Reservoir plunger position monitoring and medical device incorporating same

An infusion device, comprising:

• a housing including a voided region to receive a reservoir, the voided region including a voided portion to receive a shaft portion including a shaft coupled to a plunger of the reservoir, the shaft portion comprising a detectable feature;
• and
• a sensing arrangement proximate the voided portion to sense the detectable feature when the reservoir is inserted in the voided region, wherein:
• a resistance of the sensing arrangement is influenced by contact with the detectable feature;
• and
• the sensing arrangement comprises:
• a flexible cover layer integrated with a wall of the voided portion;
• a bottom conductive layer;
• an upper conductive layer;
• and
• a spacer layer between the bottom conductive layer and the upper conductive layer, the bottom conductive layer and the upper conductive layer being spaced apart from one another by the spacer layer in the absence of a compressive force applied to the upper conductive layer;
• the flexible cover layer overlies the upper conductive layer;
• and
• the detectable feature contacts the flexible cover layer when the reservoir is provided within the voided region of the housing to compress the flexible cover layer and the upper conductive layer to provide the resistance corresponding to a location where the flexible cover layer and the upper conductive layer are compressed by the detectable feature.

A method of operating an infusion device to deliver fluid from a reservoir including a plunger coupled to a shaft such that displacement of the shaft results in displacement of the plunger, the infusion device including a sensing arrangement to sense a detectable feature on the shaft, the method comprising:

• operating a motor having a rotor coupled to the shaft to displace the shaft in response to rotation of the rotor and deliver the fluid from the reservoir;
• obtaining a measured shaft position based at least in part on an electrical output signal provided by the sensing arrangement that is indicative of the detectable feature contacting the sensing arrangement, wherein the electrical output signal corresponds to a location of the detectable feature contacting the sensing arrangement;
• determining a remaining amount of fluid in the reservoir based on the measured shaft position;
• and
• providing a low fluid notification when the remaining amount is less than a threshold value, wherein:
• a resistance of the sensing arrangement is influenced by contact with the detectable feature;
• and
• the sensing arrangement comprises:
• a flexible cover layer integrated with a wall of the voided portion;
• a bottom conductive layer;
• an upper conductive layer;
• and
• a spacer layer between the bottom conductive layer and the upper conductive layer, the bottom conductive layer and the upper conductive layer being spaced apart from one another by the spacer layer in the absence of a compressive force applied to the upper conductive layer;
• the flexible cover layer overlies the upper conductive layer;
• and
• the detectable feature contacts the flexible cover layer when the reservoir is provided within the voided region of the housing to compress the flexible cover layer and the upper conductive layer to provide the resistance corresponding to a location where the flexible cover layer and the upper conductive layer are compressed by the detectable feature.