Abstract:
A tubing installation checking device is provided for determining proper installation of a tubing along a tube receiving channel in a peristaltic pump of the type having a tube receiving channel and a door for holding a tubing therein. The tubing installation checking device includes a pressure sensor held in the peristaltic pump positioned along the tube receiving channel downstream from the pumping mechanism for sensing pressure in the tubing and for providing a signal representing the sensed pressure. A valve is provided held in the peristaltic pump along the tube receiving channel downstream from the pressure sensor for closing the tubing when it is installed in the tube receiving channel. A computer program is provided for closing the valve, for activating the pumping mechanism for a partial pumping stroke, for receiving a first pressure signal from said pressure sensor indicating the sensed pressure after the partial pumping stroke, for holding the pumping mechanism stationary during a predetermined period of time, for receiving a second pressure signal indicating the pressure in the tubing after the predetermined period of time, for comparing the first and second pressure signals to determine whether there is leakage in the tubing indicating improper tubing installation and if so for providing an alarm signal to indicate improper tubing installation.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to peristaltic pumps and in particular to a method and device for testing proper placement of a tubing in pumping engagement prior to operation of the peristaltic pump. 
     BACKGROUND OF THE INVENTION 
     In peristaltic infusion pumps, and in particular linear peristaltic infusion pumps, appropriate placement of a tubing upon which the pumping mechanism of the pump has in the past been a manual function accomplished by the pump operator. Accurate alignment and proper installation of the tubing has been a function of operator skill and care. Because the tubing is flexible it has been possible to insert the tubing improperly close the door or other tubing capture or holding mechanism and activate the pumping mechanism with the improperly installed or misaligned tubing. Although efforts are made to always properly insert the tubing and also to use only a proper size and pump compatible wall thickness tubing, poor alignment or installation of an improper tubing can result in a malfunction or inaccurately metered fluid flow. 
     SUMMARY OF THE INVENTION 
     A tubing installation checking device and a method is provided in a peristaltic pump having a tube receiving channel and a door for holding a tubing therein. The checking device and method are for determining proper installation of a tubing along a receiving channel canal in to which the tubing is inserted for pumping engagement with a pumping mechanism. The checking device comprises a pressure sensor held in the peristaltic pump so that the pressure sensor is positioned along the tube receiving channel downstream from the pumping mechanism for sensing pressure in the tubing and for providing a signal representing the sensed pressure. A valve is also held in the peristaltic pump along said receiving channel downstream from said pressure sensor for closing a properly installed tubing in the tube receiving channel. The method is effectively implemented by a computer program operatively coupled to the peristaltic pump for activating the valve to close off fluid flow through the tubing after the tubing is installed and the door is shut, for activating the pumping mechanism for a partial pumping stroke, for receiving a first pressure signal from said pressure sensor indicative of the sensed pressure after the partial pumping stroke, for holding the pumping mechanism stationary a predetermined period of time, and for receiving a second pressure signal indicative of the pressure in the tubing after the predetermined time period, and for comparing the first and second pressure signals to determine whether there is fluid flow leakage through the tubing. If there is leakage through the tubing, such leakage is an indication of improper tubing installation and the program activates an alarm signal to indicate such improper tubing installation. 
     In an enhanced version an initial pressure is sensed in the tubing as soon as the tubing is inserted, the door is shut and the downstream valve is activated to close the tube. Then the pumping mechanism is activated for a partial pumping stroke and the first pressure is measured. The initialization pressure is compared to the first pressure to see whether the first pressure is higher as expected for a properly installed tubing. If not an initial alarm signal is provided and the remainder of the testing need not be implemented. If the first pressure is higher than the initialization pressure, then the second pressure is sensed after the predetermined period. The second pressure is compared to the first pressure to determine whether there is any drop in the pressure to indicate leaking through the tubing. 
