Research Papers

J. Mechanisms Robotics. 2016;8(4):041001-041001-7. doi:10.1115/1.4031501.

This paper proposes a trajectory generation technique for three degree-of-freedom (3-dof) planar cable-suspended parallel robots. Based on the kinematic and dynamic modeling of the robot, positive constant ratios between cable tensions and cable lengths are assumed. This assumption allows the transformation of the dynamic equations into linear differential equations with constant coefficients for the positioning part, while the orientation equation becomes a pendulum-like differential equation for which accurate solutions can be found in the literature. The integration of the differential equations is shown to yield families of translational trajectories and associated special frequencies. This result generalizes the special cases previously identified in the literature. Combining the results obtained with translational trajectories and rotational trajectories, more general combined motions are analyzed. Examples are given in order to demonstrate the results. Because of the initial assumption on which the proposed method is based, the ratio between cable forces and cable lengths is constant and hence always positive, which ensures that all cables remain under tension. Therefore, the acceleration vector remains in the column space of the Jacobian matrix, which means that the mechanism can smoothly pass through kinematic singularities. The proposed trajectory planning approach can be used to plan dynamic trajectories that extend beyond the static workspace of the mechanism.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041002-041002-10. doi:10.1115/1.4032204.

A complete stiffness analysis of a parallel manipulator considers the structural compliance of all elements, both in designed degrees-of-freedom (DoFs) and constrained DoFs, and also includes the effect of preloading. This paper presents the experimental validation of a Jacobian-based stiffness analysis method for parallel manipulators with nonredundant legs, which considers all those aspects, and which can be applied to limited-DoF parallel manipulators. The experimental validation was performed by comparing differential wrench measurements with predictions based on stiffness analyses with increasing levels of detail. For this purpose, two passive parallel mechanisms were designed, namely, a planar 3DoF mechanism and a spatial 1DoF mechanism. For these mechanisms, it was shown that a stiffness analysis becomes more accurate if preloading and structural compliance are considered.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041003-041003-8. doi:10.1115/1.4032103.

The design of cable-driven manipulators is complicated by the unidirectional nature of the cables, which results in extra actuators and limited workspaces. Furthermore, the particular arrangement of the cables and the geometry of the robot pose have a significant effect on the cable tension required to effect a desired joint torque. For a sufficiently complex robot, the identification of a satisfactory cable architecture can be difficult and can result in multiply redundant actuators and performance limitations based on workspace size and cable tensions. This work leverages previous research into the workspace analysis of cable systems combined with stochastic optimization to develop a generalized methodology for designing optimized cable routings for a given robot and desired task. A cable-driven robot leg performing a walking-gait motion is used as a motivating example to illustrate the methodology application. The components of the methodology are described, and the process is applied to the example problem. An optimal cable routing is identified, which provides the necessary controllable workspace to perform the desired task and enables the robot to perform that task with minimal cable tensions. A robot leg is constructed according to this routing and used to validate the theoretical model and to demonstrate the effectiveness of the resulting cable architecture.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041004-041004-8. doi:10.1115/1.4032104.

This paper addresses the force distribution of redundantly actuated cable-driven parallel robots (CDPRs). A new and efficient method is proposed for the determination of the lower-boundary of cable forces, including the pose-dependent lower-boundaries. In addition, the effect of cable sag is considered in the calculation of the force distribution to improve the computational accuracy. Simulations are made on a 6DOF CDPR driven by eight cables to demonstrate the validity of the proposed method. Results indicate that the pose-dependent lower-boundary method is more efficient than the fixed lower-boundary method in terms of minimizing the motor size and reducing energy consumption.

Topics: Cables , End effectors
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041005-041005-9. doi:10.1115/1.4032210.

Mobility is a basic property of a mechanism. The aim of mobility analysis is to determine the number of degrees-of-freedom (DOF) and the motion pattern of a mechanism. The existing methods for mobility analysis have some drawbacks when being applied to limited-DOF parallel mechanisms (PMs). Particularly, it is difficult to obtain a symbolic or closed-form expression of mobility and its geometric interpretations are not always straightforward. This paper presents a general method for mobility analysis of limited-DOF PMs in the framework of geometric algebra. The motion space and constraint space of each limb are expressed using geometric algebra. Then the mobility of the PM can be calculated based on the orthogonal complement relationship between the motion space and the constraint space. The detailed mobility analyses of a 3-RPS PM and a 3-RPC PM are presented. It is shown that this method can obtain a symbolic expression of mobility with straightforward geometric interpretations and is applicable to limited-DOF PMs with or without redundant constraints. Without solving complicated symbolic linear equations, this method also has computational advantages.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041006-041006-9. doi:10.1115/1.4032407.

