Showing papers on "Revolute joint published in 2008"

A neural-genetic (NN-GA) approach for optimising mechanisms having joints with clearance

Abstract: In this paper, a dimensional synthesis method for a four-bar (4R) path generator mechanism having revolute joints with clearance is presented. Joint clearances are considered as virtual massless links. The proposed method uses a neural network (NN) to define the characteristics of joints with clearance with respect to the position of the input link, and a genetic algorithm (GA) to implement the optimization of link parameters using an appropriate objective function based on path and transmission angle errors. Training and testing data sets for network weights are obtained from mechanism simulation, and Grashof’s rule is used during the optimization process as constraint. The results show that the proposed method is very efficient for the purpose of modeling the joint variables and also adjusting the link dimensions to optimize planar mechanisms with clearances.

Translational Joints With Clearance in Rigid Multibody Systems

Abstract: A computational methodology for dynamic description of rigid multibody systems with translational clearance joints is presented and discussed in this work. Over the past years, extensive work has been done to study the dynamic effect of the revolute joints with clearance in multibody systems, in contrast with the little work devoted to model translational joints with clearance. In a joint with translation clearance, there are many possible ways to set the physical configuration between the slider and guide, namely: (i) no contact between the two elements, (ii) one corner of the slider in contact with the guide surface, (iii) two adjacent slider corners in contact with the guide surface, and (iv) two opposite slider corners in contact with the guide surfaces. The proposed methodology takes into account these four different situations. The conditions for switching from one case to another depend on the system dynamics configuration. The existence of a clearance in a translational joint removes two kinematic constraints from a planar system and introduces two extra degrees of freedom in the system. Thus, a translational clearance joint does not constrain any degree of freedom of the mechanical system but it imposes some restrictions on the slider motion inside the guide limits. When the slider reaches the guide surfaces, an impact occurs and the dynamic response of the joint is modeled by contact-impact forces. These forces are evaluated here with continuous contact force law together with a dissipative friction force model. The contact-impact forces are introduced into the system's equations of motion as external generalized forces. The proposed methodology is applied to a planar multibody mechanical system with a translational clearance joint in order to demonstrate its features.

Experimental Validation of a model of an Uncontrolled Bicycle

Abstract: In this paper, an experimental validation of some modelling aspects of an uncontrolled bicycle is made. In computer models, many physical aspects of the real bicycle are considered negligible, such as the flexibility of the frame and wheels, play in the bearings, and precise tire characteristics. The admissibility of these assumptions can be checked by comparing experimental results with numerical simulation results. The numerical simulations are performed on a benchmarked bi- cycle model [1]. This model (Fig. 1) consists of four rigid bodies connected by revolute joints. The contact between the knife-edge wheels and the flat level surface is modelled by holonomic constraints in the normal direction and by non-holonomic constraints in the longitudinal and lateral direction. In the absence of a rider we assume no-hands operation. This system has three velocity degrees of freedom, the roll, the steer, and the forward speed. For the validation we consider the linearized equations of motion for small perturbations of the upright steady forward motion. Apart from flexibility and play, the greatest uncertainty to be verified in this model is the replacement of the tires by ideal rolling knife-edge wheels. Open image in new window Figure 1 Bicycle model.

A novel dynamic modelling approach for parallel mechanisms analysis

Abstract: A novel approach (recursive matrix method), which is used for kinematic and dynamic analysis of a 3-DOF parallel mechanism with revolute actuators, is established in this paper. The active links of the mechanism are actuated by three electric motors and have three independent motions. Knowing the evolution of movable platform, first we develop the positions, velocities and accelerations of all elements of the mechanism. An inverse dynamic problem is solved using the principle of virtual work. Finally, recursive relations and graphs for the torques of three actuators are determined. It showed the efficiency of the proposed method by the example.

