Set-point control with gravity compensation for robots with input/output delays

Set-point control problem for robotic manipulators when signals are exchanged via a delayed communication channel is studied in this paper. The gravitational effects, which were not considered or were assumed to be pre-compensated in the previous research, are considered in this paper. Using an appropriately defined controller with gravity compensation, it is first shown that simply utilizing the scattering variables can stabilize the closed-loop system in the presence of constant delays; however, position regulation cannot be guaranteed. Therefore, we study a new control algorithm where explicit position feedback, in conjunction with scattering variables is used, to guarantee both stability and tracking performance. Moreover, the efficacy of this architecture to handle time-varying input/output delays is also demonstrated. The proposed algorithm is numerically validated on a two-degree-of-freedom manipulator for both constant and time-varying delays.