Reasoning about nature of contact for planning manipulators tasks

Extracting information about contact between two convex bodies from the measured force vector is a prerequisite for any fine compliant motion control strategy. Contact information contains the direction and orientation of the contact surface normal and its relative location and orientation with respect to the compliant reference frame system.A method for interpreting the contact force feedback during compliant robot motion control, using kinematic screws, is presented. Domain specific rules combined with partial a priori knowledge of mating parts geometry and interpreted force signals are used to reason and make inferences about the initial contact configuration. The likely contact surfaces are predicted and point(s) or line(s) of contact are fully defined. These surfaces are idealized and represented by quadratic equations or polyhedral surfaces. The geometric properties of surfaces at the contact location are used to select the contact configuration when multiple solutions exist.An algorithm for predicting the Expected Contact Configuration (ECC) has been developed and is illustrated here with examples. Experimental validation of the developed expert system prototype, using a 6R manipulator, a six-axis force sensor, and a host computer is described.     

Six-axis force sensor evaluation and a new type of optimal frame truss design for robotic applications

The different means currently available for six-axis wrist force sensor evaluation are discussed, and a unified criteria is proposed that is based on the condition number, the overall static and dynamic stiffness of the sensor, and the strain gauge sensitivity. In this light a new frame/truss type of sensor body design is introduced. The uniqueness of the design lies in the elastic members that exhibit truss (axial deformation), as opposed to the commonly used beam (bending) behavior. Several improvements over previous designs result, including: increased force sensitivity with a consistently low condition number, increased rigidity, and improved design flexibility. In addition, a design methodology is presented that uses optimization theory in combination with finite element analysis, to yield the best possible frame/truss force sensor design for a given set of specified principal forces.     

Simultaneous shape and topology optimization of prestressed concrete beams

This paper presents a new optimization approach for the design of prestressed concrete beams. The prestressing tendon is modeled as a chain of linear segments that transfer point forces to the concrete domain according to the tendon’s angles. The concrete beam is modeled as a discretized continuum following density-based approaches to topology optimization. The shape of the tendon and the topology of the surrounding concrete are optimized simultaneously within a single problem formulation. A special filtering technique is developed in order to ensure that the tendon is covered by concrete, thus shape and topological variables are tightly coupled. Several test cases demonstrate the applicability of the proposed optimization procedure. The deformation of the optimized designs due to external loads is counteracted by the deformation due to prestressing, hence by tuning the force in the tendon the total deformation can approach zero. Consequently, the beams exhibit a compression-only response meaning that the common goal of prestressed concrete design is achieved.     

Adaptive neuro-fuzzy prediction of grasping object weight for passively compliant gripper

The development of universal grippers able to pick up unfamiliar objects of widely varying shapes and surfaces is a very challenging task. Passively compliant underactuated mechanisms are one way to obtain the gripper which could accommodate to any irregular and sensitive grasping objects. The purpose of the underactuation is to use the power of one actuator to drive the open and close motion of the gripper. The fully compliant mechanism has multiple degrees of freedom and can be considered as an underactuated mechanism. This paper presents a new design of the adaptive underactuated compliant gripper with distributed compliance. The optimal topology of the gripper structure was obtained by iterative finite element method (FEM) optimization procedure. The main points of this paper are in explanation of a new sensing capability of the gripper for grasping and lifting up the gripping objects. Since the sensor stress depends on weight of the grasping object it is appropriate to establish a prediction model for estimation of the grasping object weight in relation to sensor stress. A soft computing based prediction model was developed. In this study an adaptive neuro-fuzzy inference system (ANFIS) was used as soft computing methodology to conduct prediction of the grasping objects weight. The training and checking data for the ANFIS network were obtained by FEM simulations.     

机器人柔性腕力传感器及其检测系统

介绍了一种集被动柔顺和力传感器于一身的机器人柔性腕力传感器,该传感器采用非接触式的光电检测装置进行位置/姿态变换的检测,检测准确度高,不易受到干扰,通过USB接口与计算机进行数据传输,接口方便。     

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.     

Fuzzy rule base optimization of a compliant wrist sensor for robotic assembly

The problem of part mating and assembly with close tolerances has been addressed in the past by active or passive compliance and by force/position control. With ambient sensor and transmission noise and with imprecise measurements it is often difficult to attain high precision in manipulator positioning. A compliant wrist position sensor with a fuzzy logic rule base was designed by the author to address this problem. In this article, after a brief review of this sensor, optimization of its fuzzy rule base is discussed. The optimization results are then presented. © 1996 John Wiley & Sons, Inc.     

