Showing papers on "Revolute joint published in 2021"

A Backdrivable Kinematically Redundant (6+3)-Degree-of-Freedom Hybrid Parallel Robot for Intuitive Sensorless Physical Human–Robot Interaction

Abstract: A novel backdrivable 3-[ R ( R R- R RR)SR] kinematically redundant (6+3)-degree-of-freedom (DOF) spatial hybrid parallel robot with revolute actuators is proposed for low-impedance physical human–robot interaction. The kinematic model is developed based on the constraint conditions of the robot. It is shown that the type II (parallel) singularities can be completely avoided, thereby yielding a very large translational and orientational workspace. A workspace analysis is presented in order to demonstrate the capabilities of the robot. Mechanisms are then introduced to use the redundant DOF of the robot to operate a gripper with the robot actuators, which are mounted on or close to the base, thus reducing the inertia of the moving parts. The architecture of the robot makes it possible to use direct drive motors, thereby making the robot easily backdrivable and allowing the use of a very simple and effective controller. A prototype of the robot is then designed and built and the large workspace of the robot as well as the effortless physical human–robot interaction are demonstrated. The controller of the robot is then described, including a position control mode and a control mode for physical interaction, which does not require the use of a force/torque sensor or joint torque sensors. Because of its backdrivability and low moving inertia, the robot is particularly well-suited for physical human–robot interaction, as demonstrated in the accompanying videos.

Frictional Impact-Contacts in Multiple Flexible Links

Abstract: Multiple impacts of 2D (planar) open-loop robotic systems composed of n elastic links and revolute joints are studied in this paper. The dynamic equations of motion for such systems are derived by ...

Navigation of an n-link Revolute Robotic Arm via Hierarchal Landmarks

Abstract: This paper presents a dynamic n-link revolute robotic arm that can perform a sequence of tasks and navigate via hierarchal landmarks to its target. The stability condition with multiple Lyapunov functions for switched systems is considered. The multiple Lyapunov functions are formulated from the Lyapunov-based Control Scheme (LbCS) as a tool for analyzing Lyapunov stability. A new set of switched nonlinear, time-invariant, continuous, and stabilizing velocity controllers of the proposed Rn robotic arm are developed.

Correlation dimension and bifurcation analysis for the planar slider-crank mechanism with multiple clearance joints

Abstract: Joint clearance serves as a crucial element of nonlinearity in multibody systems. The quantization of the system chaos is conducive to not only the understanding of the nonlinear nature but the rationalization of system controlled parameters. In the present work, the system dynamics for the planar slider-crank mechanism with multiple clearance joints is depicted by the correlation dimension and bifurcation actions. Considering the obliqueness of the slider, the general configuration of the planar joint is proposed. Generalized coordinates and the Lagrangian approach are adopted to derive the dynamic motion equations. The effects of clearance size and driving speed on the bifurcations of the dynamic response are investigated. Furthermore, the fractal dimension of the strange attractor is identified by the correlation dimension from time series. Based on the Cao method, the Mutual Information (MI) function, and the Grassberger-Procaccia (G-P) algorithm, the controlled factors in the evaluation of correlation dimension are cautiously determined. Ultimately, the compound effect of translational and revolute clearance joints on the mechanism dynamics is featured. The numerical results testify that the correlation dimension of the slider displacement approximately saturates beyond a specific translational clearance value. Moreover, with the parameters used in this work, the complexity of system response seems to be more sensitive to the variation of translational clearance size than with the revolute joint.

Three-dimensional asymmetric maximum weight lifting prediction considering dynamic joint strength:

Abstract: In this study, the three-dimensional (3D) asymmetric maximum weight lifting is predicted using an inverse-dynamics-based optimization method considering dynamic joint torque limits. The dynamic joint torque limits are functions of joint angles and angular velocities, and imposed on the hip, knee, ankle, wrist, elbow, shoulder, and lumbar spine joints. The 3D model has 40 degrees of freedom (DOFs) including 34 physical revolute joints and 6 global joints. A multi-objective optimization (MOO) problem is solved by simultaneously maximizing box weight and minimizing the sum of joint torque squares. A total of 12 male subjects were recruited to conduct maximum weight box lifting using squat-lifting strategy. Finally, the predicted lifting motion, ground reaction forces, and maximum lifting weight are validated with the experimental data. The prediction results agree well with the experimental data and the model's predictive capability is demonstrated. This is the first study that uses MOO to predict maximum lifting weight and 3D asymmetric lifting motion while considering dynamic joint torque limits. The proposed method has the potential to prevent individuals' risk of injury for lifting.

