The paper presents issues associated with the experimental study of the vibration of a spot welding gun mounted on a robotic arm. The main aim of the study was to assess the vibration of the robot flange and the vibration of the mounted tool. Because of the tools’ large size and weight (up to 150 kg), manipulating it in a limited space is a challenge for programmers when defining trajectories. The article presents the results of inertial measurements of the KUKA KR120 R2500 industrial robot equipped with a pneumatic welding tool, paying particular attention to the vibrations occurring at the process points. Inertial tests on the robotic station were made using triaxial accelerometers and a high-speed camera. The methodology developed by the authors confirmed the existence of structural vibrations and allowed for defining the relationship between the robot’s motion parameters (notably velocity and acceleration) and the size of the vibrations present. The paper presents selected test results for various parameters of robot motion (speeds from 2000 mm/s to 500 mm/s and acceleration ramps ranging from 100% to 25%). In the course of the study, a disturbance was noticed in the form of a reduction in the value of maximum acceleration. This could be attributed to the appearance of the structure’s natural vibrations. Their character is not constant, and they are damped.

/pdf/experimental-study-of-the-vibration-of-the-spot-welding-gun-2jlwsmyx.pdf

Experimental Study of the Vibration of the Spot Welding Gun at a Robotic Station

Nonlinear dynamic modelling and analysis of multiple thin plates connected by long hinges

Hinged booms are widely used in astrophysics missions; however, the trajectory and deployment velocity are difficult to control. This is because the booms are usually driven by springs, which limits their application in narrow spaces. And the torque calculation of the spring is difficult. Thus, this paper presents a dynamic analysis method for hinged boom based on the Udwadia-Kalaba Equation. The method avoids Lagrange multipliers and simplifies the calculation process. Using assumed mode method (AMM) and tree topology multi-body theory to derive dynamic equation of the hinged boom. Finally, according to the Udwadia-Kalaba Equation calculates the torque required by each hinge of the hinged boom and verifies the feasibility of this method by Adams.

Dynamic Analysis of the Hinged Boom Based on Udwadia-Kalaba Equation

Hinged booms are widely used in astrophysics missions; however, the trajectory and deployment velocity are difficult to control. This is because the booms are usually driven by springs, which limits their application in narrow spaces. And the torque calculation of the spring is difficult. Thus, this paper presents a dynamic analysis method for hinged boom based on the Udwadia-Kalaba Equation. The method avoids Lagrange multipliers and simplifies the calculation process. Using assumed mode method (AMM) and tree topology multi-body theory to derive dynamic equation of the hinged boom. Finally, according to the Udwadia-Kalaba Equation calculates the torque required by each hinge of the hinged boom and verifies the feasibility of this method by Adams. 

In recent years, industries have increasingly emphasized the need for high-speed, energy-efficient, and cost-effective solutions. As a result, there has been growing interest in developing flexible link manipulator robots to meet these requirements. However, reducing the weight of the manipulator leads to increased flexibility which, in turn, causes vibrations. This research paper introduces a novel approach for controlling the vibration and motion of a two-link flexible manipulator using reinforcement learning. The proposed system utilizes trust region policy optimization to train the manipulator’s end effector to reach a desired target position, while minimizing vibration and strain at the root of the link. To achieve the research objectives, a 3D model of the flexible-link manipulator is designed, and an optimal reward function is identified to guide the learning process. The results demonstrate that the proposed approach successfully suppresses vibration and strain when moving the end effector to the target position. Furthermore, the trained model is applied to a physical flexible manipulator for real-world control verification. However, it is observed that the performance of the trained model does not meet expectations, due to simulation-to-real challenges. These challenges may include unanticipated differences in dynamics, calibration issues, actuator limitations, or other factors that affect the performance and behavior of the system in the real world. Therefore, further investigations and improvements are recommended to bridge this gap and enhance the applicability of the proposed approach.

Vibration and Position Control of a Two-Link Flexible Manipulator Using Reinforcement Learning

In this paper, the effect of flexibility on the dynamics of a two-link planar manipulator having two revolute joints is investigated. For this purpose, a mathematical model validated through experiments is obtained for a Two-link planar manipulator having two revolute joints . The mathematical model takes into account the continuous change of Eigen value due to change of configuration of the manipulator. A general expression for the frequency equation for the vibrating links has been obtained which is found to be time-dependent. The effect of this time-dependency of Eigen values of links on Joint and Tip responses is included in the assumed modes method. In this paper, the types of boundary conditions to be used for the flexible links are also researched upon and it is proposed that first four modes of vibration should be used for exactly modelling the flexible links . 

Determination of modes of vibration for accurate modelling of the flexibility effects on dynamics of a two link flexible manipulator

In this paper, trajectory control of a planar articulated flexible manipulator having two links is achieved using the technique of independent modal space control. For this, the joint torques of the manipulator are expressed as functions of joint errors and joint error derivatives. The governing equations belong to the class of second-order differential equations whose coefficients vary with time. Application of independent modal space control theory on these equations yield a method for finding the control gains for a proportional-derivative controller. The controller thus developed is described as coupled-error dynamics controller. Simulation results show that the proposed controller gives output close to that of a computed-torque controller.

S. Singh

Papers

Determination of modes of vibration for accurate modelling of the flexibility effects on dynamics of a two link flexible manipulator

Independent Modal Space Control based Trajectory Control for an Articulated Planar Manipulator with Flexible Links