It was indicated that thyristor AC voltage soft start is the best method for no-load start and light load srart,and soft starting technology integrating cycloconverter and thyristor AC voltage is appropriate to heavy load start.

The method is introduced into the study of the work space on a truck crane boom to determine the mass-center function of all the main units in the truck crane in relation to the original coordinate frame when the main units move in pace with the movement of the lifted load and to determine the mass-center function of the whole truck crane.