Showing papers on "Revolute joint published in 2004"

Dynamic Analysis for Planar Multibody Mechanical Systems with Lubricated Joints

Abstract: The dynamic analysis of planar multibody systems with revolute clearance joints, including dry contact and lubrication effects is presented here. The clearances are always present in the kinematic joints. They are known to be the sources for impact forces, which ultimately result in wear and tear of the joints. A joint with clearance is included in the multibody system much like a revolute joint. If there is no lubricant in the joint, impacts occur in the system and the corresponding impulsive forces are transmitted throughout the multibody system. These impacts and the eventual continuous contact are described here by a force model that accounts for the geometric and material characteristics of the journal and bearing. In most of the machines and mechanisms, the joints are designed to operate with some lubricant fluid. The high pressures generated in the lubricant fluid act to keep the journal and the bearing surfaces apart. Moreover, the lubricant provides protection against wear and tear. The equations governing the dynamical behavior of the general mechanical systems incorporate the impact force due to the joint clearance without lubricant, as well as the hydrodynamic forces owing to the lubrication effect. A continuous contact model provides the intra-joint impact forces. The friction effects due to the contact in the joints are also represented. In addition, a general methodology for modeling lubricated revolute joints in multibody mechanical systems is also presented. Results for a slider-crank mechanism with a revolute clearance joint between the connecting rod and the slider are presented and used to discuss the assumptions and procedures adopted.

Parallel kinematics mechanism with a concentric spherical joint

Abstract: A parallel kinematics mechanism (100) is provided for uses such as robotics or machining The mechanism has various limbs (A1, A2, A3, A4, A5) designed as elbow-linkages, at least some of which are actuatable, for moving an end component (40) with multiple workspace-to-footprint ratio and a closed-form solution for the forward kinematics The mechanism comprises a joint assembly (J1, J2) having a plurality of revolute joints for connecting to at least three limbs (5, 15) In various embodiments of the invention, the end component (40) has three, four, five and six degrees of freedom

Type Synthesis of Three-Degree-of-Freedom Spherical Parallel Manipulators

Abstract: A spherical parallel manipulator (also called an orientational parallel manipulator or rotational parallel manipulator) refers to a threedegreeof-freedom (3-DoF) parallel manipulator in which the moving platform undergoes a 3-DoF spherical motion or rotates about a fixed point. In this paper, we propose a new method for the type synthesis of non-overconstrained (isostatic) spherical parallel manipulators. In a non-overconstrained three-legged spherical parallel manipulator, each leg is composed of five revolute, prismatic and/or helical joints. Using the proposed approach, non-overconstrained three-legged spherical parallel manipulators can be obtained by the combination of a 3-RRR overconstrained spherical parallel manipulator and three four-bar Delassus linkages with at least one revolute joint. In a 3-RRR spherical parallel manipulator, each leg is composed of three revolute joints whose axes pass through the center of spherical motion. A four-bar Delassus linkage is a single-DoF four-bar linkage compo...

Adaptive regulation of amplitude limited robot manipulators with uncertain kinematics and dynamics

Abstract: Common assumptions in most of the previous robot controllers are that the robot kinematics and manipulator Jacobian are perfectly known and that the robot actuators are able to generate the necessary level of torque inputs. In this paper, an amplitude-limited torque input controller is developed for revolute robot manipulators with uncertainty in the kinematic and dynamic models. The adaptive controller yields semi-global asymptotic regulation of the task-space set-point error. The advantages of the proposed controller include the ability to actively compensate for unknown parametric effects in the dynamic and kinematic model and the ability to ensure that actuator constraints are not breached by calculating the maximum required torque a priori.

The Synthesis of Three-Degree-of-Freedom Planar Parallel Mechanisms with Revolute Joints (3-ṞRR) for an Optimal Singularity-Free Workspace

Abstract: In this paper, a method is presented for the synthesis of 3- R RR planar parallel mechanisms. The method uses a genetic algorithm while considering three different design criteria: the optimization of the mechanism workspace to approach a prescribed workspace, the maximization of the mechanism's dexterity, and the avoidance of singularities inside the mechanism workspace. It is shown that, for a given mechanism, some working modes do not have any corresponding singularity curves located inside the mechanism workspace. Furthermore, a case is presented where, for a given orientation range of the mechanism's end-effector, there are no parallel singularities located inside the workspace. Finally, two methods are described and compared to deal with the nonuniform units of the mechanism's Jacobian matrix during the dexterity computation. © 2004 Wiley Periodicals, Inc.

