Abstract:
A compact fluid dispenser for use in controllably dispensing fluid medicaments, such as antibiotics, blood clotting agents, analgesics, and like medicinal agents from collapsible containers at a uniform rate. The dispenser includes a novel stored energy source that is provided in the form of a compressible-expandable member that functions to continuously and uniformly expel fluid from the apparatus reservoir. The apparatus further includes a novel fluid flow control assembly that precisely controls the flow of the medicament solutions from the apparatus reservoir to the patient.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fluid dispensing apparatus. More particularly, the invention concerns a medicament delivery device for dispensing medicinal fluids to ambulatory patients that includes a novel stored energy source in the form of a variable force spring. The variable force spring is cooperatively associated with the collapsible reservoir of the device and functions to deliver a variable force to the reservoir that tends to urge fluid flow therefrom at a substantially constant rate. In the preferred form of the invention the stored energy source uniquely comprises an elongated, pre-stressed strip of spring material that is formed into coils and exhibits a cross-sectional mass that varies along its length. 
     DISCUSSION OF THE PRIOR ART 
     A number of different types of medicament dispensers for dispensing medicaments to ambulatory patients have been suggested in the past. Many of the devices or apparatus seek either to improve or to replace the traditional gravity flow and hypodermic syringe methods which have been the standard for delivery of liquid medicaments for many years. 
     The prior art gravity flow methods typically involve the use of intravenous administration sets and the familiar flexible solution bag suspended above the patient. Such gravametric methods are cumbersome, imprecise and require bed confinement of the patient. Periodic monitoring of the apparatus by the nurse or doctor is required to detect malfunctions of the infusion apparatus. Accordingly, the prior art devices or apparatus are not well suited for use in those instances where the patient must be transported to a remote facility for treatment. 
     With regard to the prior art, one of the most versatile and unique fluid delivery apparatus developed in recent years is that developed by one of the present inventors and described in U.S. Pat. No. 5,205,820. The components of this novel fluid delivery apparatus generally include: a base assembly, an elastomeric membrane serving as a stored energy means, fluid flow channels for filling and delivery, flow control means, a cover, and an ullage which comprises a part of the base assembly. 
     Another prior art patent issued to one of the present applicants, namely U.S. Pat. No. 5,743,879, discloses an injectable medicament dispenser for use in controllably dispensing fluid medicaments such as insulin, anti-infectives, analgesics, oncolylotics, cardiac drugs, bio-pharmaceuticals, and the like from a pre-filled container at a uniform rate. The dispenser, which is quite dissimilar in construction and operation from that of the present invention, includes a stored energy source in the form of a compressively deformable, polymeric, elastomeric member that provides the force necessary to controllably discharge the medicament from a pre-filled container, which is housed within the body of the apparatus. After having been deformed, the polymeric, elastomeric member will return to its starting configuration in a highly predictable manner. 
     SUMMARY OF THE INVENTION 
     By way of brief summary, one form of the fluid delivery device of the present invention for dispensing medicaments to a patient comprises a supporting structure; a carriage assembly interconnected with the supporting structure for movement between a first position and a second position; a pre-filled collapsible container carried by the carriage assembly, the collapsible container having accessing means for accessing the reservoir comprising a frangible member in the form of a pierceable member or shearable member. The apparatus also includes guide means connected to the supporting structure for guiding travel of the carriage assembly between the first position and said second positions; a stored energy source operably associated with the carriage assembly for moving the carriage assembly between the first and second positions; and an administration set, including an administration line interconnected with the outlet port of the collapsible reservoir. The stored energy source is cooperatively associated with the collapsible container of the device and functions to deliver a variable force to the container that tends to urge fluid flow therefrom at a substantially constant rate. In the preferred form of the invention the stored energy source uniquely comprises an elongated, pre-stressed strip of spring material that is formed into coils and exhibits a cross-sectional mass that varies along its length. 
     Another object of the invention is to provide a compact fluid delivery device of the character described in the preceding paragraph in which variation in cross-sectional mass along the length of the retractable spring can be achieved by varying the width of the pre-stressed spring along its length. 
     Another object of the invention is to provide a compact fluid delivery device of the character described in which variation in cross-sectional mass along the length of the retractable spring can be achieved by providing spaced-apart apertures in the pre-stressed spring along its length. 
     With the forgoing in mind, it is still another object of the present invention to provide a compact fluid delivery device for use in controllably dispensing fluid medicaments to ambulatory patients, such as, antibiotics, blood clotting agents, analgesics, KVO, artificial blood substitutes, resuscitation fluids, internal nutritional solutions, biologics, and like beneficial agents from pre-filled or field-filled containers at a uniform rate. 
     Another object of the invention is to provide a small, compact pre-filled fluid dispenser that is aseptically filled and sealed at the time of manufacture. 
     Another object of the invention is to provide an apparatus that is of simple construction that can be used in the field with a minimum amount of training. 
     Another object of the invention is to provide a dispenser in which a stored energy source is provided in the form of a highly novel variable force retractable member of a unique construction that provides the force necessary to continuously and uniformly expel fluid from the apparatus reservoir. 
     Another object of the invention is to provide a dispenser of the class described which includes a fluid flow control assembly that precisely controls the flow of the medicament solution to the patient. Uniquely, the container is formed as a unitary structure that includes a collapsible side wall and a pierceable closure wall that isolates the beneficial agents contained within the container reservoir from external contaminants. 
     Another object of the invention is to provide a dispenser that includes precise variable flow rate selection. 
     Another object of the invention is to provide a fluid dispenser of the class described which is compact, lightweight, is easy for ambulatory patients to use, is fully disposable, transportable and is extremely reliable in operation. 
     Another object of the invention is to provide a fluid dispenser as described in the preceding paragraphs that is easy and inexpensive to manufacture in large quantities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a generally perspective, top view of one form of the fluid delivery device of the present invention for dispensing medicaments to a patient. 
         FIG. 2  is a generally perspective, bottom view of the fluid delivery device shown in  FIG. 1 . 
         FIG. 3  is a generally perspective, exploded view of the fluid delivery device of the invention showing the top cover removed and the administration set unfurled. 
         FIG. 4  is a foreshortened, longitudinal, cross-sectional view of the device showing the reservoir in a pre-filled condition. 
         FIG. 4A  is a cross-sectional view taken along lines  4 A- 4 A of  FIG. 4 . 
         FIG. 5  is a foreshortened, longitudinal, cross-sectional view, similar to  FIG. 4 , but showing the various components of the apparatus as they appear following delivery to the patient of the fluid contained within the device reservoir with the reservoir substantially empty. 
         FIG. 6  is a top plan view of the collapsible container of this embodiment of the invention. 
         FIG. 7  is a cross-sectional view taken along lines  7 - 7  of  FIG. 6 . 
