U.S. patent application number 11/840545 was filed with the patent office on 2008-03-27 for spring guide suitable for use in, for example, an injection device.
Invention is credited to Edgar Hommann.
Application Number | 20080077090 11/840545 |
Document ID | / |
Family ID | 35811760 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080077090 |
Kind Code |
A1 |
Hommann; Edgar |
March 27, 2008 |
SPRING GUIDE SUITABLE FOR USE IN, FOR EXAMPLE, AN INJECTION
DEVICE
Abstract
An injection appliance including a housing, a product container
received by the housing and containing a product, a piston received
in the housing in such a way that it can be displaced in a forward
direction to dispense the product, a piston rod which acts on the
piston in the forward direction, and a spring which acts on the
piston rod in the forward direction, wherein, in one embodiment,
the spring includes at least two adjacent spring sections each
having a different buckling resistance in relation to the same
length when the piston rod is a forward position and, in another
embodiment, the appliance includes a spring guiding structure that
is entrained during a forward movement of the piston rod and
secures the spring against buckling, wherein, when the piston rod
is in the forward position, the guiding structure extends past an
end of the rod.
Inventors: |
Hommann; Edgar;
(Grossaffoltern, CH) |
Correspondence
Address: |
DORSEY & WHITNEY LLP;INTELLECTUAL PROPERTY DEPARTMENT
SUITE 1500
50 SOUTH SIXTH STREET
MINNEAPOLIS
MN
55402-1498
US
|
Family ID: |
35811760 |
Appl. No.: |
11/840545 |
Filed: |
August 17, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CH06/00017 |
Jan 11, 2006 |
|
|
|
11840545 |
Aug 17, 2007 |
|
|
|
Current U.S.
Class: |
604/135 ;
604/110 |
Current CPC
Class: |
A61M 2005/31518
20130101; F16F 1/12 20130101; A61M 2005/206 20130101; A61M 5/24
20130101; A61M 5/3202 20130101; F16F 1/128 20130101; A61M 2005/2013
20130101; A61M 5/2033 20130101 |
Class at
Publication: |
604/135 ;
604/110 |
International
Class: |
A61M 5/20 20060101
A61M005/20; A61M 5/00 20060101 A61M005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2005 |
DE |
20 2005 006 333.9 |
Mar 10, 2005 |
DE |
20 2005 003 847.4 |
Apr 15, 2005 |
DE |
10 2005 017 477.9 |
Claims
1. An injection device comprising: a housing; a product container
received by the housing and containing a product to be injected; a
piston received in the housing in such a way that it can be moved
in a forward direction to inject the product; a piston rod which
acts on the piston in the forward direction; a spring which acts on
the piston rod in the forward direction; and a guide that is
entrained during a forward movement of the piston rod and secures
the spring against buckling, wherein, when the piston rod is in a
forward position, the guide extends past an end of the rod.
2. An injection device comprising: a) a housing; b) a product
container accommodated by the housing, in which a plunger is
accommodated so that it can be moved in a distal direction to
dispense product; c) a plunger rod acting on the plunger in the
distal direction; d) a spring acting on the plunger rod in the
distal direction; and a guide structure for the spring, the guide
structure extending in the proximal direction beyond the plunger
rod to prevent the spring from buckling when the plunger rod is in
a most distal position.
3. The injection device as claimed in claim 2, wherein the guide
structure is driven when the plunger rod is driven distally.
4. The injection device as claimed in claim 3, wherein the guide
structure and at least one of the plunger rod and spring are in
engagement or move into engagement when the plunger rod is driven
distally, causing the guide structure to be driven as the plunger
rod is driven.
5. The injection device as claimed in claim 4, wherein the plunger
rod is able to move in the distal direction relative to the guide
structure.
6. The injection device as claimed in claim 5, wherein the guide
structure surrounds the spring.
7. The injection device as claimed in claim 5, wherein the spring
surrounds the guide structure.
8. The injection device as claimed in claim 2, wherein the guide
structure is in engagement with the spring, causing the guide
structure to be driven by the spring.
9. The injection device as claimed in claim 8, wherein the guide
structure comprises an engagement element which presses against the
spring.
