A fluid infusion device includes a fluid pump mechanism having a rotor and a stator. The rotor includes an optically detectable feature, a reference surface, and a cam element rising from the reference surface. The stator includes a cam element having a stator cam surface. The cam elements cooperate to axially displace the rotor as a function of angular position of the rotor, wherein the detectable feature rotates and axially translates as a function of angular position of the rotor. A biasing element provides force to urge the rotor cam element toward the stator cam element and toward the reference surface. A drive motor actuates the rotor to pump medication fluid from a fluid cartridge module to a body, via a subcutaneous conduit. An optical detection circuit interrogates the detectable feature during operation of the fluid pump mechanism to determine an operating condition of the fluid pump mechanism.