Workspace Analysis Research Articles

Kinematics and workspace analysis of a modified portable exoskeleton arm

In order to solve the problems such as small workspace, complicated mechanical structure and motion interferences of traditional exoskeleton arm, a modified exoskeleton mechanism is proposed by optimizing the angles between the shoulder joint axes. In this paper, the model of traditional exoskeleton arm and the modified one are both built. And the kinematic theory of the two models is analysed and discussed. Furthermore, the Monte Carlo method is used to simulate the workspace of the mechanism with the help of the Matlab software. The simulation results show that the modified exoskeleton arm has larger workspace than the traditional one. So it can better meet the needs of more application scenarios.

Kinematics and workspace analysis of a spherical exoskeleton parallel mechanism

Based on the biomechanical simulation curve of OpenSim, an open source software of biomechanical model, a spherical exoskeleton parallel mechanism with two degrees of freedom for hip joint is proposed in this paper for the rehabilitation therapy of patients with impaired leg motor function or elderly people with walking dysfunction. Firstly, the parallel mechanism is modeled and the position inverse solution of the parallel mechanism is obtained using inverse kinematics analysis. The velocity analysis expression of the mechanism is derived by deriving the inverse kinematics solution. The model is imported into the mechanical system dynamics analysis software ADAMS and matrix processing analysis software MATLAB to carry out simulation experiments. The correctness of the velocity analysis is verified by comparing the velocity simulation results of the two methods. Then, three singular types of the mechanism are analyzed according to the obtained Jacobian matrix. According to the inverse solution of the mechanism, the reachable workspace of the mechanism is obtained by programming in MATLAB with given mechanism parameters and restriction conditions. Finally, the prototype platform is built. The experimental results show that the exoskeleton hip joint using this parallel mechanism can satisfy the requirement of rotation angle of human hip joint movement, but also can be good to assist patients with leg flexion-extension movement and adduction-abduction movement, and it is helpful to carry out corresponding rehabilitation training. It also has theoretical significance and application value for the research work of human hip exoskeleton parallel mechanism.

Design and Development of a Novel 2-Degree-of-Freedom Parallel Robot

SummaryParallel robots are widely used in the fields of manufacturing, medical science, education, scientific research, etc. Many studies have been conducted on the topic already. However, shortcomings still exist, especially in certain situations. To meet the demand of good speed and load performances at the same time, this work presents a novel 2-degree-of-freedom parallel robot. The structural design, static, stiffness, and reachable workspace analysis of the robot are given in the manuscript. Experiment regarding the accuracy and speed performance is conducted, and the results are provided. In the end, potential applications of the proposed robot are suggested.

Design and Workspace Analysis of a Parallel Ankle Rehabilitation Robot (PARR).

The ankle rehabilitation robot is essential equipment for patients with foot drop and talipes valgus to make up deficiencies of the manual rehabilitation training and reduce the workload of rehabilitation physicians. A parallel ankle rehabilitation robot (PARR) was developed which had three rotational degrees of freedom around a virtual stationary center for the ankle joint. The center of the ankle should be coincided with the virtual stationary center during the rehabilitation process. Meanwhile, a complete information acquisition system was constructed to improve the human-machine interactivity among the robot, patients, and physicians. The physiological motion space (PMS) of ankle joint in the autonomous and boundary elliptical movements was obtained with the help of the RRR branch and absolute encoders. The natural extreme postures of the ankle complex are the superposition of the three typical movements at the boundary motions. Based on the kinematic model of PARR, the theoretical workspace (TWS) of the parallel mechanism was acquired using the limit boundary searching method and could encircle PMS completely. However, the effective workspace (EWS) was smaller than TWS due to the physical structure, volume, and interference of mechanical elements. In addition, EWS has more clinical significance for the ankle rehabilitation. The PARR prototype satisfies all single-axis rehabilitations of the ankle and can cover most compound motions of the ankle. The goodness of fit of PMS can reach 93.5%. Hence, the developed PARR can be applied to the ankle rehabilitation widely.

Workspace analysis of the bogie 6-degree-of-freedom dynamic simulation test bench

The bogie 6-degree-of-freedom dynamic simulation test bench can simulate various operating conditions of the bogie through coordinated movement of the three parallel 6-degree-of-freedom motion platforms; however, the motion of the platforms will be interfered by some space obstacles. In order to obtain the collision-free workspace of the 6-degree-of-freedom motion platforms, a limit boundary–search method based on the collision-detection model is proposed. The structure of three parallel 6-degree-of-freedom motion platforms is analyzed, and its inverse kinematics model is established. Considering its internal constraints, the constraint models of the actuators’ stroke and the spherical hinges angle are established. Based on the collision-detection method between convex polygons, the minimum distance-detection models between platforms and obstacles as well as between actuators and obstacles are established. Then the limit boundary–search method is used to search for all boundary points that satisfy the constraint conditions. Finally, the correctness and feasibility of the proposed method and models are verified by some simulation examples. The proposed research avoids collisions effectively and provides a reference for the optimal design of the test bench.

