Method and apparatus for protecting a pump mechanism from extraneous fluid

A plurality of finger members disposed adjacent each other are moved by a driving mechanism in a reciprocal, sequential manner. Infusion is carried out when the finger members engage an infusion tube in a peristaltic sequence. The finger members contact each other by projections formed integrally on the upper and lower surfaces of the finger members to reduce the contact surface area. A fluid diversion guiding hole is contained in a tube-pressing portion of each finger member. The guide holes of adjacent finger members are aligned to form a continuous channel for discharging leaking infusion fluid. Bevels surround the guiding holes and are inclined toward the center of the hole. Each finger member also includes a rib that is integral with and protrudes upward from the upper surface of the finger member for blocking infusion fluid from the finger members and drive mechanism. In a preferred embodiment, the projections are linear and substantially parallel with the sides of the guiding hole which are, in turn, parallel with the movement of the tube-pressing portion.

BACKGROUND OF THE INVENTION 
The invention relates generally to pump mechanisms, and more particularly, 
to a method an apparatus for protecting a pump mechanism used in an 
infusion pump from possible adverse effects caused by the entrance of 
extraneous fluid into the pump mechanism, such as adhesion of mechanism 
parts. 
An infusion system typically includes a reservoir, such as a bottle or bag, 
for holding infusion fluid, a drip chamber for monitoring the flow of 
fluid from the reservoir, infusion tubing for carrying the fluid to an 
injection needle, and an infusion pump for precisely controlling the flow 
rate of fluid through the infusion tubing. One conventional infusion pump, 
known as a linear peristaltic pump, comprises finger members that move 
into and out of contact with the tubing in a peristaltic manner so that 
they compress the infusion tube in a wavelike motion, squeezing the fluid 
as the wave progresses and thereby carry out the infusion. The finger 
members and the drive mechanism controlling the movement of the finger 
members are collectively referred to as a pump mechanism. The pump 
mechanism and a control processor with ancillary power and display systems 
comprises an infusion pump. A typical infusion pump as such is described 
in Japanese patent publication No. Sho-62-8763. 
In some cases during operation, infusion fluid, such as a liquid containing 
a sugar, leaks out of the bottle or bag and travels down the outer surface 
of the infusion tube and may enter the pump mechanism area. If the pump is 
constructed so that leaking infusion fluid is not diverted out of the 
pump, the leaking infusion fluid may accumulate in the pump mechanism, 
dry, and adhere to the pump mechanism and cause the finger members to 
stick to the driving mechanism and to each other. This sticking can cause 
the pump mechanism to malfunction and not be available when needed. 
In a typical infusion pump, adjacent finger members contact each other in a 
face-to-face manner, i. e., the upper and lower surfaces of the finger 
members rub against each other as the finger members move. As infusion 
fluid accumulates on the face-to-face surfaces of the finger members and 
begins to dry, the finger members may stick to each other and a 
malfunction of the pump mechanism may occur if the driving mechanism does 
not have sufficient power to overcome the adhesion of the fingers to one 
another. A remarkably large force may be required, depending on the nature 
of the leaking fluid, to break the face-to-face adhesive bond. This is 
especially so when an attempt is made to break the bond by moving the 
finger members in the direction parallel to the face, which is the 
direction of movement during pump operation. 
One method to eliminate this adhesive problem involves covering, with a 
rubber sheet, the portion of the finger members which compresses the 
infusion tube. Essentially the rubber sheet blocks infusion fluid from 
entering the pump mechanism. However, as the rubber sheet is continuously 
pressed against the infusion tube by the finger members, the rubber sheet 
may become swelled by the plasticizer from the infusion tube and may 
become soft and eventually break. Accordingly, the rubber sheet must be 
periodically replaced. 
