Riveting System Research Articles

Intelligent Robotic Electromagnetic Riveting Interference Connection Technology for Aircraft Assembly

Aiming at the problem that the existing automatic electromagnetic riveting equipment is difficult to adapt to the riveting of complex structures such as narrow space, an electromagnetic riveting interference connection technology based on intelligent robots is proposed. An industrial robot carrying an end-effector is used in electromagnetic riveting. First, the overall design of the electromagnetic riveting system with each integrated module is presented; Then the composition form of the electromagnetic riveting module and riveting operation principle is elaborated in detail, and the system process flow is designed; Finally, the test pieces are subjected to hole-making and interference bolt riveting tests, and the results show that the designed system can complete the electromagnetic riveting task, and the rivets and the riveted plates realize a better interference fit.

Design and Verification of Complex Intelligent Integrated Dual-robot Collaborative Drilling and Riveting System for Aircraft Assembly

A complex intelligent integrated dual-robot collaborative drilling and riveting aircraft assembly system is proposed in this paper to solve the application problem of automatic drilling and riveting in narrow spaces. Firstly, the structure of the system is described. Then, the multifunctional end effectors which include intelligent drilling and riveting units are designed. Finally, relevant experiments are designed to verify the application of the system for the automatic drilling and riveting of complex laminated materials in different aircraft. The results show that the system can well adapt to the application scenarios of aircraft automatic drilling and riveting.

A combined vertical accuracy compensation method for automatic drilling and riveting of aircraft panels with variable curvatures

PurposeAircraft structures are mainly connected by riveting joints, whose quality and mechanical performance are directly determined by vertical accuracy of riveting holes. This paper proposed a combined vertical accuracy compensation method for drilling and riveting of aircraft panels with great variable curvatures.Design/methodology/approachThe vertical accuracy compensation method combines online and offline compensation categories in a robot riveting and drilling system. The former category based on laser ranging is aimed to correct the vertical error between actual and theoretical riveting positions, and the latter based on model curvature is used to correct the vertical error caused by the approximate plane fitting in variable-curvature panels.FindingsThe vertical accuracy compensation method is applied in an automatic robot drilling and riveting system. The result reveals that the vertical accuracy error of drilling and riveting is within 0.4°, which meets the requirements of the vertical accuracy in aircraft assembly.Originality/valueThe proposed method is suitable for improving the vertical accuracy of drilling and riveting on panels or skins of aerospace products with great variable curvatures without introducing extra measuring sensors.

Deformation prediction and compensation of a dual-machine riveting system for aircraft assembly

Automatic riveting systems play a crucial role in the field of aircraft manufacturing. In the riveting process, the machine tool bears a large axial squeezing force, and the resulting deformation will inevitably affect the riveting quality. In this paper, a dual-machine riveting system is developed first, the kinematic chain model and the lower-numbered body of the system structure are constructed sequentially. Then, considering the interaction and coupling effect of the two machines in the actual riveting process, the relative stiffnesses of the dual machine in the resisting state are identified by loading tests. Based on the stiffness data at a combination of postures within the workspace, a Kriging prediction model is established to describe the relationship between stiffness and postures. According to the prediction results, the influence of rotational and translational axes on the spatial stiffness distribution of the riveting system is revealed. Finally, the online deformation compensation is realized by modifying the displacement of the feed axis on both sides. A riveting experiment is carried out, and the results demonstrate that the riveting quality is significantly improved after compensation.

The Kinematic Calibration of an Industrial Robot With an Improved Beetle Swarm Optimization Algorithm

The article proposes a kinematic calibration method based on an improved beetle swarm optimization algorithm for an industrial robot to finish drilling and riveting. Specifically, a preference random substitution method to improve the update strategy was presented, which comprises a new boundary-processing strategy that avoids stagnation states and local optimization traps by adopting a dynamic parameter adjustment strategy to increase the speed and stability of searches. The effectiveness of the proposed method was verified by simulations and calibration experiments involving a robot drilling and riveting system with an industrial robot KUKA KR500L340-2. In addition, comparisons were conducted with linear least-squares, particle swarm optimization, and beetle swarm optimization algorithms. According to the results of calibration simulations and experiments, the fitness function value of the proposed algorithm can decrease rapidly in the first 20 iterations, while the mean value of the end-effector position error is reduced from 2.95mm to 0.20mm by using the proposed algorithm. Compared with other three algorithms, the positioning accuracy is improved by more than 60%.