         FIG. 8  is an exploded, cross-sectional view of the reservoir access assembly of this form of the invention. 
         FIG. 9  is a view taken along lines  9 - 9  of  FIG. 4 . 
         FIG. 10  is a generally perspective view of a prior art retractable spring. 
         FIG. 11  is a generally perspective view of the prior art retractable spring shown in  FIG. 10  as it appears in a partially expanded configuration. 
         FIG. 12  is a generally illustrative view of the configuration of a retractable spring that would deliver a force that decreases by a factor of w 1 /w 2  as a spring returned from its fully extended configuration to its fully coiled configuration. 
         FIG. 13  is a generally graphical representation plotting pressure versus the length of the reservoir container when a constant force spring is used to compress a bellows-like reservoir container. 
         FIG. 14  is a generally graphical representation, similar to  FIG. 13 , plotting pressure versus the degree of compression for the reservoir container when the container is compressed by a constant force spring. 
         FIG. 15  is a generally illustrative view of the retractable spring of a first modified configuration. 
         FIG. 15A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 15  versus position along the length of the spring. 
         FIG. 16  is a generally illustrative view of the retractable spring of a second modified configuration. 
         FIG. 16A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 16  versus position along the length of the spring. 
         FIG. 17  is a generally illustrative view of the retractable spring of a third modified configuration. 
         FIG. 17A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 17  versus position along the length of the spring. 
         FIG. 18  is a generally illustrative view of the retractable spring of a fourth modified configuration. 
         FIG. 18A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 18  versus position along the length of the spring. 
         FIG. 19  is a generally illustrative view of the retractable spring of a fifth modified configuration. 
         FIG. 19A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 19  versus position along the length of the spring. 
         FIG. 20  is a generally illustrative view of the retractable spring of a sixth modified configuration. 
         FIG. 20A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 20  versus position along the length of the spring. 
         FIG. 21  is a generally illustrative view of the retractable spring of a seventh modified configuration. 
         FIG. 21  A is a generally graphical representation plotting force exerted by the spring shown in  FIG. 21  versus position along the length of the spring. 
         FIG. 22  is a generally illustrative view of the retractable spring of an eighth modified configuration. 
         FIG. 22A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 22  versus position along the length of the spring. 
         FIG. 23  is a generally illustrative view of the retractable spring of a ninth modified configuration. 
         FIG. 23A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 23  versus position along the length of the spring. 
         FIG. 24  is a generally illustrative view of the retractable spring of a tenth modified configuration. 
         FIG. 24A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 24  versus position along the length of the spring. 
         FIG. 25  is a generally illustrative view of the retractable spring of an eleventh modified configuration. 
         FIG. 25A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 25  versus position along the length of the spring. 
         FIG. 26  is a generally illustrative view of the retractable spring of a twelfth modified configuration. 
         FIG. 26A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 26  versus position along the length of the spring. 
         FIG. 27  is a generally illustrative view of the retractable spring of a thirteenth modified configuration. 
         FIG. 27A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 27  versus position along the length of the spring. 
         FIG. 27B  is a generally perspective view of still another form of modified spring of the invention that here comprises a modification of the thirteenth modified spring configuration shown in  FIG. 27  of the drawings. 
         FIG. 28  is a generally illustrative view of the retractable spring of a fourteenth modified configuration. 
         FIG. 28A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 28  versus position along the length of the spring. 
         FIG. 29  is a generally illustrative view of the retractable spring of a fifteenth modified configuration. 
         FIG. 29A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 29  versus position along the length of the spring. 
         FIG. 30  is a generally illustrative view of the retractable spring of a sixteenth modified configuration. 
         FIG. 30A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 30  versus position along the length of the spring. 
         FIG. 31  is a generally illustrative view of the retractable spring of a seventeenth modified configuration. 
         FIG. 31A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 31  versus position along the length of the spring. 
         FIG. 32  is a generally illustrative view of the retractable spring of a eighteenth modified configuration. 
         FIG. 32A  is a generally graphical representation plotting force exerted by the spring shown in  FIG. 32  versus position along the length of the spring. 
         FIG. 33  is a generally perspective, exploded view of the upper portion of the fluid delivery device of the invention showing the construction of one form of the rate control of assembly of the device. 
         FIG. 33A  is an enlarged, cross-sectional view of the selector housing of the device that houses the device selector member for selecting the rate of fluid flow from the fluid reservoir. 
         FIG. 33B  is a view taken along lines  33 B- 33 B of  FIG. 33A . 
         FIG. 33C  is a greatly enlarged cross-sectional view of one form of the selector member of the fluid delivery device. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Definitions: As used herein, the following terms have the following meanings: 
     Constant Force Spring 
     Constant force springs are a special variety of extension spring. They are tightly coiled wound bands of pre-hardened spring steel or stainless steel strip with built-in curvature so that each turn of the strip wraps tightly on its inner neighbor. When the strip is extended (deflected) the inherent stress resists the loading force; the same as a common extension spring, but at a nearly constant (zero) rate. The constant-force spring is well suited to long extensions with no load build-up. In use, the spring is usually mounted with the internal diameter (ID) tightly wrapped on a drum and the free end attached to the loading force. Considerable flexibility is possible with constant-force springs because the load capacity can be multiplied by using two or more strips in tandem, or back-to-back. Constant force springs are available in a wide variety of sizes. 
     Force Generating Region 
     The force generating region of the prior art constant force spring means the region of the spring in which the force is generated. More particularly, it should be understood that it is the change in radius of curvature of the prior art constant force spring that is responsible for the generation of the force produced by the spring. In fact, the radius of curvature of the prior art constant for spring changes from essentially infinity to a value equal to the radius of the spool on which the spring is wound. 
     Note that because the force generating region takes up some portion of the length of the spring it will tend to average any point-by-point changes in physical or structural properties of the spring. 
     It should also be kept in mind that this force generating region takes up some part of the total length of the spring, and that this force generating region moves as the degree of extension of the spring changes. 
     Modified Constant Force Spring (Variable Force Spring) 
     The modified constant force spring or variable force spring of the present invention comprises a spring of highly novel configuration that includes an elongated, pre-stressed strip of spring material that may be metal, a polymer, a plastic, or a composite material with built-in curvature so that, like the conventional constant force spring, each turn of the strip wraps tightly on its inner neighbor. Uniquely, the elongated pre-stressed strip of spring material exhibits a cross-sectional mass that varies along said length. This variation in cross-sectional mass along the length of the spring can be achieved in various ways, as for example, by varying the width of the pre-stressed strip along its length and by providing spaced-apart apertures in the pre-stressed strip along its length. 
