Valveless metering pump

Abstract: In a valveless positive displacement pump a piston 40 is rotated by a motor 12 and shaft 104 within a cylindrical housing 22 having a closed end. A cam arrangement 16 introduces reciprocating motion into shaft 104 as it rotates, with a dwell period between compression and suction strokes. The piston surface includes a fluid passage which extends to the end of the piston and which includes two intersecting helical slots. As the piston reciprocates (suction/compression) and rotates, the fluid passage is maintained in fluid coupling with an inlet/outlet port by a respective said helical slot, and during the subsequent dwell period the fluid coupling is transferred between the two ports via an intermediate state where both ports are sealed by the piston surface.

Description: The present invention relates generally to positive displacement pumps, particularly, to metering pumps for dispensing relatively precise volumes of fluid from a source to a receiver at accurately controlled rates and volume through the use of a valveless positive displacement piston pump coupled to a precision rotary/linear motion actuator mechanism. Valveless, positive displacement metering pumps have been successfully employed in many applications where safe and accurate handling of fluids is required. Several such pumps are discussed in U.S. Patent No. 5,020,980 to Pinkerton. As noted by Pinkerton, the valveless pumping function is accomplished by the synchronous rotation and reciprocation of a piston in a precisely mated cylinder bore. One pressure and one suction stroke are completed per cycle. A slot on the piston connects a pair of cylinder ports alternately with the pumping chamber. One port is in fluid communication with the pumping chamber on the pressure stroke and the other port is in fluid communication with the pumping chamber on the suction stroke. The piston and cylinder form a valveless positive displacement pump. These types of pumps have been found to perform accurate transfers of both gaseous and liquid fluids. In numerous types of fluid systems, the intermixing of fluids must be controlled to a high degree of accuracy. In one such system, a pump head module containing the piston and cylinder is mounted in a manner that permits it to be swiveled angularity with respect to the rotating drive member. The degree of angle controls the stroke length and in turn flow rate. The direction of the angle controls flow direction. The manner in which the pump head module is swiveled with respect to the drive member varies among the different available metering pumps. In one commercially available pump, the pump head module is secured to a plate which is, in turn, mounted to the base of the pump. The plate is pivotal about one of two pivot axis depending upon the angular orientation of the module. The base may be provided with graduations to indicate the percentage of the maximum flow rate achieved at the particular angle at which the module is directed. Maximum flow rate is achieved when the module is at its maximum angle with respect to the axis of the rotating drive member. In such a metering pump, the piston rotates and reciprocates. The piston is provided with a flat or slot which extends to the end of the priston. As the piston is pulled back and rotated, the piston slot opens to the inlet port, thereby creating suction which fills the pump chamber with fluid. As the piston reaches the highest point in the reciprocation cycle, the pump chamber is at its maximum volume capacity. Continuing the piston rotation seals the inlet port. As the inlet port is sealed and the pump chamber is full to its maximum volume capacity, the outlet port opens up. Continuing the rotation and reciprocation, the piston is forced down and the piston slot opens to the outlet port. Discharge is created and fluid is pumped out of the pump chamber. The piston bottoms at the end of the pressure stroke for maximum fluid and bubble clearing. Continuation of piston rotation seals the outlet port. As the outlet port is sealed and the pump chamber is empty, the inlet port opens to start another suction stroke. While positive displacement pumps have the capability of providing precise delivery of fluids, numerous potential problems may be encountered. For example, available positive displacement pumps may leak, may not self-align, may jam due to the build up of solids and may be inaccurate due to air bubble build up in the piston slot. In addition, pressure build up in the pump chamber at the end of each piston pressure stroke due to axial travel of the piston at the transition point between the inlet and outlet ports may induce leakage about the piston and provide a fluid communication flow path between the inlet and outlet ports. The present invention provides a metering pump comprising a cylindrical pump housing having a closed end; piston means located in the housing and defining therewith a pumping chamber, the piston surface including shaping which with the side of the housing defines fluid passage means extending to the pumping chamber; inlet port means and outlet port means in the housing which open adjacent the said piston surface; and drive means arranged to impart a reciprocal motion to the piston to provide alternate suction and compression strokes spaced