3-Dimensional profile distortion measured by stylus type surface profilometer

In this paper, the distortion effect in measured profiles caused by stylus tip radius size of stylus-typed surface profilometer was analyzed in terms of 2D and 3D. On the basis of our analysis results, we propose selection criteria for the stylus tip radius to improve the reliability of measurement results. For this purpose, a simulation algorithm has been devised and implemented for 2D and 3D measurement simulations, and the 3-dimensional surface texture used in simulation was obtained using an Atomic Force Microscope (AFM) on an actual machined surface to improve the reliability of simulation results. The simulation results are compared with the measured results from the same specimen using a roughness tester, and the validity of analysis via the simulation proposed in this study is confirmed. Cumulative power spectral analysis was performed for the 2D and 3D simulated profiles obtained from simulation. On the basis of the analysis results, an effective frequency components field using a stylus type profilometer is clarified, and the selection criteria of the stylus tip radius for measurement is proposed considering the surface texture characteristics of the specimen. The purpose of this paper is to provide a basis of a simple and effective method which could be an alternative of some engineering standard that specifies selection of stylus tip radius for the measurement using only nominal Rq for machined surface.     

Uncertainty analysis of roughness standard calibration using stylus instruments

A stylus instrument was characterized and calibrated, including a dynamic calibration of the probe. This stylus instrument was used to calibrate ten roughness standards for six surface roughness parameters. The sensitivity of each parameter of each standard to such measurement conditions as stylus geometry, measurement force, cut-off wavelength, and so forth was determined experimentally. These results were used for an uncertainty evaluation of each parameter for each roughness standard. It is shown that the manufacturers’ specification for the stylus instrument (2% uncertainty in roughness parameters) is approximately correct for the most commonly used samples and parameters, but the uncertainty may range from 0.03% (for sinusoidal profiles) to 100% (for very fine surfaces), depending upon the standard and parameter to be calibrated.     

Dynamic modelling of the fidelity of random surface measurement by the stylus method

A numerical simulation has been used to systematically investigate the characteristics of a stylus surface profiling instrument. The model bridges together previously used concepts to incorporate both tip size and tip dynamics. The dynamics incorporate a tip flight phenomenon, inferring detachment from zero value of the reaction force and the trajectory from a free vibration solution to a second order system. Tip shape is handled by a rigid kinematic model. Following brief discussions of the modelling and the process for generating test profiles with defined correlation lengths, the influences of the inherent parameters of the stylus instrument and the testing method on the measurement fidelity are examined. The tip shape effect of the stylus instrument is also considered in the dynamic measurement. It is noted that the finite tip size can increase the critical scanning speed to avoid tip flight, but decreases the signal fidelity of the measurement due to the bridging effect.     

Mechanical filtration of surface profiles

This paper presents the analysis of factors affecting the small wavelength content of profile after measurement by stylus profilometer. Three following factors are considered: the shape and size of stylus tip sampling interval, and short-wavelength cut-off. The effect of mechanical filtration of replica measurement is considered. The influence of skid is also analysed. The real and computer generated random profiles of normal and asymmetrical shapes of the ordinate distribution are the objects of investigation. 2D profiles are analysed, but the effects of tip radius size as well as the skid effect were analysed in three-dimensional surface.     

The influence of stylus flight on change of surface topography parameters

Theoretical and experimental work on stylus flight is described. The paper describes the development of a simulation model for assessing the magnitude of surface topography distortion by stylus flight. Experiments on the surfaces support the theoretical model, which predicts stylus flight. The measurements of different surface topographies (including surfaces after grinding, turning, honing, milling) were done using Talyscan 150 measuring instrument with four traversing speeds (0.5, 1, 2 and 3 mm/s). The results of theoretical considerations and experiments were compared. The effect of stylus flight on surface topography parameters of measured surfaces basing on experimental investigation was assessed. The tendency was found that slope decreased, decrease of amplitude parameters and increase of horizontal parameters took place, but these effects were different for various surface types. The simulation procedure assured good accuracy of surface topography parameters changes.Based on theoretical investigation, the effect of stylus flight and stylus tip radius on parameters of computer-generated profiles was predicted. The choice of traversing speed to different types of surfaces was done. The parameters of biggest changes caused by error in measurement due to stylus kinematics were selected.     

Methods of measuring and characterising the surface geometry of road stones

Methods of measuring and characterising random rough surfaces have always been of interest in the field of engineering. Measurement and analysis of finer scales of texture of a surface are now mainly effected by the use of a stylus instrument.Because of the finite radius of the tip of the stylus, this instrument cannot sense all the scales of texture on a surface. Evaluation of scales of texture finer than that sensed by the stylus instrument is of interest in many fields of engineering and in the prediction of hysteretic friction and of abrasion of rubber in particular. Two new methods which meet this demand to a great extent are described and their application is illustrated by actual measurements on stone surfaces. A scanning electron microscope is used in one method and an optical microscope in the other. Numerical methods of solution using electronic computers are adopted for the evaluation of texture parameters in both methods.     

