Method and apparatus for accurately dispensing liquids and solids

This application is a divisional application of U.S. patent application Ser. No. 09/229,538, filed Jan. 12, 1999, issuing as U.S. Pat. No. 6,126,039 on Oct. 3, 2000, which is a divisional application of U.S. patent application Ser. No. 08/752,768, filed Nov. 20, 1996, issuing as U.S. Pat. No. 5,857,589 on Jan. 12, 1999, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The field of the present invention is systems for calibrating devices that meter and dispense singular and plural component liquids and solids.

BACKGROUND OF THE INVENTION

Systems for mixing and dispensing singular and multi-component materials are well known in the art. Such systems typically include pumping mechanisms for pumping and metering separate materials, such as a base material and an accelerator material, in a prescribed ratio to a mixing device that thoroughly mixes these materials together. The mixed composition then flows out of a dispensing nozzle directly to the surface or point of application where the composition is desired.

When a curable composition is desired, two or more suitable materials are mixed to interact with each other to create a flowable, curable composition which will set or harden to a non-flowable state. The time required for a curable composition to harden is referred to as the “cure” time and often is a short period of time. Such resulting curable compositions have been used, for instance, as adhesives, sealants and potting materials in a wide variety of industrial applications.

Production environments can impose limitations on how a dispensing device should operate. For example, in a production environment, it is desirable for the curable composition to cure as rapidly as possible so that subsequent production operations can be performed on the production item without having to wait a significant time for curing to occur.

Further, production requirements often include the need to dispense a precise amount of a properly constituted composition. A deviation in the actual ratio of the constituent materials dispensed may alter the strength, viscosity and/or other properties and attributes of the composition. Thus, a dispensing system should dispense the desired ratio and quantity of constituent materials as accurately as possible. In many cases, the desired ratio is expressed as a function of the weight or mass of two constituent components. Nonetheless, the two constituent components are generally supplied to the mixer by volumetric metering pumps which control the volumetric ratio of the two components, rather than their weights or masses. The volumetric ratio fails to account for any changes in density and changes in mass that may occur when the components are subjected to temperature or pressure change.

Also, production items often move along a production line at a set speed. Therefore, the flow rate of the dispensed composition should be kept or maintained as constant as possible so that the time required to dispense the proper amount of composition onto or into the production item remains constant.

An assembly line operation may further require that the composition be dispensed intermittently because the composition is applied to production items that are separated spatially and temporally. Dispensing compositions intermittently may cause a loss of flow control and/or ratio control. During the first few seconds of dispensing a composition, a transient imbalance phenomenon may arise from the elasticity of materials in the dispensing system and/or changing pressures caused by cycling the dispenser. When pressure changes, the volume of stored material between the mixer and the pump changes. In other words, changes in pressure may introduce an error into the weight or mass ratio of the constituent components because a higher pressure results in a component taking less volume than the component would otherwise take, or in an expansion or shrinkage of the hoses, fittings and tubes. The loss of control may result in inaccurately dispensed quantities or ratio of materials. This loss of flow control can occur separately or in addition to the loss of ratio control. A loss of ratio control occurs when the transient imbalance phenomenon causes the dispensing system to dispense too much or too little of one constituent material, thereby resulting in an improperly constituted end product. In other words, even if the ratio control is not lost during the first few seconds of dispensing a composition, the flow control may be lost. Therefore, it is desirous to control both the ratio of constituent materials and the flow rate of dispensing of the resulting composition.

Dispensing machines may be used to create various types of compositions. A dispensing machine may be required to dispense two or more constituent materials to form a first composition and then switch to dispense either the same constituent materials in a different ratio or other constituent materials to form a second composition. Thus, it is desirable for a dispensing machine to change what materials are dispensed, the quantities of materials dispensed and/or the ratio of constituent materials while maintaining the device's ability to control accurately the quantity, ratio, flow rate and other dispensing criteria. Current dispensing systems fail to satisfy these needs and require users to shut down the dispensing machine and go through a lengthy calibration cycle in order to adjust the machine to the viscosity and/or other properties of the constituent materials.

