ring 74 by a universal joint 80 when the planes of rings 74 76 are in the same plane as base 24 and collar 78 is normal to the base the axes of rotation of universal joint 80 and revolute joints 86 and 87 are all in a single plane also center post 72 can only slide in collar 78 without any rotation platform 22 fig5 is connected to center post 72 by universal joint 89 fig7 a universal joint 89 prevents the rotation of platform 22 with respect to the longitudinal axis of center post 72 referring again to fig7 a the top end of center post 72 is attached to three active cables 88 which are used to orient the center post 72 in space fig7 a shows the mechanism without the passive cables 98 and movable platform 22 to show more clearly the active cables 88 the active cables 88 are attached at one end thereof to the tip of center post 72 referring particularly to fig7 b each of the active cables 88 is pulled and accumulated using an associated winch assembly that includes a pulley 92 and a motor 90 which rotates the pulley pulley 92 and motor 90 of each winch assembly is mounted in housing 96 which is attached to the base platform 22 and each of the cables 88 passes through a hole 94 located in the top of the associated housing 96 the tip of center post 72 can be moved to any point in the workspace by changing the length of active cables 88 the center post 72 applies a pushing force to cables 88.