Highly accurate pumping device

Abstract

A highly accurate pumping device for aspirating and dispensing variable volumes of fluid is presented. The pumping device comprises a housing with a slotted optical sensor, a stepper motor with a fine pitch lead screw, a coupling linking the stepper motor shaft and the lead screw, an anti-backlash nut, an anti-rotation arm linking the plunger with the anti-backlash nut, an end of travel sensor feature integrated in the arm, and a top which incorporates a chamber and a lead screw bearing. A seal, located in the top, seals against the plunger and the chamber. The plunger is attached to the anti-rotation arm and eccentrically aligned to the lead screw. The pumping device further includes one or more ports through which fluid may be introduced into or out of the chamber. The pumping device may be easily changed to accommodate different full-scale volume requirements due to the self-aligning features.

Description

BACKGROUND ON THE INVENTION

Many types of pumps are used to aspirate and dispense fluids. Many applications require accurately dispensing small volumes of fluid. Pumps typically are comprised of many pieces with many stringent manufacturing requirements necessary for such accurate aspirating and dispensing.

There is a need for a pump which is simple to manufacture and is able to provide accurate aspiration and dispensing of a wide range of volumes.

SUMMARY OF THE INVENTION

A highly accurate pumping device for aspirating and dispensing fluids is presented. The pumping device is comprised of a stepper motor, a lead screw, a coupler linking the stepper motor shaft to the lead screw, an anti-backlash nut coupled to the lead screw, an anti-rotation arm coupled to the anti-backlash nut, a plunger coupled to the anti-rotation arm, a top section, an end cap and a housing with a slot for the anti-rotation arm and mounts for an end-of-travel sensor. The top section is comprised of a bearing for locating one end of the lead screw, a pumping chamber, one or more ports and a recessed area for a seal, which seals against the plunger and the sides of the recessed area. The end cap is located such as to retain the seal in the recessed area of the top section. Activation of the stepper motor causes the plunger to move axially into or out of the pumping chamber thus dispensing or aspirating fluid. Accurate aspiration and dispensing of fluids is accomplished with the use of the anti-rotation slot, the anti-backlash nut and by adjusting several factors such as the pitch of the lead screw, the diameter of the plunger and the actuation of the stepper motor. Exchanging a minimal number of parts allows the pump to aspirate and dispense different volumes of fluids. The self-aligning features of the pump allow the pump to be easily reconfigured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front perspective view of the pumping device.

FIG. 1B is a rear perspective view of the pumping device.

FIG. 2 is a cross sectional view of the pumping device of FIG. 1A.

FIG. 3A is a perspective view of a first top.

FIG. 3B is a cross sectional side view of a first top in FIG. 3A showing a bearing, a seal and the end cap.

FIG. 3C is a cross sectional view of a second top without the bearing, seal and end cap.

FIG. 4 is a perspective view of the end cap.

FIG. 5A is a perspective view of the housing.

FIG. 5B is a cross sectional side view of the housing in FIG. 5A.

FIG. 5C is a rear view of the housing in FIG. 5A.

FIG. 6 is a perspective view of the anti-rotation arm.

FIG. 7 is a perspective view of the anti-backlash nut, lead screw, anti-rotation arm and a first plunger assembly.

FIG. 8A is a cross sectional view of a first plunger in FIG. 7.

FIG. 8B is a cross sectional view of a second plunger.

FIG. 9 is a perspective view of the coupler.

FIG. 10 is a perspective view of the lead screw.

FIG. 11 is a perspective view of the lead screw, anti-backlash nut, plunger, anti-rotation arm and coupler assembly.

FIG. 12A is a perspective view of a first seal.

FIG. 12B is a perspective view of a second seal.

FIG. 13 is a perspective view of the stepper motor.

FIG. 14 is a perspective view of the lead screw, anti-backlash nut, anti-rotation arm, plunger, coupler and stepper motor assembly.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIGS. 1A and 1B is a highly accurate pumping device comprised of a first top section 1, an end cap 17, a housing 7, a first plunger 18, an anti-rotation arm 6, a sensor 8 and a stepper motor 10. Also shown in FIG. 1A are an inlet port 12 and an outlet port 13. The number and location of the ports can vary. An adjustment knob 45 is attached to the motor 10 to manually adjust the position of the first plunger 18.