Some dispensing systems include vats capable of holding large amounts of a constituent material. Motor-driven agitators are placed inside the vat to maintain the material homogeneity. As the amount of material held in a vat is consumed, the agitator requires either less velocity or less current to mix the remaining material. However, in present dispensing systems, as the remaining material in a vat decreases, an agitator controlled by conventional means may over-agitate the material, resulting in frothing or the introduction of air bubbles. This frothing of the material could adversely affect the accuracy of the amount of material dispensed.

These concerns and problems may be further exacerbated when a dispensing system attempts to dispense a composition formed by mixing a solid powder with a liquid. Additional issues such as maintaining proper ratios and homogeneity arise.

Ideally, a dispensing system should be able to accurately control the ratio of each constituent material dispensed, the flow rate of each constituent material dispensed, the flow rate of the resulting composition, and the amount of the constituent materials and the resulting composition dispensed and be able to maintain such accuracy over time and various operating conditions. However, present dispensing systems fail to satisfy these attributes.

SUMMARY OF THE INVENTION

The present invention is directed to a method of calibrating a dispensing system which has a pump motor and an output nozzle. The method includes the dispensing of a certain amount of fluid which is contained. The rotation of the pump motor during dispensing is monitored. The expected amount of fluid dispensed is determined and the actual amount of fluid dispensed is weighed. A comparison is made to determine the amount of rotation of pump motor per unit measure of fluid dispensed.

Accordingly, it is an object of the present invention to provide an improved calibration system for measuring fluid dispensed based on motor rotation. Other and further objects and advantages will appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects, features and advantages to the present invention will be better understood by considering the Detailed Description of a Preferred Embodiment which follows together with the drawings, wherein:

FIG. 1

is a block diagram of a preferred embodiment of a dispensing system which dispenses a single or plural component fluid.

FIG. 2

is a cross-sectional diagram of a dispense head in the opened position.

FIG. 3

is a cross-sectional diagram of a dispense head in the closed position.

FIG. 4

is an exploded cross-sectional view of the bellows assembly.

FIG. 5

is a partially exploded cross-sectional view of the bellows assembly.

FIG. 6

is a cross-sectional view of the bellows assembly as mounted to the valve rod and rod end.

FIG. 7

is a cross-sectional view of the bellows.

FIG. 8

is a cross-sectional diagram of a preferred embodiment of the pump stator assembly.

FIG. 9

is a side view of a pressure section of the pump stator assembly of FIG.

8

.

FIG. 10

is a perspective end view of a pressure section of FIG.

9

.

FIG. 11

is an end view of a pressure section of FIG.

10

.

FIG. 12

is another side view of a pressure section of FIG.

9

.

FIG. 13

is a cross-sectional view of the pump stator assembly of FIG.

8

and illustrates the flow pattern of fluids passing through the pump stator assembly.

FIG. 14

is a cutaway view of a partial pump stator assembly having a single helix rotor within the double helix bore.

FIG. 15

is a cross-sectional view of a partial pump stator assembly and rotor.

FIG. 16

is a diagram showing the position of the single helix rotor as the rotor rotates within the double helix bore of a pump stator assembly.

FIG. 17

is an electrical block diagram of a preferred embodiment of a motor controller.

FIG. 18

is a block diagram of a preferred embodiment of a dispensing system which dispenses a powder and a single or plural component fluid.

FIG. 19

is a diagram showing how

FIGS. 20-23

connect to create a software flowchart for controlling aspects of the dispensing system.

FIGS. 20-23

are software flowcharts for controlling aspects of the dispensing system.

FIG. 24

is a software flowchart that describes the RS232 and DIP switch software for the motor controller.

FIG. 25

is a software flowchart that describes the RS232 data flow in the motor controller.

