Tulley, Matthew (Single Use Surgical Ltd, Barnsley Business Innovation Centre Innovation Wa, Barnsley South Yorkshire S75 1JL, GB)
|1.||A peristaltic pump pressure monitoring system, comprising: a) a pump rotor and stator; b) a flexible tube squeezed between the rotor and stator to drive fluid in the tube into a pressure side of the tube; c) a pressure monitor, having jaws between which the pressure side of the tube is engaged, the jaws squeezing the tube when the drive fluid is at low pressure in the tube; d) means to monitor force tending to open the jaws by expansion of the tube on increase in said pressure; and e) means to control the operation of the pump in response to said force monitoring; wherein f) said control comprises increasing the speed of the pump until a desired working pressure is reached, and switching off the pump when a maximum pressure is exceeded. A system as claimed in claim 1, in which said jaws are resiliency biased towards one another and said means monitoring said force comprises a pressure sensor actuated by separation of said jaws against said bias. A system as claimed in claim 2, in which said sensor comprises a strain gauge disposed between one jaw and the tube. A system as claimed in claim 2, in which said bias increases with said separation, said sensor detecting said increase in bias. A system as claimed in claim 4, in which said bias is a spring bias. A system as claimed in any of claims 2 to 4, in which one jaw is fixed. A system as claimed in claim 1 , in which both jaws are fixed, said monitoring means comprising a strain gauge disposed between one jaw and the tube. A system as claimed in any preceding claim, in which the jaws are openable to permit insertion of the tube and are closeable to predetermined closed position in which a specific area of tube is presented to said monitoring means. A system as claimed in any preceding claim, in which the tube is of predetermined dimensions and material characteristics, the system further comprising means to display said monitored force as pressure change within the tube. A system as claimed in claim 9, in which said display is of absolute pressure within the tube.|
The present disclosure generally relates to monitoring of pressure from peristaltic pumps.
Peristaltic pumps have been used for many years pumping relatively low volumes. They are by design positive displacement pumps with the pumped flow rate set by speed of the pump. In some situations flow interruptions downstream of the pump can result in high back pressures. These high pressures can damage the flexible tube forming the pump element or cause damage to the downstream components.
There are many pressure feedback systems used with peristaltic pumps but these usually rely on separate pressure monitoring that is either connected to the peristaltic tube or communicate with the peristaltic tube via a diaphragm or other flexible membrane. The intention usually is to separate the pressure sensor from the pumped fluid.
In many medical and pharmaceutical applications, the segregation of the pumped fluid is important to maintain purity or sterility. This cleanliness is ensured by making all of the components in contact with the liquid single use. Where a pressure monitor is required as well, this necessitates the pressure sensor or diaphragm / membrane above to also be single use.
While this gives a good technical performance for pressure measuring it does significantly increase the cost of the single use components. The proposal therefore measures the pressure inside the tube by deforming a section of the pressure tube against a force transducer
SUMMARY OF THE DISCLOSURE
The pressure inside the peristaltic pump tubing is measured by deforming the outside of the tube by a known amount against a force transducer. The initial force required to deform the tube with no pressure or flow is used as a datum for further force measurements (the force transducer is 'zeroed' when the tubing is first installed in the pump / pressure monitor. Measurements of the force therefore enable the pressure inside the pump tubing to be calculated
Variations in the tube geometry can affect the effective area flattened by the force transducer and therefore affect absolute pressure calculation, however the pressure repeatability is good, making the signal suitable for flow control of the pump. The absolute pressure is also accurate enough for over pressure sensing and the signal can be used for overpressure protection alarms.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are further described hereinafter, by way of example with reference to the accompanying drawings, in which: FIGURE 1 shows an overview of the pump and pressure monitor; and FIGURE 2 shows the pressure monitor, viewed perpendicular to the tube.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in Figure 1 , the rotation of the peristaltic pump rotor 1 squeezes the tube 2 against the stator 3. The fluid contained between the rotor 4 is forced out by this movement and is therefore positive displacement, making any downstream blockage 5 a potential cause of over pressure in the downstream tube 6.
The peristaltic tube is also pressed against a force sensor 7 by a moving anvil 8.
As shown in Figure 2, which is a transverse section across the measuring point. The top moving anvil 8 travels down to a fixed location to compress the tube 6. In doing this the tube 2 is deformed so that a flat 9 is formed against the measuring face. The width of the flat is determined by the diameter and wall thickness of the tube. The pressure inside the tube reacts with the force sensor over this width, and the length of the anvil / sensor. This pressure multiplied by the area produces the force measured by the sensor. By maintaining close tolerances on the tube dimensions and the final moving anvil position the deformed area is consistent, and so the pressure back calculated from the force is consistent.
The initial force required to deform the tube is zeroed out when the tube is installed in the pump and sensor. Correct sensing of the pressure occurs where this deformation force is constant (selection of appropriate tube materials and tube pre-forming).
Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.
Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.
The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
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