Robot-Guided End Effector for an Automated Finishing of Concrete Free-Form Surfaces

Digitalisation and automation approaches are increasingly relevant for the construction sector. Especially additive manufacturing processes based on extrusion and material jetting are expected to reduce manual labour and production costs. Additionally, with the inherent design freedom construction elements with complex free-form shapes can be created. However, high material application rates lead to coarse surfaces with the stacking of layers resulting in a staircase effect, especially for overhangs and cavities. In order to increase the overall surface quality of freely designed construction elements, the development of an automated process for post-processing surfaces is necessary. Therefore, this article proposes a novel approach for the automated finishing of free-form surfaces using robotic end effectors. By dividing a component surface into smaller sections consisting of various spine functions, a form-flexible trowel can be used for the finishing of freshly-printed components. By continuously deforming the tool edge with two linear axes, freely adjustable spline curves are achievable, which enable a processing of free-form surface. Besides the development and an initial concept for the control of the end effector, a path planning concept for a synchronous movement with a robot is presented. First results on the deformability are analysed and discussed. By minimizing lateral forces due to an elongation of the tool edge, an improvement in the adaptability to cubic splines was achieved, even for higher elongations. This enhancement increases the usablility of the developed end effector by reducing the processable radii of free-form surfaces. The article concludes by discussing application scenarios of the end effector in the construction industry as well as its limitations. By implementing a surface finishing process using the presented tool concept of a flexible trowel to reduce the staircase effect, additive manufacturing in construction can become a reality in the near future, even for components with high surface requirements.