Dexterous Workspace Research Articles

Development of a Novel Tendon-Sheath-Driven Upper Limb Exoskeleton With Elastic Joints for Assisting Surgeon-Performing Microlaryngoscopic Surgery

Abstract When performing microlaryngoscopic surgery, surgeons must maintain their arm positions for a long time, which can cause arm soreness and affect the success rate of surgery. In this study, a novel tendon-sheath-driven upper limb exoskeleton with elastic joints (TULEE) is proposed and developed to support the arms of doctors wearing the TULEE. The functional requirements of the TULEE were proposed according to the needs of microlaryngoscopic surgery, and the overall structure of the TULEE was designed. Then, the positive kinematics of the TULEE were derived based on the D–H transformation matrices, and the accuracy of the positive kinematic control was verified experimentally. The reachable workspace of the wrist joint of the TULEE was analyzed, and the dexterous workspace of the wrist was analyzed by using the condition number of the Jacobian matrix. The control strategy of the TULEE was proposed based on the principle of admittance control. Finally, an experimental prototype of the TULEE was built, and the feasibility of the control strategy was verified by a servo control experiment testing a single joint and a combined control experiment testing multiple joints. Through simulated surgical experiments, it was verified that TULEE can follow the wearer's arm movement, provide assistance for the wearer's arm movement in the following control mode, and lock the joint rotation angle in the steady-state control mode to reduce external disturbances and reduce the risk of unsuccessful surgery.

Workspace and dexterity analysis of the hybrid mechanism master robot in Sinaflex robotic telesurgery system: An in vivo experiment.

Sinaflex robotic telesurgery system has been introduced recently to provide ergonomic postures for the surgeon along with dexterous workspace for robotic telesurgery. The robot is described, and the forward and inverse kinematics are derived and validated by an experiment. The robot and operational workspaces and their dexterity are investigated and compared using the data collected during a dog vasectomy robotic telesurgery by Sinaflex. According to the simulation results, the workspace of the end effector is as large as 914.56×105mm3, which can completely cover the ergonomic human hand workspace. The dexterity of the robot for the total and operational workspace is 0.4557 and 0.6565, respectively. In terms of the workspace size and the amount of dexterity, Sinaflex master robot can be considered a good choice to fulfil the requirements of the surgeon side robot in robotic telesurgery systems.

Design of the five-bar linkage with singularity-free workspace

AbstractThis paper shows the kinematic analysis and the synthesis of the five-bar linkage with symmetrical structure and singularity-free dexterous workspace. The type synthesis of the five-bar linkage shows that the number of symmetrical structures of five-bar linkage is limited to eight structures. This study deals with the forward and inverse kinematic analysis and synthesis of the five-bar structure 5-RRRRR. The synthesis equations allow the analytical computation of the link lengths of a symmetrical five-bar linkage using only revolute joints to avoid the singularities in an imposed dexterous workspace. A numerical example of the symmetrical five-bar linkage is analyzed and synthetized theoretically and characterized by computing the performance indices. The tests on an experimental model of the five-bar linkage 5-RRRRR confirm the singularity-free dexterous workspace.

Workspace Characterization for Hybrid Tendon and Ball Chain Continuum Robots.

Continuum robots have attracted considerable attention for applications in minimally invasive diagnostics and therapeutics over the past decade [1]. The primary reason is their ability to navigate narrow and tortuous anatomical passageways, while guaranteeing safe inter- action with the anatomy. In designing such robots, an important goal is create a robot with a workspace appropriate for the clinical task. A significant limitation of many continuum designs re- lates to the minimum radius of curvature that a particular design can achieve. While multiple bending sections can be concatenated to provide more degrees of freedom, the orientations by which a point in the workspace can be approached are often limited. To overcome this limitation, this paper investigates a hybrid design that combines the advantages of tendon- actuated [2] and magnetic ball chain robots [3] as shown in Fig. 1. In this hybrid design, a proximal tendon- actuated section positions the robot with respect to the goal tip location while a distal ball chain section orients the robot tip with respect to the goal location. This abstract describes how the hybrid kinematics can be modeled and illustrates how the hybrid design possesses a dextrous workspace of finite extent.