FIG. 26

is a software flowchart that describes the motor controller timer interrupt software.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1

illustrates a block diagram of a dispensing system

1

which dispenses a single or plural component fluid. In

FIG. 1

, the dispensing system

1

has a plurality of vats

2

,

4

, each of which holds a fluid

6

,

8

that is a constituent material of the desired final product. Agitators

9

,

10

stir the fluids

6

,

8

in order to maintain the fluids as homogeneously as possible. The dispensing system

1

has a master control unit

14

which may be a CPU, microprocessor, microcontroller, arithmetic logic unit, ASIC, field programmable gate array, or other logic control circuit. The master control unit

14

receives data and commands via data interconnects

16

,

18

from a user input device

20

and/or a programming input device

22

. The user input device

20

may be a keypad, buttons, switches, barcode reader, or other input device. Depending on the input, the master control unit

14

controls various aspects of the dispensing system

1

. For example, the master control unit

14

has lines

26

,

28

for transmitting commands and receiving data from pump controllers

30

,

32

which in turn direct and manage pumps

34

,

36

. The control unit

14

calculates desired pump parameters, such as acceleration, speed and duration, based on data entered through aforementioned user input devices and from data resident in the software and hardware of the control unit. Primary items of information stored in the resident software are the dispense volume of each pump rotation, and the ratio between motor rotation and pump rotation. The software then calculates the number of motor rotations to deliver the desired quantity of material, including velocity or rotational speed. If one revolution of the pump outputs a known volume of a fluid, the pump constant, the control unit

14

calculates the tick count to control the number of revolutions and partial revolutions the pump makes and thus, direct the quantity of the fluid to be dispensed. The desired pump parameters are then downloaded to the pump controllers

30

,

32

, via the data lines

26

,

28

and stored. A signal to begin a cycle is sent simultaneously to each pump controller

30

,

32

by the control unit

14

, both pumps

34

,

36

activate under their respective programs. The motor controllers

30

,

32

then count the ticks received from absolute position encoders

38

,

40

over time to manage the rotational speed or acceleration of the pumps

34

,

36

. The absolute position encoders

38

,

40

are coupled mechanically to the shafts of the motors

39

,

41

and may operate optically, mechanically, electrically or magnetically. The encoders

38

,

40

count tick marks to detect the position of the shafts as they rotate. The encoders

38

,

40

send pulses (i.e., a number of ticks over time) representing the shaft position information to the motor controllers

30

,

32

. As later described in

FIG. 17

, the pulses enter a control circuit

190

(within the motor controllers) and are used by the control circuit

190

to control power drivers

200

and the motors

39

,

41

. Thus, the pulses from the encoders are used by the motor controllers to adjust or fine tune the operation of the motors

39

,

41

. The motor controllers

30

,

32

may send status and other information including encoder information to the master control unit

14

. Thus, the motors

39

,

41

and in turn the pumps

34

,

36

are controlled by a pump control system including the master control unit

14

, the motor controllers

30

,

32

and the encoders

38

and

40

.

If a revolution of the pump outputs a known volume of a fluid, the pump control system, either the master control unit

14

or the motor controller depending on which device is to have feedback control in a particular design, can use the encoder tick measurement of the number of revolutions and partial revolutions made by the pump and thus, calculate the expected volume of the fluid dispensed. The master control unit

14

may count the ticks from the encoders

38

,

40

over time to determine the rotational speed or acceleration of the pumps

34

,

36

. Thus, the pump control system including the encoders

38

,

40

measure pump displacement and rate to act as pump movement sensors.

The action of the pumps

34

,

36

draws fluids

6

,

8

into the pumps through vat fluid lines

42

,

44

. The fluids

6

,

8

pass into the pump fluid lines

46

,

48

and into a dispense head

49

having a separate chamber

51

for each pump fluid line

46

,

48

. From the dispense head

49

, the fluids pass into a static mixer tube

50

. The static mixer tube

50

has internal projections that mix the fluids

6

,

8

together and dispense an end product

52

through the output nozzle

53

of the static mixer tube

50

. The end product

52

may be dispensed onto a scale

54

which weighs the end product. The dispensing system

1

receives DC power from a DC power supply

56

.

