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Accepted Manuscripts

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research-article  
Pei Jiang, Shuihua Huang, Ji Xiang and Michael Z. Q. Chen
J. Mechanisms Robotics   doi: 10.1115/1.4036569
Kinematic control of manipulators with joint physical constraints, such as joint limits and joint velocity limits, has received extensive studies. Many studies resolved this problem at the second-order kinematic level, which may suffer from the self-motion instability in the presence of persistent self-motion or unboundedness of joint velocity. In this paper, a unified approach is proposed to control a manipulator with both joint limits and joint velocity limits at the second-order kinematic level. By combining the weighted least-norm (WLN) solution in the revised joint space and the clamping weighted least-norm (CWLN) solution in the real joint space, the unified approach ensures the joint limits and joint velocity limits at the same time. A time-variant clamping factor is incorporated into the unified approach to suppress the self-motion when the joint velocity diverges or the end-effector stops, which improves the stability of self-motion. The simulations in contrast to the traditional dynamical feedback control method and the recent minimum-acceleration-norm (MAN) scheme have been made to demonstrate the advantages of the unified approach.
TOPICS: Manipulators, Kinematics, Stability, Simulation, Engineering simulation, End effectors, Feedback
research-article  
Midhun S Menon, V C Ravi and Ashitava Ghosal
J. Mechanisms Robotics   doi: 10.1115/1.4036571
Hyper-redundant snake-like serial robots are of great interest due to their application in search and rescue during disaster relief in highly cluttered environments and recently in the field of medical robotics. A key feature of these robots is the presence of a large number of redundant actuated joints and the associated well-known challenge of motion planning. This problem is even more acute in the presence of obstacles. Obstacle avoidance for point bodies, non-redundant serial robots with a few links and joints and wheeled mobile robots has been extensively studied and several mature implementations are available. However, obstacle avoidance for hyper-redundant snake-like robots and other extended articulated bodies is less studied and is still evolving. This paper presents a novel optimization algorithm, derived using calculus of variation, for the motion planning of a hyper-redundant robot where the motion of one end (head) is an arbitrary desired path. The algorithm computes the motion of all the joints in the hyper-redundant robot in a way such that all its links avoid all obstacles present in the environment. The algorithm is purely geometric in nature and it is shown that the motion in free space and in the vicinity of obstacles appears to be more natural. The paper presents the general theoretical development and numerical simulations results. It also presents validating results from experiments with a 12-degree-of-freedom planar hyper-redundant robot moving in a known obstacle field.
TOPICS: Robots, Path planning, Algorithms, Robotics, Mobile robots, Optimization algorithms, Biomedicine, Emergency management, Vacuum, Computer simulation
research-article  
Aylin Gazi and Koray Korkmaz
J. Mechanisms Robotics   doi: 10.1115/1.4036570
Retractable Plate Structure (RPS) is a family of structures that is a set of cover plates connected by revolute joints. There exists wide range of possibilities related with these structures in architecture. Configuring the suitable shape of rigid plates that are able to be enclosed without any gaps or overlaps in both closed and open configurations and eliminating the possibility of contact between the plates during the deployment have been the most important issues in RPS design process. Many researchers have tried to find the most suitable shape by using kinematical or empirical analysis so far. This study presents a novel approach to find the suitable shape of the plates and their assembly order without any kinematical or empirical analysis. This approach is benefited from the 1-uniform mathematical tessellation technique that gives the possibilities of covering plate combinations without any gaps or overlaps in terms of regular polygons. In the light of this technique, the shape of the plates are determined as regular polygons and two conditions are introduced to form RPS in which regular polygonal plates are connected by only revolute joints. It should be noted that these plates are not allowed to become overlapped during deployment and form gaps in closed configuration. Additionally, this study aims to reach a single degree of freedom (Dof) RPS. It present a systematic method to convert multi DoF RPS into single DoF RPS by using the similarity between graph theory and the duality of tessellation.
