Nonlinear Disturbance Observer for External Force Estimation in a Cooperative Robot In humanrobot cooperation, where the robot shares workspace with humans, safety of the operator becomes a major concern. To this aim, the robot is required to detect forces from the human operator and the environment, and react to them accordingly. Since force sensors can be very expensive, force estimation methods are proposed. In this paper, the goal is to estimate the external forces acting on the endeffector of the robot. These forces make torques at the joint space. To estimate the applied joint space external torques, a nonlinear disturbance observer is proposed. The estimated torque can be converted into task space force, using the Jacobian matrix. The suggested method is demonstrated on a WallMoBot, which is designed to help the operator to install heavy glass panels. Simulation results and preliminary experimental results are presented to show the validity of the proposed observer in estimating the applied joint space external torques of the WallMoBot.

Sensorless Hybrid NormalForce Controller With Surface Prediction In this paper, an improved sensorless hybrid controller for constant force control along normal direction is proposed for applications including polishing, milling and deburring. No additional sensors are involved. External joint torques of all joints can be calculated from their electric current, dynamic model and friction model. With the help of dynamically consistent generalized inverse matrix, they can be converted to external forcetorque at the endeffector. The underlying force control strategy is the integration of impedance control model and explicit force control. The novel improvement is the realtime prediction algorithm of surfacexe2x80x99s shape profile and normal direction without any prior knowledge. So, this force controller has great adaptiveness to arbitrary unknown surfaces. Experiments were performed on a 7 degreesoffreedom (DOFs) robot to test the controllerxe2x80x99s capability and utility on an inclined plane and curved surface. Results prove the credibility of external force estimation. The normal force tracking accuracy is adequate for targeted applications. Realtime prediction is functional as the robot adjusts its orientation accordingly.