Patent Publication Number: US-6659728-B2

Title: Liquid dispensing pump system

Description:
BACKGROUND 
     Technical Field 
     An improved internal gear pump is disclosed. More specifically, one disclosed internal gear pump includes a controller linked to a stepper motor for enhanced dispensing accuracy. Still another disclosed internal gear pump includes an improved head design for enhanced accuracy. Further, algorithms for providing precise pump control and dispensing accuracy are also disclosed. 
     SUMMARY OF THE INVENTION 
     Internal gear pumps are known and have long been used for the pumping of thin liquids at relatively high speeds. The typical internal gear pump design includes a rotor mounted to a drive shaft. The rotor includes a plurality of circumferentially disposed and spaced apart rotor teeth that extend axially toward an open end of the pump casing. The open end of the pump casing is typically covered by a head plate or cover plate which, in turn, is connected to an idler. The idler is mounted to the head plate eccentrically with respect to the rotor teeth. The idler also includes a plurality of spaced apart idler teeth disposed between alternating idler roots. The idler teeth are tapered as they extend radially outward and each idler tooth is received between two adjacent rotor teeth. The rotor teeth, in contrast, are tapered as they extend radially inward. A crescent or sealing wall is disposed below the idler and within the rotor teeth. The crescent provides a seal to prevent the loss of fluid disposed between the idler teeth as the idler teeth rotate. The rotor teeth extend below the crescent before rotating around to receive an idler tooth between two adjacent rotor teeth. 
     The input and output ports for internal gear pumps are disposed on opposing sides of the rotor. The fluid being pumped is primarily carried from the input port to the output port to the space or roots disposed between adjacent idler teeth. This space may be loaded in two ways: radially and axially. The space is loaded radially when fluid passes between adjacent rotor teeth before being received in a root disposed between adjacent idler teeth. Further, there is typically a gap between the distal ends of the rotor teeth and the head plate or casing cover which permits migration of fluid from the inlet port to an area disposed between the head plate and the idler. After migrating into this area, the fluid can be sucked into the area or root disposed between adjacent idler teeth during rotation of the idler and rotor. 
     In order to increase the speed of such internal gear pumps, head designs have been developed to ensure complete loading of the inner most area between the idler teeth or the root disposed between the adjacent idler teeth. One such design is disclosed in U.S. Pat. No. 6,149,415. 
     However, while the head design disclosed in the &#39;415 patent and other internal gear pumps known in the art have increased the pumping rate of such internal gear pumps, such designs have been found unsatisfactory for applications where precise dispensing of relatively small amounts of liquids is required. 
     Accordingly, there is a need for an improved internal gear pump design with improved accuracy. 
     SUMMARY OF THE DISCLOSURE 
     Several embodiments of improved internal gear pumps and pumping systems are disclosed which satisfy the aforenoted need. 
     Specifically, an internal gear pump is disclosed which includes a stepper motor coupled to a drive shaft that, in turn, is coupled to a rotor. The rotor is meshed with an idler which, in turn, is mounted to a head coupled to a head plate. The improvement comprises a controller linked to the stepper motor. The stepper motor imparts a stepped rotational movement to the drive shaft wherein a single 360° rotation of the drive shaft comprises a plurality of steps. The controller sends a signal to the stepper motor to rotate the drive shaft a predetermined number of steps. The signal causes the stepper motor to rotate the drive shaft the predetermined number of steps. The controller calculates the predetermined number of steps based upon a dispensed amount that is inputted to the controller. The controller calculates the predetermined number of steps and generates the signal sent to the stepper motor based upon an algorithm derived experimentally that defines a relationship between dispense amount and a number of steps required for each dispense amount that is unique to each fluid to be pumped. 
     Typically, the relationship between dispense amount and the number of steps required is a linear relationship that can be defined experimentally with a plurality of data points for a particular liquid. A straight forward algorithm is generated for the liquid to be pumped and stored in the controller memory. 
