Freedom Parallel Manipulator Research Articles

Kinematics and dynamics analysis of a six-degree of freedom parallel manipulator

Modeling and analysis of inverse kinematics and dynamics for a novel parallel manipulator are established in this article. The manipulator is a spatial mechanism, which consists of six identical kinematic chains connecting to the moving platform. Firstly, screw theory is applied to compute the degree of freedom of this manipulator. Then the inverse position is achieved based on the homogeneous coordinate transformation principle while motion law of the moving platform is given. Furthermore, the first-order influence coefficient method is employed to obtain the Jacobian matrices of the considered manipulator and the links, so do the velocities. Afterward, the rigid-body dynamics model is derived from the Lagrange formulation. To obtain the integrated inverse dynamics model, an approach for simplified flexible dynamics analysis is proposed. Finally, simulations are conducted to compute the position and driving force of this considered manipulator, which validate the new method simultaneously.

Intelligent controller for robust orientation control of smart actuator based parallel manipulator

Flexible parallel manipulators can be used as an orienting device due to its precise positioning ability. The flexibility demands the use of non-conventional actuators and noncontact type/flexible sensors for feedback measurement. This study proposes a novel 2 Degree of Freedom (DoF) parallel manipulator actuated by shape memory alloy springs (SMA) which could be used as an orienting device for a table top Cartesian robot. To mitigate the use of contact type sensor, model based feedback is proposed to obtain SMA length for the feedback control. The inclusion of SMA actuators to parallel mechanism imposes control challenges due to nonlinearities, coupling effects, and disturbances. This work also proposes a novel control scheme based on concept of partition control law to control the SMA spring position without the use of any complex mathematical model. The proposed controller is a combination of two parts Fuzzy PID servo control and the time delay estimation (TDE) based auxiliary control. The fuzzy PID control handles the error tracking and the auxiliary control tries to cancel the nonlinearities and disturbances, thus enhancing the robustness. The performance of the proposed controller is tested for a complex trajectory under disturbances and the results are compared with existing nonlinear controllers which proves superior nature of the proposed controller.

Analysis of coupling effects on hydraulic controlled 6 degrees of freedom parallel manipulator

Analysis of coupling effects on hydraulic controlled 6 degrees of freedom parallel manipulator

Analysis of coupling effects on hydraulic controlled 6 degrees of freedom parallel manipulator

This paper presents an analysis of the coupling effects between degrees of freedom of a hydraulic controlled six DOF parallel manipulator. Based on the singular value decomposition to the properties of its joint space inverse mass matrix, the method is put forward to analyze coupling effects between degrees of freedom using a transformation matrix, the product of transposed Jabobian matrix and an orthogonal unitary matrix, of which each element represents decoupled modal space coordinates with respect to physical task space frame. The simulation results in frequency domain prove the theoretical analysis right. The analysis will provide useful information to mechanism and controller designer, to asses from concept the coupling effects between DOF in respect of the requirement for a particular application and also for the study on decoupling control strategies.

Optimization of 3-DoF Manipulators’ Parasitic Motion with the Instantaneous Restriction Space-Based Analytic Coupling Relation

This paper presents a velocity-level approach to optimizing the parasitic motion of 3-degrees of freedom (DoFs) parallel manipulators. To achieve this objective, we first systematically derive an analytical velocity-level parasitic motion equation as a primary step for the optimization. The paper utilizes an analytic structural constraint equation that describes the manipulator’s restriction space to formulate the parasitic motion equation via the task variable coupling relation. Then, the relevant geometric variables are identified from the analytic coupling equation. The Quasi-Newton method is used for the direction-specific minimization, i.e., optimizing either the x-axis or y-axis parasitic motion. The pattern-search algorithm is applied to optimize all parasitic terms from the workspace. The proposed approach equivalently describes the 3-PhRS, 3-PvRS, 3RPS manipulators. Moreover, other manipulators within a similar category can be equivalently expressed by the proposed method. Finally, the paper presents the resulting optimum configurations and numerical simulations to demonstrate the approach.

