Modeling of a Mobile Spatial Cable Robot With Flexible Cables and Investigating the Effect of Its Nonlinear Vibrations on the System Dynamics

In this paper the modeling of a novel moving cable robot is conducted considering the vibration of the cables in its nonlinear format. The robot has 6 DOFs while the controlling input number is 12. Considering the fact that the elasticity of the cables is coupled with the dynamic model of the system, their vibration effects on the robot performance and accuracy. The target of this paper is to model the robot considering the cables’ elasticity and study its effect on the robot performance. This study can be considered in designing the controller of tower cranes and decrease the swing of the cables and increasing their stability. In order to cover the mentioned aim, the continuous vibration of the cables are modeled as a nonlinear system and it is added to the moving platform dynamics. Moreover the differences between the nonlinear modeling of the cables’ vibration and estimating them as a linear system is studied and their related results are compared and analyzed. The correctness of modeling is shown by comparing the results with previous research and the superiority of modeling the cables’ vibration in its nonlinear format is verified by the aid of a series of simulation scenarios in MATLAB. Moreover, by conducting some experimental test on the manufactured moving cable robot of IUST, it is illustrated that, modeling the cables in these robots as a nonlinear system results in more accurate results. It is shown that not only considering the cables’ vibration is significant in analyzing the robot dynamic, but also it is shown that promoting the mentioned model into nonlinear one increase the accuracy of the robot modeling which sequentially can provide a stronger controller for stabilizing and controlling the end-effector within a predefined trajectory.

THE SIMPLIFIED ANALYSIS OF THE ASYMMETRIC SINGLE-PYLON SUSPENSION BRIDGE WITH RIGID CABLES

Suspension bridges are characterized by exceptional architectural expressions and excellent technical and economic properties. However, despite all advantages, suspension bridges have a few negative features. Suspension bridges with flexible cables share excessive deformation caused by the displacement of kinematic origin. In order to increase the stiffness of suspension bridges, an innovative structural solution refers to rigid cables used instead of the flexible ones. The paper describes a methodology for calculating an asymmetric single-pylon suspension bridge with rigid cables considering installation features. Also, the article presents the numerical simulation of the bridge and determines the accuracy of the proposed methodology.

Overconstrained Cable-Driven Parallel Manipulators Statics Analysis based on Simplified Static Cable Model

In recent years, cable-driven parallel manipulators (CDPM) become more and more interesting topics of robot researchers due to its outstanding advantages. Unlike traditional parallel robots, CDPMs use many flexible cables in order to connect the robot fixed frame and the moving platform instead of using conventional rigid links. Since cables used in CDPM is very light compared to rigid links, its workspace can be very large. Besides, CDPMs are often enhanced load capacity by adding redundant actuators. They also help to widen the singularity-free workspace of CDPM. On the other hand, the redundant actuators produce the underdetermined system i.e. the system has non-unique solutions. Moreover, the elasticity and bendability of flexible cable caused by self-weight and external forces act on it, resulting in the kinematic problem of CDPMs are no longer related to the geometric problem. Therefore, the system of CDPM become non-linear when the deformation of cable is considered. In this study, we introduce the simplified static cable model and use it to linearize the static model of redundantly actuated CDPM. The algorithm to solve the force distribution problem is proposed in Sect. 4. The static-workspace and the performance of those are analyzed in a numerical test.

Coordinated Control of Flexible Cables With Human-Like Dual Manipulators

Due to the flexibility and high degrees-of-freedom of flexible cables, their dynamic modeling and precise control are challenging. In this paper, the dynamic modeling and control of flexible cables with human-like dual manipulators are studied to deploy them on a plane and form the desired shapes automatically. First, we establish a dynamic model of flexible cables based on a discrete elastic rod model. This model can simulate their stretching, bending, and twisting deformations. Then, we consider the collisions, contacts, and frictions between the flexible cables and the plane, add kinematic constraints to the model, and finally obtain an implementable dynamic solution of the model. Next, we propose dynamic control schemes including parallel dual-arm control and coordinated dual-arm control to deploy the flexible cables on a plane and form the desired shapes for dual-arm controls. Finally, experimental and simulation studies are carried out to illustrate the effectiveness of the dynamic model and the validity of the control schemes. The results show that the model can successfully demonstrate the deformations of flexible cables, and the proposed control schemes can successfully manipulate flexible cables in different tasks.

