Patent Publication Number: US-2022213884-A1

Title: Mechanism for electronic adjustment of flows in fixed displacement pump

Description:
This application claims priority from U.S. provisional patent application Ser. No. 62/881,086, filed on Jul. 31, 2019. 
    
    
     FIELD OF INVENTION 
     The present invention relates to pumps used to dispense small amounts of fluids at accurate flow rates. In particular, the invention relates to a mechanism that electronically adjusts the dispensing of fluids from a pump at low flow rates. 
     BACKGROUND 
     A family of valve-less pumps, which have at their heart special mounting means, commonly referred to as a base, interposed between a drive motor and a pump head, is known in the art. These bases are typically injection molded plastic and incorporate a living hinge separating an upper base portion from a lower base portion. The upper base portion can be tilted with respect to the lower base portion by flexure of the living hinge. The relative angle between the upper and lower base portions establishes the pump output volume per revolution. This entire mechanism was previously described in commonly owned U.S. Pat. Nos. 5,020,980 and 4,941,809, and U.S. Patent Application Publication No. 2016/0245275, each of which is incorporated herein in its entirety. 
     Conventionally, the method for adjusting and setting the angle is accomplished by means of an adjusting screw engaging with pivot pins in the two portions of the base, which are positioned on the opposite side of the central axis of the base. Certain applications require pumps with the same target output per revolution. This was accomplished by substituting fixed linkage means for the adjustable screw and pivot pins. The fixed links are injection molded from plastic resin and the tooling used to mold these links allows for different lengths to be produced such that different target pump displacements can be routinely produced. An eccentric bushing providing a combination of the benefits of an adjusting screw and a fixed link is disclosed in commonly owned U.S. Patent Application Publication No. 2016/0245275. 
     These traditional methods for changing the output volume per revolution by adjusting the angle between the upper base portion and lower base portion have all required manual adjustment. This has generally made conventional pumps only convenient for use at a single output volume per revolution. 
     However, there are applications where it would be beneficial to be able to electronically adjust the output volume per revolution. This would allow an electronic system to adjust these pumps without manual intervention. U.S. Pat. No. 7,708,535 discloses a method for electronic adjustment of the angle of the base. However, the device disclosed in this patent uses rigid members to translate linear motion to angular motion. This leads to varying angular movement relative to linear movement, which leads to a complex relationship when defining the linear motion required to adjust the angle between the two portions of the base. 
     Moreover, due to the nature of the mechanism linking the piston to the motor shaft, the output volume is not a constant flow rate when the motor is rotated at a constant speed. Instead, the flow rate through the pump head is sinusoidal with the dispense to the outlet port being the positive portion of the sine wave and the aspirate from the inlet port being the negative portion of the sine wave. 
     However, there are applications where the sinusoidal nature of the dispense is not acceptable and a constant flow rate is desired. In these cases, a traditional syringe pump is generally favored for the constant flow rate it can easily provide. 
     There are also applications where a pump is used to dispense a small volume. This sometimes means that it takes a significant length of time to prime the line from the fluid source to the pump and to the dispense tip. 
     In certain cases, a pump is used to aspirate a fluid into a probe tip and dispense portions of the aspirated fluid into other receptacles. A fixed displacement pump can be used for these cases by rotating the motor in the reverse direction to aspirate. However, due to the design of the fixed displacement pump, the aspirate volume may not be the same as the calibrated dispense volume. 
     Another drawback with traditional syringe pumps is that a linear actuator is used to move the plunger to pull fluid into and push fluid out of a barrel. The accuracy of a syringe pump is generally tied to the size of the syringe barrel. The larger a syringe barrel, the lower its accuracy and precision. In order to have high accuracy at smaller volume dispenses or aspirates, a smaller barrel must be used. This is due to the smallest reliable increment of linear distance travelled in a syringe pump being related to a volume of fluid being moved. As the barrel size grows, this increment of linear distance relates to a larger volume of fluid being moved. 
     Still another drawback with pumps of the prior art relates to the need for priming such pumps. In order to decrease priming time and limit use of the syringe pump as much as possible, some systems include a priming pump with a syringe pump. The priming pump fills the lines quicker than the syringe pump and also limits the use of the syringe pump in order to increase the time between required maintenance of the syringe pump. 
     Accordingly, it would be desirable to provide a means for remote adjustment of output volume per revolution of a fixed displacement pump. It would be further desirable to provide a mechanism capable of overcoming the restrictions of sinusoidal output of a fixed displacement pump and also capable of varying output volume per revolution. It would also be desirable to overcome issues of varying aspirate volumes relative to dispense volumes in a fixed displacement pump and to overcome accuracy restrictions related to syringe pump barrel sizes, while also incorporating priming capabilities. 