High-precision and large-stroke XY micropositioning stage based on serially arranged compliant mechanisms with flexure hinges

Abstract: Compliant mechanisms are state of the art in micropositioning stages due to their many beneficial features. However, their design usually compromises between motion range, motion accuracy and design space, while mechanisms with distributed compliance are mostly applied. The further use of flexure hinges with common notch shapes strongly limits the stroke in existing high-precision motion systems. Therefore, this paper presents a high-precision compliant XY micropositioning stage with flexure hinges capable of realizing a motion range of ± 10 mm along both axes. The stage is based on a novel plane-guidance mechanism, which is optimized to realize a precise rectilinear motion of the coupler link while keeping the rotation angles of all hinges below 5 ° . The XY motion is then achieved by coupling two of these mechanisms in a serial arrangement. Next, the synthesis of the monolithic XY stage is realized by replacing all revolute joints of the rigid-body model with flexure hinges using optimized power function notch shapes. Emphasis is also placed on the embodiment design of the stage and the actuator integration to minimize possible error sources. Finally, the quasi-static behavior of the compliant stage is characterized by a simulation with a 3D FEM model and by an experimental investigation of a prototype. According to the results, the developed compliant XY micropositioning stage achieves a maximum positioning deviation of less than 10 μm in both axes and a yaw error of less than 100 μrad over a working range of 20 mm × 20 mm with a comparably compact design of the compliant mechanism of 224 mm × 254 mm.

An approach for dynamic analysis of planar multibody systems with revolute clearance joints

Abstract: Clearance is inevitable for manufacture and assembly in the revolute joints of multibody systems. Excessive value of joint clearance will lead to the poor dynamic performance of mechanism, namely noise, vibration and fatigue failure. This paper presents the development of a dynamic model for planar multibody systems with clearance joints. Based on the continuous contact law, the contact force model proposed by Lankarani and Nikravesh is employed to describe the contact–impact phenomenon between pin and hole. And, the incorporation of the friction influence on revolute joint clearance is conducted by a modified friction force model. According to the geometric relationship between contact elements, the kinematics of the multibody systems is mapped into the global coordinate systems. Additionally, an experimental test platform is set up whereby a slider–crank mechanism with two clearance joints is used as an example to demonstrate the correctness and effectiveness of the proposed approach. Finally, the effects of joint clearance on the dynamic characteristics of planar multibody systems are investigated.

Type synthesis, unified kinematic analysis and prototype validation of a family of Exechon inspired parallel mechanisms for 5-axis hybrid kinematic machine tools

Abstract: To fully disclose potential configurations of parallel mechanisms (PMs) that are performance-comparable to the commercially successful Exechon, a family of one translational two rotational (1T2R) over-constrained Exechon inspired PMs is synthesized through the screw theory. The synthesized PMs are further comparatively analyzed in terms of inverse kinematics, singularity occurrence and reachable workspace based on a unified kinematic model. The kinematic analyses indicate that the inherited overconstraints benefit for eliminating the constraint singularity of all synthesized Exechon inspired PMs and the workspace distribution of an Exechon inspired PM is closely related to its topological arrangement. Based on the kinematic evaluations, a preferred configuration of 2U P R-1R P S PM (‘R’: revolute joint, ‘U’: universal joint, ‘S’: spherical joint, ‘ P ’: prismatic actuated joint) is selected as a candidate for 1T2R spindle head. A laboratory prototype is fabricated and experimentally tested to verify the feasibility of the type synthesis and the correctness of the kinematic analyses. By integrating the selected PM with a 2-degree of freedom sliding gantry, a full scale prototype of a novel hybrid kinematic machine tool is developed to perform 5-axis machining tasks. The well match between the machined workpiece and its designed shape fully proves the engineering potential of the synthesized PMs that are expected to be employed as the functional module to construct 5-axis serial-parallel hybrid machining devices.

