Modeling of Viscoelastic Contacts and Evolution of Limit Surface for Robotic Contact Interface

Viscoelastic contact is a type of contact which includes, in addition to linear or nonlinear elastic response, time-dependent response due to relaxation or creep phenomena that govern the contact behavior. The characteristics of the time-dependent relaxation of such a viscoelastic contact are typically exponentially decaying functions, and exponentially growing functions for creep, respectively. Such contacts can be found in anthropomorphic robotic fingers, soft materials, viscoelastic skin with rigid core, and human fingers and feet. In this paper, the nature of viscoelastic contacts is investigated, and the evolution of their friction limit surfaces and of the pressure distributions at the contact interface are studied. Two cases commonly found in robotic grasping and manipulation are discussed. Based on the modeling formulation, it is found that the two important parameters of analysis and modeling for such contacts, i.e., the radius of contact area and the profile of pressure distribution, can be chosen using proposed coupling equations as the viscoelastic contact interface evolves with time. The new contribution of this paper includes a proposal of coupling equations between the two important parameters to describe the viscoelastic contact interface, and a study of the evolution of limit surfaces for viscoelastic contact interface due to temporal dependency, and the implication on grasp stability. It is found from the evolution of limit surfaces that when normal force is applied with typical viscoelastic contacts, grasp becomes more stable as time elapses. The modeling can be applied to the design of fingertips and the analysis of robotic grasping and manipulation involving viscoelastic fingers     

Development of an Underwater Robotic Inspection System using Mechanical Contact

This paper reports the development of a robotic inspection system using a mechanical contact mechanism that enhances the positioning stability of a small and lightweight underwater robot to take clear images of underwater targets and to work with manipulators for inspections under external disturbances. As described in this paper, first we perform a two‐dimensional numerical analysis based on force and moment acting on an underwater robot with a contact mechanism. Second, we experimentally investigate the friction coefficients of several soft and high friction materials for the contact points of a prototype contact mechanism to enhance the positioning stability of the robot. Based on the results of numerical analysis and the experimental investigation, we design and develop a prototype contact mechanism for an underwater robot. Moreover, we experimentally test the stability of the underwater robot with the contact mechanism in a test tank. Finally, a ship hull inspection is conducted as a field test in a port using the robot with the developed contact mechanism. The experimentally obtained results indicate that the proposed contact mechanism is a useful tool for underwater visual inspections and manipulator tasks of a small and lightweight underwater robot.     

Identification of Contact Dynamics Parameters for Stiff Robotic Payloads

This paper investigates and demonstrates the feasibility of identifying contact dynamics parameters for stiff robotic payloads using a robotic system. The contact dynamics model for stiff payloads is motivated, and theoretical parameter values and bounds are provided. Then, the effect of nonidealities such as surface roughness and plastic deformation on the theoretical values is demonstrated. A row-wise-scaled total least-squares parameter estimation algorithm is proposed and applied to experimental data measured using the special purpose dexterous manipulator task verification facility manipulator at the Canadian Space Agency. The experimental results are compared to a separate set of experiments with a material testing machine as well as finite-element modeling results. Finally, the experimental findings are generalized by providing guidelines for the maximum identifiable payload stiffness as a function of the position resolution, the maximum exertable force, and the structural stiffness of the robotic system.     

导电橡胶动态接触压力分布测量系统

叙述了应用新型导电橡胶材料的电阻－力特性研制的16×16点阵接触力传感及计算机测量系统．系统具有传感器薄，对接触面影响小，测量频率可达50次／秒等优点；由于采用直接与微机相连，软件采集的数据以三维图形显示出来而十分直观。     

An SPN-Neural Planning Methodology for Coordination of two Robotic Hands with Constrained Placement

This paper presents a planning methodology based on Stochastic Petri Nets (SPNs) and Neural nets for coordination of two robotic arms working in a space with constrained placement. The SPN planning method generates a global plan based on the states of the elements of the Universe of Discourse. The plan includes all the possible conflict-free planning paths to achieve the goals under constraints, such as specific locations on which objects have to be placed, order of placement, etc. An associated neural network is used to search the vectors of markings generated by the SPN reachability graph for the appropriate selection of plans. Moreover, it preserves all the interesting features of the SPN model, such as synchronization, parallelism, concurrency and timing of events. The coordination of two robotic arms is used as an illustrative example for the proposed planning method, in a UD space where the location of objects placement are restricted.     

Brain-Computer Interface Operation of Robotic and Prosthetic Devices

Brain-computer interfaces (BCIs) use signals recorded from the brain to operate robotic or prosthetic devices. Both invasive and noninvasive approaches have proven effective. Achieving the speed, accuracy, and reliability necessary for real-world applications remains the major challenge for BCI-based robotic control.     