     SUMMARY 
     In a first embodiment of the present invention, an electronic angle adjustment mechanism for a pump and a motor is provided. The mechanism generally includes a base, a linear actuator and a flexible member. The base has a motor flange for mounting a motor, a pump flange opposite the motor flange for mounting a pump and a hinge or hinge assembly disposed between the motor flange and the pump flange. The pump flange can be integrally formed as part of a collar that is attached to the pump housing or can be formed as part of the pump housing. The linear actuator is mounted to one of the motor flange or the pump flange of the base and the flexible member has a proximal end attached to the linear actuator and a distal end opposite the proximal end connected to the other of the motor flange or the pump flange of the base. When actuated, the linear actuator drives the flexible member in a curved path causing the motor flange and the pump flange to pivot with respect to each other about the hinge, thereby changing an angle between the motor flange and the pump flange. 
     The electronic angle adjustment mechanism can also include a cam block mounted to one of the motor flange or the pump flange, wherein the cam block has a curved support surface for guiding the flexible member in the curved path. An attachment plate can be mounted between the motor flange and the motor. The attachment plate extends outwardly from the motor parallel to the face of the motor flange and is sized to accommodate the mounting of the electronic adjustment mechanism. Preferably, the attachment plate is integrally formed as part of the motor flange. The curved support surface has a radius of curvature about a pivot point of the base hinge defined by the distance from the pivot point to the connection point of the flexible member with the other of the motor flange or the pump flange. 
     In the first embodiment, the angle adjustment mechanism preferably includes a roller bearing adjacent the cam block. The roller bearing presses the flexible member against the curved surface of the cam block. 
     The flexible member may comprise a spring steel material such that the flexible member is bendable for transitioning a linear motion of the linear actuator to a pivoting motion of the motor flange and the pump flange with respect to one another. 
     In another aspect of the first embodiment of the present invention, a motor and pump assembly is provided. The motor and pump assembly generally includes a base, a motor, a pump, a linear actuator and a flexible member. The base includes a motor flange, a pump flange opposite the motor flange and a hinge disposed between the motor flange and the pump flange. The motor is mounted to the motor flange of the base, and has a shaft rotatable about a rotation axis. The pump is mounted to the pump flange of the base, and has a piston rotatable about a rotation axis and linearly translatable along the rotation axis, wherein the pump piston is coupled to the motor shaft. The linear actuator is mounted to one of the motor flange or the pump flange of the base, and the flexible member has a proximal end attached to the linear actuator and a distal end opposite the proximal end connected to the other of the motor flange or the pump flange of the base. When actuated, the linear actuator drives the flexible member in a curved path causing the motor flange and the pump flange to pivot with respect to each other about the hinge thereby changing an angle between the rotation axis of the motor shaft and the rotation axis of the pump piston about the hinge. 
     In one aspect of the present invention, the linear actuator includes a drive rod movable along a linear axis, and a drive rod coupler attached to a distal end of the drive rod, wherein the flexible member is attached to the drive rod coupler. In this aspect, the linear actuator is preferably mounted to the motor flange and the drive rod extends parallel with the rotation axis of the motor shaft. The linear actuator can be a DC, AC, or a brushless DC motor, more preferably a stepper motor. 
     In another aspect of the present invention, a method for adjusting the angular orientation between a motor shaft of a motor and a pump piston of a pump is provided. The method generally includes providing a base between the motor and the pump, wherein the base includes a motor flange for mounting the motor, a pump flange opposite the motor flange for mounting the pump and a hinge assembly disposed between the motor flange and the pump flange, and driving a flexible member in a curved path against one of the motor flange or the pump flange with a linear actuator mounted to the other of the motor flange or the pump flange, thereby changing an angle between the motor shaft and the pump piston about the hinge assembly. 
     In a second embodiment of the electronic adjustment mechanism, the pump and motor are the same as in the first embodiment described above. The base is formed by an upper base portion and a lower base portion that are pivotably connected by a hinge or hinge assembly but a different electronic adjustment mechanism is used. In the second embodiment, the attachment plate extends outwardly from the motor and a sidewall extends downwardly. An electric motor, preferably a DC, AC, or brushless DC motor, more preferably a stepper motor, is attached to the outside of the sidewall and the motor shaft passes through the sidewall. A gear wheel with a plurality of teeth is attached to the distal end of the motor shaft. A collar is attached to the lower base portion. The collar fits around the outside of the lower base portion and is attached by a clamp, screws, bolts, an adhesive, or other known fastening devices. The collar can also be integrally formed as part of the lower base portion or pump housing and it can also have a flange extending outwardly from at least part of the exterior surface. On one side of the collar, the lower base portion is attached to the upper base portion by the hinge. Opposite the hinge, a bracket having two parallel members with a slot in between extends outwardly from the collar. On the distal ends of the two parallel members an arcuate member is attached between the two parallel members. The arcuate member curves inwardly towards the collar and has a concave surface with a plurality of teeth. The plurality of teeth on the gear wheel engage the plurality of teeth on the arcuate member and the motor controls the pivotal movement of the upper base portion in relation to the lower base portion. 
