Showing papers on "Revolute joint published in 2005"

Off-line programming of an industrial robot for manufacturing

Abstract: A procedure for the automatic generation of the robot programming used in manufacturing operations is introduced in the present paper. The off-line programming system developed here includes graphical simulation of the robot and its workcell, kinematic model of the robot, motion planning and creation of the NC code for manufacturing process. The proposed system is applied in a robot with five revolute joints for manufacturing operations and in a robot with six revolute joints for welding operations.

Towards grasping in unstructured environments: grasper compliance and configuration optimization

Abstract: This paper examines the role of grasper compliance and kinematic configuration in environments where object size and location may not be well known. A grasper consisting of a pair of two-link planar fingers with compliant revolute joints was simulated as it passively deflected during contact with a target object. The kinematic configuration and joint stiffness values of the grasper were varied in order to maximize successful grasp range and minimize contact forces for a wide range of target object size. Joint rest angles around 25-45 degrees produced near-optimal results if the stiffness of the base joint was much smaller than the intermediate joint, as confirmed experimentally.

Benchmark Results on the Linearized Equations of Motion of an Uncontrolled Bicycle

Abstract: In this paper we present the linearized equations of motion for a bicycle as, a benchmark The results obtained by pencil-and-paper and two programs are compaied The bicycle model we consider here consists of four rigid bodies, viz a rear frame, a front frame being the front fork and handlebar assembly, a rear wheel and a fiont wheel, which are connected by revolute joints The contact between the knife-edge wheels and the flat level surface is modelled by holonomic constiaints in the normal direction and by non-holonomic constraints in the longitudinal and lateral direction The rider is rigidly attached to the rear frame with hands free from the handlebar This system has three degrees of freedom, the roll, the steer, and the forward speed For the benchmark we consider the linearized equations for small perturbations of the upright steady forward motion The entries of the matrices of these equations form the basis for comparison Three diffrent kinds of methods to obtain the results are compared pencil-and-paper, the numeric multibody dynamics program SPACAR, and the symbolic software system AutoSim Because the results of the three methods are the same within the machine round-off error, we assume that the results are correct and can be used as a bicycle dynamics benchmark

Planar bipedal walking with foot rotation

Abstract: This paper addresses the key problem of walking with both fully-actuated and underactuated phases. The studied robot is planar, bipedal, and fully actuated in the sense that it has feet with revolute, actuated ankles. The desired walking motion is assumed to consist of three successive phases: a fully-actuated phase where the stance foot is flat on the ground, an underactuated phase where the stance heel lifts from the ground and the stance foot rotates about the toe, and an instantaneous double support phase where leg exchange takes place. The main contribution of the paper is to provide a provably asymptotically stabilizing controller that integrates the fully-actuated and underactuated phases of walking. By comparison, existing humanoid robots, such as ASIMO and Qrio, use only the fully-actuated phase (i.e., they only execute flat-footed walking), or RABBIT, which uses only the underactuated phase (i.e., it has no feet, and hence walks as if on stilts). The controller proposed here is organized around the hybrid zero dynamics of Westervelt et al. (2003) in order that the stability analysis of the closed-loop system may be reduced to a one-dimensional Poincare map that can be computed in closed form.

Learning-based identification and iterative learning control of direct-drive robots

Abstract: A combination of model-based and iterative learning control (ILC) is proposed as a method to achieve high-quality motion control of direct-drive robots in repetitive motion tasks. We include both model-based and learning components in the total control law, as their individual properties influence the performance of motion control. The model-based part of the controller compensates much of the nonlinear and coupled robot dynamics. A new procedure for estimating the parameters of the rigid body model, implemented in this part of the controller, is used. This procedure is based on a batch-adaptive control algorithm that estimates the model parameters online. Information about the dynamics not covered by the rigid body model, due to flexibilities, is acquired experimentally, by identification. The models of the flexibilities are used in the design of the iterative learning controllers for the individual joints. Use of the models facilitates quantitative prediction of performance improvement via ILC. The effectiveness of the combination of the model-based and the iterative learning controllers is demonstrated in experiments on a spatial serial direct-drive robot with revolute joints.

Accurate low DOF modeling of a planar compliant mechanism with flexure hinges: the equivalent beam methodology

Abstract: A methodology for accurate and efficient finite elements method (FEM) simulations of planar compliant mechanisms with flexure hinges is presented. First, using symmetry/antisymmetry boundary conditions and 3D elements, one-eighth of a single hinge is simulated to determine its true stress/stiffness characteristics. A set of fictitious beams is derived, which have the identical characteristics. This set is used in conjunction with other beams that model relatively stiff links to generate an equivalent model of an entire mechanism consisting of the beam elements only. The model has a low number of degrees-of-freedom (DOF) and appears to be more accurate than any 2D FEM models, even those with very large number of DOF. The methodology has been developed specifically for the right circular flexure hinge; however, it can be applied to all types of revolute flexure hinges.

