Syringe pump abstract
To prevent engagement and disengagement of the drive elements of
a syringe pump, a clutch element (17) is used which permanently
engages with the screw spindle (14). The clutch element (17), which
may be formed of two cog wheels (18a, 18b) or of a nut, is alternatively
blocked or released by brake elements (21). The brake elements are
actuated by an actuation button (9) via a brake tube (15) and a
pivoting lever (24). Since the clutch element (17) is permanently
engaged to the screw spindle (14) there is no mechanical play upon
initiation of the dispensing process.
Syringe pump claims
1. A motor-driven syringe pump device for controlled dosage dispensing
of a liquid from an injection syringe having a syringe piston disposed
therein and a pushing member acting on one end of said syringe piston,
said device comprising:
a casing having a mounting for a syringe;
a screw spindle transmission means for transmitting a driving force
from the motor to the syringe piston, said transmission having a
threaded screw spindle and a drive element coupled to the pushing
a clutch member permanently and rotatably engaged with the threads
of the screw spindle;
a releasable brake means for alternatively braking or releasing
said clutch member for movement along said screw spindle;
an actuation means for releasing said brake means from said clutch
member and applying said brake means to said clutch member, said
actuation means being coupled to said brake means, said brake means
being urged into contact with the clutch member by a spring which
has one end engaging said pushing member;
wherein the brake means comprises a brake tube and said spring
is disposed within the brake tube, said brake tube being disposed
within a pull-shaft, the other end of the spring engaging the brake
tube, the actuation means being disposed on the pushing component.
2. A syringe pump as claimed in claim 1 wherein the drive element
includes a tubular shaft which surrounds the screw spindle.
3. A syringe pump as claimed in claim 1 wherein the clutch member
comprises a cog wheel which engages with the screw spindle in a
4. A syringe pump as claimed in claim 1 wherein the clutch member
comprises a nut which is rotatably mounted to the drive element
through a ball bearing.
5. A syringe pump as claimed in claim 4 wherein the screw spindle
and the nut have a thread which prevents self-locking.
6. A syringe pump claimed in claim 3 wherein the brake means operates
on a front side of the cog wheel.
7. A syringe pump as claimed in claim 3 wherein the brake means
operates on a cog side of the cog wheel.
8. A syringe pump as claimed in claim 4 wherein the brake means
operates on the front side of the nut.
9. A syringe pump as claimed in claim 1 wherein the brake means
is provided with a brake lining on its contact surface.
10. A syringe pump as claimed in claim 1 wherein the pull-shaft
engages the pushing member and extends between the pushing member
and a cage, the clutch member being disposed in the cage.
Syringe pump description
This application is based upon German application P 38 38 465.5
filed Nov. 12 1988. Applicants incorporate herein the entire text
thereof by reference within the meaning of In re Fouche, 439 F.2d
1237 169 USPQ 429 (CCPA 1971).
This invention concerns a syringe pump for controlled dosage dispensing
of a liquid from an injection syringe that has a casing with a mounting,
is powered by a motor and uses a screw spindle transmission to convey
the force from the motor to the piston. The device features a drive
element which is fastened to a pushing component that presses against
the bottom plate of the syringe piston. A clutch component at the
drive element is permanently engaged to the threads of the screw
spindle, allowing it to rotate freely, whereby a brake element which
allows the clutch element to be blocked or released is provided.
The brake element can be actuated by an actuation element connected
to it via an activating gear that is biased by a spring which rests
against the pushing component.
Syringe pumps are used in clinics and in medical research to apply
small amounts of liquids to a patient over an extended period of
time. One example of such a syringe pump is known from U.S. Pat.
No. 4191187. In this case, the screw spindle is disposed axially
within the pump and is firmly connected to the casing, and holds
a bearing block which contains a clutch pin. The pin has an opening
on its inner side which contains a screw segment that can be engaged
to the screw spindle. A guiding surface is provided on the casing
parallel to the screw spindle where the bearing block is secured
in a manner which allows it to slide.
Another example of a syringe pump is described in DE-A 34 28 655.
Its casing is provided with a mounting for the syringe. It also
is driven by a motor and a transmission conveys the force of the
drive to the syringe, whereby the transmission features a drive
element which can be connected to the mobile part of the syringe
for movement. To prepare the syringe for further use after it has
been already utilized, a clutch is provided which has a disconnection
component allowing disengagement of the transmission from the drive.
