the controller 10 of fig1 includes the back panel 11 attached to its casing which consists of the top 12 , the sides 13 and 14 , the front 15 , and the bottom 16 . at the front 15 appear the on - off switch 19 and a weak - battery indicator and rate - selection switches which the figure does not show . however , the cover 20 for the rotary selection switches appears behind the front panel 15 . behind the front panel 15 appears a z - shaped metal bracket 23 . the screws 24 hold the front leg 25 of the z bracket 23 to the front panel , receiving the assistance of the posts 26 in this task . the screw 28 , along with an additional screw beneath it , similarly holds the back leg 29 of the z bracket 23 to the front panel 15 . the post 30 extends from the front panel 15 to the screw 28 to provide an attachment for the latter to the former . the front panel 15 of the controller 10 has the opening 31 into which can fit a casette . the casette generally has a greater height than does the controller . moreover , the connections leading to and from the casette extend out of the controller &# 39 ; s top and bottom , respectively . accordingly , an opening 33 in the bottom 16 and a similar opening 34 in the top 12 ( seen in fig2 ) allow for the insertion of the casette into the controller 10 through the front panel 15 . as shown in fig1 the opening 33 in the bottom panel 16 has a shape of an inverted &# 34 ; l .&# 34 ; the lateral leg of the l - shaped opening permits the movement of the casette from the left to the right . the opening 34 in the top panel 12 has the same shape as the bottom panel &# 39 ; s opening 33 . as the casette enters the controller 10 through the front panel 15 , it snugly fits between the metal plate 37 and the upper arm 38 . as shown in fig2 the lower arm 39 sits below the upper arm 38 and also serves to orient the casette . moreover , as discussed below with regards to fig4 the two arms 38 and 39 fit snugly around a protuberance on the casette to orient the latter in a vertical direction . the plate 37 and the arms 38 and 39 form part of a single metal holder . they connect together through the back piece 40 which also has the upper leg 41 and the bottom leg 42 . the top of the upper leg 41 sits inside of a groove provided in the upper track 44 . as seen in fig2 the track 44 has the thick , short section 45 which sits in front of the upper leg 41 . the screws 47 retain the upper track 42 to the back leg 29 of the z bracket 23 . similarily , the lower leg 42 sits in a groove formed in the lower track 49 . similar to the upper track 44 , the lower track 49 includes the short thick section 50 which sits in front of the lower leg 42 . its thin , long section 51 sits behind the lower leg 42 . the screws 52 attach the lower track 49 to the back leg 29 of the z bracket 23 . the grooves in the tracks 44 and 49 allow the upper and lower legs 41 and 42 to slide to the left and right in fig1 to 3 . since the legs 41 and 42 must slide to the right and left in the tracks 44 and 49 , they should encounter the minimum possible resistence as they do so . correspondingly , the tracks 44 and 49 may assist this objective by having a composition of a low - friction material such as teflon ® ( manufactured by e . i . du pont de nemours & amp ; co ., wilmington , del . the legs 41 and 42 move laterally , as does the entire metal holder 54 which includes the legs 41 and 42 , the back piece 40 , the plate 37 and the arms 38 and 39 . when the metal holder 54 occupies its leftward position shown in fig1 and 2 , it allows for the insertion of a casette between the plate 37 and the arms 38 and 39 . when the metal holder 54 has moved furthest to the right as in fig3 it places a casette in the position where the controller 10 may open and close the casette &# 39 ; s valves . furthermore , with the holder 54 in the position of fig3 a casette cannot move towards the front or the rear of the controller 10 . the shape of the openings 33 and 34 in the bottom 15 and the top 11 , respectively , prohibits this latter type of motion . preventing the casette from moving forward or backward has particular importance when the casette occupies the position that the holder 54 in fig3 would place it . there , the casette would engage the alignment pins 57 and 58 as well as the inlet valve member 59 and the outlet valve member 60 . moving the casette forward and back while engaged with these items could damage the casette and possibly the components of the controller . where the holder 54 occupies the position of fig2 and retains a casette , neither the alignment pins 57 and 58 nor the valve members 59 and 60 can engage the casette . however , the openings in the casette