Injection device

Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...

Patent

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Details

604134, 604135, A61M 520

Patent

active

061591815

DESCRIPTION:

BRIEF SUMMARY
This invention relates to injection devices, and in articular to one-shot devices which are supplied primed and with a full capsule, and which are thrown away after a single use.
It is important that after the injection has been made, the needle should be made safe, and this is usually done by retraction inside the barrel-like body of the device. This can happen automatically, with a returning spring coming into play when the injection has been made and a connection between the drive mechanism and the capsule has been broken. But it is difficult to ensure that the disconnection of the drive mechanism happens at the right time. In particular, if it happens a bit too early, the return spring will act before the full dose has been ejected. If it is does not happen too early or at just the right moment it probably will not happen at all, because once the full drive stroke has been completed, everything is stationary, and without any movement, no disconnection can be made.
Without automatic retraction, the user has to cause it, and do so in a simple and convenient manner. It is the aim of this invention to provide such a device.
According to the present invention there is provided a one-shot injection device with a barrel-like body carrying a loaded capsule having a needle at its forward end and a spring drive system which, when released, drives the capsule forwards to project the needle from the body and eject a dose through the needle, and which thereafter can cause the capsule and needle to be retracted, wherein the spring drive system comprises a drive spring, a hollow drive member acted upon by the drive spring and initially held in a rearward position by a first trigger, an abutment member between the drive member and the rear end of the plunger whose forward end forms or acts upon a piston within the capsule, a return spring acting between the capsule and the body, and a second trigger operable when the drive member is in a forward position to move the abutment member from an engaged position in relation to the drive member to a disengaged position where the return spring can act to push the abutment member rearwardly via the capsule and its plunger, thereby retracting the needle.
There are preferably removable means to shield the first trigger or to prevent it being accidentally operated when the device is primed.
The drive spring is conveniently a coil spring which when released shoots the drive member and capsule forwards, using the plunger, to project the needle and then eject the dose through the needle, the liquid contents of the capsule acting as a solid while the needle is penetrating.
The drive member can be a cylinder open at both ends and with a rearwardly facing shoulder against which the drive spring acts, the other end of the drive spring reacting against the closed rear end of the barrel.
The return spring is also conveniently a coil spring surrounding the capsule and offering little resistance to the drive spring.
In one form the abutment member is free of the drive member and in its engaged position is peripherally held against a forward facing shoulder formation of the drive member. The second trigger actuation shifts the abutment member to the disengaged position, clear of the shoulder, where it is free to be pushed rearwardly through the drive member. This shift from the engaged to the disengaged position may laterally of the barrel or rotational about the axis of the barrel.
In another preferred form the abutment member is hinged to the drive member and in its engaged position is held across a passage through the drive member by a formation diametrically opposite the hinge co-operating with a detent on the barrel. The shift from the engaged to the dishing gaged position is by the second trigger releasing said formation from the detent, thereby allowing the abutment member to hinge back and clear the passage for the plunger.
Preferably the drive member and the abutment member are integrally moulded of plastics material. A thin web then forms the hinge and will allow diametral shift of

REFERENCES:
patent: 3880163 (1975-04-01), Ritterskamp
patent: 5478316 (1995-12-01), Bitdinger et al.
patent: 5637094 (1997-06-01), Stewart, Jr.
patent: 5713866 (1998-02-01), Wilmot
patent: 5851197 (1998-12-01), Marano et al.

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