Showing papers on "Revolute joint published in 2011"

Distributed Coordinated Tracking With a Dynamic Leader for Multiple Euler-Lagrange Systems

Abstract: In this note, we study a distributed coordinated tracking problem for multiple networked Euler-Lagrange systems. The objective is for a team of followers modeled by full-actuated Euler-Lagrange equations to track a dynamic leader whose vector of generalized coordinates is time varying under the constraints that the leader is a neighbor of only a subset of the followers and the followers have only local interaction. We consider two cases: i) The leader has a constant vector of generalized coordinate derivatives, and ii) The leader has a varying vector of generalized coordinate derivatives. In the first case, we propose a distributed continuous estimator and an adaptive control law to account for parametric uncertainties. In the second case, we propose a model-independent sliding mode control algorithm. Simulation results on multiple networked two-link revolute joint arms are provided to show the effectiveness of the proposed control algorithms.

Joint stiffness identification of six-revolute industrial serial robots

Abstract: Although robots tend to be as competitive as CNC machines for some operations, they are not yet widely used for machining operations. This may be due to the lack of certain technical information that is required for satisfactory machining operation. For instance, it is very difficult to get information about the stiffness of industrial robots from robot manufacturers. As a consequence, this paper introduces a robust and fast procedure that can be used to identify the joint stiffness values of any six-revolute serial robot. This procedure aims to evaluate joint stiffness values considering both translational and rotational displacements of the robot end-effector for a given applied wrench (force and torque). In this paper, the links of the robot are assumed to be much stiffer than its actuated joints. The robustness of the identification method and the sensitivity of the results to measurement errors and the number of experimental tests are also analyzed. Finally, the actual Cartesian stiffness matrix of the robot is obtained from the joint stiffness values and can be used for motion planning and to optimize machining operations.

Numerical and experimental investigation on multibody systems with revolute clearance joints

Abstract: A comprehensive combined numerical and experimental study on the dynamic response of a slider-crank mechanism with revolute clearance joints is presented and discussed in this paper to provide an experimental verification and validation of the predictive capabilities of the multibody clearance joint models. This study is supported in an experimental work in a test rig, which consists of a slider-crank mechanism with an adjustable radial clearance at the revolute joint between the slider and the connecting rod. The motion of the slider is measured with a linear transducer and an accelerometer. Dynamic tests at different operating crank speeds and with several clearance sizes are performed. The maximum slider acceleration, associated with the impact acceleration, is used as a measure of the impact severity. The obtained results demonstrate the dynamical behavior of a multibody mechanical system with a clearance joint. Finally, the correlation between the numerical and experimental results is presented and discussed leading to validated models of clearance revolute joints.

Dual arm robot

Abstract: A robot assembly for transporting a substrate is presented. The robot assembly having a first arm and a second arm supported by a column, the first arm further having a first limb, the first limb having a first set of revolute joint/line pairs configured to provide translation and rotation of the distal most link of the first limb in the horizontal plane. The assembly further having a second arm further having a second limb, the second limb comprising a second set of revolute joint/link pairs configured to provide translation and rotation of a distalmost link of the second limb in the horizontal plane. The first limb and second limb further having proximal revolute joints having a common vertical axis of rotation and a proximal inner joint housed in a common housing. The assembly further having an actuator assembly coupled to the first set of revolute joint/link pairs and to the second set of revolute joint/link pairs to effect rotation and translation of the distalmost links of the first limb and the second limb, each of the first limb and the second limb defining, in conjunction with the actuator assembly, at least three degrees of freedom per limb, whereby the distalmost links of the first limb and the second limb are independently horizontally translatable for extension and retraction.

