Robust hybrid position/force control of redundant robots

Abstract

A nonlinear feedback control based on inverse dynamics is proposed for redundant robots with rigid or flexible joints during the execution of constrained motion tasks. Based on constrained system formalism, the presented control scheme achieves simultaneous, independent control of both position and contact force at the robot end-effector, while optimizing an objective function for redundancy resolution. Non-invariance problems are avoided by the use of a special methodology for constraint formulation. Issues related to the practical application of the proposed control algorithms, such as the design of robust controllers, are discussed. The assumed uncertainties are related to the robot as well the environment model. For flexible joint robots, it is also possible to use an inexact model for calculating those feedback variables which cannot be measured directly such as link accelerations and jerks, as well as the contact force time derivatives. The proposed approach is illustrated using an example of a three-link robot operating a moving joystick, with mixed contact conditions. The results of numerical simulation demonstrate the effectiveness of the proposed controllers.