Device for controlling fluid flow

Abstract

A device (30) for controlling fluid flow in a flexible tube (10) comprises two rotatable bobbins (22, 32), a motor (56), an encoder (64) and a processor (202). Each bobbin comprises a tube-engaging surface portion having a shape that changes around at least part of a circumference of the bobbin. The motor comprises a rotor (62) mechanically coupled to the bobbins such that operation of the motor causes rotation of the bobbins. The encoder is mechanically coupled to the rotor and configured to measure an angular displacement of the rotor. The processor determines (902) a target angular displacement of the rotor, receives (904) a measurement signal (64) indicative of the angular displacement of the rotor from the encoder, and outputs (906) a motor control signal (67) to set the angular displacement of the rotor as measured by the encoder to the target angular displacement.

Description

[0001] DEVICE FOR CONTROLLING FLUID FLOW

[0002] The present disclosure relates to a device for controlling fluid flow. More specifically, the present disclosure relates to a device suitable for controlling the flow of fluid in a flexible tube, such as a blood line in a medical setting.

[0003] Flexible tubes are typically used in a medical setting to transport fluids such as blood or solutions. A convenient way to restrict fluid flow without risking contamination by direct contact with a fluid is to squeeze a flexible tube using a clamp. Conventionally, clamps are operated manually and are releasable to remove the flow restriction on demand. Various mechanisms exist but in common they comprise tube-engaging elements that pinch or slide against an outer circumferential surface of a flexible tube to squeeze the tube.

[0004] Using manual clamps it is a challenge to reduce fluid flow rate to a particular level. This is because flexible tubes of the type usually employed in medical settings may have to be squeezed to about half their original diameter before a noticeable effect on the flow rate is observed, and may have to be squeezed further to restrict the flow.

[0005] The Applicant’s earlier patent, United Kingdom Patent No. GB 2547900, describes a clamping mechanism which improves upon manual clamping techniques. More specifically, that patent discloses a clamping mechanism in which two rotatable bobbins are mounted upon a translatable carriage. Each bobbin has a tube-engaging surface portion, the shape of which changes around the circumference of the bobbin. Axial rotation of the bobbins squeezes a tube positioned in the space between the bobbins by an amount dependent on the rotation of the bobbins, thus deforming the tube sufficiently to restrict fluid flow through the tube. This arrangement allows accurate control of the degree of deformation of the tube and, hence, accurate control of the flow rate through the flexible tube. The translatable carriage moves the bobbins along the tube as the bobbins are rotated, so as to prevent the bobbins pulling the tube. GB 2547900 is incorporated by reference herein in its entirety.

[0006] The present disclosure relates to improvements to a clamping mechanism of the type disclosed in the Applicant’s earlier patent, GB 2547900. Summary

[0007] In accordance with a first aspect of the disclosure, there is provided a device for controlling fluid flow in a flexible tube. The device comprises two rotatable bobbins, each bobbin comprising a tube-engaging surface portion, wherein the tube-engaging surface portions define boundaries of a free space between the bobbins through which a tube may extend. At least one tube-engaging surface portion has a shape that changes around at least part of a circumference of the bobbin, such that axial rotation of the bobbins reduces the free space by an amount dependent on the rotation of the bobbins. The device further comprises a motor comprising a rotor, the rotor being mechanically coupled to the bobbins such that operation of the motor causes rotation of the bobbins. The device further comprises an encoder, the encoder being mechanically coupled to the rotor and configured to measure an angular displacement of the rotor. The device further comprises a processor configured to determine a target angular displacement of the rotor, receive a measurement signal from the encoder, the measurement signal indicative of the angular displacement of the rotor, and output a motor control signal to set the angular displacement of the rotor as measured by the encoder to the target angular displacement.

[0008] In comparison to the clamping mechanism described in the Applicant’s earlier patent, GB 2547900, the device for controlling fluid flow described herein provides even more accurate control of the flow rate through the flexible tube, particularly at low temperatures and / or low flow rates.

[0009] Flexible tubing typically used in medical settings becomes stiffer as its temperature is reduced, which can increase the likelihood of motor slippage. In this context, motor slippage refers to a situation in which the rotor of a motor does not rotate when the motor receives a control signal. Motor slippage can occur sporadically at low temperatures if, in response to a particular control signal, the motor does not generate enough torque to overcome the increased stiffness of the flexible tubing. The device described herein mitigates the effects of motor slippage by detecting an error between the target displacement of the rotor and the actual displacement of the rotor, and outputting a motor control signal to reduce or eliminate that error. The device described herein can thus operate the motor to squeeze the flexible tube accurately by a desired amount, even when sporadic motor slippage occurs. This can provide improved control of the rate of flow of blood during a cardiac perfusion procedure performed under hypothermic circulatory arrest, in which a patient’s body temperature is reduced to 25°C or lower.

[0010] It is difficult to measure low flow rates through the flexible tube accurately using a flow sensor. The device described herein can use a measurement of the angular displacement of the rotor as a proxy for a flow rate measurement. Due to the mechanical coupling between the rotor and the bobbins, an angular displacement of the rotor causes a commensurate rotation of the bobbins, which in turn affects the flow rate through the flexible tube. Hence, by using a measurement of the angular displacement of the rotor as a proxy for flow rate measurement, the device disclosed herein can accurately control fluid flow at “low” flow rates. In this context, “low” flow rates are those at which a flow sensor has poor sensitivity or is otherwise inaccurate.

[0011] As used herein, the term “target angular displacement” refers to a desired angular displacement of the rotor. The target angular displacement may be chosen to achieve particular functionality. For example, the target angular displacement may be chosen to set the flow rate through the tube to a particular level. As another example, the target angular displacement may be chosen to set the bobbins to a fully-open configuration, a fully-occluded configuration, or to a particular partly-occluded configuration at an intermediate point between the fully-open and fully-occluded configurations.

[0012] Optionally, the processor may be further configured to receive a second measurement signal from the encoder, after the angular displacement of the rotor as measured by the encoder has been set to the target angular displacement. The processor may identify, based on the second measurement signal, that the angular displacement of the rotor has drifted from the target angular displacement. The processor may output a second motor control signal to reset the angular displacement of the rotor as measured by the encoder to the target angular displacement.

[0013] The bobbins may occasionally deviate from their intended position. For example, a clinician may inadvertently pull the tube, causing the bobbins to rotate unintentionally. This, in turn, can affect the flow rate through the tube by causing the free space between the bobbins to increase or decrease, which will increase or decrease the flow rate respectively. Due to the mechanical coupling between the rotor and the bobbins, the device disclosed herein can detect unintentional rotation of the bobbins by identifying that the angular displacement of the rotor has drifted (i.e. , unintentionally moved) from the target angular displacement. The device can then restore the bobbins to their intended position by actuating the motor so as to reset the angular displacement of the rotor as measured by the encoder to the target angular displacement. In this manner, deviations in the intended position of the bobbins can be rectified, and the flow rate through the tube can be maintained at a desired level.

[0014] Optionally, the processor may be further configured to receive an input indicative of a desired flow rate, and determine the target angular displacement based on the desired flow rate and a known relationship between flow rate in the flexible tube and angular displacement of the rotor.

