Workspace Of Manipulator Research Articles

A Multi-Contact-Aided Continuum Manipulator With Anisotropic Shapes

Cable-driven continuum manipulators have shown excellent benefits to work for endoluminal intervention. Demand of small diameter for confined anatomy limits the usage of multiple actuations, leading to limited DOFs and bending shapes. To address this problem, this letter proposes a multi-contact-aided continuum manipulator with anisotropic bending shapes. First, contact-aided compliant mechanisms (CCMs) are configured at different locations to introduce the specific constraints to enable the anisotropy. Then, the forward and inverse kinematic models considering contact blocks are built. The reachable workspace of the continuum manipulator is given, and simulation cases are studied to demonstrate the superiority of the proposed manipulator. Finally, a 3D-printed physical prototype is fabricated, and preliminary experiments are conducted to evaluate the model accuracy. Results show an average shape error of 1.98 mm (4.2%) and a maximum of 3.58 mm (7.6%). A robotic bronchoscopy platform integrated with the continuum manipulator is developed to conduct the airway phantom experiments. The shape deviation of the proposed manipulator from the centerline of the bronchus is 31.8% smaller than that of the constant curvature manipulator. The experiments validate the system-level feasibility and effectiveness of the developed continuum manipulator.

Deep Reinforcement Learning-Based Path Planning for Multi-Arm Manipulators with Periodically Moving Obstacles

In the workspace of robot manipulators in practice, it is common that there are both static and periodic moving obstacles. Existing results in the literature have been focusing mainly on the static obstacles. This paper is concerned with multi-arm manipulators with periodically moving obstacles. Due to the high-dimensional property and the moving obstacles, existing results suffer from finding the optimal path for given arbitrary starting and goal points. To solve the path planning problem, this paper presents a SAC-based (Soft actor–critic) path planning algorithm for multi-arm manipulators with periodically moving obstacles. In particular, the deep neural networks in the SAC are designed such that they utilize the position information of the moving obstacles over the past finite time horizon. In addition, the hindsight experience replay (HER) technique is employed to use the training data efficiently. In order to show the performance of the proposed SAC-based path planning, both simulation and experiment results using open manipulators are given.

Devising a method to analyze the current state of the manipulator workspace

This paper has proposed a program analysis method over the current state of the workspace of an anthropomorphic manipulator using the Mathcad software application package (USA). The analysis of the manipulator workspace helped solve the following sub-tasks: to calculate the limits of the grip reach, to determine the presence of "dead zones" within the manipulator workspace, to build the boundaries of the manipulator workspace. A kinematic scheme of the manipulator typically provides for at least five degrees of mobility, which is why in the three-dimensional Cartesian coordinate system the work zone boundaries represent the surfaces of a complex geometric shape. The author-devised method makes it possible to construct the projections of the boundaries of the manipulator's work zone onto the coordinate planes in the frame of reference associated with the base of the robot.
 Using Mathcad's built-in features makes it possible to effectively solve the above sub-tasks without wasting time developing specialized software. The Mathcad software application package provides for the possibility of a symbolic solution to the first problem of the kinematics of an industrial robot, that is, the program generates analytical dependences of the coordinates for special point P (pole) of the grip on the trigonometrical functions of the generalized coordinates. The resulting analytical dependences are used for kinematic and dynamic analysis of the manipulator.
 Special features in constructing mathematical models when using the Mathcad software application package have been revealed. Simulating the manipulator movement taking into consideration constraints for kinematic pairs, the drives' power, as well as friction factors, makes it possible to optimize the parameters of the manipulator kinematic scheme.
 An example of the analysis of the working space of an anthropomorphic manipulator with five degrees of mobility has been considered.
 The reported results could be used during the design, implementation, modernization, and operation of manipulators.

