Hyung-Min Son

Tunable-focus liquid lens system controlled by antagonistic winding-type SMA actuator

A new tunable-focus liquid lens system is proposed that consists of a liquid-filled PDMS (polydimethylsiloxane) membrane, special liquid injection mechanism based on a cam structure, antagonistic winding-type SMA(shape memory alloys) actuator for changing the surface curvature of the membrane, and liquid injection control system, including a digital signal processing board and actuator driver board. The focal length of the liquid lens is adjusted by changing the radius of the curvature of the liquid lens through redistributing the liquid using an injection mechanism. In the case of liquid lens systems using conventional injection mechanisms, the nonlinear relationship between the focal length change and the actuator displacement makes it difficult to control the focal length of the lens system, as there is only a narrow control range for adjusting the focal length over a wide range. In addition, miniaturization of the lens system is difficult due to the requirement of bulky and heavy actuators, such as an electrical motor and pump[7]. Thus, a relatively light and small SMA actuator is proposed for a compact lens system. This paper then provides a detailed description of the proposed tunable-focus liquid lens system, and an experimental system is also implemented. Finally, the focusing performance of the proposed liquid lens system is analyzed, and its usefulness and effectiveness verified through a series of experiments.

Biomimetic variable-focus lens system controlled by winding-type SMA actuator

Inspired by the biomechanics of the human eye, which includes a crystalline lens, ciliary muscles, and zonular fibers, the proposed variablefocus lens system consists of a PDMS lens, winding-type SMA actuator, and load arms. The PDMS lens is encircled and stretched by the load arms joined to an outer ring that is rotated by the winding-type SMA actuator, thereby changing the focal length of the lens. In contrast to other single tunable-focus lenses, the proposed system uses a gel-type PDMS lens, which is insensitive to gravity and external vibration, and can be made into a biconvex or aspheric shape. The design of the proposed system is described in detail, and experimental results demonstrate the validity of the proposed system.

Design of new quadruped robot with SMA actuators for dynamic walking

This paper presents a small-sized dynamic walking quadruped robot that uses SMA actuators. Conventional dynamic walking robots have a bulky body and are usually driven by large and heavy electrical motors or hydraulic actuators in order to produce a high output torque. Thus, to resolve this problem, a new SMA actuator is proposed with attractive features, such as a high power density, small size, and light weight. To improve the small ratio of deformation and slow response time of an SMA, the proposed actuator also has a unique winding structure for the SMA wire and reversed gear mechanism. As such, a quadruped robot for dynamic walking is introduced that is equipped with twelve SMA actuators, four 3-DOF leg mechanisms, and a rigid body. The control system for the proposed robot consists of a main control board, PWM generator board, SMA driver board, and sensor interface board

Design of biomimetic robot-eye system with single vari-focal lens and winding-type SMA actuator

This paper presents a biomimetic robot-eye system with a single vari-focal lens and winding-type SMA actuator. Based on the biomechanics of the human eye, the proposed system consists of a biconvex PDMS lens, winding-type SMA actuator, and mechanical parts, such as grippers, load arms, an outer ring, and body. In contrast to other single vari-focal lenses, the proposed PDMS lens is a gel, thereby avoiding any deflection from gravity and external vibration. Plus, the PDMS lens is circularly enclosed and elongated by load arms joined to an outer ring that is operated by a winding-type SMA actuator. While the advantages of SMA wires are their light weight and high-power density, their deformation is small. Thus, to overcome this limitation, the lever principle is conversely applied to the load arms, allowing a large elongation of the PDMS lens to adjust its focal length, even though the SMA wire is only slightly deformed. The design of the proposed system is described in detail, and experimental results demonstrate the validity of the proposed system.

New Gel-type Biomimetic Variable-focus Lens System

In this paper, we propose a new gel-type biomimetic variable-focus lens system. The miniaturization of conventional lens system is limited due to the use of a set of glass lenses for adjusting the focal length. Biologically inspired by the focus adjustment mechanism of the human eye, a gel-type single lens system with variable-focus is presented. The proposed system consists of a gel-type lens, mechanical parts such as body, rotation ring, and winding-type SMA actuator. In addition, the proposed system is designed to operate with a simple and miniaturized mechanical structure using a new attachment and driving mechanism. The focusing performance of the proposed system is verified through a series of experiments and measurements of the shape of the lens using tomography.

New variable focal liquid lens system using antagonistic-type SMA actuator

This paper presents a new variable focal liquid lens system that uses a SMA(shape memory alloy) actuator. Making a conventional variable focal liquid lens system small and light is difficult, due to the requirement of a large and heavy actuator, such as a pump or an electric motor, to distribute the liquid in the liquid lens. Plus, focal control is also difficult, due to a nonlinear focal variation in relation to a linear actuation. Thus, to solve these problems, a new actuation system is proposed for a liquid lens that uses a SMA wire and rotating piston mechanism, in which a cylindrical cam structure is adopted to create a linear relationship between the radius of the curvature of the lens and the displacement of the actuator. A winding and antagonistic-type SMA actuator is also designed to produce a large displacement and fast response time. Experiments using a prototype demonstrate the efficiency of the proposed system.

Implementation of face selective attention model on an embedded system

This paper proposes a new embedded system which can selectively detect human faces with fast speed. The embedded system is developed by using OMAP 3530 application processor which has DSP and ARM core. Since the embedded system has the limited performance of CPU and memory, we propose a hybrid system combined the YCbCr based bottom-up selective attention with the conventional Adaboost algorithm. The proposed method using the bottom-up selective attention model can reduce not only the false positive error ratio of the Adaboost based face detection algorithm but also the time complexity by finding the candidate regions of the foreground and reducing the regions of interest (ROI) in the image. The experimental results show that the implemented embedded system can successfully work for localizing human faces in real time.

Design and control of a linearity-enhanced SMA actuator

For the accurate and dexterous operation of mechanical systems, continuous-type actuation, rather than on/off-type actuation, is an indispensable function. However, conventional Ti–Ni alloys present difficulties for continuous positioning control, due to their hysteretic and abruptly changing relationship between strain and temperature. Therefore, this paper proposes a new linearity-enhanced SMA actuator using a temperature-gradient annealed alloy and an inverse hysteresis controller. In comparative experiments, the proposed controller and alloy exhibit superior performance for continuous actuation.

Biomimetic gel-type single lens system with new attachment and driving mechanism

This paper proposes a biomimetic gel-type single lens system with a new attachment and driving mechanism. As the miniaturization of conventional lens systems is limited due to the use of a set of glass lenses for adjusting the focal length, a gel-type single lens system is presented based on the focus adjustment mechanism of the human eye. The proposed system consists of a gel-type lens, mechanical part, and winding-type SMA actuator. In addition, the proposed system is designed to operate with a simple and miniaturized mechanical structure using a new attachment and driving mechanism. The focusing performance of the proposed system is verified through a series of experiments.