Syringe pump abstract
A syringe pump has an arm swung against the barrel of the syringe.
The arm is coupled to a strip mask having a row of transparent apertures
of differing length. The mask extends above a CCD array of sensing
elements and below a concave mirror, which produces a collimated
beam of radiation on the mask from an LED. The length of sensing
elements exposed to radiation through an aperture in the mask gives
an approximate indication of barrel size; the position of an edge
of the aperture gives an accurate indication. The pump compares
the barrel size with information relating size to syringe type and
produces an indication of syringe type on a display.
Syringe pump claims
What we claim is:
1. A syringe pump comprising: a mechanism for engaging and driving
a plunger of a syringe; and a sensor mechanism for sensing a size
of a barrel of the syringe, said sensor mechanism comprising: a
contact member displaceable into contact with said barrel, a mask
member, having at least a first side, coupled with said contact
member and movable in response to movement of said contact member,
and a row of a plurality of optical sensors positioned to receive
radiation transmitted by the mask member, wherein the mask member
includes a plurality of transmitting regions arranged in a row,
each transmitting region having a different length, and wherein
the pump includes a control unit responsive to at least one output
from said sensors, said control unit determining the size of the
barrel from a combination of a length of the row of sensors receiving
radiation transmitted by one of the transmitting regions and a position
of an edge of the transmitting region.
2. A pump according to claim 1 wherein the transmitting regions
are transparent apertures in the mask member.
3. A pump according to claim 1 wherein said radiation source and
said sensors are mounted on said first side of said mask member.
4. A pump according to claim 1 including a collimator for collimating
radiation falling on the mask member.
5. A pump according to claim 4 wherein the collimator is a concave
6. A pump according to claim 1 wherein the contact member is on
a swung arm.
7. A pump according to claim 6 wherein the arm is rotatable about
an axis extending parallel to the axis of the syringe.
8. A pump according to claim 1 wherein said mask member is an
elongate strip and the row of transmitting regions extends along
a length of said strip.
9. A pump according to claim 1 wherein the row of optical sensors
is provided by a CCD array.
10. A pump according to claim 1 wherein said control unit includes
information as to the barrel size of different syringes, and wherein
the control unit provides an output to a display on which an identity
of the syringe is displayed.
11. A syringe pump comprising: a mechanism for engaging and driving
a plunger of a syringe; and a sensor mechanism for sensing a size
of a barrel of the syringe, the sensor mechanism comprising a contact
member displaceable into contact with the barrel, an elongate mask
member coupled with the contact member and movable along its length
to a position dependent on the position of the contact member, said
mask member having a plurality of transparent apertures spaced along
a length of the mask, each said aperture having a different length,
a row of a plurality of optical sensors positioned under the mask
member, a radiation source arranged to direct radiation onto the
sensors through the apertures in the mask such that the length of
the row of optical sensors receiving radiation is dependent on the
aperture located above the sensors and thereby gives an approximate
indication of mask position and barrel size, and such that the position
of an edge of the aperture gives a more accurate indication of position
and barrel size.
Syringe pump description
BACKGROUND OF THE INVENTION
This invention relates to syringe pumps.
Syringe pumps are used to supply medication to a patient. A syringe
is pre-filled with the medication and this is connected to an infusion
line extending to the patient. The syringe is then loaded in the
syringe pump, which applies a force to the plunger of the syringe
to drive medication into the infusion line at a controlled rate.
The user enters information about the size of the syringe and the
dose rate, so that the pump can calculate the drive rate for the
plunger to dispense medication at the correct rate.
