1,721,052 research outputs found
Modeling of static reliability assessment in dielectric elastomer transducers subject to electric loads
No full textIn recent years, Dielectric Elastomer Transducers (DETs) have been of top-notch interest as an alternative solution to conventional mechatronic transduction systems, thanks to their features as low-cost and affordable materials, silence operation, low-power consumption, and high level of energy density. Generally, in their most uncomplicated layout, these devices form an electrostatic system, composed of a Dielectric Elastomer (DE) membrane, embedded between two opposite compliant electrodes, constituting a highly deformable capacitor capable of transforming electrical energy into mechanical and vice versa. However, DETs applicability is strongly affected by several engineering constraints. One of their principal failure modes is related to the electrical breakdown of the DE membrane, which occurs when an applied input electrical load exceeds the dielectric strength of the DE. In order to address this problem, the materials and the input load conditions must be chosen appropriately to assure a desired lifetime of operation. For this purpose, this work proposes a preliminary static reliability assessment procedure to evaluate the failure probability of a DET for static events as the electrical breakdown, with specific electric input load conditions. The resulting reliability model comprises the stochastic comparison of the dielectric strength of the DE material with the extreme values distribution of electrical loads in a specific period, aiming to forecast the reliability evaluation for a more extended period, multiple of the original one
Loading system mechanism for dielectric elastomer generators with equi-biaxial state of deformation
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Proceedings of SPIE - The International Society for Optical Engineering
Volume 9056, 2014, Article number 90561F
Electroactive Polymer Actuators and Devices, EAPAD 2014; San Diego, CA; United States; 10 March 2014 through 13 March 2014; Code 106848
Loading system mechanism for dielectric elastomer generators with equi-biaxial state of deformation (Conference Paper)
Fontana, M. , Moretti, G., Lenzo, B., Vertechy, R.
PERCRO SEES, TeCIP Institute, Scuola Superiore sant'Anna, Piazza Martiri della Libertà 33, Pisa, 5612, Italy
View references (18)
Abstract
Dielectric Elastomer Generators (DEGs) are devices that employ a cyclically variable membrane capacitor to produce electricity from oscillating sources of mechanical energy. Capacitance variation is obtained thanks to the use of dielectric and conductive layers that can undergo different states of deformation including: uniform or non-uniform and uni- or multi-axial stretching. Among them, uniform equi-biaxial stretching is reputed as being the most effective state of deformation that maximizes the amount of energy that can be extracted in a cycle by a unit volume of Dielectric Elastomer (DE) material. This paper presents a DEG concept, with linear input motion and tunable impedance, that is based on a mechanical loading system for inducing uniform equi-biaxial states of deformation. The presented system employs two circular DE membrane capacitors that are arranged in an agonist-antagonist configuration. An analytical model of the overall system is developed and used to find the optimal design parameters that make it possible to tune the elastic response of the generator over the range of motion of interest. An apparatus is developed for the equi-biaxial testing of DE membranes and used for the experimental verification of the employed numerical models
A New Parameter Selection Method for Power Skiving Tools
No full textThis paper presents a new selection method of the teeth number and the helix angle of a power skiving tool, which are basic parameters for machining internal gears. It is based on screw theory, whose use for power skiving has not been yet documented in the literature. The tool parameters are selected based on an optimization procedure of the machining process kinematics, differently from the common practice that defines them by experience. In addition, specific power skiving requirements are also considered in the selection. A working example that shows the effectiveness of the method is provided, and the optimal tool parameters are found. In particular, the results show that two different types of tool can machine the same internal gear
Power skiving manufacturing process: A review
Full text linkGears are the most widely used mechanical components for motion and power transmission; thus, gear manufacturing plays a crucial role in many industrial sectors. Amongst the different methods for gear machining, power skiving has become a highly competitive gear manufacturing process in the last few decades. This is mainly due to advances in manufacturing engineering and improvements in numerical control of electric drives. This article presents a comprehensive review on the research and development activities on power skiving that is missing in the literature. In particular, it aims at presenting the current state of the art of this manufacturing process and highlighting new advancements. The study encompasses some of the major topics, namely: new tool designs, influence of working parameters on the cutting operation, chip geometry, determination of cutting forces and tool wear. Finally, study deficiencies, practical limitations and new research directions in the field of power skiving are discussed which can serve as guidelines for new research on the topic
On Locally Optimal Redundancy Resolution using the Basis of the Null Space
No full textThis paper presents two methods for the computation of the null space velocity command in redundant robots. Both these methods resort to the solution of a constrained optimization problem. The first one is a formalization of the traditional Gradient Projection Method (GPM) which guarantees the respect of the joint bounds and a gradual activation/deactivation of the null space command. The second one, called Null Space Basis Optimal Linear Combination Method (NSBM), finds the optimal coefficients of a basis of the null space of the Jacobian, ensuring in turn that the joint bounds are respected and that the null space is activated and deactivated gradually. The two methods are applied to the case study of a welding application in which the null space command must avoid the collision between the robot and an obstacle. The comparison of the results of the case study shows that NSBM performs better than GPM. The proposed algorithms are also tested on a real robotic platform to demonstrate that their computational time is compatible with the real-time requirements of the robot
