The aim of this article is to present an overview of the most important robotic processes in which force control methods are applied. In recent years, robotization has seen a rapid increase in the use of industrial robots in tasks that require simultaneous implementation of a given path of motion and the robot's force of interaction with the environment. In the field of industrial applications, this applies to issues related to the robotization of machining or some assembly tasks, but also the complex issue of cooperation between robots and people. One of the first applications of force control systems in robots were machining tasks such as grinding or blunting of sharp edges. Currently, robots are used in the following types of machining: grinding, polishing, chamfering, blunting, light milling. The implementation of such tasks requires the use of so-called position-force hybrid control. The task of such a control system is to implement the desired trajectory of the tool movement along the edge being machined or on the machined surface and to exert an appropriate clamping force of the tool. In the field of robotic machining, an important and still valid issue is the development and implementation of control strategies that ensure the quality of the mechanical machining process of the part despite the occurrence of unmolded phenomena, caused by, for example, significant errors in the geometry of the parts with local surface disturbances or its flexibility.
Another of the basic applications of force control systems in robots are assembly tasks. In such processes, force control is particularly important, because too high interaction forces between the assembled components lead to large distortions and prevent the correct process from running. There are many papers in the literature that describe the problem of monitoring the machining process using force sensors. Monitoring the machining process is important in the industrial production of parts with a high unit cost. Any irregularity in the production of the part causing its non-compliance with the documentation is a cause of significant financial losses. Process monitoring aims to prevent irregularities during its implementation and to correct or discontinue the machining process.
Friction stir welding is a method of joining materials without using consumable materials and without melting materials. In the process of friction stir welding, a cylindrical tool with a mandrel performs a rotary motion and at the same time is slowly moved along the joint area with simultaneous clamping. An industrial robot is responsible for the movement along the joint. The friction welding process is very sensitive to the temperature in the joint area. The temperature is not controlled directly, but by three other parameters: tool feed speed, tool speed and tool clamping force. For this reason, robots used for friction welding are equipped with position-force hybrid control systems. In recent years, the issue of cooperation in the human-robot system has become more and more important. The main area of application of this approach is assembly tasks. This solution has a number of advantages, such as the possibility of using the lifting capacity of the robot to lift heavy objects and the "ingenuity" of a human to maneuver the object. The robot, thanks to force sensor, is able to detect the method of maneuvering an object desired by a human.
Summing up, it can be said that the use of force control has significantly increased the functionality of robotic systems in recent years.
Keywords: Robotics; Force Control; Robotized Machining; Robotized Process Monitoring; Robotized Assembly; Friction Stir Welding; Robot-human Cooperation
