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A special issue of Machines (ISSN 2075-1702). This special issue belongs to the section "Automation and Control Systems".

Deadline for manuscript submissions: closed (30 September 2022) | Viewed by 33071

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Special Issue Editors

Dr. Zhufeng Shao

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Guest Editor

Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
Interests: robotics; parallel mechanism; optimal design; dynamics; intelligent automation

Prof. Dr. Dan Zhang

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Guest Editor

Department of Mechanical Engineering, Lassonde School of Engineering, York University, Toronto, ON M3J 1P3, Canada
Interests: robotics and mechatronics; high-performance parallel robotic machine development; sustainable/green manufacturing systems; micro/nanomanipulation and MEMS devices (sensors); micro mobile robots and control of multi-robot cooperation; intelligent servo control system for the MEMS-based high-performance micro-robot; web-based remote manipulation; rehabilitation robot and rescue robot
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Dr. Stéphane Caro

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Guest Editor

National Centre for Scientific Research (CNRS) and the Laboratory of Digital Sciences of Nantes (LS2N), UMR CNRS, 6004 Nantes, France
Interests: design, modeling, and control of cable-driven parallel robots and reconfigurable parallel robots
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Parallel robots have been proposed, developed on the basis of serial robots, with a core feature of the parallel configuration of drive/kinematic chains. The moving platform of a parallel robot is supported and driven simultaneously by two or more kinematic chains, which provide the parallel robot with the advantages of high speed, heavy-load-bearing ability, high stiffness, and compact architecture. In recent years, parallel robots have been widely applied in industry and daily life, such as the successful commercialization of the Delta high-speed robot, the Sprint Z3 machining head, and parallel robot simulators.

Increased applications of and interests in parallel robots have driven the research community to carry out extensive investigations. On the one hand, research on the theories and methods of configuration analysis, optimization design and control has developed rapidly. On the other hand, interdisciplinary integration has brought a series of challenges and innovations, for example, cable, soft and various driving modes, serial and parallel hybrid configurations, rigid-flexible coupling/fusion, and artificial intelligence capabilities. This Special Issue will provide an international forum for professionals, academics, and researchers to present the latest developments on parallel robots.

Papers are welcome on topics related to aspects of theory, design, practice, and application, including, but not limited to:

Cable-driven parallel robots and soft parallel robots;
Hybrid robots and rigid-flexible parallel robots;
Bionic, rehabilitation, and exoskeleton robots;
Parallel machine tools and reconfigurable robots;
Configuration innovation and optimal design;
Kinematics and dynamics of new parallel mechanisms;
Accuracy improvement (kinematic calibration, vibration suppression, and dynamic compensation);
Simulation and modelling for parallel robots;
Control theory, systems, and applications;
Artificial intelligence for parallel robots;
Human–robot collaboration and novel applications.

Dr. Zhufeng Shao
Prof. Dr. Dan Zhang
Dr. Stéphane Caro
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Machines is an international peer-reviewed open access monthly journal published by MDPI.

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Published Papers (11 papers)

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Editorial

Jump to: Research

3 pages, 200 KiB

Open AccessEditorial

New Frontiers in Parallel Robots

by Zhufeng Shao, Dan Zhang and Stéphane Caro

Machines 2023, 11(3), 386; https://doi.org/10.3390/machines11030386 - 15 Mar 2023

Cited by 2 | Viewed by 2334

Abstract

In the field of parallel robots, marked by the birth and application of the Gough–Stewart parallel mechanism [...] Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

Research

Jump to: Editorial

21 pages, 3965 KiB

Open AccessEditor’s ChoiceArticle

Geometric Error Analysis of a 2UPR-RPU Over-Constrained Parallel Manipulator

by Xu Du, Bin Wang and Junqiang Zheng

Machines 2022, 10(11), 990; https://doi.org/10.3390/machines10110990 - 29 Oct 2022

