Design and manufacturing of mobile micro manipulation system with a compliant piezoelectric actuator based micro gripper

This paper presents a new design of mobile micro manipulation system for robotic micro assembly where a compliant piezoelectric actuator based micro gripper is designed for handling the miniature parts and compensation of misalignment during peg-in-hole assembly is done because piezoelectric actuator has capability of producing the displacement in micron range and generates high force instantaneously. This adjusts the misalignment of peg during robotic micro assembly. The throughput/speed of mobile micro manipulation system is found for picking and placing the peg from one hole to next hole position. An analysis of piezoelectric actuator based micro gripper has been carried out where voltage is controlled through a proportional-derivative (PD) controller. By developing a prototype, it is demonstrated that compliant piezoelectric actuator based micro gripper is capable of handling the peg-in-hole assembly task in a mobile micro manipulation system.     

Universal compliant device based on SCARA concept

The paper presents the results of the research and the development of the universal adaptive compliant device for customary assembly task robot configurations. The developed system is based on a newly developed SCARA robotic mechanism and combined properties of the SCARA concept and RCC devices. It successfully operates around its true compliance center, obtained under precisely determined conditions.     

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.     

A peg-in-hole robot assembly system based on Gauss mixture model

Using robots to assemble parts has always been a research hotspot, but the traditional analysis model of assembly mainly focuses on establishing the linear equation between the feedback force and the relative position of the peg and hole, which leads to high requirements for the material properties and geometric parameters of the assembly parts. In this paper, a new assembly strategy is proposed that learns skills from manual teaching to carry out the assembly process. A Gauss mixture model and regression is used to fit the teaching data, and then, the compliance control method is applied to conduct assembly when the geometric profile parameters and material elastic parameters of the assembly are inaccurate. Finally, the experiment was implemented under the tolerance is 0.18 mm, and the success rate reaches 100%. These findings verified the effectiveness of the compliance control method.     

基于视觉引导的SCARA机器人自动装配系统

现有生产线工业机器人抓取点固定,工件只能以固定的姿态提前摆放在固定的位置,这种装配模式很难满足复杂的工业生产要求且效率低下。设计了基于视觉引导的机器人装配系统改进原有系统。设计了机器视觉系统,实现了工件的快速识别、定位以及姿态确定功能;设计了抓放系统,实现了工件的精确抓取和安装功能;采用Visual Studio的MFC开发,实现图像处理算法,并利用Socket通信将坐标和姿态数据发送给机器人。通过实验验证本系统具有良好的稳定性和快速性,可以满足生产的要求,大幅提高生产效率。     

Robotic assembly automation using robust compliant control

Industrial robots used to perform assembly applications are still a small portion of total robot sales each year. One of the main reasons is that it is difficult for conventional industrial robots to adapt to any sort of change. This paper proposes a robust control strategy to perform an assembly task of inserting a printed circuit board (PCB) into an edge connector socket using a SCARA robot. The task is very challenging because it involves compliant manipulation in which a substantial force is needed to accomplish the insertion operation and there are some dynamic constraints from the environment. Therefore, a robust control algorithm is developed and used to perform the assembly process. The dynamic model of the robotic system is developed and the dynamic parameters are identified. Experiments were performed to validate the proposed method. Experimental results show that the robust control algorithm can deal with parameter uncertainties in the dynamic model, thus achieve better performance than the model based control method. An abnormal case is also investigated to demonstrate that the robust compliant control method can deal with the abnormal situation without damaging the system and assembly parts, while pure position control method may cause damages. This strategy can also be used in other similar assembly processes with compliant applications.     

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.     

Adaptive neuro fuzzy controller for adaptive compliant robotic gripper

The requirement for new flexible adaptive grippers is the ability to detect and recognize objects in their environments. It is known that robotic manipulators are highly nonlinear systems, and an accurate mathematical model is difficult to obtain, thus making it difficult то control using conventional techniques. Here, a novel design of an adaptive neuro fuzzy inference strategy (ANFIS) for controlling input displacement of a new adaptive compliant gripper is presented. This design of the gripper has embedded sensors as part of its structure. The use of embedded sensors in a robot gripper gives the control system the ability to control input displacement of the gripper and to recognize particular shapes of the grasping objects. Since the conventional control strategy is a very challenging task, fuzzy logic based controllers are considered as potential candidates for such an application. Fuzzy based controllers develop a control signal which yields on the firing of the rule base. The selection of the proper rule base depending on the situation can be achieved by using an ANFIS controller, which becomes an integrated method of approach for the control purposes. In the designed ANFIS scheme, neural network techniques are used to select a proper rule base, which is achieved using the back propagation algorithm. The simulation results presented in this paper show the effectiveness of the developed method.     

