Agile robotic arm for vertical applications - Evaluation, design and development

Abstract: Existing pick and place robots are either heavy or have a limited workspace for vertical operations. Since there is no robot today that are both light and have a good vertical workspace, this leads to a gap in the market. With the use of the laws of physics Cognibotics is trying to fill these gaps in the market, by developing new fast and lightweight robots. These new robots are designed to have as much of the total weight as possible close to the base. This will decrease the moment of inertia which will help make the robots faster. Cognibotics holds a patent with multiple different robotic arms that have the possibility to have a vertical workspace. This thesis will focus on evaluate these robotic arms and develop the robotic arm with the best opportunity to be fast, lightweight and have a vertical workspace. The development will focus on the overall layout of the arm, which includes the rods and joints. The sizes of the rods will be selected and for the joints, bearing type and size will be selected. The development of the joints will also include how the bearings should be mounted. In the patent, the robotic arm presented in fig. 9 is evaluated to be the best option for further development. This arm is light, has a good weight distribution (most of the weigh is close to the base) and fewer parts than the other arm, which will probably make it cheaper. The original arm presented in the patent do only have three DOF (degrees of freedom). The arm however can be modified to have a fourth actuator at the end effector for the possibility to get the last DOF, which is needed for the application this thesis applies. Based on the selected robotic arm from the patent, two concepts where made. The first concept ”concept 1”, will probably be lighter and have a better weight distribution than the second concept ”concept 2”. Based on this, the conclusion is drawn that ”concept 1” is the best option. For the selected concept, a CAD model was made. In the CAD model both the rods and the joints are designed in greater detail. A total of five different joints within the CAD model, were needed to be designed and developed. For the development of the joints, a wide arrange of bearings are used. Some of the more common bearings are angular contact ball bearings and tapered roller bearings. In one of the more complex joint, spherical roller bearings are used. For the development of the rods, a reach study was made. The lengths of the inner and outer arms is selected based on this reach study. For a good performance the size and profile of the rods was then investigated. Since one rod is carrying almost the entire weight of the robotic arm, this rod need to be bigger than the rest of the rods. When the development of the robotic arm was complete, a crude cost analysis of the robot was performed. This includes the total material cost for the robot, which includes the cost for the rods, joints (with bearings), tool mounting platform, motors, gearboxes and control systems.