On the zero dynamic of servo pneumatic actuators and its usage for trajectory planning and control

This paper deals with the trajectory generation and trajectory tracking control for a servo drive consisting of a double action pneumatic cylinder combined with one servo valve. This configuration is quite attractive for usage in automation, as servo pneumatic drives are cheaper than DC motors of comparable driving power. The main drawback is the existence of dominant nonlinearities and the fact that the described plant is characterized by a zero dynamic. Strategies for an accurate trajectory tracking, which base up on the input/output linearization are efficient, but they need the measurement of the chamber pressure. Therefore the use of pressure sensors is necessary, which increases the price of servo pneumatic drives. On the other hand, there is a great engineering gap for a suitable trajectory generation taking account of optimization aspects and system constraints. The central part of this work is the solution of the zero dynamic. Basing up on this, one is able to parameterize the chamber pressures in respect of the actual position and a limited number of its derivatives. This makes it possible to use low cost pressure sensors for the control. Illustrated measurement results prove the control benefit. Furthermore the solution of the zero dynamic allows an easy computation for an optimal trajectory generation in respect of state and input constraints, which is presented as well as some experimental results.