Showing papers on "Revolute joint published in 1996"

Method and apparatus for providing high bandwidth, low noise mechanical i/o for computer systems

Abstract: A method and apparatus (25') for providing high bandwidth and low noise mechanical input and output for computer systems. A closed-loop, five member gimbal mechanism (46, 58, 48a, 48b, 50a and 50b) provides two revolute degrees of freedom to an object about two axies of rotation. A linear axis member (40) can be coupled to the gimbal mechanism at the axes' intersection and be translated along a third axis to provide a third degree of freedom. Transducers (42) associated with the provided degrees of freedom include sensors and actuators and provide an electromechanical interface between the objet (44) and a digital processing system (14). Capstan drive mechanisms (58) transmit forces between the transducers (42) and the object (44).

Kinematics of a novel three DOF translational platform

Abstract: A novel 3-DOF parallel manipulator is presented that employs only revolute joints and constrains the manipulator output to translational motion. Closed-form solutions are developed for both the inverse and forward kinematics. The inverse kinematics produces four solutions for each leg of the manipulator. In general, the four solutions are realized in only two unique leg configurations. The forward kinematic solution is reduced to a quadratic equation. So that in general, there are two poses the manipulator can assume for a given set of input joint angles.

Passive robots and haptic displays based on nonholonomic elements

Abstract: Describes a new architecture for passive robots and haptic displays, which the authors call a programmable constraint machine (PCM). An n-DOF PCM can, under computer control, exhibit constraints (smooth, impenetrable virtual surfaces of dimensionality

Dynamic underactuated nonprehensile manipulation

Abstract: By exploiting centrifugal and Coriolis forces, simple, low-degree-of-freedom robots can control objects with more degrees-of-freedom. For example, by allowing the object to roll and slip, a one-degree-of-freedom revolute robot can take a planar object to a full-dimensional subset of its state space. We present a dynamic manipulation planner that finds manipulator trajectories to move an object from one state to another without grasping it. The trajectories have been successfully implemented on a one-degree-of-freedom direct drive arm to perform dynamic tasks such as snatching an object from a table, rolling an object on the surface of the arm, and throwing and catching.

Three degree of freedom parallel mechanical linkage

Abstract: A three degree of freedom parallel mechanism or linkage that couples three degree of freedom translational displacements at an endpoint, such as a handle, a hand grip, or a robot tool, to link rotations about three axes that are fixed with respect to a common base or ground link. The mechanism includes a three degree of freedom spherical linkage formed of two closed loops, and a planar linkage connected to the endpoint. The closed loops are rotatably interconnected, and made of eight rigid links connected by a plurality of single degree of freedom revolute joints. Three of these revolute joints are base joints and are connected to a common ground, such that the axis lines passing through the revolute joints intersect at a common fixed center point K forming the center of a spherical work volume in which the endpoint is capable of moving. The three degrees of freedom correspond to the spatial displacement of the endpoint, for instance. The mechanism provides a new overall spatial kinematic linkage composed of a minimal number of rigid links and rotary joints. The mechanism has improved mechanical stiffness, and conveys mechanical power bidirectionally between the human operator and the electromechanical actuators. It does not require gears, belts, cable, screw or other types of transmission elements, and is useful in applications requiring full backdrivability. Thus, this invention can serve as the mechanical linkage for actively powered devices such as compliant robotic manipulators and force-reflecting hand controllers, and passive devices such as manual input devices for computers and other systems.

Mechanism for control of position and orientation in three dimensions

Abstract: The subject invention provides a parallel or closed loop mechanism for moving and positioning a member in space. The mechanism includes three branches each provided with at least two link members being serially connected together by a spherical elbow joint whereby the first and second link members are rotatable with respect to each other about any axis passing through a centre of the first joint. The mechanism is provided with actuators for moving each branch and the first links of each branch are rigidly connected at an end portion thereof to the actuator means. The mechanism includes three revolute joints each defining a longitudinal axis of rotation. Each revolute joint is connected to an associated second link member so that the longitudinal axes of all third joints intersect at a point and the revolute joints are interconnected so that the three branches form three parallel or closed loops.

