Automatic precision non-contact open-loop fluid dispensing

• US 20050095723A1
• Filed: 11/04/2003
• Published: 05/05/2005
• Est. Priority Date: 11/04/2003
• Status: Active Grant

• Current Assignee: DRUMMOND SCIENTIFIC COMPANY
• Original Assignee: DRUMMOND SCIENTIFIC COMPANY
• Inventors: Canfield, Eric L., DiTrolio, Nicholas M.
• Granted Patent: US 7,396,512 B2
• Time in Patent Office: Days
• US Class Current: 436/180
• CPC Class Codes: B01L 2200/146 Employing pressure sensors
• CPC Class Codes: B01L 2200/148 Specific details about calibrations
• CPC Class Codes: B01L 2300/027 Digital display, e.g. LCD, LED
• CPC Class Codes: B01L 2400/0487 fluid pressure, pneumatics
• CPC Class Codes: B01L 3/021 Pipettes, i.e. with only one conduit for withdrawing and redistributing liquids
• CPC Class Codes: B01L 3/0213 Accessories for glass pipettes; Gun-type pipettes, e.g. safety devices, pumps
• CPC Class Codes: B01L 3/0227 Details of motor drive means B01L3/0231, B01L3/0234 take precedence
• CPC Class Codes: B01L 3/0234 Repeating pipettes, i.e. for dispensing multiple doses from a single charge
• CPC Class Codes: G01F 13/006 measuring volume in function of time
• CPC Class Codes: G01F 15/005 Valves valves in general F16K
• CPC Class Codes: G01F 15/022 using electrical means
• CPC Class Codes: G01F 15/068 with electrical means G01F15/063 takes precedence
• CPC Class Codes: G01F 23/02 by gauge glasses or other apparatus involving a window or transparent tube for directly observing the level to be measured or the level of a liquid column in free communication with the main body of the liquid
• CPC Class Codes: G01F 25/0092 for metering by volume
• CPC Class Codes: G01F 3/00 Measuring the volume flow of fluids or fluent solid material wherein the fluid passes through the meter in successive and more or less isolated quantities, the meter being driven by the flow measuring a proportion of the volume flow G01F5/00
• CPC Class Codes: Y10T 436/2575 Volumetric liquid transfer

Abstract

A rugged, all-electronic fluid dispensing system for use with pipettes or in other contexts indirectly measures fluid flow by using a non-linear system model to correlate vacuum existing at the top of a column of suspended fluid. Non-contact operation is provided to eliminate the need for contact-type closed-loop fluid flow sensing and associated potential cross-contamination risks. In one particular exemplary non-limiting illustrative implementation, an electronic controller within a gun-shaped, cordless self-contained pipetter housing dynamically calculates valve opening time based on a non-linear equation. Calibration is used to derive equation constants, and column vacuum pressure before the valve is opened is used as the independent variable to derive a valve opening time that will result in accurate dispensing of a desired programmed fluid quantity. Repetitive automatic dispensing with accuracies greater than 1% are possible within the context of a relatively inexpensive portable pipette or device without the need for mechanically-complex positive displacement arrangements.

Claims

1. A method of automatically dispensing liquid from a pipette comprising:

restricting gas flow into said pipette to thereby substantially retain a column of liquid there within;

computing a timing parameter based at least in part on (i) height of said liquid column within said pipette, and (ii) a desired quantity of said liquid to dispense; and

automatically controlling gas flow into said pipette in accordance with said timing parameter to thereby dispense substantially said desired quantity of liquid from said pipette.

2. The method of claim 1 wherein said restricting includes maintaining a valve closed, and said controlling includes opening said valve for a time period based at least in part on said timing parameter.

3. The method of claim 1 wherein said computing includes accessing a stored mathematical model.

4. The method of claim 3 wherein said computing further includes calculating said timing parameter.

5. The method of claim 3 wherein said computing further includes looking up said timing parameter from a stored table of empirical values.

6. The method of claim 1 wherein said controlling includes actuating a pump.

7. The method of claim 1 further including measuring negative pressure at the top of said column, and ascertaining liquid column height based at least in part on said measured negative pressure.

8. The method of claim 1 further including contacting said liquid only with said pipette during said aforementioned steps.

9. The method of claim 1 wherein said controlling includes using an open-loop control mechanism.

10. The method of claim 1 wherein said controlling controls said dispensing without using feedback.

11. The method of claim 1 further including decoupling said pipette from a handheld fixture and disposing of said pipette after use.

12. The method of claim 1 further including repeating said computing and controlling to repetitively dispense said desired quantity.

13. The method of claim 12 wherein said repeating is performed in response to user actuation.

14. A non-contacting, open loop automatic fluid dispensing method comprising:

programming an amount of fluid to be dispensed from a reservoir;

using a mathematical model to generate a time parameter; and

controlling dispensing of said fluid based at least in part on said time parameter,

wherein said method accurately dispenses said desired quantities over different column heights within said reservoir.