[0015] The known relationship between flow rate and angular displacement can be used to determine a target angular displacement of the rotor that results in a desired flow rate through the tube. This, in turn, can be used to set the flow rate to the desired flow rate without the need for a flow sensor which, as discussed above, may be inaccurate at low flow rates. The desired flow rate can be a user-selected value, which may be input into the processor by a user (e.g., a clinician, such as a perfusionist) via a user input device. Alternatively, the desired flow rate may be a programmatically-selected value, which can be determined by a control program in order to achieve a particular clinical result.

[0016] The known relationship between flow rate and angular displacement may be stored in a memory that is communicatively coupled to the processor. For example, the memory may store a look-up table which relates two or more flow rates to corresponding angular displacements of the rotor. In some implementations, the memory may store multiple such look-up tables, where each look-up table relates flow rates to angular displacements for a given setup. The setup may be defined in terms of properties of the flexible tube (e.g., its internal diameter, external diameter and / or material), properties of the fluid (e.g., its composition and / or viscosity), and / or temperature. Other relevant properties of the setup may be used. The values in the look-up table may be empirically determined (e.g., by measuring the flow rate achieved by a particular setup at each of a plurality of different angular displacements).

[0017] Alternatively, the known relationship between flow rate and angular displacement may be in the form of a parameterised model. The parameterised model may receive inputs including a desired flow rate and, optionally, one or more other parameters such as one or more properties of the flexible tube (e.g., its internal diameter, external diameter and / or material), one or more properties of the fluid (e.g., its composition and / or viscosity) and / or temperature. The parameterised model may output a target angular displacement that will result in the desired flow rate for a setup having whichever other parameter values are provided as inputs to the model.

[0018] The desired flow rate may be expressed in any suitable unit of measurement, such as millilitres per second or litres per minute.

[0019] Optionally, the processor may be further configured to receive an input indicative of a desired occlusion of the flexible tube, and determine the target angular displacement based on the desired occlusion and the known relationship between occlusion of the flexible tube and angular displacement of the rotor.

[0020] In this context, “occlusion” is a numerical value representing a point on a continuum between the fully-open and fully-occluded configurations of the device. Occlusion may be expressed as a percentage. For example, an occlusion of 0% corresponds to the fully-open configuration, in which the device does not restrict the flow of fluid through the flexible tube. As another example, an occlusion of 100% corresponds to the fully- occluded configuration, in which the device restricts the flow of fluid through the flexible tube to the maximum extent possible, such that flow is completely stopped or reduced to a negligible amount. As yet further examples, occlusions of 25%, 50% and 75% correspond to partially-occluded configurations, where a higher percentage value corresponds to a lower flow rate. Other occlusions between 0% and 100% are possible.

[0021] The known relationship between occlusion and angular displacement can be used to determine a target angular displacement of the rotor that results in a desired occlusion of the flexible tube. This, in turn, can be used to control the flow rate through the flexible tube without the need for a flow sensor which, as discussed above, may be inaccurate at low flow rates. Occlusion may be used as a more intuitive alternative to specifying a flow rate. The desired occlusion can be a user-selected value, which may be input into the processor by a clinician via a user input device. Alternatively, the desired occlusion may be a programmatically-selected value, which can be determined by a control program in order to achieve a particular clinical result. The known relationship between occlusion and angular displacement may be stored in a memory that is communicatively coupled to the processor. For example, the memory may store a look-up table which relates two or more occlusion values to corresponding angular displacements of the rotor. In some implementations, the memory may store multiple such look-up tables, where each look-up table relates occlusion values to angular displacements for a given setup. The setup may be defined in terms of properties of the flexible tube (e.g., its internal diameter, external diameter and / or material), properties of the fluid (e.g., its composition and / or viscosity) and / or temperature. Other relevant properties of the setup may be used. The values in the look-up table may be empirically determined (e.g., by measuring the free space between the bobbins and / or measuring deformation of the tube at each of a plurality of different angular displacements).

[0022] Alternatively, the relationship between occlusion and angular displacement may be in the form of a parameterised model. The parameterised model may receive inputs including a desired occlusion and, optionally, values of one or more other parameters such as one or more properties of the flexible tube (e.g., its internal diameter, external diameter and / or material), one or more properties of the fluid (e.g., its composition and / or viscosity) and / or temperature. The parameterised model may output a target angular displacement that will result in the desired occlusion for a setup having whichever other parameter values are provided as inputs to the model.

[0023] Optionally, the device may have a second operating mode in which the processor is configured to: determine a target flow rate of a fluid in the flexible tube; receive a flow rate signal from a flow sensor, the flow rate signal indicative of a flow rate of a fluid in the flexible tube as measured by the flow sensor; and output a third motor control signal to cause rotation of the bobbins to set the flow rate as measured by the flow sensor to the target flow rate.

[0024] The second operating mode can be provided as an alternative to a first operating mode, as described above, in which the angular displacement of the rotor is set to a target value. The encoder is not used to determine the motor control signal in the second operating mode, although may still be used to provide angular displacement measurements from which the position of the bobbins can be accurately determined. The second operating mode may provide more accurate of the flow rate through the flexible tube at higher temperatures and / or higher flow rates. In this context, “higher” flow rates are those at which the flow sensor is sufficiently accurate to allow the flow rate as measured by the flow sensor to be within a certain tolerance of the target flow rate. “Higher” temperatures are those at which temperature-induced stiffness of the flexible tubing does not result in motor slippage.

[0025] The flow sensor may be a component of the device for controlling fluid flow. Alternatively, the flow sensor may be a separate component that is configured to supply the signal indicative of the flow rate to the processor. In either case, the flow sensor is any suitable component that is configured to measure the flow rate of a fluid in the flexible tube, and to output a signal indicative of the measured flow rate.

[0026] The target flow rate can be a user-selected value, which may be input into the processor by a user (e.g., a clinician, such as a perfusionist) via a user input device. Alternatively, the target flow rate can be a programmatically-selected value, which can be determined by a control program in order to achieve a particular clinical result.

[0027] Optionally, the processor may be further configured to detect failure of the flow sensor while the device is in the second operating mode. In response to detecting failure of the flow sensor, the processor may cause the device to operate in a first operating mode. In the first operating mode, the processor determines the target angular displacement of the rotor, receives the measurement signal from the encoder, and outputs the motor control signal to set the angular displacement of the rotor as measured by the encoder to the target angular displacement.

[0028] By switching from the second operating mode to the first operating mode, the device can continue to control the flow of fluid through the flexible tube even in the unlikely event of the flow sensor failing. In this regard, “failure” does not necessarily refer to the flow sensor being completely inoperative. Rather, “failure” of the flow sensor may be detected if the flow sensor is accidentally disconnected by a user, or if the processor detects anomalous measurements from the flow sensor. Anomalous measurements may occur if gas bubbles enter the flexible tube. Optionally, the processor may be further configured to cause the device to operate in the first operating mode by determining the target angular displacement based on the target flow rate and a known relationship between flow rate in the flexible tube and angular displacement of the rotor.

[0029] The known relationship between flow rate and angular displacement can thus be used to maintain the flow rate at a previously-set target flow rate if the flow sensor fails.

[0030] Optionally, the processor may be further configured to receive an override input and, in response to the override input, cause the device to operate in the second operating mode when failure of the flow sensor has been detected.

