A stable transition controller for constrained robots

This paper addresses the problem of contact transition from free motion to constrained motion for robots. Stability of transition from free motion to constrained motion is essential for successful operation of a robot performing general tasks such as surface following and surface finishing. Uncertainty in the location of the constraint can cause the robot to impact the constraint surface with a nonzero velocity, which may lead to bouncing of the robot end-effector on the surface. A new stable discontinuous transition controller is proposed to deal with contact transition problem. This discontinuous transition control algorithm is used when switching from free motion to constrained motion. Control algorithm for a complete robot task is developed. Extensive experiments with the proposed control strategy were conducted with different levels of constraint uncertainty and impact velocities. Experimental results show much improved transition performance and force regulation with the proposed controller. Details of the experimental platform and typical experimental results are given     

Control of robotic object pivoting based on tactile sensing

Robotic manipulation of objects using the sole tactile feedback is a challenge. If the contact between the robot end effector and the manipulated object is distributed, the robot can exchange both friction forces and torques with it. The friction highly influences the motion of the object. By controlling the friction it is possible to perform complex manipulation tasks, such as moving the object with respect to the end effector by executing a controlled sliding motion. If the motion is a rotation with respect to the end effector, the corresponding maneuver is called pivoting. Control of the pivoting motion is considerably difficult, especially without any visual feedback. This paper proposes a novel method to regulate the object angular position, by means of a pivoting maneuver, through a parallel gripper endowed with force/tactile sensors. The strategy is based on a novel nonlinear observer that estimates the sliding velocity from force/torque measurements and a model of the sliding dynamics. We exploit the Limit Surface concept and the LuGre friction model to build a dynamic model of a planar slider. We show, through experimental results, that simple parallel grippers are able to execute such maneuvers that correspond to adding a virtual joint between the fingers, thus enlarging the robot workspace.     

A visual sensing application to a climbing cleaning robot on the glass surface

This paper describes a visual sensing application to a climbing robot that provides cleaning service on the glass wall of high-rise buildings. The robot uses suction cups to stick on the glass, moves with a translation mechanism, and adjusts its orientation by rotating a flexible waist. A visual sensor, composed of an oriented CCD camera and two laser diodes, is used to measure the robot’s position and orientation relative to the window frame on the glass surface. The visual sensor is also used to locate the dirt spot to be cleaned. The mathematical model and the measure methodology of the visual sensing system are discussed. Experiments are performed to calibrate the visual sensor, measure the position and orientation of the robot, and measure the location of the dirty spot. The experimental results verify the effectiveness of the proposed approach.     

Hierarchical fuzzy force control for industrial robots

In this paper, we present a hierarchical force control framework consisting of a high-level control system based on fuzzy logic and the existing motion control system of a manipulator in the low level. In order to adapt various contact conditions, an adaptable fuzzy force control scheme has been proposed to improve the performance. The ability of the adaptable force control system is achieved by tuning the scaling factor of the fuzzy logic controller (FLC). A Mitsubishi MELFA RV-M1 industrial robot equipped with a BL Force/Torque sensor is utilized for implementing the hierarchical fuzzy force control system. Successful experiments for various contact motions are carried out. Additionally, discussion of a peg-in-hole insertion is presented, and the experimental results are given     

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.     

Transmission of Force Sensation by Environment Quarrier Based on Multilateral Control

In recent years, realization of a haptic system has been strongly desired in the fields of medical treatment and expert's skill acquisition. The bandwidth of force sensing and friction compensation are very important problems for reproduction of vivid force sensation. In this paper, an environment quarrier is proposed for bilateral teleoperation instead of force sensors. The environment quarrier is a novel force-sensing method that consists of a twin robot system. Two of the same type of robot are required and they are controlled in the same position, velocity, and acceleration by bilateral acceleration control based on a disturbance observer. One robot is in contact motion and the other is unconstrained. The purity of external force is obtained by subtracting the disturbance torque in the unconstrained robot from the constrained one. The environment quarrier can observe the external force with high bandwidth and friction compensation. In this paper, the idea of multilateral control is introduced for attainment of simultaneity. Furthermore, this paper shows the controller design of the multilateral control in the modal space. The experimental results show the viability of the proposed method     

A spectral color correction framework for medical applications

This paper presents a new spectral approach to color correction for medical image analysis applications. Linear estimation with regularization by a constrained principal eigenvector method is used for calibration of the camera system and estimation of the illumination spectrum while spectral surface reflectivities are determined by Wiener inverse estimation. Nonlinear devices are handled by piecewise linear interpolation and any linear color preprocessing inside the camera is explicitly modeled. All measurement and estimation processes are combined into a spectral calibration framework for practical application in computer-assisted image analysis. The novelty of our approach lies in the generalization of the image formation model allowing for linear preprocessing inside the camera system. Such transforms would lead to erroneous results with positivity constraint based algorithms or a monochromator based measurement. We provide experimental results from a comprehensive set of reference measurements acquired with a video endoscopy system for gastroscopic application.     