Thus, the dispensing system as shown in

FIG. 1

is a two-channel system, where each channel handles the dispensing of one fluid. The first channel (channel A) includes the vat

2

, vat fluid line

42

, pump

34

, pump controller

30

, encoder

38

, pump fluid line

46

and dispense head

49

. The second channel (channel B) comprises the vat

4

, vat fluid line

44

, pump

36

, pump controller

32

, encoder

40

, pump fluid line

48

and dispense head

49

. The dispensing system may also be modified to include additional channels and include additional vats, agitators, pumps, fluid lines and other components as desired to dispense three or more component mixtures.

Pressure transducers

58

,

60

send feedback information about the pressure in the pump fluid lines

46

,

48

to the master control unit

14

so that the master control unit

14

can monitor the pressure in the pump fluid lines

46

,

48

from the output of the pumps

34

,

36

to the dispense head

49

. The ability to maintain a constant pressure from the output of each pump

34

,

36

to the dispense head

49

helps assure that the fluid is compressed uniformly and constantly so that an accurate amount of fluid is dispensed. Additionally, if there is a blockage or malfunction, the pressure transducer will signal a preset overpressure situation, and the system will shut down. Similarly, flow meters

66

,

68

measure the flow rates within the pump fluid lines

46

,

48

and transmit flow rate information to the master control unit

14

, thereby allowing the master control unit

14

to monitor the fluid flow rates. Should the flow rates differ from calibration data, the system can be shut down and an error reported.

The dispense system can also use information from the pump controllers

30

,

32

and the flow meters

66

,

68

and other feedback sensors to check the pump and plumbing for leaks and trapped air. Appropriate error messages may be issued to the user to insure optimum performance. The dispense system may change the delivered material composition, from shot-to-shot or during the time the material is being dispensed, in order, for example, to adjust material pre-cure and post cure characteristics such as the viscosity, color and thixotropic factors of the material.

The dispense head

49

has positive cutoff valves

70

which are symbolically shown in FIG.

1

. The positive cutoff valves

70

are controlled by the master control unit

14

and serve to cut off the flow of fluids in the dispense head

49

whenever appropriate (i.e., when the dispense cycle is completed). The control lines between the master control unit

14

and the positive cutoff valves

70

are not shown in FIG.

1

.

Agitators

9

,

10

in the vats

2

,

4

are driven by agitator motors

11

,

12

. The agitators

9

,

10

are illustrated as stir paddles but may be any type of agitator well known in the art. The agitators

9

,

10

run at a constant desired speed. However, as the level of the fluid in a vat

2

,

4

falls, less current is required to drive the agitator at the same speed. The master control unit

14

can detect the reduced current flow and determine the amount of fluid remaining in the vat. Alternately, the system can be made to maintain a constant current instead of constant motor speed. An additional encoder and motor controller similar to those previously described are coupled to each agitator motor so that the motor controller (and master control unit

14

) can receive rotational position information from the agitator motors. Accordingly, the master control unit

14

can determine the rotational speed of each agitator to determine the level of fluid remaining in the vat. As the fluid level in the vat falls and as the current flow to the agitator motor is kept constant, the rotational speed of the agitator motor increases. The master control unit

14

can measure the rotational speed of the agitator motor to determine the level of fluid remaining in the vat. The master control unit

14

can also decrease the current to the agitator motor when the master control unit

14

detects that the motor speed has increased. Each vat

2

,

4

has a float connected to a normally closed switch. When the fluid level falls below a certain level, the float falls and triggers the switch to open.

The dispensing system of

FIG. 1

operates as follows:

1. The user calibrates the dispensing system (as described later) and the dispensing system calculates how much the pump motors must rotate in order to dispense a unit weight of a fluid or mixture.

