The objective of the present study was to investigate the relationship between surface roughness and touch perception of surfaces with randomly spaced, irregular features. Two sets of specimens with top surfaces consisting of triangular peaks and valleys were modeled and 3D-Printed by varying the height of the peak, the depth of the valley, and the width between two intersections of the peak or valley with the center line. For one set of specimens, values of these variables were kept constant within a specimen but varied across specimens. For the other set of specimens, values of these variables were randomly selected in given ranges within a specimen while ranges were varied across specimens. The level of touch perception of each specimen was then measured using a questionnaire consisting of 16 adjectives related to touch perception and a 7-point Likert scale. Measured data were statistically analyzed and compared between different sets of specimens. Results indicated that it was inappropriate to directly apply findings of the previous studies for surfaces with regularly spaced, geometrically well-defined features to surfaces with randomly spaced, irregular features.
The electromagnetic force compensation (EMFC) measurement principle has been widely adopted in the high-precision mass metrology system due to its sensitive compliant mechanism and nanometer level position sensor. In EMFC, an electromagnetic actuator balances the gravitational weight to maintain zero (or Null) position by feedback control using a position sensor, and the weight is calculated from the current applied to the actuator. Thus, a position sensor in the EMFC system should measure the null position accurately with high sensitivity and resolution. The position sensor commonly used in EMFC balance is an optical sensor that measures the displacement of EMFC balance from the intensity of light coming through a slit using a two-segment photodiode. This paper analyzed the characteristics of an optical position sensor for EMFC balance through parametric analysis using the Fresnel diffraction model. We also evaluated the performance of the sensor and confirmed the feasibility from weighing performance of the balance prototype. Normalized sensitivity of the sensor was 0.04237 μm-1 and measured resolution was 1.09 nm. The weighing repeatability with our optical position sensor was 4.83 mg (1σ) at 10 g measurement, which was 3 times better than the repeatability with an alternative commercial sensor.
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Spectroscopic sensors have been used in the field of optics and chemical analysis, and the need for remote gas monitoring in a portable form has increased. Hence, it is essential to design, manufacture, and develop a moving mirror, which that can generate the optical path difference for spectroscopic sensor. It is important to verify whether it can satisfy design requirements for the actual spectroscopic interferometer application by evaluating its performance. In this paper, a moving mirror assembly with high-speed transfer capability for a portable spectroscopic sensor is fabricated and tested. For application to a portable spectrometer, design requirements, such as moving distance, speed, and stiffness, are set and the mechanical structure, including the voice coil motor and elastic guide, satisfying these requirements is proposed. Through finite element analysis, performance of the proposed moving mirror assembly is predicted. By testing the performance after fabrication, it is verified that the proposed mirror is capable of linear movement with travel distance of several millimeters and moving speed of tens of Hz. Optical testing result shows that the proposed moving mirror can generate linear motion with a tilting error below 10 arcsecond and can be applied to the actual spectroscopic interferometer in future.
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The aim of this research was to investigate the torque performance of the motor in an electric vehicle depending on the rotor shape and air gap. The research focused on numerical comparison of torque performance of new rotors based on the average torque and torque ripple rate, which appeared according to the number and placement of permanent magnets. This research was numerically analyzed by MAXWELL V21.1. Average torque values in cases 1, 2, and 3 were increased, but vibration and noise in cases 1 and 3 were increased as the torque ripple rate increased. Considering the average torque and torque ripple rate, the torque performance of case 2 was the most optimal. Compared with Model N, the average torque of case 2 was increased by 9.1% and the torque ripple rate was reduced by 1.5%. The torque performance according to the size of air gap was compared with the basic model of case 2, which showed the best performance. An air gap of 0.7 mm applied to Model N showed the best torque performance. An additional magnet on case 2 and air gap of 0.7 mm provided the best torque performance and improved the driving motor performance for motor durability.
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