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.

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.

Complete Dynamic Modelling of Flexible Joint Robots

2015 ◽  
Author(s):  
Yu Zhao ◽  
Cong Wang ◽  
Xiaowen Yu ◽  
Masayoshi Tomizuka
Keyword(s):  
Dynamic Model ◽  
Dynamic Modelling ◽  
High Accuracy ◽  
Industrial Robots ◽  
Motion Controller ◽  
Flexible Joint ◽  
Interaction Terms ◽  
Flexible Joint Robots ◽  
Joint Elasticity ◽  
Precision Motion

Joint flexibility is common in industrial robots that have geared joints. In order to design a precision motion controller that compensates the effects of joint elasticity, an accurate dynamic model of flexible joint robots is required. The models that are commonly used ignore the gyroscopic interactions between the motors and links. In order to evaluate the influence of the ignored gyroscopic interaction, a complete dynamic model for flexible joint robots is derived in this paper. It is shown that when to realize high accuracy for high velocity trajectory tracking, the motor inertia is non-negligible compared to link inertia, and that the neglected interaction terms must be taken into account.

Design of global tracking controllers for flexible-joint robots

1993 ◽  
Vol 10 (6) ◽  
pp. 835-846 ◽  
Author(s):  
S. Nicosia ◽  
P. Tomei
Keyword(s):  
Flexible Joint ◽  
Global Tracking ◽  
Flexible Joint Robots ◽  
Tracking Controllers

scholarly journals Extended and Unscented Kalman Filtering Applied to a Flexible-Joint Robot with Jerk Estimation

2010 ◽  
Vol 2010 ◽  
pp. 1-14 ◽  
Author(s):  
Mohammad Ali Badamchizadeh ◽  
Iraj Hassanzadeh ◽  
Mehdi Abedinpour Fallah
Keyword(s):  
Initial Conditions ◽  
Covariance Matrices ◽  
Flexible Joints ◽  
Velocity Measurements ◽  
Lagrange Equations ◽  
Robust Nonlinear Control ◽  
Flexible Joint ◽  
Flexible Joint Robots ◽  
Simulation Results

Robust nonlinear control of flexible-joint robots requires that the link position, velocity, acceleration, and jerk be available. In this paper, we derive the dynamic model of a nonlinear flexible-joint robot based on the governing Euler-Lagrange equations and propose extended and unscented Kalman filters to estimate the link acceleration and jerk from position and velocity measurements. Both observers are designed for the same model and run with the same covariance matrices under the same initial conditions. A five-bar linkage robot with revolute flexible joints is considered as a case study. Simulation results verify the effectiveness of the proposed filters.

Sign in / Sign up

Export Citation Format

Share Document