Mobile Parallel Research Articles

Advanced control algorithm considering cable interference of mobile cable-driven parallel robots (MCDPRs)

Advanced control algorithm considering cable interference of mobile cable-driven parallel robots (MCDPRs)

Structural design and coupling analysis of multimode variable coupling parallel mobile robots

Purpose There is coupling between the branches of mobile parallel robots, similar to traditional parallel mechanisms, but there is currently relatively little research on the coupling problem between the branches of mobile parallel robots. Design/methodology/approach This study optimizes the coupling analysis method of traditional parallel mechanisms, treats the mobile parallel mechanism as a whole, takes the motion of the active pair as input and the overall motion of the mobile parallel mechanism as output and analyzes the input–output characteristics of the mobile parallel mechanism. Moreover, this study applies this theory to a mobile parallel mechanism, designs control logic and finally conducts simulation and physical verification. Findings This study proposes a coupling analysis method suitable for parallel mobile robots and designs the control logic of their active pair based on the results of their coupling analysis. This study designs a multimode variable coupling parallel mobile robot, which can change the coupling of the mechanism by changing its own branch chain structure, so that it can switch between different coupling configurations to meet the different needs brought by different terrains. Originality/value The work presented in this paper propose a method for analyzing the coupling of mobile parallel robots and simplify their control logic by applying coupling theory to the design of mobile parallel robots. This study conducts simulation and physical experiments, thereby filling the gap in the coupling analysis of parallel mobile robots and laying the foundation for the research of uncoupled parallel mobile robots.

Expanding the wrench feasible workspace of quadrotor-based mobile cable-driven parallel manipulators using multi-objective optimization and machine learning

Quadrotor-based Reconfigurable Cable-Driven Parallel Manipulators (QRCDPMs) have previously been introduced as having significant potential in extending the feasible workspace of Cable-Driven Parallel Manipulators (CDPMs). However, such configurations have limitations in executing positive Z-direction trajectories resulting in non-optimal workspace and performance. This study proposes a novel Quadrotor-based Enhanced Reconfiguration Cable-Driven Parallel Manipulator (QERCDPM) that significantly enhances the Wrench Feasible Workspace (WFW). This allows for extended safe platform operation along all XYZ directions by adjusting the bottom cable exit point. Simulation results indicate that the proposed setup achieves a 96.39 % ratio of safe workspace to available workspace in various cable exit points configurations. Tension Distribution analysis for different trajectories demonstrates the proposed setup's superior cable tension management, increased flexibility and reachability. A Random Forest based Particle Swarm Optimization - Modified Frequency Bat Algorithm (RFPSOMFB) optimization algorithm is proposed, which outperforms existing methods in terms of run time and solution quality. The findings hold significance for applications requiring safe and efficient trajectory execution in dynamic and constrained environments, contributing to the evolution of multi-robot based intelligent and distributed systems.

Hybrid cable tension–length compensation algorithm for dynamic performance improvement of mobile cable-driven parallel robot

Hybrid cable tension–length compensation algorithm for dynamic performance improvement of mobile cable-driven parallel robot

MF+C: Linking suboptimal projections to detail on handheld devices

Mobile Focus + Context (mF+C) involves using a handheld device as a focus screen for content on an immersive display or mobile projector. In this work we examine how using a focus device can mitigate poor context image quality due to environmental factors. In an exploratory study we compare three techniques for linking focus and context: lens-focus (Lens), where the device works as a mobile lens held parallel to and in front of the context, center-focus (Centered), where the user holds the device in the center of the projection and pans both context and focus by swiping, and marker-focus (Marker), where the focus region is highlighted on the context, and the user pans the focus by swiping. Participants performed searching, tracing, and detail acquisition tasks with maps and electronics diagrams under a range of simulated projection conditions. All techniques were able to mitigate poor projection quality and performed comparably in time and precision, but the effectiveness of each technique was impacted by task type. There was lower variation in time between participants using Lens for tracing tasks versus the other techniques, but wider variation for searching tasks. Tasks completed using sub-optimal projections involved more time spent looking at the context image than tasks with clear projections, however this difference is less pronounced for the Lens technique. We propose a hybrid Lens-Marker approach for mobile Focus+Context applications in dynamic environments.

