Abstract:
A shape memory activated fluid control pinch valve is disclosed. The valve may be normally open or normally closed. In various embodiments of the valve, the valve may be a latching pinch valve and may operate with magnetic assistance.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to pinch valves and more specifically to a latching pinch valve utilizing shape memory alloy materials.  
       BACKGROUND  
       [0002]     In the field of fluid control various valves have been used to control the flow of the fluid. Well known in the field are two position valves which are either open or closed and proportional valves where the amount of fluid flowing is determined by the degree of openness or closure of the valve. Also known in the field are valves where the fluid flows directly through the valve and pinch valves where the valve operates on the external portion of the flow path to control the flow of the fluid along a flow path. An example of this latter case is a roller clamp used in the intravenous delivery of therapeutic solutions where the roller pinches the IV flow line based on its position along an inclined plane.  
         [0003]     Also known in the art are bistable latching valves that may either be open or closed. These bistable latching valves are of particular importance when available power for operation of the valve is limited. In the case of these bistable latching valves power need only be applied to change the state of the valve; that is, from open to closed or from closed to open. Since these valves are stable in both the open position and the closed position, no power is needed to keep the valve in either the open or the closed position. Examples of latching valves are commercially available from the Lee Company of Westbrook, Conn.  
         [0004]     Most latching valves are designed in such a manner that fluid flows through the valves. However, latching pinch valves are known, for example, solenoid latching pinch valves from the Farmington Engineering Company of Madison, Conn.  
         [0005]     Valves taking advantage of the shape changing properties of shape memory alloys are also known. Krumme in U.S. Pat. No. 4,645,489 teaches the use of a shape memory allow to control the position of a valve closure element in a proportional valve. Edelman and Ritson in U.S. Pat. No. 4,878,646 teach the use of a shape memory alloy element to release the energy of a spring to close a pinch valve in an IV fluid delivery system. In this teaching, the shape memory alloy is only used to close the valve by releasing a latch. Reopening the valve and latching the valve open is done manually. In automatic fluid control systems, where both the closing and the opening of the fluid flow path should be done automatically under the control of an operating system, such a manual “reset” of the valve of Edelman and Ritson is impractical.  
         [0006]     Recently, “closed loop” fluid systems for delivery of medications to patients have appeared where a fluid flow property is measured and the rate of fluid flow is adjusted based on the flow measurement. Notable examples are Sage, in U.S. Pat. No. 6,582,393, Connelly et al in U.S. Pat. No. 6,589,229 and Jerman in U.S. Pat. No. 5,533,412. While Connelly uses a piezoelectric pump and adjusts the output of the pump based on the monitored flow property, Sage and Jerman do not teach the details of the flow control means, although both do teach the flow measuring means. An automatic, low power, bistable latching pinch valve would be useful in the implementation of either the art of Jerman or Sage. None of the prior art teachings represent acceptable valves for use in these miniaturized fluid delivery systems where the fluid flow rate is measured and a microprocessor controls a valve based on the measured flow rate. Hence there remains a need for improved valving methods.  
       SUMMARY OF THE INVENTION  
       [0007]     A miniature microprocessor controlled pinch valve is described. The valve may be bistable or may be a latching valve. The valve is operated by shape memory alloy elements wherein current is applied to the elements to change the length of the elements thereby activating the valve. In one embodiment, the force of a spring is applied to a valve closure element such that with no power applied, the valve is normally closed. To open the valve, current is applied to the shape memory alloy element thereby decreasing its length. The force resulting from the shape change is sufficient to overcome the force keeping the valve closed, hence the valve opens. A reduced “holding” current may be used to maintain the valve in the open position. To close the valve, current is removed from the shape memory alloy element.  
         [0008]     Alternatively, in a second embodiment, the valve could be normally open with no power applied. In this case, when current is applied to the shape memory element, the valve is drawn closed since the force resulting from the shape change in the shape memory alloy is greater than the force keeping the valve open. To open the valve again, current is withdrawn from the shape memory element.  
         [0009]     In a second embodiment, two shape memory alloy elements are used to operate a bistable latching valve. The valve may be normally open or normally closed, depending on the initial placement of the pinching element. In the normally closed version of this embodiment, a first shape memory alloy element is briefly energized to latch the valve in the open position. To close the valve, a second shape memory element is briefly energized to unlatch the pinching element. In the normally open version of this embodiment, the first shape memory alloy element is briefly energized to latch the valve in the closed position. To open the valve, the second shape memory alloy element is briefly energized to unlatch the pinching element, thereby opening the valve again. In drug delivery applications, the normally closed version is usually preferred since this is the position the valve will take in the event of a power failure.  
