Coupling for an auto-injection device

A coupling for selectively securing a spring to a plunger is provided. The coupling has a first end defining a spring rest for receiving the spring and a second end defining a shoulder. The shoulder is moveable to a first position into contact with the plunger and to a second position out of contact with the plunger. The shoulder is normally in the second position and is resiliently moveable to the first position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure is related to auto-injection devices. More particularly, the present disclosure is related to a coupling for auto-injection devices for releasably securing an injection spring to a plunger rod.

2. Description of Related Art

Diseases such as AIDS, Hepatitis, and others, are increasing within the general population. The onset of these diseases has increased the desire to prevent inadvertent needle sticks during the use of syringe assemblies. Many prior art devices include self-retracting needles to mitigate inadvertent needle sticks.

Many life-threatening situations such as allergy induced anaphylactic shock, and exposure to chemical, radiological, and biological weapons can require the use of automatic injection devices. Also, many non-threatening conditions can be candidates for use of such automatic injection devices. However, the cost of the prior art automatic injection device can make such use by consumers cost prohibitive.

Typical automatic injection devices are syringe assemblies that allow the medically untrained user to automatically inject a medicine by manually trigging the automatic injection. Some prior automatic injection devices also incorporate self-retracting needles. Such automatic injection and retraction assemblies included a coupling that releasably couples an injection spring to a syringe plunger. Unfortunately, many prior couplings require tight manufacturing tolerances, which can increase the overall cost of the device.

Accordingly, there is a continuing need for auto-injection devices and couplings for such devices that overcome and/or mitigate one or more of the aforementioned and other deficiencies and deleterious effects of prior automatic injection devices.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present disclosure to provide a coupling for selectively securing a spring to a plunger. The coupling has a first end defining a spring rest for receiving the spring and a second end defining a shoulder. The shoulder is moveable to a first position into contact with the plunger and to a second position out of contact with the plunger. The shoulder is normally in the second position and is resiliently moveable to the first position.

In some embodiments, the coupling includes a first end defining a spring rest for receiving the spring and a second end defining a shoulder. The spring rest and the shoulder are radially offset from one another by a predetermined angle.

In other embodiments, the coupling includes a first end defining a pair of spring rests for receiving the spring and a second end defining a pair of shoulders. The pair of shoulders are moveable to a first position into contact with the plunger and a second position out of contact with the plunger.

A power injection assembly is also provided. The assembly includes a plunger rod, an injection spring, an inner housing, and a coupling. The plunger rod has a rib. The inner housing has a first opening and an inner diameter. The injection spring is about the inner housing and the plunger rod is in the inner diameter. The coupling has a spring rest and a shoulder. The coupling is in the inner diameter such that the spring rest extends through the first opening and receives the injection spring and such that the shoulder is compressed to a first position by the inner diameter. The shoulder is engaged with the rib in the first position.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the figures and in particular toFIGS. 1 through 3, an exemplary embodiment of an auto-injection device10according to the present disclosure is shown in an assembled state. Auto-injection device10includes a power-injection assembly12, a medicine cartridge14, and a power-retraction assembly16.

Auto-injection device10is configured to extend a hypodermic needle from within the device, inject a single, pre-measured dose of medicine from cartridge14into a user, and automatically retract the hypodermic needle into the device after the injection is completed.

Advantageously, syringe assembly10is a multi-component device that can be assembled by the user and/or medical provided (e.g., pharmacist, doctor, nurse). Since syringe assembly10does not require assembly at the time of manufacture, the present disclosure effectively separates expiry of medicine cartridge14from the expiry of syringe assembly10. For example, typical flu vaccines have an expiration date of one year. Thus, the user can maintain a supply of power injection and retraction assemblies12,16of the present disclosure, while only replacing any expired medicine cartridges14.

For example, power-injection assembly12and power-retraction assembly16can be secured to one another in a snap fit manner so that the assemblies can not be removed from one another after injection. In the illustrated embodiment, power-injection assembly12includes one or more outwardly depending tabs18that are received in a corresponding number of openings20defined in power-retraction assembly16. As power-injection assembly12is inserted into power-retraction assembly16, tabs18act on the power-retraction assembly to elastically deform the inner dimension of the tube. Once tabs18are received by openings20, the inner dimension of power-retraction assembly16resiliently returns to its original dimension to secure the tabs in the openings.