     Mass of Material 
     The term “mass of material” when used herein in connection with the modified constant force spring of the invention means the mass of material in the “force generating region” as previously defined herein. More particularly, increasing the mass of material in the “force generating region” will increase the force provided by the spring. Conversely, decreasing the mass of material in the “force generating region” will result in a reduction of the force generated by the spring. The mass in the active region can be changed by changing the thickness of the spring, the width of the spring, the density of material of the spring, or any combination of these. 
     Unitary Container 
     A closed container formed from a single component. 
     Continuous/Uninterrupted Wall. 
     A wall having no break in uniformity or continuity. 
     Hermetically Sealed Container 
     A container that is designed and intended to be secure against the entry of microorganisms and to maintain the safety and quality of its contents after pressurizing. 
     Biologic 
     A virus, therapeutic serum, toxin, antitoxin, vaccine, blood, blood component or derivative, allergenic product, or analogous product applicable to the prevention, treatment or cure of diseases or injuries of man. 
     Drug 
     As defined by the Food, Drug and Cosmetic Act, drugs are “articles (other than food) intended for the use in the diagnosis, cure, mitigation, treatment, or prevention of disease in man or other animals, or to affect the structure or any function.” 
     Drug Product 
     A finished dosage form (e.g. tablet, capsule, or solution) that contains the active drug ingredient usually combined with inactive ingredients. 
     Artificial Blood Substitutes 
     Blood Substitutes are used to fill fluid volume and/or carry oxygen and other gases in the cardiovascular system. These include volume expanders for inert products, and oxygen therapeutics for oxygen-carrying products. 
     Resuscitation Fluids 
     Infusion of hyperosmotic-hyperoncotic solutions such as hypertonic saline dextran (HSD) as used for resuscitation of traumatic shock and perioperative volume support or as an adjunct to other conventional isotonic crystalloid solutions. Where hypotension is caused by myocardial depression, pathological vasodilatation and extravascation of circulating volume due to widespread capillary leak, a resuscitative effort is attempted to correct the absolute and relative hypovolemia by refilling the vascular tree. Here resuscitation with a small volume of hypertonic-hyperoncotic solution allows systemic and splanchnic hemodynamic and oxygen transport recovery, without an increase in pulmonary artery pressure. Alternate types of normotonic, hyperoncotic, hypertonic, and hypertonic-hyperoncotic solutions can be used for systemic hemodynamic recovery. 
     KVO 
     KVO—keeping-the-vein-open in an IV set up, a phrase that refers to the flow rate of a maintenance IV line established as a prophylactic access. 
     Nutritionals 
     Dietary supplemental enteral nutrition support feeding solutions used for nasoenteric application typically used in nasogastric, nasoduodenal and nasojejunal or intravenous routes of administration. 
     Beneficial Agent 
     The term beneficial agent can include any substance or compound that is biologically active and includes any physiologically or pharmacologically active substance that produces a localized or systemic effect in humans or animals and that can be delivered by the present invention to produce a beneficial and useful result. 
     Diluent 
     A liquid that dilutes, as in an inert solution used to dilute a medicament. An inert liquid carrier of a beneficial agent. 
     Device 
     An instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or other similar or related article, including any component, part or accessory, which is intended for use in the diagnosis, cure, treatment or prevention of disease. A device does not achieve its intended purpose through chemical action in the body and is not dependent upon being metabolized to achieve its purpose. 
     Reservoir 
     A receptacle or chamber for storing a fluid. A part of a machine, apparatus, where liquid is stored. 
     Liquid Container 
     A receptacle for holding a liquid. A fluid dispenser that is carried or transported. 
     Collapsible 
     To cause to fold, break down, or fall down or inward or as in bent-over or doubled-up so that one part lies on another. 
     Collapsible Container 
     A dispensing apparatus in which one or more walls of the container are made of a material which will deform (collapse) when pressure is applied thereto; or a dispensing apparatus having a collapsible or telescoping wall structure. 
     Aseptic Processing 
     The term ‘aseptic processing’ as it is applied in the pharmaceutical industry refers to the assembly of sterilized components and product in a specialized clean environment. 
     Sterile Product 
     A sterile product is one that is free from all living organisms, whether in a vegetative or spore state. 
     Blow-Fill-Seal Process 
     The concept of aseptic blow-fill-seal (BFS) is that a container is formed, filled, and sealed as a unitary container in a continuous manner without human intervention in a sterile enclosed area inside a machine. The process is multi-stepped, pharmaceutical grade resin is extruded into a tube, which is then formed into a container. A mandrel is inserted into the newly formed container and filled. The container is then sealed, all inside a sterile shrouded chamber. The product is then discharged to a non-sterile area for packaging and distribution. 
     Integrally Formed 
     An article of one-piece construction, or several parts that are rigidly secured together and is smoothly continuous in form and that any such components making up the part have been then rendered inseparable. 
     Frangible 
     An article, item or object that is capable of being ruptured or broken, but does not necessarily imply any inherent materials weakness. A material object, under load that demonstrates a mechanical strain rate deformation behavior, leading to disintegration. 
     Luer Lock Connector 
     A connector used to connect medical apparatus. Classically, the Luer consists of a tapered barrel and a conical male part that fits into it with or without a seal. 
     Referring to the drawings and particularly to  FIGS. 1 through 3 , one form of the fluid dispensing apparatus of the present invention for dispensing medicaments to a patient is there shown and generally designated by the numeral  20 . The dispensing apparatus here comprises a supporting structure  22 , which includes a housing  24  having an upper portion  25  and a generally cylindrically shaped skirt portion  26 . Supporting structure  22  can be constructed from metal, plastic or any suitable material. Connected to portion  26  is a base segment  27 , the details of construction of which will presently be described. 
     Disposed within skirt portion  26  is a carriage assembly  28 , which is movable between a first position shown in  FIG. 4  and a second position shown in  FIG. 5 . Carriage assembly  28  here comprises a carriage  30  having a carriage flange  30   a  to which the novel stored energy means of the present invention is operably interconnected. Carriage assembly  28  is releasably locked in its first position by a novel locking means the character of which will be described in the paragraphs which follow. 
     Carried by carriage assembly  28  is a reservoir defining assembly  34  that defines a fluid reservoir  35 . As illustrated in  FIGS. 4 ,  5 , 6  and  7 , reservoir defining assembly  34  includes a top wall  34   a , a continuous bellows-like sidewall  34   b  that is connected to top wall  34   a  and a bottom wall  34   c  that is connected to side wall  34   b . Bellows-like sidewall  34   b  is movable from the expanded, starting configuration shown in  FIG. 4  to the collapsed configuration shown in  FIG. 5 . As illustrated in  FIGS. 4 and 7 , bottom wall  34   c  includes a cup-shaped portion  34   d.    
