DOSE SENSING MODULE WITH FRICTION ENHANCING MEANS

The present invention provides a sensor module adapted to be arranged in a cartridge based drug delivery device between a rotatable piston rod and a cartridge piston for capturing dose data from a dose expelling event, the sensor module (50) extending along a reference axis and comprising: a first module part (51) adapted to engage the cartridge piston and comprising anti-rotation means for establishing a frictional interface to the cartridge to impede rotation of the first module part (51) relative thereto, a second module part (54) adapted to engage the rotatable piston rod, and sensor means (52, 152, 252; 53, 153, 253) adapted to detect an extent of relative rotational motion between the first module part (51) and the second module part (54), wherein the anti-rotation means comprises a plurality of radially outwardly projecting studs (51.1; 351.1; 451.1), each comprising a contact surface (51.8; 351.8; 451.8, 451.9) adapted to establish frictional contact with an interior surface of the cartridge.