This paper presents a design and fabrication of millimeter scale walking robot using ionic polymer–metal composite (IPMC) actuator as the robot's leg for walking in terrestrial environment. A small scale of new IPMC actuator based on poly-vinylidene fluoride (PVDF)/polyvinyl pyrrolidone (PVP)/polystyrene sulfuric acid (PSSA) blend membrane was fabricated and employed in this study to sustain and drive the walking robot with sufficient force and displacement. The PVDF/PVP/PSSA based IPMC actuator with a polymer mixture ratio of 15/30/55 shows improved performances than Nafion based IPMC actuator. To enhance a traction force of the walking robot and to increase the life time of IPMC actuators, the IPMC strips are covered with a thin PDMS (polydimethylsiloxane) layer. A miniaturized terrestrial walking robot (size: 18 × 11 × 12 mm, weight: 1.3 g) with a light weight robot's body which can support 2-, 4-, or 6-IPMC-leg models was designed and implemented the walking motion on the ground at the maximum speed of 0.58 mm/s.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041007-041007-8. doi:10.1115/1.4032589.

This study proposes an innovative transmission mechanism, called parallel-type independently controllable transmission (ICT). The proposed mechanism can provide functions similar to those of infinitely variable transmission (IVT) or continuously variable transmission (CVT) mechanisms. The parallel-type ICT can transmit rotational output speed that can be independently regulated using a controller and is unaffected by the speed variation of the input shaft. Thus, a variable speed wind turbine can generate electricity with a constant frequency and improved quality. The kinematic characteristics, torque distribution, and power flow of this transmission mechanism were verified using a prototype of the ICT to demonstrate the feasibility of its application.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041008-041008-11. doi:10.1115/1.4032592.

Extended nonlinear analytical modeling and analysis of compound parallelogram mechanisms are conducted in this paper to consider the effect of the initial internal axial force. The nonlinear analytical model of a compound basic parallelogram mechanism (CBPM) is first derived incorporating the initial internal axial force. The stiffness equations of compound multibeam parallelogram mechanisms (CMPMs) are then followed. The analytical maximal stress under the primary actuation force only is also derived to determine the maximal primary motion (motion range). The influence of initial internal axial forces on the primary motion/stiffness is further quantitatively analyzed by considering different slenderness ratios, which can be employed to consider active displacement preloading control and/or thermal effects. The criterion that the primary stiffness may be considered “constant” is defined and the initial internal axial force driven by a temperature change is also formulated. A physical preloading system to control the initial internal axial force is presented and testing results of the object CBPM are compared with theoretical ones.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041009-041009-6. doi:10.1115/1.4032701.

The unified formulation of dimensional synthesis of Stephenson linkages for motion generation is the subject of this paper. Burmester theory is applied to the six-bar linkage, which leads to a unified formulation applicable for all three types of Stephenson linkages. This is made possible by virtue of parameterized position vectors, which simplify the formulation of synthesis equations. A design example is included to demonstrate the application of the method developed.

Topics: Linkages
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041010-041010-10. doi:10.1115/1.4032211.

This paper presents a novel analytical formulation for identifying the closest pair of points lying on two arbitrary cylinders in space, and subsequently the distance between them. Each cylinder is decomposed into four geometric primitives. It is shown that the original problem reduces to the computation of the shortest distance between five distinct combinations of these primitives. Four of these subproblems are solved in closed form, while the remaining one requires the solution of an eight-degree polynomial equation. The analytical nature of the formulation and solution allows the identification of all the special cases, e.g., positive-dimensional solutions, and the curve of intersection when the cylinders interfere. The symbolic precomputation of the results leads to a fast numerical implementation, capable of solving the problem in about 50 μs (averaged over 1 × 106 random instances of the most general case) on a standard PC. The numerical results are verified by repeating all the calculations in a general-purpose commercial cad software. The algorithm has significant potential for applications in the various aspects of robotics and mechanisms, as their links can be modeled easily and compactly as cylinders. This makes tasks such as path planning, determination of the collision-free workspace, etc., computationally easier.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041011-041011-9. doi:10.1115/1.4032632.

