Byoung Gook Loh

Characteristics of elliptical vibration cutting in micro-V grooving with variations in the elliptical cutting locus and excitation frequency

The characteristics of elliptical vibration cutting (EVC) in micro-V grooving in connection with variations of the elliptical cutting locus and the excitation frequency have been investigated with a cutting device consisting of orthogonally connected dual piezoelectric actuators. The elliptical cutting locus was modulated by changing the magnitude and phase difference of harmonic voltages supplied to the piezoelectric actuators, and the maximum excitation frequency used for EVC was 19 kHz. It was found that cyclic breaking of the contact between the tool and the workpiece is a pre-requisite for the merits of the EVC process to be realized. An index termed non-contact index (NCI) involving the vibration amplitude of the elliptical locus, the feed speed and the excitation frequency was defined to determine the existence of cyclic breaking of the contact under a given EVC condition. The surface roughness in the feed direction showed a tendency to increase with the vibration amplitude in the thrust direction and the square of the feed speed, and to decrease with the square of the vibration amplitude in the cutting direction and the square of the excitation frequency. The variation in the cutting resistance was in good agreement with the CR trend curve representing the contact ratio between the tool and the workpiece in EVC; in the EVC process involving breaking of the contact, marked decrease in the cutting force occurred at higher values of CR at which either slight increase in the excitation frequency or in the vibration amplitude results in significant decrease in the cutting force. Reduction in the cutting force preferably contributed to the improvement of machining quality of the micro features by inhibiting burr formation.

Characteristics of chip formation in micro V-grooving using elliptical vibration cutting

The chip and burr formation in micro V-grooving using elliptical vibration cutting (EVC) was investigated. Elliptical vibration of the cutting tool was achieved by employing two parallel piezoelectric actuators excited with two sinusoidal voltages of 90° phase difference. Changes in the shape of the chip and the cutting force, and the surface texture in micro V-grooving with EVC were investigated. It was observed that the reversal of the direction of the frictional force and the marked increase in the shear angle, which are two major characteristics of the EVC process, changed the shear flow inside the chip and reduced the cutting force, the chip thickness and the radius of curvature of the chip. When the excitation frequency of the tool was increased to an ultrasonic frequency of 65 kHz, more pronounced characteristics of EVC were observed. The cutting force in micro V-grooving with EVC at 65 kHz was reduced to approximately 10% of the cutting force magnitude under ordinary cutting. Low cutting force in the EVC process suppressed plastic deformation on the workpiece, thereby creating a micro V-groove free of burrs, which contributed to significant improvement in the form accuracy of a micro V-groove.

Control of Industrial Safety Based on Dynamic Characteristics of a Safety Budget-Industrial Accident Rate Model in Republic of Korea

Background Despite the recent efforts to prevent industrial accidents in the Republic of Korea, the industrial accident rate has not improved much. Industrial safety policies and safety management are also known to be inefficient. This study focused on dynamic characteristics of industrial safety systems and their effects on safety performance in the Republic of Korea. Such dynamic characteristics are particularly important for restructuring of the industrial safety system. Methods The effects of damping and elastic characteristics of the industrial safety system model on safety performance were examined and feedback control performance was explained in view of cost and benefit. The implications on safety policies of restructuring the industrial safety system were also explored. Results A strong correlation between the safety budget and the industrial accident rate enabled modeling of an industrial safety system with these variables as the input and the output, respectively. A more effective and efficient industrial safety system could be realized by having weaker elastic characteristics and stronger damping characteristics in it. A substantial decrease in total social cost is expected as the industrial safety system is restructured accordingly. Conclusion A simple feedback control with proportional–integral action is effective in prevention of industrial accidents. Securing a lower level of elastic industrial accident-driving energy appears to have dominant effects on the control performance compared with the damping effort to dissipate such energy. More attention needs to be directed towards physical and social feedbacks that have prolonged cumulative effects. Suggestions for further improvement of the safety system including physical and social feedbacks are also made.

Correcting distortion and rotation direction of an elliptical trajectory in elliptical vibration cutting by modulating phase and relative magnitude of the sinusoidal excitation voltages

In elliptical vibration cutting, cutting performance is largely affected by the shape and the rotational direction of a micro-scale elliptical trajectory generated at the cutting edge. In this study, change in the shape of the ellipse, which was created by two parallel piezoelectric actuators attached at the tool, was experimentally observed as the excitation frequency to the piezoelectric actuators was increased from 10 Hz to 25 kHz to investigate the effect of the excitation frequency on the elliptical trajectory. For the whole range of experimental frequencies, the major axis of the ellipse becomes tilted, and the aspect ratio of the ellipse is significantly distorted as the excitation frequency approaches the resonant frequency of the elliptical vibration cutting device. To correct the distortion and rotational direction of the elliptical trajectory, an analytical model describing the elliptical path of the tool was developed and verified with experimental results. Based on the analytical model, the distortions in the elliptical trajectories created at various frequencies were corrected for tilt and aspect ratio by changing the phase and relative magnitude of the sinusoidal excitation voltages.