A second method involves making the clearances between the finger members 
as narrow as possible so that infusion fluid is unlikely to enter the pump 
mechanism. To further ensure that fluid does not enter, a grease like 
repellent filler such as silicon may be placed in the clearances. There 
is, however, a limitation in the mechanical accuracy, and it is very 
difficult to completely block the entrance of infusion fluids. In 
addition, an upgrading of the mechanical accuracy results in higher 
production costs. Furthermore, when a repellent filler is used, there is a 
possibility that the filler may leak into other regions of the pump 
mechanism and a pump mechanism malfunction may result. 
A third method involves unitizing a cleanable and removable pump mechanism. 
When infusion fluid adheres to the inside of the pump mechanism, the 
unitary pump mechanism may be removed, cleaned and reinstalled. In unitary 
pump mechanisms, however, the mechanical connection is often times loose 
and produces high noise levels during operation. Furthermore, it is 
inconvenient for a nurse, who is very busy with daily business, to remove 
and wash the pump mechanism. 
Hence, those skilled in the art have recognized a need for a pump mechanism 
that conveniently and effectively reduces or eliminates the entrance of 
infusion fluid into the pump mechanism and reduces the detrimental effects 
of any fluid which does enter the pump mechanism. The invention fulfills 
these needs and others. 
SUMMARY OF THE INVENTION 
Briefly, and in general terms, the invention is directed to an apparatus 
and a method that protects a pump mechanism from the detrimental effects 
typically associated with the accumulation of leaking fluids within the 
pump mechanism. 
In one aspect, the invention comprises a finger member for use in a pump 
mechanism having a plurality of reciprocating finger members disposed for 
sequentially engaging an infusion tube to move fluid through the tube in a 
peristaltic manner. The pump mechanism also has a drive mechanism for 
moving the finger members. Each finger member includes an upper and a 
lower surface and a plurality of projections protruding from the upper and 
lower surfaces. The finger members are disposed so that the projections 
will be aligned with and will engage the projections of the adjacent 
fingers. 
In another aspect, the invention comprises a pump mechanism for moving 
fluid through an infusion tube. The pump mechanism includes a plurality of 
finger members, each finger member having a tube-pressing portion and 
upper and lower surfaces. Also included is a plurality of projections 
protruding from the upper and lower surfaces of each finger member. The 
finger members are disposed so that the projections of adjacent finger 
members are substantially aligned with each other and contact each other. 
Further included is a drive mechanism for moving the finger members in a 
peristaltic manner so that the tube-pressing portions sequentially engage 
the infusion tube. 
In yet another aspect, the invention comprises a method for protecting a 
pump mechanism from adhesion caused by the entry of extraneous fluid into 
the pump mechanism. The pump mechanism has a plurality of reciprocating 
finger members adjacently disposed for sequentially engaging an infusion 
tube to move fluid through the tube in a peristaltic manner. The pump 
mechanism also has a drive mechanism for moving the finger members and 
each finger member has upper and lower surfaces. The method includes the 
step of limiting the surface-area contact between adjacent upper and lower 
surfaces. Also included is the step of forming a continuous channel that 
is associated with each finger member. Further included is the step of 
diverting the fluid from the upper and lower surfaces toward and into the 
channel. 
These and other aspects and advantages of the present invention will become 
apparent from the following more detailed description, when taken in 
conjunction with the accompanying drawings which illustrate, by way of 
example, the preferred embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Turning now to the drawings with more particularity, in FIGS. 1 and 2 there 
is shown a linear peristaltic infusion pump 40 in accordance with an 
embodiment of the invention. The infusion pump 40 is equipped with a 
mechanism chamber 1 which is defined by a cover 7 at the rear and a 
partition 4. Housed within the mechanism chamber 1 are a plurality of 
movable finger members 3 disposed in an adjacent fashion. A pump chamber 
2, adjacent the mechanism chamber 1, is defined by the partition 4 and an 
openable and closable lid 5. 