Dexterous workspace optimization for a six degree-of-freedom parallel manipulator based on surrogate-assisted constrained differential evolution

Parallel manipulators are increasingly applied because of their high stiffness, load capacity, and motion precision. However, the workspace of a parallel manipulator is relatively small compared to that of a serial manipulator. Therefore, appropriate structural designs of parallel manipulators for maximizing the workspace are essential. This paper studies the dexterous workspace maximization problem of a six-degree-of-freedom (DOF) parallel manipulator. First, a constrained optimization model is formulated, in which, the objective is to maximize the dexterous workspace, and the constraints include several kinematic and dynamic indicators, and some general structural limitations. To address the highly constrained, computationally-expensive problem, a surrogate-assisted two-phase constrained differential evolution method is proposed. Its effectiveness and efficiency are verified by the superior performance over two surrogate-free evolutionary methods: differential evolution (DE) and genetic algorithm (GA), and two surrogate-assisted state-of-the-art evolutionary methods: modified constrained expected improvement (CEI) and the lower confidence bounding approach (PCLCB), on ten benchmark functions and the established real-word 6-DOF manipulator design optimization problem.

Attracting Conductive Nonmagnetic Objects With Rotating Magnetic Dipole Fields

Recent research has shown that eddy currents induced by rotating magnetic dipole fields can produce forces and torques useful for dexterous manipulation of conductive nonmagnetic objects. This control paradigm shows promise for application in the remediation of space debris. However, the resulting force from each field source always includes a repulsive component, suggesting that the object should be surrounded by field sources to some degree to ensure the object does not leave the dexterous workspace during manipulation. In this letter, we describe the ability of multiple field sources working together in a coordinated fashion to attract conductive nonmagnetic objects that are not surrounded, reminiscent of a tractor beam. This enables an object to be pulled into a dexterous manipulation workspace. We explicitly describe the nominal attractive force on spherical objects, serving as an approximation for other object geometries, as a function of the properties of the object and the field-generation system. We perform experimental verification using a water-based microgravity simulator.

Towards Autonomous Robotic Biopsy-Design, Modeling and Control of a Robot for Needle Insertion of a Commercial Full Core Biopsy Instrument.

This paper presents the design, control, and experimental evaluation of a novel fully automated robotic-assisted system for the positioning and insertion of a commercial full core biopsy instrument under guidance by ultrasound imaging. The robotic system consisted of a novel 4 Degree of freedom (DOF) add-on robot for the positioning and insertion of the biopsy instrument that is attached to a UR5-based teleoperation system with 6 DOF. The robotic system incorporates the advantages of both freehand and probe-guided biopsy techniques. The proposed robotic system can be used as a slave robot in a teleoperation configuration or as an autonomous or semi-autonomous robot in the future. While the UR5 manipulator was controlled using a teleoperation scheme with force controller, a reinforcement learning based controller using the Deep Deterministic Policy Gradient (DDPG) algorithm was developed for the add-on robotic system. The dexterous workspace analysis of the add-on robotic system demonstrated that the system has a suitable workspace within the US image. Two sets of comprehensive experiments including four experiments were performed to evaluate the robotic system’s performance in terms of the biopsy instrument positioning, and the insertion of the needle inside the ultrasound plane. The experimental results showed the ability of the robotic system for in-plane needle insertion. The overall mean error of all four experiments in the tracking of the needle angle was 0.446°, and the resolution of the needle insertion was 0.002 mm.

A manipulator size optimization method based on dexterous workspace volume

Background: Manipulators for robots are required to have high manipulability for adaptability in different tasks. However, general methods for designing manipulators with high manipulability are deficient. Here, aiming at improving the manipulability of the six degrees-of-freedom (DOF) manipulator, a method for optimizing structure size parameters based on the dexterous workspace volume is proposed. Methods: Firstly, the kinematic analysis of the manipulator is performed. Then, the manipulability of the single working point of the manipulator is judged based on reachability in different postures. The workspace of the manipulator is discretized to obtain the volume of the overall dexterous workspace. By taking the maximum volume of the dexterous workspace as the optimization goal, Genetic Algorithm (GA) is used to optimize the structure size parameters to achieve optimal manipulability. AUBO 6-DOF manipulator is defined and analyzed as an example. Results: The optimization results indicate that the dexterous workspace of the manipulator expands in volume and its manipulability is improved. The validity of the proposed optimization method is verified by comparing the distribution of dexterous workspace of the manipulator. Conclusions: This article proposes an optimization method for the structure size parameters of a 6-DOF manipulator, which can be implemented to improving the manipulability of the manipulator.