     This important reservoir defining container also includes a neck portion  34   e  which is sealed at the time of manufacture by a thin closure wall  39 . Neck portion  34   e  forms a part of the novel reservoir access means of the invention the purpose of which will presently be described. As shown in  FIG. 5 , when the bellows-like sidewall  34   b  is collapsed, the cup-shaped portion  34   d  is disposed in close proximity to the neck portion  34   e  and substantially fills the upper portion of the collapsible container. In this embodiment of the invention fluid reservoir  35  is accessible via a penetrating member  40   a  that is carried by the septum-penetrating assembly generally designated in  FIG. 4  by the numeral  40 . Penetrating member  40   a  is adapted to pierce closure wall  39  as well as a pierceable membrane  42  which is positioned over closure wall  39  by means of a closure cap  44  which is affixed to the neck portion  34   c  of the container assembly (see also  FIGS. 7 and 8 ). 
     Closure wall  39  is integrally formed with neck portion  34   e  by means of a novel aseptic blow-fill-seal technique that is also used to form reservoir defining assembly  34 . This aseptic blow-fill-seal technique comprises the continuous extrusion through an extruder head of a length of a parison in the form of a hollow tube between and through two co-acting first or main mold halves. The method includes the step of cutting off the parison below the extruder head and above the main mold halves to create an opening which allows a blowing and filling nozzle assembly to be moved downwardly into the opening in the parison for molding and thereafter filling a molded container. 
     When the container portion of the container assembly is filled with the desired amount of liquid, the blowing and filling nozzle assembly is retracted from the opening in the parison. A separate pair of co-acting second or upper sealing mold halves are then moved together around the exposed length of parison to form and seal the container upper portion. The finished container assembly, completely formed, filled, and sealed as a unitary structure is then conveyed out of the molding apparatus. Further information concerning aseptic blow-fill and blow-fill-seal techniques is available from Rommelag of Waiblingen, Germany and is discussed in U.S. Pat. No. RE 27,155 issued to Hansen. Because of the pertinence of this latter patent, U.S. Pat. No. RE 27,155 is hereby incorporated by reference as though fully set forth herein. 
     The basic unitary container and the hermetically sealed reservoir portion of the container are closed by the thin closure wall  39 . Following closure of the container by the thin closure wall  39 , the piercable septum membrane  42  is then positioned over the closure wall and the cap  44  is positioned over the piercable septum and secured to neck portion  34   e  by any suitable means such as adhesive bonding or sonic welding. It is to be understood that septum  42  can also be constructed as a slit or partially slit member. It is important to note that closure wall  39  effectively prevents the medicament contained within the fluid reservoir from coming in contact with external contaminants. 
     To controllably move the carriage assembly  28  from its first position to its second position, novel stored energy means are provided. This novel stored energy means, which is operably associated with carriage assembly, is here provided in the form of three uniquely formed variable force springs  48  ( FIG. 9 ), the character of which will presently be described. 
     As illustrated in  FIGS. 4 ,  4 A and  5  the carriage locking means includes a locking member  50  having a shank portion  50   a  which extends through a keyhole-shaped opening  28   c  provided in the carriage base  28   b  (see  FIG. 4A ). The carriage locking means also includes a finger-engaging, operating member  52  that is connected to shank portion  50   a . Operating member  52  functions to rotate locking member  50  from a transverse locking position to a release position in alignment with keyhole opening  28   c  formed in carriage base  28   b . As the operating member is rotated from a locked position to a release position, the stored energy means, or springs  48  ( FIGS. 4 and 9 ) will move the carriage from a position shown in  FIG. 4  into the position shown in  FIG. 5  and in so doing will urge the fluid contained within reservoir  35  to flow toward penetrating member  40 , into passageway  40   b  formed in the penetrating member and toward the rate control means of the invention, the construction and operation of which will presently be described. 
     Turning now to a consideration of the stored energy sources, or variable force springs  48 , which form an extremely important feature of the present invention, it is to be understood that the objective of many prior art fluid and drug delivery systems is to deliver fluid at a constant flow rate. One method for achieving a constant flow rate over time involves ensuing that the pressure driving the fluid through the device is constant, i.e., the pressure inside the fluid reservoir of the device is constant In the present invention achieving constant pressure in the bellows-like fluid reservoir  35  of the device is an accomplished in a unique manner by modifying a typical constant force spring, such as a Negator spring “NS”. Negator springs, which are of the general character illustrated in  FIGS. 10 and 11  of the drawings, are readily commercially available from a number of sources including Stock Drive Products/Sterling Instruments of new Hyde Park, N.Y. 
     The prior art Negator extension spring comprises a pre-stressed flat strip “FS” of spring material that is formed into virtually constant radius coils around itself or on a drum “Z” having a radius R- 1  ( FIG. 11 ). The area identified in  FIG. 11  of the drawings as “FGR” designates the “active region” or “the force generating region” of the constant for spring. It should be understood that in this “active region” the radius of curvature of the spring changes and it is this change in radius of curvature of the spring that is responsible for the generation of the force. In fact, the radius of curvature changes from essentially infinity to a value equal to the radius R- 1  of the spool on which the spring is wound. As will be discussed in greater detail hereinafter, increasing the mass of material in this “force generating region” will increase the force provided by the spring. Conversely, decreasing the mass of material in the “force generating region” will result in a reduction of the force generated by the spring. The mass in the active region can be changed by changing the thickness of the spring, the width of the spring, the density of material of the spring, or any combination of these. It should be further noted that because the force generating region takes up some portion of the length of the spring it will tend to average any point-by-point changes in physical or structural properties of the spring. The variable L shown in  FIG. 11  of the drawings is defined to be the distance from the force generating region to the end of the spring. When deflected, the spring material straightens as it leaves the drum (see  FIG. 11 ). This straightened length of spring actually stores the spring&#39;s energy through its tendency to assume its natural radius. 
     The force delivered by a typical prior art constant force spring, such as the Negator extension spring depends on several structural and geometric factors. Structural factors include material composition and heat treatment. Geometric factors include the thickness of the spring “T”, the change in radius of curvature of the spring as the spring is extended, and the width “W” of the spring. 
     Turning now to a consideration of the novel variable force springs of the present invention, these springs can be constructed from various materials, such as metal, plastic, ceramic, composite and alloys, that is, intermetallic phases, intermetallic compounds, solid solution, metal-semi metal solutions including but not limited to Al/Cu, Al/Mn, Al/Si, Al/Mg, Al/Mg/Si, Al/Zn, Pb/Sn/Sb, Sn/Sb/Cu, Al/Sb, Zn/Sb, In/Sb, Sb/Pb, Au/Cu, Ti/Al/Sn, Nb/Zr, Cr/Fe, non-ferrous alloys, Cu/Mn/Ni, Al/Ni/Co, Ni/Cu/Zn, Ni/Cr, Ni/Cu/Mn, Cu/Zn, Ni/Cu/Sn. These springs comprise a novel modification of the prior art constant force springs to provide variable springs suitable for use in many diverse applications With the foregoing in mind, if one wanted to produce a spring that delivered a force that increased by a factor of two as the spring returned from its fully extended conformation to its equilibrium, or fully coiled conformation, one would require that, as illustrated in  FIG. 12  of the drawings, the width of the spring change by a factor of two along its length. In the example illustrated in  FIG. 13 , the force will decrease by a factor of w 1 /w 2  as the spring changes from a fully extended configuration to a fully retracted configuration. 
     With the forgoing in mind, one form of the modified spring of the present invention can be described algebraically as follows: 
     If x denotes the position of a point along a line that is parallel to the longitudinal axis of the spring and w(x) denotes the width of the spring at that point then:
 