Feedrate scheduling of a five-axis hybrid robot for milling considering drive constraints

Abstract: Characterized by high rigidity and precision, large working space, and reconfigurability, hybrid kinematic machines are widely used in the five-axis machining of large parts in situ. The feedrate is limited by the velocity, acceleration, and jerk of actuated joints in high-speed machining due to the nonlinear motion introduced by the use of revolute joints and parallel kinematic module. To achieve a good balance between the machining accuracy and efficiency, an offline feedrate-scheduling algorithm considering the drive constraints of a five-axis hybrid machine is proposed. By adding a dimension of the curve parameter, the feedrate profile expressed by a cubic uniform B-spline is mapped into a two-dimensional curve with the redefined control points. Then, the feedrate-scheduling process is completed by iteratively modulating the control points of feedrate profile. The velocity, acceleration, and jerk of actuated joints are calculated by the kinematic analysis for a dual non-uniform rational basis spline (NURBS) toolpath. Based on this, the feedrate constraint equations are derived considering the geometry and drive constraints. The scheduled feedrate profile remains constant in most parameter intervals, while it changes smoothly in transition intervals without violating constraints. Simulations and experiments are carried out on the TriMule600/800 machining platform, and the results validate the correctness and effectiveness of the proposed algorithm.

Development of a redundant anthropomorphic hydraulically actuated manipulator with a roll-pitch-yaw spherical wrist

Abstract: The demand for redundant hydraulic manipulators that can implement complex heavy-duty tasks in unstructured areas is increasing; however, current manipulator layouts that remarkably differ from human arms make intuitive kinematic operation challenging to achieve. This study proposes a seven-degree-of-freedom (7-DOF) redundant anthropomorphic hydraulically actuated manipulator with a novel roll-pitch-yaw spherical wrist. A hybrid series-parallel mechanism is presented to achieve the spherical wrist design, which consists of two parallel linear hydraulic cylinders to drive the yaw/pitch 2-DOF wrist plate connected serially to the roll structure. Designed as a 1RPRRR-1SPU mechanism (“R”, “P”, “S”, and “U” denote revolute, prismatic, spherical, and universal joints, respectively; the underlined letter indicates the active joint), the 2-DOF parallel structure is partially decoupled to obtain simple forward/inverse kinematic solutions in which a closed-loop subchain “RPRR” is included. The 7-DOF manipulator is then designed, and its third joint axis goes through the spherical center to obtain closed-form inverse kinematic computation. The analytical inverse kinematic solution is drawn by constructing self-motion manifolds. Finally, a physical prototype is developed, and the kinematic analysis is validated via numerical simulation and test results.

Cartesian Aerial Manipulator with Compliant Arm

Abstract: This paper presents an aerial manipulation robot consisting of a hexa-rotor equipped with a 2-DOF (degree of freedom) Cartesian base (XY–axes) that supports a 1-DOF compliant joint arm that integrates a gripper and an elastic linear force sensor. The proposed kinematic configuration improves the positioning accuracy of the end effector with respect to robotic arms with revolute joints, where each coordinate of the Cartesian position depends on all the joint angles. The Cartesian base reduces the inertia of the manipulator and the energy consumption since it does not need to lift its own weight. Consequently, the required torque is lower and, thus, the weight of the actuators. The linear and angular deflection sensors of the arm allow the estimation, monitoring and control of the interaction wrenches exerted in two axes (XZ) at the end effector. The kinematic and dynamic models are derived and compared with respect to a revolute-joint arm, proposing a force-position control scheme for the aerial robot. A battery counterweight mechanism is also incorporated in the X–axis linear guide to partially compensate for the motion of the manipulator. Experimental results indoors and outdoors show the performance of the robot, including object grasping and retrieval, contact force control, and force monitoring in grabbing situations.

