The Gantry-Tau parallel kinematic machine-kinematic and elastodynamic design optimisation

Pubished version of an article in the journal: Meccanica. Also available from the publisher at: http://dx.doi.org/10.1007/s11012-010-9394-9One of the main advantages of the Gantry-Tau machine is a large accessible workspace/footprint ratio compared to many other parallel machines. The optimal kinematic, elastostatic and elastodynamic design parameters of the machine are still difficult to calculate and this paper introduces an optimisation scheme based on the geometric and functional dependencies to define the workspace and first resonance frequency. This method assumes that each link and universal joint can be described by a mass-spring-damper model and calculates the transfer function from a Cartesian force or torque to Cartesian position or orientation. The evolutionary algorithm based on the complex search method is compared to the gradient-based search function in Matlab integrated optimisation toolbox. Kinematic design obtained by optimisation according to this paper gives a 2D workspace/footprint ratio more than 1.66 and first resonance frequency is more than 50 Hz with components of an existing lab prototype at the University of Agder, Norway

Outils pour l’identification des paramètres de raideur des robots à l’aide d’un logiciel de CAO

This report proposes a CAD-based approach for identification of the elasto-static parameters of the robotic manipulators. The main contributions are in the areas of virtual experiment planning and algorithmic data processing, which allows to obtain the stiffness matrix with required accuracy. In contrast to previous works, the developed technique operates with the deflection field produced by virtual experiments in a CAD environment. The proposed approach provides high identification accuracy (about 0.1% for the stiffness matrix element) and is able to take into account the real shape of the link, coupling between rotational/translational deflections and joint particularities. To compute the stiffness matrix, the numerical technique has been developed, and some recommendations for optimal settings of the virtual experiments are given. In order to minimize the identification errors, the statistical data processing technique was applied. The advantages of the developed approach have been confirmed by case studies dealing with the links of parallel manipulator of the Orthoglide family, for which the identification errors have been reduced to 0.1%ANR COROUSS

CAD-based approach for identification of elasto-static parameters of robotic manipulators

The paper presents an approach for the identification of elasto-static parameters of a robotic manipulator using the virtual experiments in a CAD environment. It is based on the numerical processing of the data extracted from the finite element analysis results, which are obtained for isolated manipulator links. This approach allows to obtain the desired stiffness matrices taking into account the complex shape of the links, couplings between rotational/translational deflections and particularities of the joints connecting adjacent links. These matrices are integral parts of the manipulator lumped stiffness model that are widely used in robotics due to its high computational efficiency. To improve the identification accuracy, recommendations for optimal settings of the virtual experiments are given, as well as relevant statistical processing techniques are proposed. Efficiency of the developed approach is confirmed by a simulation study that shows that the accuracy in evaluating the stiffness matrix elements is about 0.1%.Comment: arXiv admin note: substantial text overlap with arXiv:0909.146

Dynamic path planning of initially unknown environments using an RGB-D camera

In this thesis an RGB-D camera was used with the goal to perform dynamic path planning in an initially unknown environment. Depth data from an RGB-D camera together with a discretizising algorithm is continuously used for maintaining an obstacle map of the environment which within the path planning algorithm D* Lite [S. Koening, 2005] is performed on the flight. Experiments were conducted on two different systems, on Combine’s hexacopter and on a Gantry Tau robot at the Robot Lab of the Department of Automatic Control, LTH. On Combine’s hexacopter different tracking algorithms such as ICP, Translation Approximation and SDF where evaluated for 3D positioning while the robots internal positioning where used on the Gantry Tau robot. For discretization purposes we compare the use of Box Approximation and Signed Distance Function (SDF) for creating the obstacle map

Outils pour l’identification des paramètres de raideur des robots à l’aide d’un logiciel de CAO

This report proposes a CAD-based approach for identification of the elasto-static parameters of the robotic manipulators. The main contributions are in the areas of virtual experiment planning and algorithmic data processing, which allows to obtain the stiffness matrix with required accuracy. In contrast to previous works, the developed technique operates with the deflection field produced by virtual experiments in a CAD environment. The proposed approach provides high identification accuracy (about 0.1% for the stiffness matrix element) and is able to take into account the real shape of the link, coupling between rotational/translational deflections and joint particularities. To compute the stiffness matrix, the numerical technique has been developed, and some recommendations for optimal settings of the virtual experiments are given. In order to minimize the identification errors, the statistical data processing technique was applied. The advantages of the developed approach have been confirmed by case studies dealing with the links of parallel manipulator of the Orthoglide family, for which the identification errors have been reduced to 0.1%ANR COROUSS

The Development and Application of a Custom Robotic Biomechanical Testing Platform Employing Real-time Load-control to Compare Spinal Biomechanical Testing Protocols: Pure Moment, Ideal Follower Load, and a Novel Trunk Weight Protocol

