Showing papers on "Revolute joint published in 1999"

A Well-Behaved Revolute Flexure Joint for Compliant Mechanism Design

Abstract: This paper describes the design of a unique revolute flexure joint, called a split-tube flexure, that enables (lumped compliance) compliant mechanism design with a considerably larger range-of-motion than a conventional thin beam flexure, and additionally provides significantly better multi-axis revolute joint characteristics. Conventional flexure joints utilize bending as the primary mechanism of deformation. In contrast, the split-tube flexure joint incorporates torsion as the primary mode of deformation, and contrasts the torsional properties of a thin-walled open-section member with the bending properties of that member to obtain desirable joint behavior. The development of this joint enables the development of compliant mechanisms that are quite compliant along kinematic axes, extremely stiff along structural axes, and are capable of kinematically well-behaved large motions.

Folding cartons with fixtures: a motion planning approach

Abstract: Packaging products such as telephones and two-way radios after assembly is a common manufacturing task. Carton folding is a packaging operation typically performed by human operators or with fixed automation. We present a flexible method to fold cardboard cartons using fixtures; a carton blank is folded by moving it through a fixture with a robot. This method uses interchangeable fixtures to enable rapid changeovers between product models. We outline an approach to design a fixture given a carton and a folding sequence. We present an implemented motion planning algorithm that generates all folding sequences for a carton by modeling it kinematically as a many degree-of-freedom robot manipulator with revolute joints and branching links. Folding fixtures constrain the carton motion to paths consisting of line segments in its configuration space. We characterize the set of valid paths for these carton robots and generate them using the motion planner. To illustrate the method, we selected a folding sequence for an example carton, designed a fixture, and demonstrated folding of the carton from blanks with an industrial robot.

Kinematic Clearance Sensitivity Analysis of Spatial Structures With Revolute Joints (

Abstract: The paper presents a new method to assess the influence of joint clearances in spatial structures that are composed of links connected by revolute joints. The method allows assessment of the amount by which joint clearances affect the rigid-body position of a generic link of the structure when an external load is exerted on the link. Unlike other procedures, the proposed method relies on the clearance-free idealization of the structure under investigation. An example shows application of the proposed method to the analysis of the structure derived from a multi-loop manipulator by freezing its actuators.

Dynamic modeling and simulation of a flexible robotic manipulator

Abstract: This work focuses on the dynamic modeling of a flexible robotic manipulator with two flexible links and two revolute joints, which rotates in the horizontal plane. The dynamic equations are derived using the Newton-Euler formulation and the finite element method, based on elementary beam theory. Computer simulation results are presented to illustrate this study. The dynamic model becomes necessary for use in future design and control applications.

Position control of a compliant mechanism based micromanipulator

Abstract: This paper addresses the modeling and control of a compliant micromanipulator for use in such fields as microsurgery, telesurgery, and microassembly. The unique flexure-based manipulator utilizes revolute flexure joints in achieving well-behaved kinematic characteristics, without the backlash and stick-slip phenomena that would otherwise impede precision control. A mathematical model of the micromanipulator is formulated, and a controller for positioning of the manipulator is derived. The model and resulting controller are unlike typical manipulator models and controllers since this manipulator is actually a controlled large range-of-motion structure with nonlinear structural dynamics. Following the development of the controller, computer simulations of the proposed controller on the manipulator are used to verify the positioning performance.

Three revolute cobot using CVTs in parallel

Abstract: Cobots are capable of producing virtual surfaces of high quality, using mechanical transmission elements as their basic element in place of conventional motors. Most cobots built to date have used steerable wheels as their transmission elements. We describe how continuously variable transmissions (CVTs) can be used in this capacity for a cobot with revolute joints. The design of an “arm-like” cobot with a three-dimensional workspace is described. This cobot can implement virtual surfaces and other effects in a spherical workspace approximately 1.5 meters in diameter. Novel elements of this cobot include the use of a power wheel that couples three CVTs that are connected in parallel.