High precision redundant robotic manipulator

Abstract: A high precision redundant robotic manipulator for overcoming contents imposed by obstacles or imposed by a highly congested work space. One embodiment of the manipulator has four degrees of freedom and another embodiment has seven degreed of freedom. Each of the embodiments utilize a first selective compliant assembly robot arm (SCARA) configuration to provide high stiffness in the vertical plane, a second SCARA configuration to provide high stiffness in the horizontal plane. The seven degree of freedom embodiment also utilizes kinematic redundancy to provide the capability of avoiding obstacles that lie between the base of the manipulator and the end effector or link of the manipulator. These additional three degrees of freedom are added at the wrist link of the manipulator to provide pitch, yaw and roll. The seven degrees of freedom embodiment uses one revolute point per degree of freedom. For each of the revolute joints, a harmonic gear coupled to an electric motor is introduced, and together with properly designed based servo controllers provide an end point repeatability of less than 10 microns.

A Revolute Joint With Linear Load-Displacement Response for Precision Deployable Structures

Abstract: NASA Langley Research center is developing key structures and mechanisms technologies for micron-accuracy, in-space deployment of future space instruments. Achieving micron-accuracy deployment requires significant advancements in deployment mechanism design such as the revolute joint presented herein. The joint presented herein exhibits a load-cycling response that is essentially linear with less than two percent hysteresis, and the joint rotates with less than one in.-oz. of resistance. A prototype reflector metering truss incorporating the joint exhibits only a few microns of kinematic error under repeated deployment and impulse loading. No other mechanically deployable structure found in literature has been demonstrated to be this kinematically accurate.

Adaptive control of flexible manipulators carrying large uncertain payloads

Abstract: An adaptive controller is presented for a manipulator with revolute joints and structurally flexible links which carries a rigid payload with unknown mass properties. Under the assumption that the payload mass is much greater than that of the manipulator, globally stable tracking of the Cartesian end-effector coordinates is established. Key ideas underlying the controller development are the passivity of a mapping involving the end-effector rates as part of the output and a fixed parameter feedforward which preserves this property. The concept of filtered error is borrowed from previous work on rigid arms and suitably modified in developing the adaptive law. Although measurements of the tip positions and rates are needed, there is no requirement for sensing of the elastic coordinates. A numerical example involving a six DOF manipulator with flexible links demonstrates excellent tracking with respect to a simulation based on the exact motion equations. © 1996 John Wiley & Sons, Inc.

Motion planning for mobile manipulators with a non-holonomic constraint using the FSP (full space parameterization) method

Abstract: The efficient utilization of the motion capabilities of mobile manipulators, i.e., manipulators mounted on mobile platforms, requires the resolution of the kinematically redundant system formed by the addition of the degrees of freedom (DOF) of the platform to those of the manipulator. At the velocity level, the linearized Jacobian equation for such a redundant system represents an underspecified system of algebraic equations, which can be subject to a varying set of contraints such as a non-holonomic constraint on the platform motion, obstacles in the workspace, and various limits on the joint motions. A method, which we named the Full Space Parameterization (FSP), has recently been developed to resolve such underspecified systems with constraints that may vary in time and in number during a single trajectory. In this article, we first review the principles of the FSP and give analytical solutions for constrained motion cases with a general optimization criterion for resolving the redundancy. We then focus on the solutions to (1) the problem introduced by the combined use of prismatic and revolute joints (a common occurrence in practical mobile manipulators), which makes the dimensions of the joint displacement vector components non-homogeneous, and (2) the treatment of a non-holonomic constraint on the platform motion. Sample implementations on several large-payload mobile manipulators with up to 11 DOF are discussed. Comparative trajectories involving combined motions of the platform and manipulator for problems with obstacle and joint limit constraints, and with non-holonomic contraints on the platform motions, are presented to illustrate the use and efficiency of the FSP approach in complex motion planning problems. © 1996 John Wiley & Sons, Inc.

Development of a spherical in-parallel actuated mechanism with three degrees of freedom with large working space and high motion transmissibility : Evaluation of motion transmissibility and analysis of working space

Abstract: For a spherical in-parallel actuated mechanism with three degrees of freedom in which the output link is connected to the base link by three connecting chains composed of an input link, a coupler link and three revolute pairs each, a transmission index (TI) is proposed based on the power transmitted from the input links to the output link. Static force analyses with consideration of elasticity of links have been carried out in the case where forces and moments are exerted on the output link as external loads. Then, mechanism synthesis is carried out considering both motion transmissibility and interferences among links, and a spherical in-parallel actuated mechanism with three degrees of freedom is proposed.