Study on the effects of transverse ultrasonic vibration on deformation mechanism and mechanical properties of riveted lap joints

In this paper, a new and special transverse ultrasonic vibration-assisted riveting (TUVR) system is developed to improve the plasticity and qualification of titanium alloy rivets. Comparing with conventional riveting (CR), the formed driven heads by TUVR are not only suffered from the riveting force and hole boundary constrain, but also the acoustic softening and dragging friction force. Consequently, to disclose the deformation mechanism and mechanical properties in driven head, a series of studies were carried out. First, the dimensions of driven head for different amplitudes and roughness were investigated. On this basis, the typical position microstructures in driven head of TUVR and CR were contrastively analyzed. Moreover, the interference sizes of laminates riveted lap joints under CR and TUVR were compared. Finally, the micro-hardness and pull-out strength in joints of two riveting processes were tested, and illustrating the mode and microstructure of failure. Results show that ultrasonic vibration can act as a new and effective auxiliary riveting method, which contributes to achieving plasticity improvement and higher mechanical properties of joints. Although the TUVR has significant effects on the deviation of the driven head, which can be restrained well with a reasonable amplitude and roughness. The grains deformation in typical positions of TUVR is much severer than CR, except in the lower shear band and difficult deformation area. Besides, the uniformity of interference sizes of riveted sample is well improved by TUVR. The experimental results show that the micro-hardness and yield load of TUVR riveted lap joints increase more than 10% and 4%, respectively.

Pose accuracy compensation of mobile industry robot with binocular vision measurement and deep belief network

It is very important to improve the absolute pose accuracy of the robot, in the automatic drilling and riveting system of mobile industrial robot. This paper presents a practical scheme to compensate for the pose accuracy of mobile industrial robot. Firstly, the binocular vision measurement of the robot pose was building, and the pose error samples were collected under the massive configuration of the robot. Secondly, the mapping model of the robot's theoretical pose and actual pose errors is established based on the deep belief network, and the pose error estimation is realized. Finally, the developed scheme has been verified on a mobile industrial robot KUKA KR500-3 of robot automatic drilling and riveting system. The proposed scheme took into account the position error and direction error of the robot into account, does not depend on the specific kinematics model of the robot, and without retrofitting with high-end encoder. The verification results showed that the maximum absolute position error and orientation error of the robot was reduced by 80.84 % from 1.524 mm to 0.292 mm and reduced by 57.29 % from 0.096 deg to 0.041 deg respectively, which can meet the requirements of the robotic automatic drilling and riveting system.

Hybrid Position/Force Control for Dual-Machine Drilling and Riveting System

The deformation of riveting machine caused by riveting force during rivet formed makes the riveting tool out of positioning, which leads to gapping underneath the rivet manufactured head and insufficient rivet drive head. This paper proposes a hybrid position/force riveting control method for the dual-machine drilling and riveting system to eliminate the negative effects of machine deformation. The cooperative work of two-side machine tool is realized by a hybrid position/force control strategy, which compensates for the force-induced deformation error without an accurate stiffness model of the riveting system. The position of pressing foot relative to the machine which represents the deformation of skin-side machine is obtained for the compensation to the displacement of skin-side actuator. Simultaneously, the advanced force control is adopted for the stringer-side actuator. The dynamics model of the stringer-side actuator in consideration of the machine deformation is established and identified. The disturbance observer (DOB) and feedforward controller are introduced as the model-based control algorithm to achieve the high-performance force control. Also, contrast experiments are conducted to validate the effectiveness of the proposed riveting control method. The results show that the rivet manufactured head can be seated in the countersink during the forming process and the gapping under the head is eliminated. The driven head height tolerance of ±0.1 mm is achieved by accurate force control.

