Dynamic and Oscillatory Motions of Cable-Driven Parallel Robots Based on a Nonlinear Cable Tension Model

In this paper, dynamic modeling of cable-driven parallel robots (CDPRs) is addressed where each cable length is subjected to variations during operation. It is focusing on an original formulation of cable tension, which reveals a softening behavior when strains become large. The dynamic modulus of cable elasticity is experimentally identified through dynamic mechanical analysis (DMA). Numerical investigations carried out on suspended CDPRs with different sizes show the effect of the proposed tension formulation on the dynamic response of the end-effector.

Download Full-text

Dynamic and Wrench-Feasible Workspace Analysis of a Cable-Driven Parallel Robot Considering a Nonlinear Cable Tension Model

Applied Sciences ◽

10.3390/app12010244 ◽

2021 ◽

Vol 12 (1) ◽

pp. 244

Author(s):

Vu N. D. Kieu ◽

Shyh-Chour Huang

Keyword(s):

Parallel Robot ◽

Mechanical Analysis ◽

Industrial Applications ◽

Parallel Robots ◽

Kinematic Equation ◽

Cable Tension ◽

End Effector ◽

Tension Distribution ◽

Workspace Analysis ◽

High Dynamics

Cable-driven parallel robots (CDPRs) have several advantages and have been widely used in many industrial fields, especially industrial applications that require high dynamics, high payload capacity, and a large workspace. In this study, a design model for a CDPR system was proposed, and kinematic and dynamic modeling of the system was performed. Experiments were carried out to identify the dynamic modulus of elastic cables based on the dynamic mechanical analysis (DMA) method. A modified kinematic equation considering cable nonlinear tension was developed to determine the optimal cable tension at each position of the end-effector, and the wrench-feasible workspace was analyzed at various motion accelerations. The simulation results show that the proposed CDPR system obtains a large workspace, and the overall workspace is satisfactory and unrestricted for moving ranges in directions limited by the X-axis and the Y-axis from −0.3 to 0.3 m and by the Z-axis from 0.1 to 0.7 m. The overall workspace was found to depend on the condition of acceleration as well as the moving ranges limited by the end-effector. With an increase in external acceleration, the cable tension distribution increased and reached a maximum in the case of 100 m/s2.

Download Full-text

Wrench-Feasible Workspace of Mobile Cable-Driven Parallel Robots

Journal of Mechanisms and Robotics ◽

10.1115/1.4045423 ◽

2020 ◽

Vol 12 (3) ◽

Cited By ~ 3

Author(s):

Tahir Rasheed ◽

Philip Long ◽

Stéphane Caro

Keyword(s):

Convex Hull ◽

Case Studies ◽

High Speed ◽

Parallel Robot ◽

Parallel Robots ◽

Static Equilibrium ◽

Equilibrium Conditions ◽

Cable Tension ◽

End Effector ◽

Novel Concept

Abstract Cable-driven parallel robots (CDPRs) hold numerous advantages over conventional parallel robots in terms of high speed and large workspace. Cable-driven parallel robots whose workspace can be further increased by the modification of their geometric architecture are known as reconfigurable cable-driven parallel robots. A novel concept of reconfigurable cable-driven parallel robots that consists of a classical cable-driven parallel robot mounted on multiple mobile bases is known as mobile CDPR. This paper proposes a methodology to trace the wrench-feasible workspace of mobile cable-driven parallel robots by determining its available wrench set. Contrary to classical cable-driven parallel robots, we show that the available wrench set of a mobile cable-driven parallel robot depends, not only on the cable tension limits but also on the static equilibrium conditions of the mobile bases. The available wrench set is constructed by two different approaches known as convex hull approach and hyperplane shifting method. Three case studies are carried out for the validation of the proposed methodology. The proposed approach is experimentally validated on a mobile cable-driven parallel robot with a point-mass end-effector and two mobile bases.