Test study and nonlinear dynamic analysis of planar multi-link mechanism with compound clearances

Abstract: Clearance of kinematic pairs and flexibility of components are unavoidable problems in engineering applications. Dynamical model of planar rigid 2 DOFs 9 bars rigid-flexible coupling mechanism with compound clearances(including revolute clearance and translational clearance) is built. Comparison of dynamic response and nonlinear characteristic of rigid mechanisms with compound clearances and rigid-flexible coupling mechanisms with compound clearances is studied with each other. Influences of various clearance sizes and driving speeds on nonlinear dynamics characteristics of rigid-flexible coupling mechanisms with compound clearances have been both researched by center trajectory diagram, phase maps, Poincare maps and bifurcation diagrams . In order to verify correctness of theoretical results, test study of 2 DOFs 9 bars mechanism with compound clearances is carried out. Influences of different clearance sizes and driving speeds on mechanism with compound clearances have been also studied by test.

On the Optimal Design of Underactuated Fingers Using Rolling Contact Joints

Abstract: The design of underactuated fingers using rolling contact joints is addressed in this article in order to increase performance in robotic and prosthetic hands applications. Rolling contact joints have proven to be a promising alternative to revolute joints by increasing the range of motion, introducing compliance and decreasing internal friction. The conditions of optimal design for fingers using such joints are however not well stated. In order to fully exploit the potential of rolling-contact-joint based fingers, their design space is extended and performance metrics adapted to underactuated fingers are used in this letter. An optimization based on these metrics is performed over the large design space using genetic algorithms to find an optimal design. The solution obtained is then used to build a prototype and its performance is compared to that predicted by the model and to a comparative design using a realistic test bench.

Complex manipulation with a simple robotic hand through contact breaking and caging.

Abstract: Humans use all surfaces of the hand for contact-rich manipulation. Robot hands, in contrast, typically use only the fingertips, which can limit dexterity. In this work, we leveraged a potential energy-based whole-hand manipulation model, which does not depend on contact wrench modeling like traditional approaches, to design a robotic manipulator. Inspired by robotic caging grasps and the high levels of dexterity observed in human manipulation, a metric was developed and used in conjunction with the manipulation model to design a two-fingered dexterous hand, the Model W. This was accomplished by simulating all planar finger topologies composed of open kinematic chains of up to three serial revolute and prismatic joints, forming symmetric two-fingered hands, and evaluating their performance according to the metric. We present the best design, an unconventional robot hand capable of performing continuous object reorientation, as well as repeatedly alternating between power and pinch grasps-two contact-rich skills that have often eluded robotic hands-and we experimentally characterize the hand's manipulation capability. This hand realizes manipulation motions reminiscent of thumb-index finger manipulative movement in humans, and its topology provides the foundation for a general-purpose dexterous robot hand.

Dynamic modelling and properties analysis of 3RSR parallel mechanism considering spherical joint clearance and wear

Abstract: The collision and wear caused by inevitable clearance in kinematic pair have an effect on the dynamic characteristics of the mechanism. Therefore, we established the dynamic model of a 3RSR (R is the revolute joint and S is the spherical joint) parallel mechanism with spherical joint clearance based on the modified Flores contact force model and the modified Coulomb friction model using Newton-Euler method. The standard quaternion was introduced in the constraint equation, and the four-order Runge-Kutta method was adopted to solve the 3RSR dynamic model. The simulation results were compared and analyzed with the numerical results. The geometrical parameters of the worn ball socket were solved based on the Archard wear model, and the geometrical reconstruction of the worn surface was carried out. The geometric reconstruction parameters were substituted into the dynamic model, which was to analyze the dynamic response of the 3RSR parallel mechanism with wear and spherical joint clearance. The simulation results show that the irregular wear occurs in the spherical joint with clearance under the presence of the impact and friction force. The long-term wear will increase the fluctuation of the contact force, thereby decreasing the movement stability of the mechanism.

An image-guided hybrid robot system for dental implant surgery.

