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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
research-article  
Yundou Xu, Liangliang Chen, Wenlan Liu, Jiantao Yao, Jialong Zhu and Yongsheng Zhao
J. Mechanisms Robotics   doi: 10.1115/1.4039341
In the deployable mechanism for a conventional truss antenna, the nodes cannot be adjusted to be uniform in atti-tude. To solve this problem, a method of adding constraint chains is proposed based on the reciprocal screw theory. By performing type synthesis of the deployable mechanisms for the truss antenna, a novel deployable mechanism is developed that not only enables complete folding and unfolding but also allows the attitude of the nodes to be made uniform. First, according to the unit division of the antenna reflection surface and the characteristic motions of the nodes, constraint chains that can be added between two adjacent nodes are synthesized based on the recipro-cal screw theory. Second, to improve the overall rigidity of the mechanism, a series of basic developable unit mech-anisms is obtained by adding virtual constraint chains, again based on the reciprocal screw theory. Next, a method of dividing the minimum combination unit of the curved-surface antenna mechanism is proposed. The design of the minimum combination unit mechanism is optimized, such that the attitude of all nodes in the final folded state can be made consistent. Finally, the feasibility of the optimized minimum combination unit mechanism is verified by simulation analysis. The proposed method for type synthesis provides a new approach to the design of deployable mechanisms for truss antennas, and novel deployable mechanisms for the curved-surface truss antenna with better performance are obtained.
TOPICS: Trusses (Building), Chain, Screws, Design, Simulation analysis, Stiffness, Reflection
research-article  
Victor Prost, Kathryn M. Olesnavage, Brett Johnson, Matthew Major and Amos G. Winter, V
J. Mechanisms Robotics   doi: 10.1115/1.4039342
An experimental prosthetic foot intended for evaluating a novel design objective is presented. This objective, called the Lower Leg Trajectory Error (LLTE), enables the optimization of passive prosthetic feet by modeling the trajectory of the shank during single support for a given prosthetic foot and selecting design variables that minimize the error between this trajectory and able-bodied kinematics. A light-weight, fully-characterized test foot with variable ankle joint stiffness was designed to evaluate the LLTE. The test foot can replicate the range of motion of a physiological ankle over a range of different ankle joint stiffnesses. The test foot consists of a rotational ankle joint machined from acetal resin, interchangeable U-shaped nylon springs that range from 1.5 Nm/deg to 24 Nm/deg, and a flexible nylon forefoot with a bending stiffness of 16 Nm^2 . The U-shaped springs were designed to support a constant moment along their length to maximize strain energy density; this feature was critical in creating a high stiffness and high-range of motion ankle. The design performed as predicted during mechanical and in vivo testing, and its modularity allowed us to rapidly vary the ankle joint stiffness. Qualitative feedback from preliminary testing showed that this design is ready for use in larger scale clinical trials to further evaluate the use of the LLTE as an optimization objective for passive prosthetic feet.
TOPICS: Trajectories (Physics), Design, Optimization, Testing, Artificial limbs, Errors, Springs, Stiffness, Nylon fabrics, Physiology, Feedback, Resins, Modeling, Density, Weight (Mass), Kinematics
research-article  
V.N. Murthy Arelekatti and Amos G. Winter, V
J. Mechanisms Robotics   doi: 10.1115/1.4039222
An estimated 230,000 above-knee amputees in India are currently in need of prosthetic devices, a majority of them facing severe socio-economic constraints. However, only a few passive prosthetic knee devices in the market have been designed for facilitation of normative gait kinematics and for meeting the specific daily life needs of above-knee amputees in the developing world. Based on the results of our past studies, this paper establishes a framework for designing a potentially low-cost, fully passive prosthetic knee device, which aims to facilitate able-bodied kinematics at a low metabolic cost. Based on a comprehensive set of functional requirements, we present an early prototype mechanism for the prosthetic knee joint. The mechanism is implemented using two functional modules: an automatic early stance lock for stability and a differential friction damping system for late stance and swing control. For preliminary validation of the knee mechanism, we carried out a field trial on four above-knee amputees in India, which showed satisfactory performance of the early stance lock. The prototype enabled smooth stance to swing transition by timely initiation of late stance flexion. Possible methods of incorporating an additional spring module for further refinement of the design are also discussed, which can enable flexion-extension during early-stance phase of the gait cycle and further reduce the metabolic energy expenditure of the user.
