A Simple Method of Surface Parameter Extraction for Gate Schottky Contact in 4H-SiC MESFETs

We investigate the effects of the surface states on the Schottky contacts in 4H-SiC MESFET. The Ti/Pt/Au gate metal contacts are deposited by electron beam evaporation and patterned by a lift-off process. Based on thermionic theory,a simple parameter extraction method is developed for determination of the surface states in metal/4H-SiC Schottky contacts. The interface state density and interface capacitance are calculated to be 4. 386 × 10^12 cm^-2 · eV^- 1 and 6. 394 × 10^-6 F/cm^2 ,which are consistent with the device＇s terminal characteristics.

Contact State Estimation Based on Surface-matching in Virtual Assembly

Contact problems are one of the most challenging fields in virtual assembly. Information of contact states could be utilized to realize compliant motion of work pieces, to analyze the contact stress, to assist positioning parts and so on. Some methods have already been proposed to estimate contact states between objects and in most of these methods contact states between objects are simplified in order to realize real-time visual reality animation. While in virtual assembly contact states between parts are required to analyze contact stress, deformation and quality. Besides the contact state estimation method for virtual assembly should be able to handle a number of complex parts in real time. There are rarely known methods which could meet this requirement till now. In this study a contact state estimation algorithm based on surface-matching for virtual assembly is proposed. Contacts between parts are categorized into six basic types according to contact region of surfaces. Based on continuous collision detection of polyhedral models a novel contact state identification algorithm which is based on surface matching is proposed. Then contact evolution algorithm, which utilizes the extern force and contact information, is implemented to handle evolution of contact state. Finally a prototype system is developed to verify the above technologies. Experiment results reveal that contact state between parts could be estimated correctly in real time virtual assembly. The proposed contact state estimation algorithm provides a complete solution to obtain the contact state between parts in virtual assembly. Information of contact state between parts could be utilized to realize contact dynamic, contact stress analysis, assembly quality analysis, and so on.

ROBOT PROGRAMMING BY DEMONSTRATION FOR TASK IN CONTACT STATE

Robot programming by demonstration (PBD) system for task in which objectrequires contact with environment is built based on the controlling skill model. The skill isdescribed in three aspects: contact state classifier, acquirement of contact states sequence andcontrolling transition between states. The classifier is developed with the support vector machineby using force sense. Sequence of states is obtained from the force signal of demonstration by theevent trigger. The velocity command of transition is achieved by linearization method. The PBDsystem is successfully built with robot controller with open architecture.

Force Based Skill Learning for Robot Tasks in Contact Conditions

To acquire human operation skill based on force sense, element contact form (ECF) is proposed to describe contact condition firstly. The skill is modeled as a sequence of discrete ECFs. Since different ECF has different force distribution, a support vector machine classifier is built to identify the contact conditions according to the force signal. Finally, the robot can obtain the skill from the human demonstration.

Effect of thickness of friction material on contact state of ultrasonic motor

Performances of ultrasonic motor (USM) considerably depend on contact state between stator and rotor.Based on an electric contact method,the effects of thickness of single homogeneous friction material and gradient friction material on contact state between stator and rotor were studied.The relative contact length was employed to describe the contact characteristics of stator and rotor.With the decrease of thickness of friction material,the contact characteristic of stator and rotor were analyzed and compared when single homogeneous friction material and gradient friction material were used.The experimental results showed that the effect of gradient friction material on contact characteristic is smaller than that of single homogeneous friction material when the thickness of friction material decreases.The result can provide experimental guidance for design and choosing of friction material for USM.

Fuzzy reasoning model using fuzzy Petri Nets for the monitoring of robotic assembly

This paper presented a fuzzy Petri net model to deal with the monitoring of robotic assembly. Based on the fuzzy Petri net model, an efficient composite reasoning mode was proposed to perform fuzzy reasoning automatiealy. It can determine whether there exists an antecedent-consequence relationship between two contact states. Furthermore, various types of sensor signals can be converted to the same form of real values between zero and one, and the contradiction among large number, high degree of truth and importance of input conditions can be resolved very well by introducing the weight factors and priorities for sensor signals. Finally, a peg- in-the-hole example was given to illustrate the reasonability and feasibility of the proposed model.

Surface activity of cancer cells:The fusion of two cell aggregates

A key feature that distinguishes cancer cells from all other cells is their capability to spread throughout the body.Although how cancer cells collectively migrate by following molecular rules which influence the state of cell-cell adhesion contacts has been comprehensively formulated,the impact of physical interactions on cell spreading remains less understood.Cumulative effects of physical interactions exist as the interplay between various physical parameters such as(1)tissue surface tension,(2)viscoelasticity caused by collective cell migration,and(3)solid stress accumulated in the cell aggregate core region.This review aims to point out the role of these physical parameters in cancer cell spreading by considering and comparing the rearrangement of various mono-cultured cancer and epithelial model systems such as the fusion of two cell aggregates.While epithelial cells undergo volumetric cell rearrangement driven by the tissue surface tension,which directs cell movement from the surface to the core region of two-aggregate systems,cancer cells rather perform surface cell rearrangement.Cancer cells migrate toward the surface of the two-aggregate system driven by the solid stress while the surface tension is significantly reduced.The solid stress,accumulated in the core region of the two-aggregate system,is capable of suppressing the movement of epithelial cells that can undergo the jamming state transition;however,this stress enhances the movement of cancer cells.We have focused here on the multi-scale rheological modeling approaches that aimed at reproducing and understanding these biological systems.

