Parallel Robot Mechanism Research Articles

Design and verification of a parallel elastic robotic leg

This paper presents the design and experimental verification of a parallel elastic robotic leg mechanism that aims to capture the dynamics of the linear mass-spring-damper model. The mechanism utilizes a wrapping cam mechanism to linearize the non-linear force resulting from the elongation of the parallel elastic element. Firstly, we explain the desired dynamics of the mass-spring-damper model, including the impact transitions, and the design of the wrapping cam mechanism. We then introduce a system identification procedure to estimate the parameters of the leg mechanism corresponding to the dynamic model. The estimated parameters are tested with a cross-validation approach to evaluate the mechanism’s performance in tracking the desired model. The experimental results show that the passive dynamics of the mechanism resemble the linear model as intended. Thus, the robot provides a basis for using parallel elastic actuation while using model-based controllers that benefit the analytic solutions of the linear model.

Transendoscopic flexible parallel continuum robotic mechanism for bimanual endoscopic submucosal dissection

In endoscopic submucosal dissection (ESD), the gastrointestinal (GI) tract warrants the surgical instruments to navigate through a long, narrow and tortuous endoscope. This poses a great challenge in developing ESD instruments with small dimensions, flexibility, and high distal dexterity. In this work, we propose the first Transendoscopic Flexible Parallel Continuum Robotic mechanism to develop a miniature dexterous flexible-stiff-balanced Wrist (FPCW). Besides, it can steer multifunctional instruments of diameters 2.5 mm to 3.5 mm, including the electrosurgical knife, injection needle, and forceps. Our FPCW instruments are adaptable to commercially available dual-channel endoscopes (diameter: <12 mm, channel width: 2.8 mm and around 3.8 mm). Furthermore, we develop a surgical telerobotic system, called DREAMS (Dual-arm Robotic Endoscopic Assistant for Minimally Invasive Surgery), by using our smallest FPCW instruments for bimanual ESD procedures. First, we conduct a series of experiments to determine the FPCW’s design and kinematics parameters and to verify the mechanical properties of the FPCW instruments’ prototypes, including workspace, stiffness, strength, and teleoperation accuracy. Second, we validate the functionality of the FPCW instruments through ex-vivo tests by performing ESD steps on porcine stomachs. Finally, we perform an invivo test on a live porcine model and showcase that our developed DREAMS can be teleoperated intuitively to perform bimanual ESD efficiently with an average dissection speed of 108.95 mm2/min at the greater curvature in gastric body, which demonstrates that our DREAMS has satisfactory maneuverability as well as accuracy and is more competitive than counterpart robotic systems.

On Research of Cable Tension Distribution Algorithm for Four Cables - Three DOF Planar Cable-Driven Parallel Robot

One of the main concerns in controlling the cable-driven parallel robot (CDPR) mechanism is dealing with the distribution of tension on each cable, which is critical to the operation of the entire cable system. It can be said that adjusting the cable tension will determine the power consumption of the motors and the stiffness of the structure. Therefore, the problem that needs to be solved is how to handle the cable tension when the end-effector moves throughout the entire workspace. The tension of each cable needs to be adjusted properly to ensure it remains the same. Moment and force act in a static state, keeping the kinematic position of the end moving platform from being deflected and the main purpose is to ensure that the robot achieves a rigid state and eliminates vibration when moving. Because of that essential demand, this article will refer to the Quadratic programming algorithm to solve the problem of tension distribution for the Planar Cable-Driven Parallel Robot consisting of 4 cables with 3 degrees of freedom. This article will be the foundation for applying this algorithm to an 8-cable robot with 6 degrees of freedom (Spatial Cable-Driven Parallel Robot for example). At the same time, in this article, the simulation results for the algorithm will also be presented in this paper.

Kinematic modeling and motion control of a parallel robotic antenna pedestal

AbstractThis paper deals with kinematic modeling and motion control of a novel antenna pedestal based on parallel robotic mechanism. Its active joints are two sliders equipped with DC motors on a circular rail. The synchronous and asynchronous motions of the two sliders enable the antenna to rotate in azimuth and pitch. In order to solve the problem of trajectory deviation caused by nonlinear friction and other uncertain disturbances, the structure of the antenna is described at the beginning, and then, the kinematic model is established based on geometry method. Then, the fuzzy PI (FPI) control system is designed based on the position feedback of the driving slider to realize the trajectory tracking of the desired curve. Finally, the parameters of the FPI controller are optimized and validated by Simulink simulation experiments. The tracking performance and the effectiveness of the control algorithm on prototype are verified by experiments of typical trajectory following control.