TOPICS: Design, Artificial limbs, Knee, Kinematics, Locks (Waterways), Engineering prototypes, Damping, Stability, Friction, Cycles, Springs, Prostheses, Developing nations
research-article  
Genliang Chen, Zhuang Zhang and Hao Wang
J. Mechanisms Robotics   doi: 10.1115/1.4039223
This paper presents a general discretization-based approach to the large de?ection problems of spatial ?exible links in compliant mechanisms. Based on the principal axes decomposition of structural compliance matrices, a particular type of elements which relate to spatial 6-degree-of-freedom (DOF) serial mechanisms with passive elastic joints, is developed to characterize the force-de?ection behavior of the discretized small segments. Hence, the large de?ection problems of spatial ?exible rods can be transformed to the determination of static equilibrium con?gurations of their equivalent hyper-redundant mechanisms. The main advantage of the proposed method comes from the use of robot kinematics/statics, rather than structural mechanics. Thus, a closed-form solution to the system overall stiffness can be derived straightforwardly for ef?cient gradient-based searching algorithms. Two kinds of typical equilibrium problems are intensively discussed and the correctness has been veri?ed by means of physical experiments. In addition, a 2-DOF planar compliant parallel manipulator is provided as a case study to demonstrate the potential applications.
TOPICS: Deflection, Rods, Equilibrium (Physics), Algorithms, Statics, Structural mechanics, Compliance, Stiffness, Compliant mechanisms, Manipulators, Robot kinematics, Structural analysis
research-article  
Xianwen Kong, Xiuyun He and Duanling Li
J. Mechanisms Robotics   doi: 10.1115/1.4039224
This paper deals with a 6R single-loop overconstrained spatial mechanism that has two pairs of revolute joints with intersecting axes and one pair of revolute joints with parallel axes. The 6R mechanism is first constructed from an isosceles triangle and a pair of identical circles. The kinematic analysis of the 6R mechanism is then dealt with using a dual quaternion approach. The analysis shows that the 6R mechanism usually has two solutions to the kinematic analysis for a given input and may have two circuits (closure modes or branches) with one or two pairs of full-turn revolute joints. In two configurations in each circuit of the 6R mechanism, the axes of four revolute joints are coplanar, and the axes of the other two revolute joints are perpendicular to the plane defined by the above four revolute joints. Considering that from one configuration of the 6R mechanism, one can obtain another configuration of the mechanism by simply renumbering the joints, the concept of two-faced mechanism is introduced. The formulas for the analysis of plane symmetric spatial triangle is also presented in this paper. These formulas will be useful for the analysis of multi-loop overconstrained mechanisms involving plane symmetric spatial RRR triads.
TOPICS: Circuits, Kinematic analysis
Technical Brief  
Genliang Chen, Hao Wang, Zhongqin Lin and Xinmin Lai
J. Mechanisms Robotics   doi: 10.1115/1.4039218
The theory of screws plays a fundamental role in the ?eld of mechanisms and robotics. Based on the rank-one decomposition of positive semide?nite matrices, this paper presents a new algorithm to identify the canonical basis of high-order screw systems. Using the proposed approach, a screw system can be decomposed into the direct sum of two subsystems, which are referred to as the general and special subsystems, respectively. By a particular choice of the general subsystem, the canonical basis of the original system can be obtained by the direct combination of the subsystems' principal elements. In the proposed decomposition, not only the canonical form of the screw system, but also the corresponding distribution of all those possible base elements can be determined in a straightforward manner.
TOPICS: Screws, Algorithms, Robotics
Editorial  
Andreas Mueller, Andrew P. Murray and Venkat Krovi
J. Mechanisms Robotics   doi: 10.1115/1.4039203
The Mechanisms and Robotics Conference has traditionally provided a vigorous and stimulating international forum for the exchange of technical and scientific information on the theory and practice of mechanical systems. The topical coverage has span areas central to mechanical systems including design (novel mechanisms and robots, synthesis); analysis (kinematics, dynamics, computational approaches, software systems), applications (from micro air vehicles, modular robotics, origami applications, medical robotics, to exoskeleton-assistive systems) and educational practices. This 4th IDETC Special Issue, containing 18 papers from researchers in five countries on three continents, seeks to capture the exciting research, emerging topics and latest results from the 41st ASME Mechanisms and Robotics (M&R) conference in archival format. We hope readers will find this Special Issue interesting and informative as we have attempted to capture the richness and diversity across the various symposia of M&R 2017. As our editorial work comes to an end, we would like to express our deep appreciation to all the authors who supported this Special Issue by contributing papers. We are also grateful to all the reviewers for their service and commitment to the journal through rigorous reviews, timely response to the tight schedule, and above all, insightful and constructive comments that helped shape the final outcome. Last but not least, our sincere appreciation goes to the Editor, Professor Vijay Kumar, for his vision, support, and valuable advice throughout this process.
