1.Main cause of crane cage fall accident caused by construction lift There are many causes causing the crane cage to fall,which can be summarized as follows: (1)the braking torque of the driving device is not enough and the safety factor is too small; (2)single drive and double(multiple)drive; (3)poor reliability of anti-fall safety device; (4)in violation of the buckle rules,not in accordance with the provisions of the product manual,the cage overload operation; (5)there is no supporting wheel on the back of the meshing place between the drive pinion and rack,or there is no locking plate on the eccentric shaft of the driving wheel; (6)the balance weight is not set; (7)other incidental causes; 2 analysis and comparison of safety devices of driving devices 2.1 brake of cage drive device The brake is a device for the floor of the crane cage parking,currently there are roughly two types:one is the standard JWZ200 block brake,the braking torque is 160N·m,is a mature product,its disadvantages are large size,brake easy to wear,such as repair and maintenance is not easy to fail.This kind of brake is mostly used in the 80's production of domestic construction lift,has been rarely used,gradually phased out;The other is a reference ALIMAK import prototype developed in the late 1980s,which is a disc friction brake connected to the drive motor.It is a pull friction brake connected to the drive motor.This kind of brake is characterized by compact structure,small size,and easy to adjust the gap between brake plates.At present domestic construction lift its this kind of brake. To make the cage reliably parked on the bent layer,to ensure that it does not fall,the brake brake device must have enough braking torque,for the cage with no balance weight of the braking torque should meet the following requirements: Row on the hoisting cage:M1=(((G+Q,R)/I)k.hanging LongXia row:M2=(((G+Q+Q1),R)/I),k Where:M1--braking torque(N·m)of the hoisting cage when it is going up;M2--braking torque(N·m)when the cage go