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Editorial

J. Mechanisms Robotics. 2016;8(5):050201-050201-1. doi:10.1115/1.4032699.
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The Mechanisms and Robotics community would like to acknowledge and honor Jian Sheng Dai, professor at the King's College London, London, UK, and a Fellow of the American Society of Mechanical Engineers (ASME), who received the 2015 ASME DED Mechanisms and Robotics Award at the 39th ASME Mechanisms and Robotics conference held on Aug. 2–5, 2015 in Boston, MA. The Mechanisms and Robotics Award is an honor that is given annually by the ASME Design Engineering Division, to engineers known for a lifelong contribution to the fundamental theory, design and applications of mechanisms and robotic systems. Professor Dai has made a lasting impact on reconfigurable mechanisms through his contributions to theoretical study, mechanism innovation, applications, and societal services and by exploring the screw system relationship for revealing constraint variation that affects mechanism reconfigurability and for establishing a mode of mobility analysis.

Topics: Robotics
Commentary by Dr. Valentin Fuster

Guest Editorial

J. Mechanisms Robotics. 2016;8(5):050301-050301-2. doi:10.1115/1.4032510.
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This second IDETC Special Issue, containing 19 papers from researchers in seven countries on three continents, seeks to capture the current interest topics and latest results from the 39th ASME Mechanisms and Robotics (M&R) conference. The topics span the synthesis and analysis of novel mechanisms and robots as well as their validation in a variety of applications. The papers are organized with contributions to the core theoretical methodologies of M&R (five papers) appearing first. The application areas that follow are micro air vehicles (MAVs) (two papers), modular robotics (three papers), origami applications (three papers), medical robotics (three papers), and exoskeleton-assistive systems (three papers).

Commentary by Dr. Valentin Fuster

Research Papers

J. Mechanisms Robotics. 2016;8(5):051001-051001-9. doi:10.1115/1.4032409.

This paper presents a metamorphic parallel mechanism (MPM) which can switch its motion between pure translation (3T) and pure rotation (3R). This feature stems from a reconfigurable Hooke (rT) joint of which one of the rotation axes can be altered freely. More than that, based on the reconfiguration of the rT joint, workspace of both 3T and 3R motion can be tunable, and the rotation center of the 3R motion can be controlled along a line perpendicular to the base plane. Kinematics analysis is presented based on the geometric constraints of the parallel mechanism covering both 3T and 3R motion. Following this, screw theory based motion/force transmission equations are obtained, and their characteristics are investigated and linked to the singularity analysis using Jacobian matrix. Motion/force transmission indices can be used to optimize basic design parameters of the MPM. This provides reference of this mechanism for potential applications requiring 3T and 3R motion.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051002-051002-9. doi:10.1115/1.4032120.

This paper proposes the use of passive force and torque limiting devices to bound the maximum forces that can be applied at the end-effector or along the links of a robot, thereby ensuring the safety of human–robot interaction. Planar isotropic force limiting modules are proposed and used to analyze the force capabilities of a two-degree-of-freedom (2DOF) planar serial robot. The force capabilities at the end-effector are first analyzed. It is shown that, using isotropic force limiting modules, the performance to safety index remains excellent for all configurations of the robot. The maximum contact forces along the links of the robot are then analyzed. Force and torque limiters are distributed along the structure of the robot in order to ensure that the forces applied at any point of contact along the links are bounded. A power analysis is then presented in order to support the results. Finally, examples of mechanical designs of force/torque limiters are shown to illustrate a possible practical implementation of the concept.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051003-051003-3. doi:10.1115/1.4032410.

This paper extends the general method to construct a singularity trace for single degree-of-freedom (DOF), closed-loop linkages to include prismatic along with revolute joints. The singularity trace has been introduced in the literature as a plot that reveals the gross motion characteristics of a linkage relative to a designated input joint and a design parameter. The motion characteristics identified on the plot include a number of possible geometric inversions (GIs), circuits, and singularities at any given value for the input link and the design parameter. An inverted slider–crank and an Assur IV/3 linkage are utilized to illustrate the adaptation of the general method to include prismatic joints.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051004-051004-8. doi:10.1115/1.4032212.

