Design, Modelling, and Kinematic Analysis of 6 DOF Articulated Robotic Arm with Spherical Wrist for Harvesting heavy Agricultural Products

Smart agriculture has risen to prominence as a significant means of agricultural production with the advent of technology. Robotic harvesting helps to pluck crops at height without endangering human lives. The spherical wrist is a mechanism commonly used in robotics that mimics the mobility and dexterity of a human wrist. In this paper, a robotic arm for harvesting heavy agricultural products like pumpkins, watermelon, etc. is designed and modeled. A 6 DOF robotic arm with 6 revolute joints and a spherical wrist is chosen as a preliminary design for this purpose. RAVebots-I robotic arm with 5 DOF and a non-spherical wrist is taken as a benchmark to compare the performance of an articulated robot having a spherical wrist. After defining the axis’ directions and link parameters, an analytical solution of forward and inverse kinematics was computed. These analytical solutions are verified in MATLAB using Robotics Toolbox. Trajectories of joint space motion between two sets of joint coordinates are plotted in MATLAB and the motion was analyzed in terms of joint coordinates, Cartesian position locus in xy-plane, and roll-pitch-yaw angles against time step. The boundaries of the workspaces of a robotic arm with a spherical and non-spherical wrist with the two sets of same points are also plotted in MATLAB. It was analyzed that workspace-boundary singularities for inner radius are fewer for robotic arm with a non-spherical wrist when the arm is folded back on its own than for articulated robotic arm with a spherical wrist. Results reveal that a key distinction between the two wrists is that the non-spherical wrist is versatile and has usually a 360° range while the spherical wrist's structure enforces a limited range of q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> to avoid singularity.