Dynamic Models of Unmanned Aerial Vehicle Manipulator Control and Stabilization

Purpose or research. Improving guidance accuracy of robotic capture mounted on an unmanned aerial vehicle and the stability of combined aerial manipulation system is the main objective of this study. In order to achieve this goal, a particular task of developing a manipulator control system that considers joint working space of manipulator and unmanned aerial vehicle has been solved. Methods. Kinematic model of a manipulator with three degrees of freedom is proposed in this work. This is a part of air manipulation system of quadrotor. Rotary movement of two successive links is performed by means of hinge joint. Direct and inverse kinematic tasks were solved for this manipulator. Equations for dynamic model were also obtained. Dynamic response of each link is sufficient for quick stabilization of the system with little re-adjustment. Self-tuning fuzzy proportional-integral-differentiating (PID) regulator was developed based on these data to control the manipulator. Control system for each manipulator link consists of a PID regulator and a fuzzy PID output using Mamdani method. Results. Simulation of developed manipulator control system was carried out in the absence of disturbances. The proposed control system satisfies specified requirements and ensures continuous and smooth movement of manipulator links in calculated trajectory. Conclusion. The developed three-link manipulator motion control method provides a horizontal mass center shift not more than 1.25 mm, which is an acceptable result for rapid stabilization of unmanned aerial manipulator and further practical experiments.

Master manipulator optimisation for robot assisted minimally invasive surgery

In robot-assisted minimally invasive surgery, the surgeon controls a robot by operating a pair of master manipulators. Thus, the performance of a master manipulator directly affects the work of the surgeon physiologically and psychologically. In order to improve the operability and quality of operation, a structure optimisation method of master manipulator is proposed. The optimisation index of workspace and dexterity of main manipulator based on ergonomics and kinematics is established, and the reasonable weight coefficient of optimisation index is determined by using combination weighting method. Experiments verified that the proposed optimisation method ensures a large workspace and good kinematic performance for the master manipulator. This improves the comfort of the surgeon and can effectively avoid the problem of cutting off master-slave communication to adjust the position of the master manipulator owing to the small workspace.

Diseño de la interfaz de control para un manipulador SCARA con efector final subactuado

The decoupled control of robots eases the generation of trajectories of position, speed and acceleration, as well as the combination of sequences of movement in the joints. The aim of this work is to develop an application for motion control, integrating a virtual model into a prototype SCARA manipulator of 4 DOF. The methodology consists: 1. Definition of the manipulator's workspace; 2. Preparation of the control diagram in LabVIEW; 3. Configuration and communication with Arduino hardware. 4. Development of the interface for simultaneous movements; 5. Configuration of the communication interface with SolidWorks. Developing such integration requires particular hardware characteristics that support simulation and communication environments between the different software mentioned, as well as the acquisition and processing of analog signals used in the control algorithm applied to the model, with Lagrange polynomials and direct and inverse kinematics modelling by the Denavit-Hartenberg method.

Reliable bounding of the implicitly defined sets with applications to robotics

The article considers approximation of solution sets to indeterminate systems for non-linear equations. We developed a method to obtain inner and outer approximations of such sets. The method uses interval analysis techniques and relies on the Krawczyk operator and its modification based on the Baumann bicentered interval extension. We developed software that efficiently constructs and visualizes the computed approximations of the solution sets for systems of non-linear equations. The software is implemented in Python programming language and is available for free download and use. Finding the solution set of indeterminate systems of equations finds at least one important application in practice: bounding the workspace of a robotic manipulator. We perform experiments for the 2-RPR robot and evaluate the tightness of the obtained approximations. As expected the Krawczyk bicentered method noticeably improves the quality of approximations as compared with the classical Krawczyk operator.

Kinematics and workspace analysis of a robotic device for performing rehabilitation therapy of upper limb in stroke-affected patients

Exoskeleton robots generally have multi-functions and one such function is doing rehabilitation therapy in upper limb and lower limb in stroke-affected patients. A novel hybrid (serial-parallel) robot manipulator was proposed in this paper for rehabilitation of upper limb and its kinematics are studied systematically. This robot manipulator intends to perform wrist flexion, wrist extension, wrist radial deviation, wrist ulnar deviation, elbow flexion, elbow extension, elbow pronation and elbow supination motions. The contemporary mechanical designs especially the kinematic structure of upper limb exoskeleton robots have a unique feature that is, almost all of them use serial manipulators, and few others used parallel manipulators. The kinematic structure of the proposed robot is that of a hybrid manipulator (two parallel manipulators connected in series) which has 4-degrees-of-freedom. It is composed of an upper 3SPS-type parallel manipulator and 2SPR-type parallel manipulator connected in series. The Jacobian and Hessian Matrix method was used to derive the manipulator kinematic formula for solving the displacement, velocity and acceleration. A 3D model of the robotic arm was constructed and analyzed by simulation. The positioning workspace of manipulator was constructed and analyzed. The 3SPS-type parallel manipulator has good kinematic characteristics while performing wrist motions. The 2SPR-type parallel manipulator produced singular configuration, while performing the desired rehabilitation elbow motions, it was found to not be suitable for usage in performing rehabilitation therapy in stroke-affected patients.