     In a third embodiment of the electronic adjustment mechanism, the pump and motor are the same as the first embodiment described above. The base is formed by an upper base portion and a lower base portion that are pivotably connected by a hinge or hinge assembly but a different electronic adjustment mechanism is used. In the third embodiment, the attachment plate extends outwardly from the motor and a sidewall extends downwardly. An electric motor, preferably a DC, AC, or brushless DC motor, more preferably a stepper motor, is attached to the outside of the member and the motor shaft passes through the sidewall. A gear wheel with a plurality of teeth is attached to the distal end of the motor shaft. A collar, as described above, is attached to the lower base portion. One side of the collar is attached to the upper base portion by the hinge. Opposite the hinge, a bracket having two parallel members with a slot in between extends outwardly from the collar. On the distal ends of the two parallel members an arcuate member is attached between the two parallel members. The arcuate member curves outwardly away from the collar and has a convex surface with a plurality of teeth. The plurality of teeth on the gear wheel engage the plurality of teeth on the arcuate member and the motor controls the pivotal movement of the upper base portion in relation to the lower base portion. 
     In a fourth embodiment of the electronic adjustment mechanism, the pump and motor are the same as the first embodiment described above. The base is formed by an upper base portion and a lower base portion that are pivotably connected by a hinge or hinge assembly but a different electronic adjustment mechanism is used. In the fourth embodiment, the attachment plate extends outwardly from the motor. A motor, preferably a DC, AC, or brushless DC motor, more preferably a stepper motor, is mounted on the attachment plate with the motor shaft extending downwardly through the plate towards the pump. A worm screw is attached to the distal end of the motor shaft. A collar, as described above, is attached to the lower base portion. One side of the collar is attached to the upper base portion by a hinge assembly. Opposite the hinge assembly, a bracket having two parallel members with a slot in between extends outwardly from the collar. On the distal ends of the two parallel members, an arcuate member is attached between the two parallel members. The arcuate member curves outwardly away from the collar and has a convex surface with a plurality of teeth. The plurality of teeth on the worm screw engage the plurality of teeth on the arcuate member and the motor controls the pivotal movement of the upper base portion in relation to the lower base portion. 
     Thus, the invention utilizes a linear actuator to allow electronic adjustment of the angle between the pump piston and the motor shaft. The linear actuator is mounted to the upper base portion and adjustably connected to the lower base portion. With this invention, the angle is adjustable electronically instead of manually. 
     By facing the piston flat to a port and varying the angle by means of the linear actuator, the pump can “syringe” fluid and dispense or aspirate at a near constant flow rate. When the linear actuator is extended, this will increase the angle between the portions of the base and the pump will aspirate through the active port. When the linear actuator is retracted, this will decrease the angle between the portions of the base and the pump will dispense through the active port. 
     With the ability to electronically adjust the angle, the angle can be manually or automatically adjusted to operate at one of several output volumes per revolution. For example, a large angle would be used for a high output volume per revolution for priming or flushing the fluid circuit. Then, the angle would be electronically adjusted to a small angle for a low output volume per revolution for small volume critical dispenses. With the ability to “syringe” fluid, a predictable and accurate aspirate and dispense volume can be achieved. 
     By varying the angle between the piston flat and the active port, varying barrel sizes can be achieved. This means that a single pump can be used to dispense fluids at rates equivalent to pumps with a large barrel size and pumps with a small barrel. 
     In still another aspect, this invention could be used like a traditional pump to prime the fluid circuit, and then operated like a syringe pump. This eliminates the need for two separate pumps and combines the syringe pump with the priming pump. 
     Features of the disclosure will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a conventional motor/pump connection utilizing adjustable flow angle hardware, according to the prior art. 
         FIG. 2  is a perspective view of a conventional motor/pump connection utilizing a fixed link, according to the prior art. 
         FIG. 3  is a cross-sectional view of a liquid pump according to the prior art. 
         FIG. 4  is a perspective view of a motor/pump connection utilizing an electronic, angle adjustment mechanism according to a first embodiment of the present invention. 
         FIG. 5  is a front view of the motor/pump connection utilizing an electronic adjustment mechanism shown in  FIG. 4 . 
         FIG. 6  is a cross-sectional view of the motor/pump connection utilizing an electronic adjustment mechanism taken along the line  6 - 6  in  FIG. 5 . 
         FIG. 7  is a perspective view of a motor/pump connection utilizing an internal gear, electronic angle adjustment mechanism according to a second embodiment of the present invention. 