Cited by 7 | Viewed by 1952

Abstract

For a 2UPR-RPU over-constrained parallel manipulator, some geometric errors result in internal forces and deformations, which limit the improvement of the pose accuracy of the moving platform and shorten the service life of the manipulator. Analysis of these geometric errors is important for restricting them. In this study, an evaluation model is established to analyse the influence of geometric errors on the limbs’ comprehensive deformations for this manipulator. Firstly, the nominal inverse and actual forward kinematics are analysed according to the vector theory and the local product of the exponential formula. Secondly, the evaluation model of the limbs’ comprehensive deformations is established based on kinematics. Thirdly, 41 geometric errors causing internal forces and deformations are identified and the results are verified through simulations based on the evaluation model. Next, two global sensitivity indices are proposed and a sensitivity analysis is conducted using the Monte Carlo method throughout the reachable workspace of the manipulator. The results of the sensitivity analysis indicate that 10 geometric errors have no effects on the average angular comprehensive deformation and that the identified geometric errors have greater effects on the average linear comprehensive deformation. Therefore, the distribution of the global sensitivity index of the average linear comprehensive deformation is more meaningful for accuracy synthesis. Finally, simulations are performed to verify the results of sensitivity analysis. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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19 pages, 9071 KiB

Open AccessArticle

Consistent Solution Strategy for Static Equilibrium Workspace and Trajectory Planning of Under-Constrained Cable-Driven Parallel and Planar Hybrid Robots

by Qingjuan Duan, Quanli Zhao and Tianle Wang

Machines 2022, 10(10), 920; https://doi.org/10.3390/machines10100920 - 10 Oct 2022

Cited by 1 | Viewed by 2117

Abstract

This paper presents a consistent solution strategy for static equilibrium workspaces of different types of under-constrained robots. Considering the constraint conditions of cable force and taking the least squares error of the static equilibrium equation as the objective, the convex optimization solution is carried out, and the static equilibrium working space of the under-constrained system is obtained. A consistent solution strategy is applied to solve the static equilibrium workspaces of the cable-driven parallel and planar hybrid robots. The dynamic models are presented and introducing parameters that are applied to make the system stable for point-to-point movements. Based on this model, the traditional polynomial-based point-to-point trajectory planning algorithm is improved by adding unconstrained parameters to the kinematic law function. The constraints of the dynamics model are incorporated into the trajectory planning process to achieve point-to-point trajectory planning for the under-constrained cable-driven robots. Finally, under-constrained cable-driven parallel robots with three cables and planar hybrid robot with two cables are taken as examples to carry out numerical simulation. The final results show that the point-to-point trajectory planning algorithm introducing parameters is effective and feasible and can provide theoretical guidance for the design of subsequent under-constrained robots. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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27 pages, 9685 KiB

Open AccessArticle

Singularity Analysis and Geometric Optimization of a 6-DOF Parallel Robot for SILS

by Doina Pisla, Iosif Birlescu, Nicolae Crisan, Alexandru Pusca, Iulia Andras, Paul Tucan, Corina Radu, Bogdan Gherman and Calin Vaida

Machines 2022, 10(9), 764; https://doi.org/10.3390/machines10090764 - 2 Sep 2022

Cited by 6 | Viewed by 2444

Abstract

The paper presents the singularity analysis and the geometric optimization of a 6-DOF (Degrees of Freedom) parallel robot for SILS (Single-Incision Laparoscopic Surgery). Based on a defined set of input/output constraint equations, the singularities of the parallel robotic system are determined and geometrically interpreted. Then, the geometric parameters (e.g., the lengths of the mechanism links) for the 6-DOF parallel robot for SILS are optimized such that the robotic system complies with an operational workspace defined in correlation with the SILS task. A numerical analysis of the singularities showed that the operational workspace is singularity free. Furthermore, numerical simulations validate the parallel robot for the next developing stages (e.g., designing and prototyping stages). Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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26 pages, 62558 KiB

Open AccessArticle

Pick–and–Place Trajectory Planning and Robust Adaptive Fuzzy Tracking Control for Cable–Based Gangue–Sorting Robots with Model Uncertainties and External Disturbances

by Peng Liu, Haibo Tian, Xiangang Cao, Xinzhou Qiao, Li Gong, Xuechao Duan, Yuanying Qiu and Yu Su

Machines 2022, 10(8), 714; https://doi.org/10.3390/machines10080714 - 20 Aug 2022