     Instead of, or in addition to, the above-described controller system, an improved head design is also disclosed. In the improved head design, the head comprises a head surface that faces towards the rotor. The head surface consists of an aperture for receiving the idler pin, a crescent disposed below the aperture and a remaining planar head surface area that surrounds the aperture and the crescent and that abuttingly engages the rotor and idler. The idler pin extends outward from the aperture in the head surface and the idler comprises a central hole that mateably receives the idler pin so that the idler abuttingly engages a first circular ring area of the head surface disposed above the crescent and around the central aperture. The rotor abuttingly engages a second circular ring area of the head surface area that extends below the crescent and partially overlaps the first circular ring area. The first and second circular ring areas are eccentric with respect to each other and account for the planar head surface area. The terms “above” and “below” are used in a relative sense. In some embodiments, the pump may be arranged where the crescent is disposed vertically above the aperture which accommodates the idler pin. Thus, the first circular ring area extends around the aperture and between the aperture and the crescent. The second circular ring area extends around the crescent wherein the crescent is disposed between the portion of the second circular ring area and the aperture. 
     In a further refinement, the head and head plate comprises a two-piece assembly wherein a wave spring is disposed between the head and the head plate and the wave spring biases the head towards the rotor. 
     In another refinement, the head and head plate are unitary in construction. 
     In a further refinement, the stepper motor is frictionally coupled to the drive shaft which, in turn, is frictionally coupled to the rotor. In a further refinement of this concept, the stepper motor is press fitted to the drive shaft which, in turn, is press fitted to the rotor. 
     In a further refinement relating to the embodiment including a controller, the controller is linked to a power supply which, in turn, is linked to the stepper motor. The above-described signal is sent from the controller to the power supply which transmits sufficient power to the stepper motor to rotate the drive shaft a predetermined number of steps corresponding to the signal. 
     In another refinement, each of the above-described steps corresponds to approximately 1.8° of rotation of the drive shaft so that one rotation of the drive shaft is approximately equivalent to 200 steps. In a further refinement, half-steps are available where each half-step corresponds approximately to 0.9° of rotation of the drive shaft so what one rotation of the drive shaft is approximately equal to 400 half-steps. Generally speaking, in depending upon the stepper motor selected, the steps can correspond to a rotation of the drive shaft ranging from about 0.5° to about 3° so that one rotation of the drive shaft can range from about 720 to about 120 steps. 
     In another refinement, instead of operating based upon an open loop utilizing an algorithm as described above, the controller can operate based upon a closed loop. In such a refinement, the controller is linked either directly or indirectly to an output mechanism which may be in the form of a scale that weighs the fluid being pumped or dispensed from the pump, a fluid level indicator in a receptacle that measures the volume of fluid being pumped or a pressure transducer that measures the pressure or flow rate of the fluid being pumped. The output mechanism generates an output signal which is communicated to the controller. Initially, the controller sends a dispense signal to the stepper motor to rotate the drive shaft. The dispense signal causes the stepper motor to rotate the drive shaft. The controller generates a stop signal and sends a stop signal to the stepper motor based upon an output signal received from the output mechanism that indicates that the dispense amount has been reached. 
     In yet another refinement, a method for controlling an internal gear pump is disclosed. The method comprises linking a controller to the stepper motor, the controller comprising a memory, deriving an algorithm experimentally that defines a relationship between dispense amount and the number of steps that is unique for each fluid to be pumped, storing the algorithm and the memory of the controller, communicating a dispense amount to the controller, calculating the number of steps in the controller for dispensing the dispense amount using the algorithm and sending a signal from the controller to the stepper motor to rotate the drive shaft the calculated number of steps. 
     Other features and advantages of the disclosed internal gear pumps, control systems therefore and methods of controlling an internal gear pump will be apparent from the following detailed description and appended claims, and upon reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The disclosed internal gear pump, control system and method of controlling an internal gear pump are illustrated more or less diagrammatically in the following drawings, wherein: 
     FIG. 1 is a sectional view of one embodiment of an improved internal gear pump linked to a control system; 
     FIG. 2 is a plan view of the pump shown in FIG. 1 schematically illustrating an output port linked to a controller; 
     FIG. 3 is a perspective view of the pump shown in FIGS. 1 and 2; 
     FIG. 4 is an exploded view of the pump shown in FIGS. 1-3; 
     FIG. 5 is a perspective view of the head of the pump illustrated in FIG. 4; 
     FIG. 6 is a sectional view of another improved internal gear pump; 
     FIG. 7 is an exploded view of the pump shown in FIG. 6; 
     FIG. 8 is a perspective view of the combination head and head plate shown in FIG. 7; 
     FIG. 9 is a sectional view of another improved internal gear pump; 
     FIG. 10 is an exploded view of the internal gear pump shown in FIG. 9; 
     FIG. 11 schematically illustrates an open loop used by the controller shown in FIG. 1; and 
     FIG. 12 schematically illustrates a closed loop that can be used by the controller shown in FIG.  2 . 
