Abstract:
The invention relates to multi-stable valves and methods for their use. The multi-stable valves may include a movable physical stop and a position arm. The physical stop may be placed in the path of the arm effectively locking the valve in at least one position upon deactivation of the valve&#39;s motivating forces. The valve may be, for example, a micro valve or a microelectromechanical device. Such a valve may be used in implantable drug infusion applications and other applications having limitations on available energy. In one exemplary embodiment, the valve comprises a membrane separating two channels. The membrane may be lifted by activation of a piezo material, opening the channels for fluid flow. A physical stop may be moved into place and the piezo material deactivated, bringing to rest the arm on the physical stop. In this manner, the valve is stabilized in the open position without requiring continuous supply of energy.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Priority is hereby claimed to U.S. Provisional Application No. 60/439,909, filed Jan. 14, 2003 and U.S. Provisional Application No. 60/439,780, filed Jan. 13, 2003, the disclosures of which are hereby incorporated herein by reference. The present application is related to the co-pending and commonly assigned U.S. patent application Ser. No. [64862/P009US/10314031], titled “Actuation System and Method for an Implantable Infusion Pump,” filed concurrently herewith, the disclosure of which is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention, in general, relates to fluid flow systems. More specifically, the invention relates to multi-stable valves and methods for use thereof in controlling dosage rates of a treatment solution in a medical application. 
     BACKGROUND OF THE INVENTION 
     Valves are used in a variety of applications, from large-scaled, bulk flow applications to relatively small flow rate applications. More recently, valves have been used in implantable devices for infusion drug treatment. Flow rates for this application usually range from tenths of milliliters per day to a few milliliters per hour. 
     Typical valves have a default position. The position may fail opened or closed in the event that energy or an actuation force is lost. In a typical fail-closed valve, a pneumatic or electric force is applied to open the valve and keep it open. For example, in a typical solenoid valve that fails closed, a current is applied to a coil, inducing a magnetic force that drives a piston against a spring, opening the valve. To keep the valve open, the current is continuously applied, consuming energy. 
     In implantable devices, the available energy is limited by the power source. In some cases, the implanted devices may be recharged through radio frequency energy collection. However, the system is still limited by the size of the battery and the frequency of available recharging. As such, a valve that requires continuous power to maintain a desired position draws down the available power, usually requiring more frequent recharging or battery replacement. 
     In addition, the continuous use of energy to maintain valve position may cause other problems. Continuous use of sensitive circuitry may cause thermal strain. In various actuation systems, continuous use may lead to leaks, stress on parts, and undesired chemical reactions that adversely affect performance of the valve. 
     As such, typical valve systems and methods for use may suffer from deficiencies in energy use and use-induced stresses. Many other problems and disadvantages of prior solutions will become apparent to one skilled in the art after comparing such prior solutions with the present invention as described herein. 
     BRIEF SUMMARY OF THE INVENTION 
     An embodiment of the invention comprises a multi-stable valve, having physical mechanisms for stabilizing the valve in several positions. In an exemplary embodiment, the valve is a bi-stable valve which can assume two positions, open and closed. In this exemplary embodiment, the valve may be a piezo driven diaphragm valve with a cantilever arm. The cantilever arm operably contacts a physical stop in either the open or closed position. During movement of the valve, the physical stop is moved from the path of the cantilever arm and replaced once the valve is in position. The valve may be actuated by various means including electrostatic, electromagnetic, magnetic torsion, electro-hydrodynamic, electro-osmosis, electrochemical, and mechanical. Furthermore, the valve may use various mechanisms in place of a physical stop, such as a permanent magnet. The valve may be a micro-electromechanical valve. However, various methods may be used to manipulate the cantilever arm and physical stop. The valve may be created on a silicon substrate or other similar materials, or it may be micro-injection molded from tooling created using methods used to construct micro-electromechanical systems. 
     In an embodiment, a multi-stable valve is employed in a drug infusion application. A system including the multi-stable valve, a treatment solution reservoir, and control circuitry may be used to treat various ailments and conditions. 
     Other embodiments comprise methods for opening and closing a valve. The method may include moving a physical stop, activating the valve, replacing the physical stop, and deactivating the valve, whereby a valve positioner engages the physical stop. The method may also comprise activating the valve, moving the physical stop, deactivating the valve, and replacing the physical stop. 
