Patent ID: 7993109

Claim:
A method of dispensing liquid from a pump, comprising: drawing a first volume of the liquid into a pumping chamber by causing a shape memory material to contract and move a piston to a first position of a plurality of positions; expelling a second volume of the liquid from the pumping chamber by causing the shape memory material to relax and move the piston to a second position of the plurality of positions; monitoring each of the plurality of positions of the piston using an encoding grid disposed on the piston, wherein a first location on the encoding grid indicates the first position of the plurality of positions of the piston and wherein a second location on the encoding grid indicates the second position of the plurality positions of the piston; and measuring a first time period, wherein the first time period is the time it takes to draw the first volume of liquid into the pumping chamber; comparing the first time period to a predetermined time period; and determining that the pump is not primed when the first time period is below the predetermined time period by a threshold amount of time.