Robust Contact Research Articles

Investigation of the dynamics of electromagnetic valves by a coupled magneto‐mechanical algorithm including contact mechanics

PurposeThe fast and flexible development of fast switching electromagnetic valves as used in modern gasoline engine demands the availability of efficient and accurate simulation tools. The purpose of this paper is to provide an enhanced computational scheme of these actuators including all relevant physical effects of magneto‐mechanical systems and including contact mechanics.Design/methodology/approachThe finite element (FE) method is applied to efficiently solve the arising coupled system of partial differential equations describing magneto‐mechanical systems. The algorithm for contact mechanics is based on the cross‐constraint method using an energy‐ and momentum‐conserving time‐discretisation scheme. Although solving separately for the electromagnetic and mechanical system, a strong coupling is ensured within each time step by an iterative process with stopping criterion.FindingsThe numerical simulations of the full switching cycle of an electromagnetic direct injection valve, including the bouncing during the closing state, are just feasible with an enhanced and robust mechanical contact algorithm. Furthermore, the solution of the nonlinear electromagnetic and mechanical equations needs a Newton scheme with a line search scheme for the relaxation of the step size.Originality/valueThe paper provides a numerical simulation scheme based on the FE method, which includes all relevant physical effects in magneto‐mechanical systems, and which is robust even for long‐term contact periods with multitude re‐opening phases.

Novel multicontact radio frequency microelectromechanical system switch in high-power–handling applications

We report a novel multicontact radio frequency (RF) microelectromechanical system (MEMS) switch with mechanical independent switch elements and microspring contacts. The consistent contact arrangement and the robust contact design can effectively increase the contact area, reduce the current density, and therefore improve the power-/current-handling capability. The working mechanism of the switch with microspring contact is investigated by CoventorWare® simulation tools. The switch, fabricated by the Cu-Ni dual-metallic-sacrificial-layer surface micromachining, is actuated at 55 V for characterization. The closing time is 11 μs, and the opening time is 13.5 μs. The isolation is -30.9 dB at 2 GHz and -11.5 dB at 20 GHz; the insertion loss is -0.12 dB at 2 GHz and -0.22 dB at 20 GHz. The contact metal is Pt-Au, and the measured switch resistance drops from 48 to 1.2 Ω when the actuation voltage increases from 40 to 65 V. The switch element handles a current of 300 mA at 0.1 Hz. The switch is an excellent candidate for microwave applications requiring high-power handling.

Flexible Field Emission of Nitrogen‐Doped Carbon Nanotubes/Reduced Graphene Hybrid Films

The outstanding flexible field emission properties of carbon hybrid films made of vertically aligned N-doped carbon nanotubes grown on mechanically compliant reduced graphene films are demonstrated. The bottom-reduced graphene film substrate enables the conformal coating of the hybrid film on flexible device geometry and ensures robust mechanical and electrical contact even in a highly deformed state. The field emission properties are precisely examined in terms of the control of the bending radius, the N-doping level, and the length or wall-number of the carbon nanotubes and analyzed with electric field simulations. This high-performance flexible carbon field emitter is potentially useful for diverse, flexible field emission devices.

Haptograph representation of real‐world haptic information by wideband force control

AbstractArtificial acquisition and reproduction of human sensations are basic technologies in communication engineering. For example, auditory information is obtained by a microphone, and a speaker reproduces it by artificial means. Furthermore, a video camera and a television make it possible to transmit visual sensation by broadcasting. On the other hand, since tactile or haptic information is subject to Newton's “law of action and reaction” in the real world, a device that acquires, transmits, and reproduces information has not been established. From this perspective, real‐world haptics is the key technology for future haptic communication engineering. This paper proposes a novel acquisition method for haptic information called a “haptograph”. The haptograph visualizes the haptic information like a photograph. The proposed haptograph is applied to haptic recognition of the contact environment. A linear motor contacts the surface of the environment and its reaction force is used to make a haptograph. A robust contact motion and sensor‐less sensing of the reaction force are attained by using a disturbance observer. As a result, an encyclopedia of the contact environment is obtained. Since temporal and spatial analyses are conducted to represent haptic information as the haptograph, intuitive recognition and evaluation are possible. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(11): 28–37, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10235

Mother-offspring dialogue in early pregnancy: Impact of adverse environment on pregnancy maintenance and neurobiology

The mother-offspring dialogue begins even before implantation and is essential to signal pregnancy, establish robust contact, and maintain embryo growth and development. Any circumstance that disrupts the dialogue risks pregnancy problems. A new look at how stress impacts on pregnancy involves its adverse effects on the key pregnancy hormones of progesterone and prolactin. These effects have far-reaching consequences on pregnancy maintenance, maternal anxiety and embryo programming. This review focuses on early pregnancy and how stress might compromise the multi-layer, two-way communication between mother and embryo.