which engage these components fall on straight lines passing through the components &# 39 ; individual centers . moreover , each of the valve members moves along the same line that leads to the appropriate opening in the casette . to provide its motion to the right and left , the metal holder 54 has the slotted opening 63 in its bottom piece 40 . the pin 64 extends into the slot 63 and contacts its sides . in turn , the pin 64 rigidly attaches to the circular disc 65 which may rotate about its center . most of the back of the disc 65 has a flat configuration which lies against the back leg 29 of the z bracket 23 . the shaft 66 , shown in fig1 passes through the back leg 29 of the z bracket 23 and rigidly adjoins the circular disc 65 . in fact , the disc 65 and the shaft 66 may simply form part of a single piece . turning the shaft 66 thus has the effect of rotating the disc 65 . moreover , the knob 57 , located on the outside of the back panel 11 , attaches firmly to the shaft 66 to allow for the manual rotation of the latter . the end of the shaft 67 closest to the disc 65 has screw threads formed on it . this allows for the attachment of the bolt 68 on the side of the bracket &# 39 ; s leg 29 opposite the disc 65 . the bolt 68 thus presses the washer 69 and 70 against one side of the leg 29 of the z bracket 23 and holds the disc 65 against the other side of the leg 29 . consequently , the bolt 68 and the washer 70 keep the disc 65 pressed against the back leg 29 in the position shown in fig2 and 3 . forming the washer 70 and the disc 65 of a low - friction material , such as teflon ®, allows them to rotate relative to the back plate 29 although the bolt 68 firmly squeezes them against it . rotate they must in order to move the holder 54 to the right and left which carries the casette from its insertion position to its operational position . specifically , after placing the casette between the plate 37 and the arms 38 and 39 , the casette and , thus , the holder 54 , must move to the right as seen in fig1 through 3 . to accomplish this , the operator turns the knob 67 to the right ( in fig1 ). this rotates the shaft 66 in the same direction and results in a clockwise rotation of the disc 65 . as the disc 65 begins to rotate , the pin 64 moves initially towards the top of the slot 63 . however , the rotation of the disc 65 causes it to contact and bear against the right side of the slot 63 . further clockwise rotation of the disc 65 forces the pin 64 to push against the right side of the slot 63 and move the holder 54 to the right . during the first half of the journey of the holder 54 from the position of fig2 to that in fig3 the pin 64 moves towards the top of the slot 63 and very nearly reaches it . during the second half of the journey , the pin 64 continues to move to the right . however , it now travels downward in the slot 63 . at the end of the journey , the pin 64 has moved the holder 54 to the position shown in fig3 . once again , however , it has a location at the bottom of the slot 63 . removing the casette from the controller 10 reverses the process which places the casette in its operational position described above . first , the attendant rotates the knob 67 to the left in fig1 . this induces a counterclockwise rotation of the disc 65 . the pin 64 , attached to the disc 65 , begins to rise in the slot 63 . it also contacts the left side of the slot 63 and moves the holder 54 to the left . for a while , the pin 64 continues to rise in the slot 63 while it moves the holder 54 to the left . subsequently , however , the pin 64 descends in the slot 63 until the holder 54 has reached the left position . when the holder 54 returns to the position shown in fig1 and 2 , the attendant may again disengage the casette and the controller from each other . since the pin 64 has a rigid attachment to the disc 65 , it travels over the circumference of a circle as it moves between the positions of fig2 and 3 . to allow for this required motion of the pin 64 , the slot 63 must have a length equal to the radius of that circle plus , of course , the width of the pin 64 itself . when the casette occupies its operational position within the controller 10 , the metal holder 54 and , thus , the pin 64 , occupy the position shown in fig3 . specifically , the pin 64 lies as far to the right at the disc 65 can move it . alternatively , if the slot 63 had its bottom located slightly below the configuration shown in the figures , the pin 64 would actually lie somewhat below its position in fig3 . in either case , to disengage the casette from the controller , the pin 64 initially moves upward and has no component of motion to the left . subsequently , of course , it does move to the left . however , physically pushing the pin 64 to the left , when in the position in fig3 cannot cause it to rotate in the counterclockwise direction . only an upward force can begin the movement of the pin 64 along its arc and , thus , produce counterclockwise rotation of the disc 65 . in particular , if the holder 54 attempted to push the pin 64 to the left in fig3 it could not effect any motion of the pin 64 or the disc 65 . moreover , when a casette sits in the holder 54 , pushing the casette to the left cannot move the pin 64 or rotate the disc 65 in the direction that would disengage the casette from the controller 10 . the pin 64 and the disc 65 prevent motion of the casette to the left which represents the direction it must move to disengage from the controller 10 . consequently , the pin 64 and the slot 63 lock the holder 54 and , thus , the casette in a position in which the controller 10 can effectively operate the inlet and outlet valves on the casette . the pin 64 and the disc 65 prevent disengagement of the casette from the controller 10 due to an inadvertant force , such as from an accidental knocking . similarly but less importantly , pin 64 in fig2 can only move upwards in order for the holder 54 to move to the right . an accidental force applied against the holder 54 or against the casette retained in the holder 54 cannot cause movement of the casette toward the engagement position . the locking of the bracket to the left of fig2 does provide a benefit , however . after the removal of the casette from the holder 54 , the holder 54 remains properly aligned with the opening 31 in the front panel 15 . there , it can readily receive the insertion of a subsequent casette . after a casette enters between the plate 37 and the arms 38 and 39 in fig1 and 2 , it receives transportation to the right until the holder 54 has the position shown in fig3 . with the holder 54 in this configuration , a casette 75 will occupy its operational position as in fig4 . the casette 75 includes the base section of plastic 76 and the plastic cover slip 77 . fused together , they hold the elastomeric membrane 78 between them . the cover slip 77 has the protuberance 81 which barely fits between the upper arm 38 and the lower arm 39 to roughly align the casette 75 in the controller 10 . in order to provide a fine adjustment of the casette 75 , the controller 10 includes the alignment pins 57 and 58 attached to the middle leg 84 of the z bracket 23 . normally , the plastic cover slip 77 occupies a position between the base plastic section 76 and the middle leg 84 . however , the base plastic section 76 includes the circular protuberances 85 and 86 which actually extend through openings 87 and 88 , respectively , in the cover slip 77 . the protuberances 85 and 86 have the depressions 89 and 90 formed in them . to closely align the casette 75 and the controller 10 , the alignment pins 57 and 58 fit into the depressions 89 and 90 . the pins 57 and 58 , thus , directly provide substantially no alignment of the cover section 77 although it normally sits between the base plastic section 76 and the middle leg 84 . however , the openings 87 and 88 in the cover slip 77 surround the protuberances 85 and 86 . this produces the necessary alignment of the cover slip 77 to both the base section of plastic 76 and the controller 10 . a critical alignment , of course , exists between the base plastic section 76 and the valve members 59 and 60 . the valve members 59 and 60 must properly sit upon the inlet valve face 93 and the outlet valve face 94 , respectively , to control the amount of fluid passing through the casette 75 . the valve seats 93 and 94 , however , form part of the base section of plastic 76 . its proper alignment results directly from the insertion of the alignment pins 57 and 58 into the openings 89 and 90 which also form part of the base plastic section 76 . alternatively , the alignment pins 57 and 58 could snugly fit into appropriately sized depressions in the cover section 77 . however , the correct alignment of the valve members 59 and 60 relative to the valve seats 93 and 94 would then depend upon the orientation of the cover slip 77 to the base plastic section 76 . the direct insertion of the pins 57 and 58 into the openings 89 and 90 in the base section 76 eliminates the need for an absolutely precise alignment between the base section 76 and the cover slip 77 . the valve members 59 and 60 must , nonetheless , move through the openings 97 and 98 in the cover slip 77 . making the openings 97 and 98 appreciably larger than needed for the valving members 59 and 60 eliminates the criticality of the alignment of the cover slip 77 