Decreasing batch sizes lead to an increasing demand for flexible automation systems in manufacturing industries. Robot cells are one solution for automating manufacturing tasks more flexibly. Besides the ongoing unifications in the hardware components, the controllers are still programmed application specifically and non-uniform. Only specialized experts can reconfigure and reprogram the controllers when process changes occur. To provide a more flexible control, this paper presents a new method for programming flexible skill-based controls for robot cells. In comparison to the common programming in logic controllers, operators independently adapt and expand the automated process sequence without modifying the controller code. For a high flexibility, the paper summarizes the software requirements in terms of an extensibility, flexible usability, configurability, and reusability of the control. Therefore, the skill-based control introduces a modularization of the assets in the control and parameterizable skills as abstract template class methodically. An orchestration system is used to call the skills with the corresponding parameter set and combine them into automated process sequences. A mobile flexible robot cell is used for the validation of the skill-based control architecture. Finally, the main benefits and limitations of the concept are discussed and future challenges of flexible skill-based controls for robot cells are provided.
The Screw Extrusion Additive Manufacturing (SEAM) technology provides output rates up to 10 kg/h, a melt pressure up to 350 bar and temperatures up to 400 °C as well as strands with an adjustable bead width between 1-8 mm. Due to a bypass nozzle, position jumps without material extrusion, local wall thickness reduction, and the control of the volume flow (0-100 %) are made possible. Further, the extruder is able to process fiber-reinforced as well as highly filled plastics and integrates a regranulation system to return bypassed material into the process. The hexapod parallel kinematic meets the process requirements, as it generates a rapid movement of the workpiece (up to 1 m/s) in 6 degrees of freedom within a large printing workspace (1100 × 800 x 600 mm3), where an additional Z-axis carries the extruder and realizes the part height. Eccentric joints provide high accuracy and stiffness while being cost-efficient at the same time. The commercial Beckhoff TwinCAT control allows G-code processing and provides an HTML based GUI for machine and extruder control. Consequently, high accuracy is achieved, which is verified by the use of a double-ball-bar measuring device and by producing a test workpiece.
Additive manufacturing (AM), often referred to as 3D printing, is a generic term describing the layered build-up of material in near net shape frequently attributed with a freedom of design that cannot be achieved otherwise. AM focuses basically on the fabrication of parts for different fields in complex high-tech applications. Examples include components for jet engines, turbines blades, and implants in the medical sector. This is often justified with tool cost savings, shorter lead-time, and overcoming the “design for manufacture” paradigm. On the other hand, a machining allowance is frequently required to counteract the inherent surface roughness and the widespread challenge of part distortion due to residual stresses. At this point, geometrical complexity and small batch sizes transform into strong cost drivers compared to conventional subtractive processing. In fact, these parts are simply hard-to-clamp and hard-to-probe. Moreover, iterative processing is frequently required due to remaining residual stresses in order to reach the target geometry; even the part envelope changes unintentionally. The current paper explores the novel approach of semiautonomous postprocessing of AM parts and components based on flexible clamping, geometry acquisition in the as-clamped position using cooperating laser profile sensors, and an adaptive milling path planning strategy to counteract unforeseen change of the part envelope.
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