         FIG. 8  is a perspective view of a motor/pump connection utilizing an external gear, electronic angle adjustment mechanism according to a third embodiment of the present invention. 
         FIG. 9  is a perspective view of a motor/pump connection utilizing a worm screw, electronic angle adjustment mechanism according to a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a conventional prior art motor  10  connected to a pump  12  via a base  14 . The motor  10  has a shaft that rotates about a rotational axis and the pump has a piston that also rotates about a rotational axis and also translates in the direction of the rotational axis. The shaft of the motor is coupled to the piston of the pump so that rotation of the motor shaft will cause rotation of the pump piston. Also, by tilting the rotational axis of the pump piston with respect to the rotational axis of the motor shaft, rotation of the motor shaft will also cause linear translation of the pump piston in a manner that is described in further detail below. A pump and motor support arrangement of this type is shown and described in commonly owned U.S. Pat. Nos. 4,941,809 and 5,020,980, the specifications of which are incorporated herein by reference in their entirety for all purposes. 
       FIG. 1  shows one prior art embodiment of an adjustable base  14 , which includes a flange attached to the motor  10  and an opposing or mating flange attached to the pump  12 . Between the two flanges is a flexible living hinge, which allows angular pivoting of the flanges with respect to the hinge. Opposite the hinge are two bosses, between which adjustable flow angle hardware is provided. In the embodiment shown in  FIG. 1 , the adjustable flow angle hardware is in the form of a screw and nut arrangement connected between pivot pins inserted in the respective bosses of the base. Rotation of the nut with respect to the screw selectively lengthens or shortens the length between the pivot pins of the bosses, thereby adjusting the angle of the motor flange with respect to the pump flange. 
       FIG. 2  shows an alternative embodiment of a prior art motor/pump connection of the prior art utilizing a base, similar to the base shown in  FIG. 1 , but utilizing a fixed link provided between the opposing bosses. Specifically, the base  14  shown in  FIG. 2 , again includes a motor mounting flange and a pump mounting flange on opposite sides of a flexible living hinge. Opposite the hinge are opposed bosses between which a fixed link is provided to set the angle between the pump and the motor. The length of the fixed link is selected based on the desired volumetric flow produced by the pump. In certain applications, a variety of fixed links of differing lengths can be provided to adjust the volume of the pump in a predetermined range. 
     Referring now to  FIG. 3 , this prior art pump and motor arrangement operates as follows. The pump  12  generally includes a pump housing  101  and a piston  118 . The pump housing  101  includes a plastic pump casing  102  having an inlet port  104  and an outlet port  106 . The pump casing  102  defines a cylindrical chamber  108  having an open end  110 . Received in the cylindrical chamber  108  is a ceramic piston liner  112  having a central longitudinal bore  114  and a transverse bore  116  communicating with the longitudinal bore  114 . The transverse bore  116  includes a liner inlet port  116   a  fluidly communicating with the inlet port  104  of the pump casing  102  and a liner outlet port  116   b  fluidly communicating with the outlet port  106  of the pump casing so that a liquid can be pumped from the inlet port  116   a , through the liner, to the outlet port  116   b  in a manner described below. 
     The pump piston  118  is axially and rotatably slidable within the central bore  114  of the piston liner  112 . One end of the piston  118  extends out of the open end  110  of the pump casing  102  and includes a coupling  120  for engagement with the shaft of the motor  10 . At its opposite end, the piston  118  is formed with a relieved or “cutout” portion  122  disposed adjacent the transverse bore  116  of the pump liner. As described below, the relieved portion  122  is designed to direct fluid into and out of the pump  12 . 
     A seal assembly  124  is provided at the open end  110  of the pump casing  102  to seal the piston  118  and the pump chamber  108 . The seal assembly  124  is retained at the open end  110  of the pump casing  102  by a gland nut  126  having a central opening  128  to receive the piston  118 . The gland nut  126  is attached to the pump casing  102  with a threaded connection  130 . 
     In operation, the motor  10  drives the piston  118  to axially translate and rotate within the central bore  114  of the piston liner  112 . In order to draw liquid into the transverse bore  116  from the inlet port  104 , the piston  118  is rotated as required to align the relieved portion  122  with the liner inlet port  116   a . The piston  118  is then drawn back as required to take in the desired volume of liquid into the central bore  114  of the pump liner  112 . Withdrawal of the piston  118  produces a negative pressure within the liner inlet port  116   a  of the transverse bore  116 , which draws in liquid from the casing inlet port  104 . The piston  118  is then rotated to align the relieved portion  122  with the liner outlet port  116   b . Finally, the piston  118  is driven forward the required distance to force liquid into the outlet port  116   b  of the transverse bore  116  to produce the desired discharge flow. 
