In this article we develop a new approach to control an omnidirectional mobile manipulator. This approach is based on a layered command structure and impedance control technique. First we define multiple control behaviors depending on the robot tasks. Two behaviors are considered here the synchronized one and the independent one. Each behavior mentioned above is described in terms of force and position models in order to allow each robot to regulate his corresponding behavior. In the case of synchronized situation, kinematic modeling is presented with particular emphasis on redundancy. We use the additional task concept to solve the control problem of these redundant holonomic systems by taking into account the external forces.