Cover for liquid delivery system with integrated plunger position sensing using focused optical beam and linear potentiometer

An apparatus for use with a pen injector, the pen injector including a transparent cylinder for housing a liquid and an at least partially opaque plunger movable along an axis of the cylinder for expelling the liquid through an outlet, the apparatus comprising:

• (a) a cap with a central bore extending along an axis, said cap configured for sliding engagement with the cylinder so as to be slidable along the cylinder parallel to the axis from a first position to a second position;
• (b) a cradle slidingly mounted within said central bore, said cradle configured for receiving an end portion of the pen injector, said cradle being spring biased towards an end position for engaging the end portion of the pen injector when said cap is in said first position, and being retractable to move together with the end portion of the pen injector as said cap slides to said second position;
• (c) a set of sensors housed in said cap so as to move together with said cap, said set of sensors comprising:
• (i) an optical sensor having an optical emitter for emitting radiation and an optical receiver for generating a first output indicative of an amount of said radiation received by said optical receiver, and
• (ii) a position sensor deployed for generating a second output indicative of a current position of said cradle within said central bore;
• and
• (d) a processing system associated with said set of sensors so as to receive at least said first output and said second output, said processing system being configured to be responsive to a variation in said first output indicative of said optical sensor reaching a known spatial relationship to the plunger to determine a corresponding current position of said cradle as indicated by said second output, and thereby to determine a location of the plunger along the cylinder,
• wherein said position sensor comprises a linear potentiometer strip deployed within said cap so as to extend parallel to said axis, and a pressure element mounted to said cradle and biased so as to press against said linear potentiometer strip.