Showing papers on "Revolute joint published in 2000"

Position feedback control system

Abstract: Disclosed is a system and method for independently evaluating the spatial positional performance of a machine having a movable member, comprising an articulated coordinate measuring machine comprising: a first revolute joint; a probe arm, having a proximal end rigidly attached to the first joint, and having a distal end with a probe tip attached thereto, wherein the probe tip is pivotally mounted to the movable machine member; a second revolute joint; a first support arm serially connecting the first joint to the second joint; and coordinate processing means, operatively connected to the first and second revolute joints, for calculating the spatial coordinates of the probe tip; means for kinematically constraining the articulated coordinate measuring machine to a working surface; and comparator means, in operative association with the coordinate processing means and with the movable machine, for comparing the true position of the movable machine member, as measured by the true position of the probe tip, with the desired position of the movable machine member.

Collision-Free Trajectory Planning for a 3-DoF Robot with a Passive Joint

Abstract: This paper studies motion planning from one zero velocity state to another for a three-joint robot in a horizontal plane with a passive revolute third joint. Such a robot is small-time locally controllable on an open subset of its zero velocity section, allowing it to follow any path in this subset arbitrarily closely. However, some paths are “preferred” by the dynamics of the manipulator in that they can be followed at higher speeds. In this paper we describe a computationally efficient trajectory planner which finds fast collision-free trajectories among obstacles. We are able to decouple the problem of planning feasible trajectories in the robot’s six-dimensional state space into the computationally simpler problems of planning paths in the three-dimensional configuration space and time scaling the paths according to the manipulator dynamics. This decoupling is made possible by the existence of velocity directions, fixed in the passive link frame, which can be executed at arbitrary speeds. We have demonstrated the motion planner on an experimental underactuated manipulator. To our knowledge, it is the first implementation of a collision-free motion planning algorithm for a manipulator subject to a second-order nonholonomic constraint.

Design, implementation, and evaluation of an under-actuated miniature biped climbing robot

Abstract: The design, implementation, and evaluation of a miniature biped robot for urban reconnaissance are presented. Design specifications for mobility, space requirement weight, sensing, and control are defined. A revolute hip joint is selected based on its enhanced mobility and capability to function in reasonably confined spaces. Small size dictates minimal weight, which is achieved by an under actuated joint structure, providing steering at only one foot, minimizing sensors, and structural optimization. The smart robotic foot supports the robot on a variety of smooth surfaces and provides feedback when a firm grip is established. Adaptable control strategies and dithering are implemented in lieu of minimal sensors and uncertainty created by backlash, gravity, and compliance in the suction feet. The robot is evaluated while performing tasks on surfaces with a variety of inclinations.

Static balancing of spatial six‐degree‐of‐freedom parallel mechanisms with revolute actuators

Abstract: The static balancing of spatial 6-degree-of-freedom parallel mechanisms or manipulators with revolute actuators is studied in this article. Two static balancing methods, namely, using counterweights and using springs, are used. The first method leads to mechanisms with a stationary global center of mass while the second approach leads to mechanisms whose total potential energy (including the elastic potential energy stored in the springs as well as the gravitational potential energy) is constant. The position vector of the global center of mass and the total potential energy of the manipulator are first expressed as functions of the position and orientation of the platform. Then, conditions for static balancing are derived from the resulting expressions. Finally, examples are given to illustrate the design methodologies. © 2000 John Wiley & Sons, Inc.

Workspace Analysis of a Six-Degrees of Freedom, Three-Prismatic- Prismatic-Spheric-Revolute Parallel Manipulator

Abstract: This paper studies the workspace of a six-degrees-of-freedom parallel manipulator of the general three-PPSR (prismaticprismatic-spheric-revolute) type. It is known that a drawback of parallel manipulators is their limited workspace. To develop parallel mechanisms with a larger workspace is of use to potential applications. The mechanism of a three-PPSR manipulator and its variations are briefly analysed. The workspace is then investigated and the effects of joint limit and limb interference on the workspace shape and size are numerically studied. The constituent regions of the workspace corresponding to different classes of manipulator poses are discussed. It is shown that the workspace of this parallel manipulator is larger than that of a comparable Stewart platform, especially in the vertical direction.

