Passive and Active Closures by Constraining Mechanisms

1999 ◽  
Vol 121 (3) ◽  
pp. 418-424 ◽  
Author(s):  
Tsuneo Yoshikawa
Keyword(s):  
Degrees Of Freedom ◽  
Contact Point ◽  
Three Dimensional ◽  
Internal Force ◽  
Existence Condition ◽  
Passive Force ◽  
Contact Points ◽  
Force Closure ◽  
Grasping And Manipulation ◽  
Form Closure

This paper provides a unified theoretical framework for analytical characterization of grasping and manipulation capability of robotic grippers and hands as well as fixing capability of fixtures and vises. The concept of passive closure and active closure for general constraining mechanisms consisting of fixed and/or articulated constraining limbs is introduced. These concepts are useful for explicitly distinguishing the two kinds of capabilities of the constraining mechanism: Passive closure represents the ability of fixing devices and active closure represents the ability of manipulating devices. Passive closure is further classified into passive form closure and passive force closure. Passive form closure is essentially the same as Reuleaux’s classical form closure and passive force closure is a substantial generalization of classical force closure to the case where articulated constraining limbs exist. Conditions for these closures to hold are studied. After a brief review of conditions for passive form closure, several conditions for passive force closure are given. One outcome is that, under the assumption that the contact points are frictionless and the active contact points are independent, for the existence of passive force closure there must be at least six (three) fixed contact points and one active contact point in the case of three-dimensional (two-dimensional, respectively) space. Finally, a necessary and sufficient condition for active closure is given for the case of frictional point contacts by constraining limbs with enough degrees-of-freedom. This condition consists of a general positioning condition of contact points and the existence condition of nonzero internal force. This condition has a quite natural physical interpretation.

Spatial Kinematic Analysis of Threaded Fastener Assembly

2005 ◽  
Vol 128 (1) ◽  
pp. 116-127 ◽  
Author(s):  
Stephen Wiedmann ◽  
Bob Sturges
Keyword(s):  
Design Space ◽  
Compliant Mechanisms ◽  
Contact Point ◽  
Three Dimensional ◽  
Vertical Movement ◽  
Initial Contact ◽  
Geometric Problem ◽  
Intelligent Sensor ◽  
Contact State ◽  
Contact Points

Compliant mechanisms for rigid part mating exist for prismatic geometries. A few instances are known of mechanisms to assemble screw threads. A comprehensive solution to this essentially geometric problem comprises at least three parts: parametric equations for nut and bolt contact in the critical starting phase of assembly, the possible space of motions between these parts during this phase, and the design space of compliant devices which accomplish the desired motions in the presence of friction and positional uncertainty. This work concentrates on the second part in which the threaded pair is modeled numerically, and contact tests are automated through software. Tessellated solid models were used during three-dimensional collision analysis to enumerate the approximate location of the initial contact point. The advent of a second contact point presented a more constrained contact state. Thus, the bolt is rotated about a vector defined by the initial two contact points until a third contact location was found. By analyzing the depth of intersection of the bolt into the nut as well as the vertical movement of the origin of the bolt reference frame, we determined that there are three types of contacts states present: unstable two-point, quasi-stable two-point, stable three point. The space of possible motions is bounded by these end conditions which will differ in detail depending upon the starting orientations. We investigated all potential orientations which obtain from a discretization of the roll, pitch, and yaw uncertainties, each of which has its own set of contact points. From this exhaustive examination, a full contact state history was determined, which lays the foundation for the design space of either compliant mechanisms or intelligent sensor-rich controls.

Multi-Agent Form Closure Capture of a Generic 2D Polygonal Object Based on Projective Path Planning

2006 ◽  
Author(s):  
Pankaj Sharma ◽  
Anupam Saxena ◽  
Ashish Dutta
Keyword(s):  
Path Planning ◽  
Contact Point ◽  
Point Contact ◽  
Object Boundary ◽  
Actual Object ◽  
Contact Points ◽  
Correct Orientation ◽  
Novel Approach ◽  
Form Closure ◽  
Multi Agent

The study of multi-agent capture and manipulation of an object has been an area of active interest for many researchers. This paper presents a novel approach using Genetic Algorithm to determine the optimal contact points and the total number of agents (mobile robots) required to capture a stationary generic 2D polygonal object. After the goal points are determined the agents then reach their respective goals using a decentralized projective path planning algorithm. Form closure of the object is obtained using the concept of accessibility angle. The object boundary is first expanded and the robots reach the expanded object goal points and then converge on the actual object. This ensures that the agents reach the actual goal points at the same time and have the correct orientation. Frictionless point contact between the object and robots is assumed. The shape of the robot is considered a circle such that it can only apply force in outward radial direction from its center and along the normal to the object boundary at the contact point. Simulations results are presented that prove the effectiveness of the proposed method.