15. The method of automatically dispensing fluid from a fluid reservoir comprising:

programming an electronic controller with a desired quantity of fluid to be dispensed;

measuring a pressure associated with the fluid reservoir;

deriving at least one open-loop control output parameter from said measured pressure and said programmed desired quantity; and

applying a signal corresponding to said derived open-loop control parameter to at least one fluid flow control element coupled to said fluid reservoir,

wherein said applying causes substantially said desired fluid quantity to be automatically dispensed.

16. The method of claim 15 wherein said reservoir comprises a pipette.

17. The method of claim 15 wherein said flow control element includes an electric valve and said control output parameter comprises opening time of said valve.

18. The method of claim 15 further including powering an electric pump.

19. The method of claim 15 wherein said reservoir provides a suspended fluid column and said measuring includes measuring the vacuum at the top of the suspended fluid column.

20. The method of claim 15 further including issuing a control output causing said reservoir to be at least partially refilled with fluid.

21. The method of claim 15 wherein said deriving includes calculating at least one non-linear equation.

22. The method of claim 15 further including a look-up table.

23. A system for automatically dispensing quantities of fluid from a reservoir, comprising:

a storage medium that stores a parameter relating to a desired quantity of fluid to be dispensed;

a pressure transducer that measures a pressure associated with the reservoir;

at least one fluid flow control element coupled to said reservoir; and

a processor coupled to said storage medium, said processor deriving at least one open-loop control output parameter from said measured pressure and said stored quantity parameter; and

applying an open-loop control signal corresponding to said derived open-loop control parameter to said fluid flow control element to control substantially said desired fluid quantity to be dispensed.

24. The system of claim 23 wherein said reservoir comprises a pipette.

25. The system of claim 23 wherein said flow control element includes an electric valve.

26. The system of claim 23 wherein said flow control element includes an electric pump.

27. The method of claim 23 wherein said transducer measures the vacuum at the top of a suspended fluid column.

28. The method of claim 23 further including means for issuing a control output causing said reservoir to be at least partially refilled with fluid.

29. An electronic, hand held fluid dispensing system for use with a laboratory pipette, comprising:

a housing capable of being held in one hand;

a coupler disposed at least partially within said housing, said coupler being adapted to be removably connected to said pipette;

a source of pressure and/or vacuum;

a valve pneumatically coupled between said source and said coupler;

at least one pressure transducer pneumatically coupled to said coupler, said pressure transducer generating at least one output; and

an electronic controller electrically coupled to control at least said valve and also electrically coupled to said pressure transducer, said electronic controller operating in an open-loop mode to control said valve in accordance with a valve controlled parameter derived from said pressure transducer output, said valve control parameter controlling said valve so that said system automatically, repetitively dispenses substantially a predetermined quantity of fluid from said pipette.

30. The system of claim 29 wherein said source comprises an electric air pump.

31. The system of claim 29 wherein said source comprises a source of atmospheric pressure.

32. The system of claim 29 wherein said source comprises a source of a pressurized gas.

33. The system of claim 29 wherein said source comprises a reversible electric pump that selectively generates suction and positive pressure, and wherein said electronic controller is coupled to selectively control said pump to generate suction to draw fluid into said pipette.

34. The system as in 29 wherein said hand-held housing is gun-shaped.

35. The system as in 29 wherein said electronic controller dynamically calculates said valve control parameter based on a non-linear mathematical model.

36. The system as in 29 wherein said electronic controller uses a look-up table to ascertain said valve control parameter based on measured pressure.

37. The system as in 29 where further including a further pressure transducer that measures pressure between said source and said valve, and wherein said electronic controller is responsive to said second pressure transducer for controlling said source to compensate for variations in the output pressure of said source.

38. The system as in 29 wherein said coupler is adapted to accept pipettes of different sizes.

39. The system as in 29 further including a graphical display disposed on said housing and coupled to said electronic controller.

40. The system as in 29 further including means for allowing an end user to program said desired quantity.

41. The system as in 40 wherein said means comprises first and second push buttons mounted on said housing, said first and second push buttons in one mode of operation being used to program said desired quantity, and in a further mode of operation being used to control aspiration and dispensing rate.

42. The system as in 40 wherein said means comprises software executed by said electronic controller that allows said electronic controller to learn said desired quantity based on user operation of said system.

43. The system as in 29 wherein said system achieves repeatable dispensing accuracies of better than 1%.

44. The system as in 29 wherein said fluid control element comprises an electronic valve with a on/off orifice, and wherein said control parameter controls the duration of opening of said valve orifice.

45. The system as in 29 wherein said fluid control element comprises a valve with a variable orifice, and wherein said control parameter controls the amount said valve orifice is opened.

46. The system as in 29 wherein said electronic controller controls said source to reduce undesired dripping of fluid from said pipette.

47. The system as in 29 wherein said electronic controller derives an indication of the angle of said pipette from vertical.

48. The system as in 29 wherein said electronic controller compensates for different fluid viscosities.