Key Engineering Materials Vols. 447-448

Abstract: There are increasing demands for polymer based microfluidic devices as polymer devices can be mass produced using the injection molding process for disposable analytical applications. However, fabrication of precision injection molds with micro features down to tens of micro meters is a challenging task. The most efficient manufacturing method for this type of high precision micro mold is the tool-based micro machining. In this paper, studies have been conducted to develop metal injection mould manufacturing technologies for polymer microfluidic device fabrication. An injection mould with a micro feature of 29m wall thickness, 20m height and 9.8mm length has been successfully achieved on brass with very precise dimensional accuracy and surface quality for molding process of polymer microfluidic devices. Polymer microfluidic chips with micro channels of 30m width have been successfully produced using the machined metal injection mould.

Abstract: Resistance microwelding is an important microjoining process used in the fabrication of microelectronics, MEMS and medical devices. However, the process is infeasible in the situation of terminating insulated copper wire to metal sheet due to the hindrance of the insulation coating in common opposed configuration. To address this problem, a revised electrode configuration is used. The effect of main process parameters (welding current, weld time and electrode force) were investigated by detailed mechanical testing and metallurgical examinations. A bonding mechanism with several main process stages (wire cold collapse, coating melting and withdrawing, and solid-state bonding) was proposed.

Abstract: This paper describes new electrostatic control countermeasures and solutions for critical electrostatic control environment for MEMS manufacturing processes, especially in MEMS’s wafer handling that needs low electrostatic voltage. This includes personnel grounding methodology, ESD event measurement, and low ion imbalance ionization to support current and future needs of the MEMS.

Abstract: This paper presents the design and development of a remote center of compliance (RCC) for a stamp holder for the micro-transfer printing process. One important aspect of the design of an automated printer to implementing the micro-transfer printing process is the generation of conformal contact between the stamp and the donor and acceptor substrates. Orientation errors during set up make this very hard to achieve with the introduction of some compliance. To introduce such compliance without the loss of overlay registration accuracy, a 2 degree of freedom (2-dof) remote centre of compliance is designed into the stamp holder so that its instantaneous rotation center at the face of the stamp. This design is implemented using flexure hinges in a configuration that makes the resulting system compact, in-expensive and easy to manufacture.

Abstract: The authors have developed a miniaturized peristaltic pump which is characterized by multi-channel, low pulsation, high pressure resistance and portability. The pump mainly consists of a disposable pumping channel unit and reusable actuating parts. The pumping channel unit, made of silicone elastomers, has eight pumping channels. The operation principle is based on the peristaltic motion of pumping channels that are occluded by the screw shaft. The shaft rotating inside the pumping channel unit has a spirally arranged projection which deforms and closes down the channels. While the shaft rotates, the pinched locations in the channels move either way according to direction of rotation, squeezing out the air inside. The maximum discharge pressure generated was about 160 kPa at rotating speeds of 30 ~ 180 rpm. A micro pneumatic actuator was fabricated to demonstrate the performance of the pump. The validity of the pump for pneumatic actuation was reported.

Abstract: This paper addresses the limitations of current hot embossing machines for mass production applications. It describes the features of a hot embossing machine in terms of machine design for handling large surfaces, embossing head for fast and precise temperature control, and the alignment mechanism for controlling the residual uniformity and planar offsets for producing microstructures uniformly on large area by means of step-and-repeat method. The developed machine demonstrated that microstructures of features size of up to 100µm could be replicated in 250s on PMMA sheet with an electroplated nickel stamp. The linear dimensions of the embossed features however were generally smaller than those in the stamp, which highlighted the importance of precision process control.

Abstract: This paper deals with an orientation control method for micro objects, which have a size in the order of 100 micro meters, by using a board stage that is vibrated in the natural frequencies of various vibration modes. Orientation control is important for manufacturing processes, such as the assembling of small parts. Since it is difficult to grip and to manipulate micro objects, a simple and reliable method is desired. In this paper, the vibration mode is used for generating different motions of the stage and for controlling the orientation of the objects on the stage. Since each vibration mode has a unique vibration motion, different motions can be selected by choosing the vibration frequency. In order to design the stage so that the objects turn toward target direction, Finite Element Method (FEM) analysis was applied. And, the designed vibration stage was fabricated using a stainless steel thin plate. Experimental results showed that the actual vibration is similar with the simulation results. As an example of the orientation control of the micro objects, some small electronics parts were tested and they could be turned toward the target directions.

Abstract: This paper describes the design and proof of concept for an active eddy current damper which is integrated into a single-axis linear motor. Although developments on active eddy current damper are well documented, none has been implemented in a linear motor. The advantage of such a system is two-fold. Firstly, the relative motion between the magnets and the conducting sheet produces eddy currents resulting in an electromagnetic force opposing the direction of motion; which can be utilized to suppress vibrations. Secondly, it is possible to enhance the damping effect of the system; Due to environmental noise, it is normally not possible to increase the D coefficient in a PID controller as much as desirable. The damper is thus able to supplement this damping effect to improve settling time. Here, we will present the damper design as well as the preliminary experiment results for both vibration suppression and motion damping.

Abstract: The modeling and compensation of hysteresis in piezoelectrically driven systems are very important for positioning and noise and vibration reduction applications. An active vacuum clamping system for a stationary wood machining center with piezo actuators for the purpose of vibration control has been developed. This active system is intended to reduce workpiece vibrations, which are excited during machining. However, the piezo actuators have an inherent hysteresis effect between input voltage and output position of the vacuum plate. The Bouc-Wen and the Classical Preisach methods are studied in this paper to model the hysteresis curves and to compensate the hysteresis effect of the integrated piezo actuator.

Abstract: Coaxial alignment is an important process in the machining of cylindrical-shape miniature components with an inner bore. It requires aligning the axis of the inner bore with respect to the machine rotational axis precisely. In this paper, we present a spindle with automated coaxial alignment capability for machining applications of the components such as ferrules and capillaries. This spindle includes a novel orientation-adjustable mechanism and a vision-guided feedback system. The adjustment mechanism consists of two pieces of flexural bearings, which can provide the spindle with 4 DOF adjustments without any backlash. The vision-guided feedback system comprises the component face image processing and the through-bore light intensity processing, both of which provide the information of translational and angular offsets. A prototype of the spindle was built to verify the technology we developed. The results show that the system can achieve superior coaxial alignment performances.