10. The injection device as claimed in claim 9, wherein the
engagement element engages between adjacent coils of the
spring.
11. The injection device as claimed in claim 2, further comprising
a guide portion which overlaps the plunger rod when the plunger rod
is in the most distal position, the plunger rod moving away from
the position overlapping with the guide portion when driven in the
distal direction and a proximal end of the plunger rod spaced at a
distance axially apart from the guide portion when the plunger rod
is in the most distal position.
12. The injection device as claimed in claim 2, wherein the plunger
rod at least substantially overlaps with the guide structure in the
distal direction when in a most proximal position.
13. The injection device as claimed in claim 2, wherein the housing
comprises a mount for the product container so that the container
can move in the distal direction and the spring acts on the product
container in the distal direction.
14. The injection device as claimed in claim 13, wherein the spring
acts on the product container via the plunger.
15. The injection device as claimed in claim 2, wherein the spring
is a coil spring with coils extending adjacent to one another in a
spiral about a spring axis, said coil spring used as a compression
spring for the injection device and having a first axial spring
portion with a first buckling resistance in a relaxed state and a
second axial spring portion with a second, higher buckling
resistance in the relaxed state.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International
Application No. PCT/CH2006/000017, filed on Jan. 11, 2006, which
claims priority to German Application No. DE 20 2005 006 333.9
filed on Feb. 18, 2005, Germany Application No. DE 20 2005 003
847.4 filed on Mar. 10, 2005 and German Application No. DE 10 2005
017 477.9 filed on Apr. 15, 2005, the contents of all of which are
incorporated in their entirety herein by reference.
BACKGROUND
[0002] The present invention relates to a device for injecting,
administering, delivering, dispensing or infusing substances, and
to methods of making and using such devices. More particularly, the
present invention relates to an injection device with a spring,
which serves as a driving spring for a conveying mechanism of the
injection device. The invention further relates to a spring used as
a compression spring, e.g., a driving spring, for an injection
device. The injection device may be an injection pen for
administering insulin, growth hormones or an osteoporosis
preparation in particular.
[0003] Mechanical springs, such as coil springs used as compression
springs, are often used in injection pens as a means of driving a
plunger in a container filled with the product to be injected in a
forward drive direction, generally the distal direction. Such use
as a driving spring is known from applications based on automatic
injection devices in particular, which represents one preferred
type of injection device for the purpose of the invention. Driving
springs of well known automatic injectors are used not only to
drive the plunger forward, but also to drive the injection needle
during the injection. This being the case, the spring is therefore
not only relaxed or the tension therein released by the distance
over which the plunger has to be driven but also by the length over
which the needle has to be driven during the injection. In such
cases, the driving spring of an automatic injector is longer than a
driving spring which is used to drive the plunger only wherein the
respective product containers must naturally be of the same length.
The longer and slimmer the injection spring is, the more critical
bending or buckling stresses can be, particularly in the case of
automatic injectors, because the spring is typically required to
expend a higher spring force in the forward drive direction than
springs which only have to drive the plunger due to the fact that
it has to drive the needle.
[0004] An automatic injector of the type to which the invention
relates in particular, although not exclusively, is known from
German patent application No. 103 51 594. With this automatic
injector, the plunger rod is provided in the form of a sleeve with
a base or shoulder at its distal end and the driving spring
projects into the sleeve in the distal direction onto the base or
shoulder. Depending on the type of product container, the plunger
rod sleeve is correspondingly slim and the spring is therefore
slimmer. In order to prevent buckling or even just an outward
deflection of the spring, the plunger rod co-operates with a
support structure on which the spring is supported in the proximal
direction to form a telescopic guide for the spring. The plunger
rod and a guide portion of the support structure extend by an
appropriate length in the distal direction in order to continue
providing a reliable guide for the plunger rod even when the
plunger rod has assumed its most distal position, having emptied
the container.
SUMMARY
[0005] One object of the present invention is to improve the
functional reliability of a driving spring of an injection device.
Another object of the invention is to provide a spring for use in
an injection device which is less susceptible to defects.