Abstract: Dental implant surgery is an effective method for remediating the loss of teeth. Robot is expected to increase the accuracy of dental implant surgery. However, most of them are industrial serial robot, with low stiffness and non-unique inverse kinematic solution, which may reduce the success rate and safety of robotic surgery. Compared to serial robot, parallel robot is more stiffness and has unique inverse kinematic. However, its workspace is small, which may not meet surgical requirements. Therefore, a novel hybrid robot dedicated to dental implant is proposed. The hybrid robot is composed of three translation joints, two revolute joints, and Stewart parallel manipulator. Stewart is used for performing surgical operation, while the joints are used for enlarging the workspace of Stewart. In order to ensure the safety of robot motion, physical human–robot interaction based on a variable admittance controller is applied in the robotic system. In addition, considering the small workspace of Stewart, an optimal model is proposed to minimize the joint movement of Stewart in adjusting the orientation of drill bit. Phantom experiments were carried out based on the prototype robot. In the experiments, the optimal model could be solved after 20 iterations, finding an ideal joint configuration. The proposed variable admittance controller could enhance comfort level effectively. The accuracy of robot is evaluated by angle, entry and exit deviation, which are 0.74 ± 0.25°, 0.93 ± 0.28 mm, and 0.96 ± 0.23 mm, respectively. The phantom experiments validate the functionality of the proposed hybrid robot. The satisfactory performance makes it more widely used in the practical dental implant surgery in the future.

Nonlinear dynamic analysis of the extended telescopic joints manipulator with flexible links

Abstract: In this paper, the open-chain arm containing flexible links connected through telescopic joints is investigated so as to replace robotic chains with revolute joints. In this manipulator, telescopic joints are considered by a simultaneous motion combination of the prismatic and revolute joints. In comparison with revolute–prismatic joints in which prismatic joint hubs are utilized, telescopic joints lack the hub, and the linear motion is generated via a gear. Accordingly, the flexible link is not placed inside the hub. In fact, the link is merely divided into two sections each at a time step. The front section which is considered in the motion equations is placed at the back of the hinge’s point. This part solely creates vibration, which probably affects the motion of other sections. This type of manipulator’s joints due to the structure benefits consists of the optimum weight, simple mechanism, extended workspace acceptable for robotic tools, industrial machinery, and domestic systems. To derive motion equations of N-link flexible manipulator with telescopic joints system, the Euler–Lagrange formulation is employed. The obtained equations are in the time-varying form, and the manipulator link length changes during motion. The derived equations are simulated for a two-link system with different elasticity values, and the results are then analyzed to verify the outcomes. The bifurcation analysis has also been used to prevent unstable vibrations and chaotic responses. It should be noticed that this type of manipulator can be used in a fast and precise mechatronics' system for utilization in space exploration, space station, and spacecraft as well.

Workspace analysis of 3-DOF U-shape base planar parallel robotic motion stage using shape memory alloy restoration technique (SMART) linear actuators

Abstract: The applications of lightweight planar parallel robotic manipulators are increasing enormously because of its various desirable characteristics such as low weight, lower inertia and higher stiffness Higher accelerations and accuracies can be achieved in planar parallel manipulators Also, shape memory alloy restoration technique (SMART)-based linear actuators are replacing huge and bulky linear actuators This study presents the kinematic design of smart linearly actuated family of U-shape base planar parallel robotic manipulator With the aid of solid modelling software, different available configurations were modelled and their workspace was analysed The developed 3-DOF motion stages (18 unique configurations) were fabricated using fused deposition modelling process, and the top three configurations having higher workspace were further experimented It is interesting to observe that the actual or experimental workspace of a particular manipulator configuration is further minimised from the predicted or feasible workspace It is due to the presence of passive links, singularities, friction between the parts, heat dissipation, force distribution, stiffness, etc The present study depicts the experimental workspace of the top three configurations, namely PPR-PRP-PRR, PRP-PPR-PRP and PRP-PPR-PRR Since none of the experimental workspace observed is equal or higher than the model workspace, an efficiency loss in terms of workspace reduction was calculated to understand the acceptability of the configurations in different domains Apart from the loss, the result disclosed that the actual workspace of all the manipulators was within the feasible workspace domain of mobile platform The PPR-PRP-PRR manipulator was found to possess highest experimental workspace than other configurations Note: P, P, and R refer to active prismatic, passive prismatic and passive revolute joints respectively

Kinematic and dynamic analysis of a 3-DOF parallel mechanism

Abstract: This paper presents a three Degrees of Freedom (DOFs) parallel manipulator with no rotational capacity. Planar kinematic pairs (revolute joint and prismatic joint) are exclusively employed in this parallel structure. The parallelogram joint in each kinematic chain assists to ensure the moving platform’s orientation is constant throughout the reachable workspace. Unlike the general parallel mechanisms, three identical kinematic limbs are degenerated to two kinematic limbs through merging two passive prismatic joints with same movement. Three active sliding joints are still required to drive this special parallel structure. Its mobility characteristic is firstly studied in detail and all possible singularity configurations are discussed by means of screw theory. The Lagrangian formulation is employed to compute the mathematical model of the inverse dynamic problem. The reachable workspace is obtained based on the inverse kinematic solutions. The distributions of the maximum joint force effect and maximum joint velocity effect are conducted. An example is provided to illustrate their trends under preset motion of the mobile platform.