TOPICS: Reactor protection systems, Plates (structures), Shapes, Manufacturing, Degrees of freedom, Design
Technical Brief  
Yu-Heng Ou and Dar-Zen Chen
J. Mechanisms Robotics   doi: 10.1115/1.4036515
A methodology to develop tension springs with zero-free-length (ZFL) characteristics is presented, and the configurations for placing the springs precisely on the manipulators are introduced. A spring-string arrangement installed between two separate links of a serial-type manipulator is employed and is divided into three regions for mounting, tensioning, and placing springs. The springs can develop ZFL characteristics if adequate length is ensured for mounting the springs. To shorten the length for placing springs, a reference length acquired from the link configurations is utilized. The minimization of the placing length can therefore be described clearly. Because the overextended springs and links resulting from the longish mounting length shroud the workspace of the other links, the springs are reorganized using pulleys and wire winding configurations to shorten the mounting length. The springs can then be arranged in alignment on the links. As achieved with this additional arrangement, comprehensive spring configurations on the manipulators can be shown. Two examples are presented after deriving the spring configurations for ZFL characteristics and the configurations with wire winding, respectively.
TOPICS: Springs, Tension, Manipulators, Wire, Winding (process), String, Pulleys
research-article  
Lingmin Xu, Qinchuan Li, Ningbin Zhang and Qiaohong Chen
J. Mechanisms Robotics   doi: 10.1115/1.4036517
Parallel manipulators with redundant actuation are attracting increasing research interest because they have demonstrated improved stiffness and fewer singularities. This paper proposes a new redundantly actuated parallel manipulator that has three degrees of freedom (DOFs) and four limbs. The proposed manipulator is a 2UPR-2PRU parallel manipulator (where P represents an actuated prismatic joint, R represents a revolute joint, and U represents a universal joint) that is actuated using four prismatic joints; two of these joints are mounted on the base to reduce the movable mass. Mobility analysis shows that the moving platform has two rotational DOFs and one translational DOF. First, the inverse displacement solution, velocity, and singularity analyses are discussed. Next, the local transmission index and the good transmission workspace are used to evaluate the motion/force transmissibility of the 2UPR-2PRU parallel manipulator. Finally, the parameter-finiteness normalization method is used to produce an optimal design that considers the good transmission workspace. It is thus shown that the motion/force transmission of the proposed manipulator is improved by optimizing the link parameters.
TOPICS: Kinematics, Design, Manipulators, Stiffness, Mechanical admittance, Displacement, Universal joints, Degrees of freedom
Errata  
Paul M. Loschak, Alperen Degirmenci, Yaroslav Tenzer, Cory M. Tschabrunn, Elad Anter and Robert D. Howe
J. Mechanisms Robotics   doi: 10.1115/1.4036457
The incorrect version of Fig 15 was published. Some control flow boxes are missing text. The correct diagram is included in PDF form.
research-article  
Marco Salerno, Amir Firouzeh and Jamie Paik
J. Mechanisms Robotics   doi: 10.1115/1.4036425
Thin foldable origami mechanisms allow reconfiguration of normally complex structures with a large volumetric change, low cost and versatility; however, there is rarely a systematic way to make them autonomously actuated due to the lack of low-profile actuators. The required actuation contradicts engineering design parameters between actuation range, actuation speed and back-drivability. This paper presents a novel approach to a fast and controllable folding by embedding the actuation system in a nominally flat platform. The design, fabrication and modelling of an electromagnetic actuation system are reported; a 1.7 mm thick single degree-of-freedom (DoF) foldable parallel structure reaching an elevation of 13 mm has been used as a proof-of-concept for the proposed methodology. We also report on the extensive test results that validate the mechanical model in terms of the loaded and unloaded speed, the blocked force, and the range of actuation.
TOPICS: Robots, Manufacturing, Engineering design, Degrees of freedom, Actuators, Design, Modeling
research-article  
Jean-Michel Boucher and Lionel Birglen
J. Mechanisms Robotics   doi: 10.1115/1.4036220
In this paper, the performance augmentation of underactuated fingers through additional actuators is presented and discussed. Underactuated, a.k.a. self-adaptive, fingers typically only relies on a single actuator for a given number of output degrees of freedom, generally equal to the number of phalanges. Therefore, once the finger is mechanically designed and built, there is little that can be done using control algorithms to change the behaviour of this finger, whether it is during the closing motion or the grasp. In this work, the authors propose to use more than one actuator to drive underactuated fingers in order to improve the typical metrics used to measure their grasp performances (such as stiffness, stability, etc.) In order to quantify these improvements, two different scenarios are presented and discussed. The first one analyzes the impact of adding actuators along the transmission linkage of a classical architecture while the second focuses on a finger with a dual-drive actuation system for which both actuators are located inside the palm. A general kinetostatic analysis is first carried out and adapted to cover the case of underactuated fingers using more than one actuator. Typical performance indices are subsequently presented and optimizations are performed to compare the best designs achievable depending on the number of actuators.