Time-optimal controls of kinematically redundant manipulators with geometric constraints

Abstract: Theoretical investigations of time-optimal control of kinematically redundant manipulators subject to control and state constraints are presented. The task is to move the end-effector along a prescribed geometric path (state equality constraints). In order to address a structure of time-optimal control, the concept of a regular trajectory derived in Pontryagin et al. (1961) and the extended state space introduced herein are used. Next, it is proved that if the dynamics of a manipulator are defined by n actuators and m path-constrained equations, where m

Determination of finger position

Abstract: A prescription is provided which specifies constraints, e.g., the type (revolute and/or prismatic) and the number of joints which may be included between any two position-sensing elements (PSEs), where the joints connect the links of a kinematically constrained multi-articulated structure, whereby the defining parameters of the structure may be determined using the spatial placement of the two PSEs and the kinematic constraints of the multi-articulated structure, and where at least the spatial placement of one link is not directly measured. Also provided are preferred placements of PSEs and goniometers on a kinematically constrained multi-articulated structure which will allow determination of the spatial placement of the links, where at least the spatial placement of one link is not directly measured. Revolute joint models of the articulations of the entire human body, as well as preferred PSE and goniometer locations, are provided. An algorithm is provided for determining the joint angles for a finger modeled as a 4-link planar manipulator with one PSE affixed to the fingertip and one PSE affixed to the metacarpus.

Determination of singularity contours for five-bar planar parallel manipulators

Abstract: From a design point of view, it is crucial to predict singular configurations of a manipulator in terms of inputs in order to improve the dexterity and workspace of a manipulator. In this paper, we present a simple, yet a systematic appoach to obtain singularity contours for a class of five-bar planar parallel manipulators which are based on five rigid links and five single degree of freedom joints – revolute and prismatic joints. The determinants of the manipulator Jacobian matrices are evaluated in terms of joint inputs for a specified set of geometric parameters, and the contours of the determinants at 0.0 plane which are the singularity contours in joint space are generated for the three types of singularities reported in the literature. The proposed approach/algorithm is simple and systematic, and the resulting equations are easy to solve on a computer. The singularity contours for all the class are presented in order to demonstrate the method. It is concluded that the proposed method is useful in trajectory planning and design of five-bar planar parallel manipulators in order to improve their dexterity and workspace.

The bounds and realization of spatial compliances achieved with simple serial elastic mechanisms

Abstract: We address the spatial elastic behavior that can be achieved through the use of a serial chain of revolute and prismatic elastic joints. We show that, regardless of the number of joints or the configuration of the links, there exists a subspace within the 21-dimensional compliance matrix space that cannot be reached by a simple serial elastic mechanism. This restriction is shown to be dual to the restriction on the stiffness matrices associated with simple parallel mechanisms. Although analogous to each other, the two restrictions correspond to different elastic behaviors. A procedure to synthesize any realizable compliance matrix with a simple serial mechanism is provided. The dualities and differences between the parallel and serial cases are discussed.

RCC characteristics of planar/spherical three degree-of-freedom parallel mechanisms with joint compliances

Abstract: A three degree-of-freedom (DOF) planar parallel manipulator has been extensively studied as the fundamental example of parallel manipulators. In this work, we explicitly show that this mechanism possesses a completely decoupled compliance characteristic at the object space, which is the important operational requirement for a RCC device. As the first condition to have a RCC point, this mechanism should maintain symmetric configurations. As the second condition, the same magnitude of revolute joint compliance should be symmetrically placed at the same joint location of each chain. We also investigate the compliance characteristics of a spherical 3 DOF mechanism which has a similar kinematic structure to the planar mechanism through simulation. It turns out that the spherical mechanism also has a RCC point at the intersection point of all nine joint axes in its symmetric configuration. Further, more general output compliance model is derived for those mechanisms with redundant joint compliances. It is expected that these two parallel mechanisms not only can be used as excellent 3 DOF RCC devices, but also can be integrated into the design of a new six DOF RCC device.