Kinematic design of a six-DOF parallel-kinematics Machine with decoupled-motion architecture

Abstract: The design of a new six-degree-of-freedom (6-DOF) parallel-kinematics machine (PKM) has been proposed. Different from the conventional Stewart-Gough platform which has six extensible legs, the new PKM employs three identical RPRS legs to support the moving platform. Since all joint axes, excluding the three spherical joints at the leg ends, are parallel to each other and perpendicular to the base plane, this 6-DOF PKM presents a promising platform structure with decoupled-motion architecture (DMA) such that translation in a horizontal plane and rotation about a vertical axis are driven by the three active revolute joints, while translation in the vertical direction and rotation about horizontal axes are driven by the three active prismatic joints. As a result, this 6-DOF 3RPRS PKM with DMA has simple kinematics, large cylindrical reachable workspace, and high stiffness in the vertical direction. These features make it appropriate for light machining and heavy parts assembly tasks. Because of the DMA, a projection technique is employed for its kinematics analysis. By projecting the manipulator onto horizontal directions and vertical planes, the kinematics issues such as the displacement, singularity, and workspace analysis are significantly simplified.

Method and apparatus for providing an interface mechanism for a computer simulation

Abstract: A mechanical interface for providing high bandwidth and low noise mechanical input and output for computer systems. A gimbal mechanism includes multiple members that are pivotably coupled to each other to provide two revolute degrees of freedom to a user manipulatable about a pivot point located remotely from the members at about an intersection of the axes of rotation of the members. A linear axis member, coupled to the user object, is coupled to at least one of the members, extends through the remote pivot point and is movable in the two rotary degrees of freedom and a third linear degree of freedom. Transducers associated with the provided degrees of freedom include sensors and actuators and provide an electromechanical interface between the object and a computer. Capstan band drive mechanisms transmit forces between the transducers and the object and include a capstan and flat bands, where the flat bands transmit motion and force between the capstan and interface members. Applications include simulations of medical procedures, e.g. epidural anesthesia, where the user object is a needle or other medical instrument, or other types of simulations or games.

Optimum synthesis of planar parallel manipulators based on kinematic isotropy and force balancing

Abstract: This paper deals with an optimum synthesis of planar parallel manipulators using two constrained optimisation procedures based on the minimization of: (i) the overall deviation of the condition number of manipulator Jacobian matrix from the ideal/isotropic condition number, and (ii) bearing forces throughout the manipulator workspace for force balancing. A revolute jointed planar parallel manipulator is used as an example to demonstrate the methodology. The parameters describing the manipulator geometry are obtained from the first optimisation procedure, and subsequently, the mass distribution parameters of the manipulator are determined from the second optimisation procedure based on force balancing. Optimisation results indicate that the proposed optimisation approach is systematic, versatile and easy to implement for the optimum synthesis of the parallel manipulator and other kinematic chains. This work contributes to previously published work from the point of view of being a systematic approach to the optimum synthesis of parallel manipulators, which is currently lacking in the literature.

Type Synthesis of 3-DOF PPR Parallel Manipulators Based on Screw Theory and the Concept of Virtual Chain

Abstract: PPR-PMs (parallel manipulators) are the parallel counterparts of the 3-DOF PPR serial robots, which are composed of two P (prismatic) joints and one R (revolute) joint. For a PPR-PM, the moving platform can rotate arbitrarily about an axis undergoing a planar translation. This paper deals with the type synthesis of 3-DOF PPR-PMs. At first, virtual chains are introduced to represent the motion patterns of 3-DOF motions and relevant results from screw theory are recalled. A method is then proposed for the type synthesis of 3-DOF PPR-PMs. Using the proposed approach, the type synthesis of 3-DOF PPR-PMs is performed in three steps, namely, the type synthesis of legs for PPR-PKCs (parallel kinematic chains), the type synthesis of PPR-PKCs, and the selection of actuated joints of PPR-PMs. The three steps are dealt with in detail consequently. The characteristics of the proposed approach is that the type synthesis of legs for PPR-PKCs is reduced to the type synthesis of 3-DOF overconstrained single-loop kinematic chains and thus easy to perform. In addition to all the 3-DOF PPR-PKCs and 3-DOF PPR-PMs proposed in the literature, a number of new 3-DOF PPR-PKCs and 3-DOF PPR-PMs are identified. It is also found that there are no PPR-PMs with identical types of legs.Copyright © 2004 by ASME

Fully-Isotropic T3R1-Type Parallel Manipulators

Abstract: The paper presents a special family of fully-isotropic parallel manipulators with four degrees of mobility. The moving platform of T3R1-type parallel manipulators has three orthogonal translations and one rotation. Only revolute and prismatic joints are used to achieve the four motions that are controlled independently by four actuators situated on the fixed base. It is shown that a one-to-one correspondence exists between the actuated joint space and the operational space of the moving platform. The Jacobian matrix of fully-isotropic T3R1-type parallel manipulators presented in this paper is the identity 4×4 matrix throughout their workspace. A method is proposed for structural synthesis based on the theory of linear transformations. The special family of fully-isotropic T3R1-type parallel manipulators includes 196 solutions. As far as we are aware this paper presents for the first time fully-isotropic parallel manipulators with four degrees of mobility.

