Abstract:
The formation of a bellows made up of a stack of a predetermined number of ring-convolutions and having an intermediate plate supported within said stack is achieved by supplying several thin metal rings, each having inner and outer edges. A pair of these metal rings are positioned in contiguous relationship and their adjacent inside edges are welded together to form a ring-convolution. This process is repeated until a sufficient number of ring-convolutions are made to eventually make the desired bellows. Before these separate ring-convolutions are fused to each other, an intermediate plate and a support ring are made. The intermediate plate is a disc of metal that is sized smaller than the inside diameter of the rings and is secured to the support ring. The support ring is then positioned between two formed ring-convolutions in contiguous relationship and the three abutting outside edges are welded to each other to form a support plate convolution. The already made ring-convolutions and the support plate convolution are then stacked in the desired order and in contiguous relationship. All not-yet welded adjacent outside edges of said ring-convolutions and said support plate convolution are then welded to form the bellows. A bottom plate is formed and welded to the outside edge of the bottommost ring-convolution and a top ring is finally welded to the uppermost convolution to complete the bellows. The top ring is meant to be welded to a base plate of an infusion pump.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of US Provisional Patent Application No. 60/731,678 filed on Oct. 31, 2005, entitled “Implantable Pump with Reservoir with Level Detector”, and US Non-Provisional patent application Ser. No. 11/552,343 filed on Oct. 24, 2006, entitled “Implantable Pump with Reservoir Level Detector”, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention generally relates to the method of manufacture of metal bellows of the type used to form a fluid reservoir in implantable infusion pumps, and more particularly, to the method of manufacture of such metal bellows having an intermediate plate to aid in accurate sensing of the volume of the bellows. 
     2) Discussion of Related Art: 
     Extremely thin-gauge titanium welded bellows are commonly used in implantable infusion pumping devices as the main drug reservoir. A pump of this type is implanted within a patient and is used to accurately administer a precise dose of a stored liquid medication either continuously or at carefully timed intervals. As is well known in the art, within these small pumps, a metal bellows holds a supply of a liquid medication and is located within a sealed rigid propellant chamber containing a pressurized gas. The surrounding pressure differential within the chamber applies an even force to the bellows, which in turn collapses against the liquid medication within in a controlled and predictable manner. The collapsing bellows applies an even force to the contained liquid medication and in doing so, forces the liquid through controlling conduits and valves located elsewhere within the pump, eventually expelling the liquid medication to a target site within the patient. The liquid typically passes through what is called a micro-channel restrictor so that even though the pressure exerted on the liquid medication is very high, it dispenses from the pump at an extremely slow and controlled rate. 
     Since these pumps are surgically implanted within a patient, they are for the most part, inaccessible for long periods of time. For this reason, electrical and magnetic signals are typically used as a means of communication between the different sensing and controlling systems within the pump and remote monitoring devices located outside the patient&#39;s body. One such sensing system is used to detect the amount of medicament remaining the fluid reservoir of the pump. For obvious health reasons, it is important to know the moment the medicament level falls to a predetermined threshold so that the patient is never without treatment, as prescribed. When the threshold is reached, a piercing conduit can be used to replenish the liquid medicament supply within the bellows by penetrating the patient&#39;s skin and an additional septum within the pump. 
     Although there are likely different sensing methods that could be used to determine the amount of medicament within the fluid reservoir of these implantable pumps, one preferred system is disclosed in U.S. Pat. No. 6,755,814, which is commonly owned by the assignee of the present invention. 
     U.S. Pat. No. 6,755,814 discloses an implantable infusion pump that has a reservoir level detector. The pump includes a housing having a base plate which separates the housing into a pump electronic chamber and a propellant chamber. A bellows mechanism is disposed within the propellant chamber. The bellows mechanism has a bottom plate and defines a collapsible fluid reservoir into which the medicament for delivery to a patient is stored. A propellant is disposed about the bellows mechanism within the propellant chamber. The propellant compresses the bellows mechanism and thereby pushes the medicament out of the bellows mechanism through a flow restrictor, a valve and an outlet of the pump. As the bellows empties, the bottom plate naturally advances towards the base plate of the pump. 