Assembly precision design for parallel robotic mechanism based on uncertain hybrid tolerance allocation

PurposeThe coupling impact of hybrid uncertain errors on the machine precision is complex, as a result of which the designing method with multiple independent error sources under uncertainties remains a challenge. For the purpose of precision improvement, this paper focuses on the robot design and aims to present an assembly precision design method based on uncertain hybrid tolerance allocation (UHTA), to improve the positioning precision of the mechanized robot, as well as realize high precision positioning within the workspace.Design/methodology/approachThe fundamentals of the parallel mechanism are introduced first to implement concept design of a 3-R(4S) &3-SS parallel robot. The kinematic modeling of the robot is carried out, and the performance indexes of the robot are calculated via Jacobian matrix, on the basis of which, the 3D spatial overall workspace can be quantified and visualized, under the constraints of limited rod, to avoid the singular position. The error of the robot is described, and a probabilistic error model is hereby developed to classify the hybrid error sensitivity of each independent uncertain error source by Monte Carlo stochastic method. Most innovatively, a methodology called UHTA is proposed to optimize the robot precision, and the tolerance allocation approach is conducted to reduce the overall error amplitude and improve the robotized positioning precision, on the premise of not increasing assembly cost.FindingsThe proposed approach is validated by digital simulation of medical puncture robot. The experiment highlights the mathematical findings that the horizontal plane positioning error of the parallel robotic mechanism can be effectively reduced after using UHTA, and the average precision can be improved by up to 39.54%.Originality/valueThe originality lies in UHTA-based precision design method for parallel robots. The proposed method has widely expanding application scenarios in industrial robots, biomedical robots and other assembly automation fields.

Silicon-based soft parallel robots 4D printing and multiphysics analysis

Four-dimensional printing has set the stage for a new generation of soft robotics. The applications of rigid planar parallel robotic manipulators are also significant because of their various desirable characteristics, such as lower inertia, higher payload, and high accuracy. However, rigid planar parallel robots are heavy and require different actuators and components. This study introduces a novel technique to produce a light three degrees of freedom soft parallel manipulator at a low cost, which can be stimulated easily. This technique allows researchers to customize the actuator’s design based on the requirement. The robot is made by 3D printing based on fused deposition modelling and a direct ink writing process. The design, development, and additive manufacturing of a soft parallel robot electrothermally driven by a linear silicon-based actuator and polylactic acid parts are presented. Silicon-based soft actuators replace the rigid conventional linear actuators in this study to drive the planar parallel manipulator. The actuation of actuators is conducted using simple heating compared to the conventional rigid actuator. Various heating approaches and configurations are compared and analysed to find the most suitable one for the effective linear stroke of the soft actuator. The finite element model is used to analyse the performance of the electrothermally silicon-ethanol soft actuators in ABAQUS. The kinematics of the planar parallel robotic manipulator are simulated in MATLAB to achieve its workspace. The final soft parallel robot mechanism and the active and passive links are fabricated and tested experimentally.

Multi-objective optimization of a redundantly actuated parallel robot mechanism for special machining

Abstract. In order to improve the accuracy and efficiency of special machining for a complex surface, a 2RPU-2SPR (where R, P, U, and S stand for revolute, prismatic, universal, and spherical joints, respectively) over-constrained redundantly actuated parallel robot mechanism is proposed. And six performance evaluation indexes are established to ensure the working performance including workspace, motion/force transmission efficiency, stiffness, dexterity, energy efficiency, and the inertia coupling index. Furthermore, a collaborative optimal configuration algorithm is conducted based on an orthogonal experimental design algorithm and a multi-objective particle swarm optimization algorithm. On the basis given above, a simulation analysis of a multi-objective optimization is conducted. Compared with two traditional, intelligent optimization algorithms of a multi-objective particle swarm optimization algorithm and an orthogonal experimental design method, the improved collaborative multi-objective optimization algorithm has a better optimization effect.

