Quasi-Static Compliance Calibration ofSerial Articulated Industrial Manipulators

This article presents a procedure for the quasi-staticcompliance calibration of serial articulated industrialmanipulators. Quasi-static compliance refers to theapparent stiffness displayed by manipulators at lowvelocitymovements, i.e., from 50 to 250 mm/s. Thenovelty of the quasi-static compliance calibration procedurelies in the measurement phase, in which thequasi-static deflections of the manipulator’s end effectorare measured under movement along a circulartrajectory. The quasi-static stiffness might be amore applicable model parameter, i.e., representingthe actual manipulator more accurately, for manipulatorsat low-velocity movements. This indicates thatthe quasi-static robot model may yield more accurateestimates for the trajectory optimization comparedwith static stiffness in the implementation phase. Thisstudy compares the static and apparent quasi-staticcompliance. The static deflections were measured atdiscretized static configurations along circular trajectories,whereas the quasi-static deflections were measuredunder circular motion along the same trajectories.Loads of different magnitudes were inducedusing the Loaded Double Ball Bar. The static andquasi-static displacements were measured using a linearvariable differential transformer embedded in theLoaded Double Ball Bar and a Leica AT901 lasertracker. These measurement procedures are implementedin a case study on a large serial articulatedindustrial manipulator in five different positions of itsworkspace. This study shows that the measured quasistaticdeflections are bigger than the measured staticdeflections. This, in turn, indicates a significant differencebetween the static and apparent quasi-staticcompliance. Finally, the implementation of the modelparameters to improve the accuracy of robots and thechallenges in realizing cost-efficient compliance calibrationare discussed.QC 20211005