     According to U.S. Pat. No. 6,755,814, a sensing circuit including a capacitor and a coil disposed within the base plate is used to form a resonant circuit. When energized, the coil generates a primary electromagnetic field, which flows through the bottom plate of the bellows mechanism and induces eddy currents therein. The strength of these eddy currents increases as the bottom plate moves closer to the coil within the base place. The eddy currents generate a secondary magnetic field, which is coupled back to the primary field. The closer the bottom plate is to the coil, the stronger the secondary magnetic field is and its influence on the primary field. This flux coupling brings about change to the inductance of the coil and thus brings about a displacement or shift of the resonance frequency of the resonant circuit depending on the distance between the coil and the bottom plate. Upon measuring the resonance frequency, which is dependent upon the inductance, well known circuitry can be employed to calculate the distance that the bottom plate of the bellows mechanism is from the base plate. This distance can then be used to determine the effective volume of the fluid reservoir and also the amount of medicament remaining within the bellow mechanism. An appropriate circuit can use this information to selectively create an alarm signal in response to a predetermined resonant frequency being reached. 
     In the prior art, such as the apparatus disclosed in U.S. Pat. No. 6,755,814, the measurement of fluid remaining in the reservoir is only accurate for the last 20 ml of fluid within the bellows mechanism. At fluid levels greater than about 20 ml and because of the increasing distance between the coil and the bottom plate at those greater volumes, the measured inductance doesn&#39;t vary sufficiently to provide accurate measurements. 
     In an effort to solve this problem, Applicant has filed US Patent Application No 2007/0106280 on Oct. 24, 1006, based on a provisional case filed Oct. 31, 2005, which is also commonly owned by the assignee of the present invention. U.S. Patent Application No. 2007/0106280 discloses an implantable infusion pump having the same main parts and operating in basically the same manner as that described above in U.S. Pat. No. 6,755,814, but further including an “intermediate plate”. This intermediate plate is secured within the bellows structure and inside the fluid reservoir and works with the resonant sensing circuit so that the volume of fluid within the bellows mechanism can be measured with a greater degree of accuracy, not only above 20 ml, but also within the critical range of between 0 and 20 ml. 
     To help explain the present invention, a quick discussion of the basic structure and operation of the pump of US Patent Application No 2007/0106280 is in order. To this end, referring now to  FIG. 1  of the present application, an implantable pump  10  in accordance with the invention disclosed in U.S. Patent Application No 2007/0106280 is shown. Pump  10  has a housing  12 . The housing is comprised of a base plate  14  and a can  13 . Can  13  is attached to the base plate  14 . Base plate  14  divides the housing into an electronics chamber  16  and a propellant chamber  18 . A bellows mechanism  20  is connected to the base plate  14  and is disposed within the propellant chamber  18 . The bellows mechanism  20  has a hermetically sealed expandable sidewall  22  and a bottom plate  24 . The bellows mechanism  20  divides the propellant chamber into a medicament-receiving portion  26  and a non-medicament receiving portion  28 . In one preferred exemplary embodiment of U.S. Patent Application No. 2007/0106280 a propellant located within propellant-receiving portion  28  applies an even force the adjacent bellows  20  causing the medicament within medicament-receiving portion  26  to be delivered to an outlet of pump  10  in a manner known to those skilled in the art. Alternatively, the pump maybe an active pump, such as, for example, a peristaltic-type pump, and the medicament in medicament-receiving portion is in fluid communication with the peristaltic pump conduit so that medicament is drawn from medicament-receiving portion  26  and subsequently delivered to the target site by way of the conduit. In this embodiment of U.S. Patent Application No. 2007/0106280, portion  28  may contain no propellant at all or a relatively small amount of propellant. 