It has been well established that kinematic mapping theory could be applied to mechanism synthesis, where discrete motion approximation problem could be converted to a surface fitting problem for a group of discrete points in hyperspace. In this paper, we applied kinematic mapping theory to planar discrete motion synthesis of an arbitrary number of approximated poses as well as up to four exact poses. A simultaneous type and dimensional synthesis approach is presented, aiming at the problem of mixed exact and approximate motion realization with three types of planar dyad chains (RR, RP, and PR). A two-step unified strategy is established: first N given approximated poses are utilized to formulate a general quadratic surface fitting problem in hyperspace, then up to four exact poses could be imposed as pose-constraint equations to this surface fitting system such that they could be strictly satisfied. The former step, the surface fitting problem, is converted to a linear system with two quadratic constraint equations, which could be solved by a null-space analysis technique. On the other hand, the given exact poses in the latter step are formulated as linear pose-constraint equations and added back to the system, where both type and dimensions of the resulting optimal dyads could be determined by the solution. These optimal dyads could then be implemented as different types of four-bar linkages or parallel manipulators. The result is a novel algorithm that is simple and efficient, which allows for N-pose motion approximation of planar dyads containing both revolute and prismatic joints, as well as handling of up to four prescribed poses to be realized precisely.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051005-051005-10. doi:10.1115/1.4032105.

This paper describes a synthesis technique that constrains a spatial serial chain into a single degree-of-freedom mechanism using planar six-bar function generators. The synthesis process begins by specifying the target motion of a serial chain that is parameterized by time. The goal is to create a mechanism with a constant velocity rotary input that will achieve that motion. To do this, we solve the inverse kinematics equations to find functions of each serial joint angle with respect to time. Since a constant velocity input is desired, time is proportional to the angle of the input link, and each serial joint angle can be expressed as functions of the input angle. This poses a separate function generator problem to control each joint of the serial chain. Function generators are linkages that coordinate their input and output angles. Each function is synthesized using a technique that finds 11 position Stephenson II linkages, which are then packaged onto the serial chain. Using pulleys and the scaling capabilities of function generating linkages, the final device can be packaged compactly. We describe this synthesis procedure through the design of a biomimetic device for reproducing a flapping wing motion.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051006-051006-11. doi:10.1115/1.4032411.

Flapping wing aerial vehicles (FWAVs) may require charging in the field where electrical power supply is not available. Flexible solar cells can be integrated into wings, tail, and body of FWAVs to harvest solar energy. The harvested solar energy can be used to recharge batteries and eliminate the need for external electrical power. It can also be used to increase the flight time of the vehicle by supplementing the battery power. The integration of solar cells in wings has been found to alter flight performance because solar cells have significantly different mechanical and density characteristics compared to other materials used for the FWAV construction. Previously, solar cells had been successfully integrated into the wings of Robo Raven, a FWAV developed at the University of Maryland. Despite changes in the aerodynamic forces, the vehicle was able to maintain flight and an overall increase in flight time was achieved. This paper investigates ways to redesign Robo Raven to significantly increase the wing area and incorporate solar cells into the wings, tail, and body. Increasing wing area allows for additional solar cells to be integrated, but there are tradeoffs due to the torque limitations of the servomotors used to actuate the wings as well changes in the lift and thrust forces that affect payload capacity. These effects were modeled and systematically characterized as a function of the wing area to determine the impact on enhancing flight endurance. In addition, solar cells were integrated into the body and the tail. The new design of Robo Raven generated a total of 64% more power using on-board solar cells, and increased flight time by 46% over the previous design. They were also able to recharge batteries at a similar rate to commercial chargers.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051007-051007-10. doi:10.1115/1.4032250.

Micro-aerial vehicles (MAVs) face limited flight times, which adversely impacts their efficacy for scenarios such as first response and disaster recovery, where it might be useful to deploy persistent radio relays and quadrotors for monitoring or sampling. Thus, it is important to enable micro-aerial vehicles to land and perch on different surfaces to save energy by cutting power to motors. We are motivated to use a downward-facing gripper for perching, as opposed to a side-mounted gripper, since it could also be used to carry payloads. In this paper, we predict and verify the performance of a custom gripper designed for perching on smooth surfaces. We also present control and planning algorithms, enabling an underactuated quadrotor with a downward-facing gripper to perch on inclined surfaces while satisfying constraints on actuation and sensing. Experimental results demonstrate the proposed techniques through successful perching on a glass surface at various inclinations, including vertical.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051008-051008-11. doi:10.1115/1.4032273.

