Abstract:
A drug delivery pump drive which uses a linear piezoelectric motor to advance a syringe piston to deliver a liquid drug and a method thereof are disclosed. The pump drive, provided in a drug delivery pump, provides silent operation and very low energy consumption compared to electric motor-based drives. The small size of the motor helps also to reduce overall size of the pump drive and the resulting drug delivery pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is filed under 35 U.S.C. §111(a) as a continuation of U.S. application Ser. No. 13/036,162, filed Feb. 28, 2011, which is a division of U.S. application Ser. No. 11/874,417, filed Oct. 18, 2007. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally related to drug delivery pumps, and in particular to a drug delivery pump drive using a linear piezoelectric motor to advance a syringe piston to deliver a liquid drug. 
     BACKGROUND OF THE INVENTION 
     Typically miniature drug delivery pumps use an electric motor and a system of many gears to reduce the high speed motors down to a slower speed. The slower speed provides the precision needed to control the very small doses of a liquid drug being delivered by means of an advancing lead screw and nut moving the syringe piston. Due to the above performance requirements, such miniature drug delivery pump use an expensive high quality electric motor and the associated high quality gears, therefore making such pumps expensive and generally not disposable in nature. In addition, concealment under clothing is problematic due to the relative size of the motor and the noise generated during operation. 
     SUMMARY OF THE INVENTION 
     It is against the above background that the present invention provides a drug delivery pump drive which uses a linear piezoelectric motor to advance a syringe piston to deliver a liquid drug. The pump drive, provided in a drug delivery pump, provides silent operation and very low energy consumption compared to electric motor-based drives. The small size of the motor helps also to reduce overall size of the pump drive and the resulting drug delivery pump. 
     In one embodiment, a drive system used to dispense a liquid drug from a drug container having a piston is disclosed. The drive system comprises a lead screw having a rotational axis and operably connected to the piston; a ratchet wheel provided along the rotational axis and operably connected to the lead screw to rotate the lead screw about the rotational axis; a piezoelectric motor having a shaft, a nut engaging the shaft, and piezoelectric elements configured to produce reciprocating linear and rotational motion of the shaft relative to the nut adjacent the rotational axis; and a pawl operably connected to the shaft and engaging the ratchet wheel such that the reciprocating linear motion of the shaft is converted into unidirectional rotary motion of the ratcheted wheel about the rotational axis which moves the lead screw and advances the piston to dispense the liquid drug from the drug container. Completion of the cycle may be confirmed either by sensing the motor shaft has reached the limits of its travel or by the successful advancement of the ratchet by one tooth. 
     In another embodiment, a method for dispensing a liquid drug from a drug container having a piston is disclosed. The method comprises providing a lead screw having a rotational axis and operably connected to the piston; providing a ratchet wheel along the rotational axis and operably connected to the lead screw to rotate the lead screw about the rotational axis; providing a piezoelectric motor having a shaft, a nut engaging the shaft, and piezoelectric elements configured to produce reciprocating linear motion of the shaft relative to the nut adjacent the rotational axis; and providing a pawl operably connected to the shaft and engaging the ratchet wheel such that the reciprocating linear motion of the shaft is converted into unidirectional rotary motion of the ratcheted wheel about the rotational axis which moves the lead screw, wherein moving the lead screw advances the piston dispensing the liquid drug from the drug container. 
     Another embodiment discloses a drive system in which the motor shaft is held to rotate but not translate while the motor body is allowed to translate but not rotate. The drive system comprises a lead screw having a rotational axis and operably connected to the piston; a piezoelectric motor having a threaded shaft, a threaded motor body engaging the shaft, and piezoelectric elements configured to produce reciprocating linear and rotational motion of the shaft relative to the nut; a housing to constrain the shaft to rotate while constraining the motor body to translate; a connection between the motor shaft and lead screw to transmit the rotational movement of the shaft to the lead screw; a nut engaging the lead screw and operably connected to the piston; whereby as the motor is activated, the shaft outputs only rotary motion which causes the nut to advance along the lead screw, advancing the piston and dispensing liquid drug from the drug container. 
