Experimental investigation on high-performance coordinated motion control of high-speed biaxial systems for contouring tasks

The recently developed global task coordinate frame (TCF) is utilized to synthesize a high-performance contouring controller with cogging force compensation for a linear-motor-driven biaxial gantry to test the practically achievable high-speed/high-accuracy contouring performance. Specifically, the approach employs the global task coordinate formulation to meet the stringent control performance requirements for high-speed and large-curvature coordinated contouring tasks. Moreover, the approach explicitly takes into account the specific characteristics of cogging forces existed in linear motors for the controller design as model compensation to further improve practical contouring performance. Physically intuitive discontinuous projection modifications are used to ensure all the on-line estimates within their known bounds. Robust control terms are also constructed to effectively attenuate the effect of model compensation errors due to various uncertainties for a theoretically guaranteed transient performance and steady-state tracking accuracy in general. Comparative experiments are carried out on an industrial linear-motor-driven biaxial gantry and the results verify the effectiveness of the proposed cogging force compensations - a contouring tracking accuracy improvement of 30% is achieved. Experimental results also validate the rather excellent contouring performance of the proposed controller for high-speed/high-accuracy contouring tasks in actual implementation in spite of various parametric uncertainties and uncertain disturbances.     

New nano-contouring measurement techniques for a nano-stage

Among the most commonly used contouring measurement methods, no measuring techniques have been available with nanometer resolution except for the grating encoder measurement system. Although the grating encoder measurement system can reach the resolution of nanometers for nano-contouring, its resolution and accuracy of measurement are limited by the manufacturing accuracy of the size of the grating etching, the size of the light-spot and the pitch of the grating. When the contouring radius is less then the pitch of the grating, the grating encoder system does not work. So, no measuring instrument could simultaneously measure the nano-stage contouring error. In this paper, three new nano-contouring measurement techniques for a nano-stage have been successfully developed by employing laser interferometers, corner cubes and some developed fixture. By specified light path arrangements, three different setting-ups are described in this paper. The measuring resolution of these techniques is 10 nm. Contouring tests with a very small radius were carried out. A 500 nm radius contouring test result was given. Since the techniques are simple, it is very easy to set up and to carry out the tests, compared to other systems. Also, the setting-up error can be ignored when the contouring radius is small. A Heidenhain measuring system was employed to verify these three new techniques. Good verification results were obtained to prove these systems.     

Graphic analysis of resources by numerical evaluation techniques (Garnet)

An interactive computer program for graphical analysis has been developed by the U.S. Geological Survey. The program embodies five goals, (1) economical use of computer resources, (2) simplicity for user applications, (3) interactive on-line use, (4) minimal core requirements, and (5) portability. It is designed to aid (1) the rapid analysis of point-located data, (2) structural mapping, and (3) estimation of area resources.     

Interpretation of regional geochemistry using optimal interpolation parameters

A collection of data analysis procedures is presented which are derived from estimation of geographic interpolation parameters. Several interpolation models are discussed along with a procedure to obtain the best model. The power parameter, p, and the search radius, c, are the standard parameters in inverse distance weighting interpolation which is appropriate for sampling patterns that are not highly irregular. The power parameter is shown to characterize the regional behavior of geochemical measurements. This characterization process can be used to associate similar types of geochemical measurements, produce optimal contour maps, derive meaningful residual maps, and highlight unusual geochemical areas by a weighted sum variable. The computer program. BESTP, (used to estimate the optimum inverse distance weighting interpolation parameters) is presented, along with an example using reconnaissance groundwater data from the Plainview Quadrangle, Texas.     

PETFAB: user-considerate FORTRAN 77 program for the generation and statistical evaluation of fabric diagrams

PETFAB is an easy-to-use FORTRAN 77 program which provides a comprehensive structural geologic fabric analysis package for use by geologists and students with little or no computer experience. User-selected options include a plot of data points on an equal-area stereonet, determination of data distribution and preferred orientation, calculation of statistical significance of fit, and contour diagrams using both fixed and variable counting areas. Creation of data files is simplified by use of an interactive utility loading program, LOADFAB. Output is generated on a lineprinter and optionally on a CALCOMP plotter.     

