Peristaltic Pump

Abstract

A peristaltic or roller pump is disclosed in which a pair of compressible tubes of unequal inside diameter are held between pumping shoes and a rotor. The rotor has a plurality of pins equally spaced along the periphery thereof. Each of the pins carries one roller thereon for occluding the larger tube. Alternate pins carrying a second roller for occluding the smaller tube. A stepping motor is employed to drive the rotor in angular increments so that a precision volume can be dispensed. The stepping motor is driven by pulses which initially have a greater interval therebetween than would occur during the normal operation thereof. In this way, the rotor can be driven with a small torque stepping motor. The ends of the tubes are rigidly held adjacent to the associated pumping shoes so that the pump will operate symmetrically with the rotor being driven in either a pick up or delivery mode.

Description

FIELD OF THE INVENTION

This invention relates to precision pumps and particularly to precision peristaltic pumps.

BACKGROUND OF THE INVENTION

Peristaltic pumps, which employ a rotor having rollers thereon for periodically occluding a liquid carrying compressible tube, have been used for a number of years to produce a flow of liquid. These pumps are normally operated with the rotor rotating at an accurately controlled speed. The accuracy of such a peristaltic pump increases as the time interval during which the pumping occurs is increased. This is because the constant speed motor which is used to drive the rotor has a start up time interval during which the rotor is not operating at its appropriate speed. The more accurate a peristaltic pump must be during a short pumping interval, the larger and more powerful the motor driving the rotor must be. This is necessary to exert sufficient torque at start up. The high torque motor, therefore, increases the cost of presently available accurate peristaltic pumps. During normal operation of the pump, however, the extra torque capability of the motor is never employed.

An additional problem encountered in present day peristaltic pumps is the backlash which is encountered when trying to reverse the direction of the pump. Most present day pumps will not run accurately in both directions.

Another additional problem encountered in present day peristaltic pumps relates to the relatively long circumferential arc through which the pumping occurs, this introduces nonuniform stretching of the compressible tubing, large areas of wear, and significant fluid turbulence, also nonreversibility.

Often times it is desirable to pump two fluids having a volume ratio of ten to one. In the past two compressible tubes have been used for such a requirement. The two tubes would have different inside diameters in order to provide the two rates of delivery. It has been found, however, that when an order of magnitude difference in pumping is desired, the ratio of diameters becomes too great.

Therefore, it is an object of this invention to provide an improved peristaltic pump.

It is a further object of this invention to provide a peristaltic pump which will be accurate at start up.

It is still a further object of this invention to provide a peristaltic pump which does not require a high torque motor to overcome start up inaccuracies.

It is yet another object of this invention to provide a peristaltic pump which will accurately dispense, hold, or pick up fluid. The accuracy can be adjusted before or during operation.

It is still another object of this invention to provide a peristaltic pump in which pumping ratios of ten to one can be achieved accurately with two compressible tubes.

It is a further object of this invention to provide a peristaltic pump having a small contact arc.

BRIEF DESCRIPTION OF THE INVENTION

With these and other objects in view the present invention contemplates a peristaltic pump in which a compressible tube is periodically occluded by a rotor, having rollers thereon, against a pumping shoe in which the rotor is driven by a motor which turns a predetermined angular amount in response to an advance signal applied thereto.

The advance signal is applied by a signal generator which when actuated by a start signal provides a stream of advance signals initially having greater time intervals between individual advance signals than occurs after the signal generator has stabilized at its normal operating rate.

In one embodiment of the invention a pair of compressible tubes of unequal inside diameter are held between the rotor and a pair of adjustable pumping shoes.

The rotor has a plurality of pins equally spaced along the periphery thereof. Each of the pins carries one roller thereon for occluding the larger tube while alternate pins carry a second roller for occluding the smaller tube. The area of contact between the rollers and the tubes occupies a small arc.

DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention can be had be referring to the following drawings and detailed description of the invention in which:

FIG. 1 is an isometric view of a peristaltic pump constructed in accordance with the teachings of this invention;

FIG. 2 is a top view of a pair of compressible tubes held between a rotor and a pair of pumping shoes;

FIG. 3 is a sectional view taken along the lines 3--3 of FIG. 2 showing both the motor driving the rotor and the rollers on the rotor for occluding the pair of compressible tubes; and

FIG. 4 is a block diagram of the circuitry which drives the motor in the peristaltic pump of this invention.

DETAILED DESCRIPTION OF THIS INVENTION

Referring now to FIG. 1, we see an isometric view of the peristaltic pump of this invention. All of the components of the pump are mounted either on top of or inside of a housing 10. A rotor 11 is mounted for rotary motion on a pumping platform 12 which sits on the housing 10. A tube supporting bracket 14 has a pair of pumping shoes 16 mounted therein and held to an adjustable range of positions by a pair of leaf springs 17 and adjusting screws 18.