TOPICS: Stability, Linkages, Degrees of freedom, Actuators, Stiffness, Control algorithms
research-article  
Jun Wu, Xiangyun Li, Qiaode Jeffrey Ge, Feng Gao and Xueyin Liu
J. Mechanisms Robotics   doi: 10.1115/1.4036222
This paper examines the problem of geometric constraints acquisition of a planar motion through a line-geometric ap- proach. In previous work, we have investigated the problem of identifying point-geometric constraints associated with a motion task which is given in a parametric or discrete form. In this paper, we seek to extend the point-centric approach to the line-centric approach. The extracted geometric con- straints can be used directly for determining the type and di- mensions of a physical device such as mechanical linkage that generates this constrained motion task.
TOPICS: Kinematics, Linkages
research-article  
Mark Naves, Dannis Brouwer and Ronald G. K. M. Aarts
J. Mechanisms Robotics   doi: 10.1115/1.4036223
Large stroke flexure mechanisms inherently lose stiffness in supporting directions when deflected. A systematic approach to synthesize such hinges is currently lacking. In this paper a new building block based spatial topology optimization method is presented for optimizing large stroke flexure hinges. This method consists of a layout variation strategy based on a building block approach combined with a shape optimization to obtain the optimal design tuned for a specific application. A derivative free shape optimization method is adapted to include multiple system boundaries and constraints to optimize high complexity flexure mechanisms in a broad solution space. To obtain the optimal layout, three predefined 3-D “building blocks” are proposed which are consecutively combined to find the best layout with respect to specific design criteria. More specifically, this new method is used to optimize a flexure hinge aimed at maximizing the frequency of the first unwanted vibration mode. The optimized topology shows an increase in frequency of a factor ten with respect to the customary three flexure cross hinge, which represents a huge improvement in performance. The numerically predicted natural frequencies and mode shapes have been verified experimentally.
TOPICS: Blocks (Building materials), Hinges, Bending (Stress), Topology, Flexure mechanisms, Shape optimization, Design, Optimization, Vibration, Stiffness, Mode shapes
research-article  
Tzu-Yu Tseng, Yi-Jia Lin, Wei-Chun Hsu, Li-Fong Lin and Chin-Hsing Kuo
J. Mechanisms Robotics   doi: 10.1115/1.4036218
In lower-limb rehabilitation, there is a specific group of patients that can perform voluntary muscle contraction and visible limb movement provided that the weight of his/her leg is fully supported by a physical therapist. In addition, this therapist is necessary in guiding the patient to switch between hip-only and knee-only motions for training specific muscles effectively. These clinic needs have motivated us to devise a novel reconfigurable gravity-balanced mechanism for tackling with the clinical demands without the help from therapists. The proposed mechanism has two working configurations, each leading the patient to do either hip-only or knee-only exercise. Based on the principle of static balancing, two tensile springs are attached to the mechanism to eliminate the gravitational effect of the mechanism and its payload (i.e., the weight of the patient’s leg) in both configurations. The gravity balancing design is verified by a numerical example and ADAMS software simulation. A mechanical prototype of the design was built up and was tested on a healthy subject. By using electromyography (EMG), the myoelectric signals of two major muscles for the subject with/without wearing the device were measured and analyzed. The results show that the myoelectric voltages of the stimulated muscles in both hip-only and knee-only motion modes are reduced when the subject is wearing the device. In summary, the paper for the first time demonstrates the design philosophy and applications by integrating the reconfigurability and static balancing into mechanisms.
