DVD Pickup Head Research Articles

Two-Dimensional Low-Frequency Optical Accelerometer With High Accuracy and Low Cross-Axis Sensitivity

Two-dimensional (2D) accelerometer is a commonly used sensor for detecting horizontal vibrations. However, their low frequency response characteristics are limited by high cross-axis sensitivity and low resolution. To address this challenge, this study proposes a new 2D optical accelerometer based on a symmetric 2D vibration pickup unit and a high-sensitivity 2D angle sensor modified from a DVD pickup head. The parameters of the symmetrical 2D pickup unit were determined through modeling and simulation, and the performance of the accelerometer was tested experimentally. Experimental data show that the accelerometer has good low frequency response characteristics in the range from 1 to 10 Hz, sensitivity is better than 2.5 V/(m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), cross-axis sensitivity is less than 0.075 V/(m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), and the resolution is better than 0.4 mm/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Moreover, the sources of uncertainty of the accelerometer were analyzed in detail and the synthetic uncertainty of the accelerometer was analyzed based on experiments. Compared with conventional techniques in this area, the proposed 2D optical accelerometer has featured the advantages, such as high accuracy and low cross-axis sensitivity, and can be widely used for low-frequency vibration monitoring in engineering applications.

(Invited) Resonator and SERS Sensing in the Field of Drug Delivery

Introduction Our research center of excellence IDUN combines research in nanosensors/centrifugal microfluidics and microfabricated devices for oral drug delivery. This allows us to explore the synergy between sensor development and search for new pharmaceutical delivery tools and materials. Our developed nanosensors get access to unique polymers and biomolecules and are able to characterize, among others, small volumes of materials and molecules, which are today not possible to analyze by any standard technologies. We will show examples of recent findings and results within drug/polymer characterization (1) and process monitoring (2) using nanomechanical sensors. Also, new applications within therapeutic drug monitoring using Surface Enhanced Raman Scattering (SERS) will be presented as well as sensor integration with centrifugal microfluidics platforms. Resonators By monitoring the resonance frequency shift of micrometer sized strings or cantilevers coated with thin layers of polymers, it is possible to monitor phase transitions using only ng of material. We have been able to observe beta relaxation of polymers (3) and drugs (2), see figure 1. These systems also allowed us to monitor degradation of biomaterials used in the fabrication of the microcontainers (4). Also, strings are inherently sensitive to temperature changes (5). The resonant frequency detunes as a function of temperature and temperature changes down to 10-5 °C can be detected. The effect has been used to perform photothermal IR spectra on samples deposited on resonating strings and resonating filters. This has been used to for example study the amorphous and crystalline forms of indomethacin (1). As an alternative to cleanroom fabricated resonators we have used single drug and collagen particles as micro mechanical resonators, thereby eliminating the need for cleanroom processing. This method additionally makes it possible to study the behavior of single crystals, which would otherwise be extremely difficult/impossible. This method has, among others, allowed us to study new phenomena in the hydration/dehydration of drugs (6). Centrifugal microfluidics The optics and mechanics from a DVD player can be used to realize compact and sensitive sensor systems. By rotating a polymer disc with integrated microfluidic channels it is possible to manipulate liquid samples such as blood – performing crucial operations like separation, valving and mixing. We integrate sensor elements such as cantilevers, nanoparticles, resonating strings and SERS substrates with centrifugal microfluidics (7). The sensors are read out by a DVD pick-up head, which can perform transmission/absorption measurements and can detect nm deflections. Also, electrodes and spectrometers are integrated on a disc platform, facilitating electrochemical/Raman measurements. Our nanopillar SERS substrate can be used for sample filtration and separation. Here the nanopillars function similarly to a filter paper in chromatography and can be used to distinguish e.g. different components in a urine sample as well as drug residuals. A SERS chip is placed in a centrifugal microfluidics platform, whereby the sample can be initially centrifuged. Subsequently half the SERS chip is exposed to the centrifuged liquid. Hereby, liquid can travel up the chip by the so-called wicking effect, and depending on affinity of molecules to the surface, different molecules will travel different lengths. Hereby, a separation is secured and the different molecules are read-out as bands on the SERS chip. Acknowledgements This research has received funding from the ERC grant agreement n° 320535 and from the Center of Excellence ’IDUN’ granted by Danish National Research Foundation, DNRF122/the Velux Foundations.

