Weibin Rong

A Flexible Experimental System for Complex Microassembly under Microscale Force and Vision-Based Control

A flexible experimental system developed for efficient and stable complex microassembly is presented. The system consists of a set of modules that can adapt their shape and function to various assembly tasks. Due to the basic limitations of microscopic vision, a wavelet-based focus measure to obtain both high precision and robust autofocusing, a control scheme with a modified Smith predicator to decrease the inherent time delay of vision systems, and microscopic vision/force integration to control the assembly tasks are proposed. A smart 3-D PVDF (Polyvinylidence Fluoride) force sensor is employed to sense the interactive force. Analysis and microassembly of three planetary gears demonstrate that this system has high flexibility.

Visual servoing with modified Smith predictor for micromanipulation tasks

A control scheme with a modified Smith predicator (MSP) for the position-based dynamic look-and-move visual servoing for the control of micromanipulation is proposed. Due to the time consuming image acquisition, transfer, and processing, the visual servoing has an inherent time delay, which seriously damage the system performance. Previously, the most common method is to decrease the primary gains to increase damping, thus making the system more robust in the presence of delays. However, the resultant response of the system is lowered, leading to a sluggish overall performance. In this paper, a control scheme with a similar structure to the Smith predictor, called modified Smith predictor is employed to eliminate the vision delay. A detailed analysis and experiments available are presented to demonstrate the vision control system with the proposed control scheme has better dynamics performance than the single vision control system.

Task-Reconfigurable System for MEMS Assembly

This paper presents a Task-reconfigurable system developed for efficient and reliable MEMS assembly. The system consists of a set of autonomous modules that can adapt their shape and function to various assembly tasks, including a distributed 6 DOF coarse positioning module, a distributed 5 DOF fine positioning module, grippers designed for different manipulation tasks with same mechanical interface, a multi-view imaging system, and control software. In order to achieve high precision and dexterity in microassembly, a hybrid vision-force control method is proposed. For easier reconfiguration, a semi-automated calibration method is applied to quick calibrating of the new reconfigurations. Analysis and 3 cases of microassembly are presented to demonstrate that this system has high reconfigurability and adaptability.

Hybrid Vision-Force Control for Automatic Assembly of Miniaturized Gear System

This paper presents the automatic microassembly of miniaturized gear system by hybrid vision-force control with the vision system and the 3-DOF force sensor feedback data. The assembly process consists of three phases, including visual positioning, searching meshing state, and inserting. Visual feedback is used to achieve the coarse positioning and guide the grasping and transporting of microparts during the visual positioning phase. During the searching phase, a fuzzy PID controller is used to control the contact force on z axis and fuzzy logic strategy is developed to search the meshing state by the force feedback on x and y axes. The tolerance compensations movement is used to support the inserting task to avoid the case of blocking and prevent the micro parts from damaging. The assembly experiment of three planetary gears validates the hybrid force control strategy.

Micromanipulation robot for automatic fiber alignment

Optical fiber alignment devices are highly necessary in optical communications. In this paper, we developed a micromanipulation robot for automatically performing optical fiber alignment task. The system consists of a precision parallel robot with 6 D.O.Fs, a nano positioning stage with 5 D.O.Fs, two microscopes, two CCD cameras, an optical power meter and a fusion device. Directed by the micro-vision system, the precision parallel robot can realize fiber alignment with 0.5 /spl mu/m resolution and 2 /spl mu/m repetitive accuracy. The nano positioning stage is actuated by piezoelectric and 10 nm resolution can be gained. Under the help of optical power meter and through optimal searching method, the fiber can be positioned precisely. With this system, a single mode optical fiber alignment task has been finished automatically. The average splice loss is about 0.016dB. The system can also realize the alignment of fiber and optical devices for its multi DOFs. It will play a key role in the field of optical engineering.

A Novel Piezo-driven Nanopositioning Mechanism for Precise Manipulating

A three-degree-of-freedom (3-DOF) novel nanopositioning mechanism was developed. The mechanism utilizes three piezoelectric actuators (PZTs) and ring plate hinges to realize nanopositioning, which are arranged in an equilateral triangle shape. The simplified modeling of the nanopositioning mechanism was discussed. The translational stiffness along z direction and rotational stiffness along x and y direction, and three natural frequencies of the nanopositioning mechanism are deduced in terms of the theory of structural mechanics. Theoretical analysis and finite element analysis (FEA) on static and dynamic behavior of the nanopositioning mechanism are performed and the comparative results of the theory, FEA and experiments show that the accuracy of theory model and the validity of FEA. An apery intelligent PI control algorithm for realizing a closed loop is discussed and a series of experiments were carried out to investigate the static and dynamic characteristics of the mechanism. Using the 3-DOF mechanism, an optical precise assembly is accomplished, which validates the feasibility of the mechanism in precise operating fields.

Considering Van Der Waals Forces in Micromanipulation Design

Van der Waals interactions are always present in handling micro objects and will influence the whole manipulation process. This paper investigates the effects of van der Waals forces on the design and planning of micromanipulation. Origins of van der Waals interactions are shown first. Van der Waals forces between micro objects of several typical configurations in micromanipulation process are characterized. The related aspects of van der Waals forces are discussed based on the theoretical analysis. Methods of control adhesion induced by van der Waals forces in micromanipulation processes are presented.

Research on integrated micromanipulator and its application in microassembly

Micromanipulator is the key component of a micromanipulating robot. According to the principle of piezoelectric scanner, a three degree-of-freedom micromanipulator driven by piezoelectric tubes is developed. The integration of mechanism, actuator and sensor is realized. The formula establishing the relationship between microdisplacement and driving voltage is given. The micropositioning control system is introduced, including the bipolar piezoelectric driver and micropositioning measuring system. Some static and dynamic characteristics of the micromanipulator are gained. Based on this, the micromanipulator is applied to a micromanipulating robot. Thanks to micro-vision and micro-force perceiving, macro-micro-positioning is performed. As a result, the peg-in-hole with diameter of 0.2 mm is finished successfully by rational microassembly strategy.

Elastic-plastic adhesive contact of fractal microparts surfaces with low adhesion parameters

The elastic-plastic adhesive contact model of microparts surfaces with low adhesion parameters is developed based on the fractal rough surfaces description. The critical transition area from elastic to plastic deformation of single asperity contact is determined by the plastic deformation condition. Based on this, the relation between the applied load and the real contact area of rough surfaces are deduced. It has been shown that the fractal dimensions whichever are less or larger than 1.5 have similar effect on the load-area relations. Small applied loads are needed to achieve the same real contact area for the larger fractal dimension in each case duo to the rough surfaces become smoother with the increase of fractal dimensions. The effect of elastic adhesion index on the relation is more remarkable at high load. For the plastic adhesion index, the effect is also prominent at high loads, but the effect trend is contrary to the elastic adhesion one. This is for the index indicates the ration of hardness to the surface adhesion work.

A Multi-Sensor System for Optical Precise Assembly

This paper presents a multi-sensor system for optical precise assembly. The system utilizes macro-micro robot for high precision assembly, which consists of a 6-DOF parallel robot for coarse positioning, a 5-DOF stage driven by piezoelectric actuators for fine positioning, a gripper, a multi-sensor system, and an optical system. Mechanism design and control system design of the coarse-fine positioning stage are discussed. In order to achieve high precision in optical assembly, a multi-sensor control system is established, which includes a micro displacement detecting module, a signal analyzing module, a vision module, and a force sensor. Some control algorithms for image recognition and signal analysis are proposed, which can monitor the optical assembly in real-time. The experimental results validate the feasibility of the optical precise assembly system