The pneumatic cylinder has internal rubber seals. When the piston moved toward the desired position, the seal sticks and slides and then attaches itselt to the cylinder wall or piston rod, near the final position. So the viscoelastic formation of the seal appears and has an affect on the control performances, such as positioning accuracy, stability and settling delay in this region.
In this report, the viscoelasticity of piston displacement caused by the seal when it attaches is examined and the effects of viscoelasticity regarding the control performance are analyzed. It is shown that the viscoelasticity becomes very large near the desired position such as within 0.02mm and as a result, piston displacement becomes very slow. The speed can not be improved using the ordinary control method. To improve the settling delay and ensure the control stability, the control method, taking account the viscoelasticity model, is induced and the various types of performance are specified. The control is composed of the feedback loops by using the response model of system including the viscoelasticity.
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