Chia-Hsiang Menq

Automated precision measurement of surface profile in CAD-directed inspection

The authors present an optimal match scheme that aligns the measurement data with the design data in CAD-directed dimensional inspection. The principle of this scheme is to determine the actual measured points on the nominal surface by minimizing the sum of the squared distances of the measurement data from the surface with respect to the parameters of a rigid body transformation. Its computational efficiency and robustness against singularity are discussed. Two applications are examined. The first is determining the design coordinate system with respect to a machine coordinate system. The second is comparative analysis for precision measurement. For determining the design coordinate system, a sensitivity measure is proposed and confirmed experimentally. For error comparative analysis, a statistical model is developed to determine the minimum number of required measurement points so that the sampled points can closely represent the entire population. >

Determination of optimal measurement configurations for robot calibration based on observability measure

The selection of measurement configurations in robot cali bration is investigated. The goal is to select a set of robot measurement configurations that will yield maximum ob servability of the error parameters in a defined position error model so that the effect of noise in parameter estimation can be minimized. The noise considered in this paper includes both measurement and modeling errors. An observability measure is used as a criterion for selecting measurement configurations for calibration. Experimental studies are per formed to demonstrate the importance of observability to parameter estimation and to verify its implications in robot calibration. Based on the defined observability measure, the optimal measurement configurations for robot calibration are determined for general open-loop planar mechanism and PUMA type robots.

Smooth-surface approximation and reverse engineering

Abstract The paper identifies the steps involved in the reverse-engineering process. The procedure begins with the division of the whole array of measurement data points into regions, according to shape-change detection. In each region, points are parameterized, and knots are selected. Smooth parametric surface approximation is obtained by the least-square fitting of B-splines. Nonlinear least-square minimization is applied for parameter optimization with simple bounds on the parameter values. The objective function minimized is the explicit error expression for the sum of the squares of error values at the data points.

Hysteresis compensation in electromagnetic actuators through Preisach model inversion

In this paper, the classical Preisach independent domain model is used to capture the essential characteristics of hysteresis nonlinearity in electromagnetic (EM) actuators made of soft ferromagnetic material. Experimental results demonstrate its ability to accurately model electromagnetic hysteresis for variations in input current, airgap, and orientation. The Preisach model is then inverted and incorporated in an open-loop control strategy that regulates the EM actuator and compensates for hysteretic effects; hysteresis-free regulation of the EM actuator is obtained, for variations in input current, airgap, and orientation. Hysteresis is also effectively compensated for desired force trajectories of frequencies up to 100 Hz. Thus, the experimental results demonstrate consistent performance of the open-loop control strategy based on Preisach model inversion, in satisfactorily regulating the output of the EM actuator to the desired trajectories.

The prediction of cutting forces in the ball-end milling process—I. Model formulation and model building procedure

Abstract This paper presents a model for the prediction of cutting forces in the ball-end milling process. The steps used in developing the force model are based on the mechanistic principles of metal cutting. The cutting forces are calculated on the basis of the engaged cut geometry, the underformed chip thickness distribution along the cutting edges, and the empirical relationships that relate the cutting forces to the undeformed chip geometry. A simplified cutter runout model, which characterizes the effect of cutter axis offset and tilt on the undeformed chip geometry, has been formulated. A model building procedure based on experimentally measured average forces and the associated runout data is developed to identify the numerical values of the empirical model parameters for the particular workpiece/cutter combination.

Automatic data segmentation for geometric feature extraction from unorganized 3-D coordinate points

A systematic approach is proposed to automatically extract geometric surface features from a point cloud composed of a set of unorganized three-dimensional coordinate points by data segmentation. The point cloud is sampled from the boundary surface of a mechanical component with arbitrary shape. The proposed approach is composed of three steps. In the first step, a mesh surface domain is reconstructed to establish an explicit topological relation among the discrete points. The topological adjacency is further optimized to recover the second order object geometry. In the second step, curvature-based border detection is applied on the irregular mesh to extract both sharp borders with tangent discontinuity and smooth borders with curvature discontinuity. Finally, the mesh patches separated by the extracted borders are grouped together in the third step. For objects with complex shape, a multilevel segmentation scheme is proposed for better results. The capability of the proposed approach is demonstrated using various point clouds having distinct characteristics. Integrated with state of art scanning devices, the developed segmentation scheme can support reverse engineering of high precision mechanical components. It has potential applications in a whole spectrum of engineering problems with a major impact on rapid design and prototyping, shape analysis, and virtual reality.

