Patent Application
20080312595
This invention relates generally to a drug pump. More particularly, the present invention relates to a multiple piece actuator for a drug pump.
Infusion devices may be used to deliver an infusion media (e.g. a medication such as insulin) to a patient. Such devices may be designed to be implanted into a patient's body to deliver predetermined dosages of the infusion media to a particular location within the patient's body, e.g. in the venous system, the spinal column, or within the peritoneal cavity. A known infusion device of the type described above includes a drive mechanism that includes a reciprocating pumping element, otherwise known as an actuator member. The reciprocating pumping element includes an actuator that has a piston portion coupled to an armature portion, also known as a piston actuator or pole. The piston portion is configured to reciprocate within a piston channel when a solenoid coil is alternately energized and de-energized. That is, when the solenoid is energized, magnetic flux causes the actuator to move very quickly (i.e. in the order of 2-3 milliseconds) until it reaches a stop member. This corresponds to the pump's forward stroke and results in the delivery of a predetermined dosage of infusion media from an outlet chamber to the patient. When the solenoid is de-energized, the lack of magnetic flux allows the actuator to return to its original position under the force of a spring or other return mechanism. This, in turn, causes the pressure in the piston chamber to fall. The reduced pressure in the piston chamber causes infusion media to flow from a reservoir through an annulus between the actuator piston and the piston cylinder wall to refill the piston chamber, thus equalizing the pressure between the reservoir and the piston chamber and preparing the pump for its next pumping or delivery stroke.
Manufacturing of the actuator as a single piece made up of the piston portion and the armature portion requires near perfect tolerances in form and perpendicularity to assure the trouble free operation of the actuator over the life of the pump. If the perpendicularity of the piston from the armature is off slightly, or the piston is not located correctly on the armature, wear issues may develop that could cause premature failure of the pump. A continued need therefore exists for actuator designs that reduce manufacturing costs and improve performance.
According to an aspect of the invention, a
more
Embodiments of the present invention will hereinafter be described in conjunction with the following drawings wherein like reference numerals denote like elements throughout.
The present invention is an actuator for a piston pump that includes a separately manufactured piston and armature. The piston and the armature are later assembled together or are inserted into the piston pump in such a manner as to cooperate during pumping. Assembling the piston and the armature as separate components may provide for improved form of the piston component when manufactured separately from the armature, due to, for example, increased simplification of the manufacturing process. In addition, effects of manufacturing the piston and the armature together, such as stress on the piston, may be reduced. Moreover, as further described below, allowing for a joint or point surface contact between the piston and the armature may reduce or eliminate the ability of the pole to induce wear on the armature, or visa versa, through stresses or through rotation of the components during the pumping process. The armature and piston may also be referred to other names without effecting the scope of the present invention, such as, for example, the armature may be known as a pole
In one embodiment, the actuator is formed as three pieces and assembled before placement in the pump. In further embodiments the actuator may be separately formed in two or more pieces and then assembled before or after placement of one or more pieces into the pump. As may be appreciated, the separate pieces of the actuator may be connected in a number of ways, including friction fitting, snapping, welding, sonic welding, soldering, gluing, etc. In further embodiments no permanent connection is necessarily be established between the piston and the armature. The term “assembled” should therefore not be limited to making a permanent or locking type engagement of the pieces of the actuator but instead may only imply arrangement of the pieces in a manner designed to perform the actuator function.
The following detailed description is of the presently contemplated mode of implementing the invention. This description is not to be taken in a limiting sense, but is merely for the purpose of illustrating the general principles of embodiments of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. The scope of the invention is defined by the appended claims.
In further embodiments, the present invention actuator member may be included in pumping systems not related to infusion devices. An implantable infusion pump, however, will be utilized in the remainder of this description for the sake of simplicity.