The preferred embodiment of the infusion pump 40 described herein is 
configured so that the finger members 3 move in a substantially horizontal 
direction, as is typical with many infusion pumps. Some pumps, however, 
may have finger members 3 that move in other directions. Furthermore, in 
the preferred embodiment the finger members 3 are stacked in a 
substantially vertical manner, although other configurations may be 
possible. 
Each finger member 3 includes a supporting portion 3a that is pivotally 
supported relative to a pivotal axis 8. The pivotal axis 8 is installed in 
the vertical direction in the mechanism chamber 1. An arm 3b extends 
horizontally along the partition 4 from the supporting portion 3a while a 
U-shaped cam-holding portion 3c projects from the arm 3b. A tube-pressing 
portion 3d projects toward the partition 4 from the cam-holding portion 
3c. The tube-pressing portion 3d communicates with the pump chamber 2 
through an opening 9 contained within the partition 4. 
A pressure plate 10 is attached to the lid 5 by a plurality of bolts 14. 
Concentric with each bolt is a spring 11. The bolts 14 movably support the 
pressure plate 10 while the springs 11 bias the pressure plate 10 away 
from the lid 5. Positioned between the pressure plate 10 and the finger 
members 3 and aligned with an opening 9 is an infusion tube 6. During 
operation, the pressure plate 10 and the accompanying force provided by 
the springs 11 provide the force necessary to hold the infusion tube 6 in 
place. 
A plurality of eccentric cams 13, one for each finger member 3, are stacked 
on a rotatable drive shaft 12 and are aligned and positioned within the 
cam-holding portion 3c. The eccentric cams 13 rotate together with the 
drive shaft 12. The finger members 3 are constructed so as to carry out 
peristaltic movements in line with the rotation of the drive shaft 12 and 
the eccentric cams 13. This motion results in substantially horizontal 
movements of the tube-pressing portion 3d centering around the pivotal 
axis 8 of the finger members 3. The infusion tube 6 is pressed, in turn, 
between the tube-pressing portion 3d and the pressure plate 10 so as to 
transfer the infusion fluid downward toward the injection needle (shown in 
FIG. 5). 
The upper end of the driving shaft 12 is connected to a motor 19 by way of 
a transmission mechanism 18. The transmission mechanism 18 includes a worm 
gear 18a; engaged with the worm gear 18a is a gear 18b. The motor 19, 
transmission mechanism 18, drive shaft 12 and eccentric cams 13 constitute 
a drive mechanism for peristaltically moving the finger members 3. An 
encoder 20 is attached to the driving shaft 12 while a rotation position 
detector 21 is aligned with the encoder 20. A guide 24 for aligning the 
infusion tube 6 and a pinch-off means 25 to pinch the pump outlet of the 
infusion tube 6 are provided. 
In a preferred embodiment as shown in FIGS. 3 and 4, the tube-pressing 
portion 3d has a guiding hole 26 which passes therethrough in the 
substantially vertical direction. The size and alignment of the guiding 
holes 26 are such that during horizontal movement of the tube-pressing 
portions 3d the guiding holes 26 form a continuous channel that runs from 
the extreme upper finger member 3 to the extreme lower finger member 3. 
The vertical channel formed by the general alignment of the guiding holes 
26 provides a path for infusion fluid, which may accumulate on the upper 
surfaces of the finger members 3, to travel and thereby be discharged 
outside the pump without adhering to the finger members or entering the 
drive mechanism. Therefore, the accumulation of infusion fluid is 
prevented and the possibility of finger members 3 sticking to each other 
is greatly reduced. 
The guiding holes 26 are made large enough so that even when a finger 
member 3 has been moved into contact with the tubing, its guiding hole 
will still have some overlap with the guiding holes of the adjacent finger 
member. 
The tube-pressing portion 3d also includes bevels 27, 28 that incline 
toward the center of the guiding hole 26 and are provided on both the 
upper and lower surfaces of the tube-pressing portion 3d. The bevels 27, 
28 tend to divert infusion fluid which enters the tube-pressing portion 3d 
toward the guiding hole 26. In an alternate embodiment the bevels 27, 28 
are provided only at the upper surface of the tube-pressing portion 3d. 
