Syringe pump abstract
The invention relates to an infusion syringe pump which by means
of a motor-gear unit drives a linearly movable drive member which
is in engagement with the syringe plunger of an infusion syringe.
According to the invention a position-defining element is connected
only to the linearly movable drive member which actuates the syringe
plunger of the infusion syringe. The position-defining element is
functionally coupled to an absolute displacement pickup which is
preferably constructed as linear potentiometer. By the control means
according to the invention the absolute position of the syringe
plunger can be determined.
Syringe pump claims
1. Infusion syringe pump comprising:
a motor-gear unit and a threaded spindle for driving a linearly
movable drive member,
an injection syringe having a syringe plunger which for its actuation
is in engagement with the drive member and
a position detecting means for determining the position of the
syringe plunger, said means having a position-defining element and
a stationary absolute displacement pickup extending along the length
of said threaded spindle,
that the position-defining element is rigidly connected to the
linearly movable drive member, and
that the position-defining element along its path of movement corresponding
to the displacement direction of the drive member is electrically
coupled to the absolute displacement pickup.
2. Infusion syringe pump according to claim 1 characterized in
that the absolute displacement pickup is constructed as linear potentiometer.
3. Infusion syringe pump according to claim 1 characterized in
that the absolute displacement pickup is constructed as inductive,
capacitive or magnetic position-defining element.
4. Infusion syringe pump according to claims 1 2 or 3 characterized
in that the absolute displacement pickup is connected to an evaluation
5. Infusion syringe pump according to claim 1 wherein said position
defining is magnetically coupled to said absolute displacement pickup.
Syringe pump description
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to an infusion syringe pump comprising a
motor-gear unit for driving a linearly movable drive member, an
injection syringe having a syringe plunger which for its actuation
is in engagement with the drive member and a position detecting
means for determining the position of the syringe plunger, said
means having a position-defining element and a stationary absolute
DE-OS 2922037 and DE-GM 8520376 disclose syringe pumps which
operate with optoelectronic detection means. These detection means
have the disadvantage that it is not possible to produce a continuous
signal so that the accuracy of the position detection is a function
of the respective code-dependent quantization of the optoelectronic
US-PS 4620848 discloses an infusion syringe pump in which a first
roller mounted stationarily on a housing is in engagement with a
syringe plunger which in turn is driven by a motor, a gearing and
a second roller whih is also mounted on the housing and which is
drivingly connected to the motor via the gearing. The first roller,
which is rotationally driven, is mounted on the housing and not
on the drive member for the syringe plunger.
Furthermore, an infusion syringe pump is known from US-PS 3701345
in which a motor drives a plunger for expelling the fluid from a
syringe cylinder. This angiographic infusion syringe pump comprises
a position control system which employs a feedback voltage signal
which is not associated with the syringe plunger speed but with
the infusion syringe plunger position. Said feedback signal is generated
by a mechanically driven potentiometer which is set in operation
by the drive motor via an additional gearing. Before performing
the injection the instantaneous position of the syringe plunger
is sensed and the position thereof used as basis reference quantity
or zero limit. The desired injection volume, corresponding voltage
limits or the desired rate are predefined proportionally to the
voltage by the operator.
As mentioned above, in this system a potentiometer is used to detect
the instantaneous position of the syringe plunger. The position
signal is compared with a control signal and the resulting difference
used to operate the motor. The motor is influenced by a voltage-limiting
circuit which prevents the motor delivering too much power. On return
of the syringe plunger into its initial position the direction of
rotation of the motor and thus of the gearing is reversed. In such
infusion syringe or injection pumps in which the injection or syringe
plunger is returned to its initial position in dependence upon the
motor-gear unit by reversal of the direction of rotation of the
motor it is admittedly possible to determine at any time an instantaneous
absolute position value of the syringe plunger; however, the construction
of the position control system is made complicated by the necessity
of an additional gearing transmission for the position control system.
The presence of an additional gearing transmission can moreover
introduce a source of error into said control system because inaccuracies
or errors of the additional gearing transmission can give rise to
a deviation of the actual position of the syringe plunger in the
syringe cylinder from the position information supplied by the position
In addition, such a pump is complicated in manipulation because
the entire drive arrangement must be moved to the initial state
when a new (filled) syringe is to be inserted.
In other known infusion injection or syringe pumps in which the
injection or syringe plunger can be returned to its zero position
independently of the motor-gear unit, such as for example described
in DE-OS 3428655 it would be desirable to have such a position
According to the invention the problem is solved in that the position-defining
or position-indicating element is rigidly connected to the linearly
movable drive member, and that the position-defining element along
its path of movement corresponding to the displacement direction
of the drive member is electrically or magnetically coupled to the
absolute displacement pickup.