     The present invention provides a method and a device for testing the proper loading of tubing into a peristaltic pump. The apparatus comprises a peristaltic pump having a tubing channel and a closeable door by which a tubing is engaged in the tubing channel of the pump. A pressure sensor is positioned adjacent to the tubing downstream from the pumping fingers, and a shutoff valve is positioned for engagement against and closure of the tubing downstream from the downstream sensor. Upon engagement of the tubing and prior to pump operation, the downstream valve closes the tubing, and the pumping fingers are engaged against the tubing and moved forward, creating a trapped pocket of fluid in the tubing downstream from the pumping fingers and upstream from the closed valve. The forward movement of the pumping fingers is stopped temporarily, and the pressure of the fluid trapped in the tubing is monitored by the downstream sensor. If the pressure signal initially increases upon movement of the pumping fingers forward and then remains constant when the movement of the pumping fingers is stopped, a good seal, and therefore proper alignment of the tubing in the pumping channel, is indicated. If the sensed pressure either does not increase when the pumping fingers are moved forward or increases and then rapidly decreases, there is an indication that either the closure valve has not closed the tubing fully or the pumping fingers do not completely collapse the tubing such that a leak is detected, indicative of misalignment or improper installation of the tubing into the peristaltic pump. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other benefits and inventions can be more fully understood and a better understanding of this invention can be obtained when the following detailed description of the preferred embodiments is considered in conjunction with the following drawings in which like numbers represent like elements and in which: 
     FIG. 1 is a perspective view of a peristaltic pump of a type for which the present invention may be applicable, in this figure a linear peristaltic pump and a tubing to be installed are depicted; 
     FIG. 2 is a perspective view of the pump of FIG. 1 with the tubing shown properly inserted into the tube receiving channel ready for the door to be shut thereby retaining the tubing in proper installation. 
     FIG. 3 is a perspective view of the pump of FIG. 1 with the tubing shown improperly inserted into the tube receiving channel prior to the door being shut whereby the tubing would be held in a position improper for pumping engagement; 
     FIG. 4 is a schematic partial cross-sectional view through the pumping mechanism showing a pumping element in relation to a tubing partially compressed against a retractable platen held in a shut door; 
     FIG. 5 is a schematic perspective view depicting a partially constructed pump cam shaft with all of the plurality of pumping elements and reshaping fingers removed except one set for clarity; 
     FIG. 6 is a schematic exploded construction view depicting the partially constructed pump assembly of FIG. 5, again with all of the plurality of pumping elements and reshaping fingers removed except one set for clarity; 
     FIG. 7 is a schematic depiction of linear peristaltic pumping elements engaged at an initial pumping position against a tubing along a tube receiving channel; 
     FIG. 8 is a schematic depiction of linear peristaltic pumping elements as in FIG. 7 with the pumping elements advanced a few steps of pumping compression against the tubing from the initial position shown in FIG. 7; 
     FIG. 9 is a graphical depiction of pressure sensed in a tubing properly installed in a peristaltic pump, downstream from the pumping elements and upstream from a closed valve as a function of time during testing for proper tubing installation according to one embodiment of the invention; 
     FIG. 10 is a graphical depiction of pressure sensed in the tubing improperly installed in a peristaltic pump, downstream from the pumping elements and upstream from a closed valve as a function of time during testing for proper tubing installation according to one embodiment of the invention; 
     FIG. 11 is a schematic partial cross-sectional view depicting one possible improper tubing installation scenario where the tubing is outside of the tube receiving channel at the pumping mechanism; 
     FIG. 12 is a schematic partial cross-sectional view, similar to FIG. 4, showing a retractable platen in a position retracted against a spring through the actuation of retraction rod; 
     FIG. 13 is a perspective view of a partially constructed cam shaft assembly with the pumping elements removed to show a platen lift cam and retraction rod; 
     FIG. 14 is a perspective view of a cam shaft schematically depicting cam rotation for positioning various cam lobes in positions for testing and /or initial calibration prior to pumping operation; 
     FIG. 15 is a schematic depiction of pumping elements and platen lifted off from contact with the tubing for initial calibration of upstream and downstream pressure sensors; and 
     FIG. 16 is a schematic depiction of pumping elements and patent advanced against a tubing in a position for beginning pumping operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a perspective view of one embodiment of a peristaltic pump according to the present invention and in particular a linear peristaltic pump  10 . The pump  10  as depicted includes a pump body  12  having a door  14  pivotally attached as at hinges  15  and  16 , for closing against an interior face  28  of the pump body  12  as shown with assembly arrows  18 ,  19  and  20 . A flexible tubing  22  is depicted having a slide clamp  24  engaged there along to prevent fluid flow while tubing  22  is outside of the pump  10 . Tubing  22  is to be installed by placing it in and along an engagement pathway or tube receiving channel  26 . Tube receiving channel  26  is formed along the interior face  28  of the pump body  12 . The slide clamp  24  is inserted (as shown with assembly line  56 ) into automatic clamp mechanism  62  by which the slide clamp  24  is released and the pump controls opening and closing flow in tubing  22 . A pumping mechanism  30 , that includes in this embodiment an assembly of linear peristaltic pumping elements  32  and reshaping fingers  34 , is mounted in the pump body  12  positioned along channel  26  for receiving and for acting upon the tubing  22  in pumping engagement. It will be noted that the reshaping fingers  34  are the subject of another patent and though beneficial for reshaping the tubing during pumping operation, are not specifically required for the operation of the current invention. 