Modeling large spatial deflections of flexible beams has been one of the most challenging problems in the research community of compliant mechanisms. This work presents a method called chained spatial-beam constraint model (CSBCM) for modeling large spatial deflections of flexible bisymmetric beams in compliant mechanisms. CSBCM is based on the spatial-beam constraint model (SBCM), which was developed for the purpose of accurately predicting the nonlinear constraint characteristics of bisymmetric spatial beams in their intermediate deflection range. CSBCM deals with large spatial deflections by dividing a spatial beam into several elements, modeling each element with SBCM, and then assembling the deflected elements using the transformation defined by Tait–Bryan angles to form the whole deflection. It is demonstrated that CSBCM is capable of solving various large spatial deflection problems either the tip loads are known or the tip deflections are known. The examples show that CSBCM can accurately predict large spatial deflections of flexible beams, as compared to the available nonlinear finite element analysis (FEA) results obtained by ansys. The results also demonstrated the unique capabilities of CSBCM to solve large spatial deflection problems that are outside the range of ansys.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041012-041012-13. doi:10.1115/1.4032811.

This paper presents the design of an underactuated robotic arm for capturing moving targets with an impact-absorbing capability. The arm consists of three joints (a base joint (BJ), a medial joint (MJ), and a distal joint (DJ)) that are driven by two actuators. A one-input dual-output planetary gear (PG) system, in which neither the ring gear nor the planetary carrier is fixed, is employed to distribute the driving torque between the MJ and DJ. As is well known, an underactuated arm may exhibit unstable grasping performance such that the arm loses contact with the target in certain grasping postures. Therefore, a method is presented for analyzing the equilibrium contact force and the relative movement trend between the target and the arm to determine the work space in which stable grasping is possible. The structural configuration parameters, such as the length ratios among the three beams and the reduction ratio of the PG system, were optimized to maximize the grasp stability work space. Subsequently, a prototype was designed and fabricated based on these optimized parameters. Experiments indicate that this arm design can effectively reduce the peak torque on the joints when grasping a moving target.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041013-041013-11. doi:10.1115/1.4032778.

The mobility of a linkage is determined by the constraints imposed on its members. The geometric constraints define the configuration space (c-space) variety as the geometric entity in which the finite mobility of a linkage is encoded. The aim of a local kinematic analysis of a linkage is to deduce its finite mobility, in a given configuration, from the local c-space geometry. In this paper, a method for the local analysis is presented adopting the concept of the tangent cone to a variety. The latter is an algebraic variety approximating the c-space. It allows for investigating the mobility in regular as well as singular configurations. The instantaneous mobility is determined by the constraints, rather than by the c-space geometry. Shaky and underconstrained linkages are prominent examples that exhibit a permanently higher instantaneous than finite DOF even in regular configurations. Kinematic singularities, on the other hand, are reflected in a change of the instantaneous DOF. A c-space singularity as a kinematic singularity, but a kinematic singularity may be a regular point of the c-space. The presented method allows to identify c-space singularities. It also reveals the ith-order mobility and allows for a classification of linkages as overconstrained and underconstrained. The method is applicable to general multiloop linkages with lower pairs. It is computationally simple and only involves Lie brackets (screw products) of instantaneous joint screws. The paper also summarizes the relevant kinematic phenomena of linkages.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041014-041014-9. doi:10.1115/1.4032865.

In the context of robot manipulation, Salisbury's taxonomy is the common standard used to define the types of contact interactions that can occur between the robot and a contacted object; the basic concept behind such classification is the modeling of contacts as kinematic pairs. In this paper, we extend this notion by modeling the effects of a robot contacting a body as kinematic chains. The introduced kinematic-chain-based contact model is based on an extension of the Bruyninckx–Hunt approach of surface–surface contact. A general classification of nonfrictional and frictional contact types suitable for both manipulation analyses and robot hand design is then proposed, showing that all standard contact categories used in robotic manipulation are special cases of the suggested generalization. New contact models, such as ball, tubular, planar translation, and frictional adaptive finger contacts, are defined and characterized. An example of manipulation analysis that lays out the relevance and practicality of the proposed classification is detailed.

