A new approach, employing sliding-mode based smooth robust compensators, has been developed for simultaneous position and force control of an uncertain robot manipulator performing constrained tasks in the presence of environmental stick-slip friction. Under the proposed approach, the robot manipulator can exert a preset amount of force on the environment while tracking along a desired trajectory with global asymptotic stability, as proved by Lyapunov＇s direct method. No exact knowledge of link parameters (including link masses, the centre of mass, and the moment of inertia of links) is required. Unlike other approaches, the one proposed here takes into consideration the environmental friction as well as its dependency on normal contact force, and compensates for the friction effect. Furthermore, the proposed controller produces smooth control action, and ensures the robot＇s smooth motion on the contact surface. A numerical example of a two-link robot performing a constrained task is presented as an illustration.