Pumps – Condition responsive control of pump drive motor – By control of electric or magnetic drive motor
Reexamination Certificate
1999-02-02
2001-05-08
Walberg, Teresa (Department: 3742)
Pumps
Condition responsive control of pump drive motor
By control of electric or magnetic drive motor
C417S036000, C417S046000, C210S634000
Reexamination Certificate
active
06227807
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a constant flow fluid pump and in particular to means and method for reduction of pressure and flow pulsations in a fluid pump by selectively controlling the rotational speed of the pump driving motor at any one of a predetermined number of discrete rotational steps around the 360° periphery of the driving motor rotation.
2. Description of the Related Art
There are many applications for analyzing blood and other fluids for which it is important to move the fluid to be examined at a uniform rate through testing/analyzing equipment, such as a flow cytometer. These fluids are usually driven by a constant pressure source. However the application of a constant pressure to a fluid may not result in a constant flow if the resistance to flow changes. For constant flow, the force pumps for driving these fluids are either of the diaphragm or reciprocating piston type of positive displacement pump that is actuated by an electric motor.
A problem with positive displacement pumps is that the rotary displacement of the electric motor must be converted to a linear displacement in order to activate the pump and thereby pump the fluid, i.e., both the diaphragm and the reciprocating piston are driven by a powered rod of some type that receives its linear motion by means of a reciprocating crankshaft. Whether it be a diaphragm pump or a reciprocating piston pump, the linear actuated rod must have its power converted from the rotary motion of the motor by means of a crankshaft/driving rod arrangement. It is well known that the output of a rotary motor driving a rod through a crankshaft arrangement, has a sinusoidal displacement output. The driving rod experiences displacement variations ranging from a minimum of zero at both top dead center and bottom dead center of its rotation through the crankshaft journal to a maximum displacement midway between top dead center and bottom dead center. It is also well understood in the Art that other parameters of the output pump also experience the same sinusoidal variation through the 360° rotation of the driving motor through the crankshaft/driving rod arrangement. For example, it is well-known that the pressure and the flow output of both a diaphragm and a reciprocating piston pump consist of a half-rectified sine wave. If the pump is driving a purely resistive load, the pressure and flow will be in phase and have their maximum value when the crank of the pump is in the middle of its upstroke, at 90° away from top dead center (TDC). After the pump passes TDC, the flow and pressure go to zero for a purely resistive load until the crank reaches bottom dead center (BDC).
Positive displacement pumps of the leadscrew drive type can provide a constant flow independent of resistance. However they must be refilled during the downstroke, during which time there is no output flow. Dual acting positive displacement pumps of the leadscrew drive type operate in tandem, so that as one pump is supplying fluid, the other pump is refilling. However these types of double acting pumps are expensive and complex.
A flow cytometer requires a pulseless flow of sheath fluid to obtain precise particle measurements. Present flow cytometers, in order to compensate for the pressure/flow variation described above, use one of two methods known in the Art to apply a pulseless flow of sheath fluid. The first is the use of a pressurized tank of sheath fluid that will even out the pulsations and the second is the use of a compliant member such as for example compressing a static volume of air through a flexible membrane. The problems with these two compensation methods is that the tank must have a very small height to prevent pressure variations from occurring as the tank empties and the tank must be sturdy enough to withstand pressure of 5-10 PSI, and that a constant pressure source doesn't provide a constant flow if the resistance to flow changes. Furthermore, the sheath fluid becomes saturated with air, which may be released as micro bubbles at the flow cell, causing the detection of false particles. The second method is equally problematic in the use of flow cytometry as well as other fluids analytical instruments in that the compliant member often is large and unwieldy and sometimes several compliant members are necessary to smooth pulsations in the flow of sheath fluid. Accordingly, it would be desirable to have a fluid pump driven by an electric motor through a crankshaft/driving rod arrangement that would have as close to a constant pressure and fluid output as possible through the 360° rotational driving range of motion of the electric motor.
SUMMARY OF THE INVENTION
Briefly, the present invention is a means and method for controlling the output flow of a fluid pump. The invention does this by controlling the radial speed of the pump motor during discreet segments of the motor's 360° angular/radial path through a revolution of the pump. The electric pump motor is controlled throughout the 360° radial path by employing a control means for controlling the speed of actuation of the radial steps of a stepper motor throughout the 360° path of rotation of the stepper motor. Control means for controlling the speed of the discreet steps of the stepper motor comprises at least a memory means, a counting means and an amplification means. The memory means may be an EPROM or other memory device for storing a series of numbers, each number representing selective speeds for which the stepper motor rotates to desired positions. The counting means which may be for example a binary counter is for retrieving the discreet numbers from the memory means for each selective position speed. The amplifying means, which may be for example a bipolar constant current driver, takes the output control signal from the counting means and amplifies it and conditions it so that it is suitable for energizing the stepper motor to rotate at the selected discreet speed necessary to achieve the selected discreet position along the 360° rotation of the stepper motor output shaft.
The motor/pump combination of the invention provides a constant or near constant flow during the upstroke of the pump. Of course, every pump outputs no flow during the downstroke time. The constant flow motor/pump of the invention compensates for this by keeping the down stoke time to {fraction (1/30)} of the upstroke time and provides a flow interruption filter to suppress this interruption of the flow during the upstroke. This flow interruption filter includes two compliant lengths of tubing separated by a resistive orifice.
REFERENCES:
patent: 3855515 (1974-12-01), Hutchins, Jr.
patent: 3985467 (1976-10-01), Lefferson
patent: 4236880 (1980-12-01), Arcibald
patent: 4242051 (1980-12-01), Mason et al.
patent: 4352636 (1982-10-01), Patterson et al.
patent: 4599046 (1986-07-01), James
patent: 4775481 (1988-10-01), Allington
patent: 4913624 (1990-04-01), Seki et al.
patent: 4990058 (1991-02-01), Eslinger
patent: 5520517 (1996-05-01), Sipin
patent: 5866004 (1999-02-01), Houck et al.
patent: 5915925 (1999-12-01), North, Jr.
Fastovsky Leonid
Walberg Teresa
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