Accepted Manuscripts

Shivanand Pattanshetti and Seok Chang Ryu
J. Mechanisms Robotics   doi: 10.1115/1.4038440
With the proliferation of successful minimally invasive surgical techniques, comes the challenge of shrinking the size of surgical instruments further to facilitate use in applications such as neurosurgery, pediatric surgery, and needle procedures. This paper introduces laser machined, multi-degree-of-freedom (DOF) hinge joints embedded on tubes, as a possible means to realize such miniature instruments without the need for any assembly. A method to design such a joint for an estimated range of motion was explored. The effects of design and machining parameters on the mechanical interference, range of motion and joint dislocation were analyzed. The extent of interference between the moving parts of the joint can be used to predict the range of motion of the joint for rigid tubes and future design optimization. The total usable workspace was also estimated using kinematic principles for a joint in series and for two sets of orthogonal joints. Our work can open up avenues to a new class of miniature robotic medical devices with hinge joints and a usable channel for drug delivery.
TOPICS: Hinges, Medical devices, Design, Surgery, Dislocations, needles, Pediatrics, Surgical tools, Neurosurgery, Optimization, Robotics, Drug delivery systems, Instrumentation, Shrinkage (Materials), Kinematics, Lasers, Machining, Manufacturing
Joseph Calogero, Mary Frecker, Zohaib Hasnain and James E. Hubbard Jr.
J. Mechanisms Robotics   doi: 10.1115/1.4038441
A method for validating rigid-body models of discrete flexible joints under dynamic loading conditions using motion tracking cameras and genetic algorithms is presented. The flexible joints are modeled using rigid-body mechanics as compliant joints: spherical joints with distributed mass and three axis torsional spring-dampers. This allows flexible joints to be modeled using computationally efficient rigid-body dynamics methods, thereby allowing a model to determine the desired stiffness and location characteristics of discrete flexible joints spatially distributed into a structure. An experiment was performed to validate a previously developed numerical dynamics model with the goal of tuning unknown model parameters to match the flapping kinematics of the leading edge spar of an ornithopter with contact-aided compliant mechanisms (CCMs) inserted. A system of computer motion tracking cameras was used to record the kinematics of reflective tape and markers placed along the leading edge spar with and without CCMs inserted. A genetic algorithm was used to minimize the error between the model and experimental marker kinematics. The model was able to match the kinematics of all markers along the spars with a root mean square error of less than 2% of the half wingspan over the flapping cycle. Additionally, the model was able to capture the deflection amplitude and harmonics of the CCMs with a root mean square error of less than 2 degrees over the flapping cycle.
TOPICS: Dynamics (Mechanics), Structural dynamics, Kinematics, Wing spars, Spar platforms, Errors, Genetic algorithms, Cycles, Deflection, Dampers, Computers, Dynamic testing (Materials), Springs, Stiffness, Compliant mechanisms
Xiangyun Li, Ping Zhao, Anurag Purwar and Qiaode Jeffrey Ge
J. Mechanisms Robotics   doi: 10.1115/1.4038305
This paper studies the problem of spherical four-bar motion synthesis from the viewpoint of acquiring circular geometric constraints from a set of prescribed spherical poses. The proposed approach extends our planar four-bar linkage synthesis work to spherical case. Using the image space representation of spherical poses, a quadratic equation with ten linear homogeneous coefficients, which corresponds to a constraint manifold in the image space, can be obtained to represent a spherical RR dyad. Therefore, our approach to synthesizing a spherical four-bar linkage decomposes into two steps. First, a pencil of general manifolds that best fit the task image points in the least squares sense can be found using Singular Value Decomposition, and the singular vectors associated with the smallest singular values are used to form the null space solution; second, additional constraint equations on the resulting solution space are imposed to identify the general manifolds that are qualified to become the constraint manifolds, which can represent the spherical circular constrains and thus their corresponding spherical dyads. After the inverse computation that converts the coefficients of the constraint manifolds to the design parameters of spherical RR dyad, spherical four-bar linkages that best navigate through the set of task poses can be constructed by the obtained dyads. The result is a fast and efficient algorithm that extracts the geometric constraints associated with a spherical motion task, and leads naturally to a unified treatment for both exact and approximate spherical motion synthesis.
