Liquid droplet dispensing

• US 20020177237A1
• Filed: 03/26/2001
• Published: 11/28/2002
• Est. Priority Date: 03/26/2001
• Status: Active Grant

• Current Assignee: Allegro Technologies Ltd. (Danaher Corporation)
• Original Assignee: Allegro Technologies Ltd. (Danaher Corporation)
• Inventors: Makarov, Sergei, Osing, Juergen, Shvets, Alexander, Shvets, Igor
• Granted Patent: US 6,669,909 B2
• Time in Patent Office: Days
• US Class Current: 436/180
• CPC Class Codes: B01L 3/0265 using valves to interrupt or meter fluid flow, e.g. using solenoids or metering valves
• CPC Class Codes: B01L 3/0268 using pulse dispensing or spraying, eg. inkjet type, piezo actuated ejection of droplets from capillaries
• CPC Class Codes: F16K 31/0651 the fluid passing through the solenoid coil
• CPC Class Codes: F16K 31/0655 Lift valves
• CPC Class Codes: F16K 37/0041 for measuring valve parameters F16K37/0033 takes precedence
• CPC Class Codes: F16K 37/005 for measuring fluid parameters F16K37/0033 takes precedence
• CPC Class Codes: G01N 9/34 by using elements moving through the fluid, e.g. vane
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve
• CPC Class Codes: Y10T 436/2575 Volumetric liquid transfer

Abstract

A dispenser (1) for liquid droplets of the order of 30 μl or less in volume. The dispenser (1) comprises a metering valve body (2) having a main bore (3) connected by a pipe (4) to a pressurised liquid delivery source (not shown). The body (2) comprises a base (5) from which is mounted a nozzle (6) projecting above the base (5) to form a valve seat (7). An actuating coil assembly (11) is mounted on the exterior of the body (2) for moving a floating valve boss (15) of a ferromagnetic material. Sensing coils (20, 21) are mounted around and spaced-apart along the body (2) forming part of a valve boss detector. The valve boss detector acts as a positional movement detector so that the opening and closing of the valve can be accurately controlled and bouncing of the valve boss (15) either against an end stop (9) or on the valve seat (7) can be greatly minimized, if not prevented fully, by careful operation of the actuating coil assembly (11).

Claims

1. A dispensing assembly for liquid droplets of the order of 30 μ

l or less in volume comprising;

a pressurised liquid delivery source;

a metering valve body connected to the liquid delivery source, the body comprising an elongate body member having an internal main bore and a base forming an apertured valve seat;

a valve boss in the bore, the cross-sectional area of the valve boss being sufficiently less than that of the main bore to permit the free passage of liquid therebetween;

a nozzle mounted on the base of the body member comprising a dispensing tip and having a nozzle bore communicating between the valve seat and the dispensing tip;

a variable power output valve boss actuator for moving the valve boss in the bore between a closed position engaging the valve seat and an open position spaced-apart from the valve boss;

a valve boss detector for determining the movement of the valve boss within the bore; and

a controller connected to the valve boss detector and to the valve boss actuator for varying the power input to the valve boss actuator depending on the movement of the valve boss within the bore.

2. A dispensing assembly for liquid droplets as claimed in claim 1 in which the valve boss detector is a position sensor.

3. A dispensing assembly as claimed in claim 1 in which at least portion of the nozzle adjacent the dispensing tip is of a hydrophobic material.

4. A dispensing assembly for liquid droplets as claimed in claim 2 comprising:

a ferromagnetic material forming part of the valve boss;

an actuating coil assembly forming the valve boss actuator; and

a Hall sensor to provide the position sensor.

5. A dispensing assembly for liquid droplets as claimed in claim 2 comprising:

a ferromagnetic material forming part of the valve boss;

at least one actuating coil assembly forming the valve boss actuator; and

two spaced-apart Hall sensors to provide the position sensor.

6. A dispensing assembly for liquid droplets as claimed in claim 2, in which the valve boss comprises a ferromagnetic material;

the valve boss actuator comprises a pair of spaced-apart actuating coil assemblies; and

one of the actuating coil assemblies comprises a source of alternating current to allow the position of the valve boss be detected by measuring the electromagnetic field generated in the other actuating coil assembly.

7. A dispensing assembly for liquid droplets as claimed in claim 2 comprising:

a valve boss including a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

a pair of spaced-apart sensing coils forming part of the valve boss detector; and

a separate excitation coil for generating an oscillating magnetic field for the valve boss detector.

8. A dispensing assembly for liquid droplets as claimed in claim 2 in which the valve boss comprises a ferromagnetic material;

the valve boss actuator comprises a pair of spaced-apart actuating coil assemblies, at least one of which is powered with alternating current and the position sensor comprises a sensing coil adjacent the body member for receiving the signal induced in the boss by the alternating current.