Position, Jacobian, decoupling and workspace analysis of a novel parallel manipulator with four pneumatic artificial muscles

This paper firstly presents a novel 4-SPS/S (active chain/passive chain) parallel manipulator (PPM) driven by four pneumatic artificial muscles (PAMs). SPS denotes a spherical pair–prismatic pair–spherical pair chain and S denotes a spherical pair chain. The PPM proposed can be utilized as shoulder, wrist, waist, hip and ankle simulators or ankle rehabilitation robot. And we present a comprehensive analysis on the PPM proposed, including degrees of freedom (DOF), position, kinematic, Jacobian, singularity, decoupling and workspace analysis. In order to decrease the influence of the maximum angle of spherical pairs in four active chains on the workspace, a novel connector for PAM is proposed. The structure of the PPM is explicitly described, and DOF of the PPM are analyzed based on constraint screw theory. The posture of the moving platform (MP) of the PPM is obtained though Z–Y–X (α–β–γ) type Euler angles and the inverse position solution is obtained. When the MP moves toward any a single Euler angle direction, the closed-form direct position solution is presented by geometric analysis. A back propagation (BP) neural network model for the whole direct position solution is established. Two methods for the Jacobian matrix, one velocity composition, one differentiation, are addressed, and the acceleration inversion is obtained. Based on the Jacobian matrix, the singularity and kinematic decoupling of the PPM are both analyzed. The geometric model of expanded PAM is introduced, and the change of diameters of four PAMs in active chains is taken into consideration when chains of the PPM interfere. Based on length ranges of four active chains, the maximum angle of spherical pairs and possible interferences between chains of the PPM, the configuration workspace is presented. Finally, the characteristic of the workspace and the influence of the maximum angle of spherical pairs in active chains on the configuration workspace are both analyzed.

Unified Kinematics of Prismatically Actuated Parallel Delta Robots

SummaryThis paper presents a unified formulation for the kinematics, singularity and workspace analyses of parallel delta robots with prismatic actuation. Unlike the existing studies, the derivations presented in this paper are made by assuming variable angles and variable link lengths. Thus, the presented scheme can be used for all of the possible linear delta robot configurations including the ones with asymmetric kinematic chains. Referring to a geometry-based derivation, the paper first formulates the position and the velocity kinematics of linear delta robots with non-iterative exact solutions. Then, all of the singular configurations are identified assuming a parametric content for the Jacobian matrix derived in the velocity kinematics section. Furthermore, a benchmark study is carried out to determine the linear delta robot configuration with the maximum cubic workspace among symmetric and semi-symmetric kinematic chains. In order to show the validity of the proposed approach, two sets of experiments are made, respectively, on the horizontal and the Keops type of linear delta robots. The experiment results for the confirmation of the presented kinematic analysis and the simulation results for the determination of the maximum cubic workspace illustrate the efficacy and the flexible applicability of the proposed framework.

Reachable workspace determination for a spatial hyper-redundant manipulator formed by several parallel manipulators

Solving the reachable workspaces of spatial hyper-redundant manipulators (SHRMs) formed by serially connected parallel manipulators is an important and challenging work. This study addresses the issue on reachable workspaces and establishes a novel CAD-VBbased workspace determination system for determining the reachable workspaces of SHRMs. The reachable workspace determination of a novel (3-RPS)+(3-SPR)+(3-RPS) SHRM, a triple delta-type SHRM, and a novel (3-RRS)+(3-SPR)+(3-RRS) SHRM shows the generality and effectiveness of the proposed approach. The system proposed in this study can contribute to reachable workspace analysis for SHRMs.

Collision-free workspace and kinetostatic performances of a 4-DOF delta parallel robot

In this paper, the mechanical interference of the 4-DOF delta parallel robot, which is designated to be used as pick-and-place robot, within its practical workspace is investigated. A new geometric algorithm is introduced which enables to identify mechanical collisions, namely the collisions of links with each other and the collision of links with the installed conveyor at the bottom of the robots workspace. Obtaining the close-to-reality workspace, upon eliminating the parts which lead to collision, is an essential and undeniable process in the workspace analysis of a pick-and-place robot. Moreover, the most common kinetostatic performance indicators including sensitivity, dexterity, and manipulability for the first time are presented and investigated for the 4-DOF delta parallel robot within the workspace.