[0031] The override input may be supplied by a user (e.g., a clinician, such as a perfusionist) via a user input device. The override input can prevent the device switching from the first operating mode to the second operating mode when the user knows that the flow sensor has not actually failed. For example, the user may activate the override input when they observe that an apparent failure of the flow sensor is caused by a small number of air bubbles in the flexible tube, and judge that the device can continue to operate safely in the second operating mode until those bubbles have passed the flow sensor.

[0032] Optionally, the processor may be further configured to receive an instruction to stop fluid flow through the flexible tube and, in response to the instruction to stop fluid flow through the flexible tube, output a fourth motor control signal to set the angular displacement of the rotor as measured by the encoder to a second target angular displacement. The second target angular displacement may correspond to a fully-occluded configuration of the device in which the bobbins maximally restrict the flow of fluid through the flexible tube.

[0033] The instruction to stop fluid flow through the flexible tube may be generated in response to an input provided by a user (e.g., a clinician, such as a perfusionist) via a user input device. Alternatively, the instruction to stop fluid flow can be automatically generated by a control program. In each case, the instruction to stop fluid flow through the flexible tube may be generated when clinical circumstances require flow to be temporarily stopped. By taking into account the angular displacement of the rotor when outputting the fourth motor control signal, the device is reliably set to its fully-occluded configuration in which the flow of fluid is stopped or reduced to a negligible amount.

[0034] Optionally, the processor may be further configured to receive an instruction to disengage from the flexible tube and, in response to the instruction to disengage from the flexible tube, output a fifth motor control signal to set the angular displacement of the rotor as measured by the encoder to a third target angular displacement. The third target angular displacement may correspond to a fully-open configuration of the device in which the bobbins do not restrict the flow of fluid through the flexible tube.

[0035] The instruction to disengage from the flexible tube may be generated in response to an input provided by a user (e.g., a clinician, such as a perfusionist) via a user input device. Alternatively, the instruction to disengage from the flexible tube may be automatically generated by a control program. In each case, the instruction to disengage from the flexible tube may be generated when clinical circumstances require fluid flow in the flexible tube to be maximised. By taking into account the angular displacement of the rotor when outputting the fifth motor control signal, the device is reliably set to its fully- open configuration in which the flow of fluid is not restricted.

[0036] Optionally, the processor may be further configured to receive an instruction to resume fluid flow through the flexible tube and, in response to the instruction to resume fluid flow in the flexible tube, output a sixth motor control signal to set the angular displacement of the rotor as measured by the encoder to the target angular displacement.

[0037] The instruction to resume fluid flow through the flexible tube may be generated in response to an input provided by a user (e.g., a clinician, such as a perfusionist) via a user input device. Alternatively, the instruction to resume fluid flow may be automatically generated by a control program. In each case, the instruction to resume fluid flow through the flexible tube may be generated after the clinical circumstances requiring fluid flow to be stopped or maximised have passed, and it is desired for fluid to flow through the flexible tube at its previous rate. The sixth motor control thus sets the angular displacement of the rotor to the target angular displacement prior to receipt of the instruction to stop fluid flow in the flexible tube or the instruction to disengage from the flexible tube. This is simpler and quicker than requiring the user to manual reset the device to its previous setting. The encoder may be an absolute encoder. The use of an absolute encoder ensures that the current rotational position of the bobbins can always be derived from the latest measurement signal received from the encoder. To put this another way, the use of an absolute encoder avoids the current rotational position of the bobbins becoming unknown during a clinical procedure.

[0038] In accordance with a further aspect of the disclosure, a cardiac perfusion system may be provided. The cardiac perfusion system comprising a device for controlling fluid flow as described herein.

[0039] The device for controlling fluid flow described herein is particularly well-suited for use in medical settings and, in particular, for use during cardiac perfusion procedures. This is because the device described herein provides accurate control of flow rate, which can be advantageous during cardiac perfusion. Moreover, the ability of the device disclosed herein to provide accurate control of flow rate at low temperatures can be particularly advantageous during a cardiac perfusion procedure performed under hypothermic circulatory arrest.

[0040] The device described herein may be used in a cardiac perfusion system to control: the flow of blood from a patient to a reservoir; the flow of blood from the venous reservoir to an oxygenator; the flow of blood from an oxygenator to the patient; or the flow of a cardioplegia agent. Multiple such devices may be used in a single cardiac perfusion system, with each device being configured to control the flow of a respective fluid.

[0041] It should be appreciated that the device for controlling fluid flow described herein can be used for other medical applications, or even for non-medical applications.

[0042] Brief Description of the Drawings

[0043] Embodiments will now be described, purely by way of example, with reference to the accompanying drawings, in which like features are denoted by like reference signs, and in which: Figure 1 is an perspective view of a device for controlling fluid flow in accordance with the present disclosure;

[0044] Figure 2 is a front view of the device shown in Figure 1 ;

[0045] Figure 3 is a side view of the device shown in Figures 1 and 2;

[0046] Figure 4 is a section view of the device along line A-A in Figure 2;

[0047] Figure 5a is a front view of the bobbins of the device shown in Figures 1 to 4, with the bobbins in a fully-open configuration;

[0048] Figure 5b is a front view of the bobbins of the device shown in Figures 1 to 4, with the bobbins in a partly-occluded configuration;

[0049] Figure 5c is a front view of the bobbins of the device shown in Figures 1 to 4, with the bobbins in a fully-occluded configuration;

[0050] Figure 6a is a side view of the bobbins of the device shown in Figures 1 to 4, with the bobbins in a fully-open configuration corresponding to that shown in Figure 5a;

[0051] Figure 6b is a side view of the bobbins of the device shown in Figures 1 to 4, with the bobbins in a partly-occluded configuration corresponding to that shown in Figure 5b;

[0052] Figure 6c is a side view of the bobbins of the device shown in Figures 1 to 4, with the bobbins in a fully-occluded configuration corresponding to that shown in Figure 5c;

[0053] Figure 7 is a schematic diagram of a control system of the device shown in Figures 1 to 4;

[0054] Figure 8 is a schematic diagram of a controller of the control system shown in Figure 7;

[0055] Figure 9 is a flow diagram of a first example of a method of controlling the device shown in Figures 1 to 4;

[0056] Figure 10 is a flow diagram of a second example of a method of controlling the device shown in Figures 1 to 4; and

[0057] Figure 11 is a flow diagram of a third example of a method of controlling the device shown in Figures 1 to 4.

[0058] Detailed Description

[0059] A device 30 for controlling fluid flow in accordance with the present disclosure will now be described with reference to Figures 1 to 4. Figures 1 to 3 are perspective, front and side views of the device 30, respectively. Figure 4 is a section view of the device 30, in which shading indicates the cut surface of the device 30. The device 30 comprises a first bobbin 22 and a second bobbin 32. The first bobbin 22 is generally cylindrical and comprises on its circumferential surface a groove 24 constituting a tube-engaging surface portion. The groove 24 has a radius that increases, relative to a central axis of rotation 28 of the first bobbin 22, along at least part of the circumference of the first bobbin 22. The shape of the groove 24 thus changes along the bobbin circumference and becomes progressively flatter. On its circumferential surface, the first bobbin 22 comprises a flattened portion 29 above the deepest portions of the groove 24. The groove 24 terminates at one end into a chamfered shoulder 27 which constitutes a sharply reduced silhouette.

[0060] The second bobbin 32 comprises a groove 34, a flattened portion 39 above the deepest portions of the groove 34, and a chamfered shoulder 37. The second bobbin 32 is a mirror image of the first bobbin 22 about the line A-A shown in Figure 2. The description of the first bobbin 22 given above is thus also applicable to the second bobbin 32.