Numerical and experimental investigation on the rivet head flushness in automatic countersunk riveting

Riveting is an important interference-fit joining technology, which has been widely applied in aircraft assembly and many manufacturing fields. The rivet head flushness is an import industrial standard for the quality evaluation of a riveted joint. It would influence the aerodynamic performance of aircraft if not carefully controlled. In this paper, a finite element model (FEM) of automatic countersunk riveting is established and the formation of rivet head flushness is studied by the simulation results. Then, based on the coordinated motion of the riveting bar and the anvil tool, several compensation strategies are proposed to reduce the rivet head flushness and ensure the riveting quality, in which the riveting bar and anvil tool feed with the same speed (RASS) strategy is considered as the most efficient one. Finally, riveting experiments are conducted on a dual-machine-based automatic drilling and riveting system. The experimental results indicate that the simulation result is accurate, and the RASS compensation strategy is applicable and effective. This paper studies the formation mechanism and compensation method of the rivet head flushness for the countersunk rivet and provides scientific guidance for the riveting process optimization in engineering applications.

New Indices for Evaluating Vibration Characteristics of Flexible-Joint Robots

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.

Squeezing force detection and signal processing for robot assisted pneumatic percussive riveting system

Abstract Researches in the literature treated the pneumatic percussive riveting as an open-loop process. Vibration signals of the percussive hammer and driven-head based dimensions cannot be used to real-time control each impacting of the pneumatic percussive riveting. The paper installs a force sensor on the bucking bar to collect the squeezing force signal in pneumatic percussive riveting. And a squeezing force based closed-loop process control method for robot-assisted pneumatic percussive riveting is proposed. After introducing the robot assisted pneumatic percussive riveting system, the squeezing force and the impacting frequency under different pneumatic pressure are investigated extensively with the constructed pneumatic percussive riveting platform. A squeezing force signal processing method based on time-frequency analysis is used to extract the characteristics of the percussive riveting such as the peak squeezing force, the impacting frequency and the number of impacts etc. Based on the peak squeezing force and the impacting frequency, the pneumatic percussive riveting process is divided into four stages in order to control the squeezing force of the robot riveting efficiently. A squeezing force based real-time feedback algorithm is proposed to control the squeezing force of each impacting by adjusting the pneumatic pressure and the feed force. The squeezing force based real time control method outlined in the paper is found to be effective and accurate. It can be used for robot-assisted pneumatic percussive riveting system, and closed-loop control of percussive riveting in sheet metal assembly.

Modeling and Optimization of Bidirectional Clamping Forces in Drilling of Stacked Aluminum Alloy Plates.

Interlayer burrs formation during drilling of stacked plates is a common problem in the field of aircraft assembly. Burrs elimination requires extra deburring operations which is time-consuming and costly. An effective way to inhibit interlayer burrs is to reduce the interlayer gap by preloading clamping force. In this paper, based on the theory of plates and shells, a mathematical model of interlayer gap with bidirectional clamping forces was established. The relationship between the upper and lower clamping forces was investigated when the interlayer gap reaches zero. The optimization of the bidirectional clamping forces was performed to reduce the degree and non-uniformity of the deflections of the stacked plates. Then, the finite element simulation was conducted to verify the mathematical model. Finally, drilling experiments were carried out on 2024-T3 aluminum alloy stacked plates based on the dual-machine-based automatic drilling and riveting system. The experimental results show that the optimized bidirectional clamping forces can significantly reduce the burr heights. The work in this paper enables us to understand the effect of bidirectional clamping forces on the interlayer gap and paves the way for the practical application.

