JPH04355147A - Ink jet recording head and driving method thereof - Google Patents

Abstract

PURPOSE:To realize the stable emission of ink and the desirable shape of an emitted ink droplet from the aspect of printing quality and to also realize the uniform emission of ink from a large number of nozzles arranged in high density. CONSTITUTION:One end of a plurality of rectangular pressure chambers 1 on the same plane communicate with a nozzle 3 and the other end thereof communicate with a common ink chamber 7 and the walls of the pressure chamber 1 are energized by the end parts of piezoelectric elements 15 having island- shaped protruding parts 13 at the centers thereof through a metal film 12. In a standby state, the piezoelectric elements 15 are in a charged state and the walls of the pressure chambers are in a preparatory displaced state and, when a printing signal is inputted, said elements 15 are rapidly discharged to further displace the walls of the pressure chambers to emit an ink droplet and gradually charged thereafter to return to the original standby state.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of an inkjet recording head suitable for an inkjet recording apparatus that performs recording by ejecting droplets, and a method for driving the same.

0002

[Prior Art] An inkjet recording head that utilizes longitudinal displacement of a piezoelectric element to displace a pressure chamber wall in the direction of the displacement, pressurizes ink within the pressure chamber, and jets ink droplets from a nozzle communicating with the pressure chamber. is published in Japanese Patent Publication No. 58-1198.
It is disclosed in Publication No. 72. However, since the natural vibration period of this type of drive unit is very short and the displacement speed is high, the disclosed drive method tends to suck air bubbles from the nozzle and lacks stability in ejection. It was also found that the ink droplets were ejected from the nozzle in a long and thin shape, and it was found that the shape of the dots on the paper surface was long and thin, degrading the print quality.

Furthermore, when a plurality of nozzles are arranged at a high density, the conventional example does not disclose a means for uniformly and reliably connecting the pressure chamber wall and the end of the piezoelectric element. It was found that it was difficult to eject ink droplets by

0004

[Problems to be Solved by the Invention] First, achieving stable and reliable ejection, second, achieving a shape of ejected ink droplets that is favorable for print quality, and furthermore, achieving consistent ink ejection from each nozzle in a large number of high-density nozzle heads. The purpose of the present invention is to realize the following.

[0005]

[Means for Solving the Problems] Accordingly, in the present invention, the pressure chambers and the flow paths communicating with the pressure chambers are set in consideration of ensuring the amount of ejected ink and the ability to discharge air bubbles, and the piezoelectric elements are attached to the walls of the pressure chambers. Constructed to provide displacement. Furthermore, as a driving method, the piezoelectric element is in a charging state in the standby state,
When a print signal is input, the pressure chamber wall is rapidly discharged to further displace the pressure chamber wall from the pre-displacement state to eject ink droplets, and then gradually charged and driven to return to the original standby state.

[0006] Furthermore, an island-like rectangular convex portion is formed on the outer wall of the pressure chamber at a substantially uniform distance from the periphery of the rectangular pressure chamber, and the convex portion is placed face down at the end of the piezoelectric element.

[0007]Furthermore, the flow passage portion was fixed outside and near both ends in the longitudinal direction of the pressure chamber by a fixing member that fixed the other end of the piezoelectric element.

[0008]

[Embodiments] The present invention will be explained in detail below according to embodiments. FIG. 1 is a perspective view of an embodiment of the flow path of an inkjet recording head according to the present invention, and FIG. 2 is a displacement plate 1 that is joined above the flow path to cover the flow path and receives displacement of the piezoelectric element.
This is an example of No. 1. FIG. 3 shows an embodiment of a drive section 20 including a piezoelectric element 15 that applies a predetermined displacement to the displacement plate 11. 4 shows the flow path in FIG. 1, the displacement plate 11 in FIG. 2, and the drive unit 20 in FIG. 3.
FIG. 5 is a perspective view of the recording head according to the present invention assembled with
4 is a sectional view taken along line A-A in FIG. 4. FIG.

In FIGS. 1 and 5, reference numeral 1 denotes a pressure chamber, and one end 4 of the pressure chamber 1 communicates with the nozzle 3 through a through hole 5.
The other end 6 of the pressure chamber 1 communicates through the throttle supply port 2 with an ink chamber 7 common to each pressure chamber. The through hole 5 is a circular flow path whose diameter is equal to the width of the pressure chamber 1. Ink enters the ink chamber 7 from an ink tank through a supply port 8. 10 is a nozzle plate having a nozzle 3, which is manufactured by electroforming or press working of a metal plate. The flow paths such as the pressure chamber 1 and the through hole 5 are made of a photosensitive resin such as a dry film. In the illustrated example, the nozzles are arranged in two rows in a staggered manner, but it is easy to arrange more than one row.