Inverse Kinematics and Dexterous Workspace Formulation for 2-Segment Continuum Robots With Inextensible Segments

The inverse kinematics (IK) problem of continuum robots has been investigated in depth in the past decades. Under the constant-curvature bending assumption, closed-form IK solution has been obtained for continuum robots with variable segment lengths. Attempting to close the gap towards a complete solution, this paper presents an efficient solution for the IK problem of 2-segment continuum robots with one or two inextensible segments (a.k.a, constant segment lengths). Via representing the robots shape as piecewise line segments, the configuration variables are separated from the IK formulation such that solving a one-variable nonlinear equation leads to the solution of the entire IK problem. Furthermore, an in-depth investigation of the boundaries of the dexterous workspace of the end effector caused by the configuration variables limits as well as the angular velocity singularities of the continuum robots was established. This dexterous workspace formulation, which is derived for the first time to the best of the authors knowledge, is particularly useful to find the closest orientation to a target pose when the target orientation is out of the dexterous workspace. In the comparative simulation studies between the proposed method and the Jacobian-based IK method involving 500,000 cases, the proposed variable separation method solved 100% of the IK problems with much higher computational efficiency.

A Lightweight Accessible Wearable Robotic Interface for Bimanual Haptic Manipulations.

Wearable devices with bimanual force feedback enable natural and cooperative manipulations within an unrestricted space. Weight and cost have a great influence on the potential applications of a haptic device. This paper presents a wearable robotic interface with bimanual force feedback that has considerably reduced weight and cost. To make the reaction force less perceivable than the interaction force, a waist-worn scheme is adopted. The interface mainly consists of a belt, a fastening tape, two serial robotic arms, and two electronics units and batteries. The robotic arms located on both sides of the belt are capable of 3-DoF position tracking and force feedback for each hand. The whole interface is lightweight (only 2.4 kg) and accessible. Furthermore, it is also easy to wear and the operator can wear it only by putting the belt on the waist and fastening the tape, reducing his/her dependency on additional assistance. The interface is optimized to obtain desirable force output and a dexterous workspace without singularity. To evaluate its performance in bimanual cooperative manipulations, an experiment in the virtual environment was conducted. The experimental results showed the subjects had more efficient and stable cooperative manipulations with bimanual force feedback than without force feedback.

Prescribed flexible orientation workspace and performance comparison of non-redundant 3-DOF planar parallel mechanisms

The functionality of a workspace is one of the most important considerations in planar parallel manipulators (PPMs) design. Dexterous workspace (DW) is the subset of the reachable workspace (RW) and it means that full rotational dexterity is preserved in every translational position in space. However, DW is impractical as PPMs cannot rotate a full 360° because of interference. This paper proposes a workspace called prescribed flexible orientation workspace (PFOW) that characterizes the orientation capability of PPMs. To optimize and compare 3 degree-of-freedom (3-DOF) PPMs, a normalized and unified performance characteristic index is built based on indices including PFOW, condition number, velocity, payload, stiffness, and transmission indices which plays a guiding role in the optimization process. The best configuration is obtained through graphical performance comparison. In general, this work presents the analysis of rotational dexterity of PPMs and provides a guidance for optimization and selection.

Research on Region Division of Large Workpiece Based on Dexterous Workspace of Robot

In order to complete the processing of large-scale workpieces, a region division of large-scale workpieces based on robot dexterous workspace is studied. The linkage coordinate system of the robot is established by D-H method, and the forward kinematics equation of the robot is obtained; Monte Carlo method is used to analyze the workspace of the robot, and MATLAB is used to program to draw the workspace and task space of the robot; Taking an example part as the object, the feature of the part is studied, and the process of determining the task space area of the workpiece in the dexterous workspace of the robot is given, and the region of the workpiece is divided based on the size of the task space and the geometric features of the workpiece.