     Regardless, in either case, the bellows mechanism of U.S. Patent Application No. 2007/0106280 includes an intermediate plate  30  disposed within the medicament-receiving portion  26 . Intermediate plate  30  has at least one through-hole  32  therein to permit medicament to pass there-through. In a preferred exemplary embodiment of U.S. Patent Application No. 2007/0106280, intermediate plate  30  has four symmetrical through-holes  32 . Those skilled in the art will readily appreciate that numerous other configurations can be used for intermediate plate  30  so long as they have the functionality to practice the specific embodiment. For example, plate  30  could be in the form of a grid. Plate  30  is preferably made of a biocompatible, non-magnetic material, such as, for example, titanium. According to U.S. Patent Application No. 2007/0106280, plate  30  could also be made of a combination of materials, such as, for example, a sandwich or layers of different materials, with the outer layer being biocompatible. U.S. Patent Application No. 2007/0106280 also discloses that intermediate plate  30  is preferably positioned 25% to 50% of the distance from the base plate  14  to the bottom plate  24  of bellow mechanism  20  at free length (e.g., when the bellows is in a stable state during its manufacturing). More preferably, intermediate plate  30  is disposed 33% to 40% of the distance from the base plate  14  to the bottom plate  24  of bellow mechanism  20 . In a currently preferred exemplary embodiment, intermediate plate  30  is disposed approximately 40% of the distance from the base plate  14  to the bottom plate  24  of bellow mechanism  20 . Thus, referring now to  FIG. 1 , the distance b divided by distance a (i.e., ratio b/a) is preferably 0.40, or 40%. 
     U.S. Patent Application No. 2007/0106280 further discloses that a coil  34  is disposed in a recess  36  on the lower surface  38  of base plate  14 . A mu-metal  40  is disposed between coil  34  and base plate  14 . Mu metals are nickel and iron alloys (usually 75% nickel, 15% iron and include copper and molybdenum) that offer very high magnetic permeability. This mu-metal  40  acts as a rear shield of the coil to limit the eddy current in the base plate  14 . In addition, coil  34  is spaced from the internal wall, which is preferably made of titanium, by a distance. Coil  34  is isolated from the medicament chamber with a biocompatible titanium ring  35 . 
     In a currently preferred exemplary embodiment of U.S. Patent Application No. 2007/0106280, the pump housing  12  is made of titanium. In addition, as stated above, intermediate plate  30  is also preferably made of titanium. The sensitivity in detecting the intermediate plate  30  increases with increasing thickness of plate  30 . However, increasing the thickness of plate  30 , increases the weight of the device and decreases the internal volume of the reservoir in the pump because intermediate plate  30  is disposed within the bellows reservoir medicament-receiving portion  26 . The plate may have a thickness ranging from 0.2 mm to 0.7 mm, with 0.5 mm being preferred in a currently preferred exemplary embodiment. The value of the inductance seen across coil  34  is affected by the location of the intermediate plate  30  and bottom plate  24 . The resonant frequency of the circuitry in which the coil  34  is placed is influenced by the inductance across coil  34 . The amount of fluid remaining in the reservoir is determined based upon the measurement of the resonant frequency, which is correlated to the inductance. Currently pending and commonly owned U.S. patent application Ser. No. 1/278,048, filed Mar. 30, 2006, and entitled “Methods and Devices for Monitoring Fluid of an Implantable Infusion Pump” discloses, inter alia, a manner of using a fluid level sensor to monitor the amount of fluid in a reservoir. The disclosure of pending U.S. application Ser. No. 11/278,048, as well as the disclosure of U.S. Patent Application No. 2007/0106280 are both in their entirety, hereby incorporated by reference. 
     It is a first object of the invention to provide a method for manufacturing the metal bellows fluid reservoir including the intermediate plate of the pump described in U.S. Patent Application No. 2007/0106280. 
