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# Accepted Manuscripts

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research-article
J. Mechanisms Robotics   doi: 10.1115/1.4038010
This paper presents the design, simulation, fabrication, and testing processes of a new microelectromechanical systems (MEMS) microgripper, which integrates an electrostatic actuator and a capacitive force sensor. One advantage of the presented gripper is that the gripping force and interaction force in two orthogonal directions can be respectively detected by a single force sensor. The whole gripper structure consists of the left actuating part and right sensing part. The actuator and sensor are fixed and linearly guided by four leaf flexures, respectively. The left arm of the gripper is driven through a lever amplification mechanism. By this structure, the displacement from the electrostatic actuator is transmitted and enlarged at the gripper tip. The right arm of the gripper is designed to detect the gripping and interaction forces using a capacitive sensor. The MEMS gripper is manufactured by SOIMUMPs process. The performance of the designed gripper is verified by conducting finite-element-analysis (FEA) simulation and experimental studies. Moreover, the demonstration of bio-cellulose gripping confirms the feasibility of the developed gripper device.
research-article
J. Mechanisms Robotics   doi: 10.1115/1.4038007
This paper develops an approach to evaluate a state-space controller design for mobile manipulators using a geometric representation of the system response in tool space. The method evaluates the robot system dynamics with control scheme and the resulting response is called the controllability ellipsoid; a tool space representation of the system's motion response given a unit input. The controllability ellipsoid can be compared with a corresponding geometric representation of the required motion task (called the motion polygon) and evaluated using a quantitative measure of the degree to which the task is satisfied. The traditional control design approach views the system response in the time domain. Alternatively, the proposed controllability ellipsoid views the system response in the domain of the input parameters. In order to complete the task, the controllability ellipse must fully span the motion polygon. The optimal robot arrangement would minimize the total area of the controllability ellipse while fully spanning the motion polygon. This is comparable to minimizing the power requirements of robot design when applying a uniform scale to all inputs. It will be shown that changing the control parameters changes the eccentricity and orientation of the controllability ellipse, implying a preferred set of control parameters to minimize design motor power. When viewed in the time domain, the control parameters can be selected to achieve desired stability and time response. When coupled with existing control design methods, the controllability ellipsoid approach can yield robot designs that are stable, responsive and minimize the input power requirements.
research-article
J. Mechanisms Robotics   doi: 10.1115/1.4038008
Principles from origami art are applied in the design of mechanisms and robotics increasingly frequent. A large part of the application driven research of these origami-like mechanisms focuses on devices where the creases (hinge lines) are actuated and the facets are constructed as stiff elements. In this paper, a design tool is proposed in which hinge lines with torsional stiffness and flexible facets are used to design passive, instead of active mechanisms. The design tool is an extension of a model of a Single Vertex Compliant Facet Origami Mechanism (SV-COFOM) and is used to approximate a desired moment curve by optimizing the design variables of the mechanism. Three example designs are presented: a Constant Moment Joint, a Gravity Compensating Joint and a Zero Moment Joint. The Constant Moment Joint design has been evaluated experimentally, resulting in a RMSE of 6.4 E-2 Nm on a constant moment value of 0.39 Nm. This indicates that the design tool is suitable for a course estimation of the moment curve of the SV-COFOM in early stages of a design process.
research-article
J. Mechanisms Robotics   doi: 10.1115/1.4038009
This paper presents a design procedure for a two-degree of freedom translational parallel manipulator, named IRSBot-2. This design procedure aims at determining the optimal design parameters of the IRSBot-2 such that the robot can reach a velocity equal to 6~m/s, an acceleration up to 20~G and an accuracy up to 20~$\mu$m throughout its operational workspace. Besides, contrary to its counterparts, the stiffness the IRSBot-2 should be very high along the normal to the plane of motion of its moving-platform. A semi-industrial prototype of the IRSBot-2 has been realized based on the obtained optimum design parameters. This prototype and its main components are described in the paper. Its accuracy, repeatability, elasto-static performance, dynamic performance and elasto-dynamic performance have been measured and analyzed too. It turns out the IRSBot-2 has globally reached the prescribed specifications and is a good candidate to perform very fast and accurate pick-and-place operations.
research-article
J. Mechanisms Robotics   doi: 10.1115/1.4037892
The paper presents a theory of vibratory locomotion, a prototype, and the results of experiments on mini robot which moves as a result of inertial excitation provided by two electric motors. The robot is equipped with elastic bristles which are in contact with the supporting surface. Vibration of the robot generates the friction force which can push the robot forward or backward. The paper presents a novel model of interaction between the bristles and the supporting surface. The friction force (its magnitude and sense) is defined as a function of the robot velocity and the robot´s vibrations. The analysis is done for a constant coefficient of friction and a smooth surface. Depending on the motors' speed, one may obtain a rectilinear or a curvilinear motion, without jumping or losing contact with the substrate. The results of the simulation show which way the robot moves, its mean velocity of locomotion, change of the slipping velocity of the bristles and its influence on the normal and the friction force. A prototype was built and experiments were performed with it.
