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This paper presents a low-cost pose measuring device capable of simultaneously measuring all six coordinates (3 translations and 3 rotations) of a rigid body with respect to a given reference frame. The proposed system consists of a mechanical chain of rigid bodies and two encoders. The mechanism is a spatial four-bar linkage system with a symmetrical Revolute-Spherical-Spherical-Revolute (RSSR) kinematic structure, where two encoders measure the rotation of the revolute joints. The mechanism is investigated theoretically and solved kinematically using a numerical estimation method. The uncertainty of the pose determination, caused by the repeatability of the sensors, is estimated, as well as the achievable measurement range. A low uncertainty is achieved by a suitable design of the proposed kinematic chain. The mechanism is easy to realize with low tolerances and the correct definition of the length of the links allows a quite large workspace. The system can be profitably used in the calibration of robots or multi-axis machine tools where the actual pose of the gripper or spindle must be measured over the workspace of the machine. An experimental prototype is described, and the first experimental results are reported. • Six-coordinate low-cost pose measuring device. • Simple RSSR kinematic structure, easy realized with high accuracy and low backlash. • Great linear and angular accuracy of about 1 ⋅ 1 0 − 5 [m] and 1 ⋅ 10−4 [rad]. • Useful for kinematic calibration of robots or multi-axis machine. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the results of a research project whose aim is investigating, from both a theoretical and an experimental point of view, all the aspects connected to the optimal design and use of a 6 DoF draw-wire sensors based measuring system in the kinematic calibration of industrial robots context. One essential operation in calibration is the measurement of the pose of the robotic gripper in a predefined set of points inside the working space. For this purpose optical devices, like laser trackers, are usually employed due to their precision, although they are very expensive. Therefore, the study of a low-cost measuring system and the investigation of the reachable performances could represent a relevant outcome in the evolution of the calibration task. With this aim the design of a wire-sensors based measuring system was developed and applied to a six revolute degrees of freedom anthropomorphic robot. In a preliminary phase, with the aid of simulations tools, the measuring system was optimized to obtain isotropic accuracy and high sensitivity, while in the following experimental phase the same system was employed for the kinematic calibration of the robot, achieving an accuracy lower than the robot repeatability, which practically represents a physical limit. [Copyright &y& Elsevier]

Abstract: Motion planning for free-flying robots can be quite complex due to the fact that any movement of the joints influences the position and the orientation of the spacecraft which carries the manipulator. Several studies have been carried out to plan joint trajectories which eliminate the effects of the dynamic disturbances. Approximate solutions to this problem have been proposed using the concept of the Disturbance Map. The authors have already studied this problem for the case of 2 DOF and 3 DOF planar robots connected with revolute joints developing an exact solution based on the concept of dynamic singularities. Aim of this paper is to extend the proposed methodology to the case of planar polar manipulators, analyzing the peculiarities of these robot arm configurations. A numerical procedure for the evaluation of zero disturbance trajectories is also presented and application examples are developed. The adoption of the proposed strategy improves the performances of spacecraft’s attitude control system. [Copyright &y& Elsevier]

• Smooth and efficient interpolation between different angular poses. • Singularity-free rotation interpolation algorithm. • C 2 angular motion generation. This paper proposes a new methodology for the interpolation of a given set of 3D rotation poses that have to be reached in successive times by preserving continuity in orientation, angular velocity and angular acceleration. The discussed algorithm ensures the generation of smooth angular trajectories without singularities. The distinctive features of the proposed approach are the straightforward formulation, the reduced computational burden and the lack of iterative procedures. The presented methodology has applications in the generation of spatial motion of mechanical systems (e.g. robotics, flying devices) or in 3D computer graphics. After a theoretical introduction, the proposed algorithm is compared with other methods available in literature and some possible applications are presented. [ABSTRACT FROM AUTHOR]