in the present invention , a tube clamp is remotely actuated by a driver via a bowden cable . in addition , an electrical continuity detector monitors an insulating layer within the bowden cable to provide an indication of wearing of the layer . fig1 illustrates a system 10 for controlling the flow rate of medical fluids transported in flexible tubing . system 10 broadly includes a slidable clamp 11 , a flexible tube 12 , a bowden cable 13 , a driver 14 , and an electrical continuity detector 15 . bowden cable 13 is coupled on one end to actuator 11 and on its other end to driver 14 . mechanical pushing or pulling forces are generated by driver 14 and transmitted by bowden cable 13 to slidable clamp 11 . slidable clamp 11 applies a variable compressive force on tube 12 . the compressive force applied to tube 12 deflects tube 12 to create an occlusion which constricts or fully blocks the flow of medical fluids in tube 12 . electrical continuity detector 15 is in electrical communication with elements of bowden cable 13 in order to provide a wear status indication of bowden cable 13 as described below . fig2 is shown as a cutaway to illustrate the internal elements of bowden cable 13 . an inner wire 21 may be comprised of a single solid body or may include a plurality of twisted strands to form a wire rope . the solid body or strands are made of a conductive metal such as steel . one or both ends of inner wire 21 may include a nipple ( not shown ) for attaching to other components . inner wire 21 is coaxially disposed within an outer casing that includes a spiral wound casing member 23 and a protective housing 24 . member 23 is made to be substantially incompressible in an axial direction but flexible in a lateral direction . one of ordinary skill in the art will recognize casing member 23 can be constructed in various ways . instead of the rectangular wire shown in fig2 , a steel wire with a round or other cross section can be used . instead of a single spiral , the coiled casing member 23 could include multiple spiral strands woven together . a seamless tubular metal material could also be used . between inner wire 21 and casing member 23 is an insulating layer in the form of a cylindrical plastic sheath 22 . in operation , casing member 23 is rigidly secured on each of its ends , while inner wire 21 is freely slidable along its longitudinal axis with respect to the outer casing . the axial movement of inner wire 21 in relation to casing member 23 enables bowden cable 13 to transmit mechanical pushing and pulling forces . insulating layer 22 is disposed between inner wire 21 and outer casing 23 for the purpose of reducing friction , but it also acts as an insulating barrier between inner wire 21 and outer wire 23 . insulating layer 22 is made from a material that is not electrically conductive such as vinyl or other polymeric material . rather than a separate tubular sheath as shown in fig2 , layer 22 may alternatively be comprised of a coated layer of insulating material applied to either the inner surface of casing member 23 as shown at 25 or the outer surface of inner wire 21 as shown at 26 . fig3 illustrates the concentration of wear in an area 27 where the bowden cable bends . along the inner radius of a bend , inner wire 21 has its most forceful contact with sheath 22 . as sheath 22 becomes worn away , increasing exposure of inner wire 21 to casing member 23 results . sliding friction of inner wire 21 goes up while electrical continuity between inner wire 21 and casing member 23 goes up ( i . e ., electrical resistance goes down ). fig4 shows the wear detection of the invention in greater detail . inner wire 21 of bowden cable 13 is coupled to driver 14 . driver 14 may use various mechanisms for applying motive force to inner wire 21 such as a rotary spindle coupled to a stepper motor , a linear motor , a double acting fluid mechanical cylinder and so on . since insulating layer 22 electrically isolates inner wire 21 and casing member 23 , the physical integrity of insulating layer 22 can be detected by examining the electrical continuity between inner wire 21 and casing member 23 as measured by electrical continuity detector 15 . detector 15 is electrically connected to casing member 23 and inner wire 21 in any suitable manner . since inner wire 21 is movable , it is preferable to make a fixed connection to a portion of inner wire 21 that is inside the housing of driver 14 where there is no interference with its movement into the outer casing . the connection to casing member 23 may preferably be made by a standalone connection just outside the housing of driver 14 . detector 15 measures an electrical property between inner wire 21 and casing member 23 , and when the measured property corresponds to a continuity greater than a threshold ( e . g ., a resistance in ohms less that a predetermined resistance ), then a warning signal 17 is generated . the electrical continuity between the inner wire and the casing member can be measured according to electrical properties other than resistance , such as capacitance or inductance . warning signal 17 may be in the form of the turning on of a warning light or may be a communicated signal that is sent to an electronic control system , for example . fig5 illustrates the monitoring and eventual decline of the physical integrity of the insulating layer of a bowden cable as a function of time . the y - axis of the graph in fig5 is a scale of electrical continuity . the x - axis is time , such as hours of operation of a bowden cable . the electrical continuity detector of the present invention measures the continuity of the insulating layer and compares it to a threshold level . the measured continuity of the insulating layer as a function of time is represented by line 31 in fig5 . line 32 represents a threshold level of continuity which is established to correspond to the level of continuity at which the insulating layer has failed or is close to failure . the threshold level may be determined empirically by experimentation . in an undamaged bowden cable the electrical resistance of the insulating layer is high , as shown by line 41 at “ t = 0 ” on the left side of the graph in fig5 . with use , the friction from the sliding of the bowden cable &# 39 ; s inner wire will induce wearing of the insulating layer so that its thickness decreases at one or more places . the resistance of the thinning insulating layer is reduced as shown by the decline in line 31 going from left to right on the graph . at a point 33 , the resistivity of the insulating layer has declined to the extent that it is equal to the threshold value represented by line 32 . point 33 represents the decline in the physical integrity of the insulating layer to the extent that the bowden cable should be repaired or replaced . fig6 illustrates an adapter 35 for connecting a bowden cable with devices at its terminations , such as a driver housing . a socket 36 receives an end of the outer casing . socket 36 and the outer casing may be threaded in order to attach them by screwing them together . crimping or adhesives could also be used . adapter 35 is formed of an insulating material , such as a plastic , in order to maintain the electrical isolation of the inner wire from the outer casing member . a passage 37 receives the inner wire which then passes into the device , such as the driver , where it is attached to one of the moving structures in the system . in order to adjust the effective length of the outer casing and thereby the tension or travel path of the inner wire , a barrel adjuster ( not shown ) or other adjustable feature may be incorporated into adapter 35 or placed at some other location , provided it maintains the electrical isolation between the inner wire and the casing member . while the invention has been described in reference to a preferred embodiment of a medical fluid tube clamp remotely actuated by a driver via a bowden cable with an electrical continuity detector to monitor the integrity of an insulating layer within the bowden cable , it should be understood by those skilled in the art that the essence of the invention may also be applied to other medical and non - medical devices . in addition , various changes may be made and equivalents may be substituted for elements thereof without departing from the essential scope of the invention . therefore , it is intended that the invention not be limited to the particular embodiment disclosed herein , but that the invention will include all embodiments falling within the scope of the claims .
a system for clamping a flexible tube containing medical fluids includes a cable assembly coupled to a remote driver and a slidable clamp that imparts a clamping force to the flexible tube . an electrical continuity detector is included to measure the wear of an internal insulating layer of the cable between a sliding inner wire and a cable casing member . an indication of the wear to the cable is generated in response to a comparison of the electrical integrity of the insulating layer with a threshold . the wear indication enables the cable to be repaired or replaced prior to a malfunction of the overall tube clamp system .