         [0010]     In a third embodiment, a pinching element is made of a material attracted to magnets. In a first position, it is held in a position such that the flow path is pinched and flow is stopped. In a second position, it is held in position such that the flow path is open and fluid flows along the flow path. Shape memory alloy wires are used to overcome the magnetic force holding the pinching element in one or the other position thereby causing it to move from one position to the other position.  
         [0011]     In any of the embodiments, the conduit for fluid flow is adapted to be removable from the pinching action of the pinching member. The valve is caused to be in the open position, allowing the fluid conduit to be removed from a position between the pinching member and a pinching plate. In this manner the fluid flow path is not breached, that is, the valve operates on the outside of the fluid path and does not touch the fluid. Such a non-contact feature is important for maintaining sterility of the flow path such as when the shape memory activated pinch valve is used in a drug delivery system.  
         [0012]     The consistent theme of this invention is the automatic or logical control of both the opening and the closing of a shape memory alloy activated pinch valve. The valve may be normally open or normally closed. In general it is a latching valve in that it has two stable positions such that zero or small amounts of energy are required to maintain the valve in either of its two stable positions. It is not, however, a proportional valve where the amount of current in the shape memory element dictates the degree of openness or closure of the valve. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0013]      FIG. 1  shows a schematic of an automatically operated normally closed shape memory alloy activated valve.  
         [0014]      FIG. 2  shows a schematic of an automatically operated normally closed bistable latching valve activated by a shape memory alloy.  
         [0015]      FIG. 3  shows a schematic of a shape memory alloy latching pinch valve with magnetic assist of opening and closing the valve. 
     
    
     DETAILED DESCRIPTION  
       [0016]     The operation of one embodiment of the invention is described with the aid of  FIG. 1 , which is a schematic of a normally closed pinch valve activated by a shape memory alloy element.  FIG. 1  has three drawings;  FIG. 1A  which shows the valve in the normally closed, unactivated state,  FIG. 1B  which shows the valve in the activated or open state, and  FIG. 1C  which shows the valve returned to the normally closed unactivated state. The shape memory alloy element is nominally a shape memory alloy wire, but other shapes of materials such as strips and coils would also be appropriate. Shown in  FIG. 1  is fluid reservoir  14  which is adapted to deliver fluid along flow path  13 . Flow path  13  may be any of compressible material such as silicone or may be of a laminate construction of sheet materials such that a fluid path is provided. This flow path is shown compressed in  FIG. 1A  between pinching element  15  and surface  12 . Pinching component  15  is shown contacting flow path  13  at two locations for redundancy. Pinching component  15  is shown cantilevered from wall  19 , such that flexure of pinching element  15  provides the force to compress flow path  13 . Other means of providing force to compress flow path  13  are possible including a compressed spring or additional mass attached to pinching component  15 . Pinching component  15  may have as few as one pinching point or may have two or more depending on the needed confidence of closure. Attached to pinching component  15  are two shape memory alloy elements  11 . Two elements  11  are shown again for redundancy, but one or more than two may also be used. Shape memory elements  11  are connected at the other end to a fixed connector block  18 . The connection provided by connector block  18  is an electrical as well as physical one so that current provided by current source  16  is provided to shape memory elements  11 . Logical circuit  17  provides signals to current source  16  in order to operate the valve at the proper times. Logical circuit  17  may receive its input from a number of sources that are not shown, such as manual input from a human interface, from a clock circuit, or from a flow sensor such as that taught in U.S. Pat. No. 6,582,393.  
         [0017]      FIG. 1A  shows the shape memory alloy activated valve in the normally closed position.  FIG. 1B  shows the valve in the open position. To activate the valve to the open position, logical circuit  17  sends a signal to current source  16  to supply current to shape memory alloy elements  11  through connector block  18 . Sending current through a shape memory alloy element raises its temperature, which causes a material phase change that results in a reduction in length of the shape memory alloy element. This shape change exerts a significant force overcoming the force causing pinching component  15  to compress flow path  13  and raising pinching component  15  above surface  12  thereby allowing fluid to flow along flow path  13 . Pinching component  15  remains in this position until such time that logic circuit  17  sends a signal to current supply  16  to discontinue providing current to shape memory allow elements  11 . Removing the current from shape memory elements  11  lowers the temperature of shape memory elements  11  thereby causing them to lengthen and return to their original length. The lengthening of shape memory alloy elements  11  allows pinching component  15  to compress fluid path  13 , thereby closing the valve. This configuration of the valve after removal of current from shape memory alloy elements  11  and the subsequent return of pinching component  15  is shown in  FIG. 1C .  