by dwell periods, and to impart a rotary motion to the piston so as to bring said fluid passage means adjacent said inlet port means during at least part of a suction stroke and to bring said fluid passage means adjacent said outlet port during at least part of said compression stroke, characterised in that said fluid passage means comprises intersecting inlet and outlet slot portions, the inlet slot portion being generally helical to maintain fluid coupling to said inlet port means during said part of said suction stroke and the outlet slot portion being generally helical to maintain fluid coupling to said outlet port means during said part of said compression stroke. The invention further provides a method of pumping a metered volume of fluid, said method comprising providing a cylindrical housing with a sealed end in which housing a piston is mounted to define a pumping chamber, said housing including an inlet port and an outlet port opening onto the cylindrical surface of the piston, said surface being shaped to define with the housing a fluid passage extending to the pumping chamber, said fluid passage means comprising intersecting inlet and outlet slot portions, the inlet slot portion being generally helical to maintain fluid coupling to said inlet port means during said part of a suction stroke and the outlet slot portion being generally helical to maintain fluid coupling to said outlet port means during said part of a compression stroke, said method further the cyclically sequential steps of (a) retracting the piston to perform a said suction stroke while said inlet port means and said fluid passage are fluidly coupled; (b) rotating said piston through a position in which neither of the port means are fluidly coupled to the fluid passage until the outlet port means is brought into fluid coupling with the fluid passage; (c) moving said piston towards said housing to perform a said compression stroke while said outlet port means and said fluid passage are fluidly coupled; and (d) rotating said piston through a position in which neither of the port means are fluidly coupled to the fluid passage until the inlet port means is brought into fluid coupling with the fluid passage. The invention enables the provision of a rotary reciprocating pump which utilises a rotary reciprocating piston as an integral valving mechanism in which the axial stroke length of the rotary piston may be precisely controlled by a cam drive mechanism. In embodiments of the invention, axial piston movement is interrupted during piston rotation, for example during at least 10° of piston rotation, or sufficient to permit transfer of fluid coupling with the piston slot between the inlet and outlet ports, so that only one fluid port is open at any given time, whereby the pressure and suction ports are never interconnected. The invention also enables the provision of a rotary reciprocating pump which may be flushed by a single rotation of the piston. US Patent Serial No. 3,230,892 (Burns) describes a rotary reciprocating pump comprising helical grooves on the surface of a reciprocating and rotating piston. However in this pump the grooves do not intersect. Further features and advantages of the invention will become apparent upon a perusal of the appended claims, to which the reader is referred, and on a reading of the following more detailed description of an exemplary embodiment of the invention, in which: Figure 1 is a longitudinal sectional view of an embodiment of metering pump according to the invention; Figure 2 is a partial sectional top plan view of the metering pump of Figure 1 showing the valve at the beginning of the intake (suction) stroke; Figure 3 is a similar enlarged partial sectional view of the metering pump of Figure 1 showing the valve at the end of the intake (suction) stroke; Figure 4 similar enlarged partial sectional view of the metering pump of Figure 1 showing the valve at the crossover point beginning the discharge (compression) stroke; Fig. 5 is a similar partial enlarged schematic view of the apparatus of the invention showing the valve at the end of the discharge stroke; and Fig. 6 is a similar partial enlarged schematic view of the apparatus of the invention showing the valve at the beginning of the intake stroke upon completion of a single rotation of the piston. Referring first to Fig. 1, the metering pump apparatus of the invention, generally identified by the reference numeral 10, is shown. One metering pump apparatus 10 is depicted in Fig. 1. It is understood, however, that one or more pump apparatus 10 may be arranged to deliver fluid from a source. For example, two pump apparatus 10 may be arranged 180° out of phase to deliver constant fluid flow from a fluid source to a receiver. The apparatus 10, as shown in Fig. 1, is driven by a motor 12 operatively connected to the pump apparatus 10. The pump apparatus 10 functions to transfer fluid from a source to a receiver at accurately controlled rates and volumes and is capable of dispensing fluid volumes in the nanoliter range. Referring still to Fig. 1, the apparatus 10 comprises a valveless positive displacement metering pump 14, a rotary/linear motion actuator 16 and a motor 12 mounted in an open framework defined by endplates 18 and 20. The pump 14 comprises a pump housing 22 which is