9. A dispensing assembly for liquid droplets as claimed in claim 2 comprising:

a ferromagnetic material forming part of the valve boss; and

a parametric oscillator circuit forming the position sensor, the circuit comprising at least one element coupled to the valve boss, the element being such as to be effected by the position of the valve boss relative thereto to change the characteristics of the oscillations.

10. A dispensing assembly for liquid droplets as claimed in claim 2, in which the valve boss comprises a ferromagnetic material encased in an electrically conducting material, the valve boss actuator comprises at least one actuating coil assembly;

and the position sensor comprises a pair of sensing coils coupled with each other by means of eddy currents induced in the boss by one of them.

11. A dispensing assembly for liquid droplets as claimed in claim 2, in which the valve boss comprises a ferromagnetic material encased in an electrically conducting material, the valve boss actuator comprises at least one actuating coil assembly;

and the position sensor comprises a pair of sensing coils surrounded by a conducting shield adjacent the body member, the two sensing coils being coupled with each other by means of eddy currents induced in the boss by one of them.

12. A dispensing assembly as claimed in claim 2 in which at least portion of the length of the nozzle is of a hydrophobic material.

13. A dispensing assembly for liquid droplets as claimed in claim 1, in which the valve boss detector is a velocity sensor.

14. A dispensing assembly for liquid droplets as claimed in claim 13, in which the velocity sensor comprises two sensing coils spaced-apart along the body member for measurement of the electromotive force generated by the moving boss which comprises a ferromagnetic material.

15. A dispensing assembly for liquid droplets as claimed in claim 13, in which the valve boss comprises a ferromagnetic material and the valve boss actuator comprises a pair of spaced-apart actuating coil assemblies, the actuating coil assemblies also being adapted for measurement of the electromotive force generated by the moving boss to provide the velocity sensor.

16. A dispensing assembly for liquid droplets as claimed in claim 13 in which the valve boss comprises a ferromagnetic material;

the valve boss actuator comprises at least one actuating coil assembly; and

the velocity sensor comprises a sensing coil adjacent the body member for measurement of the electromotive force generated by the moving boss.

17. A dispensing assembly for liquid droplets as claimed in claim 13 in which the valve boss comprises a ferromagnetic material;

the valve boss actuator comprises a pair of spaced-apart actuating coil assemblies; and

the velocity sensor comprises a sensing coil adjacent the body member for measurement of the electromotive force generated by the moving boss.

18. A dispensing assembly as claimed in claim 13, in which at least portion of the nozzle adjacent the dispensing tip is of a hydrophobic material.

19. A dispensing assembly for liquid droplets as claimed in claim 1, in which there are a plurality of nozzles mounted on the base of the body member.

20. A dispensing assembly for liquid droplets as claimed in claim 19 comprising:

a valve boss, at least portion of which is of a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

a source of current to power the actuator;

sensing means in the valve boss; and

detector to determine the electromotive force generated by the valve boss under the influence of an externally generated signal.

21. A dispensing assembly for liquid droplets as claimed in claim 19 comprising:

a valve boss, at least portion of which is of a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

a source of current to power the actuator; and

means in the detector to determine the electromotive force generated by the valve boss under the influence of an externally generated signal and in which the externally generated signal is provided by the actuating coil assembly.

22. A dispensing assembly for liquid droplets as claimed in claim 19 comprising:

a valve boss, at least portion of which is of a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

a source of current to power the actuator; and

means in the detector to determine the electromotive force generated by the valve boss under the influence of an externally generated signal and in which the electrical signal is provided by the actuating coil assembly and the sensing means comprises a sensing coil external of the body member.

23. A dispensing assembly for liquid droplets as claimed in claim 19 comprising:

a valve boss, at least portion of which is of a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

a source of current to power the actuator; and

means in the detector to determine the electromotive force generated by the valve boss under the influence of an externally generated signal and in which the externally generated signal is an additional alternating current.

24. A dispensing assembly for liquid droplets as claimed in claim 19 in which the valve boss detector is a combined position and velocity sensor.

25. A dispensing assembly for liquid droplets as claimed in claim 19 comprising:

a valve boss including a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

means in the valve boss detector for measurement of the electromotive force generated by the valve boss when moving under the influence of the current applied to the actuating coil assembly to determine the velocity of the valve boss;

means for applying the oscillating magnetic field to the valve boss; and

means in the valve boss detector for measurement of the electromotive force generated by the valve boss under the influence of the oscillating field to determine the position of the valve boss.

26. A dispensing assembly as claimed in claim 19, in which at least portion of the nozzle adjacent the dispensing tip is of a hydrophobic material.

27. A dispensing assembly for liquid droplets as claimed in claim 1 comprising:

a valve boss, at least portion of which is of a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

a source of current to power the actuator; and

means in the detector to determine the electromotive force generated by the valve boss under the influence of an externally generated signal.

28. A dispensing assembly for liquid droplets as claimed in claim 27, in which the externally generated signal is provided by the actuating coil assembly.

