Development of fixed-point two-degree-of-freedom angular error measurement system with precision improvement function.

In the field of precision industries, measuring micro-angular errors plays a crucial role in improving the accuracy of equipment. Therefore, this study aims to develop a two-degree-of-freedom (two-DOF) angular error measurement system for simultaneously measuring the assembly angle errors of the bond head in a die bonding machine. This system is based on the laser collimation method and constructed by using components such as a fiber laser and position-sensitive detectors. It utilizes the angular drift compensation of the laser beam and averaging function to improve the measurement accuracy. In addition, the mathematical model of the proposed system was established by using skew-ray tracing. Through experiments, the measuring accuracy of ±0.25 arcsec and measuring repeatability of 0.3 arcsec could be achieved.

Innovative Image Processing Method to Improve Autofocusing Accuracy.

For automated optical inspection, autofocusing microscopes play an important role in capturing clear images of the measured object. At present, the image processing part of optics-based autofocusing microscopes often has various factors, which makes it impossible to describe the image information of the semicircular (or elliptical) spot with a simple circle-finding method. Accordingly, this study has developed a novel algorithm that can quickly calculate the ideal center of the elliptical spot and effectively compensate the linearity of the focusing characteristic curve. A prototype model was used to characterize and verify the proposed algorithm. The experimental results show that by using the proposed algorithm, the autofocusing accuracy can be effectively improved to less than 1.5 µm.

Design and characterization of innovative optical prism for four-degree-of-freedom fast steering mirror active laser compensation system.

In this study, an innovative four-degree-of-freedom (4-DOF) compensation prism is designed for fast steering mirror active laser compensation systems. In addition to improving the disadvantages of the commercially available compensation systems, such as a larger number of components and longer optical paths, the proposed system has further enhanced the shortcoming of high sensitivity to the laser by using double Porro prisms as 4-DOF compensation prisms proposed in a previous study. The prism proposed in this study reduces the sensitivity to the laser while maintaining two translations and two rotations in 4-DOF control characteristic for laser, thereby improving the resolution of the system to control the laser. First, Zemax was used to build the overall system and evaluate the system characteristics. Then, the skew-ray tracing method and homogeneous coordinate transformation matrix were used to build the mathematical model of the compensation prism and analyze the sensitivity of the proposed prism to the laser. Finally, the closed-loop algorithm was established and the system was completely built on the optical table for experiments to compare the results between the laser before and after compensation by the proposed prism. In addition, the resolution of the proposed prism is compared with the double Porro prisms.

Grinding Wheel Loading Evaluation by Using Acoustic Emission Signals and Digital Image Processing.

In the manufacturing industry, grinding is used as a major process for machining difficult-to-cut materials. Grinding is the most complicated and precise machining process. For grinding machines, continuous generating gear grinding machines are widely used to machine gears which are essential machine elements. However, due to its complicated process, it is very difficult to design a reliable measurement method to identify the grinding wheel loading phenomena during the grinding process. Therefore, this paper proposes a measurement method to identify the grinding wheel loading phenomenon in the grinding process for continuous generating gear grinding machines. In the proposed approach, an acoustic emission (AE) sensor was embedded to monitor the grinding wheel conditions; an offline digital image processing technique was used to determine the loading areas over the surface of Al2O3 grinding wheels; and surface roughness of the ground workpiece was measured to quantify its machining quality. Then these three data were analyzed to find their correlation. The experimental results have shown that there are two stages of grinding in the grinding process and the proposed measurement method can provide a quantitative grinding wheel loading evaluation from the AE signals online.

Implementation and Optimization of a Dual-confocal Autofocusing System.

This paper describes the implementation and optimization of a dual-confocal autofocusing system that can easily describe a real-time position by measuring the response signal (i.e., intensity) of the front and the rear focal points of the system. This is a new and systematic design strategy that would make it possible to use this system for other applications while retrieving their characteristic curves experimentally; there is even a good chance of this technique becoming the gold standard for optimizing these dual-confocal configurations. We adopt two indexes to predict our system performance and discover that the rear focal position and its physical design are major factors. A laboratory-built prototype was constructed and demonstrated to ensure that its optimization was valid. The experimental results showed that a total optical difference from 150 to 400 mm significantly affected the effective volume of our designed autofocusing system. The results also showed that the sensitivity of the dual-confocal autofocusing system is affected more by the position of the rear focal point than the position of the front focal point. The final optimizing setup indicated that the rear focal length and the front focal length should be set at 200 and 100 mm, respectively. In addition, the characteristic curve between the focus error signal and its position could successfully define the exact position by a polynomial equation of the sixth order, meaning that the system can be straightforwardly applied to an accurate micro-optical auto-focusing system.