Dynamic behaviors of an integrated crawler mobile parallel robot in obstacle-crossing

Dynamic behaviors of an integrated crawler mobile parallel robot in obstacle-crossing

Optimal sampling-based path planning for mobile cable-driven parallel robots in highly constrained environment

Mobile cable-driven parallel robots (MCDPRs) is a novel concept of cable-driven parallel robots (CDPRs) developed by mounting several mobile bases to discrete the conventional fixed frame. However, the additional mobile bases introduce more degree-of-freedom (DoF), thereby causing the kinematic redundancy. Moreover, mobile bases are susceptible to disturbances causing inconsistent performance. Hence, path planning of MCDPRs becomes a challenging issue due to various internal and external constraints involved. In this article, an optimization-based path planning method is proposed for MCDPRs in highly constrained environments with considering kinematic stability. The proposed approach quickly generates feasible paths for coupled mobile bases by using the developed multi-agent rapidly exploring random tree (MA-RRT). In this process, the tree can share information through the heuristics method to optimize the path, and the adaptive sampling strategy is thus proposed to increase the tree growth efficiency by self-adjusting sampling space. Moreover, the developed dynamic control checking method (DCC) is integrated with MA-RRT to smooth the path and the kinodynamic constraints of mobile bases can be satisfied. To generate the path of the end-effector, two performance metrics are designed considering the kinematic and stability of the MCDPR. Based on the performance metrics, the grid-based search method is developed to generate the path for the end-effector. Finally, the convincing performance of the proposed method is revealed through the dynamic simulation software (CoppeliaSim) and real-world experiments based on a self-built MCDPR prototype.

Mobile parallel manipulator consisting of two nonholonomic carts and their path planning

Mobile manipulators are widely used to transport and manipulate objects in industrial settings. In this paper, we propose a mobile manipulator that consists of a parallel mechanism and two two-wheel-drive carts. The planar motions of the carts are transmitted to a platform through three screw pairs of the parallel mechanism, allowing the pose of the platform to be controlled by only four motors. Kinematic analysis for such a two-cart mobile manipulator gives a Jacobian matrix, reveals the effects of nonholonomic constraints, and demonstrates that the yaw angle of the platform must be limited to avoid singular and failure configurations, and that the pitch angle is quite sensitive to uncertainties. Based on these analysis results, we present a custom path planning method for the carts. This method provides a non-optimal but easily realizable path planning algorithm with low computational cost, since the complex constraint conditions of this two-cart mobile manipulator have little influence on the proposed path generation process. The path planning process consists of four steps. We describe the motions of the carts in each step and establish a path tracking control system for the carts. Some simulations are conducted to show the motions of the carts, investigate the changes in the pose of the platform, and quantitatively evaluate the sensitivity of the platform’s pitch angle. Moreover, we construct an experimental prototype and conduct experiments to verify the validity and usefulness of the proposed mechanism and path planning method.

Мобильный спелеологический параллельный робот с пространственной тактильной системой распознавания контактной поверхности

The paper considers the problem of conducting speleological studies of natural and artificial caves, including channels of the underground rivers, as well as various mine workings in dangerous or inaccessible conditions for a speleologist. In this case, external environment of the objects under study could turn out to be opaque for optical, radio, ultrasonic and other physical methods of monitoring the inner surface, for example, due to partial or complete flooding of the object with water with inhomogeneous suspensions. A solution to the problem is proposed by robotizing the research using a mobile speleological parallel robot (MSPR) with a spatial tactile system for identification of the contact surface. MSPR is created in the form of an active octahedral structure, which edges are rods with linear drives. The rod ends are pivotally connected to the corresponding vertices of the active octahedral structure ensuring its geometric invariability when the linear drives are turned off. As a result, MSPR is able to carry out contact (tactile) mapping of the inner surface under study regardless of the external environment transparency and its geodetic binding to the base coordinate system with visualization in the form of histograms. At the same time, MSPR is able to self-move along the internal surfaces regardless of their spatial orientation. MSPR and its functionalities are described, one of which is the ability to build the 3D histograms of the surrounding space bind to the base (inertial) coordinate system through the mechanical contact. The tactile system of identifying the contact surface makes it possible not only to move the MSPR, but also to tactilely monitor in the external environment that is opaque for optical, radio, ultrasonic and other physical control methods. MSPR allows robotizing speleological research in dangerous, hard-to-reach and inaccessible places for a speleologist, as well as to carry out rescue operations and ensure delivery of the required cargo.

