Wen-Yuh Jywe

Development of a laser-based high-precision six-degrees-of-freedom motion errors measuring system for linear stage

This article presents a useful measuring system for the simultaneous measurement of six-degrees-of-freedom motion errors of a moving stage. The system integrates a miniature fiber coupled laser interferometer with specially designed optical paths and quadrant detectors, capable of measuring six-degrees-of-freedom motion errors. Using this model, the proposed measuring method provides rapid performance, simplicity of setup, and preprocess verification of a linear stage. The experimental setups and measuring procedures, and a systematic calculated method for the error verification are presented in the paper. The system’s resolution of measuring straightness error component is about 25nm. The resolution of measuring the pitch and yaw angular error component is about 0.06arcs. With the comparison between the HP calibration system and the proposed system in the measuring range of 120mm, the system accuracy of measuring straightness error and angular error is within the range ±0.6μm and ±0.3arcs.

Precision modeling of form errors for cylindricity evaluation using genetic algorithms

A heuristic approach is proposed in this paper to model form errors for cylindricity evaluation using genetic algorithms (GAs). The proposed GAs method shows good flexibility and excellent performance in evaluating the engineering surfaces via measurement data involved with randomness and uncertainty. The numerical-oriented genetic operator is used as a basic representation for error modeling in the paper. The theoretical basis for the proposed Gas-based cylindricity evaluation algorithms is first presented. The performance of the method under various combinations of parameters and the precision improvement on the evaluation of cylindricity are carefully analyzed. One numerical example is presented to illustrate the effectiveness of the proposed method and to compare the Gas-based modeling results with those obtained by the least-squares method. Numerical results indicate that the proposed GAs method does provide better accuracy on cylindricity evaluation. The method can also be extended for solving difficult form error minimization and profile evaluation problems of various geometric parts in engineering metrology.

The min-max problem for evaluating the form error of a circle

There have been many studies to evaluate the form error of a circle. Most of them, such as the optimum methods and limacon model, employed the approximate solution to obtain the desired results. In this paper, three mathematical models depending on the method used to select the exact control points are constructed to evaluate the analytic solution of the minimum circumscribed circle, the maximum inscribed circle and the minimum zone circle by directly resolving the simultaneous linear algebraic equations. These new and simple mathematical methods are verified to be useful for determining the exact solution.

Development of a simple test device for spindle error measurement using a position sensitive detector

A new spindle error measurement system has been developed in this paper. It employs a design development rotational fixture with a built-in laser diode and four batteries to replace a precision reference master ball or cylinder used in the traditional method. Two measuring devices with two position sensitive detectors (one is designed for the measurement of the compound X-axis and Y-axis errors and the other is designed with a lens for the measurement of the tilt angular errors) are fixed on the machine table to detect the laser point position from the laser diode in the rotational fixture. When the spindle rotates, the spindle error changes the direction of the laser beam. The laser beam is then divided into two separated beams by a beam splitter. The two separated beams are projected onto the two measuring devices and are detected by two position sensitive detectors, respectively. Thus, the compound motion errors and the tilt angular errors of the spindle can be obtained. Theoretical analysis and experimental tests are presented in this paper to separate the compound errors into two radial errors and tilt angular errors. This system is proposed as a new instrument and method for spindle metrology.

Development of a diffraction-type optical triangulation sensor.

We propose a diffraction-type optical triangulation sensor based on the diffraction theorem and the laser triangulation method. The advantage of the proposed sensor is that it obtains not only the linear displacement of a moving object but also its three angular motion errors. The developed sensor is composed mainly of a laser source, two quadrant detectors, and a reflective diffraction grating. The reflective diffraction grating can reflect the incident laser beam into several diffractive rays, and two quadrant detectors were set up for detecting the position of 0- and + 1-order diffraction rays. According to the optical triangulation relationship between the spatial incident angles of a laser beam and the output coordinates of two quadrant detectors, the displacement and the three angular motion errors of a moving object can be obtained simultaneously.

Simple three-dimensional laser angle sensor for three-dimensional small-angle measurement.