Modular robots have captured the interest of the robotics community over the past several years. In particular, many modular robotic systems are reconfigurable, robust against faults, and low-cost due to mass production of a small number of different homogeneous modules. Faults in these systems are normally tolerated through redundancy or corrected by discarding damaged modules, which reduces the operational capabilities of the robot. To overcome these difficulties, we previously developed and discussed the general design constraints of a heterogeneous modular robotic system (Hex-DMR II) capable of autonomous team repair and diagnosis. In this paper, we discuss the design of each module, in detail, and present a new, novel elevator module. Then, we introduce a forestlike structure that enumerates every non-isomorphic, functional agent configuration of our system. Finally, we present a case study contrasting the kinematics and power consumption of two particular configurations during a mapping task.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051009-051009-15. doi:10.1115/1.4032509.

This paper presents a new model for a linear bistable compliant mechanism and design guidelines for its use. The mechanism is based on the crank–slider mechanism. This model takes into account the first mode of buckling and postbuckling behavior of a compliant segment to describe the mechanism's bistable behavior. The kinetic and kinematic equations, derived from the pseudo-rigid-body model (PRBM), were solved numerically and are represented in plots. This representation allows the generation of step-by-step design guidelines. The design parameters consist of maximum desired deflection, material selection, safety factor, compliant segments' widths, maximum force required for actuator selection, and maximum footprint (i.e., the maximum rectangular area that the mechanism can fit inside of and move freely without interfering with other components). Because different applications may have different input requirements, this paper describes two different design approaches with different parameters subsets as inputs. The linear bistable compliant crank–slider mechanism (LBCCSM) can be used in the shape-morphing space-frame (SMSF) as potential application. The frame's initial shape is constructed from a single-layer grid of flexures, rigid links, and LBCCSMs. The grid is bent into the space-frame's initial cylindrical shape, which can morph because of the inclusion of LBCCSMs in its structure.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051010-051010-11. doi:10.1115/1.4032248.

The aim of this paper is to introduce an approach for optimally organizing a variety of nonrepeating compliant-mechanism-like unit cells within a large deformable lattice such that the bulk behavior of the lattice exhibits a desired graded change in thermal expansion while achieving a desired uniform stiffness over its geometry. Such lattices with nonrepeating unit cells, called nonperiodic microarchitectured materials, could be sandwiched between two materials with different thermal expansion coefficients to accommodate their different expansions and/or contractions induced by changing ambient temperatures. This capability would reduce system-level failures within robots, mechanisms, electronic modules, or other layered coatings or structures made of different materials with mismatched thermal expansion coefficients. The closed-form analytical equations are provided, which are necessary to rapidly calculate the bulk thermal expansion coefficient and Young's modulus of general multimaterial lattices that consist first of repeating unit cells of the same design (i.e., periodic microarchitectured materials). Then, these equations are utilized in an iterative way to generate different rows of repeating unit cells of the same design that are layered together to achieve nonperiodic microarchitectured material lattices such that their top and bottom rows achieve the same desired thermal expansion coefficients as the two materials between which the lattice is sandwiched. A matlab tool is used to generate images of the undeformed and deformed lattices to verify their behavior and an example is provided as a case study. The theory provided is also verified and validated using finite-element analysis (FEA) and experimentation.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051011-051011-6. doi:10.1115/1.4032442.

Reconfigurable structures based on origami design are useful for multifunctional applications, such as deployable shelters, solar array packaging, and tunable antennas. Origami provides a framework to decompose a complex 2D to 3D transformation into a series of folding operations about predetermined foldlines. Recent optimization toolsets have begun to enable a systematic search of the design space to optimize not only geometry but also mechanical performance criteria as well. However, selecting optimal fold patterns for large folding operations is challenging as geometric nonlinearity influences fold choice throughout the evolution. The present work investigates strategies for design optimization to incorporate the current and future configurations of the structure in the performance evaluation. An optimization method, combined with finite-element analysis, is used to distribute mechanical properties within an initially flat structure to determine optimal crease patterns to achieve desired motions. Out-of-plane and twist displacement objectives are used in three examples. The influence of load increment and geometric nonlinearity on the choice of crease patterns is studied, and appropriate optimization strategies are discussed.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051012-051012-7. doi:10.1115/1.4032472.