As shown in FIG. 2 the coupler 9 connects the shaft 11 of the stepper motor 10 to the lead screw 4. The lead screw 4 is located in a first top section 1 by means of a bearing 3. The anti-rotation arm 6 is connected to the anti-backlash nut 5, which moves axially along the lead screw 4 when the stepper motor 10 is activated. A first plunger 18 is attached to the arm 6 by means of a screw 29. A first seal 14 is retained in a first top section 1 by means of an end cap 17. A first plunger 18 is moved axially through a first seal 14 when the stepper motor 10 is activated. A sensor 8 located on the housing 7 is used for determining position of a first plunger 18. The number and location of the sensor 8 on the housing may vary. The adjustment knob 45 is attached on the motor 10 distally from the housing 7.

FIG. 3A shows a first top section 1 with a plurality of holes 38 used to attach the top section 1 to the housing as described below.

FIG. 3B shows the configuration of a first top section 1. The bearing 3, which locates the lead screw as described above, is located in a hole 34. A first seal 14 is located in a recessed area 16. The end cap 17 is attached to the top section 1 such that its central hole, as described below, is axially aligned with a first chamber 31 and attached to the top section 1. The end cap 17 retains the seal 14 in the recessed area 16. An outlet port 13 is located at the top surface of the top section 1 and is axially aligned with a first chamber 31. The chamber is substantially cylindrical in shape. A conical section 33 of a first chamber 31 assists in removal of air bubbles when liquid is dispensed. The inlet port 12 is located above the seal 14 perpendicular to the chamber 31 to assist in removal of air bubbles from around the seal 14 when liquid is aspirated. A recessed area 23 is used to axially align the top section 1 with the housing as described below.

A second top section 2 is shown in FIG. 3C. A second chamber 32 allows for a different volume to be aspirated or dispensed. The chamber is substantially cylindrical in shape. A second seal, as described below, is located in a second hole 44. The outlet port 13 is axially aligned with the second chamber 32. A conical section 42 of the second chamber 32 assists in removal of air bubbles when liquid is dispensed. A hole 34 is used to locate a bearing as described above. A recessed area 23 is used to axially align the second top section 2 with the housing as described below. The inlet port 12 is located perpendicular to the chamber 31 to assist in removal of air bubbles from around the seal when liquid is aspirated as described above.

The end cap 17, shown in FIG. 4, is comprised of a central hole 41 and a plurality of holes 40 used to attach the end cap 17 to the top section. The central hole 41 is axially aligned with the chamber in the top section as described above.

FIG. 5A shows the housing 7 with a plurality of holes 39 which are used to attach the housing 7 to the top section as described above. The boss 22 is used to axially align the housing 7 with the top section as described above. A slot 25 is provided for movement of the end of travel protrusion of the anti-rotational arm as described below. A second slot 24 prevents the anti-rotation arm from rotating as described below. A plurality of holes 43 is used to attach the housing to the stepper motor as described below.

FIG. 5B shows the housing 7, which includes a boss 22 used to axially align the housing 7 with the top section as described above. A recessed area 21 is used to axially align the housing 7 with the stepper motor as described below.

A rear view of the housing 7 is shown in FIG. 5C. Mounting supports 26 and a slot 30 allow for the attachment of the sensor as described above.

The anti-rotation arm 6 is shown in FIG. 6. It contains a protrusion 37 which is used with the sensor to indicate position of the plunger as described above. A hole 46 is used to attach the plunger as described below to the anti-rotation arm 6.

FIG. 7 shows the assembly of the lead screw 4, the anti-backlash nut 5, the anti-rotation arm 6 and a first plunger 18.

FIG. 8A shows a first plunger 18 with a threaded hole 35 used to attach the plunger to the anti-rotational arm as described above. The plunger may be attached to the anti-rotation arm by means other than screws.

FIG. 8B shows a second plunger 19 with a diameter different from that of the first plunger. A threaded hole 35 is used to attach the plunger to the anti-rotation arm as described above. The plunger may be attached to the anti-rotation arm by means other than screws.

FIG. 9 shows one version of a coupler 9 that is used to connect the shaft of the stepper motor to the lead screw as described above. Other configurations of the coupler are possible.