Improving CNC contouring accuracy by robust digital integral sliding mode control

Integral sliding mode control (ISMC) has been employed and shown to improve contouring accuracy in the presence of external disturbances and model uncertainties. An ISMC controller directly reduces the tracking errors of each individual axis, thereby reducing the overall contour errors indirectly. An ISMC controller drives the system dynamics back onto the sliding surface if there exists a deviation from the predefined surface. In the design of an ISMC controller, it is crucial to choose an appropriate sliding surface as this has a great impact on system performance and on chattering. In current approaches, the sliding surface is chosen largely based on a rule of thumb which is only applicable for systems with open-loop poles having imaginary parts. In this paper, an approach is presented to design the sliding surface using principles of robust digital control so that both the regulation and robustness requirements can be satisfied. The natural frequency of the dominant closed-loop poles is chosen such that the modulus of the output sensitivity function lies within the robustness bounds. Resonant pole-zero filters are then used to reshape the output sensitivity function in specific frequency regions. Experiments showed that when the modulus of the output sensitivity function is kept within the robustness bounds, chattering can be avoided and the contour errors resulting from vibrations can be reduced. The introduction of a resonant pole-zero filter also allowed the attenuation band to be expanded so that the low frequency components of the contour errors are attenuated.     

Prediction of cutting forces and machining error in ball end milling of curved surfaces -II experimental verification

This paper presents the results of a series of experiments performed to examine the validity of a theoretical model for evaluation of cutting forces and machining error in ball end milling of curved surfaces. The experiments are carried out at various cutting conditions, for both contouring and ramping of convex and concave surfaces. A high precision machining center is used in the cutting tests. In contouring, the machining error is measured with an electric micrometer, while in ramping it is measured on a 3-coordinate measuring machine. The results show that in contouring, the cutting force component that influences the machining error decreases with an increase in milling position angle, while in ramping, the two force components that influence the machining error are hardly affected by the milling position angle. Moreover, in contouring, high machining accuracy is achieved in “Up cross-feed, Up cut” and “Down cross-feed, Down cut” modes, while in ramping, high machining accuracy is achieved in “Left cross-feed, Downward cut” and “Right cross-feed, Upward cut” modes. The theoretical and experimental results show reasonably good agreement.     

Prediction of cutting forces and machining error in ball end milling of curved surfaces -I theoretical analysis

This paper presents a theoretical model by which cutting forces and machining error in ball end milling of curved surfaces can be predicted. The actual trochoidal paths of the cutting edges are considered in the evaluation of the chip geometry. The cutting forces are evaluated based on the theory of oblique cutting. The machining errors resulting from force induced tool deflections are calculated at various parts of the machined surface. The influences of various cutting conditions, cutting styles and cutting modes on cutting forces and machining error are investigated. The results of this study show that in contouring, the cutting force component which influences the machining error decreases with increase in milling position angle; while in ramping, the two force components which influence machining error are hardly affected by the milling position angle. It is further seen that in contouring, down cross-feed yields higher accuracy than up cross-feed, while in ramping, right cross-feed yields higher accuracy than left cross-feed. The machining error generally decreases with increase in milling position angle.     

The design of an interactive graphics system for the display of meteorological fields

We describe a computer graphics system for the display of meteorological fields (such as plots of temperature and pressure). Much of the design effort has gone into the command processor which uses the usual command format of VERB PARAMETER = VALUE … The parameter and values are defined in terms of a tree sructure and the program searches as much of the tree as is necessary to make an unambiguous indentification of a token (where such an identification is possible). Because of this, commands can generally be abbreviated to the format VERB VALUE. This shortened form is possible even when the value of the command parameter is numerical. This is achieved by always specifying the units of numerical values (such as 5 days, 24 hours, 1000 millibars, etc.). The command format allows the user to manipulate a number of fields to form derived fields such as the difference of two pressure forecasts. The use of defaults for all parameters (which change as the user requests plots), reduces the amount of typing required to a minimum. A ‘Help’ facility aids the user in his choice of commands.     

Interactive 3D medical image segmentation with energy-minimizing implicit functions

We present an interactive segmentation method for 3D medical images that reconstructs the surface of an object using energy-minimizing, smooth, implicit functions. This reconstruction problem is called variational interpolation. For an intuitive segmentation of medical images, variational interpolation can be based on a set of user-drawn, planar contours that can be arbitrarily oriented in 3D space. This also allows an easy integration of the algorithm into the common manual segmentation workflow, where objects are segmented by drawing contours around them on each slice of a 3D image.Because variational interpolation is computationally expensive, we show how to speed up the algorithm to achieve almost real-time calculation times while preserving the overall segmentation quality. Moreover, we show how to improve the robustness of the algorithm by transforming it from an interpolation to an approximation problem and we discuss a local interpolation scheme.A first evaluation of our algorithm by two experienced radiology technicians on 15 liver metastases and 1 liver has shown that the segmentation times can be reduced by a factor of about 2 compared to a slice-wise manual segmentation and only about one fourth of the contours are necessary compared to the number of contours necessary for a manual segmentation.