1,720,996 research outputs found
An effective approach to model parallel robots with flexible links
No full textThis paper is focused on the development of an effective hardware and software architecture that is useful to improve the performance of slender parallel manipulators. The latter can perform high acceleration in fast pick and place applications, but their features can be also exploited in more advanced operations, where path following is a central issue. A simple and effective approach to model the elastodynamic behavior of flexible parallel manipulator is proposed, conceived to be fast and easy to implement in model-based control schemes. Moreover, a workbench architecture based on camera acquisitions is essential to calibrate the elastodynamic model and provide all the required information that are needed to improve path following of flexible mechanims
Practical range of applicability of a linear stiffness model of an elliptical flexure hinge
No full textThis paper presents the analysis of a linear stiffness model of an elliptical flexure hinge. The purpose of the study is to support the mechanical designer in choosing the geometric dimensions of the hinge based on design specifications, driven by the accuracy that can later be achieved in planning its motion using the related stiffness model. Results are presented as a comparison between the analytical model and a finite element model of the flexure hinge, showing the practical range of applicability of the analytical model and its limitations. A case study show how to design a flexure hinge of small size for micro scale robotic or mechatronic operations
Insights into Bending Stiffness Modeling of Elementary Flexure Hinges
Full text linkFlexure hinges are widely used in mechanical devices, especially for micro- or even nano-scale applications, where conventional joints based on conjugate surfaces prove unsuitable. However, to achieve accurate motion of devices whose joints are flexure hinges, knowledge of stiffness models that correlate applied forces or bending moments with the resulting displacements is required. Nonlinear bending models are typically too complex and difficult to implement. Therefore, it is preferred to use linear models, which admit analytical solutions. The purpose of this paper is to show what is lost in terms of accuracy in reducing a nonlinear bending stiffness model associated with a flexure hinge when simplifications are made to obtain an analytical solution. An analysis of the simplification process leading to a linear stiffness model and its analytical solution is presented. From this study arises an increased awareness of flexure joints in terms of the accuracy obtained with their stiffness models, suggesting important information to the user in choosing the level of complexity required to model them in a specific application. A comparison between analytical and numerical results is provided in the form of maps and tables so as to make that choice as clear as possible
Collaborative Robotics for Rehabilitation: A Multibody Model for Kinematic and Dynamic Analysis
No full textHuman-Robot Collaboration is increasing in industrial settings because of the robot’s accuracy and repeatability join perfectly with human’s problem solving to enhance the industrial productivity. Collaborative robots share the workspace with operators in order to reduce human workload and guarantee performances. The reliability and safety of these robots allow their application in the health care sector (e.g. neuromuscular rehabilitation). The cobot-assisted therapy is becoming a significant supplement to the traditional one aimed at providing intensive and repetitive rehabilitating tasks to improve the patient’s recovery. The human-robot system presented in this paper is a closed kinematic chain composed of a robotic arm attached to the human forearm through a custom handle system. The handle, designed with simple components, is used for primary rehabilitation exercises. The kinematic models of human and robotic arms presented in this study are applied to develop trajectory planning algorithm in the joint space. Robot joints torques needed for guiding the patient limb are obtained by multibody dynamic simulations, assessing the capability of the manipulator to perform the task at given speeds and loads. The tools and methods proposed in this work allow for a preliminary study on cobot-assisted-therapy by different human-cobot-working modalities
A Framework for the Study of Human-Robot Collaboration in Rehabilitation Practices
No full textCollaborative robots and humans can cooperate in different industrial processes by combining their peculiar skills: the accuracy and repeatability of the manipulators can be exploited in synergy with human intelligence and flexibility. Since the cobots are safe and reliable, they can be adopted in the health sector, in particular in rehabilitation: the cobots allow the three-dimensional manipulation of the limbs and can be easily adapted to different anthropometric parameters. The kinematic models of the human-robot system presented in this paper can be exploited to develop motion planning algorithms for rehabilitation exercises. Furthermore, the estimation of the interaction forces in the human-robot interface can be obtained by multibody dynamic simulations. The proposed methodology is a starting point for the study of the integration of cobots into current rehabilitation practices, evaluating the feasibility and providing useful ideas in order to plan different man-robot working modalities
