Development of Multi Micro Manipulation System Using IPMC Micro Grippers

This paper presents a new design of multi micro manipulation system using ionic polymer metal composite (IPMC) micro grippers for robotic micro assembly where IPMC is used as a light weight actuator for developing the micro grippers. It has the potential of large displacement, low mass force generation and misalignment compensation ability during micro manipulation. These capabilities are utilized for handling of miniature parts like pegs. The analysis of IPMC micro gripper and manipulator are carried out for developing a multi micro manipulation system that can handle pegs in micro assembly operation for shifting one to another hole position in a large work space (100 mm × 100 mm). By developing a prototype, it is demonstrated that IPMC based micro grippers are capable of handling the peg-in-hole assembly tasks in a multi micro manipulation system.     

SCARA based peg-in-hole assembly using compliant IPMC micro gripper

Robotic assembly is difficult as there always exist position errors between two mating parts. Compliance is added in a selective compliant assembly robot arm (SCARA) in the form of a two ionic polymer metal composite (IPMC) fingers based micro gripper. This micro gripper is integrated at the end effector position of a SCARA robot. Peg-hole interaction is analytically modeled and based on it the force required to correct the lateral and angular errors by IPMC is calculated. A proportional-derivative (PD) controller is designed to actuate the IPMC to get the desired force for correcting the peg position before assembly. Simulations and experiments were carried out by developing an IPMC micro gripper and using it to analyze various cases of peg in hole assembly. The experimental results prove that adding compliance through IPMC helps in peg-in-hole assembly.     

Fuzzy logic compliance control of the peg in hole insertion

Compliance control of the peg-in-hole insertion while both peg and hole are rigidly supported, is studied. Initially, the peg-in-hole operation is mathematically modelled to develop a better understanding of the existing constraints. Imitating a human operator, a compliant motion for the assembly of the peg in the hole using the heuristic approach is developed. Two basic fuzzy controllers are studied. One in which inference engine operates purely based on force/torque information received from the sensor. In the other the approximate position of the peg is also taken into account to estimate the corrective action required. The rule-bases of both controllers are developed based on the qualitative knowledge of the behaviour of the controlled process. The performance of the fuzzy controllers are compared with the performance of a non-fuzzy IF–THEN logic branching control algorithm. The results obtained are encouraging.     

Constrained gripper motion in assembly manipulation. Part II

Part II of this article elaborates one practical problem: peg-in-hole problem in assembly manipulation. The theory of constrained gripper motion explained in Part I is used to solve the dynamics of the assembly manipulation problem.     

Characterization of an electro-thermal micro gripper and tip sharpening using FIB technique

A micromachined electro-thermal gripper, first introduced by Ivanova et al. (Microelectron Eng 83:1393–1395, 2006), represents a promising candidate for the manipulation and handling of micro or even nano-scaled objects. To further optimize the performance of the device, a detailed electrical and mechanical characterization is needed. Due to the so-called duo-action gripper approach (i.e., a separate actuator for closing and opening action) these investigations focused on the maximum (minimum) opening width being 11.5 μm (3.3 μm), while in rest position a value of 4 μm is feasible. The maximum, electrical input power is limited to 80 mW/actuator element, resulting in a current density of up to 1.27 MA cm⁻² in the corresponding metal layers. When applying, however, larger current densities the probability of device failure increases substantially as in combination with an enhanced temperature of about 200°C electromigration effects occur in the metallization. Furthermore, the cut-off frequency and parasitic effects during actuation such as the z-deflection and the increase in length of each arm both showing values of up to 3 μm have been investigated as a function of operation parameters. Finally, the tips of the gripper were sharpened using Focused Ion Beam technique to a radius of less than 1 μm for gripping operations in space-restricted environments or for the manipulation or handling of sub-μm scaled objects.     

Modeling, analysis, and performance evaluation of a robotic grippersystem for limp material handling

This paper presents an analytical model of a flat surfaced robotic gripper designed to automate the process of reliable, rapid and distortion-free limp material handling. The designed gripper prototype is integrated with an industrial robot manipulator. The gripper geometry and its grasp stability are justified. Performance of the overall system is experimentally tested, based on a set of industry dictated operational constraints. It is found that the gripper system has high reliability, grasp stability, and that it is capable of rapid rates of manipulation.     