Autonomous Learning of the Robot Kinematic Model

Abstract: Robotics systems are becoming more and more autonomous and reconfigurable. In this context, the design of algorithms capable of deriving kinematics and dynamics models directly from data could be particularly useful. In this article, we present an algorithm that learns a forward kinematics model of a robot starting from a time series of visual observations. Our strategy can be applied to any robot with serial kinematics composed of revolute and prismatics joints. First, the algorithm identifies the robot kinematic structure, i.e., a high-level description of the robot geometry that defines the connections between the rigid-bodies composing the robot. Then, the algorithm derives the forward kinematics relying on a Gaussian process (GP) model. More precisely, the GP model is based on a polynomial kernel, defined exploiting the kinematic structure previously identified. The effectiveness of the proposed solution has been tested via extensive Monte Carlo simulations, as well as via experiments on a real UR10 robot.

Novel Manipulability for Parallel Mechanisms with Prismatic-Revolute Actuators, GA-DP Trajectory Planning Application

Abstract: Performance measures have been utilized for numerous applications in robotics research In this paper, the manipulability and dexterity indices have been focused These indices have been used successfully when parallel robots have either completely revolute or prismatic joints But, in a manipulator with both revolute and prismatic joints, these may not be used because of the dimensional inconsistency of the components in the Jacobian matrix Moreover, in the kinematic or dynamic case, for manipulability and dexterity analysis, the Euclidean norm for the velocity inputs is considered while the velocity inputs for active joints are generally independent; therefore, the manipulability and dexterity indices are explained based on the infinity-norm Thus, the final solution is represented by the new concept of mixed manipulability polytope Next, an example of the 3-RPC parallel robot is analyzed based on the notion of this index As an application, the index is applied for trajectory planning in multi-objective optimal control For this, one of the direct methods of optimal control, dynamic programming (DP), is selected But for the DP, the genetic algorithm (GA) is used for searching the optimum path This analysis is applied for a novel PU-3RPR redundant parallel manipulator First, the parallel mechanism is introduced, and the kinematics and Jacobian analysis is discussed Then the objective function that minimizes the pseudo kinetic energy and maximizes the index, is adopted for an optimization problem Finally, the trajectory of the PU-3RPR redundant parallel mechanism is planned by the proposed GA-DP method

Mathematical modelling and virtual decomposition control of heavy-duty parallel-serial hydraulic manipulators.

Abstract: This paper proposes a novel modelling approach for a heavy-duty manipulator with parallel$-$serial structures connected in series. Each considered parallel$-$serial structure contains a revolute segment with rigid links connected by a passive revolute joint and actuated by a linear hydraulic actuator, thus forming a closed kinematic loop. In addition, prismatic segments, consisting of prismatic joints driven by hydraulic linear actuators, also are considered. Expressions for actuator forces are derived using the Newton$-$Euler (N$-$E) dynamics formulation. The derivation process does not assume massless actuators decoupled from manipulator links, which is common in the Lagrange dynamics formulation. Actuator pressure dynamics are included in the analysis, leading in total to a third-order system of ordinary differential equations (ODEs). The proposed model in the N$-$E framework, with fewer parameters than its predecessors, inspires revision of the virtual decomposition control (VDC) systematic process to formulate a control law based on the new model. The virtual stability of each generic manipulator revolute and prismatic segment is obtained, leading to the Lyapunov stability of the entire robot.

Dynamic analysis of mechanical system considering radial and axial clearances in 3D revolute clearance joints

Abstract: In the dynamic modeling and simulation of mechanical system with revolute clearance joint, it is usually assumed that the revolute joint is planar joint with radial clearance, but the axial clearan...