A collaborative path planning method for mobile cable-driven parallel robots in a constrained environment with considering kinematic stability

Mobile cable-driven parallel robot (MCDPR) is a variant of cable-driven parallel robots (CDPRs) by mounting several mobile bases to replace the conventional fixed frame. The novel modification of adding mobile bases leads MCDPRs being highly flexible and have great potential for complex environments. However, the issue of coupled mobile bases introduces actuated kinematic redundancies which present challenges for path planning. In this paper, we propose a collaborative path planning method for MCDPRs, and it allows the robot to deal with complex internal and external constraints in a high-dimensional state space efficiently. The proposed method quickly generates feasible paths for coupled mobile bases using the adaptive goal-biased rapidly exploring random tree (RRT) method, in which the adaptive sampling method is developed to enhance efficiency. Based on the feasible path of the mobile base, we proposed a grid-based search method to determine the position of the end-effector with considering the stability and kinematic performances. Furthermore, the planned paths are post-processed with the cubic splines to obtain continuous profiles for the robot. Finally, the proposed method is validated through the dynamic simulation software (CoppeliaSim) and experiments based on a MCDPR prototype with an eight-cable-driven parallel robot mounted on four mobile bases.

Innovative Mobile Parallel Octahedral Ice-Breaker to Remove Ice and Snow from Cable-Stayed Bridges

Innovative Mobile Parallel Octahedral Ice-Breaker to Remove Ice and Snow from Cable-Stayed Bridges

Feasibility Design and Control of a Lower Leg Gait Emulator Utilizing a Mobile 3-Revolute, Prismatic, Revolute Parallel Manipulator

Abstract Design and control of lower extremity robotic prostheses are iterative tasks that would greatly benefit from testing platforms that would autonomously replicate realistic gait conditions. This paper presents the design of a novel mobile 3-degree-of-freedom (DOF) parallel manipulator integrated with a mobile base to emulate human gait for lower limb prosthesis evaluation in the sagittal plane. The integrated mobile base provides a wider workspace range of motion along the gait direction and reduces the requirement of the parallel manipulator’s actuators and links. The parallel manipulator design is optimal to generate the defined gait trajectories with both motion and force requirements using commercially available linear actuators. An integrated active force control with proportional integral derivative (PID) control provided more desirable control compared to traditional PID control in terms of error reduction. The novelty of the work includes the methodology of human data-oriented optimal mechanism design and the concept of a mobile parallel robot to extend the translational workspace of the parallel manipulator with substantially reduced actuator requirements, allowing the evaluation of prostheses in instrumented walkways or integrated with instrumented treadmills.

Actuation-Coordinated Mobile Parallel Robots With Hybrid Mobile and Manipulation Functions

Abstract Mobile robots with manipulation capability are a key technology that enables flexible robotic interactions, large area covering and remote exploration. This paper presents a novel class of actuation-coordinated mobile parallel robots (ACMPRs) that utilize parallel mechanism configurations and perform hybrid moving and manipulation functions through coordinated wheel actuators. The ACMPRs differ with existing mobile manipulators by their unique combination of the mobile wheel actuators and the parallel mechanism topology through prismatic joint connections. Common motion of the wheels will provide mobile function while their relative motion will actuate the parallel manipulation function. This new concept reduces actuation requirement and increases manipulation accuracy and mobile motion stability through coordinated and connected wheel actuators comparing with existing mobile parallel manipulators. The relative wheel location on the base frame also enables a reconfigurable base size with variable moving stability on the ground. The basic concept and general type synthesis are introduced and followed by kinematics and inverse dynamics analysis of a selected three limb ACMPR. A numerical simulation also illustrates the dynamics model and the motion property of the new mobile parallel robot (MPR) followed by a prototype-based experimental validation. The work provides a basis for introducing this new class of robots for potential applications in surveillance, industrial automation, construction, transportation, human assistance, medical applications, and other operations in extreme environment such as nuclear plants, Mars, etc.

Design of a mobile binary parallel robot that exploits nonsingular transitions

Sliding-frame mobile robots used for autonomously inspecting metallic structures consist of two bodies connected by few joints. They move by alternately adhering one body to the structure while moving the other body to the next position. Sliding-frame robots are simpler and offer safer adhesion than legged and wheeled robots, and their control can be simplified using binary actuators that adopt only two stable states. However, most existing sliding-frame robots require continuous actuators to reach targets with precision, since binary actuators impose steps of fixed length. To solve this, this paper presents a new sliding-frame robot consisting of two bodies connected through a 2RPR-PR kinematic chain driven by two binary actuators. The 2RPR-PR chain can perform nonsingular transitions, which is the ability of many parallel robots to switch between different poses corresponding to the same state of its actuators, without crossing singularities. Thanks to this, the poses reachable by the proposed robot are doubled, granting it a denser workspace and more accuracy than similar robots, using only two binary actuators. The feasibility of the proposed robot is shown through a prototype.

