Abstract:
Pivotal platform apparatus (10) includes a frame member (12), a platform member (14) being pivotally attached to the frame member and having a first rotational inertia, and a reaction member (20) being pivotally attached to the frame member and having a second rotational inertia. A pair of crossed taut elements (40a and 40b) provide means for transmitting reverse rotation pivotal movement between the platform member and the reaction member so that the inertia of the reaction member balances the reaction of the platform member to provide a reactionless scan mechanism. A pair of motors (26a and 26b), each having pole pieces (30a and 30b) attached to the reaction member, and each having motor coils (28a and 28b) attached to the frame member, provide means for rotationally positioning the reaction member.