FIG. 10 shows the lead screw 4. The proximal end 28 is connected to the coupler as described above. The distal end 27 is inserted into the bearing as described above. The proximal end 28 and the distal end 27 may be of same or different diameters.

FIG. 11 shows an assembly consisting of the lead screw 4, the anti-backlash nut 5, the anti-rotation arm 6, a first plunger 18 and the coupler 9. The anti-backlash nut is self-adjusting to take out any backlash between the lead screw and the motor.

A first seal 14 is shown in FIG. 12A. The seal is a u-cup shape with an internal diameter sized for the first plunger. The outer diameter seals against the recessed area of the top section as described above.

A second seal 15 is shown in FIG. 12B. The seal is a u-cup shape with an internal diameter sized for the second plunger. The outer diameter seals against the recessed area of the top section as described above.

The stepper motor 10 is shown in FIG. 13. A boss 20 on the motor is used to axially align the motor to the housing as described above. A wiring connector 36 provides for power to the motor.

FIG. 14 shows the arrangement between the stepper motor 10, the coupler 9, the lead screw 4, the anti-backlash nut 5, the anti-rotation arm 6 and a first plunger 18. The stepper motor 10 turns the coupler 9 which in turn rotates the lead screw 4. The anti-backlash nut 5 travels axially along the lead screw 4. The anti-rotation arm 6, connected to the anti-backlash nut 5, moves with the anti-backlash nut 5. The slot in the housing described above prevents the anti-rotation arm 6 from rotating as the lead screw 4 is rotated. Thus, the plunger 18 is moved in an axial direction into and out of the chamber to dispense and aspirate fluids as described above.

The above described pumping device, using the anti-rotation arm, the anti-rotation slot of the housing, the anti-backlash nut with appropriate modifications to the lead screw pitch, plunger diameter and stepper motor control and other features, provides accurate and reliable aspiration and dispensing volumes. The self-aligning features allow the pump to be easily reconfigured to accommodate different full stroke volumes. The self-aligning features, together with the few number of parts, provide for substantial cost savings in the manufacture of the pumping device.

Having described preferred embodiments of the invention, it will become apparent to those of reasonable skill in the art that other embodiments incorporating the above described features may also be developed. Accordingly, it is submitted that the present invention not be limited to the described embodiments but rather by the scope and spirit of the appended claims.

Claims

1. A highly accurate pumping device comprising:

a housing including an integral anti-rotation groove and mounting location for a slotted optical sensor;

a first top removably coupled to said housing;

a first chamber within a portion of said first top, said first chamber having a cone shape at one end;

a first plunger displaceable within a portion of said first chamber, which, in combination with said first chamber, is adapted for aspirating and dispensing;

ports within said first top, said ports allowing for the introduction of liquid into or out of said first chamber;

a coupler linking the lead screw and stepper motor shaft;

a stepper motor attached to said housing, which turns said lead screw for the purpose of moving said first plunger into or out of said first chamber;

2. The pumping device of claim 1 further comprising an anti-rotation arm removably coupled to an anti-backlash nut, the anti-rotation arm having an end of travel protrusion that interacts with a slotted optical sensor.

3. The pumping device of claim 1 wherein said first plunger is removably coupled to said anti-rotation arm.

4. The pumping device of claim 1 comprising a first seal disposed around said first plunger and against a surface of a recessed area of said first top.

5. The pumping device of claim 1 wherein one port is located proximally to said first seal and oriented with its axis perpendicular to the axis of said first chamber to allow incoming fluid to clear away residual air bubbles from said first seal.

6. The pumping device of claim 1 wherein one port is located distally from said first seal and axially aligned with said first chamber.

7. The pumping device of claim 1 comprising an end cap disposed to restrain said first seal in said first top.

8. The pumping device of claim 1 comprising a bearing disposed in a hole in said first top, said bearing axially aligned with said lead screw, through which one end of said lead screw protrudes.

9. The pumping device of claim 1 further comprising:

a second plunger having a different size than said first plunger;

a second top with a second chamber having a different size than said first chamber;

a second seal having a different size than said first seal, said second seal disposed in recessed area in said second top and restrained by an end cap; said second top, said second plunger and said second seal adapted to aspirate or dispense a second volume of liquid.