Type synthesis of 6-DOF mobile parallel link mechanisms based on screw theory

Type synthesis of 6-DOF mobile parallel link mechanisms based on screw theory

Mobile parallel robot machine for heavy-duty double-walled vacuum vessel assembly

Purpose This paper aims to present a detailed mechanical design of a seven-degrees-of-freedom mobile parallel robot for the tungsten inert gas (TIG) welding and machining processes in fusion reactor. Detailed mechanical design of the robot is presented and both the kinematic and dynamic behaviors are studied. Design/methodology/approach First, the model of the mobile parallel robot was created in computer-aided design (CAD) software, then the simulation and optimization of the robot were completed to meet the design requirements. Then the robot was manufactured and assembled. Finally, the machining and tungsten inert gas (TIG) welding tests were performed for validation. Findings Currently, the implementation of the robot system has been successfully carried out in the laboratory. The excellent performance has indicated that the robot’s mechanical and software designs are suitable for the given tasks. The quality and accuracy of welding and machining has reached the requirements. Originality/value This mobile parallel industrial robot is particularly used in fusion reactor. Furthermore, the structure of the mobile parallel robot can be optimized for different applications.

Kinematics Analysis and Optimization of a Multi-Mode Mobile Parallel Mechanism

Kinematics Analysis and Optimization of a Multi-Mode Mobile Parallel Mechanism

Design and Multi-Objective Optimization of a Dexterous Mobile Parallel Mechanism for Fusion Reactor Vacuum Vessel Assembly

The present paper proposed a newly designed dexterous mobile parallel mechanism for fusion reactor vacuum vessel assembly, the robot system has advantages in terms of compact design, the capability to carry out heavy-duty machining tasks, is easy to evacuate, and has less space occupation than other robot systems in existence. Despite different robot systems having been studied in the fusion reactor, there is still a lack of research on mechanism development for vacuum vessel assembly, which is attractive to future fusion reactors. In the fusion reactor, the robot systems will carry out different tasks, such as welding and machining. The assembly tasks of the vacuum vessel will be performed from inside of the vacuum vessel on-site. Then the paper introduced the single-objective and multi-objective optimization design of the proposed mechanism, the optimized objective was considered to be a combination of parallel mechanism dynamic machining force, dexterity, stiffness and workspace volume. The design variables were derived from the geometry of the fixed and movable platforms, which include mass, inertia, the sizes of the platforms, and distances between universal joints located on the platforms. In the multi-objective optimization, non-dominated sorting genetic algorithm II was adopted and different trajectories were designed to simulate the machining process, which further turns the local optimization problem into a global optimization problem. Finally, the optimized results were extracted and analyzed. Simulation results indicated the effectiveness of the proposed multi-objective optimization approaches and multi-objective optimization was found to be more reliable than single-objective optimization.

Motion Control and Trajectory Planning for Obstacle Avoidance of the Mobile Parallel Robot Driven by Three Tracked Vehicles

SUMMARYThis paper proposes a mobile parallel robot (MPR) and focuses on obstacle avoidance. When analyzing the collision-free trajectories, the coupling constraints caused by the parallel mechanism and the obstacle should be emphatically solved. The solution is to divide the problem into two steps. First, the genetic algorithm is employed to search and optimize the feasible trajectories under the mechanism constraint of the MPR. Then the trajectory tracking controller is designed to make the tracked vehicles move cooperatively and track a trajectory asymptotically. Finally, simulations and experiments are carried out to verify the effectiveness of the solution.

Design and implementation of a mobile parallel robot for assembling and machining the fusion reactor vacuum vessel

Abstract The present paper introduces a mobile robot machine for the fusion reactor and presents its implementation. The task of the robot is to carry out assembly work inside the fusion reactor vacuum vessel, the assembly work consists of scanning, machining, splice plate transportation, welding, nondestructive testing (NDT), defect welding point cutting and re welding. To better meet the requirements of the fusion reactor configuration, the structure and the kinematics of the mobile parallel robot have been optimized for the fusion reactor access. In this paper, the overall design of the mobile parallel robot is first presented, followed by calculation and simulation of the static, kinematic and workspace model of the mobile parallel robot. Finally, the implementation process of the mobile parallel robot is introduced. Compared with the similar mobile parallel robot developed by the same research group and demonstrated in ITER, the new designed robot machine is more reliable and more easily realizable, and, moreover, it is suitable for assembling work in different environments.