Topics: Kinematics , Friction
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041015-041015-7. doi:10.1115/1.4032976.

The parallelogram-based remote center of motion (RCM) mechanism used for robotic minimally invasive surgery (MIS) manipulators generates a relatively large device footprint. The consequence being larger chance of interference between the robotic arms and restricted workspace, hence obstruct optimal surgical functioning. A novel mechanism with RCM, dual-triangular linkage (DT-linkage), is introduced to reduce the occupied space by the linkage while keeping sufficient space around the incision. Hence, the chance of collisions among arms and tools can be reduced. The concept of this dual-triangular linkage is proven mathematically and validated by a prototype. Auxiliary mechanisms are introduced to remove the singularity at the fully folded configuration. The characterized footprints of this new linkage and the one based on parallelograms are analyzed and compared.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041016-041016-11. doi:10.1115/1.4032975.

This paper presents the development of a compact, modular rotary series elastic actuator (SEA) design that can be customized to meet the requirements of a wide range of applications. The concept incorporates flat brushless motors and planetary gearheads instead of expensive harmonic drives and a flat torsional spring design to create a lightweight, low-volume, easily reconfigurable, and relatively high-performance modular SEA for use in active impedance controlled devices. The key innovations include a Hall effect sensor for direct spring displacement measurements that mitigate the negative impact of backlash on SEA control performance. Both torque and impedance controllers are developed and evaluated using a 1-degree-of-freedom (DoF) prototype of the proposed actuator package. The results demonstrate the performance of a stable first-order impedance controller tested over a range of target impedances. Finally, the flexibility of the modular SEA is demonstrated by configuring it for use in five different actuator specifications designed for use in the uBot-7 mobile manipulator requiring spring stiffnesses from 3 N · m/deg to 11.25 N · m/deg and peak torque outputs from 12 N · m to 45 N · m.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041017-041017-12. doi:10.1115/1.4033157.

This paper deals with a research work that aims to develop a new three degrees-of-freedom (DoF) hybrid mechanism for humanoid robotics application. The proposed hybrid mechanism can be used as a solution not only for several modules in humanoid robots but also for other legged robots such as quadrupeds and hexapods. Hip and shoulder mechanisms are taken as examples in this paper; torso and spine mechanisms, too, can be based on the proposed solutions. In this paper, a detailed analysis of the required performances of the hip and shoulder mechanisms is first carried out. Then, using a kinematic synthesis, a novel solution for the hip mechanism is proposed based on one rotary and two linear actuators. Improving this solution allows us to fulfill the requirements induced by the large motion ranges of the shoulder module, leading to a new management of the linear actuators contributions in the motion/force achievement process. Kinematic and geometrical models of a generic hybrid mechanism are achieved and used to get the optimized solutions of both hybrid mechanisms addressed in this paper.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041018-041018-8. doi:10.1115/1.4033251.

Precision-point synthesis problems for design of four-bar linkages have typically been formulated using two approaches. The exclusive use of path-points is known as “path synthesis,” whereas the use of poses, i.e., path-points with orientation, is called “rigid-body guidance” or the “Burmester problem.” We consider the family of “Alt–Burmester” synthesis problems, in which some combination of path-points and poses is specified, with the extreme cases corresponding to the classical problems. The Alt–Burmester problems that have, in general, a finite number of solutions include Burmester's original five-pose problem and also Alt's problem for nine path-points. The elimination of one path-point increases the dimension of the solution set by one, while the elimination of a pose increases it by two. Using techniques from numerical algebraic geometry, we tabulate the dimension and degree of all problems in this Alt–Burmester family, and provide more details concerning all the zero- and one-dimensional cases.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041019-041019-11. doi:10.1115/1.4033158.

