Patent ID: 7878931

Claim:
In a motorized operator for moving a barrier between open and closed positions, a frame including spaced apart generally parallel elongated frame plates, spaced apart frame members interconnecting said frame plates, an electric motor mounted on said frame in a fixed position, a motor output shaft projecting through one of said frame plates, an intermediate shaft mounted for rotation on said frame in bearings supported on respective ones of said frame plates, an output shaft mounted for rotation on said frame in spaced apart bearings supported on said frame plates, respectively, said bearings for said intermediate shaft and for said output shaft being fixed on said frame plates, respective chain sprockets mounted on said intermediate shaft and said output shaft and a chain trained over said sprockets, said output shaft further comprising a second sprocket disposed between said parallel elongated frame plates for moving a door, and a third sprocket drivingly connected to a sprocket disposed on separate and spaced apart rotatable limit switch shaft, respective pulleys mounted on said motor output shaft and said intermediate shaft and a stretchable endless drive belt trained over said pulleys, said stretchable endless drive belt formed of an elastic polyamide cord and being stretchable between about two percent to ten percent of its nominal length, whereby said intermediate shaft is driven by said motor, the distance between axes of rotation of said motor output shaft and said intermediate shaft is fixed and a predetermined tension in said stretchable belt is fixed.