mounted to the endplate 18 by a plurality of screws 24 which extend through the pump housing 22 and are threadably received within holes 26 formed in the endplate 18. The cylindrical pump housing 22 includes an axial bore 28 and a counter bore 30. A cylindrical pump housing liner 32 is received within the counter bore 30. The one end of the cylindrical liner 32 abuts against a shoulder 34 forming the inner end of the counter bore 30. The opposite end of the liner 32 projects slightly out of the counter bore 30 and is closed by an endcap 36 which is secured against the end face of the liner 32 and mounted to the cylindrical housing 22 by threaded screws 24. Appropriate o-ring seals or the like (not shown in the drawings) are incorporated at the contact of the endcap 36 with the end face of the liner 32 for forming a fluid tight seal therewith. The liner 32 is provided with an axial passage 38 for slidably and rotatably receiving a piston 40 therein. The cylindrical housing 22 is provided with diametrically opposite, internally threaded fluid ports 42 and 44. The ports 42 and 44 taper inwardly terminating in radial passages 46 and 48. The radial passages 46 and 48 have smaller diameters than the ports 42 and 44 and extend through the cylindrical housing 22 to the counter bore 30. The radial passages 46 and 48 are in alignment with radial passages 50 and 52 formed within and extending through the cylindrical liner 32. The diameters of the passages 50 and 52 are equal to the diameters of the radial passages 46 and 48 and are sized for mating alignment with crossover slots 54 and 55 formed on the piston 40 to be described in greater detail later herein. As noted above, the pump apparatus 10 of the invention comprises three primary components: the positive displacement pump 14, the cam actuator 16, and the motor 12. These three components are supported in axial alignment by end plates 18 and 20. The support framework further includes flange members 60 and 62 which are coupled to the end plates 18 and 20 by mounting bolts 64 and 66, which collectively form the open framework structure of the pump apparatus 10. The spacing between the end plates 18 and 20 is maintained by cylindrical spacers 68 journaled about the mounting bolts 64 and 66 as shown in Fig. 1. The motor 12 is mounted to the end plate 20 by mounting screws 70 which extend through a circumferencial mounting flange 13 of the motor 12 and are threadably received within threaded holes formed in the endplate 20. A rotor shaft 72 projects from the motor 12 through an opening 74 in the end plate 20. A cylindrical drive shaft coupling 76 is mounted about the rotor shaft 72 and is coupled thereto by a set screw 78 which extends through the coupling 76 and engages a flat face 80 formed on the rotor shaft 72. Projecting from the flat planar surface 82 of the coupling 76 are a pair of drive coupling pins 84 (best shown in Fig. 1A). Referring now to the cam actuator 16 supported axially between the motor 12 and the pump 14, the cam actuator 16 comprises flanged cylindrical end numbers 90 and 92 threadably mounted to support frame members 60 and 62, respectively, by mounting screws 94. The flanged end members 90 and 92 are mounted on opposite ends of a cylinder 96, which when assembled with the end members 90 and 92 define a cam chamber 98. The end members 90 and 92 are provided with cylindrical extensions 100 and 102 projecting toward each other and forming a cam passageway or track 103 therebetween. A cam drive shaft 104 extends through the cam chamber 98 and through axial bores formed in the end members 90 and 92 and the support frame members 60 and 62. Bushings 106 extending through the axial bores of the end members 90 and 92 and the support frame members 60 and 62 are journaled about the cam shaft 104. The internal diameters of the bushings 106 are slightly larger than the diameter of the cam shaft 104 thereby permitting the cam shaft 104 to rotate and reciprocate freely in the bushings 106. The cam shaft 104 includes an enlarged portion 108 formed at about the midpoint of the cam shaft 104. The enlarged portion 108 is provided with an axial opening extending perpendicular to the rotational axis of the cam shaft 104 for receiving a connector pin 110 therethrough. A spacer 112 mounted about the connector pin 110 provides a support shoulder for a ball bearing retainer ring 114. An internal, flanged retainer ring 116 cooperates with the ring 114 for forming a raceway for ball bearings 118 received between the rings 114 and 116. The flanged retainer ring 116 is internally threaded for coupling with the connector pin 110. The retainer ring 114 is sized to travel in the cam track 103 defined between the cylindrical extensions 100 and 102 of the cam actuator end members 90 and 92. The cam shaft 104 projects outward from each end of the cam actuator chamber 98. A motor coupling 120 is secured to one end of the drive shaft 104 by set screw 122. The coupling 120 is provided with slots 124 extending therethrough. Bushings 126 are received within the slots 124 for receiving the pins 84 projecting from the motor drive coupling 76. The bushings 126 slide freely on the pins 84, thereby permitting the pins 84 to move longitudinally during reciprocal movement of the cam shaft 104 and simultaneously imparting rotational