A
drug delivery device comprising comprising a delivery unit (3) and a drive unit (4), the delivery unit comprising a
drug container (5) and a pumping
system (8) having a pump engine (38) with a
stator (29) and a pump rotor (31) configured to effect an axial
piston stroke as a function of the rotation about an axis of rotation of the pump rotor relative to the
stator for pumping liquid out of the
drug container, the drive unit comprising a housing (2), an
electronic control system (6), a pump drive (7) including a motor (16), a motor output transmission shaft (17) driven in rotation by the motor (16), a rotor position
sensing system (9), and a
coupling (21) slidably coupled to the motor output transmission shaft (17) driven in rotation by the motor output transmission shaft, the
coupling (21) having a pump side interface (39) engaged with a drive
coupling interface (40) of the pump rotor (31) configured for transmitting torque from the motor (16) to the pump rotor (31) and for effecting an
axial displacement following an
axial displacement of the pump rotor (31), the
electronic control system (6) comprising a
motor drive circuit having a delivery control module, the delivery control module receiving an axial position measurement of the pump rotor (31) as a function of the rotational position of the pump rotor. The delivery control module is configured to emit an alarm condition defining an
occlusion event of the
drug delivery device triggered after an axial position of the rotor is measured as a value above an
occlusion position threshold, or after an
axial displacement amplitude of the rotor is measured below an
occlusion displacement threshold, for at least two revolutions of the pump rotor (31) within a window in a range of at least three to no more than ten revolutions.