Modeling and simulation of percussive impact for robotic riveting system

Riveting is one of the major joining methods used in assembly,and the robotic riveting has been gradually introduced into aircraft industry.In this paper,a method is presented for modeling and simulation of percussive robotic riveting.In percussive riveting,vibration always exists.When an impact force is employed,a forced vibration will be induced.If it resonates with a robot natural frequency,the vibration will cause damage to the robot.The main content of this paper is divided into three parts.Firstly,a robot dynamic model is established to compute the driving torque for each joint.Secondly,vibration responses under impact are analyzed for the percussive riveting process.Thirdly,the effect of riveting on robot vibration is studied over the robot workspace.The purpose of this paper is to discuss the suitable regions for riveting where the robot vibration is very minimal.It is shown that based on the presented method an appropriate trajectory can be planned for robotic riveting.     

A Comparative Study of Friction Self-Piercing Riveting and Self-Piercing Riveting of Aluminum Alloy AA5182-O

In this paper, self-piercing riveting (SPR) and friction self-piercing riveting (F-SPR) processes were employed to join aluminum alloy AA5182-O sheets. Parallel studies were carried out to compare the two processes in terms of joint macrogeometry, tooling force, microhardness, quasi-static mechanical performance, and fatigue behavior. The results indicate that the F-SPR process formed both rivet–sheet interlocking and sheet–sheet solid-state bonding, whereas the SPR process only contained rivet–sheet interlocking. For the same rivet flaring, the F-SPR process required 63% less tooling force than the SPR process because of the softening effect of frictional heat and the lower rivet hardness of F-SPR. The decrease in the switch depth of the F-SPR resulted in more hardening of the aluminum alloy surrounding the rivet. The higher hardness of aluminum and formation of solid-state bonding enhanced the F-SPR joint stiffness under lap-shear loading, which contributed to the higher quasi-static lap-shear strength and longer fatigue life compared to those of the SPR joints.     

自激励式电磁铆接铆钉镦头变形试验研究

目的掌握自激励式电磁铆接驱动力的作用方式,确定合理的工艺参数,探究铆钉变形规律。方法以2A10半圆头铆钉为研究对象,通过试验方法研究放电电压、放电电容及线圈结构对线圈放电电流和铆钉镦头变形的影响。结果自激励式电磁铆接驱动力源于两放电线圈电流的相互作用,两放电电流可分别进行独立控制。随着放电电压升高,线圈放电电流幅值增加,周期略有增加,铆钉镦头的变形量增加,相同放电能量下,放电电容值增加使放电电流幅值降低,周期增大,铆钉镦头变形量存在最大值;放电线圈匝数较多,导线宽度较小时,铆钉镦头变形量更大。结论自激励式电磁铆接是一种动力源可控的连接方法,为铆接驱动力的产生引入新方式,实现了铆接驱动力的主动控制,提高了控制的灵活性,其能量利用率较感应式高,为高强度大直径铆钉的成形提供一种有效的方式。铆钉变形是铆接驱动力幅值在一定时间下的作用效果,要综合考虑放电电流幅值与作用时间的关系。     

基于钉杆变形均匀性的锥形半圆头铆钉优化设计研究

目的 针对铆接过程中铆钉钉杆发生镦粗变形,其变形的均匀性影响连接接头力学性能的问题,提出一种钉杆带有锥度的变径铆钉,以改善钉杆变形的均匀性.方法 基于三维有限元仿真方法,对准静态铆接过程进行仿真,获取锥形与常规半圆头铆钉在铆接后钉杆变形情况,同时对比分析板材残余应力变化情况.最后建立由钉杆变形均匀度与铆钉尺寸以及镦头高...     

磁阻型电磁铆接工艺研究

目的 为了掌握磁阻型电磁铆接新技术,研究工艺参数对铆接驱动力的影响规律.方法 通过改变放电电压、线圈导线截面尺寸和弹丸尺寸等参数进行磁阻型电磁铆接试验研究,分析各参数对直径为8 mm的2A10铆钉镦头变形的影响,与感应式电磁铆接的成形铆钉进行对比.结果 随着放电电压的升高,铆钉镦头变形量增加;相同放电能量下,导线截面尺...     