     Thus, each rotation of the motor shaft rotates the piston of the pump. Due to the angular orientation between the pump and the motor, each rotation of the motor shaft further causes the pump piston to reciprocate in the axial direction to alternately draw in and push out fluid to transfer fluid between an inlet and an outlet of the pump. The amplitude of the piston stroke determines the volume of the fluid delivered between the inlet and the outlet of the pump. By varying the angle of the pump with respect to the motor, the stroke of the piston is adjusted, thereby adjusting the volume of the fluid transferred between the inlet and the outlet. 
     In such prior art pump and motor arrangements, the angle of the pump  12  with respect to the motor  10  is adjustable via the base  14  to provide a desired volumetric flow of the pump with each rotation of the motor shaft. Therefore, it is desirable to provide a base  14  which is adapted for adjusting the angle between the axis of the pump and the motor shaft. 
     As used herein, a “stepper motor,” also known as step motor or stepping motor, is an electric motor that divides a full shaft rotation into a number of steps of essentially uniform magnitude when driven from a sequentially switched DC power supply. 
     As used herein, the term “worm drive” is a gear arrangement in which a worm or worm screw meshes with an arcuate (i.e., curved) member with a plurality of teeth. The worm screw and arcuate member are arranged in parallel along their longitudinal axes and the threads of the worm screw engage the teeth of the arcuate member. Rotation of the worm screw in a clockwise direction causes the arcuate member to move in a first direction and rotation of the worm screw in a counterclockwise direction causes the arcuate member to move in the opposite direction. 
     As used herein, the terms “hinge,” “hinge assembly,” and “living hinge” refer to a movable joint or mechanism having one or more components, which connect(s) the upper base portion and lower base portion to change the angular relationship between their longitudinal axes. 
     As used herein, the term “living hinge” refers to a type of hinge made from an extension of the parent material (typically plastic). The living hinge “bridge” is the thin section of plastic that acts as a connection between two larger plastic sections, i.e., the upper base portion and the lower base portion. Preferably, the upper and lower base portions and the living hinge “bridge” will be made of one continuous piece of plastic. Since it is very thin and typically made from a flexible plastic, the living hinge is also able to rotate about one axis 180 degrees or more. 
     Referring now to  FIGS. 4-6 , an adjustable pump and motor assembly  20  with an angle adjustment actuator  60  according to a first embodiment of the present invention is shown. The adjustable pump and motor assembly  20  includes a conventional motor  22  connected to a fixed displacement pump  24  (as described above with reference to  FIG. 3 ) via a base  26  with a pivotably connected upper base portion  46  and a lower base portion  48 . The motor  22  has a shaft  28  that is connected to a spindle coupling  32  and the shaft  28  rotates the spindle coupling  32  about a rotational axis. The pump  24  has a piston  30  that also rotates about a rotational axis and also translates in the direction of its rotational axis. One end of the piston  30  is connected to the spindle coupling  32 . 
     The shaft  28  of the motor  22  is coupled to the piston  30  of the pump  24  via the spindle coupling  32  so that rotation of the motor shaft  28  will cause rotation of the pump piston  30 . Also, by tilting the rotational axis of the pump piston  30  with respect to the rotational axis of the motor shaft  28 , rotation of the motor shaft  28  will also cause linear translation of the pump piston  30  and increase or decrease the volume of the chamber  35  at the distal end of the piston  30 . 
     The end of the pump piston  30  closer to the motor shaft  28  is attached to a pin  34  that is perpendicular to the pump piston  30  and connected to a spherical bearing  36 . The spherical bearing  36  is retained or captured in a hollow portion of the spindle coupling  32 . When the spindle coupling  32  is rotated by the motor shaft  28 , the spherical bearing  36  and pin  34  assembly translates the rotational movement of the spindle coupling  32  to the pump piston  30 . Rotation of the spindle coupling  32  rotates and reciprocates the pump piston  30  inside the cylinder  38  of the pump  24  in a linear direction along the axis of the pump piston  30 . As the pump piston  30  moves linearly, the spherical bearing  36  rotates in the hollow of the spindle coupling  32 . The reciprocal rotation of the pump piston  30  over a 180-degree arc switches the piston flat  44  between a first position facing the first port  40  and a second position facing the second port  42 . In the first position, the piston flat  44  allows fluid to flow from the first port  40  into the chamber  35 . As the pump piston  30  rotates 180-degrees, the first port  40  is closed off and the piston flat  44  moves to the second position and dispenses the fluid from the chamber  35  through the second port  42 . As the pump piston  30  reciprocally rotates in the cylinder  38  between opposing ports  40 ,  42 , the piston flat  44  is open to only one port  40 ,  42  at a time. 