Syringe pumps may include a syringe barrel sensor, which provides
a measure of the diameter of the syringe loaded in the pump. A display
is derived from the output from the barrel size sensor so that the
user can-check that he has correctly identified the syringe. The
Series 3000 syringe pump sold by SIMS Graseby of Watford, England
includes a syringe barrel sensor having an arm that is swung into
contact with the outside of the barrel. The arm is coupled to a
mask that is movable between a row of five LEDs and a row of five
photodiodes. The outputs of the photodiodes give an indication of
the position of the mask and hence the size of the barrel of the
syringe. Such an arrangement gives an approximate indication of
the size of the syringe but is not sufficiently accurate to distinguish,
for example, between two syringes from different manufacturers having
similar external diameters.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an alternative
According to the present invention there is provided a syringe
pump including means for mounting a syringe, means for engaging
and driving a plunger of the syringe, and a sensor mechanism for
sensing the barrel size of the syringe, the sensor mechanism including
a contact member displaceable into contact with the outer surface
of the barrel, a mask member coupled with the contact member and
movable in response to movement of the contact member, and a row
of a plurality of optical sensing means positioned to receive radiation
transmitted by the mask member, the mask member including a plurality
of transmitting regions arranged in a row, each transmitting region
having a different length, and the pump including means responsive
to the outputs from the sensors to determine the size of the barrel
from the combination of the length of the row of sensing means receiving
radiation transmitted by one of the transmitting regions and the
position of an edge of the transmitting region.
The transmitting regions are preferably transparent apertures in
the mask member. The pump may include a radiation source mounted
on the same side of the mask member as the sensing means. The pump
may include means for collimating radiation falling on the mask
member, such as a concave reflector. The contact member is preferably
on a swung arm, which may be rotatable about an axis parallel to
the axis of the syringe. The mask member is preferably an elongate
strip and the row of transmitting regions preferably extends along
the length of the strip. The mask member may have five transmitting
regions and the row of optical sensing means may be provided by
a CCD array. The pump preferably includes information of the barrel
size of different syringes such that the syringe type used can be
identified from its barrel diameter, and the pump may include a
display on which the syringe type is displayed.
A syringe pump according to the present invention will now be described,
by way of example, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the pump schematically;
FIG. 2 is a perspective view of a part of the pump with its interior
exposed to show the syringe barrel sensor;
FIG. 3 is a side elevation view of the syringe barrel sensor; and
FIG. 4 is an elevation view from one end of the syringe barrel
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference first to FIG. 1 the pump includes an outer housing
1 with a recess 2 on its front surface shaped to receive a syringe
3 of conventional kind and which may be of a variety of different
sizes. The syringe 3 contains a medication liquid 4 that is dispensed
to a patient via an infusion line 5 by pushing in the plunger 6
of the syringe. The pump has a conventional drive mechanism 7 such
as including a lead screw driven by a motor, coupled with an engaging
mechanism for engaging the head 8 of the plunger 6. The drive mechanism
7 is driven by a control unit 9 which receives inputs from a keypad
10 or other user input means, and from a syringe barrel size sensor
mechanism 20 which is described in detail below. The control unit
9 also provides an output to a display 11.
With reference now also to FIGS. 2 to 4 the syringe barrel size
sensor mechanism 20 includes a swung arm 21 mounted at one end on
a shaft (not shown) extending parallel to and to one side of the
axis of the syringe 3 so that the arm is rotatable about an axis
parallel to the axis of the syringe. The other end of the arm has
a contact finger 22 positioned to contact the outside of the barrel
of the syringe 3. The shaft of the mechanism 20 is connected axially
to a freely rotatable ring 23. A coiled spring 24 connected with
the ring 23 urges it in a sense such that the arm 21 swings down
until its finger 22 contacts the syringe barrel. The ring 23 has
a rod retainer 25 at the edge of the ring projecting parallel to
the axis of rotation of the ring. The retainer 25 secures one end
of a mask 30 extending generally transverse to the syringe axis.
It will be appreciated that rotation of the arm 21 will cause a
corresponding rotation of the ring 23 and a linear movement of the
mask 30 along its length.