机器人激光扫描系统现场标定技术

针对机器人激光 扫描系统现场标定问题,提出了一种基于交比不变性的线结构光传感器标定方法,允许平 面参 照物在传感器测量空间中自由移动,通过摄像机拍摄多幅平面参照物的图像即可对光平面进 行标定;同时, 提出一种定点变位姿的机器人手眼关系标定方法,采用一个直径已知的标准球作为手眼标定 参照物,控制 机器人分别以纯平移运动和变姿态运动的方式带动视觉传感器对标准球的球心坐标进行测量 ,根据固定点 约束标定手眼关系。实验结果表明,本文标定方法有效、快速,可以用于机器人激光扫 描系统现场标定。     

Eye-to-hand approach on eye-in-hand configuration within real-time visual servoing

This paper presents a framework of hand-eye relation for visual servoing with more precision, mobility, and global view. Mainly, there are two types of camera utilization for visual servoing: eye-in-hand and eye-to-hand configurations. Both have own merits and drawbacks regarding to precision and view limit that oppose each other. Based on both behaviors, this paper employs a mobile manipulator as the second robot to hold the camera. Here, the camera architecture is eye-to-hand configuration for the main robot, but mainly behaves as eye-in-hand configuration for the second robot. Having this framework, the drawback of each configuration is resolved by the benefit of the other. Here, the camera becomes mobile with more precision and global view. In addition, since there is no additional camera, the vision algorithm can be kept simple. In order to gain real-time visual servoing, this paper also addresses real-time constraints on vision system and data communication between robot and vision. Here, a hexagon pattern of artificial marker with a simplified image processing is developed. A grasp positioning problem is considered with position-based dynamic look and move visual control through object pose estimation. The system performance is validated by the experimental result.     

Localization of a mobile robot using the image of a moving object

This paper proposes a new approach for determining the location of a mobile robot using the image of a moving object. This scheme combines data from the observed position, using dead-reckoning sensors, and the estimated position, using images of moving objects captured by a fixed camera to determine the location of a mobile robot. Using the a priori known path of a moving object and a perspective camera model, the geometric constraint equations that represent the relation between image frame coordinates for a moving object and the estimated robot's position are derived. Since the equations are based on estimated position, measurement error may exist. However, the proposed method utilizes the error between the observed and estimated image coordinates to localize the mobile robot, and the Kalman filtering scheme is used for the estimation of the mobile robot location. The proposed approach is applied for a moving object on the wall to show the reduction of uncertainty in the determining of mobile robot location.     

任意位姿平面靶标实现立体视觉传感器标定

提出一种基于任意位姿平面靶标的立体视觉传感器标定新方法。利用平面标定参照物,并允许其在测量空间内自由移动,结合镜头畸变的摄像机标定数学模型,实现传感器中摄像机标定;在立体视觉传感器三维测量模型基础上,引入特征点约束优化传感器结构参数,同时实现了传感器现场标定。该方法降低了标定设备的成本,灵活方便,切实可行。实验结果表明,该方法标定精度高,已标定传感器测量空间距离的相对误差优于0．3％。     

CAD-guided sensor planning for dimensional inspection in automotive manufacturing

This paper addresses the vision-sensor-planning problem in part-dimensional inspection of automotive parts. First, a CAD-guided camera-planning system is developed, which utilizes the CAD information of inspected parts and a camera model to plan camera viewpoints. A recursive algorithm, which combines two existing vision-sensor-planning approaches, is developed to find feasible viewpoints. Second, to improve the performance of the eye-in-hand robot and reduce the computational cost of the robot placement problem, a new approach is developed to integrate the kinematics constraint into vision sensor planning. Experimental and simulation results demonstrate the effectiveness of our vision-sensor-planning system.     

Experimental study of contact transition control incorporatingjoint acceleration feedback

Joint acceleration and velocity feedbacks are incorporated into a classical internal force control of a robot in contact with the environment. This is intended to achieve a robust contact transition and force tracking performance for varying unknown environments, without any need of adjusting the controller parameters. A unified control structure is proposed for free motion, contact transition, and constrained motion in view of the consumption of the initial kinetic energy generated by a nonzero impact velocity. The influence of the velocity and acceleration feedbacks, which are introduced especially for suppressing the transition oscillation, on the postcontact tracking performance is discussed. Extensive experiments are conducted on the third joint of a three-link direct-drive robot to verify the proposed scheme for environments of various stiffnesses, including elastic (sponge), less elastic (cardboard), and hard (steel plate) surfaces. Results are compared with those obtained by the transition control scheme without the acceleration feedback. The ability of the proposed control scheme in resisting the force disturbance during the postcontact period is also experimentally investigated     