Hybrid Visual Servoing for Rivet-in-hole Insertion Based on Super-twisting Sliding Mode Control

Aiming at solving the rivet-in-hole insertion problem of the complement riveting process, a novel hybrid visual servoing controller is proposed for an automatic drilling and riveting system, in which, combination of visual and laser sensor feedback is adopted to determine the relative pose errors of the rivet with respect to the hole. To compensate the system uncertainties, a super-twisting sliding mode controller (STSMC) is designed to provide continuous control inputs, and the end-effector can move to the desired pose by exponentially decreasing the feature errors. The proposed control scheme not only guarantees the stability of the control system but also provides a robust and quick rivet spot-positioning in the presence of manipulator errors and external disturbances of the riveting system. Finally, rivet-in-hole insertion experiments were conducted, the results show that accurate positioning can be achieved within a finite time (1~5s) which meets the demand of high-efficiency and flexibility in the riveting process since it can achieve global convergence from any initial camera pose as long as the hole is in the field-of-view (FOV) and the laser displacement sensors are in the working range at the beginning.

Elastic-plastic analysis and riveting energy control for dual-robot pneumatic riveting system

To ensure the riveting quality and avoid riveting defects such as overdriven head or underdriven head, elastic and plastic mechanical analysis of the riveting process has been studied and a riveting energy control method is proposed in this paper. According to the target size of the driven head, the material properties, and the interference, the total riveting energy is calculated. Then, the relation of riveting duration and riveting energy is established to realize the control of the riveting impact energy in practical engineering. Furthermore, plastic dynamic impact buckling of the rivet is also analyzed to get impact buckling critical speed. Due to the dual-robot posture adjustment and countersunk self-centering ability, the working axes of the riveting tools, rivet, and hole are found to be well coaxial. The analysis shows there is little phenomenon of rivet bending in the dual-robot pneumatic riveting system and the impact buckling critical speed is much higher than the piston impact speed. Finally, finite element model is built for riveting dynamic simulation and dual-robot pneumatic riveting cell for fuselage panel assembly is developed to obtain experimental results. The comparison shows the proposed method has a good performance. The research results enhance the knowledge of energy effect of dual-robot pneumatic riveting, and thus offer positive guidance for practical application in aircraft assembly.

Design of DOB-based riveting force controller for dual-machine horizontal drilling and riveting system

A dual-machine horizontal automatic drilling and riveting system for aircraft panel assembly is presented in this paper. Two cooperative machines are adopted, like a two-robot system, to achieve the unobstructed workspace, so it can be applied in an efficient assembly line. Different from the current deign wisdom to ensuring the riveting accuracy by increasing the machine stiffness, which detrimentally results in higher masses to be moved and sophisticated reinforcements being used, this paper proposes a disturbance observer (DOB) based design method of riveting force controller for adaptive riveting with high accuracy driven heads, reducing the dependence of automatic riveting on high stiffness of machine. This method simplifies the force-induced deformation error compensation problem to a force control problem, which has rarely been studied before in literature. The separate layout leads to weak machine stiffness in the whole workspace and the stiffness varies with machine pose greatly, which makes it difficult to establish an accurate force-induced deformation error compensation model. To make the riveting machine precisely generate the desired force under such stiffness-varying conditions, a robust control algorithm is designed: the disturbance observer is introduced to address the robust stability against model parameter variance caused by the change of system stiffness with pose, and the feedforward controller can achieve the high-bandwidth force control to ensure the riveting efficiency. The model identification experiments are carried out for different machine stiffness. Validation riveting experiments have been conducted to verify the proposed controller on the dual-machine riveting system. The results show that, compared with previous displacement control, the proposed force controller can ensure the consistency of driven heads through accurate force control.

Sensor-Based Control Using an Image Point and Distance Features for Rivet-in-Hole Insertion

This paper addresses the problem of stabilizing the machine at a pose specified by a reference image and four laser sensor readings. The system configuration combining monocular vision and laser pointers is applied for pose estimation of the end-effector as well as providing the control objective. Specific features are selected to reflect the pose of the end-effector in Cartesian space, and an adaptive controller is designed to implement the alignment between the end-effector and a stationary object for further assembly. The complete control scheme is assessed through simulations and experiments conducted on an automatic drilling and riveting system, the results demonstrate that the assembly task can be accomplished accurately and efficiently even with coarsely calibrated camera and laser pointers. Furthermore, decoupled results can be gained thanks to the selected features.

