Stability and shock control of expandable articulated arm in tokamak vessel

For safe and precise operation of a polyarticulated arm in a tokamak toroidal vessel, (highly symmetrical) automatically preprogrammed toroidal pantographic expansion from rest position to working place is considered. Arm expansion also generates vibrations due to excitation of internal bending and torsion modes of the structure, impairing the system capability of meeting precise operating requirements. However, a (regular) feedback control law of generalized PD (proportional plus derivative) type is shown to exist, which globally stabilizes the vibrations. As its analytical expression for uniform (not accelerated) expansion and retraction only depends on measurements of arm tip displacement and velocity, such a feedback can be possibly implemented on experimental apparatus in order to ease the manipulation of the arm. When a shock like effect is acting on the arm tip, a new specific control can be applied at joints to counteract the torque created by the shock on a very short electrical time scale, whereas its residual effect is shown to be handled by the regular feedback control law