    
    
     It should be understood that the drawings are not necessarily to scale and that embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the disclosed pumps, control system or control method, or which render other details difficult to perceive, may have been omitted. It should be understood, of course, that the concept disclosed herein are not necessarily limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     Turning to FIGS. 1-4, one embodiment of an improved gear pump  15  is disclosed. The pump  15  includes a stepper motor  16  coupled to a drive shaft  17 . The drive shaft  17  is received in a rotor  18 . The rotor  18  is meshed with an idler  19  that is mounted to a head  21  by way of an idler pin  22 . The idler pin extends through the head  21  into the head cover plate  23 . The head  21  is biased toward the rotor  18  by a wave spring  24 . Seals are illustrated at  25 - 27 . The casing  28  and head plate  23  define a pump chamber  29  which accommodates the rotor  18 , idler  19  and head  21 . An input port  31  and an output port  32  are shown in FIG.  2 . In the internal gear pump design disclosed herein, the input and output ports are interchangeable. Further, one advantage of the disclosed design is that the input and output ports  31 ,  32  can be disposed in a variety of locations on the casing  28 . 
     As best seen in FIG. 5, the head  21  includes a crescent  33  and an aperture  34  for accommodating the idler pin  22 . Other than the crescent  33  and the aperture  34 , the head  21  presents a planar surface area  36  for engaging one side  37  of the idler  19  (see FIG. 4) and the ends  38  of the teeth  39  of the rotor  18  (see also FIG.  4 ). By presenting a uniform flat planar surface area  36 , the head  21  greatly improves the accuracy of the pump  15 . 
     Returning to FIG. 1, the accuracy of the pump  15  is further enhanced by use of a controller  41  to control the action of the stepper motor  16 . Specifically, the stepper motor  16  rotates the shaft  17  in a stepped manner whereby a plurality of steps are required to rotate the shaft  17  one rotation or 360°. The size of the steps can vary, depending on the motor  16 . In one preferred embodiment, each step is 1.8° so that one complete rotation of the shaft  17  represents 200 steps. In another preferred embodiment, the steps are half this size or half-steps so that each smaller step or half-step is 0.9° of rotation so that one complete rotation of the drive shaft is equivalent to 400 steps. It should be noted that these two step sizes are mere examples and that the step size can range depending upon the accuracy required and the motor  16  selected. For accurate or precise dispensing pumps wherein inaccuracies of 5% or less are desired or inaccuracies within 1%, the step size should be small, ranging from about 0.5° to about 3° so that one rotation of the drive shaft ranges from about 720 steps to about 120 steps. 
     In the embodiment illustrated in FIG. 1, the controller  41  is linked to a power supply or motor driver  42 . The controller sends a signal to the motor driver  42  which supplies the sufficient power to the stepper motor  16  to rotate the shaft  17  the predetermined or requested number of steps. Data may be inputted to the controller  41  directly or through a data input terminal or personal computer or lap-top computer as shown at  43 . 
     The algorithms and control methodology utilized by the controller  41  will be discussed below with reference to FIG.  11 . Further, the controller  41  or a different controller  44  may be coupled to an output port  32 . It will be noted that the controller  41  as shown in FIG. 1 is used to calculate a predetermined number of steps based upon an inputted dispense amount. One open loop algorithm that can be utilized for the controller  41  is illustrated in FIG.  11  and discussed in detail below. In contrast, the controller  44  receives a dispense amount directly or from a data input source  45  and controls the operation of the stepper motor  16  based upon output readings such as the weight of the liquid dispensed, a flow rate reading, a pressure reading or a volume or liquid level reading. One suitable closed loop algorithm that can be utilized by such a controller  44  is discussed below with respect to FIG.  12 . 
     Turning to FIGS. 6-8, an alternative pump  15   a  is disclosed. Parts analogous to the pump  15  disclosed in FIGS. 1-5 will be referenced with like reference numerals but with the suffix “a.” Like the pump  15 , the pump  15   a  includes a stepper motor  16   a  that is coupled to drive shaft  17   a  which, in turn, is coupled to a rotor  18   a . One preferred coupling method is to use a press-fit connection. The rotor  18   a  is a mesh with an idler  19   a  which, in turn, is trapped between the rotor  18   a and the head  21   a . The idler  19   a  is mounted to an idler pin  22   a . Again, seals are shown at  25 - 27   a . Instead of being a separate part from the head plate  23   a , the head  21   a  and head plate  23   a  are unitary in construction as shown in FIGS. 6-8. 
