Abstract:
A precision fluid dispensing system that can be effectively used for accurate fluid dispensing in peristaltic pumps if roller control is used. Peristaltic pumps can be combined with pinch valves allowing a dispense tube to be open while a source tube is blocked. Controlled roller movement is used to move the next roller to the same starting position as the previous roller was on the previous dispense, the dispense pinch valve is closed and the source valve is opened. The system uses roller positioning where the each roller is properly positioned so that each dispense cycle starts in the same position. The precision and accuracy is better than 0.3% total.

Description:
BACKGROUND 
       [0001]    This application is related to, and claims priority from, U.S. Provisional Patent Application No. 61/978,911 filed Apr. 13, 2014. Application 61/978,911 is hereby incorporated by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to peristaltic pumps and more particularly to a precision fluid dispensing using peristaltic roller control. 
       DESCRIPTION OF THE PRIOR ART 
       [0003]    Peristaltic pumps find use for fluid dispensing in many fields where pump contamination is a concern, aggressive fluids can be used, slurries that can pass through the peristaltic pump or minimizing shear in shear sensitive fluids. A peristaltic pump mostly uses rollers to squeeze, occlude, flexible tubing against a pressure shoe forcing fluid to move between rollers. It is generally assumed in the art that it is very difficult to achieve accurate, repeatable precision dispensing with this type of pump due to roller progression, We have found that this is true except where each cycle can be repeated with the rollers in the same place for the start of a dispense. This is usually one complete revolution of the pump or when a roller is in the same position at the end of a dispense cycle. The cyclic nature of roller progression of peristaltic pumps is shown  FIGS. 1A-1B . The results indicate a cyclic nature of the peristaltic pump system where the rollers progress for each dispensing cycle. This is shown in  FIGS. 1A-1B . Testing of the three roller system, as shown in  FIG. 1A , shows that with each 180 degree index of the pump, there are two groups of weight determinations. 
         [0004]    Complete and rotations indicate that the pump repeats very accurately as roller progression has been removed from  FIG. 3 . Looking at  FIG. 1A , it can be seen that the cycle repeats for approximately every 21 cycles. If the rollers are located at any additional fraction of a complete rotation, roller control is needed so that for each dispense the roller can start in the same position. It would be very advantageous to use roller control to achieve accurate dispensing with a peristaltic pump. 
       SUMMARY OF THE INVENTION 
       [0005]    A peristaltic system of the present invention can be effectively used for accurate fluid dispensing in peristaltic pumps if roller control is used. Peristaltic pumps can be combined with pinch valves allowing a dispense tube to be open while a source tube is blocked. When roller movement is used to move the next roller to the same starting position the dispense pinch valve is closed and the source valve is opened. After dispenses and prior to exercising valves, a drip retention is used moving a fluid back from the dispensing tips so when the pinch valve is used the valve actuation safely moves the fluid in the tube. Upon releasing the valve opening the tube to dispensing the fluid moves back to its earlier position. Shown in  FIG. 4 , is the valve conditions for various connections. 
         [0006]    The present invention uses roller positioning where the each roller is properly positioned so that each dispense cycle starts in the same position. The data for this dispensing with the rollers being in the same original position shows that the precision and accuracy is less than 0.3% total whereas most conventional systems only report the precision and accuracy at better than 1.0%. This also depends on the dispensing volume, tubing set and pump/motor being used.  FIG. 5  shows roller positioning. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0007]    Attention is now directed to several drawings that illustrate features of the present invention: 
           [0008]      FIG. 1  shows 3-Roller Pump Cycles. 
           [0009]      FIG. 2  shows 4-Roller Pump Cycles. 
           [0010]      FIG. 3  shows Half Index Cycles. 
           [0011]      FIG. 4  shows a representative Valve Diagram 
           [0012]      FIG. 5  shows a Four Roller Pump—Position Control. 
           [0013]      FIG. 6  shows a Cole Parmer MiniFlex and Watson-Marlow 313 &amp; 114 Pumps. 
           [0014]      FIG. 7  shows a Lexium Motor and Watson-Marlow 114 Pump. 
           [0015]      FIG. 8  shows a Lexium Motor Wiring Diagram. 
           [0016]      FIG. 9  shows an External Sensor 
           [0017]      FIG. 10  shows Portion Dispensing. 
