Parallel Robot System Research Articles

Correlation of damage score in PTOA with changes in stress on cartilage in an ovine model

There is a high risk of developing osteoarthritis (OA) following traumatic injury to the knee. Severe ligament injuries can disrupt the integrity of the multicomponent knee at both biological and biomechanical levels. We hypothesize changes in cartilages stresses could lead to tissue damage and development of OA. The in-vivo gait kinematics of the stifle (knee) joint of four adult female ovine subjects were recorded prior to and at ten-and-twenty weeks following partial ACL-MCL transection. The subjects were sacrificed and the experimental joint from each subject was mounted on a parallel robotic system programmed with the kinematic findings. Ten custom-built Fibre Bragg Grating optic sensors were arranged to measure contact stresses on the surface of the tibial plateau articular cartilage. These sensors provide the first accurate stress measurements in a joint during gait replication using the previously recorded in-vivo kinematics. The relationship between the results obtained and observed focal damage was assessed. The locations on the tibial plateaus that experienced the greatest change in contact stresses corresponded with the locations of focal damage development. No direct link was detected between individual animal differences in kinematics and variations in stress magnitudes or the development of focal cartilage damage. The findings highlight the importance of mechanical stress determinants in the integrated set point for the knee (with individual variation), and how injury-related stress changes correlate with development of PTOA.

Joint-Space Characterization of a Medical Parallel Robot Based on a Dual Quaternion Representation of SE(3)

The paper proposes a mathematical method for redefining motion parameterizations based on the joint-space representation of parallel robots. The study parameters of SE(3) are used to describe the robot kinematic chains, but, rather than directly analyzing the mobile platform motion, the joint-space of the mechanism is studied by eliminating the Study parameters. From the loop equations of the joint-space characterization, new parameterizations are defined, which enable the placement of a mobile frame on any mechanical element within the parallel robot. A case study is presented for a medical parallel robotic system in which the joint-space characterization is achieved and based on a new defined parameterization, the kinematics for displacement, velocities, and accelerations are studied. A numerical simulation is presented for the derived kinematic models, showing how the medical robot guides the medical tool (ultrasound probe) on an imposed trajectory.

Nonlinear Robust Control of a Stewart Parallel Robot

In this paper, the control problem of a Stewart parallel robot is investigated, and a sliding mode control method based on self-tuning sliding mode disturbance compensator and double power reaching law is presented. The presented control method can realize fast regulation of a Stewart parallel robot system, and has good robustness and adaptability towards the system uncertainties. The design of a self-tuning sliding mode disturbance compensator is included in the presented control method. The designed sliding mode disturbance compensator does not need the upper bound information of the system uncertainties, and can accurately estimate the system uncertainties. The double power reaching law can not only ensure fast convergence of the system states, but also maintain the continuity of the sliding mode controller. Lyapunov stability theory is adopted to prove the stability of the closed-loop control system, and the validity of the presented control method is verified by a numerical simulation test.

Backstepping Sliding Mode Robust Control for a Wire-Driven Parallel Robot Based on a Nonlinear Disturbance Observer

Based on a nonlinear disturbance observer, a backstepping sliding mode robust control is proposed for a wire-driven parallel robot (WDPR) system used in the wind tunnel test to dominate the motion of the end effector. The control method combines both the merits of backstepping control and sliding mode robust control. The WDPR is subject to different types of disturbances, and these disturbances will affect the motion precision of the end effector. To overcome these problems, a nonlinear disturbance observer (NDO) is designed to reject such disturbances. In this study, the design method of the nonlinear disturbance observer does not require the reliable dynamic model of the WDPR. Moreover, the design method can be used not only in the WDPR but also in other parallel robots. Then, a backstepping design method is adopted and a sliding mode term is introduced to construct a desired controller, and the disturbances are compensated in the controller to reduce the switching gain and guarantee the robustness. For the sake of verifying the stabilization of the closed-loop system, the Lyapunov function is constructed to analyze the stabilization of the system. Finally, the feasibility and validity of the proposed control scheme are proved through both simulation and experimental results.

Systematic Design of a Parallel Robotic System for Lower Limb Rehabilitation

This paper presents the design of an innovative robotic system for lower limb post-stroke rehabilitation of bed confined patients during the acute stage of the treatment. To establish the particularities of each targeted joint motion, experimental measurements are performed on healthy subjects. The acquired data is used to determine the operational workspace, namely the limits of the anatomic joints motion for the lower limb. Based on the prescribed operational workspace, an innovative parallel robotic architecture is designed for achieving the rehabilitation of the lower limb. A detailed kinematic modelling and analysis is carried out to demonstrate the robot capability to safely achieve the required motions. The design of the robotic rehabilitation device is discussed in detail alongside with numerical simulations for validating its performance while performing medically relevant rehabilitation motions.

