Abstract: A crane safety apparatus for displaying a schematic diagram of a part of a crane mechanism on a two-dimensional screen dynamically as the crane mechanism is operated, and displaying on the same screen a predetermined operation zone as a visually discriminative zone pattern. The operation zone pattern is displayed on the screen in response to the key command by an operator during a selected crane operation mode, while referring to the schematic crane mechanism diagram currently displayed on the screen.

Abstract: Rope extension is detected as a rope shift distance at predetermined time intervals. A rope extension amount is obtained as the accumulated value of the shift distances. The rope shift accumulated value is automatically reset to 0 when a hook structure reaches an overhoist position to renew the reference position of the rope extension amount and to correct any measurement errors of the rope extension amount. From this rope extension amount, a hanging length of the hook structure from a boom or jib top is obtained and used to calculate a hook lifting distance. The calculated hook lifting distance, or hook structure position, is displayed on a display screen relative to a fixed index or pattern. An operator can monitor the state of the hook structure from the display.