Patent Description:
Handheld injection devices for the injection of a medicament into a patient can be powered through many different mechanisms, including springs, electric motors, etc. Such injection devices can be utilized to insert a needle of the injection device into a patient and/or actuate a plunger through a cartridge attached to the needle so as to inject the medicament into the patient. The power sources utilized in such injection devices can be relatively powerful, and thus it can be desirable to control the amount of force applied by the power source to the cartridge and/or plunger. However, design interests and other limitations can impose significant constraints on any mechanism utilized to limit force transfer. Such design interests and limitations can include a desire to minimize the size of the overall injection device, requisite device complexity, and the use of materials inefficient for bulk manufacturing.

As such, there is a need for a handheld injection device that includes a system for limiting force transfer from a power source.

<CIT> discloses an injection device with a needle which, when the device is operated, is first caused to project, then liquid is forced out through it, and finally the needle is automatically retracted. The needle extends forwardly from a capsule that can slide longitudinally within a barrel-like body, a relatively weak spring normally maintaining the capsule and needle retracted. A more powerful spring acts oppositely on a plunger formed by rod parts which, when released, shoots the capsule forward by acting on the liquid therein, and then forces the liquid out through the projecting needle. At the end of the forward stroke the plunger and capsule are decoupled and the weak spring returns the exhausted capsule and its needle to the retracted position. A lost motion connection provided by a piston of the rod part acts as a damper in a cylinder of the rod part, to ensure that the full dose is ejected from the needle before decoupling occurs.

<CIT> discloses a low retraction activation force plunger sub-assembly for an automatic injector which includes: a plunger outer having one or more engagement prongs, a plunger inner having a shoulder, and a plunger biasing member retained in a first energized state between said plunger outer and plunger inner when the engagement prongs of the plunger outer are releasably engaged with the shoulder of the plunger inner. An automatic injector includes a housing, an activation mechanism, an actuation mechanism, and a syringe cartridge having the plunger sub-assembly and a needle assembly, wherein the actuation mechanism comprises an actuation biasing member residing in an initial energized state substantially within an upper portion of an actuation pill. A method of assembling the automatic injector includes the steps of: assembling the plunger sub-assembly and inserting the plunger sub-assembly into the housing such that a proximal end of the plunger sub-assembly contacts the actuation pill.

<CIT> discloses an auto-injector for administering a medicament and a method for operating it, the auto-injector comprising: a tubular chassis and a carrier subassembly, comprising a tubular carrier slidably arranged in the chassis. The carrier contains a syringe, a drive spring and a plunger for forwarding load of the drive spring to a stopper arranged in the syringe. The syringe is locked for joint axial translation with the carrier. A control spring is connectable to the carrier by first interlock means for needle insertion, wherein the whole carrier subassembly is advanced. Second interlock means are arranged for releasing the drive spring when the carrier has at least almost reached an injection depth thus delivering the medicament. The first interlock means are arranged for decoupling the control spring from the carrier and coupling it to the chassis for advancing it over the needle into a needle safe position.

The invention lies in the injection device of claim <NUM>. Further embodiments are given in the dependent claims.

A further aspect of the present disclosure outside the subject-matter of the claims is a method of disconnecting a power source of an injection device from a plunger actuation assembly, where the plunger actuation assembly is configured to drive a plunger disposed within a chamber of a cartridge, the chamber being configured to hold a medicament. The method includes actuating the power source to drive the plunger actuation assembly a first distance, where a second disengagement element is configured to couple the plunger actuation assembly to the power source, and translationally decoupling a first disengagement element from the plunger actuation assembly. The method also includes driving the plunger actuation assembly a second distance and translationally decoupling, via the first disengagement element, the second disengagement element and the power source from the plunger actuation assembly.

The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. The drawings show illustrative embodiments of the disclosure. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown.