Modeling and Analysis of Soft Bionic Fingers for Contact State Estimation

Contact state estimation is significant for evaluating grasp stability of bionic hands,especially in unknown environments or without visual/tactile feedback.It still remains challenging,particularly for soft bionic hands without integrating complicated external sensors on soft fingers.Focusing on this issue,a proprioceptive-sensing-based systematic solution is proposed to estimate the contact state of soft bionic fingers in a single grasp.A kinematic model for soft fingers is first developed to capture the joint rotation angles and tendon displacement.A kinetostatic model is further built to estimate the contact force when soft fingers come in contact with objects.On this basis,a system stiffness model for soft fingers during preshaping and initial contact with objects is proposed to perceive the contact state.Moreover,an instantaneous stiffness model for soft fingers when initial contact occurs is developed for estimating the contact position on certain phalanges,especially the contact position along the distal phalange.The proposed proprioceptive-sensing-based approach is the first application in soft fingers without integrating complicated external sensors,which makes them concise and practical.Experiments are carried out to demonstrate the effectiveness and efficiency of our proposal.

Dynamic friction energy dissipation and enhanced contrast in high frequency bimodal atomic force microscopy

Dynamic friction occurs not only between two contact objects sliding against each other,but also between two relative sliding surfaces several nanometres apart.Many emerging micro-and nano-mechanical systems that promise new applications in sensors or information technology may suffer or benefit from noncontact friction.Herein we demonstrate the distance-dependent friction energy dissipation between the tip and the heterogeneous polymers by the bimodal atomic force microscopy(AFM)method driving the second order flexural and the first order torsional vibration simultaneously.The pull-in problem caused by the attractive force is avoided,and the friction dissipation can be imaged near the surface.The friction dissipation coefficient concept is proposed and three different contact states are determined from phase and energy dissipation curves.Image contrast is enhanced in the intermediate setpoint region.The work offers an effective method for directly detecting the friction dissipation and high resolution images,which overcomes the disadvantages of existing methods such as contact mode AFM or other contact friction and wear measuring instruments.

A tree-shaped motion strategy for robustly executing robotic assembly tasks

An assembly robot needs to be capable of executing an assembly task robustly under various uncertainties.To attain this goal,we use a task sequence tree model originally proposed for manual assembly.This model regards an assembly task under uncertainties as a transformation of the contact state concept.The concept may contain several contact states with probabilities but these are transformed through a series of task elements into the contact state concept having only the goal state at the end.The transformed contact state concept can be classified according to the terminal condition of each task element.Thus,the whole assembly task can be designed as a tree-shaped contingent strategy called a task sequence tree.This paper proposes a systematic approach for reconfiguring a task sequence tree model for application to a robotic assembly task.In addition,by taking a 2D peg-in-hole insertion task to be performed by a robot equipped with a force sensor as an example,we confirm that the proposed approach can provide a robust motion strategy for the task and that the robot can actually execute the task robustly under bounded uncertainty according to the strategy.

Study on the pipe friction resistance in long-distance rock pipe jacking engineering

Previous studies on pipe friction resistance are mainly concentrated in the soil layer,whereas the study on that in the rock stratum is limited.To estimate the pipe friction resistance in the rock stratum,the calculation models of pipe friction resistance and their applica-tion conditions were compared first.Then the friction resistance calculation model for pipe jacking in the rock stratum was established and simplified.Lastly,the measured(FM)and the computed(FN)pipe friction resistance was compared to validate the simplified friction resistance calculation model.The following conclusions can be drawn:(1)The existing calculation methods of pipe friction resistance can be well verified in the soil layer but cannot be applied in the rock stratum.(2)Sediment,pipe–rock friction coefficient and mud buoyancy are the main factors affecting the pipe friction resistance in long-distance rock pipe jacking engineering.(3)The simplified calculation model established by Deng et al.can estimate the pipe friction resistance in different rock strata at different jacking stages with satisfac-tory outcomes.Further research on the pipe-rock friction coefficient in different rock strata with different pipe–rock contact conditions merits further investigation to better predict the pipe friction resistance in the rock stratum.The research results have certain practica-bility and can provide a reference for similar projects.

Wettability and Surface Free Energy Analyses of Monolayer Graphene

Recently Rafiee et al. experimentally demonstrated the wetting transparency of graphene, but there is still no comprehensive theoretical explanation of this physical phenomenon. Since surface free energy is one of the most important parameters characterizing material surfaces and is closely related to the wetting behavior, the surface free energy of suspended monolayer graphene is analyzed based on its microscopic formation mechanism. The surface free energy of suspended monolayer graphene is shown to be zero, which suggests its super-hydrophobicity. Neumann's equation of state is applied to further illustrate the contact angle, θ, of any liquid droplet on a suspended monolayer graphene is 180 o. This indicates that the van der Waals(vd W) interactions between the monolayer graphene and any liquid droplet are negligible; thus the monolayer graphene coatings exhibit wetting transparency to the underlying substrate. Moreover, molecular dynamics(MD) simulations are employed to further confirm the wetting transparency of graphene in comparison with experimental results of Rafiee et al. These findings provide a fundamental picture of wetting on ideal single atomic layer materials, including monolayer graphene. Thus, these results provide a useful guide for the design and manufacture of biomaterials, medical instruments, and renewable energy devices with monolayer graphene layers.