     SUMMARY OF THE INVENTION 
     The formation of a bellows made up of a stack of a predetermined number of ring-convolutions and having an intermediate plate supported within said stack, according to the present invention is achieved by starting with a supply of thin metal rings, each ring having a first outer diameter defining a first outer edge and a first inner diameter, defining a first inner edge. A pair of these metal rings are positioned one on top of the other in a contiguous relation to each other and their adjacent inside edges are welded together to form a ring-convolution. This process is repeated until a sufficient number of ring-convolutions are made to eventually make the desired bellows. Before these separate ring-convolutions are fused to each other, an intermediate plate and a support ring are made. The intermediate plate is a disc of metal that is sized smaller than the inside diameter of the rings and is secured to the support ring. The support ring is then positioned between two formed ring-convolutions in contiguous relationship and the three abutting outside edges are welded to each other to form a support plate convolution. The already made ring-convolutions and the support plate convolution are then stacked in the desired order and in contiguous relationship. All not-yet welded adjacent outside edges of said ring-convolutions and said support plate convolution are then welded to form the bellows. A bottom plate is formed and welded to the outside edge of the bottommost ring-convolution and a top ring is finally welded to the uppermost convolution to complete the bellows. The top ring is meant to be welded to a base plate of an infusion pump. The method includes steps for holding the rings to be welded into a jig and thereafter moving the jig with respect to the welder, or moving the welder with respect to the jig. The welder preferably includes the use of a laser wherein the output beam of the laser may be easily moved along the held rings by appropriate optics, but the welder may also be an arc-TIG type. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1 , labeled “Prior Art” is a cross-sectional elevation view of an infusion pump having an intermediate plate which is used to help explain the operation of the infusion pump including a metal bellows; 
         FIG. 2  is a perspective section view of the bellows of the infusion pump of  FIG. 1 , showing detail of upper and lower rings, an intermediate ring, an intermediate plate, a top ring and a bottom plate; 
         FIG. 3  is a perspective view of an upper ring and a lower ring being assembled together, according to the method of manufacture of the present invention; 
         FIG. 4  is perspective view of a schematic illustration showing a welding process according to the methods of manufacture of the present invention, wherein an inner edge of an upper ring is fused to an inner edge of a lower ring, creating a “convolution”; 
         FIG. 5  is an enlarged partial section view of a fused convolution of  FIG. 4 , according to the method of manufacture of the present invention, showing details of the fused inner edge of the two rings; 
         FIG. 6  is a perspective view of a schematic illustration showing the intermediate plate being fused to an intermediate-plate support ring, according to the method of manufacture of the present invention; 
         FIG. 7  is an enlarged partial section view of a fused intermediate subassembly, according to the method of manufacture of the present invention, showing details of the fused inner edges of the two convolutions and intermediate ring; 
         FIG. 8  is an elevation assembly view of the entire bellow assembly showing the relative positioning of each convolution and intermediate subassembly, top convolution and bottom plate, according to the method of manufacture of the present invention; 
         FIG. 9  is a perspective view of the fully assembled bellows made by the method of manufacture of the present invention; 
         FIG. 10  is a perspective assembly view of an intermediate plate, a support ring, and a sensor coil according to a second embodiment of the invention; and 
         FIG. 11  is a cross-sectional perspective view of the intermediate plate, a support ring, and sensor coil of  FIG. 10  shown with the intermediate plate welded to the support ring, according to the second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 2 and 9 , a bellows  100  (cross-sectional view in  FIG. 2 ) is shown including a plurality of upper diaphragm rings  102  (hereinafter called “upper rings”) edge-welded to a plurality of lower diaphragm rings  104  (hereinafter called “lower rings”, a top ring  106 , a bottom plate  108 , an intermediate plate  110  and an intermediate-plate support ring  112 . The bellows  100  shown in  FIG. 9  is manufactured primarily by welded pre-cut and formed parts together in a predetermined order, as described below. 
     According to the method of manufacture of the present invention, each upper and lower ring  102 ,  104 , top ring  106 , bottom plate  108 , an intermediate plate  110  and an intermediate-plate support ring  112  is made by cutting a predetermined shape from an appropriate bio-compatible material, such as titanium, stainless steel, an appropriate composite, alloy, or a laminate made up of different metals and/or composites. 
     All the main parts of the bellows  100 , including rings  102 ,  104 , bottom plate  108 , top ring  106 , intermediate plate  110 , and intermediate ring  112  are preferably made from titanium. The material thickness of upper and lower rings  102 ,  104 , top ring  106  and intermediate-plate support ring  112  is within the range of 0.06 mm and 0.12 mm depending on the size and design parameters of the pump assembly, with 0.8 mm being a preferred thickness of these parts in this exemplary embodiment. The thickness of the intermediate plate  110  will also vary depending on design factors and materials selected. As mentioned above, the thicker the intermediate plate, the more accurately it will “communicate” with coil  34  (shown in  FIG. 1  and described above in the background section of this application), but the heavier the pump will become and also the less volume available within the reservoir for liquid medication. In this exemplary embodiment, intermediate plate  110  is 0.5 mm thick, but may vary from 0.2 mm and 0.7 mm thick. 