Joint coupling design of underactuated hands for unstructured environments

Abstract: This paper examines joint coupling in underactuated robotic grippers for unstructured environments where object properties and location may not be well known. A simplified grasper consisting of a pair of two-link planar fingers with compliant revolute joints was simulated as it grasped a target object. The joint coupling configuration of the gripper was varied in order to maximize successful grasp range and minimize contact forces for a wide range of target object sizes and positions. The number of actuators was also varied in order to test performance for varying degrees of underactuation. A normal distribution of object position was used to model sensing uncertainty and weight the results accordingly. There are three main results: distal/proximal joint torque ratios of around 1.0 produced the best results, both for cases in which sensory information available for the task was poor and when sensing was good; an actuator for each gripper finger performs no better than a single actuator for both fingers; and that for good sensing, the gripper should be positioned off-center from the object, resulting in an increased lever arm and lower unbalanced contact forces on the object.

Modeling 3D revolute joint with clearance and contact stiffness

Abstract: The clearances in the kinematic joints are due to deformations, wear, and manufacturing errors; the accurate modeling of these effects in multibody analysis is a complex issue but in many practical applications, it is mandatory to take into them into account in order to understand the actual behavior of mechanical systems. In this paper, the authors present a general computer-aided model of a 3D revolute joint with clearance suitable for implementation in multibody dynamic solvers. While a perfect revolute joint imposes kinematic constraints, the proposed revolute joint with clearance leads to a force constraint. The revolute joint has been modeled by introducing a nonlinear equivalent force system, which takes into account the contact elastic deformations. The model depends on the structural and geometrical properties of materials in contact that have been investigated using finite element models. The purpose is to give a general approach to study the influence of actual joints on kinematic, dynamic, and structural behavior of mechanisms. The proposed model has been applied in dynamic simulations of a spatial slider-crank mechanism.

Synthesis of Deployable/Foldable Single Loop Mechanisms With Revolute Joints

Abstract: This paper presents a geometric approach for design and synthesis of deployable/foldable single loop mechanisms with pure revolute joints. The basic kinematic chains with symmetric mobility are first synthesized, and an intuitive geometric method is proposed for the mobility analysis of these kinematic chains. The deployable/foldable single loop mechanisms can be regarded as a combination of the basic kinematic chains with nontrivial mobility intersection, under this approach, the 5R to 8R single loop mechanisms with symmetric mobility are synthesized systematically. The method for determining the positions of the joint axes on polyhedral links is also proposed, so that the mechanism can be fully deployed or fully folded without suffering from physical interference. Under this framework, a class of novel deployable/foldable single loop mechanisms is developed. The computer-aided design models for typical examples are built to illustrate their feasibility. [DOI: 10.1115/1.4004029].

A nonlinear series elastic actuator for highly dynamic motions

Abstract: A novel revolute nonlinear series elastic actuator called the HypoSEA is presented. The actuator uses a hypocycloid mechanism to stretch a linear spring in a nonlinear way. The actuator is optimized for highly dynamic tasks such as running and jumping, as it features a 120Nm torque capability and more than 30J of passive energy storage. When combined with a suitable controller, using the spring as an energy buffer can greatly reduce the work done by the rotor during periodic motions. The design has exceptionally low reflected mechanical impedance, making it robust against repeated impact loads. The nonlinear stiffening spring is optimized for the nonlinearities typically found in revolute-jointed hopping robots, and may be adjusted offline using a pretensioning mechanism. Finally, the low effective stiffness around the zero-torque equilibrium allows for extremely sensitive force control.

Design Adaptive Fuzzy Inference Sliding Mode Algorithm: Applied to Robot Arm

Abstract: The developed control methodology can be used to build more efficient intelligent and precision mechatronic systems. Three degrees of freedom robot arm is controlled by adaptive sliding mode fuzzy algorithm fuzzy sliding mode controller (SMFAFSMC). This plant has 3 revolute joints allowing the corresponding links to move horizontally. Control of robotic manipulator is very important in field of robotic, because robotic manipulators are Multi-Input Multi-Output (MIMO), nonlinear and most of dynamic parameters are uncertainty. Design strong mathematical tools used in new control methodologies to design adaptive nonlinear robust controller with acceptable performance in this controller is the main challenge. Sliding mode methodology is a nonlinear robust controller which can be used in uncertainty nonlinear systems, but pure sliding mode controller has chattering phenomenon and nonlinear equivalent part in uncertain system therefore the first step is focused on eliminate the chattering and in second step controller is improved with regard to uncertainties. Sliding function is one of the most important challenging in artificial sliding mode algorithm which this problem in order to solved by on-line tuning method. This paper focuses on adjusting the sliding surface slope in fuzzy sliding mode controller by sliding mode fuzzy algorithm.

