Synthesis of a Reconfigurable Four-Bar Mechanism With Variable Joints

This article introduces a reconfigurable four-bar mechanism. The mechanism uses a rotational-translational variable joint to switch between a RRRR four-bar and a RRRP1 four-bar. The ability to transition between two types of four-bar mechanisms allows the reconfigurable four-bar mechanism to complete a rigid body guidance task not possible by either a RRRR four-bar mechanism or a RRRP four-bar mechanism. The reconfigurable mechanism reduces the number of required actuators in the mechanism.

Performance Characterization of Multifunctional Wings With Integrated Solar Cells for Unmanned Air Vehicles

Flapping wing unmanned air vehicles (UAVs) are small light weight vehicles that typically have short flight times due to the small size of the batteries that are used to power them. During longer missions, the batteries must be recharged. The lack of nearby electrical outlets severely limits the locations and types of missions that these UAVs can be flown in. To improve flight time and eliminate the need for electrical outlets, solar cells can be used to harvest energy and charge/power the UAV. Robo Raven III, a flapping wing UAV, was developed at the University of Maryland and consists of wings with integrated solar cells. This paper aims to investigate how the addition of solar cells affects the UAV. The changes in performance are quantified and compared using a load cell test as well as Digital Image Correlation (DIC). The UAV platform reported in this paper was the first flapping wing robotic bird that flew using energy harvested from on-board solar cells. Experimentally, the power from the solar cells was used to augment battery power and increase operational time.

Dimensional Synthesis of a Novel 2T2R Parallel Manipulator for Medical Applications

This paper deals with the dimensional synthesis of a novel parallel manipulator for medical applications. This parallel mechanism has a novel 2T2R mobility derived from the targeted application of needle manipulation. The kinematic design of this 2T2R manipulator and its novelty are illustrated in relation to the percutaneous procedures. Due to the demanding constraints on its size and compactness, achieving a large workspace especially in orientation, is a rather difficult task. The workspace size and kinematic constraint analysis are considered for the dimensional synthesis of this 2T2R parallel mechanism. A dimensional synthesis algorithm based on the screw theory and the geometric analysis of the singularities is described. This algorithm also helps to eliminate the existence of voids inside the workspace. The selection of the actuated joints is validated. Finally, the dimensions of the structural parameters of the mechanism are calculated for achieving the required workspace within the design constraints of size, compactness and a preliminary prototype without actuators is presented.

A Novel Synthesis Method of Polygon-Scaling Mechanisms

A polygon-scaling mechanism is a single DOF (degree-of-freedom) mechanism for scaling a polygon. This paper presents a tetragon-elements based synthesis method of polygon-scaling mechanisms. According to movable conditions of radial scaling elements, four basic tetragon elements (rhombus element, parallelogram element, kite element and general tetragon element) are proposed. For a given polygon, these four types of elements can be selected based on the characteristics of target polygons to construct polygon-scaling mechanisms in a straightforward manner. Using this synthesis method, some planar 1-DOF scaling mechanisms are obtained with the characteristics of retracting and deploying. Their 3D models are also presented to proof the validity of the proposed method. Finally, a table of tetragon elements with the characteristics of their associated polygon-scaling mechanisms is summarized using which polygon-scaling mechanisms can be easily constructed.

Design and Analysis of a Tendon-Driven, Under-Actuated Robotic Hand

There has been continuous research and development to add more actuators into robotic hands to increase their dexterity. However, dexterous hands require complex control and are more costly to build. Therefore, many researchers and commercial enterprises have begun developing under-actuated robotic hands with fewer actuators and passive mechanical adaptation to not only reduce complexity and cost, but to also achieve better grasp performance in unstructured settings. This paper presents the design and analysis of the Valkyrie hand — a four fingered, tendon-driven, and under-actuated robotic hand that balances dexterity and simplicity with total 14 joints, and six degrees of actuated freedom. A derivation is provided of general dynamic and static equations for the analysis of a tendon driven mechanism, based on Euler-Lagrange formulation. The equations were used to evaluate the design parameters’ impact on the hand grasp shape and closing effort, and also validated against a design case study.