Easily manageable, electrothermally actuated silicon micro gripper

This paper presents a new batch process to fabricate thermally driven silicon micro grippers for handling and manipulation objects smaller than 25 μm. To achieve a robust gripper gearing with fine gripping tips, silicon on insulator (SOI) technology is used. The flexure gearing is driven by two integrated thermal expansion actuators that are moving in opposite directions and are actuated by Joule heating. In addition, a customized gripper mounting mechanism is presented, which offers fast and easy gripper handling, resulting in reduced tooling time and lower costs for the user. Finally, the experimental results and electrical characteristics for the sophisticated gripper design are presented.     

Micro parts assembly system with micro gripper and RCC unit

This paper presents a new micro assembly system, which is composed of a micro gripper, a micro remote center compliance (RCC) unit, a voice coil motor-driving mechanism and precision motion stages. The micro gripper is actuated by two shape memory alloy (SMA) wires, and its grip is 1 mm. The micro RCC unit has low translational and rotational stiffness sufficient for micro parts assembly. The voice coil motor-driving mechanism can generate linear motion with an adjustable stiffness, and it can also measure external force in the moving direction. An algorithm for the automatic assembly of micro parts is also proposed, and assembly experiments are performed.     

Enhanced adaptive motion tracking control of piezo-actuated flexure-based four-bar mechanisms for micro/nano manipulation

This paper establishes and investigates an enhanced adaptive motion tracking control methodology for piezo-actuated flexure-based four-bar micro/nano manipulation mechanisms. This control methodology is proposed for tracking desired motion trajectories in the presence of unknown or uncertain system parameters, non-linearities including the hysteresis effect, and external disturbances in the motion systems. In this paper, the equations for the modelling of a flexure-hinged four-bar micro/nano mechanism are established. These include the angular stiffness, ‘static’ linear stiffness, equation of motion, and lowest structural resonance of the mechanism. In addition, a lumped parameter dynamic model that combines the piezoelectric actuator and the micro/nano mechanism is established for the formulation of the proposed control methodology. The stability of the control approach is analysed, and the convergence of the position and velocity tracking errors to zero is proven theoretically. A precise tracking performance in following a desired motion trajectory is also demonstrated in the experimental study. An important advantage of this control methodology is that the approach requires only a knowledge of the estimated lumped system parameters in the physical realisation. This proposed motion tracking control methodology is very attractive for the implementation of high performance flexure-based micro/nano manipulation control applications.     

微位移系统中压电陶瓷驱动器迟滞建模

针对超精密微位移系统中压电陶瓷驱动器的迟滞非线性问题,提出了一种基于遗传反向传播(BP)神经网络的压电陶瓷迟滞非线性建模方法.通过电涡流位移传感器获取压电陶瓷驱动器不同电压值下所对应的位移值;利用六次多项式拟合获得迟滞的数学模型,从而建立基于遗传BP神经网络的迟滞,模型.实验结果显示:该迟滞模型在神经网络测试下的最大误差为0.082 1 μm,平均绝对误差为0.0158 μm.表明,所建的迟滞模型能够较精确地反映出压电陶瓷驱动器的迟滞特性,同时为微位移控制系统设计提供了一定的理论基础.     

Design of a low-cost five-finger anthropomorphic robotic arm with nine degrees of freedom

The aim of this work was to design and demonstrate a dexterous anthropomorphic mobile robotic arm with nine degrees of freedom using readily available low-cost components to perform different object-picking tasks for immobile patients in developing nations. The robotic arm consists of a shoulder, elbow, wrist and five-finger gripper. It can perform different gripping actions, such as lateral, spherical, cylindrical and tip-holding gripping actions using a five-finger gripper; each finger has three movable links. The actuator used for the robotic arm is a high torque dc motor coupled with a gear assembly for torque amplification, and the five-finger gripper consists of five cables placed like tendons in the human arm. The robotic arm utilizes a controller at every link to trace the desired trajectory with high accuracy and precision. Digital implementation of the control algorithm is done on an Atmel Atmega-16 microcontroller using trapezoidal approximation and Newton's backward difference methods. The arm can be programmed or controlled manually to perform a variety of object-picking tasks. A prototype of the robotic arm was constructed, and test results on a variety of object-picking tasks are presented.     