     The basic shape of each ring  102 ,  104 ,  106 ,  112 , bottom plate  108  and intermediate plate  110  is formed by cutting prescribed shapes from sheet titanium using any of a variety of known processes including stamping, laser-cutting, or water-jet abrasive cutting, however, a simple stamping process is preferred, owing to the speed and accuracy this well known process typically offers. The stamping machine preferable cuts the ring shape from stock sheet material in one smooth stroke, leaving clean sharp edges. 
     Once cut, each ring  102 ,  104 ,  106 ,  112 , bottom plate  108  and intermediate plate  110  are formed to a desired shape using an appropriate forming process and machine, such as using a forming press. 
     A forming press, which is well known, employs two opposing forming dies which, in use are pressed firmly into opposing sides of an interposed metal blank to shape the blank. The dies are forced together using tremendous pressure and at times with applied heat so that the metal blank will be forced to take on the shape of the dies. 
     As is well known, combination machines are available that allow stamping and forming of a ring shape in one stroke. This would be preferred to simplify the manufacturing process. 
     The details of the cutting and forming processes are not shown in the figures of the present application since these processes are well known. The main parts of the bellows of the present invention may be made using any of a variety of processes, the specific details of which are beyond the scope of the immediate invention. 
     When the upper and lower rings  102 ,  104  are formed, each will have a distinctive concentric wave pattern of predetermined height, width and pitch formed therein. Also, upper ring  102  will have a radial slant wherein an outer edge  103  will reside within a higher plane to that of an inner edge  105 . Conversely, lower ring  104  will be formed with an opposite radial slant so that an outer edge  107  will reside in a plane that is lower than that of an inner edge  109 . This detail of rings  102 ,  104  is best shown in  FIG. 3 . Of course, the specific shapes of rings  102 ,  104  may vary according to the details of design. The rings may include several “waves” and may in some instances be formed symmetric so that an upper ring  102  is merely an inverted lower ring  104 . Rings of any shape can be used with the steps of the present method without departing from the invention. 
     Top Ring 
     As described above, in this exemplary embodiment of the invention, different sets of dies would be required to form upper ring  102 , lower ring  104 , bottom plate  108 , top ring  106  and intermediate-plate support ring  112 . For example, top ring  106  is formed in a similar manner to upper and lower rings  102 ,  104 , but is preferably larger in outside diameter and includes particular concentric pattern that allows it to be easily fused to base  14  (refer to  FIG. 1  and the description above). 
     Intermediate Plate 
     In this exemplary embodiment, intermediate plate  110  is preferably flat and requires no specific forming, however, as shown in  FIGS. 2 and 6 , intermediate plate  110  is preferably provided with four large openings  114 , which allow liquid medication to flow freely above and below intermediate plate  110  within fluid reservoir during the operation of the pump. The large openings  114  are preferably formed by a stamping process. 
     Intermediate-Plate Support Ring 
     Also, as shown in  FIGS. 2 and 6 , intermediate-plate support ring  112  is formed to include a shallow dish and is thereafter stamped using a stamping machine to cut out preferably four large sections  116 , as shown, to define four similarly shaped support arms  118 . Each arm  118  is formed extending from the center to the outer ring, like spokes of a bicycle wheel. Support arms  118  are used to support intermediate plate  110 , as described below. 
     As shown in  FIG. 6 , intermediate plate  110  is secured to support arms  118  of intermediate-plate support ring  112  using any appropriate welding technique, such as spot welding. In this exemplary embodiment, four spot welds  120  are preferably formed, one weld to each arm  118 . Spot welding is a well known and commonly used technique to quickly and effectively secure two metal parts to each other using local heat transmission. The details of this process are beyond the scope of this invention and are therefore not described in any great detail. Once intermediate plate  110  is welded to intermediate-plate support ring  112 , intermediate plate subassembly  122  is formed. 