     These and other features and advantages of the invention will be more fully understood from the following description of various embodiments of the invention taken together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of the various embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  is an exploded perspective view of a drug delivery pump drive embodiment using a linear piezoelectric motor positioned parallel to an axis of rotation of a lead screw arrangement according to the present invention; 
         FIG. 2  is an exploded perspective view of another drug delivery pump drive embodiment using a linear piezoelectric motor positioned parallel to an axis of rotation of a lead screw arrangement according to the present invention; 
         FIG. 3  is an exploded perspective view of a drug delivery pump drive embodiment using a linear piezoelectric motor positioned perpendicular to an axis of rotation of a lead screw arrangement according to the present invention; 
         FIG. 4  is an exploded perspective view of another drug delivery pump drive embodiment using a linear piezoelectric motor positioned perpendicular to an axis of rotation of a lead screw arrangement according to the present invention; 
         FIG. 5  is a perspective view of another drug delivery pump drive embodiment using a linear piezoelectric motor in a housing to drive a lead screw arrangement according to the present invention; and 
         FIG. 6  is a perspective view of a miniature drug delivery pump embodiment using a drug delivery pump drive using a linear piezoelectric motor to advance a syringe piston to deliver a liquid drug according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of the embodiments of the invention, skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiment(s) of the present invention. Accordingly, the drawings are merely schematic representations, intending to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. The invention will be described with additional specificity and detail through the accompanying drawings. The description of the invention may contain, for example, such descriptive terms as up, down top, bottom, right or left. These terms are meant to provide a general orientation of the parts of the invention and are not meant to be limiting as to the scope of the invention. 
     With reference to  FIG. 1 , an embodiment of a drug delivery pump drive  100  using a linear piezoelectric motor  12  is shown. It is to be appreciated that such a drug delivery pump drive  100  is suitable for use in an infusion pump application to accurately pump a liquid drug. A suitable linear piezoelectric motor is described in U.S. Pat. No. 6,940,209, the disclosure of which is herein incorporated fully by reference. In one embodiment, the motor  12  has a 3.5×3.5×15 mm footprint, which is about 20% the size of conventional electrical micro-motors. The motor  12  provides an adjustable stroke that can be precisely controlled in a range up to about 4 mm and in a speed range up from about 0.001 to about 3 mm/s. Typical input power (moving) is about 300 mW. 
     In use, the application of a drive signal  14  from a controller  16  via wires  18  causes piezoelectric elements  20  in the motor  12  to vibrate or be driven through a range of motion which induces friction between contacting and constrained motor members, such as a threaded rod or shaft  22  and a motor body  24  which acts like a nut  25 . In particular, the friction generated between the shaft  22  and the motor body  24 , which houses the piezoelectric elements  20 , causes the shaft  22  to rotate about the motor body  24 , thereby producing linear movement of the shaft  22  relative to the motor body  24 . As the motor body  24  in the illustrated embodiment is fixed to a base  26  within a drug delivery or infusion pump  28 , the shaft  22  will advance and apply a force axially (i.e., pushing) in either direction (e.g., up and down) depending on the drive signal  14 . In one embodiment, the push force applied by the shaft is about 2 Newtons using a 100 VAC RMS sinusoidal drive signal. 
     In the illustrated embodiment of  FIG. 1 , it is to be appreciated that the shaft  22  of the motor  12  is mounted parallel to a rotational axis X of a lead screw  30 . The motor  12  drives a linear slider  32  in both directions (e.g., up and down) parallel to the rotational axis X. The slider  32  is mounted slidably to a pair of braces  34  which is also fixed to the base  26 . The slider  32  has an integral pin  36 . A cam  38  is mounted rotatably to the base  26  and located coaxially to the lead screw  30 . It is to be appreciated that the cam  38  may rotate in both directions (e.g., right and left) about the rotational axis X. The cam  38  has an integral track  40  that receives the pin  36 . The track  40  is helical or angled from the rotational axis X, so that oscillating axial motion (e.g., up and down) of the pin  36  causes oscillating radial movement of the cam  38  about the rotational axis X. 
     A ratchet wheel  42  is located coaxially and fixed at an end of the lead screw  30 . The ratchet wheel  42  and/or the lead screw  30  is mounted rotatably and coaxially to the cam  38 . A pair of pawls  44 ,  46  allows the ratchet wheel  42  to be rotated in only one direction designated by symbol Z about the rotational axis X. The first pawl  44  is mounted at a first end  48  to the cam  38  and is located adjacent the ratchet wheel  42  such that a free end  50  of the first pawl  44  cooperates with the saw-like teeth  52  of the ratchet wheel  42 . The second pawl  46  is fixed at first end  54 , such as for example, to the base  26 , and located also adjacent the ratchet wheel  42  such that a free end  56  cooperated with the teeth  52  of the ratchet wheel  42  and prevents the ratchet wheel from freely rotating in the opposite direction to the direction Z. 