A compliant end-effector coupling for vertical assembly: design and evaluation

Many manipulation tasks require compliance, i.e. the robot's ability to comply with the environment and accomplish force as well as position control. Examples are constrained motion tasks and tasks associated with touch or feel in fine assembly. Few compliance-related tasks have been automated, and usually by active means of active compliance control: the need for passive compliance offered by the manipulator itself has been recognized and has led to the development of compliant end-effectors and/or wrists. In this paper we present a novel passively compliant coupling, the compliant end-effector coupling (CEEC), which aids automated precision assembly. It serves as a mechanical interface between the end of the robot arm and the end-effector. The coupling has 6 degrees of freedom. The design of the coupling is based on a “lock and free” assembly idea. The coupling is locked and behaves like a stiff member during robot motion, and is free (compliant) during constrained motion. It features an air bearing, a variable stiffness air spring and a center-locking mechanism. The end-effector assembly, being centrally unlocked, will float within the designed compliance limits assisted by the air bearing. These frictionless and constraint-free conditions facilitate a fast correction of any initial lateral and angular misalignments. In a peg insertion assembly, such accommodation is possible provided that the tip of the peg is contained within the chamfer of the hole. A variable stiffness air spring was incorporated in the design to allow variable and passive vertical compliance. This vertical compliance allows the accommodation of angular and vertical errors. The center-locking mechanism will return the end-effector assembly to its initial position upon an error correction. In a robot application program, the CEEC can be locked during rapid motion to securely transport a part or be set free during assembly or disassembly processes when the motions are constrained.     

Piecewise strategy and decoupling control method for high pose precision robotic peg-in-hole assembly

Existing compliance control methods take the force/moment precision as the only metric but do not explicitly guarantee the pose precision between assembly objects. In this paper, we first find significant time-variant and coupling characteristics in the process of modelling peg-in-hole assembly. Then, piecewise strategy and decoupling control (PSDC) method is proposed to explicitly improve the pose precision between the peg and hole. During designing PSDC controller, given the time-variant characteristic of assembly, piecewise strategy is utilized to improve the rapidity and stability of control, which is the basis of the pose precision. Given the coupling characteristic of assembly, an identification method of modelling error on the equation of output is proposed and the corresponding decoupling module is designed to avoid the system error on the pose between the peg and hole. Finally, the simulation and experiment results demonstrate that PSDC method achieves higher pose precision assembly in a force-guided compliance control framework.     

微操作机器人的视觉伺服控制

视觉伺服控制是微操作机器人实现精确运动,完成自动操作的必要手段．本文介绍 了实现微操作机器人视觉伺服控制的方法．首先论述了微操作机器人的视觉伺服结构,并以 建立的面向生物工程的双手微操作机器人系统为例,介绍了基于二维显微视觉信息的三自由 度柔性铰链微操作机器人的运动学建模方法,针对压电驱动器控制器的特点提出了基本的PI D视觉伺服控制规律实现方法,并进行了点到点运动和圆轨迹跟踪实验．实验结果表明,视 觉伺服控制克服了由于标定以及环境等因素导致的运动模型不准确而引入的误差．     

Assembly task execution using visual 3D surface reconstruction: An integrated approach to parts mating

This paper is focused on assembly tasks executed by an industrial robotic manipulator in the presence of uncertainties. The goal is to achieve higher levels of autonomy and flexibility of robotic systems in the execution of such tasks. In particular, as a well-established paradigm of assembly tasks, a Peg-in-Hole task has been considered, where the pose of the target object with respect to the robot is known with uncertainties far larger than the task tolerance, e.g., due to manual positioning of the object in the workcell. The proposed approach is based on the reconstruction of the object surface by means of a number of point clouds provided by a depth sensor. The reconstruction is then compared with a known CAD model of the surface, in order to localize the position and tilt of the holes. Finally, the peg insertion is performed in two steps: a search phase, in which the peg tip gently slides on the surface following a trajectory described by Lissajous functions, and a mechanical coupling phase, in which a compliant behavior is imposed to the peg. Experiments on a collaborative manipulator confirm that the proposed approach allows to achieve a better degree of autonomy and flexibility for a class of robotic tasks in partially structured environments.     

A compliant self-adaptive gripper with proprioceptive haptic feedback

Grippers and robotic hands are an important field in robotics. Recently, the combination of grasping devices and haptic feedback has been a promising avenue for many applications such as laparoscopic surgery and spatial telemanipulation. This paper presents the work behind a new self-adaptive, a.k.a. underactuated, gripper with a proprioceptive haptic feedback in which the apparent stiffness of the gripper as seen by its actuator is used to estimate contact location. This system combines many technologies and concepts in an integrated mechatronic tool. Among them, underactuated grasping, haptic feedback, compliant joints and a differential seesaw mechanism are used. Following a theoretical modeling of the gripper based on the virtual work principle, the authors present numerical data used to validate this model. Then, a presentation of the practical prototype is given, discussing the sensors, controllers, and mechanical architecture. Finally, the control law and the experimental validation of the haptic feedback are presented.     