A pair of projections 29 are formed integrally on both the upper and lower 
surfaces of the tube-pressing portion 3d. Preferably, these projections 29 
are linear and are substantially parallel with the sides of the guiding 
hole 26 and are substantially parallel with the horizontal movement of the 
tube-pressing portion 3d. The linear projections 29 of vertically adjacent 
finger members 3 are in contact with each other and remain so even during 
the peristaltic movement of the finger members 3. This keeps the finger 
members 3 in a linear contacted state, even during horizontal movement, 
and thereby provides a continuous guide for diverting infusion fluid as 
well as a substantially reduced surface area of contact between adjacent 
fingers. 
Each linear projection 29 is positioned between an edge of the 
tube-pressing portion 3d, which is substantially parallel with the 
horizontal movement of the tube-pressing portion, and a side of the 
guiding hole 26, which is also substantially parallel with the horizontal 
movement of the tube-pressing portion. Accordingly, infusion fluid is 
directed toward the guiding hole 26 by the projections, and each 
projection limits fluid from flowing over the edges of the tube-pressing 
portion 3d. 
As shown in FIG. 1, a pair of upper linear projections 30 is integrally 
formed on the upper opening-facing side of the partition 4 at the opening 
9 and protrude downward. Likewise, a pair of lower linear projections 36 
are integrally formed on the lower opening-facing sides of the partition 4 
at the opening 9 and protrude upward. The linear projections 29 of the 
extreme upper and lower finger members 3 contact the upper linear 
projections 30 and the lower linear projection 36, respectively. An upper 
guide groove 31 and a lower guide groove 32 are provided on the 
pump-chamber-facing side of the partition 4. The guide grooves 31, 32 
incline toward the mechanism chamber 2 and thereby aid in diverting 
infusion fluid down along the infusion tube 6 and out the infusion pump 
40. The upper guide groove 31 assists in diverting or channeling the 
leaking fluid through the guiding holes 26 in the finger members 3 while 
the lower guide groove 32 diverts or channels the leaking fluid back to 
the fluid tubing so that it leaves the pump 40. 
A weir-like rib 33, as shown in FIG. 3, is integrally formed on the upper 
and lower surfaces of each finger members 3. The height of the rib 33 is 
less than the linear projection 29 so that the ribs 33 of adjacent finger 
members 3 do not contact each other during the horizontal movement of the 
finger members 3. The ribs 33 nevertheless prevent infusion fluid from 
flowing to the support portion 3a, arm 3b and cam-holding portion 3c of 
the finger member 3. The ribs 33 retain the fluid in the region 
surrounding the guiding hole 26 and thereby protect the portions of the 
finger members 3 that interface with the drive mechanism from exposure to 
leaking fluid and from adhering to each other were that fluid to dry on 
those portions. The ribs 33 also tend to divert the fluid toward the 
guiding holes 26 so that it flows downward and away from the mechanism. 
The vertical grooves 34 as shown in FIG. 2, are formed in the surface of 
the partition 4 facing the mechanism at both edges of the partition 4 near 
the opening 9. The vertical grooves 34 channel infusion fluid, which may 
be present on the upper surface of the finger members 3, downward and out 
of the infusion pump 40. 
A plurality of supporting projections 35, substantially equidistant from 
the pivotal axis 8, are integrally formed on the upper and lower surfaces 
of the pivotally supporting portion 3a of the finger members 3. The 
supporting projections 35 of adjacent finger members 3 are in contact with 
each other. The supporting projections 35 have the same height as the 
linear projection 29, thereby allowing the horizontal posture of the 
finger members 3 to be maintained. 