Described herein is an injection device <NUM> powered by a power source <NUM> for injecting a medicament into a patient. Certain terminology is used to describe the injection device <NUM> in the following description for convenience only and is not limiting. The words "right," "left," "lower," and "upper" designate directions in the drawings to which reference is made. The words "inner" and "outer" refer to directions toward and away from, respectively, the geometric center of the description to describe the injection device <NUM> and related parts thereof. The words "forward" and "rearward" refer to directions in a longitudinal direction L and a direction opposite the longitudinal direction L along the injection device <NUM> and related parts thereof. The terminology includes the above-listed words, derivatives thereof and words of similar import. Unless otherwise specified herein, the term "longitudinal" is used to describe a longitudinal directional component of various components of the injection system <NUM> as designated by the longitudinal direction L, while the term "radial" is used to describe a radial directional component of the injection system <NUM> that is perpendicular to the longitudinal direction L as designated by the radial direction R. The radial direction R includes the radial direction R as shown in each figure, as well as any other direction that is perpendicular to the longitudinal direction L.

<FIG> depict an injection device <NUM> according to an embodiment of the current disclosure. The injection device <NUM> is configured to be manually held and actuated by a patient. The injection device <NUM> can include a substantially hollow housing <NUM>, which can be comprised of molded plastic or metal, for example. The housing <NUM> can be substantially elongate along the longitudinal direction L, and can define a cavity <NUM> therein, where components of the injection device <NUM> are configured to be supported by the housing <NUM> within the cavity <NUM>. A portion of the housing <NUM> can be transparent to allow patient monitoring of the contents of a cartridge <NUM> contained within the housing <NUM>, where the cartridge <NUM> will be described further below. A cap <NUM> can be releasably attached to the housing <NUM>, where the cap <NUM> is configured to shield certain components of the injection device <NUM> to maintain sterility of certain components and/or protect a patient from unintended needle contact. The cap <NUM> can be molded from plastic, though other materials are contemplated. Additionally, as depicted the cap <NUM> can be substantially transparent. However, it is also contemplated that the cap <NUM> can be opaque and comprise a variety of colors and/or markings as desired.

The housing <NUM> is configured to at least partially contain a cartridge <NUM>, where the cartridge <NUM> is prefilled with a medicament to be injected into a patient. The depicted injection device <NUM> can be supplied to an end patient with a cartridge <NUM> preinstalled within the housing <NUM>, though it is contemplated that in other embodiments the cartridge <NUM> can be removable from within the housing <NUM> and replaced. The cartridge <NUM> has a body <NUM> that extends from a first end 50a to a second end 50b opposite the first end 50a along the longitudinal direction L. The cartridge <NUM> further defines a chamber <NUM> therein, where the chamber <NUM> extends from a proximal opening <NUM> defined at the first end 52a of the body <NUM> to a distal opening <NUM> defined at the second end 52b of the body <NUM>. The injection device <NUM> can further include a needle <NUM> extending from the cartridge <NUM>. The injection device <NUM> can further include a elastomeric tip cap (not shown) that can be disposed around the needle <NUM> so as to create a sterile seal on the needle <NUM>, as well as a rigid needle shield (not shown) that can be utilized to hold the tip cap in place and allow for removal of the tip cap and rigid needle shield. A coupler <NUM> can be attached to the second end 52b of the body <NUM>, where the coupler <NUM> is configured to secure the needle <NUM> to the cartridge <NUM>. Though a coupler <NUM> is specifically shown as attaching the needle <NUM> to the cartridge <NUM>, it is contemplated that the cartridge <NUM> can be alternatively configured without the coupler <NUM>. For example, in such embodiments the needle <NUM> can be directly attached to the cartridge <NUM>. When attached the cartridge <NUM>, the needle <NUM> can be in fluid communication with the distal opening <NUM>, and thus the chamber <NUM>, such that medicament can flow through the needle <NUM> from the cartridge <NUM> and into a patient upon actuation of the injection device <NUM>. In addition to the cap <NUM>, the injection device <NUM> can include a needle shield <NUM> attached to the housing <NUM>, where the needle shield <NUM> is configured to selectively shield the patient from the needle <NUM>. The injection device <NUM> can further include a return spring <NUM> disposed at least partially within the needle shield <NUM>, where opposing ends of the return spring <NUM> are configured to engage the needle shield <NUM> and cartridge <NUM>, respectively. The function of the return spring <NUM> will be described in greater detail below.