In a preferred embodiment the absolute displacement pickup is constructed
as linear potentiometer.
In addition, the absolute displacement pickup may be a capacitive
or magnetic position-defining element.
Furthermore, the absolute displacement pickup is connected to an
Due to the preferably rigid connection of the position-pickup element
to the drive member driving the syringe plunger the possible source
of error of the defective auxiliary gear in US-PS 3701345 can
be eliminated. Consequently, due to the direct tapping off of the
instantaneous plunger position extensive freedom from error can
Infusion syringe pumps which can move the syringe plunger into
any desired initial position independently of the motor-gear unit
can be provided with a drive spindle leading to the motor-gear unit
and a drive member which by an actuating element can be disengaged
from the drive spindle by rotation about its longitudinal axis and
thus pulled forwardly or rearwardly independently of the motor-gear
unit, as is the case in DE-OS 3428655. By reengagement of the
drive member the latter can be locked again in any desired position.
Due to the fixed connection the position-indicating or position-pickup
element is displaced with the drive member and correlated thereto
represents the position of the drive member and thus the syringe
The invention will be explained in detail hereinafter with the
aid of an example of embodiment.
DESCRIPTION OF THE DRAWING
The enclosed drawing shows an infusion syringe pump according to
the invention in which the syringe plunger is movable independently
of the motor-gear unit into any desired initial position.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The infusion injection pump comprises a motor-gear unit 1 which
drives a threaded spindle 2 which projects from an end face of the
motor-gear unit 1 and on which a linearly movable drive member 3
The infusion syringe 4 consists of a syringe cylinder 5 and a syringe
plunger 6 having a plunger rod 7. The front end of the syringe cylinder
5 is inserted into a holder 8 which in the case of the example is
mounted on the motor-gear unit 1 of the infusion syringe pump. The
rear end of the plunger rod 7 is inserted into a further holder
9 which is disposed on the linearly movable drive member 3. If the
linearly movable drive member 3 is moved in the direction towards
the motor-gear unit 1 the syringe plunger 6 in the syringe cylinder
5 is displaced and the injectate is expelled through the syringe
outlet 10. The syringe outlet is connected via a (not shown) flexible
tube to the patient.
Such an infusion syringe pump is described in DE-OS 3428655
to the disclosure of which reference is made.
A position-defining element 11 is arranged on the linearly movable
drive member 3 in such a manner that said element is coupled functionally
to an absolute displacement pickup 12 in particular is in engagement
therewith. Said absolute displacement pickup 12 is constructed in
a particular embodiment of the invention as linear potentiometer
as shown in the drawing. The absolute displacement pickup 12 may
also be formed by a known inductive capacitive or magnetic position-indicating
As also apparent from the drawing the absolute value pickup 12
extends parallel to the longitudinal axis of the threaded spindle
2 or to the displacement direction of the drive member 3.
Furthermore, the absolute displacement pickup 12 is connected to
an evaluating unit 13 via the line 14 which in turn is connected
via a line 15 to the motor-gear unit 1.
Likewise, the ends of the linear potentiometer are connected via
the lines 14 to the evaluating unit 13 and form together with the
position-defining element 11 a voltage divider, said element 11
being formed as wiping contact.
The evaluating unit 13 defines the input voltage U.sub.e of the
absolute displacement pickup 12 that is the linear potentiometer,
and at the same time stores said voltage. The position-defining
element 11 on the linearly movable drive member 3 is now also at
a predetermined position of the linear potentiometer which at this
point taps off a certain output voltage signal U.sub.a and passes
said signal to the evaluating unit 13. Said output voltage U.sub.a
is proportional to the position of the position-defining element
11 and thus to the instantaneous position of the syringe plunger
6 in the syringe cylinder 5 and after corresponding conversion indicates
the coordinates thereof on the movement or position axis.
Infusion pumps are usually designed for a certain type of syringe
or injection needle and for technical safety reasons only approved
for one such type. Consequently, the output voltage U.sub.a indicates
for the approved syringe type the absolute coordinate of the syringe
plunger provided the syringe is properly inserted into the receiving
means 8 and 9.
On the other hand, after appropriate calibration another type of
syringe can however also be employed.
The necessary and usual infusion-relevant parameters are centered
into the evaluating unit before and during the infusion operation.
Consequently, the value tapped off at the linear potentiometer can
itself indicate the remaining amount of infusion in the syringe
5 or, via the entered advance rate, the remaining infusion time.
The circuits and components of the evaluating unit 13 correspond
to the state of the art.
Moreover, the evaluating unit 13 as indicated in the drawing by
the line 15 can also be used for controlling the motor-gear unit