Parallel Manipulator Research Articles

A Portable Cable-Suspended Parallel Robot and Its Applications in Indoor Inspection

A Portable Cable-Suspended Parallel Robot and Its Applications in Indoor Inspection

Parallel Continuum Delta: On the Performance Analysis of Flexible Quasi-Translational Robots

In the field of rigid parallel manipulators, the Delta parallel robot is one of the most popular choices in the industry due to its ability to adapt to a wide range of applications, particularly pick-and-place tasks. In this paper, the authors present novel designs of Delta-type continuum parallel manipulators with flexible bars, solving both their direct and inverse kinematics, as well as obtaining the associated workspace. The continuum parallel manipulators, unlike conventional robots, incorporate certain flexible elements, such as slender rods that make up the kinematic chains of the Delta manipulators proposed in this work. As a consequence of the flexibility of these rods, a purely translational movement will not be generated, since it is necessary to analyze the zones of the workspace where a parasitic motion related to the inclination of the moving platform compromises the task devised. In addition, an experimental prototype of the Keops-Delta continuum manipulator has been built, and several experimental tests have been carried out to validate the proposed theoretical model.

Kinematic Reliability of Manipulators Based on an Interval Approach

Robotic manipulators inevitably experience the impact of uncertainties and errors, such as dimensional tolerances and joint clearances. Therefore, this paper proposes a novel method based on an interval approach to evaluate the kinematic reliability of manipulators. Kinematic reliability quantifies the probability of positioning errors that fall within allowable boundaries. As a result, reliability evaluates the probability that the interval end-effector error produced by dimensional tolerances exceeds an acceptable rate. The proposed reliability index is based on the interval error that conveys an alternative approach to the kinematic reliability methods based on probabilistic frameworks reported in the literature based on probabilistic approaches. The obtained numerical results demonstrate the viability of the proposed methodology by evaluating the reliability of a serial manipulator subjected to joint clearances and a parallel manipulator with dimensional tolerances.

Redesign of a Balance Rehabilitation Device Based on a Parallel Continuum Mechanism

In the present work, a parallel continuum manipulator for trunk rehabilitation tasks for patients who have suffered a stroke was analyzed and redesigned. The manipulator had to perform active assistance exercises for the motor recovery of the patient. Based on this background, a series of requirements were defined, which determined the design framework during the modeling of the manipulator. Finally, an improved prototype was built and tested to verify that the model can properly characterize the behavior of the manipulator. Such tests were carried out using a self-made dummy that replicates the simplifying hypotheses and conditions assumed in the mathematical model.

A novel real-time tension distribution method for cable-driven parallel robots

Abstract The tension distribution problem of cable-driven parallel robots is inevitable in real-time control. Currently, iterative algorithms or geometric algorithms are commonly used to solve this problem. Iterative algorithms are difficult to improve in real-time performance, and the tension obtained by geometric algorithms may not be continuous. In this paper, a novel tension distribution method for four-cable, 3-DOF cable-driven parallel robots is proposed based on the wave equation. The tension calculated by this method is continuous and differentiable, without the need for iterative computation or geometric centroid calculations, thus exhibiting good real-time performance. Furthermore, the feasibility and rationality of this algorithm are theoretically proven. Finally, the real-time performance and continuity of cable tension are analyzed through a specific numerical example.

A parallel mechanism-based virtual biomechanical shoulder robot model: Mechanism design optimization and motion planning

This paper presents the design and optimization process of a Virtual Biomechanical Shoulder Robot Model (VBSRM) based on a 6-4 parallel mechanism. To address the challenges posed by parallel manipulators and the specific biomechanical constraints of the shoulder joint, a comprehensive design analysis is conducted. First, a kinematic model of the VBSRM is developed, followed by an investigation of its geometric model. To obtain an optimal VBSRM design, performance objectives such as condition number, norm of actuator force, and stiffness are identified and optimized. Initially, only condition number of the robot mechanism is optimized using Genetic Algorithm and performance objectives from the optimal design are analyzed. Later, the three objectives are grouped to form a single function and a single objective-based optimization is also conducted. However, further investigation revealed the conflicting nature of the objectives and hence these were simultaneously optimized using the Non-dominated Sorting Genetic Algorithm (NSGA II). The results obtained from various optimization routines are compared and it is found that the results from the NSGA II provide a better tradeoff between the performance objectives. The motion trajectories from the optimal design of the VBSRM are later analyzed vis-à-vis human shoulder motions for its intended use as a robotic model of the human shoulder joint in various applications.

