Mohebullah Wali

Improving the speed of a pneumatic stage through positive feedback of calculated stage jerk signal

In this paper, a pneumatic stage is concerned. The stage is moved between two parallel guideways which are fixed on the base plate. The base plate is activated by four coil-type spring isolators. The positive feedback of calculated stage jerk signal (PFBCSJS) is proposed to speedup the stage positioning. This control scheme results in the reduction of stage mass, which leads the positioning speed to improve. The stage jerk signal is calculated by using the relative position and base plate acceleration signals which are respectively measured by an optical encoder and an accelerometer. The reason of using calculated stage jerk signal is to circumvent the use of accelerometer on the stage. This is because if an accelerometer is used, its cable tension for short length or contact to surroundings for long length will respectively make safety or noise problems. Moreover, its output might be saturated for the fast and long stroke positioning due to the lower level of its maximum detection sensitivity. The effectiveness of the proposed control scheme is evidently verified through the experimental results.

Combining the positive stage and base plate jerk feedback schemes to speedup a pneumatic stage

In this paper, the stage jerk feedback (SJFB) with positive polarity is proposed to reduce the stage mass in a pneumatically actuated positioning system. Reduction of stage mass, from one side, results in the high speed positioning which is the main objective of this study. However, on the other hand, it results in an overshoot in the positioning response, which can be compensated through the stiffness gain of the outer loop controller. Moreover, the system becomes easily unstable by further increasing the SJFB gain due to the positive polarity of this controller. This issue is solved by coupling the conventional controller, namely, the base plate jerk feedback (BPJFB) scheme with positive polarity. The experimental results show the effectiveness of both schemes. In addition, based on the experimental estimation, the SJFB has a significant role on the stage mass reduction.