Nonlinear Dynamics and Chaotic Motions in Feedback-Controlled Two-and Three-Degree-of-Freedom Robots

Abstract: The dynamics of a feedback-controlled rigid robot is most commonly described by a set of nonlinear ordinary differential equations. In this paper we analyze these equations, representing the feedback-controlled motion of two- and three-degrees-of-freedom rigid robots with revolute (R) and prismatic (P) joints in the absence of compliance, friction, and potential energy, for the possibility of chaotic motions. We first study the unforced or inertial motions of the robots, and show that when the Gaussian or Riemannian curvature of the configuration space of a robot is negative, the robot equations can exhibit chaos. If the curvature is zero or positive, then the robot equations cannot exhibit chaos. We show that among the two-degrees-of-freedom robots, the PP and the PR robot have zero Gaussian curvature while the RP and RR robots have negative Gaussian curvatures. For the three-degrees-of-freedom robots, we analyze the two well-known RRP and RRR configurations of the Stanford arm and the PUMA manipulator respectively, and derive the conditions for negative curvature and possible chaotic motions. The criteria of negative curvature cannot be used for the forced or feedback-controlled motions. For the forced motion, we resort to the well-known numerical techniques and compute chaos maps, Poincare maps, and bifurcation diagrams. Numerical results are presented for the two-degrees-of-freedom RP and RR robots, and we show that these robot equations can exhibit chaos for low controller gains and for large underestimated models. From the bifurcation diagrams, the route to chaos appears to be through period doubling.

Design and analysis of a 3-DOF micromanipulator

Abstract: A unique design for a 3-DOF micromanipulator is presented. The new design contains only revolute joints, and it incorporates rotation of the upper platform of the mechanism, which effectively uses the length of the end-effector to increase workspace volume. The forward and inverse kinematics problems for the device are solved, and a method for calculating the Jacobian is presented. Finally, a prototype of the manipulator was fabricated and tested experimentally to compare with the theoretical results.

The planning of suboptimal collision-free robotic motions

Abstract: A method of planning sub-optimal collision-free motion for redundant manipulators is presented. It is based on using a penalty function approach and scaling the robot dynamic equation to satisfy actuator constraints. The proposed method allows real time computations. A computer example involving a planar redundant manipulator of three revolute kinematics pairs which operates in a work space with obstacles, is also presented.

Multibody Dynamics of Very Flexible Damped Systems

Abstract: An efficient multibody dynamics formulation is presented for simulating the forward dynamics of open and closed loop mechanical systems comprised of rigid and flexible bodies interconnected by revolute, prismatic, free, and fixed joints. Geometrically nonlinear deformation of flexible bodies is included and the formulation does not impose restrictions on the representation of material damping within flexible bodies.

Friction model of a revolute joint for a precision deployable spacecraft structure

Abstract: An analytical model is presented for predicting breakaway friction torque in a precision deployable spacecraft structure joint incorporating preloaded angular contact bearings. The model is based on the Todd/Johnson tribological friction model of friction within ball bearings (Todd, M. J., and Johnson, K. L., "A Model for Coulomb Torque Hysteresis in Ball Bearings," International Journal of Mechanical Science^ Vol. 29,1987, pp. 339-354) and includes the effects of Coulombic microslippage between the bearing components and material hysteretic damping. A new nondimensional parameter is developed to quantify the effects of bearing preload, geometry, and material properties. It is analytically shown that bearing friction can be minimized for a specific bearing contact angle considering both rolling and sliding friction components. Additionally, steady-state bearing friction is calculated to vary nonlinearly with assembly preload. Analytical prediction of bearing friction is correlated with measured data.

The kinematic design of a 3-dof hybrid manipulator

Abstract: This paper focuses on the kinematic properties of a new three-degree-of-freedom hybrid manipulator. This manipulator is obtained by adding in series to a five-bar planar mechanism (similar to the one studied by Bajpai and Roth [1]) a third revolute passing through the line of centers of the two actuated revolute joints of the above linkage (Figures 2 & 3). The resulting architecture is hybrid in that it has both serial and parallel links. Fully-parallel manipulators are known for the existence of particularly undesirable singularities (referred to as parallel singularities) where control is lost [4] and [6]. On the other hand, due to their cantilever type of kinematic arrangement, fully serial manipulators suffer from a lack of stiffness and from relatively large positioning errors. The hybrid manipulator studied is intrinsically stiffer and more accurate. Furthermore, since all actuators are located on the first axis, the inertial effects are considerably reduced. In addition, it is shown that the special kinematic structure of our manipulator has the potential of avoiding parallel singularities by a suitable choice of the « working mode », thus leading to larger workspaces. The influence of the different structural dimensions (e.g. the link lengths) on the kinematic and mechanical properties are analysed in view of the optimal design of such hybrid manipulators.

