Research On Key Techniques Of Stabilized Parallel Shipment Platform With Folding Branches

Ships at sea are affected by complex oceanic sea conditions such as waves and sea breeze,and it is difficult to implement cargo transshipment under high sea conditions,which seriously affects marine supply and overpass operations.The overseas stable receiving technology has become relatively mature abroad,and China has only begun to pay attention to the development and application of related technologies in recent years.At present,it is hard to see mature domestic products on the market.The stable delivery and transfer platform at sea is mostly in the form of a parallel robot,and it also exist in the form of serial and hybrid structure.During the process of analyzing the cargo transshipment,it was found that the roll,pitch and heave motions of the ship have the greatest impact on the receiving process.Ship’s swaying and swaying,require a translational compensation capability for parallel platforms.In the analysis of the structure and operation of the existing domestic and foreign receiving platforms,it is found that the cargo needs to be lifted or assisted by the front lift when it is transferred from the receiving platform to the deck.In the case of ships under the high sea or without such equipment,this is Always a pain point.Therefore,to synthesize the above-mentioned degrees of freedom,working space,and the requirements of actual goods handling operations,a parallel platform with six degrees of freedom and folding branches is proposed,the main research contents are as follows:Firstly,a branching mechanism model based on Screw Theory is established,and the mechanical equivalent of the folding branch is analyzed.Based on this,the positive and inverse solutions of the parallel mechanism are deduced.Secondly,because there are many joints with folded branches,and the joint clearance has a great influence on the system control accuracy and motion noise in practical engineering.In this paper,the gap is replaced by the connecting rod to establish a branch mechanism model considering the gap,and we optimize the joint-error-sensitive structural parameters of the branch dip.The folding mechanism contains closed-loop sub-chains,and the force conditions are complex.This paper analyzes the force conditions at each joint by statics,which provides a reference for mechanical structure design.Thirdly,through the dynamic simulation analysis results under condition of the extreme wave cycles,the output and speed information of the driving branch was obtained.The hydraulic system of the receiving platform was designed as aboved,and the key components were calculated and selected.Based on the mutual verification of theoretical simulation and the product manual,the transfer function of the position servo control of the hydraulic cylinder and the parameters of the PI controller was deduced by the engineering setting theory method and the mechanical-hydraulic co-simulation,by which we also obtain the control controls the error curve in each degree of freedom..Finally,by analyzing the movement characteristics of the receiving process ship in the earth coordinate system,an incomplete compensation compensation strategy for the detrended term is proposed.This method compensates for the movement of the ship which influence cargo transshipment most and also avoids the parallel platform movement beyond the working space.