Singularities are one of the most important issues affecting the performance of parallel mechanisms. Therefore, analysis of their locations and closeness is essential for the development of a high-performance mechanism. The screw theory based motion/force transmission analysis provides such a closeness measure in terms of the work performed between specific mechanism twists and wrenches. As such, this technique has been applied to many serial chain parallel mechanisms. However, the motion/force transmission performance of parallel mechanisms with mixed topology chains is yet to be examined. These chains include linkages in both series and parallel, where the parallel portion is termed a closed-loop subchain (CLSC). This paper provides an analysis of such chains, where the CLSC is a planar four-bar linkage. In order to completely define the motion/force transmission abilities of these mechanisms, adapted wrench definitions are introduced. The proposed methodology is applied to a family of two degrees-of-freedom planar axis-symmetric parallel mechanisms, each with a different CLSC configuration. The presented analysis provides the first complete motion/force transmission analysis of such mechanisms.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):041020-041020-14. doi:10.1115/1.4033159.

The paper examines the static behavior of the inverted planetary roller screw (PRS) through numerical and experimental studies. The numerical analysis of the inverted PRS is first presented to capture the global and local deformations in different configurations. Using a three-dimensional finite element (3D FE) method, a sectorial model of the mechanism is built involving an entire roller. The model describes the static behavior of the system under a heavy load and shows the state of the contacts and the in-depth stress zones. The current work also investigates the axial stiffness (AS) and the load distribution (LD) under both compressive and tensile loadings. It is shown that the LDs are not the same at each contact interface of the roller and that they depend on the configuration of the system. Also, the nut is less stressed than the screw shaft because of their contact curvatures. In parallel, complementary experiments are carried out to measure the axial deflection of the screw shaft and the rollers in five cases with different numbers of rollers. In each situation, the mechanism is under the same equivalent axial and static load. The tests reveal that rollers do not have the same behavior, the difference certainly being due to manufacturing and positioning errors that directly affect the number of effective contacts in the device. This stresses the fact that the external load is unequally shared over rollers and contacting threads. By introducing the notion of an equivalent roller, the results are used to validate the previous numerical model of an inverted PRS. As they provide a better understanding of the inverted PRS, these investigations are useful to improve the existing analytical models of the device.

Topics: Screws , Stress , Rollers , Thread
Commentary by Dr. Valentin Fuster

Technical Brief

J. Mechanisms Robotics. 2016;8(4):044501-044501-11. doi:10.1115/1.4032404.

The object of this work is the development of an innovative wire actuator in collaboration with Velan ABV S.p.A., which will be mainly used in applications in which high efficiency and linear behavior are desirable specifications. In this work, the main features of the proposed actuator, which is protected by a patent, are evaluated and compared with respect to a conventional solution consisting of a scotch yoke (SY) transmission system. The comparison is performed using both the simulation results and the experimental data. In order to identify the efficiency and the dynamical response of the innovative actuator, the authors have designed a hydraulic test rig, which can be configured to perform different testing procedures. In this way, it is possible to perform both static tests to identify actuator efficiency, and dynamic ones, in which an assigned load or a valve impedance function is simulated to verify the response of the tested actuator in realistic conditions. Finally, the proposed test rig has been successfully employed to perform both reliability and fatigue tests in which the actuator is subjected to realistic and repetitive loads.

Topics: Actuators , Valves , Design
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):044502-044502-4. doi:10.1115/1.4032405.

In this study, we analyze different actuation configurations for bionic hands in order to improve their level of anthropomorphism. We used a previously developed benchmark, the anthropomorphism index (AI), for 15 different actuation configurations of hands from one to five actuators. By comparing the AI of these configurations, we obtained important conclusions regarding the actuation strategy of the anthropomorphic hands with a limited number of actuators. Results show that the actuation configuration is very important for increasing the level of anthropomorphism of the hands. It is shown that with an appropriate actuation configuration, a configuration with lower number of actuators can result in a higher AI than a configuration with higher number of actuators. We also showed the best actuation configurations for each category of 1–5 actuators. Results can be used as a guideline for development of hands with high anthropomorphism in terms of grasping postures.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):044503-044503-9. doi:10.1115/1.4032777.

We report on the model-based development of a climbing robot that is capable of performing dynamic vertical and lateral climbing motions. The robot was designed based on the two-arm vertical-climbing model inspired by the dynamic climbing motion of cockroaches and geckos, with the extension of introducing the arm sprawl motion to initiate the lateral climbing motion. The quantitative formulation of the model was derived based on Lagrangian mechanics, and the numerical analysis of the model was conducted. The robot was then built and controlled based on the analysis results of the model. The robot can perform the behaviors predicted by the model in which the climbing speed decreases when the swing magnitude increases, and the lateral climbing motion can be initiated when the arm sprawl motion is introduced. The experimental validation of the robot confirms that though the reduced-order two-arm model is abstract and ignored various empirical details, the model is sufficient to predict the robot behavior. This conclusion further suggests that the behavior development of the robot can indeed be explored and evaluated by using the simple climbing model in the simulation environment in place of extensive trial-and-error on the physical robot.