TOPICS: Robotics, Vehicles, Computer software, Shapes, Biomedicine, Exoskeleton devices, Kinematics, Dynamics (Mechanics), Robots, Engineering teachers, Design, Performance
research-article  
Gregory S. Chirikjian, Robert Mahony, Sipu Ruan and Jochen Trumpf
J. Mechanisms Robotics   doi: 10.1115/1.4039121
For more than a century, rigid-body displacements have been viewed as affine transformations described as homogeneous transformation matrices wherein the linear part is a rotation matrix. In group-theoretic terms, this classical description makes rigid-body motions a semi-direct product. The distinction between a rigid-body displacement of Euclidean space and a change in pose from one reference frame to another is usually not articulated well in the literature. Here we show that, remarkably, when changes in pose are viewed from a space-fixed reference frame, the space of pose changes can be endowed with a direct product group structure, which is different than the semi-direct product structure of the space of motions. We then show how this new perspective can be applied more naturally to problems such as monitoring the state of aerial vehicles from the ground, or the cameras in a humanoid robot observing motions of its hands.
TOPICS: Rotation, Aircraft, Displacement, Humanoid robots
research-article  
Yan Xie, Jingjun Yu and Hongzhe Zhao
J. Mechanisms Robotics   doi: 10.1115/1.4039065
Compliant universal joints have been widely employed in high-precision fields due to plenty of good performance. However, the stiffness characteristics, as the most important consideration for compliant mechanisms, are rarely involved. In this paper, a deterministic design for a constraint-based compliant parallel universal joint with constant rotational stiffness is presented. First, a constant stiffness realization principle is proposed by combination of the freedom and constraint topology (FACT) method and beam constraint model (BCM) to establish a mapping relationship between stiffness characteristics and topology configurations. A parallel universal joint topology is generated by the constant stiffness realization principle. Then the analytical stiffness model of the universal joint with some permissible approximations is formulated based on the BCM, and geometrical prerequisites are derived to achieve the desired constant rotational stiffness. After that, finite element analysis (FEA), experimental testing and detailed stiffness analysis are carried out. It turns out that the rotational stiffness of the universal joint can keep constant with arbitrary azimuth angles even if the rotational angle reaches up to ±5°. Meanwhile, the acceptable relative errors of rotational stiffness are within 0.53% compared with FEA results and 2.6% compared with experimental results, which indicates the accuracy of the theoretical stiffness model and further implies the feasibility of constant stiffness realization principle on guiding the universal joint design.
TOPICS: Universal joints, Design, Stiffness, Topology, Finite element analysis, Testing, Approximation, Errors, Compliant mechanisms
research-article  
Arkadeep Narayan Chaudhury and Ashitava Ghosal
J. Mechanisms Robotics   doi: 10.1115/1.4039001
Multi-fingered hands have the capability of dexterous manipulation of grasped objects and thus significantly increase the capabilities of a robot equipped with multi-fingered hands. Inspired by a multi-jointed human finger and the hand, we propose a six-degree-of-freedom model of a three-fingered robotic hand as a parallel manipulator. Two kinds of contact, namely point contact with friction and rolling without slipping between the finger tips and the grasped object, are considered. The point contact with friction is modeled as a three-degree-of-freedom spherical joint and for rolling without slipping, we use the resultant non-holonomic constraints between the grasped object and the fingers. With realistic limits on the joints in the fingers and dimensions of finger segments, we obtain the well-conditioned workspace of the parallel manipulator using a Monte Carlo based method. Additionally, we present two new general results -- it is shown that maximum position and orientation workspace is obtained when the cross sectional area of the of the grasped object is approximately equal to the area of the palm of the hand and when rolling without slipping is allowed the size of of the well-conditioned workspace is significantly larger (~ 1.2 - 1.5 times). We also present representative experiments of manipulation by a human hand show that the experimental results are in reasonable agreement with those obtained from simulations.