Rolling Contact Motion Generation and Control of Robotic Fingers

Dexterity in human hand is connected with the fingertip rolling ability. In this work we consider rolling motion of spherical robotic fingertips as one of the control objectives together with the set point position control and force trajectory tracking. The generation of a rolling motion trajectory is proposed and a control solution is designed which achieves prescribed transient and steady state tracking behavior. The proposed control law is structurally and computationally simple and does not utilize the dynamics of the robot model or its approximation. A simulation of a five degrees of freedom robot show excellent contact rolling performance even at cases of adverse friction conditions while alternative controllers lead to contact sliding. Experiments with a KUKA LWR4 + are performed to validate the proposed method.     

A Framework for Automatic Generation of a Contact State Graph for Robotic Assembly

Dynamic manipulation of an active object is introduced as a general model of hopping and juggling tasks. In this setting, juggling and hopping are two extreme cases of this general model. Behavioral resemblance of these two tasks is afterwards extended to a detailed mathematical analogy between them. Then the analogy is exploited to develop a unified and abstract planning framework for juggling and hopping. To this end, dynamic manipulation of an active object is decomposed into three distinct phases and two transitions: Carry I, Free flight and Carry II phases. These phases are analogous to Lift off, Free flight and Touch down in hopping. In the next step, a mathematical model for each phase is developed. It is shown that dynamic grasp (in Carry phases of juggling) and foot stability (in Support phases of hopping) conditions share similar sets of dynamic equations. Accordingly, Lift off/Release and Touch down/Catch conditions in hopping/juggling are derived. It is shown that analogous strategies can be developed for Lift off and Release. The analogy is held for Touch down and Catch conditions as well. It is discussed that in the planning framework the initial and the goal configurations of the three phases are set in a model-based and forward manner. To do so, Touch down/Landing time, Free flight duration and robot/object maneuvers during Free flight are used as free parameters for planning in order to ensure foot stability in hopping and dynamic grasp in juggling along with other constraints.     

Monolithic Friction and Contact Handling for Rigid Bodies and Fluids Using SPH

We propose a novel monolithic pure SPH formulation to simulate fluids strongly coupled with rigid bodies. This includes fluid incompressibility, fluid–rigid interface handling and rigid–rigid contact handling with a viable implicit particle-based dry friction formulation. The resulting global system is solved using a new accelerated solver implementation that outperforms existing fluid and coupled rigid–fluid simulation approaches. We compare results of our simulation method to analytical solutions, show performance evaluations of our solver and present a variety of new and challenging simulation scenarios.     

薄膜式土压力分布传感器研发及试验研究

在岩土力学与工程领域,随着对土压力荷载大小与分布研究的深入,新型土压力传感器的研发愈显重要.本文利用导电敏感复合材料研制了一种新型薄膜式土压力分布传感器,其总厚度小于0.2 mm.首先介绍了传感器的设计原理及结构,初步测试结果表明,双层结构传感器的灵敏度相对更高.然后,通过大型模型试验实测检验了研发的双层结构土压力分布传感器的基本性能.新型传感器具有测点面积小(可实现大密度测试)、T/D小(对土体扰动小)、引线方便以及弯曲挠度大(适合弯曲表面压力测试)等特点.综合来看,它用于土压力分布测试初步是可行的,具有进一步深入研究的价值.     

Design and Implementation of a Multi Sensor Based Brain Computer Interface for a Robotic Wheelchair

In this study, design and implementation of a multi sensor based brain computer interface for disabled and/or elderly people is proposed. Developed system consists of a wheelchair, a high-power motor controller card, a Kinect camera, electromyogram (EMG) and electroencephalogram (EEG) sensors and a computer. The Kinect sensor is installed on the system to provide safe navigation for the system. Depth frames, captured by the Kinect’s infra-red (IR) camera, are processed with a custom image processing algorithm in order to detect obstacles around the wheelchair. A Consumer grade EMG device (Thalmic Labs) was used to obtain eight channels of EMG data. Four different hand movements: Fist, release, waving hand left and right are used for EMG based control of the robotic wheelchair. EMG data is first classified using artificial neural network (ANN), support vector machines and random forest schemes. The class is then decided by a rule-based scheme constructed on the individual outputs of the three classifiers. EEG based control is adopted as an alternative controller for the developed robotic wheelchair. A wireless 14-channels EEG sensor (Emotiv Epoch) is used to acquire real time EEG data. Three different cognitive tasks: Relaxing, math problem solving, text reading are defined for the EEG based control of the system. Subjects were asked to accomplish the relative cognitive task in order to control the wheelchair. During experiments, all subjects were able to control the robotic wheelchair by hand movements and track a pre-determined route with a reasonable accuracy. The results for the EEG based control of the robotic wheelchair are promising though vary depending on user experience.     