Download Full-text

New Sensor Device to Accurately Measure Cable Tension in Cable-Driven Parallel Robots

Sensors ◽

10.3390/s21113604 ◽

2021 ◽

Vol 21 (11) ◽

pp. 3604

Author(s):

Guillermo Rubio-Gómez ◽

Sergio Juárez-Pérez ◽

Antonio Gonzalez-Rodríguez ◽

David Rodríguez-Rosa ◽

Lis Corral-Gómez ◽

...

Keyword(s):

Parallel Robots ◽

Control Algorithms ◽

Cable Tension ◽

End Effector ◽

New Device ◽

Fixed Frame ◽

Serial Robots ◽

Sensor Device ◽

Wide Range ◽

Improved Accuracy

Cable-driven parallel robots are a special type of robot in which an end-effector is attached to a fixed frame by means of several cables. The position and orientation of the end-effector can be controlled by controlling the length of the cables. These robots present a wide range of advantages, and the control algorithms required have greater complexity than those in traditional serial robots. Measuring the cable tension is an important task in this type of robot as many control algorithms rely on this information. There are several well-known approaches to measure cable tension in cable robots, where a trade-off between complexity and accuracy is observed. This work presents a new device based on strain gauges to measure cable tension specially designed to be applied in cable-driven parallel robots. This device can be easily mounted on the cable near the fixed frame, allowing the cable length and orientation to change freely, while the measure is taken before the cable passes through the guiding pulleys for improved accuracy. The results obtained from the device show a strong repeatability and linearity of the measures

Download Full-text

Smallest Maximum Cable Tension Determination for Cable-Driven Parallel Robots

IEEE Transactions on Robotics ◽

10.1109/tro.2020.3043684 ◽

2021 ◽

pp. 1-20

Author(s):

Hussein Hussein ◽

Joao Cavalcanti Santos ◽

Jean-Baptiste Izard ◽

Marc Gouttefarde

Keyword(s):

Parallel Robots ◽

Cable Tension

Download Full-text

Simultaneous base and tool calibration for self-calibrated parallel robots

Robotica ◽

10.1017/s0263574702004101 ◽

2002 ◽

Vol 20 (4) ◽

pp. 367-374 ◽

Cited By ~ 16

Author(s):

Guilin Yang ◽

I-Ming Chen ◽

Song Huat Yeo ◽

Wee Kiat Lim

Keyword(s):

Parallel Robot ◽

Parallel Robots ◽

Sufficient Accuracy ◽

Least Square ◽

Mobile Platform ◽

Calibration Model ◽

End Effector ◽

The World ◽

Kinematic Transformation ◽

Kinematic Errors

In this paper, we focus on the base and tool calibration of a self-calibrated parallel robot. After the self-calibration of a parellel robot by using the built-in sensors in the passive joints, its kinematic transformation from the robot base to the mobile platform frame can be computed with sufficient accuracy. The base and tool calibration, hence, is to identify the kinematic errors in the fixed transformations from the world frame to the robot base frame and from the mobile platform frame to the tool (end-effector) frame in order to improve the absolute positioning accuracy of the robot. Using the mathematical tools from group theory and differential geometry, a simultaneous base and tool calibration model is formulated. Since the kinematic errors in a kinematic transformation can be represented by a twist, i.e. an element of se(3), the resultant calibration model is simple, explicit and geometrically meaningful. A least-square algorithm is employed to iteratively identify the error parameters. The simulation example shows that all the preset kinematic errors can be fully recovered within three to four iterations.

Download Full-text

Modal Kinematic Analysis of a Parallel Kinematic Robot with Low-Stiffness Transmissions

Robotics ◽

10.3390/robotics10040132 ◽

2021 ◽

Vol 10 (4) ◽

pp. 132

Author(s):

Paolo Righettini ◽

Roberto Strada ◽

Filippo Cortinovis

Keyword(s):

