Design and Simulation of an Inverted 2RPU–RPS Parallel End Effector for a Compact Maize Seeding Robot

Terrain-induced chassis motion can disturb the soil-entry attitude and soil engagement of seeding components on compact agricultural robots. This study develops an inverted 2RPU–RPS rallel mechanism for a maize seeding robot to regulate the end effector without levelling the entire chassis. The mechanism supports the disc opener and terminal seed tube and provides one vertical translation and two rotations. A nonlinear inverse-kinematic model, a unilateral penetration–downforce model, constrained electric-cylinder dynamics, and a coordinated feedforward–PI controller are established. The roll and pitch loops combine chassis-attitude feedforward compensation with end-effector error feedback, while the vertical loop regulates the opener downforce using a stiffness-based penetration reference and force feedback. MATLAB/Simulink simulations are conducted under isolated attitude disturbances, vertical terrain excitation, and multi-row operation. With maximum chassis roll and pitch disturbances of 4.49° and 3.35°, the end-effector RMSE values are 0.109° and 0.114°, respectively. At a prescribed downforce of 400 N, the downforce RMSE is 11.07 N and the mean disc-opener penetration is 34.99 mm. During the 300 s multi-row simulation, the mean penetration remains 34.96 mm and the downforce RMSE is 12.65 N. The results indicate that the strategy can attenuate chassis-induced disturbances and maintain stable soil engagement under the adopted modelling assumptions.