Daegeun Park

Design of a variable-stiffness flapping mechanism for maximizing the thrust of a bio-inspired underwater robot

Compliance can increase the thrust generated by the fin of a bio-inspired underwater vehicle. To improve the performance of a compliant fin, the compliance should change with the operating conditions; a fin should become stiffer as the oscillating frequency increases. This paper presents a novel variable-stiffness flapping (VaSF) mechanism that can change its stiffness to maximize the thrust of a bio-inspired underwater robot. The mechanism is designed on the basis of an endoskeleton structure, composed of compliant and rigid segments alternately connected in series. To determine the attachment point of tendons, the anatomy of a dolphins fluke is considered. Two tendons run through the mechanism to adjust the stiffness. The fluke becomes stiffer when the tendons are pulled to compress the structure. The thrust generated by a prototype mechanism is measured under different conditions to show that the thrust can be maximized by changing the stiffness. The thrust of the VaSF device can approximately triple at a certain frequency just by changing the stiffness. This VaSF mechanism can be used to improve the efficiency of a bio-inspired underwater robot that uses compliance.

Electromyographic analysis of upper limb muscles during standardized isotonic and isokinetic robotic exercise of spastic elbow in patients with stroke.

Although it has been reported that strengthening exercise in stroke patients is beneficial for their motor recovery, there is little evidence about which exercise method is the better option. The purpose of this study was to compare isotonic and isokinetic exercise by surface electromyography (EMG) analysis using standardized methods. Nine stroke patients performed three sets of isotonic elbow extensions at 30% of their maximal voluntary isometric torque followed by three sets of maximal isokinetic elbow extensions with standardization of mean angular velocity and the total amount of work for each matched set in two strengthening modes. All exercises were done by using 1-DoF planner robot to regulate exact resistive torque and speed. Surface electromyographic activity of eight muscles in the hemiplegic shoulder and elbow was recorded. Normalized root mean square (RMS) values and co-contraction index (CCI) were used for the analysis. The isokinetic mode was shown to activate the agonists of elbow extension more efficiently than the isotonic mode (normalized RMS for pooled triceps: 96.0±17.0 (2nd), 87.8±14.4 (3rd) in isokinetic, 80.9±11.0 (2nd), 81.6±12.4 (3rd) in isotonic contraction, F[1,8]=11.168; P=0.010) without increasing the co-contraction of muscle pairs, implicating spasticity or synergy.

Development of A Meal Assistive Exoskeleton made of Soft Materials for polymyositis patients

Main goal of this research is to design and fabricate an exoskeleton type assistive device for polymyositis patients, which is extremely compact, lightweight and also comfortable. In order to achieve this goal, the target motion of the device is focused on eating motion which is one of the most important task of daily life. Also, the exoskeleton is designed with soft materials such as fabric, rubber, wire and other compliant materials. The most rigid component used in the exoskeleton is a supporting part made of flexible board. By adopting these materials and concentrating on specific target motion, the number and size of the actuators can be reduced so that total complexity, weight and size of the device decrease. Also, the characteristics of soft material allows comfortable wearing sensation, low cost and good appearance. Therefore, the device becomes affordable and convenient. Polymyositis patients are chosen as the target user since the characteristics of their symptom can reduce complexity of the exoskeleton. Also a special controller is designed to utilize the available motion of the polymyositis patients. Some experiments are conducted to evaluate the performance of the exoskeleton.

Development of a Multi-functional Soft Robot (SNUMAX) and Performance in RoboSoft Grand Challenge

This paper introduces SNUMAX, the grand winner of the RoboSoft Grand Challenge. SNUMAX was built to complete all the tasks of the challenge. Completing these tasks required robotic compliant components that could adapt to variable situations and environments and generate enough stiffness to maintain performance. SNUMAX has three key components: transformable origami wheels, a polymer-based variable stiffness manipulator, and an adaptive caging gripper. This paper describes the design of these components and how they worked together to allow the robot to perform the contest’s navigation and manipulation tasks.

Design and Simulation of the Adjustable Weight bearing system to adjust the torque change by the distal joint on 2DOF body limb

In daily life, arm motions are important for many activities. However, many people suffer from arm impairment because of such conditions as muscle disease and spinal cord injury and experience inconvenience in daily life. We present a new type of adjustable weight bearing system by considering the torque change by the 2-DOF system. In this system, we choose the tendon-driven mechanism for transmitting the weight bearing force from the weight bearing system to the upper arm. Also, we use soft materials such as fabric for the wearing part to minimize joint misalignment and avoid an unfamiliar appearance. In this paper, we suggest the design of the adjustable weight bearing system and simulate the joint torque on shoulder and elbow joint to show the effect of the system.

Evaluation of an improved soft meal assistive exoskeleton with an adjustable weight-bearing system for people with disability

These days, many people suffer from impairments caused by diseases and accidents. Impaired arm function is one of the biggest problem interrupting the activities of daily living for these people. To assist these people with the activities of daily life, many assistive devices for arm motion have been developed. However, many issues arise in their use in actual life, such as the need for customization, costs, and appearance. We focus on the soft meal assistive exoskeleton to minimize the two main issues for typical rigid body devices, structural complexity and cost. We use soft materials and apply the concept of target-oriented rehabilitation to reduce complex arm motions to simple motions. Also, we apply the adjustable weight-bearing system to the soft meal assistive exoskeleton to reduce the required motor power, which is one of the main challenges to reducing running time, size and costs. To evaluate improvement, we measured motor current, which indicates the motor power when the soft meal assistive exoskeleton pulls the upper arm to generate the desired trajectory.

Design and manufacturing a robotic dolphin to increase dynamic performance

Robotic fish and dolphin have been studied to increase their dynamic performance, especially the velocity of a robotic dolphin. There are lots of parameters to increase the velocity of the robotic dolphin such as increasing an oscillating frequency, the area of a caudal fin, or the oscillatory amplitude and so on. The efficient and easy way to increase the thrust is to use a compliant caudal fin. Using the flexible caudal fin, the velocity of the robotic dolphin can increase. Furthermore, using a novel variable stiffness mechanism, the stiffness of the caudal fin can be varied depending on an oscillating frequency to maximize the thrust. We introduce the design and manufacturing of a robotic dolphin which has a variable stiffness mechanism.

Preliminary study for a soft wearable knee extensor to assist physically weak people

To assist the walk of the physically weak people is important to increase their quality of life because it can expand their activity area. We present a soft wearable knee extensor, called Knee Tendon-suit, which assist the knee extension during climbing stairs. To achieve our goal, we used the tendon-driven mechanism for transmitting the actuation force and the anchor structure for transmitting the actuation force to the body. Measuring Electromyography (EMG) at the femoral muscles and the tension at the anchor, we verified performance of the Knee Tendon-suit as the first preliminary result.

Sensorless admittance control of cycle ergometer for rehabilitation

This paper proposes a new control scheme for the cycle ergometer, sensorlsss admittance control. The Proposed control algorithm consists of admittance controller, exercise intensity and speed adjustment controller, and interaction torque estimator which can decrease the cost of the cycle ergometer while providing the advantages of impedance control. With impedance control, the device can provide various dynamic responses by tuning impedance to various rehabilitation exercise scenarios. The admittance controller is adopted instead of the impedance controller for stability. The disturbance observer is established with a friction model and dynamic model of the device to estimate the interaction torque without torque sensor. Some experiments are conducted to verify the performance of the interaction torque estimator and to verify the performance of the sensorless admittance controller. The results show that the torque was well estimated for the different ratio of impedance with the passive operation mode and the auto operation mode.