     In the provided drive arrangement of the first illustrated embodiment, it is apparent that the oscillating (e.g., up and down) movement of the shaft  22  of the motor  12  about the motor body  24  causes the incrementing of the ratchet wheel  42  one tooth at a time. The tooth-by-tooth rotation of the ratchet wheel  42  causes the lead screw  30  to also rotate about the rotational axis X. As shown, the lead screw  30  is only free to rotate and is prevented from translating axially. A threaded nut  58  engages the lead screw  30 . 
     The threaded nut  58  is provided with a projection or key portion  60  which is situated in a slot or keyway  62  that is mounted, for example, to the base  26 . In this manner, the nut is prevented by the keyway  62  from rotating about the rotational axis X with the ratchet wheel  42  and lead screw  30  but is free to translate incrementally along axis X. The incremental advancement of the threaded nut  58  along the keyway  62  causes a plunger or piston  64  to be pushed into a syringe-like drug cartridge or container  66 . The pushing of the piston  64 , via incremental advancement of the nut  58 , causes a liquid drug to be expelled from the container  66  in a controlled manner. 
       FIG. 2  shows another embodiment of a pump drive  200  according to the present invention wherein the lead screw  30  and the ratchet wheel  42  are not fixed together as in the previous embodiment illustrated by  FIG. 1 . In this alternative embodiment, the ratchet wheel  42  provides a threaded nut portion  68  which rotates about the lead screw  30 . The cam  38  provides a cavity  70  which accommodates a first portion of the lead screw  30 . A second portion of the lead screw  30  extends from the cavity  70  through the threaded nut portion  68  of the ratchet wheel  42 , and through a through bore or cavity  72  in a retainer  74 . The retainer  74  serves to constrain the ratchet wheel  42  from translating up the rotational axis X as it rotates the threaded nut portion  68  about the lead screw  30 . The retainer  74  also provides a key portion  76  situated in the cavity  72 . The key portion  76  rides in a keyway  78  provided in the lead screw  30 . In this manner, the lead screw  30  is constrained to translate, but not rotate incrementally, along rotational axis X. The incremental advancement of the lead screw  30  along the rotational axis X with each tooth-by-tooth rotation of the ratchet wheel  42  causes the piston  64  to be pushed into the container  66 , thereby expelling the liquid drug from the container  66  in a controlled manner. 
       FIG. 3  shows still another embodiment of a pump drive  300  according to the present invention. In this embodiment, the shaft  22  of the motor  12  is mounted perpendicular to the rotational axis X. The motor body  24  is mounted to the base  26  and supports the shaft  22  above the base  26 . The shaft  22  is mounted between opposing tabs on the rocker  80  above the base  26 . Accordingly, the motor  12  drives and rotates the rocker  80  in both directions (e.g., right and left) around the rotational axis X. 
     The rocker  80  mounts the first pawl  44  such that as the motor  12  oscillates the rocker  80  back and forth around the rotational axis X, the first pawl  44  rotates the ratchet wheel  42  in the advancing direction Z. The second pawl  46  is mounted or otherwise fixed to the base  26  such that the ratchet wheel  42  cannot rotate in the direction opposite to the advancing direction Z. In this embodiment, the lead screw  30  is fixed to rotate with the ratchet wheel  42 . It is to be appreciated that in another embodiment, the lead screw  30  and ratchet wheel  42  may be a unitary piece. For brevity, as the pump drive  300  advances the piston  64  in the same manner as described above with reference to the pump drive  100  shown by  FIG. 1 , no further discussion is provided about this embodiment. 
     Another embodiment of a pump drive  400  is shown by  FIG. 4 , with the shaft  22  of the motor  12  mounted perpendicular to the rotational axis X. In this embodiment, as in the illustrated embodiment of  FIG. 2 , the lead screw  30  is configured to translate about the rotational axis X but is constrained to rotate as mentioned previously in an above section. It is to be appreciated that in another embodiment, pawl  44  and rocker  80  may be a unitary piece. For brevity, as the pump drive  400  advances the piston  64  in the same manner as described above with reference to the pump drive  200  shown by  FIG. 2 , no further discussion is provided about this embodiment. 
