Kinetostatic Analysis of a Simple Cable-Driven Parallel Crane

This paper introduces the concept of a new planar Cable-Driven Parallel Crane (CDPC) for lifting and carrying payloads with a moving hoist mechanism connected in parallel to the ceiling. In contrast to bridge-crane, CDPC is inexpensive and practicable for diverse tasks with simple assembly setup. The hoist mechanism is an under-constrained moving-platform articulated through a bi-actuated cable circuit, namely, a cable loop. The hoist is connected to a suspended moving-platform with four degrees of freedom. The power is transmitted directly from the motors fixed on frames to the hoist through the cable loop. Therefore, the dynamic performance of the robot is increased due to lower inertia of the moving-platform. However, the moving-platform undergoes some parasitic inclinations because of the cable loop. This paper investigates the parasitic inclination and its effect on the positioning of the payload. The workspace of the CDPC is studied in terms of static equilibrium. Moreover, the geometrico-static and elasto-static models of the CDPC are presented.

Dynamic Analysis of Slider Mechanisms With Consideration of Frictional Effect in the Slider

This paper deals with dynamic analysis of three methods for the slider in mechanisms. Three methods are introduced under three conditions (the influence of friction force is considered, the slider’s center of mass is not coincide with the hinge point, the slider and its guide have rotation motion). The dynamic analyses of the crank slider mechanism and the flying shear mechanism are given as examples by a developed software based on Visual C++ environment, and application scope of the three methods is concluded at the end of the paper. These results are useful for analyzing and designing mechanisms with sliders, such as choosing suitable slider materials or actuators.

Mobile Robot Regulation With Image Based Visual Servoing

The development of image processing algorithms grew exponentially over the past few decades with improvements in vision sensors and computational power. In this paper, a visual servo controller is designed and developed using the image-based method for a differential drive robot. The objective is to reach a desired pose relative to a target object placed in the world frame with four feature points. A full system model that includes the mobile base and camera is presented along with the design of a proportional controller. The system is implemented in the Husky A200 Robot by Clearpath Robotics. MATLAB Simulation and experimental results are analyzed and discussed with conclusion and future works recommendation in the end.

A Study on the Influence of Planar Mechanism Design on Energy Use During Controlled Movements

This paper presents a study on the energy utilization of planar automation mechanisms that operate with controlled moves. Designers of factory automation for pick & place tasks often select multiple degree-of-freedom robotic devices. With multiple degrees-of-freedom, task flexibility is available, but many operations require little or no flexibility. The majority of research on the energy usage of these robot devices for pick & place tasks focuses on path planning. The study presented in this paper explores the energy savings in using low degree-of-freedom devices and the influence of design parameter selection. Energy predictor equations are developed and confirmed through experimentation. Various positioning mechanisms of differing dimensions are studied for trends in energy utilization. Lastly, an actuator control strategy is proposed for further reducing energy requirements. The study concludes that energy usage can be substantially decreased in pick & place applications by reducing the degrees of freedom of the device, implementing a prudent mechanism architecture, ideally selecting mechanism dimensions and optimally controlling the actuator(s).

Three-Position Rigid Body Guidance Using Specified Moving Pivots for a Four-Bar Mechanism With Variable Topology

This paper provides an algorithm allowing a designer to perform three position rigid body guidance with specified moving pivots for a 4R-RRRP mechanism with variable topology (MVT). A mechanism with variable topology is a mechanism that changes from one topological state to another due to a change in joint geometry. Both a graphical approach and an algebraic solution are presented. An example is provided in which a circuit defect in a 4R mechanism can be avoided using a 4R-RRRP mechanism. Two additional examples are provided that show the results of this new theory. Practical applications for this theory are found in many industries including manufacturing, aerospace, and healthcare.

