Accepted Manuscripts

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
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
Aaron Yu, Fengfeng (Jeff) Xi and Amin Moosavian
J. Mechanisms Robotics   doi: 10.1115/1.4036221
This paper presents a new method for kinematic modeling and analysis of a six degree-of-free¬dom (DOF) parallel robot enclosed by a number of rigid sliding panels, called panel en¬closed mechanism. This type of robots has been seen in applications where mechanisms are covered by changeable surfaces, such as aircraft morphing wings made of variable ge-ometry truss manipulators. Based on the traditional parallel robot kinematics, the proposed method is developed to model the motions of a multiple segmented telescopic rigid panels that are attached via an extra link to the base and platform of a driving mechanism. Through this modeling and analysis, non-linear formulations are adopted to optimize orientations adjacent sliding panels during motion over the workspace of the mechanism. This method will help design a set of permissible panels used to enclose the mechanism free of collision. A number of cases are simulated to show the effectiveness of the proposed method. The effect of increased mobility is analyzed and validated as a potential solution to reduce panel collisions.
TOPICS: Kinematics, Robots, Trusses (Building), Collisions (Physics), Design, Modeling, Aircraft, Manipulators, Robot kinematics, Shapes, Wings, Mechanical admittance
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
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
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
Frederick Sun and Jonathan B. Hopkins
J. Mechanisms Robotics   doi: 10.1115/1.4035993
This paper introduces a general method for analyzing flexure systems of any configuration, including those that cannot be broken into parallel and serial subsystems. Such flexure systems are called interconnected hybrid flexure systems because they possess limbs with intermediate bodies that are connected by flexure systems or elements. Specifically, the method introduced utilizes screw algebra and graph theory to help designers determine the freedom spaces (i.e., the geometric shapes that represent all the ways a body is permitted to move) for all the bodies joined together by compliant flexure elements within interconnected hybrid flexure systems (i.e., perform mobility analysis of general flexure systems). This method also allows designers to determine (i) whether such systems are under-constrained or not and (ii) whether such systems are over-constrained or exactly-constrained (i.e., perform constraint analysis of general flexure systems). Although many flexure-based precision motion stages, compliant mechanisms, and microarchitectured materials possess topologies that are highly interconnected, the theory for performing the mobility and constraint analysis of such interconnected flexure systems using traditional screw theory does not currently exist. The theory introduced here lays the foundation for an automated tool that can rapidly generate the freedom spaces of every rigid body within a general flexure system without having to perform traditional computationally expensive finite element analysis. Case studies are provided to demonstrate the utility of the proposed theory.
TOPICS: Bending (Stress), Screws, Mechanical admittance, Algebra, Space, Finite element analysis, Shapes, Compliant mechanisms
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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