Abstract : The application of AC frequency converter speed control system for tower cranes improves the service life of the structural components and mechanisms of tower cranes, further ensures construction safety, and brings convenience to operators. This article details the selection of frequency converters and motors for tower cranes and the advantages of using frequency conversion systems in tower cranes.
Keywords : Tower crane; Speed control system; Variable frequency technology; Application
With the continuous improvement of the mechanization level of tower cranes (hereinafter referred to as tower cranes) and the expansion of their application fields, the requirements for the technical level of tower cranes are becoming increasingly higher. The advanced technology of AC variable frequency speed control has been gradually promoted and applied to tower cranes in recent years. In early 1997, our factory began to apply AC variable frequency speed control technology to the slewing mechanism of the QTD150 tower crane, selecting Y-series ordinary motors, standard planetary reducers, Japanese Fuji AC frequency converters, and configuring braking units. The product was exported to Malaysia and performed very well. In the first half of 1998, the QTZ250 tower crane used in the Qinshan Nuclear Power Plant, a key national project, tested and applied variable frequency technology in its three main mechanisms (hoisting, slewing, and trolley luffing). The hoisting mechanism used a 55kW variable frequency motor, a German Siemens AC frequency converter, and an encoder (due to the immaturity of the central controller product, the hoisting mechanism used a dual-speed wound-rotor motor instead). The slewing trolley traction mechanism also used a variable frequency motor, all using German Siemens AC frequency converters. These are still in use on customer construction sites. Customers are quite satisfied with the performance of AC frequency conversion technology. At the end of 2001, our factory developed the QTK60 tower crane. The hoisting mechanism, slewing mechanism, and traveling mechanism of the product all adopt AC frequency conversion speed control technology. The hoisting mechanism uses J and Y series 22kW ordinary motors, and the slewing and traveling mechanisms use Y series 4kW ordinary motors. All use standard reducers and Yaskawa AC frequency converters, and are equipped with programmable controllers. The product is still in use on the construction site of Shanghai No. 7 Construction Company. Operators have reported that the machine runs smoothly, has a low failure rate, and the overall performance and safety devices meet the requirements of national standards. With the accumulation of experience in AC frequency conversion technology and the absorption and digestion of advanced foreign technologies, our factory has applied frequency conversion technology to QTZ5013, QTZ80G, QTZ5613, QTZ160, QTZ250, QTK60, and QTD150 tower cranes.
1. Tower crane speed control scheme
Since the 1990s, the working radius of tower cranes has been continuously increasing, and the lifting height and lifting capacity have been continuously increasing. This has placed new demands on the performance of the three major mechanisms of tower cranes: slewing, trolley luffing, and hoisting. These demands can be summarized in several aspects: ① improving the slow positioning function; ② improving the smoothness of mechanism starting, braking, and speed regulation; ③ increasing the working speed of the mechanism; ④ improving the overall safety and reliability of the machine. To meet these requirements, conventional stepped speed regulation schemes are no longer sufficient. Stepless speed regulation schemes mainly include voltage regulation speed regulation, slip speed regulation, hydraulic speed-regulating DC generator sets, and AC frequency conversion speed regulation. A comparative analysis of several stepless speed regulation schemes is presented below.
For details, please click: Discussion on the Market Application of Variable Frequency Technology in Tower Cranes