A description of the implantable infusion pump and how it is placed in the body may help to provide some further context for the present invention. The device 10 may include a generally disc-shaped housing 14. While a generally circular disc-shaped embodiment is illustrated in
The housing 14 includes a reservoir 16 for holding a volume of infusion medium, such as, but not limited to, a liquid medication to be administered to the patient. Housing 14 may also contain a drive mechanism 18 (e.g. a pump), a power source 13, and control electronics 20. Pump 18 may be configured to receive infusion media from reservoir 16 via a pump inlet 22. Inlet structure 22 may provide a closeable and sealable fluid flow path to the reservoir 16 in the reservoir portion of the housing. The inlet structure 22 may include a port for receiving a needle through which fluid may be transferred to the infusion device, for example, to fill or re-fill the reservoir 16 of the device with the infusion media or a rinsing fluid as will be more fully discussed below. In particular embodiments, the inlet structure 22 may be configured to re-seal after a fill or re-fill operation, and to allow multiple re-fill and re-seal operations. One example of an inlet structure 22 is described in U.S. Pat. No. 6,652,510, titled “Infusion Device and Reservoir for Same,” which is incorporated by reference herein in its entirety and for everything it teaches and discloses. However, further embodiments may employ other suitable inlet structures, including, but not limited to, those described in U.S. Pat. Nos. 5,514,103 and 5,176,644, each to Srisathapat et al.; U.S. Pat. No. 5,167,633 to Mann et al.; U.S. Pat. No. 4,697,622 to Swift; and U.S. Pat. No. 4,573,994 to Fischell et al., also incorporated by reference. Representative examples of reservoir housing portions and reservoirs which may be employed in embodiments of the invention are described in the above referred to U.S. Pat. No. 6,652,510, and further embodiments may employ other suitable reservoir configurations, including, but not limited to, those described in the above referred to U.S. Pat. Nos. 5,514,103; 5,176,644; 5,167,633; 4,697,622; and 4,573,994.
Pressure Sensing in Implantable Medical Devices (Miesel), which describes infusion systems that may be modified for use accordance with the methods of the present invention.
The medical device 10 and catheter 12 are typically implanted by a clinician (e.g., surgeon) within the body 15 during a surgical procedure. While the present invention also contemplates embodiments wherein the catheter is implanted with a proximal end outside the body 15 so that it may attach to an external infusion device, the remainder of this description is, for the sake of brevity, directed to implantable infusion systems that are entirely implanted in the body 15 of the patient.
Before implantation of the medical device 10, the catheter 12 may be positioned such that the fluid delivered to the patient through the catheter 12 reaches a selected internal delivery location 17 within the body 15 of the patient. As depicted, the infusion system is implanted such that the delivery site 17 is located within the intrathecal space of the spinal canal. As may be appreciated, the infusion systems of the present invention may be used to deliver fluid to any other selected internal delivery location, e.g., epidural, etc.
Catheter 12 may preferably disgorge fluid at other than at its distal end. For example, catheter 12 may intentionally have a delivery region that is not proximate the distal end of the catheter 12, e.g., a hole or valve positioned somewhere before reaching the distal end of the catheter 12. Thus, catheter 12 may be placed in patient with a delivery region of catheter 12 placed in or near to, generally proximate to, the selected internal delivery site 17.
A proximal end of the catheter 12 may be tunneled through the tissue to the device implant location and coupled to a catheter port of the medical device 10. If implanted, the medical device 10 is typically positioned subcutaneously, e.g., from 1 centimeter (0.4 inches) to 2.5 centimeters (1 inch) beneath the skin, where there is sufficient tissue for supporting the medical device 10, e.g., with sutures or the like.
The medical device 10 is, in the illustrated embodiment, operable to infuse a fluid from an enclosed reservoir 16 into the body 15 through the catheter 12.
In order to fully understand the present invention, a more detailed explanation of an example embodiment pump in which the invention may be utilized may be first helpful.
As illustrated in
In particular embodiments, both the drive mechanism 18 and the reservoir 16 may be hermetically sealed. In such embodiments, the housing 14 containing drive mechanism 18 and control electronics 20 may be made from titanium or titanium alloy or other biocompatible metals. The reservoir portion 16 of the housing may be made from similar metals or a biocompatible and infusion medium compatible plastic that allows for the desired hermeticity.
The drive mechanism 18 may include mechanical and electromagnetic components that inhabit a volume of space within the housing 14 in which the components reside and operate. The device 10 is configured such that, once implanted, it functions for a relatively long period of time to administer infusion medium to the patient to periodically be replenished from the outside of patient's body.
As used herein, the term “therapeutic substance” refers to a substance intended to have a therapeutic effect on the patient, e.g., pharmaceutical compositions, genetic materials, biologics, and other substances. “Pharmaceutical compositions,” as used herein, may include chemical formulations intended to have a therapeutic effect such as intrathecal antispasmodics, pain medications, chemotherapeutic agents, and the like. Pharmaceutical compositions are often configured to function effectively in an implanted environment by possessing various characteristics including: stability at body temperature to retain therapeutic qualities; concentration to reduce the frequency of replenishment; and the like. “Genetic materials,” as used herein, may include substances intended to have a direct or indirect genetic therapeutic effect such as genetic vectors, genetic regulator elements, genetic structural elements, DNA, and the like. “Biologics,” as used herein, may include substances that are living matter, or derived from living matter, and offer a therapeutic effect to the patient such as stem cells, platelets, hormones, biologically produced chemicals, and the like. “Other substances” may include most any other substance that is intended to have a therapeutic effect, yet does not clearly fit within one of the categories identified above. Examples of other substances may include saline solutions, fluoroscopy agents, and the like.