SYNTHESIS OF A NOVEL FIVE-DEGREES–OF-FREEDOM PARALLEL KINEMATIC MANIPULATOR

This paper presents the design and analysis of a novel five degrees-of- freedom (DOF) parallel kinematic manipulator (PKM) for part-handling, sorting, general positioning, and robotic machining applications. The 2- R(Pa-IQ)RR, R(Pa-IQ)R manipulator has two rotational DOFs, one parasitic rotation, and three translational DOFs. In comparison with other 5- and 6- DOF PKMs, this PKM possesses three pairs of coplanar legs that contain nested kinematic chains, and it makes exclusive use of revolute and prismatic joints. The inverse kinematic analysis is a novel extension of the geometric (vector) method with the analysis of inner and outer kinematic chains. The forward kinematic analysis was solved using the Newton Raphson (NR) method. The results of the forward and inverse kinematic analyses were validated with SolidWorks ® and MATLAB ® simulations.

Development and Validation of Finite Element Analysis Model (FEM) of Craniovertebral Junction: Experimental Biomechanical Cadaveric Study.

Experimental Cadaveric Biomechanical Study. To establish an experimental procedure in cadavers to estimate joint stiffness/stability at craniovertebral junction (CVJ) region with various implant systems and to develop/validate an indigenous cost effective 3D-FEM (three-dimensional finite element model) of CVJ region. Finite element analysis (FEM) tools can provide estimates of internal stress and strain in response to external loading of various implant systems used in CVJ fixations. Experimental setup for conducting biomechanical movements on CVJ region of cadaver was developed using cost effective innovative tools. A manually actuated seven- degrees of freedom parallel manipulator motion testing system (MA7DPM) was designed and developed to impart designed trajectories and to conduct various biomechanical motion studies at CVJ region for the present study. FEM model of CVJ region was developed and subsequently validated with CVJ morphometry data of 15 human subjects of Asian origin. Validated FEM was subjected to force motion studies at the CVJ region. The force-motion maps obtained from the FEM studies were subsequently validated against biomechanical experiment results from cadaveric experiment results obtained with three different implant fixations. A cost effective biomechanical tool (which did not require decapitation of cadaveric head) and a customised chair (to place cadaver in sitting position during conduct of biomechanical movements simulating real-life scenario) was indigenously designed and developed. Developed biomechanical tool (MA7DPM) for this study is likely to be useful for stress-testing analysis of various implant systems for individual patients undergoing surgery at CVJ region in near future. 5.

Comparative Kinematic Analysis and Design Optimization of Redundant and Nonredundant Planar Parallel Manipulators Intended for Haptic Use

SUMMARYThis paper investigates a comparative kinematic analysis between nonredundant and redundant 2-Degree Of Freedom parallel manipulators. The nonredundant manipulator is based on the Five-Bar mechanism, and the redundant one is a 3-RRR planar parallel manipulator. This study is aimed to select the best structure for a haptic application. This latter requires a mechanism with a desired workspace of 10 cm × 10 cm and an admissible force of 5 N in all directions. The analysis criteria are the accuracy of the forward kinematic model and the required actuator torques. Thereby, the geometric parameters of the two structures are optimized in order to satisfy the required workspace such that parallel singularities are overcome. The analysis showed that the nonredundant optimally designed manipulator is more suitable for the haptic application.

