Tower crane originated in Western europe. A rotary crane boom mounted on the upper part of the tower of the tower. Large working space,Website:://.xqcranes.com, mainly for housing construction materials in the vertical and horizontal transportation and installation of building components. Made of three parts, metal structure, working mechanism and electrical system. The metal structure comprises a tower body, a movable arm and a base. Working mechanism of lifting, luffing, slewing and walking four parts. The electrical system comprises a motor, controller, power distribution cabinets, connection lines, signals and lighting devices.Jib tower crane form sub horizontal type and press type .Jib tower crane is horizontal, the trolley along the horizontal dynamic variation range of operating arm, pagoda type crane with luffing movement. The dynamic arm is long, but the greater weight arm. Boom for the pressure rod, luffing mechanism and the traction actuating arm pitching amplitude, amplitude motion than horizontal smooth, but its relatively small weight.The lifting weight of the tower crane varies with the extent of the range. The product of the weight and the amplitude of the load torque is the main technical parameters of the crane. Through the rotary mechanism and a rotary supporting, tower crane lifting height, and the inertial mass of a turn and walk. Therefore, it is necessary have good speed performance, special hoisting mechanism to light load fast, heavy and slow, installation in place fretting. General in addition to the use of resistance speed, but also often use eddy current brakes, frequency modulation, variable pole, controlled silicon and mechanical and electrical combination of speed control.