Towards autonomous soft grasping of deformable objects using flexible thin-film electro-adhesive gripper
No full textAutonomous robotic grasping is a fundamental skill for the next generation of robots. It is a challenging problem as it requires many steps to succeed, ranging from detecting the target location to selecting the grasp pose configuration to have a stable grasp. Grasping fragile objects or objects with variable shapes is a more complex task with respect to the traditional pick and place of solid objects, and robots typically do not have a reliable sense of touch. In such cases, a retention action, which can be obtained by electro-adhesion, is typically preferred over a compression force in order to avoid damaging the objects. The proposed work presents a robotic manipulation grasping system that leverages a gripper realized with the flexible thin-film electro-adhesive (EA) devices technology and a vision pipeline based on an RGB-D camera to detect the grasp pose configuration and track the target during the holding phase to check whether the task has been successfully completed. Thanks to the properties of the EA gripper, vision is the only perception cue needed to successfully grasp the target without damaging it since the gripper can automatically adapt its shape to the surface of the target delicately wrapping its two fingers around the object. Several tests have been done to assess the capabilities of the proposed robotic system, picking and placing deformable objects, comparing the EA gripper with a traditional parallel jaw gripper. The gripper is particularly suitable to handle objects where two parallel flat surfaces are available for grasping. Future works will attempt to improve the grasping of non flat objects
On the profile change of conical skiving tools after re-sharpening
Full text linkGear skiving is a productive process for manufacturing internal gears that has been spreading among companies in recent years. In gear skiving, conical shaped tools are used to avoid interference during machining. However, due to the conical shape, both the tool tip diameter and the tool profile change after re-sharpening, leading to a change in cutting performances during the tool service life. This paper aims at investigating the impact of the profile change on the process through simulations and experiments. Sensitive tools to profile change are identified and a strategy to reduce the difference in cutting performances is proposed
Dielectric elastomer materials for large-strain actuation and energy harvesting: A comparison between styrenic rubber, natural rubber and acrylic elastomer
Full text linkThis paper compares the performance of commercially available membranes made of styrenic rubber, natural rubber and acrylic elastomer for dielectric elastomer transducers (DETs) operating in the large strain regime. Following a detailed description of the adopted experimental set-up and procedures, the results of a comprehensive electro-mechanical characterization of the three materials are reported to highlight the following dependencies: dielectric strength versus stretch, electrical conductivity versus electric field, dielectric constant versus stretch, stress versus stretch and strain rate. This includes the fitting of the experimental data with constitutive equations which provide material property values that can be used for model-based analysis, design and control of dielectric elastomer actuators and generators operating at large levels of strain amplitudes (like, for instance, transducers featuring actuation and generator strains over 50%) or in the presence of large pre-strains (over 50%). Performance metrics relying on the identified constitutive parameters are introduced in order to discuss the specific pros and cons of the considered elastomers for the development of practical DETs
Design and Control of the Rehab-Exos, a Joint Torque-Controlled Upper Limb Exoskeleton †
Full text linkThis work presents the design of the Rehab-Exos, a novel upper limb exoskeleton designed for rehabilitation purposes. It is equipped with high-reduction-ratio actuators and compact elastic joints to obtain torque sensors based on strain gauges. In this study, we address the torque sensor performances and the design aspects that could cause unwanted non-axial moment load crosstalk. Moreover, a new full-state feedback torque controller is designed by modeling the multi-DOF, non-linear system dynamics and providing compensation for non-linear effects such as friction and gravity. To assess the proposed upper limb exoskeleton in terms of both control system performances and mechanical structure validation, the full-state feedback controller was compared with two other benchmark-state feedback controllers in both a transparency test—ten subjects, two reference speeds—and a haptic rendering evaluation. Both of the experiments were representative of the intended purpose of the device, i.e., physical interaction with patients affected by limited motion skills. In all experimental conditions, our proposed joint torque controller achieved higher performances, providing transparency to the joints and asserting the feasibility of the exoskeleton for assistive applications
Control of an oscillating water column wave energy converter based on dielectric elastomer generator
No full textThis paper introduces a model-based control strategy for a wave energy converter (WEC) based on dielectric elastomer generators (DEGs), i.e. a device that can convert the energy of ocean waves into electricity by employing deformable elastomeric transducers with variable capacitance. The analysed system combines the concept of oscillating water column WEC with an inflated circular diaphragm DEG (ICD-DEG). The device features strongly nonlinear dynamics due to the ICD-DEG electro-hyperelastic response and the compressibility of the air volume comprised between the water column and the ICD-DEG, while the hydrodynamic loads can be approximated as linear. The optimal control solution that maximises the power extraction of the device is numerically investigated in the case of monochromatic waves over the typical frequency and amplitude ranges of sea waves. The more realistic case of panchromatic waves is also analysed through the implementation, in simulation environment, of a real-time controller. This regulator is based on a simple sub-optimal control logic that is deduced from the monochromatic case. The performance of the proposed control strategy is illustrated in comparison with unoptimised algorithms
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