     The port  40 ,  42  that is open to the piston flat  44  is considered the active port. The reciprocating motion pulls fluid in from and pushes fluid out of the active port. The reciprocation and rotation is timed to pull fluid in from one port and push fluid out of the opposite port. Preferably, the piston flat  44  reciprocates by rotating about 180 degrees between the ports  40 ,  42 . Modifying the angle that the pump piston  30  is held relative to the motor shaft  28  adjusts the volume in the chamber  35  at the bottom of the pump piston  30  so that the output volume per revolution can be calibrated to a desired output volume. 
     As also discussed above, the angle between the axis of the pump piston  30  and the motor shaft  28  is determined by means of the base  26  having an upper base portion  46  and a lower base portion  48  pivotably connected to one another via a hinge  50 . The upper base portion  46  has a flange  52  that attaches to the motor  22 , and the lower base portion  48  has a flange  54  that holds the pump head  24  that houses the piston  30  and cylinder  38 . The hinge  50  allows the upper base portion  46  to be tilted relative to the lower base portion  48  in a direction indicated by arrow  47  in  FIG. 4 . Typically, the base  26 , including the upper base portion  46  and lower base portion  48 , are injection molded together with a living hinge  50 . However, it is within the scope of the invention for these portions to be molded separately with a pinned hinge instead. 
     The piston  30  extends into the cylinder  38  and forms a chamber  35  between the distal end of the piston  30  and the bottom of the cylinder  38 . The volume of the chamber  35  changes as the piston  30  travels up and down in the cylinder  38 . Adjusting the angle between the axis of the pump piston  30  and the motor shaft  28  adjusts the travel distance of the piston  30  and determines the maximum volume of the chamber  35  and the flow rate. 
     Adjustment of the angle between the motor shaft  28  and the pump piston  30  is achieved with an electronic adjustment mechanism  59  according to a first embodiment of the present invention shown in  FIGS. 4-6 . The electronic adjustment mechanism  59  includes a linear actuator  60  attached to one of the flanges of the base  26 .  FIGS. 4-6  are directed to a first embodiment of the present invention, wherein a linear actuator  60  attached to the motor flange  52  of the upper base portion  46 . However, it is conceivable for the actuator  60  to be attached to the opposite pump flange  54 , wherein the arrangement of the remaining associated components described herein would be reversed. 
     The linear actuator  60  is preferably an electronic device capable of translating a linear actuator drive rod  62  in precise increments along a linear axis  64  extending parallel to the rotational axis of the motor shaft  28 . One type of linear actuator for use in the present invention is known in the art as a captive nut linear actuator. 
     The motor flange  52  on the upper base portion  46  is preferably attached to the motor  22  by an attachment plate  66 . The attachment plate  66  extends outwardly from the motor  22  and is sized and shaped to allow mounting of the linear actuator  60  of the electronic angle adjustment mechanism  59  to an upper surface  68  of the attachment plate  66 . The mounting of the linear actuator  60  and the motor  22  on the upper surface  68  of the attachment plate  66  and mounting of the motor flange  52  on a lower surface  70  of the attachment plate  66  can be accomplished with conventional fasteners, such as bolts with threaded connections in respective components. Preferably, the attachment plate  66  extends outwardly from the motor  22  and is formed from a single sheet of metal and shaped to accommodate the electronic angle adjustment mechanism  59 . 
     Attached to a distal end of the linear actuator drive rod  62  of the linear actuator  60  is a drive rod coupler  72 . The drive rod coupler  72  extends outwardly from the linear actuator  60  in the axial direction along the longitudinal axis  64 . The drive rod coupler  72  further extends axially through an opening provided in the attachment plate  66  between the upper and lower surfaces. Attached to a distal end of the drive rod coupler  72 , opposite the drive rod  62  is a flexible member  74 . 
     The flexible member  74  is preferably made from a material having the strength to transfer the linear force imparted by the drive rod  62  along its longitudinal axis  64 , yet flexible enough to allow for some slight bending, as will be discussed further below. A suitable material for the flexible member, for example, is spring steel. 
     The flexible member  74  has a first end attached to the distal end of the drive rod coupler and a second end, opposite the first end, connected to the lower flange  54  of the base  26 . Thus, linear motion of the linear actuator drive rod  62  will cause linear motion of the flexible member  74  in the same direction. Because the linear actuator  60  is connected to the upper base portion  46  and the flexible member  74  is connected to the lower base portion  48 , linear motion of the flexible member  74  will cause the lower base portion  48  to pivot with respect to the upper base portion  26  about the hinge  50 . 
     The flexible member  74  initially extends from the drive rod coupler  72  in a direction along the linear axis  64  of the linear actuator drive rod  62 . However, the flexible member  74  is permitted to begin to bend at a point along the longitudinal axis  64  beyond the drive rod coupler  72 . Such bending of the flexible member  74  is desirable to compensate for the arc shaped path of travel of the end of the lower flange  54  opposite the base hinge  50 . 