TOPICS: Robots, Excitation, Friction, Engineering prototypes, Vibration, Electric motors, Motors, Simulation
Errata
Mark Plecnik
J. Mechanisms Robotics   doi: 10.1115/1.4037804
Table 1 lists some example homotopy startpoints and endpoints. Although the "Roots obtained" in Table 1 are valid solutions of the target system, they do not correspond with the printed "Startpoints" and "Start system parameters" when a homotopy is constructed with the ? parameter listed in the caption. Corrected endpoints are printed below.
research-article
Leila Notash
J. Mechanisms Robotics   doi: 10.1115/1.4037803
For under-constrained and redundant parallel manipulators, the actuator inputs are studied with bounded variations in parameters and data. Problem is formulated within the context of force analysis. Discrete and analytical methods for interval linear systems are presented, categorized and implemented to identify the solution set, as well as the minimum 2-norm least square solution set. The notions of parameter dependency and solution subsets are considered. The hyperplanes that bound the solution in each orthant characterize the solution set of manipulators. While the parameterized form of the interval entries of the Jacobian matrix and wrench produce the minimum 2-norm least square solution for the under-constrained and over-constrained systems of real matrices and vectors within the interval Jacobian matrix and wrench vector, respectively. Example manipulators are used to present the application of methods for identifying the solution and minimum norm solution sets for actuator forces/torques.
TOPICS: Redundant manipulators, Manipulators, Actuators, Jacobian matrices, Linear systems, Analytical methods
research-article
J. Mechanisms Robotics   doi: 10.1115/1.4037760
Flapping wing air vehicles (FWAVs) offer a new flight mode compared to the traditional rotary or fixed wing platforms. Recent advances in FWAVs have produced platforms that offer motion control in wings, which is used to explore aerobatic maneuvers. Dive is one of the the simplest maneuvers to explore using wing motion control capabilities. This maneuver can serve as a building block for designing more complex aerobatic maneuvers. This paper is focused on design of dive maneuvers that can be performed outdoors with a minimal amount of on-board computing capability. We present a simple computational model that provides accuracy of 5 m in open loop operation mode for outdoor dives under wind speeds of up to 3 m/s. This model is executed using a low power, on-board processor. We have also demonstrated that the platform can independently execute roll control through tail positioning, and dive control through wing positioning to produce safe dive behaviors. These capabilities were used to successfully demonstrate autonomous dive maneuvers on the Robo Raven platform developed at the University of Maryland.
TOPICS: Modeling, Wings, Unmanned aerial vehicles, Motion control, Design, Wind velocity, Blocks (Building materials), Flight, Vehicles
research-article
J. Mechanisms Robotics   doi: 10.1115/1.4037619
The paper presents a simple and effective kinematic model and methodology to assess the extent of the position uncertainty caused by joint clearances for any linkage and manipulator connected with revolute or prismatic pairs. The model is derived and explained with geometric rigor based on Ting's rotatability laws. It offers a simple prismatic joint clearance link model that catches the translation and oscillation characteristics of the slider within the clearance and separates the geometric effect of clearances from the input error. It is a general method, which is effective for multiloop linkages and parallel manipulators. It settles the dispute on the position uncertainty effect to parallel and serial robots due to joint clearance. The discussion is illustrated and carried out through symmetric planar eight-bar parallel robots. It finds that at a target position, the uncertainty region of a three degree-of-freedom three-leg parallel robot is enclosed by a hexagon with curve edges, while that of its serial counterpart is enclosed by a circle within the hexagon. A numerical example is presented. The finding and proof, though only based on three-leg planar 8-bar parallel robots, have a wider implication suggesting that based on the kinematic effect of joint clearance, parallel robots tends to inherit more position uncertainty than their serial counterparts. The use of more loops in linkages as well as parallel robots cannot fully offset the adverse effect on position uncertainty caused by the use of more joints.
TOPICS: Clearances (Engineering), Linkages, Manipulators, Uncertainty, Robots, Kinematics, Oscillations, Degrees of freedom, Errors
research-article
J. Mechanisms Robotics   doi: 10.1115/1.4037567
Space robots require compact Joint Drive Systems (JDS), typically comprising of actuator, transmission, joint elements that can deliver high torques through stiff mechanical ports. Today's conventional space drive systems are made from off-the-shelf actuators and multi-stage transmissions that generally involve 3-6 stages. This current practice lacks a system-level integration that accounts for the actuator structure, size and output force, transmission structure, gear ratio and strength, and often leads to long and bulky assemblies with large number of parts. This paper presents a new robotic hardware that integrates the robot's joint drive system into one compact device that is optimized for its size and maximum torque density. This is done by designing the robotic joint using a special transmission which, when numerically optimized, can produce unlimited gear-ratios using only two stages. The design is computerized to obtain all the solutions that satisfy its kinematic relationships within a given actuator diameter. Compared to existing flight actuators, the proposed design could lead to shorter assemblies with significantly lower number of parts for the same output torque. The theoretical results demonstrates the potential of an example device, for which a proof-of-concept plastic mockup was fabricated, that could deliver more than 200 Nm of torque in a package as small as a human elbow joint. The proposed technology could have strong technological implications in other industries such as powered prosthetic and rehabilitation equipment.
TOPICS: Torque, Actuators, Design, Robotics, Gears, Density, Kinematics, Robots, Hardware, Gates (Closures), Artificial limbs, Flight, Human elbow

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