By forming the pressure chamber 1 into a rectangular shape as shown in the figure, it is possible to shorten the distance between adjacent nozzles, achieve high density, and arrange pressure chambers of a size necessary to obtain the amount of ink to be ejected. By making one end of the pressure chamber 1 the through hole 5 to the nozzle and the other end the constriction part 2, air bubbles will not remain in the pressure chamber.

In FIG. 2, the displacement plate 11 is a metal film 1.
2, an island-shaped convex portion 13 formed on the outer wall of the pressure chamber 1, and an outer peripheral portion 14 on the outside of the pressure chamber. The metal film 12 is preferably made of stainless steel, nickel, beryllium, titanium, etc., and has a thickness of 1 to 10 μm, preferably 2 to 5 μm.
It is μm. By using the metal film 12, the thickness can be uniformized over all the pressure chambers with high precision, so the stress applied to the metal film 12 can be managed and the discharge characteristics of each pressure chamber can be made uniform. The island-shaped convex portion 13 must be formed at a precisely constant distance from the outer periphery of the pressure chamber 1 when it is joined on the flow path, and must be formed to have a constant thickness. The protrusions 13 and the outer circumference 14 are preferably made of photosensitive resin, and after laminating the photosensitive resin on the metal film 12, exposure and development are performed to determine the position and thickness of the protrusion 13 and the outer circumference 14 with high precision. can be formed into The width of the convex portion 13 is 1/2 of the pressure chamber width.
or less.

In the driving section 20 of FIG. 3, numeral 15 denotes a stacked piezoelectric element, which is arranged in a high-density line corresponding to the arrangement of each pressure chamber 1. A non-overlapping portion of both electrodes on about half of one side of the piezoelectric element 15 is bonded to a fixing plate 16, and the fixing plate 16 is further firmly bonded or mechanically bonded to a second fixing plate 17. At this time, the free end surface 18 of the piezoelectric element 15 is on the same plane as the end surface 19 of the second fixing plate 17, or several μm to 10
Assemble accurately using a jig so that it protrudes by a micrometer. The fixed plate 16 to be bonded to the piezoelectric element 15 can be made of ceramic, metal, or plastic material. The piezoelectric element 15 is installed so that the stacking direction thereof corresponds to the longitudinal direction of the pressure chamber 1.

As shown in FIGS. 4 and 5, the displacement plate 11 is precisely positioned and joined on the flow path of the pressure chamber 1, etc., and the drive unit 20 in FIG. 3 is also mounted on the displacement plate 11. After precise positioning, it is installed using adhesive. That is, the displacement plate 11 is installed so that the convex part 13 is located exactly in the center of the pressure chamber 1, and the end surface 18 of the piezoelectric element 15 is placed on the convex part 13. The end surface 18 and convex portion 13 of the piezoelectric element 15 are also connected to the end surface 19 of the second fixed plate 17 and the displacement plate 1.
The outer circumferential portion 14 of 1 is joined. In particular, the end face 19 and the outer circumference 14 are joined and fixed outside the pressure chamber 1 and as close as possible. Moreover, the displacement plate 11 is fixed above the aperture supply port 2 while avoiding the ink chamber 7 so that the displacement plate 11 does not bend.

As will be described later, when the drive unit 20 is assembled and when ink is ejected, the drive unit 20 turns the displacement plate 11 upside down and deforms the flow path and even the nozzle plate 10. However, as shown in the figure, by fixing both ends of the pressure chamber, particularly both longitudinal ends of the pressure chamber having a long span, it is possible to prevent deformation from extending to the flow path and the nozzle plate 10.

FIG. 6 is a cross-sectional view taken along line BB in FIG. 4, and shows a slightly exaggerated deflection of the displacement plate 11 that occurs when the drive section is assembled with an adhesive. The displacement plate 11 in each pressure chamber is configured to be deflected in a range of about 0 to 15 μm. With respect to the joint surface between the end surface 19 of the fixed plate 17 and the outer peripheral portion 14 of the displacement plate, it is inevitable that the height of each convex portion 13 will vary by several μm, and the end surface 18 of the piezoelectric element 15 will also vary. By applying the deflection, the convex portion 13 on the outer wall of each pressure chamber and the free end surface 18 of the piezoelectric element can be reliably joined without separating.

