Improvements in door operators

摘要

A gearbox for an operator of a closure such as a door. The gearbox includes an input shaft (18) and an output shaft (20) each of which is journalled for rotation by bearings (16 and 17). A drive boss (23) is mounted by pin (24) to each shaft. A toothed sprocket (25) is engaged in a driving manner with shaft (18) via boss (23) while similarly toothed sprocket (26) is engaged with shaft (20) via boss (23). A toothed belt (27) extends about the drive sprockets to transfer drive from the input shaft (18) to the output shaft (20). The toothed sprockets (25 and 26) are of different sizes and interchangeable on the bosses (23) of the respective shafts (18 and 20) to facilitate a change in the gear ratio of the gearbox.