Final answer:
Anti-two block devices are crane safety systems designed to prevent the hook assembly from colliding with the boom point, which could cause dangerous situations like cable breakage or crane collapse. They use sensors and alarms to detect and stop this from happening.
Step-by-step explanation:
Anti-two block devices are safety systems used on cranes to prevent a condition known as two-blocking, which occurs when the lower load block, or hook assembly, is raised too high and comes into contact with the upper block, or boom point. This can lead to dangerous situations, including the potential for the crane's cable to break or the entire crane to collapse. Anti-two block devices work by providing a warning signal or automatically stopping the crane's hoisting motion to prevent the blocks from colliding.
Function of Anti-Two Block Devices
These devices typically consist of a sensor mounted on the boom or jib of the crane that detects when the hook assembly is approaching too closely to the boom point. An alarm or cutoff mechanism is triggered when the sensing device detects the hook's proximity, thereby preventing the occurrence of a two-block situation.