In this paper, a methodology is proposed to obtain a stable control law for the manipulators which perform contact tasks. The methodology is based on unified approach of the Lyapunov direct method. The subject manipulators are varied from a simple linear manipulator to a nonlinear 3-dimensional re-dundant multi-link manipulator, which are interacting with a flexible wall with collision pheonomena at the contact of tasks. The stability and response of the system are examined by parameter studies of numerical simulations adequately. As the demands for rapid motion of robotics has been increasing in the field of industry to achieve higher efficiency, collision has become a problem to be solved, because every task includes contact when a manipulator acts on an object. The contact, or collision, is analyzed and proved to be stable on the manipulator tasks.