 w ( x )=(constant) x  
 
This describes the case wherein the width varies linearly with x as is shown in  FIG. 12  of the drawings.
 
     However, it is to be observed that the relationship between a position along the longitudinal axis of the spring and the width of the spring at that position need not be linear as shown in  FIG. 12 . Further, the width of the spring could be any arbitrary function of x. Thus:
 
 w ( x )= f ( x )
 
where (x) denotes an arbitrary function of x.
 
     Using this concept a spring can be designed that can be used to controllably compress a bellows type reservoir, such as reservoir  35 , which when compressed by the modified spring exhibits a pressure vs. degree of compression curve of the character shown in  FIG. 14 . Stated another way, it is apparent that the concept can be employed to design a spring that generates a pressure that is independent of the degree of compression of the bellows-type reservoir. 
     By way of example, suppose that the pressure vs. degree of compression curve for a bellows-like container when compressed by a constant force spring is exemplified by the curve P(x) and the force of the constant force spring is identified as “FCFS”. Further assume that the drop in pressure as the container is compressed is due to the force “BF(x)”, which is the force required to compress the container. Then the net force producing the pressure in the container can then be written:
 
 F ( x )= FCFS−BF ( x )
 
     Assume for simplicity that the area on which the force F acts is constant and is represented by “A”. Then the pressure in the bottle is:
 
 P ( x )=( FCFS−BF ( x ))/ A  
 
This equation describes, in functional form, the curve labeled P(x) in  FIG. 14 , and includes explicitly the contributions of the two forces generating the pressure within the reservoir  35  of the bellows-like container, that is the force due to the spring and the force due to the bellows-like container.
 
     The foregoing analysis allows one to design a spring, the force of which changes in such a way that the sum of all forces generating the pressure in the container is independent of the degree of the compression of the container, i.e., independent of the variable x. The force delivered by such a spring can be stated as:
 
 F ( x )= FCFS+AF ( x )
 
Where “FCFS” is the force delivered by the original constant force spring and AF(x) is an additional force whose functional form is to be determined. Thus, the modified spring can be thought of as being composed of two parts, one part delivers the force of the original constant force spring (a force independent of x) and the other delivers a force that depends on the variable x.
 
     For this system the net force generating the pressure in the reservoir of the bellows-like container is stated as:
 
 FS ( x )= F   ms ( x )− BF ( x )= FCFS+AF ( x )− BF ( x )
 
Assuming that:
 
AF(x)=BF(x) for all x.
 
Then the total force compressing the container is:
 
 FS ( x )= FCFS+AF ( x )− AF ( x )= FCFS  
 
which force is independent of the degree of compression of the container, and wherein the pressure within the container is independent of the degree of compression of the container.
 
 P   ms ( x )=( FCFS+AF ( x )− AF ( x ))/ A=FCFS/A  
 
Where P ms (x) denotes the pressure in the fluid reservoir when the modified spring of the invention is used.
 
