Design Of Heavy Duty Mainpulator For Loading And Unloading Crankshafts And Trajectory Planning For Three Working Procedures

Six-cylinder crankshaft is an important component of diesel engine and withstandcomplex force conditions. To make such a crankshaft, the processing quality is alwayshighly required. Consequently, this leads to complicated the process technology andfrequent delivery, loading and unloading. Moreover, the crankshaft mass is alwaysapproaching200kg. These conditions make it imperative to design a heavy-dutymanipulator arm to load and unload the crankshafts to facilitate the renovation of theautomatic production line. This paper mainly designed a heavy-duty manipulator toautomatically load and unload the crankshaft between three production processes: themilling of the end faces plus drilling of center holes, mass centering machine, andlathing outside diameter of crankshafts. A trajectory planning and optimization analysiswas further conducted.The design targets were firstly confirmed based on the study of production field.After the comparison of configuration characteristics of the current manipulator at homeand abroad, a5-DOF articulated heavy-duty manipulator configuration was determined.In view of the manipulability, an optimization of the length of the manipulator’s rodswas conducted. After the weigh and judgement of performances of different motors andreducing mechanisms, we adopted YASKAWA AC servo electric machine and RVspeed reducer. We then employed link lever mechanisms and V type jaw combinationsto design the end clamper. The analysis of motion space shows that the manipulator canmeet the space demands of the production field. A spring balance cylinder was designedat the shoulder joint to balance the self gravity effect of the manipulator, so as toimprove control characteristics. Besides, the parameters of balance system areoptimized based on the simplified dynamic model. After the optimization, the shoulderjoints peak driving moment of the balance system is reduced from9679.5N·m to2498.0N·m.In order to optimize the dynamic characteristics of the manipulator, a dynamicmodel of the manipulator rigid body, together with the rigid flexible coupling modelconsidering flexible joints are established. The correctness is subsequently verified byADAMS. Based on the validated dynamic model, dynamic parameters and performanceof the manipulator system are analyzed. With corresponding dynamic performanceindex and lightweight body as the optimization objective function, the dimensionparameters of each member bars of manipulator are optimized. Body weight is reducedby about30%with the optimized member bar dimension parameters. The optimizationalso improved the dynamic performance of the body to a certain degree. A finiteelement model of the optimized manipulator arm is further established. Static and modal analysis of the model were conducted, with the results showing that the optimizedmanipulator bars meet the design requirements.In the path planning algorithm and path optimization of the manipulator arms, afterfinishing the comparison of the two common trajectory planning algorithms, the spatialmulti-point spline interpolation algorithm is chosen as the basic algorithm. Combiningthe dynamic model of manipulator arm, the trajectory planning algorithm is optimizedwith the consuming time and consuming energy as the optimization objective. Theoptimization results prove that this algorithm has certain advantages in reducing boththe run time and the energy consumption. Based on the loading and unloadingoperations requirements of three working procedure of the six-cylinder crankshaftproduction line, the joint simulation experiment for the trajectory planning of theheavy-duty manipulator is conducted by SolidWorks, ADAMS and MATLAB. Theresults show that the manipulator arm is able to meet the work field demands ofcrankshaft machining. The manipulator arm could transport the workpieces in a quickand steady way.