Joint analysis in rapid fabrication of non‐assembly mechanisms

Abstract: Purpose – The main purpose of this study is to develop a systematic method that can minimize joint clearance for non‐assembly mechanism fabrication using a layer‐based fabrication technology.Design/methodology/approach – Joint clearance is one of the key factors affecting a mechanism's performance. Hertz theory is adopted to analyze the joint clearance‐penetration displacement relationship and the impact force‐displacement relationship. This analysis has indicated the importance of reducing joint clearance. To reduce joint clearance in layer‐based fabrication, a drum‐shaped roller is proposed for pin joint design in non‐assembly mechanism fabrication. Compared to cylindrical pin joint design, a drum‐shaped roller joint results in less impact force in mechanism operation. Furthermore, the joint clearance can also be drastically reduced.Findings – Large joint clearance could introduce instability into the dynamic behaviour of a mechanism. By applying a drum‐shaped roller, the instability could apparently be...

Design and fabrication of miniature compliant hinges for multi-material compliant mechanisms

Abstract: Multi-material molding (MMM) enables the creation of multi-material mechanisms that combine compliant hinges, serving as revolute joints, and rigid links in a single part. There are three important challenges in creating these structures: (1) bonding between the materials used, (2) the ability of the hinge to transfer the required loads in the mechanism while allowing for the prescribed degree(s) of freedom, and (3) incorporating the process-specific requirements in the design stage. This paper presents the approach for design and fabrication of miniature compliant hinges in multi-material compliant mechanisms. The methodology described in this paper allows for the concurrent design of the part and the manufacturing process. For the first challenge, mechanical interlocking strategies are presented. For the second challenge, the development of a simulation-based optimization model of the hinge is presented, involving functional and manufacturing constrains. For the third challenge, the development of hinge positioning features and gate positioning constraints is presented. The developed MMM process is described, along with the main constraints and performance measures. This includes the process sequence, the mold cavity design, gate selection, and runner system development. A case study is presented to demonstrate the feasibility of creating multi-material mechanisms with miniature hinges serving as joints through MMM process. The approach described in this paper was utilized to design a drive mechanism for a flapping wing micro air vehicle. The methods described in this paper are applicable to any lightweight, load-bearing compliant mechanism manufactured using multi-material injection molding.

A scalable joint-space controller for musculoskeletal robots with spherical joints

Abstract: In the long history of robotics research, the most prominent problem has always been, to develop robots that can safely operate in human-centered environments. One way towards the goal of a safe, and human-friendly robot, is to incorporate more and more of the flexibility that can be found in humans, by mimicking the internal mechanisms. In this work we propose a scalable joint-space control scheme based on computed torque control for an anthropomimetic robot. To achieve this, the dynamic system model of the robot is decomposed into hierarchical subsystems, using scalable modeling algorithms where possible. Machine learning techniques were employed to tackle the problem of muscle force to joint torque mapping. The developed control scheme has been evaluated using the highly refined simulation of an anthropomimetic robot arm featuring 11 muscles, a revolute elbow joint and a spherical shoulder joint. We show trajectory tracking based on a low-level muscle and a high-level joint control scheme, taking into account the coupling between the joints due to inertial reactions and bi-articular muscles.

