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Alunda Ouma Bernard,황재석,신동철,Bai Dong 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5
Many different types of elastomeric rings have been developed to suit various needs in industry. The X-ring was introduced as a resultof the limitations of O-rings that twist, especially during dynamic application. A better understanding of the behavior and the stressdistribution of the X-ring under a uniform squeeze rate and internal pressure is needed. We analyzed the contact stresses and internalstresses developed in an X-ring before and after forcing-out by using the photoelastic experimental hybrid method, ascertained thepacking ability of an X-ring, and studied the failure criterion of an X-ring under uniform squeeze rate and internal pressure. Forcing-outin the X-ring occurred when the internal pressure was 3.92 MPa. After forcing-out, at an internal pressure of 5.88 MPa, the two lobes onthe upper contact surface merged one contact side of the upper side immensely. Even after extrusion of the X-ring, the X-ring can be usedto effectively contain the fluid. This is because the effects of extrusion on the X-ring affected the stress distribution of only two lobesclose to the assembly gap and the two lobes are merge into one lobe. In addition, our experimental results show that the maximum shearfailure criterion is suitable for the prediction of failure in X-ring seals.
Internal stress distribution of X-ring using photoelastic experimental hybrid method
Alunda Ouma Bernard,황재석,신동철,임현석 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.5
Sealing elements are essential parts of many machines, and are used to prevent the loss of a fluid or gas. When such fluids are notproperly sealed, catastrophic failures may result. Many different types of rings have been developed to suit various industrial needs. Considerableresearch has been done on the O-ring. We analyze the internal stresses developed in an X-ring under a uniform squeeze rate of20%, which is suitable for static applications, using a photoelastic experimental hybrid method. The internal pressures applied were 0.98,1.96, 2.94, 3.92, 4.90, and 5.88 MPa. We show that sealing rings with X geometry have considerably higher internal stresses than O-ringseals. In addition, we demonstrate that after extrusion, for an internal pressure of 5.88 MPa, the two lobes on the upper contact surfacemerge, thereby increasing the contact length of the upper side significantly. Extrusion in the X-ring occurred when the internal pressurewas 4.90 MPa.
Bernard Ouma Alunda,루크오두어르오티에노,Melody CHEPKOECH,변지수,이영중 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.2
The optical beam de ection sensor remains the most popular force detection method used in atomic force microscopy. With the recent development of short cantilevers, a means for measuring small de ections at high frequencies has become a challenge. Minimizing the noise level of the readout electronics without signicantly limiting the detection bandwidth still remains a challenge. In this work, a recently proposed trans-linear readout circuit-based technique, in which necessary analog arithmetics are done in the current domain instead of the voltage domain, is compared to a more traditional trans-impedance readout circuit-based topology. Our developed trans-impedance readout circuit recorded a noise oor of 9:48 1013 V2 Hz1 compared to 1:41 1011 V2 Hz1 for the trans-linear readout circuit. Also, the measured 3 dB bandwidth of 11 MHz for the transimpedance readout circuit was slightly higher than the 10 MHz for the trans-linear readout circuit. Trans-impedance readout circuits, with proper circuit design considerations and careful selection of electronic parts, still remain competitive for use in high-speed operations in atomic force microscopy.
A Novel Two-axis Parallel-kinematic High-speed Piezoelectric Scanner for Atomic Force Microscopy
Bernard Ouma Alunda,Yong Joong Lee,Soyeun Park 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.5
High-speed atomic force microscopy permits the capture of static, as well as the dynamic, processes present in various physical phenomena. Unlike visualizing static processes, capture of dynamic processes requires high-speed scanning in all three dimensions. Despite the recent increased interest in high-speed atomic force microscopy, relatively few reports concerning piezoelectric actuatordriven scanners for high-speed scanning have been published. In this paper, we propose a novel design for a high-speed two-dimensional piezoelectric scanner unit by combining the positive features developed from works published in the literature. The proposed design ensures high vertical stiffness by utilizing compliant double-hinged flexure that minimizes cross-coupling and parasitic motions. Any high-speed scanner design requires a compromise between the two main competing parameters: maximum scan size and speed. The performance of the proposed scanner was evaluated by using numerical simulations with finite element analyses in terms of the mechanical resonance frequencies and the scan range. Finally, the results from the numerical simulations are compared with the experimental measurements.