抛光过程游离单颗磨粒与光学元件间滚动摩擦接触分析

针对游离单颗磨粒与光学元件滚动接触过程中摩擦、磨损机理分析的不足及如何 有效控制滚动单颗磨粒对光学元件亚表面损伤的影响等问题,基于滚动接触理论,提出了一种 具有分形特征表面的单颗磨粒与光学元件双粗糙面间的摩擦、磨损接触模型,并运用有限元仿 真分析微观动态滚动的接触过程。通过对不同剪切强度下接触力、接触应力、磨粒角度及其对 亚表面损伤的影响等分析,发现随着剪切强度的增强,磨粒与光学元件表面接触界面间的摩擦 系数将减小,最佳的磨粒角度为105°~120°,并且分形特征的单颗磨粒对亚表面损伤的影响要 大于球形特征单颗磨粒,这说明了研究分形特征游离单颗磨粒滚动接触的必要性和重要性,为 更加深刻了解滚动接触过程的摩擦机理提供了借鉴意义。     

Modeling,Sensing, and Interpretation of Viscoelastic Contact Interface

Soft robotics is important in the next generation of robots because of the rapidly increasing need for robotics in biomedical applications and the advantages of providing a soft interface for interaction with the physical environment in service robots and other applications. It is indispensable to understand the fundamental behavior of such contact interface, typically viscoelastic, in order to accurately predict the actual elastic and temporal responses of the contact and to successfully control it. Viscoelasticity is a phenomenon of time-dependent strain and/or stress in soft materials. It is therefore important to model such behavior and to study the effects of such time-dependent strain and stress on stability and behavior at the contact interface. The contribution of this paper is the introduction of a novel latency model, which is a nonlinear model with differential equations that govern viscoelastic materials. Latency model describes various features of viscoelastic materials, such as stress relaxation and strain creep. The theoretical modeling was supported by experimental results in which we found two types of relaxation. Type I relaxation is well documented in existing literature but Type II relaxation has not been elaborated previously with the physical insights provided in this paper. The proposed theory can unify both types of time-dependent relaxation responses for modeling, sensing, and interpretation of viscoelastic contact interface.     

AFDX总线10M接口电气参数极限适应性测试方法

AFDX(航空电子全双工交换式以太网)作为新型机载数据总线应用于大中型飞机,其通信接口电气参数的极限适应性测试是一项重要测试内容.提出一种10M标准AFDX总线信号发生器实现方案,采用4路非归零(NRZ)编码模拟双极性差分曼彻斯特编码,产生符合ARINC664规约要求的总线数据信号,并实现数据信号的传输速率、差分信号幅度、上升/下降时间等电气特性参数连续可调,满足AFDX总线10M接口电气参数极限适应性测试需求.     

Development of Mine Hands: Extended Prodder for Protected Demining Operation

The over 100 million landmines and unexploded ordnance (UXO) are buried in disaster-affected countries.Although significant efforts have been made at addressing this problem, few have resulted in practical removal tools, especially in the hazardous, yet essential, LV-3 survey.     

均衡时间压力的人机界面信息编码

复杂系统人机交互中,在紧迫的时间压力下,操作者能否迅速而准确地对界面承载的大量信息作出反应是界面设计中有待研究的课题.文中针对时间压力对认知行为的影响,研究如何合理地使用编码方式达到界面优化设计.基于主观工作负荷测量法中变量的水平描述和视觉凝视,将时间压力设定为大、适中和小3种水平,对应的呈现时间分别为200 ms,600 ms和1 000 ms;通过实验分析时间压力对颜色和形状编码的认知影响,结果表明,在1000 ms以内的时间压力下,颜色编码比形状编码的认知容量大、认知速度快.最后以A320飞机的电子集成监控系统仿真界面设计为例,验证了颜色编码在多个信息量快速识别中的改进作用.     

基于Profibus-PA的差压变送器通信接口设计

Profibus-PA是一种广泛应用于过程控制领域的现场总线.文中以模块化的设计思想为指导,采用西门子专用协议芯片SIM1-2和DPC31,为差压变送器的仪表控制器设计开发了Profibus-PA通信接口,将仪表控制器作为从站接入Profibus总线,实现现场总线的控制系统.实验结果表明,运用该接口模块可以实现Profibus-PA主从站之间的非循环数据通信,主站的可靠性和通用性较好,能够嵌入应用到所有的现场设备中.     

机器人导航系统的设计与开发磁

论文介绍了一个机器人导航系统,该系统将机器人的地图路径生成、机器人移动、机器人避障功能加以分离,当传感器发现规划路径不能继续时,可以对路径进行动态调整。仿真实验表明该系统结构能够完成基本的导航任务。