Risk Management for the Reliability of Robotic Assisted Treatment of Non-resectable Liver Tumors

Hepatic cancers represent an important worldwide health issue where surgery alone in most cases is not a feasible therapeutic solution since most tumors are non-resectable. Despite targeted therapies showing positive results in other areas of cancer treatment, in the case of liver tumors, no low-risk delivery methods have been identified. Based on a risk assessment approach, this paper proposes a technical solution in the form of a robotic system capable of achieving a reliable delivery method for targeted treatment, focusing on the patient safety and therapeutic efficiency. The design of the robotic system starts from the definition of the design constraints with respect to the medical protocol. An analytical hierarchy process is used to prioritize the data correlated with the technical characteristics of a new robotic system, aiming to minimize risks associated with the medical procedure. In a four-phase quality function deployment, the technical solution is evaluated with respect to the quality characteristics, functions, subsystems, and components aiming to achieve a safe and reliable system with high therapeutic efficiency. The results lead to the concept of HeRo, a parallel robotic system for the reliable targeted treatment of non-resectable liver tumors.

Complete Geometric Analysis Using the Study SE(3) Parameters for a Novel, Minimally Invasive Robot Used in Liver Cancer Treatment

The paper presents a complete geometric analysis of a novel parallel medical robotic system designed for minimally invasive treatment of hepatic tumors using brachytherapy, ablation or targeted chemotherapy. An algebraic method based on the study parameters of the special Euclidean transformation Lie group SE(3) was used to determine the mechanism kinematics singularities and workspace. Moreover, two particular medical tool manipulations for the minimally invasive medical procedures are defined in terms of the Study parameters. The first manipulation of the medical tool refers to the linear insertion (of e.g., needles) and the second one is the remote center of motion manipulation of specific medical instruments (e.g., ultrasound probes). The constraint equations of the robotic system are derived and then, the operational workspace is illustrated for the novel parallel robotic system. Lastly, a numerical simulation is presented showing the behavior of the robotic system manipulating the ultrasound probe constrained by the remote center of motion. The geometric analysis of the operational workspace and the numerical simulation show promising results that validate the novel robotic system (safe-wise) for the medical procedure.

Analysis of the effect of system parameters for combined nonlinear cable elongation characteristics in CDPR

The polymer cable is a widely used material in the cable-driven parallel robot (CDPR) system because of its many advantages such as high sensitivity, large workspace and so on. However, the accurate control of CDPR is not easy because of complicated response of the cable. In our previous study, the integrated cable model was derived. Based on the model, parametric studies were progressed in this paper. While operating CDPR, various parameters such as length, applied tension, and tensile rate can be changed and dominantly affect the dynamics of CDPR. For this reason, parametric study was based on these parameters. In this investigation, dynamic creep, hardening factor and short-term recovery were saturated as processing cyclic load. Each saturation rate was dominantly influenced by cable length and applied tension. As the tensile rate was increased, the dynamic creep was decreased. The hysteresis was the characteristic combining all of dynamics. So, the hysteresis also had saturation trends. When the exerted tension was decreased, the length of cable could be reduced or elongated because the creep and recovery occur at the same time.

Trajectory Tracking and Control Algorithm for Precision Parallel Robot

When the state of the robot reaches the smooth sliding plane, the current algorithm will generate high-frequency chattering, resulting in larger tracking error and longer response time. To solve these problems, we have proposed a trajectory tracking and control algorithm based on exponential reaching rate. The coordinate system of parallel robot system is established, and the kinetic energy and potential energy of the system are calculated. The results are brought into the Lagarnge equation to find the dynamic model of the system. The power amplifier, electro-hydraulic servo valve, hydraulic cylinder and its load are taken as generalized controlled objects, and the hydraulic servo system model is established. The exponential approaching rate is introduced to design the dynamics model and the trajectory tracking sliding controller of the hydraulic servo system model. By adjusting the upper and lower bounds of the external disturbance of the controller, the control rate is changed, the buffeting occurrence is reduced, and the response time is shortened, to realize the low error tracking of any trajectory of the robot. The experimental results show that the trajectory of the robot can be adjusted quickly and the desired trajectory is better tracked by the end.

