Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B17/00—Pumps characterised by combination with, or adaptation to, specific driving engines or motors
  • F04B17/03—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors
  • F04B17/04—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors using solenoids
  • F04B17/042—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors using solenoids the solenoid motor being separated from the fluid flow
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
  • F04B49/06—Control using electricity
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B2203/00—Motor parameters
  • F04B2203/04—Motor parameters of linear electric motors
  • F04B2203/0407—Force
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B2205/00—Fluid parameters
  • F04B2205/05—Pressure after the pump outlet

Definitions

• the present invention relates, generally, to reciprocating pumps, and more particularly, relates to a magnetic direct drive reciprocating pump apparatus for liquid chromatography chemical analysis.
• At least one return spring is employed to act on the piston member in the direction opposite of the solenoid magnetic field.
• Typical of these patented solenoid- type electromagnetic pumps may be found in U.S Patent Nos. : 4,838,771; 4,352,645; 4,252,505; 4,080,552; 4,021,152; 3,804,558; 3,514,228 and 2,806,432.
• the spring augmented solenoid pumps cause several operational problems.
• the coils of the return spring may rub against a piston shaft or other exposed surfaces during operation to substantially increase friction and severely hamper operation thereof.
• the spring force acting on the piston must be overcome by the electromagnetic force driving the piston in the opposite direction during the during the push or flush stroke. This force imbalance tends to cause erratic fluid flow so that the pump flow rate is neither substantially constant nor smooth.
• the refill or pull stroke may be too fast such that an internal cushion or bumper is necessary to absorb and cushion contact as the spring fully withdraws the piston from the chamber.
• piston installation misalignment where the piston member is slightly skewed from the chamber longitudinal axis may cause the piston to rub against various components during operation.
• Such adverse contact includes rubbing against the back-up washers, as well as side loading against the solenoid and seals.
• Another object of the present invention is to provide an electromagnetic pump apparatus with reduced operating frictional forces.
• Still another object of the present invention is to provide an electromagnetic pump apparatus with increased efficiency and longer operational life.
• Yet another object of the present invention is to provide an electromagnetic pump apparatus enabling hydraulic pressure measurement thereof.
• the present invention provides a magnetic direct drive pump apparatus including a pump head defining a chamber, and an elongated guide shaft having a piston member disposed in the chamber for reciprocal movement thereof along a guide axis of the guide shaft .
• An annular magnet is included having a central opening and a central axis generally co-axial with the guide axis of the guide shaft. The annular magnet is formed to internally generate a first magnetic field which is aligned along the central axis.
• a drive magnet is coupled to the guide shaft at a position through the annular magnet central opening. Further, the drive magnet internally generates an independent drive magnetic field which is aligned to cooperate with the first magnetic field.
• At least one of the annular magnet and the drive magnet is selectively capable of reversing the polarity of the respective magnetic field to one of attract and repulse the other magnet for controlled reciprocal movement of the piston member in and out of the chamber free of additional external forces driving the piston member.
• the annular magnet is provided solenoid coil is included which generates a bi-directional electromagnetic field in response to the respective direction of current flow therethrough.
• the drive magnet is preferably provided by a permanent magnet.
• the present invention further includes a method for measuring the hydraulic pressure of a pumped fluid by measuring the force applied to the piston assembly for movement thereof in the chamber. Subsequently, depending upon the particular method, the hydraulic pressure or force is calculated by canceling either the seal stiction force between the seal and the piston assembly or the seal friction therebetween.
• the method includes the steps of A) retaining the piston assembly at a first position along the path toward and away from the chamber in the presence of a first seal stiction formed between the seal and the piston assembly. This retainment is accomplished by applying a driving force at a first level to the piston assembly in a first direction opposite the hydraulic pressure force of the pumped fluid acting thereon in an opposite second direction.
• the next step includes B) incrementally increasing or decreasing the driving force from the first level to a second level at which the piston assembly just overcomes the first seal stiction.
• the piston assembly breaks the first seal stiction, and measurably moves in either the first direction or the second direction along the path away from the first position.
• the direction of the movement depends upon the direction and magnitude of the force applied to the piston assembly, and the magnitude of the hydraulic pressure.
• the present invention further includes the steps of the C) measuring the driving force at the second level, and D) thereafter, retaining the piston assembly at a second position along the path in the presence of a second seal stiction formed between the seal and the piston assembly. This is accomplished by incrementally decreasing or increasing the driving force in the first direction or the second direction to a third level.