FIG. 7 is a perspective view of one laminated piezoelectric element 15, in which thin layers of piezoelectric material 28 are laminated with electrode layers 21 in between, as shown, one electrode 23 and the other electrode 24. When an electric field is applied between them, they contract in the longitudinal direction in proportion to the piezoelectric constant d31, and when discharged, they return to their original state.

Next, the driving method will be explained. FIG. 8 shows an example of drive waveforms, in which 25 is a standby state in which the piezoelectric element is charged, 26 is a discharge period, and 27 is a recharging period. The displacement plate 11 is further rapidly displaced from the standby state as shown in FIG. 6 in the direction of arrow A by the discharge 26, pressurizing the ink in the pressure chamber and ejecting ink droplets from the nozzles. As the battery is subsequently recharged, the pressure chamber returns to its standby state.

Comparing the above driving method with a method of ejecting ink by first expanding the pressure chamber and then contracting the pressure chamber, it is found that with this method, an ejected ink droplet shape with a large main drop and small satellite drops is obtained; Therefore, more circular and larger dots can be obtained on the paper. The fact that satellite drops are small and have a slow ejection speed and are susceptible to bending ink droplets means that even if they bend, the effect on printing is small. More importantly, if a piezoelectric element having small pressure chambers arranged in high density and having high rigidity as described above is used as a drive source, a large negative pressure will be generated in the pressure chamber, but the drive method of this method It was found that if this was done, air bubbles would not be sucked in from the nozzle, and the discharge could be continued stably for a long period of time, even during intermittent use.

[0019]

As explained above, the inkjet recording head according to the present invention uses a laminated piezoelectric element to displace the pressure chamber wall in the direction of displacement of the piezoelectric element, and it is possible to arrange the nozzles at a very high density, while at the same time We were able to stabilize the ejection, improve the shape of the ejected ink droplets, and improve the variation in the ejection characteristics of multiple nozzles.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a flow path of the present invention.

FIG. 2 is a perspective view of a displacement plate used in the recording head of the present invention.

FIG. 3 is an explanatory diagram of a drive unit used in the recording head of the present invention.

FIG. 4 is a perspective view of a recording head according to the invention.

FIG. 5 is a sectional view taken along line A-A in FIG. 4;

FIG. 6 is a sectional view taken along line BB in FIG. 4;

FIG. 7 is an explanatory diagram of a laminated piezoelectric element.

FIG. 8 is an explanatory diagram of drive waveforms of the present invention.

[Explanation of symbols]

1 Pressure chamber 2 Throttle supply port 3 Nozzle 7 Ink chamber 10 Nozzle plate 11 Displacement plate 12 Metal film 13 Convex part 15 Piezoelectric element 20 Drive section 25 Drive waveform standby state 26 Discharge part of drive waveform 27　Drive waveform charging part 28 Adhesive

Claims (4)

[Claims] 1. An inkjet that utilizes the displacement of a laminated piezoelectric element to displace the wall of a pressure chamber in the direction of the displacement, pressurizes ink within the pressure chamber, and jets ink droplets from a nozzle communicating with the pressure chamber. In the recording head, the pressure chambers have a plurality of rectangular shapes on the same plane, and one end of each pressure chamber communicates with a nozzle, and the other end communicates with a common ink chamber through an aperture supply port. An inkjet recording head characterized in that a substantially central portion thereof is placed face down at an end portion of the piezoelectric element. 2. An island-like rectangular convex portion is formed on the outer wall of the pressure chamber at a substantially uniform distance from the periphery of the rectangular pressure chamber, and the convex portion is placed face down at the end of the piezoelectric element. The inkjet recording head according to claim 1. 3. A fixing member for fixing the other end of the piezoelectric element, and fixing the outside and the vicinity of both longitudinal ends of the pressure chamber by the fixing member or a second fixing member connected to the fixing member. The inkjet recording head according to claim 1. (1) In the standby state, the piezoelectric element according to claim 1 is in a charging state, and the pressure chamber wall according to claim 1 is in a pre-displacement state, and (2) when a printing signal is input, the piezoelectric element is rapidly discharged. and further displaces the pressure chamber wall to eject an ink droplet, (
3) A method for driving an inkjet recording head, which comprises gradually charging the head and returning to the standby state of (1).