JPS6363379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink supply device for an inkjet head in which the head is scanned, and a device for suppressing ink pressure fluctuations in an ink supply pipe connected to the head to obtain stable ink pressure. aim at something.

In a device such as an ink jet head that ejects ink for recording, one of the important issues is to maintain the ink meniscus at the ink ejection port in a stable state. Particularly in ink-on-demand type ink jet heads, the state of the meniscus of the ink ejection opening is one of the factors that determines the minimum driving voltage required for ink ejection. Furthermore, when the ink pressure fluctuations generated in the ink supply pipe connected to the head are propagated inside the head, the state of the meniscus at the ink ejection port becomes extremely unstable, causing the following serious drawbacks. That is, when the pressure fluctuation of the ink acts on the positive pressure side, the meniscus of the ink ejection port is pushed toward the recording paper side and flies as a droplet. This phenomenon is noticeable in heads with airflow effects.
On the other hand, the meniscus of the ink ejection port that acts on the negative pressure side becomes concave toward the inside of the head and ruptures, allowing air to enter the inside of the head in the form of bubbles. If air bubbles exist inside the head, the ink pressure waves generated by the electro-vibration conversion element are absorbed by the air bubbles, making ink ejection unstable and, in severe cases, causing inability to eject. The minimum value of the ink pressure fluctuation that has such an adverse effect as described above is a small value of ±0.05 kg/cm ² in an ink-on-demand type head.

The ink pressure fluctuations that make the meniscus of the ink ejection port unstable as described above are mostly caused by vibrations and impacts of the ink supply tube, so it is necessary to smooth the movement of the ink supply tube. However, this alone cannot sufficiently suppress ink pressure fluctuations. That is, when the ink supply pipe undergoes accelerated movement, a relative movement occurs between the ink supply pipe and the ink, resulting in pressure fluctuations that are propagated to the head. This will be explained in more detail with reference to FIG.

FIG. 1a shows a scanning system of heads and ink supply tubes. An ink supply tube 2 is connected to the head 1 in a U-shape on one side, and scans between and and indicated by dotted lines in the figure. At this time, the ink pressure fluctuation at point A, that is, head 1
The pressure fluctuations propagated therein and the scanning speed of the head 1 are shown in FIG. 1b, with time on the horizontal axis.
The states in which the head 1 is in the positions , , , in FIG. 1a correspond to the positions , , and in FIG. 1b, respectively. In the state of a, that is, when the head 1 is moving at a constant velocity, the pressure fluctuation at point A is almost 0 (as in b). However, the state of a,
In other words, when head 1 starts to decelerate, stops, and then accelerates in the opposite direction again, the inertia of the ink in the ink supply tube (upper part of the horizontal U-shape) that was moving to the left causes pressure to rise to the positive pressure side at point A. Variation occurs (b
of). On the other hand, in condition a, the ink supply tube was moving to the right (upper part of the U-shaped sideways)
There is almost no ink pressure fluctuation within the cylinder, and on the contrary, when the ink at point A is accelerated to the left, the ink at point A is pulled, and the pressure fluctuation occurs slightly on the negative pressure side (b). Therefore, in the head scanning system as shown in FIG. 1, when the head comes to the position , the pressure fluctuation at point A becomes the largest, and the state of the meniscus at the ink ejection port becomes unstable. The head is on the left,
FIG. 2 shows a head scanning system in which the ink pressure fluctuations are the same when reaching the right end.

The ink supply pipe 2 is connected to the first ink supply pipe 2 as shown in FIG.
Place the one in the picture on the opposite side to create a symmetrical loop shape. By making the ink supply tube 2 into a loop shape, the ink inside the tube 2 moves, albeit slightly, within the loop when subjected to acceleration, so the pressure fluctuation at point A is as shown in Figure 1. Since it is smaller than that of b and is symmetrical, the same value is shown for the position of b.