Empirical Quasi-Static and Inverse Kinematics of Cable-Driven Parallel Manipulators Including Presence of Sagging

Cable-driven parallel manipulators (CDPMs) have been of great interest to researchers in recent years because they have many advantages compared to the traditional parallel robot. However, in many studies they lack the cable’s elasticity that leads to flexible cables just being considered as extendable rigid links. Furthermore, an external force acts on the extremities of cable and the self-weight is relevant to the length of it. Experimentally, a small change in length produces a huge change in tension act on the entire cable. By this property, the adjusting length of cable is often added to the traditional inverse kinematic solution in order to reduce the tension force exerted on the cable. This means that the load on the actuator is also reduced. Because of the relationship between tension that acts on the cable and its length, the kinematic problem itself does not make sense without concerning the static or dynamic problems. There is often interest in planning forces for actuators and the length of cables based on a given quasi-static trajectory of the moving platform. The mentioned problem is combined with the quasi-static problem with the inverse kinematic problem of CDPM. In this study, we introduce a novel procedure to produce the quasi-static model and inverse kinematic model for CDPM with the presence of sagging by using both an analytic approach and empirical approach. The produced model is time-efficient and is generalized for spatial CDPM. To illustrate the performance of the proposed model, the numerical and experimental approaches are employed to determine particular solutions in the feasible solutions set produced by our model in order to control the two redundant actuators’ CDPM tracking on a certain desired trajectory. Its results are clearly described in the experimental section.

Friction and Wear Mechanism Analysis of Polymer Flexible Cable Using a High Natural Frequency Piezoelectric Sensor

The friction and wear of flexible cables are the main factors that cause electrical breakdown and insulation aging, and they greatly reduce the reliability and safety of robots. In order to enhance the reliability and safety of the robot, it is of great necessity to investigate the friction and wear mechanisms of the flexible cable. In this research, the friction and wear mechanisms have been discussed. The effects of relative speed, ambient temperature, and positive pressure on the flexible cables are considered by an orthogonal frictional movement. The cable friction force has been measured by a piezoelectric sensor with high natural frequency characteristics. The relations among friction and different factors affecting friction have also been discussed. The results show that the relative speed and the ambient temperature are the main factors affecting the friction and wear of the cable; the main form of flexible cable wear is mechanical-force chemical friction and wear. Those discoveries will greatly deepen the understanding of the friction and wear mechanisms of flexible cables, and will be beneficial to robot cable-reliability design.

ASSESSMENT OF SEISMIC PERFORMANCE OF SUBMERGED FLOATING TUNNEL UNDER MULTI-SUPPORT SEISMIC EXCITATIONS

Submerged floating tunnel (SFT) is an innovative structural solution for the transportation infrastructure through sea straits, fjords, and inland waters and is an economical alternative to the long-span cable-supported bridge, immersed tunnel, or underground tunnel. An SFT is a massive cylindrical structure that floats at a certain depth below the water surface and subjected to extreme environmental conditions, such as waves, tsunamis and earthquakes. The seismic assessment of SFT supported by mooring cables, under multi-support seismic excitations needs to be evaluated in more detail. The time domain dynamic problem of SFT moored by inclined mooring cables/anchors is formulated and the geometric non-linear dynamic analysis of SFT subjected to hydrodynamic and seismic excitations is performed in this paper. The prototype of SFT to be constructed in Qindao Lake of China is analysed under multi-support seismic excitations. It was found that due to the fluid environment and flexible cables the effective seismic forces are dissipated well and SFT is stable under the spectrum compatible ground motions. However, the lateral component of seismic excitations produce larger responses compared to longitudinal one and may be critical for other case studies.