Dynamic Impact of Spherical Joint Clearances on a Delta Parallel Robot Behavior

Clearances in robot kinematic joints, which are functionally required, can have a significant influence on dynamic behavior and on optimal design, implicitly. Consequently, this paper aims to highlight the influence of clearances in the upper and lower spherical joints of a Delta parallel robot on trajectory accuracy and motor torques, under dynamic conditions with high speeds and accelerations. The employed method involves CAD modeling of the Delta robot's mechanical system in CATIA software and simulating its dynamic behavior in ADAMS software, using a representative trajectory where the end-effector's speed and acceleration reach the robot maximum admissible values. Considering different clearance values and various scenarios (clearances only in the upper spherical joints, only in the lower ones, and cumulatively), the simulation results highlighted a major kinematic and dynamic influence of the clearances from the upper spherical joints (with errors up to 0.05% for speeds, 0.06% for accelerations, and up to 0.19% for torques) and a relatively insignificant influence of those in the lower joints (with errors up to 0.00018% for speeds, 0.00041% for accelerations, and up to 0.172% for torques). The cumulative effect of these clearances was also analyzed, concluding that a little non-linear coupling impact was identified.