Traceability and correlation in roundness measurement

A new method for the calibration of Flick standards for roundness measuring instruments has been developed through the use of a Form Talysurf stylus instrument. The method incorporates circular fits and the convolution of the standardized probe geometry over the fitted arcs using the “Kilroy's Cat” function. The method yields stable results, and an error budget documents the low uncertainty of the method. Major uncertainty contributors are the traceability of the Form Talysurf and the roughness of the Flick standard. It is shown that the tip radius has a significant effect on the results obtained in roundness measurement, even on such simple artifacts as the Flick standard. This underlines the importance of implementing a standardized tip radius. The influence of Gaussian versus 2RC filters is also documented.     

Measurements of stylus radii

In stylus measurements of surface texture the measured results for roughness depend on the stylus radius. Therefore it is important to determine the stylus radius. Since stylus tips are not perfectly spherical, the local radius of curvature varies significantly over the surface which makes the determination of an effective radius difficult. Both the techniques used to generate stylus profiles and the subsequent algorithms used to derive an effective radius are discussed. Comparisons are made between three techniques: sharp-edge traces, optical microscopy and scanning electron microscopy. Several algorithms, including that prescribed by the American National Standard ANSI B46-1, are discussed. It is concluded that the radius scale method is accurate, unambiguous and easy to use for routine measurements in the laboratory.     

Statistical behaviour of surface profiles

Since the surface profiles obtained by stylus instruments may be considered as a random process, it is possible to represent these profiles by statistical parameters and functions. The usual geometrical parameters from surface profiles used for the specification of roughness do not completely give the nature of the profile. To obtain a better comparison of the profiles, their statistical similarities may be studied, but the number of such parameters used for the specification of surface profiles should, however, be limited for practical applications. Use of the autocorrelation functions allows the periodic and random nature of the profile to be established, but a simple quantitative value for these functions has yet to be developed. The paper analyses a few statistical parameters obtainable from surface profiles to determine their real significance. An analysis of the statistical behaviour of the profile features is also included.     

A new stylus instrument with a wide dynamic range for use in surface metrology

An instrument has been developed which can measure not only radius of curvature but also form deviation and surface texture at the same time. A computer is used to mathematically separate the form from the texture. The technique can be applied to the measurement of cross track curvature of bearing raceways and to other precision components whose form is defined as a circular arc, or a straight line, in which case angle will be measured instead of radius. The measurement of other forms such as parabolic, elliptical, hyperbolic and aspheric are the subject of continuing development. The instrument provides a distinctive and useful advance in measurement by the stylus method, offering possible solutions to many obdurate problems in the field of surface metrology     

Amplitude-wavelength maps for X-ray computed tomography systems

Amplitude–wavelength (AW) maps or “Stedman diagrams” are often used to provide a graphical representation of the limitations and capabilities of surface measuring instruments. This paper presents an approach for setting the parameter constraints of X-ray computed tomography (CT) in terms of resolution and measuring range for the purpose of representing the performance of industrial CT systems on an AW map. Such AW map will allow instrument users to quickly compare the CT instrument performance to other measuring systems. Examples of the construction of AW maps for different working capabilities of X-ray CT systems, and based on experimental data, are provided. Polypropylene, aluminum, and steel are three workpiece materials considered for determining some of the limitations of measuring capability for the maps developed in this paper. Although the limiting boundaries of the AW plots presented in this paper set a generalized measure of performance for comparisons with other measuring instruments, they may evolve with more comprehensive models of the limiting factors in X-ray CT.     

二维轮廓测量仪的系统建模及标定

在分析轮廓测量仪测量原理的基础上,建立了二维轮廓测量系统的数学模型,构造了轮廓测量仪的硬件结构。研究了差动式电感传感器的输出特性,在此基础上提出了采用标准组合量块的传感器标定方法。分析了触针测头形状对被测轮廓数据的影响,并提出了对测头半径的两种数据修正方法。经实例验证,所采用的系统数学模型和传感器标定方法满足测量系统的要求。     

The Measurement of Surface Roughness and Profiles on Metals

A study of an optical and two stylus-type instruments for measuring surface finish was conducted. The stylus-type instruments are demonstrated to be inaccurate on metals that have a Rockwell hardness less than C-66. The inaccuracy is attributed primarily to surface damage caused by the stylus. The optical instrument causes no surface damage. Stylus-type instruments are proven also to be unsatisfactory for rating relative degree of roughness unless gross roughness differences are considered.

The interpretation of interferographs is discussed.     

Stylus-laser surface calibration system

A stylus-laser surface calibration system was developed to calibrate the NIST sinusoidal roughness Standard Reference Materials (SRM) 2071-2075. Step height standards are used to calibrate the stylus instrument in the vertical direction, and a laser interferometer is mounted on the traversing unit of the stylus instrument to calibrate the instrument in the horizontal direction. The calibration uncertainty (±2δ) for SRM 2075 is ±1.2% for roughness calibrations ((R_a = 1 μm), and ±0.06% for spatial wavelength calibrations (S_m = 800 μm).     

