Novel Design of a Rotation Centre Auto-Matched Ankle Rehabilitation Exoskeleton with Decoupled Control Capacity

This paper presents a novel ankle rehabilitation exoskeleton for post-stroke patients, with its rotational centre automatically conforming with ankle complex once people wear it. This exoskeleton has 2 rotation DOFs and is able to provide 2 different rotation patterns by reconfiguring. In the combined-rotation pattern arrangement, the mechanism can generate all three kinds of rotations that the ankle complex is naturally capable of realising. Among these rotational motions, adduction/abduction rotation is coupled motion. This rotation can be further reduced, or eliminated, by minimizing the distance between the lower connection points of the actuated links and the human ankle complex, and vice versa. For the other rotation pattern, a 90-degree arrangement of the side link offers decoupled motion control of the mechanism. Numerical studies reveal that the required rehabilitation workspace for dynamical gait exercises can be achieved with high dexterity, without generating singularities. Further investigations indicate that this mechanism has great potential for rehabilitating post-stroke patients of a wide range of heights and weights.

Kinematic design of a translational parallel mechanism based on sub-kinematic chain determined workspace superposition

This paper presents the kinematic design of a translational parallel mechanism (PM) named Vari-Orthoglide by means of the workspace superposition, according to the sub-kinematic chain (SKC) based PM composition principle. The main topological characteristics of the manipulator with two SKCs under study, such as the position and orientation (POC) characteristics, degree of freedom (DOF) and coupling degree are analyzed, which turns out that the coupling degree equals to 1, implying the partially decoupled motion. With the topological characteristics based kinematic modeling principle, a symbolic model of the kinematics is established to derive its symbolic direct and inverse kinematic solutions. Based upon the direct kinematic solution, the workspaces for the two SKCs can be efficiently found. Moreover, the singularity loci are identified for finding the singularity-free workspace, where a regular workspace is fitted as the task workspace as expected. The presented work shows an approach to design translational parallel mechanisms considering motion decoupling and regular workspace, applicable to other types of parallel mechanisms.

Structure Synthesis of a Class of Parallel Manipulators with Fully Decoupled Projective Motion

This paper describes the structure synthesis of a special class of parallel manipulators with fully decoupled motion, that is, a one-to-one correspondence between the instantaneous motion space of the end-effector and the joint space of the manipulator. A notable finding of this study is that a fully decoupled design can be achieved for parallel manipulators with any number of degrees of freedom (DOFs) when the rotational DOF of the end-effector is expressed in the form of a projective angle representation. On the basis of the geometrical reasoning of the projective motion interpreted by screw algebra, a systematic approach is developed for synthesizing the structures of f-DOF (f ≤ 6) parallel manipulators with fully decoupled projective motion. Several 2-, 3-, 4-, 5-, and 6-DOF parallel manipulators with fully decoupled projective motion were designed for illustrating the developed method.

Decoupled Hydrodynamic Models and Their Outdoor Identification for an Unmanned Inland Cargo Vessel with Embedded Fully Rotatable Thrusters

Expanding the automation level of the freshly introduced fleet of self-propelled Watertruck+ barges, which house fully-rotatable embedded thrusters, might increase their ability to compete with their less sustainable but dominating road-based alternatives. Hydrodynamic motion models, which reveal the manoeuvring capabilities of these barges, can serve as inputs for many pieces of this automation puzzle. No identified motion models or hydrodynamic data seem to be publicly available for the hull design and the novel actuation system configuration of these barges. Therefore, this study offers: (i) decoupled motion model structures for these barges for surge, sway, and yaw, with a focus on the thruster and damping models; (ii) two identification procedures to determine these motion models; (iii) all the experimental data, generated outdoors with a scale model barge to identify (i) based on (ii). In addition, the identified surge models were compared with both computational and empirical data. These comparisons offer more physical insights into the identified model structures and can aid in the model selection for which the desired complexity and accuracy evidently depend on their envisaged application. Finally, this methodology need not be limited to the vessel and actuation types utilised by us.