         [0018]     A second embodiment of the invention is shown in  FIG. 2 . This second embodiment is a latching valve in that it may be in either position, the open position or the closed position without requiring any power to maintain that position.  FIG. 2A  shows the valve in the closed position with pinching element  15  pressing flow path  13  against surface  12 . Fluid to be controlled by the valve flows in flow path  13  from a fluid supply (not shown) similar to that shown in  FIG. 1 . Pressure to close flow path  13  may be provided by the mass of the pinching element  15 , by pinching element  15  made of a flexible material and being already flexed in the position shown in  FIG. 2A  or by a spring (not shown but which is well known in the art) forcing pinching element  15  against flow path  13 . When the decision is made to open the valve, logic circuit  17  signals current source  16  to supply current to shape memory alloy elements  25  through interface block  24 . As in the previous embodiment, the number of shape memory alloy elements may vary according to the force requirements. This current causes shape memory alloy elements to shorten in length, moving latching element  23  to the position shown in  FIG. 2C . The force keeping latching component  23  in the position shown in  FIG. 2A  may be provided by a spring (not shown) or may be due to stored elastic energy of the material of latching component  23 .  
         [0019]     Once latching element  23  is in the position shown in  FIG. 1C , logic circuit  17  signals current source  16  to supply shape memory alloy elements  21  through interface block  22 . This current causes shape memory alloy elements  21  to shorten in length, thereby raising pinching component  15  away from surface  12  and opening flow path  13 . Once pinching component  15  is raised away from surface  12 , current supply  16  withdraws current from shape memory alloy elements  25  allowing latching element  23  to resume its initial position. With pinching component  15  raised and latching component  23  in its original position, as shown in  FIG. 1B , latching component  23  holds pinching component  15  away from surface  12 , allowing fluid to flow in flow path  13 . Current supply  16  now removes current to shape memory alloy elements  21 . In this state, no current is supplied to any of the shape memory alloy elements, yet the valve remains open.  
         [0020]     Alternatively, this opening step may be taken without activating shape memory alloy elements  25  with an appropriate shape of latching component  23 . As shown in  FIG. 2A , when current is applied to shape memory alloy elements  21  to pull pinching component  15  away from surface  12 , the motion of pinching element  15  away from surface  12  will also move latching element  23  to the right as it slides against latching component  23 . Given the force provided with latching component  23  to urge it to the position shown in  FIG. 2A , once pinching element is above the latching component  23  as shown in  FIG. 2B , latching component will return to the position shown in  FIG. 2A  thereby engaging pinching component  15  and holding it away from surface  12 .  
         [0021]     To close the valve, logic circuit  17  signals current source  16  to supply current to shape memory alloy elements  25  through interface block  24 . This current causes shape memory alloy elements  25  to shorten in length, moving latching component  23  to the position shown in  FIG. 2C . Latching component  23  in this position is no longer able to hold pinching component  15  above surface  12  so it springs back to its lower position where it compresses flow path  13  against surface  12 , closing the valve. When logic circuit  17  signals current source  16  to stop the flow of current to shape memory alloy elements  25 , they lengthen again, and latching component  23  returns to the position shown in  FIG. 2A  such that the valve is now ready to be opened again with signals from logic circuit  17 .  
         [0022]     A third embodiment of the invention is shown in  FIG. 3 . The shape memory alloy activated valve is designed to open or close flow path  13  by pinching flow tube  13  between pinching component  33  and pinch block  31 . This third embodiment latches the valve in the open or closed position by using magnets  31 , which is also pinch block  31 , and magnet  32 . Shown in  FIG. 3A  is the valve in the normally closed position with pinching component  33  pressing against flow path  13 . At a selected time current source  36  activates shape memory alloy wires  35  causing the wires shorten. This shortening of shape memory alloy wires  35  causes pinching component  33  to move upward. When pinching component  33  moves upward, it is pulled further upward by the magnetic field of magnet  32 , causing pinching component  33  to come to rest as shown in  FIG. 3B . In this way the valve is opened by a single short pulse of current from current source  36  and is held upon by magnet  32 .  
         [0023]     When a time arrives when the valve is to be closed, current from current source  37  activates shape memory alloy wires  34  causing them to shorten. The shortening of shape memory alloy wires  34  causes pinching component  33  to move downward. As pinching component  34  moves downward, the magnetic field of pinch block and magnet  31  pulls it down further causing it to come to rest firmly in the grip of magnet  31 , closing the valve as shown in  FIG. 3C . In one embodiment of the magnetically assisted valve of  FIG. 3 , magnet  31  exerts a larger magnetic force on pinching component  33  than magnet  32  thereby providing additional assurance that the valve is normally in the closed state.