Drug delivery device with an improved mechanism for controlling the delivery rate

A method, comprising:

• determining a target rotational speed for an electric motor of a drug delivery device in terms of pulse frequency based on a target delivery rate for delivery of a fluid medicament through an outlet of a reservoir of the drug delivery device;
• comparing the target rotational speed with a minimum rotational speed for detecting a back-emf signal of the electric motor;
• in response to the target rotational speed being less than the minimum rotational speed:
• defining a ratio between an on state and an off state of the electric motor such that the electric motor is operated in the on state at the minimum rotational speed and at zero speed in the off state;
• modulating the on state and the off state to drive a delivery mechanism and cause the fluid medicament to be delivered at the outlet of the reservoir at the target delivery rate;
• and
• in response to the target rotational speed being equal to or greater than the minimum rotational speed:
• operating the electric motor continuously in the on state at the target rotational speed in order to drive the delivery mechanism and cause the fluid medicament to be delivered at the outlet of the reservoir at the target delivery rate.