To obtain a guide which does not tilt, the bearing block holds an
elongated guiding part which sits on the screw spindle, and the
disconnection component of the clutch is fastened to the guiding
part and the bearing block in a manner which allows it to slide.
Engagement and disengagement of the disconnection component is
done manually by means of a connection piece, which is disposed
outside the casing, and by means of a drive element attached to
the connection piece which extends into the casing and is forced
against the disconnection component. The drawback of such clutches
is that they do not always contact exactly the opposite section
of the thread and therefore need engagement control. As the clutch
meets the screw spindle, a considerable amount of time may pass
until it actually engages and until the play of the mechanism is
eliminated and the bearing block actually starts to move.
DE-A 34 39 322 describes an infusion pump which has a wheel ratchet
that allows free movement in one direction and interacts with a
latch. The latch can only be actuated indirectly by pulling a handle
which causes a certain movement of the latch via the wheel ratchet.
This arrangement allows the rod of the syringe piston to be moved
only in the direction opposite to the dispensing direction, since
in the dispensing direction the rod is blocked by the latch, which
cannot be activated to release the brake when movement in the dispensing
direction takes place. This, however, is not the purpose of the
syringe pump of DE-A 34 39 322 because it is the purpose of the
latch to prevent the syringe piston from being accidentally pushed
by the force of the spring alone.
The required latch makes a definite calibration of the piston in
the dispensing direction impossible (e.g. when the syringe is not
completely filled and the piston should be brought up to the liquid
before the actual dispensing process begins).
Therefore it is the purpose of this invention to create a syringe
pump of the kind described above, whose brake element can be actuated
directly and which allows a calibration of the syringe piston in
the direction of dispensing as well as in the reverse direction.
This is achieved in an arrangement where the rod features a brake
shaft in the drive element, having a spring which is connected with
the brake shaft at one end, and where the actuation element is disposed
on the pushing component.
Since a syringe pump in accordance with this invention allows the
brake element to be actuated directly by the actuation element,
independently from the movement of the drive element, it is possible
to adjust the syringe piston in the direction of dispensing as well
as in the reverse direction, prior to the actual injection process.
The drive element preferably includes a tubular pull-shaft disposed
around the spindle.
In one preferred embodiment, the clutch element is formed of a
cog wheel which engages the spindle like a comb.
In another preferred embodiment, the clutch element is formed of
at least one nut which is attached to the tubular shaft by means
of a ball bearing.
Syringe pumps in accordance with this invention also have the advantage
that no separation of the drive element from the screw spindle is
necessary when the drive element is slid manually along the screw
spindle. The clutch element, i.e. the cog wheel or the nut, remains
engaged with the thread of the screw spindle so there is no mechanical
play after the syringe is inserted and the pushing component is
fixed against the bottom pressure plate of the syringe. Thus, the
actual translational movement of the pushing component is not retarded.
To move the drive element and the pushing component manually, only
the brake element must be released so that the cog wheel and the
nut, respectively, are released. The clutch element then can turn
upon the screw spindle during manual sliding, whereby the clutch
elements remain engaged with the screw spindle. After securing the
pressure plate and the syringe to the pushing component, the brake
element is actuated to fix the clutch element in its position. In
this manner, the position of the drive element relative to the screw
spindle is defined and subsequent rotating motion of the screw spindle
is translated into the desired movement of the drive element. There
is no mechanical play at the beginning of the rotary movement of
the screw spindle so the movement of the screw spindle is directly
conveyed to the drive element and the syringe piston. This saves
time and allows safer handling of the syringe pump.
To ensure that the nut can rotate freely after releasing the brake
element the pitch of spindle and nut is set large enough to prevent
The brake element may connect at the cog side or--if a larger braking
surface is desired--at the front side of the cog wheel. If a nut
is used as a clutch element, the brake element preferably connects
at the front side of the nut. To achieve optimum braking effect,
the brake element may be equipped with brake lining on the contact
A connector, which is biased by a spring, links the brake element
to an actuation element at the pushing component for actuation.