to either the base section 76 or to the controller 10 . fig4 shows a close fit between the alignment pin 57 and the opening 89 . at the other end of the drawing , however , the pin 58 appears to have a loose fit within the opening 90 . in fact , the opening 90 has an oblong shape which allows motion in its inside of the pin 58 in the direction towards and away the opening 89 at the casette &# 39 ; s other end . the opening 90 , however , fits close to the pin 58 in the direction into and out of the paper . when the pin 57 sits in the opening 89 , the only allowed motion of the casette 75 relative to the controller 10 involve a rotation around the pin 57 . the close fit of the opening 90 to the front and back of the pin 58 , as seen in fig4 specifically prevents this type of motion . thus , the looseness of the oblong opening 90 does not detract from the precise alignment of the casette 75 in the controller 10 . it merely eliminates the criticality of the distance of the pin 58 away from the pin 57 . similarly , the opening 87 in the cover slip 76 tightly fits around the circular protuberance 85 of the basic plastic section 76 . at the other end , the cover section 76 has an oblong opening 88 which allows some leeway to the circular protuberance 86 . again , the sides of the sides of the oblong opening 88 closely approach the protuberance 86 . no misalignment between the two sections of plastic can result . it merely lowers the exactness with which the manufacturing process must locate the opening 88 relative to the protuberance 86 . the controller 10 and the casette 75 operate cyclicly . the cycle of operation begins with the closing of the outlet port 101 . this occurs when the outlet valve member forces the membrane 78 to seat upon the outlet valve face 94 . retracting the inlet valve member 59 allows the membrane 78 to contract to the configuration shown in fig4 . this opens the inlet port 102 . fluid may then flow from the inlet channel 103 through the inlet port 102 . it arrives at the metering chamber 103 located between the membrane 78 and the portion 104 of the base section 76 located between the inlet and outlet ports 102 and 101 , respectively . as the fluid enters the metering chamber 103 , the membrane 78 expands until it contacts the concave depression formed in the cover plastic section 77 . at this point , the membrane 78 can expand no further and , consequently , the metering chamber 103 has reached its maximum volume . the slot 107 in the cover plastic section 77 allows for the equalization of the air pressure between the cover section 77 and the membrane 78 . fig5 shows the configuration of the membrane 78 in the region of the outlet port 101 when the valve member 60 has closed it . as shown there , the valve member 60 has extended towards the outlet valve face 94 . when it moves in that direction , it contacts the membrane 78 , stretches it , and forces it to seat tightly upon the valve face 94 . with the membrane 78 seated upon the face 94 , no fluid can pass out the outlet port 101 . to continue the cycle of operation , the controller inserts the inlet valve 59 until it stretches the membrane 78 sufficiently to seat upon the valve face 93 of the inlet port 102 . then , the controller retracts the outlet valve member 60 which allows for the contraction of the membrane 78 in the region of the outlet port 101 . as the membrane 78 there contacts , it moves away from the outlet valve face 94 which , thus , opens the outlet port 101 . with the outlet port 101 open , the fluid from the metering chamber 104 may pass through the outlet port 101 , the outlet channel 110 , and to the patient . the controller completes the cycle of operation by again inserting the outlet valve member 60 to cause the membrane 78 to close the outlet port 101 . when all of the fluid from the metering chamber 104 has passed out of the casette 75 , the middle portion of the membrane 78 contracts to the flat position shown in fig4 . to move the valving members 59 and 60 , the controller 10 includes the e - frame electromagnet , shown generally at 117 in fig1 to 3 . screws and posts 119 attach the electromagnet 117 to the front leg 25 of the z - shaped bracket 23 . as seen in fig2 and 3 , the electromagnet 117 includes the coil 118 which surrounds the magnet &# 39 ; s middle leg 119 . the back 120 of the magnet 117 connects its middle leg 119 to its side legs 120 and 121 . when current flows along the leads 122 to the magnet 117 , it induces the ends of both the legs 120 and 121 to become magnetic poles of the same type . thus , the side legs 120 and 121 may both have a north pole at their ends . reversing the current in the leads 122 causes the opposite