An approximation method for stiffness calculation of robotic arms with hybrid open- and closed-loop kinematic chains

Abstract

Industrial robots have advantages of large workspace, compact structure, and good flexibility, but the stiffness of the robot is relatively weak due to the compliance of reducers and its series structure. In this article, a five-degree-of-freedom robot with non-backlash driving is presented. A parallelogram structure with diagonal driven is used for robotic arms which is useful to improve the overall stiffness of the robot. First, the detailed structure of the robot is introduced, and the kinematic characteristics of the robot are analyzed. Second, a stiffness approximation method is proposed to evaluate the stiffness of the robot in the global workspace. The overall deformations under certain external loads which are composed of deflection deformations and stretching deformations are calculated based on the strain energy method and the properties of the components. The effectiveness of the approximation method used for evaluating the stiffness of the robot which has hybrid open-and closed-loop kinematic chains is verified through the finite element analysis results and the experimental results. Finally, the stiffness evaluation results show that the stiffness of the proposed robot is better than that of the industrial robot, which makes it more suitable for most of the industrial applications, such as handling, palletizing, and drilling.

Joint stiffness identification of industrial serial robots using 3D digital image correlation techniques

“…where R is a 3 � 3 rotation matrix, and t is a 3 � 3 translation column matrix. 28 From equation (11), it can be inferred that determination of R and t is an issue of solving the overdetermined linear equations. The method of SVD (Singular Value Decomposition) based on least square criterion is used to calculate R and t, which fit the two sets of points best.…”

“…Sun and Fang proposed a stiffness approximation method to evaluate robot stiffness based on the strain energy method and the material properties of the robot structures. 11 Due to simplification and idealization, the identification results deviate far from the reality. The second method described by Abele et al 12 is to clamp all joints except for the one evaluated, which ensures that only one joint at a time is loaded.…”

Optimization of Installation Position for Complex Space Curve Weldments in Robotic Friction Stir Welding Based on Dynamic Dual Particle Swarm Optimization

“…The integration of general industrial robots with FSW equipment has become an inevitable trend in the development of FSW [6]. However, due to the high welding force in FSW and the limited end stiffness of serial industrial robots, stability during FSW decreases, leading to welding errors from excessive end displacement and reduced welding quality due to vibration [7][8][9]. These factors have become the main obstacles hindering the further development and widespread application of RFSW technology.…”

“…Traditional FSW equipment utilizing CNC machines typically features high stiffness, making the mechanical structure largely unaffected by fluctuations in welding force [26]. However, in RFSW systems employing serial industrial robots, excessive welding force fluctuations may lead to end vibrations, undermining welding stability and quality [8].…”

Adaptive Identification of Legged Robotic Kinematic Structure

“…Current works mostly focuses on identifying the manipulator stiffness of industrial robotic arms [13], [14], [15] which are much more rigid compared to legged robots. In addition, work has been done in identifying flexible joint stiffnesses on the Canadarm [16].…”