A fuzzy tuning approach for controller parameters of a parallel manipulator based on clustering analysis

A fuzzy tuning approach for controller parameters of a parallel manipulator based on clustering analysis

A Six‐Axis Asymmetric Parallel Manipulator Co‐Driven by Direct‐Drive and Geared Motors for Enhanced Force‐Sensing Capability

This article introduces a novel six‐axis parallel manipulator co‐driven by motors with and without geared reducers. The design leverages the high stiffness provided by the geared motors and the high force‐sensing capability of the direct drives. When the geared motors move synchronously with their direct‐drive counterparts, the manipulator mimics a Delta robot's spatial translation, while the direct drives double as high‐performance force sensors. An asymmetric design of the manipulator is proposed to allocate a larger portion of torque to the geared motors, raising the overall stiffness of the mechanism. Relations between the external force to the driving torque are derived and the torque redistribution effect of the asymmetric design is illustrated numerically. Experimental results on prototypes of both the symmetric design and the asymmetric design show that direct drives consistently exhibit much higher linearity in the force‐to‐torque relationship compared to the geared drives, and also confirm that asymmetric design alleviates the torque burden on the direct drives. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Evaluation of Two Tension Sensors for Cable‐Driven Parallel Manipulators

Evaluation of Two Tension Sensors for Cable‐Driven Parallel Manipulators

Error analysis of a coaxis five-bar parallel mechanism

Abstract With societal advancement, robots are increasingly being deployed in production processes. Currently, high-precision robots predominantly found in the market are delta parallel robots. Common parallel robots, including delta robots, generally suffer from the drawback of having a smaller workspace compared to serial robots. Contrasted with other types of parallel robots, coaxis parallel robots feature a larger workspace, thereby offering greater potential for application. This paper focuses on a coaxis five-bar parallel mechanism as the subject of investigation. Firstly, by employing the perturbation method to model the errors in the parallel mechanism, a mapping relationship between error sources and the errors of the mechanism’s end-effector was derived. Then a sensitivity analysis of each error source was performed statistically, yielding sensitivity metrics. Last, under conditions where the magnitudes of errors are identical, the end-effector error of a coaxis parallel mechanism is notably larger compared to that of a common parallel mechanism. This makes it more essential to conduct precision design on coaxis parallel robots in the future study.

A novel cross-receptive field fusion cascade network with adaptive mask update for transfer health state diagnosis of manipulators

Manipulators, particularly planar parallel manipulators, are widely employed in high-end precision equipment to conduct precise positioning and operation tasks due to their advantages of high stiffness, high precision, and high load. Moreover, they are also frequently exposed to changeable working circumstances, which significantly cause inconsistent health state data distribution. Although transfer learning can successfully offset the above distribution discrepancies, it remains unclear how to identify and quantify the source domain knowledge’s contribution to the transfer process. To overcome these challenges, a novel transfer health state diagnosis framework, named cross-receptive field fusion cascade network with adaptive mask update (CFFCN-AMU), is developed and employed for manipulators. Specifically, a unique cross-receptive field fusion cascade module (CFFCM), in which the receptive field self-evaluator and channel attention mechanism are jointly designed, is constructed initially to achieve adaptive extraction and fusion of cascaded features. Subsequently, in the target domain fine-tuning stage, an adaptive mask update (AMU) strategy is implemented to evaluate the contribution of source domain knowledge and selectively guide the parameter updating process. Finally, some mechanistic model-driven cross-working condition transfer scenarios are investigated. Multiple sets of excellent transfer diagnosis results fully illustrate the transferability and superiority of the constructed CFFCN-AMU model.

Grasping Control for Kinematically Redundant Parallel Robots With a Remotely Operated Gripper

Grasping Control for Kinematically Redundant Parallel Robots With a Remotely Operated Gripper

Fuzzy Adaptive Whale Optimization Control Algorithm for Trajectory Tracking of a Cable-Driven Parallel Robot

Fuzzy Adaptive Whale Optimization Control Algorithm for Trajectory Tracking of a Cable-Driven Parallel Robot

Fuzzy adaptive impedance control for the two-layered vertical cable-driven parallel robot

This study unveils a novel two-layered vertical octahedron cable-driven parallel robot (TLVO CDPR), distinctively engineered for effective force interactions with vertical surfaces while preventing collision with cables. It pioneers an innovative control strategy integrating a position-based fuzzy adaptive impedance controller with a fuzzy Proportional – Integral – Derivative (PID) controller, adeptly managing both the pose and contact force of the robot. While dual control application is often found in rigid-link robots, it remains a largely unexplored frontier in the realm of CDPRs, despite its critical importance in sectors like manufacturing and assembly. The fuzzy adaptive mechanism significantly boosts impedance control efficacy in the face of unpredictable, non-uniform working surfaces, ensuring algorithmic stability and convergence. Concurrently, fuzzy logic is harnessed to optimize PID controller performance. The forward kinematics challenge is efficiently tackled using a least squares method coupled with an Inertial Measurement Unit (IMU), ensuring swift and precise solutions. The robustness and adaptability of the robot and its control systems are thoroughly validated through extensive experimental trials, involving diverse trajectories and varying uncertainties on vertical working surfaces.

