Patent ID: 7145742
Filing Date: 2006-12-05
Classification: G11B

Abstract:
1. A control apparatus for controlling retraction of a device carried on a moveable member actuated by an electric motor after a sudden power loss, the control apparatus comprising: a measuring circuit for measuring a back electromotive force (back EMF) from the electric motor during a measuring phase, wherein the back EMF from the electric motor is related to an actual velocity of the moveable member; a controller which receives the back EMF from the electric motor and provides a control signal for controlling a magnitude of a drive current based on a commanded velocity signal and the back EMF from the electric motor, wherein the controller includes a proportional integral controller including a proportional compensation portion and an integral compensation portion, the proportional compensation portion and the integral compensation portion each having as an input the difference between the commanded velocity and the back EMF from the electric motor; and a current control loop for providing a command current signal based on the control signal and a sensed current through the electric motor, and for providing the electric motor with the drive current during a driving phase based on the command current signal.