Liguo Chen

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.

An Integrated Parallel Micromanipulator with Flexure Hinges for Optical Fiber Alignment

A novel six degree-of-freedom (DOF) parallel micromanipulator with flexure hinges driven by piezoelectric actuators is presented for optical fiber alignment. The micromanipulator is designed based on integration of mechanism, driver and measurement. The 6-SPS mechanism is used to develop the parallel robot, the mechanical parameters of the structure are optimized, and the working space and stiffness analysis is given. Then the modularization of driver and sensor and the controller are integrated together with our own defined internal bus. Finally, the pose of the parallel robot is measured in open loop control and close loop control condition, and the error compensation is executed. Experimental results indicate that the liner precision of the system is 10 nm and the rotation precision of the system is 0.0001deg. The robot has high positioning precision and high reliability, and it can be used expediently in optical fiber alignment system for the high compact structure.

Automated Precise Liquid Dispensing System for Protein Crystallization

Recently, high throughput protein crystallization requires that the volumes of sample solution in crystallization experiments should be reduced to increase the screening chance with a given amount of sample. This leads to the developments of automated liquid handling instruments that can transfer submicroliter volumes of fluid. In this paper, an automated solenoid based liquid handling system was developed, which could dispense submicroliter reagent without touching off. Also, the non-contact liquid dispensing process was investigated with computational fluid dynamics (CFD) models, which makes us understand the droplet breakup process more detailedly and makes dispensing droplet fall off successfully without attaching to the nozzle. The system is composed of assembled syringes, pneumatic devices, stepper motor, solenoid valve and other miscellaneous devices. The noncontact reagent dispensing is accomplished by rapidly opening and closing the solenoid valve while applying fluid pressure to it and the volume modulation is possible by altering the opening time of the valve and the flow rate. Experiments were carried out with different dispensing volumes, coefficient of variance (CV) has been shown to be below 3% at 1 mul and approach 8% at 50 nl.

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.

Design, identification, and control of piezoactuated positioning mechanism based on adaptive inverse method

Precision positioning mechanisms using piezoelectric stack actuators have a very wide range of applications. However, loss of tracking positioning precision in piezoelectric actuators occurs as a result of hysteresis during long-range applications and creep effects. This paper proposes two models that can simultaneously describe the hysteresis and creep phenomena of a piezoelectric actuator. Based on the hysteresis model and creep model, an adaptive inverse control approach is presented for improving the tracking performance of piezo-nanopositioning. The inverse controller is identified by using least mean square algorithm. The realization of the adaptive inverse controller for the linearization of a piezoelectric actuator is formulated. Finally, a tracking control experiment of piezoelectric actuators for a desired trajectory is performed according to the proposed method. The experimental results demonstrate that the positioning precision is noticeably improved in open-loop operation compared with the conventional open-loop control without any compensation.

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.

Piezoelectric Actuated Precise Positioning System Based on a New Hysteresis Model

The need for precise positioning technique draws significant attention for optical engineering, semi-conductor industry, biotechnology, and nanotechnology, etc. This paper presents a novel piezoelectric (PZT) actuated precision fast positioning system (PFPS), which consists of control module, PZT driving module, precision fast positioning mechanism (PFPM), and micro-displacement measure module. It provides fast and precise control in tilt and piston movements. The driving, mechanism and measure integrative model of the PPS is built. Due to the inherent hysteresis nonlinearity, the PZT actuator always causes positioning error in the open-loop operation and instability in the closed-loop operation. In order to improve the positioning accuracy and response speed, a control method for PZT actuator based on a PID feedback controller with a feedforward compensation is proposed. Finally, the tracking control experiments of piezoelectric actuators for a desired sinusoidal trajectory are performed according to the proposed control method. The experimental results demonstrate that the positioning precision is noticeably improved. The maximum error in tracking a sinusoidal signal is lowered about one order of magnitude in comparison with only using PID

A novel nanoliter liquid dispensing technology for protein crystallization

Recently, high-throughput protein crystallization requires the ability to transfer submicroliter volumes of sample with a large range of viscosities. In this paper, a solenoid-based non-contact liquid handling instrument with high-speed flow sensor was developed to meet this requirement. The flow sensor-driven dispenser with feedback control automatically compensates for encountered differences or changes in sample viscosity by adjusting the valve opening time or system pressure. Also, the non-contact liquid dispensing process was investigated with computational fluid dynamics (CFD) models, which make us understand the droplet breakup process in more detail and make dispensing nanoliter droplet fall off successfully without attach to the nozzle. Experiments were carried out with different dispensing volumes, coefficient of variance (CV) has been shown to be below 3% at 1 mul and approach 8% at 50 nl.

Research on Vacuum Capture Based on Closed-loop Control for Bio-microdissection

A new vacuum-capture method was presented to pick and place the sample exactly for bio-microdissection. The main forces acting on micro-objects were analyzed and some equations of operation force condition were derived. A proportional valve and a fine pressure sensor were added to the vacuum unit to improve its pick and place capability. The measured operation pressures were controlled as the feedback signal by the vacuum unit based on closed-loop control. The good effect was gotten by the united control of PC and date traffic card to adjust the operation press. Experimental results validate the pick-place performance of vacuum-capture method based on closed-loop control for bio-microdissection