magnetic pole to appear at the ends of the legs 120 and 121 . following the example given above , reversing the current in the leads 122 produces a south magnetic pole at the ends of the legs 120 and 121 . adjacent to the end of the leg 120 sits the permanent magnet 125 , while the permanent magnet 126 has a location in proximity to the end of the other side leg 122 . both of the permanent magnets 125 and 126 connect to the same rocker arm 127 . however , the magnets 125 and 126 present opposite magnetic poles to the e - frame electromagnet 117 . in other words , if the permanent magnet 125 has its north pole lying closest to the end of the side leg 120 , then the permanent magnet 126 has its south pole lying closest to the end of the side leg 121 . as stated above , the current passing along the leads 122 and through the coil 118 can cause the ends of both side legs 120 and 121 to become south magnetic poles . when that occurs , the south magnetic pole on the side leg 120 attracts the north magnetic pole on the permanent magnet 125 . simultaneously , the south magnetic pole on the leg 121 repels the south pole on the permanent magent 126 to produce the configuration shown in fig2 . reversing the direction of the current in the leads 122 and the coil 118 produces the opposite effect , or north magnetic poles at the ends of the side legs 120 and 121 . in this instance , the resulting north magnetic pole on the side leg 120 repels the north magnetic pole of the permanent magnet 125 . further , the north magnetic pole on the side leg 121 attracts the south magnetic pole on the permanent magnet 126 . this reversal of attraction and repulsion causes the rocker arm 127 to rotate about its pivot point 128 located on a line passing through the center leg 119 of the e - frame electromagnet 117 . the rocker arm 127 will continue to rotate until the permanent magnet 126 makes actual contact with the side leg 121 and produces the configuration shown in fig3 . in general , the rotating of the rocker arm 127 about its pivot point 128 moves the valve members 59 and 60 to open and close the inlet and the outlet valves on the casette 75 . to provide the interconnection between the rocker arm 127 and the valve members 59 and 60 , the spring member 131 attaches to the former with the aid of the screw 132 . additional screws at the pivot point 128 attach the side 133 of the spring member 131 to the middle leg 119 electromagnet 117 . the spring member 131 in turn has the two legs 135 and 136 . each of the legs 135 and 136 has a slot in its end barely large enough to allow it to fit into grooves provided near the end of the movable valve member 59 and 60 , respectively . the end of the valve members 59 and 60 with these grooves lie on the same side of the middle leg 84 of the z bracket 23 as the rocker arm 127 . fig1 shows the slot in the leg 135 with barely sufficient room to enter the groove in the end of the inlet valve member 59 . as the rocker arm rotates about the pivot point 128 between the two positions shown in fig2 and 3 , the spring member 131 rotates between its two positions , which also appear in those figures . in the position in fig2 the leg 136 of the connecting member 131 lies closer to the middle plate 84 and thus to the casette that the holder 54 would retain . this situation , in particular , receives illustration in fig4 . the leg 136 thus projects the outlet valve member sufficiently far through the plate 84 to cause the membrane 78 to close off the outlet port 101 . the other leg 135 of the spring member 131 retracts the inlet valve member 59 which , in turn , opens the inlet port 102 . when the connecting member changes its position from that of fig2 to that in fig3 the opposite result occurs . specificially , it thrusts the inlet valve member 59 through the middle plate 84 to close the inlet valve . it then retracts the outlet valve member 60 sufficiently to allow the casette &# 39 ; s outlet 101 to open . the composition of the spring member 131 should provide it with a modicum of inherent resiliency or &# 34 ; springiness &# 34 ;. moreover , it should have a location sufficiently close to the middle plate 84 that a leg 135 or 136 must flex when forcing a valve member , 59 or 60 , respectively , to close its appropriate valve in the casette . as a result , when the rocker arm 127 changes positions , the spring member causes the other valve member to start moving and close off its valve in the casette . the other leg , during this time , starts to unbend , but keeps its valve member in the position where its valve stays closed . thus , the spring member 131 , with the flexing legs 132 and 133 and a close location to the middle plate 84 , when