Pumps – Expansible chamber type – Elongated flexible chamber wall progressively deformed
Reexamination Certificate
2002-02-21
2003-08-26
Freay, Charles G. (Department: 3746)
Pumps
Expansible chamber type
Elongated flexible chamber wall progressively deformed
C417S022000, C417S042000, C417S044100
Reexamination Certificate
active
06609900
ABSTRACT:
TECHNICAL FIELD
The present invention is directed to a dynamic brake with backlash control, and more particularly, to a dynamic brake with backlash control for use with a peristaltic pump.
BACKGROUND OF THE INVENTION
Peristaltic pumps, also referred to as roller pumps, are commonly utilized in medical applications. For instance, such pumps are often employed during cardiovascular surgery to facilitate circulation of blood between a patient and a heart-lung machine. Other common medical uses are the transfer of blood between a patient and a kidney dialyzer, and intravenous feeding of IV solutions. Generally, peristaltic pumps are simply structured, generate a constant flow, and employ disposable tubes as a member for fluid transfer.
Peristaltic pumps are relatively simple in construction and typically include a housing having rollers which progressively compress a flexible tube at spaced intervals against an arcuate surface or raceway so as to flatten or locally reduce the cross-sectional area of the tube. In this manner, fluid leading to the flexible tube is continuously forced through the flexible tube by one or another of the rollers as it proceeds along the flexible tube over the arcuate surface or raceway.
A conventional roller pump
10
, as shown in
FIG. 1
, comprises a drive mechanism
14
furnished with a drive shaft
12
, a rotating shaft
16
which rotates according to the rotation of drive shaft
12
, and a hollow pump head
20
fixed to a housing
18
to which drive mechanism
14
is attached. This pump head
20
integrally incorporates a bearing block
24
through which rotating shaft
16
is inserted and rotatably supported by a pair of bearings
22
and a stator
26
arranged on the upper portion of bearing block
24
. On the upper surface of stator
26
is formed a recess
28
through which the upper end of rotating shaft
16
is protruded. While this recess
28
is radially and outwardly spaced at a certain distance from the outer circumferential surface of rotating shaft
16
, its inner circumferential surface
28
a
is coaxial with rotating shaft
16
.
A rotor assembly
30
is attached to the upper portion of rotating shaft
16
in such a way as to be placed inside recess
28
of stator
26
and to stay opposite the inner circumferential surface
28
a
thereof. This rotor
30
is fixed to rotating shaft
16
through a bolt
32
, and is so constructed as to integrally rotate along with rotating shaft
16
. On the outer circumferential surface of rotor
30
, at least one roller
34
is arranged so as to rotate about its own axes. A tube
36
which is filled with blood or other fluid material is placed between rotor
30
and stator
26
. Tube
36
is clamped between respective rollers
34
, which are attached to rotor
30
, and inner circumferential surface
28
a
of stator
26
, thereby maintaining tube
36
in a closed state at the point at which it is clamped.
Thus, in a conventional roller pump
10
, rotor
30
is rotated by the rotational motion of rotating shaft
16
driven by drive mechanism
14
, and the clamped portions of tube
36
move according to the revolution of rollers
34
around rotating shaft
16
. Therefore, fluid inside tube
36
is transferred according to the revolution of rollers
34
. The rate of rotation of the rotating shaft
16
and hence the rollers
34
is normally adjustable so that the pumping rate of the fluid within tube
36
can be adjusted. However, the pumping rate can also be adjusted by adjusting the degree to which the rollers compress the flexible tube. This can be done in peristaltic pump assemblies by providing an adjustment mechanism for adjusting the distance between the axes of the rollers and hence the distance between the roller surface and the inner circumferential surface
28
a
of stator
26
. Another important reason for peristaltic pumps to be adjustable in this fashion is that the compressibility, size, and other qualities of the flexible tube can vary considerably.
Referring also to
FIG. 2
, the operation of a typical roller pump
10
is illustrated. Although roller pumps are typically capable of rotating in either direction, the solid arrow in
FIG. 2
indicates that roller pump
10
is rotating in a clockwise direction to force blood through the tube or fluid conduit
36
. Generally, the roller pump
10
continues to rotate until the motor drive circuitry (not shown) is disabled. When this occurs, the roller pump coasts to a gradual stop. After the roller pump has come to a complete stop, it is desirable if the rollers
34
a
,
34
b
,
34
c
are left free to move (i.e., rotate). This is desirable because it allows the roller pump to be hand-operated (i.e., hand-cranked), if that should become necessary.
However, when the rollers are left free to move, it is common for the roller pump to experience some recoil, that is, some amount of counter rotation (e.g., 20 degrees of counter rotation) immediately after the rollers reach zero RPM. In
FIG. 2
, the counter rotation is depicted by the “broken line” arrow. The recoil, referred to herein as backlash, is due to the fact that the rollers are left free to move, and because there is a certain amount of counter pressure in the fluid conduit which opposes the normal rotation (e.g., clockwise rotation) of the roller pump. Backlash may cause air to be introduced into the conduit. This highly undesirable condition may lead to an air embolism or even death of the patient.
Some roller pumps employ a continuously applied brake to prevent backlash due to counter rotation. A continuously applied brake is an electrical or mechanical brake which is continuously applied to stop the motor within the pump. The brake is never removed until it is deemed necessary for the pump to begin moving the rollers again, so as to move fluid in the pump. These pumps may activate the continuously applied brake as soon as the motor drive circuitry receives a signal to stop the pump. While the continuously applied brake does, to some extent, prevent backlash, it also prevents the rollers from freely moving after the rollers have stopped rotating. In this instance, the continuously applied brake would preclude the option of hand operating the roller pump.
Accordingly, there is a need in the art for an improved braking feature for a roller pump, which substantially reduces the occurrence of backlash yet allows the roller pump to be hand operated if necessary.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an intelligent, momentary dynamic brake for use in a roller pump to prevent backlash.
It is also an object of the present invention to provide intelligent, momentary dynamic braking in a roller pump without jeopardizing the ability to hand operate the pump after the rollers have stopped rotating.
In a first embodiment of the present invention, the aforementioned and other objects are achieved by a roller pump that includes means for activating a dynamic brake when the roller pump decelerates below a predefined pump speed. The pump also includes means for deactivating the dynamic brake when pressure in the fluid conduit of the roller pump subsides.
In another embodiment of the present invention, the aforementioned and other objects are achieved by a method for preventing backlash in a roller pump. The method involves determining whether the speed of the roller pump is less than a predefined roller pump speed threshold. When it has been determined that the speed of the roller pump is less than the predefined roller pump speed threshold, a dynamic brake is activated. Then, after a predefined period of time has elapsed, the dynamic brake is deactivated.
REFERENCES:
patent: 4705668 (1987-11-01), Kaltenbach et al.
patent: 4781548 (1988-11-01), Alderson et al.
patent: 4910682 (1990-03-01), Wolff et al.
patent: 5657000 (1997-08-01), Ellingboe
patent: 5996650 (1999-12-01), Phallen et al.
Danielson David
Griewski Richard A.
Lucke Lori E.
Solak Timothy P.
Terumo Cardiovascular Systems Corporation
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