Reconfigurable Parallel Mechanism Research Articles

Construction and forward kinematics of a novel reconfigurable parallel mechanism

In this paper, a kind of hybrid kinematics chain with variable constraints is constructed by using a 6R spatial bifurcated chain and 4-DOF serial limbs, by using them, a 3-DOF Reconfigurable Parallel Mechanisms (RPM) was constructed, which has four motion modes: 3T, 2T1R, 2R1T, and 3R motion modes. Using screw theory, the change of wrench system in the hybrid kinematics chain caused by the reconfiguration of the 6R bifurcated chain is analyzed, which affects the wrench system of the moving platform (MP), and thus causes the reconfiguration of the parallel mechanism (PM). The triangular pyramid fixed to the MP was found as auxiliary geometry and used to intuitively describe the constraint relationship between joint axes in limbs. The latter was used to establish a unified forward kinematics model of the RPM in four motion modes. The general forward kinematics solution procedure for this type of RPM is given. The overall Jacobian matrix was obtained by screw theory for singularity analysis. The condition number of the Jacobian matrix measures the degree to which the mechanism is close to the singular configuration. Based on the Monte Carlo simulation, point cloud images representing the workspace of RPM were obtained.

Design and kinematical performance analysis of a novel reconfigurable parallel mechanism with three remote center-of-motion modes

In view of the demands for variability and safety in surgical procedures, this paper presents a novel reconfigurable parallel mechanism (RPM) capable of performing three remote center-of-motion (RCM) modes: 1R1T, 2R1T, and 3R1T. One of the RCM modes can transform into two distinct configurations from the switch configuration, in which one configuration offers a rotational degree-of-freedom (DOF) and a translational DOF in the YOZ plane, and the other configuration provides identical DOFs in the XOZ plane. A novel device is introduced for switching between the active and passive modes of the revolute joint, which serves as the basis for the RPM reconfiguration process. Utilizing screw theory, the mobility and actuation scheme of the RPM in each configuration are analyzed. Inverse kinematic analysis and Jacobian matrices are then carried out. Subsequently, kinematical performances, such as singularity, workspace, and dexterity, are studied. All results indicate that the proposed RPM has the ability to switch motion modes without requiring reassembly and can effectively meet the diverse demands of surgical procedures based on specific minimally invasive surgery (MIS) requirements.

A new reconfigurable parallel mechanism using novel lockable joints for large scale manufacturing

A new reconfigurable parallel mechanism using novel lockable joints for large scale manufacturing

Analysis and design method of a class of reconfigurable parallel mechanisms by using reconfigurable platform

This paper proposes a method to design reconfigurable parallel mechanisms by applying reconfigurable platforms. According to the requirements of convenience and reliability, the basic rules for designing a reconfigurable platform are proposed. Based on a planar four-bar mechanism, single- and double-stage mechanisms are designed based on DOF (Degree of Freedom) formulation, and the single- and multi-loop reconfigurable platforms are both presented. For the spatial reconfigurable platform, the F1 (one independent force), C1 (one independent couple), F2C1 (two independent forces and one independent couple), and F1C2 (one independent force and two independent couples) over-constrained mechanisms are designed according to screw theory. To meet the multi-limb, parallel-mechanism structural requirement, single-loop over-constrained mechanisms are developed to multi-loop over-constrained mechanisms. Finally, a typical reconfigurable parallel mechanism is selected. Both the kinematics and performance analysis are investigated, and dimension synthesis based on multi-objective optimization is explored using some global indices.

Configuration switch and path selection between Schönflies motion and non-Schönflies motion based on quotient manifold of novel reconfigurable parallel mechanisms

This paper investigates configuration switch and path selection of novel reconfigurable parallel mechanisms with two double-four-bar modular linkages in terms of subgroups SE(2), SO(3) and X(z). The motion representation of reconfigurable parallel mechanisms with three motion branches is proposed based on intersection operation of manifold generated, and the switching principle of motion generators is presented to realize the switching of the three motion branches of the reconfigurable parallel mechanism through the transformation of the submanifold generated by the suitable common motion generators. Two double-four-bar modular linkages are designed to constitute a subchain in terms of the switching principle, and the configuration transformation of the subchain is proposed with respects to the configuration switch of each modular linkage following different forms of the quotient submanifold generated. A reconfigurable parallel mechanism is synthesized by means of rearranging the configurations of two modular linkages of three identical subchains. Especially, the paths of three configurations of a reconfigurable parallel mechanism are selected to satisfy switching.