Using a game engine for simulation in ergonomics analysis, design and education: An exploratory study

Among the possible approaches for building virtual environments (VE), researchers have recently started employing game engines (GE). Although there are already studies reporting the usage of GE-based VEs, their potential for supporting a more comprehensive workspace analysis (considering the physical, organizational and cognitive aspects of work) has yet to be better understood. The main goal of this paper is to investigate how a GE-based simulation of a real workplace (a local control room in an oil refinery) can be used as a tool by practitioners and researchers in evaluating work conditions. Participants (n = 38) were recruited to explore the simulation and evaluate the workplace dimensions represented. A comparison between the scores participants attributed to the work dimensions and the scores assigned by the ergonomics consultant was performed through a statistical test to verify whether they significantly differed or not. Out of the 10 aspects evaluated, only 3 presented significant differences, thus showing that GE suitability for ergonomics analysis is conditioned to the aspects represented. Qualitative data analysis highlighted participants' perception of GEs potential as an analysis and educational tool, as well as a medium for fostering communication and stakeholder involvement in the design process.

Kinematička i analiza radnog prostora paralelnog uređaja za rehabilitaciju pacijenata sa povredom vratne kičme

Kinematička i analiza radnog prostora paralelnog uređaja za rehabilitaciju pacijenata sa povredom vratne kičme

On the Maximization of Joint Velocities and Generalized Reactions in the Workspace and Singularity Analysis of Parallel Mechanisms

SummaryAn approach for calculating the maximum possible absolute values of joint velocities or generalized reactions in a leg of a parallel mechanism has been considered in this paper. The Jacobian analysis and the Screw theory-based methods have been used to acquire the result. These values are calculated for the “worst” directions of the external load or end-effector’s velocity for each leg. The feasibility of using these parameters as the measures of closeness to different types of parallel mechanism singularity is discussed. Further, how this approach is related to the state-of-the-art methods has been illustrated. The key aspect of the discussed approach is that the normalization of vectors or screws is carried out separately for angular and linear components. One possible advantage of such an approach is that it deals only with the kinematic and statics of the mechanism while still providing physically meaningful and practically applicable measures. Case studies of a 3-Degrees Of Freedom translational parallel mechanism and a planar parallel mechanism are presented for illustration and comparison.

Structure synthesis and workspace analysis of a telescopic spraying robot

Spraying robot is a kind of important industrial equipments. However most of them cannot flexibly change their workspace. In order to obtain a spraying robot with extremely large workspace but a small storage space, we synthesize an innovative mobile robot with a telescopic forearm. First, the structure of a four-side deployable arm to generate straight line motion for the mobile robot is proposed. It adequately enlarges the workspace and reduces the storage space because of the stretchable structure. Based on the new structure, the homogeneous transformation matrix and Jacobian matrix of the forward and inverse kinematics are deduced in details for workspace evaluation. Geometry analysis indicates that the four-side deployable structure effectively extends the arm of the robot, and therefore it has much larger workspace than its existing counterparts do.

Retraction: Using artificial neural network for forward kinematic problem of under-constrained cable robots

Cable-Driven Parallel Robot has many advantages. However, the problems of cable collision between each other and environment, the lack of proper structure and non-positive cable tension prevent the spread of them. In this work, a neural network (NN) model of under constrained cable robots is presented with external forces applied to the end-effector (EE) for computing the position of it. As in under-constrained robot’s kinematics and statics are innately coupled together, and they contemporaneously should be considered the forward kinematic problem of the robot change to an optimization problem. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The main contribution of this paper has three goals. First, a method is used toward kinematic problem of the under constrained cable robot modeling using four bar linkage kinematic concept, which could be used in online control approaches for real-time purposes. Second, in order to track the position of end-effector, an online PD controller is designed by the three error criteria methods such as IAE, ISE and ITSE. Finally, as the third contribution, NN control approach is applied in order to validate the model. A model is created based on the robot’s geometry and dynamic to solve the forward kinematics problem. So, the forward kinematic problem is solved offline and used online. Moreover, an analysis of workspace is performed which discovers that the solution of the forward kinematic problem of the under-constrained cable robots is unique in this case. In addition, a modified local linear model tree algorithm for nonlinear system modelling are proposed. The results show the effectiveness of the proposed approach in modeling the under constrained cable robot.

Workspace analysis for a five degrees of freedom hybrid engraving plotter

At present, there is a little research on the workspace of the hybrid mechanism, and the further development of the engraving plotter is hindered due to the limitation of the workspace. In order to clearly understand the workspace of the hybrid engraving plotter, and verify whether the workspace meets the industrial production needs, the five degrees of freedom hybrid engraving plotter is analysed and studied. First, the structure of the engraving plotter is analysed and simplified, and then the direct equation is deduced by the analytic method. Second, according to the engraving plotter direct solution equation, the boundary of workspace is determined and the volume is calculated by using the optimisation algorithm. In order to understand the change of workspace in different z planes, the workspace of the parallel part is intercepted by some planes, which are parallel to XOY; thus, the authors know that the cut plane area of the workspace increases with the increase of Z values. Finally, the influence of the mechanism parameters is discussed on the dexterity. These theoretical knowledge will make important research significance for guiding engineering practice.