Topics: Robots
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):044504-044504-8. doi:10.1115/1.4032863.

This article proposes a cam mechanism with a translating follower that has dual concave faces, and also demonstrates how to design such a mechanism. This is a positive-drive cam mechanism because the dual concave faces of the follower can simultaneously contact the cam at any instant. The contact forces and the contact stresses of the mechanism are analyzed to illustrate the nature and the capability of reducing contact stress of this novel follower. This cam mechanism is found to have lower contact stress over the constant-breadth and the constant-diameter cam mechanisms.

Topics: Stress , Design , Pressure , Rotation
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):044505-044505-7. doi:10.1115/1.4032812.

This study presents a topology optimization method for design of complaint mechanisms with maximum output displacement as the objective function. Unlike traditional approaches, one special characteristic of this method is that the volume fraction, which is defined as the calculated volume divided by the full volume, remains the same value throughout the optimization process based on the proposed pseudodensity and sensitivity number update scheme. The pseudodensity of each element is initially with the same value as the prespecified volume fraction constraint and can be decreased to a very small value or increased to one with a small increment. Two benchmark problems, the optimal design of a force–displacement inverter mechanism and a crunching mechanism, are provided as the illustrative examples to demonstrate the effectiveness of the proposed method. The results agree well with the previous studies. The proposed method is a general approach which can be used to synthesize the optimal designs of compliant mechanisms with better computational efficiency.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):044506-044506-9. doi:10.1115/1.4032593.

The solution for positive wire tension vector in the presence of uncertainties in design parameters and error in data is investigated for parallel manipulators. The minimum 2-norm non-negative solution and enclosures for the vector of wire tensions are formulated utilizing the perturbed and the interval forms of Jacobian matrix and platform wrench. Methodologies for calculating the minimum 2-norm non-negative solution set of wire tension vector, for interval Jacobian matrix and interval external wrench, are presented. Example parallel manipulators are simulated to investigate the implementation and effectiveness of these methodologies while relating their results.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2016;8(4):044507-044507-3. doi:10.1115/1.4032910.

A vast number of mechanisms have been synthesized to augment the requirements of automation industry, but still there is need to invent useful mechanisms. To bridge this gap and to fulfill the requirement of motion between two extreme positions, various planar kinematic linkage mechanisms have been proposed by different researchers. In this paper, an effort has been made to propose a mechanism along with its analytical dimensional synthesis that makes use of two binary links having two offset tracing points. The proposed mechanism transmits motion between two extreme positions by alternately temporarily fixing a different binary link in two distinct stages. The analytical equations have been written using dyadic and triadic approach of mechanism synthesis for common standard kinematic task of path generation. The proposed method is noniterative and reduces the solution space.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Mechanisms Robotics. 2016;8(4):045001-045001-10. doi:10.1115/1.4032700.

Various stair-climbing or cleaning mechanisms have been proposed or developed in the past decades. Most of them are big-sized, complex, and/or expensive, which hinder their practical application. In this study, a new stair-cleaning robot is proposed and developed. In the new robot, a pair of legs is used for stair climbing. Rotating around the main body, the legs of the robot drive the feet to execute revolving but translational motions, thereby allowing the robot to climb. The new robot is highly compact compared with most traditional stair-cleaning or climbing robots, because only one motor is utilized to drive the climbing mechanism and the legs can be retracted at both sides of the robot when it is not climbing. Its compact structure enables the new robot to move along the riser to do cleaning on the stairs, which is a prominent advantage over most similar robots. The cleaning device is designed similar to that of current ground cleaning robots. The sensing and control system is designed for successful stair climbing and avoidance of falls and collisions. Experiments show that the new robot has high success rates in climbing up or down common types of stairs, and thus can do cleaning on the related stairs.

Topics: Stairs , Robots
Commentary by Dr. Valentin Fuster

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