Development of a High-Precision Multifunctional Probe for Measuring Microstructures

An increasing number of micro/nano-components with complex structures have emerged in recent years. Different kinds of feature sizes usually exist in a single component and require the use of instruments with nanometer-level accuracy. The traditional types of equipment cannot meet the current demands because of their lack of function and effectiveness. In this study, a multifunctional probe is designed by combining the interference and focusing principles. The Linnik principle is adopted in the interferometry module for its high vertical resolution and large horizontal range and its ability to measure surface topography. The focusing module modified from a Blue-ray DVD pickup head has a high horizontal resolution and a large vertical range suitable for measuring step height and line/groove width. The two modules share a polarizing beam splitter and an objective lens to reduce probe size. Then, the probe is manufactured, calibrated, and verified by measuring the surface topography with a reference height of 100 nm, a step height of approximately $4~\mu \text{m}$ , and a diameter of approximately $25~\mu \text{m}$ . The proposed probe has a high resolution and large range in 3D and can measure high-precision components with multiple features.

Utilization of CD and DVD Pick-Up Heads for Scratch Inspection of Magnetic Disk in Dynamic State Using Microcontroller

A non-destructive technique to inspect a scratch on all magnetic disks in the beginning process of hard disk drive (HDD) manufacturing by using CD and DVD pick-up heads as the detector is proposed. It requires a 100% disk inspection of micrometer-sized scratches in a quick measurement with low cost inventing. Most of the previous studies were in static state but this is the first time to be done in dynamic study using the microcontroller in order to promptly serve for industrial utilization. The size, position, and shape characteristic of scratches are examined using light reflection technique. The results show that, when the laser beam is targeted on a magnetic disk in a position, either scratch or non-scratch, the reflected light intensity differs. The DVD pick-up head can detect the width and the surface characteristic of the scratches, which is similar to the results from scanning electron microscope (SEM) for all scratches sizes less than 100 µm. It is also found that using a DVD pick-up head provides a better resolution of shape characteristic and roughness of scratches surface than a CD pick-up head. Hence, the scratch size of 10s µm scale on the magnetic disk can be accurately characterized by this proposed technique, which can be further utilized for magnetic disk inspection in the hard disk drive manufacturing process.

(Invited) Resonator and SERS Sensing in the Field of Drug Delivery

Introduction Our research center of excellence IDUN combines research in nanosensors/centrifugal microfluidics and microfabricated devices for oral drug delivery. This allows us to explore the synergy between sensor development and search for new pharmaceutical delivery tools and materials. Our developed nanosensors get access to unique polymers and biomolecules and are able to characterize, among others, small volumes of materials and molecules, which are today not possible to analyze by any standard technologies. We will show examples of recent findings and results within drug/polymer characterization (1) and process monitoring (2) using nanomechanical sensors. Also, new applications within therapeutic drug monitoring using Surface Enhanced Raman Scattering will be presented as well as sensor integration with centrifugal microfluidics platforms. Resonators By monitoring the resonance frequency shift of micrometer sized strings or cantilevers coated with thin layers of polymers, it is possible to monitor phase transitions using only ng of material. We have been able to observe beta relaxation of polymers (3) and drugs (2), see figure 1. These systems also allowed us to monitor degradation of biomaterials used in the fabrication of the microcontainers (4). Also, strings are inherently sensitive to temperature changes (5). The resonant frequency detunes as a function of temperature and temperature changes down to 10-5 °C can be detected. The effect has been used to perform photothermal IR spectra on samples deposited on resonating strings and resonating filters. This has been used to for example study the amorphous and crystalline forms of indomethacin (1). Centrifugal microfluidics The optics and mechanics from a DVD player can be used to realize compact and sensitive sensor systems. By rotating a polymer disc with integrated microfluidic channels it is possible to manipulate liquid samples such as blood – performing crucial operations like separation, valving and mixing. We integrate sensor elements such as cantilevers, nanoparticles, resonating strings and surface enhanced Raman scattering (SERS) substrates with centrifugal microfluidics (6). The sensors are read out by a DVD pick-up head, which can perform transmission/absorption measurements and can detect nm deflections. Also, electrodes and spectrometers are integrated on a disc platform, facilitating electrochemical/Raman measurements. Acknowledgements This research has received funding from the ERC grant agreement n° 320535 and from the Center of Excellence ’IDUN’ granted by Danish National Research Foundation, DNRF122/the Velux Foundations.