Optimal motions of redundant manipulators with state equality constraints

Abstract: An approach to the time optimal control of a kinematically redundant manipulator subject to state equality constraints is proposed. The solution is based on an approximation of the prior control set by means of a strictly convex set, with arbitrary accuracy in the Hausdorff sense. This approach produces continuous optimal controls which may be used to provide nominal inputs for online control. Furthermore, the corresponding optimal controls thus obtained retain (in a limit) a bang-bang form if the error of approximation approaches 0. A computer example involving a planar redundant manipulator of three revolute kinematic pairs whose the end-effector moves along a prescribed geometric path, is given.

Tracking control in the presence of nonlinear dynamic frictional effects: robot extension

Abstract: We extend the observer/control strategies previously published by Vedagarbha et al. (1997) to an n-link, serially connected, direct drive, rigid link, revolute robot operating in the presence of nonlinear friction effects modeled by the Lu-Gre model. In addition, we also present a new adaptive control technique for compensating the nonlinear parametrizable Stribeck effects. Specifically, an adaptive observer/controller scheme is developed which contains a feedforward approximation of the Stribeck effects. This feedforward approximation is used in a composite controller/observer strategy which forces the average spare integral of the position tracking error to an arbitrarily small value.

Robustness of the minimal control synthesis algorithm to non-linear plant with regard to the position control of manipulators

Abstract: This paper presents new, more rigorous, proofs of the stability and robustness of the adaptive minimal control synthesis (MCS) and decentralized MCS (DMCS) algorithms, applied to plant subject to internal state-dependent non-linear disturbances. The concept of arbitrary dissipativity, and the restriction on the high frequency gain of the plant introduced by Hodgson and Stoten in 1996, is used as a basis for the analysis. We also extend the stability result to the position control of manipulators composed of prismatic and revolute joints, by making use of the passive structure of the manipulator dynamics.

An efficient Method for Synthesis of Planar Multibody Systems Including Shape of Bodies as Design Variables

Abstract: A point contact joint has been developed and implemented in a joint coordinate based planar multibody dynamics analysis program that also supports revolute and translational joints. Further, a segment library for the definition of the contours of the point contact joints has been integrated in the code and as a result any desired contour shape may be defined. The sensitivities of the basic physical variables of a multibody system, i.e., the positions, velocities, accelerations and reactions of the system with respect to the automatically identified independent design variables may be determined analytically, allowing design problems where the shape of the bodies are of interest to be handled in both a general and efficient way.

Tenth world congress on the theory of machines and mechanisms

Abstract: In this paper Rapid Prototyping techniques have been used to fabricate mechanisms and evaluate their design faster. Prototypes of revolute, prismatic and spherical joints have been built using the Stereolithography machine SLA 190 of the Department of Mechanical and Aerospace Engineering at Rutgers University. In addition, a three legged six degree of freedom rapid prototype of a parallel manipulator has been fabricated. These rapidly prototyped mechanisms and joints have been fabricated in one step, without requiring assembly while they maintained their desired mobility. As far as the authors are aware, this is the first time that multi-joint, multi-degree-of-freedom mechanisms have been rapidly prototyped without requiring any assembly after their fabrication.

Optimum design of a three-dimensional serial robot manipulator

Abstract: A systematic and mathematical optimization methodology is presented for the optimal design of a three link, revolute joint, three-dimensional manipulator which must perform specific prescribed tasks. The objective of interest is the minimization of average torque requirement. In particular circular and eccentric closed task paths are considered. The optimization is carried out with the link lengths and the positional coordinates of the base taken as the five design variables, and subject to assembly and geometric constraints imposed on the system. In particular restrictions are placed on the joint angle between the links and on the link lengths. The minimization is successfully performed by the application of Snymans robust dynamic trajectory method for unconstrained optimization, to a penalty function formulation of the constrained problem.

