Brake mechanism for motor driven projection screen

Claim 1

In an electric motor unit for rotatably driving the roller of a projection screen apparatus, the motor unit including a stator for establishing a magnetic field when electrically actuated, and a rotor rotatably mounted within the stator and provided with limited axial movement from an inoperative position to an operative position in alignment with the magnetic field, said rotor having aligned journals at its opposite ends with one of said journals having an exposed end portion projecting outwardly of the motor unit and the other of said journals being operatively connected to rotate the roller of the projection screen apparatus, a brake mechanism for preventing rotation of the rotor and the roller when electric current to the stator is discontinued, comprising: a brake supporting member mounted exteriorly of the motor unit adjacent the exposed end portion of said one journal, said member having an outwardly facing braking surface; a braking element secured to said exposed end portion and having an inwardly facing braking surface in confronting relation to said outwardly facing braking surface; spring means normally urging the rotor toward inoperative position and normally urging the inwardly facing braking surface into frictional braking engagement with the outwardly facing braking surface, electric actuation of the stator causing the rotor to be moved to its operative position in opposition to said spring means so as to move the exposed end portion of the one journal and said braking element outwardly to separate the two braking surfaces, and subsequent discontinuance of electric current to the stator permitting the rotor to be shifted to inoperative position with the surfaces in braking engagement to prevent rotation of the rotor journals and the screen roller; and means for adjustably positioning the braking element axially of the exposed end portion to vary the force exerted by the spring means.