Cited by 8 | Viewed by 2700

Abstract

A suspended cable–based parallel robot (CBPR) composed of four cables and an end–grab is employed in a pick–and–place operation of moving target gangues (MTGs) with different shapes, sizes, and masses. This paper focuses on two special problems of pick–and–place trajectory planning and trajectory tracking control of the cable–based gangue–sorting robot in the operation space. First, the kinematic and dynamic models for the cable–based gangue–sorting robots are presented in the presence of model uncertainties and unknown external disturbances. Second, to improve the sorting accuracy and efficiency of sorting system with cable–based gangue–sorting robot, a four-phase pick–and–place trajectory planning scheme based on S-shaped acceleration/deceleration algorithm and quintic polynomial trajectory planning method is proposed, and moreover, a robust adaptive fuzzy tracking control strategy is presented against inevitable uncertainties and unknown external disturbances for trajectory tracking control of the cable–based gangue–sorting robot, where the stability of a closed-loop control scheme is proved with Lyapunov stability theory. Finally, the performances of pick–and–place trajectory planning scheme and robust adaptive tracking control strategy are evaluated through different numerical simulations within Matlab software. The simulation results show smoothness and continuity of pick–and–place trajectory for the end–grab as well as the effectiveness and efficiency to guarantee a stable and accurate pick–and–place trajectory tracking process even in the presence of various uncertainties and external disturbances. The pick–and–place trajectory generation scheme and robust adaptive tracking control strategy proposed in this paper lay the foundation for accurate sorting of MTGs with the robot. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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16 pages, 2568 KiB

Open AccessArticle

Fractional Order KDHD Impedance Control of the Stewart Platform

by Luca Bruzzone and Alessio Polloni

Machines 2022, 10(8), 604; https://doi.org/10.3390/machines10080604 - 24 Jul 2022

Cited by 9 | Viewed by 2357

Abstract

In classical impedance control, KD, the steady-state end-effector forces are imposed to be proportional to the end-effector position errors through the stiffness matrix, K, and a proper damping term is added, proportional to the first-order derivatives of the end-effector position errors according to the damping matrix, D. This paper presents a fractional-order impedance control scheme, named KDHD, in which an additional damping is added, proportional to the half-order derivatives of the end-effector position errors according to the half-derivative damping matrix, HD. Since the finite-order digital filters which implement in real-time the half-order derivatives modify the steady-state stiffness of the end-effector—which should be defined exclusively by the stiffness matrix—a compensation method is proposed (KDHDc). The effectiveness of this approach is validated by multibody simulation on a Stewart platform. The proposed impedance controller represents the extension to multi-input multi-output robotic systems of the PDD^1/2 controller for single-input single-output systems, which overperforms the PD scheme in the transient behavior. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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31 pages, 1863 KiB

Open AccessArticle

Dynamic Modeling, Workspace Analysis and Multi-Objective Structural Optimization of the Large-Span High-Speed Cable-Driven Parallel Camera Robot

by Yu Su, Yuanying Qiu, Peng Liu, Junwei Tian, Qin Wang and Xingang Wang

Machines 2022, 10(7), 565; https://doi.org/10.3390/machines10070565 - 14 Jul 2022

Cited by 15 | Viewed by 3518

Abstract

Since most of the cable-driven parallel manipulators (CDPMs) are small in dimension or low in speed, the self-weight or inertia of the cable is neglected when dealing with the problems of kinematics, dynamics and workspace. The cable is treated as a massless straight line, and the inertia of the cable is not discussed. However, the camera robot is a large-span high-speed CDPM. Thus, the self-weight and inertia of the cable cannot be negligible. The curved cable due to the self-weight is modeled as a catenary to accurately account for its sagging effect. Moreover, the dynamic model of the camera robot is derived by decomposing the motion of the cable into an in-plane motion and an out-plane motion, based on which an iterative-based tension distribution algorithm and a workspace generation algorithm are presented. An optimization model is presented to simultaneously improve the workspace volume, anti-wind disturbance ability and impulse of tensions on the camera and pan–tilt device system (CPTDS) by selecting the proper optimal variables under the linear and nonlinear constraints. An improved genetic algorithm (GA) is proposed, and the simulation results demonstrate that the improved GA offers a stronger ability in global optimization compared to the standard genetic algorithm (SGA). The ideal-point method is employed to avoid the subjective influence of the designer when performing the multi-objective optimization, and a remarkable improvement of the performance is obtained through the optimization. Furthermore, the distribution characteristics of the optimization objects are studied, and some valuable conclusions are summarized, which will provide some valuable references in designing large-span high-speed CDPMs. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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18 pages, 8149 KiB