     Referring now to  FIGS. 3 ,  4 , and  5 , an upper ring  102  and a lower ring  104  are secured to each other along their respective inner edges  105 ,  109 . This is done by mounted each ring into an appropriate rotatable holding jig (not shown), which is well known in the art. The rotatable holding jig is designed to firmly hold upper ring  102  with respect to lower ring  104  so that the inner edge  105  of upper ring  102  aligns and abuts with inner edge  109  of lower ring  104 . The holding jig is designed to clamp onto both rings  102 ,  104  in such a manner that the entire circumference of both inner edges  105 ,  109  of both rings are accessible to a welder and so that the inner edges are held together in an intimate contiguous relationship. 
     As these two rings are held by the holding jig, the jig is rotated at a controlled rotation rate and a welder is applied to effectively fuse the adjacent inner edges  105 ,  109  of each ring together along the entire inside circumference of the ring pair. 
     The conventional approach to joining such rings has been to use tungsten inert gas (TIG) to weld both the inside and outside joints. Unfortunately, TIG welding is relatively slow and may produce inconsistent quality welds. TIG welding also introduces a high level of heat energy to the metal structures which must be appropriately absorbed (using copper “chill rings”) and diverted from the rings to prevent warping damage to the ring structures. To this end, a more precise and less heat-invasive laser welding process is preferably used to fuse the upper and lower rings to each other. 
     Referring to  FIG. 4 , a schematic of a laser-welder is illustrated showing an upper ring  102  secured to a lower ring  104  (jig not shown, for clarity). The two rings  102 ,  104  are set into a controlled rotation (represented by arrow  130 ) about a central axis  132 . In a first laser welding arrangement, a first laser diode  134  is positioned above upper ring  102  so that an output beam  136  contacts a portion of upper ring immediately adjacent to inner edge  105 . Similarly, a second laser diode  138  is positioned below lower ring  104  so that an output beam  140  contacts a portion of lower ring immediately adjacent to inner edge  109 . Both beams  136  and  140  may operate together in a continuous manner or may pulse at controlled intervals and durations, as is well known in the art. The output of each laser  134 ,  138  is focused onto a target area preferably located immediately adjacent to the respective inner edges  105 ,  109  of each secured ring  102 ,  104 . 
     As is well known, the focusing arrangement can be accomplished using computer controlled mirrors and lenses situated as necessary between lasers  134 ,  138  and the target area on the rings  102 ,  104  being held in the jig. Each outputs of laser  134 ,  138  is in the form of an energy pulse, which can be digitally shaped using appropriate optics and computer control. The pulse has sufficient energy to weld the two secured rings  102 ,  104  together within the target area of focus. Of course, although two lasers are shown in this example and in  FIG. 4 , a single laser may also be used. In such instance, the energy of the single laser pulse is controlled to be insufficient to penetrate the both rings  102 ,  104 , but sufficient to effectively fuse the two rings together. 
     An infrared or other sensor can be coupled to the output optics of the laser to receive a signal indicative of the temperature achieved in the weld puddle at the top ring pair within the focus area to serve as an indicator of the weld function. A suitable feedback can be coupled to the sensor and to the laser source controls for supplying a corrective signal to the laser source. 
     The digital programming of the present invention may control the laser output so that an initial energy burst is followed by a rest phase. During subsequent bursts, more or less energy may be applied following a prescribed program designed for the particulars of the two rings  102 ,  104 , until the two rings located at the target area are properly fused to each other. The pulsed bursts will produce a generally circular or elliptical spot weld. The lasers continue to spot weld the edges until the entire inside circumference has been welded. Of course, to create an effective and required hermetic seal, each spot weld will have to overlap with adjacent spot welds, as is known in the art. The locations for sequential spot welds are preferably separated sufficiently so that there is very little, if any, residual thermal energy present in the ring at the second location due to prior activity of the laser. In this way, each welded spot can be supplied with about the same amount of energy without any significant risk of delivering too much energy. The sequentially welded areas can be adjacent to each other, however such positioning can, in certain circumstances, tend to induce thermal warps in the delicate thin metal rings  102 ,  104 . 
     As the holding jig rotates the ring pair with respect to the beams,  136 ,  140 , the energy produced by the beams effectively fuses upper ring  102  to lower ring  104  along the combined respective inner edges  105 ,  109 . The welding continues until a continuous and hermetically-tight bond is formed along the entire circumference of both upper and lower rings. 