Orientation Capability, Error Analysis, and Dimensional Optimization of Two Articulated Tool Heads With Parallel Kinematics

Abstract: Because of the increasing demand in industry for A/B-axis tool heads, particularly in thin wall machining applications for structural aluminium aerospace components, the three-degree-of-freedom articulated tool head with parallel kinematics has become very popular. This paper addresses the dimensional optimization of two types of tool head with 3-P V P H S and 3-P V RS parallel kinematics (P, R, and S standing for prismatic, revolute, and spherical joint, respectively; the subscripts V and H indicating that the direction of the P joint is vertical or horizontal, and the joint symbol with underline means the joint is active) by considering their orientation capability and positioning accuracy. We first investigate the tilt angle of the spherical joint, the orientation capability, and the error of one point from the mobile platform caused by input errors. Optimization of the 3-P V P H S tool head is easy. For the 3-P V RS tool head, a design space is developed to illustrate how the orientation capability and error index are related to the link lengths. An optimization process is accordingly presented. Using the optimization method introduced here, it is not difficult to find all the possible optimal solutions.

Global analysis of the double-gimbal mechanism

Abstract: The double-gimbal mechanism (DGM) is a multibody mechanical device composed of three rigid bodies, namely, a base, an inner gimbal, and an outer gimbal, interconnected by two revolute joints. A typical DGM, where the cylindrical base is connected to the outer gimbal by a revolute joint, and the inner gimbal, which is the disk-shaped payload, is connected to the outer gimbal by a revolute joint. The DGM is an integral component of an inertially stabilized platform, which provides motion to maintain line of sight between a target and a platform payload sensor. Modern, commercially available gimbals use two direct-drive or gear-driven motors on orthogonal axes to actuate the joints. Many of these mechanisms are constrained to a reduced operational region, while moresophisticated models use a slip ring to allow continuous rotation about an axis. Angle measurements for each axis are obtained from either a rotary encoder or a resolver. The DGM is a fundamental component of pointing and tracking applications that include missile guidance systems, ground-based telescopes, antenna assemblies, laser communication systems, and close-in weapon systems (CIWSs) such as the Phalanx 1B.

Stiffness Characteristics of Carton Folds for Packaging

Abstract: Recent studies for packaging using cartons have modeled carton folds as equivalent mechanisms by considering creases as revolute joints and panels as links. This raises the interest in the study of stiffness characteristics of creases, which have a variable stiffness in contrast to a constant stiffness of a revolute joint and subsequently that of a whole carton fold. This paper investigates the stiffness characteristics of creases and reveals for the first time the folding motion and moment diagram in carton manipulation. Three characteristic stages were provided to characterize the crease stiffness, which has a variable value during carton manipulation. The paper further investigates the integrated stiffness of a combination joint and develops the integrated stiffness of a complete carton fold. The study is then extended to the integrated stiffness of a type of carton folds.

Gravity Compensation, Static Balancing and Dynamic Balancing of Parallel Mechanisms

Abstract: The balancing of parallel mechanisms is addressed in this chapter. First, the notions of static balancing, gravity compensation and dynamic balancing are reviewed. A general mathematical formulation is then developed in order to provide the necessary design tools, and examples are given to illustrate the application of each of the concepts to the design of parallel mechanisms. Additionally, some limitations of the techniques currently used for the balancing of parallel mechanisms are pointed out.

A Family of Kinematically Redundant Planar Parallel Manipulators

Abstract: Parallel manipulators feature relatively high payload and accuracy capabilities compared to their serial counterparts. However, they suffer from small workspace and low maneuverability. Kinematic redundancy for parallel manipulators can improve both of these characteristics. This paper presents a family of new kinematically redundant planar parallel manipulators with six actuated-joint degrees of freedom based on a 3-PRRR architecture obtained by adding an active prismatic joint at the base of each limb of the 3-RRR manipulator. First, the inverse displacement of the manipulators is explained, then their reachable and dexterous workspaces are obtained. Comparing the proposed redundant manipulators to the original 3-RRR nonredundant manipulator, both reachable and dexterous workspaces are substantially larger. Next, the Jacobian matrices of the manipulators are derived, and different types of singularities are analyzed and demonstrated. It is shown that the vast majority of singularities can be avoided by using kinematic redundancy.

