Injection devices

Details Injection devices Injection devices

1995-01-18

1997-07-01

Rimell, Sam

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

604135, 604131, A61M 520, A61M 5315

Patent

active

056432143

DESCRIPTION:

BRIEF SUMMARY
This invention relates to injection devices.
Often, when a sequence of injections is carried out, each time the entire contents of a capsule are ejected through the needle in a single stroke of a plunger. However, there are other circumstances where only a small amount of fluid should be used, and it is not always practical or economic to make a number of very small capsules and injection devices to cater for this. There is therefore a need for an injection device which can produce repeated measured doses from a single capsule. It is the aim of this invention to provide one.
According to the present invention there is provided an injection device with an elongate barrel-like body for giving a sequence of injections of liquid from a capsule, the capsule being carried therein in a manner allowing longitudinal movement between limiting positions, having a needle at one, forward end and a plunger extending rearwardly from the other end whose operation causes emission of doses through the needle, the device comprising spring drive means with a limited travel which, when energised, engages the plunger at a first position thereon and urges it forwardly, the drive in a first phase carrying the capsule from a rear to a forward limit, by virtue of a substantial hydraulic lock, to project the needle from the body, and in a second phase forcing the plunger alone on to eject a dose, manually operable priming means to re-energise the drive means and withdraw the capsule to its rear limit, the plunger being carried with the capsule until the spring drive means re-engages the plunger at a second position more rearward thereon than the first position, and means for releasably holding the spring drive means energised after priming.
Thus, on the forward stroke, the plunger first pushes the capsule forwards to its limit by acting on the liquid in the capsule which is effectively solid, and then carries on more slowly to eject one dose. The plunger is then stopped, but at a position further forward with respect to the capsule than before that operation. For the next dose, the priming means pulls back the plunger and capsule and re-energises the spring drive means, which is temporarily held by a trigger mechanism. But before it achieves this, the capsule carrier will reach its rearward limit, while the drive means has its relationship to the plunger adjusted to compensate for the emission of one dose. The device is then ready for the next injection.
Preferably, the plunger and drive means have pawl and ratchet interengagement, positive in the drive direction, the ratchet teeth generally being on the plunger while the pawl is on the drive means.
The capsule may be mounted in a carrier capable of longitudinal movement within the body, limited by stops. It too preferably has a pawl to engage the ratchet teeth, and it will then also have a lost motion connection with the drive means. During the first phase of the drive stroke the carrier is driven directly via the plunger, the liquid and the capsule and the lost motion connection contributes nothing. But during the second phase of the drive stroke, with the carrier arrested, the carrier pawl has its engagement with the teeth shifted to the rear as the lost motion connection allows relative movement between the drive means and the carrier. After injection and when the device is primed again, the lost motion connection ensures that both carrier and drive means are withdrawn by different amounts, allowing the pawl of the drive means to have its engagement with the teeth shifted to the rear. These shifts, and the scope of the lost motion, correspond to the movement of the plunger relative to the capsule when ejecting a single dose.
Conveniently, the drive means includes a tubular member sleeved over the plunger with coil spring means encircling it and effectively reacting against the body. The priming means may simply be a knob on the end of the tubular member accessible at the rear end of the body.
The means for releasably holding the drive means may be a trigger device carried by the

REFERENCES:
patent: 4394863 (1983-07-01), Bartner
patent: 5114406 (1992-05-01), Gabriel
patent: 5300030 (1994-04-01), Crossman

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