Design and control of a shape memory alloy wire bundle actuator

Abstract: In this paper, the design and control of a novel shape memory alloy (SMA) actuator that possesses impressive payload lifting capabilities are presented. The actuator consists of 48 nickel-titanium SMA wires mechanically bundled in parallel forming one powerful artificial muscle. This new linear actuator can apply up to 100 lbf (445 N), which is approximately 300 times its weight, over a maximum distance of 0.5 in. (1.27 cm). The actuator was tested in two different loading configurations - linear displacement and operation of a revolute joint. A PID based controller with the addition of an input shaping function was developed for each loading configuration with excellent results, maintaining steady state error within ± 0.004 in. (0.1 mm) for linear motion and ± 1o for revolute joint rotation. This powerful, compact, and lightweight actuator shows promise for use in space, medical, and other macro-robotic applications.

A simplified inverse kinematic model calculation method for all 6r type manipulators

Abstract: An inverse kinematic model of a manipulator - equipped with an end effector - is a function which allows to calculate a manipulator configuration corresponding to a given end effector location (position and orientation). In this paper, we consider the case of 6 R type manipulators having a single open kinematic chain structure and six revolute joints R. The first method, which brought back the determination of this model to the computation of the roots of a polynomial equation whose degree - equal to sixteen - is minimal, was proposed in 1988 by Lee and Liang. Nevertheless, Lee and Liang's technique was extremely complicated and necessitated divisions which prevent it from being used in any case. Here, we present a simplified method for this calculation, which does not involve any division; as a consequence it works in any case. We present also an example of a particular, but non academic, manipulator for which we actually obtain sixteen different real configurations corresponding to a particular given end effector location; this result demonstrates that the degree of the previous polynomial equation cannot be reduced.

Time-optimal motions of robotic manipulators

Abstract: An approach to planning time-optimal collision-free motions of robotic manipulators is presented. It is based on using a negative formulation of the Pontryagin Maximum Principle which handles efficiently various control and/or state constraints imposed on the manipulator motions, which arise naturally out of manipulator joint limits and obstacle avoidance. This approach becomes similar to that described by Weinreb and Bryson, as well as by Bryson and Ho if no state inequality constraints are imposed. In contrast to the penalty function method, the proposed algorithm does not require an initial admissible solution (i.e. an initial admissible trajectory) and finds manipulator trajectories with a smaller cost value than the penalty function approach. A computer example involving a planar redundant manipulator of three revolute kinematic pairs is included. The numerical results are compared with those obtained using an exterior penalty function method.

Analysis and Synthesis of Schatz Six-Revolute Mechanisms

Abstract: Based on geometrical intuition and computer graphics, we present the formation of two kinds of Schatz six-revolute mechanisms and two types of algebraic surfaces on which the corresponding reciprocal screw axes lie under any possible configurations. Then, we derive the general kinematic closed-form solutions and show the absence of stationary configuration of both mechanisms using four-by-four matrix and differential algebra. Moreover, the parametric formulations of coupler-point motion provide a complete higher-order analysis of the coupler curve. In practical application, this mechanism is further used for the dimensional synthesis, path and motion generation synthesis, by the nonlinear programming optimization method. At last, two numerical examples are taken to illustrate the design algorithm.

Geometric Calibration of Robots Using Multiple Plane Constraints

Abstract: This paper revisits the problem of the calibration of the geometric parameters of robots using plane constraint methods. Although such methods have been studied by many authors, there exist some ambiguities concerning the identifiable parameters and the number of required planes. This study shows that, for a robot with revolute joints only, four planes are necessary to obtain the same identifiable parameters as the open-loop method using the Cartesian coordinates of the terminal point as calibration data, while three planes are sufficient for a robot with at least one prismatic joint. Experimental results are given for a Puma 560 robot.