     When the tubing  22  is manually inserted into channel  26  (as shown by assembly line  58 ), the door  14  is closed shut as by pivoting about hinges  15  and  16  and latched against interior face  28 . The door  14  functions as a tubing holder to capture and hold the tubing  22  into channel  26 . Also shown is a retractable spring loaded platen  36  formed into and movably attached to the inside face  38  of door  14 . When door  14  is shut, platen  36  is positioned adjacent to the pumping mechanism  30  and is pushed by spring action against interior face  28 . Thus the platen  36  provides both the indicated tubing holding function and also provides a backing support surface for the pumping mechanism  30 . Door  14  may be latched into a closed position using latches  40 A,  40 B,  42 A and  42 B. Also an upstream pressure sensor  44  and a downstream pressure sensor  46  are positioned and attached to the pump  10  along the channel  26 , on either side of the pumping mechanism  30 . Upstream and downstream are determined with respect to the pumping direction of flow to the patient and the position of the sensor (or the valve as the case may be) relative to pumping mechanism  30 . Also held in door  14  are spring loaded pressure sensor supports, including upstream pressure sensor support  48  and downstream pressure sensor support  50 . According to the invention and as depicted in the embodiment of FIG. 1, there is a downstream valve  52  for selectively closing or opening fluid flow through the tubing  22 . The downstream valve  52  is downstream from both the pumping mechanism  30  and from the downstream sensor  46 . A spring loaded valve backing plate  54  is provided correspondingly positioned opposite from valve  52  at the inside face  38  of door  14 . The operation of the pressure sensors  44  and  46  and the operation of the valve  52  will be more fully discussed below. 
     FIG. 2 depicts the pump of FIG. 1 with the tubing  22  shown properly inserted into the tube receiving channel  26  ready for the door  14  to be shut thereby retaining the tubing in proper installation for pumping engagement with pumping mechanism  30  and for proper operation with valve  52  and pressure sensors  44  and  46 . 
     FIG. 3 is a perspective view of the pump  10  of FIG. 1 with the tubing  22  shown improperly inserted and partially out of the tube receiving channel  26  prior to the door  14  being shut, whereby the tubing  22  would be improperly installed as it would be held in a position that is not proper for pumping engagement. In this depiction of an improperly installed tubing  22 , such tubing  22  is shown out of tube receiving channel  26  at a portion of its length adjacent to pumping mechanism  30 . It will be understood that the flexible tubing  22  might also be outside of channel  26  elsewhere along its length. It might also be understood that tubing  22  might be kinked. Further it will be understood that an improper installation might include installing a tubing  22  that was too small in diameter or that had a wall thickness that was too thin or a wall thickness that was too thick for proper pumping engagement. All of these and other improper installations of tubing into a peristaltic pump might be detected according to the present invention. 
     FIG. 4 depicts a schematic partial cross-sectional view of pumping mechanism  30  in relation to a tubing  22  partially compressed against the retractable platen  36  held in door  14 . One of a plurality of pumping elements  32 , is shown in this embodiment as a reciprocally moveable rectangular shaped plate. According to this embodiment of the invention applied to a linear peristaltic pump  10 , pairs of reshaping fingers  34   i  and  34   ii  are shown pivotal attached and activatable into and out of reshaping contact with the tubing  22 . The reciprocal movements of adjacent pumping elements  32  activate the reshaping contact. The reciprocation position of the pumping element  32  in FIG. 4 corresponds generally to a position with pumping element  32  partially compressed against tubing  22 . The amount of compression is controlled according to the rotation position  297  of cam lobe  262 . It can be seen that pumping element  32  has a flat top surface  230 . Flat top surface  230  is parallel to the backing support surface provided by platen  36 . 