Hole position quick modification method for automatic drilling and riveting system considering workpiece pose deviation

Workpiece pose deviation is inevitable during automatic drilling and riveting in aircraft assembly, and it either leads to increased time cost or decreased position accuracy with the present methods. This study aims to propose a quick modification method to modify the coordinates of assembly holes based on online detection of the position of pre-assembly holes considering the effect of abnormal data caused by workpiece pose deviation. In the case of hole-making in the double curvature skin region of three pre-assembly holes, the space transformation matrix is determined using the unit quaternion method in accordance with the on-line detection of the hole position coordinates. In the case of more than three assembly holes with abnormal data, a new modification method using a random sampling consistency RANSAC algorithm is used to optimize the spatial transformation matrix and eliminate the abnormal data effectively. This method has been integrated into automatic drilling and riveting systems. Numerical simulation and experiment tests were conducted, and the result comparison showed that the method has obvious positive effect dealing with the abnormal data considering component pose deviation, which proves the effectiveness of the method.

End stiffness modeling for automatic horizontal dual-machine cooperative drilling and riveting system

Aircraft panel automatic drilling and riveting system is the key equipment to realize aircraft panel assembly with high efficiency and quality. In practical application, automatic drilling and riveting system should bear cyclic riveting force with large load, which means such systems must have enough stiffness to deal with this situation. The stiffness of each components in automatic drilling and riveting system reflects as the end stiffness finally; in the meanwhile, end stiffness and riveting ability of the system will be affected when the posture of the system changes. According to this situation, stiffness matrixes related to mechanics characteristic of motion axes, transmission parts, inner-side working head, and outer-side working head of automatic horizontal dual-machine cooperative drilling and riveting system are established, in which the Jacobi matrix method, point transformation matrix method, and finite element analysis are applied. Finally, the static end stiffness model is proposed based on multi-body small deflection theory. The end stiffness model has been validated through experimental measurement, and the stiffness relationship of dual-machine tool system was obtained, which applied important data for structure optimization and control system design.

Prediction and compensation of force-induced deformation for a dual-machine-based riveting system using FEM and neural network

Force-induced deformation of machine tools has a great influence on the workpiece dimension and surface quality. For the dual-machine-based riveting system, the great squeezing force during riveting process not only causes structural deformation of the machine tools but also leads to inaccurate positioning of the riveting bar and dimension deviation of riveted joints. Moreover, the force-induced deformation usually changes with the varying poses of the machine tools, which makes it more difficult to predict precisely. In this paper, an efficient prediction and compensation method of force-induced deformation is developed based on finite element modeling (FEM) and artificial neural network. Firstly, a series of finite element models at selected poses are established to obtain the deformation data. Then, a force-induced deformation prediction model is established through radial basis function neural network with adaptive genetic algorithm optimization (AGA-RBF). Furthermore, a basic strategy is proposed to compensate for the predicted error through the motion commands modification. Finally, a contrast experiment is carried out to verify the feasibility and efficiency of the proposed method.

Influence of the deformation of riveting-side working head on riveting quality

Automatic drilling and riveting system has been widely used in aircraft manufacture field to satisfy the increasing demands of assembly quality. During the automatic riveting process, the riveting-side working head is the key component to perform the action of pressing rivet and its deformation has a great impact on riveting quality. In this paper, firstly, a theoretical model is established to investigate the factors influencing the deformation of riveting-side working head according to its structure and working situation. Then, the FE models with different squeezing displacements and riveting angles are established to analyze the effort of deformation of the riveting-side working head on driven head dimension, interference, and deformation of riveted hole on panels. Lastly, experiments are performed to verify the simulation results. The results show that the deformation of the riveting-side working head has a significant impact on the final riveting quality, and it can be compensated by increasing the riveting displacement.