Slip-ring motor can be used in conjunction with time delay relays for floor operated cranes to improve their travelling quality during start and inching.
为改善地面操作起重机的起动、点动运行性能，可选用绕线型电动机加外延时继电器控制。
2
The series of electric control devices developed in 70s for overhead travelling and gantry cranes has several shortcomings.