From Dataset Creation to Defect Detection: A Proposed Procedure for a Custom CNN Approach for Polishing Applications on Low-Performance PCs
Full text linkThis study focuses on training a custom, small Convolutional Neural Network (CNN) using a limited dataset through data augmentation that is aimed at developing weights for subsequent fine-tuning on specific defects, namely improperly polished aluminum surfaces. The objective is to adapt the network for use in computationally restricted environments. The methodology involves using two computers—a low-performance PC for network creation and initial testing and a more powerful PC for network training using the Darknet framework—after which the network is transferred back to the initial low-performance PC. The results demonstrate that the custom lightweight network suited for a low-performance PC effectively performs object detection under the described conditions. These findings suggest that using tailored lightweight networks for recognizing specific types of defects is feasible and warrants further investigation to enhance the industrial defect detection processes in limited computational settings. This approach highlights the potential for deploying AI-driven quality control in environments with constrained hardware capabilities
Modelling and control of a spherical robotic device
No full textThe researchers at the Polytechnic University of Marche developed a spherical parallel manipulator designed for the orientation of parts or tools: the paper presents the first experimental results on such innovative machine. A model of the prototype robot has been realised by means of commercial multibody software then both open-loop and closed loop dynamics has been studied. The relative simplicity of machine kinematics allowed also to experiment the use of controllers with compensation of gravitational terms
Simulation assessment of the performance of a redundant SCARA
Full text linkThe present paper analyses the potential dynamic performance of a novel redundant SCARA robot, currently at the stage of a functional design proposed by a renowned robot manufacturer. The static and dynamic manipulability of the new concept is compared with the conventional model of the same manufacturer by means of computer simulation in typical pick and place tasks arising from industry. The introduction of a further revolute joint in the SCARA robot kinematics leads to some improvements in the kinematic and dynamic behaviour at the expense of a greater complexity. In this paper, the potential of a redundant SCARA architecture in cutting cycle-times is investigated for the first time in performing several tasks. It is shown that, in order to exploit the possible enhancements of the redundant structure, the whole manipulator, mechanics and control must be redesigned according to specific tasks aiming at the optimization of their cycle-time
A collision avoidance strategy for redundant manipulators in dynamically variable environments: On-line perturbations of off-line generated trajectories
No full textIn this work, a comprehensive control strategy for obstacle avoidance in redundant manipulation is presented, consisting of a combination of off-line path planning algorithms with on-line motion control. Path planning allows the avoidance of fixed obstacles detected before the start of the robot’s motion; it is based on the potential fields method combined with a smoothing process realized by means of interpolation with Bezier curves. The on-line motion control is designed to compensate for the motion of the obstacles and to avoid collisions along the kinematic chain of the manipulator; it is realized by means of a velocity control law based on the null space method for redundancy control. A new term is introduced in the control law to take into account the speed of the obstacles as well as their position. Simulations on a simplified planar case are presented to assess the validity of the algorithms and to estimate the computational effort in order to verify the transferability of our approach to a real system
Collaborative robot sensorization with 3D depth measurement system for collision avoidance
No full textHuman-Robot Collaboration (HRC) and Machine Vision are some of the most promising technologies of Industry 4.0. Collaborative robots are quickly gaining ground in the industrial network, due to their possibility of working side by side with humans, in a shared space, without physical barriers. However, the knowledge of the environment is required to adapt the robot motion and guarantee the operator safety. This paper presents a preliminary study for a bigger project regarding the implementation of a full obstacle avoidance strategy into a robotic system for industrial purposes. The system adopted consists of a vision system based on Intel Realsense cameras, an algorithm providing obstacle representation as elementary geometric shapes and an obstacle avoidance strategy used for the motion control of the robot. The continuous monitoring of the operators, objects and robots present in the workstation with the vision system ensures the stability and security of the system
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