On Isotropic Sets of Points in the Plane. Application to the Design of Robot Archirectures

Abstract: Various performance indices are used for the design of serial manipulators One method of optimization relies on the condition number of the Jacobian matrix The minimization of the condition number leads, under certain conditions, to isotropic configurations, for which the roundoff-error amplification is lowest In this paper, the isotropy conditions, introduced elsewhere, are the motivation behind the introduction of isotropic sets of points By connecting together these points, we define families of isotropic manipulators This paper is devoted to planar manipulators, the concepts being currently extended to their spatial counterparts Furthermore, only manipulators with revolute joints are considered here

Nonholonomic Motion Planning for Coupled Planar Rigid Bodies with Passive Revolute Joints.

Abstract: Motion planning for coupled rigid bodies in a horizontal plane is investigated. The rigid bodies are serially connected by passive revolute joints. The dynamic constraints on the system are second-order nonholonomic constraints. We attempted to control those n coupled rigid bodies by the translational acceleration inputs at the first joint. If each rigid body is hinged at the center of percussion, it is possible to compose a positioning trajectory by connecting rotational and translational trajectory segments. Each rigid body can be rotated about its center of percussion one after another. When all of the rigid bodies are aligned on a straight line, they can be translated. The algorithm for positioning is presented. Simulations show that the coupled planar rigid bodies can reach the desired configuration by the constructed inputs.

Design and analysis of a new haptic device using a parallel mechanism

Abstract: Presents the design and analysis of a 6 degree-of-freedom new haptic device for interfacing with virtual reality by using a parallel mechanism. The mechanism is composed of three pantograph mechanisms that are driven by ground-fixed servomotors and stand perpendicularly to the base plate, three spherical joints between the top of the pantograph mechanisms and connecting bars, and three revolute joints between connecting bars and a mobile joystick handle. Forward and inverse kinematic analyses have been performed and the Jacobian matrix is derived. Performance indices such as GPI (global payload index), GCI (global conditioning index), translation and orientation workspaces, and sensitivity are evaluated to find optimal parameters in the design stage. The proposed haptic mechanism has better load capability than those of pre-existing haptic mechanisms due to the fact that motors are fixed at the base. It has also wider orientation workspace mainly due to a RRR type spherical joint.

Multiped walking robot

Abstract: PROBLEM TO BE SOLVED: To provide a multiped walking robot having a freedom in arrangement of a driving system for an articulated part while securing the articulated part with the sufficient power and rigidity. SOLUTION: A body 22 of a robot 21 is provided with first turning shafts 31 having the axial direction parallel to the side surface of the body 22 and turning the legs 24A-24D within the vertical surface against the side surface. The legs 24A-24D are provided with second turning shafts 32 having the axial direction vertical to the side surface of the body 22 and the turning the legs 24A-24D within the parallel surface against the side surface. By constructing first joint parts 28 with these first and second turning shafts 31, 32, the body 22 is secured the degree of freedom in the width direction, so as to adopt a cylindrical motor 30 as a driving system of the revolute joint parts 28 for improving a power performance while improving the rigidity of the revolute joint part 28 by widening the face width of a gear.

Snake-like motions of multibody systems over a rough plane

Abstract: Motions of multibody systems over a rough horizontal plane are investigated. The system under consideration is a linkage consisting of several rigid bodies connected by revolute joints with vertical axes. Control torques are created by actuators installed at the joints. Dry friction forces between the linkage and the plane act upon the system. It is shown that the multibody system can move in an arbitrary direction: lengthwise, sideways, and rotate. Different modes of motion of two-link, three-link, and multilink systems are investigated. The control laws for periodic and wave-like motions are proposed. The displacements and speed of motions are estimated, and optimal parameters are obtained which maximize the average speed. The results of computer simulation are presented. The obtained results are discussed with respect to motions of snakes and other animals, as well as to possible applications to mobile robots.

Method for winding outer revolute coil and winder

Abstract: PROBLEM TO BE SOLVED: To simplify a structure of an outer revolute coil winder and to improve productivity. SOLUTION: The outer revolute coil of the winder 1 is extended at both ends of a wire material 11 from an outermost peripheral layer of the coil. The winder 1 comprises a drum core (winding core) 4 rotating at an axis as a center to wind the material 11, a flyer 43 revolving around the axis, and a second tensioner (wire material locking mechanism) 61 for locking the material 11 supplied from a first tensioner (wire material supplying mechanism) 51 via the core 4. The method for winding the outer revolute coil comprises the steps of rotating the drum core 4 and the flyer 43 in the same direction to wind the wire material 11 supplied from the first tensioner 51 on the core 4, and revolving the flyer 43 around the axis to wind the wire material 11 fed from the second tensioner 61 on the core 4.