According to one preferred embodiment of the invention, a brake
tube may be held in the tubular pull-shaft, by means of a spring
which is fastened to the brake tube on one end and to the pushing
component on the other. On this brake tube there is a lever which
is connected with the actuation button in a fashion allowing pivotal
movement of the lever. When the actuation button is pressed, the
brake tube is pressed against the force of the spring and the brake
element is released from the clutch element. Releasing the actuation
button causes the spring to push the brake tube into its initial
position so the brake element presses against the clutch element
and blocks it.
The drive element is preferably provided with a cage to hold the
clutch elements, located at the side of the drive element facing
the pushing component.
Examples for the preferred embodiments of this invention are explained
in more detail below with the use of illustrations. The following
items are shown:
FIG. 1 A top plan view of a syringe pump.
FIG. 2 A bottom plan view of the syringe pump, according to FIG.
FIG. 3 A partial cross-section of the clutch according to a first
FIG. 4 A partial cross-section of the clutch according to another
preferred embodiment of the invention.
The casing (20) of the syringe pump depicted in FIGS. 1 and 2 is
provided with a mounting (7) on its upper side which partially encircles
the syringe (3). The position of the syringe is fixed by a shoulder
of the syringe (5) which is disposed between a holder (31) and a
mounting (7). The syringe piston (4) is connected to the pushing
component (8) by a pressure plate (6).
The pushing component (8) is fastened to the drive element (2).
As can also be seen in FIG. 1 a button (9) is connected to the
pushing component (8) for actuation of the brake. The brake will
be described in more detail below.
FIG. 2 is a representation of the syringe as seen from the bottom.
A motorized drive (11) is connected to the screw spindle (14) via
the two cog wheels 12 and 13. The drive may be an electric motor
which is attached to the casing (20).
The screw spindle is part of the transmission, which also includes
the cog wheels (12 13) and the clutch element (17). The screw spindle
(14) is disposed parallel to the axis of the motor, one end of which
is held in the clutch element in a manner that allows rotary movement.
The other end is held in a bearing stand (32) that is fastened to
the casing and which allows rotary movement of the screw spindle
but prevents it from shifting axially. As can be seen in FIG. 3
the clutch element is disposed in a cage (28). To prevent distortion
of the tubular shaft (10) during rotation of the screw spindle (14),
the tubular shaft (10) and cage (28) are connected to a distortion
preventing rod (16), which is fastened to the casing (20) parallel
to the screw spindle by means of a sliding guide (29).
FIG. 3 shows one preferred embodiment of the clutch. The clutch
element (17), in this example, is formed of the two cog wheels (18a,
18b), which are contained in cage 28 in a bearing that allows rotary
movement. These cog wheels (18a, 18b) are permanently engaged with
the thread of screw spindle 14. To alternatively block or release
the two cog wheels, two brake elements (21) are provided in the
shape of a pipe flange. The brake elements (21) are made from a
unitary piece and of a shape complementary to brake tube 15 and
are provided with brake lining (22) on the contact surface. The
brake tube is disposed in tubular pull-shaft 10 which is fastened
to the pushing component (8). The brake tube (15) also extends into
pushing component 8 and has a pivoting lever (24) at its end which
is connected to brake tube 15 at point 26 and to pushing component
8 at point 33 in a manner which allows a pivotal movement. The
upper end of the lever (24) is connected to the actuation button
(9). In brake tube 15 there is another spring (23), which is fastened
to plate 27 of the brake tube on one end and connected to pushing
component 8 at the other end via a wire (25).
When the actuation button (9) is pressed, the brake tube (15) shifts
to the left against the force of spring 23 so the brake elements
release the cog wheels (18a, 18b). The actuation button (9) is pressed
until pushing component 8 has reached the desired position. In this
process, the cog wheels (18a, 18b) slide in the thread of the screw
spindle (14). When the desired position is reached, the actuation
button is released and spring 23 pressed brake tube 15 back into
its initial position where the brake (21) elements block the cog
wheels (18a, 18b).
FIGS. 4 shows another preferred embodiment. In this embodiment,
the clutch element is formed of a nut (19) which is held in cage
28 by ball bearings, allowing rotary movement. The front side of
nut 19 is preferably oblique so that a larger surface exists between
brake element 21 and the nut. This brake element (21) also has the
shape of the pipe flange and is provided with brake lining. The
shape of the brake elements (21) is complementary to that of the
brake tube (15) and is connected with the actuation element in the
same manner as described in FIG. 3. The operation of this brake
element as well as the actuation of brake element 21 is analogous
to what has been described in FIG. 3.