           [0018]      FIG. 11  shows Watson-Marlow 114 Rollers 
       
    
    
       [0019]    Several drawings and illustrations have been presented to aid in understanding the present invention. The scope of the present invention is not limited to what is shown in these figures. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Peristaltic pumps can accurately dispense fluids if roller control is used to position each roller to the same starting position for each dispense. A motor is used to move the rotor containing the rollers. In order to index rollers to the next dispensing position, it is necessary to close off the tube used to dispense fluid and open a source tube to the pump so that a roller position can take place without fluid dispensing. A roller can be moved in either direction once the source tube is activated, and the dispense tube closed. The present invention uses the forward motor direction so the each roller is moved in the direction of an output of the system. This puts the tubing in the same direction as a dispense move, and not the drip retention direction. 
         [0021]    The present invention is designed so that upon each dispense, the number of counts from a stepper motor or an encoder is known. External sensors such as proximity or optical sensors can also be used. A typical stepper motor is made by Lexium. This Lexium stepper motor has 51,200 micro steps per revolution which can be used in determining roller positions. Using a 4-roller pump, the number of steps between each roller is 51,200/4 or 12,800 steps. Knowing the number of rollers, or by sensing each roller in the system, the dispense count after subtracting full revolutions can be used to move the next roller into position. 
         [0022]    Steps between roller repeat positions based on a Lexium motor with 51,200 steps per revolution.
       2 Roller Pumps—51,200/2=25,600 Steps between rollers   3 Roller Pumps—51,200/3=17,066.667   4 Roller Pumps—51,200/4=12,800   6 Roller Pumps—51,200/6=8,533.33333   8 Roller Pumps—51,200/8=6,400   10 Roller Pumps—51,200/10=5,120   16 Roller Pumps—51,200/16=3,200       
 
         [0030]    If a 4-roller pump is used, the progression can be up to 12,800 steps for each dispense. If 12,800 steps, or and even multiple that is being used for each dispense, then there is no roller correction. Otherwise, for example, assume that the total dispense amount is 288,800 steps for a 4-roller pump. Knowing this value, the next roller can be advanced to the same roller position as in the previous cycle by moving 12,800 micro-steps. Thus, 288,800/12,800=22.5625 roller moves. Discarding the full roller moves, the fraction is 0.5625 or 7200 steps beyond the roller start position. With 12,800 steps between rollers—7,200 is equal to 5,600 steps to bring the next roller into the same start position. If the number of rollers does not divide into the 51,200 possible motor micro-steps evenly, then another calculation can be made. Assume that the pump has three rollers, or 17,066.667 steps between each roller. The calculation is made with 17,066 steps for the first two dispense positions, and then the last move is for 17,068 steps making the step count of 17,066+17,066+17,068=51,200 or one complete motor revolution. 
         [0031]    While the preferred motor is a stepper motor, any type of motor may be used including a linear motor or solenoid or other type of actuator. 
         [0032]    The pump system also needs to have valve control so that dispense and source valves can be actuated. The use of Lexium motors, the smart motors have input and output built into the motors and can be programmed to operate the pump system correctly. The following sequence is used for accurate dispensing: 
         [0033]    1. The pump system is primed allowing all the tubes to fill with the dispensing fluid. First the dispensing leg of tubing is primed, and then the source tubing. This also allows the tube to “wear in” if a new tube is being used. 
         [0034]    2. The “Z” pulse of the encoder is found, and the motor is stopped. Each motor has a different “Z” pulse as the motor shafts are not registered to a known position. 
         [0035]    3. A step offset from this position is used for the starting point of each dispense. Usually this is at the 10:00 position for the roller, but may be different based on pump type. 
         [0036]    4. Several dispenses are made before a weight determination is made. After these dispenses, a single dispense is made and the weight determined. Specific gravity must be known for each fluid. This is repeated several times, and an average is determined where by the corresponding steps can be assigned. 
         [0037]    5. The valve(s) are set without excitation with the dispensing valve open and the source valve closed. 
         [0038]    6. A drip retention is selected where the fluid is reversed resulting in a movement of the fluid back from the end of the output nozzle. This drip retention is also automatically entered into the dispense calculation. 
         [0039]    7. The first dispense has the valves in the not excited values, and at the end of the drip retention, each of the valves is actuated where the dispense valve is closed and the source valve opened. 
         [0040]    8. A several dispenses are made before a weight verification is made assuring that the system is setup correctly. 
