Pulseless liquid delivery system using a pulsatile pump

• US 5,971,713 A
• Filed: 12/29/1998
• Issued: 10/26/1999
• Est. Priority Date: 01/07/1997
• Status: Expired due to Fees

• Current Assignee: Howard L. North Jr
• Original Assignee: Howard L. North Jr
• Inventors: North, Howard L. Jr.
• Primary Examiner(s): Thorpe, Timothy S.
• Assistant Examiner(s): Gartenberg, Ehud
• Application Number:
  US09/222,057
• Time in Patent Office: 301 Days
• Field of Search: 417/32, 417/36, 417/37, 417/44.9, 417/63, 73/149, 73/290 R, 73/168
• US Class Current: 417/36
• CPC Class Codes: F04B 11/0033 with a mechanical spring
• CPC Class Codes: F04B 2201/0808 Size of the dead volume
• CPC Class Codes: F04B 2203/0201 Current
• CPC Class Codes: F04B 49/16 by adjusting the capacity of dead spaces of working chambers
• CPC Class Codes: G01N 15/1404 Handling flow, e.g. hydrodynamic focusing

Abstract

A liquid supply system including a diaphragm pump, a novel liquid accumulator providing exceptionally high volume compliance, and a control of accumulator volume within narrow limits by continuous control of the pump motor. The accumulator achieves high volume compliance by arranging the kinematics of a main spring loading the accumulator to have a negative spring rate equal to the sum of all other positive spring rates produced by a second spring used to adjust the accumulator pressure, by the diaphragm, and by a pivot for a sensor lever. This lever moves with the diaphragm to actuate an optical sensor producing an signal indicative of small changes in liquid volume in the accumulator. This signal continuously modulates the power to the motor driving the pump so as to maintain the accumulator volume lose to a datum valve. This close control of liquid volume in a high compliance accumulator provides substantially pulse-free constant pressure liquid delivery from a pulsatile pump. The second spring may be adjusted to modify this constant pressure without disturbing the balance between positive and negative spring rates. Adjustment may be automatic in response to a variable such as liquid temperature whereby liquid pressure is automatically increased with lower liquid temperature to maintain liquid flow substantially constant through a flow cytometry apparatus used for particle analysis.

Claims

1. In a liquid delivery system of the type comprising a supply reservoir, a pump, and an outlet useful for supplying from said outlet a liquid under pressure, the improvement wherein there is interposed between said pump and said outlet a) a liquid accumulator means incorporating both pressure regulating means and volume sensing means and b) a control means responsive to said volume sensing means for providing substantially continuous modulation of power to a pump drive means whereby substantially constant and pulse-free liquid pressure is produced over a range of liquid flow from zero up to the maximum capacity of said pump.

2. The liquid delivery system of claim 1 wherein said pump includes at least one pumping diaphragm with inlet and outlet check valves and said pump driving means produces reciprocating motion of said pumping diaphragm.

3. The liquid delivery system of claim 1 wherein said pressure regulating means includes a housing enclosing a flexible diaphragm exposed on one side to said liquid pressure and loaded on the opposite side by an opposing force means whereby small increases in liquid volume within said housing cause said opposing force to either decrease or remain substantially constant.

4. The liquid delivery system of claim 3 wherein said opposing force means includes a pivotably supported sensor lever loaded by force from an extension spring pivotably attached to said sensor lever at a point so located that as said sensor lever executes small movements about said pivot in response to increases in liquid volume in said accumulator, the fractional increase in said spring force is equal to or less than the fractional decrease in the distance from the line of action of said spring force to said pivot, thus producing zero or negative changes in the moment about said pivot thereby producing zero or negative changes respectively in the force on said diaphragm connected to said sensor lever.

5. The liquid delivery system of claim 4 further including an additional spring acting on said sensor lever to increase the liquid pressure wherein said negative changes in force on said diaphragm substantially equal the sum of all positive changes in force on said diaphragm produced by said diaphragm, said pivot, and said additional spring due to small movements about said pivot produced by increases in liquid volume in said liquid accumulator.

6. The liquid delivery system of claim 4 wherein said sensor lever pivot is comprised of a thin sheet of rigid material fastened on one side to a support member and fastened on the opposite side to said sensor lever thus permitting small rotational movements of the sensor lever about a virtual pivot within the elastic limit of said rigid material.

7. The liquid delivery system of claim 1 wherein the liquid accumulator means has a volume compliance as defined by Equations 1, 2 and 3:

##EQU7## where for pivot support (44);

E=Young=s modulus of elasticity--psi

w=width--inches

t=thickness--inches

h=height--inches ##EQU8## and wherein the value of H is selected to be equal to the value derived from Equations 4 and 5;

##EQU9##

8. The liquid delivery system of claim 7 wherein the value of H is selected to approximate the value derived from Equations 4 and 5.

9. The liquid delivery system of claim 5 wherein said additional spring has the end distal to said sensor lever pivotably attached to to linearly movable means whereby said additional spring force acting on said sensor lever may be adjusted to produce vatiations in said regulated pressure.

10. The liquid delivery system of claim 9 wherein said linearly movable means comprises a knob integral with a threaded member, supported to resist linear motions and to permit rotational motion, engaged with threads in a slidable member supported to resist rotational motion, said slidable member pivotably coupled to said additional spring whereby rotational motion of said knob produces variations in said regulated liquid pressure.

11. The liquid delivery system of claim 9 wherein said linearly movable means comprises a linear electric stepper motor actuator whereby electric voltage pulses extend or retract the output shaft of said actuator with said additional spring pivotably coupled to said output shaft whereby said electric voltage pulses produce variations in said regulated liquid pressure.

12. The liquid delivery system of claim 11 wherein said electric voltage pulses are produced by a control means producing a position of said output shaft predetermined by the liquid temperature at said liquid delivery system outlet.

13. The liquid delivery system of claim 12 wherein said control means comprises a memory device selected from a group consisting of look-up tables and electrically programmable memories where a predetermined number of electrical pulses are defined by said memory device with said liquid temperature as input signal.

14. The liquid delivery system of claim 3 wherein said volume sensing means comprises a device to continuously sense some portion of the displacement of said diaphragm in said pressure regulating means and produce an electrical signal substantially proportional to said displacement and thus sunstantially proportional to liquid volume change producing said diaphragm displacement.

15. The liquid delivery system of claim 14 wherein said device includes a light source means and a light sensing means with said sensor lever interposed therebetween, whereby said sensor lever, being operably connected to said diaphragm, produces changes in light received by said light sensing means proportional to displacement of said diaphragm thereby providing an input signal to said control means.

16. The liquid delivery system of claim 14 wherein said control means comprises amplifying means operably disposed to regulate the power to said pump drive means whereby discharge of said pump is regulated throughout at least 90% of each discharge cycle of said pump and whereby the liquid volume in said pressure regulating means is maintained substantially constant.