it changes its position , causes the open valve to close before it allows the closed valve to open . this prevents a period of time during which both valves in the casette could open and permit an unknown amount of fluid to pass to the patient . if no current flows along the leads 122 to the coil 118 , no magnetic pole will appear at the end of either the side legs 120 or 121 . however , the permanent magnetic poles 125 and 126 still remain . both of these would then exert an attractive force upon the ferromagnetic material of the side legs 120 and 121 . the pole creating the greater force would move to and actually contact the leg nearest it while the other pole would then move from its leg . however , the permanent magnetic poles 125 and 126 have very nearly the same strength . thus , the pole lying closer to the e - frame would actually move towards its leg . accordingly , with no current in the electromagnet 117 , a magnetic bistable device results ; either the permanent pole 125 makes contact with the e - frame to create the configuration shown in fig2 . or , the magnetic pole 126 would attract itself to the bottom leg 121 to produce the situation in fig3 . one of these two situations must result because of the bistable magnetic device created by the permanent magnets 125 and 126 in proximity to the electromagnet 117 without any current in it . moreover , each of the situations in fig2 and 3 place one of the movable valve members 59 or 60 in a position where it closes its valve in the casette . in fig2 the outlet would close will , in fig3 the inlet would close . thus , one of the valves in the casette would necessarily have to close as long as the casette remained engaged in the controller 10 . this occurs even if no current passed to the electromagnet 117 . under no circumstances would the controller 10 allow fluid to pass in an uncontrolled manner to the patient . in the figures , the magnetic bistable device includes the ferromagnetic material of the electromagnetic 117 . other powering devices , however , could move the rocker arm 127 . examples include mechanical or pneumatic motive means . nonetheless , placing ferromagnetic material in the locations of the side legs 120 and 121 and permanent magnets 125 and 126 on the rocker arm 127 would still produce the magnetic bistable device . this would continue to assure the closure of at least one valve in a casette placed in the controller 10 . when using the electromagnet 117 , the rocker arm 127 with its pivot point 128 should not make direct contact with the middle leg 119 of the electromagnet 117 . if it did contact , it could provide a shunt for the magnetic field through the middle leg 119 of the electromagnet 117 . the shunt would provide a circuit between the permanent magnet making actual contact with a side leg . the shunt would reduce the field strength of the other side leg which repels the other permanent magnet . moreover , displacing the rocker arm 127 slightly from the middle leg 119 of the electromagnet 117 prevents the grinding of the two components and the concommitant production of coarse fillings between them which could interfere with the free rotation of the rocker arm 127 . instead of having the two attached permanent magnets 125 and 126 , the rocker arm 127 may simply take the form of a long permanent magnet having its poles near the location of the magnets 125 and 126 . that would assure the rocker arm 127 of magnetic poles of equal strength . moreover , such a permanent magnet could not have an induced pole at its middle . consequently , the magnetic field could not shunt across the middle of the rocker arm 127 to the middle leg 119 of the electromagnet 117 . however , the rocker arm 127 should still remain slightly removed from the middle leg 119 . this prevents the grinding of the two together as the rocker arm 127 rotates and the production of filings from either component to interfere with the free rotation of the rocker arm 127 . fig6 shows a metal holder 41 with arms 143 and 144 slightly different from the arms 38 and 39 of the prior figures . the openings 145 and 146 in the arms 143 and 144 , respectively , allow the alignment pins 147 and 148 to pass through and reach the casette 75 . as shown in fig7 the alignment pins 147 and 148 form part of an alignment block 149 which sits behind the middle leg 150 of a z bracket corresponding to the bracket 23 of fig1 . the bracket &# 39 ; s middle leg 150 has the similar openings 151 and 152 through it . these again allow the alignment pins 147 and 148 to reach the casette . the snap rings 157 and 158 clamp on to the alignment pins 147 and 148 . they affix the alignment block 149 to the z bracket &# 39 ; s middle