Ink feeding circuit device for raster drawing machines

DESCRIPTION

Ink supply circuit device in raster drawing machines.

Scope

The object of the present invention is a damping device that allows the inkjet head to be isolated from the pernicious influences caused by overpressures and depressions, due to the effect of the inertia of the fluid that feeds the printing head, as well as the vibrations that originate during the operation of the drawing machine. The device is applicable to any drawing or printing machine using inkjet technology. State of the art

Raster-type drawing machines that use inkjet heads are widely known, but these machines (plotters) intended to work with large scanning distances on the heads, such as the one described in patent ES-9701193, work in conditions Difficult speed and acceleration in order to achieve high productivity. Usually these movements have sections of acceleration, constant speed and deceleration. In these changes of speed, pressure waves occur in the ink table subjected to the movement that produce situations of malfunction in the head. To reduce the mobile mass to the minimum necessary, the printing head is fed from a deposit far away from it, of sufficient size to allow great autonomy of the drawing machine, for this reason, oscillations occur that can greatly exceed the working range of the head preventing Its correct operation.

Summary of the invention

The present invention relates to a damping device, for pressure changes in the ink supply circuit to the print head. The device is formed by ducts provided with bifurcations, in which a gas that acts as a damper of the pressure wave is housed, while the ink is displaced through the main duct.

Description of the figures

Fig. 1.- Overview of the drawing machine.

Fig. 2.- Depression-time graph.

Fig. 3.- Scheme of the power circuit. Detailed Description

The device object of the invention is applied on a drawing machine (10) of the raster type as shown in Fig. 1 These drawing machines, have movement in the head holder (23) follow the plane (20), in two directions X and Y.

In the head holder (23), the ink jet head (1) is located and away from it, in a stationary area, a reservoir (2) responsible for supplying the ink (3). From the reservoir (2) to the head (1), located in the head holder (23), there is usually a significant amount of ink (4), contained in the conduction (31), which is subject to the movements of the head holder ( 23) mounted on the bridge (22).

The printing head (1) works so that, when applying electrical pulses on the walls that form the channels constructed of piezoelectric material, these are deformed producing a pressure that ejects the ink drop (5) it contains. The print head (1) requires that the ink level in the feed tank (2) be below the level (6) of the lowest nozzle, that is, it works with some millibars in depression.

The pressure waves produced in the ink table (4) by the accelerations or decelerations, generate a pressure (27) Fig. 2 at the entrance to the printhead (1), as shown in the depressioan-time graph of fig. 2 On said graph, the stable permissible zone (7) of the printhead (1) can be seen.

If a firing order is generated, that is, an electric pulse, when the head (1) is subjected to a pressure (27) that falls outside its permissible zone (7), a write failure occurs, consisting of the no ink drop or a defective shot.

The ink supply circuit incorporates a gaseous damper (9) so that the energy associated with the pressure wave (27) is used in the compression of the gas that is enclosed in the damping chamber (14). In Fig. 3, the ink supply circuit to the printhead (1) and the constructive form of the damper are observed. The ink supply circuit is constituted by a reservoir (2) with a lower opening (16), through which the ink (3). The ink is sent to the print head (1) through a generally flexible conduit (31), which at its end near the print head (1), intercalates a gas buffer (9) and joins the head (1) at the entrance mouth (17).

The gas damper (9), is formed by a tube (21) inside which a gas is housed and the ink surface (19) The space occupied by the gas constitutes the damping chamber (14).

The gas damper is oriented with the tube (21) in the vertical direction (25) and above the level (30) of the ink conduit (31), so that the gas always remains in said tube (21). ), both because of its lower density, as well as the opposition to the change produced by the surface tension in the meniscus formed on the surface (19), between the liquid fluid (4) and gas phases.

When the ink (3) is oil-based, the gas can get air.

The damping chamber (14) is sized so that its volume is sufficient to reduce the pressure wave (27) Fig. 2, to a value admissible by the head (1) generating a minimum rebound. This reduction is essentially based on a reversed function of the square volume of gas and the velocity of the pressure wave. The exposed device generates a certain rebound produced by expanding the gas again, but it is already produced with pressure values ​​(28) Fig. 2, much smaller, as can be seen in Fig. 2, and which do not interfere with the operation of the head (1). The device is located in the vicinity of the head so that its effectiveness is greater

ES 1 040 834 U