     Referring to FIG. 9, instead of the press-fit between the drive shaft  17 ,  17   a  and rotors  18 ,  18   a  as shown in FIGS. 1 and 6 with respect to embodiments  15 ,  15   a , the rotor  18   b  is mechanically connected to the stepper motor  16   b  by way of the coupling  47 . Instead of a drive shaft  17  or  17   a , the rotor  18   b  includes its own shaft section  48 . The bushing  49  and mechanical seals  51 - 53  are utilized instead of the o-ring seals  25 - 25   a  and  26 ,  26   a  as described above. Again, the head  21   b  and head plate cover  23   b  are unitary in construction similar to the embodiment  15   a  discussed above. 
     Turning to FIGS. 11 and 12, algorithms for use by a controller  41  based upon input data (see FIG. 1) or controller  44  based upon output data (see FIG. 2) are illustrated respectively. 
     FIG. 11 discloses an open-loop control process wherein at step  61 , a dispense amount is inputted to the controller  41  either directly or through a data input terminal such as a personal computer or lap-top computer  43 . Using an algorithm programmed into its memory, the controller  41  calculates the number of steps required to dispense the amount inputted with the pump  15 ,  15   a  or  15   b . The algorithm is generated from experimental test results wherein a plurality of data points are generated for a plurality of dispense amounts in corresponding steps. It has been found with the pump designs  15 ,  15   a  and  15   b  and variations thereof that the relationship between dispense amount and number of steps is generally linear. Accordingly, a trend line is developed with a slope. For example, the dispense amount y may be related to the number of steps x by way of the formula: y=mx+b wherein b is a y-axis intersect value. Accordingly, the controller  41  calculates the number of steps required for pumping the dispense amount at  62 . At step  63 , the controller  41  either directly activates the stepper motor  16 ,  16   a  or  16   b  or activates the stepper motor  16 ,  16   a ,  16   b  through a power supply or motor driver  42 . To dispense the liquid for the predetermined number of steps at step  64 , the controller, either directly or through the power supply  42  accelerates the motor to an operating speed at step  65 , holds the speed at step  66 , decelerates the motor at step  67  and deactivates the motor at step  68  after the drive shaft  17 ,  17   a  or rotor  18   b  has been rotated the appropriate amount corresponding to the predetermined number of steps calculated at step  62 . The controller then awaits for additional dispense amount input at steps  69 . 
     It will be noted that steps  63 - 68  may be combined into a single step or divided further into additional individual steps, depending upon the controller  41  design, power supply  42  design and stepper motor  16 ,  16   a ,  16   b  design. 
     Referring to FIG. 12, a closed loop control system is illustrated schematically that is based upon an output signal. At step  71 , a dispense amount is inputted to the controller  44  either directly or through a data input terminal  45  as described above. The controller  44  activates the stepper motor  16 ,  16   a , or  16   b  at step  72 . The dispensing begins at step  73  where, at step  74 , the motor is accelerated to operating speed and maintained at that speed at step  75 . At this point, output signals are generated at step  76  and communicated back to the controller  44 . The output signals may be generated by a scale that weighs the amount of fluid dispensed, a flow meter that measures the amount of fluid dispensed, a pressure transducer that measures the pressure of the liquid being dispensed, or a level indicator which communicates to the controller the level of liquid in a container of a known volume thereby enabling the controller to generate the volume of liquid dispensed. If the amount of liquid dispensed is close to the inputted dispensed amount at  77 , the controller then checks again to see if the dispense amount has been reached at  78  and, if not, the stepper motor  16 ,  16   a  or  16   b  is decelerated at  79  before the closed loop represented by steps  76 - 79  is repeated. If the dispensed amount has been reached at step  78 , the motor is stopped at  80  and shut down at  81  before the controller  44  awaits for additional input at  82 . 
     Obviously, variations of the open loop and closed loop methodologies described in FIGS. 11 and 12 will be apparent to those skilled in the art. The use of these methodologies with and without the pump design refinements above lead to an improved accuracy for internal gear pump operation. 
     From the above description, it is apparent that the deficiencies of the prior art have been overcome. While only certain embodiments have been set forth and described, other alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of the present disclosure.