Читать книгу Smart Systems for Industrial Applications - Группа авторов - Страница 43

Pneumatic system has numerous advantages, such as smooth construction, consistency, ruggedness, and easy maintenance [3]. They are commonly used in automated industries. Due to essential compressible gas, there is a difficulty in controlling the gas out flow using valve, chamber friction, and inconstancy in system parameters. They are fundamentally nonlinear time-varying systems [3, 10]. In practical, PID controller is used to modify the acceleration feedback and compensate the nonlinearity. The flexibility of PID control is weak, when the reference and other conditions of the system changes considerably [6]. The proposed method will give satisfactory solution about uncertain conditions. Error changes due to the different conditions and the changes in throttle control. For other intelligent control techniques, it provides better result, but high cost, related to PID control [19]. The FOC has the better response than classical PID controllers [3, 6]. The FOPID controller is established by system with fractional-order control and IPID [1]. The tuning of control parameters is more tough in FOPID than IPID. In FOPID whose parameters are not optimized accurately, it will give poor performance of the system [1, 2]. In NPID controllers, the variation of nonlinear gain is exploited for greater accuracy [8].

In conventional pneumatic servo systems have been used in many fields [14, 17], such as the active suspension system on the Shinkansen bullet train, moulding machines for glass lenses, and amusement robots, because of the numerous advantages of high power, compliant property, and good force controllability. However, the characteristic of a pneumatic servo is nonlinear, which make control difficult [21, 22]. Therefore, control methods of a pneumatic servo, applying advanced control theories such as fuzzy control or robust control, have been investigated.

Pneumatic position servo system comprises of cylinder (Figure 2.1), variable resistor, solenoid valves, air pump, and piston. The compressed air is pumped through air pump and passed through the chamber A or Bin the cylinder, where the valve is regulating the flow level. The incoming valve regulates the mass flow in each chamber to get pressure difference among two chambers [15]. The difference in pressure will drive the piston and payload and the velocity of the system load is controlled by rheostat with the piston [1, 4]. The aim of the controller is to track the position of the piston and payload through a desired path [2] and its dynamic characteristics are represented by a fractional-order model. A 230-V supply is stepped down to 5 V using step down transformer and rectified using bridge rectifier and then given to variable resistor. The PIC microcontroller receives the position of the piston and converts it from analog to digital form before it is given to PC using serial bus. A 12-V relay board is used for tripping the supply when the position of the load is not at zero in initial position.

Figure 2.1 Pneumatic position servo system.