一种高分辨力柔性触觉传感器

本文描述了一种基于全内反射原理，用透明橡胶材料作为波导板的柔性触觉传感器。该传感器除具有一般刚性波导板触觉传感器的高分辨力等特点外，还具有柔性好，力灵敏阈值低，不怕碰撞等特点，该传感器特别适合装在智能机器人手爪上，为机器人系统高效率地获取物体形状，位置和姿态信息，实现智能抓握物体，操作物体等功能提供了有效的手段。     

Developing genetic programming techniques for the design of compliant mechanisms

Compliant mechanisms achieve desired force and displacement characteristics through elastic deformation of their structure. Current research in the synthesis of compliant mechanism topology has pursued multiobjective optimization using gradient-based search methods. This paper will explore the use of a random-guided search method for multiobjective optimization of compliant mechanisms through genetic programming techniques. The combination of genetic algorithms and compliant mechanisms is an effective and interesting combination of two biologically inspired engineering design areas. This paper will describe and demonstrate the successful use of genetic programming to create a general design tool for topological synthesis of compliant mechanisms. Features that exploit the implementation of genetic algorithms to compliant mechanism design, such as multiple criteria specification, multiple-design parameter variation, and final selections from a family of solutions will be presented and discussed. Finally, the use of this design tool will be demonstrated on several familiar examples for validation and discussion.     

六维柔性腕力传感器的设计研究

本文主要介绍了六维柔怀腕力传感器的结构检测原理，用ＲＰＹ方法建立了移动体对基座的变换矩阵，并根据ＰＳＤ检测的位置信号求解出变换矩阵。在此基础上，建立了力向量与位姿向量的关系式，通过刚度矩阵的标定获得力信息。最后介绍了腕力传感器的数据采集及处理系统。     

Ultra-low-power components for an RFID Tag with physical and chemical sensors

In this work the development and optimization of the main components for a multisensing flexible Tag with RFID communication capabilities and integrated physical and chemical sensors for logistic datalogging applications will be reported. For this specific scenario, several constraints must be considered: power consumption must be limited for long-term operation, reliable ISO compliant RFID communication must be implemented, and special encapsulation issues must be faced for reliable sensor integration. In this work, the developments on application specific electronic interfaces and on ultra-low-power Metal OXdide semiconductor (MOX) gas sensors will be reported. The electronics for sensor control and readout as well as for RFID communication are based on an ultra-low-power MSP430 microcontroller from Texas Instruments together with a custom RFID front-end based on analog circuitry and a CPLD digital device, and are designed to guarantee a passive ISO15693 compliant RFID communication in a range up to 6 cm. A thin film battery for sensor operation is included, thus data acquisition and storage can be accomplished when no reader field is present. This design allows the user to access both the traceability and sensor information even when the on-board battery is exhausted. The physical sensors for light, temperature and humidity are commercially available devices, while for chemical gas sensing innovative MOX sensors are developed, based on ultra-low-power micromachined hotplate arrays specifically designed for flexible Tag integration purposes. A single MOX sensor requires only 8.9 mW for continuous operation, while temperature modulation and discontinuous sensor operation modes are implemented to further reduce the overall power consumption. The development of the custom control and RFID front-end electronics, together with innovative ultra-low-power MOX sensor arrays with flexible circuit encapsulation techniques will be described.     

High-resolution low-cost optoelectronic instrument for supervising grape must fermentation

In a globalized world, the quality–cost ratio for wine is a key factor for winemakers in order to be competitive. Therefore, the fermentation process of grape must should ideally be continuously supervised to achieve a wine that meets the expected quality standards, avoiding undesirable states which may contribute to raise the cost. However, the traditional procedure followed by winemakers to monitor the fermentation process is not automated as winemaking is monitored manually by enologists, who must extract and analyze fermenting must samples at least twice a day from each fermentation tank during the whole fermentation process. An optoelectronic device has been developed in order to contribute to the automation of the wine fermentation process. It is capable of measuring both the fermentation kinetics and the maceration of wine during the whole fermentation by means of refractometric techniques and absorbance measurements in the visible spectrum, respectively. Moreover, as the refractive index is not measured by enologists during the fermentation (they rely on density measurements instead), it has been validated as an indicator for monitoring the fermentation kinetics according to both predictions derived from analytical calculations and from experimental data obtained in several fermentations with the optoelectronic device and other analytical techniques. The system consists of a laser diode and a PSD (position sensitive detector) for refractive index measurements, LEDs and photodiodes for color measurements, and a temperature sensor useful to reference the data to 20 °C. It also comprises a frame holder, some conditioning circuits and a data acquisition board.     

Compliant grasping with passive forces

Because friction is central to robotic grasp, developing an accurate and tractable model of contact compliance, particularly in the tangential direction, and predicting the passive force closure are crucial to robotic grasping and contact analysis. This paper analyzes the existence of the uncontrollable grasping forces (i.e., passive contact forces) in enveloping grasp or fixturing, and formulates a physical model of compliant enveloping grasp. First, we develop a locally elastic contact model to describe the nonlinear coupling between the contact force with friction and elastic deformation at the individual contact. Further, a set of “compatibility” equations is given so that the elastic deformations among all contacts in the grasping system result in a consistent set of displacements of the object. Then, combining the force equilibrium, the locally elastic contact model, and the “compatibility” conditions, we formulate the natural compliant model of the enveloping grasp system where the passive compliance in joints of fingers is considered, and investigate the stability of the compliant grasp system. The crux of judging passive force closure is to predict the passive contact forces in the grasping system, which is formulated into a nonlinear least square in this paper. Using the globally convergent Levenberg‐Marquardt method, we predict contact forces and estimate the passive force closure in the enveloping grasps. Finally, a numerical example is given to verify the proposed compliant enveloping grasp model and the prediction method of passive force closure. © 2005 Wiley Periodicals, Inc.     