Adjusting screw 18 is used to calibrate the volume picked up or dispensed. Adjustment is needed to compensate for mechanical variations in the rotor, support bracket, rollers, tubing inside diameter, outside diameter, concentricity and elasticity, fluid viscosity and temperature.

A pair of compressible tubes 19 and 21 are mounted between the rotor 11 and the pumping shoes 16 being held in place by the tube support bracket 14. An end bracket 22 is mounted on the end of the tube support bracket 14 to give additional strength to hold the tube 19 in place. A centering groove is sometimes used with smaller diameter tubing, this aligns the tube on the shoe and holds it in position.

The tubes 19 and 21, before being mounted in the tube support bracket 14, have "ears" 23 and 24 (see FIG. 2) molded thereon for holding the tube 19. The spacing of the "ears" 23 and 24 can be varied as a means of pretensioning the tubing 19 and 21 and setting the pick up or delivery accuracy to compensate for manufacturers tolerances on the inside and outside diameters of the tubes.

A "tube lubricant" is always used in area between "ears," lubricant reduces tube wear and decreases motor torque requirement.

In this embodiment, the inside diameter of the tube 19 is approximately 4 times as great as the inside diameter of the tube 21. It is desired to have a ratio of volumes picked up or delivered from the tubes 19 and 21 of 10 to one. The rate at which fluid is moved in a peristaltic pump is generally determined by the inside diameter of the pumping tube and the rate at which the tube is occluded. Therefore, in accordance with this invention (see FIG. 3, in particular) the rotor 11 is provided with 24 roller bearing pins designated 26 peripherally located thereon and having equal spacing therebetween. Each of the roller bearing pins 26 carry a small roller 27 seen on the right hand side thereof in FIG. 3. Each time the rotor 11 makes one complete revolution, the tube 21 is occluded 24 times against its pumping shoe 16. Alternate roller bearing pins 26 are provided with large rollers 28 while those in between are provided with spacer members 29. The large rollers 28 have the same outside diameter as the small rollers 27 and occlude the large tube 19 against its pumping shoe 16 each time it passes adjacent thereto. Therefore, for each revolution of the rotor 11 the large tube 19 is occluded 12 times by the large rollers 28. The spacers 29 have smaller outside diameters than the rollers 27 and 28 and do not occlude the large tube 19 but serve merely to hold the smaller roller 27 on the roller bearing pin 26 aligned with the smaller tube 21. In this way, it is assured that with an approximately four to one ratio of inside diameter between the tubes 10 and 21 a ratio of fluids will be passed thereby at a rate of 10 to one.

The peristaltic pump shown in FIGS. 1 through 3 is controlled by circuitry shown in FIG. 4 in which common elements have common designations. As has been pointed out above, the rate at which fluid is passed from the pump tubes 19 and 21 is generally determined by the inside diameters thereof and the rate at which the tubes 19 and 21 are occluded against the respective pumping shoes 16 by the rollers 28 and 27 respectively. The providing of twice the number of rollers 27 as 28 on the rotor 11 insures that the tube 21 will be occluded at twice the rate of the tube 19. This insures the maintenance of a proper ratio of pumping from the tubes 19 and 21. In order to provide accurate absolute volume pumping, the movement of the rotor 11 must be accurately controlled.

In the prior art, the rotor 11 was controlled by a motor having an accurate speed control. In accordance with the present invention, a stepping motor 31 is employed to control the rotor 11. A stepping motor will rotate a fixed angular increment for each stepping signal applied thereto, and then hold its position when voltage remains.

The peristaltic pump of this invention is operatable in several modes. In one mode the peristaltic pump is controlled to dispense a fixed volume of fluid rather than operate for a fixed amount of time. In a second mode the peristaltic pump is operated to pick up a fixed amount of fluid rather than operate for a fixed amount of time. It should be understood that the dispense and pick up functions are performed by operating the rotor 11 in opposite directions. In most present day peristaltic pumps the hysteresis and backlash of the motor and tubing render bidirectional operation to be unsatisfactory in practice. In this peristaltic pump the inclusion of the "ears" 23 and 24 on the tubes and other mounting techniques including the end bracket 22 enable accurate operation of the pump in both a dispense or pick up mode.