Branch three-leg five-DOF (degree of freedom) parallel mechanism containing double-compound drive

Abstract: The invention discloses a branch three-leg five-DOF (degree of freedom) parallel mechanism containing a double-compound drive. The branch three-leg five-DOF parallel mechanism comprises an engine base, a movable platform and a single-drive branched chain for connecting the engine base and the movable platform and two compound drive branched chains with the same structure, both ends of each of three branched chains are symmetrically distributed in a regular triangle shape, wherein the single-drive branched chain is composed of two universal pairs and a drive translation pair to form a UPU-type series structure branched chain. Each compound drive branched chain is composed of two revolute pairs, a drive translation pair and a spherical hinge to form an RRPS-type compound drive series structure branched chain, and axial lines of two revolute pairs are vertical to each other to form a universal pair, wherein one revolute pair is connected with the engine base and coaxially connected with a drive motor, and the spherical hinge is connected with the movable platform. The branch three-leg five-DOF parallel mechanism is strong in bearing capacity, good in stability, large in working space, high in flexibility, simple in structure, less in movable branched chain, hard to interference, free from automatic jogging, high in precision, close to a frame in drive and easy to control.

Task space control of mobile manipulators

Abstract: This study offers the solution of the end-effector trajectory tracking problem subject to state constraints, suitably transformed into control-dependent ones, for mobile manipulators. Based on the Lyapunov stability theory, a class of controllers fulfilling the above constraints and generating the mobile manipulator trajectory with (instantaneous) minimal energy, is proposed. The problem of manipulability enforcement is solved here based on an exterior penalty function approach which results in continuous mobile manipulator controls even near boundaries of state constraints. The numerical simulation results carried out for a mobile manipulator consisting of a non-holonomic unicycle and a holonomic manipulator of two revolute kinematic pairs, operating in a two-dimensional task space, illustrate the performance of the proposed controllers.

Closed-form inverse kinematics of 6R milling robot with singularity avoidance

Abstract: For a 6R milling robot, it is necessary to convert the postprocessing cutter locations (CL) into the robot’s revolute joint variables. This paper introduces an algorithm for calculating the forward and inverse kinematics of a 6R robot according to the CL data generated by conventional CAD/CAM systems. A redundant mechanism is analyzed to avoid the singular configurations and joint limits. The Denavit–Hartenberg (D–H) convention is referred to for developing the forward kinematics, and a closed-form solution of the inverse kinematics is presented by means of kinematic decoupling. A fundamental approach with modifying factor for avoiding singularity are developed with regard to three-axis and five-axis CL data. A gap bridging strategy is applied to reduce the jerk motion caused by tool retraction and cut paths connection. Finally, the result is conducted to simulation and machining test to verify the algorithms.

Inverse kinematics by numerical and analytical cyclic coordinate descent

Abstract: Cyclic coordinate descent (CCD) inverse kinematics methods are traditionally derived only for manipulators with revolute and prismatic joints. We propose a new numerical CCD method for any differentiable type of joint and demonstrate its use for serial-chain manipulators with coupled joints. At the same time more general and simpler to derive, the method performs as well in experiments as the existing analytical CCD methods and is more robust with respect to parameter settings. Moreover, the numerical method can be applied to a wider range of cost functions.

A Microcontroller Based Four Fingered Robotic Hand

Abstract: In this paper we deal with the design and development of a Four Fingered Robotic Hand (FFRH) using 8-bit microcontroller, sensors and wireless feedback. The design of the system is based on a simple, flexible and minimal control strategy. The robot system has 14 independent commands for all the four fingers open and close, wrist up and down, base clockwise and counter clockwise, Pick and Place and Home position to move the fingers. Implementation of pick and place operation of the object using these commands are discussed. The mechanical hardware design of the Robotic hand based on connected double revolute joint mechanisms is briefed. The tendoning system of the double revolute joint mechanism and wireless feedback network provide the hand with the ability to confirm to object topology and therefore providing the advantage of using a simple control algorithm. Finally, the results of the experimental work for pick and place application are enumerated.