Continuing with <FIG>, the injection device <NUM> includes a power pack housing <NUM> disposed within the cavity <NUM> of the housing <NUM> and attached to the housing <NUM>. In one embodiment, the power pack housing <NUM> is a separate component from but integral with the housing <NUM>, though it is contemplated that the power pack housing <NUM> and the housing <NUM> could be monolithic. The power pack housing <NUM> can have a body <NUM> that extends from a first end 67a to a second end 67b opposite the first end 67a along the longitudinal direction L. The power pack housing <NUM> can also include an outer surface 67c and an inner surface 67d opposite the outer surface 67c, where the inner surface 67d defines a channel <NUM> extending through the body <NUM> from the first end 67a to the second end 67b. The channel <NUM> can have a generally circular cross-section and can define varying diameters across its length, i.e., can be tiered along the longitudinal direction L. In one instance, the inner surface 67d can define a ledge <NUM> facing the channel <NUM>, where the function of the ledge <NUM> will be described further below. The ledge <NUM> can define a stepped region of the inner surface 67d where two portions of the channel <NUM> having differing diameters meet. The ledge <NUM> can extend substantially circumferentially about the entirety of the inner surface 67d, though it is contemplated that the ledge <NUM> may only extend partially about the inner surface 67d.

The injection device <NUM> can further include a proximal housing <NUM> disposed within the cavity <NUM> of the housing <NUM> and attached to the housing <NUM>. The proximal housing <NUM> can define a chamber <NUM> therein, where the chamber <NUM> is configured to receive certain components of the injection device <NUM>, as will be described below. Specifically, the injection device <NUM> includes a power source <NUM> configured to be at least partially received within the chamber <NUM> of the proximal housing <NUM> and configured to drive the plunger actuation assembly <NUM> such that the plunger <NUM> forces the medicament from the chamber <NUM>, as will be described further below. In the depicted embodiment, the power source <NUM> comprises a power pack spring <NUM>. However, it is contemplated that the power source <NUM> can be differently configured. For example, it is contemplated that the power source <NUM> can alternatively comprise an electromechanical motor, pneumatic actuator, etc..

The power pack spring <NUM> extends from a first end 150a to a second end 150b opposite the first end 150a along the longitudinal direction L. The power pack spring <NUM> can comprise a metal coiled spring, and can be configured to expand from a first length (such as shown in <FIG>) to a second length (such as shown in <FIG>) so as to operate certain aspects of the injection device <NUM>, as will be described further below. In the depicted embodiment, the power pack spring <NUM> is a single spring. However, it is contemplated that in other embodiments the power pack spring <NUM> can comprise a set or series of springs. The first end 150a of the power pack spring <NUM> can engage a ledge <NUM> defined by the proximal housing <NUM>, while the second end 150b of the power pack spring <NUM> can engage a portion of a second disengagement element <NUM>, which will be described further below. The exact embodiment of power pack spring <NUM> utilized in the injection device <NUM> can be a design choice to account for the specific force and/or spatial requirements of a particular injection device.

The injection device <NUM> also includes a plunger <NUM> disposed within the chamber <NUM> of the cartridge <NUM>, where the plunger <NUM> is configured to selectively force the medicament from the chamber <NUM>. The plunger <NUM> can comprise a conventional rubber or elastomeric plunger, where the plunger is configured to form a fluid seal with the inner surface of the cartridge <NUM> to prevent the medicament from flowing past the plunger <NUM> and escaping the cartridge <NUM>. Though the plunger <NUM> creates a fluid seal with the cartridge <NUM>, the plunger <NUM> can be translatable through the chamber <NUM> of the cartridge <NUM> along the longitudinal direction L. To accomplish this, the injection device <NUM> includes a plunger actuation assembly <NUM> is configured to drive the plunger <NUM>. In the depicted embodiment, the plunger actuation assembly <NUM> can be comprised of a plurality of interconnected rods having varying diameters. However, it is contemplated that in other embodiments, the plunger actuation assembly can be comprised of a single, integrally formed body. The plunger actuation assembly <NUM> can include a first portion 100a and a second portion 100b connected to the first portion 100a and extending from the first portion 100a along the longitudinal direction L. The second portion 100b can define a diameter that is larger than the diameter of the first portion 100a. The diameter of each of the first and second portions 100a, 100b can be the same or differ along their lengths as desired. Though a plunger actuation assembly <NUM> including two portions is explicitly disclosed, it is contemplated that in other embodiments the plunger action assembly can be comprised of more or less than two portions, such as one portion, three portions, four portions, etc. Initially, the plunger actuation assembly <NUM> can be spaced from the plunger <NUM>, and can engage the plunger <NUM> only after some initial displacement caused by the power source <NUM>. However, it is also contemplated that the plunger actuation assembly <NUM> can be initially attached to the plunger <NUM>.