Open AccessArticle

Kinematic and Dynamic Modeling and Workspace Analysis of a Suspended Cable-Driven Parallel Robot for Schönflies Motions

by Ruobing Wang, Yanlin Xie, Xigang Chen and Yangmin Li

Machines 2022, 10(6), 451; https://doi.org/10.3390/machines10060451 - 6 Jun 2022

Cited by 12 | Viewed by 3480

Abstract

In recent years, cable-driven parallel robots (CDPRs) have drawn more and more attention due to the properties of large workspace, large payload capacity, and ease of reconfiguration. In this paper, we present a kinematic and dynamic modeling and workspace analysis for a novel suspended CDPR which generates Schönflies motions. Firstly, the architecture of the robot is introduced, and the inverse and forward kinematic problems of the robot are solved through a geometrical approach. Then, the dynamic equation of the robot is derived by separately considering the moving platform and the drive trains. Based on the dynamic equation, the dynamic feasible workspace of the robot is determined under different values of accelerations. Finally, experiments are performed on a prototype of the robot to demonstrate the correctness of the derived models and workspace. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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20 pages, 4170 KiB

Open AccessArticle

Kinematic Calibration of Parallel Robots Based on L-Infinity Parameter Estimation

by Dayong Yu

Machines 2022, 10(6), 436; https://doi.org/10.3390/machines10060436 - 1 Jun 2022

Cited by 7 | Viewed by 2649

Abstract

Pose accuracy is one of the most important problems in the application of parallel robots. In order to adhere to strict pose error bounds, a new kinematic calibration method is proposed, which includes a new pose error model with 60 error parameters and a different kinematic parameter error identification algorithm based on L-infinity parameter estimation. Parameter errors are identified by using linear programming to minimize the maximum difference between predictions and workspace measurements. Simulation results show that the proposed kinematic calibration has better kinematic parameter error estimation and fewer pose errors when measurement noise is less than kinematic parameter errors. Experimental results show that maximum position and orientation errors, respectively, based on the proposed method are decreased by 86.48% and 87.85% of the original values and by 14.32% and 18.23% of those based on the conventional least squares method. The feasibility and validity of the proposed kinematic calibration are verified by improved pose accuracy of the parallel robot. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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24 pages, 8777 KiB

Open AccessArticle

Analysis of 3-DOF Cutting Stability of Titanium Alloy Helical Milling Based on PKM and Machining Quality Optimization

by Xuda Qin, Mengrui Shi, Zhuojie Hou, Shipeng Li, Hao Li and Haitao Liu

Machines 2022, 10(5), 404; https://doi.org/10.3390/machines10050404 - 21 May 2022

Cited by 6 | Viewed by 2619

Abstract

Aiming at the requirements of titanium alloy holes in aircraft industry, the 3-DOF cutting stability and surface quality optimization of parallel kinematic manipulator (PKM) are studied. The variation of natural frequencies with the end-effector position of the PKM is analyzed. The cutting force model of titanium alloy helical milling based PKM is developed, and the cutting force coefficients are identified. The prediction model for 3-DOF the stability of helical milling based on the PKM is established through a Semi-Discrete method, and the stability lobes are obtained. The correctness of the stability lobes is verified by subjecting the cutting force signal to time-frequency transformation and roughness detection. The step-cutter is used for machining process improvement to enhance the stability domain. The method proposed in this paper can provide a reference for further optimization of the prediction and optimization of the milling process of difficult-to-process materials based on PKM in the future. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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19 pages, 7069 KiB

Open AccessArticle

Elasto-Dynamic Modeling of an Over-Constrained Parallel Kinematic Machine Using a Beam Model

by Hélène Chanal, Aurélie Guichard, Benoît Blaysat and Stéphane Caro

Machines 2022, 10(3), 200; https://doi.org/10.3390/machines10030200 - 10 Mar 2022

Cited by 3 | Viewed by 2483

Abstract

This article deals with the development of a simple model to evaluate the first natural frequencies of over-constrained parallel kinematic machines (PKMs). The simplest elasto-dynamic models are based on multi-body approaches. However, these approaches require an expression of the Jacobian matrices that may be difficult to obtain for complex PKMs. Therefore, this paper focuses on the determination of the global mass and stiffness matrices of an over-constrained PKM in stationary configurations without the use of Jacobian matrices. The PKM legs are modeled by beams. Because the legs are connected to a moving platform and the mechanism is over-constrained, constraint equations between the parameters that model the deformation of each leg are determined according to screw theory. The first natural frequencies and associated modes can then be determined. It should be noted that the proposed method can be easily used at the conceptual design stage of PKMs. The Tripteor X7 machine is used as an illustrative example and is characterized experimentally. Full article

(This article belongs to the Special Issue New Frontiers in Parallel Robots)

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