초록 ▼

Reservoir volume in a drug delivery device is sensed by providing a capacitor, the capacitance of which varies with bellows position or, alternatively, with the amount of propellant liquid absorbed in a dielectric material. In one embodiment, a capacitance is provided between a surface of the bellow

Reservoir volume in a drug delivery device is sensed by providing a capacitor, the capacitance of which varies with bellows position or, alternatively, with the amount of propellant liquid absorbed in a dielectric material. In one embodiment, a capacitance is provided between a surface of the bellows, which acts as a first capacitor plate, and a conductive surface disposed proximate the bellows, which acts as a second capacitor plate. As the bellows moves from its extended full position to its collapsed empty position, the area of overlap, and therefore the capacitance between the first and second plates varies from a maximum value to a minimum value. In another embodiment, a variable capacitor is provided with an absorbent material. The absorbent material absorbs the liquid phase of the propellant in the pump housing and acts as a dielectric between two stationary conductive plates provided in the housing. The amount of liquid propellant absorbed in the absorbent material varies with the reservoir volume. When the reservoir is in its full, expanded position, more liquid propellant is absorbed in the absorbent material. When the reservoir is in its compressed empty position, more of the propellant exists as vapor within the pump housing and therefore less liquid propellant is absorbed in the absorbent material. The dielectric properties of the capacitor are therefore higher and the capacitance is therefore maximized when the reservoir is in its full, extended position. Conversely, the dielectric properties are lower and the capacitance minimized when the reservoir is in its compact, empty position.

대표청구항 ▼

[What is claimed is:] [1.]a housing;an expansible reservoir within the housing for containing a supply of drug, the reservoir defining a volume;a propellant contained in the housing as both a liquid phase and a vapor phase so as to maintain a substantially constant vapor pressure force on the reserv

[What is claimed is:] [1.]a housing;an expansible reservoir within the housing for containing a supply of drug, the reservoir defining a volume;a propellant contained in the housing as both a liquid phase and a vapor phase so as to maintain a substantially constant vapor pressure force on the reservoir as the reservoir volume changes;a capacitor disposed within the housing, the capacitor having a capacitance and comprising an absorbent dielectric for absorbing the liquid phase of the propellant and having dielectric properties that vary with the amount of absorbed liquid phase of the propellant, whereby the capacitance of the capacitor changes with variations in the reservoir volume.