Referring to <FIG>, the injection device <NUM> includes a first disengagement element <NUM>. The first disengagement element <NUM> can define a body <NUM> that can be substantially disc-shaped, such that the body <NUM> defines a channel 114a extending therethrough. The channel 114a can be specifically sized such that the channel 114a is configured to receive a portion of the plunger actuation assembly <NUM>. Specifically, the channel 114a can be configured to receive the first portion 100a of the plunger actuation assembly <NUM>, such that the first disengagement element <NUM> is concentrically disposed around the first portion 100a of the plunger actuation assembly <NUM>. The first disengagement element <NUM> can also define at least one tab <NUM> extending longitudinally from the body <NUM>, and each tab <NUM> can include a protrusion <NUM> extending inwards therefrom along the radial direction R. As a result, each tab <NUM> and protrusion <NUM> combination can collectively substantially define a hook-like shape. In the depicted embodiment, the first disengagement element <NUM> can include four tabs <NUM> circumferentially spaced apart, and likewise four corresponding protrusions <NUM>. However, in other embodiments, it is contemplated that the first disengagement element <NUM> can include different numbers of tabs <NUM> and protrusions <NUM>, such as one, two, three, five, six, seven, etc. As depicted, the tabs <NUM> are equidistantly circumferentially spaced apart. In other embodiments, the tabs <NUM> can be non-equidistantly spaced apart circumferentially. Each component of the first disengagement element <NUM> can be comprised of a substantially flexible material, such as plastic, though other materials are contemplated, such that portions of the first disengagement element <NUM> are configured to flex during operation, notably the tabs <NUM>.

As shown in <FIG>, the second portion 100b of the plunger actuation assembly <NUM> defines at least one external groove 104a extending radially inwards, where the at least one protrusion <NUM> of the first disengagement element <NUM> is configured to engage the at least one external groove 104a to translationally couple the first disengagement element <NUM> to the plunger actuation assembly <NUM>. Generally, the second portion 100b of the plunger actuation assembly <NUM> will include a number of external grooves 104a that corresponds to the number of protrusions <NUM> of the first disengagement element <NUM>. For example, in the depicted embodiment, the second portion 100b of the plunger actuation assembly <NUM> can define four external grooves 104a, where each protrusion <NUM> is configured to engage a respective one of the four external grooves 104a. As the tabs <NUM> and protrusions <NUM> can be equidistantly circumferentially spaced apart, so too can the external grooves 104a. Though it is contemplated that the external grooves can alternatively be non-equidistantly circumferentially spaced apart about the second portion 100b of the plunger actuation assembly <NUM>, the spacing of the external grooves 104a and the tabs <NUM> and protrusions <NUM> will generally correlate. In operation, the protrusions <NUM> can be selectively decoupled from the corresponding external grooves 104a, so as to translationally decouple the first disengagement element <NUM> from the plunger actuation assembly <NUM>.

