Preferable Workspace for Fatigue Life Improvement of Flexible-Joint Robots Under Percussive Riveting

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Yuwen Li ◽  
Shuai Guo ◽  
Fengfeng (Jeff) Xi
Keyword(s):  
Fatigue Life ◽  
Endurance Limit ◽  
Industrial Robots ◽  
Structural Dynamic ◽  
End Effector ◽  
Flexible Joint Robots ◽  
Structural Dynamic Model ◽  
Life Improvement ◽  
Aerospace Assembly ◽  
Human Operators

This paper proposes a method to find the preferable workspace for fatigue life improvement of robots with flexible joints under percussive riveting. The development is motivated by the growing interest in using industrial robots to replace human operators for percussive riveting operations in aerospace assembly. A most important characteristic of robotic percussive riveting is the repetitive impacts generated by the percussive rivet gun. These impacts induce forced vibrations to the robot, and the joint shaft fatigue due to the resulting stress cycles must be prevented. This paper aims at finding the preferable workspace for fatigue life improvement of the robot, that is, the end-effector positions where the joint stresses are below the endurance limit. For this purpose, a structural dynamic model is established for the robot under percussive riveting. Then, an approximate analytical solution is formulated for the torsional stresses of the robot joints. Once the distributions of the stresses are obtained over the workspace, the preferable workspace for fatigue life improvement can be found by comparing the stresses with the endurance limit. Simulation studies are carried out for a mobile robot under percussive riveting. It is found that the dynamic response of the robot to the percussive riveting varies dramatically over the workspace. The method is then used to obtain the preferable positions of the robot end-effector for fatigue resistance.

scholarly journals New Indices for Evaluating Vibration Characteristics of Flexible-Joint Robots

2020 ◽  
Vol 10 (14) ◽  
pp. 4895
Author(s):  
Ping Zhang ◽  
Yuwen Li
Keyword(s):  
Harmonic Excitation ◽  
Vibration Characteristics ◽  
Industrial Robots ◽  
Structural Vibration ◽  
Elastic Displacement ◽  
Structural Dynamic ◽  
Flexible Joint ◽  
Flexible Joint Robots ◽  
External Process ◽  
Aerospace Assembly

Structural vibration is a significant consideration for robotic applications such as machining where the robot is subject to large dynamic loading. Aiming at providing an efficient means to evaluating the vibration characteristics of industrial robots for these applications, this work proposes two new indices to quantify the elastic displacement of the tool mounted on the robot caused by the vibrations induced by external process loading for flexible-joint robots. For this purpose, a structural dynamic model is first developed to derive the frequency responses of the tool displacement. Then, the displacement-force and displacement-torque frequency response ratios are defined, which represent the mapping from the amplitudes of an external harmonic force and torque to the amplitude of tool displacement respectively. The upper bounds of the two ratios are used as evaluation indices for the vibration characteristics of the robot, which represent the worst situation of the tool displacement due to harmonic excitation with amplitude of unit force and unit torque respectively. With these indices, an efficient method is provided to predict whether the tool misalignment caused by periodic loading is acceptable for process quality requirement. Numerical simulation demonstrates the effectiveness of the proposed method for a robotic riveting system being developed for aerospace assembly.

scholarly journals Fatigue Life Improvement of Cracked Aluminum 6061-T6 Plates Repaired by Composite Patches

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1421
Author(s):  
Armin Yousefi ◽  
Saman Jolaiy ◽  
Reza Hedayati ◽  
Ahmad Serjouei ◽  
Mahdi Bodaghi
Keyword(s):  
Fatigue Life ◽  
Fatigue Behavior ◽  
Weight Ratio ◽  
High Strength ◽  
Plastic Strain Amplitude ◽  
Composite Patch ◽  
Life Improvement ◽  
Cracked Structures ◽  
Aluminum Plates ◽  
High Flexibility

Bonded patches are widely used in several industry sectors for repairing damaged plates, cracks in metallic structures, and reinforcement of damaged structures. Composite patches have optimal properties such as high strength-to-weight ratio, easiness in being applied, and high flexibility. Due to recent rapid growth in the aerospace industry, analyses of adhesively bonded patches applicable to repairing cracked structures have become of great significance. In the present study, the fatigue behavior of the aluminum alloy, repaired by a double-sided glass/epoxy composite patch, is studied numerically. More specifically, the effect of applying a double-sided composite patch on the fatigue life improvement of a damaged aluminum 6061-T6 is analyzed. 3D finite element numerical modeling is performed to analyze the fatigue performance of both repaired and unrepaired aluminum plates using the Abaqus package. To determine the fatigue life of the aluminum 6061-T6 plate, first, the hysteresis loop is determined, and afterward, the plastic strain amplitude is calculated. Finally, by using the Coffin-Manson equation, fatigue life is predicted and validated against the available experimental data from the literature. Results reveal that composite patches increase the fatigue life of cracked structures significantly, ranging from 55% to 100% for different applied stresses.