TOPICS: Gravity (Force), Knee, Muscle, Design, Weight (Mass), Electromyography, Computer software, Simulation, Engineering prototypes, Signals, Springs, Switches
Technical Brief  
Jianyou Han and Guangzhen Cui
J. Mechanisms Robotics   doi: 10.1115/1.4036219
This paper presents a solution region synthesis methodology to perform the dimensional synthesis of spatial 5-SS (spherical-spherical) linkages for six specified positions of the end-effector. Dimensional synthesis equations for an SS link are formulated. After solving the synthesis equations, the curves of moving and fixed joints can be obtained, and they are called moving and fixed solution curves, respectively. Each point on the curves represents an SS link. Considering the limited ranges of joints at the first position, we can obtain the feasible solution curves. The link length curves can be obtained based on the feasible solution curves. We determine three SS links by selecting three points meeting the requirements on link length curves. Then the solution region is built by sorting and adding feasible solution curves and projecting the feasible solution curves on the line. In this paper, the 5-SS linkage is formed by five SS links, which connect the base and end-effector. We use linear actuator to drive the 5-SS linkage, and there are infinite ways to add the linear actuator in theory. To simplify the way of adding linear actuator, we provide 20 feasible ways. The linkage is analyzed whether it is defective, when different linear actuators are added. The feasible solution region can be obtained by eliminating defective linkages and linkages that fail to meet the other requirements from the solution region. The validity of the formulas and applicability of the proposed approach is illustrated by example.
TOPICS: Linkages, Actuators, End effectors
research-article  
Venkatasubramanian Kalpathy Venkiteswaran, Omer Anil Turkkan and Hai-Jun Su
J. Mechanisms Robotics   doi: 10.1115/1.4035992
This paper seeks to speed up the topology optimization using a pseudo-rigid-body (PRB) model, which allows the kinetostatic equations explicitly represented in nonlinear algebraic equations. PRB models can not only accommodate large deformations, but more importantly reduce the number of variables compared to beam theory or finite element methods. A symmetric 3R model is developed and used to represent the beams in a compliant mechanism. The design space is divided into rectangular segments while kinematic and static equations are derived using kinematic loops. The use of the gradient and hessian of the system equations leads to a faster solution process. Integer variables are used for developing the adjacency matrix, which is optimized by a genetic algorithm. Dynamic penalty functions describe the general and case-specific constraints. The effectiveness of the approach is demonstrated with the examples of a displacement inverter and a crimping mechanism. The approach outlined here is also capable of estimating the stress in the mechanism which was validated by comparing against Finite Element Analysis. Future implementations of this method will incorporate other pseudo-rigid-body models for various types of compliant elements and also try to develop multi-material designs.
TOPICS: Topology, Compliant mechanisms, Optimization, Kinematics, Deformation, Stress, Finite element methods, Design, Finite element analysis, Euler-Bernoulli beam theory, Algebra, Displacement, Genetic algorithms
research-article  
Dion Hicks, Taufiqur Rahman and Nicholas Krouglicof
J. Mechanisms Robotics   doi: 10.1115/1.4035879
Voice coil actuators are simple electro-mechanical devices which are capable of generating linear motion in response to an electrical input. The generic cylindrical design of commercially available actuators imposes a large variety of limitations on the end-user. The most prominent is the requirement to design and fit extra components to the actuator in order to increase functionality. To solve this issue, a novel voice coil actuator was created which reconfigures the standard cylindrical design with one of a rectangular structure. The novel actuator incorporates planar magnets in a modified Halbach array configuration to ensure compactness and an exceptionally intense, uniform magnetic field. The moving coil is substituted with a printed circuit board encompassing numerous current conducting traces. The board contains a miniature linear rail and bearing system, unified drive electronics and highly adaptive position feedback circuitry resulting in a compact, highly dynamic and accurate device. In pursuit of optomechatronic applications, two distinct parallel kinematic mechanisms were developed to utilize the high dynamics and accuracy of the novel actuator. These devices were configured to function in only rotational degrees of freedom and because of their underlying kinematic structures can be referred to as parallel orientation manipulators. In particular, two structures were defined, 2-PSS/U and 3-PSS/S in order to constraint their payloads to two and three degrees of rotational freedom, respectively. The resultant manipulators are highly dynamic, precise and fulfill size, weight and power requirements for many applications such as sense and avoidance and visual tracking.
TOPICS: Actuators, Design, Kinematics, Manipulators, Rails, Electronics, Printed circuit boards, Weight (Mass), Dynamics (Mechanics), Electromechanical devices, Magnets, Magnetic fields, Degrees of freedom, Feedback, Bearings

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