Bang-bang impact control using hybrid impedance/time-delay control

For stabilization of a robot manipulator upon collision with a stiff environment, a nonlinear bang-bang impact controller is developed. Under this control, a robot can successfully achieve contact tasks without changing the control algorithm or controller gains throughout all three modes: free space, transition and constrained motion. It uses a robust hybrid impedance/time-delay control algorithm to first absorb impact forces and stabilize the system. This control input alternates with zero when no environment force is sensed due to loss of contact. This alternation of control action repeats until the impact transient subsides and steady state is attained. After impact transient, the hybrid impedance/time-delay control algorithm is again utilized. This bang-bang control method provides stable interaction between a robot with severe nonlinear joint friction and a stiff environment, and achieves rapid response while minimizing force overshoots. During contact transition, we employ one simple control algorithm that switches only to zero and maintains the same gains, while other controllers use more than one control algorithm or different control gains. It is shown via experiments that overall performance is superior or comparable to more complicated existing impact force control techniques.     

Vision-based nonlinear tracking controllers with uncertainrobot-camera parameters

This paper considers the problem of position tracking control of planar robot manipulators via visual servoing in the presence of parametric uncertainty associated with the robot mechanical dynamics and/or the camera system. Specifically, by assuming exact knowledge of the mechanical parameters, we design an adaptive camera calibration controller that compensates for uncertain camera parameters and ensures global asymptotic position tracking. We then develop an adaptive robot controller that accounts for parametric uncertainty throughout the entire robot-camera system while producing global asymptotic position tracking. Experimental results illustrating the viability of the adaptive controllers and extensions regarding robust control and redundant robot manipulators are also included     

Measurement of pull-off force for planar contact at the microscale

At the microscale, surface forces influence the behaviour of micro-objects more than volumic forces. During micro-assembly processes, contacts occur between a microgripper and a micro-object or between a substrate and a micro-object. The pull-off force, which represents the force required to break a contact, is one of the predominant problems in micro-assembly. Current force measurements are mostly focused on sphere-plane geometries, and models are based on nanoscale theories. The aim of this letter is to propose an evaluation of the pull-off force for a planar contact, which is the most frequent kind of contact in micro-assembly. Experimental force measurements based on a capacitive microforce sensor and micro/nano robotic systems are carried out. The proposed device enables the study of pull-off forces according to the preload force and the contact angle. Finally, experimental results are discussed and compared with a model.     

用于微摩擦测试的微力传感器及其制作

微构件表面的摩擦状况和磨损机理与宏观构件有较大的区别，需一种能够测量微米尺度样品摩擦特性的专用仪器。给出了一种新型硅微力传感器的设计原理、结构、制作工艺及其弱信号采集方法。静态性能测试结果表明，传感器最大输出电压2000μV，重复性约为1．3％，灵敏度约为65V／N，分辨率为46μN，总精度为2．3％，基本上满足了微摩擦测试的需要。实验及计算表明，通过优化微力传感器的结构，改进芯片的封装，可以大大减少其体积，并提高其各项性能指标。     

结构光内参数和机器人手眼关系的同时标定

为实现对复杂工件的快速在线测量,构建了基于结构光的机器人视觉测量系统,提出一种该系统中结构光测头内参数和手眼关系同时标定的方法。标定时,在机器人工作空间内固定一个平面靶标作为参考物,精确控制机器人末端带动结构光测头做平移运动和变位姿运动,获取不同位姿下的靶标图像。通过平移运动,同时标定结构光测头内参数和手眼关系中的旋转矩阵;通过变位姿运动,同时标定摄像机内参数和手眼关系中的平移向量。考虑到旋转矩阵和平移向量分离标定会存在误差累积,采用非线性优化方法对手眼关系做进一步优化。对标准球及工件进行扫描测量实验,实验结果表明该标定方法简单高效,能保证测量系统具有较高的测量精度,适用于工业现场。     

Vision-based active sensor using a flexible beam

Proposes a vision-based active sensing system, termed vision-based active antenna. This is composed of a camera, a flexible beam whose force-deformation characteristic is known, and an actuator for rotating the beam. The camera observes the beam deformation, including the contact information, while the beam is in contact with an object. By solving a set of equations based on the information acquired through the camera, the sensor can detect the contact location, the contact force, and the stiffness of the object, even though the contact point is hidden by occlusion. For two particular versions, we show some experimental results to verify the basic idea     

无线传感网络下的井下无线监控系统

通过对无线传感网络相关原理及软硬件操作系统的描述,阐释了井下无线监控系统的基本框架,并对其工作原理进行了细致分解和证明。即在.net开发平台上,实现网眼2000摄像头的图像采集,并将图像通过无线传感器网络实时传输。在pc端用c#编程实现网络图像的接收与实时显示,从而构成整套井下网络监控系统,为地下无人采矿技术提供有效的数据和图像无线传输方法,为实现矿山的数字信息化服务。