On the front panel of the housing (see FIG. 1) two sets of push buttons 32 and 33 are arranged. In order to operate the peristaltic pump to pick up a predetermined volume of fluid, one of the push buttons 32 is depressed indicating the volume to be picked up. A pick up switch 34 (see FIGS. 1 and 4) is employed to actuate a pick up flip-flop 36 through a pick up gate 37 and a diode 38 and transmit an initial count 39 as determined by the state of the push buttons 32. The pick up gate 47 also actuates a four-phase generator and direction control circuit 41 which determines the direction which the stepping motor will operate. The pick up flip-flop 36 enables the step pulse enable gate 42 to operate a step pulse generator 43. The step pulse generator 43 is an oscillator which provides periodic pulses to the four-phase generator direction control circuitry for stepping the stepping motor 31 once for each pulse applied to the four-phase generator and direction control 41. The step pulse enable gate also energizes a power level control 44 which applies power to the stepping motor 31. Therefore, it is seen that the power to the stepping motor 31 is controlled by the power level control 44 while the direction and timing of the stepping motor 31 is controlled by the four-phase generator and direction control circuitry 41 which in turn is driven by the step pulse generator 43.

The output of the step pulse generator 43 is also applied to a pick up count "and" gate 46. The pick up "and" gate 46 has been enabled by the pick up flip-flop 36 over leads 47 and 48 to pass the signal supplied thereto by the step pulse generator 43. It should be observed that a dispense count gate 49 to which the signal from the step pulse generator 43 is also applied is presently disabled. The output from the pick up count gate 46 is applied by a lead 51 to the pick up counter 39 which counts the pulses applied thereto until the number initially inserted therein by the pick up push buttons is reached.

At that time a pulse is applied on an output lead 52 thereof which resets the pick up flip-flop 36 to disable the step pulse enable gate and the pick up count gate 46. The disabled step pulse enable gate 42 turns off the step pulse generator 43 and the power level control circuitry 44. Therefore, it is seen that through this circuitry the stepping motor 31 and therefore the rotor 11 is operated through a fixed angular increment as determined by the push buttons 32 without regard to the time interval of operation.

In accordance with this invention to minimize the starting torque necessary for the stepping motor 31, the step pulse generator 43 is designed to provide pulses initially at a slower rate than it does at its steady state value. In this way, the time interval between pulses for stepping at the beginning of pumping is longer than during normal operation so that the initial torque build up can be done slowly thereby enabling the stepping motor 31 to be smaller that would be necessary if fast start up were required.

In a like manner when the dispense start button 53 is actuated, a dispense gate 54 signals the four-phase generator and directional circuitry 41 to operate in the dispense direction and also triggers the dispense flip-flop 56 to enable the step pulse enable gate 42 and the dispense count gate 49. The step pulse enable gate 42 operates the same circuitry in the same manner as when enabled by the pick up flip-flop 36 except that now the dispense count gate 49 passes the pulses from the step pulse generator 43 to the dispense counter 57 rather than having the pick up count gate 46 pass the pulses from the step pulse generator 43 to the pick up counter 39. When the dispense counter 57 reaches the preset count a signal appearing on the lead 58 resets the dispense flip-flop 56. During the counting of the dispense counter 57, the four-phase generator and direction control circuitry 41 drives the stepping motor 31 in the dispense direction which is opposite to the pick up direction.

Each time the pick up flip-flop 36 or the dispense flip-flop 56 is triggered the output therefrom is applied to a push button lockout "or" gate 59 which disables the pick up "and" gate, the dispense "and" gate and the add "and" gate 62. In this way, the controls of the peristaltic pump are rendered insensitive to manipulation during the pumping cycle.

Several additional features have been included in the peristaltic pump of this invention which are accomplished by simple additions to the circuitry. The first is the add mode. This mode is employed to extend the preselect pumping range of the pump. In this mode, the pulse generator 43 will continue to operate until the total of the numbers set by both sets of the push buttons 32 and 33 have been achieved. This mode is actuated by depressing the add button 61 which passes a signal through the add "and" gate 62 so long as the push button lockout "or" gate 59 is not actuated. The add "and" gate 62 operates both the pick up flip-flop 36 and the dispense flip-flop 56. The dispense flip-flop 56 is operated through a diode 63 while the pick up flip-flop 36 is operated through a diode 64. In this embodiment it is desired that the add mode operate for dispensing fluid rather than picking up fluid. Therefore, the diode 63 is connected directly to the input of the dispense flip-flop 56 and therefrom to the four-phase direction control circuitry 41.

In this mode the dispense count gate 49 is disabled by the pick up flip-flop 36 over a lead 66. Therefore, the pick up counter 39 is counted down until a pulse is provided thereby to reset the pick up flip-flop 36. The resetting of the pick up flip-flop 36 removes the signal from the lead 66 disabling the dispense count gate 49. Thereafter the signal from the dispense flip-flop 56 enables the dispense count gate 49 until the dispense counter 57 provides a pulse on the output lead 58 thereof disabling the dispense flip-flop 56. In this way it is seen that the peristaltic pump will operate until the step pulse generator 43 provides a number of pulses equal to the sum of the initial counts stored in a pick up counter 39 and the dispense counter 57.

