US3903939A

US3903939A - Fluidic deposition control

Info

Publication number: US3903939A
Authority: US
Inventors: Charles G Pickett
Original assignee: Bio Medical Sciences Inc
Current assignee: Bio Medical Sciences Inc
Priority date: 1974-04-01
Filing date: 1974-04-01
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09

Abstract

The deposition of liquid material by displacement of tubular needle is controlled in-line through directing a stream of pressured fluid at deposited material which has solidified, sensing the change in back pressure relative to a preselected value by means of proportional fluidic element, and increasing or decreasing the pressure under which the material is deposited in response to decrease or increase, respectively, in the back pressure. An apparatus for in-line control of the deposition includes a fluidic probe, a proportional center dump fluidic element, a source of pressure and a vessel in which the material to be deposited is held under a closed head space.

Description

Sept. 9, 1975 FLUIDIC DEPOSITION CONTROL Charles G. Pickett, Andover, NJ.

Bio-Medical Sciences, Inc., Fairfield, NJ.

Filed: Apr. 1, 1974 Appl. No.: 457,121

Inventor:

Assignee:

US. Cl 141/1; 117/37 R; 118/8; 137/805; 141/153; 141/198 Int. Cl. B65B 3/26; F15C 4/00 Field of Search 117/37 R; 118/8; 137/805, 137/836, 557; 141/1, 11, 31, 94, 95, 82, 83, 138, 139, 153, 198, 237, 270, 279, 284

[56] References Cited UNITED STATES PATENTS 3,581,754 6/1971 Adams 137/805 Primary Examiner-Richard E. Aegerter Assistant Examiner-Frederick R. Schmidt Attorney, Agent, or F irm-Anthony Lagani, Jr.

ABSTRACT The deposition of liquid material by displacement of tubular needle is controlled in-line through directing a stream of pressured fluid at deposited material which has solidified, sensing the change in back pressure relative to a preselected value by means of proportional fluidic element, and increasing or decreasing the pressure under which the material is deposited in response to decrease or increase, respectively, in the back pressure. An apparatus for in-line control of the deposition includes a fluidic probe, a proportional center dump fluidic element, a source of pressure and a vessel in which the material to be deposited is held under a closed head space. I

8 Claims, 1 Drawing Figure 37 as k 42 43 TO REJECT FLUIDIC DEPOSITION CONTROL DETAILED DESCRIPTION The present invention pertains to a method and device for controlling material deposition in manufacturing procedures.

US. Pat. No. 3,810,779 and its Belgian counterpart No. 784,429, describe a method and apparatus for depositing precisely metered quantities of a liquid on a surface. In this technique, a tubular needle is positioned vertically over the surface on which the deposition is to occur. A reservoir of the liquid to be deposited is maintained above the surface and in communi cation with the needle with the surface level of the reservoir or pool being at or slightly below the lower tip of the needle. In this relationship, no head pressure is exerted in the liquid at the lower tip end of the needle and as a result of capillary action, the needle remains filled with liquid at all times. The needle is then displaced downwards and as a consequence of the resultant head pressure and kinetic action, a globule or ball of liquid is formed at the tip of the needle. The downward displacement of the needle terminates as the globule makes contact with the surface and as the needle is then retracted to its initial position, adhesion of the liquid to the surface results in the deposition of the globule of liquid on the surface.

This technique has proven especially valuable in those mass production procedures in which a plurality of extremely accurate amounts of liquid must be deposited on a surface, as in the production of disposable thermometers of the type described in US. Pat. No. 3,665,770. The control and reproducibility of such factors as the inside diameter of the needle, the uniform displacement distance the needle travels and the maintenance of a substantially uniform level of liquid in the reservoir have permitted a degree of deposition control heretofore unobtainable. For example, for a plurality of deposits, this technique permits control of the amount deposited to from 25 to 30 ug for i l sigma limits, 50 to 60 ug for i 2 sigma limits and 75 to 90 ug for i 3.0 sigma limits. Even greater control however would be desirable.

The present invention provides a method and apparatus for achieving improved control in this technique. The invention has as one objective the in-line control of deposition based on corrective quality monitoring. A further objective is the direct fluidic examination of each deposition and not only rejection of those items which are clearly unacceptable but more importantly, the positive adjustment of the deposition system through fluidic means to correct any deviation trends appearing in a series of such depositions.

These and other objectives will be apparent from the following description and the accompanying drawing which is a schematic representation of the system and the apparatus. 9

Referring to the drawing, surface 11 having cavities l2 and 13 formed therein as by embossing, punching, casting or the like, is positioned under tubular needles 14 and 15. The nature and number of cavities as well as the nature of the surface is relatively unimportant although the present device permits a large number of accurate simultaneous deposits. Tubular needles l4 and 15 are rigidly fixed to sliding block assembly 16 which is mounted for vertical travel with respect to an upright support (not shown). The position and movement of needles 14 and 15 in the sliding block assembly with respect to surface 11 is identical with that described in US. Pat. No. 3,810,779. The upper end of needles 14 and 15 is connected to a reservoir-refill system. While this system is shown only for needle 14, it will be understood that a parallel system is connected to needle 15 and to every needle mounted in sliding block assembly 16, of which there may be as many as 50, or more. Flexible tube 17 is connected at one end to needle 14 and at the other to holding vessel 18. Vessel 18 is operable to maintain the deposition material 19 contained therein in a liquid condition; e.g., the material may be maintained in a mblten condition at a temperature above its melting point, in a solution in a readily vaporized solvent, or the like. A refill reservoir 20 is in turn connected to vessel 18 through conduit 21. A pair of

thermistors

22 and 23 are positioned within vessel 18 and are in electrical connection with comparator unit 24. When the level of liquid 19 falls below the level of thermistor 23, the unbalance in the electrical bridge of comparator 24 activates and opens solenoid operated valve 25. As the level of liquid 19 rises and reaches thermistor 22, the bridge of comparator 24 is brought back into balance and valve 25 is closed. As a result, the level of liquid 19 is always maintained within two predetermined limits. The foregoing elements are essentially identical with those described in US. Pat. No. 3,810,779. In contrast to the prior art device, vessel 18 is not in communication with the atmosphere but rather has a closed head space, shown generally at 26. Moreover, vessel 18 need not be positioned so that the surface of liquid 19 is at or slightly below the tip of needles l4 and 15.

Following displacement of the needles 14 and 15 downward in a unitary motion and deposition of liquid material 19A in cavities l2 and 13 of surface 11, the surface is advanced and the next cavities to be filled are moved into position under needles 14 and 15. As the filled cavities are moved away from the filling station, the liquid material is solidified. For molten material, this is accomplished either by allowing the materials to assume ambient temperature or through passage of the material through a chilling station (not shown). When a solvent system is employed, the solvent can be evaporated or a coagulant may be added. After the material has solidified, the surface is passed under fluidic probe 31. A plurality of fluidic probes can be provided, one for each deposition system. In the example shown, the material deposited in cavity 12 by needle 14 is positioned under fluidic probe 31 while the material deposited in cavity 13 by needle 15 is positioned under fluidic probe 32. By disposing the fluidic probes in the same configuration as the cavities (and the deposition needles), these positionings are accomplished simultaneously.

Fluidic probe 31 is in communication with a source of pressurized fluid (not shown) such as a compressed air which is introduced into the system as at 33. Since each fluidic probe has a parallel circuit, of which only one is shown in the drawing, a single source of pressurized fluid can be passed through distributing valve 34, each outlet port of which is associated with a fluidic circuit and fluidic probe. After distribution, the pressurized fluid is conveyed through conduit 35 to parallel

variable restrictors

36 and 37. The output from variable restrictor 36 is in turn taken through conduit 38 to fluidic probe 31 and through conduit 39 to the first control port 40 of proportional fluidic element 41. Input port 42 of fluidic element 41 is connected to vari able restrictor 37 through conduit 43. The fluid emerging from the second control port 44 of fluidic element 41 is allowed to exhaust, as is that emerging from first output port 45. Second output port 46 of fluidic control 41 is connected through conduit 47 to the head space of reservoir 18. Damping

volumes

48 and 49 can be introduced into conduit 47, and damping volume 50 into conduit 47. Manometer 51 and high-low pressure transducer 52 can be connected to the fluidics circuit for purposes described hereafter.

In operation, fluidic probe 31 serves as a back pressure sensor, being responsive to changes in the distance .between the probe and a surface passing beneath it.

Fluidic element 41 is a monostable centered dump proportioning fluidic element which in turn is sensitive to changes in back pressure in fluidic probe 31. By adjustment of variable restrictor 36, the system is brought into balance for a desired back pressure in fluidic probe 31 with the pressurized fluid output from variable restrictor 37 exiting through

ports

45 and 46 of fluidic element 41. The pressure difference between the material in the lower tip end of needle 14 and the surface of liquid material 19 in vessel 18 can be initially controlled through adjustments in the height of vessel 18 and then finely controlled by adjustment of variable restrictor 37. This latter feature is possible because of closed head space 26 and is in contrast to the prior art devices in which the material in the vessel was under atmospheric pressure and changes in the developed head were effected solely through raising and lowering the vessel relative to the lower tip end needle.

So long as the level of solidified deposited material 19B remains constant, no change in the back pressure sensed by fluidic probe 31 will occur and consequently fluidic element 41 remains in balance. Consequently the pressure exerted in head space 26 also remains substantially constant at its initially set value. Some change in the pressure in head space 26 will of course occur as the level of liquid 19 drops in the course of deposition but this change, which can be observed in manometer 51, is minimized by placing

thermistors

22 and 23 closely together for activation of the refill mechanism more frequently but for shorter intervals.

Should fluidic probe encounter a cavity in which the surface of deposited material 19B is higher than that under which the system was brought into balance, an increase in back pressure in fluidic probe 31 and

conduits

38 and 39 will result. This back pressure increase is sensed by fluidic element 41 with the result that a proportional amount of the pressurized fluid entering port 42 is deflected from output port 46 to output port 45. The pressure communicated to head space 26 by conduit 47 is accordingly reduced, again as can be seen on manometer 51. Since the force necessary to overcome the capillary resistance within tube 17 and needle 14 is determined by the difference in pressure at the surface of liquid material 19 and that at the lower tip end of needle 14, the above reduction in pressure in closed head space 26 results in a corresponding reduction in the amount of material deposited, thereby correcting the condition which initially triggered this adjustment, namely a higher level of deposited material.

Should fluidic probe 31 encounter deposited material the level of which is below that at which the system was balanced, a decrease in back pressure in fluidic probe results. This reduction in back pressure has the effect of diverting a greater amount of the pressurized fluid passing through input port42 from output port 45 to output port 46. Consequently, the pressure of the fluid pressing through conduit 47 to head space 26 is increased and the amount of material deposited upon displacement of tubular needle is increased. Thus the pressure in closed head space 26 will be increased or decreased proportionally to the decrease or increase respectively of the back pressure sensed by fluidic probe 31.

Because the surface passing under fluidic probe 31 may vary for reasons other than different levels of deposited material, as for example the undepressed surfaces around the cavities, and since each of these will be sensed by fluidic probe 31, it is desirable to introduce damping volumes such as are shown at 48, 49 and 50. Damping

volumes

48 and 49 have the effect of minimizing the individual changes in back pressure sensed by fluidic probe 31. Repeated deviations in back pressure will have a cumulative effect on these damping volumes and thus a series of underfilled or overfilled cavities will effect a proportional change in pressure through fluidic element 41. Damping volume 50 serves a similar function, operating however on the main pressure line rather than the control pressure line. v

High-low pressure transducer 52 can be introduced into the system for item reject purposes. Thus the main fluidic circuit operates as an in-line control of deposition through corrective quality monitoring and not as an accept-reject control system. Transducer 52 on the other hand is introduced to detect pre-set maximum and minimum values for changes in the back pressure. A cavity which is grossly overfilled will result in an increase in back pressure considerably greater than that normally encountered and a totally empty cavity will similarly result in a significantly greater decrease in back pressure. These changes are sensed by the proportionating fluidic element 41 and the resultant large decrease or increase, respectively, in the pressure in conduit 47 will activate transducer 52 for reject of that particular item. Appropriate circuitry can be added for interruption of the entire process in the case of successive rejects. I

The foregoing description and drawing represent a typical embodiment of the present invention but are not intended as limitations on the scope thereof, it being apparent that the invention can be practiced to obvious modifications and rearrangements without departing from the essential spirit thereof.