2. The user enters program mode to set up shot parameters.

3. In response, the master control unit

14

queries the user for various parameters of the dispense cycle.

4. The user inputs the desired ratio of component fluids, the shot size of the end product, and either the flow rate or the time duration of the dispense cycle.

5. The master control unit

14

determines the proper pump parameters in order to feed constituent materials at the desired rate and downloads instructions to the pump controllers

30

,

32

.

6. The user initiates a dispense cycle by depressing a foot pedal, button or switch. The system can also be initiated by a signal from a pressure transducer to dispense more fluid.

7. The master control unit

14

starts the dispense cycle by opening the positive cutoff valves

70

in the dispense head

49

and by starting the pumps

34

,

36

.

8. The pump controllers

30

,

32

, flow meters

66

,

68

and pressure transducers

58

,

60

feed back information about the rotational speed of the pumps, flow rates and pressures to the master control unit

14

. The pump controllers

30

,

32

self monitor for accuracy and feed errors back to the master control unit

14

. The master control unit

14

uses this information to monitor the pump for correct rotational speed, flow rates and pressures.

9. The pressure transducers

58

,

60

check for blockages in the pump fluid lines

46

,

48

and shut down the dispensing system to prevent damage to the system if the detected pressure exceeds a pressure limit set point (i.e., an overpressure condition).

10. The pumps

34

,

36

and the positive cutoff valves

70

maintain the proper pressure in pump fluid lines

46

,

48

by functioning as positive cutoffs between shot cycles. When the dispense cycle ends, the master control unit

14

closes the positive cutoff valves

70

and stops pumps

34

,

36

.

11. The master control unit

14

analyzes received information and determines whether a dispense cycle was successfully completed.

12. Should there be a need to modify the pump function to insure correct dispense characteristics, the master control unit

14

sends new commands to the pump controllers

30

,

32

.

13. Steps 6-12 are repeated as needed for different quantities, ratios and durations.

FIG. 2

is a cross-sectional diagram of a dispense head

49

. The dispense head

49

is a combination manifold/on-off valve that controls the flow of fluids. The dispense head

49

includes a bellows assembly

80

.

FIG. 4

illustrates an exploded cross-sectional view of the bellows assembly

80

and

FIG. 5

depicts a cross-sectional view of a partially constructed bellows assembly

80

. The bellows assembly

80

includes a bellows

82

. The bellows

82

is a compressible corrigated metal alloy sleeve that is shown in greater detail in FIG.

7

. As shown in

FIG. 7

, the bellows

82

has two ends

84

,

86

. Returning to

FIGS. 4 and 5

, a valve rod

88

is inserted into a center hole of the bellows

82

. The bellows

82

slides freely along the length of the valve rod

88

. The valve rod

88

is also inserted into an aperture of a rod seal ring

90

. The rod seal ring

90

is not affixed to the valve rod

88

and is also free to slide back and forth along the length of the valve rod

88

.

FIG. 6

is a cross-sectional view of the bellows assembly

80

and shows how the bellows assembly

80

is affixed to the valve rod

88

and the rod seal ring

90

. One end

84

of the bellows

82

is hermetically sealed to the raised lip

92

of the valve rod

88

by welding, soldering, brazening or other means. The other end

86

of the bellows

82

is similarly hermetically sealed by welding, soldering, brazening or other means to the rod seal ring

90

. Thus, as the valve rod

88

extends and retracts from the rod seal ring

90

, the valve rod

88

alternately compresses and expands the bellows

82

.

A seat/rod seal

94

slides over and around an end of the valve rod

88

and abuts the raised lip

92

of the valve rod

88

. A retaining screw

96

enters the opening of the seat/rod seal

94

and screws into mating threads

98

of the valve rod

88

. The retaining screw

96

holds the seat/rod seal

94

in place.