[0006] In one embodiment, the present invention comprises an
injection device comprising a housing, a product container received
by the housing and containing a product to be injected, a piston
received in the housing in such a way that it can be moved in a
forward direction to inject the product, a piston rod which acts on
the piston in the forward direction, a spring which acts on the
piston rod in the forward direction, and a guide that is entrained
or in use during a forward movement of the piston rod and secures
the spring against buckling, wherein, when the piston rod is in a
forward position, the guide extends past an end of the rod.
[0007] In one embodiment, the present invention comprises an
injection appliance including a housing, a product container
received by the housing and containing a product, a piston received
in the housing in such a way that it can be displaced in a forward
direction to dispense the product, a piston rod which acts on the
piston in the forward direction, and a spring which acts on the
piston rod in the forward direction, wherein, in one embodiment,
the spring includes at least two adjacent spring sections each
having a different buckling resistance in relation to the same
length when the piston rod is a forward position and, in another
embodiment, the appliance includes a spring guiding structure that
is entrained during a forward movement of the piston rod and
secures the spring against buckling, wherein, when the piston rod
is in the forward position, the guiding structure extends past an
end of the rod.
[0008] In one embodiment, the present invention comprises a device
for injecting a liquid product, comprising a housing, a product
container mounted in the housing with a plunger accommodated in it,
a plunger rod and a spring acting on the plunger rod. In some
embodiments, the spring acts on the plunger rod in the distal
direction, which in turn acts on the plunger. The spring acts as a
compression spring and extends lengthways in the distal direction,
i.e., its axial or longitudinal length measured in the distal
direction is significantly larger than its width measured
perpendicular thereto.
[0009] In accordance with some embodiments of the present
invention, the spring has at least two spring portions of differing
buckling resistance disposed adjacent to one another in the distal
or longitudinal direction, namely a first spring portion and a
second spring portion with a different, e.g., higher buckling
resistance than the first spring portion. In some embodiments, the
buckling resistance of the second spring portion is sufficiently
high that a guide for the spring can be dispensed with in the
second spring portion and may not be implemented in some
embodiments. In such embodiments, the plunger rod or the container
guides or guide a distal spring portion, which may form the first
spring portion or one of several first spring portions. While in
some embodiments the second spring portion can be used to bridge a
distance of the spring which requires no guide during and after
driving the plunger rod forward, it is at least the first spring
portion which drives the plunger rod forward because the spring is
softer in the first spring portion than in the second spring
portion due to the lower buckling resistance. Accordingly, in some
embodiments the difference in length between the tensed and the
relaxed state of the spring is bigger in the first spring portion
than in the second spring portion.
[0010] In some preferred embodiments, the spring has at least one
other axial spring portion with a lower buckling resistance. The at
least one other spring portion may correspond to the first spring
portion in terms of buckling resistance and spring stiffness. If
the spring has at least two spring portions with a lower buckling
resistance, for example two identical first spring portions in
terms of spring stiffness and buckling resistance, which may be of
the same or different lengths, the forward driving movement is
advantageously distributed to these several axial spring portions
with a lower buckling resistance. The second axial spring portion
may bridge a distance without any guide whatsoever, although in
some preferred embodiments it is guided at one of its axial ends at
least at both axial ends, including when the plunger rod is in the
most distal position.
[0011] In some preferred embodiments, if the spring has two axial
spring portions with a lower buckling resistance, the second axial
spring portion is disposed between these two spring portions. In
other embodiments, the spring has spring portions of higher
buckling resistance axially alternating with spring portions of
lower buckling resistance. Such a spring is able to bridge several
distances which have no guide and optimum use can be made of the
spring action within distances which are guided.
[0012] One spring, in accordance with the present invention, is a
compression spring as such and is provided in the form of a coil
spring with a plurality of coils, which extend in a spiral along a
spring axis. The differing degrees of buckling resistance in such
springs may be obtained in various ways. For example, the
cross-section of the spring wire may be larger in the second axial
spring portion than in the first axial spring portion, and the same
applies if even more different axial spring portions are provided.