The mask 30 comprises a stiff strip of opaque material, such metal
or plastics, having a row or series of five apertures 31 to 35 spaced
apart from one another along the length of the mask. The apertures
31 to 35 are of rectangular shape, each having the same width. The
length, however, of each aperture 31 to 35 along the mask differs
one from the other.
The mask 30 extends lengthways above an optical sensor in the form
of a CCD array 40. The CCD array 40 comprises a row of 103 individual
sensor elements or pixels 41 extending along its length. The length
of the array 40 is greater than that of the longest one of the apertures
31 in the mask 30. The output of the array 40 is supplied to the
control unit 9. An LED 42 is mounted below and to one side of the
mask 30 and is oriented to direct its radiation upwardly. A concave
mirror 43 mounted vertically above the mask 30 is positioned to
be illuminated by the LED 42. The optical properties of the concave
mirror 43 are such that it reflects a beam of radiation, collimated
in a plane including the length of the mask 30 vertically downwardly
onto the mask 30 and hence onto any of the pixels 41 of the CCD
array 40 exposed through apertures 31 to 35 of the mask. Because
the radiation illuminating the CCD array 40 is collimated, it ensures
that sharply-defined shadows are produced by the edges of the apertures
31 to 35. The output of the CCD array 40 is a series of analogue
signal levels each representing the level of light falling on different
ones of the elements 41. This is clocked out of the CCD array 40
and supplied to the control unit 9 which compares the level on
each element 41 to determine whether or not the element is illuminated
through an aperture 31 to 35 or is shadowed by opaque regions of
the mask 30. The control unit 9 performs an algorithm that reads
the outputs of the elements 41 it turn to determine where dark changes
to light and where it changes to dark again. This provides information
on the length of the aperture 31 to 35 through which light falls
on the array 40 so that the particular aperture above the array
can be identified to give an approximate, unique indication of the
position of the mask 30. The position of the boundary between the
light and dark regions defines the edge of the aperture 31 to 35
and this enables the position of the mask 30 to be determined with
high accuracy. Determining the position of the mask 30 from the
edge boundary alone, however, would not give a unique indication
of mask position.
FIG. 2 shows the arm 21 raised to its maximum extent for syringes
3 of the largest size, and the mask 30 is shown at one end of its
travel, with the longest of the apertures 31 positioned above the
array 40. For smaller syringes, the arm 21 has a lower position
and the mask is pulled through the array 40 to a different position.
The assembly is calibrated by inserting two circular bars, in place
of a syringe, the bars having different, known diameters at opposite
ends of the range of syringe sizes. This information may be used
in a linear equation, a look-up table or a combination of both to
determine the size of syringes of other diameters. The face of the
finger 22 contacting the syringe barrel is profiled such as to linearize
the output of the array 40.
The present invention enables the diameter of syringe barrels to
be measured to high accuracy, typically to about 0.4mm. This accuracy
is sufficient to enable a majority of current syringes to be identified
uniquely and enables syringes from different manufacturers to be
distinguished one from the other, even when these have the same
nominal capacity. The control unit 9 contains a library of different
syringes and information as to their diameters. The output from
the array 40 is used to calculate the diameter of the syringe 3
and this is compared against the table to determine which syringe
is loaded. The control unit 9 provides a signal to the display 11
indicating the identity of the syringe loaded, for example "Baxter
10 ml", and prompts the user to confirm that this is correct
by pressing an appropriate key on the keypad 10. Alternatively,
the pump could utilize the information about syringe size as a check
against information input to the pump by the user.
The present invention enables improved safety in the use of syringe
pumps since there is less risk that the user will incorrectly enter
details of the syringe and hence that the pump will dispense an
It will be appreciated that the invention could be modified in
various different ways, especially as to the manner of illumination
of the mask. It is not essential that the mask be a straight strip,
it could be curved if appropriately curved sensor arrays are available.
The mask member could have transmitting regions formed by reflective
regions, rather than by transparent regions. The contact member
engaging the outside of the barrel could be movable linearly rather