An Algorithm for Force-Closure Grasping of Three-Fingered Hand

2011 ◽  
Vol 250-253 ◽  
pp. 3965-3970
Author(s):  
Qing Yun Liu ◽  
Bo Jiang ◽  
Xiao Liu Yu
Keyword(s):  
Full Rank ◽  
Existence Condition ◽  
Robot Hand ◽  
Relative Location ◽  
Equilibrium Relation ◽  
Geometrical Characteristics ◽  
Contact Points ◽  
Force Closure ◽  
Internal Forces ◽  
Hand Force

On the assumption of FCWF model, the conditions of three-fingered robot hand force-closure grasping are equivalent to grasp matrix be full rank and exist rigorous internal forces. Based on the analysis to the geometrical characteristics of contact points, the existence condition of the frictional sectors is established. By means of studying the relative location relationships between the frictional sector borderlines and their intersections, the existence condition of the concurrent polygon of three internal forces is presented. Taking the equilibrium relation of internal forces into consideration, a general algorithm using vector calculation for force-closure grasping is established. An example is given to illustrate the validity of the algorithm.

Pantograph/Catenary Contact Formulations

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Shubhankar Kulkarni ◽  
Carmine M. Pappalardo ◽  
Ahmed A. Shabana
Keyword(s):  
Degrees Of Freedom ◽  
Contact Point ◽  
Three Dimensional ◽  
Realistic Model ◽  
Wind Loading ◽  
Elastic Contact ◽  
Spin Moment ◽  
Aerodynamic Forces ◽  
Contact Formulation ◽  
Catenary System

In this investigation, the pantograph/catenary contact is examined using two different formulations. The first is an elastic contact formulation that allows for the catenary/panhead separation and for the analysis of the effect of the aerodynamic forces, while the second approach is based on a constraint formulation that does not allow for such a separation by eliminating the freedom of relative translation in two directions at the catenary/panhead contact point. In this study, the catenary system, including the contact and messenger wires, is modeled using the nonlinear finite element (FE) absolute nodal coordinate formulation (ANCF) and flexible multibody system (MBS) algorithms. The generalized aerodynamic forces associated with the ANCF position and gradient coordinates and the pantograph reference coordinates are formulated. The new elastic contact formulation used in this investigation is derived from the constraint-based sliding joint formulation previously proposed by the authors. By using a unilateral penalty force approach, separation of the catenary and panhead is permitted, thereby allowing for better evaluating the response of the pantograph/catenary system to wind loading. In this elastic contact approach, the panhead is assumed to have six degrees-of-freedom with respect to the catenary. The coordinate system at the pantograph/catenary contact point is chosen such that the contact model developed in this study can be used with both the fully parameterized and gradient deficient ANCF elements. In order to develop a more realistic model, the MBS pantograph model is mounted on a detailed three-dimensional MBS rail-vehicle model. The wheel/rail contact is modeled using a nonlinear three-dimensional elastic contact formulation that accounts for the creep forces and spin moment. In order to examine the effect of the external aerodynamic forces on the pantograph/catenary interaction, two scenarios are considered in this investigation. In the first scenario, the crosswind loading is applied on the pantograph components only, while in the second scenario, the aerodynamic forces are applied on the pantograph components and also on the flexible catenary. For the configuration considered in this investigation, it was found that the crosswind assists the uplift force exerted on the pantograph mechanism, increasing the mean contact force value. Numerical results are presented in order to compare between the cases with and without the wind forces.

Three-Dimensional Kinematic Analysis of a Two Actuated Spoke Wheel Robot Based on Its Equivalency to a Serial Manipulator

2008 ◽  
Author(s):  
Ping Ren ◽  
Ya Wang ◽  
Dennis Hong
Keyword(s):  
Inverse Kinematics ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Forward Kinematics ◽  
Future Research ◽  
Ground Contact ◽  
Contact Points ◽  
Prismatic Joints ◽  
Forward Kinematic ◽  
The Relationship

In this paper, the inverse and forward kinematics of a novel mobile robot that utilizes two actuated spoke wheels is presented. Intelligent Mobility Platform with Active Spoke System (IMPASS) is a wheel-leg hybrid robot that can walk in unstructured environments by stretching in or out three independently actuated spokes of each wheel. First, the unique locomotion scheme of IMPASS is introduced. Then the configuration of the robot when each of its two spoke wheels has one spoke in contact with the ground is modeled as a two-branch parallel mechanism with spherical and prismatic joints. An equivalent serial manipulator of the 2-SP mechanism with the same degrees of freedom is proposed to solve for the inverse and forward kinematic problems. The relationship between the physical limits of the stroke of the spokes (effective spoke length) and the limits of its equivalent degree of freedom is established. This approach can also be expanded to deal with the forward and inverse kinematics of other configurations which has more than two ground contact points. Several examples are used to illustrate the method. The results obtained will be used in the future research on the motion planning of IMPASS walking in unstructured environment.

