Surgery – Instruments – Surgical mesh – connector – clip – clamp or band
Patent
1996-09-16
1999-03-09
Lewis, William
Surgery
Instruments
Surgical mesh, connector, clip, clamp or band
A61M 500
Patent
active
058793607
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to improvements in infusion devices and more particularly to improvements to the drive head of a syringe pump.
BACKGROUND OF THE INVENTION
Various forms of syringe pump are commercially available and have been proposed in the patent literature. Examples of such patent literature include our own patents, such as U.S. Pat. Nos. 4,741,732 Crankshaw et al and 5,034,994 Crankshaw et al.
A head switch which operates when the drive head or pusher makes contact with the plunger flange of the syringe is required to permit:
(1) Sizing of syringes by identifying correct engagement of the drive head in the empty and filled positions to permit calculation of the internal volume of the syringe from data entered by the operator;
(2) Identification of operator interference with the drive head;
(3) Detection of separation of the syringe plunger from the drive head, which may occur with spontaneous delivery of fluid, or siphoning, from the syringe in excess of that caused by the pusher;
(4) Disengagement of the drive head and hence depressurization of the contents of the syringe prior to the sounding of an occlusion alarm.
In each of the above patents, a conventional microswitch with dual contacts was utilized. While such switches are reliable, it is necessary to incorporate a small lever to reduce the actuating force to the 10 to 20 gram range. A force above 10 gram is necessary to avoid spurious actuation if the position of the syringe pump is changed suddenly. On the other hand the actuating force must be less than 20 gram so that the plunger of a small syringe is not operated by the switch before contact has been sensed. Even with the smallest switch available, the lever must travel an excessive distance before the switch operates. This leads to unacceptable delays in sensing the contact or the release of the pusher with the drive head. A further disadvantage of a microswitch is the difficulty of rendering it waterproof without considerably increasing the force necessary to operate it.
SUMMARY OF INVENTION AND OBJECTS
It is an object of a first aspect of the present invention to provide a sensor which operates as a means for sensing contact between a device for exerting a force and an object, such as the drive head or pusher of a syringe pump and the plunger of the syringe, in a mariner which ameliorates the above stated disadvantages.
In a first aspect, the invention provides a force sensor for a device which exerts a force on an object, comprising spaced conductive members, insulating means carrying conductive elements covered by dielectric materials to define with said conductive members a pair of capacitors, biasing means for maintaining one of said dielectric materials closely adjacent to or in contact with one of said conductive members, the other conductive member being spaced to define an air gap between the other dielectric material and the other conductive member, means for applying a contact force to said insulating means to move said insulating means towards said other conducting member to close said air gap to thereby change the capacitance of one of said capacitors, and means for utilizing said change in capacitance to detect the application of said force to said sensor.
In one form of the invention, the sensor is a contact sensor capable of detecting forces between about 10 and 20 grams, and in this form, the air gap is small and the biasing means requires only a small force of about 10 grams to cause movement of the insulating means to close the air gap.
The insulating means is preferably in the form of an insulating disk having conductive plates, such as copper plates, fixed to its opposite surfaces with a thin dielectric layer overlying the conductive plates. A small spring supplies the biasing force which holds the dielectric on one side of the insulating disk in engagement with one of the conductive members thereby leaving a small air gap between the other dielectric covering and the other conductive member. An actuating button is secured to the di
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Lewis William
The University of Melbourne
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