Modelling lubricated revolute joints in multibody mechanical systems

Abstract: This work deals with the modelling of lubricated revolute joints in multibody mechanical systems. In most machines and mechanisms, the joints are designed to operate with some lubricant fluid. The high press- ures generated in the lubricant fluid act to keep the journal and the bearing apart. Moreover, the thin film formed by lubricant reduces friction and wear, provides load capacity and adds damping to dissipate undesirable mech- anical vibrations. In the dynamic analysis of journal-bearings, the hydrodynamic forces, which include both squeeze and wedge effects, produced by the lubricant fluid oppose the journal motion. These forces are obtained by integrating the pressure distribution evaluated with the aid of Reynolds' equation written for the dynamic regime. The hydrodynamic forces are nonlinear functions of journal centre position and velocity relative to the bearing centre. In a simple way, the hydrodynamic forces built up by the lubricant fluid are evaluated from the state of variable of the system and included into the equations of motion of the mechanical system. Results for an elementary slider-crank mechanism, in which a lubricated revolute joint connects the connecting rod and slider, are used to discuss the assumptions and procedures adopted.

Tactile efficiency of insect antennae with two hinge joints

Abstract: Antennae are the main organs of the arthropod tactile sense. In contrast to other senses that are capable of retrieving spatial information, e.g. vision, spatial sampling of tactile information requires active movement of the sense organ. For a quantitative analysis of basic principles of active tactile sensing, we use a generic model of arbitrary antennae with two hinge joints (revolute joints). This kind of antenna is typical for Orthoptera and Phasmatodea, i.e. insect orders that contain model species for the study of antennal movements, including cricket, locust and stick insect. First, we analyse the significance of morphological properties on workspace and sampling acuity. It is shown how joint axis orientation determines areas out of reach while affecting acuity in the areas within reach. Second, we assume a parametric set of movement strategies, based on empirical data on the stick insect Carausius morosus, and investigate the role of each strategy parameter on tactile sampling performance. A stochastic environment is used to measure sampling density, and a viscous friction model is assumed to introduce energy consumption and, thus, a measure of tactile efficiency. Up to a saturation level, sampling density is proportional to the range or frequency of joint angle modulation. The effect of phase shift is strong if joint angle modulation frequencies are equal, but diminishes for other frequency ratios. Speed of forward progression influences the optimal choice of movement strategy. Finally, for an analysis of environmental effects on tactile performance, we show how efficiency depends on predominant edge direction. For example, with slanted and non-orthogonal joint axis orientations, as present in the stick insect, the optimal sampling strategy is less sensitive to a change from horizontal to vertical edge predominance than with orthogonal and non-slanted joint axes, as present in a cricket.

Application of Workspace Generation Techniques to Determine the Unconstrained Motion of Parallel Manipulators

Abstract: Due to clearances in their passive joints, parallel manipulators always exhibit some unconstrained motion at the end effector. The amount of unconstrained motion depends on the pose of the manipulator and can increase significantly at or near singular configurations. This paper shows precisely how much unconstrained end effector motion exists at the end effector for a large class of parallel manipulators, namely those with passive revolute and/or spherical joints, if all the joint clearances are known. This includes the planar 3RRR, and, in approximation the Gough-Stewart and the Hexa manipulators. For the analysis, the passive joints are assumed to be revolute or spherical because these are the simplest cases. However the general framework also applies to other joint types, although leading to more complex calculations. For most manipulators, determining the amount of end effector motion can be transformed to a workspace generation problem. Therefore, general workspace generation techniques can be utilized.