[0061] The first bobbin 22 and the second bobbin 32 are rotatably disposed next to each other, such that the circumferential surfaces of the bobbins 22, 32 face each other. The grooves 24, 34 define boundaries of a free space 15. A tube 10 can extend through the free space 15, as shown in Figures 5a to 5c. The tube 10 is not part of the device 30, but is instead a replaceable (and optionally disposable) component that is supplied separately from the device 30. The tube 10 can be any suitable resiliently-deformable tube whose internal volume decreases when a compressive force is applied to the external surface of the tube, and which returns to its previous internal volume when the compressive force is removed. When the flattened portion 29 of the first bobbin 22 and the flattened portion 39 of the second bobbin 32 are aligned to face each other as shown in Figure 2, the flattened portions 29, 39 provide a passage 55 through which the tube 10 may be inserted into, and removed from, the free space 15 between the bobbins 22, 32. The device 30 may comprise a housing (not shown) to support the tube 10 on either side of the bobbins 22,32, and to maintain the tube 10 in a defined spatial relationship relative to the bobbins 22, 32.

[0062] With reference to Figures 5a to 5c, the area of the free space 15 between the bobbins 22, 32 can be varied by causing the bobbins to rotate. This, in turn, can affect the flow of a fluid through a tube 10 positioned within the free space 15. In Figure 5a, the bobbins 22, 32 are oriented such that the deepest portions of the grooves 24, 34 face one another. In this orientation, the area of the free space 15 between the bobbins 22, 32 is at its maximum, and the tube 10 is subject to little or no deformation from the bobbins 22, 32. Figure 5a is thus described as a “fully-open” configuration of the device 30, because the bobbins 22, 32 do not deform the tube 10 sufficiently to affect the flow of a fluid through the tube 10.

[0063] To reduce the area of the free space 15, the bobbins 22, 32 are rotated about their respective axes 28, 38 in the directions indicated by arrows 36, 35. It will be noted that the direction of rotation of the first bobbin 22 is opposite to that of the second bobbin 32. Figure 5b shows the bobbins 22, 32 after both have been rotated about their respective axes 28, 38 by approximately forty-five degrees. In this orientation, shallower portions of the grooves 24, 34 face one another, and the free space 15 between the bobbins 22, 32 is reduced with respect to that in the fully-open configuration. The circumferential surfaces of the bobbins 22, 32 bear against and compress the tube 10, which causes the tube 10 to deform as shown in Figure 5b. When the tube is deformed, its internal cross-sectional area is reduced and the rate at which a fluid can flow through the tube 10 is reduced. Figure 5b is thus described as a “partially-occluded” configuration of the device 30, because the bobbins 22, 32 deform the tube 10 sufficiently to reduce the flow of a fluid through the tube 10, but without completely stopping the flow.

[0064] Further rotation of the bobbins 22, 32 about their respective axes 28, 38 in the directions indicated by arrows 36, 35 causes the area of the free space 15 to be progressively reduced. Consequently, the rate at which a fluid can flow through the tube 10 is also progressively reduced.

[0065] When the bobbins 22, 32 have rotated about their respective axes 28, 38 by approximately one hundred and eighty degrees, the chamfered shoulders 27, 37 face one another as shown in Figure 5c. In this orientation, the area of the free space 15 between the bobbins 22, 32 is at its minimum, and the tube 10 is deformed by the bobbins 22, 32 to such an extent that fluid cannot flow through the tube 10. Figure 5c is thus described as a “fully-occluded” configuration of the device 30, because the bobbins 22, 32 completely stop the flow of a fluid through the tube 10 (or at least reduce the rate of fluid flow through the tube to a negligible amount). It should be appreciated that the bobbins 22, 32 have a number of intermediate orientations between the two extremes of the fully-open and full-occluded configurations. Due to the progressively flattening shapes of the grooves 24, 34, each intermediate orientation of the bobbins 22, 32 corresponds to a different area of the free space 15. The deformation of the tube 10 is thus dependent upon the orientation of the bobbins 22, 32. Moreover, the rate of fluid flow through the tube 10 is also dependent upon the orientation of the bobbins 22, 32, but the relationship between the rate of fluid flow and the orientation of the bobbins 22, 32 is nonlinear. The rate of fluid flow through the tube 10 can thus be varied by rotating the bobbins 22, 32. The rate of fluid flow can be decreased by rotating the bobbins 22, 32 about their respective axes 28, 38 in the directions indicated by arrows 36, 35. The rate of fluid flow can be increased by rotating the bobbins 22, 32 about their respective axes 28, 38 in directions opposite to those indicated by arrows 36, 35.

[0066] A mechanism for causing the bobbins 22, 32 to rotate will now be described with reference to Figures 1 to 4. The device 30 comprises a frame 40 and a carriage 46. The frame 40 supports other components of the device 30, including the carriage 46. The carriage 46 supports the bobbins 22, 32. The carriage 46 is moveable with respect to the frame 40. More specifically, the carriage 46 can translate with respect to the frame 40 along a linear path generally indicated by arrow 18. Although the figures show the arrow 18 pointing in only one direction, it should be appreciated that the carriage 46 is capable of translational motion in both directions along the linear path. Translation of the carriage 46 causes rotation of the bobbins 22, 32, as explained in more detail below.

[0067] The first bobbin 22 is secured to a first end of a first axle 23, with the first axle 23 and first bobbin 22 able to rotate about a common axis 28. A first pinion 25 is at a second end of the first axle 33. Similarly, the second bobbin 32 is secured to a first end of a second axle 33, with the second axle 33 and second bobbin 32 being able to rotate about a common axis 38. A second pinion 45 is at a second end of the second axle 33. The first pinion 25 and the second pinion 45 each have teeth, which mesh with teeth of a first toothed rack and a second toothed rack 44, respectively. Only the second toothed rack 44 is visible in the drawings, but it will be appreciated that the first toothed rack extends parallel to the second toothed rack 44. The first and second toothed racks extend substantially perpendicular to the axes 28, 38 of the first and second bobbins 22, 32, and substantially parallel to the tube 10 in use. The carriage 46 comprises a first carriage portion 46a and a second carriage portion 46b. The second carriage portion 46a can be seen in Figure 4, but is omitted from Figures 1 to 3 to avoid obscuring other features of the device 30. In an alternative implementation, which is not shown in the drawings, the carriage 46 does not have distinct first and second portions 46a, 46b, but instead has a unitary construction. The first carriage portion 46a comprises an internal screw thread 47a. The second carriage portion 46b is rigidly coupled to the first carriage portion 46a such that translation of the first carriage portion 46a causes an equal translation of the second carriage portion 46b. The first axle 23 and second axle 33 extend vertically through respective bores in the second carriage portion 46b. The first axle 23 and second axle 33 are able to rotate freely within their respective bores in the second carriage portion 46b. However, when the second carriage portion 46b undergoes a translational motion, the internal surfaces of its bores bear upon the first axle 23 and the second axle 33, causing the first bobbin 22 and the second bobbin 32 to translate.