Kinematic Analysis and Dimension Optimization of a New Reconfigurable Parallel Mechanism With 1R2T and 2R1T Operation Modes

Abstract This paper introduces a novel reconfigurable parallel mechanism (RPM) consisting of two PRU limbs (P denotes a prismatic joint, R denotes a revolute joint, U denotes a universal joint) and one PUU limb. The proposed RPM can evolve into two distinct configurations from the switch configuration, in which one configuration has one rotational degree-of-freedom (DOF) and two translational DOFs, and the other configuration has two rotational DOFs and one translational DOF. First, the DOFs of the RPM in each configuration are analyzed using screw theory. Then, position modeling for the RPM is carried out. Inverse position solutions and forward position solutions are derived. Further, performance evaluation and optimization are conducted using the motion/force transmission method. Finally, a prototype is developed, and preliminary experiments are carried out. The proposed RPM has the potential to be used in applications with multi-task requirements.

Mobility of overconstrained parallel mechanisms with reconfigurable end-effectors

Reconfigurable parallel mechanisms have legs or end-effectors with additional degrees of freedom or with the ability to change their mobility. This allows them to reconfigure into a variety of conventional parallel mechanisms. One type of reconfigurable parallel mechanism can be obtained by replacing the end-effector with a closed-loop linkage. The parts of this linkage that are connected to the legs may be considered as the end-effectors, having their own mobility relative to the base and a coupled mobility with each other. Classical methods for mobility analysis cannot be directly applied to this type of mechanism. This article presents a general method to calculate and represent the coupled mobility of the multiple end-effectors using nullspace operations on a matrix of mobility. The nullspace approach provides an efficient way to calculate the mobility in a closed-loop chain while the matrix of mobility allows for calculating the multiple end-effectors mobility interaction. The general method can be performed analytically to obtain insights on the mechanism in any configuration, or algorithmically to obtain numerical values of the mobility in a particular configuration. Two illustrative examples showcasing the method are presented.

A novel reconfigurable parallel mechanism constructed with spatial metamorphic four-link mechanism

In this paper, a spatial metamorphic four-link mechanism (SMM) based on the metamorphic universal joint is proposed. By adjusting the axis position of the universal joint, three kinds of SMMs are constructed. Each kind of SMM has different bifurcation and metamorphic characteristics. Starting from the motion characteristics of each phase of SMM based on the screw theory, a reconfigurable hybrid limb is constructed by combining it with the series branch which can provide a constraint force and a constraint couple. The constraint changes of metamorphic hybrid limbs corresponding to different phases of SMM are analyzed. This leads to the design of a new type of reconfigurable parallel mechanism (RPM), in which the platform is connected to the base by three reconfigurable hybrid limbs. The results show that the performance of the RPM can be changed from 6 degrees of freedom (DOFs) to 5, 4, and 3 DOFs.

A Reconfiguration Algorithm for the Single-Driven Hexapod-Type Parallel Mechanism

This paper presents a hexapod-type reconfigurable parallel mechanism that operates from a single actuator. The mechanism design allows reproducing diverse output link trajectories without using additional actuators. The paper provides the kinematic analysis where the analytical relationships between the output link coordinates and actuated movement are determined. These relations are used next to develop an original and computationally effective algorithm for the reconfiguration procedure. The algorithm enables selecting mechanism parameters to realize a specific output link trajectory. Several examples demonstrate the implementation of the proposed techniques. CAD simulations on a mechanism virtual prototype verify the correctness of the suggested algorithm.