     In designing the modified spring of the present invention, the information contained in the pressure vs. displacement curve when the container is compressed by a constant force spring can be used to determine how the cross-sectional mass, in this case the width of the spring, must vary as a function of x in order that the pressure in the container when compressed with the modified spring remains constant. 
     The force delivered by the spring being linearly dependent on the width of the spring if all other things remain constant, thus:
 
AF(x)=(constant)w(x)
 
Substituting this into equation:
 
 P ( x )=( FCFS−BF ( x ))/ A , then:
 
 P ( x )=( FCFS−AF ( x ))/ A =( FCFS −constant) w ( x )) A  
 
However, it is to be observed that FCFS/A−P(x) is just the difference between the two curves shown in  FIG. 14 , FCFS/A being the horizontal line. Thus, the modification to the width, denoted w(x), of the original constant force spring is proportional to the difference between the two curves shown in  FIG. 14 . In other words, the shape of the change in the width of the spring as a function of x is similar to the difference between the two curves as a function of x. Furthermore, one can simply “read off” the shape of the curve w(x) from the pressure vs. displacement curve.
 
     The broader utility of a variable force spring, whose width defines the specific force, may be that the spring design can be appropriately constructed to deliver a non-linear and highly variable force to meet a specific requirement. In this way, a spring that has a width that simply decreases as it is unrolled could be used. Alternatively, the spring could have an increasing width, followed by a width that decreases again during its distention. The spring force provided is therefore highly tunable to meet a variety of applications and requirements, simply by constructing a spring of specific width at the desired distension. Although a virtually infinite number of designs are possible, by way of non-limiting example, several differently configured springs are illustrated in  FIGS. 15 through 30  of the drawings. 
     Referring to  FIG. 15  of the drawings one form of variable force spring having varying cross-sectional mass along its length is there illustrated. In this instance, the varying cross-sectional mass is achieved by a constant force spring that has been modified to exhibit varying width along its length. As shown in  FIG. 15A , which is a plot of Force versus “L”, where “L” is the distance from the force generating region of the spring to the end of the spring, the spring provides a decreasing force as it is retracted. Conversely, the spring depicted in  FIG. 16  of the drawings, which also achieves varying cross-sectional mass by a spring exhibiting varying width along its length, provides a greater force as it retracts (see  FIG. 16A ). 
     With regard to the spring depicted in  FIG. 17 , this spring achieves varying cross-sectional mass by a constant force spring that has been modified to exhibit varying width along its length and also to exhibit at least one area of reduced width along its length. As illustrated in  FIG. 17A  of the drawings, as this spring rolls up from the extended position shown in  FIG. 17 , it will provide gradually less force, followed by a non-linear reduction in force at the area designated in  FIG. 17  as  55 , followed again by a non-linear increase in force, and finally at the point at which it is almost completely retracted, exhibits a gradually decreasing force. 
       FIG. 18  is a generally illustrative view of the retractable spring of a modified configuration somewhat similar to that shown in  FIG. 15  of the drawings. In this latest spring configuration the varying cross-sectional mass is once again achieved by a constant force spring that has been modified to exhibit varying width along its length. As illustrated in  FIG. 18A , which is a generally graphical representation plotting force exerted by the spring shown in  FIG. 18  versus “L”, the spring provides a decreasing force as it is retracted. 
       FIG. 19  is a generally illustrative view of still another form of retractable spring wherein the varying cross-sectional mass is achieved by a constant force spring that has been modified to exhibit varying width along its length. More particularly, this latest form of the modified spring exhibits a tapered body portion  57 . As illustrated in  FIG. 19A , which is a generally graphical representation plotting force exerted by the spring shown in  FIG. 19  versus “L”, that is the distance from the force generating region of the spring to the end of the spring., the spring provides a decreasing force as it is retracted. 
       FIG. 20  is a generally illustrative view of the yet another form of retractable spring wherein the varying cross-sectional mass is achieved by a constant force spring that has been modified to exhibit varying width along its length. More particularly, this latest form of the modified spring exhibits a tapered body portion  59 , which unlike the body portion  57  of the spring shown in  FIG. 19  tapers downwardly rather than upwardly. As illustrated in  FIG. 20A , which is a generally graphical representation plotting force exerted by the spring shown in  FIG. 20  versus “L”, the spring provides a decreasing force as it is retracted. 
     With regard to the spring depicted in  FIG. 21 , this spring, which is somewhat similar to the spring configuration shown in  FIG. 17  of the drawings, achieves varying cross-sectional mass by a constant force spring that has been modified to exhibit varying width along its length and also to exhibit a plurality of areas of reduced width along its length. As illustrated in  FIG. 21A  of the drawings, as this spring rolls up from the extended position shown in  FIG. 21 , it will provide gradually less force, followed by a non-linear reduction in force at the area designated in  FIG. 21  as  60 , followed again by a non-linear increase in force, followed by a non-linear reduction in force at the area designated in  FIG. 21  as  60   a  and finally at the point at which it is almost completely retracted, once again exhibits a gradually decreasing force. 
     Referring next to  FIG. 22  of the drawings, the spring there depicted, which is somewhat similar to the spring configuration shown in  FIG. 21  of the drawings, achieves varying cross-sectional mass by a constant force spring that has also been modified to exhibit varying width along its length and also to exhibit a plurality of areas of reduced width along its length. However, as illustrated in  FIG. 22A  of the drawings, as this spring rolls up from the extended position shown in  FIG. 22 , it will provide gradually increased force, followed by a non-linear decrease in force at the area designated in  FIG. 22  as  61 , followed again by a non-linear increase in force, followed by a non-linear decrease in force at the area designated in  FIG. 22  as  61   a  and finally at the point at which it is almost completely retracted, once again exhibits a gradually increasing force. 
     Turning next to  FIG. 23  of the drawings, the spring there depicted is also somewhat similar to the spring configuration shown in  FIG. 21  of the drawings. However, the spring shown in  FIG. 23  does not exhibit a tapered body portion like that of the spring illustrated in  FIG. 21 . Rather, the spring achieves varying cross-sectional mass by a constant force spring that has also been modified only to exhibit a plurality of areas of reduced width along its length. As illustrated in  FIG. 23A  of the drawings, as this spring rolls up from the extended position shown in  FIG. 23 , it will provide a slightly decreased force, followed by a non-linear decrease in force at the area designated in  FIG. 23  as  63 , followed again by a non-linear increase in force, followed by a non-linear decrease in force at the area designated in  FIG. 23  as  63   a , followed again by a non-linear increase in force, followed by a non-linear decrease in force at the area designated in  FIG. 23  as  63   b  and finally at the point at which it is almost completely retracted, once again exhibits a gradually decreasing force. 
