Cooperative manipulators are two or more serial manipulators which cooperate in grasping and manipulating an object and form a parallel robotic system. They are commonly used in assembling, coaxialization, moving an objectetc. Grasping an intermediary object is a complicated subject in analysis and synthesis of cooperative manipulator, since its analysis is mostly depended to the manner that the object is grasped by the arms fingertips In the case of frictional grasping, the elimination of undesired slippage of fingertips on the object due to the environmental factors, and also contribution of the fingertips geometry in the dynamical model of the system are some of the issues that makes its analysis complicated. This study deals with frictional grasping of an object by use of two planar manipulators controlling the undesired slippages. In line with this purpose, first the dynamical and kinematical equations of cooperative manipulators and the object as a unified system are extracted taking into account the fingertips geometry and frictional contacts as well as moving the object on the desired trajectory. Then by studying the variety of possible contact conditions the inequality equation corresponding to contact conditions are converted into a single differential equation with switching coefficients. Since the contact conditions change system degrees of freedom, the system’s dynamics are multiphase and consequently a multiphase controller must be designed in order to control the system, the system dynamical equations are transferred to a set of input-output equations. The inputs are actuators torques while the outputs are object kinematics parameters and end-effectors slippage. A computed torque like control law is used to eliminate undesired slippage and to track the object motion on the predefined trajectory. The control performance is analyzed using numerical simulation. Generally, the present study is an extension to Mr. Shahram Hadian Jazi, phd thesis which study the contribution and effects of finger-tips geometry. Considering a circular geometry for finger-tips the numerical results showed increasing or decreasing the finger-tips radius, does not change the results trends. Key Words Friction; cooperative arm; fingertip geometry