A Portable Intuitive Haptic Device on a Desk for User-Friendly Teleoperation of a Cable-Driven Parallel Robot

This paper presents a compact-sized haptic device based on a cable-driven parallel robot (CDPR) mechanism for teleoperation. CDPRs characteristically have large workspaces and lightweight actuators. An intuitive and user-friendly remote control has not yet been achieved, owing to the unfamiliar multiple-cable configuration of CDPRs. To address this, we constructed a portable compact-sized CDPR with the same configuration as that of a larger fully constrained slave CDPR. The haptic device is controlled by an admittance control for stiffness adjustment and implemented in an embedded microprocessor-based controller for easy installation on an operator’s desk. To validate the performance of the device, we constructed an experimental teleoperation setup by using the prototyped portable CDPR as a master and larger-size CDPR as a slave robot. Experimental results showed that a human operator can successfully control the master device from a remote site and synchronized motion between the master and slave device was performed. Moreover, the user-friendly teleoperation could intuitively address situations at a remote site and provide an operator with realistic force during the motion of the slave CDPR.

Development of a control architecture for a parallel three-axis robotic arm mechanism using CANopen communication protocol

Based upon the CANopen communication protocol and the LabVIEW graphic programing procedures, this paper develops a closed-loop control architecture for a parallel three-axis (Delta) robotic arm mechanism. The accomplishments include prototyping a parallel three-axis robotic arm mechanism, assembling servomotors with associated encoders and gearsets, coding CANopen communication scripts for servomotor controllers and a host supervision GUI, coding forward/inverse kinematics scripts to compute the required servomotor rotations and the coordinates of a movable platform or the mechanism, coding tracking error compensation scripts for effective closed-loop griper control, and coding integration scripts to command and supervise the mechanism motion on the LabVIEW-based host GUI. During the development stage, this research designed and prototyped the parallel three-axis robotic arm mechanism based upon basic Delta robot kinematics. To control the mechanism effectively and accurately, this study implemented the CANopen communication protocol, which characterizes high speed and stable transmission. The protocol applies to the CANopen communication channels among the controllers and the host supervision GUI. On the LabVIEW development platform, the coded supervision GUI performs issuing/receiving messages to the CANopen-based controllers. The controllers excite the servomotors and actuate the parallel mechanism to track prescribed trajectories in a closed-loop control fashion. Meanwhile, an electromagnet attached to the movable platform of the robotic mechanism performs satisfactory picking/placing object actions.

300-N Class Convex-Based Telescopic Manipulator and Trial for 3-DOF Parallel Mechanism Robot

We designed a new telescopic manipulator that uses a clustered elastic convex tape. The manipulator has an ultra-wide expansion range and toughness against mechanical stress. Compared to conventional linear actuators, our convex-type manipulators have high extension range and are very lightweight. Moreover, they are compact when rolled up. The telescopic manipulators designed in the previous study had insufficient output due to structural problems and were unstable. In this study, we report a Type-K telescopic manipulator mechanism (Makijaku-Ude Type-K), which is a redesigned manipulator that can be easily used with a 300-N class power, and applied the mechanism to a three degrees-of-freedom spatial parallel-mechanism robot.

Mechanism and Model of a Soft Robot for Head Stabilization in Cancer Radiation Therapy.

We present a parallel robot mechanism and the constitutive laws that govern the deformation of its constituent soft actuators. Our ultimate goal is the real-time motion-correction of a patient's head deviation from a target pose where the soft actuators control the position of the patient's cranial region on a treatment machine. We describe the mechanism, derive the stress-strain constitutive laws for the individual actuators and the inverse kinematics that prescribes a given deformation, and then present simulation results that validate our mathematical formulation. Our results demonstrate deformations consistent with our radially symmetric displacement formulation under a finite elastic deformation framework.

Design and Analysis of a Novel Planar Translational Parallel Robotic Mechanism with Three Limbs

A novel planar translational parallel robotic mechanism with three limbs is designed. The degree of freedom (DOF) and output characteristics of mechanism are studied based on the screw theory. The mathematic models including position, velocity and acceleration are derived according to different forms of the actuated inputs. When the linear displacements of two cylindrical joints are selected as the actuated inputs, the velocity Jacobian is an identity matrix and the mechanism has fully isotropic kinematics characteristics. Singularity of the mechanism is discussed and all singular configurations are explored. Finally, kinematics simulation of the mechanism is carried out by ADMAS and MATLAB software, and the kinematic curves are drawn.