leg 150 . the alignment block 149 also has the protuberances 159 and 160 oriented in the same direction as the alignment pins 147 and 148 . the middle leg 150 has the openings 161 and 162 into which fit the protuberances 159 and 160 . the other side of the mounting block 150 has the protuberances 165 and 166 . these generally fall at the same location as the protuberances 159 and 160 , but on the other side . the opening 167 passes through the mounting block 149 and centers itself in the proturberances 159 and 165 . the second opening 168 also passes through the alignment block 159 and has a central location in the protuberances 160 and 166 . the openings 167 and 168 serve a dual purpose . first , they guide the valving members 59 and 60 to their proper locations relative to the inlet 102 and the outlet 101 on the casette 75 . secondly , the alignment block 149 has a composition of a low frictional material . delrin 500 cl ®, an acetal resin manufactured by the e . i . du pont de nemours & amp ; co ., represents a good example of such a material . its surface has a low coefficient of friction . the valving members 59 and 60 protract and retract to operate the valves on the casette . sliding on the material of the alignment block 149 , they encounter substantially no frictional resistence from the surfaces of the openings 167 and 168 . fig8 shows the front of the alignment block 149 prior to its assembly on the z bracket &# 39 ; s middle leg 150 . this surface shows the alignment pins 147 and 148 , the protuberances 159 and 160 , and the openings 167 and 168 . the side view of fig9 shows these components as well as the protuberances 165 and 166 on the side of the alignment block 149 opposite to the protuberances 159 and 160 . the openings 167 and 168 through these protuberances appear in phantom in the figure . fig9 also shows a small ridge 170 on the back of the alignment block 149 . the ridge 170 provides the alignment block 149 with greater structural rigidity . fig1 shows the ridge 170 passing down the middle of the back of the alignment block 149 . as suggested above , the alignment pins 147 and 148 provide the fine alignment of the casette 75 within the controller 10 . the openings 167 and 168 guide the valving members 59 and 60 as they operate the openings 101 and 102 in the casette 75 . consequently , the same section of material that aligns the casette also guides the valve members . the alignment pins 147 and 148 do not attach to a separate section of material which then either guides the valve members or would include further sections of material to perform that function . the resulting alignment would then not only depend upon the orientation of the casette relative to the alignment pins 147 and 148 . the casette &# 39 ; s proper placement would also depend upon the correct orientation of the pins 147 and 148 to , for example , the z bracket &# 39 ; s middle leg 150 . utilizing the single molded block 149 assures the correct orientation of the alignment pins 147 and 148 to the guiding openings 167 and 168 .
improvements in infusion controlling apparatus used in limiting the flow rate of an intravenous solution to a patient . the improvements provide coarse and fine orientations of a casette through which the solution passes relative to a controller which valves the casette &# 39 ; s inlet and outlet to provide measured volumes of fluid . the coarse alignment device includes spaced apart metal sections which grasp onto the casette and move it towards the controller &# 39 ; s valving members . as the casette reaches the valving members , protuberances on the controller fit into indentations on the casette , as the fine adjustment . the indentations into which the protuberances fit form part of the casette &# 39 ; s base section of plastic notwithstanding the location of a cover slip between these two items . the valving members couple to a rocker arm which pivots about a point located at its middle and has magnetic poles at its ends . the rocker arm &# 39 ; s pivot point over the center leg of an e - frame electromagnet allows the arm to rotate between two orientations in which one of its magnetic poles contacts a side leg of the e - frame electromagnet . current passing through a coil located on the center leg of the electromagnet moves the rocker arm between these positions , depending upon the current &# 39 ; s direction . with no current in the coil , the arm &# 39 ; s magnets and the e - frame provide a bistable magnetic device in which the rocker arm forces one of the valving members to close either the casette &# 39 ; s inlet or its outlet . this prevents the uncontrolled passage of fluid through the casette to the patient .