Mass Flow Rate Control with Compensation of Nonlinearity using Valve Internal Variables

As pneumatic actuators have several advantages such as a high thrust-to-weight ratio and low cost, they are widely used in automated industrial operations, especially in point-to-point positioning applications. However, they have a substantial disadvantage of large time delay and highly nonlinear characteristics due to the air dynamics and the valve structure. Since these factors degrade the control performance of pneumatic drive systems, pneumatic actuators are rarely used in precise positioning applications. In particular, it is not easy to control the mass flow rate of air that passes through a valve because its characteristics depend on the pressure difference between entrance and exit ports and have a hysteresis originating from a solenoid. Thus, this paper applies a new electromagnetically controlled valve with an internal sensor to resolve these nonlinearity problems. The proposed mass flow rate control system with a new inner loop can compensate for the nonlinearity without mass flow rate feedback control.