Three‐dimensional discrete element simulation for granular materials

2006 ◽  
Vol 23 (7) ◽  
pp. 749-770 ◽  
Author(s):  
Dawei Zhao ◽  
Erfan G. Nezami ◽  
Youssef M.A. Hashash ◽  
Jamshid Ghaboussi
Keyword(s):  
Search Algorithm ◽  
Contact Point ◽  
Three Dimensional ◽  
Engineering Application ◽  
Discrete Element ◽  
Content Type ◽  
Polyhedral Particles ◽  
Contact Points ◽  
Neighbor Search ◽  
Force Calculation

PurposeDevelop a new three‐dimensional discrete element code (BLOKS3D) for efficient simulation of polyhedral particles of any size. The paper describes efficient algorithms for the most important ingredients of a discrete element code.Design/methodology/approachNew algorithms are presented for contact resolution and detection (including neighbor search and contact detection sections), contact point and force detection, and contact damping. In contact resolution and detection, a new neighbor search algorithm called TLS is described. Each contact is modeled with multiple contact points. A non‐linear force‐displacement relationship is suggested for contact force calculation and a dual‐criterion is employed for contact damping. The performance of the algorithm is compared to those currently available in the literature.FindingsThe algorithms are proven to significantly improve the analysis speed. A series of examples are presented to demonstrate and evaluate the performance of the proposed algorithms and the overall discrete element method (DEM) code.Originality/valueLong computational times required to simulate large numbers of particles have been a major hindering factor in extensive application of DEM in many engineering applications. This paper describes an effort to enhance the available algorithms and further the engineering application of DEM.

Mobility and Geometrical Analysis of a Two Actuated Spoke Wheel Robot Modeled as a Mechanism With Variable Topology

2008 ◽  
Author(s):  
Ya Wang ◽  
Ping Ren ◽  
Dennis Hong
Keyword(s):  
Degrees Of Freedom ◽  
Contact Point ◽  
Future Research ◽  
Coordinate Systems ◽  
Line Geometry ◽  
Geometrical Analysis ◽  
Constraint Equations ◽  
Contact Points ◽  
Different Types ◽  
Variable Topology

In this paper, the mobility and geometrical analysis of a novel mobile robot that utilizes two actuated spoke wheels is presented. Intelligent Mobility Platform with Active Spoke System (IMPASS) is a wheel-leg hybrid robot that can walk in unstructured environments by stretching in or out three independently actuated spokes of each wheel. First, the unique locomotion scheme of IMPASS is introduced and the definitions of the coordinate systems are developed to describe the kinematic configurations. Since this robot is capable of utilizing its metamorphic configurations to implement different types of motion, its topology structures are classified into different groups based on the cases of ground contact points. For each contact point case, the mobility analysis is performed using the conventional Gru¨bler and Kutzbach criterion. However, as for the cases in which the structure is overconstrained, the Modified Gru¨bler and Kutzbach criterion based on reciprocal screws are implemented to obtain the correct number of degrees of freedom. Line geometry is adopted to assist in the process. Additionally, the geometrical constraint equations of the robot are derived. The results in this work lay the foundation of the future research on inverse and forward kinematics, instantaneous kinematics, dynamics analysis and motion planning of this unique locomotion robot.

scholarly journals Beyond Soft Hands: Efficient Grasping With Non-Anthropomorphic Soft Grippers

2021 ◽  
Vol 8 ◽  
Author(s):  
Yufei Hao ◽  
Yon Visell
Keyword(s):  
Degrees Of Freedom ◽  
Robotic Systems ◽  
Human Hand ◽  
Detailed Knowledge ◽  
New Techniques ◽  
Research Directions ◽  
Challenging Tasks ◽  
Force Closure ◽  
Grasping And Manipulation ◽  
And Control