However, in some preferred embodiments, the variation in buckling
resistance is obtained by varying the pitch of the spring coils, in
which case the pitch in the first spring portion is higher than in
the second spring portion, at least when the spring is in the
relaxed state, so that the coils in the second spring portion lie
closer to one another than in the first spring portion. In some
preferred embodiments, the spring is dimensioned so that the coils
in the second spring portion lie against one another in a block
when the plunger rod assumes its most distal position having
emptied the product container. If the spring has several axial
spring portions of lower buckling resistance or several spring
portions of both types, what was said about the first and second
spring portions above applies to the other axial spring
portions.
[0013] In some embodiments, the buckling resistance of the spring
portions is defined for the same axial length in each case for each
spring portion, i.e., the buckling resistance is based on a unit of
length. In the situation where spring portions have different
lengths, the length of the shorter spring portion, or if there are
more than two different spring portions, the length of the shortest
spring portion, may be used as the reference length. If the
different spring portions are homogeneous across their entire
length, is in some preferred embodiments, the characteristic
"buckling resistance" may simply be replaced by the characteristic
"bending strength" which does not depend on length. However, in
situations where the spring portions of differing buckling
resistance are not homogeneous across their respective length, the
higher buckling resistance of the at least one second spring
portion is also combined with a higher bending strength across its
length in each cross-section.
[0014] In some preferred embodiments, the spring in accordance with
the invention is used as the driving spring as described above. In
principle, however, it may advantageously be installed in any
situation where it is necessary to contend with bending or buckling
stress.
[0015] Although a spring in accordance with the invention may
advantageously be used without a guide in the second spring portion
or the several axial spring portions of higher buckling resistance,
a guide or guide structure for the spring can be provided in
accordance with the invention. In some embodiments, the guide is
driven with the plunger rod as it is driven forward. When the
plunger rod assumes a selected or its most distal position having
emptied the container, the spring projects in the proximal
direction beyond the plunger rod and is prevented from buckling by
the guide or guide structure. The guide structure is advantageously
may be used in combination with a spring in accordance with the
present invention. If a guide structure is provided, however, it is
also possible to use a conventional spring as an alternative,
comprising axial spring portions each with an identical buckling
resistance, e.g., an identical buckling resistance everywhere
across or along the entire spring length.
[0016] A guide structure in accordance with the present invention
may be of a bellows-type design, for example, guiding the spring at
certain points. In some embodiment, the guide may be of an axially
stiff design or generally tubular. In some preferred embodiments,
the guide structure comprises a single part and, in combination
with the plunger rod, forms a guide telescope with the plunger rod
serving as a first telescopic portion and the guide structure
serving as a second telescopic portion. In principle, the guide
structure may also have several parts, and may itself form a guide
telescope.
[0017] The plunger rod can advantageously be moved in the distal
direction relative to the guide structure. So that providing the
guide structure does not require making the injection device longer
in the distal-proximal direction or at least making it necessary to
make it considerably longer, it is of advantage if the plunger rod
partially or totally overlaps with the guide structure in its most
proximal position and the overlap is reduced by the forward driving
action of the plunger rod.
[0018] In some preferred embodiments, the present invention may
applied advantageously to automatic injectors, e.g., injection
devices wherein an injection needle is automatically pushed forward
relative to the housing when triggered, until it projects forward
by a sufficient length beyond the housing or a needle guard which
can be moved relative to the housing to permit an injection, and
wherein the product is automatically conveyed out of the container
when triggered. A spring in accordance with the invention may
constitute the driving spring of an automatic injector and drive
the injection needle, beyond the container, and the plunger
forward. The driving spring of an automatic injector of this type
usually extends longitudinally in the distal direction, which means
that automatic injectors may be susceptible to the problem of
buckling or flexing of the spring to a specific degree unless
counter-measures are taken.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a first exemplary embodiment of an injection
device prior to triggering;
[0020] FIG. 2 shows the injection device of the first embodiment
after triggering;
[0021] FIG. 3 shows a second exemplary embodiment of an injection
device prior to triggering;
[0022] FIG. 4 shows the injection device of the second embodiment
after triggering;
[0023] FIG. 5 shows a third exemplary embodiment of an injection
device prior to triggering; and
[0024] FIG. 6 shows the injection device of the third embodiment
after triggering.