TOPICS: Kinematics, Linkages, Manifolds, Algorithms, Design, Computation
Wei Li and Jorge Angeles
J. Mechanisms Robotics   doi: 10.1115/1.4038306
The subject of this paper is twofold: the kinematics and the isotropic design of six-dof, 3-CCC parallel-kinematics machines (PKMs). Upon proper embodiment and dimensioning, the PKMs discussed here, with all actuators mounted on the base, exhibit interesting features, not found elsewhere. One is the existence of an isotropy locus, as opposed to isolated isotropy points in the workspace, thereby guaranteeing the accuracy and the homogeneity of the motion of the moving platform (MP) along different directions within a significantly large region of their workspace. The conditions leading to such a locus are discussed in depth; several typical isotropic designs are brought to the limelight. Moreover, the kinematic analysis shows that rotation and translation of the MP are decoupled, which greatly simplifies not only the kinetostatic analysis, but, most importantly, their control. Moreover, it is shown that the singularity loci of this class of mechanism are determined only by the orientation of their MP, which also simplifies locus evaluation and eases its representation.
TOPICS: Kinematics, Machinery, Design, Mechanical admittance, Isotropy, Kinematic analysis, Dimensions, Actuators, Rotation
Design Innovation Paper  
Kyle W. Eastwood, Peter Francis, Hamidreza Azimian, Arushri Swarup, Thomas Looi, James M. Drake and Hani E. Naguib
J. Mechanisms Robotics   doi: 10.1115/1.4038254
This work presents a novel miniature contact-aided compliant joint mechanism that can be integrated into millimeter-sized manual or robotic surgical instruments. The design aims to address the trade-off between notched-tube compliant joints’ range-of-motion and stiffness, while also ensuring a compact form-factor. The mechanism is constructed from a nitinol tube with asymmetric cutouts and is actuated in bending by a cable. The innovative feature of this design is the incorporation of a contact-aid into the notched-tube topology which acts to both increase the stiffness of the joint and change the shape that it undertakes during bending. Using finite element modelling (FEM) techniques, we present a sensitivity analysis investigating how the performance of this contact-aided compliant mechanism (CCM) is affected by its geometry, and derive a kinematics and statics model for the joint. The FEM simulations and the kinematic and static models are compared to experimental results. The design and modelling presented in this study can be used to develop new miniature dexterous instruments, with a particular emphasis on applications in minimally invasive neurosurgery.
TOPICS: Design, Surgery, Finite element model, Stiffness, Kinematics, Modeling, Finite element methods, Robotics, Statics, Cables, Simulation, Engineering simulation, Finite element analysis, Instrumentation, Topology, Surgical tools, Compliant mechanisms, Neurosurgery, Tradeoffs, Geometry, Nickel titanium alloys, Sensitivity analysis, Shapes
Technical Brief  
Pengfei Gui, Liqiong Tang and Subhas Mukhopadhyay
J. Mechanisms Robotics   doi: 10.1115/1.4038219
This paper presents a novel mechanism of tree climbing robotic system for tree pruning. The unique features of this system include the passive and active anti-falling mechanisms which prevent the robot from falling to the ground under either static or dynamic situations, the capability to vertically or spirally climb up a tree trunk and the flexibility to suit different trunk sizes. The CAD models of the robotic mechanism, static and kinematic analysis, climbing simulation and testing of the physical model are stated in detail. This research work reveals that this novel tree climbing mechanism can be served as a platform for tree pruning robot.
TOPICS: Robotics, Robots, Simulation, Computer-aided design, Testing, Kinematic analysis
Technical Brief  
Wyatt Felt and C. David Remy
J. Mechanisms Robotics   doi: 10.1115/1.4038220
In this work, we present a closed-form model which describes the kinematics of Fiber Reinforced Elastomeric Enclosures (FREEs). A FREE actuator consists of a thin elastomeric tube surrounded by reinforcing helical fibers. Previous models for the motion of FREEs have relied on the successive compositions of ``instantaneous'' kinematics or complex elastomer models. The model presented in this work classifies each FREE by the ratio of the length of its fibers. This ratio defines the behavior of the FREE regardless of the other parameters. With this ratio defined, the kinematic state of the FREE can then be completely described by one of the fiber angles. The simple, analytic nature of the model presented in this work facilitates the understanding and design of FREE actuators.
TOPICS: Kinematics, Fibers, Actuators, Design, Elastomers
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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