Differentially Flat Designs of Underactuated Open-Chain Planar Robots

Abstract: A fully actuated system can execute any joint trajectory. However, if the system is underactuated, not all joint trajectories are attainable. For such systems, it is difficult to characterize attainable joint trajectories analytically. Numerical methods are generally used to characterize these. This paper investigates the property of differential flatness for underactuated planar open-chain robots and studies dependence on inertia distribution within the system. It is shown that certain choices of inertia distributions make an underactuated open-chain planar robot with revolute joints feedback linearizable, i.e., also differentially flat. Once this property is established, trajectory between any two points in the state space can be planned, and a controller can be developed to correct for errors. To demonstrate the proposed methodology in hardware, experiments with an underactuated 3-DOF planar robot are also presented.

The relationship between joint strength and standing vertical jump performance.

Abstract: The effect of joint strengthening on standing vertical jump height is investigated by computer simulation. The human model consists of five rigid segments representing the feet, shanks, thighs, HT (head and trunk), and arms. Segments are connected by frictionless revolute joints and model movement is driven by joint torque actuators. Each joint torque is the product of maximum isometric torque and three variable functions of instantaneous joint angle, angular velocity, and activation level, respectively. Jumping movements starting from a balanced initial posture and ending at takeoff are simulated. A matching simulation reproducing the actual jumping movement is generated by optimizing joint activation level. Simulations with the goal of maximizing jump height are repeated for varying maximum isometric torque of one joint by up to +/-20% while keeping other joint strength values unchanged. Similar to previous studies, reoptimization of activation after joint strengthening is necessary for increasing jump height. The knee and ankle are the most effective joints in changing jump height (by as much as 2.4%, or 3 cm). For the same amount of percentage increase/decrease in strength, the shoulder is the least effective joint (which changes height by as much as 0.6%), but its influence should not be overlooked.

Kinematic Synthesis of Planar, Shape-Changing Rigid-Body Mechanisms

Abstract: This paper presents a kinematic procedure to synthesize planar mechanisms, composed of rigid links and revolute joints, capable of approximating a shape change defined by a set of curves. These "morphing curves", referred to as design profiles, differ from each other by a combination of rigid-body displacement and shape change. Design profiles are converted to piecewise linear curves, referred to as target profiles, that can be readily manipulated. In the segmentation phase, the geometry of rigid links that approximate the shapes of corresponding segments from each target profile is determined. In the mechanization phase, these rigid links are joined together at their end points with revolute joints to form a single chain. Dyads are then added to reduce the number of degrees of freedom (DOF's) to any desired value, typically 1. The approach can be applied to any number of design profiles that can be approximated with any number of rigid links, which can then be used to construct a mechanism with any number of DOF's. Naturally, greater difficulty is encountered for larger numbers of design profiles and/or links and for more dramatic changes in shape. The procedure is demonstrated with examples of single-DOF mechanisms approximating shape changes between two and three design profiles.

Kinematics analysis, design, and control of an Isoglide3 Parallel Robot (IG3PR)

Abstract: The paper presents a novel structure of the Isoglide3 parallel robot (IG3PR), as an effective robotic device with three degrees of freedom manipulation The IG3PR manipulator offers the characteristics, advantageous relative to the other parallel manipulators (light weight construction), while on the other hand alleviates some of the traditional weaknesses of parallel manipulators, (extensive use of spherical joints and coupling of the platform orientation and position) The presented IG3PR robot employs only revolute (rotary) and prismatic (sliding) joints to achieve the translational motion of the moving platform The pivotal advantages of the presented parallel manipulator are the following: all of the actuators can be attached directly to the base; closed-form solutions are available for the forward and inverse kinematics; and the moving platform maintains the same orientation throughout the entire workspace In addition to these comparative improvements, the paper presents an innovative user interface for high-level control of the Isoglide3 parallel robot The novel IG3PR was verified and tested, and results in MATLAB, Simulink, and SimMechanics were presented

