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

A drug delivery device including

• a reservoir configured to contain a fluid medicament to be delivered by advancing a piston in the reservoir at an advancement speed defining a delivery rate for the medicament through an outlet of the reservoir,
• an electric motor configured to drive a delivery mechanism by rotation to advance the piston,
• a control unit configured to control a rotational speed and an on state and an off state of the electric motor,
• wherein the control unit is configured to determine the rotational speed based on a back-electromagnetic force (back-emf) signal provided from the electric motor while the electric motor is operating in a monitoring mode,
• wherein the control unit is configured to control the rotational speed of the electric motor to be, while in the on state, above a minimum speed such that a back-emf signal can be detected in the monitoring mode, and wherein the control unit is configured to modulate the on state and the off state of the electric motor to adjust the delivery rate to a target delivery rate,
• wherein the delivery mechanism comprises a piston rod that abuts the piston in the reservoir, and wherein the piston rod is advanced at the advancement speed by the delivery mechanism,
• wherein the reservoir includes a cartridge comprising the piston that is configured to be linearly advanced in the cartridge by the delivery mechanism towards an outlet of the cartridge, and
• wherein the electric motor includes a brushless direct-current (DC) motor, and wherein the control unit is configured to control the on state by providing a driving voltage to a stator coil of the DC motor, wherein provision of the driving voltage to the stator coil of the DC motor is configured to cause application of a driving torque to a rotor of the DC motor to cause rotation of the rotor.

A method, comprising:

• using a control unit to determine a rotational speed of an electric motor of a drug delivery device based on a back-electromagnetic force (back-emf) signal provided from the electric motor while the electric motor is operating in a monitoring mode;
• determining, using the control unit, a target rotational speed for the electric motor 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, using the control unit, the target rotational speed with a minimum rotational speed detected by the control unit as the back-emf signal of the electric motor while the electric motor is operating in the monitoring mode;
• in response to the target rotational speed being less than the minimum rotational speed, using the control unit to:
• define a ratio between an on state and an off state such that the electric motor is operated in the on state at the minimum rotational speed and at zero speed in the off state;
• cause the electric motor to operate in an alternating fashion to modulate between the on state and the off state based on the ratio in order to drive a delivery mechanism and cause advancement of a piston of the drug delivery device, wherein advancement of the piston is configured to cause the fluid medicament to be delivered at the outlet of the reservoir at a delivery rate that is based on the target delivery rate;
• and
• in response to the target rotational speed being equal to or greater than the minimum rotational speed, using the control unit to:
• cause the electric motor to operate continuously in the on state at the target rotational speed in order to drive the delivery mechanism and cause advancement of the piston of the drug delivery device, wherein advancement of the piston is configured to cause the fluid medicament to be delivered at the outlet of the reservoir at the delivery rate that is based on the target delivery rate,
• wherein the delivery rate varies between 0.1 ml/min and 10 ml/min.