Study On The Pneumatic Servo Gun Flexible Loading Method Based On The Sliding Mode Strategy

As an important kind of manufacturing technology in the welding of thin plate,resistance spot welding is widely used in automobile manufacture,aviation,aerospace and other fields.After several decades of development,pneumatic welding technology has been more mature.But with the development of the automobile industry,its own shortcomings gradually exposed and it has been unable to meet the development requirements of the modern manufacturing industry.Servo welding drive mechanism is a new type of driving mechanism developed in recent years.And it can achieve high-precision positioning of the welding torch.At present,only NORGREN from the UK and SMC from Japan have introduced the pneumatic servo spot welding gun.The research results of pneumatic servo gun technology currently mainly concentrated in foreign countries,and the domestic research on pneumatic servo gun is relatively fewer,especially the study on the flexible loading method of the pneumatic servo gun.In order to improve the welding efficiency of resistance spot welding process and prevent the large impact force damaging the workpiece when the electrode approaching,this paper studys on the flexible loading method of the welding gun electrode and the following aspects of the research work are mainly carried out:Firstly,starting with the position servo system,the modeling of the pneumatic servo gun system researched in the topic has been completed,including the proportional valve selected and the system controlled by the valves.On this basis,the unknown parameters of the system transfer function are identified by using the least square method.It lays the foundation for the flexible loading method of the electrode.Secondly,the collision between the welding electrodes is analysed.And according to the existing welding technology,the technical index that needs to be realized in the paper is put forward.According to the characteristics of the pneumatic servo gun system,a method of using sliding mode variable structure control to realize the electrode flexible loading is proposed.In order to offset the shortcoming of sliding mode variable structure control,the idea of subsection sliding mode variable structure control is proposed.The concept and calculation method of the optimal buffer distance are given.Finally,the feasibility of the proposed method is verified by the simulation of the system flexible loading process.The cushioning effect of PID control,sliding mode variable structure control and subsection sliding mode variable structure control method are compared by experiments.The experimental results show that subsection sliding mode variable structure control can effectively reduce the impact of welding electrode on the basis of keeping loading process time short.The technical indexes proposed in this paper are basically realized.The experiment is carried out under different feed distance and different air supply pressure,which proves that the method is robust.The above experimental results show that this method has a certain application value.