Visual Control of Planar Parallel Robots Without Using Velocity Measurements

This work proposes an image-based visual servoing scheme applied to a class of overactuated planar parallel robots with revolute joints. A Proportional Derivative algorithm computes torques for the robot active joints. The Derivative action operates at the joint level and the Proportional action works at the visual level. A linear filter provides velocity estimates from active joint position measurements, and Lyapunov Stability theory allows concluding closed loop stability. Experimental results on a laboratory prototype show that the proposed approach permits using higher gains compared with a control law relying on velocity estimates generated using visual measurements; moreover, these experiments also show that the closed loop system is robust in face of kinematic uncertainty.