     Alternatively, also shown in  FIG. 4 , instead of rotating the holding jig, the laser beam may be optically directed around the inner edge of both rings so that the edges are again effectively fused to each other. One way to do this is to position a laser  150  so that an output beam  152  is directed along central axis  132 , perpendicular to the plane in which both rings  102 ,  104  contact each other, as they are both held by holding jig. A mirror  156  is attached to the shaft of a motor  158  at a 45 degree angle and positioned to capture and reflect the output beam  152  to contact the inner edges  105 ,  109  of both rings  102 ,  104 . As the motor  158  rotates mirror  156 , the output beam  152  of laser  150  will move along the inner edges  105 ,  109  and fuse them together, forming a clean weld bead. Again, as before, the output of laser  150  may be pulsed to create small spot welds that are produced in an overlapping relationship to create a hermetic seal. 
     To improve the quality of the resulting welds, all of the welding steps disclosed in this application are preferably performed with the working parts located either within an evacuated chamber (within a vacuum) or in the presence of an inert gas, as understood by those skilled in the art. 
     U.S. Patent Application 2003/0226247, filed Oct. 28, 2002 and U.S. Pat. No. 6,040,550 both disclose methods of fusing bellow rings to each other. The rings of this present application may be fused using the processes described in these two identified applications. The entirety of both U.S. Patent Application 2003/0226247 and U.S. Pat. No. 6,040,550 are hereby incorporated by reference. 
     Regardless how the inner edge  105  of upper ring  102  is hermetically fused to the inner edge  109  of lower ring  104 , forming a “convolution”  160 , the process is repeated with different upper and lower rings  102 ,  104 , to form a sufficient number of convolutions  160  necessary to assemble the entire bellows  100 . Of course the number of convolutions required will vary depending on the design of the particular bellows. A bellows that is used as a fluid reservoir within an implantable infusion pump will typically include between 6 and 12 convolutions. 
     Referring to  FIG. 2  and using the same process described above and shown in  FIG. 4 , an inside edge  111  of top plate  106  is fused to an adjacent inside edge  109  of a lower ring  104  to form a top convolution  162 . 
     According to an important aspect of the present invention, and referring to  FIGS. 7 ,  8 ,  9  and  10 , an outer edge  164  of intermediate plate subassembly  122  is fused to two opposing convolutions  160  at an outer edge  103 ,  107  of the respective upper and lower ring which make up the convolutions. As above, an appropriate holding jig (not shown) is used to hold intermediate plate subassembly  122  between two convolutions  160  so that outer edge  164  of intermediate plate subassembly  122 , outer edge  103  of the lower ring  104  of one convolution  160  and outer edge  107  of upper ring  102  of the other convolution each align and abut with each other. Once the three outer edges are properly held and aligned within the holding jig, the output beam  166  of an appropriate laser  168  is directed along the combined edges so that as the holding jig rotates, all three outer edges,  164 ,  103 , and  107  are effectively fused to each other forming a hermetic seal therealong, creating assembly  170 , shown in  FIG. 7  (in partial section view). As described above in connection with lasers  134 ,  138 , the laser  168  may include appropriate optics to help guide and focus the output beam as required and may follow the same pulse programming as that described above. 
     Referring now to  FIG. 8 , an assembly view of bellows  100  is shown to illustrate how the different parts that make up the bellows are put together in final assembly. The final assembly of this exemplary embodiment is performed using the outside-edge laser welding process described above. 
     To being the final assembly, top convolution  162  and a convolution  160  are positioned in an appropriate holding jig, similar to the ones described above so that top ring  106  faces away from convolution  160 . Outer edge  107  of lower ring  104  of top convolution  162  is positioned into contact with outer edge  103  of upper ring  102  of convolution  160 . The two outer edges are then laser welded using the outer-edge welding process described above. 
     Once welded together, the assembly continues by laser welding subassembly  170  (which contains intermediate plate  110  and intermediate-plate support ring  112 ), outer-edge to outer-edge. Next, another convolution  160  is laser welded outer-edge to outer-edge using the same process. In this exemplary embodiment, four additional convolutions  160  are laser welded, outer-edge to outer-edge. Finally, the outer edge of bottom plate  108  is laser welded to the outer edge  107  of lower rig  104  to complete the assembly. 
