ON THE SEMIACTIVE CONTROL OF A STEWART PLATFORM WITH FLEXIBLE JOINTS
Abstract
The mathematical model of a Stewart platform is presented in order to apply the piezoelectic semiactive control to ensure the stability of its movements. In the case of the Stewart platform, there is a difference between a single-input and single-output system (SISO) and a multi-input and multi-output system (MIMO). To eliminate multiple input and output couplings and to convert a MIMO system into a SISO system, the system is decoupled into six single-axis systems. The nodal model of a single bar with included PZT actuator is defined. The first vibration mode of this nodal model is a rigid mode, and the corresponding natural frequency is zero. A structure with a rigid vibration mode is unstable and therefore needs control to remove it from this vibration mode. The piezoelectric semiactive control of a Stewart platform with 6 piezoelectric vibration isolation elements, in the (5-250) Hz range is discussed. The control is achieved by eliminating the rigid vibration mode that leads to instability.