A numerical algorithm to determine straightness error, surface roughness, and waviness measured using a fiber optic interferometer (original) (raw)

An error separation technique for measuring straightness motion error of a linear slide

Measurement Science and Technology, 2000

A novel measurement system for on-machine determination of the straightness motion error and profile of a precision linear slide for active error compensation (AEC) purposes has successfully been developed. The characteristics of the proposed measurement method are: (i) the profile is determined under on-machine conditions requiring no pre-calibration; and (ii) a novel approach involving representation of the test section of the profile by one cycle of a periodic function is facilitated by specially arranging three sensors to form a stationary stage. In this paper, the principles and operation of the measurement method are presented. The approach of defining a periodic function to deal with the problem of non-periodicity of a profile is then described. A preliminary analysis of the sensor measurement errors is also given. Finally, the measurement system consisting of three non-contact capacitive sensors is built and evaluated experimentally on a laboratory lathe and good reproducibility of profile results is obtained.

Techniques of multi-degree-of-freedom measurement on the linear motion errors of precision machines

Any axis of precision machines possesses sixdegree-of-freedom (6-DOF) motion errors, also called the geometric errors, due to manufacturing tolerances and assembly errors, namely three linear and three angular errors. Conventional optical instruments allow measurement of only one or two errors at a time. In order to achieve fast measurement, many multi-degree-of-freedom measurement (MDFM) systems have been developed over the past 20 years, from three-degree-of-freedom (3-DOF) to 6-DOF. This article summarizes reports of optical measurement techniques of MDFM systems for precision linear, planar and XYZ stages. Comments are also given for the applicability to practical uses.

Modal Analysis, Metrology, and Error Budgeting of a Precision Motion Stage

Journal of Manufacturing and Materials Processing, 2018

In this study, a precision motion stage, whose design utilizes a single shaft supported from the bottom by an air bearing and voice coil actuators in complementary double configuration, is evaluated for its dynamic properties, motion accuracy, and potential machining force response, through modal testing, laser interferometric metrology, and spectral analysis, respectively. Modal testing is carried out using two independent methods, which are both based on impact hammer testing. Results are compared with each other and with the predicted natural frequencies based on design calculations. Laser interferometry has been used with varying optics to measure the geometric errors of motion. Laser interferometry results are merged with measured servo errors, estimated thermal errors, and the predicted dynamic response to machining forces, to compile the error budget. Overall accuracy of the stage is calculated as peak-to-valley 5.7 µm with a 2.3 µm non-repeatable part. The accuracy measured is in line with design calculations which incorporated the accuracy grade of the encoder scale and the dimensional tolerances of structural components. The source of the non-repeatable errors remains mostly equivocal, as they fall in the range of random errors of measurement in laser interferometry like alterations of the laser wavelength due to air turbulence.

Calibration of an interferometric on-machine probing system on an ultra-precision turning machine

Measurement, 2018

Surface measurement is fundamental to further enhance accuracy and efficiency in ultra-precision machining. Advanced on-machine measurement (OMM) is evolving as the key enabling technology for autonomous and intelligent manufacturing. The present work integrates an interferometric probing system on an ultra-precision turning machine. However, due to relatively harsh environment in the machine tools, metrology characteristics of surface measuring instrument would deviate from those tested in laboratories. In order to improve the performance of on-machine measurement system, it is necessary to calibrate the OMM system and compensate the systematic errors. Three major error sources, including on-machine vibration, machine tool kinematic errors, and linearity errors are investigated according to the characteristics of interferometric single point OMM. For on-machine vibration, a theoretical study of the relationship between sampling frequency, scanning parameters, vibration frequency and topography frequencies of interest is first presented. Static and scanning vibration tests are performed in order to select the proper sampling frequency. Machine scanning error is mapped for OMM correction with the proposed kinematic error modelling measurement and compensation method. Calibration of the response curve and linearity error correction is conducted by measuring a radially distributed step height sample on the machine. Experimental investigation is conducted which proves the validity of proposed calibration methodology and the effectiveness of OMM. After the calibration process, OMM results agree well with calibrated offline measurements.