Effect of Number of Digits on Human Precision Manipulation Workspaces.

Precision manipulation, or moving small objects held in the fingertips, is likely the most heavily utilized class of dexterous within-hand manipulation and adds greatly to the capabilities of the human hand. This article focuses on studying the effects of varying the number of digits used on the resulting manipulation abilities, in terms of translational workspaces and rotational ranges, by manipulating two circular objects, 50 mm and 80 mm in diameter. In general, as the number of digits in contact with the object increases, the results show a significant reduction in precision manipulation workspace range for four of the six translation and rotation directions and no significant change in the other two, suggesting that for these particular metrics, more fingers result in a reduction in performance. Furthermore, while two digits results in the largest workspaces for five of the six translation and rotation axes, the lack of ability to control rotation in the distal-proximal direction suggests that three digits may be more desirable for overall precision manipulation dexterity.

Development of a Planar Haptic Robot With Minimized Impedance.

Several studies have reported that stroke survivors displayed improved voluntary planar movements when forces supporting the upper limb increased, and when impeding forces decreased. Earlier haptic devices interacting with the human upper limb were potentially impacted by undesired residual friction force and device inertia. To explore natural, undisturbed voluntary motor control in stroke survivors, we describe the development of a Decoupled-Operational space Robot for wide Impedance Switching (DORIS) with minimized mechanical impedances. This design is based on a novel decoupling mechanism separating the end effector from a manipulator. While the user manipulates the end effector freely inside the workspace of the decoupling mechanism, to which a manipulator of the robot is attached, the robot detects such change in position using a lightweight linkage system. The manipulator of the robot then follows such movements of the end effector swiftly. Consequently, the user can explore the extended workspace, which can be as large as the manipulator's workspace. Since the end effector is mechanically decoupled from the manipulators and actuators, the user can remain unaffected by the mechanical impedances of the manipulator. Mechanical impedances perceived by the user and bandwidth of the control system were estimated. The developed robot was capable of detecting larger maximum acceleration and larger jerk of the reaching movement in chronic stroke survivors with hemiparesis. We propose that this device can be utilized for evaluating voluntary motor control of the upper limb while minimizing the impact of robot inertia and friction forces on limb behavior.

Research on Path Calculation and Simulation System of Variable Parameter Manipulator

The simulation software of manipulator is generally developed by manufacturers, and the products are only suitable for the specific company, but cannot be used in universal. Aiming at this problem, this paper establishes a mathematical model with attributes through parametric design. The standard D-H parameter method is used to model the kinematics of the manipulator. Based on the expert system, the intelligent path planning of the manipulator is carried out, and the trajectory control instructions of the manipulator are generated. According to the Monte Carlo method of point cloud, the workspace of manipulator is obtained, and the bounding box technology is used for real-time collision detection. Taking the welding work as an example, the parametric modelling and trajectory planning simulation of the manipulator are realized, and a general off-line programming platform is established.

Singularity-free spheres in the position and orientation workspaces of Stewart platform manipulators

This paper presents the computation of singularity-free regions in the position and orientation workspaces of Stewart platform manipulators (SPMs). Notwithstanding several previous publications in this regard, certain issues persist, such as the unavailability of analytical solutions and the consequent lack of accurate estimates of the numbers of solutions in various cases; the improper use of an incompatible metric while finding such regions inside SO(3) or SE(3). In this paper, the singularity-free regions have been envisaged as spheres in either R3 or SO(3). An analytical formulation for identifying such singularity-free spheres (SFSs) is presented. Several algebraic methods are explored to solve the resulting set of polynomial equations, leading to valuable insights into the numbers of (finite, complex) solutions to this problem, in both the position and the orientation workspaces. A physically meaningful and mathematically sound metric is used while computing the SFS in the orientation workspace. The formulation and computational algorithms have been demonstrated by identifying the SFSs (in R3 as well as SO(3)) for multiple architectures of the SPM through implementations in the C language.