     The completed bellows  100  is shown in  FIG. 9 . 
     Referring now to  FIGS. 10 and 11 , an intermediate plate  200 , a support ring  202  and an exemplary sensor coil  204  are shown according to a second embodiment of the invention. Sensor coil  204  is similar to coil  34  of  FIG. 1  (Prior Art) and described above in the Background of the Invention section of this application. Coil  204  is made from a coil of wire and is located within the pump assembly (not shown in  FIGS. 10 and 11 . Coil  204  is electrically connected to a well known sensing circuit (not shown). Coil  204  (like coil  34 ) essentially functions as an inductive proximity sensor and uses the inductive influence of intermediate plate  200  to determine the distance between the plate and the coil. 
     As can be seen in the figures, intermediate plate  200  is ring shaped having an outside diameter defining an outer edge  206  and having an inside diameter defining an inner edge  208 . Support ring  202  includes a support ledge  210  which is sized and shaped to receive intermediate plate  200 . Support ledge  210  defines an inner edge  212  having an inside diameter. Inside diameter of inner edge  212  is less than the outside diameter of intermediate plate  200 , but greater than the inside diameter of intermediate plate  200 . This will allow an overlap between support ledge  210  and intermediate plate  200 . This overlap allows intermediate plate  200  to be spot welded to support ledge  210  and also support ring  202 . 
     By being ring shaped, intermediate plate  200  offers a large central opening  214  which allows the liquid medication located within the bellows to move freely around intermediate plate  200 . Ring shaped intermediate plate  200  is preferably shaped similarly to ring-shaped sensor coil  204  so that it remains effective at communicating with sensor coil  204  so that the magnitude of collapse of the bellows can be accurately sensed, as described above in the Background of the Invention section of this application. The ring shape of intermediate plate  200  according to this embodiment also allows the plate to be as light as possible so that its presence does not adversely influence the movement of the bellows. 
     Once the intermediate plate  200  is welded to support ring  202 , support ring may be welded to the other rings which make up the bellows as described above in the method of manufacture of the present invention. Intermediate plate  200  and support ring  202  may be made using the same steps described above used to manufacture intermediate plate  110  and intermediate support plate  112  and can also be made from one of the same selection of materials, preferably titanium. Sensor coil  204  is shown in  FIGS. 10 and 11  as exemplary to help explain this embodiment of the invention. Sensor coil  204  can take on other shapes. The point of this second embodiment is to minimize the size and weight of the intermediate plate  200  without effecting its communication with sensor coil  204 . 
     In operation, a sensing circuit (not shown) including a capacitor is electrically connected to coil  204  which is disposed within the base plate of the pump (not shown). This sensing circuit is used to form a resonant circuit. When energized, coil  204  generates a primary electromagnetic field, which flows through the intermediate plate  200  and induces eddy currents therein. The strength of these eddy currents increases as the intermediate plate  200  plate moves closer to coil  204 . As is well known, the eddy currents generate a secondary magnetic field, which is coupled back to the primary field. The closer intermediate plate  200  is to coil  204 , the stronger the secondary magnetic field is and its influence on the primary field. This flux coupling brings about change to the inductance of coil  204  and thus brings about a displacement or shift of the resonance frequency of the resonant circuit depending on the distance between the coil and intermediate plate  200 . Upon measuring the resonance frequency, which is dependent upon the inductance, well known circuitry can be employed to calculate the distance that the intermediate plate of the bellows mechanism is from the base plate. This distance can then be used to determine the effective volume of the fluid reservoir and also the amount of medicament remaining within the bellow mechanism. An appropriate circuit can use this information to selectively create an alarm signal in response to a predetermined resonant frequency being reached. 
     It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims. For example, the above described steps illustrate the method of manufacturing an exemplary metal bellows  100 , according to the invention, wherein intermediate plate  110  is positioned between the second and third convolution  160  from top ring  106  and further includes five additional convolutions  160  between bottom plate  108  and intermediate plate  110 . Other arrangements can similarly be assembled without departing from the invention.