Force estimation and control of Delta Robot for assembly

Force Control in robotic manipulators generally requires the use of a relatively expensive Force/Torque sensor to close the control loop. A trend to create low-cost robots arose in recent years, and hence the need to reduce the use of expensive sensors; i.e., avoid the use of a F/T sensor. In this work, two disturbance observers to estimate the external forces (a disturbance) in parallel kinematic machines are proposed. In the paper, the external force is estimated through a Nonlinear Disturbance Observer and an Extended Kalman Filter. The estimated force is used in a force controller with an inner position controller. The fact that the estimated external force (contact force) can be estimated to an accuracy of ±0.3N, and that it can be used for direct force control algorithms is shown.