Grasping and manipulation are challenging tasks that are nonetheless critical for many robotic systems and applications. A century ago, robots were conceived as humanoid automata. While conceptual at the time, this viewpoint remains influential today. Many robotic grippers have been inspired by the dexterity and functionality of the prehensile human hand. However, multi-fingered grippers that emulate the hand often integrate many kinematic degrees-of-freedom, and thus complex mechanisms, which must be controlled in order to grasp and manipulate objects. Soft fingers can facilitate grasping through intrinsic compliance, enabling them to conform to diverse objects. However, as with conventional fingered grippers, grasping via soft fingers involves challenges in perception, computation, and control, because fingers must be placed so as to achieve force closure, which depends on the shape and pose of the object. Emerging soft robotics research on non-anthropomorphic grippers has yielded new techniques that can circumvent fundamental challenges associated with grasping via fingered grippers. Common to many non-anthropomorphic soft grippers are mechanisms for morphological deformation or adhesion that simplify the grasping of diverse objects in different poses, without detailed knowledge of the object geometry. These advantages may allow robots to be used in challenging applications, such as logistics or rapid manufacturing, with lower cost and complexity. In this perspective, we examine challenges associated with grasping via anthropomorphic grippers. We describe emerging soft, non-anthropomorphic grasping methods, and how they may reduce grasping complexities. We conclude by proposing several research directions that could expand the capabilities of robotic systems utilizing non-anthropomorphic grippers.

scholarly journals Climbing parrots achieve pitch stability using forces and free moments produced by axial-appendicular couples

2021 ◽  
Author(s):  
Lindsey L. Reader ◽  
David R. Carrier ◽  
Franz Goller ◽  
Michael R. Isaacs ◽  
Alexis Moore Crisp ◽  
...  
Keyword(s):  
Contact Point ◽  
Natural Habitat ◽  
Three Dimensional ◽  
Large Radius ◽  
Pitching Moment ◽  
Free Moments ◽  
Contact Points ◽  
Multiple Contacts ◽  
Discrete Contact ◽  
Free Moment

During vertical climbing, the gravitational moment tends to pitch the animal's head away from the climbing surface and this may be countered by 1) applying a correcting torque at a discrete contact point, or 2) applying opposing horizontal forces at separate contact points to produce a free moment. We tested these potential strategies in small parrots with an experimental climbing apparatus imitating the fine branches and vines of their natural habitat. The birds climbed on a vertical ladder with four instrumented rungs that measured three-dimensional force and torque, representing the first measurements of multiple contacts from a climbing bird. The parrots ascend primarily by pulling themselves upward using the beak and feet. They resist the gravitational pitching moment with a free moment produced by horizontal force couples between the beak and feet during the first third of the stride and the tail and feet during the last third of the stride. The reaction torque from individual rungs did not counter, but exacerbated the gravitational pitching moment, which was countered entirely by the free moment. Possible climbing limitations were explored using two different rung radii, each with low and high friction surfaces. Rung torque was limited in the large-radius, low-friction condition, however, rung condition did not significantly influence free moments produced. These findings have implications for our understanding of avian locomotor modules (i.e., coordinated actions of the head-neck, hindlimbs, and tail), the use of force couples in vertical locomotion, and the evolution of associated structures.

Influence of rail flexibility in a wheel/rail wear prediction model

2016 ◽  
Vol 231 (1) ◽  
pp. 57-74 ◽  
Author(s):  
Javier F Aceituno ◽  
Pu Wang ◽  
Liang Wang ◽  
Ahmed A Shabana
Keyword(s):  
Prediction Model ◽  
Rigid Body ◽  
Contact Point ◽  
Three Dimensional ◽  
Contact Forces ◽  
Wear Model ◽  
Material Loss ◽  
Wear Prediction ◽  
Contact Points ◽  
Rail Wear

The aim of this paper is to study the influence of rail flexibility when a wheel/rail wear prediction model that computes the material loss based on an energy approach is used. The wheel/rail wear model used in this investigation is a simplified combined wear hypothesis that is based on the frictional energy loss in the contact patch. In order to account for wear and its distribution in a profiled wheel surface, the contact forces, creepages and location of the wheel/rail contact points are first calculated using a fully nonlinear multibody system (MBS) and three-dimensional contact formulations that account for the rail flexibility. The contact forces, creepages and contact point locations are defined as nonlinear functions of the rail deformations. These nonlinear expressions are used in the wear calculations. The wear distribution is considered to be proportional to the normal force in the contact area. Numerical simulations are first performed in order to compare between the results obtained using the simplified wheel/rail wear model and the results obtained using Archard’s wear model with a focus on sliding when the track is modeled as a rigid body. This simplified wear model is then used in the simulation of the MBS vehicle model in the case of a flexible body track, in which the rails are modeled using the finite element floating frame of reference approach and modal reduction techniques. The effect of the rail deformation on the wear results are examined by comparing these results with those obtained using the rigid-body track model.

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