Novel AR-based interface for human-robot interaction and visualization

Intuitive and efficient interfaces for humanrobot interaction(HRI) have been a challenging issue in robotics as it is essential for the prevalence of robots supporting humans in key areas of activities.This paper presents a novel augmented reality(AR) based interface to facilitate human-virtual robot interaction.A number of human-virtual robot interaction methods have been formulated and implemented with respect to the various types of operations needed in different robotic applications.A EucUdean distance-based method is developed to assist the users in the interaction with the virtual robot and the spatial entities in an AR environment.A monitor-based visualization mode is adopted as it enables the users to perceive the virtual contents associated with different interaction methods,and the virtual content augmented in the real environment is informative and useful to the users during their interaction with the virtual robot.Case researches are presented to demonstrate the successful implementation of the AR-based HRI interface in planning robot pick-and-place operations and path following operations.     

Optimization of cycle time and kinematic energy in a robot/conveyor system with variable pick-up locations

In automated manufacturing, a robot/conveyor system uses a robot to pick up parts that continuously arrive from a moving conveyor. To improve system efficiency, a variable pick-up location approach directs the robot to pick up parts before they reach the end of conveyor at a fixed point. The trade-off between robot move cycle time and kinematic energy is balanced by an optimization model based on optimum control theory in minimizing both simultaneously. Simulation results of several numerical examples show that the variable pick-up location approach consistently outperforms the conventional fixed pick-up method. Both cycle time and kinematic energy are reduced. The research results may be used for robot system planning by providing guidelines to detailed trajectory planning. Future research can include applications to the control of other robotic systems, such as manufacturing cells.     

Numerical and experimental studies of the riveting process

As one of important mechanical joining methods, rivet joints are widely used in buildings, bridges, aircrafts and automotives and in many other fields. Many variables have influences on the response of the rivet joints, such as the geometry of the joints, the material parameters of the parts, the clearance of the assembly, etc. In this paper, a finite element numerical model is developed for the analysis and optimization of the riveting process. Our approach is three-dimensional in order to be able to model non axisymmetric situations of riveting and testing of the joint strength. Four different sizes of solid rivets are considered for simulation and experimental study of the process. The comparison of the results between the numerical simulations and the experiments allows us to validate our approach.     

Multi-actor perspectives on human robotic collaboration implementation in the heavy automotive manufacturing industry - A Swedish case study

Implementing an industrial collaborative robot for Human-Robot Collaboration (HRC) in the automotive manufacturing industry is an emerging technology-driven solution aiming to increase production efficiency and reduce the human operator's ergonomic load. Successful implementation of innovative technology depends on technical feasibility and on the acceptance by the affected actors. Many studies exist that focus on the technical aspects of HRC, however, research that focuses on understanding the multi-actor concerns of HRC adoption is rare. In an effort to support the successful adoption of industrial collaborative robots, this study aims to understand the concerns of the various actors who work at the operational and management levels influencing future HRC adoption in the heavy automotive manufacturing industry.A literature review was conducted to understand the HRC implementation challenges and the methods used to investigate multi-actor involvement in advance of, and during, the implementation stage. After reviewing existing studies, the actor analysis method was selected to present the actors' perceptions using the action, factor, and goal (AFG) list to understand different actors’ opinions of HRC adoption, using a Swedish heavy vehicle manufacturing company case study.The case study results showed that the actors from the same organization had different concerns but mostly positive expectations for future HRC adoption. The actors’ perception map shows the details pertaining to Actions, Concerns, and Goals as well as the logical flow between these elements in regards to HRC future adoption. The involvement of different actor groups prior to new solution implementation contributes to a holistic view of potential implementation influences and challenges in the organization. Actor analysis can provide a set of analysis processes that comply with multi-actor perceptions to understand future adoption challenges from different perspectives. In the next step, safety-related issues and under-development standardization are the key challenges of HRC implementation.     