movement to the cam shaft 104 through the motor coupling 120. At the opposite end of the cam shaft 104, a piston coupling 130 is secured to the end of the cam shaft 104 by set screws 132. The coupling 130 includes an axial bore 134 and an axial counter bore 136. The end of the cam shaft 104 abutts against a circumferential shoulder 138 of the counter bore 136. The distal end of the piston 40 is received in the axial bore 134 and abutts against the end of the cam shaft 104. The end of the coupling 130 is partially slotted at 140 so that the coupling 130 may be clamped about the end of the piston 40 by tightening up the clamp screw 142 for mechanically connecting the piston 40 to the cam shaft 104. Upon assembly of the components of the apparatus 10 shown in Fig. 1, the proximal end of the piston 40 projects through the bore 28 of the pump housing 22 and into the liner 32. Sealing about the piston 40 is accomplished by use of an O-ring 144 received in a circumferential recess formed in the axial bore 28 of the pump housing 22. Referring again to Fig. 1, it will be observed that the piston 40 of the invention is provided with helical slots 54 and 55 which crisscross each other. The helical slots 54 and 55 are etched into a portion of the surface of the piston 40 which may be formed of ceramic material or any other suitable materials. The helical slot 54 includes an angularly extending slot portion 57 which extends to the end face of the piston 40 as best shown in Fig. 2. As a result of the geometric form of the slots 54 and 55, fluid pumping is accomplished in accordance with the sequence shown in Figs. 2-6. For purposes of illustration, passage 50 extending through the liner 32 is in fluid communication with inlet port 42 formed in the pump housing 22. Liner passage 52 is in fluid communication with the discharge port 44. The inlet port 42 and discharge port 44 are directly opposite each other, 180° apart, on the cylindrical pump housing 22. The piston 40 and the cylindrical liner 32 are machined to provide a liquid tight seal therebetween. Upon actuation of the motor 12, the piston 40 rotates in the clockwise direction relative to the orientation of the pump 10 as shown in Fig. 1. Upon rotation, the piston 40 is simultaneously retracted by the cam shaft 104 which is pulled backward as the cam ring 114 moves along the cam passageway 103. In the position shown in Fig. 2, the inlet passage 50 is open to the helical slot 55. As the piston 40 is rotated, fluid enters the slots 54 and 55 in the direction of the arrows shown in Fig. 2 and fills the piston chamber 150. The simultaneous rotation and retraction of the piston 40 maintains the fluid passage 50 in alignment with the helical slot 55 so that fluid flows into the piston chamber 150. Retraction of the piston 40 for maintaining the rotational alignment of the helical slot 55 with the fluid passage 50 is accomplished by the travel of the cam shaft cam ring 114 in the cam track 103 in the direction of the arrow shown in Fig. 3. As the cam ring 114 travels along the cam track 103, the cam shaft 104 retracts toward the motor 12 thereby retracting the piston 40 within the cylindrical liner 32. Referring now to Fig. 3, it will be observed that upon rotation of the cam shaft 104 through 150°, the piston 40 has reached its maximum retracted position and the inlet passage 50 is aligned with the end of the slot 55. Rotation of the cam shaft 104 another 30°, from 150° to 180°, positions the outlet passage 52 in alignment with the slot 54 as shown in Fig. 4. The piston 40 however does not move axially during this 30° rotation because the cam track 103 includes a segment 105, through 30° of rotation, which is perpendicular to the rotational axis of the cam shaft 104 thereby enabling the piston 40 to he rotated for alignment with the outlet passage 52 but remaining axially stationary. Further rotation of the cam shaft 104 from 180° to 330° changes the direction of axial travel of the cam shaft 104 toward the pump 14, which simultaneously advances the piston 40 into the piston chamber 150 and forces the fluid in the piston chamber 150 to be discharged through the discharge passage 52 as shown in Figs. 4 and 5. During rotation of the piston 40 from 180° through 330°, the discharge passage 52 is in rotational alignment with the helical slot 54 providing a fluid passage for discharging fluid to a receiver. At the end of the discharge stroke, the inlet passage 50 is offset by 30° from the helical slot 55 as shown in Fig. 5. Rotation of the piston 40 through 360° aligns the inlet passage 50 with the helical slot 55 as shown in Fig. 6 and the suction/discharge cycle is repeated. Again, the piston 40 does not move axially during the 30° rotation of the piston 40 between 330° and 360° because the cam track 103 includes a second segment 107, through 30° of rotation, which is perpendicular to the rotational axis of the cam shaft 104 thereby enabling the piston 40 to be rotated for alignment with the inlet passage 50 but remaining axially stationary. Thus, no pressure build up occurs in the piston chamber 150 when both the inlet passage 50 and the outlet passage 52 are closed by the piston 40 as it is rotated to complete the suction/discharge cycle. While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims which follow.

