US Patent 7252388 Projector with tilt-angle detecting capability

A projector includes two range sensors of a phase difference method. The range sensors are laid out near a projection lens in such a way that a line connecting the centers of two photo-sensor arrays incorporated in one of the range sensors crosses a line connecting the centers of two photo-sensor arrays incorporated in the other range sensors approximately at the right angles. A control section controls those range sensors to measure distances to a plurality of ranging points on a screen. The control section computes the tilt angle of the screen based on the measured distances and supplies the computed tilt angle to a trapezoid correcting section and an optical mechanism section.