Patent ID: 7993300

Claim:
A method for ensuring a constant target speed of a battery driven electrical motor, the battery driven electrical motor for moving a piston rod in an injection device so as to inject a set dose of medicine from the injection device, the method comprising: setting a first target speed to be reached by the piston rod, determining whether the first target speed can be reached, and, if the first target speed can be reached, maintaining the first target speed until the set dose of medicine has been injected from the injection device, and if the first target speed cannot been reached, setting a second target speed, determining whether the second target speed can be reached, and if the second target speed can be reached, maintaining the second target speed until the set dose of medicine has been injected from the injection device, and if the second target speed cannot be reached, setting a third target speed, determining whether the third target speed can be reached, and, if the third target speed can be reached, maintaining the third target speed until the set dose of medicine has been injected from the injection device, and, if the third target speed cannot been reached, shutting down the motor.