Ink jet recording head

Details Ink jet recording head Ink jet recording head

2002-10-31

2004-04-13

Nguyen, Judy (Department: 2861)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

Reexamination Certificate

active

06719411

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording head, and more particularly to a compact ink jet recording head with a high density of ink ejecting nozzles.
2. Description of the Related Art
Ink jet recording heads include a piezoelectric actuator and an ink chamber filled with ink. The piezoelectric actuator expands or contracts in accordance with a voltage applied thereto. This expansion or contraction applies pressure to ink in the ink chamber and ejects ink droplets from a nozzle in fluid communication with the ink chamber. To insure that the proper pressure is applied to the ink, the piezoelectric actuator must be capable of generating a certain amount of displacement.
In view of the requirement that a plurality of piezoelectric actuators be mounted on each recording head, the piezoelectric actuator needs to be very small. Accordingly, the piezoelectric actuator must be applied with a high voltage in order to obtain sufficient displacement to properly eject ink droplets. This causes problems such that the electronic components that make up the drive circuitry of the piezoelectric actuators need to be durable to a high voltage. Also, because the piezoelectric actuators can come into contact with ink, the piezoelectric actuators need to have high dielectric properties.
One solution to the above problems is using a piezoelectric actuator of a type in which a plurality of piezoelectric elements are stacked. Such type of piezoelectric actuator can use a lower voltage, so can overcome the above-described problems. However, the fixed end of the piezoelectric actuator must be fixed to a housing, and also needs to be very rigid when fixed to insure that displacement generated by the piezoelectric actuator is efficiently transmitted to the ink chamber.
Specifically, the fixed end of the piezoelectric actuator is rigidly secured to the housing while adjusting the position of the free end of the piezoelectric actuator to be in confronting relation with a nozzle. The free end of the piezoelectric actuator is attached to a diaphragm that defines an ink chamber. The diaphragm is also supported by the housing. To assemble the recording head, a plurality of piezoelectric actuators is mounted to be in alignment with the nozzle array. However, assembling the recording head in this manner is difficult due to the piezoelectric actuators being so small in size. Increasing the size of the piezoelectric elements would raise production costs because a large amount of piezoelectric plates is needed.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the above-described problems and to provide an ink jet recording head that enables a reduction in the amount of piezoelectric plate consumed, so that costs can be lowered, without lowering efficiency of the piezoelectric actuators, even if the piezoelectric actuators are only roughly fixed to the housing, and that also enables accurately and easily positioning the piezoelectric actuators with respect to the member that defines an ink channel.
To achieve the above and other objects, there is provided an ink jet recording head that includes a base having a mass mB (kg), a piezoelectric actuator, a nozzle plate formed with a nozzle, a diaphragm having a spring module kd, and an ink chamber in fluid communication with the nozzle. The piezoelectric actuator having a fixed end secured to the base and a free end opposite the fixed end contracts and extends in response to a drive signal having an edge rising time T
fall
(s). The free end of the piezoelectric actuator is attached to the diaphragm. The ink chamber has an inner space to be filled with ink having a spring module ki. The inner space is increased and decreased to eject the ink from the nozzle in accordance with contraction and expansion of the piezoelectric actuator. With the ink jet recording head thus constructed, a relation of 2×mB/T
fall
2
≧5.0 e
6
(N/m) is met according to the invention.
It is desirable that the piezoelectric actuator be formed with a plurality of piezoelectric elements and a plurality of electrically conductive plates alternately stacked one on the other. The plurality of electrically conductive plates serve as electrodes to which the drive signal is applied.
In addition to the above-noted relation, when the base is fixedly secured by a fixing material having a spring module kc
2
, a relation of 2×mB/T
fall
2
≧kc
2
is met according to another aspect of the invention. Further, various components of the ink jet recording head may be selected to satisfy a relation of (kd|ki)/[2×mB/T
fall
2
+kc
2
}≧5.02 e
−2
.


REFERENCES:
patent: 4364068 (1982-12-01), Lewis
patent: 5381171 (1995-01-01), Hosono et al.
patent: 6186619 (2001-02-01), Usui et al.

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