Apparatus for steering a vehicle

Abstract: A steering system (10) for a vehicle (12) may include an actuator having a rotary to linear actuator (214), a movable linear section (216), and an interface (212) between the rotary to linear actuator (214) and the linear section (216). The interface (212) may include one or more cylindrical joints (244), revolute joints (272), compliant members (324, 376, 410, 412, 414, 416), or a block on a plane (424, 436) wherein the total degrees of freedom for the system including the rotary to linear actuator (214), rack (216), and interface (212) may be one, while the interface (212) may be limited to three degrees of freedom.

Control-Based Solution to Inverse Kinematics for Mobile Manipulators Using Penalty Functions

Abstract: This study offers the solution at the control feedback level to the inverse kinematics problem subject to state equality and inequality constraints for mobile manipulators. Based on the Lyapunov stability theory, a class of controllers generating the mobile manipulator trajectory whose attractor attained in a finite time, fulfills the above state constraints. The problem of both holonomic manipulability enforcement and collision avoidance is solved here based on an exterior penalty function approach which results in continuous mobile manipulator velocities near obstacles. The numerical simulation results carried out for a mobile manipulator consisting of a nonholonomic wheel and a holonomic manipulator of two revolute kinematic pairs, operating in both a constraint-free task space and task space including obstacles, illustrate the performance of the proposed controllers.

Kinematic Calibration of a Cartesian Parallel Manipulator

Abstract: In this paper, a prototype Cartesian Parallel Manipulator (CPM) is demonstrated, in which a moving platform is connected to a fixed frame by three PRRR limbs. Due to the orthogonal arrangement of the three prismatic joints, it behaves like a conventional X-Y-Z Cartesian robot. However, because all the linear actuators are mounted at the fixed frame, the manipulator may be suitable for applications requiring high speed and accuracy. Using a geometric method and the practical assumption that three revolute joint axes in each limb are parallel to one another, a simple forward kinematics for an actual model is derived, which is expressed in terms of a set of linear equations. Based on the error model, two calibration methods using full position and length measurements are developed. It is shown that for a full position measurement, the solution for the calibration can be obtained analytically. However, since a ball-bar is less expensive and sufficiently accurate for calibration, the kinematic calibration experiment on the prototype machine is performed by using a ball-bar. The effectiveness of the kinematic calibration method with a ball-bar is verified through the well- known circular test.

Geckobot and Waalbot: Small-Scale Wall Climbing Robots

Abstract: This paper proposes two small-scale agile wall climbing robots able to navigate on smooth vertical surfaces which use adhesive materials for attachment. Geckobot is a lizard-inspired climbing robot with similar kinematics to a gecko climbing gait. Waalbot uses two actuated legs with rotary motion and two passive revolute joints at each foot. Due to their compact design, a high degree of miniaturization is possible. Each has onboard power, computing, and wireless communication which allow for semi-autonomous operation. Various aspects of func- tioning prototype design and performance are discussed in detail, including leg and feet design and gait dynamics. Geckobot and Waalbot prototypes can climb 85 and 90 slopes respectively, and steer to any angle reliably. These robots are intended for inspection and surveillance applications and, ultimately, space missions.

Compliant device for nano-scale manufacturing

Abstract: The present invention is directed to a compliant device (18) comprising a support body (50), a floating body (52), and a plurality of flexure arms (54, 56, 58, 60). Each of the plurality of transfer arms (54, 56, 58, 60) is connected between the support body (50) and the floating body (52) to transfer a load therebetween in parallel. To that end, the flexure arms (54, 56, 58, 60) having first and second sets of flexure joints (62, 64, 66, 68). The first set of flexure joints (62, 64) facilitating rotational movement of said flexure arm (54, 56, 58, 60) about a first axis extending along a first direction. The second set of flexure joints (66, 68) arranged to facilitate rotational movement of the flexure arm (54, 56, 58, 60) about a second axis, extending along a second direction that is transverse to the first direction. The flexure joints (62, 64, 66, 68) are revolute joints.

