Laser interferometric system for six-axis motion measurement

This article presents the development of a precision laser interferometric system, which is designed to achieve six-axis motion measurement for real-time applications. By combining the advantage of the interferometer with a retroreflector and that of the interferometer with a plane mirror reflector, the system is capable of simultaneously measuring large transverse motions along and large rotational motions about three orthogonal axes. Based on optical path analysis along with the designed kinematics of the system, a closed form relationship between the six-axis motion parameters of the object being measured and the readings of the six laser interferometers is established. It can be employed as a real-time motion sensor for various six-axis motion control stages. A prototype is implemented and integrated with a six-axis magnetic levitation stage to illustrate its resolution and measurement range.     

Large travel ultra precision x-y-/spl theta/ motion control of a magnetic-suspension stage

This paper presents an indirect adaptive-control approach and its implementation for realizing large travel ultra precision x-y-theta motion control of a magnetic-suspension stage, which is actuated by ten electromagnets and is capable of six-degrees-of-freedom motion. Feedback linearization of the nonlinear force relationship of the electromagnet in terms of the coil current and the air gap is implemented. Due to modeling errors, perfect feedback linearization is not possible, and parameter variations of the feedback-linearized system are demonstrated through closed-loop system identification. Each axis of the feedback-linearized system is then modeled as a double integrator having gain value depending on the position of the stage and subjected to a disturbance. For the purpose of large travel x-y-theta motion control, an indirect adaptive-control algorithm is designed and implemented for each axis of the feedback-linearized system. The developed control algorithm consists of three procedures: a) real-time parameter estimation; b) model cancellation; and c) nominal linear control. Experimental results demonstrate that the indirect adaptive controllers have superior tracking ability when compared to constant gain robust linear H/sup /spl infin// controllers.     

Automatic recognition and suppression of holes on mold bases for finite element applications

Engineering with Computers - As the required accuracy of mold flow analysis has recently increased, it has become necessary to consider all components of a mold base and to generate solid meshes...     

Robust Single Molecule Magnet Monolayers on Graphene and Graphite with Magnetic Hysteresis up to 28 K

The chemical functionalization of fullerene single molecule magnet Tb₂@C₈₀(CH₂Ph) enables the facile preparation of robust monolayers on graphene and highly oriented pyrolytic graphite from solution without impairing their magnetic properties. Monolayers of endohedral fullerene functionalized with pyrene exhibit magnetic bistability up to a temperature of 28 K. The use of pyrene terminated linker molecules opens the way to devise integration of spin carrying units encapsulated by fullerene cages on graphitic substrates, be it single-molecule magnets or qubit candidates.     

Integrated laser/CMM system for the dimensional inspection of objects made of soft material

The applications of the coordinate measuring machines (CMMs) with a contact trigger probe to the dimensional inspection of manufactured products are restricted to the parts made of hard material, such as steel. By combining the laser and CMM, the applications of the CMMs can be extended to the inspection of objects made of soft materials, such as foils, plastics, wood, wax and clay materials. In this research, replacing the contact probe with an inexpensive laser sensor is attempted so as to eliminate the possible deflection of the component being measured when using contact probe. By combining a laser sensor with the existing automated inspection environment, a CAD-directed, three-dimensional coordinate sampling system which can perform non-contact dimensional inspection is developed.     

A new approach to modeling the substrate current of pre-stressedand post-stressed MOSFET's

In this paper, we propose a closed form expression of a new and accurate analytical substrate current model for both pre-stressed and post-stressed MOSFET's. It was derived based on the concept of effective electric field, which gives a more reasonable impact ionization rate in the lucky-electron model. This effective electric field, composed by two experimentally determined parameters, can be regarded as a result of nonlocal heating effects within devices. This model shows a significant improvement to the conventional local field model. One salient feature of the present model is that it allows us to characterize the time evolution of the substrate current of stressed MOSFET's for the first time. Experimental verification for a wide variety of MOSFET's with effective channel lengths down to 0.3 μm shows that the new model is very accurate and is feasible for any kind of MOS device with different drain structures. The present model can be applied to explore the hot carrier effect in designing submicrometer MOS devices with emphasis on the design optimization of a device drain engineering issue. In addition, the present model is well suited for device reliability analysis and circuit level simulations     

A unified least-squares approach to the evaluation of geometric errors using discrete measurement data

This paper presents a unified least-squares approach to the best fit of geometric features and evaluation of dimensional errors. The study originated from the need for advanced algorithms for the dimensional measurement of high precision manufactured parts. The proposed algorithm differs from traditional least-squares in that no linearization or approximation is employed and that it is general to all kinds of geometric features. Instead of computing a substitute best fit feature, the algorithm inversely transforms the measurement coordinates to best fit the nominal geometry. The sum of the squared errors in the surface normal direction is thus minimized with respect to the parameters of a rigid body transformation. Form tolerances are then evaluated using the peak-to-valley deviations after the best fit. To examine the uncertainty of the transformation obtained, sensitivity analysis was investigated to relate transformation errors to dimensional errors. A sensitivity measure is used to estimate the joint effect of the measurement locations and the number of measurement data on the accuracy of the coordinate transformation. Computer simulations have been performed on different geometric features to study the robustness and efficiency of the algorithm. Application to the measurement of high precision fuel injectors is also presented.     

Recognition of virtual loops on 3D CAD models based on the B-rep model

Loops are critical elements in boundary representation (B-rep) models because they link all edges corresponding to a face. Loops can be used in feature recognition for identifying depressions or protrusions. In real 3D CAD models, however, features typically lie across multiple faces, which is beyond the data structure of current B-rep models. This study presents a virtual loop concept to account for all loop types used in CAD models, and develops algorithms for recognizing them. In accordance with the complexity of the recognition algorithm, this study defines three types of loop: single, virtual, and multivirtual. A single loop is the current loop recorded in the B-rep model. A virtual loop lies across faces that are at least G¹ continuous. Finally, a multivirtual loop lies across faces that are either G⁰ or G¹ continuous. The proposed loop structure provides a more complete data structure for recognizing various types of features in feature-recognition modules. Several realistic CAD models are presented to confirm the feasibility of the proposed loop-recognition and feature-recognition methods.