     It will be understood that a plurality of side by side pumping elements  32  are aligned along the tube receiving channel  26  and are activated by a plurality of corn lobes driven by a cam shaft  260 . Each cam lobe  262  is off-set from the next cam lobe sequentially compress tubing  22  against platen  36  to force fluid there through. The fluid is moved ahead of the sequentially compressing pump elements  32  in a direction downstream from the portion of the tubing  22  that at any given time is fully compressed by at least one of the pumping elements  32 . Behind the fully compressed portion of the tubing  22 , the pumping elements  32  sequentially retract to allow new fluid to enter into the tubing  22 . The reshaping fingers  34   i  and  34   ii  are shown in a position partially engaged with the sides of flexible tubing  22 . The respective reshaping jaws  232   i  and  232   ii  contact and reshape the tubing  22  as pumping elements  32  retract from compressing the flexible tubing  22 . This motion of the reshaping fingers  34   i  and  34   ii  is automatically accomplished using projection  293  having angled surface  294  and projection  295  having angled surface  296  formed on pumping element  32 . A third projection  297  centrally located on pumping element  32  provides angled surface  298  and angled surface  299 . The projections  293 ,  295  and  297  have approximately the same thickness as reshaping fingers  34   i  and  34   ii  and with their angled surfaces together form actuator channels  280   i  and  280   ii  which act against portions  282   i  and  282   ii  of reshaping fingers  34   i  and  34   ii . Thus reshaping fingers  34   i  and  34   ii  are pivoted on pivot connector rods  256   i  and  256   ii  as the next adjacent pumping element  32  reciprocates compressing tubing  22  and retracting from tubing  22  in pumping action. The pumping element  32  shown in FIG. 4 is one of a plurality of pumping elements  32  and corresponding sets of reshaping fingers  34  held in the pumping assembly  30  within rectangular housing  56 . The pumping element  32  also has slots  266   i  and  266   ii  formed to accommodate guided reciprocal motion relative to the connection pivot rods  256   i  and  256   ii.    
     Other features of construction maybe further understood with reference to the schematic prospective view in FIG. 5 depicting a portion of pump  10  including a camshaft  260 , a mount  271  for motor  270 , one of the plurality of pumping plates  32  and one pair of the plurality of reshaping fingers  34  attached along connection rods  256   i  and  256   ii . The other structure comprising pump  10  has been removed from view in FIG. 5 for clarity of understanding. 
     Further details of the structure according to FIG. 5 may also be understood with reference to FIG.  6 . FIG. 6 is a schematic exploded assembly view of that portion of the pump  10  that is depicted in FIG.  5 . Again the multiple pumping elements and reshaping fingers are represented with only one set for clarity. It will be understood that each of the plurality of cam lobes  262  will engage a pumping element  32  and a corresponding set of reshaping fingers  34   i  and  34   ii.    
     It has been found that before pumping operation is activated it is desirable to run the inventive proper tubing installation testing method and certain other initial tests. For purposes of demonstrating the inventive test to determine whether the tubing  22  is properly installed, reference may be had to both FIG.  4  and FIG.  7 . In FIG. 7 a portion of the components of a linear peristaltic pump are schematically depicted as they engage the tubing  22 . In this view the plurality of pumping elements  32  comprise twelve pumping elements that are separately labeled with reference numbers  191  through  202 . As an advantageous starting point for such initialization test, the cam lobes  262  are rotated to a position for initiation of a pumping stroke. This position is shown in FIG. 7 with pumping elements  192  and  193  in the full pumping extension so that elements  200  and  201  are open and pumping elements  192  and  193  are closed. The tubing  22  is loaded into the tube receiving channel  26 , the door  14  is shut, as shown in FIG.  4 . The downstream valve  52  remains closed or is activated to a closed position and the platen  36  is extended to abut against tubing  22  in a pumping position. The platen  36  is biased by spring  235  into its pumping engagement position against the interior face  28  of door  14 . Such an initial pumping position is schematically depicted in FIG.  7 . 
