the Japanese Patent Application Laid Open No. 5-318595. In this method, as shown in
FIG. 21
, a diode switching circuit for controlling a required AC electric signal by applying DC signal to the diode comprises a resistor (Ra
1
) connected in series with an inductive element (La
2
) and in parallel to a capacitor (Ca
1
) as the driving device of inkjet printing head for recording using ink mist. In this circuit, in parallel to the printing head (HEAD), an AC element inductance (La
1
) is provided at the output side of diode (Da
1
) but a DC element capacitor is not used in order to minimize the propagation loss of AC electric signal (which is the signal output from an RF amplifier (RFA)).
Also in order to facilitate switching of an amplified RF signal, the method described in the Japanese Patent Application Laid Open No. 10-199995 discloses the RF switching provided with high-voltage CMOS diode.
In this RF switching circuit, RF switching elements such as high voltage diode and varactor are used since RF signal amplified by the radio frequency amplifier circuit has to be switched. As an example, as shown in
FIG. 22
, in the ink ejector mechanisms (ink-drop emitting mechanisms) arranged in one row for accelerating printing speed, a group of oscillators AcT having a plurality of columns of oscillators may be operated as a printing head. A controller CT for line control is connected at the controller side of each of the plurality of oscillators Ac
1
to Acn. A group of circuits ROW having a plurality of column switching circuits are connected at the input side of the plurality of oscillators Ac
1
to Acn. Each of the plurality of column switching circuit RW
1
to RWn may be selectively operated by the selection signal from the column selection signal output circuit SEL. AC electric signal (signal output from the RF signal source RF and amplified by the RF amplifier RFA) is also input to each of the column switching circuits RW
1
to RWn. In this circuit, RF switching elements such as high-voltage diode and varactor are required for the RF signal amplified by the RF amplifier RFA to be switched in each of respective column switching circuit RW
1
to RWn.
However in this arrangement the problems of decrease of energy efficiency and degradation of isolation between columns may not be avoided, since the RF signal is switched by the RF switches after amplification, even if such RF switching elements as a hi
Hiratsuka Masashi
Kondoh Yoshinao
Mihara Akira
Takahashi Kunihiro
Barlow John
Dudding Alfred
Fuji 'Xerox Co., Ltd.
Morgan & Lewis & Bockius, LLP
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