Mobile manipulators are robot systems capable of combining logistics and manipulation tasks. They thus fulfill an important prerequisite for the integration into flexible manufacturing systems. Another essential feature required for modern production facilities is a user-friendly and intuitive human-machine interaction. In this work the goal of code-less programming is addressed and an intuitive and safe approach to physically interact with such robot systems is derived. We present a natural approach for hand guiding a sensitive mobile manipulator in task space using a force torque sensor that is mount close to the end effector. The proposed control structure is capable of handling the kinematic redundancies of the system and avoid singular arm configurations by means of haptic feedback to the user. A detailed analysis of all possible singularities of the UR robot family is given and the functionality of the controller design is shown with laboratory experiments on our mobile manipulator.
Impact and the resulting contact forces can be determined by dynamic simulation once a validated model for the robot and of the contact area of the human is available. Methods for the identification of relevant geometric and dynamic parameters of the robot model are well established. While the experimental validation of constitutive models for human body contact is still topic of ongoing research, which gave rise to the ISO/TS 15066 guidelines, adequate models are already available for computational simulation of human-robot contact scenarios. However, dynamical simulations cannot be applied to exhaustively explore and assess all possible contact scenarios with the robot workspace. In this paper, first the model used for impact simulation is described and simulation as well experimental results are reported for contact at a predefined location. Then, the ability of the presented model to predict the measured contact force is discussed.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs Licence 4.0, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Abstract-Electric power steering (EPS) systems assist the driver during manoeuvres by applying an additional steering torque generated by an electric motor. Although there are many advantages for electric actuated steering systems including fuel efficiency, they are known to deteriorate the feel of the steering as experienced by the driver. This paper presents a sliding mode observer based estimation concept which provides signals to evaluate and improve perception and feel of the steering as experienced by the driver. The proposed strategy is based on a physically motivated dynamic model of a power steering system and the measurements considered are typically available in any modern vehicle. The performance of the estimator is investigated using numerical simulation as well as experimental results obtained using a laboratory steering testbed.
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