The ink pressure fluctuation at point A near the head shown in FIGS. 1 and 2 increases with the scanning speed and acceleration of the head 1. When the scanning of the head 1 is sub-scanning as in a cylindrical scanning system, the scanning speed is slow and hardly any problem occurs. However,
In the case of main scanning, such as in a plane scanning method, this problem becomes more important.

The object of the present invention is to block and alleviate ink pressure fluctuations in the vicinity of the head, particularly during acceleration and deceleration of head scanning, so that the fluctuations do not propagate to the head.

The present invention is characterized in that a fluid control valve having a movable element is provided inside a chamber having two openings. FIG. 3 shows an embodiment of the invention. 3 is a tubular body whose inner diameter is largest at the center and smallest at both ends.
Inside the body 3, there is a spherical movable element 4, such as a steel ball, which has a diameter smaller than the inner diameter of the center part and larger than the inner diameters of both ends. In this device,
FIG. 4 shows the pressure fluctuation at point A and the scanning speed of the head when the head 1 is scanned. Now, if the speed when the head 1 is scanned to the left in Fig. 3 is given as Move to the left side of 3 and close the opening on the left side to prevent pressure fluctuations from propagating. Conversely, when acceleration as shown in FIG. 4 is applied, the opening on the right side of the body 3 is closed to prevent pressure fluctuations from propagating. The state in Figure 4, i.e. head 1
is scanning at a constant speed, the spherical movable element 4
is located approximately at the center of the body 3 and does not block the ink supply pipe 2.

The most important feature of this fluid control valve is that the head 1
The acceleration/deceleration with the largest pressure fluctuation propagated to
The movable element 4 blocks the ink supply pipe 2, making it difficult for pressure fluctuations to be propagated to the head 1. In reality, some pressure fluctuation is propagated toward the head 1 until the spherical movable element 4 closes the opening, but the amount is small as shown in FIG. In order to more completely block pressure fluctuations, it is necessary to make the movement stroke of the spherical movable element 4 as short as possible, and to minimize the difference between the diameter of the spherical movable element 4 and the inner diameter of the central part of the body 3. , must be determined with consideration to securing the minimum ink supply amount.

Further, FIG. 5 shows an example in which the present invention is applied to the head scanning system shown in FIG. 2, and FIG. 6 shows the pressure fluctuation at that time. In this case, the fluid control valve is connected to the ink supply pipe 2 near the head 1, which is branched from the head 1.
be installed respectively. The operation is the same as that shown in FIG. 3, and the explanation will be omitted. Since the head scanning system shown in FIGS. 3 and 4 is symmetrical, more stable ink pressure can be obtained.

As explained above, the present invention is an ink supply device characterized in that a part of the ink supply pipe near the head is equipped with a fluid control valve having a movable element inside a chamber having two openings. It is possible to sufficiently block and alleviate ink pressure fluctuations that occur during acceleration and deceleration of head scanning.

[Brief explanation of drawings]

FIGS. 1a and 1b are a schematic diagram showing a scanning system of an ink supply device in a conventional ink jet head recording apparatus and its operating characteristic diagram, respectively, and FIGS.
b is a schematic diagram showing the scanning system of another conventional ink supply device and its operating characteristic diagram, FIG. 3 is a partially sectional side view of the ink supply device in an embodiment of the present invention, and FIG. FIG. 5 is a partially sectional side view of another embodiment of the ink supply device according to the present invention, and FIG. 6 is an explanatory diagram of the operation of the ink jet recording device shown in FIG. be. 1... Head, 2... Ink supply pipe, 3... Body, 4... Spherical movable element.

Claims (1)

[Claims] 1. An ink supply pipe leading to a reciprocating ink jet head branches into two directions, and a chamber having two openings in a portion of each ink supply pipe near the head has a diameter larger than that of the two openings,
A valve is provided with a spherical movable element having a diameter smaller than the inner diameter of the central portion of the chamber, and when acceleration is applied to the ink supply pipe, the movable element blocks the supply path to the head. Ink supply device.