     Referring now to  FIG. 24  of the drawings, the spring there depicted, is also somewhat similar to the spring configuration shown in  FIG. 21  of the drawings. However, the spring shown in  FIG. 24  exhibits both a non-tapered body portion such as that of the spring shown in  FIG. 23  and also exhibits a tapered body portion like that of the spring illustrated in  FIG. 21 . In this instance, the spring achieves varying cross-sectional mass by a constant force spring that has been modified to exhibit a reduced width along its length and has also been modified to exhibit a plurality of areas of reduced width along its length. As illustrated in  FIG. 24A  of the drawings, as this spring rolls up from the extended position shown in  FIG. 24 , it will provide a generally linear force, followed by a non-linear decrease in force at the area designated in  FIG. 24  as  67 , followed again by a non-linear increase in force, followed by a generally linear force, followed by a non-linear decrease in force at the area designated in  FIG. 24  as  67   a , followed again by a non-linear increase in force, followed by a non-linear decrease in force at the area designated in  FIG. 24  as  67   b  and finally at the point at which it is almost completely retracted, once again exhibits a generally linear force. 
     Referring next to  FIG. 25  of the drawings, the spring there depicted achieves varying cross-sectional mass by a constant force spring that has been modified to exhibit an increased width along its length and has also been modified to exhibit a plurality of areas of reduced width along its length. As illustrated in  FIG. 25A  of the drawings, as this spring rolls up from the extended position shown in  FIG. 25 , it will provide an increase in force, followed by a non-linear decrease in force at the area designated in  FIG. 24  as  68 , followed again by a non-linear increase in force, followed by a gradually increasing force, followed by a non-linear decrease in force at the area designated in  FIG. 25  as  68   a , followed by an increase in force and finally at the point at which it is almost completely retracted, once again exhibits a substantially increase in force. 
     Turning next to  FIG. 26  of the drawings, the spring there depicted is somewhat similar to the spring configuration shown in  FIG. 23  of the drawings and does not exhibit a tapered, central body portion like that of the spring illustrated in  FIG. 21 . Rather, the spring achieves varying cross-sectional mass by a constant force spring that has been modified in its central body portion to exhibit a plurality of areas of reduced width along its length and uniquely exhibits an outwardly tapered end portion. As illustrated in  FIG. 26A  of the drawings, as this spring rolls up from the extended position shown in  FIG. 26 , it will provide an increase in force at the area designated in  FIG. 26  as  69 , followed by a decrease in force, followed by an increase in force at the area designated in  FIG. 26  as  69   a , followed again by a decrease in force and finally at the point  69   c  at which it is almost completely retracted, will exhibit a gradually increasing force. 
     Referring to  FIG. 27  of the drawings still another form of variable force spring having varying cross-sectional mass along its length is there illustrated. In this instance, the varying cross-sectional mass is achieved by a constant force spring wherein the force generating region of the spring has been modified to include a plurality of spaced-apart apertures “AP” along its length. As shown in  FIG. 27A , which is a schematic plot (not to scale) of force versus cross-sectional mass, the spring uniquely provides an increasing force in a stair step fashion as it is retracted. It is to be understood, that the apertures formed in the pre-stressed strip of spring material can be located in any desired configuration and can be both transversely and longitudinally spaced-apart to provide the desired force as the spring is retracted. 
       FIG. 27B  is a generally perspective view of still another form of the retractable spring of a modified configuration that is somewhat similar to that shown in  FIG. 27  of the drawings. However, in this latest spring configuration the spring comprises a novel laminate construction made up of a first laminate FL and a second interconnected laminate SL. The varying cross-sectional mass is once again achieved by providing a plurality of the elongated transversely and longitudinally spaced-apart apertures, or slits. 
     Turning next to  FIG. 28 , still in other form of variable force spring having varying cross-sectional mass along its length is there illustrated. In this instance, the varying cross-sectional mass is once again achieved by a constant force spring wherein the force generating region of the spring has been modified to include a plurality of spaced-apart, generally circular shaped apertures “AP- 4 ” along its length. As shown in  FIG. 28A , which is a plot of force versus cross-sectional mass, the spring uniquely provides a decrease in force, followed by an increase in force, followed again by a lengthy decrease in force, followed by an increase in force and then followed by another decrease in force. 
     Referring to  FIG. 29 , still in other form of variable force spring having varying cross-sectional mass along its length is there illustrated. In this instance, the varying cross-sectional mass is once again achieved by a constant force spring wherein the force generating region of the spring has been modified to include a plurality of spaced-apart, generally circular shaped apertures “AP- 1 ”, “AP- 2 ” and “AP- 3 ” along its length. As shown in  FIG. 29A , which is a plot of force versus cross-sectional mass, the spring uniquely provides the desired variable decrease in force followed by the desired variable increase in force as it is retracted. 
     Turning to  FIG. 30 , still in other form of variable force spring having varying cross-sectional mass along its length is there illustrated. In this instance, the varying cross-sectional mass is once again achieved by a constant force spring wherein the force generating region of the spring has been modified to include a plurality of spaced-apart, generally circular shaped apertures “AP- 1 ”, “AP- 2 ”, “AP- 3 ” and “AP- 4 ” along its length. As shown in  FIG. 30A , which is a plot of force versus cross-sectional mass, the spring uniquely provides the desired variable decrease in force as it is retracted. 
     Referring to  FIG. 31 , still in other form of variable force spring having varying cross-sectional mass along its length is there illustrated. In this instance, the varying cross-sectional mass is once again achieved by a constant force spring wherein the force generating region of the spring has been modified to include a plurality of transversely and longitudinally spaced-apart, generally circular shaped apertures of increasing diameter in a direction away from the force generating region. As shown in  FIG. 31  A, which is a plot of force versus cross-sectional mass, the spring uniquely provides the desired variable decrease in force as it is retracted. 