Kinematics, workspace and optimal design of a novel 4RSS + PS parallel manipulator

In this paper, a novel four degrees of freedom (DOFs) parallel manipulator (PM) is introduced and its kinematics, workspace and optimal design are systematically studied. The manipulator is called 4RSS + PS PM having four active RSS type legs and one passive PS type leg. R, S and P stand for revolute, spherical and prismatic joints, respectively, and R denotes the actuated revolute joints. Moving platform of the manipulator has three rotational motions along with one translational motion (3R1T). As an advantage, rotational motion of the moving platform around the axis of its translational motion has no limitation. This makes the manipulator so suitable for machining applications in holes, cylinders and so on. Closed form solutions are found for the inverse and forward position kinematics problems of the manipulator. The manipulator workspace is determined numerically in a 3D space. A special design of the manipulator free of inverse and forward kinematic singularities is specified. Kinematic dexterity analysis is carried out based on the condition number of the manipulator Jacobian matrix showing that the manipulator has no singularity inside the workspace. Two architecture optimizations are also presented to achieve a maximum workspace volume of the manipulator, and to find a workspace with a desired value of kinematic dexterity.

Acausal Approach to Motion Cueing

Motion simulators have been used extensively by both industry and academia to train pilots, conduct psychological experiments on drivers, understand the perception of motion by humans, and cater to the burgeoning gaming industry among others. Working of a motion simulator can be summarized in following three steps: first, acquisition of motion signals; second, motion cueing: signal processing to generate motion references, and third, control: tracking the desired references. A motion cueing algorithm (MCA) acts as a bridge between the actual motions and the ones recreated by the simulator. Mathematically, MCA is constituted of the following four operations: scaling, saturation, filtering, and tilt-coordination (involves filtering too). The existing MCAs make use of causal filters to process the signals, thereby precluding the possibility of utilizing future motion signals to emulate pre-recorded scenarios. We present a new approach to generate motion cues by explicitly making use of future motion signals and causal linear filters. It is due to the usage of future motion signals (not the filter), we call the presented methodology as acausal cueing algorithm (ACA). Unlike most of the existing works on motion cueing, we choose to present the developed methodology using discrete-time models to facilitate its quick implementation by industry and other researchers in the future. The veracity of the presented methodology is examined by actuating a motion simulator (seven degrees of freedom parallel manipulator) based on the references generated by the ACA in response to test trajectories. The conducted experiments assert better performance of the ACA (over MCA) in the beginning, which eventually degrades in the last few seconds due to unavailability of future motion signals.

The Dexterity Analysis of a Spatial Three-Degree of Freedom Parallel Manipulator with Constrained Branch

The Dexterity Analysis of a Spatial Three-Degree of Freedom Parallel Manipulator with Constrained Branch

Development of a Self-tuning PID Controller on Hydraulically Actuated Stewart Platform Stabilizer with Base Excitation

Stewart platform is a six degrees of freedom (DOF) parallel robot manipulator with rather high powerto- weight ratio and more accurate positioning that of conventional serial-link robots. Nevertheless, modelling and control of parallel Stewart platform is so abstruse and significant for vibration isolation, especially in the case with base excitation in stabilizers. In this paper a clear nonlinear dynamic model of hydraulically actuated Stewart platform with 6-DOF is presented via Kane’s method. The dynamics of Stewart platform embedded with hydraulic actuator equations is utilized to design a modern control scheme with the aim of vibration isolation. In order to attenuate upper platform vibration under uncertain base excitation profile, a novel neural network based selftuning PID (NN-PID) control scheme is implemented. Following numerical simulation results, the proposed control method satisfies vibration isolation of the upper platform under uncertain base excitation and shows well robustness against external disturbances. It is concluded that the controller is of fine adjustability and can isolate a wide range of external disturbances.

Spatial Three Degree of Freedom Parallel Manipulator Forward Kinematic Position Analysis

This work presents forward kinematic position analysis of a spatial three degree of freedom parallel manipulator, which has three symmetric loops. The three loops consist of an actuated sliding links- rotational and spherical joints. The actuated sliding links are attached to inclined base platform via rotational joints. The limbs are connected from rotational joints to moving platform by spherical joints. The degree of freedom of a spatial parallel manipulator is analyzed via kutzbach criterion. The forward kinematic position analysis carried out by using 3-coupled trigonometric equations which are formulated with side and behaviour constraints of the manipulator. There are many difficulties in solving the system of non-linear equations in kinematics of manipulator therefore by using MATLAB the three non-linear coupled algebraic equations are solved. The forward position kinematic analysis part is used in the development procedure of spatial parallel manipulator to check, the required and obtained positions of the moving platform of the developed manipulator.