DETAILED DESCRIPTION
[0025] FIGS. 1 and 2 illustrate an injection device in accordance
with one embodiment of the present invention. Both show the same
longitudinal section, FIG. 1 showing an initial state prior to
triggering and FIG. 2 after triggering. The injection device is an
automatic injector, which automatically effects the entire
injection once placed on the injection site and triggered, i.e.,
piercing by the injection needle and dispensing of a product or
substance to be injected or delivered.
[0026] Disposed in a housing 1 of the injection device is a
container 2 filled with the product to be injected, accommodated so
that it is able to move in the distal direction V along a central
longitudinal axis L of the injection device. The container 2 may be
an ampoule of the type commonly used with such devices, with an
outlet at a distal end and a plunger 3 which seals the container 2
at the proximal end. The plunger 3 is accommodated so that it can
move in the container 2 along the axis L to dispense the product
through an injection needle 4 fitted on the distal end of the
container 2 and projecting in the distal direction V due to a
driving action in the distal or forward direction V. The injection
needle 4 is provided in the form of a cannula, i.e., with a hollow
cross-section, but could also have a solid cross-section with at
least one flow passage at the outer or peripheral surface. The
injection needle 4 is surrounded by a needle guard 18 extending
beyond its distal tip. The needle guard 18 forms both a visible
screen, i.e., it blocks any view of the injection needle 4, and
serves as a protection against piercing by the injection needle
4.
[0027] The container 2 is accommodated in a container holder 5. The
container holder 5 tightly or closely surrounds the container 2.
The housing 1 guides the container 5 so that it can move axially.
The container 2 engages round the container holder 5 by a container
flange formed at or near the proximal end so that a force acting on
the container 2 in the distal direction V is transmitted to the
container holder 5.
[0028] In addition to the plunger 3, a conveying mechanism of the
injection device comprises a plunger rod 10 and a driving spring
12. The driving spring 12 is a coil spring and when the injection
device is triggered acts as a compression spring in the distal
direction V on the plunger rod 10, which transmits the spring force
to the plunger 3. The driving spring 12 projects in the distal
direction V into the hollow cylindrical plunger rod 10, where it
sits against a base of the plunger rod 10. The plunger rod 10 is
provided in the form of a slim, thin-walled sleeve with a base
which is likewise thin. The base could also be replaced by a
narrow, inwardly projecting shoulder; it is merely necessary to
ensure that the driving spring 12 is reliably supported. The base
sits in a loose abutment contact with the rear face of the plunger
3. In the proximal or rearward direction, the driving spring 12 is
supported on a support and guide structure 8. When the driving
spring 12 is in the tensed state, virtually its entire length is
accommodated in the plunger rod 10 and it projects beyond the
plunger rod 10 in the proximal direction as far as necessary for it
to be supported.
[0029] The driving spring 12 is held in the tensed state by a
retaining mechanism. The retaining mechanism can be released. It
comprises a blocking element 6, a spring 7, the support and guide
structure 8, a snapper 9a and a retaining element 11 connected to
the plunger rod 10. The retaining element 11 is an outwardly
directed flange formed on the end of the sleeve wall of the plunger
rod 10. The retaining element 11 engages behind an elastic
resilient lug 8a of the support and guide structure 8 when the
device is in the initial state. In the initial state, the resilient
lug 8a is bent elastically radially inwardly, engaging with the
retaining element 11. Back-snapping is prevented by a co-operating
surface of a snapper sleeve 9, which is an elastic flexible lug
constituting the snapper 9. The snapper sleeve 9 is joined to the
housing 1 so that it can not move axially and surrounds the support
and guide structure 8. At its proximal end, its snapper 9a has a
thicker region disposed radially inwardly, by which it locates in a
recess in an external face of the support and guide structure 8.
The sleeve-shaped blocking element 6 blocks the snapper 9a in this
engagement. The spring 7 acts on the blocking element 6 in the
proximal direction. In the initial state, the blocking element 6 is
locked in the position blocking the snapper 9a. The lock can be
released by operating a trigger element.