     Referring to  FIG. 32 , still in other form of variable force spring having varying cross-sectional mass along its length is there illustrated. In this instance, the varying cross-sectional mass is once again achieved by a constant force spring wherein the force generating region of the spring has been modified to include a plurality of transversely and longitudinally spaced-apart, generally circular shaped apertures of decreasing diameter in a direction away from the force generating region. As shown in  FIG. 32  A, which is a plot of force versus cross-sectional mass, the spring uniquely provides the desired variable increase in force as it is retracted. 
     Considering further the operation of the device of the invention, with the apparatus in the configuration shown in  FIG. 4 , and with the fluid reservoir  35  filled with the medicament or diluent to be dispensed to the patient, the dispensing operation can be commenced by removing the top cover  77 , which is snapped over a cover connector  77   a  that is provided on a connector member  79 . With the cover removed as depicted in  FIG. 5  of the drawings, the administration line  58   a  of the administration set  58  can be unwrapped from the guide sleeve  79   a  that extends from connector member  79  and about which it has been coiled (see  FIG. 4 ). Removal of the top cover  77  also exposes selector member housing  80  that houses the important selector member  82  of the invention, the operation of which will presently be described. 
     To control the flow of medicinal fluid from reservoir  35  toward the administration set  58  of the invention and then on to the patient, flow control means are provided. This novel fluid flow control means, comprises two cooperating components, namely a rate control means for controlling the rate of fluid flow from the collapsible reservoir and an operating means for controlling fluid flow between the collapsible reservoir and the rate control means. 
     Considering first the operating means of the invention, it can be seen by referring to  FIG. 4  of the drawings, selector member housing  80  carries a tear strip  84  which retains the selector member housing  80  in its first position and comprises the part of the operating means of the invention. When the tear strip is removed, a rotary force exerted on threaded selector member housing  80  will controllably move the housing along with the penetrating member  40   a , which also comprises a part of the operating means of the invention, into the second penetrating position shown in  FIG. 5 . As the penetrating member moves into the second position, it will pierce the membrane  42  as well as the closure wall  39  in the manner shown in  FIG. 5 . Piercing of the membrane and the closure wall opens a fluid communication path from reservoir  35  to the rate control means of the invention via central fluid passageway  40   b  formed in penetrating member  40   a.    
     Once the carriage locking means of the invention, which also comprises a part of the operating means of the invention, has been manipulated in the manner previously described to release the carriage  28 , the carriage will move upwardly due to the urging of the variable force springs  48  and in so doing will collapse the container  34  in the manner shown in  FIG. 5  of the drawings. As the container collapses, the fluid contained within reservoir  35  will flow outwardly of the reservoir through the outlet  36 , into the passageway  40   b  of the piercing member  40   a , through a filter  83  which is carried by the septum-penetrating assembly  40  and then onward toward the rate control assembly  84  of the rate of control means of the invention. 
     Considering in greater detail the important rate control means of the invention, this important means comprises a novel rate control assembly  84  the construction of which is the best seen in  FIG. 31  of the drawings. Rate control assembly  84  here comprises a rate control plate  86  that is provided with circuitous fluid channels  86   a ,  86   b ,  86   c ,  86   d ,  86   e  and  86   f , each of which is of a different geometry including channel length, depth, width and geometry. During the fluid delivery step, as the fluid flows from reservoir  35  into the inlet  86   p  of rate control plate via the orifice  88   a  of the rate control cover  88 , each of the circuitous fluid channels will fill with the medicinal fluid to be dispensed to the patient. From the circuitous fluid channels, the fluid will flow into outlet passageways  90   a ,  90   b ,  90   c ,  90   d ,  90   e ,  90   f  and  90   p  respectively formed in rate control cover  90 . From these outlet passageways, the fluid flows into and fills circumferentially spaced-apart fluid passageways  94   a ,  94   b ,  94   c ,  94   d ,  94   e  and  94   f  formed in selector housing  80  (see also  FIG. 16B ). 
     As best seen by referring to  FIGS. 33 and 33C , selector member  82  is provided with an inlet passageway  96  and an outlet passageway  98  that is interconnected with inlet passageway  96  by means of an axially extending stub passageway  100  which, in turn, is connected to a circumferentially extending channel passageway  102  formed in selector member  82  ( FIG. 33C ). With this construction, by rotating the selector member  82 , inlet passageway  96  can be selectively brought into index with one of the radial extensions  104  of the axially extending passageways formed in selector member housing  82  thereby providing fluid communication between outlet passageway  98  and the selected one of the circuitous flow passageways formed in rate control plate  86  via annular channel passageway  102  and the selected axially extending passageway formed in the selector member housing  80 . Since outlet passageway  98  is in fluid communication with the administration set  58  of the invention via passageway  106  ( FIG. 33A ), the rate of fluid flow toward the patient can be precisely controlled by selecting a rate control passageway of appropriate configuration and length that is formed in rate control plate  86 . 
     More particularly, the desired flow rate can be selected by controllably rotating the selector member  82 , which is secured in position by a selector member retainer component  110 , to the desired flow rate indicated by the indicia “I” that is imprinted on the selector member retainer component  110  (see  FIG. 33 ). 
     To recover any medicament that may remain in reservoir  35  following the fluid delivery step, a pierceable septum  113 , which is carried by selector member  82 , can be conveniently pierced using a conventional syringe, or like apparatus (not shown). Piercing of septum  113  opens communication between reservoir  35  and the syringe via inlet  115   a  of a central passageway  115 , via the rate control assembly  84 , via passageway  115   a  and via passageway  40   b  of penetrating member  40   a  so that any remaining medicament can be readily extracted from reservoir  35 . 
     It is to be noted that the movable components of the dispensing apparatus typically carry conventional “O”-rings to provide appropriate sealing of the components within the apparatus with their mating parts. Throughout the drawings these “O”-rings are identified as “O”. 
     In the present form of the invention, administration set  58 , which comprises a part of the dispensing means of the invention for delivering medicinal fluids to the patient, includes, in addition to administration line  58   a , a conventional “Y”-site injection septum or port  58   b , a conventional gas vent and particulate filter  58   c  and a line clamp  58   d . Provided at the distal end of the administration line is a Luer connector  58   e  of conventional construction ( FIG. 3 ) which enables the apparatus to be interconnected with the patient in a conventional manner. 
     Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.