Modeling and simulation for fatigue life analysis of robots with flexible joints under percussive impact forces

Nie, Song-Liang; Li, Yuwen; Guo, Shuai; Song, Tao; Xi, Fengfeng

doi:10.1016/j.rcim.2015.04.001

Cited by 16 publications

(9 citation statements)

References 17 publications

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“…Note that the force in (26) can be in different directions relative to the inertial frame for different parts with transformation (21). The robot is used for the assembly in a cuboid-shaped operation workspace as drawn in Figure 10.…”

Section: Rivet Gunmentioning

confidence: 99%

“…Since the natural frequencies of an industrial robot strongly depend on its configuration [15] and its stiffness varies significantly in different directions [16,17], the vibration characteristics depend on the robot configuration and the direction of external force. It has been found that structural vibrations of the robot can cause tool misalignment [18], damage the surface quality [19], and reduce the fatigue lives of the tool and the robot [20,21]. Furthermore, the system can become instable due to the interaction between the robot vibrations and the process forces [22,23] and the stability condition can be affected by some process parameters such as feed rate and spindle speed [24,25].…”

Section: Introductionmentioning

confidence: 99%

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New Indices for Evaluating Vibration Characteristics of Flexible-Joint Robots

Zhang

2020

Applied Sciences

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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.

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Section: Rivet Gunmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New Indices for Evaluating Vibration Characteristics of Flexible-Joint Robots

Zhang

2020

Applied Sciences

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“…The resulting forced vibrations of the robot structure lead to much more complicated dynamics behaviors than many other robotic tasks such as pick-and-place and welding where static or very low contact forces act on the robot. First, the forced vibrations of the robot can seriously affect the process, for example, by decreasing the efficiency [17], damaging the surface quality [18], causing tool misalignment [19], and reducing the fatigue lives of the tool and the robot to a great extent [20,21]. Second, not only static but also inertial forces are important for these applications.…”

Section: Introductionmentioning

confidence: 99%

Workpiece Pose Optimization for Milling with Flexible-Joint Robots to Improve Quasi-Static Performance

Qin

Xiong

2019

Applied Sciences

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Although industrial robots are widely used in production automation, their applications in machining have been limited because of the structural vibrations induced by periodic cutting forces. Since the dynamic characteristics of an industrial robot depends on its configuration, the responses of the robot structure to the cutting forces are affected by how the workpiece is placed within the workspace of the robot. This paper presents a method for workpiece pose optimization for a robotic milling system to improve the quasi-static performance during machining. Since the milling forces are time-varying due to the characteristics of the multi-tooth and discontinuity of milling, these forces can excite vibrations inside the robot structure. To address this issue, a structural dynamics model is established for industrial robots, considering their joint flexibility, and a milling force formulation is incorporated into the robot dynamics model to investigate the forced vibrations of the flexible joints. Then, the quasi-static performance of the robotic machining system is evaluated by the vibration-induced offset of the cutter tool that is mounted on the end-effector. Finally, an optimization approach is given for the workpiece pose to minimize the cutter tool offset under the periodic milling force. A numerical simulation demonstrates that the optimal workpiece pose can significantly reduce the overall tool offset during machining and can lower the variation of the tool offset along the milling path.

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“…The lifespan of a robot varies greatly with respect to the level and frequency of loading. Nie et al 15 discussed and modelled the fatigue life of robots with flexible joints subjected to percussive impact forces. Zaheer and Islam 16 evaluated the fatigue reliability of a universal joint in an articulated offshore mechanism.…”

Section: Introductionmentioning

confidence: 99%

Modelling and verification of fatigue damage for compliant mechanisms

Liu¹,

Ran³

et al. 2018

Robotica

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SUMMARYThis paper presents a model-based approach for the first time to identify the crack location for the hinge-based planar RRR compliant mechanism, a parallel micro-motion stage driven by piezoelectric (PZT) actuators. However, cracks more likely occur on a flexure hinge because it usually undergoes a periodic deformation in service, which eventually compromises mechanism's performance, positioning accuracy for instance. In this work, the pseudo-rigid-body method is used to develop kinematic and dynamic models of the RRR mechanism both in healthy and damaged conditions, where the crack is considered in terms of the rotational compliance of a flexible hinge. The crack location is determined by measuring PZT elongations, which represents the driving toque deviation because of the crack presence. Numerical simulation is conducted to verify the proposed approach, and the results show good match of the identified crack location with the assumed location. Finally, experiments on the RRR mechanism with a prefabricated crack is performed to further validate the proposed models; the experimental results yield a good consistence.

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Modeling and simulation for fatigue life analysis of robots with flexible joints under percussive impact forces

Cited by 16 publications

References 17 publications

New Indices for Evaluating Vibration Characteristics of Flexible-Joint Robots

New Indices for Evaluating Vibration Characteristics of Flexible-Joint Robots

Workpiece Pose Optimization for Milling with Flexible-Joint Robots to Improve Quasi-Static Performance

Modelling and verification of fatigue damage for compliant mechanisms

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