[0068] The second carriage portion 46b is slidably disposed upon a guide rail 48. The guide rail 48 extends substantially perpendicular to the axes 28, 38 of the first and second bobbins 22, 32, and substantially parallel to the tube 10 in use. The guide rail 48 serves to constrain translational motion of the carriage 46, such that the carriage 46 can translate only along the linear path generally indicated by arrow 18. This, in turn, constrains translational motion of the first bobbin 22 and the second bobbin 32, such that they can translate only along the linear path generally indicated by arrow 18. The guide rail 48 is rigidly mounted to the frame 40.

[0069] A lead screw 42 extends substantially perpendicular to the axes 28, 38 of the first and second bobbins 22, 32. The lead screw 42 also extends substantially parallel to the first and second toothed racks, and substantially parallel to the tube 10 in use. The lead screw 42 has an external screw thread 47b, which engages with the internal screw thread 47a of the first carriage portion 46a. Although the external screw thread 47b is only visible along a small region of the lead screw 42 in Figure 4, it should be appreciated that the external screw thread 47b extends along substantially the entire length of the lead screw 42. A motor 56 is rigidly attached to the frame 40. The motor 56 comprises a rotor 62, which is configured to rotate when the motor 56 operates. The motor 56 can cause the rotor 62 to rotate in either a clockwise direction or an anticlockwise direction. The rotor 62 may comprise a shaft. In the implementation shown in Figure 4, a first end 63a of the rotor 62 is rigidly coupled to an end of the lead screw 42. Thus, rotation of the rotor 62 causes an equal rotation of the lead screw 42. In other implementations, the lead screw 42 and rotor 62 may not be distinct components, but may instead have a unitary construction. The motor 56 may be a stepper motor, or may be any other suitable type of motor.

[0070] An encoder 64 is coupled to the rotor 62 of the motor 56. As shown in Figure 4, the encoder 64 is directly coupled to a second end 63b of the rotor 62, the second end 63b being opposite to the first end 63a of the rotor 62 to which the lead screw 42 is coupled. In an alternative implementation, the encoder 64 may be interposed between the body of the motor 56 and the lead screw 42. In another alternative implementation, the encoder 42 may be coupled to an end of the lead screw 42 that is distal from the motor 56, such that the encoder 64 is indirectly coupled to the rotor 62 by the lead screw 42. Regardless of its location, the encoder 64 is configured to measure an angular displacement (in other words, a rotation) of the rotor 62. The encoder 64 is further configured to output a measurement signal indicative of the measured angular displacement of the rotor 62. The encoder 64 may thus be an electronic component known in the art as a rotary encoder or a shaft encoder. The manner in which the measurement signal is used by the device 30 is explained below with reference to Figures 7, 9 and 10.

[0071] To rotate the bobbins 22, 32, and thereby to control fluid flow in the tube 10, a motor control signal is supplied to the motor 56. The motor control signal causes the motor 56 to operate and, more specifically, causes the rotor 62 of the motor 56 to rotate. Rotation of the rotor 62 causes rotation of the lead screw 42. As the lead screw 42 rotates, its external screw thread 47b cooperates with the internal screw thread 47a of the first carriage portion 46a, causing the first carriage portion 46a to translate along the lead screw 42. The direction in which the first carriage portion 46a translates is dependent upon the direction of rotation of the rotor 62, and may be in either the direction of the arrow 18 or in the opposite direction thereto. Translation of the first carriage portion 46a causes translation of the second carriage portion 46b, which in turn causes translation of the bobbins 22, 32. As the bobbins 22, 32 translate, the pinions 25, 45 engage with the toothed racks, which causes the pinions 25, 45 to rotate. Rotation of each pinion 25, 45 causes rotation of a respective axle 23, 33, which in turn causes rotation of a respective bobbin 22, 32. In this manner, rotation of the rotor 62 of the motor 56 causes both a translational motion and a rotational motion of the first bobbin 22 and second bobbin 32. The direction in which each bobbin 22, 32 rotates is dependent upon the direction of rotation of the rotor 62. The angle through which each bobbin 22, 32 rotates is dependent upon the angular displacement of the rotor 62.

[0072] Figures 6a to 6c illustrate how the bobbins 22, 32 translate and rotate to control fluid flow in the tube 10. Only the second bobbin 32 is shown in Figures 6a to 6c, but it will be appreciated that the translational and rotational motion of the first bobbin 22 will be similar to that of the second bobbin 32. More specifically, the translational motion of the first bobbin 22 will be identical to that of the second bobbin 32, as shown in Figures 6a to 6c. The first bobbin 22 will rotate through the same angle as the second bobbin 32 at each of the bobbin positions shown in Figures 6a to 6c, but the direction of rotation of the first bobbin 22 will be opposite to that of the second bobbin 32.

[0073] In Figure 6a, the first bobbin 22 and the second bobbin 32 are in the fully-open configuration, corresponding to Figure 5a. The bobbins 22, 32 have not translated with respect to the frame 40 or the tube 10. In this configuration, the bobbins 22, 32 do not deform the tube 10 and do not restrict fluid flow through the tube 10.

[0074] In Figure 6b, the first bobbin 22 and the second bobbin 32 have been counter-rotated about their respective axes 22, 38 by approximately forty-five degrees. The first bobbin 22 and the second bobbin 32 are in the partially-occluded configuration, corresponding to Figure 5b. In contrast to Figure 6a, the bobbins 22, 32 have also translated with respect to the frame 40 and the tube 10 by an amount proportionate to their angle of rotation. The direction of translation is indicated by the arrow 18.

[0075] In Figure 6c, the first bobbin 22 and the second bobbin 32 have been counter-rotated about their respective axes 22, 38 by approximately one hundred and eighty degrees. The first bobbin 22 and the second bobbin 32 are in the fully-occluded configuration, corresponding to Figure 5c. The bobbins 22, 32 have translated further than shown in Figure 6b. In some implementations, the bobbins 22, 32 may have translated along the entire length of the lead screw 42 when in the fully-occluded position, such that further translation in the direction of arrow 18 (deliberately omitted from Figure 6c) is not possible. In this configuration, deformation of the tube 10 by the bobbins 22, 32 is at a maximum. Fluid flow through the tube 10 is blocked, or at least reduced to such an extent that the flow rate of fluid through the tube 10 is negligible.

[0076] In the positions shown in Figures 6b and 6c, the grip of the grooves 24, 34 on the tube 10 can be considerable. In the absence of the translational movement of the bobbins 22, 32 relative to the tube 10, contemporaneous gripping and rotating could pull the tube 10 along its length, which could in turn risk pulling the tube 10 out of other equipment to which it is connected. Translation of the bobbins 22, 32 eliminates (or at least reduces) the tendency of the bobbins 22, 32 to pull on the tube 10. Instead of pulling the tube 10 relative to stationary bobbins, the bobbins 22, 32 roll along the tube 10 while gradually restricting fluid flow.

[0077] A control system of the device 30 will now be described with reference to Figure 7. As shown in Figure 7, the device 30 comprises a controller 66 in addition to the bobbins 22, 32, motor 56, and encoder 64 described above. The device 30 may optionally further comprise a user input device 68 and / or a flow sensor 70.

[0078] The controller 66 is shown in more detail in Figure 8. The controller 66 comprises a processor 202 and a memory 204. The processor 202 can be any suitable type of data processing device, such as a microprocessor, microcontroller or application specific integrated circuit (ASIC). The processor 202 is communicatively coupled to the memory 204. The memory 204 can include a volatile memory, a non-volatile memory, or both volatile and non-volatile memories. The memory 204 stores a control program 206. The control program 206 includes processor-executable instructions that, when executed by the processor 202, cause the controller 66 to perform any or all of the methods described below with reference to Figures 9, 10 and 11 .