In some embodiments, the fluid contained within a reservoir 16 of the medical device 10 may be replenished periodically after device implantation. Typically, replenishment is accomplished with a non-coring needle (not shown) connected to a syringe filled with the fluid. The needle may be inserted through the patient's skin and into a self-sealing septum located within the housing of the medical device 10.
Referring to
As shown in
When assembled, the coil cup 40 may be located in the hollow interior of the housing member 32, with the central portion 36 of the housing 32 extending through channel 42 of the coil cup 40 as shown in
The drive mechanism 18 may also include an actuator member 58, which may include an armature portion 60 and a piston portion 62. The actuator member 58 is most often made of a generally rigid, biocompatible and infusion medium compatible material having a relatively high magnetic permeability such as, but not limited to, ferrous materials, ferritic stainless steel with high corrosion resistance, or the like.
As illustrated in
The collar 61 may further include an interior rib 110 and an exterior rib 112. The interior and exterior ribs 110 and 112, may be molded into the collar 61 to effectuate placement or friction fitting of the collar 61 into the armature portion 60 and attachment of the piston portion into the collar 61. The collar 61 may be made of any desired material but may be preferably made of a flexible material such as rubber or a pliable plastic. Materials may include natural or synthetic rubber, Neoprene, Teflon, latex, silicon based materials, or the like. In addition, the material should be compatible with whatever liquids are being pumped.
The armature portion 60 in the present embodiment may be a generally flat disk with a receiving portion 114 for receiving the collar 61. The receiving portion 114 is generally formed in the center of the armature portion 60 and may include a groove 116 for receiving the exterior rib 112 of collar 61. The receiving portion 114 in some embodiments may or may not be created through the entire armature portion 60. The receiving portion 114 may also be molded into the armature portion 60.
The piston 62 may also include a groove 118 for securing the piston 62 to the collar 61 through interaction with the interior rib 110. The groove 118 may be formed in shoulder 120 at the end of the piston 62. The piston 62, shoulder 120, and groove 118 may be formed as on unitary structure or as separate structures and attached together. As may be appreciated, the piston 62, collar 61, and armature 60, and the corresponding grooves and ribs thereon, are formed of a size and shape whereby each piece will cooperate in an interlocking fashion with the corresponding pieces. As may be further appreciated, a number of different corresponding shapes may be utilized to effectuate a friction fit of the various components.
Flexible materials for formation of the collar 61 may allow for a non-rigid relationship to exist between the armature portion 60 and the piston portion 62. The collar 61 may be stiff enough to retain the components in a desired position but flexible enough to allow for some movement of the piston 62 relative to the armature 60. Such a flexible relationship between the components may allow for reduced wear in the components and reduced requirements that the pieces be manufactured to relatively narrow manufacturing tolerances.
The armature 60 cooperates with the inner and outer walls of the coil cup 40 to provide a flux path for electromagnetic flux. The spacing between the pole surfaces on the armature 60 and the pole surfaces on the coil cup walls define gaps in the flux path. In particular embodiments, the spacing between the surface of outer pole 70 of the armature 60 and the surface of outer pole 52 of the outer wall 50 of the coil cup 40 is greater than the spacing between the surface of inner pole 72 of the armature and the pole surface 48 of the inner wall 46 of the coil cup (or the barrier 74) when the actuator is in the retracted position shown in
The radial struts 68 in the armature provide radial paths for electromagnetic flux between outer and inner pole sections 70 and 72 of the armature. The configuration of openings is most often designed to provide a sufficient conductor for electromagnetic flux and yet minimize or reduce viscous resistance to actuator motion. With reference to
The actuator spring 78 in the illustrated embodiment is a coil spring disposed around the piston portion 62 of the actuator 58 adjacent the armature portion 60. One end of the coil spring abuts the armature portion 60 of the actuator, while the opposite end of the coil spring abuts a shoulder 81 in the piston channel 38 of the housing 32. In this manner, the actuator spring 78 imparts a spring force between the housing and the actuator 58 to urge the actuator toward its retracted position shown in
In the illustrated embodiment, by using a coil spring 78 located around and coaxial with the piston portion 62 and disposed partially within the piston channel 38, the actuator spring may have minimal or no contribution to the overall thickness dimension of the drive mechanism. However, in other embodiments, actuator springs may have other suitable forms and may be located in other positions suitable for urging the actuator toward its retracted position shown in
The drive mechanism 18 may further include a cover member 80 which attaches to the housing member 32 over the open side of the housing member and the barrier 74. The cover member 80 is most often made of a generally rigid, biocompatible and infusion medium compatible material having a relatively low magnetic permeability (being relatively magnetically opaque) such as, but not limited to, titanium, stainless steel, biocompatible plastic, ceramic, glass or the like.
