Patent ID: 7993108

Claim:
A method of pumping a liquid, comprising: applying at least one electrical pulse to a shape memory alloy to overcome a bias force of a first spring coupled to the shape memory alloy to move a piston from a first position of a pumping cycle to a second position of the pumping cycle such that a liquid is drawn into a chamber when the piston is moved from the first position to the second position and expelled from the chamber when the piston is moved from the second position to the first position; detecting a stressed state of the shape memory alloy resulting from the shape memory alloy overcoming a bias force of a second spring coupled to the shape memory alloy; detecting an occlusion by monitoring an amount of time required to move the piston from the first position to the second position using an encoding grid disposed on the piston and comparing the amount of time to move the piston from the first position to the second position to a first predetermined time period; and modifying the at least one electrical pulse when at least one of the stressed state is detected or the occlusion is detected.