TOPICS: Friction, Dimensions, Robots, Simulation, Engineering simulation, End effectors, Manipulators, Monte Carlo methods
research-article  
Pablo C. Lopez-Custodio, Jian S Dai and José M. Rico
J. Mechanisms Robotics   doi: 10.1115/1.4039002
This paper for the first time investigates a family of plane-symmetric Bricard mechanisms by means of two generated toroids. By means of their intersection, a set of special Bricard mechanisms with various branches of reconfiguration are designed. An analysis of the intersection of these two toroids reveals the presence of coincident conical singularities which lead to the design of plane-symmetric linkages that evolve to spherical 4R mechanisms. By examining the tangents to the curves of intersection at the conical singularities it is found that the mechanism can be reconfigured between the two possible branches of spherical 4R motion without disassembling it and without needing the usual special configuration connecting the branches. The study of tangent intersections between concentric singular toroids also reveals the presence of isolated points in the intersection which suggests that some linkages satisfying the Bricard plane-symmetry conditions are actually structures with zero finite degrees of freedom but with higher instantaneous mobility. This paper is the second part of a paper submitted in parallel by the authors in which the method is applied to the line-symmetric case.
TOPICS: Linkages, Degrees of freedom, Design, Mechanical admittance
research-article  
Pablo C. Lopez-Custodio, Jian S Dai and José M. Rico
J. Mechanisms Robotics   doi: 10.1115/1.4038981
This paper for the first time investigates a family of line-symmetric Bricard mechanisms by means of two generated toroids and reveals their intersection that leads to a set of special Bricard mechanisms with various branches of reconfiguration. The discovery is made in the concentric toroid-toroid intersection. By manipulating the construction parameters of the toroids any possible bifurcation point is explored. This leads to the common bi-tangent planes that present singularities in the intersection set. The study reveals the presence of Villarceau and secondary circles in the toroids intersection. Therefore, a way to reconfigure the Bricard linkage to two different types of Bennett mechanism is uncovered. Further a linkage with two Bricard and two Bennett motion branches is explored. In addition, the paper reveals the Altmann linkage as a member of the family of special line-symmetric Bricard linkages studied in this paper.
TOPICS: Construction, Linkages, Bifurcation
research-article  
Carlotta Mummolo, William Peng, Carlos Gonzalez and Joo H. Kim
J. Mechanisms Robotics   doi: 10.1115/1.4038978
A theoretical-algorithmic framework for the construction of balance stability boundaries of biped robots with multiple contacts with the environment is proposed and implemented on a robotic platform. Comprehensive and univocal definitions of the states of balance of a generic legged system are introduced with respect to the system's contact configuration. Theoretical models of joint-space and center of mass (COM)-space dynamics under multiple contacts, distribution of contact wrenches, and robotic system parameters are established for their integration into a nonlinear programming problem. In the proposed approach, the balance stability capabilities of a biped robot are quantified by a partition of the state space of COM position and velocity. The boundary of such a partition provides a threshold between balanced and falling states of the biped robot with respect to a specified contact configuration. A COM state outside of the stability boundary represents the sufficient condition for falling, from which a change in the system's contact is inevitable. Through the calculated stability boundaries, the effects of different contact configurations (single support and double support with different step lengths) on the robot's balance stability capabilities can be quantitatively evaluated. In addition, the balance characteristics of the experimental walking trajectories of the robot with various speeds are analyzed in relation to their respective stability boundaries. The proposed framework provides a contact-dependent balance stability criterion for a given system, which can be used to improve the design and control of walking robots.
TOPICS: Stability, Robots, Robotics, Nonlinear programming, Dynamics (Mechanics), Construction, Center of mass, Design
research-article  
Xinsheng Zhang, Pablo Lopez-Custodio and Jian S Dai
J. Mechanisms Robotics   doi: 10.1115/1.4038218
The kinematic chains that generate the planar motion group with the prismatic-joint direction always perpendicular with the revolute-joint axis in each chain, have shown their effectiveness and manifested the charm in type synthesis and mechanism analysis in parallel mechanisms. This paper extends the traditional PRP kinematic chain generating the planar motion group to a relatively general case, in which one of the prismatic joint-direction is not necessarily perpendicular with the revolute-joint axis, leading to the discovery of a helical motion with a variable pitch in this kinematic chain. The displacements of such PRP chain generate a submanifold of the Schoenflies motions subgroup. This paper investigates for the first time this type of motion. Following the extraction of a helical motion from this PRP kinematic chain, this paper investigates the bifurcated motion in a 3-PUP parallel mechanism by changing the active geometrical constraint in its configuration space. The method used in this contribution simplifies the analysis of such parallel mechanism without resorting to in-depth geometry analysis and screw theory. Further, a parallel platform which can generate this PRP type of motion is presented. An experimental test is set up based on a 3D printed prototype of the 3-PUP parallel mechanism to detect the inconspicuous translation of the helical motion.
TOPICS: Parallel mechanisms, Kinematic chains, Chain, Geometry, Screws, Engineering prototypes

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