Design of a Measurement System for Six-Degree-of-Freedom Geometric Errors of a Linear Guide of a Machine Tool.

This paper proposes a system utilizing a Renishaw XL80 positioning error measuring interferometer and sensitivity analysis design to measure six-degree-of-freedom (6 DOF) geometric errors of a machine tool's linear guide. Each error is characterized by high independence with significantly reduced crosstalk, and error calculations are extremely fast and accurate. Initially, the real light path was simulated using Zemax. Then, Matlab's skew ray tracing method was used to perform mathematical modeling and ray matching. Each error's sensitivity to the sensor was then analyzed, and curve fitting was used to simplify and speed up the mathematical model computations. Finally, Solidworks was used to design the set of system modules, bringing the proposed system closer to a product. This system measured actual 6 DOF geometric errors of a machine tool's linear guide, and a comparison is made with the Renishaw XL-80 interferometer measurements. The resulting pitch, yaw, horizontal straightness, and vertical straightness error deviation ranges are ±0.5 arcsec, ±3.6 arcsec, ±2.1 µm, and ±2.3 µm, respectively. The maximum repeatability deviations for the measured guide's pitch, yaw, roll, horizontal straightness, vertical straightness, and positioning errors are 0.4 arcsec, 0.2 arcsec, 4.2 arcsec, 1.5 µm, 0.3 µm, and 3 µm, respectively.

Design and Characterisation of a Fast Steering Mirror Compensation System Based on Double Porro Prisms by a Screw-Ray Tracing Method.

This study proposes a novel FSM compensation system for four degrees of freedom (DOF) laser errors compensation, which has the advantage of shorter optical path length, fewer elements and an easier set-up process, meaning that it can be used at different locations. A commercial software, Zemax, is used to evaluate the function of the proposed FSM compensation system and the mathematical modelling of the proposed FSM compensation system is established by using a skew-ray tracing method. Finally, the proposed FSM compensation system is then verified experimentally using a laboratory-built prototype and the result shows that the proposed FSM compensation system achieves the ability to compensate the 4 DOF of the laser source.

Design of a Measurement System for Simultaneously Measuring Six-Degree-Of-Freedom Geometric Errors of a Long Linear Stage.

This study designs and characterizes a novel precise measurement system for simultaneously measuring six-degree-of-freedom geometric motion errors of a long linear stage of a machine tool. The proposed measurement system is based on a method combined with the geometrical optics method and laser interferometer method. In contrast to conventional laser interferometers using only the interferometer method, the proposed measurement system can simultaneously measure six-degree-of-freedom geometric motion errors of a long linear stage with lower cost and faster operational time. The proposed measurement system is characterized numerically using commercial software ZEMAX and mathematical modeling established by using a skew-ray tracing method, a homogeneous transformation matrix, and a first-order Taylor series expansion. The proposed measurement system is then verified experimentally using a laboratory-built prototype. The experimental results show that, compared to conventional laser interferometers, the proposed measurement system better achieves the ability to simultaneously measure six-degree-of-freedom geometric errors of a long linear stage (a traveling range of 250 mm).

An Optical Sensor for Measuring the Position and Slanting Direction of Flat Surfaces.

Automated optical inspection is a very important technique. For this reason, this study proposes an optical non-contact slanting surface measuring system. The essential features of the measurement system are obtained through simulations using the optical design software Zemax. The actual propagation of laser beams within the measurement system is traced by using a homogeneous transformation matrix (HTM), the skew-ray tracing method, and a first-order Taylor series expansion. Additionally, a complete mathematical model that describes the variations in light spots on photoelectric sensors and the corresponding changes in the sample orientation and distance was established. Finally, a laboratory prototype system was constructed on an optical bench to verify experimentally the proposed system. This measurement system can simultaneously detect the slanting angles (x, z) in the x and z directions of the sample and the distance (y) between the biconvex lens and the flat sample surface.

