Integral Resonant Control for vibration damping and precise tip-positioning of a single-link flexible manipulator

Peer reviewedPostprin

Velocity dependence of joint friction in robotic manipulators with gear transmissions

This paper analyses the problem of modelling joint friction in robotic manipulators with gear transmissions at joint velocities varying from close to zero until their maximum appearing values. It is shown that commonly used friction models that incorporate Coulomb, (linear) viscous and Stribeck components are inadequate to describe the friction behaviour for the full velocity range. A new friction model is proposed that relies on insights from tribological models. The basic friction model of two lubricated discs in rolling-sliding contact is used to analyse viscous friction and friction caused by asperity contacts inside gears and roller bearings of robot joint transmissions. The analysis shows different viscous friction behaviour for gears and pre-stressed bearings. The sub-models describing the viscous friction and the friction due to the asperity contacts are combined into two friction models; one for gears and one for the pre-stressed roller bearings. In this way, a new friction model [1] is developed that accurately describes the friction behaviour in the sliding regime with a minimal and physically sound parametrisation. The model is linear in the parameters that are temperature dependent, which allows to estimate these parameters during the inertia parameter identification experiments. The model, in which the Coulomb friction effect has disappeared, has the same number of parameters as the commonly used Stribeck model [2]. The model parameters are identified experimentally on a St ¨aubli RX90 industrial robot

Predicting the Post-Impact Velocity of a Robotic Arm via Rigid Multibody Models: an Experimental Study

Accurate post-impact velocity predictions are essential in developing impact-aware manipulation strategies for robots, where contacts are intentionally established at non-zero speed mimicking human manipulation abilities in dynamic grasping and pushing of objects. Starting from the recorded dynamic response of a 7DOF torque-controlled robot that intentionally impacts a rigid surface, we investigate the possibility and accuracy of predicting the post-impact robot velocity from the pre-impact velocity and impact configuration. The velocity prediction is obtained by means of an impact map, derived using the framework of nonsmooth mechanics, that makes use of the known rigid-body robot model and the assumption of a frictionless inelastic impact.The main contribution is proposing a methodology that allows for a meaningful quantitative comparison between the recorded post-impact data, that exhibits a damped oscillatory response after the impact, and the post-impact velocity prediction derived via the readily available rigid-body robot model, that presents no oscillations and that is the one typically obtained via mainstream robot simulator software. The results of this new approach are promising in terms of prediction accuracy and thus relevant for the growing field of impact-aware robot control. The recorded impact data (18 experiments) is made publicly available, together with the numerical routines employed to generate the quantitative comparison, to further stimulate interest/research in this field

A Contribution to Validation and Testing of Non-Compliant Docking Contact Dynamics of Small and Rigid Satellites Using Hardware-In-The-Loop Simulation