Step height measurements using a combination of a laser displacement gage and a broadband interferometric surface profiler

Interferometry XI: Applications, 2002

We describe techniques for measuring step heights between separated, nominally plane-parallel surface regions of a precision-engineered part. Our technique combines a broadband, 10-micron wavelength scanning interferometric profiler with a HeNe laser displacement gage. The infrared wavelength accommodates machined metal parts having a surface roughness in excess of what would be possible with a visible-wavelength interferometer. The combination of broadband interferometry, which removes fringe order ambiguity, with a laser displacement gage makes it possible to determine the relative heights of surfaces separated by several mm with a 2-σ uncertainty of 0.3 micron. We present the instrument theory, experimental implementation and results of instrument testing.

Enhancement of accuracy of multi-axis machine tools through error measurement and compensation of errors using laser interferometry technique

Mapan-journal of Metrology Society of India, 2010

The present era is witnessing advancement in digital electronics and microprocessor which enables manufacturing sector capable to produce complex components within small tolerance zone in the tune of nanometre and at one machining center. All motion control systems have some form of position feed back system fitted with the machine. Such systems are not generally accurate due to the errors in the positioning performance of the machine tool which will change over time to time due to wear, damage and environmental effects. The complex structure of multi-axis CNC machine tools produce an inaccuracy at the tool tip caused by kinematic parameter deviations resulting in manufacturing errors, assembly errors or quasi-static errors. Analysis of these errors using a laser measurement system provides the manufacturers a way to achieve better accuracy and hence higher quality output from these processes. In this communication, techniques to measure the linear positional errors of axes of CNC machine tools by a laser interferometer calibration system and accuracy enhancement using the data obtained from the calibration cycle by feeding into the machine’s controller with the help of linear error compensation package are discussed.

Impact of measurement procedure when error mapping and compensating a small CNC machine using a multilateration laser interferometer

Precision Engineering, 2014

This paper deals with the accuracy of compensation of machine tools using a tracking interferometer using the multilateration method. The measurement strategy and thermal drift compensation of the measurements are studied. It shows that most effects of temperature are accurately compensated by the laser tracking interferometer software. However, thermal drifts of accessories are not taken into account, and are therefore not corrected. To validate the robustness of procedures, the geometrical errors of the same machine tool were measured by five measurement strategies using the same equipment. Each strategy is devised and carried out independently by a different person from several institutions. For each strategy, the geometrical compensations were applied to a set of nominal tool path points. The difference, between the nominal points and the compensated or uncompensated points was calculated. This criterion was used to discuss the procedures employed by the participants. (J.-M. Linares). laser tracking interferometer. The error mapping is based on measurement strategies which in most cases are based on measures of geometrical entities (point, plan, cylinder or sphere).

A 2D Optical Displacement Transducer to Measure Nanometric Errors in Precision Machines

This work presents an innovative and portable optical measurement system based on a radial ESPI interferometer, capable to measure small displacements with a nanometric uncertainty. The system is fully automated, very portable and light weighted (~0.6 kg). Almost no surface preparation is required for 2D displacement measurement, what makes it very convenient for measuring directly on the work piece surface. In the current configuration, the system has a measurement range of ± 2 μm, and its calibration using a modified Michelson interferometer has showed an uncertainty U95 = ± 0.008 μm. The experiments revealed that the optical system is reliable and time efficient, having a strong potential to be applied in other situations where it is necessary to measure small displacements, with very low uncertainties. By combining three of those devices it is possible to measure all the six rigid body displacement and rotation components. Here, it is demonstrated its performance to measure the ...

Calibration of an Interferometric Surface Measurement System on an Ultra-Precision Turning Lathe

2017

On-machine measurement avoids the time-consuming transposition operations between the measurement and machine coordinates. The present work integrates an interferometric probing system on an ultra-precision turning machine. Due to the relatively harsh environment in the machine tools, metrological characteristics of the surface measurement instrument would deviate from those tested under standard laboratory conditions. In order to improve the performance of on-machine measurement systems, it is necessary to calibrate the on-machine measurement (OMM) system and compensate for any systematic errors. Three key issues, including on-machine vibration, machine tool kinematics error, and linearity error are discussed in this study. Experimental investigation is conducted to prove the validity of proposed calibration methodology and the effectiveness of on-machine measurement.