[0079] Returning to Figure 7, the controller 66 is communicatively coupled to the motor 56 and the encoder 64. For example, the controller 66 may be coupled to the motor 56 and encoder 64 by one or more electrically conductive wires, which may be in the form of a bus. The controller 66 is configured to output a motor control signal 67 to the motor 56. As discussed above, the motor control signal 67 causes the rotor 62 of the motor 56 to rotate. The controller 66 is also configured to receive a measurement signal 65 from the encoder 64. As discussed above, the measurement signal 65 indicates an angular displacement of the rotor 62. Thus, a rotation of the rotor 62 caused by the motor control signal 67 is measured by the encoder 64, which in turn provides a measurement signal 65 to the controller 66. A closed control loop is thereby formed.

[0080] By virtue of the mechanical coupling between the rotor 62 of the motor 56 and the bobbins 22, 32, any movement of the rotor 62 and / or the bobbins 22, 32 is detectable as a change in the angular displacement measured by the encoder 64. In more detail, the mechanical coupling between the rotor 62, lead screw 42, carriage 46, axles 23, 32, pinions 25, 45, toothed racks and bobbins 22, 32 permits little or no mechanical slippage, such that the angular displacement as measured by the encoder 64 always provides an accurate indication of the current position of the bobbins 22, 32.

[0081] In one example implementation, the encoder 64 is an incremental encoder. In this implementation, the encoder 64 measures the occurrence and direction of rotation of the rotor, but does not measure the absolute angular displacement of the rotor 62. The measurement signal output by the encoder 64 in this implementation is a pair of quadrature-encoded pulse trains. Each pulse indicates that the rotor 62 has rotated through a certain angle determined by the angular resolution of the encoder 64. The phase relationship between the two pulse trains indicates whether the rotor 62 has rotated in a clockwise or anticlockwise direction. The measurement signal output by an incremental encoder does not, by itself, provide sufficient information to determine the absolute position of the bobbins 22, 32. To allow the absolute position of the bobbins 22, 32 to be determined, one or more further position sensors are used in addition to the incremental encoder. The one or more further position sensors may be configured to detect the position of the carriage 46. In one example, the one or more further position sensors comprise a pair of Hall effect sensors, where one Hall effect sensor is mounted to the frame 40 near each of the two extremes of movement of the carriage 46. A permanent magnet may be mounted on the carriage 46. When the carriage 46 is at one extreme of movement (e.g., in the position shown in Figures 1 to 4), the permanent magnet causes a first one of the Hall effect sensors to output a signal. When the carriage 46 is at the other extreme of movement (e.g., towards the left of Figures 3 and 4), the permanent magnet causes the other one of the Hall effect sensors to output a signal. The Hall effect sensors may be digital sensors, such that neither sensor outputs a signal when the carriage 46 is at an intermediate position between the two extremes of movement. To determine the position of the carriage 46, the carriage 46 is moved (by operating the motor 56) until one of the Hall effect sensors outputs a signal; this indicates that the carriage 46 is positioned at one of its extremes of movement. Starting from this known position of the carriage 46, the processor 202 counts the pulses output by the encoder 64 when operation of the motor 56 causes each subsequent movement of the carriage 46. The position of the carriage 46 can be derived from the number of pulses counted, and the position of the bobbins 22, 32 can be calculated from the position of the carriage 46 as so derived. Other suitable position sensors, such as micro switches, could be used instead of Hall effect sensors to detect the position of the carriage 46. In one example, the incremental encoder has a resolution of 1 ,000 pulses per revolution, which allows the carriage 46 to be positioned with an accuracy of 0.5 microns.

[0082] In an alternative implementation, the encoder 64 is an absolute encoder. In this implementation, the encoder 64 measures the absolute angular displacement of the rotor 62. The measurement signal output by the encoder 64 in this implementation is a binary word indicative of the absolute angular displacement of the rotor 62. The absolute encoder may be a single-turn encoder, in which the measurement signal is indicative of an angular displacement between 0 and 360°. Alternatively, the absolute encoder may be a multi-turn encoder, in which the measurement signal is indicative of an angular displacement between 0 and an upper value that is greater than 360°. The measurement signal output by an absolute encoder directly relates to the absolute position of the bobbins 22, 32. The position of the bobbins 22, 32 can be calculated from the most recent measurement signal from the absolute encoder.

[0083] A motor driver (not shown) may optionally be interposed between the controller 66 and the motor 56. The motor driver is configured to convert the motor control signal 67 output by the controller 66 into a signal meeting the current, voltage and / or timing requirements needed to cause the motor 56 to operate correctly.

[0084] The user input device 68 can be any suitable device that is configured to receive one or more inputs 69 from a user, and to convey those inputs 69 to the controller 66. For example, the user input device 68 may comprise a keyboard, a keypad, a touchscreen display, or one or more discrete buttons. The inputs 69 received via the user input device 68 may include, but are not limited to: an input indicative of a desired flow rate through the tube 10; an input indicative of desired occlusion of the tube 10; an override input to prevent the device 30 from switching from a second operating mode (as shown in Figure 10) to a first operating mode (as shown in Figure 9); an input indicative of an instruction to stop fluid flow through the tube 10; an input indicative of an instruction to disengage the bobbins 22, 32 from the flexible tube 32; and / or an input indicative of an instruction to resume fluid flow through the flexible tube 10.

[0085] The flow sensor 70 can be any suitable component that is configured to measure the flow rate of a fluid in the tube 10, and to output a flow rate signal 71 indicative of the measured flow rate to the controller 66. The flow sensor 70 may be a non-invasive flow sensor is fitted to an external surface of the tube 10, but which does not come into contact with the fluid within the tube. For example, the flow sensor 70 may be an ultrasonic sensor.

[0086] A first example of a method 900 of controlling fluid flow in a flexible tube using the device 30 is illustrated in Figure 9. The method 900 is performed by the processor 202 of the controller 66. For ease of reference, the method 900 of Figure 9 is referred to as the first operating mode of the device 30.

[0087] The method 900 begins at operation 902, at which a target angular displacement of the rotor 62 is determined. The target angular displacement is a desired angular displacement of the rotor, and may be chosen to achieve particular functionality (e.g., a particular flow rate through the tube 10). The target angular displacement of the rotor 62 can be determined in a number of ways.

[0088] In a first example implementation of operation 902, a user provides a user input indicative of a desired flow rate via the user input device 68. For example, the user may specify a desired flow rate of one litre per minute. The processor 202 then determines a target angular displacement of the rotor 62 that will result in the flow rate specified by the user. The processor may determine the target angular displacement based on the desired flow rate and a known relationship between flow rate in the tube 10 and angular displacement of the rotor 62. The known relationship may be stored in a look-up table in the memory 204. Alternatively or additionally, the known relationship between flow rate and angular displacement may be in the form of a parameterised model. In this case, the processor 202 calculates the target angular displacement based upon the desired flow rate as specified by the user, and any other values of the model’s parameters. The values of the model’s parameters may be input by a user via the user input device 68 and / or may be stored in the memory 204.