HZD-based control of a five-link underactuated 3D bipedal robot

Abstract: This paper presents a within-stride feedback controller that achieves an exponentially stable, periodic, and fast walking gait for a 3D bipedal robot consisting of a torso, revolute knees, and passive (unactuated) point feet. The walking surface is assumed to be rigid and flat; the contact between the robot and the walking surface is assumed to inhibit yaw rotation. The studied robot has 8 DOF in the single support phase and 6 actuators. In addition to the reduced number of actuators, the interest of studying robots with point feet is that the feedback control solution must explicitly account for the robot?s natural dynamics in order to achieve balance while walking. We use an extension of the method of virtual constraints and hybrid zero dynamics (HZD), a very successful method for planar bipeds, in order to determine a periodic orbit and an autonomous feedback controller that realizes the orbit, for a 3D (spatial) bipedal walking robot. The effect of output selection on the zero dynamics is highlighted and a pertinent choice of outputs is proposed, leading to stabilization without the use of a supplemental event-based controller.

An Adaptive Regulator of Robotic Manipulators in the Task Space

Abstract: This note addresses the problem of position control of robotic manipulators both nonredundant and redundant in the task space. A computationally simple class of task space regulators consisting of a transpose adaptive Jacobian controller plus an adaptive term estimating generalized gravity forces is proposed. The Lyapunov stability theory is used to derive the control scheme. The conditions on controller gains ensuring asymptotic stability are obtained herein in a form of simple inequalities including some information extracted from both robot kinematic and dynamic equations. The performance of the proposed control strategy is illustrated through computer simulations for a direct-drive arm of a SCARA type redundant manipulator with the three revolute kinematic pairs operating in a two-dimensional task space.

Evolutionary design of modular robotic arms

Abstract: This paper proposes a method for task based design of modular serial robotic arms using evolutionary algorithms (EA). We introduce a 3D kinematics and a global optimization for both topology and configuration from task specifications. The search features revolute as well as prismatic joints and any number of DOF to build up a solution without using any design knowledge. A study of the evolution dynamics gives some keys to set evolution parameters that enable artificial evolution. An adapted algorithm dealing with the topology/configuration search tradeoff is proposed, descibed, and discussed. Illustrations of the algorithms results are given and conclusions are drawn from their analysis. Perspectives of this work are given, extending its reach to control and complex system design.

A modular robotic system for industrial applications

Abstract: Purpose – The aim of this paper is the development of a modular robotic system for generic industrial applications, including assembly.Design/methodology/approach – A library of robotic modules has been designed; they are divided into two categories: link modules, not actuated, and joint modules, actuated; the library is characterized by a relatively low number of elements, but allows the assembly of a wide variety of medium‐size serial robots.Findings – The prototypes of two joint modules (a revolute joint module and a wrist module) and of some link modules have been realized. The behaviour of several serial robots composed of the designed modules has been assessed by multibody simulation. The results confirm the goodness of the proposed approach.Research limitations/implications – The two prototype modules are under test in combination with simplified modules. The further steps of the research programme will be the completion of the prototype library, and an experimental campaign on different serial cha...

A Constrained Lagrange Formulation of Multilink Planar Flexible Manipulator

Abstract: In this article, the closed-form dynamic equations of planar flexible link manipulators (FLMs), with revolute joints and constant cross sections, are derived combining Lagrange’s equations and the assumed mode shape method. To overcome the lengthy and complicated derivative calculation of the Lagrangian function of a FLM, these computations are done only once for a single flexible link manipulator with a moving base (SFLMB). Employing the Lagrange multipliers and the dynamic equations of the SFLMB, the equations of motion of the FLM are derived in terms of the dependent generalized coordinates. To obtain the closed-form dynamic equations of the FLM in terms of the independent generalized coordinates, the natural orthogonal complement of the Jacobian constraint matrix, which is associated with the velocity constraints in the linear homogeneous form, is used. To verify the proposed closed-form dynamic model, the simulation results obtained from the model were compared with the results of the full nonlinear finite element analysis. These comparisons showed sound agreement. One of the main advantages of this approach is that the derived dynamic model can be used for the model based end-effector control and the vibration suppression of planar FLMs.

