15 results
Now showing1 - 10 of 15
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On using inertial measurement units for solving the direct kinematics problem of parallel mechanismsIn this paper, we investigate the accuracy and the computational efficiency of an IMU-based approach for solving the direct kinematics problem of parallel mechanisms with length-variable linear actuators under dynamic conditions. By avoiding to measure the linear actuators’ lengths and by using orientations instead, a comprehensive, low-cost sensor structure can be obtained that provides a unique solution for the direct kinematics problem. As a representative example, we apply our approach to the planar 3-RPR parallel mechanism, where P denotes active prismatic joints and R denotes passive revolute joints, and investigate the achievable accuracy and robustness on a specially designed experimental device. In this context, we also investigate the effect of sensor fusion on the achievable accuracy and compare our results with those obtained from linear actuators’ lengths when the Newton-Raphson algorithm is used to compute the manipulator platform’s pose iteratively. Finally, we discuss the applicability of inertial measurement units (IMUs) for solving the direct kinematics problem of parallel mechanisms.Publicationtype: Journal ArticleScopus© Citations 1 485 471 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On the origin of passive rotation in rotational joints, and how to calculate itIn this paper, a computation method for the output shaft’s rotation of a passive rotational joint, especially of one that is deployed on a parallel mechanism, is investigated. As an alternative to typical geometric or screw theory methods, we propose a new approach that is based on the comparison between any passive rotational joint with a reference spherical joint. As examples, we apply our method to a universal joint and a novel double joint whose passive rotation is difficult to calculate with traditional methods. c 2019 The Authors Proceedings in Applied Mathematics & Mechanics published by Wiley-VCH Verlag GmbH & Co. KGaA WeinheimPublicationtype: Conference Paper286 271 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Performance evaluation of a sensor concept for solving the direct kinematics problem of general planar 3-RPR parallel mechanisms by using solely the linear actuators’ orientationsIn this paper, we experimentally evaluate the performance of a sensor concept for solving the direct kinematics problem of a general planar 3-RPR parallel mechanism by using solely the linear actuators’ orientations. At first, we review classical methods for solving the direct kinematics problem of parallel mechanisms and discuss their disadvantages on the example of the general planar 3-RPR parallel mechanism, a planar parallel robot with two translational and one rotational degrees of freedom, where P denotes active prismatic joints and R denotes passive revolute joints. In order to avoid these disadvantages, we present a sensor concept together with an analytical formulation for solving the direct kinematics problem of a general planar 3-RPR parallel mechanism where the number of possible assembly modes can be significantly reduced when the linear actuators’ orientations are used instead of their lengths. By measuring the orientations of the linear actuators, provided, for example, by inertial measurement units, only two assembly modes exist. Finally, we investigate the accuracy of our direct kinematics solution under static as well as dynamic conditions by performing experiments on a specially designed prototype. We also investigate the solution formulation’s amplification of measurement noise on the calculated pose and show that the Cramér-Rao lower bound can be used to estimate the lower bound of the expected variances for a specific pose based exclusively on the variances of the linear actuators’ orientations.Publicationtype: Journal ArticleScopus© Citations 3 255 296 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A sensor concept for solving the direct kinematics problem of parallel mechanismsPublicationtype: Doctoral Thesis112 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Passive Rotation of Rotational Joints and Its Computation MethodThis paper discusses the equivalence condition of the input and output rotation of a passive rotational joint and provides a general method to compute the output rotation angle. In a Stewart-Gough platform, the fixed base platform is usually connected to the moveable manipulator platform by six identical kinematic chains consisting of rotational joints and linear actuators. When using lead screws for the linear actuators, possible passive rotations of the rotational joints can be harmful because they may lead to additional length variations of the linear actuators or cause extra stresses if the rotations are obstructed. This paper provides a for computing these passive rotations by using vector comparison and demonstrates its application on the examples of a universal joint, a Rzeppa joint, and a Tracta joint.Publicationtype: Conference Paper209 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Assembly Modes of General Planar 3-RPR Parallel Mechanisms when Using the Linear Actuators’ OrientationsIn this paper, we show that the number of possible assembly modes for the general planar 3-RPR parallel mechanism, where P denotes active prismatic joints and R denotes passive revolute joints, can be significantly reduced when using the linear actuators’ orientations in-stead of their lengths. The linear actuators’ lengths lead to a univariate polynomial which can have up to six different solutions and thus provides up to six assembly modes. By measuring the orientations of the linear actuators, provided, e. g., by inertial measurement units, only two assembly modes exist. Furthermore, by using two orientations of the linear actuators in addition to the moveable manipulator platform’s orientation, only one assembly mode remains.Publicationtype: Conference Paper321 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Performance of an IMU-Based Sensor Concept for Solving the Direct Kinematics Problem of the Stewart-Gough Platform(2018-12-27); ; The direct kinematics problem of the Stewart-Gough platform can be solved by measuring the manipulator platform's orientation and two of the linear actuators' orientations instead of the six linear actuators' lengths. In this paper, the effect of measurement errors on the calculated manipulator platform's pose is investigated using the Cramer-Ran lower bound and extensive experiments on a state-of-the-art Stewart-Gough platform. Furthermore, different algorithms and filters for one-time as well as continuous pose determinations are investigated. Finally, possible sensor fusion concepts for the one-time pose determination are presented to increase the robustness against noise and measurement errors.Publicationtype: Conference Paper138 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Closed-form Solution for the Direct Kinematics Problem of the Planar 3-RPR Parallel MechanismIn general, it is not possible to determine the actual manipulator platform's pose of a parallel mechanism from its active joints' coordinates. This problem is usually solved by using additional numerical procedures or by additional system information from auxiliary sensors, providing several weaknesses including initial pose estimations, reference drives, or workspace limitations. In this paper, we therefore introduce a closed-form solution for the direct kinematics problem of the planar 3-RPR parallel mechanism by using only the orientations of two active joints and the manipulator platform, where P denotes active prismatic joints and R passive revolute joints.Publicationtype: Conference Paper165 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Comparison of three methods of length compensation in a parallel kinematic and their equivalence conditionsThis paper is a further development of a previous work (PAMM 16, 51-52). In this paper, we derive an analytical formulation of the linear actuators' length variations for a 2-1-2 DOF joint designed parallel hexapod based on Riebe and Ulbrich's method (Arch. Appl. Mech. 72, 817-829) and the Euler angles based matrix method. The equivalence conditions as well as the computation errors are given and compared with a quaternion based method.Publicationtype: Conference PaperScopus© Citations 2 263 290 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On the direct kinematics problem of parallel mechanismsThe direct kinematics problem of parallel mechanisms, that is, determining the pose of the manipulator platform from the linear actuators’ lengths, is, in general, uniquely not solvable. For this reason, instead of measuring the lengths of the linear actuators, we propose measuring their orientations and, in most cases, also the orientation of the manipulator platform. This allows the design of a low-cost sensor system for parallel mechanisms that completely renounces length measurements and provides a unique solution of their direct kinematics.Publicationtype: Journal ArticleScopus© Citations 9 332 403