Speckle reduction in laser imaging applications using rotating magneto-optical disk.

Effective methods for speckle reduction are essential in improving the image quality of laser imaging applications. Accordingly, the present study proposes a novel technique for reducing the speckle contrast in laser imaging applications by means of the magneto-optic Kerr effect induced by a rotating magneto-optical (MO) disk. The performance of the proposed method is evaluated experimentally using a laboratory-built prototype model. The experimental results show that the rotating MO disk can reduce the speckle contrast of the captured image by 60% of the previous value. As a result, the proposed method yields an effective improvement in image quality. Overall, the proposed method provides a promising solution for improving the performance of a wide range of laser imaging applications.

Chaotic phase space differential algorithm for real-time detection of ventricular arrhythmias: application in animal model.

Life-threatening ventricular arrhythmias remain the main cause of death among patients with cardiovascular diseases. Efforts have been spent on early detection of such fatal cardiac signs. We have previously reported a novel chaotic phase space differential (CPSD) algorithm in discriminating VPC, VT, and VF from normal sinus rhythm with both good sensitivity and specificity. In this article, we apply this algorithm on the rat model of calcium induced ventricular tachycardia. Peaked CPSD values can be observed along with the occurrence of ventricular tachycardia. In addition, minor ECG changes such as new onset S wave or sinus arrhythmia can also be noted on CPSD tracing. We believe that the CPSD algorithm not only is capable of detecting lethal ventricular arrhythmias, but also is potentially a good tool for long-term monitoring the change of ECG signals.

Jacobian and Hessian matrices of optical path length for computing the wavefront shape, irradiance, and caustics in optical systems.

The first- and second-order derivative matrices of the ray (i.e., ∂R¯(i)/∂X¯(0) and ∂(2)R¯(i)/∂X¯02) and optical path length (i.e., ∂OPL(i)/∂X¯(0) and (2)OPL(i)/∂X¯02) were derived with respect to the variable vector X¯(0) of the source ray in an optical system by our previous papers. Using the first and second fundamental forms of the wavefront, these four matrices are used to investigate the local principal curvatures of the wavefront at each boundary surface encountered by a ray traveling through the optical system. The proposed method not only yields the data needed to compute the irradiance of the wavefront but also provides the information required to determine the caustics. Importantly, the proposed methodology is applicable to both axisymmetric and nonaxisymmetric optical systems.

Determination of the linear equations of position-sensing detectors for small motion measurement systems.

Small motion measurement systems are widely used in industry measurement fields to measure small positional/angular motions. These systems usually consist of two parts: a measuring assembly and a reference assembly. The position-sensing detectors (PSDs) are embedded in either measuring assembly or reference assembly to sense the variations of laser light incidence points when there are any small positional/angular motions. To use these systems, it is necessary to determine the linear equations of PSD readings, which relate the six-degrees-of-freedom small positional/angular motions and PSD readings. The purpose of this paper is to derive these equations based on the paraxial raytracing method. Two measurement systems are used as illustrative examples to validate the proposed methodology. The methodology of this study will be useful for system design of PSD-based measurement systems and their applications.

The differential method of phase space matrix for AF/VF discrimination application.

The advances in electrocardiographic (ECG) technology have facilitated the development of numerous successful clinical applications and commercial monitoring products for diagnosing disease and monitoring health. All of these demand the development of smart algorithms and computational resources for the real-time, early indication of critical cardiac conditions. This study presents the development of a Complex Phase Space Difference (CPSD) algorithm with differential method to analyze spatial and temporal changes in reconstructed phase space matrix, and derives an index for real-time monitoring. We used total of 5306 data segments from MIT-BIH, CU, and SCDH databases and clinical trial data to determine the optimal working parameters and verified the classification capability by using a quantitative index of this algorithm. With threshold values set to 2.0 and 6.0, this method can successfully differentiate normal sinus rhythm (NSR) signals (1.48+/-0.21), low risk of atrial fibrillation (AF) signals (3.71+/-0.99) and high risk of ventricular fibrillation (VF) signals (9.38+/-2.22). It is the first real-time algorithm that reports the best performance to distinguish AF and VF with sensitivity of 97.9% and specificity of 98.4%. With self-normalization, the algorithm is not subjected to the inter-variability or sampling size effects. Its computational scheme only requires matrices addition and subtraction, and thus significantly reduces the complexity for real-time implementation. It will be able to adopt in different scenarios of tele-healthcare and implantable applications.