Referring to <FIG>, the injection device <NUM> includes a second disengagement element <NUM>. The second disengagement element <NUM> can define a body <NUM> that can be substantially disc-shaped, such that the body <NUM> defines a channel 134a extending therethrough. The channel 134a can be specifically sized such that the channel 134a is configured to receive a portion of the plunger actuation assembly <NUM>. Specifically, the channel 134a can be configured to receive the first portion 100a of the plunger actuation assembly <NUM>, such that the second disengagement element <NUM> is concentrically disposed around the first portion 100a of the plunger actuation assembly <NUM>. The second disengagement element <NUM> can also define at least one tab <NUM> extending longitudinally from the body <NUM>, and each tab <NUM> can include a protrusion <NUM> extending inwards therefrom along the radial direction R. In the depicted embodiment, the second disengagement element <NUM> can include eight tabs circumferentially spaced apart, and likewise eight corresponding protrusions. However, in other embodiments, it is contemplated that the second disengagement element <NUM> can include different numbers of tabs and protrusions, such as five, six, seven, nine, ten, eleven, etc. As depicted, the tabs <NUM> are equidistantly circumferentially spaced apart. In other embodiments, the tabs <NUM> can be non-equidistantly spaced apart circumferentially. Each component of the second disengagement element <NUM> can be comprised of a substantially flexible material, such as plastic, though other materials are contemplated, such that portions of second disengagement element <NUM> are configured to flex during operation, notably the tabs <NUM>. The second disengagement element <NUM> can be coupled to the plunger actuation assembly <NUM> and the power pack spring <NUM>, and thereby configured to transfer force from the power pack spring <NUM> to the plunger actuation assembly <NUM> and connected components.

As shown in <FIG>, the first portion 100a of the plunger actuation assembly <NUM> defines at least one external groove 104b extending radially inwards, where the at least one protrusion <NUM> of the second disengagement element <NUM> is configured to engage the at least one external groove 104b to translationally couple the second disengagement element <NUM> to the plunger actuation assembly <NUM>. The at least one external groove 104b is spaced from the at least one external groove 104a along the longitudinal direction L. Generally, the first portion 100a of the plunger actuation assembly <NUM> will include a single external groove 104b that extends substantially continuously circumferentially about the plunger actuation assembly <NUM>. Alternatively, the at least one external groove 104b can include a number of external grooves 104b that corresponds to the number of tabs <NUM> of the second disengagement element <NUM>. In operation, the protrusions <NUM> can be selectively decoupled from the corresponding external groove 104b, so as to translationally decouple the second disengagement element <NUM> from the plunger actuation assembly <NUM>.

With reference to <FIG> and <FIG>, the operation of the injection device <NUM> will be described in detail. Initially, the patient can detach the cap <NUM> from the housing <NUM>, thus providing access to the needle shield <NUM>. Then, the patient can grasp the housing <NUM> and place the distal end of the needle shield <NUM> against their skin, achieving the orientation shown in <FIG>. Next, the patient can actuate the injection device <NUM>. To do this, the patient presses on the housing <NUM> of the injection device <NUM> in the distal direction. This decouples an activation cap <NUM> from a snap feature of the plunger actuation assembly <NUM>, thus allowing retaining tabs <NUM> to bias inwards. By biasing inwards, the retaining tabs <NUM> allow expansion of the power pack spring <NUM>.

Upon actuation of the injection device <NUM>, the power pack spring <NUM> can begin to longitudinally expand. As the first end 150a of the power pack spring <NUM> is translationally fixed due to engagement with the ledge <NUM> of the proximal housing <NUM>, the power pack spring <NUM> can expand through longitudinal movement of its second end 150b. As the second end 150b of the power pack spring <NUM> contacts a portion of the second disengagement element <NUM>, which is (at the moment) translationally fixed to the plunger actuation assembly <NUM>, the power pack spring <NUM> transfers longitudinal force to the second disengagement element <NUM>, which likewise transfers this force to the plunger actuation assembly <NUM>. The plunger actuation assembly <NUM> forces the first disengagement element <NUM>, the cartridge <NUM>, plunger <NUM>, and needle <NUM> axially along the longitudinal direction L.

After the power pack springe <NUM> has driven the first and second disengagement elements <NUM>, <NUM>, cartridge <NUM>, plunger <NUM>, plunger actuation assembly <NUM>, and needle <NUM> axially a first distance D<NUM> along the longitudinal direction L the cartridge <NUM> is blocked from further movement by the needle shield <NUM>. This may occur before, after, or coincidental with the needle <NUM> being inserted into the skin of the patient. At this time, once the first disengagement element <NUM> has been driven the first distance D<NUM>, the first disengagement element <NUM> is configured to engage the ledge <NUM> of the power pack housing <NUM>. Engagement between the first disengagement element <NUM> and the ledge <NUM> causes the tabs <NUM> of the first disengagement element <NUM> to bias outwards. As the tabs <NUM> bias outwards, the protrusions <NUM> are moved radially out of engagement with the external grooves 104a of the plunger actuation assembly <NUM>. As a result, the first disengagement element <NUM> is no longer engaged with the plunger actuation assembly <NUM>, and is thus translationally decoupled from the plunger actuation assembly <NUM>.

