Chen Liguo

Tracking control of piezoelectric actuator based on a new mathematical model

A major deficiency of piezoelectric actuators is that their open-loop control accuracy is seriously limited by hysteresis. In this paper, a novel mathematical model is proposed to describe hysteresis precisely and a new parameter called turning voltage is introduced. It was found experimentally that the shapes of hysteresis curves are decided by the value of the turning voltage. A computer-based inverse control approach under open-loop operation based on the mathematical model was applied to suppress the inherent hysteresis to within ±1% full span range of a stack piezoelectric actuator and the performance of the piezoelectric actuator is noticeably improved.

Hybrid Control of Vision and Force for MEMS Assembly System

In this paper, we present a MEMS assembly system under hybrid control of vision and force feedback. The construction of a micro-vision system is introduced in detail and a new micro-force sensor was developed. The strategies of integrating force and vision feedback have been investigated experimentally and impact experimental results are presented. A task of pin in hole of Phi 0.1mm was completed. Using force feedback alone, at least twice as many searching steps are needed, while based on the hybrid control of micro-vision and micro-force feedback, one searching step is enough

Adaptive inverse control for piezoelectric actuator with dominant hysteresis

Piezoelectric actuator controlled by voltage shows serious hysteresis phenomena, which severely degrades the positioning accuracy. Based on Prandtle-Ishlinskii hysteresis operator, an adaptive inverse control approach is presented for reducing hysteresis. The weights of the model are identified by using LMS algorithm. The realization of an inverse feedforward controller for the linearization of a piezoelectric actuator is formulated. Experiments were performed on a micro-positioning system driven by piezoelectric actuators. The results show that the presented adaptive inverse control lowers the non-linearity error from about 17.3 to about 2% in comparison to the conventionally open-loop control.

Modeling and design of a novel precision tilt positioning mechanism for inter-satellite optical communication

The compact precise tilt positioning mechanism (PTPM) determines the performance of inter-satellite optical communication systems. This paper presents a novel structural design of a PTPM in which the tilt movement is implemented by the elastic deformation of a flexure ring. The flexure ring promises zero friction and zero clearance. The stiffness model of the flexible ring was built based on an analysis of the structural mechanics. Then a dynamic model is presented based on the Lagrange equation. A modal analysis and an experimental investigation were performed. The error between the three methods is less than 10%.

Capillary Forces between Submillimeter Spheres and Flat Surfaces at Constant Liquid Volumes

We investigate the capillary forces between submillimeter spheres and flat surfaces at constant liquid volumes theoretically and experimentally. An iterative method is used to estimate the capillary force with contact angles as the boundary conditions and the constant volume as a constraint. The theoretical analysis shows that the maximum capillary force between them decreases with the increase of the liquid bridge volume at small contact angles. The experimental results show that the force is smaller than the theoretical values at the initial separation distances. It is also observed that the force first increases and then decreases with an increasing separation distance in some cases. These phenomena of capillary forces hysteresis are explained according to the wetting hysteresis.

Key Techniques of Micromanipulation Devices for MEMS Assembling and Packaging

The characteristics of micro electro mechanical system(MEMS)assembling and packaging process are analyzed,and the development status of machining devices is given.According to the characteristics of MEMS industry development,the key techniques of MEMS assembling and packaging devices are described,including database of technological parameters,fast precision positioning,modular working tools,fast micro-vision,flexible clamping and automatic material handling techniques.The composition structure and working principle of an anodized bonding device for MEMS pressure sensor and a wire bonding device are introduced,and some experimental results are given.At last,the development trend of MEMS assembling and packaging techniques and devices are discussed.

Zoom Microscope Based Micropositioning for MEMS Sensor Packaging System

This paper presents a zoom microscope based micropositioning system using feedback of multiple magnification images caught through a CMOS cameras mounted on an optical microscope. The requirement for real-time autofocusing for zoom microscope is proposed based on the analysis of zoom microscope model. In order to guarantee the accurate micropositioning of MEMS sensor packaging system, high magnification optical microscope is used. However, the small field-of-view of optical microscope essentially limits the workspace of the micromanipulator and the low depth-of-field makes it difficult to handle micro parts. To overcome these obstacles and increase the precision of micropositioning system, a zoom microscope is chosen to gain multiple magnification images. With low magnification, objects can be identified and located roughly. The precise position of objects can be calculated accurately with high magnification image. At last the autofocusing experiment and micro parts centering experiments are executed based on the micropositioning strategy. This micropositioning method, which base on zoom microscope, can also be used in micromanipulation and microassembly system

Robotic Liquid Handling System for Microdispensing of Highly Viscous Reagent

A robotic liquid handling system is developed for dispensing highly viscous reagent with nanoliter volumes. The robot in question is of immediate need in protein crystallization research and in electronics packaging field. In this paper, the system structure is introduced which mainly consists of three modules: motion control module, dispense control module and droplet volume measure module. Highly viscous reagent can be dispensed in nanoliter through controlling the dispense control module and the motion control module correctly, and the volume of micro-drop can be measured based on robotic vision technique. The factors that influence the successful delivery of nanoliter volumes of highly viscous reagent are discussed through analysis of the dispensing process. And the two critical values that the dispense height should be kept are derived. Finally, three kinds of reagent with different viscosity are used for dispensing experiments to verify the theoretical results. The accuracy of the system has been shown to be below 7%, and the coefficient of variance (CV) has been shown to be below 10%.

Vision based Integrated System for Automated Anodic Bonding of MEMS Sensors

Piezoresistive silicon pressure sensors are widely used in automotive, aerospace and medical equipment industries. Batch bonding of the sensors is limited by the manual manipulation required specially trained technicians. In order to reduce the production costs and simultaneously obtain high production quality, a vision based integrated system for automated anodic bonding is presented. This system consists of a vision subsystem, macro/micro stages, a vacuum micromanipulator, and some additional subsystems. The macro/micro stage performs fine positioning and bonding under the navigation of the vision, the vacuum micromanipulator integrated with smart force sensor can perform highly-precise bonding tasks and a nondestructive transportation of the chip and the quartz base. To perform manipulations automatically, a control system, including a task planning level and a real-time execution level, was developed. The automated batch bonding is validated by further experiment

Ultrasonic Vibration Microdissection System for Molecular Analysis of Tissue

Molecular techniques are transforming our understanding of cellular function and disease. However, accurate molecular analysis methods will be limited if the input DNA, RNA, or protein is not derived from pure population of cells or is contaminated by the wrong cells. Ultrasonic vibration microdissection provides the technology to procure pure population of targeted cells from tissue sections for subsequent analysis. It is a bio-manipulation system, which includes manipulator unit and control unit. Ultrasonic vibration microdissection is based on mechanical effect of ultrasound. We employed the multiplayer piezoelectric actuator for generating the ultrasonic vibration for cutting. With the help of ultrasound effect, an extremely fine microneedle was set in motion at a high frequency and low amplitude (approx. 16-50 kHz, and 0-3 mum) to cut the tissue. Experimental results show that embedded tissue, even thicker sections, can be quickly and precisely cut. Research indicates that Ultrasonic vibration microdissection is completely safe for DNA, RNA and protein analysis etc