Two-speed continuous tangent screw

摘要

An adjustment mechanism for a telescope of a theodolite. The mechanism includes a worm gear that is coupled to a friction gear of the theodolite. The friction gear is coupled to the telescope so that any rotation of the gear will induce a corresponding movement of the scope. The worm gear is coupled to a linear screw and an outer sleeve. The linear screw has a shaft that can push the worm gear and rotate the friction gear to provide a fine movement of the telescope. The linear screw also has a stop that engages an arm of the sleeve. Continued rotation of the linear screw rotates the engaged sleeve and the worm gear to provide a coarse movement of the telescope. The linear screw is connected to a knob which can be rotated by an operator. The operator can induce a coarse movement of the telescope by turning the linear screw so that the stop engages the sleeve. The operator can induce a fine movement of the telescope by rotating the knob in a reverse direction so that the linear screw pushes the worm gear and rotates the friction gear.