Robust contact force controller for slip prevention in a robotic gripper

Grasping a soft or fragile object requires the use of minimum contact force to prevent damage or deformation. Without precise knowledge of object parameters, real-time feedback control must be used with a suitable slip sensor to regulate the contact force and prevent slip. Furthermore, the controller must be designed to have good performance characteristics to rapidly modulate the fingertip contact force in response to a slip event. In this paper, a fuzzy sliding mode controller combined with a disturbance observer is proposed for contact force control and slip prevention. The controller is based on a system model that is suitable for a wide class of robotic gripper configurations. The robustness of the controller is evaluated through both simulation and experiment. The control scheme was found to be effective and robust to parameter uncertainty. When tested on a real system, however, chattering phenomena, well known to sliding mode research, was induced by the unmodelled suboptimal components of the system (filtering, backlash, and time delays), and the controller performance was reduced.

A Robust Position and Force Control Strategy for 7-DOF Redundant Manipulators

This paper is concerned with robust position and contact force control for 7-DOF redundant robot arms. An outer-inner loop controller, called the augmented hybrid impedance control scheme is developed. A 6-DOF force/torque sensor is used to measure the interaction forces. These are fed back to the outer-loop controller that implements either a force or an impedance controller in each of the 6 DOF of the tool frame. The force controller is provided with a force set point, and desired inertia and damping are introduced in the force control loop to improve transient performance. The inner loop consists of a Cartesian-level potential difference controller, a redundancy resolution scheme at the acceleration level, and a joint-space inverse dynamics controller. Experimental results for two 7-DOF robot arms (redundant, dextrous, isotropically enhanced, seven-turning pair robot (REDIESTRO) and Mitsubishi PA10-7C) are given to illustrate the performance of the force control strategy. A successful application of the proposed scheme to a surface cleaning task is described using the REDIESTRO, while position and force tracking experiments are described for the Mitsubishi PA10-7C robot.

An efficient and robust contact algorithm for a compliant contact force model between bodies of complex geometry

Dynamic analysis of many mechanical systems often involves contacts among rigid bodies. When calculating the contact force with a compliant contact force model, a penetration depth and a contact reference frame (a contact point and normal and tangent directions) should be determined from the geometrical information of the rigid body surfaces. In order to improve the speed and robustness of the contact analysis, this paper proposes a contact search algorithm for surfaces composed of triangles. This algorithm is divided into two parts, the pre-search and the detailed search. In the pre-search, a bounding box tree and an overlap test are used to find intersecting triangle pairs, and triangle connectivity information is used to identify and separate multiple contact regions. Then an efficient and robust detailed search algorithm is proposed, where the penetration depth and contact reference frame are determined from the results of the pre-search. Finally, the contact force for each contact region is calculated from a modified compliant contact force model. Numerical examples are also presented to illustrate the accuracy and performance.

Field Emission and Optical Properties of ZnO Nanowires Grown Directly on Conducting Brass Substrates

Large-area and uniform ZnO nanowires have been produced directly on a conducting brass substrate by annealing a Cu0.66Zn0.34 foil under a mixture of argon and oxygen. The morphology, structure, and composition of the ZnO nanowires are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. The ZnO nanowires with diameters of about 40-70 nm and lengths up to micrometers grow preferentially along the [001] direction. Since the Cu0.66Zn0.34 foil serves as both the Zn source and substrate, the synthesis and assembly of the ZnO nanowires on a conducting substrate is accomplished in one step, and good intrinsic adhesion and robust electrical contact between the ZnO nanowires and conducting substrate are realized. This ZnO configuration forms an ideal field emitter and good field emission properties are corroborated in this study. Photoluminescence studies indicate that these ZnO nanowires have good optical quality exhibiting strong ultraviolet (UV) emission at 383 nm and a weak visible emission band centered around 485 nm at room temperature. The good field emission and optical properties suggest that ZnO nanowires fabricated by this method have promising applications in nano-optoelectronic and field emission devices.

Implicit Contact Handling for Deformable Objects

AbstractWe present an algorithm for robust and efficient contact handling of deformable objects. By being aware of the internal dynamics of the colliding objects, our algorithm provides smooth rolling and sliding, stable stacking, robust impact handling, and seamless coupling of heterogeneous objects, all in a unified manner. We achieve dynamicsawareness through a constrained dynamics formulation with implicit complementarity constraints, and we present two major contributions that enable an efficient solution of the constrained dynamics problem: a time stepping algorithm that robustly ensures non‐penetration and progressively refines the formulation of constrained dynamics, and a new solver for large mixed linear complementarity problems, based on iterative constraint anticipation. We show the application of our algorithm in challenging scenarios such as multi‐layered cloth moving at high velocities, or colliding deformable solids simulated with large time steps.