After the first disengagement element <NUM> is translationally decoupled from the plunger actuation assembly <NUM>, the power pack spring <NUM> continues to exert force on the plunger actuation assembly <NUM> due to continued coupling via the second disengagement element <NUM>. As the cartridge <NUM> is prevented from continued longitudinal movement, the force applied by the power pack spring <NUM> is transferred via the plunger actuation assembly <NUM> to the plunger <NUM>, which is forced longitudinally through the chamber <NUM> of the cartridge <NUM> (which is currently in a fixed position) a second distance D<NUM> to force the medicament from the chamber <NUM>, through the needle <NUM>, and into the patient. After the plunger actuation assembly <NUM> is driven by the power pack spring <NUM> the second distance D<NUM>, the plunger <NUM> reaches a final position within the cartridge <NUM>. This final position may be the distal end of the chamber <NUM>, as shown in <FIG>, or may be proximal to the distal end of the chamber <NUM> and correspond to a predetermined maximum amount of medicament to be injected into a patient.

While the plunger actuation assembly <NUM> is being driven the second distance D<NUM>, the first disengagement element <NUM> is in a fixed position due to its translational disengagement from the plunger actuation assembly <NUM>. While the first disengagement element <NUM> is longitudinally spaced from the second disengagement element <NUM> a set distance as they are driven the first distance D<NUM>, after the first and second disengagement elements <NUM>, <NUM> are driven the first distance D<NUM>, the longitudinal spacing between the first and second disengagement elements <NUM>, <NUM> decreases. This is because the second disengagement element <NUM> remains translationally coupled to the power pack spring <NUM> as the plunger actuation assembly <NUM> is driven the second distance D<NUM>, while the first disengagement element <NUM> is in a set longitudinal position, and thus the plunger actuation assembly <NUM> moves longitudinally relative to the first disengagement element <NUM>. After the plunger actuation assembly <NUM> and the second disengagement element <NUM> are driven the second distance D<NUM>, the first disengagement element <NUM> engages the second disengagement element <NUM>. This engagement between the first and second disengagement elements <NUM>, <NUM> is configured to bias the tabs <NUM> of the second disengagement element <NUM> outwards, such that the protrusions <NUM> of the second disengagement element <NUM> disengage the external groove 104b of the plunger actuation assembly <NUM>, thus translationally decoupling the second disengagement element <NUM> from the plunger actuation assembly <NUM>. This position is shown in <FIG>, and corresponds to an end of the injection operation after a desired amount of the medicament has been injected.

After the second disengagement element <NUM> translationally decouples from the plunger actuation assembly <NUM>, the power pack spring <NUM> ceases to drive the plunger actuation assembly <NUM>. This is because force from the power pack spring <NUM> was previously transferred to the plunger actuation assembly <NUM> through the second disengagement element <NUM>. Throughout driving the above-mentioned components through the first and second distances D<NUM>, D<NUM>, the return spring <NUM> exerts a continuous force on the cartridge <NUM> in a direction opposed to that applied by the power pack spring <NUM>. Despite this, the power pack spring <NUM> is configured to exert sufficient force to overcome the counterforce applied by the return spring <NUM>. However, after the second disengagement element <NUM> is translationally decoupled from the plunger actuation assembly <NUM>, there is no force applied to the plunger actuation assembly <NUM> by the power pack spring <NUM> to counteract the force applied by the return spring <NUM> on the cartridge <NUM>. As such, as shown in <FIG>, the return spring <NUM> is configured to translate the cartridge <NUM>, plunger <NUM>, and plunger actuation assembly <NUM> proximally through the housing <NUM> along the longitudinal direction L a third distance D<NUM>. Simultaneously, this drives the needle <NUM> back within the needle shield <NUM> so as to protect a patient from unintended contact with the needle <NUM> after an injection is complete.