• the method includes the step of E) incrementally decreasing or increasing the driving force from the third level to a fourth level at which the piston assembly just overcomes the second seal stiction.
• the direction of the movement depends upon the direction and magnitude of the force applied to the piston assembly, and the magnitude of the hydraulic pressure.
• the present invention includes the step of F) measuring the driving force at the fourth level; and G) calculating the hydraulic pressure from the second level and the fourth level of driving force by canceling the opposite acting forces of the first seal stiction and the second seal stiction.
• the method includes the steps of: A) moving the piston assembly from a first position to a second position along the path in the chamber to attain a substantially constant first velocity of the piston assembly proximate the second position in the presence of a first seal friction between the seal and the piston assembly. This is accomplished by applying a continuous driving force to the piston assembly in a first direction along the path.
• the next steps includes B) measuring the driving force at a first level proximate the second position during movement of the piston assembly in step A at the substantially constant first velocity; and C) moving the piston assembly from proximate the second position to the first position along the path in the chamber to attain a substantially constant second velocity of the piston assembly proximate the first position.
• This constant second velocity occurs in the presence of a second seal friction between the seal and the piston assembly and is accomplished by applying the continuous driving force to the piston assembly in a second direction along the path opposite the first direction.
• the present invention further includes the step of D) measuring the driving force at a second level proximate the first position during movement of the piston assembly in step C at the substantially constant second velocity; and finally E) calculating the hydraulic pressure from the first level and the second level of driving force by canceling the opposite acting forces of the first seal friction and the second seal friction.
• each the seal stiction cancellation method and the seal friction cancellation method are performed on electromagnetically driven pump devices having solenoid coils magnetically driving the reciprocating piston assembly.
• each pump device includes an independent drive magnet coupled to the piston assembly and having an independent, internally generated drive magnetic field aligned to cooperate with a bi ⁇ directional magnetic field of the solenoid coil.
• a drive current is applied to the solenoid coil in one direction to drive the piston assembly along the path in the first direction, and in a reverse direction to drive the piston assembly along the path in the opposite second direction.
• the generated drive force applied to the piston assembly is proportionate to the drive current applied to the coil.
• FIGURES 1 and 2 are a schematic sequence of an electromagnetic direct drive pump apparatus constructed in accordance with the present invention, and illustrating the movement of the piston assembly and the corresponding polarities of the magnets.
• FIGURE 3 is a schematic of an alternative embodiment of the electromagnetic direct drive pump apparatus of FIGURE 1 having a dual piston configuration.
• FIGURE 1 where a magnetic direct drive pump apparatus, generally designated 10, is illustrated including a pump head 11 defining a chamber 13.
• the pump apparatus includes a piston assembly 15 having an elongated guide shaft 16 and a plunger or piston member 17 disposed in chamber 13 for reciprocal movement therein in the direction of a guide axis 18 of guide shaft 16.
• An annular magnet, generally designated 20, is included having a central opening 21 and a central axis 22 generally co-axial with the guide axis 18 of guide shaft 16.
• Annular magnet 20 is formed to internally generate a first magnetic field which is aligned along central axis 22.
• a drive magnet, generally designated 23, is coupled to guide shaft 16 at a position through annular magnet central opening 21.
• drive magnet 23 internally generates an independent drive magnetic field which is aligned to cooperate with the first magnetic field. At least one of the annular magnet 20 and the drive magnet 23 is selectively capable of reversing the polarity of the respective magnetic field to one of attract and repulse the other magnet for controlled reciprocal movement of piston member 17 in and out of the chamber 13 free of additional external forces driving piston member 17.
• a direct drive pump apparatus 10 having a drive magnet capable of generating its own magnetic field, as opposed to the mere magnetized permeable slug member of the prior art, several operational advantages are attainable.
• movement of the piston member in both directions along the central axis can be effected by magnetic cooperation between the drive magnet and the annular magnet.
• the solenoids of conventional solenoid pumps in contrast, are generally only capable of driving the pistons in a single direction (i.e., toward the central equilibrium position between the solenoid) , and require additional spring members to urge the pistons in the opposite direction (i.e., away from the center of the solenoid) .
• annular magnet 20 is provided by a solenoid coil which generates a bi-directional electromagnetic field in response to the respective direction of current flow therethrough (i.e., to reverse the polarity) .