Type Synthesis of Reconfigurable Parallel Mechanisms for Ankle Rehabilitation with Completely Decoupled Actuated Limb

Type Synthesis of Reconfigurable Parallel Mechanisms for Ankle Rehabilitation with Completely Decoupled Actuated Limb

Position, velocity, and acceleration analyses of a reconfigurable parallel mechanism (hexapod) equipped with a single motor

Parallel mechanisms represent complex mechanical systems, which possess several important properties: high load capacity, increased accuracy, multitasking, and high reliability. A class of parallel mechanisms with a circular guide is known in engineering technique. Their design properties provide the end-effector with an increased rotational angle around one of the axes, as well as the ability to manipulate heavy objects. Reconfigurable parallel mechanisms (RPMs) form another class of mechanisms with several distinct features. Such devices can vary their motion pattern, change workspace shape and dimensions, and move avoiding singular configurations. This study provides a novel variation of a reconfigurable parallel mechanism (hexapod) with a circular guide, in which the end-effector movement is controllable by a single drive. The study presents a virtual prototype of this hexapod and shows the solution of the forward and inverse problems on positions, velocities, and accelerations. In addition, the study provides the singularity analysis.

Virtual and Physical Prototyping of Reconfigurable Parallel Mechanisms with Single Actuation

The paper presents novel models of reconfigurable parallel mechanisms (RPMs) with a single active degree-of-freedom (1-DOF). The mechanisms contain three to six identical kinematic chains, which provide three (for the tripod) to zero (for the hexapod) uncontrollable DOFs. Screw theory is applied to carry out mobility analysis and proves the existence of controllable and uncontrollable DOFs of these mechanisms. Each kinematic chain in the synthesized mechanisms consists of planar and spatial parts. Such a design provides them with reconfiguration capabilities even when the driving link is fixed. This allows reproduction of diverse output trajectories without using additional actuators. In this paper, the model of a mechanism with six kinematic chains (hexapod) has been virtually and physically prototyped. The designing and assembling algorithms are developed using the detailed computer-aided design (CAD) model, which was further used to carry out kinetostatic analysis considering complex geometry of mechanism elements and friction among all contacting surfaces of joints. The developed virtual prototype and its calculation data have been further applied to fabricate mechanism elements and assemble an actuated full-scale physical prototype for future testing.

Dimensional (Parametric) Synthesis of the Hexapod-Type Parallel Mechanism with Reconfigurable Design

The study provides a solution to a dimensional synthesis problem for a hexapod-type reconfigurable parallel mechanism, which can change its configuration to realize different trajectories of its output link while having a single drive. The work presents an original procedure to find the dimensions of some mechanism’s links and their initial configuration to reproduce these trajectories. After describing the mechanism, the paper examines kinematic relations representing the basis for the subsequent synthesis algorithm. Next, the obtained expressions are extended and provide a system of equations to be solved. The structure of this equation system allows it to be solved effectively by numerical methods, which is demonstrated with an example. The proposed algorithm of dimensional synthesis does not require solving the optimization problems, in contrast to the familiar methods of dimensional synthesis of parallel mechanisms. Further, the suggested approach to the synthesis problem allows finding solution in a fast and computationally efficient manner.

Special Section: Design, Analysis and Actuation of Reconfigurable Parallel Mechanisms

Abstract This Editorial is for the Focused Section with 11 papers aiming to share research efforts in design, theory, development, and applications for Reconfigurable Parallel Mechanisms (RPMs) building on work first presented at the 4th International Conference on Fundamental Issues, Applications and Future Research Directions for Parallel Mechanisms / Manipulators / Machines (World Parallel 2020).

Constraint and Mobility Change Analysis of Rubik\u2019s Cube-inspired Reconfigurable Joints and Corresponding Parallel Mechanisms