SQP Optimization of 6dof 3x3 UPU Parallel Robotic System for Singularity Free and Maximized Reachable Workspace

The determination of kinematic parameters for a parallel robotic system (PRS) is an important and a critical phase to maximize reachable workspace while avoiding singular configurations. Stewart Platform (SP) mechanism is one of the widely known PRS and it is used to demonstrate the proposed technique. In the related literature, GCI (Global Condition Index) and LCI (Local Condition Index) are the commonly used performance indexes which give a measure about the dexterity of a mechanism. In this work, Sequential Quadratic Programming (SQP) method is used to optimize kinematic parameters of a 6dof 3x3 UPU SP in order to reach maximum workspace satisfying small condition numbers. The radius of mobile and base platforms and the lengths of the legs used in the platform are chosen as kinematic parameters to be optimized in a multiobjective optimization problem. Optimization is performed at different stages and the number of optimized kinematic parameters is increased at each level. In conclusion, optimizing selected kinematic parameters at once by using SQP technique presents the best results for the PRS.

Geometric Parameter Calibration for a Cable-Driven Parallel Robot Based on a Single One-Dimensional Laser Distance Sensor Measurement and Experimental Modeling.

A cable-driven parallel robot has benefits of wide workspace, high payload, and high dynamic response owing to its light cable actuator utilization. For wide workspace applications, in particular, the body frame becomes large to cover the wide workspace that causes robot kinematic errors resulting from geometric uncertainty. However, appropriate sensors as well as inexpensive and easy calibration methods to measure the actual robot kinematic parameters are not currently available. Hence, we present a calibration sensor device and an auto-calibration methodology for the over-constrained cable-driven parallel robots using one-dimension laser distance sensors attached to the robot end-effector, to overcome the robot geometric uncertainty and to implement precise robot control. A novel calibration workflow with five phases—preparation, modeling, measuring, identification, and adjustment—is proposed. The proposed calibration algorithms cover the cable-driven parallel robot kinematics, as well as uncertainty modeling such as cable elongation and pulley kinematics. We performed extensive simulations and experiments to verify the performance of the suggested method using the MINI cable robot. The experimental results show that the kinematic parameters can be identified correctly with 0.92 mm accuracy, and the robot position control accuracy is increased by 58%. Finally, we verified that the developed calibration sensor devices and the calibration methodology are applicable to the massive-size cable-driven parallel robot system.

Solving the pulley inclusion problem for a cable-driven parallel robotic system: Extended kinematics and twin-pulley mechanism

For a cable-driven parallel robot system, the robot kinematic models usually assume that the cable connection in the system comprises ideal fixed points on the base and an end-effector. However, the cables are usually guided around pulleys, so the pulley geometry can induce movable connection points when operating the robot system. Some previous studies have addressed the influence of the geometry of the guiding pulleys on the parallel cable robot’s kinematics, and extended pulley kinematics have been proposed by considering the pulley radius. However, the inverse kinematics of the extended pulley kinematics may hinder the implementation of an actual system, especially owing to the real-time computation capacity. Hence, in this study, to solve the pulley kinematic inclusion problem for a cabledriven robotic system and to improve the position control performance, we investigated the actual pulley kinematic effect and we proposed two methods for a fully constrained planar cable robot. Comparison and evaluations based on simulations and experiments using the proposed methods in terms of the end-effector posture demonstrated their validity for solving pulley inclusion problems for a cabledriven parallel robot.

Algae Harvesting from Large Outdoor Ponds Using a Novel Parallel Robot System

This paper presents a novel method for effective, economical, energy-efficient algae harvesting from large (1-4 acre) outdoor circulating raceway pond systems: a portable 4-cable-suspended robot. Algae, used as an alternative energy crop to produce biofuels (and other consumer products), still remains too expensive. One of the greatest expenses in processing algae is the harvesting process. To replace the typical energy-intensive pumping of the entire pond water through algae filters, we propose using a cable-suspended robot to collect algae, which largely then drains of water while the robot translates the product to a collection point. An additional benefit of our concept, in additional to lower harvesting cost, is that the algae still growing in the pond is not shocked as in the current pumping process, leading to better, healthier yields. Further, the proposed robot system is portable, capable of harvesting multiple ponds while algae continues to grow.

TOWARDS A FAIL-SAFE PROSTATE BIOPSY PARALLEL ROBOT USING ALGEBRAIC GEOMETRY

The paper presents the description of the singular loci for a parallel robotic system designed for transperineal prostate biopsy, using algebraic geometry. Singular configurations define the conditions where a robot has an uncontrollable behavior, by losing or gaining degrees of freedom, and must be avoided in exploitation. The proposed approach ensures the complete description of all mathematical singular configurations with a double role, for enabling structural optimization, and a real-time PLC configuration as a fail-safe tool for the robot during exploitation. The method used for singularity analysis uses Study parameters to obtain the mathematical model, and algebraic geometry to solve the model. A clear separation is made between the theoretical singularities and the physically possible ones, and the findings of this research are compared to previews research regarding the parallel robot presented in this paper.