Herein, we discuss the folding of highly compliant origami structures—“Soft Origami.” There are benefits to be had in folding compliant sheets (which cannot self-guide their motion) rather than conventional rigid origami. Example applications include scaffolds for artificial tissue generation and foldable substrates for flexible electronic assemblies. Highly compliant origami has not been contemplated by existing theory, which treats origami structures largely as rigid or semirigid mechanisms with compliant hinges—“mechanism-reliant origami.” We present a quantitative metric—the origami compliance metric (OCM)—that aids in identifying proper modeling of a homogeneous origami structure based upon the compliance regime it falls into (soft, hybrid, or mechanism-reliant). We discuss the unique properties, applications, and design drivers for practical implementation of Soft Origami. We detail a theory of proper constraint by which an ideal soft structure's number of degrees-of-freedom may be approximated as 3n, where n is the number of vertices of the fold pattern. Buckling and sagging behaviors in very compliant structures can be counteracted with the application of tension; we present a method for calculating the tension force required to reduce sagging error below a user-prescribed value. Finally, we introduce a concept for a scalable process in which a few actuators and stretching membranes may be used to simultaneously fold many origami substructures that share common degrees-of-freedom.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051013-051013-11. doi:10.1115/1.4032213.

In this paper, we introduce a strategy for the design and computational analysis of compliant DNA origami mechanisms (CDOMs), which are compliant nanomechanisms fabricated via DNA origami self-assembly. The rigid, compliant, and flexible parts are constructed by bundles of many double-stranded DNA (dsDNA) helices, bundles of a few dsDNA helices or a single dsDNA helix, and single-stranded DNA (ssDNA) strands, respectively. Similar to its macroscopic counterparts, a CDOM generates its motion via deformation of at least one structural member. During the motion, strain energy is stored and released in the compliant components. Therefore, these CDOMs have the advantage of suppressing thermal fluctuations due to the internal mechanical energy barrier for motion. Here, we show that classic pseudorigid-body (PRB) models for compliant mechanism are successfully employed to the analysis of these DNA origami nanomechanisms and can serve to guide the design and analysis method. An example of compliant joint and a bistable four-bar CDOM fabricated with DNA origami are presented.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051014-051014-9. doi:10.1115/1.4032272.

In this paper, we present a novel flexible endoscope (FE) which is well suited to minimally invasive cardiac surgery (MICS). It is named the cardioscope. The cardioscope is composed of a handle, a rigid shaft, a steerable flexible section, and the imaging system. The flexible section is composed of an elastic tube, a number of spacing disks, a constraint tube, and four wires. It employs the constrained wire-driven flexible mechanism (CWFM) with a continuum backbone, which enables the control of both the angulation and the length of the flexible section. Compared to other endoscopes, e.g., rigid endoscope (RE) and fixed-length FE, the cardioscope is much more dexterous. The cardioscope can bend over 180 deg in all directions, and the bending is decoupled from the distal tip position. Ex vivo tests show that the cardioscope is well suited to MICS. It provides much wider scope of vision than REs and provides good manipulation inside confined environments. In tests, the cardioscope successfully explored the full heart through a single hole, which shows that the design is promising. Despite being designed for MICS, the cardioscope can also be applied to other minimally invasive surgeries (MISs), such as laparoscopy, neurosurgery, transnasal surgery, and transoral surgery.

Topics: Design , Endoscopes , Wire
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051015-051015-10. doi:10.1115/1.4032591.

Robot-assisted minimally invasive surgery (MIS) has gained popularity due to its high dexterity and reduced invasiveness to the patient; however, due to the loss of direct touch of the surgical site, surgeons may be prone to exert larger forces and cause tissue damage. To quantify tool–tissue interaction forces, researchers have tried to attach different kinds of sensors on the surgical tools. This sensor attachment generally makes the tools bulky and/or unduly expensive and may hinder the normal function of the tools; it is also unlikely that these sensors can survive harsh sterilization processes. This paper investigates an alternative method by estimating tool–tissue interaction forces using driving motors' current, and validates this sensorless force estimation method on a 3-degree-of-freedom (DOF) robotic surgical grasper prototype. The results show that the performance of this method is acceptable with regard to latency and accuracy. With this tool–tissue interaction force estimation method, it is possible to implement force feedback on existing robotic surgical systems without any sensors. This may allow a haptic surgical robot which is compatible with existing sterilization methods and surgical procedures, so that the surgeon can obtain tool–tissue interaction forces in real time, thereby increasing surgical efficiency and safety.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051016-051016-9. doi:10.1115/1.4032249.