     In one embodiment of the invention, the pumping mechanism  30  is moved forward a few degrees of rotation or a portion of a step or a few steps of pumping element compression, as schematically depicted in FIG.  8 . As shown schematically in FIG. 8, pumping elements  194  and  195  become fully extended compressing against tubing  22  if it is properly installed. Although the pumping elements are advanced forward a significant amount in the schematic depiction of FIG. 8 (corresponding to about 60 to 90 degrees of rotation), it will be understood that the actual amount of forward rotation may be a much smaller amount depending upon the sensitivity of the sensor  42  and so that the pumping mechanism is not damaged by an excessive amount of pressure build-up in tubing  22 . A first test pressure P 1  is advantageously sensed as soon as the predetermined forward rotation is stopped. The pumping mechanism is then held without rotation for a predetermined length of time and a second test pressure P 2  is sensed at the downstream pressure sensor  46 . The magnitude of the first pressure P 1  is compared to the magnitude of the second test pressure P 2 . If there is leakage through the tubing  22  at either the pumping mechanism  30  or at the valve  52 , the second test pressure P 2  will be lower than the first test pressure P 1 , thereby indicating improper tubing installation. An alarm will be activated if the first test pressure P 1  and the second test pressure P 2  are found to be different. If the first and second test pressures P 1  and P 2  are the same, there is no indication of an improper tubing installation. 
     In another embodiment, after the tubing  22  is loaded, the door  14  is shut, the platen  36  is extended, and the downstream valve  52  is closed, an initial short time period may be permitted to allow the pressure to stabilize. The initial pressure P(i) in tubing  22  is then sensed at downstream sensor  46  after the short time period for stabilization. This may be further understood referring to FIG. 9, which is a graphical depiction of the sensed test pressure measurements as a function of time. The initial time period to allow the pressure to stabilize is shown as the period from t1 to t2. An initialization test pressure is then sensed in the tubing  22  by sensor  46  at time t2. This initialization test pressure corresponds to the pressure P(i) shown at t2 in FIG.  9 . After the initialization test pressure P(i) is sensed at t2, the pump is then rotated forward a few degrees of rotation (again represented by several steps of pumping element compression) during a period of time t2 to t3 shown in FIG.  9 . The pumping mechanism  30  is then stopped. Again, as shown schematically in FIG. 8, pumping elements  194  and  195  are fully extended compressing against tubing  22 . The first test pressure P 1  is advantageously sensed at t3 as soon as the predetermined forward rotation is stopped. 
     In this embodiment a first test pressure P 1  is sensed at t3 and is compared to the initialization pressure P(i) to determine whether the first test pressure P 1  is higher than the initialization pressure P(i). Where the tubing is properly installed there will be a pressure build-up between the pumping elements and the closed downstream valve  52 . If the first test pressure P 1  is not higher than initialization pressure P(i), an alarm is signaled, to indicate at least one condition of improper tubing installation. For example if the tubing  22  is positioned entirely outside of the tube receiving channel  26  so that either the pumping mechanism  30  does not engage the tubing or the valve  52  does not engage the tubing, a pressure increase from time t2 to time t3 might not be sensed. When there is no sensed pressure increase resulting from the partial forward pump rotation, an alarm is signaled and the test may be stopped to allow the operator to correct the improper installation. 
     If the first test pressure P 1  at t3 is higher than the initialization pressure Pi at t2, the test continues to determine whether another improper installation condition exists. The pumping mechanism is then held without rotation for another predetermined length of time t3 to t4. At time t4, a second test pressure P 2  is sensed at the downstream pressure sensor  46 . The magnitude of the first pressure P 1  is compared to the magnitude of the second test pressure P 2 . If the tubing is properly installed there will be no leaking and the pressure will hold so that P 2  will be equal to P 1  as shown in FIG.  9 . If the first and second test pressures are the same there is no indication of an improper installation. If there is a leak at either the pumping mechanism or at the valve  52 , the second test pressure will be lower than the first test pressure indicating improper tubing installation as shown graphically in FIG.  10 . Thus an alarm will be signaled if the first test pressure P 1  and the second test pressure P 2  are found to be different. 