Reliability of roughness measurements using contact stylus instruments with particular reference to results of recent research at the Physikalisch-Technische bundesanstalt

Even today international comparison measurements of surface roughness show differences of 40% and more, as they did more than 10 years ago. However, within the framework of the Deutscher Kalibrierdienst, differences occurring in comparison measurements do not exceed 5%. At the end of 1982, a project of the European Communities was started for the purpose of also carrying out comparison measurements yielding small differences. The prerequisites are the following: clearly defined surface roughness parameters including details of the measurement conditions required and calibration and testing of the contact stylus instruments before the comparison measurements are made.In recent years the contacting process, the interaction between stylus and surface, has been the subject of very thorough investigations at the Physikalisch-Technische Bundesanstalt. Elastic and plastic deformations of the surface were examined. The parameters of influence are the geometry of the stylus tip and of the surface under examination, the properties of the materials, the static and dynamic measuring forces and the rate of feed. Calculation methods for optimizing these parameters are stated in order to keep the resulting measurement errors as small as possible. A new contactless measuring method is described which is based on the evaluation of scanning electron microscopy stereo pairs. An error analysis makes precision measurements possible which up to now could not be carried out at all. Examples examined have shown that sometimes, particularly on finely ground surfaces, measurements with contact stylus instruments on surfaces with R_z values below 1 μm can be very significantly in error.     

Noncontact roughness measurement of turned parts using machine vision

The surface roughness of turned parts is usually measured using the conventional stylus type instruments. These instruments, although widely accepted, have several limitations such as low speed measurement, contacting in nature, requiring vibration-free environment, etc. Machine vision methods of roughness measurement are being developed worldwide due to their inherent advantages, including noncontact measurement, high information content, rapid measurement, and surface measurement capability. In past research, area-based light scattering method and gray scale line intensity measurement have been developed for roughness assessment using machine vision. Such methods, however, produced redundant data when applied to measure roughness of turned parts. In this paper, an alternative method of roughness measurement using the 2-D profile extracted from an edge image of the workpiece surface is proposed. Comparison with a stylus type instrument shows a maximum difference of 10% in the measurement of average roughness R _a using the vision method.     

Surface probing simulator for the evaluation of CMM probe radius correction software

Scanning coordinate metrology is largely based on recording the position of a spherical tip which is maintained in contact with the surface to be measured. The coordinate measuring machine (CMM) software converts these tip coordinates into coordinates of points on the measured surface, a process called probe radius correction. In order to investigate the probe radius correction accuracy of specific CMM software in scanning measurements, a surface probing simulator is developed. It calculates the coordinates of probe tip center points (virtual indicated measured points) as raw measurement data by numerically probing a known virtual surface. An iterative solution based on geometric criteria is used to achieve the necessary tangential contact conditions. Various sculptured surface profiles, probe radii, and scanning increments can then be simulated. These raw data are then fed to the CMM software where the probe radius correction is performed. The CMM results are then compared with the known surface to evaluate the probe radius correction accuracy of the CMM built-in algorithm. The simulator allows a rapid CMM software capability check for a variety of situations and may pinpoint shortfalls that may be avoided through alternative measurement procedures. It may also be used to motivate the development of new probe radius correction techniques and assist in their evaluation. Tests were conducted on a Zeiss and a Mitutoyo CMM to demonstrate the usefulness of the simulator.     

Ball tip–stylus tilt correction for a stylus profilometer

Ball tip and stylus tilt are two error sources found in coordinate measurement machines (CMMs). The magnitude of these errors is dependent on the ball tip radius and the degree of misalignment between the stylus motion axis and lateral referencing plane determined by the x and y axes of the CMM used. It is shown that these two errors are actually coupled and that their correction can be accomplished in one process. The overall benefit and versatility of this correction routine on a more general basis are given.     

Laser optical roughness measurement

A method for non-contacting profile assessment and roughness measurements of engineering surfaces is presented. The well known effect of focusing a light beam on the surface is used, at the same time compensating for the effect on the measuring results of varying material colours by appropriately processing the measuring signal. The sensor and the transducer are connected with the data-processing unit of a stylus instrument, which provides for a simple procedure of recording the roughness profile and calculating standard roughness parameters from it. The measuring results thus obtained agree well with the results of traditional stylus instruments.     

An analysis of the reference lines of the surface profile and its true replica

The roughness of surfaces normally not accessible by conventional stylus instruments is often measured by a replica technique. The replica surface is the mirror image of the original surface. This paper deals briefly with an analysis of the reference lines used in practice for roughness measurements from surface profiles of original as well as replica surface. A statistical analysis of surfaces produced by different processes and of their true replicas is reported.