[0089] In a second example implementation of operation 902, a user provides a user input indicative of a desired occlusion via the user input device 68. The term “occlusion” is used herein to describe a numerical value representing a point on a continuum between the fully-open and fully-occluded configurations of the device 30. Occlusion may be expressed as a percentage. For the example, the user may specify a desired occlusion of 50%, which corresponds to a partially-occluded configuration halfway between the fully-open configuration shown in Figures 5a and 6a and the fully-occluded configuration shown in Figures 5c and 6c. The processor 202 then determines a target angular displacement of the rotor 62 that will result in the occlusion specified by the user. The processor may determine the target angular displacement based on the desired occlusion and a known relationship between occlusion and angular displacement of the rotor 62. The known relationship may be stored in a look-up table in the memory 204. Alternatively or additionally, the known relationship between flow rate and angular displacement may be in the form of a parameterised model. In this case, the processor 202 calculates the target angular displacement based upon the desired occlusion as specified by the user, and any other values of the model’s parameters. The values of the model’s parameters may be input by a user via the user input device 68 and / or may be stored in the memory 204.

[0090] The result of operation 902 is a target angular displacement rotor 62, which represents the angle of the rotor 62 with respect to an arbitrary datum that will achieve a particular functionality. For example, the target angular displacement may be determined to be thirty degrees clockwise with respect to the arbitrary datum.

[0091] The method 900 continues at operation 904, at which a measurement signal 65 is received from the encoder 65. The measurement signal 65 indicates the current angular displacement of the rotor 62. Continuing the earlier example, the measurement signal may indicate that the rotor 62 is currently oriented sixty degrees clockwise with respect to the arbitrary datum. The method 900 then proceeds to operation 906, at which the processor 202 outputs a motor control signal 67 to set the angular displacement of the rotor 62 as measured by the encoder 64 to the target angular displacement. Operation 906 may include the processor determining the motor control signal 67 needed to rotate the rotor 62 from its current angular displacement as measured by the encoder 64 to the target angular displacement. Continuing the earlier example in which the target angular displacement is determined to be thirty degrees clockwise with respect to the arbitrary datum and the rotor 62 is currently oriented sixty degrees clockwise with respect to the same arbitrary datum, the processor 202 determines that the rotor needs to be rotated thirty degrees anticlockwise. In a simplified example in which the motor 56 is a stepper motor with an angular resolution of one degree, the processor 202 may then determine that the motor control signal 67 should consist of thirty pulses to rotate the rotor 62 from its current angular displacement to the target angular displacement. The processor 202 then outputs the motor control signal 67 as thus determined.

[0092] The method 900 optionally then returns to operation 904, as indicated by arrow 908, at which another measurement signal 65 is received from the encoder 64. The processor 202 can then compare the actual angular displacement of the rotor 62, as measured by the encoder 64 after the motor control signal was output at operation 906, to the target angular displacement. If there is an error in the angular displacement of the rotor 62 (i.e., the actual angular displacement is not equal to, or not within a particular tolerance of, the target angular displacement) the method returns to operation 906 and outputs a further motor control signal 67 to correct the error. An error in the angular displacement of the rotor 62 may have a number of possible causes. One possible cause is motor slippage, which can result in the rotor 62 failing to reach the target angular displacement. Another possible cause is unintentional movement of the bobbins 22, 32, which may occur if a clinician inadvertently pulls the tube 10. The encoder 64 allows such errors to be detected and corrected, and thus provides accurate control over the flow rate through the tube 10.

[0093] At any time while the method 900 is being performed, the processor 202 may receive an instruction that requires it to determine a new target angular displacement of the rotor 62. For example, a user may provide a user input indicative of a new desired flow rate or a new desired occlusion via the user input device 68. In this case, the method returns to operation 902 and reiterates. In some cases, the processor 202 may receive an instruction to stop fluid flow through the tube 10 or an instruction to disengage from the tube 10 while performing the method 900. In these cases, the method returns to operation 902, whereupon the processor 202 determines a new target angular displacement of the rotor 62 that causes the device to be in the fully-occluded configuration (as shown in Figures 5c and 6c) or the fully-open configuration (as shown in Figures 5a and 6a), respectively. The processor 202 may subsequently receive an instruction to resume fluid flow through the tube 10. The method returns to operation 902, whereupon the processor 202 determines a new target angular displacement of the rotor 62 that thus sets the angular displacement back to its target angular displacement prior receiving the instruction to stop fluid flow or the instruction to disengage from the tube 10.

[0094] A second example of a method 1000 of controlling fluid flow in a flexible tube using the device 30 is illustrated in Figure 10. The method 1000 is performed by the processor 202 of the controller 66. For ease of reference, the method 1000 of Figure 10 is referred to as the second operating mode of the device 30.

[0095] The method 1000 begins at operation 1002, at which a target flow rate of a fluid in the tube 10 is determined. The target flow rate may be chosen to achieve a particular clinical result. For example, a user may provide a user input indicative of a target flow rate via the user input device 68.

[0096] The method 1000 continues at operation 1004, at which a flow rate signal 71 is received from the flow sensor 70. The flow rate signal 71 indicates the rate of fluid flow through the tube 10.

[0097] The method 1000 then proceeds to operation 1006, at which the processor 202 outputs a motor control signal 67 to set the flow rate as measured by the flow sensor 70 to the target flow rate. For example, if the flow rate as measured by the flow sensor 70 is less than the target flow rate, the processor 202 may output a motor control signal 67 that moves the bobbins 22, 32 towards the fully-open configuration. Conversely, if the flow rate as measured by the flow sensor 70 is greater than the target flow rate, the processor 202 may output a motor control signal 67 that moves the bobbins 22, 32 towards the fully-closed configuration. The processor 202 uses feedback from the flow sensor 70, as generally indicated by arrow 1008, to maintain the flow rate as measured by the flow sensor 70 at the target flow rate.

[0098] A third example of a method 1100 of controlling fluid flow in a flexible tube using the device 30 is illustrated in Figure 11. The method 1100 is performed by the processor 202 of the controller 66. The method 1100 of Figure 11 combines the first and second operating modes of the device 30.

[0099] The method 1100 may begin at operation 1102, at which the processor 202 causes the device 30 to operate in the first operating mode. That is, at operation 1102, the processor 202 performs some or all of the operations of method 900. Whilst operating in the first operating mode, the processor 202 may receive an instruction to operate in accordance with the second operating mode. For example, the user provide an input via the user input device 68 to direct the device 30 to operate in accordance with the second operating mode. In response to receiving the instruction to operate in the second operating mode, the method proceeds to operation 1104. The method 1100 need not begin at operation 1102, but could instead begin at operation 1104.

[0100] At operation 1104, the processor 202 causes the device 30 to operate in the second operating mode. That is, at operation 1 104, the processor 202 performs some or all of the operations of method 1000.

[0101] At operation 1106, the processor 202 detects failure of the flow sensor 70 while operating in the second operating mode. For example, the processor 202 may detect the absence of a signal from the flow sensor 70, which may occur if the flow sensor 70 is accidentally disconnected by a user. As another example, the processor 202 may detect anomalous measurement signals from the flow sensor 70, such as unexpectedly high or low measurements of flow rate, or rapidly varying measurements of flow rate.