     In yet another embodiment, the pressure in the tubing  22  maybe continuously monitored over the test time periods. When the monitored pressure is stabilized, the pumping mechanism may be advanced. If the monitored pressure increases either after a predetermined amount of forward pump rotation or after a predetermined increase in the monitored pressure, the rotation can be stopped. the pressure continues to be monitored. If there is no increase in the monitored pressure, an alarm may be signaled to indicate improper tubing installation and to allow correction. If pump rotation is stopped without an alarm signal the pressure continues to be monitored either over a predetermined period of time to determine if a constant pressure is maintained or until there is a sufficient drop in the monitored pressure to indicate a leak and thus to indicate improper installation of the tubing. If the pressure does not hold, an alarm will be signaled to indicate the improper installation condition and to allow the operator to correct the condition before pumping continues. Thus, by monitoring the pressure continuously over the test period, the total time required to find an improperly installed tubing condition might be shortened where a significant amount of leakage is detected very quickly. 
     One example of a misaligned tubing  22  is depicted in the perspective view of FIG. 3 and a corresponding side cross-sectional view FIG.  11  . In the instance of such misalignment the tubing position may be such that the platen  36  is held away from its proper position against the interior face  28  when the door  14  otherwise appears to be properly closed. In this situation the pumping elements  32  would not fully collapse the tubing  22 . In an alternative example of an improperly loaded tubing, the valve  52  might not fully close the tubing. In either of these situations, leakage through the tubing should be indicated by the inventive testing mechanism and method. If there is a large amount of leakage or if the sensor  46  is not in contact with the tubing, the pressure will not increase significantly from a first test pressure P 1  to a higher second test pressure P 2 . If there is only a small amount of leakage through the tubing  22  at either the pumping elements  32  or at the valve  52 , a significantly higher second pressure P 2  might be reached, however the higher pressure will not be held steady for any significant amount of time. Thus, if P 1  is approximately equal to P 2  or if P 2  decreases during the holding period, an alarm will be sounded, and the pump will be inactivated until the improper installation of the tubing is corrected. 
     In a situation where a tubing is too large, the improper size will likely be noticed before the door is closed because the size of channel  26  will not allow a significantly larger tubing to be inserted. If the tubing is small enough to fit into the channel  26  yet too large to allow proper closure by valve  52  or by pumping elements  32 , the inventive proper tubing installation testing device and method will detect leakage. If the tubing is much too small it might also be noticed visually or it will be seen that no pressure will be built up during the proper installation pressure testing sequence. In the situation where the tubing is only slightly too small, or the wall thickness is not compatible with the pumping mechanism, the last part of the proper installation test will likely fail because the tubing will not be fully collapsed by either the valve  52  or by the pumping elements  32 . Thus, the second test pressure P 2  will not hold during the last part of the test. Such a situation will not be correctable by simply realigning the tubing and the operator, after a repeated failure of the proper installation test, may be prompted to check the tubing size. 
     In an additional calibration stage, preferably with the knowledge that the tubing  22  is properly installed as determined above, the upstream pressure sensor  44  should be calibrated to the downstream pressure sensor. To do this, the tubing  22  should be completely open and not compressed by the pumping elements. FIG. 12 depicts a schematic partial cross-sectional view similar to FIG. 4 showing retractable platen  36  in a position retracted against spring  235  through the actuation of retraction rod  237 . The retraction rod  237  acts against one end of platen  36  with an opposite end of platen  36  pivotally connected at  239  to door  14 . Thus, retraction rod  237  pushes platen  36  off of flexible tubing  22 . It is noted that platen  36  is pushed off of tubing  22  regardless of the pumping position of cam lobes  262  or the position of any of the plurality of pumping plates  32 . Platen  36  is pushed or lifted a sufficient distance to allow flexible tubing  22  to become open through the resilience of flexible tubing  22 . Platen  36  is also a part of a slidable platen safety housing  58  that is strongly biased to a desired position, as with bias spring  60 . If the magnitude of force on the platen  36  is too large and greater than the amount of force require for complete compression of spring  235 , then damage is avoided by sliding movement of the platen into the safety housing  58  against the strong bias spring  60 . 
     FIG. 13 schematically depicts the pumping camshaft  260  and the drive motor  270  as well as the platen  36 , the actuating rod  237  and a platen lifting assembly. The platen lifting rod  237  is connected to a lever  233  that pivots at  231  in response to a cam follower  229  actuated by a lift cam  227 . Lift cam  227  is mounted through a one-way clutch assembly  250  to camshaft  260 . Thus reverse rotation of motor  270  is required to engage clutch  250  and thereby rotate lift cam  227 . Similarly cam lobes  262  are mounted to cam  260  through a one-way clutch mechanism  261  that engages only in the forward motor rotation direction, (opposite direction from engagement of clutch  250 ). Thus, reverse rotation to engages clutch  250  and disengages rotation of cam shaft  260  and cam lobes  262 . 