In the assembled state, syringe assembly10preferably maintains cartridge14hermetically sealed between power-injection and retraction assemblies12,16. For example, power-injection assembly12can include a sealing member22such as, but not limited to an o-ring. Once power-injection assembly12and power-retraction assembly16are secured together, sealing member22cooperates with the interior of the power-retraction assembly to form a hermetic radial seal. In the illustrated embodiment, sealing member22is positioned below openings20defined in power-retraction assembly16to provide the hermetic seal below the snap fit connection between tabs18and openings20.

The operation of the power-injection assembly12is described with simultaneous reference toFIGS. 4 through 8. Injection assembly12includes an injection spring24, a plunger rod26, an activation device28, a coupling30, and a housing11that houses the spring24, plunger rod26, coupling30, and inner housing56(FIG. 7). Injection spring24is disposed about plunger rod26and is drivingly engaged to the plunger rod by coupling30.

Activation device28has an upper end32and a lower end34. Injection assembly12is activated by depressing activation device28in direction48. In addition, activation device28can include an outer shroud36. Outer shroud36and injection assembly12can include one or more cooperating guides (not shown) that permit depression of activation device28only after the activation device has been rotated to a predetermined position. In sum, outer shroud36and injection assembly12can work together to require movement in two directions, rotation and depression, in order to activate injection spring24. In a preferred embodiment, shroud36includes a number of longitudinal ribs39to assist the user in rotation. In this manner, injection assembly12is particularly suited for use in situations where the user may lack typical manual dexterity, such as can be the case where the user is wherein protective gloves.

Lower end34is configured to selectively couple the energy from injection spring24to drive plunger rod26. In the illustrated embodiment, plunger rod26includes a driving end38and a locking end40. Locking end40includes two tines42that are resiliently biased outward so that the tines are remote from one another. Driving end38is configured to act on medicine cartridge14in a known manner. For example, driving end38can act on medicine cartridge14as described in U.S. Pat. No. 6,387,078.

Injection assembly12includes a locking member44that engages tines42when the tines are normally biased from one another. Activation device28includes a releasing surface46defined at lower end34. Force applied to upper end32of activation device28in direction48causes releasing surface46to compress tines42toward one another such that the tines are disengaged from locking member44.

Injection spring24is maintained in a normally compressed or stressed condition. Upon release of tines42from locking member44, the stored energy in spring24drives plunger rod26in an injection direction48.

Coupling30includes a first end50and a second end52. First end50forms a spring rest or seat51upon which injection spring24rests as shown inFIG. 4.

Second end52(shown inFIGS. 5 and 6) is an outwardly biased spring member having a shoulder53for engaging plunger rod26. During assembly, second end52is compressed inward towards plunger rod26until shoulder53engages a rib54defined on plunger rod. Thus, second end52is moveable between a compressed or first position (FIG. 5) and a normal or second position (FIG. 6). Second end52is normally in the second position, but has sufficient resiliency such that the second end can be elastically urged to the first position.

During movement of plunger rod26in injection direction48, second end52is maintained in the compressed position and, thus, shoulder53is maintained engaged with rib54so that the force of injection spring24is transmitted through coupling30to plunger rod26.

After plunger rod26has traveled a predetermined distance, second end52is allowed to bias outward away from rod26so that shoulder53disengages from rib54as shown inFIG. 6. Thus, second end52moves from the compressed position to the normal position due to its own resiliency once plunger rod26travels the predetermined distance to disengage shoulder53from rib54. Once shoulder53is disengaged from rib54, the force of injection spring24is no longer transmitted through coupling30to plunger rod26.

Preferably, coupling30includes a pair of spring rests51and a pair of shoulders53. Here, spring rests51are, preferably, diametrically opposed to one another. Similarly, shoulders53are, preferably, diametrically opposed to one another. Moreover, spring rests51are, preferably, radially offset from shoulders53and circumferentially offset from the shoulder53by a predetermined angle, preferably about 90 degrees. In this manner, each spring rest51is circumferentially offset from each shoulder53by about by about 90 degrees.