The current research of reconfigurable parallel mechanism mainly focuses on the construction of reconfigurable joints. Compared with the method of changing the mobility by physical locking joints, the geometric constraint has good controllability, and the constructed parallel mechanism has more configurations and wider application range. This paper presents a reconfigurable axis (rA) joint inspired and evolved from Rubik's Cubes, which have a unique feature of geometric and physical constraint of axes of joint. The effectiveness of the rA joint in the construction of the limb is analyzed, resulting in a change in mobility and topology of the parallel mechanism. The rA joint makes the angle among the three axes inside the groove changed arbitrarily. This change in mobility is completed by the case illustrated by a 3(rA)P(rA) reconfigurable parallel mechanism having variable mobility from 1 to 6 and having various special configurations including pure translations, pure rotations. The underlying principle of the metamorphosis of this rA joint is shown by investigating the dependence of the corresponding screw system comprising of line vectors, leading to evolution of the rA joint from two types of spherical joints to three types of variable Hooke joints and one revolute joint. The reconfigurable parallel mechanism alters its topology by rotating or locking the axis of rA joint to turn all limbs into different phases. The prototype of reconfigurable parallel mechanism is manufactured and all configurations are enumerated to verify the validity of the theoretical method by physical experiments.

Analysis and control for a new reconfigurable parallel mechanism

This article proposes a new reconfigurable parallel mechanism using a spatial overconstrained platform. This proposed mechanism can be used as a machine tool. The mobility is analyzed by Screw Theory. The inverse kinematic model is established by applying the closed-loop equation. Next, the dynamic model of the presented mechanism is established by Lagrange formulation. To control the presented mechanism, some controllers have been used. Based on this dynamic model, the fuzzy-proportion integration differentiation (PID) controller is designed to track the trajectory of the end effector. For each limb, a sliding mode controller is applied to track the position and velocity of the slider. Finally, some simulations using ADAMS and MATLAB are proposed to verify the effectiveness and stability of these controllers.

Neural Network and Performance Analysis for a Novel Reconfigurable Parallel Manipulator Based on the Spatial Multiloop Overconstrained Mechanism

To meet the different requirements in the industrial area, a novel reconfigurable parallel mechanism is proposed based on the spatial multiloop overconstrained mechanism. The configurations can be changed by driving the low-DOF (degree-of-freedom) overconstrained mechanism. The mobility of this mechanism is investigated. And the kinematic model and Jacobian matrix are both established. Based on the Jacobian matrix, the workspace, stiffness, and conditional number are all analyzed. To focus on the application in the industrial area, this paper proposes a method to establish the relationship between the performance and the structural parameters by using the modified BP neural network. Based on this method, the structural parameters can be chosen by the requirements of the special task in the industrial area. Finally, some numerical examples are presented to verify the method.

Type synthesis of multi-mode mobile parallel mechanisms based on refined virtual chain approach

Mechanisms with multiple operation and multiple locomotion modes are applied to implementing the different tasks and adapting to the changes in terrains as well. Based on this application, this paper presents a refined virtual chain approach which is applied to the type synthesis of a class of multi-mode mobile parallel mechanisms (PMs). This approach is based on screw theory to synthesize the branches with coaxial rotating components under different constraint conditions. The geometric orientations of the different constraint conditions in a plane can be changed by using coaxial rotating components. Meanwhile, the inactive joints in branches are determined. By means of this approach, a number of symmetrical and asymmetrical reconfigurable PMs with four branches are obtained. The four of the multi-mode PMs are sketched as examples and the operation and locomotion modes for the mechanisms are discussed.

Classification of Reconfigurable Parallel Mechanisms

The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the characteristic parameters of each type. On that basis, individual calculation templates are developed for formalized design of reconfigurable parallel mechanisms.

Kinematic modeling and optimization of a new reconfigurable parallel mechanism

This paper investigates a new reconfigurable parallel mechanism consisting of three SvPS kinematic limbs. Induced by phase changes of a metamorphic spherical variable-axis joint (Sv), the SvPS limb is capable of changing to two typical configurations, of which one exerts no constraint and the other exerts a constraint force to the moving platform. Reconfiguration of the three limbs enables the 3-SvPS parallel mechanism to have four distinct configurations with degrees of freedom (DOFs) varying from 3 to 6. Analytical model of position and workspace analysis of the reconfigurable parallel mechanism are first investigated. In terms of the screw theory, a unified Jacobian matrix covering all the mobility configurations is established and utilized for analyzing singularity of the parallel mechanism in different configurations. Further, performance analysis and optimization are explored using the motion/force transmission method. The 3-SvPS parallel mechanism can be used as structure of reconfigurable robotic machine center with adaptability to changing task requirements.