The main components of the overhead crane include three parts like the lifting mechanism, the operating mechanism and the metal structure. The most basic part of the crane is the lifting mechanism,whose main components are three-phase asynchronous motors, brake units, decelerators, reels and pulleys. When the lifting mechanism is running, asynchronous motor outputs power through the reduction gear to make the drum rotate, so that steel cable twines round the drum or releases from the drum to pull up and down the goods. The role of the operating mechanism is to move the load horizontally or to  change the horizontal working position of the crane, which generally refers to the front and rear travel mechanism and the  left and right traverse mechanism. Their general components are three-phase  asynchronous  motor,  decelerators,  brake  units,   frames  and  wheels.   Metal construction is the main load-bearing components of the crane, whose role is to support the various parts and bear all the work load. When the bridge crane is working, its cart  runs back and forth along the rails on both sides of the elevated platform and its crab runs horizontally along the rails on the bridge, thus forming a rectangular trajectory. Make full use of the space under the bridge, then we can lift heavy objects without being hindered by the ground equipment in a certain space. Due to the requirements of the actual operation, the bridge crane must constantly move intermittently, that is, reciprocatingly changing in grasping materials, moving and unloading materials. Therefore, the design of the bridge crane control circuit is to design control methods for lifting mechanism, crane  cart and crane crab.

In this paper, the subject study is about the design of the control circuit  of the overhead crane. The MM440 inverter is used to govern the speed of the heavy objects’ moving. The Siemens S7-300 is used as the core control to control the bridge crane’s front and rear travelling, left and right sideswaying and lifting and lowering. The brakes are used to solve problems about the weight hover and the hook. The use of limit devices, overload protections, short circuit protections, alarms and the other protective  measures  is  to enhance the safety of production. The application of PLC and frequency converter in the control system of the bridge crane will make the modern production more accurate, more efficient   and more secure.

Keywords: overhead crane;crane cart;crane crab; lifting mechanism; variable frequency  speed control

目 录

第一章绪论 1

1.1研究背景及意义 1

1.2桥式起重机控制系统的研究现状与发展 1

1.2.1传统继电器控制桥式起重机的局限性 1

1.2.2可编程控制器的特色与优势 2

1.2.3桥式起重机速度控制技术及其研究发展 2

1.3本文的主要内容 3

第二章行车主电路设计 5

2.1走行及横移主电路设计 5

2.1.1大车前后走行拖动方式及特点 5

2.1.2大车主电路设计 5

2.1.3小车拖动方式及主要特点 6

2.1.4小车主电路设计 6

2.2上升下降主电路设计 7

2.2.1提升机构上提下放拖动方式及特点 7

2.2.2提升机构主电路设计