Neville Ka-shek Lee

Analysis and design of polysilicon thermal flexure actuator

An analytical model that can accurately predict the performance of a polysilicon thermal flexure actuator has been developed. This model is based on an electrothermal analysis of the actuator, incorporating conduction heat transfer. Heat radiation from the hot arm of the actuator to the cold arm is also estimated. Results indicate that heat radiation becomes significant only at high input power, and conduction heat losses to both the substrate and the anchor are mainly responsible for the operating temperature of the actuator under routine operations. Actuator deflection is computed based on elastic analysis of structures. To verify the validity of the model, polysilicon thermal flexure actuators have been fabricated and tested. Experimental results are in good agreement with theoretical predications except at high input power. An actuator with a 240 µm long, 2 µm thick, 3 µm wide hot arm and a 180 µm long, 12 µm wide cold arm deflected up to 12 µm for the actuator tip at an input voltage of 5 V while it could be expected to deflect up to 22 µm when a 210 µm long cold arm is used.

Efficient sampling for surface measurements

Abstract The sample size is directly proportional to the time taken during inspection, while the error due to discretization relates to the quality of the process. This paper investigates two deterministic sequences of numbers, as sample coordinates, by presenting their computations and their applications to metrology. Results show a dramatic improvement in both the number of and the error in measurements.

A simple approach to characterizing the driving force of polysilicon laterally driven thermal microactuators

Based on the elastic analysis of structures, a simple approach to calculating the driving force for polysilicon laterally driven thermal microactuators is presented by using their deflection. The driving force obtained through the deflection is compared with available results measured by force testers fabricated on the same substrate as the microactuators. Reasonable agreement has been achieved. The approach allows one to predict the driving force for the microactuators as their deflection is designed.

HIGH-RESOLUTION MULTIDIMENSIONAL DISPLACEMENT MONITORING SYSTEM

The possibility of using quadrant detectors to develop a new optical system that can monitor all six degrees of freedom of mechanical workpieces with very high resolution is investigated. A prototype system based on this approach has been designed and built. Although the system is not fully optimized, our proposed system has already demonstrated some promising results. Using a thermally compensated laser source together with a pinhole spatial filtering system, we have demonstrated that lateral resolution better than 50 nm and angular displacement resolution better than 0.25 ?rad is achievable with this system.

Automated configuration of parametric feeding tools for mass customization

Abstract Mass customization is a dominant new trend in modern manufacturing, where by industries are required to produce umpteen variations of products at costs approaching those achievable in mass production. Among the methods to tackle this demand is development of flexible tooling which operates at high throughput rates. A suite of such tools called MPATS (a Modular, Parametric, Assembly Tool Set) is developed for this. The paper introduces MPATS, and also describes a computer-aided planning system to automatically configure MPATS.

A modular, parametric vibratory feeder: a case study for flexible assembly tools for mass customization

A new class of parametric and modular flexible tools is proposed to improve the setup times of assembly lines. The methodology is especially effective in dealing with problems of mass customization. In addition to improvements in the setup time, the methodology, MPATS (modular, parametric assembly tool sets) has other potential advantages such as lower tooling costs as well as faster tooling lead times compared to conventional assembly systems utilizing custom made tools. To demonstrate the feasibility of the methodology, a prototype tool set is designed and presented in this paper. The prototype tool set focuses on the most common of feeding and orienting tools: vibratory bowl feeders.

Effects of Surface Roughness on Multi-Station Mechanical Alignment Processes

A theoretical simulation study was performed to study how surface roughness of the workpiece and datum can affect the locating precision of multiple station manufacturing processes using a mechanical alignment system. Our analysis shows that geometric consideration, a factor that has not been treated before, is extremely important for many multi-station applications. As expected, the level of alignment precision decreases when the level of surface roughness of the workpieces increases. Our analysis also shows that the effect of the sample roughness on the level of alignment precision depends heavily on the difference in the relative positions of the datum between different workstations.

Effect of mechanical alignment system on assembly accuracy

Mechanical means of positioning are frequently used in mechanical assembly processes. However, very little attention has been paid to the proper design and selection of mechanical alignment systems (MAS) for assembly processes. In this paper, we study the performance of different MAS in terms of assembly accuracy in the presence of the form error, surface waviness and surface roughness of the references surfaces. In particular, simulation models are used to investigate how the datum pin configuration, datum pin location and datum geometry of the MAS would affect the assembly accuracy in the presence of surface errors of the workpieces. Our investigation can provide insight into how to design MAS for optimum performance for assembly accuracy. Our analysis shows that over an order of magnitude of difference in assembly accuracy can exist between using properly designed MAS and poorly design MAS.

Effect of Datum Securing Method on Precision of Mechanical Alignment System

In this research, the achievable precision level using mechanical datums for manufacturing has been studied, Specifically, the effect of how a datum is secured in a mechanical alignment system was studied with the aid of a high-resolution multidimensional optical position monitoring system developed for the purpose. The study shows that the way datum is secured can be a major factor affecting the alignment precision of a mechanical alignment system. For a datum prepared by randomly inserting dowel pins into precision bored holes, a common practice in industry, the precision level was found to be worse than 10 μm. The results also show that the precision level can be readily improved by addressing this major cause of inaccuracy. Different methods depending on manufacturing requirements and constraints have been proposed. Some of these simple procedures lead to more than an order of magnitude improvement in alignment precision.

Beacon placement strategies in an ultrasonic positioning system

Ultrasonic Positioning Systems (UPSs) are widely used to detect, locate, or track targets. One of the key factors that determines the performance of a UPS is beacon placement. In this article, beacon placement strategies for a two-dimensional array in the xy-plane above the target with an adaptive height are studied and optimized as a function of the beacon’s characteristics and application requirements in terms of positioning precision and particularly reliability. The effect of positioning requirements on placement is also investigated. It is shown that for triangle or square placements or a hexagon placement with a low precision requirement, the optimal side length of each placement pattern is restricted by the upper bounds of the geometry and reliability, and the placement pattern is valid only when there is a gap between those upper bounds and the lower bound specified by the precision requirement. However, for a hexagon placement with a high precision requirement, the optimal side length is restricted by the upper bound imposed by the precision requirement. The use of a high beacon height with respect to the target allows positioning requirements to significantly reduce the optimal side length. In addition to the beacon height, another important factor is the beacon placement pattern, such as triangle, square, or hexagon. A comparison of the obtained results shows that under a loose precision requirement, triangle placement is the best; when it is moderate, either square or hexagon placement is preferred; and if the precision requirement is stringent, only hexagon placement is feasible. From the comparison of beacon placement strategies, an 18% reduction in the numbers of beacons is readily achievable for commonly available beacons.