[0030] To trigger the injection device, the trigger element is
operated and the lock of the blocking element 6 is released as a
result. The blocking element 6 moves in the proximal direction
relative to the housing 1, support and guide structure 8 and
snapper 9a due to the force of the spring 7 and releases the
snapper 9a. Since the force of the tensed driving spring 12 acts on
the support and guide structure 8, the support and guide structures
8 pushes in the proximal direction against the snapper 9a, which is
still engaged but has already been released by the blocking element
6, so that it bends elastically outwardly, thereby releasing the
engagement between the snapper 9a and the support and guide
structure 8. The recess of the support and guide structure 8 and
the portion of the snapper 9a engaging in the recess are shaped so
that the engaging portion is able to slide out of engagement due to
the spring force of the support and guide structure 8 acting in the
proximal direction by bending the snapper 9a outwardly.
[0031] After the engagement is released, the driving spring 12
pushes in the proximal direction in the initial phase after
releasing the support and guide structure 8 until it reaches a stop
9b formed by the snapper sleeve 9. When the support and guide
structure 8 has reached the stop position or, optionally, shortly
before moving into the stop position, the resilient lug 8a, which
until now has been in engagement with the retaining element 11,
snaps radially outwardly out of engagement so that the plunger rod
10 is released. The driving spring 12 is now able to push the
plunger rod 10 in the distal direction V relative to the housing 1.
Due to the static friction acting between the plunger 3 and the
side wall of the container 2, the container 2 and together with it
the container holder 5 are moved in the distal direction V in what
is now the second displacement phase after triggering. During this
movement, the injection needle 4 moves out from the housing 1 into
a farthest distal position. The forward movement is restricted by
the container holder 5 moving into abutment with a co-operating
stop. When the container holder 5 moves into abutment with the
co-operating stop, the static friction between the plunger 3 and
the container 2 is overcome, and the driving spring 12 pushes the
plunger 3 in the container 2 forward in the distal direction V
during a third displacement phase so that the product is dispensed.
The displacement phases or movements described above may take place
one after the other without any overlap or may at least partially
overlap with one another in time. In some embodiments, the moved
parts are mounted so that the conveying stroke of the plunger 3
does not start until the piercing movement of the injection needle
4 has ended.
[0032] FIG. 2 illustrates the injection device after an injection.
The container 2 has been emptied. The plunger 3 and the injection
needle 4 each assume their most distal position. The driving spring
12 is relaxed other than a minimum tension needed to drive the
plunger 3 forwardly. In this state, the residual tension extends
across a part of or the major part of the total length of the
injection device measured from the distal end of the housing 1 as
far as the proximal end of the injection device.
[0033] After the injection, and after the injection needle 4 has
been removed from the body tissues and the injection device moved
away form the injection site, the needle guard 18 snaps relative to
the container holder 5 and the injection needle 4 in the distal
direction as far as a guard position in which the needle guard 18
fully surrounds the injection needle 4 to beyond the tip. In the
guard position, the needle guard 18 is locked in position prior to
triggering the injection device, so that it is not able to move in
the proximal direction relative to the injection needle 4. In the
guard position after the injection, the lock is effected by an
abutment contact of the proximal end of the needle guard 18 and a
distal end of a locking element 19 as the needle guard 18 is moved
with its proximal end in front of the locking element 19 after the
injection needle 4 has been extracted, thereby releasing the
pressure induced by the action of a spring, not illustrated. Prior
to the injection, this movement of the needle guard 18 is prevented
by a blocking mechanism which automatically releases as the
container 2 is moved.
[0034] As may be seen from FIG. 2, the driving spring 12 has axial
spring portions 12a and 12b, in which the spring coils lie next to
one another at different distances. In the middle spring portion
12b, all the spring coils lie in a block in contact with one
another in the axial direction in the state of residual tensioning,
while he spring coils in the two outer spring portions 12a are
spaced apart from one another. The two outer spring portions 12a
differ from one another in terms of their length. Due to the fact
that the spring coils in the middle spring portion 12b lie closer
together, a higher buckling resistance is obtained across the
length of the spring portion 12b than in the two outer spring
portions 12a, and their buckling resistance is defined on the basis
of the length of the middle spring portion 12b compared with each
of the part-portions. The higher buckling resistance also means
higher spring stiffness, so that the spring work needed to drive
the plunger 3 and the injection needle 4 is effected in the two
outer axial spring portions 12a. There, the driving spring 12
expands axially when relaxed. In the embodiment illustrated as an
example in which the spring coils in the middle spring portion 12b
still lie in a block when the plunger 3 is in its most distal
position, the entire spring work is effected in the two outer
spring portions 12a. In other embodiments, however, it would also
be conceivable for the driving spring 12 to be relaxed in the
middle spring portion 12b, albeit less than in the outer spring
portions 12a and at the cost of buckling resistance.