• drive magnet 23 is preferably provided by a permanent magnet member generating its own magnetic field, such as a neodymium iron boron magnet.
• annular magnet could be a permanent magnet while the drive magnet may be provided an electromagnet.
• both magnets could be provided by electromagnets, having cooperating polarities, without departing from the true spirit an nature of the present invention.
• piston assembly 15 is formed to reciprocate along the guide shaft axis 18 which is substantially co-axial with the central axis 22 of the annular coil 20.
• drive magnet 23 is also preferably positioned for reciprocating movement along the central axis 22 at an orientation generally positioned substantially central to the solenoid annulus. This positions the drive magnet well within the electromagnetic field of the solenoid coil to enable continuous interaction between the two magnetic fields ⁇ i.e., the electromagnetic field of the solenoid coil and that of the drive magnet) .
• drive magnet 23 is positioned between two opposing spider members 25, 25' which mount the drive magnet to the ends of guide shaft 16 and piston member 17, respectively.
• a lower distal end of piston member 17 is reciprocally positioned in the elongated chamber 13 of pump head 11.
• sample fluid can be pumped from a first passage 26 in pump head 11 through chamber 13 and to second passage 27.
• Check valves 28, 28' i.e., intake valve 28 and exhaust valve 28'
• These valves may be provided by mechanical or electro ⁇ mechanical valves commonly employed in the field. In the preferred embodiment, however, valves 28, 28' are gravity operated valves.
• annular seal 30 is provided mounted to pump head 11 which slidably supports piston member 17 to deter contact with the chamber walls during reciprocating motion thereof.
• Annular seal 30 is preferably provided by TEFLON * for reduced friction, and further is formed to seal chamber 13 from the environment, while further preventing fluid flow therefrom. It will be appreciated that seal 30 could be fixedly mounted to piston member 17 such that the seal is in sliding contact with the inner walls forming pump chamber 13.
• FIGURE 1 illustrates that the permanent drive magnet is oriented to position its Positive pole (PJ and Negative pole (N p ) co-axially along central axis 22. While FIGURE 1 illustrates the drive magnet Positive pole (P p ) at the bottom of the drive magnet, while the Negative pole (N p ) is positioned at an upper end thereof, it will be appreciated that the polarities may be switched without departing from the true spirit and nature of the present invention.
• Solenoid coil 20 collectively generates a bi ⁇ directional electromagnetic field depending upon the -In ⁇ direction of current flow therethrough.
• the current To drive piston assembly 15 in the direction of arrow 31 in FIGURE 1 (during the push or flush stroke) , the current must flow through coil in the proper direction to generate a Positive pole (P c ) at a bottom portion of solenoid coil 20, while the Negative pole (N c ) is positioned at a top portion of the coil. Accordingly, the Positive pole (P P ) of drive magnet 23 is repelled by the lower Positive pole (P c ) of solenoid coil 20.
• the dual magnet approach of the present invention enables a more controlled movement of the piston assembly in either direction along the central axis 22.
• the magnetic force induced on the piston assembly is generally constant through a substantial portion of the interaction between the magnets along the central axis.
• the magnetic force induced on the piston assembly is generally constant during reciprocal displacement of the piston member along the central axis. This substantially simplifies controlled movement of the piston assembly.
• the electromagnetic force induced on the permeable slug is proportional to the square of the current flow through the coil.
• the magnetic force acting on the slug substantially increases as the slug moves toward the stationary magnetic structure of the solenoid, and substantially decreases as the slug moves away from the stationary magnetic structure of the coil.
• a guide member 33 is included as a second guide bearing support (FIGURES 1 and 2) for piston assembly 15.
• Guide member 33 is provided by a slip- sleeve member defining a bore 35 formed and dimensioned for sliding receipt of the guide shaft 16 therethrough. This provides sliding support and alignment of the guide shaft, and hence piston member 17, during reciprocal movement thereof.
• the piston assembly is vertically oriented to reciprocate along a substantially vertical guide axis 18. This orientation reduces friction, or more importantly, variations in friction to enhance smoother reciprocating operation, and hence, fluid flow.
• a displacement sensor 36 is included cooperating with and responsive to reciprocating movement of guide shaft 16.
• One such sensor is a variable cylindrical capacitor positioned just past the guide shaft distal end, as shown in FIGURES 1 and 2, which is formed and dimensioned for sliding receipt of guide shaft 16 therein.