Returning to

FIG. 2

, each bellows assembly

80

is shown as mounted in a separate chamber

51

within the dispense head

49

. The dispense head

49

has two inlets

100

. The inlets

100

receive fluids

6

,

8

from the pump fluid lines

46

,

48

, and go perpendicularly into the illustration of

FIG. 2. A

pneumatic valve actuator includes air cylinder

101

having a piston

102

which moves freely within the air cylinder

101

. Screws

103

pass through passages in the free piston

102

and engage the mating screw threads

99

of the valve rods

88

to attach the valve rods

88

to the air cylinder

101

. Each air chamber

104

of the air cylinder

101

has at least one air port (not shown) that allows air to be pumped into or out of the chamber. As shown in

FIG. 2

, the piston

102

is in its rightmost position (i.e., in a position furthest away from the valve nose

106

). The piston

102

has an O-ring groove

108

for holding a dynamic O-ring which acts as an air seal between chambers of the air cylinder

101

. When air is selectively pumped into the chambers

104

such that the air pressure in the rightmost chamber sufficiently exceeds the air pressure in the leftmost chamber, the piston

102

travels leftward towards the valve nose

106

. This leftward motion of the piston

102

pushes the valve rod

88

leftward and expands the bellows

82

. When the piston

102

extends the valve rods

88

leftward, the seat/rod seal

94

compresses into the tapered bore of the valve seat

110

, thereby closing off the flow of fluids in the dispense head

49

. The rod seal ring

90

is held in place within a cavity of the dispense head

49

and has an O-ring groove

112

for holding a static O-ring. The static O-ring acts as a fluid seal to prevent fluid in the dispense head

49

from leaking around the rod seal ring

90

. The resulting closed position configuration is shown in FIG.

3

. Instead of a pneumatic actuator such as the air cylinder, the system may utilize an electronic actuator such as a solenoid to move the valve rods

88

. The system may also use any other actuator well known in the art.

The bellows assembly

80

in

FIG. 3

is in the closed position because there is no gap between the seat/rod seal

94

and the valve seat

110

, thereby preventing fluid from flowing into the exit passages

114

and into the static mixer tube

50

. A raised surface

116

on the piston

102

prevents the piston surface from completely engaging the inner surface of the air cylinder

101

when the piston

102

is in its leftmost position. The raised surface

116

maintains at least some minimal air gap between part of the piston surface and the air cylinder surface so that the piston surface does not “stick” to the air cylinder surface.

To open the bellows assembly

80

, the piston

102

is moved away from the valve nose

106

so that the valve rod

88

moves relative to the rod seal ring

90

. This relative movement of the valve rod

88

to the rod seal ring

90

compresses the bellows

82

. The resulting configuration of the bellows assembly

80

is the open position shown in

FIG. 2

where the gap between the seat/rod seal

94

and the valve seat

110

permits fluid to pass into the exit passages

114

. Hence, the fluid coming from the inlets

100

may enter the dispense head

49

and flow out of the exit passages

114

of the dispense head

49

. The opening and closing of the bellows assembly

80

act as a positive cutoff valve

70

.

The valve seat

110

may be made of stainless steel or other suitable material. The seat/rod seal

94

may be formed of teflon or other suitable material that is deformable and yet highly impervious to chemicals. The valve body

118

, valve nose

106

, piston

102

and air cylinder

101

are made of aluminum or other suitable material.

The dispense head

49

has no dynamic sealing surfaces. The primary sealing mechanism is the bellows assembly

80

. A significant advantage of such a dispense head is that none of the components which come in contact with the fluids being dispensed also come into contact with any moving or dynamic sealing surfaces. Potential contamination may arise from moisture in the air which can cause the fluids to crystallize, or from contamination in the fluids themselves. Therefore, the dispense head of

FIG. 2

advantageously eliminates movement between any mechanical components of the dispense head

49

in the valve chamber and any fluid seal, thereby eliminating the possibility that a seal would be destroyed by the fluids or by abrasive contamination in the fluids.