     Still another embodiment of a pump drive  500  is shown by  FIG. 5 , which in this embodiment the shaft  22  is held to rotate but not translate by a housing  87  while the motor body  24  is allowed to translate but not rotate. The pump drive  500  further comprises the lead screw  30  having a rotational axis X and operably connected to the piston  64  via nut  58 . A connection  89  between the shaft  22  and lead screw  30  transmits the rotational movement of the shaft  22  to the lead screw  30 . In the illustrated embodiment, the connection  89  is a pair of gears mounted respectively to the shaft  22  and lead screw  30 . In other embodiments the connection  89  between the shaft  22  and lead screw  30  may be made, for example, by a spur gear reduction set, a worm gear, and the likes, with or without a ratcheting pawl or other suitable clutching arrangement. The retainer  74  in this embodiment serves to constrain the lead screw  30 , via restraining the gears of the connection  89  from translating along the rotational axis X as the lead screw  30  is rotated. Accordingly, as the motor  12  is activated, the shaft  22  outputs only rotary motion which causes the nut  58  to advance along the lead screw  30 , thereby advancing the piston  64  and dispensing liquid drug from the container  66 . 
     In the illustrated embodiment shown by  FIG. 5 , an encoder wheel  82  provided with markings or other features is mounted to the shaft  22  and read by an adjacent encoder  84 . In this manner, the encoder  84  tracks the revolutions of the shaft  22  and hence movement of nut  58 , and provides the controller  16  with the revolution information such that the motor  12  is regulated to dispense only a desired amount of the drug from the container  66 . In other pump drive embodiments, the encoder wheel  82  (or markings) and encoder  84  may be placed on and provided adjacent, respectively, any other moving component of the infusion pump  28  which can provide an indication of the amount of liquid drug dispensed from the container  66 , such as for example, the motor body  24 , the lead screw  30 , a component of connection  89 , or piston  64 . 
     In all the illustrative pump drive embodiments shown by  FIGS. 1-5 , a battery  86  is provided to power the infusion pump  28 . The battery  86  is held between a pair of electrical terminal posts  88  which are wired to provide power to the controller  16 . Other electrical component, such as for example, an on/off button  90  ( FIG. 6 ) and a small/large dose selection switch  92  ( FIG. 6 ) may also be provided as input to the controller  16  to provide the stated function to the infusion pump  28 . 
     As shown by  FIG. 6 , a pump drive  600  according to any one of embodiments of the pump drive  100 ,  200 ,  300 ,  400 , and  500  shown by  FIGS. 1-5 , is conveniently used in a miniature drug delivery pump  128 . In the illustrated embodiment, the battery  86  is a size AAAA, which is about 42.5 mm long and about 8.3 mm in diameter, weighing around 6.5 grams. Output of alkaline batteries in this size is about 1.5 volts, 625 mA·h. Although elements in the figures may be exaggerated in portion to other components, it is to be appreciated that the approximate relative size between the drug delivery pump  128  and the battery  86  is intended to be shown in the embodiment illustrated by  FIG. 6 . Accordingly, as shown, the miniature drug delivery pump  128  is not much larger than the AAAA battery  86 , and is in one embodiment about 61 mm long, about 32 mm wide, and 15.5 mm in height, and weighs about 32 grams, with the container  66  holding about 2 ml of a liquid drug. Such dimensions of the drug delivery pump  128  is about one third the size of existing conventional drug delivery pumps. The small size of the drug delivery pump  128  due to the reduction in size and components of the pump drive  500  as well as the drive&#39;s silent operation, makes it easier for the patient to conceal the drug delivery pump under clothing. 
     In the illustrated embodiment shown by  FIG. 6 , the drug delivery pump  128  provides a scaled window  94  through which a portion of piston  64  is visible and by which the patient may use to meter/monitor the delivery of the liquid drug from the container  66 . The container  66  includes an injection site  96  which is used to connect a spike connector  98  of an administration set  102  to the drug delivery pump  128 . The spike connector  98  is connected to a fluid conduit  104  which at the distal end connects to a catheter  106 , which enters the patient&#39;s intravenous system through the skin for delivery of the liquid drug. 
     Although not limited to, some of the noted advantages of the present invention are as follows: the inherent precision of the motion from the piezoelectric motor which can be used to accurately deliver very small doses (i.e., about 100 nL), nearly silent operation, fewer moving parts, and smaller parts. Such advantages result in an overall compact and low cost drug delivery pump for the consumer. 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The above embodiments disclosed were chosen and described to explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.