• the capacitance between the shaft and the sleeve vary linearly with respect to the depth of insertion.
• a simple circuit is employed to translate capacitance to voltage upon which the real displacement can be calculated. It will be understood that other displacement sensors may be employed as well such as linear potentiometers and photo detectors.
• Coupled between the displacement sensor and the solenoid coil is a real-time servo control loop or mechanism (not shown) .
• This mechanism is employed to sense the displacement and position of piston assembly 15 and, thus, adjust the current applied to the solenoid coil.
• the solenoid coil is thus controlled during each stroke such that the piston assembly displacement vs. time curve matches the desired profile.
• the direct drive pump apparatus 10 of the present invention enables measurement of the starting and ending position of each stroke with substantial repeatability.
• This arrangement furthermore, is capable of automatically overriding changes or variations in friction and pressure in the system.
• the servo control mechanism can adjust the coil current so that the next stroke is increased by an amount compensating for the deficit. Accordingly, long term variations can be effectively compensated so that the pump apparatus 10 operates at substantially constant flow rates as great a 10 ml/min, with higher efficiency.
• a dual piston configuration may be included which is particularly suitable for use as a dual analytical pump apparatus.
• guide shaft 16 includes a second opposite piston member 17' positioned on and opposite side of solenoid coil 20.
• Piston member 17' reciprocates in chamber 13' of a second pump head 11' .
• the second opposite piston member simultaneously pulls the pumped fluid into the corresponding chamber.
• a displacement sensor is not illustrated in FIGURE 3, one may be provided - 16 - between either piston member and the solenoid. Further, a guide member may be provided as well.
• dual, single piston pump apparatus may be employed which would eliminate many of the constraints inherent in the current rotary single cam motors. For instance, since the proper stroke overlap is dependent upon hydraulic pressure, a dual, single piston pump apparatus of the present invention can accurately control the overlap to eliminate the pressure pulses at the crossover. Further, during the refill stroke, the piston speed can be varied to facilitate proportioning accuracy. This is especially true since the pressure feedback of the servo control mechanism of the present invention is more efficient than for a rotary-motor pump since gear lash hysteresis is eliminated. Further, the movement and acceleration of the drive magnet is very high resulting in near instantaneous response.
• a method for measuring the hydraulic pressure of the pumped fluid through the piston assembly is provided without the application of pressure transducers.
• By measuring the drive force applied to the pump assembly during selected segments of the piston stroke either the seal stiction forces or the seal friction forces can be effectively canceled in an empirical equation. This equation enables calculation of the hydraulic force, and hence pressure, acting on the piston.
• a method for calculating the hydraulic pressure of the pumped fluid in the pump assembly by measuring the drive force applied to the piston assembly to initiate movement thereof in the chamber. By measuring the respective drive force to initiate movement of the piston assembly in both directions along the chamber, the hydraulic force is calculated by subsequently canceling out the seal stiction forces (which will be in opposite directions) between the seal and the piston assembly, and further by subtracting the weight of the piston assembly therefrom.
• the method includes the steps of A) retaining piston assembly 15 at a first position along the path toward and away from the chamber in the presence of a first seal stiction formed between seal 30 and piston assembly 15. This retainment is accomplished by applying a driving force at a first level to the piston assembly in a first direction (arrow 31 in FIGURE 1) opposite the hydraulic pressure force of the pumped fluid acting thereon in an opposite second direction (arrow 32 in FIGURE 2) .
• the next step includes B) incrementally increasing or decreasing the driving force from the first level to a second level at which piston assembly 15 just overcomes the first seal stiction.
• the piston assembly breaks the first seal stiction formed between seal 30 and piston assembly 15, and measurably moves in either the first direction or the second direction along the path away from the first position.
• the direction of the movement depends upon the direction and magnitude of the force applied to the piston assembly, and the magnitude of the hydraulic pressure.
• the present invention further includes the steps of the
• the method includes the step of E) incrementally decreasing or increasing the driving force from the third level to a fourth level at which the piston assembly just overcomes the second seal stiction.
• the direction of the movement depends upon the direction and magnitude of the force applied to the piston assembly, and the magnitude of the hydraulic pressure.
• the direction of measurable movement will be in the second direction or the first direction, opposite the direction of travel in step B, along the path away from the second position.