Methods for highly accurate gripping of flexible micro parts

Today, handling and assembly of flexible micro-components such as thin wires or glass fibres with diameters down to a few micrometers and lateral dimensions up to a few meters is an important challenge in hybrid micro-assembly (Brecher and Peschke 2004). Production of flow sensors for respirators in medical engineering or coupling a fibre to an active visual component in optical data communication are examples of such applications. Such products have one thing in common: The assembly of their most sensitive functional components is often carried out manually since the handling and positioning technology either has to be specially developed and is costly or is non-existent (Weck and Peschke 2003). However, in most cases the manual assembly is very time consuming and its repeatability and positioning accuracy is not adequate (Carrozza et al. 2000); Petersen (2003). This disadvantage is obvious especially in the assembly of hybrid micro-optical telecommunication systems such as switches or power splitters, because the required mounting tolerances are less than a micron. A deviation of 100 nm in the alignment between the optical components and the glass fibres leads to noticeable and non-tolerable losses when coupling light into the fibres. With this background, fundamental studies are carried out at Fraunhofer IPT for the optimization of gripper geometry, gripper materials and gripping parameters for handling flexible micro-components such as glass fibres. The aim of these studies, shown in chapter 2 of this paper, is primarily to investigate the effects on the reproducibility of the positioning when gripping these highly sensitive micro-components and to derive gripper optimization strategies. A further aim is to develop a large scale integrated, adaptive, rugged and economical gripper system particularly for handling and alignment of flexible micro-components accurate to the sub-micron level. This gripper system can be used on conventional robot systems for carrying out micro-assembly operations. The robot system carries out the pre-positioning, the positioning tolerances necessary for the micro-assembly are subsequently realised directly at the tip of the gripper with a multi-axes system integrated into the gripper. Positioning systems that achieve the required positioning increments in the sub-micron range are existent (Scheller 2001). The problem of such systems is that they are normally highly sensitive against mechanical impact. Also their gripper integration is problematical due to a high weight and size dimensions in the decimetre range for each axis. In this paper the development of a highly robust gripper-integrable multi-axes system is presented.     

基于分层控制的移动机器人最优运动规划

研究移动机器人在带有多移动障碍物的动态环境中的运动规划问题，基于分层最控制理论，提出了一种新的运动规划方法来解决移动机器人的导航与避障问题，仿真实例证明了该方法的有效性。     

State-of-the-Art control strategies for robotic PiH assembly

Nowadays, industrial robots have been widely applied for performing position-controlled tasks with minimum contact such as spot welding, spray painting, packing, and material handling; however, performing high-tolerance assembly tasks still poses a great challenge for robots because of various uncertainties of the parts to be assembled such as fixtures, end effector tools, or axes. From this perspective, the advancement of research and development has led to cutting-edge robotic technologies for industrial applications. To understand the technological trend of industrial robots, investigated the state-of-the-art robotic assembly technologies to identify the limitations of existing works and clarify future research directions in the field. This paper especially interested on typical peg-in-hole (PiH) assemblies, as PiH methods provide insights for further development of robot assemblies. The assembly control strategies for PiH operations is classified by based on the types and features of the assemblies, and the literature in terms of the contributions of these studies is compared to PiH assembly. Finally, the control strategies for robotic PiH assemblies are discussed in detail, and the limitations of the current robotic assembly technologies are discussed to identify the future direction of research for the control of robotic assembly.     

Microscale and nanoscale robotics systems [Grand Challenges of Robotics]

Depending on their overall size, sensing and actuation precision, part or tool size, and task space, robotic systems can be classified as microrobotics or nanorobotics, respectively. Micro/nanorobotics represents these two different scale robotics areas jointly while keeping their clear scale differences in mind. At its current early infancy, the field of micro/nanorobotics has two major research thrust areas. Analogous to the manipulation area in macroscale robotics, the first area explores new methods for programmable manipulation and assembly of micro- and nanoscale entities. Here, the overall micro/nanorobotic system size can be very large, while only the manipulation tools, manipulated objects, and sensing, actuation, and manipulation precision are required to be at the micro/nanoscale. On the other hand, the second research area focuses on overall miniaturization of mobile robots down to mum overall sizes with various locomotion capabilities such as flying, swimming, walking, hopping, rolling, and climbing. In these mobile robotic systems, overall system size is very limited, which induces severe constraints in utilized actuators, sensors, motion mechanisms, power sources, computing power, and wireless communication capability. These two research thrusts are described in detail in the following sections