Low-frequency Accelerometer Based on DVD Pick-up Head and Cantilever

Low-frequency Accelerometer Based on DVD Pick-up Head and Cantilever

Design of RBF neural network adaptive PID controller of DVD pick-up head

Design of RBF neural network adaptive PID controller of DVD pick-up head

A visual non-contact focusing probe for the measurement of micro cavities

The dimensional measurement of micro cavity profile to nanometre resolution is difficult because the edge is not able to be detected accurately with a microscope due to diffraction limit. With a touch-trigger probe on a micro-CMM, the probe cannot enter into the cavity if the tip-ball diameter is larger than the cavity size. In this paper, a vision-assisted non-contact focusing probe is presented to deal with this problem. A blue-ray DVD pickup head is adopted as the focusing sensor which is based on the principle of light reflection. Assisted by a nanopositioning stage, the focusing signal can detect the edge when the spot passes through it. In order to know the measuring point, a CCD is used for viewing the relative position between the focused spot and the edge. Experimental tests of the probe were carried out in association with a micro-coordinate measuring machine. The edge position is obtained up to a resolution of 1 nm with standard deviation of about 26 nm. This performance is beyond the diffraction limit of optical microscopes.

Inexpensive laser-induced surface modification in bismuth thin films

In this work, we present results on texturing a 500nm thick bismuth film, deposited by sputtering onto a glass slide using a low-cost homemade, near-infrared pulsed laser platform. A 785nm laser diode of a CD–DVD pickup head was precisely focused on the sample mounted on a motorized two-axis translation stage to generate localized surface microbumps on the bismuth films. This simple method successfully transferred desired micropatterns on the films in a computer-numerical control fashion. Irradiated zones were characterized by atomic force microscopy and scanning electron microscopy. It was observed that final results are strongly dependent on irradiation parameters.

Development of a Non-Contact Focusing Probe for the Measurement of Micro Cavities

The measurement of microcavities is a challenging task if the cavity is smaller than the diameter of the micro touch-trigger probe. This paper presents a noncontact method using a blue-ray DVD pickup head as the sensor. It is based on a focusing principle holding that reflected light intensity is maximal when the tested surface is at the focus point of the probe. When a focused beam scans the edge of the cavity, reflected light intensity is gradually reduced. Theoretical analysis is used to derive the light intensity equation for when the focused beam is passing along the edge. Experimental tests of the developed probe were carried out in association with a nanopositioning stage. The edge position is obtained up to a resolution of 1 nm and a standard deviation of about 30 nm. This performance is beyond the diffraction limit of optical microscopes.