• the present invention includes the step of F) measuring the driving force at the fourth level; and G) calculating the hydraulic pressure from the second level and the fourth level of driving force by canceling the opposite acting forces of the first seal stiction and the second seal stiction.
• the forces acting on the piston assembly to initiate movement thereof in the chamber from a fixed position are the hydraulic forces (H) , the drive force (D) , the gravitational force (i.e., the weight (W) ) and the seal stiction forces (S s ) .
• the hydraulic force is essentially equal to the sum of the weight of the piston assembly, the drive force necessary to break free of the first seal stiction (in the "seal stiction" method) and the seal stiction force itself.
• the seal stiction cancellation method is performed on an electromagnetically driven pump device such as the apparatus above-described. Accordingly, the driving force applied to the piston assembly is generated by the drive current flowing through the solenoid coil in one direction to drive the piston assembly along the path in the first direction, and in a reverse direction to drive the piston assembly along the path in the opposite second direction. It will be understood that the generated drive force applied to the piston assembly is proportionate to the drive current flowing through the coil. Hence, incrementally increasing or decreasing the drive current incrementally increases or decreases the drive force applied to the piston assembly proportionately.
• the "seal stiction" cancellation method of the present invention may be commenced by initiating movement of piston assembly 15 from the fixed first position in either the first direction (arrow 31 in FIGURE 1) or the second direction (arrow 32 in FIGURE 2) .
• the driving force initially urges piston member 17 into chamber 13 in the first direction
• step D the driving force will cause piston member 17 to reverse direction and back out of chamber 13.
• the driving force initially urges piston member 17 out of chamber 13 in the second direction 32 along axis 18.
• the driving force will cause piston member 17 to reverse direction and move back into chamber 13.
• the seal stiction forces will be substantially equal and opposite in direction which enables cancellation thereof.
• the effective magnitude and direction of the driving force causing movement or retainment of piston assembly 15 relative chamber 13 is a function of the magnitude of the hydraulic pressure relative the gravitational forces and the seal stiction forces.
• the hydraulic pressure is relatively small, the gravitational forces and the seal stiction forces urged upon the piston assembly will have greater impact on the direction and magnitude of the driving force required to move the piston assembly along the path than the hydraulic force. Accordingly, to move the piston assembly into the chamber in the first direction
• the drive force generally must be directed in the second direction combining the drive force with the hydraulic force to oppose the weight of the piston assembly.
• the drive force may only need to be reduced, still directed in the second direction, from the drive force level required to retain the piston assembly relative chamber 13.
• the drive force may have to be reversed in direction (i.e., in the first direction) .
• the direction of drive forces urged upon the piston assembly to effect similar movements thereof may need to be reversed.
• the drive force generally must be directed in the first direction, combining the drive force with the weight of the piston assembly to oppose the greater hydraulic force urging the piston member out of the chamber.
• the drive force may only need to be reduced, still directed in the first direction, from the drive force level required to retain the piston assembly relative chamber 13.
• the drive force may have to be reversed in direction (i.e., in the second direction) .
• the present invention can be employed to cancel the seal stiction forces in an effort to determine the sum of the hydraulic forces measured during movement in the first direction and the second direction.
• the intake valve 28 will be closed while the exhaust valve 28' will be opened for the duration thereof.
• the hydraulic pressure may vary during substantial movement of the piston assembly along the path of chamber 13, the pressure variation resulting from the relatively short displacement of the piston assembly during the seal stiction measurement technique is insignificant.
• the calculating step further includes the step of multiplying the sum of the second current and the first current by the empirical constant (C) to convert the current summation into the hydraulic pressure.
• Another step includes subtracting the weight of the piston assembly from the hydraulic force value .
• the method may further include the step of extending the piston member of the piston assembly beyond the typical stopping point of a normal stroke in an effort to clear debris built up on the seal. This tends to slough off the debris from the spot where the initial backward stiction measurement was made to prevent the debris from interfering with one of the strokes.
• this method includes the step of A) moving the piston assembly 15 from a first position to a second position along the path in chamber 13 to attain a substantially constant first velocity of piston assembly 15 proximate the second position in the presence of a first seal friction between seal 30 and the piston assembly 15. This is accomplished by applying a continuous driving force to the piston assembly in a first direction along the path.