A simple three-dimensional (3D) laser angle sensor for 3D measurement of small angles based on the diffraction theorem and on ray optics analysis is presented. The possibility of using position-sensitive detectors and a reflective diffraction grating to develop a 3D angle sensor was investigated and a prototype 3D laser angle sensor was designed and built. The system is composed of a laser diode, two position-sensitive detectors, and a reflective diffraction grating. The diffraction grating, mounted upon the rotational center of a 3D rotational stage, divides an incident laser beam into several diffracted rays, and two position-sensitive detectors are set up for detecting the positions of +/-1st-order diffracted rays. According to the optical path relationship between the three angular motions and the output coordinates of the two position-sensitive detectors, the 3D angles can be obtained through kinematic analysis. The experimental results show the feasibility of the proposed 3D laser angular sensor. Use of this system as an instrument for high-resolution measurement of small-angle rotation is proposed.

Sliding-Mode Tracking Control With DNLRX Model-Based Friction Compensation for the Precision Stage

This paper concerns the development of a sliding-mode tracking controller with friction compensation for a precision positioning stage with cross-roller guides. Experiments including prerolling and rolling friction regimes are conducted, and then a two-stage parameter estimation algorithm is used to identify the parameters of a friction dynamic model (Dynamic NonLinear Regression with direct application of eXcitation, DNLRX, model). This model allows the estimation of the friction force in combination with the system dynamics against displacement, and can be used as a feed-forward controller to compensate for the friction effect. To compensate for model error and uncertain disturbances, an integral sliding-mode controller with a disturbance estimation scheme is designed and combined with the DNLRX feed-forward controller to control the motion of a precision stage. Experimental results show that with the proposed controller, tracking performance can be improved.

Speed motion-sensorless with adaptive control approach of linear induction motor unknown resistance and payload

In this paper, we will propose a nonlinear adaptive controller for a linear induction motor to achieve speed tracking. A nonlinear transformation is proposed to facilitate controller design. In this controller, only the primary currents are assumed to be measured. The secondary flux and speed observers are designed to relax the need offlux and speed measurement. Besides, the very unique end effect of the linear induction motor is also considered and is well taken care of in our controller design. Stability analysis based on Lyapunov theory is also performed to guarantee that the controller design here is stable. Also, the computer simulations and experiments are done to demonstrate the performance of Nomenclature.

An optoelectronic measurement system for measuring 6-degree-of-freedom motion error of rotary parts

This paper presents an optoelectronic measurement system for measuring 6 degree-of-freedom (DOF) motion error of rotary parts. It comprises a pyramid-polygon-mirror, three laser diodes and three 2-axis position sensing detectors (PSD). The laser/PSD pairs are arranged evenly around the pyramid-polygon-mirror, which is mounted rigidly on and aligned axially with the rotary part to be measured. Laser rays from the laser diodes are reflected off the respective mirrors to the respective PSDs. The incidence point of the laser ray on the PSDs surface varies with the pose of the pyramid-polygon-mirror, allowing the PSD to register variation in the mirror and, thereby, the rotary part. With appropriate orientation of the lasers and PSDs, this system can measure variation (error) during rotation of a rotary part. By use of skew-ray tracing and first order Taylor series expansion, the system achieves measurement of translational and rotational motion errors for each Cartesian axis. To validate the proposed methodology, a laboratory prototype system is built. System verification and stability tests are conducted to evaluate its performance. Stability test results show that measurement errors and maximum crosstalk are within +/-1 mum in translation and +/-1.5 arc sec in rotation.

Verification and evaluation method for volumetric and positional errors of CNC machine tools

This paper provides a testing device and an automatic sampling technique for fast checking of volumetric errors of CNC machine tools. With the proposed automatic sampling technique, the verification work is carried out automatically and reliably. Furthermore, the analyzed result obtained via the traditional least-squares method is not the minimum zone solution, and may overestimate the volumetric error. Thus, genetic algorithms (GAs) are employed to obtain the minimum zone solution in this paper. Experimental test results show that the proposed method is superior to the least-squares method.