Measurement of multi-directional azimuth and tilt angles using an improved DVD pickup head with a CMOS sensor: A simulation design study

We present a new detection method for an improved DVD pickup head system capable of measuring the multidirectional azimuth and small tilt angles. A complementary metal-oxide semiconductor (CMOS) sensor is used to capture images and analyze the slight shift of the central position of the beam shape when the test plane rotates to create a tilt angle and angular signal. The proposed detection method can determine the azimuth angle of the test plane from 0° to 360° at intervals of 5°. The tilt angle measurement is varied from 0° to 4.2° at intervals of 0.3°. The simulation results show that the improved DVD pickup head system can recognize multi-directional azimuth angles of the test plane under a small tilt.

3-D measurement and evaluation of surface texture produced by scraping process

The scraping process involves traditional manual work and is an important technique for producing flat bearing surfaces with lubricating grooves on a sliding surface. In order to meet the requirements of precision engineering, the scraped surface should have an equally distributed pattern with a required number of high points per unit area while retaining good flatness. In the machine tool manufacturer’s workshop, however, the quality inspection of scraped surfaces still depends on human eyes. In this study, a 2-D evaluation system is first developed using image processing so that the peak points per area of square inch (PPI) and the percentage of points (POP) can be quantified as parameters. A vision-assisted laser focus probe system is then developed to measure the 3-D form of the scraped profiles. The laser probe is made of a DVD pickup head based on the astigmatic principle. Driven by an XY stage, the entire scraped profile can rapidly be scanned. The quality of the scraped surface can thus be interpreted in a more scientific manner. Based on the measured 3-D data, new evaluation methods are proposed for five parameters, namely the PPI, POP, height of points (HOP) or depth of surroundings (DOS), flatness, and oil retention volume. Experiments show that the 3-D system is consistent with the 2-D system. It not only reveals more surface quality parameters but also uncovers more characteristic surface phenomena than the 2-D image system.

Automated determination of best focus and minimization of optical path difference in Linnik white light interferometry

It is difficult to search for interference fringes in Linnik white light interferometry with an extremely short coherence length because of the optical path mismatch of two interference arms and the defocus of the reference mirror and the test surface. We present an automated method to tackle this problem in this paper. The determination of best foci of the reference mirror and the test surface is implemented by the astigmatic method based on a modified commercial DVD pickup head embedded in the interference system. The astigmatic method is improved by setting a threshold value in the sum signal to truncate the normalized focus error signal (NFES). The truncated NFES has a monotonic relationship with the displacement of the test surface, which removes the position ambiguity of the test surface during the autofocus process. The developed autofocus system is confirmed experimentally with a dynamic range of 190 μm, average sensitivity of 70 mV/μm, average standard deviation of 0.041 μm, displayed resolution of 4.4 nm, and accuracy of 55 nm. The minimization of the optical path difference of two interference arms is carried out by finding the maximum fringe contrast of the image captured by a CCD camera with the root mean square fringe contrast (RMSFC) function. The RMSFC function, combined with a 4×4 pixel binning of the CCD camera, is recommended to improve the computational efficiency. Experimental tests show that the automated method can be effectively utilized to search for interference fringes in Linnik white light interferometry.

Research on the Application of DVD Pick-Up Head in Three-Dimensional Optical Storage

Two-photon three-dimensional optical data storage is an effective method for high capacity data storage. Based on DVD pick-up head and two-photon absorption, two-photon three-dimensional optical disk storage system is built, and operating principle of the overall system is in detail. In the servo module of three-dimensional optical disk storage system, DVD circuit control board (MT1389SE) is conducted on three-point improvement: extract focus servo error signal and servo error signal, increase four communications interfaces，increase photoelectric detectors; the extraction of focus and track servo signal on reading and writing module is analyzed in detailed. The measured principles and methods of the voice coil motor characteristic curve of Sanyo DVD pick-up head (SF-HD60S) are analyzed in detailed by using dual-frequency laser interferometer, which can be well meet the layer selection requirements of three-dimensional optical storage. DVD pick-up head applied in three-dimensional optical storage overcomes the limitations of three-dimensional scanning stage, integrates with existing DVD servo technology, and lays a solid foundation for practical use of two-photon three-dimensional optical storage.