A Study on the Feasibility of Robotic Harvesting for Chile Pepper

This paper presents a study on the robotic harvesting of New Mexico type chile pepper, in a laboratory setting, using a five degrees of freedom (DoF) serial manipulator. The end-effector of the manipulator, a scissor-type cutting mechanism, was devised and experimentally tested in a lab setup which cuts the chile stem to detach the fruit. Through a MATLAB™-based program, the location of the chile pepper is estimated in the robot’s reference frame, using Intel RealSense Depth Camera. The accuracy of the 3D location estimation system matches the maximum accuracy claimed by the manufacturer of the hardware, with a maximum error to be in Y-axis, which is 5.7 mm. The forward and inverse kinematics are developed, and the reachable and dexterous workspaces of the robot are studied. An application-based path planning algorithm is developed to minimize the travel for a specified harvesting task. The robotic harvesting system was able to cut the chile pepper from the plant based on 3D location estimated by MATLAB™ program. On the basis of harvesting operation, on 77 chile peppers, the following harvesting indicators were achieved: localization success rate of 37.7%, detachment success rate of 65.5%, harvest success rate of 24.7%, damage rate of 6.9%, and cycle time of 7 s.

Structural design of a microsurgery-specific haptic device: neuroArmPLUSHD prototype

A microsurgery-specific haptic interface with articulated structure, possessing 3 active, 4 passive and 3 supplementary degrees of freedom (DOFs), was designed and developed. The system includes a 3-DOF active serial linkage design, mimicking the human upper extremity. It is combined with a microsurgery-specific end-effector, comprised of a 3-DOF passive gimbal mechanism and a 1-DOF passive exchangeable surgical toolset. The spherical gimbal workspace twinned with the larger linkage arm workspace allow accurate and delicate movements to maneuver the surgical tool in narrow corridors, corresponding to conventional surgery. The structural design of the device is based on kinematic performance measures aimed to enhance ergonomics and mitigate training limitations of novice end-users. A supplementary 3-DOF adjustable base further improved ergonomics for end-users of different sizes. Force feedback was provided to improve safety, i.e. avoidance of force errors in execution of surgical tasks. This haptic interface provides high positional and output force resolution (0.92–1.46 mm in Cartesian coordinate system and 0.2 N, respectively), wide range of allowable force (up to 15 N), high global manipulability (0.77), global isotropy (0.68) and stiffness (2.3 N/mm). The work, indeed, introduces a novel kinematic performance index, Dexterous Conditioning Index (DCI), based on the volume of dexterous workspace, correlating to ease of use and decreased singularity. Accordingly, the proposed haptic device demonstrates a high level of accuracy, haptic feedback, dexterous workspace, and performance, ideal for implementation in robot-assisted microsurgery.

On the elastodynamics of a five-axis lightweight anthropomorphic robotic arm

This paper presents elastodynamic modeling and analysis for a five-axis lightweight robotic arm. Natural frequencies are derived and visualized within the dexterous workspace to show the overall performances and compare them to the frequencies when the robotics is with payload. The comparison shows that the payload has a relatively small influence to the first- and second-order frequencies. Sensitivity analysis is conducted, and the system's frequency is more sensitive to the second joint stiffness than the others. Moreover, observations from the displacement response analysis reveal that the robotics produces linear elastic displacements of the same level between the loaded and unloaded working modes but larger rotational deflections under the loaded working condition. The main contribution of this work lies in that a systematic approach of elastodynamic analysis for serial robotic manipulators is formulated, where the arm gravity and external load are taken into account to investigate the dynamic behaviors of the robotic arms, i.e., frequencies, sensitivity analysis, and displacement responses, under the loaded mode.

Atlas motion platform split-axle mecanum wheel design

The Atlas motion platform was conceptually introduced in 2005 as a 2.90 m diameter thin-walled composite sphere housing a cockpit. Three active mecanum wheels provide three linearly independent torque inputs enabling the sphere to enjoy a 100% dexterous reachable workspace with unbounded rotations about any axis. Three linearly independent translations of the sphere centre, decoupled from the orientation workspace, are provided by a translational three degree-of-freedom platform. Small-scale and half-scale demonstrators introduced in 2005 and 2009, respectively, gave us the confidence needed to begin the full-scale design. Actuation and control of the Atlas full-scale design is nearing completion; however, resolution of several details have proven extremely elusive. The focus of this paper is on the design path of the 24 passive mecanum wheels. The 12 passive wheels below the equator of the sphere help distribute the static and dynamic loads, while 12 passive wheels above the equator, attached to a pneumatically actuated halo, provide sufficient downward force so that the normal force between the three active wheel contact patches and sphere surface enable effective torque transfer. This paper details the issues associated with the original twin-hub passive wheels and the resolution of those issues with the current split-axle design. Results of static and dynamic load tests are discussed.