FIG. 8

is a diagram of the pump stator assembly

130

of the progressive cavity pumps

34

,

36

. The pump stator assembly

130

is essentially comprised of multiple interlocking pressure sections

140

that have been inserted into a metal hollow tube housing

132

with a locking end cap at both ends. A threaded front end cap

142

receives the last pressure section

140

at the front end of the stator assembly

130

. A retainer

144

attaches to tube housing

132

and the last pressure section

140

at the rear end of the stator assembly

130

. A threaded rear end cap

146

then attaches to the tube housing

132

.

FIGS. 9-12

illustrate different views of a pressure section

140

of the pump stator assembly

130

.

FIG. 9

is a side view of the pressure section

140

;

FIG. 10

is a perspective end view of the pressure section

140

;

FIG. 11

is an end view of the pressure section

140

of

FIG. 10

;

FIG. 12

is another side view of the pressure section

140

;

FIG. 13

is a cross-sectional view of the pump stator assembly of FIG.

8

and illustrates the resulting double helix flow pattern of fluids passing through the pump stator assembly.

Each pressure section

140

is made of teflon or other suitably deformable, durable, yet highly chemically resistant and abrasion resistant material. Each pressure section

140

has a concentric 360 degree double helix bore

141

running through its center. A first helix thread

138

and a second helix thread

139

of the bore are shown in FIG.

13

. The helix threads wind down the length of the bore

141

, are opposed to each other by 180 degrees and cross each other every 180 degrees. Essentially, each pressure section

140

has one crossing of the double helix threads. To manufacture the double helix bore, a solid teflon rod is provided, a circular bore is drilled through the rod, and two helix threads are carved out of the bore of the rod.

Each pressure section

140

has pins

148

which mate with holes

150

of an adjacent pressure section

140

to interlock the pressure sections together and to maintain the radial alignment between adjacent pressure sections. The pressure section

140

has an O-ring groove

152

. An O-ring (not shown) made of teflon or other suitably deformable yet durable material fits into the O-ring groove

152

between adjacent pressure sections to seal each pressure section. When the end caps

142

,

146

are tightened to compress the pressure sections

140

together, the O-rings expand outward against the walls of the metal tube housing

132

.

A rotor or screw

134

having a single helix thread is inserted through the double helix bore

141

of the interlocked pressure sections

140

. The interaction of the single helix rotor

134

and the double helix bore

141

creates the pumping action.

FIGS. 14-16

illustrate how the single helix rotor operates within the double helix bore of a pump stator assembly.

FIG. 14

is a cutaway view of a partial pump stator assembly having a single helix rotor within the double helix bore.

Referring to

FIG. 14

, the single helix thread of the rotor

134

engages portions of the double helix threads

138

,

139

to create sealing lines

136

. Fluid may be carried between a pair of sealing lines

136

. As the rotor

134

turns within the double helix bore

141

, the sealing lines

136

move down the length of the bore, thereby transporting the fluid and creating a progressive cavity pump. The desired total number of turns in the double helix threads of the bore of the stator pump assembly

130

depends on the desired pump characteristics.

FIG. 15

is a cross-sectional view of a rotor in a partial pump stator assembly (where the lines through the pump stator assembly do not represent the pressure sections but are used to correlate

FIG. 15

to FIG.

16

).

FIG. 15

illustrates the sealing lines

136

formed by the contacts between the rotor

134

and the double helix threads of the bore

141

as well as the cavity

137

formed between adjacent sealing lines.

FIG. 16

is a diagram showing the position of the single helix rotor as the rotor rotates within the double helix bore of a pump stator assembly.