A method to improve the productivity of legged manipulators performing on-site manufacturing tasks on large-scale structures

Legged manipulators that combine legged robots with manipulators have emerged as a new solution to large-scale structure on-site manufacturing tasks. However, the productivity of legged manipulators is strongly affected by the positioning and repositioning process. This paper aims to improve the productivity of legged manipulators by reducing the required positioning and repositioning times. By treating a legged manipulator that attaches all feet to the ground as a virtual parallel robot, the workspace of the on-board manipulator can be enlarged while the end-effector maintains the motion precision. By choosing working positions that enable a legged manipulator to cover more processing regions with the enlarged workspace at a time, the required positioning and repositioning times can be reduced. The proposed method is implemented through a variant of a genetic algorithm to find the minimum set of working positions that enable a hexapod manipulator to accomplish welding tasks on a large-scale structure. Simulation results show that the required working positions of the hexapod manipulator are reduced significantly and thus higher productivity can be obtained. The flowchart to implement the proposed method is expected to improve the productivity of other kinds of legged manipulators that perform on-site manufacturing tasks.

3D modeling of an object located in the underwater robot’s manipulator workspace using a point cloud

Operations involving direct contact of the robot’s gripping device with surrounding objects are among the hardest in the field of robotics engineering. Therefore, minimizing the risk of tool damage and processing disruption is important. This can be achieved by using the information about the position of the object in question relative to the grip and its geometric parameters. In this paper, a method of describing an object located in the workspace of an underwater robot with solids of revolution is proposed. It is done using a noisy and incomplete point could, which is obtained with a stereoscopic system located on the terminal link of the underwater robot’s manipulator.

Dynamics-Based Algorithm for Reliable Assembly Mode Tracking in Parallel Robots

Finding the current pose of the end-effector of a parallel robot is a problem, since its forward geometric model generally has several solutions. Current methods to address this problem operate mainly under the assumption that the robot never changes its assembly mode nor gets close to Type 2 singularities. Nonetheless, recent works proved that a parallel robot can change its assembly mode, thanks to dedicated trajectory generation and control. Such a feature allows increasing the operational workspace of such manipulators. Hence, correctly tracking the end-effector pose while crossing Type 2 singularities is mandatory for a practical usage of this workspace enhancement method. However, on Type 2 singularities, several solutions of the forward geometric model merge, making current tracking methods ineffective. To fill this gap, we propose a two-step pose tracking methodology. First, a differential inclusion based on kinematics and dynamics is solved. Second, joint measurements are used to tighten resulting enclosures. The effectiveness of this method is discussed, thanks to experimental data gathered on a planar parallel robot.

An Ergonomic Shared Workspace Analysis Framework for the Optimal Placement of a Compact Master Control Console

Master-Slave control is commonly used for Robot-Assisted Minimally Invasive Surgery (RAMIS). The configuration, as well as the placement of the master manipulators, can influence the remote control performance. An ergonomic shared workspace analysis framework is proposed in this letter. Combined with the workspace of the master manipulators and the human arms, the human-robot interaction workspace can be generated. The optimal master robot placement can be determined based on three criteria: 1) interaction workspace volume, 2) interaction workspace quality, and 3) intuitiveness for slave robot control. Experimental verification of the platform is conducted on a da Vinci Research Kit (dVRK). An in-house compact master manipulator (Hamlyn CRM) is used as the master robot and the da Vinci robot is used as the slave robot. Comparisons are made between with and without using design optimization to validate the effectiveness of the ergonomic shared workspace analysis technique. Results indicate that the proposed ergonomic shared workspace analysis can improve the performance of teleoperation in terms of task completion time and the number of clutching required during operation.