Use of the chord method for analyzing workspaces of a parallel structure mechanism

The size and shape of the mechanism working area are one of the most important criteria of its performance. Known approaches to the analysis of the workspace, such as the geometric method or the discretization method, have a number of features that limit their effective application. This paper considers the optimization chord method for determining the working areas of various types on the example of a planar parallel mechanism. The simulation results for maximum, constant orientation and dextrous workspaces are presented.

A deep learning based automatic surface segmentation algorithm for painting large-size aircraft with 6-DOF robot

PurposeThis paper aims to achieve automatically surface segmentation for painting different kinds of aircraft efficiently considering the demands of painting robot.Design/methodology/approachThis project creatively proposed one method that accepts point cloud, outputs several blocks, each of which can be handled by ABB IRB 5500 in one station. Parallel PointNet (PPN) is proposed in this paper for better handling six dimensional aircraft data including every point normal. Through semantic segmentation of PPN, each surface has its own identity information indicating which part this surface belongs to. Then clustering considering constraints is applied to complete surface segmentation with identity information. To guarantee segmentation paintable and improve painting efficiency, different dexterous workspaces of IRB 5500 corresponding to different postures have been analyzed carefully.FindingsThe experiments confirm the effectiveness of the proposed surface segmentation method for painting different types of aircraft by IRB 5500. For semantic segmentation on aircraft data with point normal, PPN has higher precision than PointNet. In addition, the whole algorithm can efficiently segment one complex aircraft into qualified blocks, each of which has its own identity information, can be painted by IRB 5500 in one station and has fewer edges with other blocks.Research limitations/implicationsAs the provided experiments indicate, the proposed method can segment one aircraft into qualified blocks automatically, which highly improves the efficiency in aircraft painting compared with traditional approaches. Moreover, the proposed method is able to provide identity information of each block, which is necessary for application of different paint parameters and different paint materials. In addition, final segmentation results by the proposed method behaves better than k-means cluster on variance of normal vector distance.Originality/valueInspired by semantic segmentation of 3 D point cloud, some improvements based on PointNet have been proposed for better handling segmentation of 6 D point cloud. By introducing normal vectors, semantic segmentation could be accomplished precisely for close points with opposite normal, such as wing upper and lower surfaces. Combining deep learning skills with traditional methods, the proposed method is proved to behave much better for surface segmentation task in aircraft painting.

A Head Control Strategy of the Snake Robot Based on Segmented Kinematics

Head control is important for snake robots to work in an unknown environment. However, the existing methods of head control have certain application limitations for snake robots with different configurations. Thus, a strategy for head control based on segmented kinematics is proposed. Compared with the existing head control strategies, our strategy can adapt to different structures of snake robots, whether wheeled or non-wheeled. In addition, our strategy can realize the accurate manipulation of the snake robot head. The robot body is divided into the base part, neck part and head part. First, parameters of backbone curve are optimized for enlarging the area of the support polygon. Then the desired pose for the head link and the dexterous workspace of the head part can in turn derive the desired position and direction of the end frame for the neck part. An optimization algorithm is proposed to help the end frame of the neck part approach a desired one and obtains the joint angles of the neck part. When the actual frames of the neck part are determined, the dexterous workspace of the head part will cover the desired pose of the head link. Then the TRAC-IK inverse kinematics algorithm is adopted to solve the joint angles of the head part. To avoid the collision between the body and the ground, a trajectory planning method of the overall body in Cartesian space is proposed. Finally, simulations validate the effectiveness of the control strategy.

Optimization design for a compact redundant hybrid parallel kinematic machine

Abstract Designing a machine tool that simultaneously satisfies the requirements of high rigidity, large dexterous workspace and small footprint is challenging. This paper proposed a redundant hybrid manipulator as a machine tool with these features. The design attempted to integrate the advantages of a PKM (parallel kinematic mechanism), SKM (serial kinematic mechanism) and redundancy mechanism. The geometric parameters of the manipulator were elaborately tuned to overcome intrinsic and extrinsic singularities with an optimal machining plane. High-accuracy and complex-shape machine results have been experimentally verified. The advantage is the ability to shorten the required strokes of the linear actuators effectively. This change not only improves the performance in terms of rigidity, accuracy and dynamics of the entire mechanism but also reduces the cost of the materials and the performance ratio. The second is to decrease the overall machinery-footprint-to-workspace ratio and lower the manufacturing cost via occupied floor space reduction and layout flexibility of the production line.