Working robot device

Abstract: PROBLEM TO BE SOLVED: To provide a working robot device having a means capable of compensating a work position at a high speed and with high precision in accordance with positional deviation of an object for work when works such as welding, painting and assembly are done by a tip of a robot hand. SOLUTION: A camera and a lighting system are provided on a revolute joint of a robot arm, and image processing is applied to an image photographed by the camera when light is applied on the object for work from the lighting system to compensate a position of the tip of the robot hand based on the results.

Robot and revolute joint device for robot

Abstract: PROBLEM TO BE SOLVED: To provide a robot provided with natural motion and excellent power of expression with a small degree of freedom. SOLUTION: This man-like robot is composed of upper limbs, lower limbs and a body part, and each hip joint connecting the lower limb and the body part has a degree of freedom obtained by a hip-joint yaw shaft, a hip-joint roll shaft and a hip-joint pitch shaft to execute the leg-type movement by two- leg walking of the lower limbs. By arbitrarily setting the offset of the hip-joint yaw shaft to the axial direction of the roll, the influence of the movement of the center of gravity in accompany with the change of the use configuration of the robot is absorbed, and the balance of weight of the upper limbs and the lower limbs can be flexibly adjusted. A waist part is minimized, and the well-proportioned man-type robot is provided. The interference of left and right footplates in the turning of direction can be prevented.

Analytic geometric design of spatial r-r robot manipulators

Abstract: This paper studies the geometric design of spatial two degrees of freedom, open loop robot manipulators with revolute joints that perform tasks, which require the positioning of the end-effector in three spatial locations. This research is important in situations where a robotic manipulator or mechanism with a small number of joint degrees of freedom is designed to perform higher degree of freedom end-effector tasks. The loop-closure geometric equations provide eighteen design equations in eighteen unknowns. Polynomial Elimination techniques are used to solve these equations and obtain the manipulator Denavit and Hartenberg parameters. A sixth order polynomial is obtained in one of the design parameters. Only two of the six roots of the polynomial are real and they correspond to two different robot manipulators that can reach the desired end-effector poses.

Optimum Balancing of Shaking Force and Shaking Moment for Spatial RSSR Mechanism Using Genetic Algorithm.

Abstract: In this paper, we propose a new method, the comprehensive mass distribution method, for an optimum balancing of the shaking force and shaking moment of spatial RSSR mechanism (a spatial four-bar mechanism with two Revolute and two Spherical joints). The method consists of two parts : (1) optimizing the mass distribution of the link itself, and (2) adding weights to the end of the link. A genetic algorithm as an optimization technique is used in this study. Some examples are given, and the results show that the balancing effectiveness of the new method is better than that achieved by the conventional method and the weight of the mechanism is decreased. The shapes of optimized links are obtained using the small element superposing method.

Synthesis of spatial compliances with simple serial elastic mechanisms

Abstract: We address the spatial elastic behavior that can be achieved through the use of a serial chain of revolute and prismatic elastic joints. We show that, regardless of the number of joints or the configuration of the links, there exists a subspace within the 21-dimensional compliance matrix space that cannot be reached by a simple serial elastic mechanism. This restriction is shown to be dual to the restriction on the stiffness matrices associated with simple parallel mechanisms. Although analogous to each other, the two restrictions correspond to different elastic behaviors. A procedure to synthesize any realizable compliance matrix with a simple serial mechanism is provided. The dualities and differences between the parallel and serial cases are discussed.

A planar flexible robotic manipulator

Abstract: Presents the dynamic modelling 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, which is used to discretize the displacements such that the small motion is represented in terms of nodal displacements. Computer simulation results are presented to illustrate this study. The dynamic model becomes necessary for use in future design and control applications.