Study on Residual Vibration Suppress of a 3-DOF Flexible Parallel Robot Mechanism.

Residual vibration suppression of a 3-DOF flexible parallel robot mechanism is implemented in this paper. Considering the direct and inverse piezoelectric effect of PZT (lead zirconium titanate) material, a general motion equation is established which includes an input equation of PZT actuators and an output equation of PZT sensors. A strain and strain rate feedback (SSRF) controller is designed based on the established general motion equation. A numerical simulation is implemented to verify the effectiveness of the SSRF controller in driving the proposed robotic mechanism. The simulation results reveal that the SSRF controller can decrease the elastic vibration displacement of the flexible links rapidly and improve the position accuracy of the moving platform. In the experimental study, one scheme with three passive flexible links is controlled by the SSRF controller at the same time as the performance of the introduced solutions. The experimental results show that the strain and strain rate feedback controller is able to effectively suppress the residual vibration of the 3-DOF flexible parallel robot mechanism. The results of the numerical simulation and experiment are completely consistent.

Design and analysis of a six degrees of freedom serial–parallel robotic mechanism with multi-degree of freedom legs

A novel mobile serial–parallel mechanism with legs for in-pipe use is proposed. The mobile robotic mechanism is composed of two identical three-universal joint–prismatic joint–universal joint parallel mechanisms connected in series and two gripping modules. The proposed parallel mechanism has two rotational freedoms and one translational freedom. In addition, the parallel mechanism can achieve continuous and equivalent rotation. The singularities of the parallel mechanism are analyzed. The overall serial–parallel mechanism has six degrees of freedom, and each gripping module has four degrees of freedom. Each parallel mechanism in the waist module is driven by three servo-electric cylinders and each leg mechanism in the gripping modules is controlled by a linear actuator. The robotic mechanism can perform peristaltic movement and turning in space. The robotic mechanism possesses a simple structure and high flexibility, along with the merits of serial–parallel mechanism. In this article, analytic models for the kinematics and dynamics of the robotic mechanism are derived. Additionally, numerical examples are given, and their solutions are validated based on results obtained by SimMechanics and Adams.

Body-Mounted Robot for Image-Guided Percutaneous Interventions: Mechanical Design and Preliminary Accuracy Evaluation.

This paper presents a body-mounted, four degree-of-freedom (4-DOF) parallel mechanism robot for image-guided percutaneous interventions. The design of the robot is optimized to be light weight and compact such that it could be mounted to the patient body. It has a modular design that can be adopted for assisting various image-guided, needle-based percutaneous interventions such as arthrography, biopsy and brachytherapy seed placement. The robot mechanism and the control system are designed and manufactured with components compatible with imaging modalities including Magnetic Resonance Imaging (MRI) and Computed Tomography (CT). The current version of the robot presented in this paper is optimized for shoulder arthrography under MRI guidance; a Z-shaped fiducial frame is attached to the robot, providing accurate and repeatable robot registration with the MR scanner coordinate system. Here we present the mechanical design of the manipulator, robot kinematics, robot calibration procedure, and preliminary bench-top accuracy assessment. The bench-top accuracy evaluation of the robotic manipulator shows average translational error of 1.01 mm and 0.96 mm in X and Z axes, respectively, and average rotational error of 3.06 degrees and 2.07 degrees about the X and Z axes, respectively.

ASİMETRİK ÜÇ SERBESTLİK DERECELİ BİR DÜZLEMSEL PARALEL ROBOT MEKANİZMASININ KİNEMATİK ANALİZİ

In this study, kinematic analysis of a planar parallel robot mechanism with three degrees of freedom (DOF) was performed. The difference of the selected mechanism from the other planar mechanisms is that it has an asymmetric leg structure. In order to provide the asymmetry, a leg of 3-R P R (R: Revolute joint, P : Active prismatic joint) symmetrical planar robot mechanism was replaced by a R RR (R: Active revolute joint) type leg and the asymmetrical planar parallel robot named R P R2 R RR1 mechanism has been obtained. Inverse kinematics, Jacobian matrix and singularity free workspace analysis were performed for the proposed mechanism. In addition, the performance of this mechanism is compared with the 3-R P R mechanism, which is a symmetric planar parallel robot mechanism. According to the obtained results, it has been shown that the workspace of the proposed mechanism is better than the 3-R P R mechanism in terms of both the number of points that can be reached by the end-effector and the limit values of the orientation angle.