A Global Adaptive Learning Control for Robotic Manipulators

Abstract: This paper addresses the problem of designing a global adaptive learning control for robotic manipulators with revolute joints and unknown dynamics. The reference signals to be tracked are assumed to be smooth and periodic with known period. By developing in Fourier series expansion the input reference signals of every joint, an adaptive learning PD control is designed which 'learns’ the input reference signals by identifying their Fourier coefficients: global asymptotic tracking and local exponential tracking of both the input and the output reference signals is obtained when the Fourier series expansion of each input reference signal is finite, while arbitrary small tracking errors are achieved otherwise. The resulting control is not model based and depends only on the period of the reference signals and on some constant bounds on the robot dynamics.

Development of a Robust Nonlinear Observer for a Single-Link Flexible Manipulator

Abstract: Accurate measurements of all the state variables of a given system are often not available due to the high cost of sensors, the lack of space to mount the transducers or the hostile environment in which the sensors must be located. The purpose of this study was to design a robust sliding mode observer that is capable of accurately estimating the state variables of the system in the presence of disturbances and model uncertainties. It should be emphasized that the proposed observer design can handle state equations expressed in the general form. The performance of the nonlinear observer is assessed herein by examining its capability of predicting the rigid and flexible motions of a compliant beam that is connected to a revolute joint. The simulation results demonstrate the ability of the observer in accurately estimating the state variables of the system in the presence of structured uncertainties and under different initial conditions between the observer and the plant. Moreover, they illustrate the deterioration in the performance of the observer when subjected to unstructured uncertainties of the system. Furthermore, the nonlinear observer was successfully implemented to provide on-line estimates of the state variables for two model-based controllers. The simulation results show minimal deterioration in the closed-loop response of the system stemming from the usage of estimated rather than exact state variables in the computation of the control signals.

A multibody dynamics benchmark on the equations of motion of an uncontrolled bicycle

Abstract: In this paper we present the linearized equations of motion for a bicycle as a benchmark. The results obtained by pencil-and-paper and two programs are compared. The bicycle model we consider here consists of four rigid bodies, viz. a rear frame, a front frame being the front fork and handlebar assembly, a rear wheel and a front wheel, which are 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 directions. The rider is rigidly attached to the rear frame with hands free from the handlebar. This system has three degrees of freedom: the roll, the steer, and the forward speed. For the benchmark we consider the linearized equations for small perturbations of the upright steady forward motion. The entries of the matrices of these equations form the basis for comparison. Three different kinds of methods to obtain the results are compared: penciland-paper, the numeric multibody dynamics program SPACAR, and the symbolic software system AutoSim. Because the results of the three methods agree within the machine round-off error, we assume that the results are correct and can be used as a bicycle dynamics benchmark.

Design, Modeling, Control, and Evaluation of a Hybrid Hip Joint Miniature Climbing Robot:

Abstract: The subject of this paper is the design, control, and evaluation of a biped-climbing robot featuring a new hybrid hip joint. The hybrid hip provides both prismatic and revolute motion, discretely, to the robot, using a single actuator. This is intended to improve its adaptability in confined environments and its capability to maneuver over and around obstacles. Optimization of the hybrid hip joint relative to robot size, weight, and actuation limits is considered while maximizing range of motion. The mechanical structure of the robot is discussed, as well as forward and inverse kinematics for motion planning. Reachable robot workspace in both revolute and prismatic phases of the hybrid hip joint is analyzed. Different robot locomotion strides are developed and dynamic controller requirements are considered. Experimental evaluation of the robot walking and climbing on and between surfaces with different inclinations is conducted to evaluate performance and repeatability of the system.

Kinematic analysis and implementation of a spherical 3-degree-of-freedom parallel mechanism

Abstract: A new spherical-type 3-degree-of-freedom parallel mechanism consisting of a two degree-of-freedom parallel module and a serial module is proposed. Two alternative designs for the serial sub-chain are suggested and compared. The first design employs RU joint arrangement for the serial sub chain structure. The second design incorporates a gear chain to drive the distal revolute joint of the serial sub-chain from the base platform of the mechanism. This modification significantly improves kinematic characteristics of the mechanism within its workspace. Firstly, the closed-form solutions of both the forward and the reverse position analysis are derived. Secondly, the first-order kinematic model with respect to three inputs which are located at the base is derived. Thirdly, it is confirmed through simulation that the modified mechanism has much more improved isotropic characteristic throughout the workspace of the mechanism. Lastly, the proposed mechanism is implemented to verify the results from this analysis.