     The bending of the flexible member  74  can be facilitated by a cam block assembly  76  and a roller bearing assembly  78 . The cam block assembly  76  includes a bracket  80  mounted to the lower flange  54  of the base  26  opposite the base hinge  50 . Any attachment means can be used. For example, a conventional screw fastener engaged in a threaded hole formed in the lower flange  54  will be sufficient. 
     The cam block assembly  76  further includes a cam block  82  supported by the bracket  80 . The cam block  82  has a curved support surface  84  facing the flexible member  74 . The curved support surface  84  of the cam block  82  has a radius of curvature about the pivot point of the base hinge  50  defined by the distance from the pivot point to the intersection point of the flexible member  74  with the lower flange  54  of the base  26 . With the flexible member  74  bearing against the curved support surface  84  of the cam block  82 , the flexible member  74  will traverse a curved path coinciding with the path of the distal end of the lower flange  54  about the base hinge  50 . 
     The roller bearing assembly  78  includes a bracket  86  mounted to the attachment plate  66 . The bracket  86  rotatably supports a roller bearing  88  positioned opposite the cam surface  84  of the cam block  82 . In this regard, the roller bearing  88  can be rotatably mounted on a pin fixed to the roller bearing assembly bracket  86 . The roller bearing  88  here is used to help constrain the flexible member  74  against the curved support surface  84 . One or more springs (not shown) could also be included with the roller bearing assembly  78  to provide an ongoing bias on the roller bearing  88  for pressing the flexible member  74  against the cam block  82 . Without the roller bearing  88 , the flexible member  74  would only be constrained by the drive rod  62  and would therefore, be susceptible to bending outwardly. 
     As can be appreciated from the description above, at least some embodiments of the present invention include a controller that is coupled to the motor  22  and the linear actuator  60  via respective electrical lines  90 ,  92 . One such example of a controller is a computer device that enables dynamic control of the linear actuator  60  and causes the electronic adjustment mechanism  59  to be precisely and repeatably modified. As such, the volume of fluid dispensed is extremely accurate, repeatable, and dynamic. One skilled in the art will appreciate that the invention may be practiced by one or more computing devices and in a variety of system configurations, including in a networked configuration. 
     A second embodiment of the electronic adjustment mechanism  259  of the present invention is shown in  FIG. 7 . The attachment plate  266  is mounted between the motor  222  and a motor flange  252  on an upper base portion  226  and extends outwardly on one side of the motor  222 . The upper base portion  246  and a lower base portion  248  connected to the pump  224  are pivotably connected by a hinge  250 . A sidewall  268  on one side of the attachment plate  266  extends downwardly from the motor  222  towards the pump  224 . An electric motor  260  is attached to the outside of the sidewall  268  and the motor shaft  262  passes through the sidewall  268 . A gear wheel  274  with a plurality of teeth  276  is attached to the distal end of the motor shaft  262   
     A collar  254  is attached to the lower base portion  248  and one side of the collar  254  is attached to the upper base portion  246  by the hinge  250 . Opposite the hinge  250 , a bracket  278  having two parallel members  280 ,  282  extends outwardly from the collar  254 . On the distal end of the two parallel members  280 ,  282 , an arcuate member  284  is attached between the two parallel members  280 ,  282 . The arcuate member  284  curves inwardly towards the collar  254  and has a plurality of teeth  286  on the concave, inward surface. The plurality of teeth  276  on the gear wheel  274  engage the plurality of teeth  286  on the arcuate member  284  and the motor  260  controls the pivotal movement of the upper base portion  246  in relation to the lower base portion  248 . 
     A third embodiment of the electronic adjustment mechanism  359  of the present invention is shown in  FIG. 8 . The attachment plate  366  is mounted between the motor  322  and a motor flange  352  on an upper base portion  346  and extends outwardly on one side of the motor  322 . The upper base portion  346  and a lower base portion  348  connected to the pump  324  are pivotably connected by a hinge  350 . A sidewall  368  on one side of the attachment plate  366  extends downwardly from the motor  322  towards the pump  324 . An electric motor  360  is attached to the outside of the sidewall  368  and the motor shaft  362  passes through the sidewall  368 . A gear wheel  374  with a plurality of teeth  376  is attached to the distal end of the motor shaft  362 . 
     A collar  354  is attached to the lower base portion  348  and one side of the collar  354  is attached to the upper base portion  346  by the hinge  350 . Opposite the hinge  350 , a bracket  378  having two parallel members  380 ,  382  extends outwardly from the collar  354 . On the distal end of the two parallel members  380 ,  382 , an arcuate member  384  is attached between the two parallel members  380 ,  382 . The arcuate member  384  curves outwardly away from the collar  354  and has a plurality of teeth  386  on the convex, outward surface. The plurality of teeth  376  on the gear wheel  374  engage the plurality of teeth  386  on the arcuate member  384  and the motor  360  controls the pivotal movement of the upper base portion  346  in relation to the lower base portion  348 . 