Structural – parametric synthesis of a parallel manipulator with two grips

This paper describes the methods of structural-parametric synthesis of a parallel manipulator PM with two grippers, which can be used for reloading operations between two adjacent main technological equipment in a cold stamping technological line. This PM is formed by connecting two grippers end – effectors with a base using two passive and one negative closing kinematic chains (CKC).

A deep learning approach for pose error prediction in parallel robots

Parallel robots are increasingly favored in industrial automation due to their high precision, stability, and rigidity in high-speed and heavy-load tasks. However, factors such as manufacturing tolerances, assembly deviations, loads, and environmental conditions can lead to pose inaccuracies, manifesting as both geometric and non-geometric errors. Traditional model-driven approaches effectively predict geometric errors but often neglect non-geometric factors, potentially impacting the overall accuracy. This paper presents a deep learning-based method for comprehensive pose error prediction in parallel robots, addressing both geometric and non-geometric errors. The proposed approach employs an encoder-decoder network that takes target pose inputs and outputs predicted pose errors. The encoder integrates multi-layer convolutional sparse coding (CSC) blocks and efficient channel attention (ECA) modules to extract features from the network inputs. Monte Carlo dropout is utilized to estimate prediction uncertainties, enhancing the reliability of the network predictions. Experimental validation on a Stewart platform demonstrates the high accuracy and robustness of the method under various loading conditions. Comparative analyses with several typical models affirm the superior performance of the proposed network, indicating its potential to improve the operational accuracy and reliability of parallel robots in high-precision applications.

Complex motion design and control of aircraft model suspended with cable-driven parallel robot at high AoAs

Complex motion design and control of aircraft model suspended with cable-driven parallel robot at high AoAs

Kinematic analysis, workspace definition, and self-collision avoidance of a quasi-spherical parallel manipulator

Abstract Bilateral teleoperation has witnessed significant development since the mid-20th century, addressing challenges related to human presence in environments with constraints or a lack of skilled professionals. This article presents the kinematic and self-collision analyses of the quasi-spherical parallel manipulator, a three-legged parallel robot used as a haptic master device. The device is designed for remote center of motion-constrained operation in the telesurgical field. Inverse and forward kinematics are thoroughly analyzed to study working modes, singular configurations, and implement a haptic control architecture. The research explores the operative and reachable workspaces of the possible working modes, comparing them to find the most suitable one. Results highlight how the addition of the self-collision phenomenon impacts the working mode choice, drastically reducing most of the modes’ operative workspaces. An anti-collision control algorithm is finally introduced to maintain the architecture within its reachable workspace.

A novel type of parallel manipulator with flexible morphing platform

Abstract Parallel manipulators with flexible morphing platform (FMP) provide potential solution in various application fields, such as shape-morphing underwater robot, deformable wings, and human–machine interfaces. However, there is still lack of effective approach for the design and analysis of such novel type of parallel manipulator. In this article, a 9-UPS redundant actuation parallel manipulator with flexible morphing moving platform is designed as a representative of this kind of manipulator. Correspondingly, a deformation estimation and shape control approach for the FMP is presented. The proposed deformation estimation approach is designed based on the bending energy, which can achieve high calculation efficiency and avoid complex mechanical definition and calculation. And the proposed shape control approach is realized by utilizing a nonrigid ICP match algorithm, which can continuously deform the morphing platform to an arbitrary target surface. A prototype of the 9-UPS parallel manipulator is fabricated and analyzed as verification. The experiment results show that the proposed approach offers a promising avenue for the deformation estimation and shape control of the morphing platform.

Analytical determination of the optimal effective regular workspace of a 6-6 Stewart platform manipulator for a specified orientation workspace

This article presents an analytical method to identify the largest effective regular workspaces (ERWs) of a class of 6-6 Stewart platform manipulators for a given orientation workspace. The ERWs are modelled as spheres. The orientation workspace is specified in terms of ranges of Euler angles, as is the standard practice in the parallel robot industry. The radius of the said sphere is maximised through an optimisation problem, which is solved analytically. Consequently, the results obtained are exact in nature. The analytical formulation of the problem and its exact solutions constitute the novel theoretical contributions of this article. Moreover, since the results hold good over a given subset of SO(3), the proposed method obviates the need for numerical scanning of the orientation workspaces in design-related computations, thus improving the accuracy, robustness, as well as computational efficiency. Finally, the significance of the neutral height in harnessing the desired extents of position and orientation workspaces has been established through parametric studies. The formulations are illustrated via applications to Stewart platform manipulators of three distinct platform dimensions.