Patent ID: 7599612

Claim:
A method of determining with an electronic drive unit a radius of a cylindrical roller tube driven by an electric motor controlled by the electronic drive unit and a thickness of a material wound around the roller tube, the material having a proximal end attached to the roller tube and a distal end movable in a plane, the method comprising the steps of: determining a first distance from an initial position of the distal end to a first position of the distal end; determining a second distance from the initial position of the distal end to a second position of the distal end; determining with the electronic drive unit a first number of revolutions of the roller tube required for moving the distal end from the initial position to the first position; determining with the electronic drive unit a second number of revolutions of the roller tube required for moving the distal end from the initial position to the second position; and determining with the electronic drive unit the radius and the thickness using the first distance, the first number of revolutions, the second distance, and the second number of revolutions.