Patent ID: 7386900

Claim:
A frame elevating mechanism, comprising: a first frame configured to be supported on a floor surface; a second frame oriented above said first frame and configured to be moveably supported by said first frame; first and second drive mechanisms capable of operating at variable speeds for selectively adjusting an elevation of said second frame, with said first drive mechanism controlling an elevation of a first end of said second frame and said second drive mechanism controlling an elevation of a second end of said second frame, said first drive mechanism configured to initially operate at a first maximum operating speed and said second drive mechanism configured to initially operate at a second maximum operating speed that is substantially equal to said first maximum operating speed; at least one angle sensor located on said second frame for determining an angle of inclination of said second frame; and a control unit for selectively controlling the elevation of said second frame; wherein during a change in elevation of said second frame, said control unit repeatedly compares a starting angle of inclination of said second frame to a present angle of inclination of said second frame, and if not substantially equal, adjusts the operating speed of one of said drive mechanisms to compensate.