The human lumbar spine has been the subject of biomechanical study for many decades owing to the numerous medical cases resulting in the development of various corrective surgical procedures and medical devices intended to relieve patient discomfort. Spinal biomechanics is a broad field containing but not limited to the in vitro study of cadaveric tissue utilizing testing platforms used to apply motion- or load-profiles to tissue in the investigation of the various kinetic or kinematic responses, respectively. The particular arena field of this research concerns the field of robotics as it applies to testing platforms and how they are applied to lumbar spine biomechanical testing. The in vivo spine is subject to six degrees of freedom (DOF) of motion as a consequence of the applied loads of surrounding musculature which apply component loads in 6 DOF. However current in vitro standard protocols apply isolated loads primarily in the anatomical planes. Although the primary goal of in vitro testing may not be the simulation of in vivo circumstances, the accurate recreation of the in vivo loading environment would reveal much regarding the passive biomechanics of the spine. To accomplish such a goal, it would be ideal to utilize a platform capable of providing 6 DOF of controlled mobility as well as capable of apply controlled load in those 6 DOF. The Musculoskeletal Research Laboratory has developed such a system. The system’s load-control capabilities were validated by simulating two standard biomechanical protocols, the pure moment and the ideal follower load on 6 L4-L5 single motion segment units. The robotic performance of the system was evaluated by measuring the tracking errors during testing, or the difference between experimental forces being applied and the forces commanded by the custom motion programs executed during protocol simulation. The biomechanical data that was recorded and compared to the literature for validation was rotational range of motion in the sagittal plane and anatomical point translation. Translation data proved to be difficult to compare effectively to the literature due to the sparseness of comparable numbers. There was also interest in the platform’s ability to control protocols. To test this hypothesis, three different biomechanical protocols were simulated and there biomechanical results were compared: pure moment, ideal follower load, and trunk weight. The system provided stable, good load-control in during combined motions involving all 6 DOF. The tracking errors observed were low compared to other published robotic biomechanical platforms. The mean combined flexion-extension rotational range of motion in the sagittal plane for the pure moment protocol, the ideal follower load, and the trunk weight protocols were 8.2°(±2.5°), 7.6°(±2.9°), and 7.4°(±2.8°), respectively. There were statistically significant differences in the absolute translational data across the protocols but when comparing relative changes due to flexion and extension only, there are no significant differences across protocols. In conclusion to this research the platform developed and validated in the current study adequately provides the capabilities of 6 DOF coordinated motion and 5 DOF coordinated load-control. It is sufficient to simulate the standard spine biomechanical test protocols of pure moment and ideal follower load on single segments. It is also a good tool for comparing the effects of particular protocols on the passive biomechanics of human cadaveric tissue. To the author’s knowledge, this is the first publication of a fully robotic system adequately controlling a non-zero dynamic force vector while a bending protocol was being applied to a human spinal segment. This research is limited to the sagittal plane and single lumbar spine motion segment units

Industrial Robotics

This book covers a wide range of topics relating to advanced industrial robotics, sensors and automation technologies. Although being highly technical and complex in nature, the papers presented in this book represent some of the latest cutting edge technologies and advancements in industrial robotics technology. This book covers topics such as networking, properties of manipulators, forward and inverse robot arm kinematics, motion path-planning, machine vision and many other practical topics too numerous to list here. The authors and editor of this book wish to inspire people, especially young ones, to get involved with robotic and mechatronic engineering technology and to develop new and exciting practical applications, perhaps using the ideas and concepts presented herein

Stiffness modeling for perfect and non-perfect parallel manipulators under internal and external loadings

International audienceThe paper presents an advanced stiffness modeling technique for perfect and non-perfect parallel manipulators under internal and external loadings. Particular attention is paid to the manipulators composed of non-perfect serial chains, whose geometrical parameters differ from the nominal ones and do not allow to assemble manipulator without internal stresses that considerably affect the stiffness properties and also change the end-effector location. In contrast to other works, several types of loadings are considered simultaneously: an external force applied to the end-effector, internal loadings generated by the assembling of non-perfect serial chains and external loadings applied to the intermediate points (auxiliary loading due to the gravity forces and relevant compensator mechanisms, etc.). For this type of manipulators, a non-linear stiffness modeling technique is proposed that allows to take into account inaccuracy in the chains and to aggregate their stiffness models for the case of both small and large deflections. Advantages of the developed technique and its ability to compute and compensate the compliance errors caused by the considered factors are illustrated by an example that deals with parallel manipulators of the Orthoglide family

Proceedings of the NASA Conference on Space Telerobotics, volume 4

Papers presented at the NASA Conference on Space Telerobotics are compiled. The theme of the conference was man-machine collaboration in space. The conference provided a forum for researchers and engineers to exchange ideas on the research and development required for the application of telerobotic technology to the space systems planned for the 1990's and beyond. Volume 4 contains papers related to the following subject areas: manipulator control; telemanipulation; flight experiments (systems and simulators); sensor-based planning; robot kinematics, dynamics, and control; robot task planning and assembly; and research activities at the NASA Langley Research Center