Method And Apparatus For Aerodynamic Switching

Abstract

Filaments of fluid are stimulated with transducers to cause them to break up into uniformly spaced drops. The lengths of the filaments before they break up into drops are regulated by controlling the stimulation energy supplied by the transducers, with high amplitude stimulation resulting in short filaments and low amplitude stimulation resulting in long filaments. A flow of air is generated across the paths of the fluid at a point intermediate the ends of the long and short filaments. The air flow affects the trajectories of the filaments before they break up into drops more than it affects the trajectories of the drops themselves. Therefore, by controlling the lengths of the filaments the trajectories of the drops can be controlled, or switched, from one path to another. In a non-contacting coating system this provides means for directing some drops into a catcher while allowing other drops to be applied to a receiving member.

Description

BACKGROUND OF THE INVENTION

One form of noncontacting coating system, as disclosed in U.S. Pat. No. 3,560,641, employs a coating head which includes a series of closely spaced orifices through which filaments of coating material are projected under pressure. The filaments tend to break up into fine drops and the size and spacing of the drops can be closely controlled by imposing a high frequency vibration on the coating material supply system. An electrostatic deflecting field is positioned downstream of the orifices, and charge rings are positioned intermediate the orifices and the deflecting field to selectively apply charges to the filaments at the point at which they break up into drops. Charged drops are then deflected as they pass through the deflecting field while uncharged drops pass through the deflecting field without being affected thereby. By providing means for catching either the deflected or the nondeflected drops and controlling which drops are to be deflected, a patterned coating, such as printing, can be applied to a receiving member moving past the coating head.

SUMMARY OF THE INVENTION

The present invention provides a simplified system for switching drops of fluid along alternate trajectories without the use of electrostatic deflecting fields or the necessity of charging the fluid drops. This is accomplished by applying variable amplitude stimulation energy to the fluid filament. This causes the fluid filament to break up into drops at a frequency equal to the stimulation frequency but with a break off point which shifts with changes in applied stimulation energy. A high amplitude stimulation will result in a relatively short filament and a low amplitude stimulation will produce a relatively long filament.

An air flow is generated across the path of the fluid at a point intermediate the downstream ends of the long and short filaments. It has been observed that an unbroken fluid filament is affected by laterally blowing air to a greater extent than the trajectory of the drops themselves. Thus by selectively applying high and low amplitude stimulation to the fluid stream the path of the drops can be switched between two alternate trajectories. This principle may be applied to a single fluid filament or alternatively may be used for switching drops from a plurality of filaments.

In a noncontacting coating system this permits some drops to be applied to a receiving member while others are intercepted by a catcher. The stimulation energy can be applied to the fluid by means of a transducer driven by an amplifier capable of being switched from low or no amplification to relatively high amplification and controlling the amplifier in accordance with whether or not it is desired to switch a drop along a deflected or non-deflected path.

The air flow across the fluid path can be generated by means of a manifold operating under either positive pressure or a vacuum. In either case the air flow generated will affect the paths of the filaments more than the paths of the drops and control of the drop trajectories is thereby obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing, somewhat schematically, apparatus in accordance with the present invention;

FIG. 2 is a diagram illustrating a control circuit;

FIG. 3 illustrates graphically the selective amplification of the signals transmitted to the transducers; and

FIG. 4 is a cross sectional view showing the effect of amplitude variation on the length of the fluid filaments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As seen in FIG. 1 of the drawings, apparatus in accordance with the present invention includes a coating head 10 having a manifold 12 mounted over an orifice plate 14. A gasket 16 is interposed between the manifold and orifice plate and an inlet conduit 18 communicates with the interior of the manifold to supply coating material thereto. The orifice plate 14 is provided with a series of orifices 20, including an enlarged outer portion 22 and a portion 24 of restricted cross sectional area.

Mounted on the lower surface of the orifice plate 14, concentrically with respect to the restricted portion 24 of the orifices, are a series of transducers 26. Each of the transducers 26 is connected by means of lines 28 to amplifiers 30 (see FIG. 2 of the drawings). Each of the amplifiers 30 is driven by a constant amplitude power source 32 with which they are connected by means of the lines 34. The amplifiers 30 are preferably of the type which will transmit the signal from the source 30 at either different levels of amplification or transmit the signals amplified and unamplified.