Design of a dual-axis optoelectronic level for precision angle measurements

The accuracy of machine tools is mainly determined by angular errors during linear motion according to the well-known Abbe principle. Precision angle measurement is important to precision machines. This paper presents the theory and experiments of a new dual-axis optoelectronic level with low cost and high precision. The system adopts a commercial DVD pickup head as the angle sensor in association with the double-layer pendulum mechanism for two-axis swings, respectively. In data processing with a microprocessor, the measured angles of both axes can be displayed on an LCD or exported to an external PC. Calibrated by a triple-beam laser angular interferometer, the error of the dual-axis optoelectronic level is better than ±0.7 arcsec in the measuring range of ±30 arcsec, and the settling time is within 0.5 s. Experiments show the applicability to the inspection of precision machines.

Self-aligned cantilever positioning for on-substrate measurements using DVD pickup head

In this paper, we present a novel approach for measuring the resonant frequency of cantilevers fabricated in polymeric materials. We re-designed the use of a commercial DVD-ROM pickup head and combine it with a glass–polymer substrate in order to obtain a light and portable device to measure the resonant frequency of polymer cantilevers. The use of the Pyrex-SU-8 clamping substrate allows an easy replacement of the cantilever chips and a fast alignment process to the DVD-ROM laser beam. We show measurements of thermal noise for SU-8 and TOPAS cantilevers in air and liquid environment.

A hybrid scanning probe microscope (SPM) module based on a DVD optical head

The development of a highly sensitive (sub-nanometer) and multi-platform scanning probe microscope (SPM) module is presented. The module is based on an optical DVD pick-up head and uses its astigmatic detection scheme to detect the vertical displacement of the SPM cantilevers. The complete hybrid SPM module is capable of scanning in SPM intermittent contact, SPM contact and optical profilometry modes. The module can be used in a modified optical microscope or be implemented in a stand-alone system. Measurement results prove that the mechanical stability of this SPM module is high enough for atomic resolution imaging. Both scanning-sample and scanning-probe-type SPM setups have been tested based on this SPM module. The noise level and drift rate in the z-direction of the stand-alone system are 10 pm (rms) and 0.2 nm min−1, respectively.

Development of an optical accelerometer for low-frequency vibration using the voice coil on a DVD pickup head

In this paper, an economical and highly sensitive optical accelerometer using a commercial optical pickup head is proposed. In the proposed design, the moving part of a voice coil motor (VCM) built in the DVD pickup head is used as the seismic mass which combines with the optical system of the DVD pickup to form an accelerometer. This system not only reduces the design complexity and the manufacturing process but also obtains good measurement effect. Experimental results have shown that the accelerometer at low frequency has a sensitivity of 24.362 V/g.

Autofocusing System for Optical Microscope Based on DVD Pick-Up Head

This paper presents an autofocusing system for an optical microscope (OM) based on a low-cost, highly-sensitive laser focusing probe integrated with a precision stepper positioning stage. During the OM measurement procedure, the laser focusing probe detects variations in the distance between the glass substrate containing the specimen of interest and the OM objective lens and generates a driving signal to adjust the position of the OM via the precision positioning stage such that a precisely-focused image is obtained. The experimental results show that the integrated laser focusing probe and positioning stage complete the autofocusing process within 0.5 seconds.

Development of a compact optical system for microarray scanning using a DVD pickup head

We present a compact optical system using a commercially available DVD pickup head for microarray scanning. Our instrument successfully provides a low-cost, compact, and simple microarray scanning optical system in comparison to conventional ones due to the use of small-sized optical components and the implementation of a simple autofocusing system using an embedded voice coil motor. The performance of this system was validated by using a microarray slide with spots of fluorescent dyes. It was confirmed that our optical head performed satisfactorily and was suitable for practical use in microarray scanners. This result provides evidence of the superiority of our microarray scanning optical system over conventional ones because of its space-saving properties and cost effectiveness.