Spacecraft (S/C) docking is the last and most challenging phase in the contact closure of two separately flying S/C. The design and testing of S/C docking missions using software-multibody simulations need to be complemented by Hardware-In-The-Loop (HIL) simulation using the real docking hardware. The docking software multibody simulation is challenged by the proper modeling of contact forces, whereas the HIL docking simulation is challenged by proper inclusion of the real contact forces. Existing docking HIL simulators ignore back-reaction force modeling due to the large S/C sizes, or use compliance devices to reduce impact, which alters the actual contact force. This dissertation aims to design a docking HIL testbed to verify docking contact dynamics for small and rigid satellites by simulating the real contact forces without artificial compliance. HIL simulations of docking contact dynamics are challenged mainly by: I. HIL simulation quality: quality of realistic contact dynamics simulation relies fundamentally on the quality of HIL testbed actuation and sensing instrumentation (non-instantaneous, time delays, see Fig. 1) II. HIL testbed design: HIL design optimization requires a justified HIL performance prediction, based on a representative HIL testbed simulation (Fig. 2), where appropriate simulation of contact dynamics is the most difficult and sophisticated task. The goal of this dissertation is to carry out a systematic investigation of the technically possible HIL docking contact dynamics simulation performances, in order to define an appropriate approach for testing of docking contact dynamics of small and rigid satellites without compliance and using HIL simulation. In addition, based on the investigations, the software simulation results shall be validated using an experimental HIL setup. To achieve that, multibody dynamics models of docking S/C were built, after carrying out an extensive contact dynamics research to select the most representative contact model. Furthermore, performance analysis models of the HIL testbed were built. In the dissertation, a detailed parametric analysis was carried out on the available models’ design-spaces (e.g., spacecraft, HIL testbed building-blocks and contact dynamics), to study their impacts on the HIL fidelity and errors (see Fig. 1). This was done using a generic HIL design-tool, which was developed within this work. The results were then used to identify the technical requirements of an experimental 1-Degree-of-Freedom (DOF) HIL testbed, which was conceived, designed, implemented and finally utilized to test and validate the selected docking contact dynamics model. The results of this work showed that the generic multibody-dynamics spacecraft docking model is a practical tool to model, study and analyze docking missions, to identify the properties of successful and failed docking scenarios before it takes place in space. Likewise, the 'Generic HIL Testbed Framework Analysis Tool' is an effective tool for carrying out performance analysis of HIL testbed design, which allows to estimate the testbed’s fidelity and predict HIL errors. Moreover, the results showed that in order to build a 6DOF HIL docking testbed without compliance, it is important to study and analyze the errors’s sources in an impact and compensate for them. Otherwise, the required figure-of-merits of the instruments of the HIL testbed would be extremely challenging to be realized. In addition, the results of the experimental HIL simulation (i.e., real impacts between various specimen) serve as a useful contribution to the advancement of contact dynamics modeling

Identification of geometrical and elastostatic parameters of heavy industrial robots

The paper focuses on the stiffness modeling of heavy industrial robots with gravity compensators. The main attention is paid to the identification of geometrical and elastostatic parameters and calibration accuracy. To reduce impact of the measurement errors, the set of manipulator configurations for calibration experiments is optimized with respect to the proposed performance measure related to the end-effector position accuracy. Experimental results are presented that illustrate the advantages of the developed technique.Comment: arXiv admin note: substantial text overlap with arXiv:1311.667

Predicting the post-impact velocity of a robotic arm

Starting from the recorded dynamic response of a 7DOF torque-controlled robot while intentionally impacting a rigid surface, we investigate the possibility of predicting the post-impact robot velocity from the ante-impact velocity and configuration. The velocity prediction is obtained by means of an impact map, derived using the framework of nonsmooth mechanics, that makes use of the known rigid-body robot model and the assumption of a frictionless inelastic impact. The main contribution is proposing a methodology that allows for a meaningful quantitative comparison between the recorded post-impact data, that exhibits a damped oscillatory response after the impact, and the post-impact velocity prediction derived via the rigid-body robot model, that presents no oscillations. The results of this approach are promising and the recorded impact data (18 experiments) is made publicly available, together with the numerical routines employed to generate the quantitative comparison, to further stimulate research in this field

Control system design for robots used in simulating dynamic force and moment interaction in virtual reality applications

This dissertation presents an approach to simulating the dynamic force and moment interaction between a human and a virtual object using a robotic manipulator as the force transmitter. Accurate control of the linear and angular accelerations of the robot end effector is required in order for the correct forces and moments to be imparted on a human operating in a computer generated virtual environment. A control system has been designed which is robust in terms of stability and performance. This control system is derived from abbreviated linear and nonlinear models of the manipulator dynamics which are efficient enough for real-time implementation yet retain a sufficient level of complexity for accurate calculations. An efficient multiple-input multiple-output (MIMO) pole placement scheme has also been devised which locates the pre-specified system eigenvalues. The controller gains are given as explicit functions of a desired trajectory to be followed and, thus, are time varying such that the overall closed-loop system is rendered time-invariant. Key software elements were automatically derived and output in compiler-ready form demonstrating the feasibility of automatic, computer generated control laws for complex robotic systems. Test results are given for a PUMA 560 used to impart dynamic forces on a user operating in a virtual environment

Attitude and Position Control of a Flapping Micro Aerial Vehicle

International audienc