Structure Synthesis of Parallel Manipulators With Fully Decoupled Projective Motion and Any Degrees of Freedom

This paper presents the structure synthesis of a special class of parallel manipulators with motion decoupleability. The manipulator is synthesized by grouping a motion constraint leg and a set of constraint-free legs. The desired motion, i.e., the output degrees of freedom (DOFs), of the end-effector is expressed by a projective angle representation. It was found that the fully decoupled design for parallel manipulators with any DOFs is achievable when the output motion is described by the projective angles. A synthesis procedure is proposed based on the reasoning of the screw systems and reciprocal screws of the decoupled motion. Several design examples of fully decoupled 2-, 3-, 4-, 5-, and 6-DOF parallel manipulators are provided.

Design and Optimization of a Three Degrees-of-Freedom Spatial Motion Compliant Parallel Mechanism With Fully Decoupled Motion Characteristics

This paper presents a novel three degrees-of-freedom (DOF) compliant parallel mechanism (CPM) with a fully decoupled spatial motion (θX−θY−Z) and optimized mechanical properties. To design the CPM using the beam-based structural optimization method, several novel criteria for synthesizing three-legged CPMs with fully decoupled motions are derived. The obtained results suggest that the synthesized CPM delivers a diagonal compliance matrix, a large workspace of 10deg×10deg×7mm, fast dynamic response of ∼100Hz, and good stiffness performance whereby the translational and rotational stiffness ratios are ∼3600 and ∼570, respectively. A prototype of the synthesized CPM is fabricated using one of the three-dimensional (3D) printing technologies, electron beam melting (EBM). Experimental results have shown that the 3D printed CPM can produce the full workspace with deterministic mechanical properties whereby the highest deviations between the theoretical and experimental results are 11.2% and 1% for stiffness and dynamic behaviors, respectively. Importantly, the decoupled-motion characteristic is also verified via an energy approach, i.e., the energies of the undesired parasitic motions are minor (<1%) as compared with the energy of the desired motion. In addition, several comparisons are conducted to clarify the advantages of the synthesized CPM to the existing designs. All these investigations suggest that the proposed CPM can be used in precision positioning systems due to the good stiffness characteristics, large workspace, fast dynamic response, and decoupled output motions.

Topological Design of an Asymmetric 3-Translational Parallel Mechanism With Zero Coupling Degree and Motion Decoupling

In this paper a new asymmetric 3-translational (3T) parallel manipulator, i.e., RPa(3R) 2R+RPa, with zero coupling degree and decoupled motion is firstly proposed according to topology design theory of parallel mechanism (PM) based on position and orientation characteristics (POC) equations. The main topological characteristics such as POC, degree of freedom and coupling degree are calculated. Then, the analytical formula for the direct and inverse kinematic are directly derived since coupling degree of the PM is zero. The study of singular configurations is simple because of the independence of the kinematic chains.

Design and analysis of a new flexure-based XY stage

This article presents the design, modeling, and experimental testing of a novel piezo-driven XY stage with parallel, decoupled, and compact kinematic structure. The structural design of the stage is based on a hybrid compliant mechanism employing the right-circular double-rocker mechanism and the leaf-type parallelogram mechanism. The proposed XY stage is capable of producing a large workspace range, an excellent decoupled motion, and a suitable resonant frequency. By means of the pseudorigid-body-model method, the theoretical models of the XY stage are derived. Using the finite element analysis simulations, the optimal structural parameters are acquired, and the theoretical models are analyzed and validated. A prototype of the proposed stage was finally manufactured, and several experimental investigations were performed to validate its performances. The experimental results show that the XY stage has a large amplification ratio of 7.48 and a large workspace range of 150.3 µm × 147.9 µm. In addition, the parasitic motion along the y-axis ( x-axis) accounts for 0.94% (0.74%) of the x-axis ( y-axis) motion, which indicates that the stage possesses excellent decoupling characteristics.