Syringe/plunger coupling

Details Syringe/plunger coupling Syringe/plunger coupling

1999-02-05

2001-03-06

Kennedy, Sharon (Department: 3763)

Surgery

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

Treating material introduced into or removed from body...

C604S121000, C604S218000

Reexamination Certificate

active

06196999

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to injectors for injecting fluid into animals.
BACKGROUND OF THE INVENTION
During many medical procedures, various fluids are injected into patients for purposes of diagnosis or treatment. An example of one such fluid is contrast media used to enhance angiography or CT imaging. The injectors used in these procedures are automated devices that expel the fluid from a syringe, through a tube, and into the subject.
Injectors suitable for these applications must have relatively large volume syringes and be capable of producing relatively large flow rates and injection pressures. For this reason, injectors for such applications typically include large, high mass injector motors and drive t rains. These are typically housed in an injection head, which is supported by a floor, wall, or ceiling mounted arm.
In many such injectors the syringes are replaceable. In one exemplary injector, to replace the syringe, a front face plate which facilitates coupling between the syringe plunger and the plunger drive ram is moved, the used syringe detached, and a fresh syringe attached.
When a used syringe is removed, a replacement syringe is installed on the injector. The rearward face of the syringe plunger has a coupling element referred to as a button. This button is mushroom-shaped and consists of an extension protruding from the rearward face of the syringe plunger, topped by a cap. When the new syringe plunger is inserted, the button contacts the plunger coupling engagement jaws located on the forward end of the plunger drive ram. These jaws then snap around the button of the syringe plunger, thereby connecting the syringe plunger to the plunger drive ram.
This “jaw and button” coupling mechanism in an injector does not result in a perfect fit between the jaws on the plunger drive ram and the button on the rearward face of the syringe plunger. The ends of the jaws are not completely snug around the cap of the button on the rearward face of the syringe plunger. This results in some amount of “backlash” between the mating sections of the coupling mechanisms. Due to this spacing the syringe plunger does not move cooperatively with the plunger drive ram upon motorized, automated movement of the plunger drive ram. Rather, the jaw and button embodiment features an initial movement of the plunger drive ram and a subsequent responsive movement of the syringe plunger. Thus, there is an element of lag time, albeit small, in deploying the syringe plunger to inject fluids to a subject. This is an unfortunate problem because many medical applications require an extremely high degree of accuracy, especially in the timing and volume of substances injected into the body. The lag time inherent in the jaw and button arrangement creates a reduced degree of accuracy.
Accordingly, to improve accuracy, there is a need for a coupling mechanism for the syringe plunger and plunger drive ram where movement of the syringe plunger is directly cooperative with movement of the plunger drive ram, allowing for enhanced accuracy in the volume of a fluid injected into a subject.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide an apparatus which allows for increased accuracy in the injection of fluids into human or other animal subjects. In accordance with this objective, improvements are made on the syringe plunger/plunger drive ram coupling mechanisms of the typical injector using replacement syringe plungers.
In particular, an injector in accordance with the invention features a new method for engaging the syringe plunger allowing for increased accuracy due to its tight, backlash-free grip. As opposed to the use of the jaw and button coupling arrangement in the prior art, the coupling mechanism of the present invention is a cam cleat. This cam cleat coupling mechanism creates a tight grip between the mating elements of the syringe plunger and plunger drive ram, thereby reducing lag time between movement of the plunger drive ram and the syringe plunger. Thus, the syringe plunger moves cooperatively with the plunger drive ram whether extending or retracting. This results in increased accuracy in the volume of fluid injected into a subject and aids in the efficient removal of air from the syringe.
In one specific disclosed embodiment, the coupling mechanism located on the end of the plunger drive ram that engages the syringe plunger is an inwardly facing pair of jaws forming the cam cleat. This cam cleat engages a cylindrical extension located on the rearwardly facing surface of the syringe plunger. This cylindrical extension is generally knurled. The cylindrical extension is centrally located and protrudes along the longitudinal axis of the syringe plunger parallel to the direction of the plunger's movement. The cam cleat structure on the forward end of the plunger drive ram forms a connection between the syringe plunger and plunger drive ram when it is engaged by the cylindrical extension, during insertion of the syringe plunger into the syringe. As the motorized drive shaft moves the plunger drive ram forward into contact with the syringe plunger, the two pawls of the cam cleat rotate away from the cylindrical extension while still remaining in contact with it. The toothed faces of the pawls grip onto the knurled extension protruding from the syringe plunger. Each pawl of the cam cleat contains a tension spring so that although the cylindrical extension can be freely inserted to the pawls of the cam cleat, it cannot be removed by longitudinal motion due to the grip of the cam cleat. Thus, once coupled, the mechanism remains engaged during longitudinal motion of the drive to cause the syringe plunger to cooperatively move forward or backward with the plunger drive ram.
In alternate embodiments of the invention, the extension protruding rearwardly from the syringe plunger need not be cylindrical, i.e., circular in cross-section. It may have a rectangular, oval, football-like, or any other cross-sectional shape amenable to insertion between the two pawls of the cam cleat coupling mechanism.
Disengagement of the syringe plunger from the plunger drive ram occurs by relative movement of the syringe plunger in a direction perpendicular to the motion of the plunger drive ram. By this movement, the cylindrical extension on the rearward face of the syringe plunger is pulled away from the pawls of the cam cleat. In the specific disclosed embodiment, this disengagement occurs by movement of a face plate located between the pressure jacket of the injector and the injector housing. In other embodiments, an asymmetrical coupling is provided that engages and disengages the syringe plunger upon rotational movement of the syringe with respect to the drive.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.


REFERENCES:
patent: 4677980 (1987-07-01), Reilly et al.
patent: 4738664 (1988-04-01), Prindle
patent: 4911695 (1990-03-01), Lindner
patent: 5004460 (1991-04-01), Gimeno
patent: 5007904 (1991-04-01), Densmore et al.
patent: 5269762 (1993-12-01), Armbruster et al.
patent: 5279569 (1994-01-01), Neer et al.
patent: 5322511 (1994-06-01), Armbruster et al.
patent: 5484414 (1996-01-01), Pace
patent: 5535746 (1996-07-01), Hoover et al.
patent: 5658261 (1997-08-01), Neer et al.
patent: 5865805 (1999-02-01), Ziemba
patent: 5868710 (1999-02-01), Battiato et al.
patent: 0 709 106 A2 (1996-01-01), None
patent: 0 709 106 A3 (1996-11-01), None

Affiliated with

Also associated with

Rating

Syringe/plunger coupling does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Syringe/plunger coupling, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Syringe/plunger coupling will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2541884