29. A dispensing assembly for liquid droplets as claimed in claim 27, in which the electrical signal is provided by the actuating coil assembly and the sensing means comprises a sensing coil external of the body member.

30. A dispensing assembly for liquid droplets as claimed in claim 27, in which the electrically generated signal is an additional alternating current.

31. A dispensing assembly as claimed in claim 27, in which at least portion of the nozzle adjacent the dispensing tip is of a hydrophobic material.

32. A dispensing assembly for liquid droplets as claimed in claim 1, in which there are a plurality of metering valve bodies all connected to the one controller.

33. A dispensing assembly for liquid droplets as claimed in claim 1, in which there are a plurality of additional metering valve bodies each having an additional variable power output valve boss actuator and in which the controller is connected to each of the additional valve boss actuators for varying the power input to each of the additional valve boss actuators depending on the position of the other valve boss within its bore.

34. A dispensing assembly for liquid droplets as claimed in claim 1 comprising:

a valve boss including a ferromagnetic material;

at least one actuating coil assembly forming the valve boss actuator;

means in the valve boss detector for measurement of the electromotive force generated by the valve boss when moving under the influence of the current applied to it to determine the velocity of the valve boss;

means for applying the oscillating magnetic field to the valve boss; and

means in the valve boss detector for measurement of the electromotive force generated by the valve boss under the influence of the oscillating field to determine the position of the valve boss.

35. A dispensing assembly for liquid droplets as claimed in claim 1 in which the valve boss detector is a combined position and velocity sensor.

36. A dispensing assembly for liquid droplets as claimed in claim 1, in which the valve boss sensor is an acceleration sensor.

38. A method as claimed in claim 37, in which the valve seat engaging force is sufficient to prevent the valve boss from disengaging from the valve seat.

39. A method as claimed in claim 37, in which in the fully open position, the valve boss engages the boss stopper and then the additional steps are performed of:

on sensing the valve boss being about to contact the boss stopper, exerting a variable boss stopper engaging force on the valve seat to cause zero boss velocity; and

on sensing the valve boss is stationary, exerting the valve open retaining force on the valve boss.

40. A method as claimed in claim 39, in which the boss stopper engaging force is sufficient to prevent the valve boss from disengaging from the valve stopper.

41. A method as claimed in claim 37, in which the position of the valve boss within the main bore is determined from the velocity of the valve boss and the time travelled.

42. A method as claimed in claim 37, in which the viscosity of the liquid is determined from the force required to move the valve boss at a sensed velocity through the main bore.

43. A method as claimed in claim 37, in which the volume of droplet dispensed is measured by measuring the difference between the opening force and the closing force.

44. A method as claimed in claim 43, in which the volume is calculated as:

45. A method as claimed in claim 43, in which the volume is calculated from:

46. A method as claimed in claim 43 in which the density of a liquid being dispensed is obtained by measuring the current required to move the boss at a constant relatively low velocity and the density is calculated from

I*k_m=V_b*g*(P_b−

P_l)

I=current through the actuating coils

k_m=coefficient dependent on actuating coils

V_b=volume of boss

P_b=density of boss

P_l=density of liquid

g=acceleration due to gravity.

47. A method as claimed in claim 43, in which the presence of the liquid being dispensed is detected by monitoring the difference between the opening force and the closing force for each droplet dispensed.

37. A method of dispensing liquid droplets of the order of 30 μ

l or less in volume in a dispensing assembly using a pressurised delivery source feeding a metering valve body, the valve body comprising an elongate body member having an internal main bore, a base forming an apertured valve seat and a boss stopper in the main bore spaced-apart from the base;

a valve boss comprising ferromagnetic material in the main bore, the cross-sectional area of which is sufficiently less than that of the main bore to allow the passage of liquid therebetween, a nozzle mounted on the base comprising an elongate needle-like member having a nozzle bore communicating between the valve seat and a dispensing tip and a variable power actuator for moving the valve boss in the bore between a closed position in engagement with the valve seat and an open position spaced-apart from the valve seat, the variable power actuator moving the valve boss by applying an electrical field to the valve boss, recording the position of the valve boss within the main bore of the body member throughout the dispensing cycle and using the information on the position of the valve boss within the bore to vary the force to be exerted on the valve boss between a highest force on engagement and disengagement of the valve boss with the valve seat and lower force needed to keep the valve boss in spaced relationship with the valve seat to maintain the valve open; and

then sequentially carrying out the steps of;

opening the metering valve by exerting a disengaging force on the valve boss to separate the valve boss from the valve seat;

on sensing the opening of the metering valve, exerting an opening force to remove the valve boss to a fully open position remote from the valve seat;

exerting a valve open maintaining force on the valve boss to retain the valve boss in the fully open position;

exerting a closing force on the valve boss to move the valve boss close to the valve seat;

on sensing the valve boss being about to contact the valve seat, exerting a valve seat engaging force on the valve boss; and

on sensing the valve boss is stationary, exerting a valve closed retaining force on the valve boss.