         [0041]    Roller control can be used with various pumps and tubing sets as shown in the following examples where a MiniFlex pump,(left view) from Cole Parmer is used along with Watson-Marlow 313 and 114 pumps (right view). Other pumps and tubing can use the technology. 
         [0042]    The system should be wired so that once the computer is removed, a trigger signal can used to the I/O to exercice each dispense cycle (however, direct computer control of the motor position is within the scope of the present invention). The motor output needs to trigger a opto-amplifier which can handle the current necessary for each of the valve actuations. In the configurations shown in  FIG. 5 , the motor is coupled to the pump using a Helical coupler allowing a small amount of misalignment while not allowing rotational slip.  FIG. 7  shows the model for the 100 system. 
         [0043]    The Lexium motor was programmed through the RS485 port using custom Lexium code. 
         [0044]      FIG. 8  is a wiring diagram for an embodiment of the present invention. 
         [0045]    Roller control can be accomplished using external sensors such as a Banner reflector sensor as shown in  FIG. 9 . The sensor can count the number of rollers in a given system and then position rollers for dispensing. 
         [0046]    Using roller control, a peristaltic pump can also be used as a “soft walled syringe pump” if the portion of the pump where the roller meets the pressure shoe has enough fluid volume. A Watson-Marlow 520 pump system can demonstrate the use of pulsation free dispensing while the roller is in contact with the pressure shoe. The 520 pumps use two rollers that come in contact with the pressure shoe. Preferred tube internal diameters showing volumes using 0.005 tube diameter for 0.0 to 0.02 ml, 0.008 diameter for 0.0 to 0.05 ml, 1.6 tube diameter for 0.0 to 0.2ml, 4.8 tube diameter for 0.0 to 1.6 mL and 8.0 tube diameter for 0.0 to 4.5 mL. In  FIG. 10 , a 1.6 mm internal diameter silicon tube can be seen for one full revolution of the pump. The curve represents 5 dispensing cycles where points 1 through 7 can be used for a 0.02 mL pump. Linear pumps can be effectively used for this application. 
         [0047]    Pulsation reduction can be achieved by adding more custom rollers to the pump rotor as the sixteen roller 313 Watson-Marlow pump, or the eight rollers to a 114 pump. A drawing of the pump is shown in  FIG. 11 . The rotors containing the rollers are made of aluminum and manufactured in one CNC Lathe setup. 
       SUMMARY OF FEATURES  
       [0048]    Some of the features of the present invention can be summarized as follows: 
         [0049]    A precision fluid dispensing system that includes a peristaltic pump with two or more rollers mounted on a rotor configured to execute a sequence of single dispenses; a motor rotationally driving at a rotor containing the rollers; an encoder or external sensor cooperating with the rotor so that the encoder or external sensor determines an absolute circumferencial position of the rollers with respect to the tubing. After each single dispense in the sequence of single dispenses, the motor positions the next roller to a position that has an identical angular position with respect to the tubing as the previous roller had before the dispense. The fluid dispensing system is set up so that each single dispense represents one movement of one of the rotor (pressing one of the rollers against the tubing). The precision fluid dispensing system is set up so the sequence of single dispenses along with an optional partial dispense results in a total dispense of a predetermined quantity of fluid. In this present invention, if a stepper motor is used, the stepper motor has a fixed number of micro-steps per revolution; each peristaltic pump has a fixed number of driven rollers, and the number of micro-steps in a single dispense equals the number of micro-steps per revolution divided by the number of driven rollers when this is an integer. In the present invention, if a stepper motor is used, the optional partial dispense has a number of micro-steps equal to the total number of steps required for the total dispense modulo the number of steps in a single dispense. Finally, when the number of micro-steps per motor revolution divided by the number of rollers is not an integer, the number of micro-steps in each single dispense is the number of micro-steps per revolution divided by the number of rollers truncated to the next lower integer for each single dispense except the last single dispense in a motor revolution, with the last single dispense in the motor revolution containing a number of micro-steps needed to bring the total number of micro-steps per motor revolution to the fixed number of micro-steps per revolution. 
         [0050]    Several descriptions and illustrations have been presented to aid in understanding the present invention. One with skill in the art will realize that numerous changes and variations may be made without departing from the spirit of the invention. Each of these changes and variations is within the scope of the present invention.