An improved device delivers a fluid medicament to the subcutaneous tissue of a user. The device is better suited for patients with Parkinson's Disease and other central nervous system disorders, than conventional infusion devices. The device can include a reusable part including a drive component (e.g., motor) and control electronics and a disposable part including a medicament reservoir. Medicament can be evacuated from the medicament reservoir by a plunger assembly that includes a plunger attached to a lead screw that is rotated by a nut, all within the disposable part. The device can be fluidically coupled with the tissue via a flexible cannula. Various embodiments relate to an improved cannula insertion mechanism that delivers the cannula under a force applied by a spring. Various embodiments relate to improved filling of the device, for example, using a vial adapter and an automated filling station.