Normal contact stiffness identification-based force compensation for a hardware-in-the-loop docking simulator

Docking is a very important and challenging space operation. To ensure the safety and reliability of the docking, the thorough ground verification is necessary. Hardware-in-the-loop (HIL) simulation is a good choice, especially when the geometric structure of the docking device is complex. However, the HIL simulation suffers from energy increase and instability since time delay in the system is unavoidable. In this study, a six degree-of-freedom (DOF) parallel robot is used as the motion simulator to physically perform the contact in the simulation. To achieve system stability and high fidelity, a normal contact stiffness identification-based force compensation method is proposed. The contact force is compensated through identifying the time-varying stiffness along the normal direction of the contact surface. The 6-DOF force-moment compensation algorithm for the HIL parallel robot system is presented in detail. Simulations and experiments are both carried out, and the results show that the proposed compensation method is effective.

Development of a parallel robotic system for transperineal biopsy of the prostate

Abstract. Prostate cancer is the second deadliest form of cancer, even though it is less invasive and easily curable in early stages, due to the lack of an efficient and accurate diagnosis strategy. To date, the standard diagnosis procedure involves a blind biopsy with a high rate of false negative results. In order to overcome these limitations, the paper proposes the development of a novel parallel robotic structure for transperineal prostate biopsy that enables an accurate diagnosis through ultrasound-guided targeted tissue sampling. The robotic system consists of two parallel modules, each with 5 degrees of freedom (DOFs): one module guiding the transrectal ultrasound probe (TRUS) and the other guiding the biopsy gun. The two modules are designed to work together in order to help the physician with the tissue sampling of the prostate. The singular configurations of both robotic modules are analyzed and solutions for avoiding them are provided. The experimental model of the robotic structure is described along with the initial test results, which evaluate the robot accuracy for several medically relevant sets of coordinates.

Lyapunov-based adaptive control of a cable-driven parallel robot

This paper proposes a novel approach to the model reference adaptive control (MRAS) of a four-cable robot. A linear model is considered instead of the nonlinear model of cable-driven parallel robot system with assuming that the linear model parameters are unknown. Then, a simple control law and proper Lyapunov function are defined. Regarding to Lyapunov function, the proposed control ensures the stability of the closed-loop system. Finally, the properties of the proposed method such as performance tracking and rejecting external disturbance are demonstrated by simulations.

Lyapunov-based adaptive control of a cable-driven parallel robot

This paper proposes a novel approach to the model reference adaptive control (MRAS) of a four-cable robot. A linear model is considered instead of the nonlinear model of cable-driven parallel robot system with assuming that the linear model parameters are unknown. Then, a simple control law and proper Lyapunov function are defined. Regarding to Lyapunov function, the proposed control ensures the stability of the closed-loop system. Finally, the properties of the proposed method such as performance tracking and rejecting external disturbance are demonstrated by simulations.

Development of a Customized High-Speed Delta Robot

The Robot industry is playing one of the key roles of global market and economic development of Taiwan. In recent years, the Taiwan official is inspired and has encouraged the development of the emerging industry. This study focuses on developing the industrial 3-axis Delta parallel robot system due to its advantages of high-precision, high-speed, high repeatability, long life span, and stable mechanism. For shortening the product development time, different geometric design software, Solidworks and RecurDyn, are employed to accomplish the key components design, simulation, and analysis. The practical implementation uses the Taiwan-made key components including servo motor, actuator, transmission elements, and various controllers. It is hopefully expected that Taiwan can keep up with the torrent of the global 4th industry revolution and develop the cutting-edge robot system which will create drastic profits for Taiwan.

A Novel Shoulder Exoskeleton Robot Using Parallel Actuation and a Passive Slip Interface

This paper presents a five degrees-of-freedom (DoF) low inertia shoulder exoskeleton. This device is comprised of two novel technologies. The first is 3DoF spherical parallel manipulator (SPM), which was developed using a new method of parallel manipulator design. This method involves mechanically coupling certain DoF of each independently actuated linkage of the parallel manipulator in order to constrain the kinematics of the entire system. The second is a 2DoF passive slip interface used to couple the user upper arm to the SPM. This slip interface increases system mobility and prevents joint misalignment caused by the translational motion of the user's glenohumeral joint from introducing mechanical interference. An experiment to validate the kinematics of the SPM was performed using motion capture. The results of this experiment validated the SPM's forward and inverse kinematic solutions through an Euler angle comparison of the actual and command orientations. A computational slip model was created to quantify the passive slip interface response for different conditions of joint misalignment. In addition to offering a low inertia solution for the rehabilitation or augmentation of the human shoulder, this device demonstrates a new method of motion coupling, which can be used to impose kinematic constraints on a wide variety of parallel architectures. Furthermore, the presented device demonstrates a passive slip interface that can be used with either parallel or serial robotic systems.