[0035] In the spring portions 12a, the driving spring 12 is guided
or at least secured during the entire driving movement. The plunger
rod 10 serves as a guide because the spring coils lie against its
internal surface. The support and guide structure 8 forms a guide
in the wider sense, i.e., it prevents excessive bending or buckling
of the proximal spring portion 12a. To this end, the support and
guide structure 8 forms a guide portion 8b, on the internal surface
of which the plunger rod 10 is guided via its retaining element 11.
Accordingly, there is a slight radial distance between the driving
spring 12 and the guide portion 8b once the plunger rod 10 has been
extracted but it is sufficient to prevent the driving spring 12
from bending.
[0036] When the plunger rod 10 assumes a selected or its most
distal position as illustrated in FIG. 2, it is extracted from the
guide portion 8b and there is an axial clearance distance between
the plunger rod 10 and the support and guide structure 8. The
driving spring 12 is neither guided nor secured to prevent bending
or buckling across the length of this distance. The spring portion
12b bridges this distance, thereby also preventing any excessive
bending or buckling of the driving spring 12 across its length. To
improve reliability, the spring portion 12b projects in the distal
direction V by a short distance farther into the plunger rod 10 and
in the proximal direction also a short distance into the guide 8b.
This further enhances reliability of the prevention of bending and
buckling.
[0037] In respect of the driving spring 12 in the embodiment
described as an example herein, it should be pointed out that it
may be wound from the same spring wire with the same overall
cross-section and with the same material properties across its
entire length. The increased buckling resistance is therefore
exclusively attributable to the smaller pitch of the coils in the
spring portion 12b. The pitch in the spring portions 12a overall is
the same. The pitch is also constant in the spring portion 12b. In
the middle portion, therefore, the bending resistance is higher
overall than in the outer spring portions 12a.
[0038] The axial distance between the plunger rod 10 and the
support and guide structure 8 corresponds to the length by which
the injection device is shorter than an otherwise identical
injection device in which the driving spring is guided or secured
across its entire length in the conventional manner in the relaxed
state.
[0039] If the container holder 5 or optionally the container 2
directly is not locked in its most distal position to prevent a
movement in the proximal direction relative to the housing 1, the
specific buckling resistance of the spring 13 prevents the spring
13 from buckling, if a force directed in the proximal direction is
applied to the needle guard 18 and acts on the container 2 and
ultimately the spring 13 due to the abutment contact between the
needle guard 18 and locking element 19 and its abutment contact
with the container holder 5. However, the buckling resistance of
the spring 13 is also advantageous even during the piercing
movement of the injection needle 4 and the conveying movement of
the plunger 3.
[0040] FIGS. 3 and 4 illustrate a second exemplary embodiment of an
injection device, in which, when the plunger 10 is extracted, the
axial distance is bridged by a guide or guide structure 15 which
prevents any excess bending or buckling of the driving spring 13 in
this region. FIG. 3 illustrates the injection device in the initial
state prior to triggering and FIG. 4 shows the device after
triggering and emptying the container 2.
[0041] The driving spring 13 has adjacent spring portions 13a and
13b alternating in the axial direction wherein the buckling
resistance of the spring portions 13b is higher than that of the
spring portions 13a based on identical lengths in each case. The
spring portions 13a and 13b are respectively shorter than the
corresponding spring portions 12a and 12b of the first embodiment
described above. The more buckling resistant spring portions 13b
are significantly shorter than the axial distance between the
support structure 8 and the plunger rod 10 disposed in the most
distal position, and the guide structure 15 is therefore provided
to help prevent any excessive bending or buckling of the driving
spring 13 in this region.
