An electrically powered drive system for a medical device includes a motor, a gear box driven by the motor, a driving member for moving a part of the device, a crank mechanism, and a push-pull mechanism. The crank mechanism includes first and second crank arms each having a connection end and a distal end. The first crank arms distal end is pivotally connected to the driving member. The second crank arms connection end is pivotally connected to the first crank arms connection end. The second crank arms distal end is pivotally connected to a stationary member. The push-pull mechanism is connected to and driven by an output member of the gear box to drive the crank mechanism to move the driving member between a retracted position and an extended position.
