Structured Design of a Novel End-Effector for a Bush Trimming Robot

The European TrimBot 2020 project researches the robotics and vision technologies to prototype the first autonomous outdoor garden trimming robot. The robot navigates over different terrains, approaches boxwood plants and trims them to a desired shape. The robot platform is based on a modified Bosch robot lawnmower,which navigates autonomously using 3D-based vision scene analysis. During trimming a robotic arm is controlled by visual servo in order to trim the bush. A novel end-effector had to be designed to guarantee flexibility of the manipulator, precision of trimming and smoothness of the trimmed bush surface. This paper describes the structured design of this bush trimmer. When faced with a design problem with many interconnecting system elements, structured design is a tool to be used to iteratively and step by step guide the designers in making the right design choices at the right moment during the different design phases. First, preliminary research is done to analyse the problem and to assess the goals of the end-effector. Second, the functions are determined and working principles are found and put into a coherent structure. Finally, this leads to a composition of several preliminary designs of which the most promising one is determined. This design is built as a working prototype. Next to this, 3D-Computer Aided Design (CAD) tools and rapid prototyping is used to test ideas along the design process. The final design, based on contra-rotating blades, was discussed in terms of how and to what extent it has met the requirements, objectives and functions found during the structured design process. Moreover, the results of lab and field tests have shown the first functional results and points of improvements have been identified. A novel trimming method, by contra-rotating blades, has been found using structured design which meets the demands and limitations of other system components of the robot.