The bore

141

of the pressure sections

140

has an interference fit with the rotor

134

. That is, although the maximum outer dimension of the rotor

134

exceeds the minimum inner dimension of the bore

141

of the pressure sections

140

, the flexibility of the pressure sections

140

permits the rotor to fit within the bore

141

. The interference fit creates a seal between the rotor

134

and the bore

141

by eliminating the gap between the rotor and the bore. Lack of a gap means that fluids are prevented from leaking back through the bore

141

of the pump. When fluid leaks back through the bore

141

, the pump operates inefficiently and inaccurately. The interference fit also results in minimized slippage of the rotor

134

relative to the bore

141

. Thus, the interference fit results in a positive displacement pump wherein every rotation of the pump outputs an accurate and known volume of fluid. Because the pump is a constant displacement pump, the pressure of the system rises or falls to a steady state depending on the viscosity and flow rate of the material being pumped, and the dynamic back pressure of the system through which the fluid is dispensed. As this pressure is different for each output requirement, it is imperative that the pressure be maintained between cycles to insure accurate shot-to-shot dispense reproducibility.

By contrast, as pressures change unexpectedly in prior art devices, the fluid is compressed differently which results in a non-constant amount of fluid being dispensed. This problem with non-constant pressures is prevalent in prior art systems because as the dispense rate changes, the pressure changes. For example, a rotor that moves within a smooth bore may suffer from leakage and pressure changes. In such a pump, if fluid is poured into the bore having the rotor, the fluid will flow down the thread of the rotor, down the bore and out of the pump. The sealing lines of the double helix pump help prevent fluid from “pouring” through the pump.

Notably, each pressure section

140

can maintain a constant pressure even when the rotor

134

is static. When the rotor

134

rotates, the fluid being dispensed is transported through the pump stator assembly

130

from one pressure section to the next. The resulting progressive cavity pump is able to maintain high pressure, is volumetrically accurate and has a pulseless output flow. The pump is able to maintain constant volume of the fluids being dispensed, thereby insuring the accuracy of the dispensing characteristics. The flexible nature of the interlocked pressure sections and the metal hollow tube housing

132

of the pump also help limit the tendency of the rotor

134

to nutate or twist during rotation of the rotor

134

.

FIG. 17

is an electrical block diagram of a preferred embodiment of the motor controller

180

of the present invention. The motor controller

180

may be used to drive any motor described herein. The motor

182

is a permanent magnet DC brush or brushless motor and in particular, a 48 volt ½ horsepower motor. The motor

182

is mechanically connected to an encoder

186

. The encoder detects the absolute position of the motor shaft and sends this position information

188

to the control circuit

190

. The control circuit

190

can use the position information to determine the rotational speed or acceleration of the motor. The control circuit

190

sends various control signals

192

and “ready” control signals

194

to a multiplexor

196

. The ready signals

194

allow the control circuit

190

to turn off any specific power driver

200

if the power driver suffers a non-catastrophic failure. Signals from the multiplexor

196

pass to various power drivers

200

. A DC-to-DC converter

212

converts a 48 volt power supply to 5 volts which runs various electronics in the system and also sends 48 volts to the power drivers

200

. The power drivers

200

are semiconductor devices that use low level inputs (i.e., signals from the multiplexor

196

) to control relatively high current level outputs (i.e., lines

220

,

222

) to control the motor

182

.

Three of the input signals are the brake control signal

202

, direction control signal

204

and the pulse width modulation (PWM) control signal

206

. The brake control signal

202

causes the power drivers

200

to short the lines

220

,

222

going to the motor

182

which uses back electromotive force (emf) to dynamically brake or stop the motor

182

as quickly as possible. The direction control signal

204

tells the power drivers

200

whether to reverse the direction of the motor

182

. The pulse width modulation control signal

206

carries a train of pulses and the power drivers

200

count the number of pulses over time. As the number of pulses per unit time increases, the power drivers

200

output increasingly higher voltages up to a maximum of 48 volts to speed up the motor

182

accordingly. As the number of pulses per unit time falls, the power drivers

200

reduce the output voltage to slow down the motor

182

.

The power drivers

200

have current feedback lines