A New Perspective on O(n) Mass-Matrix Inversion for Serial Revolute Manipulators

Abstract: This paper describes a new algorithm for the efficient mass-matrix inversion of serial manipulators. Whereas several well-known O(n) algorithms already exist, our presentation is an alternative and completely different formulation that builds on Fixman’s theorem from the polymer physics literature. The main contributions here are therefore adding a new perspective to the manipulator dynamics literature and providing an alternative to existing algorithms. The essence of this theory is to consider explicitly the band-diagonal structure of the inverted mass matrix of a manipulator with no constraints on link length, offsets or twist angles, and then build in constraints by appropriate partitioning of the inverse of the unconstrained mass matrix. We present the theory of the partitioned mass matrix and inverse of the mass matrix for serial revolute manipulators. The planar N-link manipulator with revolute joints is used to illustrate the procedure. Numerical results verify the O(n) complexity of the algorithm. Exposure of the robotics community to this approach may lead to new ways of thinking about manipulator dynamics and control.

A three-DOF translational manipulator with decoupled geometry

Abstract: A new 3-DOF translational parallel manipulator is presented in this paper. This manipulator has decoupled motion in for x, y, and z axes, and employs only revolute joints. The structure and kinematics of the manipulator are studied. The mechanism singularity is examined and the calibration methods are presented.

Unified Modelling Theories for the Dynamics of Multidisciplinary Multibody Systems

Abstract: A major goal of research in multibody dynamics is to develop formulations that automatically generate and solve the governing equations of motion for a system of rigid and flexible bodies, given only a description of the system. Much progress has been made in multibody dynamics research over the last few decades and nowadays, there are several commercially-successful computer programs (e.g. Adams, Dads) that automatically analyze the dynamics of multibody mechanical systems. However, these same programs, and the theoretical formulations on which they are based, are not capable of modelling general multidisciplinary applications in which a multibody system is coupled to other physical domains, e.g. electrical or pneumatic. There are numerous important applications of multidisciplinary multibody systems, including vehicles with active suspensions and traction control, mechatronic systems, and micro-electromechanical systems (MEMS). The design of these multidisciplinary applications would be greatly facilitated by algorithms that could automate their dynamic analysis. There are two distinct approaches that have been proposed for modelling and simulating the dynamics of multidisciplinary multibody systems. The first is based on coupled simulations, or “co-simulation”, in which two separate simulation programs or subroutines are coupled numerically. The advantage of co-simulation is that one can use existing programs that are very well-developed for their particular domain. However, numerical stability problems may arise during a co-simulation [20] and, more importantly, there is no underlying mathematical framework that one could use to generate analytical models of these multidisciplinary applications. The second approach is to apply a unified systems theory to the dynamic modelling of multidisciplinary multibody systems. This paper focuses on this second approach for several reasons:

Robust control system design for SCARA robots using adaptive pole placement

Abstract: SCARA robots generally have two revolute joints and one prismatic joint. One of the fundamental motions of the robots is horizontal transportation of a load by actuating the two revolute joints. Residual vibration of the prismatic joint generally occurs in the transportation, and it should be suppressed. In this paper, we propose an adaptive controller design for the transportation. The controlled object is modeled as a nonlinear double-input quadruple-output system with unknown mass of load. The controlled object is separated into two single-input double-output systems, which allows us to design an integral controller providing performance robustness with respect to estimation error of the mass. Experimental results demonstrate the effectiveness of the proposed method.

A new family of hybrid 4-DOF parallel mechanisms with two platforms and its application to a footpad device

Abstract: This paper proposes a new family of 4-degrees-of-freedom (DOF) parallel mechanisms with two platforms and its application to a footpad device that can simulate the spatial motions of the human foot. The new mechanism consists of front and rear platforms, and three limbs. Two limbs with 6-DOF serial joints ( P -S-P-P) are attached to each platform and are perpendicular to the base plate, while the middle limb is attached to the revolute joint that connects the front and rear platforms. The middle limb is driven by the 2-DOF driving mechanism that is equivalent to active serial prismatic and revolute joints ( Pe - Re ), or prismatic and prismatic joints ( Pe - Pe ) with two base-fixed prismatic actuators. Since the middle limb perpendicular to the base plate has 3-DOF serial joints ( Pe - Re -R or Pe - Pe -R), two new 4-DOF parallel mechanisms with two platforms can generate pitch motion of each platform, and roll and heave motions (1T-3R) or pitch motion of each platform and two translational motions (2T-2R) at both platforms, according to the type of the 2-DOF driving mechanism. Kinematic analyses of the 1T-3R mechanism were performed, including inverse and forward kinematics and velocity analysis. Based on the 1T-3R mechanism, a footpad device was designed to generate foot trajectories for natural walking. © 2005 Wiley Periodicals, Inc.