Kinematic analysis of a PPPR spatial serial mechanism with geometric errors

The present study focuses on the kinematic analysis of a PPPR spatial serial mechanism with a large number of geometric errors. The study is implemented in three steps: (1) development of a map between the end-effector position error and geometric source errors within the serial mechanism kinematic chains using homogeneous transformation matrix; (2) selection of geometric errors which have significant effects on end-effector positioning accuracy by sensitivity analysis; (3) kinematic analysis of the serial mechanism within which the geometric errors are modelled as interval variables. The computational algorithms are presented for positioning accuracy analysis and workspace analysis in consideration of geometric errors. The analysis results show that the key factors which have significant effects on end-effector position error can be identified efficiently, and the uncertain workspace can also be calculated efficiently.

Modeling and Workspace Analysis of Six Degree of Freedom Manipulator

Designed a 6-DOF manipulator according to this requirement. According to D-H method, the coordinate system was established for each joint of manipulator and the connecting rod parameters. Set up a kinematic model of the manipulator. Then the attitude and position of the end effector were deduced by homogeneous transformation, and the accuracy of the kinematics equation was verified by simulation and mathematical calculation. After that, according to the mapping of joint space to work space, Monte Carlo method was used to analyze the workspace of the manipulator. Finally, the 3D map of workspace was drawn in MATLAB. It provides a reference for follow-up robotic trajectory planning, motion control and parameter optimization.

Research and Realization of a Master-Slave Robotic System for Retinal Vascular Bypass Surgery

Retinal surgery continues to be one of the most technical demanding surgeries for its high manipulation accuracy requirement, small and constrained workspace, and delicate retinal tissue. Robotic systems have the potential to enhance and expand the capabilities of surgeons during retinal surgery. Thus, focusing on retinal vessel bypass surgery, a master-slave robot system is developed in this paper. This robotic system is designed based on characteristics of retinal vascular bypass surgery and analysis of the surgical workspace in eyeball. A novel end-effector of two degrees of freedom is designed and a novel remote center of motion mechanism is adopted in the robot structure. The kinematics and the mapping relationship are then established, the gravity compensation control strategy and the hand tremor elimination algorithm are applied to achieve the high motion accuracy. The experiments on an artificial eyeball and an in vitro porcine eye are conducted, verifying the feasibility of this system.

Image-Guided Dual Master–Slave Robotic System for Maxillary Sinus Surgery

The pathway to the maxillary sinus is anatomically curved and narrow. Thus, the conventional approach using a straight endoscope and surgical tools is difficult to diagnose and treat some blind regions of the maxillary sinus through the nostrils. Such cases are usually dealt with by an approach with an external incision that causes large invasive surgery. In order to approach the blind regions without any external incision, a new bendable device and an image-guided robotic approach for the maxillary sinus surgery are required. This work reports design, development, and validation of an image-guided dual master–slave robotic system for the maxillary sinus surgery. Initially, specifications of the robotic system for sinus surgery are decided by analysis of the anatomical structure of the sinus. A method for determining the design parameters of continuum type salve robot is also presented. Based on the specifications and the design parameter determining method, a compact design of bendable dual slave robotic system for inspection and biopsy operation of the maxillary sinus area is devised and workspace analysis for verifying the robot design is conducted. The performance of the dual master–slave system equipped with flexible devices is validated through several phantom tests. The results suggest that bendable end-effectors and navigation software are useful to navigate and treat blind regions inside general sinus areas as well as the maxillary sinus.

Geometric isotropy indices for workspace analysis of parallel manipulators

This paper addresses the isotropy of a workspace in terms of its geometric shape. Workspace isotropy analysis plays a crucial role in improving the quality of workspace for parallel manipulators. When a parallel manipulator is installed on a moving platform (e.g., satellites, aircrafts, ships, etc.), the geometry of its workspace is critical to achieve the planned tasks. This paper proposes three novel workspace isotropy indices, namely, translational workspace isotropy index (TWII), rotational workspace isotropy index (RWII), and entire workspace isotropy index (EWII), for workspace isotropy analysis in terms of the geometric shape of the workspace. All three indices are mathematically defined. TWII and RWII can be applied to both planar and spatial parallel manipulators with movable bases while EWII can work for planar parallel manipulators with movable bases. Random rotational disturbances are applied to the movable bases of multiple parallel manipulators in simulation. Simulation results show that the proposed workspace isotropy indices are effective in evaluating how isotropic the geometric shape of a workspace is. They are good at reflecting the robustness of a parallel manipulator to rotational disturbances to its movable base. The proposed indices can also be used as guidelines for the optimal design of parallel manipulators.