The Control of a Multifingered Hand Actuated with ER Fluids VIOREL STOIAN, MIRCEA IVANESCU, DORIN POPESCU Mechatronics Department University of Craiova ALINA NIRVANA POPESCU, DECEBAL POPESCU Computer Department University Politehnica of Bucharest ROMANIA Abstract: - The paper proposes a new fluid controller for the fingers of an electro-mechanical hand with nonconventional actuators based on the properties of ER fluids. The controller is based on the viscosity control of the ER fluids by on electrical field. The motion control is divided into two parts: a conventional control determined by the second Lyapunov method for the pressure control of the ER fluid and a non-conventional control obtained by the viscosity control. It is proved that the stability of the motion on a switching manifold is assured if some constraints determined by the non-linear elements of the system are verified. Key-Words: - Multifingered hand, ER fluids, Second Lyapunov method, Non-conventional control. 1 Introduction An important disadvantage with traditional robot manipulators is that for a given gripper, only a small class of objects can be grasped. This limitation is sometimes overcome by equipping the robot arm with a tool changer, which allows different grippers to be used. Another disadvantage appears in assembly task, which require precise movements. For overcome these difficulties we propose to use multifingered robot hands as an alternative method. The extra degrees of mobility in a multifingered hand make it possible to grasp a large class of objects with a single end effector. This structure of the hand complicates both the kinematic and dynamic analyses of the system. In particular, since the hand is in contact with the object being manipulated, we must study the kinematics and dynamics of mechanical systems with contact constraints. Additionally, the increased degrees of mobility of the system increase the difficulty of planning a feasible grasp to perform a given task. Some ElectroRheological (ER) fluid consists of a suspension of hydrophilic (water-retaining) particles suspended in a hydrophobic (water- repelling) dielectric fluid. This suspension is placed between electrodes for application of an electric field. In an electric field the particles polarize and inter particle forces then lead to the formation of chains, which tend to orient perpendicular to the electrode gap. With enough particles and a field of sufficient strength, the fibrils will bridge the gap and cause an appreciable increase in the viscosity of the suspension. There are a great number of papers ([1], [3], [4], [6], [18]) which describe the two major methods of exploiting the ER effect in practical devices: "valve method" and "clutch method". 2 ER Fluid Actuated Multifingered Hand-Model 2.1 Technological structure of the ER based finger–model The general form of a finger model is shown in Fig. 1. It is a cylinder made of fiber-reinforced rubber. There are three internal chambers in the cylinder, each of them containing the ER fluid with an individual control circuit. The deformation in each cylinder is controlled by an independently electro-hydraulic pressure control