     As such, several embodiments are described. Other aspects, advantages and novel features of the present invention will become apparent from the detailed description of the invention when considered in conjunction with the accompanying drawings. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram depicting an exemplary embodiment; 
         FIGS. 2A ,  2 B and  2 C are schematic diagrams depicting an exemplary embodiment of a valve system, according to the invention; 
         FIG. 3  is a schematic diagram depicting an exemplary embodiment of a valve system according to the invention; 
         FIGS. 4A ,  4 B and  4 C are schematic diagrams depicting an exemplary embodiment of a valve system, according to the invention; 
         FIGS. 5A ,  5 B,  5 C,  5 D,  5 E and  5 F are schematic diagrams depicting exemplary embodiments of a physical stop; and 
         FIGS. 6A and 6B  are block flow diagrams depicting exemplary methods for use. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Valves are used in various applications from large scale flow to small scale flow applications. In cases in which available energy is limited or in which the size of the valve changes the behaviors and dynamics in the materials associated with the valve&#39;s manufacture, continuous application of forces to maintain a valve position may cause unnecessary energy usage and damage to valve parts. One such application is the infusion of drugs and pharmaceuticals through implantable drug infusion systems. 
       FIG. 1  is a schematic diagram depicting an exemplary embodiment. The system  10  depicts a treatment solution pump and reservoir  12  coupled to a valve  14 . Valve  14  controls fluid flow through catheter  16  to treatment location  18 . Control circuitry  20  may, through communications link  22 , influence the position of valve  14  in accordance with a prescription or desired flow rate. These elements ( 12 ,  14 , and  20 ) may be implanted in a patient. As such, power for the operations of these elements is limited by an available battery power or by the frequency of replenishing the power, if available. 
     In applications such as system  10 , the flow rates and thus the sizes of the elements of the valve may be significantly smaller than bulk fluid flow applications. In some embodiments, valve  14  is a micro-electromechanical valve or a micro valve formed on a substrate. A bi-stable valve system may reduce the amount of energy required by valve  14  to produce a desired flow rate because bi-stable valve systems usually only use energy during opening and closing and not in maintaining position. In addition, the stable open and stable closed positions may reduce stresses on those parts associated with the activation of valve  14 . 
       FIGS. 2A ,  2 B, and  2 C depict exemplary embodiments of bi-stable valve system  30 . In the illustrated embodiments the valve assembly is formed on substrate  32  having openings  44  and  46 . Valve seat  34 , incorporated into a diaphragm, acts to block at least one of the openings, here opening  44 , in the closed position. Valve seat  34  and the associated diaphragm of the illustrated embodiment are connected to cantilever arm  38  through connecting material  36 . Piezo material actuator  40  is coupled to cantilever arm  38 . Stop  42  is located in proximity to the distal end of cantilever arm  38  and in the path of cantilever arm  38 . 
       FIG. 2A  depicts valve system  30  as closed. Valve seat  34  rests against opening  44 , blocking a fluid path between openings  44  and  46 .  FIG. 2B  depicts the opening or activation of valve system  30 . Stop  42  is removed from the path of the distal end of cantilever arm  38 . Piezo material  40  is activated, and valve seat  34  is moved to allow fluid flow between openings  44  and  46 . During this activation, valve system  30  consumes energy through the continued activation of piezo material  40 . 
       FIG. 2C  depicts the stable open position of valve system  30 . In this figure, stop  42  is moved into place. Cantilever arm  38  rests against stop  42  upon deactivation of piezo material  40 . In this manner, fluid may flow through openings  44  and  46  while valve system  30  does not consume energy. 
     To close valve system  30 , piezo material  40  may be reactivated, lifting cantilever  38  from stop  42 . Stop  42  may then be removed from the path of cantilever arm  38 . Piezo material  40  may be deactivated, lowering cantilever arm  38 . Then, stop  42  may be moved back into the path of the distal end of cantilever arm  38 . 
     Although an embodiment incorporating a piezo material actuator, cantilever arm, and stop has been described above, the actuating means associated with a valve assembly of the present invention may take various forms, including, but not limited to, electrostatic, electromagnetic, magnetic torsion, thermal, electro-hydrodynamic, electroosmosis, electrochemical, and mechanical. Further, the valve systems of the present invention may be developed in various size ranges including micro valves and micro-electromechanical devices, among others. According to embodiments, valve assemblies may be manifolded to create a variety of desirable valve options. 
       FIG. 3  depicts an alternate embodiment in valve system  50 . In this embodiment, substrate  52  has openings  64  and  66 . Membrane  54  extends between openings  64  and  66  in a closed position. Membrane  54  is connected through connector  56  to cantilever arm  58 . Piezo material  60  is located on cantilever arm  58  in the illustrated embodiment. Physical stop  62  is located in the path of the distal end of cantilever arm  58 . Activation of piezo material  60  causes cantilever arm  58  to move upwards bringing membrane divider  54  up and establishing a fluid flow path through openings  64  and  68 . In this exemplary embodiment, physical stop  62  may be moved from the path of the distal end of cantilever arm  58  during activation and replaced to stabilize valve system  50  in an open position. Thus, valve system  50  may be placed in an open position without continuous activation of piezo material  60  or continuous use of energy. 