In this regard control means 36 is provided connected to the amplifier by means of lines 38 to control the output of the amplifiers. Thus, as seen in FIG. 3 if the amplifiers 30 are driven by the power source 32 at a constant amplitude, as indicated at 40, the output from the amplifiers 30 may be varied between high and low amplification as indicated at 42 or, as noted above, between amplified and unamplified signals, by means of the control device 36. The effect of driving the transducers 26 at different energy inputs is indicated in FIG. 4 of the drawings. As indicated in FIG. 4, driving the transducer 26a at relatively high amplitude results in a relatively short filament 44a, with the filament 44a breaking up into discrete, substantially uniformly sized and spaced drops 46 at a break down point L.sub.h downstream of the orifice plate 14. On the other hand, the transducer 26b being driven at a relatively low amplitude results in a relatively long filament 44b which breaks up into drops 46 at a distance L.sub.1 downstream of the orifice plate 14.

As seen in FIG. 1 of the drawings a deflecting fluid manifold 48 having an elongated opening 50 formed in its wall is positioned downstream of the orifice plate to generate an air flow across the path of the liquid being projected from the orifices 24. The flow may be generated by either pressurizing the interior of the manifold to provide a flow of deflecting fluid away from the manifold or by placing the interior of the manifold under vacuum to provide a flow of deflecting fluid toward the manifold.

In either case the flow of deflecting fluid intersects the paths of the coating material filaments or drops in the region indicated in FIG. 4 of the drawings as L.sub.d, this being the region between the lower end of the relatively short coating filaments 44a and the lower ends of the relatively long coating filaments 44b. Positioned downstream of the manifold 48 is a catcher 52 having an upstanding sidewall 54, which together with an opposed portion of the top wall 56 defines an elongated, drop ingesting slot 58. Preferably the interior of the catcher 52 is placed under negative pressure to withdraw therefrom any coating material passing through the slot 58 into the interior of the catcher.

Beneath the catcher a receiving member 60 is conveyed in the direction indicated by the arrow by any convenient means, such as take up and feed rollers (not shown). Because the trajectory of the filament 44b of working fluid or coating material is affected by the flow of deflecting fluid to a greater extent than the trajectories of the drops 46, it will be seen that by shifting the point of intersection of the working and deflecting fluids the drops 46 can either be directed into the catcher 52 or allowed to pass the catcher 52 and be applied to the receiving member 60.

This accomplished in accordance with the present invention by varying the amplitude at which the transducers 26 are driven. Therefore, the deflecting fluid will intersect a filament of the working fluid if it is desired to deflect the working fluid a relatively large amount. By driving the transducers at a relatively high amplitude the deflecting fluid intersects the path of the drops of working fluid and consequently deflects the working fluid a relatively small amount.

It will be seen, therefore, that the present invention provides a system for switching drops of fluid without the necessity of charging the drops of fluid or establishing an electrostatic deflecting field for the deflection thereof.

While the methods herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention.

Claims

What is claimed is:

1. Apparatus of the type described comprising:

a. means for projecting a filament of working fluid,

b. stimulation means for breaking the working fluid filament up into a succession of discrete, substantially uniform sized and spaced drops of working fluid,

c. means for generating a flow of deflecting fluid intersecting the path of said working fluid, and

d. means for shifting the point of intersection of said working fluid and said deflecting fluid upstream and downstream of the point of break up of said filament into said discrete drops.

2. The apparatus of claim 1 wherein:

a. said shifting means comprises means for shifting said point of break down upstream and downstream of said point of intersection of said working fluid and said switching fluid.

3. The apparatus of claim 2 wherein:

a. said means for shifting said point of break up comprises means for controlling power input to said stimulation means.

4. The apparatus of claim 3 wherein:

a. said stimulation means comprises transducer means associated with said filament.

5. The apparatus of claim 1 wherein:

a. said deflecting fluid generating means comprises means for generating a flow of gas across said path of said working fluid.

6. The apparatus of claim 1 wherein:

a. said working fluid projecting means comprises means for projecting a filament of coating material.

7. The apparatus of claim 6 further comprising:

a. means for catching portions of said coating material deflected by said deflecting fluid a predetermined amount.

8. The apparatus of claim 7 further comprising:

a. means for transporting a receiving member past said coating material projecting means.

9. The apparatus of claim 7 further comprising:

a. a plurality of said coating material projecting means, and

b. said deflecting fluid generating means comprising means for substantially simultaneously intersecting the paths of the coating material projected by all of said coating material projecting means.

10. A method of switching comprising:

a. projecting a filament of working fluid,

b. stimulating said working fluid to cause it to break up into a series of discrete, substantially uniformly sized and spaced drops of working fluid,

c. generating a flow of deflecting fluid into intersection with said working fluid, and

d. varying the point of intersection of said working and deflecting fluids relative to the point of break-up said filament into discrete drops.

11. The method of claim 10 wherein:

a. said step of varying the point of intersection of said working and deflecting fluids with respect to said point of break-up comprises varying the length of said filament.

12. The method of claim 11 wherein:

a. said step of varying said filament length comprises controlling the degree of stimulation of said working fluid.