Workspace Limiting Strategy for 6 DOF Force Controlled PKMs Manipulating High Inertia Objects

This article describes an efficient and effective strategy for limiting the workspace of a six degrees of freedom parallel manipulator, with challenging motion smoothness requirements due to both the high inertia objects carried by the end effector and the pose references coming from a force feedback loop. Firstly, a suitable formulation of the workspace is studied, distinguishing between different conventions and procedures. Thereafter a discrete and analytical formulation of the workspace is obtained and developed in order to suit this application. Having obtained the limits, a methodology to evaluate the robot pose is discussed, taking into account the reference pose buffering technique and the real time pose estimation through the numeric solution of the nonlinear forward kinematics equations. The safety algorithm designed checks the actual robot pose and future poses to be commanded, and takes control of the reference pose generation process, if an exit of the safety workspace is detected. The result obtained is a soft compliant surface within which the robot is free to move, but outside of which a “force field” pushes the robot end-effector to return smoothly. To reach this objective, the control deflects the end effector trajectory safely and smoothly and moves it back to within the workspace limits. Nevertheless, this preserves the continuity of the velocity and controls the acceleration, to avoid dangerous vibrations and shocks. Simulation and experimental result tests are conducted to verify the algorithm effectiveness and the efficient implementation.

PID Control and Stability Analysis of an ith leg of a Six Degree of Freedom Machining Bed

Process of material removal from work piece to get desired shape is usually termed as machining. Operations such as milling, drilling and turning are categorized as machining. Current spindle techniques allow quick material removal. Performance envelope is limited in such case for higher spindles. The high speed tools are also vulnerable to external and internal vibrations. Cuts made and parts created in existence of these vibrations will result in dimensional inaccuracy and imprecise measurements. A solution of these problems is to restrict the tool motion in a single dimension and instead give Six-DOF to the machine bed. A six degree of freedom robotic mechanism is proposed to tackle this problem to be used as a bed for machining. Proposed machining bed is a six degree of freedom parallel manipulator known as Stewart Platform, in which the tool is fixed and work piece is mounted on a movable top plate which gives controlled motion in six degrees of freedom. Overview of design for a six degree of freedom machining bed is discussed in this paper. The analysis of machining bed is done on MATLAB®. Close loop response, stability through Bode Plot, Nyquist Plot and Root Loci and selection of a controller when working in open loop conditions is discussed in detail in this paper. The results verify that a six degree of freedom bed can be used for the purpose of machining.

Studies on Stewart platform manipulator: A review

This paper presents a compilation of previous studies on the Stewart platform, which is a class of six degree of freedom parallel manipulators. The abstraction of a parallel manipulator is appropriated for the entire class of it. The paper focuses on the studies in the different fields which are closely checked to determine the direction of research and identify the solved problem areas. A significant investigation has been presented to discuss the existing methods for the analysis of the Stewart platform manipulator due to their unique applications. Studies on analysis and design of the Stewart platform manipulator using flexible joints are included. Modeling and analysis of parallel manipulators by Matlab SimMechanics environment are also highlighted.

Mechatronic design, experimental setup, and control architecture design of a novel 4 DoF parallel manipulator

ABSTRACTAlthough parallel manipulators started with the introduction of architectures with six degrees of freedom, a vast number of applications require less than six degrees of freedom. Consequently, scholars have proposed architectures with three and four degrees of freedom, but relatively few four degrees of freedom parallel manipulators have become prototypes, especially of the two rotation and two translation motion types. In this article, we explain the mechatronics design, prototype, and control architecture design of a four degrees of freedom parallel manipulators with two rotation and two translation motions. We chose to design a four degrees of freedom manipulator based on the motion needed to complete the tasks of lower limb rehabilitation. To the author’s best knowledge, parallel manipulators between three and six degrees of freedom for rehabilitation of lower limb have not been proposed to date. The developed architecture enhances the three minimum degrees of freedom required by adding a four degrees of freedom, which allows combinations of normal or tangential efforts in the joints, or torque acting on the knee. We put forward the inverse and forward displacement equations, describe the prototype, perform the experimental setup, and develop the hardware and control architecture. The tracking accuracy experiments from the proposed controller show that the manipulator can accomplish the required application.