Modeling, Optimization, and Experimentation of the ParaGripper for In-Hand Manipulation Without Parasitic Rotation

Recently, underactuated robotic hands have been exploited for dexterous in-hand manipulation, after having been proven efficient in performing versatile adaptive grasps. However, the reported in-hand manipulation skills are usually associated with parasitic motion, which may complicate control and application of the hand. This paper presents the modeling, optimization and experimentation of the ParaGripper, an underactuated gripper capable of performing in-hand manipulation without parasitic rotation. The underactuated finger uses two serially connected parallelograms to ensure pure translation of the fingertips. If the object remains stationary within the fingertips, the gripper can translate the object without parasitic rotation. The kinematics and kinetostatics of the hand–object system are derived and the manipulation workspace is optimized. The ParaGripper is designed and fabricated according to suitable optimal parameters. Experiments show that the ParaGripper could perform non-parasitic in-hand manipulation and versatile adaptive grasps.

A continuum manipulator for continuously variable stiffness and its stiffness control formulation

Continuum manipulators can accomplish tasks in cluttered and unstructured environments due to their slenderness. Balancing the workspace and stiffness of the slender continuum manipulator is a primary design concern. Thus, studies have been consistently dedicated to designing continuum manipulators with high or variable stiffness. This paper proposes a 2-segment continuum manipulator with adjustable stiffness based on continuously constrained bending curvature. The manipulator's stiffness is further enhanced via redundant backbone arrangement using the concept of dual continuum mechanism during the design phase. The Cosserat rod theory is used for the kinestatic model to calculate the tip stiffness of the manipulator. A stiffness control formulation utilizes the configuration redundancy of the manipulator to achieve stiffness variation control in a desired direction at a target position. The design concepts, system construction, kinestatic models, stiffness control formulation and experimental validations are presented. The experimental results showed that the tip stiffness of the manipulator can be adjusted in various directions with an enhancement up to 10.83 times of the minimal stiffness, indicating the efficacy of the proposed design and the stiffness control formulation.

STABILITY ANALYSIS OF SOFTWARE MANIPULATOR MOVEMENTS USING MATHCAD

Abstract. The method of the stability analysis of the manipulator program movements with use of Mathcad applied programs package is offered. On the basis of the manipulator’s kinematic scheme, the matrices of homogeneous transformations of Denavit Hartenberg are formed and a mathematical model of the extended control object is drawn up. An outline of an extended object control system consisting of a manipulator and an actuator is presented. For example, the linear equations of the manipulator, actuators, meter and controller are considered. The task of synthesizing the manipulator control algorithm is to determine the coefficients of the matrix transfer function of the controller that satisfy the conditions of stability and quality of transients. Mathematical modeling of manipulator programmatic movements was performed using the Matchad application package. The analysis of simulation results allows us to evaluate: manipulator workspace, control system performance, grip positioning accuracy, dependence of grip positioning error on the nature of load and the law of motion. A change in the dynamic characteristics of an extended control object causes a change in the controllability of systems, for the considered example rang Q = 2, i.e. the system is fully controllable.
 This method can be used to analyze the manipulation of the manipulator at the design stage; allows to determine the influence of design, kinematic and dynamic parameters on the manipulation of the manipulator and perform mathematical modeling of the manipulator motion. Calculation examples are given that confirm the expediency and effectiveness of using the Mathcad application software package to solve this type of problem.

Simulation based calculation of the inverse kinematics solution of 7-DOF robot manipulator using artificial bee colony algorithm

This paper presents an artificial bee colony algorithm for solving the inverse kinematics of 7-degree-of-freedom robotic arm which has been newly designed and not used in the literature. The kinematics analysis of this manipulator which has an excessive number of joints, is quite complex. In this study, artificial bee colony, which is one of the swarm-based heuristic algorithms, has been used for inverse kinematics solution and its results have been analyzed in terms of position error and calculation time. In order to ensure the accuracy of the algorithm, calculations have been also carried out in 100 different points selected from the workspace of the robot manipulator. The results have been compared with particle swarm optimization, which is another swarm algorithm in terms of position error and computation time. The results obtained by computer simulation clearly show that the artificial bee colony algorithm produces effective results compared with the literature.