Analysis of Parasitic Motion in Compliant Mechanisms Using Eigenwrenches and Eigentwists

Parasitic motion is undesired in precision mechanisms, it causes unwanted kinematics. These erroneous motions are especially apparent in compliant mechanisms. Usually an analysis of parasitic motion is only valid for one type of mechanism. Kinematic information is imbedded in the compliance matrix of any mechanism; an eigenscrew decomposition expresses this kinematic information as screws. It uses screw theory to identify the lines along which a force yields a parallel translation and a rotation yields a parallel moment. These lines are called eigenwrenches and eigentwists. Any other load on the compliant mechanism will lead to parasitic motion. This article introduces two parasitic motion metrics using eigenscrew decomposition: the parasitic resultant from an applied screw and the deviation of an actual degree of freedom from a desired degree of freedom. These metrics are applicable to all compliant mechanism and allow comparison between two compliant mechanisms. These metrics are applied to some common compliant mechanisms as an example.

Design, Modeling, and Experimental Drag Characterization of a Bio-Inspired, Shape-Adapting Underwater Vehicle

Autonomous underwater vehicles (AUVs) have shown great promise in fulfilling surveillance, scavenging, and monitoring tasks, but can be hindered in expansive, cluttered or obstacle ridden environments. Traditional gliders and streamlined AUVs are designed for long term operational efficiency in expansive environments, but are hindered in cluttered spaces due to their shape and control authority; agile AUVs can penetrate cluttered or sensitive environments but are limited in operational endurance at large spatial scales. This paper presents the prototype testbed design, modeling, and experimental hydrodynamic drag characterization of a novel self-propelled underwater vehicle capable of actuating its shape morphology. The vehicle prototype incorporates flexible, buckled fiberglass ribs to ensure a rigid shape that can be actuated by modulating the length of the semi-major axis. Tools from generative modeling are used to represent the vehicle shape by using a single control input actuating the vehicles length-to-diameter ratio. By actuating the length and width characteristics of the vehicle’s shape to produce a desired drag profile, we derive the feasible speeds achievable by shape actuation control. Tow-tank experiments with an experimental proto-type suggest shape actuation can be used to manipulate the drag by a factor between 2.15 and 5.8 depending on the vehicle’s operating speed.

Kinematics Analysis and Motion Control of a Mobile Robot Driven by Three Tracked Vehicles

In this paper, a mobile robot named VicRoB with 6 degrees of freedom (DOFs) driven by three tracked vehicles is designed and analyzed. The robot employs a 3-PPSR parallel configuration. The scheme of the mechanism and the inverse kinematic solution are given. A path planning method of a single tracked vehicle and a coordinated motion planning of three tracked vehicles are proposed. The mechanical structure and the electrical architecture of VicRoB prototype are illustrated. VicRoB can achieve the point-to-point motion mode and the continuous motion mode with employing the motion planning method. The orientation precision of VicRoB is measured in a series of motion experiments, which verifies the feasibility of the motion planning method. This work provides a kinematic basis for the orientation closed loop control of VicRoB whether it works on flat or rough road.

On Locomotion of a Laminated Fish-Inspired Robot in a Small-to-Size Environment

Many different robots have been designed and built to work under water. In many cases, researchers have chosen to use a bioinspired platforms. In most cases, the main goal of the fish inspired robots has been set to autonomously swim and maneuver in an environment spacious compared to the fish’s size. In this paper, the identification & control of a low-cost fish-inspired robot is studied with goal of building a mechanism to not only swim in water but able to interact with its narrow environment. The robotic fish under study uses tail propulsion as main locomotion. Moreover, proper propulsion regimes are identified and used to model and control thrust generated by propulsion.

Unified Rotational and Translational Stiffness Characterization of Compliant Shell Mechanisms

Compliant shell mechanisms utilize spatially curved thin-walled structures to transfer or transmit force, motion or energy through elastic deformation. To design with spatial mechanisms designers need comprehensive characterization methods, while existing methods fall short of meaningful comparisons between rotational and translational degrees of freedom. This paper presents two approaches, both of which are based on the principle of virtual loads and potential energy, utilizing properties of screw theory, Plücker coordinates and an eigen-decomposition, leading to two unification lengths that can be used to compare and visualize all six degrees of freedom directions and magnitudes of compliant mechanisms in a non-arbitrary physically meaningful manner.