Fatigue Life Improvement of Welded Elements and Structures by Ultrasonic Impact Treatment

2011 ◽  
Author(s):  
Yuriy Kudryavtsev ◽  
Jacob Kleiman
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Fatigue Testing ◽  
Highway Bridges ◽  
Surface Layers ◽  
Ultrasonic Impact Treatment ◽  
Stress Relieving ◽  
Life Improvement

The ultrasonic impact treatment (UIT) is relatively new and promising process for fatigue life improvement of welded elements and structures. In most industrial applications this process is known as ultrasonic peening (UP). The beneficial effect of UIT/UP is achieved mainly by relieving of harmful tensile residual stresses and introducing of compressive residual stresses into surface layers of a material, decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the material. The UP technique is based on the combined effect of high frequency impacts of special strikers and ultrasonic oscillations in treated material. Fatigue testing of welded specimens showed that UP is the most efficient improvement treatment as compared with traditional techniques such as grinding, TIG-dressing, heat treatment, hammer peening and application of LTT electrodes. The developed computerized complex for UP was successfully applied for increasing the fatigue life and corrosion resistance of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials. The UP could be effectively applied for fatigue life improvement during manufacturing, rehabilitation and repair of welded elements and structures. The areas/industries where the UP process was applied successfully include: Shipbuilding, Railway and Highway Bridges, Construction Equipment, Mining, Automotive, Aerospace. The results of fatigue testing of welded elements in as-welded condition and after application of UP are considered in this paper. It is shown that UP is the most effective and economic technique for increasing of fatigue strength of welded elements in materials of different strength. These results also show a strong tendency of increasing of fatigue strength of welded elements after application of UP with the increase in mechanical properties of the material used.

Knowledge Recommendation System for Human-Robot Collaborative Disassembly Using Knowledge Graph

2021 ◽  
Author(s):  
Yang Hu ◽  
Yiwen Ding ◽  
Feng Xu ◽  
Jiayi Liu ◽  
Wenjun Xu ◽  
...  
Keyword(s):  
Recommendation System ◽  
Industrial Robots ◽  
Knowledge Graph ◽  
Disassembly Process ◽  
Knowledge Based ◽  
Manufacturing Efficiency ◽  
Human Operators ◽  
Traditional Manufacturing ◽  
Human Robot Collaboration

Abstract In recent years, more and more attention has been paid to Human-Robot Collaborative Disassembly (HRCD) in the field of industrial remanufacturing. Compared with the traditional manufacturing, HRCD helps to improve the manufacturing flexibility with considering the manufacturing efficiency. In HRCD, knowledge could be obtained from the disassembly process and then provides useful information for the operator and robots to execute their disassembly tasks. Afterwards, a crucial point is to establish a knowledge-based system to facilitate the interaction between human operators and industrial robots. In this context, a knowledge recommendation system based on knowledge graph is proposed to effectively support Human-Robot Collaboration (HRC) in disassembly. A disassembly knowledge graph is constructed to organize and manage the knowledge in the process of HRCD. After that, based on this, a knowledge recommendation procedure is proposed to recommend disassembly knowledge for the operator. Finally, the case study demonstrates that the developed system can effectively acquire, manage and visualize the related knowledge of HRCD, and then assist the human operator to complete the disassembly task by knowledge recommendation, thus improving the efficiency of collaborative disassembly. This system could be used in the human-robot collaboration disassembly process for the operators to provide convenient knowledge recommendation service.

Finding Features of Positioning Error for Large Industrial Robots Based on Convolutional Neural Network

2021 ◽  
Author(s):  
Daiki Kato ◽  
Kenya Yoshitugu ◽  
Naoki Maeda ◽  
Toshiki Hirogaki ◽  
Eiichi Aoyama ◽  
...  
Keyword(s):  
Neural Network ◽  
Convolutional Neural Network ◽  
Production Systems ◽  
Industrial Robot ◽  
Three Dimensional ◽  
Industrial Robots ◽  
Numerical Control ◽  
Robot Motion ◽  
Positioning Error ◽  
End Effector

Abstract Most industrial robots are taught using the teaching playback method; therefore, they are unsuitable for use in variable production systems. Although offline teaching methods have been developed, they have not been practiced because of the low accuracy of the position and posture of the end-effector. Therefore, many studies have attempted to calibrate the position and posture but have not reached a practical level, as such methods consider the joint angle when the robot is stationary rather than the features during robot motion. Currently, it is easy to obtain servo information under numerical control operations owing to the Internet of Things technologies. In this study, we propose a method for obtaining servo information during robot motion and converting it into images to find features using a convolutional neural network (CNN). Herein, a large industrial robot was used. The three-dimensional coordinates of the end-effector were obtained using a laser tracker. The positioning error of the robot was accurately learned by the CNN. We extracted the features of the points where the positioning error was extremely large. By extracting the features of the X-axis positioning error using the CNN, the joint 1 current is a feature. This indicates that the vibration current in joint 1 is a factor in the X-axis positioning error.

MIG Brazing as a Means of Fatigue Life Improvement

2004 ◽  
Vol 48 (9-10) ◽  
pp. 28-40 ◽  
Author(s):  
J. S. Lepistö ◽  
G. B. Marquis
Keyword(s):  
Fatigue Life ◽  
Life Improvement

scholarly journals Detachable Robotic Grippers for Human-Robot Collaboration

2021 ◽  
Vol 8 ◽  
Author(s):  
Zubair Iqbal ◽  
Maria Pozzi ◽  
Domenico Prattichizzo ◽  
Gionata Salvietti
Keyword(s):  
Degrees Of Freedom ◽  
Tactile Feedback ◽  
Industrial Robots ◽  
Physical Interaction ◽  
Robot Arm ◽  
Robotic Hands ◽  
End Effector ◽  
External Power ◽  
Self Powered ◽  
Automatic Tool

Collaborative robots promise to add flexibility to production cells thanks to the fact that they can work not only close to humans but also with humans. The possibility of a direct physical interaction between humans and robots allows to perform operations that were inconceivable with industrial robots. Collaborative soft grippers have been recently introduced to extend this possibility beyond the robot end-effector, making humans able to directly act on robotic hands. In this work, we propose to exploit collaborative grippers in a novel paradigm in which these devices can be easily attached and detached from the robot arm and used also independently from it. This is possible only with self-powered hands, that are still quite uncommon in the market. In the presented paradigm not only hands can be attached/detached to/from the robot end-effector as if they were simple tools, but they can also remain active and fully functional after detachment. This ensures all the advantages brought in by tool changers, that allow for quick and possibly automatic tool exchange at the robot end-effector, but also gives the possibility of using the hand capabilities and degrees of freedom without the need of an arm or of external power supplies. In this paper, the concept of detachable robotic grippers is introduced and demonstrated through two illustrative tasks conducted with a new tool changer designed for collaborative grippers. The novel tool changer embeds electromagnets that are used to add safety during attach/detach operations. The activation of the electromagnets is controlled through a wearable interface capable of providing tactile feedback. The usability of the system is confirmed by the evaluations of 12 users.

Robot end effector based on electrostatic adsorption for manipulating garment fabrics

2021 ◽  
pp. 004051752110418
Author(s):  
Wenqian Feng ◽  
Yanli Hu ◽  
Xin rong Li ◽  
Lidong Liu
Keyword(s):  
Adsorption Capacity ◽  
Structural Parameters ◽  
Garment Industry ◽  
Industrial Robots ◽  
Force Model ◽  
Adsorption Effect ◽  
Electrostatic Adsorption ◽  
End Effector ◽  
Application Range ◽  
Capacity Model

To improve the effectiveness of industrial robots in the textile and garment industry, it is necessary to expand the application range of electrostatic adsorption end effectors and solve the problem of automatically grasping and transferring fabrics during garment processing. Taking weft-knit fabric as an example, this paper begins by analyzing the factors that influence the electrostatic adsorption capacity, and then constructing an electrostatic adsorption capacity model based on the fabric characteristics. Next, the shape arrangement and structural parameters of the electrode plate are optimized by taking the electrostatic adsorption force model and maximizing the adsorption force per unit area. Finally, the adsorption effect of the electrostatic adsorption end effector is verified by simulation and experiment. The verification results show that the electrode with a comb-shaped arrangement and optimized structural parameters can adsorb clothing fabric well and meets the requirements of clothing automated production lines. This study provides a new method for solving the problem of automatically grasping and transferring fabrics and provides technical support for improving automation in the garment industry.

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