Optimization For Pivots Position Of Luffing Mechanism Of Aerial Work Platform

Luffing mechanism is the working body for changing the workable radius of construction machinery which can extend working range and improve the working productiveness. Aerial work platform boom commonly use hydraulic cylinder to achieve luffing motion by three-pivot luffing mechanism. To improve the performance of luffing mechanism to adapt to the complex operating conditions, a typical folding boom luffing mechanism which is composed of a hydraulic cylinder and many linkages is given in the paper. With the same working height assured, this luffing mechanism which shortens the length of main boom and the stroke of the luffing, increases the working range is widely used in aerial work platform. After of the novel style of luffing mechanism being adopted, stress characteristics of the slew bearing is improving, and the backward stability and operational flexibility are rising. However, there are large number of pivots in the luffing mechanism which increase the difficulty of pivots layout. The force calculation of pivots is more complex than three-pivot luffing mechanism. Up to now, the method of program analogy or reference to similar design are generally applied on product design which however can not guarantee to achieve both economic and safe design goals. Therefore, the paper presents a method to calculate and optimize the mechanical characteristic of folding boom luffing mechanism, and provides an important basis for pivots layout and structural design.Based on SWHT series aerial work platform project developed by Dalian University of Technology and Hunan Sunward Intelligent Machinery Co.Ltd. The paper mainly completed following contents:(1) By conducting the analysis model of luffing mechanism of aerial work platform, the geometric relationship and static equation of luffing mechanism were established, function expressions of key pivots of luffing mechanism was given.(2) In this thesis, the mathematical model was established in which the coordinates of pivots of luffing system was regarded as variables and the pursuit of minimum of force of luffing cylinder as the objective function. The optimization calculation was presented by using genetic algorithm toolbox of MATLAB. (3) By applying the method of rigid-flexible coupling, a rigid-flexible model of the luffing mechanism was established in which upright, folding boom, balance bar and power bar of luffing mechanism were regarded as flexible body.(4) In this thesis, the simulation for the nonlimited condition of luffing mechanism was performed with ADAMS, curves of the varying force with angle of luffing mechanism key pivots were given and compared with the static calculation result gained from MATLAB. In addition, the stress and displacement curves of flexible body in luffing mechanism were acquired, and provided as a basis for the reasonable layout of pivots and decrease in the weight of the mechanism. The optimization results were credible, and have been used in practical project.