[0042] Apart from the driving spring 13 and the guide structure 15
as well as an associated modification made to the guide portion 8b,
the injection device of the second embodiment corresponds to the
embodiment described as a first example and the same reference
numbers are used to denote the same components. Reference may
therefore be made to the descriptions given above.
[0043] The guide or guide structure 15 is an integral,
intrinsically stiff sleeve, which is mounted in a sliding seating
on the external surface of the plunger rod 10. It has two sleeve
portions merging into one another, namely a distal or forward
portion with a first internal diameter and a proximal or rear
sleeve portion with a second, larger internal diameter. The
proximal portion is longer than the distal portion. By its distal
sleeve portion, the guide structure sits in sliding contact on the
plunger rod 10. It is also in contact with it by its distal end in
the initial state as well as the rear face of the container 2 at
least when the plunger rod 10 is disposed in the distal direction
V. The external face of the guide structure 15 is smooth and is in
sliding contact with an internal face of the guide portion 8b. In
principle, however, an annular gap could also be formed between the
guide structure 15 and the guide portion 8b.
[0044] In the initial state, the plunger rod 10 fully overlaps with
the guide structure 15. The guide structure 15 is also at least
substantially accommodated in the support and guide structure 8.
The guide structure 15 does not therefore requires that the
injection device has to be made longer.
[0045] When the injection device is triggered, the displacement
sequence described in connection with the first embodiment is set
in motion. The sliding seating of the guide structure 15 on the
plunger rod 10 is designed so that the guide structure 15 is driven
by the plunger rod 10 as well during the driving movement of the
container 2 and always remains in contact with the container 2.
Once the container holder 5 has reached its stop position, the
plunger rod 10 pushes the plunger 3 in the distal direction V
during the final displacement phase until the container 2 has been
emptied. During the final displacement phase, the plunger rod 10
moves in sliding contact relative to the guide structure 15 until
it has reached its most distal position. The guide structure 15
forms a driving shoulder due to the transition between the distal
portion and the proximal portion, against which the retaining
element 11 of the plunger rod 10 moves into abutment at least when
the plunger rod 10 is in the most distal position. This driving
engagement ensures that the guide structure 15 is moved during the
injection far enough in the distal direction V to bridge the
resultant distance between the plunger rod 10 and the support and
guide structure 8.
[0046] A third exemplary embodiment of an injection device is
illustrated in FIGS. 5 and 6. The injection device based on the
third embodiment has a guide structure 16, which is accommodated
inside the plunger rod 10 when the device is in the initial state.
Apart from the guide structure 16, the injection device of the
third exemplary embodiment is the same as the injection device of
the second embodiment and reference may be made to the descriptions
given above.
[0047] The guide structure 16 is provided in the form of a guide
bar. It is approximately the same length as the tensed driving
spring 13. An engagement element 16a is formed on the distal end of
the guide structure 16. The engagement element 16a is a thicker
region and in this embodiment a spherically shaped thicker region
of the guide bar. The engagement element 16a sits in a pressing
contact with the driving spring 13. The thickness of the engagement
element 16a as measured perpendicular to the longitudinal axis L is
dimensioned so that the coils of the driving spring 13 are able to
slide over the engagement element 16a in the distal direction V
during a driving movement of the plunger rod 10, but the sliding
movement is made more difficult to the degree that the guide
structure 16 is driven along a part of the distance travelled by
the plunger rod 10 before reaching its most distal position. The
engagement element 16a lightly engages in the intermediate space
between axially adjacent spring coils. When the plunger rod 10 is
in its most distal position, the guide structure 16 bridges the
axial clearance distance between the plunger rod 10 and the support
and guide structure 8, which also reliably prevents any bending or
buckling, namely due to a guiding action, i.e., a securing action
within the driving spring 13.
[0048] Embodiments of the present invention, including preferred
embodiments, have been presented for the purpose of illustration
and description. They are not intended to be exhaustive or to limit
the invention to the precise forms and steps disclosed. The
embodiments were chosen and described to provide the best
illustration of the principles of the invention and the practical
application thereof, and to enable one of ordinary skill in the art
to utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. All
such modifications and variations are within the scope of the
invention as determined by the appended claims when interpreted in
accordance with the breadth they are fairly, legally, and equitably
entitled.
* * * * *