Comparative study of two types of parallel kinematic flexure scanners for atomic force microscopy
Alunda, Bernard Ouma,Lee, Yong Joong,Park, Soyeun Informa UK (TaylorFrancis) 2018 Instrumentation science & technology Vol.46 No.1
<P>A little consideration will show that a scanner is one of the most critical components of any atomic force microscope (AFM), and properly designing a scanner remains a challenging aspect in the minds of developers. We closely examined two types of flexure-based parallel kinematic scanners (push-pull and push-only configurations) as they have been applied to AFM. The custom-fabricated scanners have been installed on a commercial AFM while keeping other parameters identical except for the scanners. The results show that intrinsically there is no significant difference in performance of both scanner designs. However, it was found that preloading conditions more critically affect the performance of the push-pull scanner than the push-only scanner. In addition, the Prandtl-Ishlinskii model has been applied to model the obtained hysteresis curves for both scanners. The application of the inverse of the Prandtl-Ishlinskii model improved the linearity of the measured hysteresis. Although both scanners possess similar characteristics and can operate at higher speeds than commercial scanners in reduced scan areas, simpler operating requirements and the monolithic construction make the push-only scanner a preferred choice for AFM.</P>
Alunda Bernard Ouma,황재석 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.8
The square ring has over the past few years been used as an alternative sealing element to the O-ring, which has been used widely for a long time. The square ring geometry is believed to be especially suitable for axial static applications because its square form remains practically constant under high pressures, has a high resistance to extrusion, not sensitive to gap extrusion and high leak tightness. Some of these fundamental properties that are crucial in the design of a square ring can be justified by analysis of the stress distribution of the square ring under various loading conditions, especially under a combined loading of uniform squeeze and internal pressure. In order to justify these properties a stress frozen square ring under this combined loading condition of uniform squeeze rate and internal pressure was analyzed using the photoelastic experimental hybrid method to obtain the contact and internal stresses. This research confirmed that contrary to the established theory, the square ring extrudes at a lower pressure of 1.96 MPa. The photoelastic experimental hybrid method can adequately be used for stress analysis of square ring seals. Internal pressure plays a significant role in the design of the seals. As the internal pressure increases, the internal stresses also increase. Maximum internal stresses were observed in the region close to the extrusion gap at points 2 and 2’. The square ring experienced contact stress singularity on the upper end of the contact surface (point 2’) on the front side and at point 2 on the upper side. The upper region experienced the largest contact stresses as well as internal stresses and so the fracture criterion of maximum shear stress should be applied in this region.
Design and Fabrication of a Low-Cost Teaching Atomic Force Microscope with 3D Printed Parts
Melody CHEPKOECH,Bernard Ouma Alunda,루크오두어르오티에노,박상준,Clare Chisu Byeon,이영중 한국물리학회 2019 새물리 Vol.69 No.2
Over the past decade, additive manufacturing and three-dimensional (3D) printing have had a profound impact on manufacturing. With the emergence of affordable 3D printers, rapid prototyping has been quite accessible to researchers in academic and industrial laboratories. As a consequence, the number of laboratory instruments that have been assembled with 3D printed parts has risen. We present an atomic force microscope (AFM) constructed with as many 3D printed parts as the design would permit. Due to its simplicity, the proposed AFM is suitable for assembly by undergraduate students in a project-based laboratory course setting. The images of compact disc (CD) data tracks and standard samples obtained using the proposed low-cost AFM effectively demonstrate its nanoscale imaging capability.