Robust Ohmic contact junctions between metallic tips and multiwalled carbon nanotubes for scanned probe microscopy

We demonstrate a simple method that uses a scanning electron microscope for making a reliable low resistance contact between a single multiwalled carbon nanotube and a metallic tungsten probe tip or a Si cantilever. This method consists of using electron beam induced decomposition of background gases and voltage pulses to remove contaminants. The electrical quality of the contact is monitored in situ by measuring the current flow at constant bias or by observing the decay of current fluctuations. The quality of the contacts is confirmed via current-voltage spectroscopy. This method produces very stable, low resistance, mechanically robust contacts with high success rates approaching 100%.

Educator and Participant Perceptions and Cost Analysis of Stage-tailored Educational Telephone Calls

Objective To identify strengths and weaknesses of nutrition education via telephone calls as part of a larger stage-of-change tailored intervention with mailed materials. Design Evaluative feedback was elicited from educators who placed the calls and respondents who received the calls. Setting An internet and telephone survey of 10 states in the midwestern United States. Participants 21 educators in 10 states reached via the internet and 50 young adults reached via telephone. Variables Measured and Analysis Rankings of intervention components, ratings of key aspects of educational calls, and cost data (as provided by a lead researcher in each state) were summarized via descriptive statistics. Results, Conclusions, and Implications Educational calls used 6 to 17 minutes of preparation time, required 8 to 15 minutes of contact time, and had a mean estimated cost of $5.82 per call. Low-income young adults favored print materials over educational calls. However, the calls were reported to have positive effects on motivating participants to set goals. Educators who use educational telephone calls to reach young adults, a highly mobile target audience, may require a robust and flexible contact plan.

Electrical Switching Using Compliant Metal Infiltrated Multi-Wall Nanotube Arrays

ABSTRACTThe topology of conventional noble-metal-coated switch counterfaces creates modes of switch failure via fouling, arcing, and local melting when impacted. To avoid these failure phenomena, compliant conductive contact surfaces of vertically aligned multi-wall nanotube arrays grown on conductive substrates have been fabricated. Infiltration of the array by noble metal results in a robust compliant switch contact surface. Cyclic hot-switch testing of the nanotube based switch, via modified nano-indentation, results in performance surpassing conventional designs with stable resistance of 0.4Ω over 3000 cycles. Investigating the physical performance of the array shows the array is compacted less than 3% over the first 500 cycles with no observable compaction through the remaining cycles. The improvement in performance of the nanotube based switch is attributed to the ability for the compliant contact surface to conform to the probe tip geometry, increasing the effective contact surface area.

Haptograph Representation of Real-World Haptic Information by Wideband Force Control

Artificial acquisition and reproduction of human sensations are basic technologies of communication engineering. For example, auditory information is obtained by a microphone, and a speaker reproduces it by artificial means. Furthermore, a video camera and a television make it possible to transmit visual sensation by broadcasting. On the contrary, since tactile or haptic information is subject to the Newton's “law of action and reaction” in the real world, a device which acquires, transmits, and reproduces the information has not been established. From the point of view, real-world haptics is the key technology for future haptic communication engineering.This paper proposes a novel acquisition method of haptic information named “haptograph”. The haptograph visualizes the haptic information like photograph. The proposed haptograph is applied to haptic recognition of the contact environment. A linear motor contacts to the surface of the environment and its reaction force is used to make a haptograph. A robust contact motion and sensor-less sensing of the reaction force are attained by using a disturbance observer. As a result, an encyclopedia of contact environment is attained. Since temporal and spatial analyses are conducted to represent haptic information as the haptograph, it is possible to be recognized and to be evaluated intuitively.

A finite element formulation of non-smooth contact based on oriented volumes for quadrilateral and hexahedral elements

This paper concerns the finite element modeling of contact between solid bodies, with a special emphasis on the treatment of non-smooth conditions. A new approach for the formulation of the contact constraint that allows for a simple and unified treatment of all potential contact scenarios in the presence of large deformations is presented. Based on the calculation of an oriented volume, this approach possesses the ability to resolve complicated contact scenarios efficiently, while being simple to implement and more widely applicable than the contact formulations available to-date. We show that the formulation boils down to a node-to-surface gap function that works effectively for non-smooth contact situations. The numerical implementation using the midpoint rule shows the need to guarantee the conservation of the total energy during impact, for which a Lagrange multiplier method is used. The result is a robust contact detection and resolution algorithm.

