Abstract : Bridge cranes use frequency converters as the variable frequency speed control power supply for the drive system motors and PLCs as the control devices for the drive system. This organically combines the advantages of frequency converters, such as large starting torque, good speed regulation performance, convenient control, and multiple protections, with the reliable and flexible control characteristics of PLCs, thus improving the operating performance and reliability of bridge cranes. This is currently a more ideal control mode. Keywords: PLC; frequency converter; drive system With the development of new technologies and control equipment, bridge cranes generally use frequency converters as variable frequency speed control power supplies, replace the original wound-rotor asynchronous motors with squirrel-cage asynchronous motors, and use PLCs as control devices for contactless control. This control mode improves speed regulation performance and increases system reliability. This article analyzes the specific application of frequency converters and PLCs in the system through an example. [b]1 Composition, characteristics and control requirements of the bridge crane drive system 1.1 Composition of the bridge crane running mechanism[/b] (1) Trolley drive system: Drives the entire crane to move left and right along the direction of the workshop (with the driver's sitting direction as a reference). (2) Trolley towing system: drags the hook and load along the bridge frame to move back and forth. (3) Hook towing system: drags the load to move up and down. Large cranes (over 10t) have two hoisting mechanisms: main hoisting mechanism (main hook) and auxiliary hoisting mechanism (auxiliary hook). Usually, the main hook and auxiliary hook cannot lift loads at the same time. [b][align=center]For details, please click: PLC and frequency converter control modes of bridge cranes[/align][/b]