Forward displacement analysis and uncertainty configurations of parallel manipulators with a redundant branch

Abstract: The effect of adding a redundant branch in terms of reduction of the number of assembly modes and elimination of potential uncertainty configuration types is investigated for a class of parallel manipulators. Considered is a broad class that includes all three-branch manipulators where each branch is comprised of a serial arrangement of three main-arm joints supporting a common payload platform through a passive spherical branch end joint-group. The addition of a redundant branch effectively yields a four-branch manipulator class. Considered in particular is a 3-4 form of the manipulator where two branch ends meet at one point on the mobile platform. Symmetric main-arm joint sensing and actuation (two sensed/acutated main-arm joints per branch) is utilized. Synthetic geometry is used to study the number of assembly configurations of the resulting 3-4 four-branch parallel manipulators. It is presented that the number of assembly modes of three-branch parallel manipulators with passive spherical branch end joints can be reduced by utilizing a redundant branch. It is shown that there exist up to eight and up to four assembly modes when all unsensed joints are revolute and when all unsensed joints are prismatic, respectively. Combinations of unsensed prismatic and revolute joints are also investigated. It is determined that there are up to eight and up to four assembly modes when the unsensed main-arm joint of one of the concurrent branches is prismatic and when the unsensed joints of both concurrent branches are prismatic joints, respectively. Resolving the potential assembly modes require only the consideration of, at highest, second-order single-variable polynomials. In addition, kinematic design considerations allowing reduction of feasible assembly modes are discussed. The investigation of potential uncertainty configuration types is based on examining degeneracies of the screw systems formed by wrenches associated with the forces that the actuated-joints can apply. All linear dependency cases that could potentially cause uncertainties for the class of four-branch manipulators are identified. It is shown that while significantly reducing potential uncertainty configuration types, the addition of a redundant branch number cannot eliminate all potential dependency (uncertainty) cases completely. For the remaining potential uncertainty configuration types, the characteristics of the corresponding unconstrained instantaneous degrees of freedom are discussed.

A Passive Mechanism that Improves Robotic Positioning through Compliance and Constraint

Abstract: This paper presents the design of a passive robotic wrist that is capable of establishing and maintaining an accurate position relative to a workpart edge through compliance and constraint (force guidance). In previous work, we have shown that, through proper selection of a manipulator's impedance, a manipulator's end-effector can be guided to its desired relative position despite errors in its commanded position. The selected proper impedance is attained here through the design of a passive micromanipulator that is mounted on the end-effector of a conventional manipulator. The micromanipulator consists of three linkages connected by revolute joints and torsional springs. The outermost linkage contacts the workpart at multiple locations providing multidirectional unilateral kinematic constraint. This kinematic constraint in conjunction with the compliance provided by the torsional springs causes the linkage to be re-positioned so that any existing misalignment (that inevitably occurs) is eliminated and a unique planar position/orientation with respect to the workpart edge is attained. Here, we present the procedure used in the parametric design of this mechanism. The desired compliant properties identified in task space (using Cartesian variables ( x , y , and θ ) for force and motion) are extended here to joint space (using joint variables ( θ 1 , θ 2 ), and θ 3 ) for torque and motion). The appropriate micromanipulator link lengths, initial linkage angles, and the appropriate torsional spring constants are selected using an optimization procedure. Computer simulation of the constrained manipulator/workpart interaction demonstrates that the desired force guidance behavior is attained.

Reexamination of the DCAL controller for rigid link robots

Abstract: In this paper, we present two DCAL-like (Desired Compensation Adaptation Law)' controllers for link position tracking of n-link, rigid, revolute robot manipulators. First, we use a simplified stability analysis to illustrate global asymptotic link position-velocity tracking for a DCAL-like controller with nonlinear feedback. The proof is simplified by employing a different structure for the nonlinear feedback than that originally proposed' and by making use of the nonlinear damping control design tool. 2 We then use the nonlinear damping tool to show that a DCAL-like controller with linear feedback can guarantee semi-global 2 asymptotic link position-velocity tracking. The proposed nonlinear and linear feedback DCAL-like controllers are experimetally tested and compared using the Integrated Motion Inc. 2-link direct drive robot manipulator.