Rotation friction pressing riveting of AZ31 magnesium alloy sheet

A kind of joining method for magnesium alloys, rotation friction pressing riveting (RFPR), is proposed in this paper. In RFPR operation, a rivet with a plug rotating at high speed is brought to contact with the riveted sheets, generating frictional heat between the rivet and riveted sheets, which softens the sheet materials and enables the rivet to be drilled into the sheets under reduced force. When fully inserted, the rivet is stopped rotating, and the plug is immediately pressed into the shank of the rivet by a punch. The expansive deformation of the rivet shank occurs under the action of the plug, thereby forming a mechanical interlock between the rivet and the sheets to fasten the sheets together. The studies show that RFPR of AZ31 magnesium alloy sheet can be carried out at ambient temperature, and provides the joints with superior shear strength and fatigue property when compared with self-piercing riveting (SPR). The effects of the operating parameters of RFPR process on the quality of the joints were investigated in the study. The results shows that while the rivet rotation speed little affects the shear strength of RFPR joints, the punch pressure has a significant influence on the mechanical properties of the RFPR joints. A numerical analysis was also performed to understand the effect of the punch pressure on the interlock between the rivet and the sheets, and the stress and strain distribution inside the sheet materials around the rivet. The results show that the interlock increased with the punch pressure and there is residual compressive stress inside the sheet materials, which seems to explain the good fatigue property of RFPR joints observed.     

Fatigue life prediction model for riveted lap joints

Applicability of currently available approaches to predict the fatigue life of riveted joints in aircraft structures is limited to cases when the actual joint, for which the predictions are made, and the reference joint, for which the prediction model has been tuned, differ only in the geometry. It is required that the riveting process should be similar for the actual and reference case, but the similarity criterion cannot be formulated in a precise way. In the prediction model developed by the authors and presented in this paper the influence of riveting on the fatigue life of a joint is unambiguously characterized by measurable quantities, namely rivet hole expansion and the load transfer distribution. Hence, the similarity of the riveting processes for the reference and actual joint is no longer required, which considerably extends the transferability of the reference results. A validation of the model is performed by comparing fatigue lives computed and observed in over 80 fatigue tests on aluminium alloy, lap joint specimens with three rivet rows, typical for aircraft fuselage skin connections in the longitudinal direction. Various combinations of production variables, such as sheet material and thickness, the squeeze stress and rivet type, were involved. A significant improvement in the present model prediction accuracy compared to a model which disregards the effect of riveting has been noted. Specifically, underestimates or overestimates of the fatigue life observed for the latter model in the case when hole expansion of the actual joint is larger or smaller respectively than for the reference joint are avoided with the present approach.     

The driven rivet head dimensions as an indication of the fatigue performance of aircraft lap joints

Solid aluminium alloy rivets are used in joints of aircraft structures. Riveting implies a squeezing process of the rivet stem with large plastic deformations to form the driven rivet head. The dimensions of the driven rivet head (diameter D and height H) depend on the applied squeeze load F_sq. High squeeze loads are beneficial for the fatigue properties of riveted joints. The present investigation is focused on the relation between F_sq and the rivet head dimensions during controlled squeezing. Measurements of D or H will then allow estimation of the applied squeeze load for quality control of the riveting process with respect to the fatigue properties of the joint. Extensive test series were carried out with five rivet materials, three rivet diameters and two sheet materials (2024-T3 and Glare). An equation was derived for F_sq(D) and F_sq(H) based on assuming a zero volume change of the rivet during plastic deformation. The two material constants in the equations were empirically determined for the rivet materials. A satisfactory correlation was obtained.     

Optimized work control process to improve safety and reliability in a risk-based and deregulated environment

This paper provides an overview of strategic models to assist power generating plants to improve their work control processes. These models include mechanisms to continually keep the process up to date. Included in the work control process are elements for system cost/performance analysis, life-cycle maintenance planning, on-line scheduling and look-ahead techniques, and schedule implementation to conduct work on the asset. The paper also discusses how risk management associated with work control issues that effect the safety and reliability, as well as O and M costs, is integrated into this strategy.The work control process is a pervasive and critical element in the successful implementation of operations and work management programs. While providing a method to implement maintenance activities in a cost-effective manner, the work control process improves plant safety and system reliability.     

Development of an adaptive robotic welding system†

The paper is concerned with the development of an adaptive robotic arc welding system for the production of high integrity, full penetration butt welds from one side. Development of statistical process models and computer simulation of an adaptive strategy incorporating the models is discussed. Practical implementation of the strategy in a robot welding system, utilizing a commercial sensor and standard industrial robot is described.     

A framework for CAD-based geometric reasoning for robot assembly language†

For automatic robot programming, world modelling of the robot's environment is one of the most important phases of the task planning. World modelling requires that the robot know the environment in which it operates, including the spatial configuration of all objects in the task environment. In robotic assembly planning at the task level, representation of these objects requires symbolic feature and shape identification of the objects to be assembled by the robot. In this paper, we present a framework for reasoning about objects based on their shapes and features and the representation of such objects for robotic assembly planning when the modelling is done on a CAD system. We show the importance of AI languages in the communication of constructive solid geometry (CSG) based information from modellers. Finally, we present the schematic for a formalism, based on Prolog, for expressing object properties and assembly situations.     

Failure of aluminium self-piercing rivets: An experimental and numerical study

The present paper investigates the fracture mechanisms of AA7278-T6 aluminium self-piercing rivets under compression during the riveting process. First, a microstructure investigation was conducted to disclose the grain structure and the particle distribution of the extruded aluminium alloy. Transmission electron micrographs revealed precipitate free zones along grain boundaries. Uniaxial tensile tests in three different directions with respect to the extrusion direction revealed anisotropy of the alloy in strength and ductility and a change in fracture mode with tensile direction. The behaviour of the alloy under compression was studied experimentally using upsetting tests and self-piercing riveting tests. Micrographs of the deformed specimens provided insight into the influence of the microstructure on the deformation and fracture of the alloy under compression. Second, numerical analyses were carried out using a 2-D axisymmetric model in LS–DYNA in an attempt to investigate the role of different physical variables on the final failure of the rivet. The numerical results revealed that constituent particles, precipitate free zones, and friction between the rivet and plates are important for strain localisation and fracture in the rivet.     

Automated robotic programming for products with changes

To achieve mass customization, a manufacturing system needs to accomplish a variety of manufacturing processes of different products for the same product family. One of the critical issues is to develop an automatic program for process planning, so that the required product variations can be tackled appropriately in the same manufacturing system. In the current paper, robotic motion planning for automatic coating process is investigated, the state of the art in this area is reviewed and a new methodology is proposed for path generation, trajectory planning and integrated system simulation.     

Review of robotic end-effector with force control

With the intelligent development of manufacturing industry, industrial robots are more and more widely used for continuous contact operation, such as polishing, sanding, burring and assembling. End-effector with force control is a critical component of robots used for hybrid force/position control and continuous contact operation, which has an important effect on the operation quality and application field extension. In view of the above situation, it is of great importance for developing new robotic end-effector of high-performance to investigate the state, analyze the characteristics and key technology, and forecast the trends of development. The background of end-effector with force control was introduced firstly, and then the composition & classification, working mode and operation principle was presented. The key technologies of end-effector with force control were refined, including the comprehensive theory and optimization technique of parallel manipulator configuration, design technique of constant force compensatory actuator, technique of compensation of mass force, technique of flexible collision and technique of decoupling control. Furthermore, the mechanical, pneumatic, electrically driven end-effector with force control of single-DOF and multi-DOF was detailed summarized, as well as the advantages and disadvantages. The technology trends of the end-effector with force control include high precision and frequency response, electric driving, multi-DOF flexibility, high load capacity, integration and intellectualization. Analysis shows that the mechanical or pneumatic end-effector with force control is widely used nowadays, which has the disadvantages of large lagging, low control precision and response and can only realize constant force control of single-DOF. As a result, research on intelligent and electrically driven robotic end-effector with force control of high precision, response and multi-DOF will play an important role for the improvement of force control precision, surface adaptability, quality and efficiency of processing & assembly, and effectively promote the intelligent operation level of industrial robots.     

Feature-driven,process-based approach to the integration of CAD /CAM in wireframe models

This paper presents a structure for an integrated CAD/CAM system in wireframe models than can be simultaneously used for product design and manufacture of prismatic components. A feature-driven, process-based design methodology, which derives its basis from traditional geometry-based design, feature-based design, deterministic and expert heuristic manufacturing knowledge, is proposed. This methodology provides an integrated modelling environment for automation of downstream manufacturing applications such as process planning and NC code generation. Representation of features in the design database is not limited to geometry alone but includes material, tooling and machine specifications and is based on a process-to-geometry mapping. Research shows that informational completeness of a CAD database depends on application; and for manufacturing tasks, the vocabulary of the process describing the means of making a part should be mapped directly to the feature-based geometry. This effort answers key issues in integrating CAD and CAM in the most widely used wireframe modelling systems.     

Prototype models for two-dimensional layout design of robot systems

This paper provides a structure for analysis and design of layouts for robotic systems. Unique features are identified and classified; prototype models are formulated to clarify specific design issues. These models formalize the existing qualitative literature dealing with robot systems, augment other quantitative approaches by demonstrating application of mathematical programming, and suggest topics of research to develop efficient solution algorithms.