Development of a 2-dof uterine manipulator with LED illumination system as a new transvaginal uterus amputation device for gynecological surgeries

Background: Hysterectomy, the most common major gynecological operation worldwide, consists of removal of the uterus and can be performed abdominally, vaginally, or laparoscopically. A uterine manipulator is a key device used for uterine manipulation and cannulation in hysterectomies. The challenges of conventional manipulators are to move the uterus in two distinct planes and to identify cervical landmarks during circular cut and coagulation.Material and methods: In this study, a structural synthesis of the two degrees of freedom parallel manipulator was performed considering the constraints noted by surgeons. Computer-aided design and assembly of the manipulator, the cervicovaginal cap with LEDs, and the external parts were performed before rapid prototyping. The final design of the uterine manipulator was then manufactured from stainless steel and tested on an artificial uterus model using a test chamber.Results: This article presents the design, production and testing processes of an innovative manipulator with a motion capability up to 80° workspace both in the sagittal and coronal planes and an illumination system, easily detectable by the laparoscope, was successfully implemented on the manipulator’s cervical cap in order to overcome the drawbacks of conventional uterine manipulators.Conclusions: Despite all the current studies and uterine manipulators on the market, no research has incorporated all the features mentioned above.

Kinematic analysis and design of a novel 3T1R 2-(PRR)2RH hybrid manipulator

A 4-DOF (degrees of freedom) parallel manipulator with three translations and one rotation (3T1R) is very useful in industry. Most of the 3T1R parallel manipulators have limited rotational capabilities that usually have a range less than 90°. A novel 3T1R 2-(PRR)2RH hybrid manipulator with full rotational capability is proposed in this paper. The fixed platform of the hybrid manipulator connects the moving platform by two identical actuated (PRR)2RH kinematic chains. The full rotational capability is achieved by using two coaxial helical (H) joints with equal but opposite pitch connected to the moving platform. Mobility analysis, inverse and forward kinematics, singularity analysis and workspace of this manipulator are presented. Based on a homogenized Jacobian matrix, condition number and global dexterity index are used to evaluate the kinematic performance of the 2-(PRR)2RH hybrid manipulator. The connection among the workspace volume, the global dexterity index and the layout angle of the manipulator are disclosed. The parameter-finiteness normalization method is then used to produce an optimal design of link parameters. The results provide theoretical foundations for application of this novel manipulator.

Optimal selection of the supporting points of large component aligned and positioned by parallel manipulator

Large components such as wing sections should be aligned and positioned in a desired position prior to the final manufacturing or assembly, so a digital alignment and position device based on six degree of freedom parallel manipulator with several prismatic-prismatic-prismatic-spherical branches was designed and fabricated to meet the needs. The digital alignment and position device is an alignment device based on the parallel manipulator, and it is also a positioning and holding fixture for large components manufacturing or assembly. In order to effectively and efficiently select the supporting points of large component where the digital alignment and position device branch is connected with, the performance of the parallel manipulator and the fixture should be comprehensively analyzed at the same time. The global performance indices such as the dexterity index, the bearing capacity index, and the stiffness index are calculated based on the mechanism Jacobean matrix of the parallel manipulator, and the positioning stability index is calculated based on the position Jacobean matrix of the fixture. The results show that the global performance indices are not related to the pose, but the positioning stability index is; in addition, all indices rely on the originally selected supporting points and provide the basis for the effective selection of the supporting points for large component aligned and positioned by the digital alignment and position device, which is based on parallel manipulator with prismatic- prismatic-prismatic-spherical pairs.