Zhao Shengdun

Adaptive PID controller based on online LSSVM identification

The paper proposes a proportional-integral-derivative (PID) controller based on least squares support vector machines (LSSVM) identifier (PID_LSSVMI). The PID parameters of the adaptive controller are adjusted by gradient information of LSSVM for online identification of nonlinear time-varying system. To illustrate the efficiency of the proposed controller, the simulation experiments are made to compare performance of three controllers, namely, PID_LSSVMI controller, classical PID controller, and PID controller based neural network. The results show that the proposed control method is effective and can achieve better control performance in control loop of nonlinear time-varying system.

Study of utilizing differential gear train to achieve hybrid mechanism of mechanical press

The problems of hybrid input of mechanical press are studied in this paper, with differential gear train as transmission mechanism. It is proposed that “adjustable-speed amplitude” or “differential-speed ratio” is the important parameters for the hybrid input mechanism. It not only defines the amplitude of the adjustable speed, but also determines the ratio of the power of the servomotor to the power of the conventional motor. The calculating equations of the ratio of transmission in all axes, the power of two motors, and the working load distribution are deduced. The two kinds of driving schemes are put forward that the servomotor and the conventional motor simultaneously drive and the servomotor and the conventional motor separately drive. The calculating results demonstrate that the latter scheme can use much lower power of the servomotor, so this scheme makes manufacture and use cost much lower. The latter scheme proposes a feasible way to apply the hybrid mechanism of mechanical press in practice engineering.

Application of flexible tolerance genetic algorithm for optimum design of double-crank mechanism

A hybrid method, a flexible tolerance genetic algorithm (FTAGA), is applied in this paper to solve a complicated engineering problem concerning synthesis optimization of a double-crank mechanism. FTAGA is based on the combination of adaptive genetic algorithm (AGA) and flexible tolerance method (FTM) and exploits the advantages of both optimization algorithms. It can efficiently and reliably obtain more accurate global optima for complex, nonlinear, high-dimension, and multimodal optimization problems subject to nonlinear constraints. The successful use of FTAGA for the optimum design of a double-crank mechanism demonstrates that FTAGA is applicable to solve more real-world problems.

Analysis of aerodynamic characteristic on cylinder exhaust of pneumatic frictional clutch

The pneumatic frictional clutch is one of chief devices on the mechanical processing apparatus, thus its aerodynamic characteristic during normally working and the compressed air exhausting is discussed. Considering the effect of the back-moving spring in the cylinder on exhausting, and four cases of sonic or subsonic exhaust with constant volume or varying volume, the mathematical model and numerical simulation program is presented. The results of the verified experiment carrying on the experimental platform of the mechanical press of type JH23–63 shows that the analytical results is in a good agreement with the experimental results, with the maximum and average of relative error less than 10.1% and 4.9%, respectively. The increase of the speed and maximal speed at the nozzle as well as the exhaust time vary with the increase of the initial pressure in a cylinder. Below the given error range, the aerodynamic characteristic such as the pressure fluctuation, speed at the nozzle and exhaust time can be easily analyzed by using the presented mathematical model and numerical simulation program.

A new approach to damage modelling and fracture analysis for metal bar with V-shaped notch

Variant-frequency vibration cropping is a new approach of low-stress manufacturing technology, which utilizes the stress concentration effect of V-shaped notch to realize the regular fracture of metal bar under conditions of low cycle fatigue. The material fracture process has a great effect on the manufacturing quality obtained by this cropping method. Aiming at the geometric shape of fracture surface and the initial cracked angle, a new approach to the damage modelling is proposed for the metal bar with V-shaped notch. Based on the relationship of stress-field components for different loads derived from the solid mechanics and the Von-Mises yield criterion under conditions of low cycle fatigue, the stress state is determined for the damage modelling. Through the definition of the damage variable and the damage coefficient, the damage modelling process is discussed according to the numerical analysis results, and the plastic slip zone is obtained near the V-shape notch. Finally, the geometric shape of fracture surface and the initial cracked angle are analysed in terms of the damage model. To verify the analysis result, experiments on the material of steel C45e are conducted, and the initial cracked angle is measured.

Optimization for the Process Parameters of Hydroforming Using Genetic Algorithm in Combination with FE Codes

Hydroforming is relatively a new technology to manufacture ball valve shell, and the process parameters in hydroforming have the critical effects on the final part quality. In this paper, a novel method of optimization for the process parameters is developed. On basis of the quality demand of parts, the objective function is defined. Using the stress ratios as the optimization variables, the genetic algorithm in combination with FE codes is applied to search the optimal process parameters. According to the optimal process parameters, the verified experiment is carried out. The results show that genetic algorithm is a feasible optimization method for obtaining the optimal process parameters in hydroforming.