In "Conventional On-Off Control" with the intentional deadzone, many efforts have been tried to improve the system performance, especially, stability and accuracy. For an electro-pneumatic on-off servo-mechanism, most of such efforts are to compose of the many feedback loops - not only position feedback, but also velocity, acceleration, pressure, and dynamic pressure feedback loops, etc. But such efforts make the system complex and expensive.
In this thesis, an efficient control technique is developed to ease with such complexities as well as to enhance the servo performance, requiring only the position feedback. The pneumatic valve used here is of newly developed special type, consisted of two poppet valve. The "Conventional On-Off Control" is turned into the "Modified On-Off Control" in such a way that the valve is operated like a dither by adjustable pulse signals when the error signal is outside the deadband and simultaneously inside the pulseband, whereas in other region the valve is operated by the conventional on-off scheme. To investigate the performance of this control configuration a series of experiments are conducted for the various system parameters, which include the deadband, pulseband, pulse width, pulperiod. The experimental results show that the "Modified On-Off Control" technique substantially increases the system stability and thus reduces the minimum stable deadband. The implication of this result indicates that the positioning accuracy can be effectively improved by a simple control technique.