Precision motion control of a magnetic suspension actuator using a robust nonlinear compensation scheme

This paper presents a robust nonlinear compensation algorithm for realizing large travel in magnetic suspension systems suffering from parameter variations and external disturbance forces. A geometric feedback linearization technique that utilizes the complete nonlinear description of the electromagnetic field distribution is employed to obtain large travel. Robustness to uncertainties in the feedback linearized system is achieved through the development of a discrete-time delay-control-based compensation algorithm. In comparison to previous developments, the new scheme removes the constraints of triangularity conditions in compensation of unmatched uncertainties. The performance of this algorithm is experimentally investigated on a magnetic suspension system. In each of the experiments, the controller is designed using the approximate nonlinear model of the system, which is significantly different from the actual plant model. For a fixed set of gains, the robust nonlinear controller accurately stabilizes the system for a large range of ball positions. In trajectory tracking performance evaluation, the controller provides tracking accuracies that are of the same order of magnitude as the accuracy of the position sensor. Finally, when the suspended ball is impressed with an external disturbance force, the controller provides adequate model regulation and rejection of disturbance forces, demonstrating high stiffness control. The experimental results, therefore, verify the consistent performance of the algorithm in realizing large travel in spite of parameter variations and external disturbances.

B-Rep model simplification by automatic fillet/round suppressing for efficient automatic feature recognition

Abstract The CAD models of real-world mechanical parts usually have many fillets and rounds that are essentially important to ensure the manufacturability and assembability. In feature-based modeling, fillets and rounds are often referred as secondary features that are used to modify the local details of the primary features such as holes, slots and pockets. Although the major shape of the primary features may not be affected, fillets and rounds can greatly change the geometric and topological patterns of the primary features. The geometric and topological variations can result in inefficient feature semantics classification in feature recognition. When feature interactions occur, it may become even worse to identify the regular patterns of the primary features. In addition, the fillets and rounds consist of no-linear surfaces such as cylindrical surfaces, spherical surfaces and toroidal surfaces, which bring the difficulties in volumetric feature extraction by half-space partition. In order to facilitate volumetric feature extraction and feature semantics classification, we pre-process the input B-Rep models by suppressing fillets and rounds before the feature recognition. Thus the input B-Rep models can be simplified without altering the major shapes of primary features, the targets of the feature recognition. The B-Rep simplification can be viewed as the reverse process of the edge blending in feature-based design. In this paper, several issues on fillet/round suppressing are discussed and a relatively general and robust approach is proposed to suppress blendings in B-Rep models of mechanical parts before the surface feature recognition and volumetric feature extraction.

CMM feature accessibility and path generation

In this paper, the accessibility of coordinate measuring machines (CMM) and path generation in dimensional inspection are studied. The objective is to develop an algorithm which can determine all the feasible probe orientations for the inspection of a workpiece using a touch trigger probe. The feasible probe orientations ensure that when the probe tip is in contact with the workpiece there should be no collision with either the touch probe or the probe stylus. The algorithm should be able to handle internal holes and complex surfaces and be capable of extending to multiple surfaces. After solving for the probe orientations, a heuristic method determines the number of probe orientations required to inspect the workpiece. It then picks the optimal probe orientation and creates a collision-free inspection path based on the information for probe orientation.

Ultra precision motion control of a multiple degrees of freedom magnetic suspension stage

A general framework for ultra precision motion control of magnetic suspension actuation systems with large travel ranges in multiple degrees of freedom (DOF) is presented. It encompasses the development of nonlinear electromagnetic force model for 6-DOF actuation, and the design of the necessary control architecture for ultra precision motion control of magnetic suspension actuation systems. A 6-DOF magnetic suspension stage (MSS) was designed and fabricated to illustrate the developed framework. The MSS consists of multiple electromagnets that are located around the flotor and are utilized to suspend and modulate its position and orientation. The control architecture takes the six control parameters provided by a laser measuring system and intends to control the 6-DOF motion by regulating the current in the electromagnets. The developed robust nonlinear control architecture consists of three components: 1) feedback linearization; 2) force distribution; and 3) H/sub /spl infin// robust controllers for each DOF of motion. Several experiments are designed to illustrate the desired characteristics of the developed system.