     The purpose of retracting platen  36  is, in part, to calibrate the pump signals from sensors  44  and  46  as will be more fully understood with reference to FIGS. 13 and 14. FIG. 14 is a schematic perspective depiction of the camshaft  260  with a lifting cam  227  as well as lifting cam index wheel  249  and volume equalization timing wheel  300 . For purposes of clarity of explanation, the convention will be adopted herein to consider forward motor rotation as counter-clockwise rotation viewing the camshaft  260  from the left hand side of FIGS. 13 and 14. According to this convention the pumping cam lobes  262  are driven with counter-clockwise rotation of motor  270  and of camshaft  260  and the platen lifting cam  227  is driven with clockwise rotation of motor  270  and correspondingly camshaft  260 . In FIG. 14 the rotation arrow  252  depicts clockwise rotation. Preferably, when the pump is initially started, and each time the door  14  is opened and then shut, an automatic initialization procedure is undertaken including testing for proper tubing installation and then calibration of the pressure sensors  44  and  46 . This will include clockwise rotation of cam  260 , engaging clutch  250 , and rotating platen cam  227  until the index notch  251  of index wheel  249  is in a proper position for raising cam follower  229  thereby actuating lever arm  233  to pivot lift actuator  237  against platen  36 . In FIG. 14 clockwise rotation as a arrow  252  causes clutch  250  to engage platen cam  227 . Clockwise rotation continues only until notch  251  of index wheel  249  is located at the proper platen liftoff position. 
     FIG. 15 schematically depicts a lifted platen  36  so that tubing  22  is opened entirely along the pumping mechanism. The tubing  22  is released regardless of the position at which the operation was stopped. Thus, for example as in FIG. 15 where the pumping plates  200  and  201  are in a down position so that tubing  22  would normally be closed if platen  36  was not lifted, the tubing  22  becomes opened as shown. With the platen  36  lifted, the valve  52  is also brought to a closed position pushing against spring loaded back plate  54 . With the tubing  22  closed downstream from both pressure sensors  44  and  46  and with the tubing  22  opened there between, the pressure inside of tubing  22  corresponds to the upstream pressure normally determined by the head height of a medical solution bottle or reservoir (not shown). Pressure sensors  44  and  46  may be constructed as strain gauge sensors such that the pressure inside of flexible tubing  22  corresponds to the expansion or contraction of tubing  22  relative to its normal size due to increased or decreased pressure of the fluid inside. With backing plates  48  and  50  biased against fixed surfaces on the face  28  of pump  10 , the expansion of tubing  22  due to internal pressure maybe accurately measured with sensors  44  and  46 . By equalizing the pressure inside of tubing  22  at both the upstream pressure sensor  44  and at the downstream sensor  46  and without any pumping action taking place, the sensory input from  44  may be equalized with the sensory input of  46 . Thus the operational relative pressure detected after the initial equalization will be accurately reflected both with respect to upstream sensor  44  and downstream sensor  46 . 
     Reverse direction rotation is initiated in camshaft  260  such that a clutch is engaged for forward (counter-clockwise) rotation of camshaft  260 . Thus, through the use of a timing wheel  300  and appropriate one direction clutches, the cam lobes  262  can be conveniently brought to desired positions for testing proper tubing installation and for calibration of the pressure sensors. 
     When the installation testing and the sensor calibration is completed, to begin pumping the mechanism is moved in reverse the final quarter of rotation. Thus, to initialize pumping the motor  270  rotates again in a reverse direction about ninety degrees of rotation so that platen lift cam  227  and downstream valve cam  52  both move to the opposite positions as shown in FIG.  16 . This advances the platen  36  against tubing  22  so that platen  36  abuts by strong spring tension against face  28 . Also downstream valve  52  is opened through the action of cam  253  so that tubing  22  is open downstream from the pumping mechanism  30  and fluid pumping may begin. 
     Other alterations and modifications and equivalents of the invention and its elements will likewise become apparent to those of ordinary skill in the art upon reading the present disclosure, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventors are legally entitled.