Now referring to <FIG>, a method <NUM> of disconnecting the power pack spring <NUM> of the injection device <NUM> from the plunger actuation assembly <NUM> is shown. As stated above, the plunger actuation assembly <NUM> is configured to drive the plunger <NUM> that is disposed within the chamber <NUM> of the cartridge <NUM>, where the chamber <NUM> is configured to hold a medicament. Method <NUM> begins with step <NUM>, which involves actuating the power pack spring <NUM> to drive the plunger actuation assembly <NUM> distally a first distance D<NUM>, where the second disengagement element <NUM> is configured to couple the plunger actuation assembly <NUM> to the power pack spring <NUM>. Step <NUM> can also include driving the cartridge <NUM> the first distance D<NUM>. In step <NUM>, the first disengagement element <NUM> can be translationally decoupled from the plunger actuation assembly <NUM>. Step <NUM> can further include engaging the first disengagement element <NUM> with the ledge <NUM> defined by the power pack housing <NUM>, thus biasing at least one tab <NUM> of the first disengagement element <NUM> outwards and disengaging a protrusion <NUM> extending from the at least one tab <NUM> from at least one external groove 104a of the plunger actuation assembly <NUM>. After step <NUM> and/or step <NUM>, the needle <NUM> can be inserted a predetermined distance into the patient.

Then, step <NUM> includes driving the plunger actuation assembly <NUM> distally a second distance D<NUM>. This step specifically involves driving the plunger <NUM> via the plunger actuation assembly <NUM> through the chamber <NUM> of the cartridge <NUM> to inject the medicament into the patient through the needle <NUM>. During step <NUM>, the cartridge <NUM> can be translationally fixed relative to the plunger actuation assembly <NUM>. Further, during step <NUM>, the first disengagement element <NUM> can be translationally fixed relative to the plunger actuation assembly <NUM>. After step <NUM>, in step <NUM> the second disengagement element <NUM> can be translationally decoupled, via the first disengagement element <NUM>, from the power pack spring <NUM> and the plunger actuation assembly <NUM>. Step <NUM> can include engaging the first and second disengagement elements <NUM>, <NUM>, thus biasing at least one tab <NUM> of the second disengagement element <NUM> outwards and disengaging a protrusion <NUM> extending from the at least one tab <NUM> of the second disengagement element <NUM> from at least one external groove 104b of the plunger actuation assembly <NUM>. Following step <NUM>, in step <NUM> the cartridge <NUM> and the plunger actuation assembly <NUM> are driven by the return spring <NUM> proximally a third distance D<NUM>. After step <NUM>, the needle <NUM> is retracted from the patient and into the needle shield <NUM>, thus protecting a patient from unintended contact with the needle <NUM> following a completed injection.

Claim 1:
An injection device, comprising:
a housing (<NUM>);
a power pack housing (<NUM>) disposed within the housing (<NUM>);
a cartridge (<NUM>) defining a chamber (<NUM>) configured to hold a medicament;
a plunger (<NUM>) disposed within the chamber (<NUM>);
a plunger actuation assembly (<NUM>) configured to drive the plunger (<NUM>);
a power source (<NUM>) configured to drive the plunger actuation assembly (<NUM>) such that the plunger (<NUM>) forces the medicament from the chamber (<NUM>);
a first disengagement element (<NUM>) translationally fixed relative to the plunger actuation assembly (<NUM>); and
a second disengagement element (<NUM>) coupled to the plunger actuation assembly (<NUM>) and to the power source (<NUM>), wherein the second disengagement element (<NUM>) is translationally fixed relative to the plunger actuation assembly (<NUM>),
wherein the first disengagement element (<NUM>) is configured to:
translationally decouple from the plunger actuation assembly (<NUM>) by an engagement with the power pack housing (<NUM>) when the power source (<NUM>) drives the plunger actuation assembly (<NUM>) a first distance, and
translationally decouple the second disengagement element (<NUM>) from the plunger actuation assembly (<NUM>) by an engagement with the second disengagement element (<NUM>) when the power source (<NUM>) drives the plunger actuation assembly (<NUM>) a second distance.