The cover member 80 defines an interior volume 82 between the barrier 74 and the inner surface of the cover member. The armature portion 60 of the actuator member 58 resides within the interior volume 82 when the cover is attached to the housing. The armature 60 is moveable in the axial direction within the volume 82 between the retracted position shown in
An adjusting stop 84, or adjustable plunger, may be located within the cover 80 for contacting the armature 60 when the armature is in the fully retracted position shown in
As shown in
The actual radial spacing between the piston portion 62 and the wall of the channel 38 to achieve such results depends, in part, on the overall dimensions of those components, the pressure differentials created in the mechanism, and the viscosity of the infusion medium.
The valve assembly 96 in the embodiment of
The valve member 102 is most often made of generally rigid, biocompatible and infusion medium compatible material, such as, but not limited to, titanium, stainless steel, biocompatible plastic, ceramic, glass, gold, platinum or the like. A layer of silicon rubber or other suitable material may be attached to the rigid valve member material on the surface facing the channel 38 to help seal the opening to channel 38 when the valve member is in the closed position shown in
The valve spring 106 is most often made of biocompatible and infusion medium compatible material that exhibits a suitable spring force such as, but not limited to, titanium, stainless steel, MP35N cobalt steel or the like. In the illustrated embodiment, the valve spring 106 is a coil spring. In other embodiments, other suitable valve spring configurations may be employed, including, but not limited to, helical, flat, radial, spiral, barrel, hourglass, constant or variable pitch springs or the like.
In the present embodiment, drive mechanism 18 employs electromagnetic and/or mechanical forces to move between a retracted, or first, position and a forward, or second, position, to cause infusion medium to be drawn into and driven out of the pump 18 and the infusion device 10 in a controlled manner.
The position of the actuator 58 in the retracted position may be adjusted by adjusting the position of the stop 84. In one particular embodiment, adjusting the stop 84 includes adjusting a threaded cylindrical member that engages corresponding threads in a stop aperture in the cover member 80 to allow adjustment in a screw-thread manner. An exposed end of the stop 84 may be provided with a tool-engagement depression for allowing engagement by a tool, such as a screw-driver, Allen wrench or the like, from outside of the cover member 80. By engaging and rotating the stop 84 with a suitable tool, the depth that the stop extends into the cover member 80 may be adjusted to adjust the retracted position of the armature portion 60 and therefore the piston 62 in the piston channel 38. In one particular embodiment, adjustments of the stop 84 are made during manufacture. In that embodiment, the adjusted position is set by welding or otherwise adhering the stop 84 in the adjusted position during the manufacture. In other embodiments, the stop 84 is not set and welded during manufacture to allow adjustment of the stop 84 after manufacture.
The piston 162 and the armature 160 may be placed into the pump 10 such that the piston 162 resides in the central piston channel 38 in the desired position for pumping. The engagement surface 166 may interact with the convex contact surface 168 at any point along the convex surface. Such a contact may be a point contact. Furthermore, though the armature 160 and the piston 162 are two separate pieces, continuous or near continuous contact between the piston 162 and the armature 160 is achieved because of the force exerted on the piston 162 and the armature 160 by springs 78 and 106 and by the electromagnetic force generated when current is passed through the coil 54. However, the point of contact may vary somewhat without inducing any undesired lateral or rotational forces on the armature 160 or the piston 162 because of the point contact. Moreover, the present embodiment may allow for more degrees of freedom between the armature 160 and the piston 162. Armature 160 may move laterally without causing movement of the piston 162, therefore reducing the strain and wear transferred to the piston 160 and piston channel 38 during the pumping stroke.
The socket 268 may be of a desired shape, depth, and width to engage the contact nub 266, in a manner similar to a ball and socket. Even if the armature 260 moves a little during the pumping stroke the socket 268 on the piston 262 will still engage the contact nub 266 for operation of the pumping stroke. Depending on the amount of friction and the force being applied by the armature 260 during the pumping stroke the socket 268 and contact nub 266, when contacting at an imperfect alignment, may slip the assembly back into the desired orientation or may effectuate the stroke in the non-aligned orientation.
During assembly, the piston 262 may be placed in the central piston channel 38 and the armature 260 placed in a corresponding position to effectuate the desired pumping action. The mating surfaces formed by the nub 266 and the socket 268 may reduce the lateral movement of the piston 262 caused by the armature 260 and therefore reduce strain and wear. Moreover, more lenient manufacturing tolerances may also be allowed. As with the previous embodiment, contact is continuously or almost continuously maintained through the action of the springs 78, 106 and the electromagnetic force due to coil 54.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing exemplary embodiments of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.