       FIGS. 4A ,  4 B and  4 C depict alternate valve embodiments. Valve system  130  of the illustrated embodiment comprises substrate  132  with openings  144  and  146 . Membrane  134  separates openings  144  and  146 , preventing fluid flow in the closed position. Connector  136  connects membrane  134  to cantilever arm  138 . Piezo material  140  is located on cantilever arm  138  of the illustrated embodiment. Physical stop  142  is located in the path of the distal end of the cantilever arm  138 . On cantilever arm  138  is conductive material  150 . Correspondingly, on physical stop  142  are one or more electrical contacts  152 . 
     As seen in a  FIG. 4A , the membrane  134  divides openings  144  and  146 , preventing fluid flow. Contacts  152  and conductive material  150  remain out of communication. However, as seen in  FIG. 4B , once valve system  130  is open, contacts  152  and conductive material  150  close a circuit. 
       FIG. 4C  depicts one exemplary embodiment of contacts  152  and conductive material  150 . When conductive material  150  bridges contacts  152  residing on physical stop  142 , a circuit is closed, indicating the position of valve system  130 . 
     However, various sensors and contact configurations may be used to ascertain the state of valve system  130 . For example, contacts  152  may be located on cantilever arm  138  and conductive material  150  located on physical stop  142 . In an alternate embodiment, one contact may be located on physical stop  142  and an opposite contact located on cantilever arm  138 . However, various indicators and sensors may be used to indicate the position of the valve. 
       FIGS. 5A ,  5 B,  5 C,  5 D,  5 E and  5 F are schematic diagrams depicting various exemplary embodiments of a physical stop as may be utilized according to the present invention.  FIG. 5A  depicts physical stop  210  that moves in a horizontal plane relative to a cantilever arm.  FIG. 5B  also depicts physical stop  220  that moves in a horizontal plane relative to a cantilever arm. Such an assembly as physical stop  220  may also be used as a physical stop for multiple valves. In this exemplary embodiment, cantilever arms  222 ,  224  and  226  may associated with individual valves. Those valves with cantilever arms resting on the physical stop may be activated. Physical stop  220  moves to the side. Then, valves associated with cantilever arms  222 ,  224  and,  226  are positioned in their desired states. Cantilever arms  222 ,  224  and,  226  effectively move between the extensions of physical stop  220 . Once the valves are in position, physical stop  220  may be replaced and the valves deactivated, stabilizing them in the desired positions. 
       FIG. 5C  depicts an alternate embodiment in physical stop  230  in which a set of lever arms is rotated to move physical stop  230  in and out of position. In another exemplary embodiment, as seen in  FIG. 5D , physical stop arm  240  is motivated in a vertical plane in a sweeping or bending motion.  FIG. 5E  depicts an alternate embodiment in which physical stop arm  250  is motivated in the vertical plane such that the path of cantilever arm  252  is left clear upon moving physical stop  250 . 
     In a further exemplary embodiment as seen in  FIG. 5F , physical stop  260  may partially rotate to a position in which the path of cantilever arm  262  is left open. Physical stop  260  is shown as a circle, missing a quarter and can be moved or rotated to a position where the missing quarter is in the path of cantilever arm  262 . Once cantilever arm  262  is in the desired position, physical stop  260  may again be rotated into a position in which a physical part of the circle exists. 
       FIGS. 6A and 6B  depict exemplary methods. In  FIG. 6A , exemplary method  290  includes moving the stop as seen in block  292 . As seen in the configurations above, such a method may be used when the valve is in the closed position and the cantilever arm is not touching the physical stop. Next, the valve actuator is activated as seen in block  294 . In embodiments, such as those illustrated in  FIGS. 2 ,  3  and  4 , piezo material is activated, causing the cantilever arm to move in a vertical direction. The stop can be replaced as seen in block  296 . Then, the valve actuator is deactivated as seen in block  298 . The deactivation causes the cantilever arm to rest against the physical stop, creating a second stable position for the valve. In this position, the valve does not require the continuous use of energy or cause continuous strain on moving parts. However, an embodiment can be envisioned in which the method  290  of  FIG. 6A  acts to close the valve. 
       FIG. 6B  is a block flow diagram depicting another exemplary method  300 . The valve actuator is activated as seen in block  302 . In the examples seen above, activation of piezo material can raise the cantilever arm from the physical stop. The physical stop can then be moved as seen in block  304 . Moving the physical stop leaves the path of the distal end of the cantilever arm open, allowing the valve to close on deactivation. The valve actuator is then deactivated as seen in block  306 , effectively closing the valve. The stop can be replaced as seen in block  308 . However, various embodiments can be envisioned that enable a valve to open with the method  300  of  FIG. 6B . 
     As such, a multi-stable valve and method for operation are described. In view of the above detailed description of the present invention and associated drawings, other modifications and variations will now become apparent to those skilled in the art. It should also be apparent that such other modifications and variations can be effected without departing from the spirit and scope of the present invention. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.