A method for stiffness analysis of overconstrained parallel robotic mechanisms with Scara motion

This paper presents a general method for analyzing stiffness of overconstrained parallel robotic mechanisms with Scara motion. In the method, the stiffness model of a limb is derived by applying Castigliano's second theorem to strain energy of the limb with a structural decomposition strategy, and the stiffness matrix of a parallel mechanism is established based on stiffness models of limbs and the static equilibrium equation of the moving platform. Comparisons show that the stiffness model obtained from the proposed method is very close to the counterpart obtained from finite element analysis (FEA). In addition, a new index is proposed to evaluate stiffness performance of a parallel mechanism in a given configuration based on strain energy under external unit forces and moments. With this index, the dimensions of a parallel mechanism can be optimized and the path of a given task can be planned to obtain high stiffness.

A method for stiffness modeling of 3R2T overconstrained parallel robotic mechanisms based on screw theory and strain energy

Stiffness (or compliance) performances of three-rotation and two-translation (3R2T) overconstrained parallel mechanisms have an important influence on their applications in bio-inspired robots with precision operations. However, it is difficult to build stiffness models of the class of mechanisms due to fairly complicated structures, and an effective and efficient modeling method has not been reported. This paper presents an approach to stiffness modeling of 3R2T overconstrained parallel robotic mechanisms. First, expressions of applied wrenches exerted on limbs and joints of a mechanism under an external load are solved based on screw theory. Then, the stiffness matrix of a limb is derived by applying Castigliano’s second theorem to strain energy of the limb, which is solved by introducing a strategy of structural decomposition. Third, the stiffness model of a mechanism is built based on stiffness matrices of all limbs and the principle of virtual work on the moving platform. Finally, the effectiveness of the proposed method is verified based on the fact that the computational compliance matrices are very close to those from finite element analysis (FEA) models. The proposed method can be used to build conveniently stiffness models with high accuracy for 3R2T overconstrained parallel mechanisms in precision positioning applications.

Design and Analysis of 6-DOF Triple Scissor Extender Robots With Applications in Aircraft Assembly

A new type of parallel robot mechanism with an extendable structure is presented, and its kinematic properties and design parameters are analyzed. The triple scissor extender (TSE) is a six-degree-of-freedom robotic mechanism for reaching high ceilings and positioning an end effector. Three scissor mechanisms are arranged in parallel, with the bottom ends coupled to linear slides, and the top vertex attached to an end effector plate. Arbitrary positions and orientations of the end effector can be achieved through the coordinated motion of the six linear actuators located at the base. By changing key geometric parameters, the TSE's design can yield a specific desired workspace volume and differential motion behavior. A general kinematic model for diverse TSEs is derived, and the kinematic properties, including workspace, singularity, and the Jacobian singular values, are evaluated. From these expressions, four key design parameters are identified, and their sensitivity upon the workspace volume and the Jacobian singular values is analyzed.A case study in autonomous aircraft assembly is presented using the insights gained from the design parameter studies.

Mobility analysis for parallel manipulators based on intersection of screw manifolds

In order to overcome the exceptional cases of the classical CGK formula for mobility analysis, a novel approach based on intersection of screw manifolds is proposed in this paper. This approach can deal with both the mobility of the moving platform and the full-cycle mobility. Furthermore, this approach can identify the redundant and passive mobilities, and guide the allocation of actuators. The procedure of the intersection operation of screw manifolds is presented in detail using the proposed concept of the complementary screw. And in special conditions, the intersection of two screw manifolds can be achieved instantly without the calculation of complementary screws. Moreover, this approach needs no investigation of the structures and properties of subgroups or submanifolds, and needs no reference to tables that are generalized to demonstrate operational rules for intersection of two subgroups. The proposed notion of the intersection of screw manifolds has the explicit kinematic sense, so that the nature of the mechanical motion of parallel robotic mechanisms can be profoundly understood.