Research On The Structure Design And Grinding Force Control System Of The Piston Skirt Grinding Machine

With the rapid development of modern manufacturing technology,profound changes are taking place in the field of machine tool processing,whose related research is continuously deepening towards high precision,high efficiency,intelligence and green development.Pistons are important components in engines,the production requirements of pistons are strict because they usually work too fast,are subjected to large forces and bear alternating loads.However,for some quality problems of piston surface,such as burrs on the piston skirt,manual removal is often used in production,but this treatment method has disadvantages such as incomplete removal,scratched workpieces and low efficiency.At present,the domestic research on the piston skirt grinding machine and grinding force is very limited,so further research in this area may be expected to improve the processing quality and efficiency of the piston skirt.In this thesis,the grinding force of the piston skirt grinding machine was studied,the mathematical model of the grinding force was obtained,and the constant force control research on the normal grinding force was determined.A special machine tool for piston skirt grinding was designed,which realized both longitudinal and transverse grinding.The aerodynamic force control system of the piston skirt grinding machine was designed and established,the effect of pole configuration optimization and PID control was compared,and the time optimal control method was introduced to improve the dynamic performance of the system.The main research contents are as follows:(1)The grinding force of the piston skirt grinding machine was studied,and the theoretical calculation method of the piston skirt grinding force was proposed.The grinding force on the piston skirt was divided into chip formation force and friction force,the force state of a single abrasive particle is studied,and the unit grinding force formula was deduced.The properties of abrasive particles and contact between abrasive particles and the workpiece were analyzed,and the model of the chip forming force was obtained.The mathematical model of the friction force was deduced,and the calculation model of the grinding force of the piston skirt was obtained.The relevant parameters were substituted for example analysis,analyzed the main factors affecting of the grinding force,and it is concluded that the normal force was the main force affecting the grinding process,which should be controlled by constant force control.(2)The overall scheme and mechanical structure of the piston skirt grinding machine were designed.The overall processing plan of the special machine was analyzed,the grinding amount of the machine was calculated,the overall structure of the machine was determined,the transmission system was designed.Combined with the calculation formula of the grinding force of the piston skirt,the maximum load of the machine was determined,and the calculation result was used as the control value of the grinding force control system.(3)The pneumatic system of the piston skirt grinding machine was designed and simulated.The schematic diagram of the aerodynamic force control system of the special machine was designed,and the working principle of the system is expounded.The pneumatic system was designed,and the corresponding calculation and selection of each component in the system were made.To verify whether the designed system was reasonable,its performance was checked and simulated and analyzed by AMESim.(4)Modeling and simulation of the aerodynamic force control system of the piston skirt grinding machine were carried out.The three equations of the aerodynamic force control system of the special machine were established,and the mathematical modelling of the system was completed.The stability of the control system was analyzed by using the Bode diagram,the Nyquist diagram and the Lyapunov method,and it was determined that the system could be controlled and observed,which was simulated and analyzed by MATLAB.(5)The control strategy of the aerodynamic force control system of the piston skirt grinding machine was studied,and the time optimal control method based on the system was proposed.The pole configuration and PID control method were used to optimize the control system.Aiming at the situation that the system response is still lagging and unstable,the time optimal control method is introduced,the performance index of time optimal control was set,and the control quantity was constrained.The objective function was reduced in order,the optimal control model was established,and the time optimal control response curve of the system was obtained.The results showed that the system could be stable and its performance was greatly improved.The main innovations of this thesis are as follows:(1)The theoretical calculation method of the piston skirt grinding force was proposed.According to the derivation process of general grinding force,the theoretical derivation method of piston skirt grinding force was proposed,and the grinding force of the piston skirt was estimated.(2)The piston skirt grinding machine and its aerodynamic force control system were designed.The system mainly ground the piston skirt longitudinally and laterally,removed the burr and allowance of the skirt,and realized the special machining and constant force grinding of the piston skirt,and meets the requirements of the grinding process.(3)The time optimal control theory was applied to the aerodynamic force control system of the piston skirt grinding machine.The optimal control objective was set,the boundary conditions of the control law were determined,the objective function was reduced in order,and the optimal control model was established.The time optimal control method of the system was obtained,and the performance of the force control system was significantly improved after the optimization.