Kinematics of the translational 3-URC mechanism

Abstract: The use of less than six degrees of freedom (dof) mechanisms instead of six-dof ones is always recommended when the application makes it possible, since their architectures and control are simpler to manufacture and implement respectively. Three-dof mechanisms constitute an important subset of less-than-six-dof mechanisms, since either translational or spherical motion can be obtained through three-dof spatial mechanisms and many industrial applications require the only translational or spherical motion. This paper presents a new translational parallel mechanism (TPM), named translational 3-URC. The new mechanism belongs to the parallel architectures with 3-URC topology, which contain another architecture that is a spherical parallel wrist. The proposed TPM is not overconstrained and has three equal legs whose kinematic pairs are three revolute pairs and one passive cylindrical pair per leg. Its actuated pairs are three revolute pair located on the frame. The position and velocity analyses of the translational 3-URC will be addressed and solved. Its singularity conditions will be written in explicit form and geometrically interpreted.

Closed-loop tape springs as fully compliant mechanisms - preliminary investigations

Abstract: The paper introduces tape springs as elements of fully compliant mechanisms. The localized folds of tape springs serve as compact revolute joints, with a very small radius and large range of motion, and the unfolded straight segments serve as links. By exploiting a tape spring’s ability to function as both links and joints, we present a new method of realizing fully compliant mechanisms with further simplification in their construction. Tape springs, typically found in carpenter tape rules, are thin-walled strips having constant thickness, zero longitudinal curvature, and a constant transverse curvature. The paper presents a closed-loop tape spring mechanism. By representing its folds as idealized revolute joints and its variable length links as sliding joints connecting rigid links, we present a modified Gruebler’s equation to determine its kinematic and idle degrees of freedom. To realize practical utility of tape spring mechanisms, we propose a simple actuation scheme incorporating shape memory alloy (SMA) wire actuators and successfully demonstrate its performance with a proof-of-concept prototype. The paper also presents potential applications for actuated tape spring mechanisms including a large displacement translational mechanism, planar positioning mechanisms, bi-stable, multi-stable, and variable stiffness mechanisms.Copyright © 2004 by ASME

Graphical Methods to Locate the Secondary Instant Centers of Single-Degree-of-Freedom Indeterminate Linkages

Abstract: This paper presents graphical techniques to locate the unknown instantaneous centers of zero velocity of planar, single-degree-of-freedom, linkages with kinematic indeterminacy. The approach is to convert a single-degree-of-freedom indeterminate linkage into a two-degree-of-freedom linkage. Two methods are presented to perform this conversion. The first method is to remove a binary link and the second method is to replace a single link with a pair of links connected by a revolute joint. First, the paper shows that a secondary instantaneous center of a two-degree-of-freedom linkage must lie on a unique straight line. Then this property is used to locate a secondary instant center of the single-degree-of-freedom linkage at the intersection of two lines. The two lines are obtained from a purely graphical procedure. The graphical techniques presented in this paper are illustrated by three examples of single-degree-of-freedom linkages with kinematic indeterminacy. The examples are a ten-bar linkage with only revolute joints, the single flier eight-bar linkage, and a ten-bar linkage with revolute and prismatic joints.Copyright © 2004 by ASME

Geometric Design of 3R Robot Manipulators for Reaching Four End-Effector Spatial Poses

Abstract: In this paper, the four-precision-point geometric design problem of serial-link robot manipulators with three revolute joints is solved using a polynomial continuation method. At each precision point, the end-effector spatial locations are defined. The dimensions of the geometric parameters of the 3R manipulator are computed so that the manipulator’s end-effector will be able to reach these four pre-specified locations. Denavit and Hartenberg parameters and 4 × 4 homogeneous matrices are used to formulate the problem and obtain the design equations. Three of the design parameters are set as free choices and their values are selected arbitrarily. Two different cases for selecting the free choices are considered and their design equations are solved using polynomial homotopy continuation. In both cases for free choice selection, 36 distinct manipulators are found, the end-effectors of which can reach the four specified spatial positions and orientations.

A Parallel 5 DOF Positioner for Semi-Spherical Workspaces

Abstract: In this paper, a new five-degree-of-freedom parallel manipulator is described and modeled. This structure has been specially designed for medical applications that require in the same time mobility, compactness and accuracy around a functional point. The purpose of this robotic device is to help practitioners to perform accurate needle insertions while preserving them from harmful intra-operative X-ray imaging devices. The system is built from revolute joints, among which only five joints are actuated to convey the required five degrees of freedom to its moving platform. A numerical simulation of the workspace and a physical prototype are presented.Copyright © 2004 by ASME

A new configuration of a six degrees-of-freedom parallel robot for MEMS fabrication

Abstract: This paper deals with the difficulties that arise in the realization of micro-mechanisms by MEMS fabrication technique e.g.: fabrication of joints and actuators, joints clearance, lifting the structure from the 2D silicon wafer plane. It then introduces a new structure of a six degrees-of-freedom parallel robot that is suitable for MEMS fabrication. The robot consists of linear actuators located at the base and only revolute joints, both of which are easier to manufacture in MEMS technology. The hybrid kinematic structure contains three single loop sub-mechanisms connected in parallel to the moving platform, and the solution of its inverse kinematics which yields 4,096 solutions is presented.

