JPH064332B2 - On-demand type inkjet head - Google Patents

Description

The present invention relates to an on-demand type inkjet recording head, and more particularly to a structure of electrical connection between a piezo element and a control circuit.

Conventionally, for electrical connection between a piezo element and a control circuit, a lead wire or the like is soldered to an electrode of the piezo element for signal transmission. With this connection structure, in a head having a plurality of piezo elements, it takes time and labor to solder each piezo element, and the vibration characteristics of the piezo element change depending on the amount of soldering, and uniform ink ejection is achieved. It had the drawback that it could not be done.

The applicant of the present invention has found that as a method of eliminating this drawback, Japanese Patent Laid-Open No.
It has been proposed that a flexible printed circuit board (FPC) as shown in Japanese Patent Application Laid-Open No. 7-41968 is directly pressed onto the piezo element to establish electrical connection with the control circuit.

In this structure, as shown in FIG. 5, the FPC 3 is brought into contact with the piezo element 2 on the head body 1, and the FPC 3 is pressed from outside by the head cover 4 via the elastic member 5. 6
Is a supply port for supplying ink to a pressure chamber (not shown) formed in the head body 1.

According to FIG. 5, it is possible to eliminate the above-mentioned problems in the soldering configuration in terms of workability and vibration characteristics.

The present invention is a further improvement of the conventional technique, and an object thereof is to ensure the connection between the electrodes of the piezo elements arranged corresponding to the pressure chambers and the FPC and to further improve the vibration characteristics of the inkjet head. To provide.

The present invention is directed to a piezo element and an FP arranged corresponding to a pressure chamber.
It is characterized in that an elastic member having conductivity is arranged between Cs.

One embodiment of the present invention is shown in FIG. FIG. 1 is a side view in which respective members constituting the inkjet head of the present invention are disassembled for easy understanding.

1 to 3 show a fifth example shown as a conventional example.
Members having the same numbers as those in the figure have the same functions.

Reference numeral 10 is an elastic member having conductivity, which is a feature of the present invention. As is clear from the figure, the FPC 3 is applied to the piezo element 2 of the head body 1 via the conductive elastic member 10, and the head cover 4 is pressed from both sides of the back surface of the FPC 3 via the elastic member 5 to fix it. The pressed state is shown in FIG. Further, as shown in FIG. 3, the FPC 3 has a connecting portion 39 that comes into contact with the electrodes of the piezo element 2 and a wiring portion 37 that connects to an external circuit (driving circuit or the like). Is coated.

The conductive member 10 may be a metal spring or the like in addition to the conductive polymer material and the conductive rubber, as long as it has elasticity. Above all, conductive rubber is optimal because it is thin, has good connection performance, and does not require man-hours for assembling. If this conductive rubber is mixed with metal or carbon and has conductivity only in the plate thickness direction, or that has conductivity only at the contact area with the piezo element, it can be sized to cover the piezo element and covered. Good.

As described above, according to the present invention, by interposing the elastic conductive member between the FPC and the piezo element,
Even if the individual piezo elements are uneven, or if the connection portion 39 of the FPC is lower than the insulating coating 38, the FP is surely
Electrical connection between the C connecting portion 39 and the piezo element 2 can be achieved.

Further, even if a voltage is applied to the piezo element 2 and the piezoelectric element 2 bends in the direction opposite to the conductive member 10, the piezo element 2 and the connecting portion 39 do not come into contact with each other because they are elastically pressed.

FIG. 4 shows the vibration characteristics (curve A) of the vibration system when the electrical connection of the conventional example was performed and the vibration characteristics (curve B) of the vibration system when the electrical connection of the present invention was performed. Has been done. As is clear from the figure, in the structure in which the elastic conductive member is interposed between the piezo element and the FPC of the present invention, the harmonic components are removed and the vibration is further attenuated as compared with the conventional example. It is possible to obtain good vibration characteristics and stable ink ejection characteristics. The improvement or stabilization of the vibration characteristics according to the configuration of the present invention will be described in detail below.

The wall of the pressure chamber in which the piezo element of the head is installed is thin enough to transmit the deflection of the piezo element to the pressure chamber, and the pressure source (vibration system) formed by this thin wall and the piezo element is used. ) Has a constant natural period, which also determines the ejection characteristics of the head. However, the characteristic of the natural period of the vibration system greatly changes the characteristics due to a delicate load.
Having a load on the piezo element or varying the load for each pressure chamber affects the ejection speed by making the natural period of the vibration system different. Further, having a load on the piezo element or varying the load for each pressure chamber reduces the amount of flexural displacement, affects the amount of ink, and causes the amount of displacement to vary from pressure chamber to pressure chamber.

The oscillating system consisting of the piezo element and the wall also functions as one wall surface that receives the pressure of the pressurizing chamber, and the thinly formed wall functions as the only compliance (softness) imparting part for the pressurizing chamber. ing.

The magnitude of this compliance is an important factor that determines the ejection characteristics such as the ejection speed of the ink droplets, the ejection amount, and the vibration period of the pressure wave. Impairing its softness due to electrical continuity lowers compliance, resulting in higher pressure, faster ejection speed, and less ejection stability. Further, the decrease in compliance also has a problem that it is easily affected by crosstalk and disturbance.

The present invention has been able to solve the above problems, can reduce the pressing force on the wall of the pressurizing chamber, and can even the pressing force between the pressure chambers, vibration The characteristics are improved, and further, the ink ejection characteristics are stabilized without being deteriorated, so that the ink ejection characteristics can be improved.

[Brief description of drawings]

FIG. 1 is an exploded side view showing an embodiment of the present invention, FIG. 2 is a partially enlarged view showing a state in which they are in close contact with each other, and FIG. 3 is a detailed view of an FPC. FIG. 4 is a diagram showing a comparison of vibration characteristics of the vibration system of the conventional example and the vibration system of the present invention. FIG. 5 shows a conventional example. DESCRIPTION OF SYMBOLS 1 ... Head body, 2 ... Piezo element 3 ... FPC, 4 ... Head cover 5 ... Elastic member 10 ... Elastic conductive member

Claims (1)

[Claims] 1. A nozzle which ejects ink, a pressure chamber which communicates with the nozzle, and a piezo element which is arranged in correspondence with the pressure chamber, and which is generated by applying a voltage to the piezo element. An on-demand type inkjet head that ejects ink droplets from the nozzles by utilizing flexure, a flexible printed board for connection between the piezo element and a control circuit that selectively generates a voltage signal, and the flexible printed board. A first elastic member having conductivity, which is arranged between the piezoelectric element and which relaxes pressing on the piezoelectric element; a second elastic member laminated on the flexible printed circuit board; and a second elastic member. A fixing member that is laminated on the member and presses and fixes the second elastic member, the flexible printed board, and the first elastic member in the direction of the piezoelectric element. An on-demand type ink jet head having: