ACTIVE VALVE AND ACTIVE VALVING FOR

PUMP

BACKGROUND

[0001] This application is related to US Patent Application Serial Number 11,024,930, filed December 30, 2004, entitled "METHOD AND APPARATUS FOR

SCAVENGING ENERGY DURING PUMP OPERATION", which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION

[0003] The present invention pertains to an active valve for a pump.

[0004] RELATED ART AND OTHER CONSIDERATIONS

[0005] Many types of pumps have been devised for pumping fluid, such as (for example) piston pumps, diaphragm pumps, peristaltic pumps, just to name a few. These pumps have different types of actuators and moving parts which act upon fluid in a pumping chamber. Typically the pumping chamber is defined by a pump body which has an inlet port and an outlet port. Communication of fluid through the inlet port and into the chamber, and out of the output port, is usually gated by one or more valves.

[0006] What is needed, and an object of the present invention, is apparatus, method, and/or technique for providing effective valving for a pump.

BRIEF SUMMARY [0007] A pump comprises a pump body; an actuator; and, one or more active valves. The pump body at least partially defines a pumping chamber which has an inlet port and an outlet port. The actuator is situated at least partially in the pumping chamber for

acting upon a fluid in the pumping chamber. The active valve selectively opens and closes a port with which it is aligned, e.g., either the inlet port or the outlet port.

[0008] In some embodiments the active valve comprises a piezoelectric element which responds to voltage for the selective opening and closing of its aligned port. In an illustrated embodiment, the piezoelectric element is a piezoceramic film. In one implementation of the pump, both the inlet valve and the outlet valves are active valves. In another implementation of the pump, only one of the valves is an active valve and the other is a passive valve, e.g., the inlet valve is an active valve but the outlet valve is a passive valve (e.g., is influenced by flow of fluid in the pump).

[0009] In other active valve embodiments, active valves operate in accordance with magnetic forces. In various implementations of the magnetically activated active valve embodiments, one or more of the inlet valve and the outlet valve are formed from a flexible material and have electric conductors or wiring embedded or otherwise formed therein in a coil shape to form a magnetic field. In addition, the ports which host the magnetically activated active valves have a magnet (e.g., permanent magnet) formed therearound. In some embodiments, when an electric current is applied to the circuit in the valve, the direction of electric flow in the conductors in the flexible valve is such that the magnetic field created thereby attracts the magnetic field extant at the port opening to close the valve. When the electric field is not applied, the valve can open (e.g., by fluidic conditions created in the pumping chamber by the diaphragm). In other embodiments, when an electric current is applied to the circuit in the valve, the direction of electric flow in the conductors in the flexible valve is such that the magnetic field created thereby repels the magnetic field extant at the port opening to open the valve. When the electric field is not applied, the valve can close. In yet other embodiments, the direction of electric current can be switched to selective create attracting and repelling fields for closing and opening of the valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[00010] The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the

same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

[00011] Fig. IA and Fig. IB are sectioned side views of a first example embodiment of a pump having active valves, Fig. IA showing a displaced state of an active inlet valve and a non-displaced state of an active outlet valve; and Fig. IB showing a non- displaced state of the active inlet valve and a displaced state of the active outlet valve.

[00012] Fig. 2 is a sectioned side view of an example, non-limiting embodiment of a piezoelectric wafer which can comprise an active valve for a pump.

[00013] Fig. 3 is a plan view taken along line 3-3 of Fig. IB.

[00014] Fig. 4 is a sectioned side view of another example embodiment of a pump having active valves and a timer for controlling duration of valve operation.

[00015] Fig. 5 A and Fig. 5B are sectioned side views of yet another example embodiment of a pump having an active valve, Fig. 5A showing a displaced state of an active inlet valve and a non-displaced state of a passive outlet valve; and Fig. 5B showing a non-displaced state of the active inlet valve and an opened state of the passive outlet valve.

[00016] Fig. 6 is a sectioned side view of the example pump embodiment of Fig. 5 A and Fig. 5B but having a timer for controlling duration of valve operation.

[00017] Fig. 7 is a sectioned side view of the example pump embodiment of Fig. 5 A and Fig. 5B showing a mode of operation in which an active inlet valve is kept open after self-priming of the pump, and wherein a passive outlet valve opens an outlet port.

[00018] Fig. 8 A and Fig. 8B are sectioned side views of an example embodiment of a pump having magnetically activated active valves, Fig. 8A showing a displaced state of an active inlet valve and a non-displaced state of an active outlet valve; and Fig. 8B showing a non-displaced state of the active inlet valve and an opened state of the active outlet valve.

[00019] Fig. 8Al and Fig. 8A2 are enlargements of an inlet port region and an outlet port region, respectively, of Fig. 8 A.

[00020] Fig. 9A and Fig. 9B are sectioned side views of another example embodiment of a pump having magnetically activated active valves, Fig. 9A showing a displaced state of an active inlet valve and a non-displaced state of an active outlet valve; and Fig. 9B showing a non-displaced state of the active inlet valve and an opened state of the active outlet valve.

[00021] Fig. 10 is a plan view taken along line 10-10 of Fig. 8 A.

DETAILED DESCRIPTION OF THE DRAWINGS [00022] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[00023] The pumps described herein comprise a pump body for at least partially defining a pumping chamber; an actuator which acts upon a fluid in the pumping chamber; and at least one active valve for the pump. In some embodiments, the active valve has a piezoelectric element which is selectively responsive to voltage for opening and closing a port of the pump body with which the active valve is aligned. In other embodiments, the active valve is a magnetically-activated active valve.

[00024] Pump 20 of Fig. IA and Fig. IB is described generally, and as such is meant to be representative of many different pump configurations which can host the inventive advancement described herein. Pump 20 comprises a body which includes a pump body base 22 and a pump body lid or cover 24. For the particular geometry shown in Fig. IA and Fig. IB, the pump body, including both its pump body base 22 and a pump body cover 24, are essentially cylindrical (e.g., circular as seen from the top). A

pumping chamber 28 is formed in the pump body, and an actuator is provided for drawing fluid into pumping chamber 28 and pumping fluid out of pumping chamber 28.

[00025] It just so happens that the form of the actuator illustrated in Fig. IA and Fig. IB is a diaphragm 26. However, it should be understood that, for this and subsequently described embodiments, the actuator need not be a diaphragm but could take other forms such as, for example, a piston-type actuator or even a peristaltic type actuator, for example. In the particular case that the actuator is actually a diaphragm, the diaphragm 26 can be clamped, adhered, fastened, or welded, preferably about its periphery, to a seat or other surface of the pump body.

[00026] The pump body 22 of the example pump 20 of Fig. IA and Fig. IB has an inlet port 29 which is selectively opened and closed by inlet valve 30 with which it is aligned. Similarly, pump body 22 has an outlet port 31 which is selectively opened and closed by outlet valve 32, the outlet valve 32 being aligned or situated for opening and closing of outlet port 31. The inlet valve 30 admits the fluid into the pumping chamber 28, whereas the outlet valve 32 permits fluid to be discharged from the pumping chamber 28. In the embodiment of Fig. IA and Fig. IB, both of the valves 30 and 32 are active valves in that they are actively driven, e.g., by an external signal or circuit, and are not merely passively responsive to phenomena (e.g., fluidic phenomena) occurring in the pumping chamber 28.

[00027] The valves of pump 20 (e.g., either inlet valve 30 or outlet valve 32) comprise a deformable or flexible member which is a piezoelectric member (e.g., piezoceramic film). That is, one or both of valves 30, 32 comprise a piezoelectric element 40 that preferably constitutes a working portion of the valve. As explained subsequently, the piezoelectric member comprising the valve preferably has electrodes sputtered or otherwise formed on its opposing major surfaces.

[00028] In whatever form it takes, application of a voltage to piezoelectric element 40 causes a flexure, stress, or compression in a piezoelectric wafer 42 which comprises piezoelectric element 40. The flexure, stress, or compression in piezoelectric wafer 42 causes the piezoelectric element 40 to deflect or displace, thereby moving the valve which it comprises, either to a port closing position or to a port opening position. In the particular implementation shown in Fig. IA and Fig. IB, application of a non-zero

voltage to the valve causes flexure of the piezoelectric element 40 and thus an opening of the port that otherwise would be covered by the valve.

[00029] The piezoelectric element 40 preferably comprises a multi-layered laminate 42. The multi-layered laminate can comprise a piezoelectric wafer which is laminated by an adhesive between an unillustrated metallic substrate layer and an unillustrated outer metal layer. The structure of the multi-layered laminate and a process for fabricating the same are described in one or more of the following (all of which are incorporated herein by reference in their entirety): PCT Patent Application PCT/USO 1/28947, filed 14 September 2001; United States Patent Application Serial Number 10/380,547, filed March 17, 2003, entitled "Piezoelectric Actuator and Pump Using Same"; United States Patent Application Serial Number 10/380,589, filed March 17, 2003, entitled "Piezoelectric Actuator and Pump Using Same".

[00030] As illustrated in Fig. 2, the piezoelectric element 42 (which can be included in inlet valve 30 and/or outlet valve 32) has thin electrodes 44 sputtered or otherwise formed on its two opposing major surfaces. The electrodes 44 can be formed of Nickel or Silver, or other appropriate conductive metal. One of the electrodes 44 is a positive electrode; the other electrode 44 is a negative electrode. The positive and negative electrodes 44 are engaged by respective positive and negative leads 46.

[00031] The piezoelectric element 40 can be mounted to, affixed to or on, or incorporated into the valve in various ways. Fig. 3 shows the inlet port 29 from the perspective of the pumping chamber 25. In the example illustration of Fig. 3, the valve 30 has a shoulder portion 47 which is proximate a sidewall of pump body 22, and a distal portion 48 which flexibly extends over inlet port 29. At its shoulder portion 47 valve 30 may be secured to the floor of pump body 22 by an adhesive, by spot welding (as indicated by dotted lines 49), or by mechanical clamping, for example. Other geometric configurations of the valve and other mounting techniques are also possible. The foregoing discussion of inlet valve 30 is also applicable, at least in some embodiments, to outlet valve 32.

[00032] The positive and negative leads 46 are connected to control circuit 50. The control circuit 50 includes a power supply 51 (e.g., battery) or other type of charge storage device (e.g., capacitance). In one example implementation, the control circuit

50 has a switch 52 which is selectively closed to provide voltage to the inlet valve 30, and a switch 53 which is selectively closed to provide voltage to the outlet valve 32.

[00033] Fig. IA shows inlet valve 30 being flexed in response to application of nonzero voltage to the piezoelectric element 40 of inlet valve 30 for permitting fluid to enter into pumping chamber 28. In Fig. IA the outlet valve 32 remains unflexed for covering outlet port 31. Fig. IB, on the other hand, shows inlet valve 30 remaining unflexed for covering inlet port 29 while also showing movement of outlet valve 32 in response to application of voltage to the piezoelectric element 40 of outlet valve 32 for permitting expulsion of fluid from pumping chamber 28 through outlet port 31.

[00034] Fig. 4 shows a variation of the pump of 20 of the embodiment of Fig. IA and Fig. IB, i.e., pump 120. In the variation of Fig. 4, control circuit 50 includes a timer 54 which times or controls the duration of opening and/or closure of switch 52 and/or switch 53, and thus the opening and closing of inlet valve 30 and/or outlet valve 32. The timer 54 can take any suitable form, from a simple circuit or delay line to a microprocessor, and is operated, sequenced, or programmed in accordance with a desired operation of the pump 120, e.g., to match the frequency of operation of pump 120. In one mode of operation, the timer 54 likely operates the two switches 52 and 53 with differing signals and thus differing timings, so that the inlet valve 30 and outlet valve 32 are not necessarily open at the same time. Fig. 4 basically corresponds to Fig. IA in showing opening of active inlet valve 30. Those skilled in the art will appreciate that the active outlet valve 32 of the Fig. 4 embodiment can be opened or activated by appropriate signal or voltage as aforediscussed in conjunction with Fig. IB. Moreover, the opening and controlling of switches 53 can be accomplished via any suitable means, such as (for example) solenoids, Hall Effect devices, relays, or transistors, bearing in mind that switches do not necessarily need to be mechanical but can be partially or entirely electrical.

[00035] Fig. 5 A and Fig. 5B show another embodiment of a pump having one valve which is an active valve and another valve which is a passive valve. In the particular example implementation of Fig. 5A and Fig. 5B, pump 320 has an active inlet valve 30 but a passive outlet valve 332. In another implementation, the outlet valve may be active and the inlet valve may be passive.

[00036] Fig. 5 A shows a displaced state of the active inlet valve 30 and a non-displaced state of the passive outlet valve 332. Fig. 5B shows a non-displaced state of the active inlet valve 30 and an opened state of the passive outlet valve 332. The active inlet valve 30 is driven by a signal or voltage to selectively cover and open inlet port 29. The passive outlet valve 332 opens and closes over outlet port 31 in response to phenomena occurring (e.g. fluidic phenomena) in pumping chamber 28. In essentially all other respects except the valving and the circuitry 350 for driving the inlet valve 30, the pump structure is illustrated as being substantially the same as the generic, representative embodiment of Fig. 1.

[00037] Further, as shown in the variation depicted in Fig. 6, the circuitry 250 can include a timer 354 which times or controls the duration of opening and/or closure of switch 52, and thus the opening and closing of active inlet valve 30.

[00038] In one mode of operation of a pump such as pump 320 of Fig. 5 A and Fig. 5B, the active inlet valve 30 may be activated to open inlet port 29 while passive outlet valve 332 remains closed. Then, after the pump 320 has been self-primed by sufficient admission of fluid through inlet port 29, the active inlet valve 30 is kept open (in view of the self-priming) and passive outlet valve 323 operates (e.g., opens and closes) in accordance with phenomena occurring in the pumping chamber 28. For example, Fig. 7 shows the active inlet valve 30 being kept open (in view of completion of the self- priming) and passive outlet valve 323 being open in response to phenomena in the pumping chamber 28. At a subsequent moment in time as dependent upon conditions in the pumping chamber, the passive outlet valve 323 closes outlet port 31 (not illustrated). Then, yet subsequently, when conditions again favor opening of outlet port 31, the passive outlet valve 323 does again open outlet port 31.

[00039] As one example way of implementing pumps of any of the foregoing example embodiments, the actuator 26 can be a diaphragm and/or include a piezoelectric layer, with the piezoelectric layer causing the displacement of diaphragm 26 when an electric field is applied to the piezoelectric layer. The electric field is supplied to the piezoelectric layer of diaphragm 26 by a power supply such as power supply 54.

[00040] Most of the structural features of the pumps are described above merely for providing an example context for explaining how active valves operate. As such, no

particular emphasis or criticality should be assigned to any of the structural elements or position of elements of pump 20. For example, the structure and positioning of the inlet valves and outlet valves are not necessarily germane. The person skilled in the art will appreciate that one or more of the inlet valve and outlet valve can be oriented so that the direction of fluid flow through the valve(s) is parallel to the displacement direction arrow 36 (e.g., one or more of inlet valve and outlet valve are formed in a bottom wall of pump body base 22). Alternatively, one or more of the inlet valve and the outlet valve can be oriented so that the direction of fluid flow through the valve(s) is perpendicular to the displacement direction arrow 36 (e.g., one or more of inlet valve and outlet valve is formed in a sidewall of pump body base 22).

[00041] Moreover, the shape, size, or other configuration of the pump body and its pump body base 22 and pump body lid 24 are variable. Variously shaped pump bodies, with or without myriad auxiliary or surface features, could be utilized.

[00042] Examples of diaphragm type structures which include a piezoelectric layer, and methods of fabricating the such diaphragms and pumps incorporating the same, as well as various example pump configurations with which the present invention is compatible, are illustrated in the following (all of which are incorporated herein by reference in their entirety): PCT Patent Application PCT/USOl/28947, filed 14 September 2001; United States Patent Application Serial Number 10/380,547, filed March 17, 2003, entitled "Piezoelectric Actuator and Pump Using Same"; United

States Patent Application Serial Number 10/380,589, filed March 17, 2003; and United States Provisional Patent Application 60/670,692, filed April 13, 2005, entitled "Piezoelectric Diaphragm Assembly with Conductors On Flexible Film"

[00043] It will be further appreciated that it is possible to control the voltage amplitude applied to the active valves described herein for controlling an opening distance by which the valve displaces relative to the respective port. Thus, a degree of opening effected by the valve is controllable or adjustable, and thus also the flow of fluid through the valve and the pump is adjustable and controllable.

[00044] In other active valve embodiments, active valves operate in accordance with magnetic forces. Two illustrative examples of differing embodiments of magnetically

activated active valves are illustrated, such as a first embodiment shown in Fig. 8 A and Fig. 8B and a second embodiment shown in Fig. 9A and Fig. 9B.

[00045] For sake of simplicity, valve bodies 22 and diaphragms 26 are shown in similar manner as previous embodiments, although it will be understood from previous explanations that such features are not limited. The magnetically activated active valve embodiments differ from previous embodiments in that the active valves do not necessarily include a piezoelectric layer or member. Rather, the active valves of the magnetically activated active valve embodiments are formed from a flexible material and have electric conductors or wiring embedded or otherwise formed therein in a coil shape to form a magnetic field. In addition, the ports which host the magnetically activated active valves have a magnet (e.g., permanent magnet) formed therearound. In some embodiments, when an electric current is applied to the circuit in the valve, the direction of electric flow in the conductors in the flexible valve is such that the magnetic field created thereby attracts the magnetic field extant at the port opening to close the valve. When the electric field is not applied, the valve can open (e.g., by fluidic conditions created in the pumping chamber by the diaphragm). In other embodiments, when an electric current is applied to the circuit in the valve, the direction of electric flow in the conductors in the flexible valve is such that the magnetic field created thereby repels the magnetic field extant at the port opening to open the valve. When the electric field is not applied, the valve can close. In yet other embodiments, the direction of electric current can be switched to selective create attracting and repelling fields for closing and opening of the valve.

[00046] Fig. 8A and Fig. 8B illustrate inlet port 29(8) as having a magnet 60 positioned around at least a portion thereof. If inlet port 29(8) is circular, then magnet 60 is annular in shape and substantially surrounds inlet port 29(8). A similar magnet 62 can be provided at outlet port 31(8).

[00047] Fig. 10 shows, from the perspective of the pumping chamber, inlet valve 30(8) which selectively opens and closes inlet port 29(8) of Fig. 8 A. Fig. 10 illustrates the electrical conductor 64 which is formed or embedded in inlet valve 30(8). The electrical conductor 64 comprises two parallel segments 66, 68 which extend from respective attachment points 70 and 72 toward a distal end of valve 30(8). An intermediate coiled segment 74 connects parallel segments 66, 68. The coiled segment

74 extends over and around the mouth of inlet port 29(8), and is preferably aligned over the magnet 60.

[00048] In an example implementation, valves such as inlet valve 30(8) described above can be realized by a flex circuit which has the embedded conductor. Such a flex circuit needs to flexible enough to displace sufficiently to accommodate fluid flow, and yet sufficiently non-permeable so that fluid does not flow or seep therethrough when the valve is closed.

[00049] Although the foregoing description of the magnet 60 and the electrical conductor has been illustrated in Fig. 10 and specifically described with regard to the inlet valve 30(8), it will be appreciated that the outlet valve 32(8) of the same embodiment can be similarly formed, as well as one or both of the inlet valves and outlet valves of the ensuing embodiments (e.g., the embodiment of Fig. 9 A and Fig. 9B).

[00050] In the embodiment of Fig. 8A and Fig. 8B, a power supply is connected so that a closed electric circuit results in electric current flow through conductor 64 in inlet valve 30(8) and outlet valve 32(8) in a direction which causes magnetic attraction of the valve to the magnet 60 in the respective port 29(8) and 31(8). In particular, Fig. 8A shows an intake stroke of the pump in which the electrical circuit for conductor 64 of inlet valve 30(8) is open so that valve 30(8) is not magnetically attracted to magnet 60 of inlet port 29(8), with the result that fluid can enter through inlet port 29(8), e.g., under action of the diaphragm in the pumping chamber. At outlet port 31 (8), on the other hand, in the intake stroke the electrical circuit for conductor 64 of outlet valve 32(8) is closed so that electrical current does flow through the conductor 64 of valve 32(8), whereby outlet valve 32(8) is magnetically attracted to magnet 60 of outlet port 31 (8), with the result that the valve 32(8) closes outlet port 31 (8) so that fluid is not permitted to leave.

[00051] Fig. 8B shows an exhaust stroke which follows the intake stroke of Fig. 8 A. In the exhaust stroke, the electrical circuit for conductor 64 of inlet valve 30(8) is closed so that electrical current does flow through the conductor 64 of valve 30(8), whereby inlet valve 30(8) is magnetically attracted to magnet 60 of inlet port 29(8), with the result that the valve 30(8) closes inlet port 29(8) so that fluid is not permitted to enter.

At outlet port 31(8), on the other hand, in the exhaust stroke the electrical circuit for conductor 64 of outlet valve 32(8) is open so that valve 32(8) is not magnetically attracted to magnet 60 of outlet port 31(8), with the result that fluid can exit through outlet port 31(8).

[00052] In the embodiment of Fig. 8A and Fig. 8B, as well as in ensuing embodiments, a separate power supply is depicted for each of the inlet valve and the outlet valve. It will be appreciate that other power supply arrangements can alternatively be provided, such as utilizing a same power supply for both the inlet valve and the outlet valve. Further, the closing and opening of the electrical circuit for the inlet valve is depicted by a simple switch Sj and the closing and opening of the electrical circuit for the outlet valve is depicted by a simple switch S ₀ . It will be appreciated that such switches can take the forms of one or more switches as described in conjunction with previous embodiments, and even include an electronic controller or the like which either times or is coordinated with the timing of the pumping action of the pump.

[00053] In the embodiment of Fig. 9A and Fig. 9B, direction of flow of electrical current for each of inlet valve 30(9) and outlet valve 32(9) is selectable so that, for differing pump strokes, each valve can either experience magnetic attraction for closing a port or magnetic repulsion for opening a port. For example, during the intake stroke shown in Fig. 9A, the conductor 64 in inlet valve 30(9) is connected to a power supply such that the electrical current flowing through conductor 64 is in a direction to create a repulsive magnetic field for inlet valve 30(9), thereby opening inlet port 29(9) for fluid to enter the pumping chamber during the intake stroke. During the intake stroke at the outlet port 31(9), on the other hand, the conductor 64 in outlet valve 32(9) is connected to a power supply such that the electrical current flowing through conductor 64 is in a direction to create an attractive magnetic field for outlet valve 32(9), thereby closing outlet port 31 (9) for precluding fluid from leaving the pumping chamber during the intake stroke.

[00054] Fig. 9B shows the exhaust stroke which follows the intake stroke of Fig. 9A. In the exhaust stroke shown in Fig. 9B, the conductor 64 in inlet valve 30(9) is connected (e.g., to another power supply) such that the electrical current flowing through conductor 64 is in an opposite direction relative to the intake stroke to create an attractive magnetic field for inlet valve 30(9), thereby closing inlet port 29(9) to

preclude fluid from entering the pumping chamber during the intake stroke. During the exhaust stroke at the outlet port 31 (9), on the other hand, the conductor 64 in outlet valve 32(9) is connected (e.g., to another power supply) such that the electrical current flowing through conductor 64 is in an opposite direction relative to the intake stroke to create a repulsive magnetic field for outlet valve 32(9), thereby opening outlet port 31(9) for permitting fluid to leave the pumping chamber during the intake stroke.

[00055] In the embodiments which feature the magnetically-activated active valves, the magnets at the ports need not necessarily surround the ports, but may merely be positioned proximate thereto. The magnet provided at the port need not necessarily be a permanent magnet, although provision of a permanent magnet simplifies the electronics design. The flexible material comprising the flexible valves can be any suitable material for forming flex circuits, for example, so long as the material is essentially fluid-impervious.

[00056] Moreover, it is also possible essentially to reverse the positioning of the elements in the embodiments of Fig. 8 A, Fig. 8B and Fig. 9A, Fig. 9B by providing, for example, a magnetic material in the valve and a electrical coil about the port covered by the valve.

[00057] While embodiments of the invention have been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements.