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Machine tools with multiple degrees of freedom and parallel kinematics offer tremendous opportunities for new kind of processes but at the same time also a lot of control challenges. They are subject to uncertainties in the form of kinematic errors, elasticities and thermal deflections. Their kinematic non-linearity requires the application of model-based control concepts whose full effectiveness can only be unlocked through controls in the task space. In particular, kinematic singularities occur in forming machines such as presses, which make closed-loop control at corresponding operating points considerably more difficult. In this paper, we use the example of a servo-driven press with three ram degrees of freedom to show how parallel kinematic machine tools can be controlled via inverse differential kinematics models in task space and to what extent the controls can benefit from scheduled gain factors. The results are validated both simulatively and experimentally. In the experimental tests, three-dimensional tool paths are traced that can be used to carry out orbital forging processes. Furthermore, the example of a punch hole rolling process demonstrates that the ram pose is controlled more accurately, which also has positive effects on the resulting workpiece geometry. The performance of the developed gain scheduling task space control is compared with that of a robust and non-robust control with static gains. • Parallel kinematic machine tools are hard to control in task space • Task space control requires integration of sensors in the vicinity of the TCP • Controlling the bearing position of the TCP platform allows gain scheduled control • Gain scheduled control with better performance than conventional control • Superiority of the control also visible in produced workpiece geometries [ABSTRACT FROM AUTHOR]

Robotic manipulators are known for their numerous degrees of freedom with which they can manipulate objects in task space. With the help of model-based control concepts, it is possible to precisely closed-loop control their pose, thus meeting high positioning accuracy requirements. As a result, they are ideally suited for carrying out flexible activities in manufacturing processes in which freely programmable tool paths are required, such as pick and place, welding or assembly tasks. If high forces have to be applied in manufacturing processes, as is the case in bulk forming processes, robots can no longer be used due to low stiffness and moderate force provision. The development of flexible forming machines with several degrees of freedom overcomes this problem. Machine tools such as the 3D Servo Press have three ram degrees of freedom and can provide forces of up to 1600 kN, but require highly accurate position control in task space. For this reason, this paper shows how control concepts from robotics can be applied to machine tools with high stiffness, high provided forces and multiple degrees of freedom. The functionality of the control is validated using the example of upsetting tests in which off-center forces are applied to the ram and the control counteracts tilting of the ram. [ABSTRACT FROM AUTHOR]