Computational method for deriving the geometric point spread function of an optical system.

The distribution of the ray density of the spot diagram formed in the image plane is called the geometric point spread function (PSF). It plays an important role in the image formation theory, since it describes the impulse response of an optical system to a source point. However, the literature contains very few techniques for deriving the PSF of optical systems. Accordingly, this study presents a method based on an irradiance model for computing the geometric PSF of an optical system by considering the energy conservation along a single light ray. It is shown that the proposed method obtains a reliable and accurate estimate of the PSF and enables the computation of the centroid and root-mean-square radius of the focus spot on the image plane. In addition, compared to existing ray-counting methods presented in the literature, in which the quality of the PSF solution depends on the number of rays traced and the grid size used to mesh the image plane, the proposed irradiance-based method requires just one tracing operation. Overall, the results presented in this study confirm that the proposed method provides an ideal solution for calculating the merit function and modulation transfer function of an optical system.

The development and evaluation of the Citizen Telehealth Care service System: case study in Taipei.

Because of the rapid aging population in Taiwan and the trend of fewer children, people are looking into technical solutions for continuous/intermittent monitoring of vital signs in the home setting environment and the interactions between family members. In this study we developed a smart medical services system for managing chronic disease, called Citizen Telemedical Care service System (CTCS). The system integrates biosignal measurement, hypertension risk estimation expert system, clinic appointment service, video communication service, medical assistance referral, health frequency program record, and health/hygiene education. The demo version CTCS is exhibited in the center of INSIGHT opened for visit and trial use. In order to verify the demand and acceptability of the system and services, we have interviewed 251 volunteers with a questionnaire survey with the help from Taipei City Government. The results showed that people have positive expectation about the service program for health care and the capability of home devices. They also expressed high motivation on learning to use the system and to participate in the program. According to the evaluation results, the system is processing a small user test led by Taipei City Government, in order to further verify the acceptability and satisfaction of the system.

Miniaturized auto-focusing VCM actuator with zero holding current.

In keeping with consumers' preferences for electronic products of ever smaller size and enhanced functionality, it is necessary to reduce the profile of the auto-focusing actuators used in camera phones without sacrificing their performance. Accordingly, this study modifies the Voice Coil Motor (VCM) actuator proposed by the current group in a previous study (C. S. Liu and P. D. Lin, Opt. Express, 16, 2533-2540, 2008) to accomplish a miniaturized auto-focusing actuator for cell phone camera modules with minimal power consumption. The proposed device comprises a VCM, a closed-loop position control system, a magnetoconductive plate, and a lens support structure to drive the lens to the optimal focusing position. The experimental results show that the actuator has a zero holding current when maintaining the lens in the specified focusing position. Overall, it is shown that compared to existing VCM actuators, the proposed actuator has bo a higher power efficiency and an improved positioning repeatability.

A miniaturized low-power VCM actuator for auto-focusing applications.

In keeping with consumer preferences for ever smaller electronic products, a requirement exists for compact, high-performance auto-focusing actuators for the camera modules deployed in cell phones. Accordingly, the present study proposes a miniaturized electromagnetic-based actuator comprising a voice coil motor (VCM) and a closed-loop position control system in which an auto-focusing capability is achieved by using a position feedback signal generated by a Hall element to dynamically adjust the position of the lens module. The experimental results show that the holding current required to maintain a lens module weighing 200 mgw in the vertical position is 17 mA +/- 2 mA. Compared to conventional VCM actuators deployed in cell phone camera applications, the actuator presented in this study has a smaller size (6.5 mm x 6.5 mm x 4 mm) and an improved power efficiency. In particular, the miniaturized actuator reduces the holding current required to maintain the lens module in the focusing position by around 75% of that required in a traditional actuator.