High Speed ◽

Parallel Robots ◽

Maximum Speed ◽

Kinematic Structure ◽

End Effector ◽

New Approach ◽

Working Space ◽

Modes Of Vibration ◽

Parallel Kinematic ◽

Actuated Joints

Several industrial robotic applications that require high speed or high stiffness-to-inertia ratios use parallel kinematic robots. In the cases where the critical point of the application is the speed, the compliance of the main mechanical transmissions placed between the actuators and the parallel kinematic structure can be significantly higher than that of the parallel kinematic structure itself. This paper deals with this kind of system, where the overall performance depends on the maximum speed and on the dynamic behavior. Our research proposes a new approach for the investigation of the modes of vibration of the end-effector placed on the robot structure for a system where the transmission’s compliance is not negligible in relation to the flexibility of the parallel kinematic structure. The approach considers the kinematic and dynamic coupling due to the parallel kinematic structure, the system’s mass distribution and the transmission’s stiffness. In the literature, several papers deal with the dynamic vibration analysis of parallel robots. Some of these also consider the transmissions between the motors and the actuated joints. However, these works mainly deal with the modal analysis of the robot’s mechanical structure or the displacement analysis of the transmission’s effects on the positioning error of the end-effector. The discussion of the proposed approach takes into consideration a linear delta robot. The results show that the system’s natural frequencies and the directions of the end-effector’s modal displacements strongly depend on its position in the working space.

Download Full-text

DYNAMIC RESPONSE EVALUATION OF A FRAMED TYPE TURBO-GENERATOR FOUNDATION INCORPORATING DYNAMIC MODULUS AND OPERATING SPEED VARIATIONS

International Journal of Structural Stability and Dynamics ◽

10.1142/s0219455404001288 ◽

2004 ◽

Vol 04 (03) ◽

pp. 379-402 ◽

Cited By ~ 3

Author(s):

N. LAKSHMANAN ◽

K. MUTHUMANI ◽

N. GOPALAKRISHNAN ◽

K. SATHISH KUMAR

Keyword(s):

Dynamic Response ◽

Dynamic Modulus ◽

Dynamic Performance ◽

Normal Operation ◽

Synthesis Process ◽

Operating Speed ◽

Turbine Generators ◽

Analysis Methodology ◽

Modal Synthesis ◽

Turbo Generator

Framed type foundation structures supporting turbo-generator machinery in a power plant have stringent vibration limits to ensure proper functioning of turbine generators without any breakdown. Current dynamic analysis methodology for such dynamically sensitive structures involves modal synthesis considering a single value of operating speed for the machinery and a uniform dynamic modulus for the frame material, which cannot be realized in site conditions. Such variations in the dynamic modulus across the whole structure and running speed of the machinery during normal operation have a profound impact on its dynamic performance which may result in alarmingly increasing amplitudes leading to subsequent breakdown of the machinery. A new methodology is outlined that combines the effects of the two variations by way of considering an enhanced range of speeds on either side of the operating speed for the modal synthesis process. This study shows the effects of variations in the dynamic modulus and operating speed on the peak dynamic response of a typical framed turbo-generator foundation structure. The modal synthesis process adopted in the study includes the significant modes in the sub-resonant range and a band of modes around the operating speed to obtain the peak response of the framed structure.

Download Full-text

Synthesis of Spatial RPRP Closed Linkages for a Given Screw System

Journal of Mechanisms and Robotics ◽

10.1115/1.4003846 ◽

2011 ◽

Vol 3 (2) ◽

Cited By ~ 9

Author(s):

Alba Perez-Gracia

Keyword(s):

Design Method ◽

Parallel Robots ◽

Synthesis Problem ◽

Dimensional Synthesis ◽

End Effector ◽

Serial Chain

The dimensional synthesis of spatial chains for a prescribed set of positions can be applied to the design of parallel robots by joining the solutions of each serial chain at the end-effector. This design method does not provide with the knowledge about the trajectory between task positions and, in some cases, may yield a system with negative mobility. These problems can be avoided for some overconstrained but movable linkages if the finite-screw system associated with the motion of the linkage is known. The finite-screw system defining the motion of the robot is generated by a set of screws, which can be related to the set of finite task positions traditionally used in the synthesis theory. The interest of this paper lies in presenting a method to define the whole workspace of the linkage as the input task for the exact dimensional synthesis problem. This method is applied to the spatial RPRP closed linkage, for which one solution exists.

Download Full-text