Nonstructural geometric discontinuities in finite element/multibody system analysis

Abstract: Existing multibody system (MBS) algorithms treat articulated system components that are not rigidly connected as separate bodies connected by joints that are governed by nonlinear algebraic equations. As a consequence, these MBS algorithms lead to a highly nonlinear system of coupled differential and algebraic equations. Existing finite element (FE) algorithms, on the other hand, do not lead to a constant mesh inertia matrix in the case of arbitrarily large relative rigid body rotations. In this paper, new FE/MBS meshes that employ linear connectivity conditions and allow for arbitrarily large rigid body displacements between the finite elements are introduced. The large displacement FE absolute nodal coordinate formulation (ANCF) is used to obtain linear element connectivity conditions in the case of large relative rotations between the finite elements of a mesh. It is shown in this paper that a linear formulation of pin (revolute) joints that allow for finite relative rotations between two elements connected by the joint can be systematically obtained using ANCF finite elements. The algebraic joint constraint equations, which can be introduced at a preprocessing stage to efficiently eliminate redundant position coordinates, allow for deformation modes at the pin joint definition point, and therefore, this new joint formulation can be considered as a generalization of the pin joint formulation used in rigid MBS analysis. The new pin joint deformation modes that are the result of C0 continuity conditions, allow for the calculations of the pin joint strains which can be discontinuous as the result of the finite relative rotation between the elements. This type of discontinuity is referred to in this paper as nonstructural discontinuity in order to distinguish it from the case of structural discontinuity in which the elements are rigidly connected. Because ANCF finite elements lead to a constant mass matrix, an identity generalized mass matrix can be obtained for the FE mesh despite the fact that the finite elements of the mesh are not rigidly connected. The relationship between the nonrational ANCF finite elements and the B-spline representation is used to shed light on the potential of using ANCF as the basis for the integration of computer aided design and analysis (I-CAD-A). When cubic interpolation is used in the FE/ANCF representation, C0 continuity is equivalent to a knot multiplicity of three when computational geometry methods such as B-splines are used. C2 ANCF models which ensure the continuity of the curvature and correspond to B-spline knot multiplicity of one can also be obtained. Nonetheless, B-spline and NURBS representations cannot be used to effectively model T-junctions that can be systematically modeled using ANCF finite elements which employ gradient coordinates that can be conveniently used to define element orientations in the reference configuration. Numerical results are presented in order to demonstrate the use of the new formulation in developing new chain models.

Curved surface contact patches with quantified uncertainty

Abstract: We introduce a set of 10 bounded curved-surface patch types suitable for modeling local contact regions both in the environment and on a robot. We present minimal geometric parameterizations using the exponential map for spatial pose both in the usual 6DoF case and also for patches with revolute symmetry that have only 5DoF. We then give an algorithm to fit any patch type to point samples of a surface, with quantified uncertainty both in the input points (including nonuniform variance, common in data from range sensors) and in the output patch. Finally, we outline how such patches can be composed into a spatial patch map of the available contact surfaces both on and around a robot.

Physics-based modeling of an anthropomimetic robot

Abstract: The control of tendon-driven robots using techniques from traditional robotics remains a very challenging task that has been so far only successfully achieved for small-scale setups comprising exclusively revolute joints [1, 2]. Hence, we propose a fundamentally different approach. Instead of deriving an analytical robot model using either the Newton-Euler or Lagrangian formulation we suggest to employ physics-based simulation engines to simulate the peculiar dynamics of this emerging class of robots and to use the simulated robot model as an internal model for robot control [3]. In this paper, we present the reverse-engineered derivation of a detailed physics-based model of an anthropomimetic robot implemented on CALIPER [4], a simulation framework developed within the EU-funded project ECCEROBOT [5]. The model comprises an accurate model of the skeleton derived from laser scan data, as well as of artificial ligaments and muscles. The individual sub-models are validated separately against measurements and the successful integration of all sub-models is demonstrated by executing a limb movement which requires the parallel control of multiple muscles.