Electrically injected quantum dot photonic crystal microcavity light emitters and microcavity arrays

Progress in the design, fabrication and characterization of electrically injected photonic-crystal quantum-dot microcavity light sources is described. In the devices investigated in this study, the carriers are injected directly into the photonic crystal microcavity, avoiding the surface state recombination in the photonic crystal pattern. A novel and robust air-bridge contact technology is demonstrated. Spectral linewidths ∼2–3 nm are observed from hexagonal microcavities of varying sizes in the output spectra of oxide-clad microcavity devices. Narrower linewidths ∼1.3 nm are observed from air-clad devices. Results on arrays of densely packed oxide-clad photonic crystal microcavities are also presented. Spectral characteristics of oxide-clad and air-clad devices are compared.

ELECTRICAL PROPERTIES OF Pb(Zr,Ti)O3 FERROELECTRIC CAPACITOR ON TiN/W PLUG STRUCTURE

ABSTRACT We investigated the electrical properties of ferroelectric Pb(Zr,Ti)O3(PZT) capacitor on TiN/W storage node contact plug that is capacitor over bitline(COB) cell structure for a high density ferroelectric memory. In order to protecting TiN/W contact plug from oxidation failure during furnace annealing of PZT capacitor, the oxidation barrier of Ti1 − x Al x N (x∼ 0.25) film was interposed at between Pt/IrO2/Ir bottom electrode and TiN/W plug of the COB cell, resulting in the robust contact resistance property of 27 ohm per contact plug after furnace annealing performed at 600°C in O2 ambient for 90 min. The remanent polarization value and leakage current density of the fully integrated PZT capacitor with a top electrode area of 1.8 × 1.8 um2 on TiN/W contact plug showed 32 μ C/cm2 and 2.5 × 10− 6A/cm2, respectively.

Controlled formation of individually seeded, electrically addressable silicon nanowire arrays for device integration

The formation of large-scale arrays of individually seeded, electrically addressable Si nanowires with controlled dimension, placement, and orientation is demonstrated. Electron beam evaporated gold nanoparticles were used for nanowire synthesis. By controlling the lithography and metal deposition conditions, nanowire arrays with narrow size distributions have been achieved. Low-energy postgrowth ion beam treatment has been utilized to control the orientation of Si nanowires. This process also leads to the attachment of nanowires on the substrate. Fabrication of planar devices with robust metal contact formation becomes feasible. The method enables efficient and economical integration of nanowires into device architectures for various applications.

Design and experimental evaluation of a QFT contact task controller for electro‐hydraulic actuators

AbstractThis paper presents design and experimental evaluation of a robust contact task controller for an electro‐hydraulic actuator that operates under significant system uncertainties and nonlinearities. The designed controller allows the actuator to follow a free space trajectory, and upon contact with an uncertain environment exert a desired force, by stably passing through the transition phase from free space to constrained space. The scheme is essentially the combination of two distinct control laws that are individually designed for position regulation in free space and force regulation during sustained contact. Both controllers are designed, using a nonlinear approach within the framework of quantitative feedback theory (QFT), to satisfy a priori specified stability, tracking and disturbance rejection specifications. They are then combined with a simple switching law to form a contact task controller. Due to the existence of a switching, the resulting control system is non‐smooth. The stability of the controller is then analysed using an extended version of Lyapunov's second method under the condition of existence and uniqueness of Filippov's solution. Experiments, performed on a typical industrial hydraulic actuator, include motion through free space, contact with the environment and the transition between the two. The proposed QFT contact task control scheme enjoys the simplicity of fixed‐gain controllers, is easy to implement, requires very little computational effort, is robust to the variation of hydraulic functions as well as environmental stiffness, and results in responses with good performance in both transient and steady‐state periods. Additionally, the controller only requires measured contact force and actuator position as feedback; this makes the controller attractive for industrial implementation. Copyright © 2006 John Wiley & Sons, Ltd.

Robust contact force estimation for robot manipulators in three-dimensional space

Information on contact forces in robot manipulators is indispensable for fast and accurate force control. Instead of expensive force sensors, estimation algorithms for contact forces have been widely developed. However, it is not easy to obtain the accurate values due to uncertainties. In this article, a new robust estimator is proposed to estimate three-dimensional contact forces acting on a three-link robot manipulator. The estimator is based on the extended Kalman filter (EKF) structure combined with a Lyapunov-based adaptation law for estimating the contact force. In contrast to the conventional EKF the new estimator is designed such that it is robust to the deterministic uncertainties such as the modelling error and the sensing bias. The performance of the proposed estimator is evaluated through simulations of a robot manipulator and demonstrates robustness in estimating the contact force. The estimation results show that it can be potentially used to replace the expensive force sensors in robot applications.