     A fourth embodiment of the electronic adjustment mechanism  459  of the present invention is shown in  FIG. 9 . The attachment plate  466  is mounted between the motor  422  and a motor flange  452  on an upper base portion  446  and extends outwardly on one side of the motor  422 . The upper base portion  446  and a lower base portion  448  are pivotably connected by a hinge  450 . A motor  460  is mounted on the attachment plate  466  with the motor shaft  462  extending downwardly through the plate  466  towards the pump  424 . A worm screw  474  with a continuous spiral thread  476  is attached to the distal end of the motor shaft  462 . 
     A collar  454  is attached to the lower base portion  448  and one side of the collar  454  is attached to the upper base portion  446  by a hinge  450 . Opposite the hinge  450 , a bracket  478  having two parallel members  480 ,  482  extends outwardly from the collar  454 . On the distal end of the two parallel members  480 ,  482 , an arcuate member  484  is attached between the two parallel members  480 ,  482 . The arcuate member  484  curves outwardly away from the collar  454  and has a plurality of teeth  486  on the convex, outward surface. The continuous spiral thread  476  on the worm screw  474  engages the plurality of teeth  486  on the arcuate member  484  and the motor  460  controls the pivotal movement of the upper base portion  446  in relation to the lower base portion  448 . 
     Embodiments of the present invention embrace one or more computer readable media, wherein each medium may be configured to include or includes thereon data or computer executable instructions for manipulating data. The computer executable instructions include data structures, objects, programs, routines, or other program modules that may be accessed by a processing system, such as one associated with a general-purpose computer capable of performing various different functions or one associated with a special-purpose computer capable of performing a limited number of functions. Computer executable instructions cause the processing system to perform a particular function or group of functions and are examples of program code means for implementing steps for methods disclosed herein. Furthermore, a particular sequence of the executable instructions provides an example of corresponding acts that may be used to implement such steps. Examples of computer readable media include random-access memory (“RAM”), read-only memory (“ROM”), programmable read-only memory (“PROM”), erasable programmable read-only memory (“EPROM”), electrically erasable programmable read-only memory (“EEPROM”), compact disk read-only memory (“CD-ROM”), or any other device or component that is capable of providing data or executable instructions that may be accessed by a processing system. 
     For example, the computer device may be a personal computer, a notebook computer, a personal digital assistant (“PDA”) or other hand-held device, a workstation, a minicomputer, a mainframe, a supercomputer, a multi-processor system, a network computer, a controller, a processor-based consumer electronic device, or the like. 
     As a result of the present invention, a mechanism for remote adjustment of the output volume per revolution of a fixed displacement pump is provided. By extending the linear actuator, the angle and output volume per revolution of the pump is increased. By retracting the linear actuator, the angle and output volume per revolution of the pump is decreased. 
     Moreover, by using a flexible member instead of a rigid member to link between the linear actuator and the upper base portion, a proportional relationship is established between the linear motion of the linear actuator and the angular motion of the upper base portion relative to the lower base portion. Also, the ability for electronic adjustment of flow allows the fixed displacement pump to utilize a large output volume per revolution to prime the lines, and then switch to a low output volume per revolution for the required small volume dispenses without manual intervention. 
     The present invention further overcome issues of varying aspirate volumes relative to dispense volumes in a fixed displacement pump. Traditionally, these pumps have only been used to move fluid by rotation of the main motor. With the ability to electronically adjust the angle of the base, a new method to move fluid with a syringing motion becomes possible. With the piston flat open to one port, extending the linear actuator increases the angle of the base and pulls fluid into the pump head. In contrast, by retracting the linear actuator, the angle of the base decreases and pushes fluid out of the pump head. Furthermore, due to the flexible member, the linear motion has a proportional relation to the angular motion, which in turn has a proportional relation to the output volume. This extension and retraction gives a predictable aspirate and dispense volume from the active port. 
     In addition, by introducing the electronic adjustment of the angle for the syringing function in valve-less pumps, it is possible to adjust the barrel size by varying the angle of the piston flat relative to the active port. 
     Also, with the ability to both operate as a traditional syringe pump and a traditional fixed displacement pump, the variable displacement pump can prime the lines by operating like a traditional fixed displacement pump and give constant flow rate dispenses by operating like a traditional syringe pump. 
     While various embodiments of the present invention are specifically illustrated and/or described herein, it will be appreciated that modifications and variations of the present invention may be effected by those skilled in the art without departing from the spirit and intended scope of the invention.