The peristaltic pump additionally has a dispense repeat cycle in which an oscillator designated dispense repeat cycle oscillator 67 periodically sets the dispense flip-flop to operate as described above and lock out the push buttons 34, 53 and 61. In this mode the frequency of the dispense repeat cycle oscillator 67 is controlled by a control know 67a (see FIG. 1). The oscillator 67 controls the period of time between successive actuations of the dispense flip-flop 56. The dispense control buttons 33 control the amount of fluid dispensed during each pumping interval. In this way, the peristaltic pump can be run on what appears to be a continuous basis.

It should be understood that the above embodiment is merely illustrative of the principles of this invention and that numerous other embodiments will become obvious to those of ordinary skill in the art.

Claims

What is claimed is:

1. A peristaltic pump including:

a housing;

a rotor having a peripheral edge mounted for rotation on said housing;

a plurality of rollers mounted on said rotor along said peripheral edge;

a pumping shoe mounted on said housing;

a compressible tube mounted between said pumping shoe and said rotor so that said rollers sequentially occlude said compressible tube against said pumping shoe;

said peristaltic pump characterized by;

a motor responsive to an incrementing signal for turning said rotor a fixed angular increment; and

means responsive to a first start signal for repeatedly generating said incrementing signal;

said incrementing signal generating means normally generates said incrementing signal at a first rate and initially generates said incrementing signal at a second rate, said second rate being lower than said first rate.

2. The peristaltic pump as defined in claim 1 further characterized by:

said incrementing signal generating means varying said generation of said incrementing signal from said second rate to said first rate.

3. The peristaltic pump as defined in claim 2 further characterized by:

means for periodically generating said first start signal.

4. A peristaltic pump including:

a housing;

a rotor having a peripheral edge mounted for rotation on said housing;

a plurality of rollers mounted on said rotor along said peripheral edge;

a pumping shoe mounted on said housing;

a compressible tube mounted between said pumping shoe and said rotor so that said rollers may sequentially occlude said compressible tube against said pumping shoe;

said peristaltic pump characterized by:

a motor responsive to an incrementing signal for turning said rotor a fixed angular increment;

first means enabled by said first start signal; settable to a first preset count, for counting said incrementing signal to disable said incrementing signal generating means.

5. The peristaltic pump as defined in claim 4 further characterized by:

said incrementing signal generating means normally generates said incrementing signal at a first rate and initially generates said incrementing signal at a second rate, said second rate being lower than said first rate.

6. The peristaltic pump as defined in claim 4 further characterized by:

means for generating a second start signal; and

said motor is responsive to said rotor in a first direction and said incrementing signal and said second start signal to turn said rotor in a second direction.

7. The peristaltic pump as defined in claim 6 further characterized by:

second means enabled by said second start signal, settable to a second preset count, for counting said incrementing signal to disable said incrementing signal generating means.

8. The peristaltic pump as defined in claim 7 further characterized by:

means for generating a third start signal; and

means responsive to said third start signal for disabling said incrementing signal generating means after the occurrence of incrementing signals equal to the sum of said first and second preset counts.

9. The peristaltic pump as defined in claim 8 further characterized by:

said incrementing signal generating means normally generates said incrementing signal at a first rate and initially generates said incrementing signal at a second rate, said second rate being lower than said first rate.

10. The peristaltic pump as defined in claim 9 further characterized by:

said incrementing signal generating means varying said generation of said incrementing signal from said second rate to said first rate.

11. In combination:

a housing;

a rotor having a peripheral edge mounted for rotation on said housing;

a plurality of roller bearing pins mounted on said rotor along said peripheral edge;

first and second adjustable pumping shoes mounted on said housing;

first and second compressible tubes mounted between said first and second adjustable pumping shoes respectively and said roller bearing pins;

a first plurality of rollers moiunted on each of said plurality roller bearing pins to occlude said first compressible tube against first pumping shoes;

a second plurality of rollers mounted on some of said plurality roller bearing pins to occlude said second compressible tube against said second pumping shoe;

said first compressible tube having a first inside diameter and said second compressible tube having a second inside diameter smaller than said first inside diameter;

said second plurality of rollers are arranged on alternate ones of said plurality of roller bearing pins; and

means responsive to a start signal for repeatedly generating incrementing signal; said incrementing signal generating means normally generates said incrementing signal at a first rate and initially generates said incrementing signal at a second rate, said second rate being lower than said first rate.