Sensor-guided micro assembly of active micro systems by using a hot melt based joining technology

This article presents (the most) recent results of the subprojects B4 and B8 of the Collaborative Research Center 516—Design and Manufacturing of Active Micro Systems—which are concerned with the assembly of active micro systems. While subproject B4 investigates sensor guided assembly processes, subproject B8 develops suitable assembly techniques on the basis of non-viscous adhesive systems (hot melts). Process development focuses on the suitability for automation, process times and the applicability of batch processes. The article discusses certain hot melt application techniques that are suitable for batch production, a sensor-guided assembly system as well as different approaches for heat conduction in an automated assembly process for hot melt coated micro components.     

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.     

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.     

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.     

视觉引导技术在SCARA机器人装配任务中的应用

基于实际生产项目,提出了一种针对平面关节型机器人(SCARA)平面装配任务的手眼标定方法。对线性标定法的输出通过多次迭代使得累积误差和逐渐减小,相较于使用线性标定法来进行手眼标定,视觉定位的平均定位误差降低了0. 4 mm,最大定位误差降低了0. 6 mm。在使用SCARA机器人进行毫米(mm)级作业时,使用迭代线性标定法比传统的线性标定法有更高的视觉定位精度。同时,末端执行器完成对目标工件的抓取任务之后,使用解线性方程的思想求解SCARA机器人完成装配任务的末端位姿,通过实际工程项目的验证,装配成功率可达98. 6%。     

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.     

Adaptive robotic assembly of compliant aero-structure components

The application of robotics to the assembly of large aero-structures has been limited by the large size and inherent compliance of the components involved. The compliance of the components is significant and simple ‘pick and place’ approaches cannot be used due to the inherent dimensional variability between mating parts. The research described in this paper aims to solve this problem by using a non-contact sensing system to measure part deformation and misalignment in real time. The acquired data can then be processed through a mathematical algorithm to calculate the relative component positions required for optimal assembly. The data can also be used to check gross distortion of components and to reject those outside the specification limits. Existing part-to-part holes were used to provide alignment for individual components within the structure. A series of experiments were performed to investigate the feasibility of the method. Results are presented along with a discussion of the problems that may be encountered during robotic assembly. The experimental results show that robots when combined with non-contact metrology can be used for the assembly of compliant aero-structure components within required tolerance limits.     

Support vector regression methodology for prediction of input displacement of adaptive compliant robotic gripper

The prerequisite for new versatile grippers is the capability to locate and perceive protests in their surroundings. It is realized that automated controllers are profoundly nonlinear frameworks, and a faultless numerical model is hard to get, in this way making it troublesome to control utilizing tried and true procedure. Here, a design of an adaptive compliant gripper is presented. This design of the gripper has embedded sensors as part of its structure. The use of embedded sensors in a robot gripper gives the control system the ability to control input displacement of the gripper and to recognize specific shapes of the grasping objects. Since the conventional control strategy is a very challenging task, soft computing based controllers are considered as potential candidates for such an application. In this study, the polynomial and radial basis function (RBF) are applied as the kernel function of Support Vector Regression (SVR) to estimate and predict optimal inputs displacement of the gripper according to experimental tests and shapes of grasping objects. Instead of minimizing the observed training error, SVR _poly and SVR _rbf attempt to minimize the generalization error bound so as to achieve generalized performance. The experimental results show that an improvement in predictive accuracy and capability of generalization can be achieved by the SVR approach compared to other soft computing methodology.     

Design and kinetostatic modeling of a compliant gripper for grasp and autonomous release of objects

A gripper with an embedded compliant bistable mechanism (BM) for gripping and autonomous release of objects is developed. Due to adhesion forces, objects might stick to the end effector of a gripper upon release, where a shaking operation may be employed to release the objects. Vibration of the end effector induced by an impact pestle adjacent to the shuttle mass of the BM may achieve autonomous release of objects adhered to the end effector. Gripping and autonomous release of objects are accomplished when the BM moves between its two stable equilibrium positions. An analytical model is developed to predict the kinetostatic behavior of the BM and to assist in the design of the gripper.     

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.     

A novel selective-area gripper for layered assembly of laminated objects

A novel method for precise handling of sheet materials is described in the context of a solid freeform fabrication method. Individual cross-sections of a three-dimensional part are laser-cat from sheet material. A robot, using a selective-area vacuum gripper, extracts each desired cross-section from the waste material, and stacks it precisely to create three-dimensional layered objects. Details of the gripper design are presented, along with characterization of its performance and results of its use within a rapid prototyping system.     

Proposal of a shape adaptive gripper for robotic assembly tasks

This paper proposes a novel robotic gripper used for assembly tasks that can adaptively grasp objects with different shapes. The proposed hand has a combined structure between two kinds of shape adaptive mechanisms where one is the granular jamming and the other is a multi-finger mechanism driven by a single wire. Due to the effect of the two shape adaptive mechanisms, the pose of a grasped object does not change during an assembly operation. The proposed hand has four fingers where two are the active ones and the other two are the passive ones. The pose of the grasped object can be uniquely determined since the passive fingers are used to orient an object placed on a table before the active fingers are closed to grasp it. Assembly experiments of some kinds of parts are shown to validate the effectiveness of our proposed gripper.