Experimental Validation of End-Effector Position Accuracy and Repeatability of a Waste-Sorting Delta Robot

The positioning accuracy of Delta robots depends on the agreement between the kinematic model and actual arm motion, particularly in systems driven by open-loop stepper motors with belt transmissions. This study experimentally validated a simplified kinematic model for a waste-sorting Delta robot by evaluating angular accuracy and end-effector distance precision and repeatability. A closed-form inverse kinematics model was formulated to map target coordinates to arm angles and stepper microsteps and implemented on an Arduino Mega 2560. Angular accuracy was assessed by comparing model-computed arm angles with digital inclinometer measurements at three target points corresponding to waste-bin locations, with 10 repetitions per point. Distance precision and repeatability were evaluated through 10 repeated movements between two points 82 mm apart, with pen-marked positions measured using ImageJ. The results showed a mean angular accuracy of 98.71%, a mean distance precision of 99.88%, and distance repeatability of ±0.39 mm. Angular errors were systematic and varied across arms, with the largest mean error of 1.72° observed in arm 2. The end-effector displacement estimated from these errors ranged from 3.6 to 5.8 mm, remaining below the 25 mm radius of the waste-bin opening. These findings provide experimental support for the feasibility of the simplified kinematic model for waste placement at the tested positions and indicate potential for improving positioning accuracy through per-arm error compensation.