What is claimed is:

1. 1n the method of material deposition in a cavity of a surface in which material to be deposited is maintained in a liquid condition in a vessel, and is communicated to a tubular needle which is displaced downward towards the cavity for formation and deposition in the cavity of a globule of the liquid material, the improvement for in-line control of the amount of material deposited which comprises a. maintaining a source of pressurized fluid in communication with a fluidic probe and with a proportional fluidic element said element comprising a first control port, a second control port, an input port, a first output port and a second output port; said pressurized fluid communicating with said element through the first control port of said element,

b. directing pressurized fluid from said probe towards the surface of solidified deposited material said probe and said surface being in spacial relationship to one another so as to create a back pressure in said probe, changes in said back pressure being sensed by the fluidic element,

c. supplying a pressurized fluid to the input port of the fluidic element,

d. maintaining said liquid material in said vessel under a closed head space and e. communicating the pressure of the fluid exiting at.

the second output port of said fluidic element to the vessel head space, the pressure in said head space thereby being increased or decreased proportionally to the decrease or increase respectively of the back pressure in said probe.

2. The method as defined in claim 1 wherein there are a plurality of spaced cavities on said surface and said surface is advanced from a first station at which said liquid material is deposited to a second station at which pressurized fluid is directed at said material after solidification, including damping said changes in back pressure.

3. The method as defined in claim 2 including damping the pressure changes exiting from said output port prior to communicating said changes to said head space.

4. In a material deposition system in which a globule of liquid material is formed and deposited on a surface from a tubular needle by displacement of the needle toward the surface, the improvement comprising a vessel in communication with said needle and operable to maintain said material in a liquid state under a closed head space and a source of pressurized fluid in communication with a fluidic probe means operable to direct a stream of said pressurized fluid at the surface of solidified deposited material, said probe means being spacially oriented with said surface so as to generate a back pressure in said probe; said pressurized fluid being in communication with the head space of said vessel and said fluidic probe through a fluidic proportionating means said fluidic proportionating means being operable to increase or decrease the pressure of fluid delivered to the head space proportionately to the decrease or increase respectively in the back pressure developed in said probe.

5. A material deposition system according to claim 4 including means operable to damp said changes in back pressure developed at said probe.

6. A material deposition system according to claim 4 including means operable to damp the pressure changes developed at said fluidic means prior to communication of said pressure changes to said head space.

7. A material deposition system according to claim 4 wherein said fluidic proportionating means is a center dump fluidic element.

8. A material deposition system according to claim 4 including transducer means in communication with said fluidic proportionating means and operable to signal pressure changes exceeding preselected maximum and minimum values.

Claims

1. In the method of material deposition in a cavity of a surface in which material to be deposited is maintained in a liquid condition in a vessel, and is communicated to a tubular needle which is displaced downward towards the cavity for formation and deposition in the cavity of a globule of the liquid material, the improvement for in-line control of the amount of material deposited which comprises a. maintaining a source of pressurized fluid in communication with a fluidic probe and with a proportional fluidic element said element comprising a first control port, a second control port, an input port, a first output port and a second output port; said pressurized fluid communicating with said element through the first control port of said element, b. directing pressurized fluid from said probe towards the surface of solidified deposited material said probe and said surface being in spacial relationship to one another so as to create a back pressure in said probe, changes in said back pressure being sensed by the fluidic element, c. supplying a pressurized fluid to the input port of the fluidic element, d. maintaining said liquid material in said vessel under a closed head space and e. communicating the pressure of the fluid exiting at the second output port of said fluidic element to the vessel head space, the pressure in said head space thereby being increased or decreased proportionally to the decrease or increase respectively of the back pressure in said probe.