A sensor fusion and support vector machine based approach for recognition of complex machining conditions

During the machining process of thin-walled parts, machine tool wear and work-piece deformation always co-exist, which make the recognition of machining conditions very difficult. Existing machining condition monitoring approaches usually consider only one single condition, i.e., either tool wear or work-piece deformation. In order to close this gap, a machining condition recognition approach based on multi-sensor fusion and support vector machine (SVM) is proposed. A dynamometer sensor and an acceleration sensor are used to collect cutting force signals and vibration signals respectively. Wavelet decomposition is utilized as a signal processing method for the extraction of signal characteristics including means and variances of a certain degree of the decomposed signals. SVM is used as a condition recognition method by using the means and variances of signals as well as cutting parameters as the input vector. Information fusion theory at the feature level is adopted to assist the machining condition recognition. Experiments are designed to demonstrate and validate the feasibility of the proposed approach. A condition recognition accuracy of about 90 % has been achieved during the experiments.     

空间机器人捕获航天器操作的避撞柔顺复合自抗扰控制

讨论空间机器人在轨捕获非合作航天器过程避免关节受冲击力矩破坏的避撞柔顺控制问题.在机械臂与关节电机之间配置一种弹簧类柔顺装置—–旋转型串联弹性执行器(RSEA),其作用在于:1)在捕获碰撞阶段,可通过其内置弹簧的变形吸收碰撞产生的能量;2)在镇定运动阶段,结合避撞柔顺策略适时开、关电机,以保证关节所受冲击力矩受限在安全...     

遥操作机器人客户端仿真系统的设计与实现

该文面向空间机器人遥操作,应用三维预测仿真和遥传感器反馈监控技术,建构了遥操作机器人的客户端仿真系统.实现了简单的柔顺力控制操作的仿真.操作员通过仿真系统面向的虚拟环境离线编程,实现对遥操作任务的预演.同时基于遥传感器反馈信息的识别,实现了对远端任务执行进程的监控和状态流图显示.在模拟的大时延情况下,操作员能够在客户端通过局域网控制实验室中的机器人完成精密插孔装配等任务.为进行大时延遥操作提供了算法实验平台.     

Six-DOF micro-manipulator based on compliant parallel mechanism with integrated force sensor

This paper describes the design of a micro-scale manipulator based on a six-DOF compliant parallel mechanism (CPM), which is featured by piezo-driven actuators and integrated force sensor capable of delivering six-DOF motions with high precision and providing real-time force information for feedback control. Particularly, the position and screw-based Jacobian analyses of the CPM are presented. Then, the compliance model and the workspace evaluation of the CPM are proposed in order to account for the compliance and obtain design guidelines. Finally, the integrated sensor is introduced. The static features of such a mechanism include high positioning accuracy, structural compactness and smooth and continuous displacements.     

Development of a piezoelectric polymer film sensor for plantar normal and shear stress measurements

We have developed a new sensor prototype for plantar pressure measurements during gait. The mechanical stress at the plantar surface has two components, pressure acting normal to the surface and shear stress acting tangential to the surface. The shear stress can be further divided into anterior–posterior (AP) and medial–lateral (ML) components. The developed sensor simultaneously measures both normal and shear stresses. It utilizes commercial polyvinylidenefluoride (PVDF) material and consists of four separate sensor elements. This paper presents the sensor development and calibration for each force components. A shaker providing dynamic excitation force was used in the calibration. Average sensitivities computed from the results were (12.6 ± 0.8) mV/N for the normal force, (223.9 ± 20.3) mV/N for the AP shear force and (55.2 ± 11.9) mV/N for the ML shear force. A preliminary plantar pressure measurement was also done. The results obtained were promising. However, the sensor developed here is the first prototype. In future, a matrix sensor based on this principle is planned to be constructed.     

双层预紧式6维力传感器预紧力对精度影响分析

针对传统Stewart结构6维力传感器性能的不足,设计并研制了一种双层预紧式6维力传感器,并进行了精度分析与实验研究.首先,介绍了该6维力传感器的结构特点,基于螺旋理论建立了其数学模型以及预紧力的数学描述形式.为了提高传感器的测量精度,在分析预紧支路结构的基础上,通过增大预紧力来降低由于预紧支路结构变形产生的误差.其次,对不同预紧力下预紧支路的结构变形进行了有限元仿真.最后研制并开发了6维力传感器样机和标定系统,进行了不同预紧力情况下的标定实验.通过增大预紧力,传感器的最大Ⅰ类误差和Ⅱ类误差分别由满量程的2.73%、2.43%降低到0.41%、0.64%.实验结果表明,增大预紧力有效地降低了预紧支路变形带来的测量误差,提高了传感器的测量精度,从而验证了理论分析与仿真的正确性.