Chien Hung Liu

Development of an optical three-dimensional laser tracker using dual modulated laser diodes and a signal detector

Laser trackers are widely used in industry for tasks such as the assembly of airplanes and automobiles, contour measurement, and robot calibration. However, laser trackers are expensive, and the corresponding solution procedure is very complex. The influence of measurement uncertainties is also significant. This study proposes a three-dimensional space position measurement system which consists of two tracking modules, a zero tracking angle return subsystem, and a target quadrant photodiode (QPD). The target QPD is placed on the object being tracked. The origin locking method is used to keep the rays on the origin of the target QPD. The position of the target QPD is determined using triangulation since the two laser rays are projected onto one QPD. Modulation and demodulation are utilized to separate the coupled positional values. The experiment results show that measurement errors in the X, Y, and Z directions are less than ±0.05% when the measured object was moved by 300, 300, and 200 mm in the X, Y, and Z axes, respectively. The theoretical measurement error estimated from the measurement model is between ±0.02% and ±0.07% within the defined measurable range. The proposed system can be applied to the measurements of machine tools and robot arms.

The Development of a Triple Ball Bar System for Calibration of CNC Machine Tools

Abstract The accuracy of machine tools restricts the dimensional accuracy of parts processed thereon. It is, therefore, necessary to monitor the errors of machine tools constantly. Normally, it takes a long set-up time before one can observe the machine tool and monitor its errors. The cost of such delays is inevitably high. As for CNC, the conventional measurement system is capable of measuring one-dimensional signals, as a laser interferometer does, and two-dimensional signals, as a grid encoder does. Three-dimensional measurement techniques, however, are far from being well developed and are not yet well known. This paper proposes a triangulation method incorporating three built-in linear-scale ball bars that requires less set-up time and lower costs than the laser ball bar system, and is capable of acquiring three-dimensional signals with greater accuracy with the extension bars, so that large volumes can be checked.

Note: Development of a high resolution six-degrees-of-freedom optical vibrometer for precision stage.

A high resolution six degrees of freedom (6-DOF) optical vibrometer is proposed. 6-DOF vibrations can be simultaneously measured using the proposed optical vibrometer, which reduces measurement time and number. The performance of the proposed vibrometer is verified by experiments. The results show that the accuracy of the proposed optical vibrometer is ±30 nm∕200 nm and ±0.04 arcsec∕0.1 arcsec at 1000 Hz.

The development of A 3‐dimensional vibration measuring system with corner cubes and quadrant detectors (Invited)

Abstract In this paper, a new optical 3‐dimensional vibrometer is presented. This system is composed of two orthogonally set up corner cubes (CC), a collimated laser source, two quadrant detectors (QD) and three beam‐splitters (BS). The corner cubes are designed to be fixed to the vibrating object and reflect the laser source onto the quadrant detectors. Due to the optical characteristics of the corner cubes, the measuring results of the QD can be magnified twice and it is not affected by micrometer‐angle. So, the three‐dimensional vibration amplitude can be obtained. The resolution is about 50 nm. This system is characterized by three‐dimensional measurement, high resolution, low cost, simple set up and wide bandwidth.

Characteristics of ZnO-based MSM photodetectors with ZnO cap layer on flexible substrates

In this work, both of ZnO based metal-semiconductor-metal photodetectors with and without ZnO cap layer were fabricated on flexible substrates (polyethylene terephthalate, PET) for comparative analysis. The ZnO films were prepared by a low temperature sputtering process. The photodetector with ZnO cap layer (stack structure: ZnO/Ag/ZnO/PET) shows a much higher UV-to-visible rejection ratio of 1.56×103 than one without. It can be attributed to the photocurrents significantly enhanced under UV light illumination in such a novel structure. With an incident wavelength of 370 nm and 3 V applied bias, the responsivities of both photodetectors with and without ZnO cap layer are 3.80×10−2 and 2.36×10−3 A/W, respectively, which correspond to quantum efficiencies of 1.13 % and 0.07 %. The Schottky barrier height on Ag/ZnO interfaces is also obtained to be 0.782 eV.

Development of a Three-Degrees-of-Freedom Laser Linear Encoder for error measurement of a High Precision Stage

The laser linear encoders are widely used as positioning sensor for a precision linear moving stage. In this paper, a Three-Degrees-Of-Freedom Laser Linear Encoder based on diffraction and interference was developed. It can simultaneously measure the linear displacement and two angular errors of a linear moving stage. The displacement is measured using a polarization interference technique and the two angular errors is also measured based on the near-axis optical theorem. This paper has describes a laser linear encoder that can detect displacements relative to an external grating scale with accuracy about 150 nm for a measuring range plusmn1000 mum and can detect angular errors with accuracy about 1 arsec for a measuring range plusmn100 arsecs.

Development of a Laser Based Dual-Axial Five-Degrees-of-Freedom Measurement System for an X-Y Stage

This paper presents a new precision multi-DOF measurement system which has been developed and implemented for the simultaneous measurement of 5DOF motion errors (two linear positions, as well as pitch, roll and yaw) of an X-Y stage. In this paper, the 3DOF laser interferometer was produced by designing the optical path from the one-degrees-of-freedom laser interferometer. The system employs two three-degree-of-freedom interferometers to detect two position errors and three angular errors of the X-Y stage. The experimental setups and measuring procedure and a systematic calculated method for the error verification are presented in the paper. The resolution of measuring the angular errors component is about 0.055 arcsec.Copyright