Dynamic Modeling and Simulation of Robot Manipulators: The Newton-Euler Formulation

Abstract: Dynamic modeling means deriving equations that explicitly describes the relationship between force and motion in a system. To be able to control a robot manipulator as required by its operation, it is important to consider the dynamic model in design of the control algorithm and simulation of motion. In general there are two approaches available; the Euler-Lagrange formulation and the Newton-Euler formulation. This thesis explains briefly the differences of the formulations, and then research the Newton-Euler method in detail. A complete derivation of the method is derived, and an automated framework for applying the method on any serial manipulator with revolute joints is presented. By using the framework, the Newton-Euler formulation is applied on a modern industrial manipulator with six degrees of freedom. The dynamic parameters of the system are estimated, and the validity of the resulting dynamic model is verified by several simulations in open and closed loop. The simulations show that the system is unstable in open loop, and that it achieves global asymptotic stability in closed loop with gravity compensation, by including PD controllers with independent joint control. The latter is a confirmation of a mathematical proof based on a Lyapunov stability analysis, which is presented as well. Equivalent simulations of the dynamic model of the same manipulator derived by the standard Euler-Lagrange formulation show that the efficiency of recursive procedures is way higher that treating the manipulator as a whole. A suggestion for future work is performing thorough dynamic parameter identification. An improved model can ultimately be implemented in the controller of the manipulator, and optimized for a specific job task.

Modelling and analysis of a three-revolute parallel micro-positioning mechanism:

Abstract: This article presents the modelling and analysis methodologies of a three-degree-of-freedom (DOF) flexure-based mechanism. The mechanical design and working principle of a three revolute parallel mechanism is briefly provided. The kinematics of the proposed mechanism is established by simplifying flexure hinges into the revolute joints. The relationship of velocity between the Cartesian space and joint space is established. For small displacements of piezoelectric actuators, this velocity mapping can be simplified as the displacement relationship for the flexure-based mechanism. Two simplified methodologies, linearizing triangular functions and constant Jacobian, are utilized to conduct computational analysis for the flexure-based mechanism. The reachable workspace and theoretical resolution are also investigated. A novel empirical displacement mapping model is proposed based on finite-element analysis. Experiments are carried out to verify the established models of the three-DOF flexure-based mechanism. The maximum reachable workspace can reach up to approximately±68 and±76 µm in x and y directions, and the translational and rotational resolutions of the flexure-based mechanism are approximately 3 nm and 0.4 µrad, respectively.

Consistent bond graph modelling of planar multibody systems

Abstract: Modelling of mechanisms is not a trivial task because the goal is not only to obtain consistent kinematics but also to get proper dynamic loads. Therefore, a modular modelling approach is preferred for large and complex mechanisms. This paper discusses modular bond graph modelling of planar mechanical systems composed of rigid bodies, which are constrained together through a set of joints. Bond graph models of revolute joints with clearance and/or flexibility and mass distribution in prismatic or slider joints are de- veloped. Bond graph models obtained from hierarchical composition of subsystem models are then used to calculate the dynamic loads. Two separate mechanisms are considered as illustrative examples and their bond graph models are validated through numerical simulations.

Gantry type five axes numerical control machine tool

Abstract: The invention discloses a gantry type five axes numerical control machine tool, belonging to the machining field of a numerical control mechanism. The technical scheme is as follows: the traditional vertical rod is replaced by an X-direction guide way, so that support force to a beam is great, and the beam can be ensured to be stably move along the X-direction guide way; an automatic bidirectional revolute joint which is fixedly connected with a Z axes servo drive assembly can drive an electrical main shaft to rotate around a horizontal A axes and along the C axes of an electrical main shaft;and the Z axes servo drive assembly also can move along the beam to realize the move of a Y axes. Therefore, under the condition that a work table prevents from rotating and moving, namely, under thecondition that the work table is static relative to the ground, the numerical control machine tool skillfully realizes the five axes numerical control machining, conquers the defect of large floor space caused by the move and the rotation of the work table, and can realize the numerical control machining of a large component with high precision.