Double revolute coil, its winding method and winding equipment

Abstract: PROBLEM TO BE SOLVED: To make a double revolute coil thinner, by constituting the double revolute coil of double layered winding of a flat type wire. SOLUTION: A wire member A is a rectangular flat type wire constituted of a long surface a1 and a short surface a2. A fixed side winding-up jig 1, a movable side winding-up jig 2 and a wire storing equipment 4 are simultaneously rotated and driven in the arrow direction by operating a rotation driving equipment 6, and the winding of a first layer is performed. When the winding of the first layer is finished, windings of the first layer are mutually fusion- welded by heating the windings, and the wire member A connected with a wire supplying equipment 3 is cut at a specified position. A movable winding center part is protruded by a specified dimension by operating a protruding equipment. In this state, the fixed side winding-up jig 1 and the movable side winding-up jig 2 are simultaneously rotated and driven, and the winding of a second layer is performed. The rotating direction at this time is made opposite to that of the first layer.

Slider crank mechanism based robot arm

Abstract: The slider crank mechanism based robot arm consists of a robot waist (2) rotating with respect to the robot base (1) and a closed kinematic chain planar mechanism which is connected to the robot waist by a revolute joint. The closed kinematic chain planar mechanism is principally constructed as a special design of a centric or eccentric slider (6) crank (4) mechanism. The slider crank (4) mechanism based robot arm (3) has similar structural and topological properties as both spherical and anthropomorphic robot manipulators and can be alternatively transformed from one another.

Fundamental properties of rigid serial manipulators for control design

Abstract: We investigate certain fundamental properties of serial-link mechanical manipulators, as related to the control design. The manipulator has rigid links with revolute and/or prismatic joints. These properties include the upper bounds of the inertia matrix, Coriolis and centrifugal terms, and gravitational term. As an illustrative example, a robust control is proposed based on this analysis. The generic properties are also readily applicable to other control designs.

Inverse control and stabilization of free-flying flexible robots

Abstract: SUMMARY The question of control and stabilization of flexible space robots is considered. Although, this approach is applicable to space robots of other configurations, for simplicity, a flexible planar two-link robot, mounted on a rigid floating platform, is considered. The robotic arm has two revolute joints and its links undergo elastic deformation in the plane of rotation. Based on nonlinear inversion technique, a control law is derived for controlling output variables describing the position and orientation of the platform and the joint angles of the robot. Although, the inverse controller accomplishes reference trajectory tracking, it excites the elastic modes of the arm. For the vibration suppression, three different stabilizer are designed. Using linear quadratic optimal control theory, a composite stabilizer for stabilization of the rigid and flexible modes and a decoupled flexible mode stabilizer are designed for regulating the end point of the robot to the target point and vibration suppression. Stabilization using only elastic mode velocity feedback is also considered. For large maneuvers, first the inverse controller is active, and the stabilizer is switched for regulation when the motion of the robot lies in the neighborhood of the terminal equilibrium state. Simulation results are presented to show that in the closed-loop system including the inverse controller and each of the stabilizers, trajectory tracking and stabilization of elastic modes are accomplished.

Nanometer Regularity in the Mechanics of a Precision Deployable Spacecraft Structure Joint

Abstract: The nonlinear microdynamics of a precision deployable space structure revolute joint incorporating angular contact ball bearings are investigated. Using a controlled-displacement force-state mapping method, it is shown that the hysteresis of thejoint approaches material damping levels asthemotions approach nanometer levels, both in extension and rotation. This suggests that structuresdeveloped from such a joint will beasymptotically linear at nanostrain motions. Moreover,thejointhasregularmicrodynamicsfordisplacementsof nanometersand rotations of microradians. No mechanical irregularities are detected to at least 5 nm of extensional resolution and 20 nrad of rotational resolution. For extensions of 1 πm or less, the axial stiffness shows negligible hysteresis, which within the resolution of the test, is comparable to material damping. In rotation, the joint exhibits nonlinear rotational behavior consistent with Todd/Johnson hysteresis loops (Todd, M. J., and Johnson, K. L., “ A Model for Coulomb Torque Hysteresis in Ball Bearings,”International Journal of Mechanical Science , Vol. 29, 1987, pp. 339 ‐354) and is repeatable down to torques of 10 π-N-m. The data support the conclusion that machined irregularities in the bearing component surfaces result in smooth, rather than irregular, microdynamic response.