Dynamic contact force/torque observer: Sensor fusion for improved interaction control

Abstract

The potential areas of application for robots have gradually extended beyond the classical industrial settings in largescale enterprizes: nowadays, the integration of robots into daily life has become a central development in robotics. Here, one major challenge is the physical interaction with unknown and/or changing environments. Such an interaction requires knowledge of the exchanged contact forces and torques. To this end, robotic systems are typically equipped with force/torque sensors at the wrist. By using force control schemes that rely on measurements from these sensors, conventional manipulation tasks are successfully executed. In particular, for dynamic manipulation tasks, however, the problem arises that the inertial forces/torques of the end effector have a non-negligible effect on the measurements of the wrist sensor. This degrades the performance of the interaction control and constitutes a safety risk since the actual interaction forces/torques deviate from the desired values. As a solution to this problem, the paper discusses four contact force/torque observer designs: two approaches are based on the extended Kalman filter (EKF) and two approaches are based on the unscented Kalman filter (UKF). For both types, EKF and UKF, two different measurement vectors are considered: the first one only uses pose and force/torque measurements, whereas the second one also uses acceleration measurements to determine the contact forces and torques. The four observer designs are evaluated in simulation and experiment for six-degree-of-freedom (DOF) tasks.

Compensation of Load Dynamics for Admittance Controlled Interactive Industrial Robots Using a Quaternion-Based Kalman Filter

“…Similar approaches have been applied in human body tracking [11], [12], but still without considering second order derivatives. Even in [13], that describes quaternion-based Kalman filters embedding also the estimation of environmental F/T acting on a robotic tool, angular accelerations are not included in the estimated state, with the result that F/T estimation errors are larger than those presented in this paper. In next sections, we will define more precisely the statement of the problem that we aim to address and the proposed overall control scheme.…”

Design and Implementation of Plastic Deformation Behavior by Cartesian Impedance Control Based on Maxwell Model

“…(ii) Feedback information of the external force . Normally, external forces can be gauged by F/T force sensors or estimated by contact force/torque observers [20].…”

Simultaneous State and Parameter Estimation Based Actuator Fault Detection and Diagnosis for an Unmanned Helicopter

“…For better estimation performance, the unscented Kalman filter was proposed to improve the accuracy, consistency and efficiency of the Kalman filter. The UKF uses a set of sigma points to represent the distribution of random variables; the sigma points are then propagated through the nonlinear dynamics, and the mean and covariance of the propagated random variable can be calculated using the propagated sigma points (Xiong et al, 2006;Kandepu et al, 2008;Julier and Uhlmann, 2004;Bätz et al, 2013).…”

“…Campbell et al (2007) used a square root sigma point filter and a square root extended set-membership filter (ESMF) for fault estimation on for fixed-wing UAVs. Many comparisons have already been made for these methods (Zhou and Han, 2007;Bätz et al, 2013;Cui et al, 2005).…”