Kuang-Chao Fan

A new minimum zone method for evaluating straightness errors

Abstract A new minimum zone method for straightness error analysis is proposed in this article. Based on the criteria for the minimum zone solution and strict rules for data exchange, a simple and rapid algorithm, called the control line rotation scheme, is developed for the straightness analysis of planar lines. Extended works on the error analysis of spatial lines by the least parallelepiped enclosures are also described. Some examples are given in terms of the minimum zone and least-squares. Finally, this easy-to-use method is illustrated by an example that demonstrates that, for a planar line, the minimum zone solution can even be found without the use of a computer.

Development of a low-cost autofocusing probe for profile measurement

In this research, a low-cost and precision autofocus laser probe system was developed. Modified from the pickup head of a commercially available DVD as a basis, it can detect the focus error signal (FES) of the object with a built-in four-quadrant photodiode. The FES will feed back to the developed controller, through which the objective lens can be adjusted in position automatically to remain in focus, driven by a voice coil motor (VCM). The driving current (converted from servo-FES) of the VCM and the objective lens displacement are one to one linearly related within several hundred micrometres. Because of this relationship, the surface profile and the surface roughness of the tested object can be realized. Calibrated results showed that the designed probe has 200 µm linearity range, 0.2 µm accuracy, 0.1 µm resolution and standard deviation of 0.2 µm on average. Some examples are given to show the applicability of this probe system.

Sensitivity analysis of the 3-PRS parallel kinematic spindle platform of a serial-parallel machine tool

The special configuration of a serial-parallel type machine tool possesses five degrees of freedom and provides more flexibility in NC machining. The parallel spindle platform plays the key role in manipulating three directions of movement. In this study, the inverse kinematics analysis of the platform is derived first. A sensitivity model of the spindle platform subject to the structure parameters is then proposed and analyzed. All the parameters influencing the position and orientation of the spindle platform are discussed based on the sensitivity model and the simulated examples. Critical parameters to the accuracy of the cutter location can then be found, which are the slider position, the strut length, and the tool length.

Flexible Temperature Sensor Array Based on a Graphite-Polydimethylsiloxane Composite

This paper presents a novel method to fabricate temperature sensor arrays by dispensing a graphite-polydimethylsiloxane composite on flexible polyimide films. The fabricated temperature sensor array has 64 sensing cells in a 4 × 4 cm2 area. The sensor array can be used as humanoid artificial skin for sensation system of robots. Interdigitated copper electrodes were patterned on the flexible polyimide substrate for determining the resistivity change of the composites subjected to ambient temperature variations. Polydimethylsiloxane was used as the matrix. Composites of different graphite volume fractions for large dynamic range from 30 °C to 110 °C have been investigated. Our experiments showed that graphite powder provided the composite high temperature sensitivity. The fabricated temperature sensor array has been tested. The detected temperature contours are in good agreement with the shapes and magnitudes of different heat sources.

A 6-degree-of-freedom measurement system for the accuracy of X-Y stages

A precision 6-degree-of-freedom measurement system has been developed for simultaneous on-line measurements of six motion errors of an X-Y stage. The system employs four laser Doppler scales and two quadrant photo detectors to detect the positions and the rotations of an optical reflection device mounted on the top of the X-Y stage. Compared to the HP5528A system, the linear positioning accuracy of the developed measurement system is better than 60.1 mm to the range of 200 mm and the vertical straightness error is within 61.5 mm for the measuring range of 60.1 mm. The yaw and pitch errors are about 61 arcsec, and the roll error is about 63 arcsec within the range of 650 arcsec.

Development of a low-cost micro-CMM for 3D micro/nano measurements

A high-precision and low-cost micro-CMM (coordinate measuring machine) is under development. The expected measuring range is 25 × 25 × 10 mm3 and the resolution is 1 nm. In order to enhance the structural accuracy, some new ideas are integrated into the design, such as the arch-shape bridge for better stiffness and thermal accuracy, and the co-planar stage for less Abbe error. The linear diffraction grating interferometer and subdivision technique is proposed for position sensing to nanometre resolution. The focusing probe on the laser interferometer feedback spindle is structured in the Z-axis to guarantee the nanometre stability. In this report, the detailed design principles of the developed micro-CMM are described. The performance evaluation of each module of the prototype micro-CMM is presented. The positioning resolution of each axis to 1 nm can be achieved by combining the coarse and fine motion control on a piezo-ceramic linear motor. The Z-axis measurement can be controlled to within 15 nm repeatability. Parts of the positioning repeatability of the co-planar stage have been achieved to 30 nm. Some problems due to current techniques will be addressed.

The development of a low-cost focusing probe for profile measurement

A high-precision optical probe based on the principle of focusing-range detection is developed in this research. The probe adopted for use was directly taken from the pick-up head of a CD player. Because its principle is similar to that of the autofocusing probe, the characteristics of each component of the head were investigated and its conversion into a focusing probe was attempted. The S-curve within the focusing range can be analysed, revealing the linear relationship between the normalized focus-error signal (FES) and the measured distance. The system accuracy of the probe was found. Within the measurement range of 10 µm the linearity error was about 1%, the standard deviation was about 34 nm and the frequency response was about 8 kHz. Some practical applications were carried out, namely profile measurements of a step height, a CD surface and a silicon-wafer grating. All results were highly consistent with the nominal values.

Intelligent planning of CAD-directed inspection for coordinate measuring machines

Abstract A method of CAD-directed inspection path planning for coordinate measuring machines is developed in this study. With the general three-dimensional objects designed in a surface model by the use of AutoCad, the measuring points on each specified surface are generated automatically with even distribution. The probe inspection path is planned to touch each measuring point from a normal direction. With the swept-volume analysis of the probe path, any possible collisions can be detected and a new detoured path generated. This system is developed on the personal computer to make it more applicable to small- and medium-sized companies.

Development of a high-precision straightness measuring system with DVD pick-up head

Al ow-cost and high-precision straightness measurement system using a DVD pick-up head has been developed in this research. By removing its objective lens the pick-up head of a commercial DVD player possesses excellent properties of stable laser power, collimated laser beam, circular Gaussian distribution and sensitive photodetectors. A moving knife-edge piece is placed between the pick-up head and a plane mirror. According to the knife-edge principle, the non-shaded part of the laser beam will be reflected back and focused onto the four-quadrant photodetector of the pick-up head. The four-quadrant signals are added to measure the returned laser power. Theoretical analysis based on the circular Gaussian distribution theory and regression method can attain the straightness error of the knife-edge while it moves along the beam direction. This low-cost system can apply to the straightness measurement of precision coordinate measuring machines and NC machine tools. Experimental results showed the achieved accuracy is better than ±0.2 µ mw ithin the measuring range of 200 µm.

Development of a multiple-microhole aerostatic air bearing system

New types of aerostatic air bearing and linear slide systems have been developed. The prototype of a multiple-microhole, instead of a porous-type, air bearing was developed and the surface roughness was improved by finished process. Instead of the conventional drilling process, the air bearing pads were fabricated by using microfabrication technology in this research. The spectral element method was employed to simulate the pressure distribution of air bearing and a comparison was made with experimental results. A granite straight edge was used as linear slide to guide the moving table that was supported by the developed air bearing system. A laser interferometer system was used to assess the performance of the stage.