• the next steps includes B) measuring the driving force at a first level proximate the second position during movement of piston assembly 15 in step A at the substantially constant first velocity; and C) moving the piston assembly from proximate the second position to the first position along the path in chamber 13.
• the velocity of the piston assembly should be a substantially constant second velocity.
• This constant second velocity occurs in the presence of a second seal friction between seal 30 and piston assembly 15 and is accomplished by applying the continuous driving force to piston assembly 15 in a second direction along the path opposite the first direction.
• the present invention further includes the step of D) measuring the driving force at a second level proximate the first position during movement of piston assembly 15 in step C at the substantially constant second velocity.
• the method includes the step of E) calculating the hydraulic pressure from the first level and the second level of driving force by canceling the opposite acting friction forces of the first seal friction and the second seal friction.
• the direction and magnitude of the force applied to piston assembly 15 for movement thereof along chamber 13 is a function of the magnitude of the hydraulic pressure relative the gravitational forces and the seal friction forces.
• the forces acting on the piston assembly during reciprocating movement thereof in the chamber at a substantially constant velocity are the hydraulic forces (H) , the drive force (D) , the gravitational force (i.e., the weight (W) ) and the seal friction forces (S F ) .
• the hydraulic force is essentially equal to the sum of the weight of the piston assembly, the drive force necessary to move the piston assembly at a substantially constant velocity along the path, and the seal friction force itself.
• the seal friction cancellation method is performed on an electromagnetically driven pump device such as the apparatus above-described. Accordingly, the driving force applied to the piston assembly is generated by the drive current flowing through the solenoid coil in one direction to drive the piston assembly along the path in the first direction, and in a reverse direction to drive the piston assembly along the path in the opposite second direction. It will be understood that the generated drive force applied to the piston assembly is proportionate to the drive current flowing through the coil. Hence, incrementally increasing or decreasing the drive current incrementally increases or decreases the drive force applied to the piston assembly proportionately.
• the "seal friction" cancellation method of the present invention may be initially performed by movement of piston assembly 15 at a substantially constant velocity from either the first position to the second position in the chamber, or from the second position to the first position. In either instance, however, the seal friction forces will be substantially equal and opposite in direction which enables cancellation thereof.
• the intake valve 28 will be closed while the exhaust valve 28' will be opened for the duration thereof.
• the hydraulic pressure may vary during substantial movement of the piston assembly along the path of chamber 13, the pressure variation resulting from the relatively short displacement (about .01 inch) of the piston assembly during the seal stiction measurement technique is insignificant.
• the calculating step further includes the step of multiplying the sum of the second current and the first current by the empirical constant (C) to convert the current summation into the hydraulic pressure.
• Another step includes subtracting the weight of the piston assembly from the hydraulic force value.
• Step A is accomplished by applying the drive current at a substantially constant first quantity which corresponds to generating a driving force at the first level.
• this embodiment of the present invention includes the step of : after step B and before step C, retaining piston assembly 15 in chamber 13 proximate the second position to enable the a direction change of the piston assembly either from the first direction of movement to the second direction, or from the second direction of movement to the first direction.
• the retaining step is accomplished by incrementally decreasing or increasing the driving force in the first direction or the second direction from the first level to a third level. This is caused by incrementally increasing or decreasing the drive current from the first quantity to a third quantity.
• the third quantity of the current through the solenoid coil corresponds to the generation of the third level of the driving force.
• Step C is accomplished by incrementally increasing or decreasing the driving force in the second direction or the first direction from the third level to the second level, which of course is accomplished by incrementally increasing or decreasing the drive current from the third quantity to a second quantity.
• step E is accomplished by calculating the hydraulic force acting on the piston assembly from the first quantity of drive current and the second quantity of drive current.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Electromagnetic Pumps, Or The Like (AREA)
• Measuring Fluid Pressure (AREA)
• Compressors, Vaccum Pumps And Other Relevant Systems (AREA)

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• 1997
  • 1997-01-28 EP EP97904001A patent/EP0880649A4/en not_active Withdrawn
  • 1997-01-28 JP JP52935097A patent/JP3248728B2/ja not_active Expired - Fee Related
  • 1997-01-28 WO PCT/US1997/001286 patent/WO1997030288A2/en active Search and Examination
  • 1997-01-28 AU AU18421/97A patent/AU697945B2/en not_active Expired
  • 1997-01-28 CA CA002245889A patent/CA2245889C/en not_active Expired - Lifetime

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