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What kinds of limit devices must the tower crane have?
Tower cranes must have lifting weight limiters, moment limiters, height limiters, travel limiters, amplitude limiters, etc.
(1) Lifting weight limiter: also known as overload limiter, is a kind of safety device that can make the crane not overloaded. When the lifting weight exceeds the rated lifting weight, it can automatically cut off the power supply of the lifting mechanism to stop or issue alarm. Lifting limiters are mechanical and electronic.
(2) Torque limiter: For a luffing crane, only a certain amount of lifting weight is allowed in a certain range. If it is overweight, the crane has a risk of tipping over. Torque limiter is a protection device developed based on this feature. At a certain amplitude, if the load exceeds its corresponding weight, the circuit is cut off, so that the lift cannot be performed and the stability of the crane is ensured. Torque limiters are mechanical, electronic and compound.
(3) height limiter: also called hook height limiter. They are usually mounted on the boom's head. When the hook is lifted to the extreme position, the lever is lifted. Pressing the lower limit switch breaks the circuit and stops it. When the brake is closed, the hook can only fall.
(4) Travel Limiter: A safety device that prevents a crane from crashing or restricts travel within a certain range. It is generally mounted on the inside of the active trolley and is mainly equipped with a limit switch that can be toggled. In addition, a fixed limit position baffle is installed at the end of the track (at a limited position in operation). When the tower crane reaches this position, the limit baffle touches the trigger of the limit switch, cuts off the power for controlling the travel, and then closes The tower crane can only be operated in the opposite direction at the time of the brake.
(5) Amplitude Limiter: Also called the amplitude limit or amplitude indicator, an amplitude indicator is attached to the boom of a general jib crane. It consists of a fixed circular dial, with a vertical movable pointer in the center of the disk. When changing the amplitude, the pointer indicates the nominal lifting weight at various amplitudes. When the boom moves to the upper and lower limit positions, the lower limit switch is pressed separately, the main control circuit is cut off, and the amplitude modulation motor is stopped to reach the limit position.