Telescopic boom

Claim 1

A telescopic structure comprising a plurality of elongated slidably fitted concentric tubular sections including: (a) a first tubular housing section having at the outer surface of its one end a drive mechanism comprising a first gear wheel mounted for rotation about a fixed axis on said housing section and protruding through a slot formed therein, said first housing further having a first gear rack extending longitudinally along its internal surface; (b) a second tubular section having an outside dimension smaller than the first housing section and having a second gear rack formed on its external surface for engagement with the first gear wheel mounted on and protruding through the housing section, whereby on rotation of said first gear wheel said second section is moved longitudinally relative to said tubular housing section; said second section further comprising longitudinally spaced first sprocket wheels mounted for rotation adjacent opposite ends of said second section, an endless first chain extending about said sprocket wheels for moving thereby, a first pair of said first sprocket wheels being mounted for rotation on a transversely extending shaft carrying a second gear wheel which protrudes through an opening in said second section for engagement with the first gear rack on the internal surface of said housing section; whereby on longitudinal movement of said second section caused by the rotation of said first gear wheel of said housing section, said second gear wheel will rotate to impart a movement to the endless first chain; (c) a third section having an outside dimension smaller than the second section and means for engaging the endless first chain of the second section so as to be moved longitudinally relative to said second section upon movement of said first chain when said second section is caused to move by the rotation of said first gear wheel on the housing section.