Parallel Robots with Adaptronic Components

Abstract: Performance in high-speed mechanisms can be increased by means of a lightweight design. But, quite often, the resulting structures have the drawback of being susceptible to vibrations. This can be overcome by applying a smart-structures technology. In this work, an application to parallel mechanisms is presented, in which undesired vibrations are reduced by integrated piezoceramic (PZT) actuators and sensors, which are driven by a proper control system. As a basis for the development of suitable control laws, a proper simulation approach is to be used which is capable to model the mechanism's dynamic behavior correctly, taking into account large motions. The multibody approach fulfills these requisites. The paper deals with the development of a fast C++-coded S-function in MATLAB/ SIMULINK for a five revolute joint mechanism chosen as a test platform. This routine incorporates a multibody model with changing states. The flexibility of the bodies is taken into account in a modal form. The corresponding parameters are read from data files which can be generated by suitable preprocessors of proprietary multibody software packages like SIMPACK. The created model is compared with an equivalent SIMPACK-model and an interpolation-based control strategy is discussed.

Singularity robust inverse dynamics of planar 2-RPR parallel manipulators:

Abstract: In planar parallel robots, limitations occur in the functional workspace because of interference of the legs with each other and because of drive singularities where the actuators lose control of the moving platform and the actuator forces grow without bounds. A 2-RPR (revolute, prismatic, revolute joints) planar parallel manipulator with two legs that minimizes the interference of the mechanical components is considered. Avoidance of the drive singularities is in general not desirable since it reduces the functional workspace. An inverse dynamics algorithm with singularity robustness is formulated allowing full utilization of the workspace. It is shown that if the trajectory is planned to satisfy certain conditions related to the consistency of the dynamic equations, the manipulator can pass through the drive singularities while the actuator forces remain stable. Furthermore, for finding the actuator forces in the vicinity of the singular positions a full rank modification of the dynamic equation...

Modeling and simulation of planar flexible link manipulators with rigid tip connections to revolute joints

Abstract: This paper presents the basis of a mathematical model for simulation of planar flexible-link manipulators, taking into consideration the effect of higher stiffness zones at the link tips. The proposed formulation is a variation of the finite segment multi-body dynamics approach. The formulation employs a consistent mass matrix in order to provide better approximation than the traditional lumped masses often encountered in the finite segment approach. The formulation is implemented into a computational code and tested through three examples; cantilever beam, rotating beam and three-link manipulator. In these examples, the length of the rigid tips at both sides of each link ranges from 0p to 6.25p of the whole link length. The zones of higher stiffness at the link tips are treated as short rigid zones. The effect of the rigid zones is averaged along with some portions of the flexible links, thereby allowing further simplification of the dynamic equations of motion. The simulation results demonstrate the effectiveness of the proposed modeling technique and show the importance of not ignoring the effect of the rigid tips.

Optimum grasp of planar and revolute objects with gripper geometry constraints

Abstract: This work presents a new methodology for synthesizing force-closure two-finger and three-finger grasps for planar and revolute parts. Most real world objects can be modeled using such parts. The grasp synthesis explicitly takes into account the gripper geometry constraints, but unlike previous related work, we optimize several grasp quality criteria simultaneously, rather than individually. The methodology also has two distinct features that makes it complete: corners are considered to ensure every existing grasp is found and an accessibility check is made around the part contour to avoid synthesizing impossible grasps. The algorithm is therefore practical while it ensures high quality grasps. Results are presented for grasp synthesis of several objects with SARAH, an under-actuated three-finger robotic hand.

Experimental investigation of clearance effects in a revolute joint

Abstract: This paper deals with the effects of clearances in revolute joint s. Experimental data is acquired from a testbed made of a four-bar mechanism of crank-rocker type, with motorized crank and clearance between rod and rocker. Since the revolute joint pair s can be changed, different values of clearance can be tested. Also the radius of the crank, the length of the truss and the angular speed of the crank can be changed, in order to investigate different settings. During test sessions, rocker and rod accelerations are acquired wit h accelerometers, and output graphs are compared to the numerical results coming from off-l ine multibody simulations. Surface wear on the axle and bushing of the revolute joint is measured either with a micrometer tool, either with a three-dimensional surface roughness tester. Wear does not affect the entire surface of the shaft, but mostly happens on spec ific spots, as predicted by our numerical model.