Towards Statically Balanced Compliant Joints Using Multimaterial 3D Printing

Compliant joints are widely used in mechanisms when accurate movements are required. With no assembly requested, they are also a great tool for mesoscale robotics, a field in which compactness and large joint amplitudes are necessary features. In this paper, an original multi-material compliant revolute joint is presented. Taking advantage of multi-material 3D printing, it exhibits a novel design with the integration of an hyper-elastic material. Thanks to a helical shape design, a large range of motion is obtained, and the incompressibility of the hyper-elastic material is used to improve the stiffness properties of the joint while keeping it compact. The spring effect of compliant joints makes mechanism actuation more difficult. The proposed joint is therefore designed with an integrated static balancing system in order to minimize actuation torques. The balancing system is composed of a bistable mechanism, which geometry optimization is presented. Experimental assessment demonstrate that the joint possesses a range of motion of 120°, and the balancing system reduces actuation moments by almost 60%.

Autonomous Loitering Control for a Flapping Wing Miniature Aerial Vehicle With Independent Wing Control

Flapping wing miniature aerial vehicles (FWMAVs) offer advantages over traditional fixed wing or quadrotor MAV platforms because they are more maneuverable than fixed wing aircraft and are more energy efficient than quadrotors, while being quieter than both. Currently, autonomy in FWMAVs has only been implemented in flapping vehicles without independent wing control, limiting their level of control. We have developed Robo Raven IV, a FWMAV platform with independently controllable wings and an actuated tail controlled by an onboard autopilot system. In this paper, we present the details of Robo Raven IV platform along with a control algorithm that uses a GPS, gyroscope, compass, and custom PID controller to autonomously loiter about a predefined point. We show through simulation that this system has the ability to loiter in a 50 meter radius around a predefined location through the manipulation of the wings and tail. A simulation of the algorithm using characterized GPS and tail response error via a PID controller is also developed. Flight testing of Robo Raven IV demonstrated the success of this platform, even in winds of up to 10 mph.

Analysis of Optimal Cable Configurations in the Design of a 3-DOF Cable-Driven Robot Leg

The operational workspace of a cable-driven serial robot is largely dictated by the choice of cable placement and routing. As robot complexity increases with additional cables and degrees of freedom, the problem of designing a cable architecture can quickly become challenging. This paper builds upon a previously described methodology to identify and analyze optimal cable configurations, expanding the approach to a 3-DoF robot leg driven by four cables. The methodology is used to analyze configuration trends in the routing and placement of the cables which achieve the desired range of motion for the robot. The results of the analysis are used to inform the design of a cable architecture which is shown to be capable of controlling the robot through the desired task.

Stiffness and Stability Characteristics of Small Satellite Deployables With Integrated Tape-Spring Booms

Currently, the small satellite mechanisms that are used to deploy sensors and antennae in space have been restricted to simple one arm pin jointed members or telescopic mechanisms. This means, to deploy multiple sensors, multiple actuators and controllers are required. However, simple rigid link mechanisms, like the 6-bar hexagonal mechanism described in this paper, give the freedom to incorporate a greater number of sensor platforms in one deployable structure and also helps reduce the number of actuators. In fact, by the use of boom technology, the entire mechanism can be deployed by a single tape-spring boom. Further, to make these structures more robust and stiffer at the joints, rotational springs can be used. In this paper, an attempt is made to study the stiffness and stability of such mechanisms at their equilibrium points. Also since the positions and orientations of the sensor platforms are critical, it is shown through a few examples how these parameters can be adjusted just by tweaking the preloads of the rotational springs. The tape-spring boom — which is bi-stable in nature — offers further stiffness to the structure in its deployed state. It is well known now and also well established by the theory of mechanics of materials that by arranging multiple tape springs in certain orientations within the boom; a boom can be obtained with significant axial and flexural stiffness in its deployed state. Through modal analyses at equilibrium and by looking at the characteristics of the Hessian of the potential energy function, it is also shown how this significantly rigid boom affects the stiffness and stability of the structure. Herein, the force method of matrix analysis for deployable structures is used for analyses. This paper also discusses the possibilities of the system failing due to insufficient actuation force by the boom — the condition where the boom does not reach its second stable position.

Multi-Objective Design Optimization of the Leg Mechanism for a Piping Inspection Robot

This paper addresses the dimensional synthesis of an adaptive mechanism of contact points ie a leg mechanism of a piping inspection robot operating in an irradiated area as a nuclear power plant. This studied mechanism is the leading part of the robot sub-system responsible of the locomotion. Firstly, three architectures are chosen from the literature and their properties are described. Then, a method using a multi-objective optimization is proposed to determine the best architecture and the optimal geometric parameters of a leg taking into account environmental and design constraints. In this context, the objective functions are the minimization of the mechanism size and the maximization of the transmission force factor. Representations of the Pareto front versus the objective functions and the design parameters are given. Finally, the CAD model of several solutions located on the Pareto front are presented and discussed.