Claims: A metering pump (14) comprising a cylindrical pump housing (22) having a closed end; piston means (40) located in the housing and defining therewith a pumping chamber (38), the piston surface including shaping which with the side of the housing defines fluid passage means extending to the pumping chamber; inlet port means (42, 46) and outlet port (44, 48) means in the housing which open adjacent the said piston surface; and drive means (12, 16) arranged to impart a reciprocal motion to the piston to provide alternate suction and compression strokes spaced by dwell periods, and to impart a rotary motion to the piston so as to bring said fluid passage means adjacent said inlet port means during at least part of a suction stroke and to bring said fluid passage means adjacent said outlet port during at least part of said compression stroke, characterised in that said fluid passage means comprises intersecting inlet and outlet slot portions (55, 54), the inlet slot portion (55) being generally helical to maintain fluid coupling to said inlet port means during said part of said suction stroke and the outlet slot portion (54) being generally helical to maintain fluid coupling to said outlet port means during said part of said compression stroke. A metering pump according to any preceding claim wherein the drive means comprises motor means (12) operatively coupled to the piston means by cam actuator means. A metering pump according to claim 2 wherein the cam actuator means comprises a drive shaft (104) which is coupled to the motor means and secured to the piston means for transmitting rotary motion from the motor to the piston means, said drive shaft including cam means (16) for causing said drive shaft and piston means to undergo said reciprocal motion upon rotation of said drive shaft by said motor means. A metering pump according to claim 3 wherein said cam means comprises a cam track (103) spaced from and extending about said drive shaft, and a cam follower (114) secured to said drive shaft and engaging said cam track to cause said drive shaft to reciprocate as it rotates. A metering pump according to any preceding claim wherein said fluid passage means is brought adjacent said inlet port means during substantially the whole of a suction stroke and adjacent said outlet port during substantially the whole of said compression stroke. A metering pump according to any preceding claim wherein said inlet port means and said outlet port means open adjacent to, and are substantially sealed by, an unshaped portion of said piston surface during at least part of each dwell period. A metering pump according to any preceding claim wherein said rotary motion continues during at least part of said suction stroke and/or said compression stroke. A method of pumping a metered volume of fluid, said method comprising providing a cylindrical housing (22) with a sealed end in which housing a piston (40) is mounted to define a pumping chamber (38), said housing including an inlet port (42, 46) and an outlet port (44, 48) opening onto the cylindrical surface of the piston, said surface being shaped to define with the housing a fluid passage extending to the pumping chamber, said fluid passage means comprising intersecting inlet and outlet slot portions (55, 54), the inlet slot portion (55) being generally helical to maintain fluid coupling to said inlet port means during said part of a suction stroke and the outlet slot portion (54) being generally helical to maintain fluid coupling to said outlet port means during said part of a compression stroke, said method further comprising the cyclically sequential steps of (a) retracting the piston to perform a said suction stroke while said inlet port means and said fluid passage are fluidly coupled; (b) rotating said piston through a position in which neither of the port means are fluidly coupled to the fluid passage until the outlet port means is brought into fluid coupling with the fluid passage; (c) moving said piston towards said housing to perform a said compression stroke while said outlet port means and said fluid passage are fluidly coupled; and (d) rotating said piston through a position in which neither of the port means are fluidly coupled to the fluid passage until the inlet port means is brought into fluid coupling with the fluid passage.

Inventors: STEARNS STANLEY D, WERNER PAUL, STEARNS, STANLEY D., WERNER, PAUL
Applicants: STEARNS STANLEY D, WERNER PAUL, STEARNS, STANLEY D., WERNER, PAUL
Application year: 1997
Main classification: F04B7
IPC codes: F04B7