In this paper, we present the design, fabrication, and testing of a robot for automatically positioning ultrasound (US) imaging catheters. Our system will point US catheters to provide real-time imaging of anatomical structures and working instruments during minimally invasive procedures. Manually navigating US catheters is difficult and requires extensive training in order to aim the US imager at desired targets. Therefore, a four-degree-of-freedom (4DOF) robotic system was developed to automatically navigate US imaging catheters for enhanced imaging. A rotational transmission enables 3DOF for pitch, yaw, and roll of the imager. This transmission is translated by the 4DOF. An accuracy analysis calculated the maximum allowable joint motion error. Rotational joints must be accurate to within 1.5 deg, and the translational joint must be accurate within 1.4 mm. Motion tests then validated the accuracy of the robot. The average resulting errors in positioning of the rotational joints were 0.04–0.22 deg. The average measured backlash was 0.18–0.86 deg. Measurements of average translational positioning and backlash errors were negligible. The resulting joint motion errors were well within the required specifications for accurate robot motion. The output of the catheter was then tested to verify the effectiveness of the handle motions to transmit torques and translations to the catheter tip. The catheter tip was navigated to desired target poses with average error 1.3 mm and 0.71 deg. Such effective manipulation of US imaging catheters will enable better visualization in various procedures ranging from cardiac arrhythmia treatment to tumor removal in urological cases.

Topics: Robots , Catheters
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051017-051017-8. doi:10.1115/1.4032214.

This paper presents studies of an upper body assistive device designed to aid human load carriage. The two primary functions of the device are: (i) distributing the backpack load between the shoulders and the waist and (ii) reducing the dynamic load of a backpack on the human body during walking. These functions are targeted to relieve stress applied on the shoulders and the back, and also reduce the dynamic loads transferred to the lower limbs during walking. These functions are achieved by incorporating two modules—passive and active—within a custom fitted shirt integrated with motion/force sensors, actuators, and a real-time controller. The relevant modeling and controller design are presented for dynamic load compensation. Preliminary evaluation of the device was first performed on a single subject, followed by a pilot study with ten healthy subjects walking on a treadmill with a backpack. Results show that the device can effectively transfer the load from the shoulders to the waist and also reduce the dynamic loads induced by the backpack during walking. Reduction in peak and total normal ground reaction forces, leg muscle activations, and oxygen consumptions was observed with the device. This suggests that the device can potentially reduce the risk of musculoskeletal injuries and fatigue on the lower limbs associated with carrying heavy loads and provide some metabolic benefits.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051018-051018-12. doi:10.1115/1.4032274.

Assisted motor therapies play a critical role in enhancing functional musculoskeletal recovery and neurological rehabilitation. Our long-term goal is to assist and automate the performance of repetitive motor-therapy of the human lower limbs. Hence, in this paper, we examine the viability of a light-weight and reconfigurable hybrid (articulated-multibody and cable) robotic system for assisting lower-extremity rehabilitation and analyze its performance. A hybrid cable-actuated articulated-multibody system is formed when multiple cables are attached from a ground-frame to various locations on an articulated-linkage-based orthosis. Our efforts initially focus on developing an analysis and simulation framework for the kinematics and dynamics of the cable-driven lower limb orthosis. A Monte Carlo approach is employed to select configuration parameters including cuff sizes, cuff locations, and the position of fixed winches. The desired motions for the rehabilitative exercises are prescribed based upon motion patterns from a normative subject cohort. We examine the viability of using two controllers—a joint-space feedback-linearized PD controller and a task-space force-control strategy—to realize trajectory- and path-tracking of the desired motions within a simulation environment. In particular, we examine performance in terms of (i) coordinated control of the redundant system; (ii) reducing internal stresses within the lower-extremity joints; and (iii) continued satisfaction of the unilateral cable-tension constraints throughout the workspace.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(5):051019-051019-9. doi:10.1115/1.4032270.

This paper presents the design evolution of the sensing and force-feedback exoskeleton robotic (SAFER) glove with application to hand rehabilitation. The hand grasping rehabilitation system is designed to gather kinematic and force information from the human hand and then playback the motion to assist a user in common hand grasping movements, such as grasping a bottle of water. Grasping experiments were conducted where fingertip contact forces were measured by the SAFER glove. These forces were then modeled based on a machine learning approach to obtain the learned contact force distributions. Using these distributions, fingertip force trajectories were generated with a Gaussian mixture regression (GMR) method. To demonstrate the glove's effectiveness to manipulate the hand, experiments were performed using the glove to demonstrate grasping capabilities on several objects. Instead of defining a grasping force, contact force trajectories were used to control the SAFER glove in order to actuate a user's hand while carrying out a learned grasping task.

Commentary by Dr. Valentin Fuster

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