A two-DOF manipulator with adjustable compliance capabilities and comparison with the human finger

Abstract: This article addresses compliance control issues and develops an actuator that modulates the stiffness and independently sets the angular positioning of a revolute joint. The capability to decouple the position from the compliance modulations is instrumental in a wide range of robotic contact operations. It is shown that a five input control scheme fully characterizes the position and compliance of a two-DOF manipulator. In an effort to characterize the control capabilities of a human finger, the compliance values of the proximal and middle joints are assessed experimentally. The results of the experiment show that a five input control is evidently within the human finger capabilities. In an effort to enhance the compliance capabilities of robotic systems, the authors believe that the newly developed actuation scheme will impact the automation of manufacturing tasks in which contact operations are inevitable. © 1996 John Wiley & Sons, Inc.

A Multi Level Approach to Synthesis of Planar Mechanisms

Abstract: A multi level approach to synthesis of planar mechanisms is presented. The approach covers both structural and dimensional synthesis of planar rigid body mechanisms containing revolute and translational joints. The synthesis is based on four different criteria. Firstly the type of mechanism is chosen with a view to get the simplest mechanism that satisfactorily fulfills the remaining three criteria. Two of these criteria are formulated as constraints on the kinematic behavior and the total area occupied by the mechanism, respectively. The fourth criteria is simply the desired minimization of the reactive forces/moments that appear in the mechanism. The desired kinematic behavior is based on a finite number, typically 1, ..., 6, of points in time (positions of the mechanism) where the position and orientation of up to two output bodies may be prescribed. The constraints on occupied areas are labelled territory constraints and formulated as a number of restricted areas (boxes). A synthesis is automatically performed at five levels. At the first level the structure of the mechanism is decided. At the second level initial dimensions for the given type of mechanism are found by random checking. At the third level the constraints on the kinematic behavior is fulfilled. At the fourth level the territory constraints are taken into account and, finally, at the fifth level the minimization of reactions is carried out. The entire approach has been implemented in a software package SYNMEC that runs on PCs and constitutes a way of performing the synthesis of a mechanism that is general and flexible with respect to both the type of mechanism that may be synthesized as well as the desired behavior upon which the synthesis is based.

Rapid analysis manipulator program (RAMP) as a design tool for serial revolute robots

Abstract: This paper describes a program (RAMP) which facilitates robot design analysis, project management, and design documentation. Requirements for such a program are proposed, and the literature is investigated. Design of the program is discussed in an object-oriented manner, and the system-level objects are described. The extent and method of implemented analysis objects is presented in more detail. Examples of use are discussed in terms of component selection, deflection analysis, and end-effector position error. Finally, the future augmentation of RAMP is described.

Dynamics of multibody tracked vehicles using experimentally identified modal parameters

Abstract: The mode shapes, frequencies, and modal mass and stiffness coefficients of multibody systems such as tracked vehicles can be determined using experimental identification techniques. In multibody simulations, however, knowledge of the modal parameters of the individual components is required, and consequently, a procedure for extracting the component modes from the mode shapes of the assembled system must be used if experimental modal analysis techniques are to be used with general purpose multibody computer codes. In this investigation, modal parameters (modal mass, modal stiffness, modal damping, and mode shapes), which are determined experimentally, are employed to simulate the nonlinear dynamic behavior ofa multibody tracked vehicle which consists of interconnected rigid and flexible components. The equations of motion of the vehicle are formulated in terms of a set of modal and reference generalized coordinates, and the theoretical basis for extracting the component modal parameters of the chassis from the modal parameters of the assembled vehicle is described. In this investigation, the track of the vehicle is modeled as a closed kinematic chain that consists of rigid links connected by revolute joints, and the effect of the chassis flexibility on the motion singularities of the track is examined numerically. These singularities which are encountered as the result of the change in the track configuration are avoided by using a deformable secondary joint instead of using the loop-closure equations.