Analytical Solution of the Forward Position Analysis of Parallel Manipulators That Generate 3-RS Structures

Abstract: In this work the forward position analysis (FPA) of 3-RS structures (R, S, P and C = revolute, spherical, prismatic and cylindrical, respectively) is carried out applying recursively the Sylvester dialytic elimination method. The analytical solution provided in this contribution yields 16 possible poses of the moving platform given the limb lengths of the manipulator and it is applicable to a wide class of parallel manipulators, e.g., the 3-RP*S mechanism, 3-CP*S mechanism, 6–3 Gough–Stewart platforms and 3-RR*S mechanism. A case study is included which consists of solving the FPA of a 3–3 Gough–Stewart platform, also known as an octahedrical mechanism.

Stratified Deformation Space and Path Planning for a Planar Closed Chain with Revolute Joints

Abstract: Given a linkage belonging to any of several broad classes (both planar and spatial), we have defined parameters adapted to a stratification of its deformation space (the quotient space of its configuration space by the group of rigid motions) making that space “practically piecewise convex”. This leads to great simplifications in motion planning for the linkage, because in our new parameters the loop closure constraints are exactly, not approximately, a set of linear inequalities. We illustrate the general construction in the case of planar nR loops (closed chains with revolute joints), where the deformation space (link collisions allowed) has one connected component or two, stratified by copies of a single convex polyhedron via proper boundary identification. In essence, our approach makes path planning for a planar nR loop essentially no more difficult than for an open chain.

A Study of Joints Suitable for Lamina Emergent Mechanisms

Abstract: One way to save space and reduce cost in a competitive environment is to use ortho-planar compliant mechanisms which can be made from sheets of material, or lamina emergent mechanisms (LEMs) One major challenge associated with LEM design, however, is creating joints with the desired motion characteristics, especially where complex spatial mechanism topologies are required This paper presents some important considerations for designing joints for LEMs A technique commonly used in robotics, using serial chains of revolute and prismatic joints to approximate the motion of complex joints, is presented for use in lamina emergent mechanisms Important considerations such as linkage configuration and simple prototyping are also discussedCopyright © 2008 by ASME

A Load Independent Pseudo-Rigid-Body 3R Model for Determining Large Deflection of Beams in Compliant Mechanisms

Abstract: Modeling flexible beams that undergo large deflection is one of the key steps in analyzing and synthesizing compliant mechanisms. Geometric nonlinearities introduced by large deflections often complicate the analysis of mechanism systems comprising such members. Several pseudo-rigid-body (PRB) or multi segment models in the literature have been proposed to approximate the tip deflection and slope. However these models are either dependent on external loads or too complicated to analyze. They are neither appropriate for analyzing mechanisms in which loads change significantly as they move, nor for synthesizing mechanisms where a parametric model is preferred. In this paper, a load independent PRB 3R model which comprises of four rigid links joined by three revolute joints and three torsion springs is proposed. The traditional PRB 1R models are first studied for both small deflection beams and large deflection beams. These studies provide fundamental insights to the geometric nonlinearity of large deflection beams. Numerical integration is applied to compute tip deflections for various loads. A three-dimensional search routine has been developed to find the optimal set of characteristic radius factors for the proposed PRB 3R model. Detailed error analysis and comparison against the result by the numerical integration and the PRB 1R model are accomplished for different load modes. The benefits of the PRB 3R model include (a) high accuracy for large deflection beams, (b) load independence which is critical for applications where loads vary significantly and (c) explicit kinematic and static constraint equations derived from the model. To demonstrate the use of the PRB 3R model, a compliant 4-bar linkage is studied and verified by a numerical example. The result shows a maximum tip deflection error of 1.2% compared with the FEA model.© 2008 ASME