Spring rests51are, preferably, axially offset from shoulders53by a predetermined distance so that coupling30has an axial length. In this manner, spring rests51are disposed forward relative to shoulders53along the axial length so that spring24encompasses a portion of the axial length.

For applications involving auto-injection devices10for small dose volumes deposited at shallow depths, the demand on injection spring24, in terms of the spring rate and extension length, are not very severe. Thus, injection spring24can be incorporated into power-injection assembly12with a reasonable set of device proportions (e.g., length and diameter). However, in cases with auto-injection devices10that must deliver larger dose volumes deposited at deeper needle penetration depths, the demand on injection spring24, in terms of the spring rate and extension length, can be severe. In these applications, injection spring24requires a long travel and high spring rate. This combination of high spring rate and long travel typically requires injection spring24to be a long, slender spring positioned in straight line sequence with the plunger, which unfortunately leads to power-injection assembly12having an undesireably long length. Alternately, the combination of high spring rate and long travel typically requires injection spring24to have a large diameter.

Advantageously, coupling30is particularly suited for use with such large diameter springs. Specifically, coupling30has spring rests51that are disposed radially outward from the coupling and are disposed forward of shoulders53. In this manner, injection spring24encompasses a portion of the axial length of coupling30so that the larger diameter spring axially overlaps at least a portion of plunger rod26. According, coupling30finds particular use with large diameter springs to mitigate the overall length of power-injection assembly12.

In the illustrated embodiment, injection assembly12includes an inner housing56shown inFIG. 8. Inner housing56defines has a first opening58through which spring rest51extends to engage injection spring24. First opening58extends along inner housing56in the injection direction48. Preferably, inner housing56has a pair of first openings58that are defined through the inner housing diametrically opposed to one another to receive a pair of diametrically opposed spring rests51.

Inner housing56has an inner diameter60that is sufficient to maintain second end52of coupling30in the compressed position and, thus, engaged with plunger rod26. Thus, second end52is outwardly biased against inner diameter60of inner housing56. The force of injection spring24is sufficient to overcome the friction between second end52and housing56.

Inner housing56also includes a second opening62. Preferably, inner housing56has a pair of second openings62that are defined through the inner housing diametrically opposed to one another. Second opening62is offset from first opening58by the same predetermined angle that offsets spring rest51from shoulder53. Thus, second opening62is aligned with shoulder53of coupling30.

Second opening62is defined at a predefined position along injection direction48where it is desired for coupling30to disengage injection spring24. Thus, after plunger rod26has traveled to the point where second end52of coupling30is at second opening62, the second end52is no longer maintained in the compressed position by inner diameter60, which allows the second end to resiliently bias outward to the first position through the second opening and move shoulder53out of engagement with rib54.

Advantageously, coupling30can be made of any material having sufficient resiliency to bias second end52outward at second opening62. For example, coupling30can be made of spring steel stamped into the desired shape such as that illustrated inFIG. 7. Accordingly, coupling30can be made less expensively and with lower manufacturing tolerances than previous couplings.

In this manner, injection spring24drives plunger rod26in injection direction48until second end52of coupling30reaches second opening52. The resiliency of coupling30causes the coupling to expand through second opening52and disengage shoulder53from rib54of plunger rod26as seen inFIG. 6. The disengagement of coupling30from plunger rod26frees the plunger rod from the force of injection spring24and, thus, allows the plunger rod to be moved in a direction opposite injection direction48by retraction assembly16.

Retraction assembly16can operate in a known manner. For example, power-retraction assembly16can include a retraction spring (not shown) that has a spring force lower than the spring force of injection spring24. Thus, injection spring24overcomes the force of the retraction spring as long as coupling30engages plunger rod26to the injection spring. However, once second end52of coupling30is disengaged from plunger rod26and the force of injection spring24is no longer transmitted through the coupling to the plunger rod, the force of the retraction spring is sufficient to urge medicine cartridge14in a direction opposite injection direction48, thus automatically retracting the hypodermic needle of cartridge14into device10.