In operation, an infusion tube 6, as shown in FIG. 5, in which an infusion 
fluid flows down from a drip chamber 15, is gradually compressed from 
upward to downward by the tube-pressing portion 3d of the finger members 3 
which are peristaltically driven by the rotating eccentric cams 13, 
thereby causing the infusion fluid to be sent to the injection needle 17. 
The eccentric cams 13 are rotated by a drive shaft 12 which is driven by 
the motor 19. Although not shown, additional support would be provided to 
the infusion fluid bottle 16, such as by a portable pole hanging 
apparatus. The bottle 16 is connected to the infusion tube 6 through the 
drip chamber 15 at the upstream end of the infusion tube 6. 
Should some infusion fluid leak from the infusion fluid bottle 16, it may 
travel along the outer surface of the infusion tube 6 and enter the 
infusion pump 40. If protection against such fluid were not present, the 
leaking fluid may accumulate on the tube-pressing portion 3d of the 
fingers 3 and dry. It is well known that the greater the surface area to 
which adhesive is applied, the greater force is required to break the 
adhesive bond. Generally, the adhesive force between two objects is 
lessened in a point-to-point, line-to-line, point-to-face, or line-to-face 
contact. Sufficient adhesive strength will not exist and the objects can 
be more easily separated. Given the line-to-line contact as provided by 
the small linear projections 29 between adjacent tube-pressing portions 3d 
of the finger members, the adhesive bond of any dried infusion fluid will 
be relatively weak. This weak bond is more easily broken as the finger 
members 3 are urged into their peristaltic movement by the driving shaft 
12. Accordingly, any sticking of the finger members 3 is overcome and a 
smooth, continuous peristaltic motion is maintained. 
Any infusion fluid which may accumulate on the tube-pressing portion 3d of 
the finger members 3 is diverted toward the guiding hole 26 by the bevels 
27, 28 and once inside the guiding hole 26, the fluid is diverted downward 
through adjacent guiding holes 26 in adjacent finger members 3 and is 
discharged through the lower guide groove 32. In some cases the quantity 
of infusion fluid which enters the tube-pressing portion 3d of the finger 
portion 3 is too great and does not flow downward through the guiding 
holes 26. In this case, the rib 33 blocks the flow of infusion fluid into 
the cam-holding portion 3c and the drive mechanism and the fluid is 
diverted toward the vertical grooves 34 and is thereby guided downward and 
out the infusion pump 40. 
Therefore, not only does the protective apparatus in accordance with the 
invention protect the driving mechanism from leaking fluid from the tubing 
or elsewhere, the apparatus also provides reduced-size contact surfaces 
between adjacent moving fingers so that any adherence between those 
fingers can be overcome by the driving mechanism. The projections in 
accordance with the invention present a much lowered surface area for such 
fluid. This results in a weaker bond that can be more easily broken by the 
driving mechanism. Greater mechanical accuracy is not required thus 
leading to lowered manufacturing costs. Rubber sheets, with their 
attendant expense, are also not needed. 
The projections on the fingers that not only provide the reduced-sized 
contact surfaces also tend to divert leaking fluid that may interfere with 
the correct operation of the pumping mechanism to a specifically designed 
fluid channel that will guide such fluid out of the pump. Additional 
channels are provided for moving leaking fluid away from the fingers and 
the other parts of the driving apparatus. Furthermore, the driving 
mechanism need not be removable for cleaning thus permitting the 
efficiency of a permanently mounted mechanism. Lower noise levels can be 
designed as well as lower manufacturing costs due to this mounting 
arrangement. 
In the above description, a preferred embodiment of the invention is 
incorporated in an infusion pump. The invention, however, is also 
applicable to other mechanisms in which extraneous fluid may enter and 
interfere with the operation of the mechanism. 
While several particular forms of the invention have been illustrated and 
described, it will be apparent that various modifications can be made 
without departing from the spirit and scope of the invention. Accordingly, 
it is not intended that the invention be limited, except as by the 
appended claims.