A wearable intravenous infusion device facilitating ambulation: a pre-clinical report

Abstract A wearable ambulatory intravenous infusion device (AIVD) has been developed to facilitate the ambulation of patients. To enhance ambulation, a wearable AIVD was designed and a prototype was developed that consists of an air bag, a reciprocating air pump, a drip rate sensor, and a microprocessor-based controller. Using air pressure as a source for actuation greatly contributes to decreasing the weight of the proposed device and the power consumption. Experimental results show that the proposed infusion device can provide a variety of flow rates ranging from 36–90 mL h−1 with less than a 10% error. A series of experiments were performed with the prototype of the proposed device at a wide range of flow rates and the results verify that the accuracy and controllability of the prototype is comparable with those of the current intravenous infusion devices available. It is expected that the AIVD significantly contributes to the early recovery of patients by offering a convenient and cost-effective means of ambulation.

Correcting Distortion of Elliptical Trajectory for Maximizing Cutting Performance in Elliptical Vibration Cutting

To maximize cutting performance of elliptical vibration cutting (EVC) (also known as two-dimensional vibration assisted cutting), the elliptical trajectory of a cutting tool needs to be corrected. In this study, the effect of the shape of the elliptical trajectory on the machining characteristics of EVC is investigated. Various elliptical trajectories were created by modulating the relative phase and magnitude of the sinusoidal input voltages to the piezoelectric actuators and the effect of tilt angle of the elliptical trajectory on the machining quality such as the cutting resistance and machining quality is experimentally observed in successive micro-V grooving as the tilt angle is changed between 0o, 30o, -30o, and 90o. It is found that the tilt angle significantly affects both the cutting resistance and machining quality.

Smartphone-based O2 Deficiency Monitoring Device

O2-deficiency related accidents occur every year and the most effective way to prevent them is to measure O2 concentration in air with a properly-calibrated O2 monitoring device before entering low-O2 areas. An electro-chemical sensor, Texas Instrument gas platform, and iPhone are used to construct a smartphone-based O2 monitoring device. The smartphone based O2 measuring approach offers advantages of small size, accessibility, internet-connectivity, and programmability in comparison to conventional O2 measuring devices. Multiple gas sensors can be conveniently interfaced to single smartphone, allowing for creating a network of gas sensors distributed across workplaces and remote monitoring via existing mobile communication network. To check proper function of the O2 monitoring device the sensor was exposed to shallow and deep human breaths. The readings decreased immediately after being exposed to exhalation and recovered during inhalation to a calibrated level of 20.9%. When readings decreased below a preset warning value of 19.5%, a low O2 warning was successfully activated on the smartphone.

A On-site Monitoring Device of Work-related Musculoskeletal Disorder Risk Based on 3D-Camera

A 3D camera-based on-site work-related musculoskeletal disorder risk assessment(WMDs) tool has been developed. The device consists of Kinect a 3D camera manufactured by Microsoft, a servo-motor, and a mobile robot. To complement inherent narrow field of view(FOV) of Kinect, Kinect is rotated according to PID servo-control algorithm by a servo-motor attached underneath, to track movement of a subject, producing skeleton-based motion data. With servo-control, full 360 degrees tracking of a test subject is possible by single Kinect. It was found from experimental tests that the proposed device can be successfully employed for on-site WMDs risk assessing tool.

Ergonomics-based Design of 7 Degrees of Freedom Motion Capture Device

The design of a 7 degree of freedom motion capture device(MCD) has been presented. The newly designed MCD overcomes the shortcomings of the existing CADEN-7 exoskeleton robot by implementing various ergonomic design. To improve ease of operation, light-weight high-strength materials such as carbon pipes and engineering plastics were used to reduce weight of the MCD and arm-length adjustment mechanism was also added. The MCD showed consistent measurement results in designed experiments involving change of arm posture from nominal configuration to either elbow-side or arm-front configurations. Furthermore, captured motion in more natural tennis swing appeared to agree well with visual observations made.