[0102] In response to detecting failure of the flow sensor 70, the processor 202 determines (at operation 1108) whether an override input has been received. The override input is an input which instructs the processor 202 not to switch to the first operating mode when failure of the flow sensor 70 is detected. The override input may be provided by a user via the user input device 68. The control program 206 may have a default value stored therein which treats the override input as having being received, or having not been received, in the absence of a user input via the user input device 68.

[0103] If an override input has not been received, the processor 202 causes the device 30 to operate in the first operating mode. That is, the processor 202 reverts to operation 1102, whereupon it performs some or all of the operations of method 900. On the other hand, if an override input has been received, the device 30 continues to operate in the second operating mode. That is, the processor 202 reverts to operation 1104, whereupon it performs some or all of the operations of method 1000. The override input may be received at any time while the device 30 is operating in the second operating mode, so the processor 202 may cause the device 30 to switch to the first operating mode if failure of the flow sensor 70 is still detected during a subsequent iteration of operation 1106. Conversely, the override input may be cancelled at any time while the device 30 is operating in the first operating mode, so the processor 202 may cause the device 30 to switch back to the second operating mode when the failure of the flow sensor 70 has been resolved.

[0104] The device 30 can advantageously be incorporated into a cardiac perfusion system to control the flow rates of various fluids. Cardiac perfusion is a medical procedure involving extracorporeal oxygenation of a patient’s blood. Cardiac perfusion is performed, for example, when a patient is unable to oxygenate their own blood by breathing, such as during heart and / or lung surgery. An example of a cardiac perfusion system in which the device 30 can be used comprises a venous reservoir, one or more pumps, and an oxygenator. In use, the cardiac perfusion system receives deoxygenated blood from a patient via a venous line, and stores the deoxygenated blood in the venous reservoir. A pump drives deoxygenated blood from the venous reservoir and through the oxygenator. As blood passes through the oxygenator, gases dissolved in the blood (e.g., carbon dioxide) are exchanged with other gases (e.g., oxygen), so as to convert deoxygenated blood to oxygenated blood. The pump (or another pump) returns oxygenated blood to the patient via an arterial line. The cardiac perfusion system 100 may optionally further comprise any or all of: a cardioplegia device to stop the patient’s heart; a heater-cooler device to regulate the temperature of blood; and a gas blender to mix gases supplied to the oxygenator. A device 30 as disclosed herein can be positioned on any or all of the blood lines (e.g., the venous line and / or the arterial line) to control the flow rate of blood. Alternatively or in addition, a device 30 as disclosed herein can be positioned on a cardioplegia line to control the delivery of a cardioplegic agent.

[0105] It will be understood that the invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the claims. In particular, the sequence of operations shown in Figures 9, 10 and 11 are merely exemplary. Any of the operations shown in methods 900, 1000 and 1100 may be performed in a different order that achieves substantially the same result. The mechanical coupling between the rotor 62 of the motor 56 and the bobbins 22, 32 shown in Figures 1 to 6 is intended purely as an example, and other suitable mechanical coupling arrangements can be used. The profile of the bobbins 22, 32 is shown in Figures 1 to 6 is intended purely as an example, and bobbins 22, 32 having different shapes could be used to achieve different results (e.g., to provide a different relationship between the angle of rotation of the bobbins 22, 32 and the resulting occlusion of the tube 10).

Claims

CLAIMS1 . A device for controlling fluid flow in a flexible tube, the device comprising: two rotatable bobbins, each bobbin comprising a tube-engaging surface portion, wherein the tube-engaging surface portions define boundaries of a free space between the bobbins through which a tube may extend, and wherein at least one tube-engaging surface portion has a shape that changes around at least part of a circumference of the bobbin, such that axial rotation of the bobbins reduces the free space by an amount dependent on the rotation of the bobbins; a motor comprising a rotor, the rotor being mechanically coupled to the bobbins such that operation of the motor causes rotation of the bobbins; an encoder, the encoder being mechanically coupled to the rotor and configured to measure an angular displacement of the rotor; and a processor configured to determine a target angular displacement of the rotor, receive a measurement signal from the encoder, the measurement signal indicative of the angular displacement of the rotor, and output a motor control signal to set the angular displacement of the rotor as measured by the encoder to the target angular displacement.

2. A device in accordance with claim 1 , wherein the processor is further configured to: after the angular displacement of the rotor as measured by the encoder has been set to the target angular displacement, receive a second measurement signal from the encoder; identify, based on the second measurement signal, that the angular displacement of the rotor has drifted from the target angular displacement; and output a second motor control signal to reset the angular displacement of the rotor as measured by the encoder to the target angular displacement.

3. A device in accordance with claim 1 or claim 2, wherein the processor is further configured to: receive an input indicative of a desired flow rate; anddetermine the target angular displacement based on the desired flow rate and a known relationship between flow rate in the flexible tube and angular displacement of the rotor.

4. A device in accordance with any of the preceding claims, wherein the processor is further configured to: receive an input indicative of a desired occlusion of the flexible tube; and determine the target angular displacement based on the desired occlusion and the known relationship between occlusion of the flexible tube and angular displacement of the rotor.

5. A device in accordance with any of the preceding claims, wherein the device has a second operating mode in which the processor is configured to: determine a target flow rate of a fluid in the flexible tube; receive a flow rate signal from a flow sensor, the flow rate signal indicative of a flow rate of a fluid in the flexible tube as measured by the flow sensor; and output a third motor control signal to cause rotation of the bobbins to set the flow rate as measured by the flow sensor to the target flow rate.

6. A device in accordance with claim 5, wherein the processor is further configured to: detect failure of the flow sensor while the device is in the second operating mode; and in response to detecting failure of the flow sensor, cause the device to operate in a first operating mode in which the processor determines the target angular displacement of the rotor, receives the measurement signal from the encoder, and outputs the motor control signal to set the angular displacement of the rotor as measured by the encoder to the target angular displacement.

7. A device in accordance with claim 6, wherein the processor is further configured to cause the device to operate in the first operating mode by determining the target angular displacement based on the target flow rate and a known relationship between flow rate in the flexible tube and angular displacement of the rotor.

8. A device in accordance with claim 6 or claim 7, wherein the processor is further configured to: receive an override input; and in response to the override input, cause the device to operate in the second operating mode when failure of the flow sensor has been detected.

9. A device in accordance with any of the preceding claims, wherein the processor is further configured to: receive an instruction to stop fluid flow through the flexible tube; and in response to the instruction to stop fluid flow through the flexible tube, output a fourth motor control signal to set the angular displacement of the rotor as measured by the encoder to a second target angular displacement, wherein the second target angular displacement corresponds to a fully-occluded configuration of the device in which the bobbins maximally restrict the flow of fluid through the flexible tube.

10. A device in accordance with any of the preceding claims, wherein the processor is further configured to: receive an instruction to disengage from the flexible tube; and in response to the instruction to disengage from the flexible tube, output a fifth motor control signal to set the angular displacement of the rotor as measured by the encoder to a third target angular displacement, wherein the third target angular displacement corresponds to a fully-open configuration of the device in which the bobbins do not restrict the flow of fluid through the flexible tube.

11. A device in accordance with claim 9 or claim 10, wherein the processor is further configured to: receive an instruction to resume fluid flow through the flexible tube; and in response to the instruction to resume fluid flow in the flexible tube, output a sixth motor control signal to set the angular displacement of the rotor as measured by the encoder to the target angular displacement.

12. A cardiac perfusion system comprising a device for controlling fluid flow in accordance with any of the preceding claims.

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